Rules for Scoring Respiratory Events in Sleep: Update of the 2007 AASM Manual for the Scoring of Sleep and Associated Events

3.1.1 Detection of Apnea and Hypopnea—General Considerations

The task force recommends a few changes and clarifications in the technical considerations section of the respiratory scoring rules chapter (Tables 2, 3, and 4). The 2007 scoring manual did not specify the sensor for detection of apnea and hypopnea during positive airway pressure (PAP) titration. PAP devices used for titration during polysomnography (PSG) have the ability to output an analog or digital signal from the internal flow sensor.13 Use of this signal to detect apnea and hypopnea during PAP titration is recommended in both the positive airway pressure and noninvasive positive pressure ventilation (NPPV) titration clinical guidelines.14,15 Flattening of the inspiratory portion of the flow waveform provides evidence of airflow limitation and increased upper airway resistance.13,16 Based on consensus and clinical evidence, the task force recommends that the PAP device flow signal should be used to score apneas or hypopneas during PAP titration. Of note, the magnitude of oral airflow, if present, during a PAP titration with a nasal mask is not estimated by the PAP flow signal.

Table 2 Recommended sensors for routine respiratory monitoring

Table 3 Alternative sensors for scoring respiratory events during diagnostic study

Table 4 Other sensors for respiratory monitoring

While the 2007 scoring manual lists the use of respiratory inductance (inductive) plethysmography (RIP) sensors17–19 as alternative sensors for scoring apnea and hypopnea, the specific RIP signals to be used were not clearly specified. The available RIP signals include the dual RIP belt signals (thorax and abdomen), the RIPsum (sum of the thorax and abdomen belt signals) and the RIPflow (the time derivative of the RIPsum signal).18–20 Deflections in the RIPsum signal provide an estimate of tidal volume when RIP is calibrated.18,19,21 In uncalibrated RIP, deflections in the RIPsum signal allow detection of a relative change in tidal volume compared to baseline breathing.9,19,22 If the RIPsum signal is not available, a reduction in tidal volume can be inferred if there is a reduction in the excursions of the thoracic and abdominal belts.9,22 Of note, the pattern of undiminished excursions in the signals from the thoracoabdominal belts that are out of phase during an event is also consistent with a reduction in tidal volume (RIPsum). The RIPflow signal is a semi-quantitative estimate of airflow in calibrated RIP, and relative airflow in uncalibrated RIP.19,20,23–25 Calibration of the RIP signal is usually not performed in routine clinical PSG unless the technology for calibration during natural breathing26 is available. During apnea, the RIPsum and RIPflow signals show absent or minimal excursions, and during hypopnea, the excursions are diminished compared to baseline breathing.18,19 Of note, airflow limitation can be inferred from subtle qualitative changes in the inspiratory portion of the thorax RIP, abdominal RIP, and RIPsum signals,27 or from flattening of the inspiratory portion of the RIPflow waveform.19,20,28 The recommended RIP signals for scoring apnea and hypopnea events are specified in Tables 2 and 3.

The 2007 scoring manual recommends use of the nasal pressure signal for scoring hypopnea in both adults and children. While the detection of hypopnea depends on the reduction in the amplitude of the signal, the inspiratory portion of the nasal pressure waveform provides additional useful information. Flattening of the shape of the inspiratory nasal pressure waveform is a surrogate for airflow limitation19,24,29–31 and is included in the respiratory effort related arousal (RERA) rules in the 2007 scoring manual.1 Visualization of flattening of the signal requires that the nasal pressure signal be recorded either as a DC signal or an AC signal with a low-frequency filter setting (cutoff frequency) that is sufficiently low (frequency cutoff 0.03 Hz or lower) (Figure 1).30 Snoring can also be detected as oscillations superimposed on the unfiltered nasal pressure signal32 if an appropriate high-frequency filter setting is used (100 Hz).1 The task force recommends that appropriate high and low filters settings be specified for nasal pressure recording in future revisions of the scoring manual.

3.1.2 Sensors for Apnea Detection

In the 2007 scoring manual the recommended sensor for detecting apnea in both adults and children is an oronasal thermal sensor (Table 1 for definition of recommended). Oronasal thermal sensors have the advantage of being able to detect both nasal and oral airflow. Thermal sensors detect a change in temperature between inhaled and exhaled gas. Here thermal airflow sensors include thermistors, thermocouples, or polyvinylidene fluoride (PVDF) sensors.19,33–35 The task force found no evidence to change this recommendation for diagnostic sleep studies, although it broadened the definition of thermal sensors to include PVDF sensors.

The 2007 scoring manual recommends somewhat different alternative sensors for apnea detection in adults (nasal pressure transducer or RIP) and children (nasal pressure transducer, end-tidal PCO₂, and summed RIP) (Table 1 for definition of alternative). The nasal pressure signal is not the recommended sensor for apnea detection as the signal may show decrease excursions (decreased amplitude) during mouth breathing.32 Due to the non-linear characteristics of the nasal pressure signal (proportional to the flow squared), the signal underestimates low flow rates and could result in a hypopnea appearing to be an apnea.36 A square root transformation of the nasal pressure signal more closely approximates flow and minimizes this problem.

As noted above, the excursions of the RIPsum and RIPflow signals usually have minimal amplitude during apnea.18,19,23 However, during obstructive apnea continued excursions in the RIPsum or RIPflow signals may be seen if the thorax and abdominal belt signals do not precisely sum to zero. This problem is minimized by calibration of the RIP signals; however, even the calibrated RIPsum may not remain accurate due to belt movement or changes in patient position.37

Studies have evaluated the accuracy of RIPsum or RIPflow as a surrogate of tidal volume/airflow to detect apneas and hypopneas in adults23,38 and children.25 These studies usually analyzed the combination of apneas and hypopneas.23,38 That is, a separate analysis for apneas and hypopneas was not performed. In one study of calibrated RIP, the use of the RIPsum and RIPflow signals to determine the apnea hypopnea index (AHI) showed good agreement with a pneumotachograph (accurate flowmeter).23 Another study using uncalibrated RIP to determine the AHI found the intermeasurement agreement between use of the RIPsum and pneumotachograph to be considerably lower than between nasal pressure and pneumotachograph.38 A separate analysis for apnea and hypopnea detection was not performed. Respiratory belts utilizing a PVDF sensor can also provide a sum signal as well as thoracoabdominal signals. One study in adult patients being evaluated for suspected obstructive sleep apnea (OSA) suggests that the PVDFsum signal may have utility as a method for apnea/hypopnea detection independent of direct airflow monitoring (nasal pressure or thermistry).6 The PVDFsum signal identified apnea based on a reduction in signal amplitude to 10% of baseline and hypopnea by a 50% reduction in signal. There was good agreement between classification of patients with an AHI ≥ 5/hour using PVDFsum compared to detection of airflow by thermistry and nasal pressure. In a separate part of the study, ten normal subjects simulated central and obstructive apneas while monitored with a pneumotachograph, RIP belts, and PVDF belts. Respiratory events defined as > 50% drop in signal amplitude were identified and compared. The PVDF sensor performed as well as the RIP when compared against the pneumotachograph in terms of the total number of respiratory events that were detected. Further evidence for the utility of the PVDF signals (thoracoabdominal belts or sum) to detect apnea/hypopnea is needed.

In summary, there is evidence that RIPflow or RIPsum (in adults and children) or PVDFsum (in adults only) may be used as an alternative sensor for apnea detection with the understanding that most studies analyzed the combination of apneas and hypopneas. Calibration of RIP may improve the accuracy of RIPflow and RIPsum, but a head-to-head comparison of AHI results using the same sensor, with and without calibration, has not been performed. Further comparisons between PVDFsum, RIPsum, or RIPflow, and an oronasal thermal sensor for detection of apneas (both central and obstructive) are needed.

The end-tidal PCO₂ signal is listed as an alternative sensor for apnea detection in pediatric patients in the 2007 scoring manual. A more accurate description of the signal is exhaled PCO₂, but the phrase end-tidal PCO₂ monitoring is widely used. Monitoring of exhaled PCO₂ is routinely performed during pediatric PSG, and the absence of signal deflections (no CO₂ exhaled) has been used to score apneas (Figure 2).1,39 The side stream method is most commonly used and consists of gas suctioned via a nasal cannula to an external sensor at bedside. Mouth breathing and occlusion of the nasal cannula can impair the ability of end-tidal PCO₂ monitoring to detect apnea. One must remember that the magnitude of signal excursion depends entirely on the highest value of PCO₂ in the exhaled breath rather than the magnitude of tidal volume or flow. Signal excursions can persist during inspiratory apnea if small expiratory puffs with a high PCO₂ are present.40 A large study in infants compared the ability of the RIPsum, end-tidal PCO₂, and oronasal thermistor monitoring to detect apnea.39 End-tidal PCO₂ detected 182 of 196 apneas detected by either a thermistor or RIPsum.

After review of the existing evidence, the task force decided upon recommended (Table 2) and alternative (Table 3) sensors for apnea detection. The task force concluded that the recommended sensor for apnea detection during diagnostic study should continue to be an oronasal thermal sensor in adults and children [Recommended] (Consensus). The task force also reached consensus on specification of the nasal pressure signal or the RIPsum or RIPflow signals from calibrated or uncalibrated RIP as the alternative (sensor) signals for apnea detection during diagnostic study in adults and children [Recommended] (Consensus). In adults the PVDFsum signal may also be used as an alternative sensor for apnea detection, although the ability to differentiate obstructive apneas versus hypopneas has not been defined [Acceptable] (Adjudication). The end-tidal PCO₂ is another alternative apnea sensor in children if other sensors are not functioning or not available [Acceptable] (Consensus). As noted in the previous section, the PAP device flow signal is the recommended signal for apnea detection during PAP titration. Alternative sensors for apnea detection during PAP titration studies are not specified.

3.1.3 Sensors for Hypopnea Detection

Hypopnea detection requires a sensor to reliably detect a reduction in airflow or tidal volume. The gold standard for airflow detection is a pneumotachograph, usually placed in the outlet of a mask over the nose and mouth, which measures the pressure drop across a linear resistance.9,19,23,24,40 However, this technology is not practical for clinical studies. The 2007 scoring manual recommends a nasal pressure transducer with or without square root transformation as the recommended sensor for detection of airflow for identification of hypopnea in adults.1 In children the untransformed nasal pressure signal is recommended. The 2007 scoring manual also recommends somewhat different alternative hypopnea sensors for adults (calibrated or uncalibrated RIP, oronasal thermal sensor) and children (oronasal thermal sensor).

As noted above, nasal pressure monitoring (nasal cannula connected to a pressure transducer) provides a signal proportional to the square of the flow.36 A square root transformation of the signal provides a more accurate estimate of flow, but the accuracy of the transformed nasal pressure signal typically deteriorates over a night of monitoring due to factors such as changes in catheter position.23 The effect of using a transformed rather than untransformed nasal pressure signal on the apnea hypopnea index is usually small; the AHI based on the transformed signal is slightly lower.1,23 The utility of nasal pressure monitoring has been documented in a significant number of publications19,23–25,29–32 and is sensitive to even subtle changes in airflow. The inspiratory portion of the nasal pressure waveform can display flattening, a surrogate of airflow limitation when using appropriate filter settings. As noted above, the major disadvantage of nasal pressure monitoring is the inability to detect or estimate the magnitude of oral airflow.32

Oronasal thermistors and thermocouples detect the presence of airflow due to a change in sensor temperature, as exhaled gas is warmed to body temperature. The signal from these thermal devices is not proportional to flow33,41 and often overestimates flow as flow rates decrease.33 Excursions in the signal typically show some decrement during hypopnea, although not as prominent as those in the nasal pressure signal.19 Thermal sensors using polyvinylidene fluoride (PVDF) film produce a signal that is roughly proportional to the temperature difference between the two sides of the film and have a faster response time than thermistors or thermocouples.34,35 One study comparing the ability of an oronasal PVDF airflow sensor to a pneumotachograph in ten patients with OSA found that the output of a PVDF airflow sensor tracked the magnitude of changes in flow with reasonable accuracy.34 Although this study did not directly compare the PVDF sensor to traditional thermal sensors, it does suggest that PVDF sensors more accurately estimate the magnitude of airflow.34 While the inspiratory PVDF waveform may not routinely exhibit flattening during airflow limitation, PVDF sensors have the advantage over nasal pressure sensors of being able to detect oral airflow. One can also argue that hypopnea definitions are based on changes in amplitude rather than signal contour. A limitation of the evidence for using PVDF airflow sensors for hypopnea detection is the small number of patients that have been studied. A study of PVDF airflow sensors in children has yet to be published.

As noted above, the calibrated or uncalibrated RIP signals (RIPsum, RIPflow, thorax and abdominal belt excursions) also decrease during hypopnea.18–20,22–24 Studies of uncalibrated9,22,38 and calibrated RIP23,24 have shown reasonable accuracy in detection of hypopnea. However, in some very obese patients inspiration is associated with small thoracoabdominal excursions making use of RIP for detection of hypopnea more difficult. Heitman et al.38 found the event by event device agreement between a pneumotachograph and the nasal pressure signal to be higher than between the pneumotachograph and the RIPsum (uncalibrated RIP). Clark and coworkers found the nasal pressure signal to be more sensitive for detection of airflow limitation than RIPflow (calibrated RIP).25 Thurnheer et al.23 found the bias in AHI between nasal pressure (transformed or untransformed) and a pneumotachograph to be similar to that between RIPflow (calibrated RIP) and the pneumotachograph. One might expect calibration of RIP to improve the accuracy of hypopnea detection, but this is rarely performed in clinical PSG. Another issue is that not all commercially available PSG systems provide a RIPsum and/or a RIPflow signal. As noted in the discussion of apnea sensors, the PVDFsum signal (from PVDF effort belts) appears to have utility for detection of apneas and hypopneas based on a single study in adults. As with other hypopnea sensors, the PVDFsum does not appear to be as sensitive for detecting events (based entirely on flow) as nasal pressure.6 The ability of PVDFsum to detect hypopnea when combined with arterial oxygen desaturation remains to be determined.

Given the above considerations, the task force was able to reach consensus on the recommended (Table 2) and alternative (Table 3) sensors for hypopnea detection in adults and children during diagnostic polysomnography. The task force recommends that the recommended sensor for detection of airflow for identification of hypopnea in adults and children continue to be a nasal pressure transducer (with or without square root transformation) [Recommended] (Consensus). The simplicity and sensitivity of nasal pressure and the ability for scorers to easily recognize changes in flow based on changes in shape as well as amplitude are distinct advantages. Alternative sensors for identification of hypopnea in adults and children include oronasal thermal sensors (including PVDF airflow sensors) or calibrated or uncalibrated RIP (RIPsum, RIPflow, dual thoracoabdominal RIP belts) [Recommended] (Consensus). The PVDFsum is an alternative hypopnea sensor to be used in adults only [Acceptable] (Adjudication). As noted earlier, the PAP device flow signal is the recommended signal for hypopnea detection during PAP titration. Alternative sensors for hypopnea detection during PAP titration studies are not specified.

3.1.4 Sensors for Detection of Respiratory Effort

The 2007 scoring manual recommends esophageal manometry or calibrated or uncalibrated respiratory inductance plethysmography for detection of respiratory effort in adults and children. Esophageal manometry is the gold standard for detection of respiratory effort, and the signal excursions provide an estimate of the magnitude of effort.8,9,42 However, esophageal manometry is rarely used in clinical practice due to its invasiveness and patient discomfort. Instead, the monitoring of thoracoabdominal excursions is used to detect the presence of respiratory effort. The magnitude of these excursions may or may not be proportional to esophageal pressure excursions, yet for routine clinical sleep monitoring, the detection of respiratory effort to differentiate central and obstructive apnea is the major concern. Failure to detect respiratory effort when present may result is the incorrect classification of an obstructive apnea as central. In one study of 22 patients with OSA using strain gauge sensors positioned on the chest and abdomen, 422 events were classified as central apneas; however, 156 of the events were reclassified as obstructive based on esophageal pressure tracings.43

The 2007 scoring manual did not specify the use of dual effort belts (thoracoabdominal belts) for detection of respiratory effort. Nevertheless, this is standard clinical practice for a number of reasons. Some patients have larger excursions in either the thorax or abdominal belts during the night, and this can vary with body position. If one effort belt fails, the other still provides information about respiratory effort. During biocalibration the polarity of belt signals is adjusted so that belt distension results in signal excursion in the same direction for both belts. Use of dual belts has the additional advantage of the ability to demonstrate paradoxical motion of the thorax and abdomen and adds the ability to identify events as obstructive18,19,44 (Figure 2).

The technology available for respiratory effort belts includes strain gauges, impedance plethysmography, inductance plethysmography (RIP), and belts with piezoelectric or PVDF sensors.6,18,19,43 An advantage of the RIP technology is that inductance of the band and ultimately the signal output depends on the entire surface area enclosed by the band. Effort belts with piezoelectric or PVDF sensors typically utilize a single sensor between belt material surrounding the thorax or abdomen. The signal depends on variations in the tension on the sensor which may or may not reflect the magnitude of thoracoabdominal excursions. Studies have shown that RIP belts are able to detect subtle changes in respiratory effort27,28 and out of phase (paradoxical) motion of the thorax and abdomen excursions is often noted during obstructive apnea or hypopnea.18,44 Calibration of RIP signals should improve the accuracy of this sensor technology for detection of respiratory effort.18 However, even calibrated RIP may not detect feeble respiratory effort in some patients with misclassification of obstructive apneas as central.44 Of note, many of the studies documenting the accuracy of RIP used belts from one or two manufacturers, yet RIP belts are currently supplied by many different manufacturers, and information on the specific technology used for a given belt is not available to the clinician. Validation studies for each type of RIP belt would increase confidence that their performance is similar to the belts used in previous investigations.

Prior to publication of the 2007 scoring manual, many sleep centers used piezoelectric effort belts. Today use of RIP belts has replaced piezoelectric belts in most sleep centers. The task force found scant evidence directly comparing RIP and piezoelectric effort belts with respect to the AHI or detection of central apnea.45,46 Montserrat et al. did find that subtle changes in piezoelectric belt signals were useful in detecting subtle increases in respiratory effort.16 A recent study directly compared RIP belts and effort belts using a PVDF sensor.6 Monitoring was performed with both types of belts in place in 50 adult patients referred for evaluation of possible obstructive sleep apnea (OSA). Respiratory events were scored using montages with either RIP or PVDF belt signals visible to detect respiratory effort. Although there were differences in the AHI values between the sensor types in some patients, overall the results obtained by both technologies were very similar. The average number of central apneas, obstructive apneas, hypopneas, and the overall AHI as determined using RIP versus PVDF belts for respiratory effort detection were almost identical and showed a high level of agreement as assessed by the κ statistic. Thus, PVDF sensor effort belts appear to adequately detect respiratory effort in adults.6 Unlike RIP signals, there have been no studies of PVDF belts in children. More validation studies directly comparing effort belts with different technology (RIP versus piezoelectric, RIP versus PVDF) are needed.

The 2007 scoring manual includes surface diaphragmatic/intercostal electromyography (EMG) as an alternative sensor for detection of respiratory effort. Bursts of the diaphragmatic/intercostal EMG signal are noted with each inspiration. Similar monitoring methods as those used for recording of anterior tibial muscle EMG can be used. However, unlike leg EMG, the diaphragmatic/intercostal EMG signal is often contaminated with prominent electrocardiographic activity. There continues to be scant literature on the use of surface EMG to detect respiratory effort.47,48 Although diaphragmatic/intercostal EMG monitoring is potentially useful as an adjunct to other methods of detecting respiratory effort, the task force felt that more research in this area is needed.

Given the above considerations, the task force decided to uphold the 2007 manual recommendation that esophageal manometry or calibrated or uncalibrated dual thoracoabdominal RIP belts be used for detection of respiratory effort in adults and children (Table 2) [Recommended] (Consensus). It was concluded that dual thoracoabdominal PVDF belts may be used to detect respiratory effort in adult patients but with a lower level of recommendation due to limited published evidence (Table 2) [Acceptable] (Adjudication).

3.1.5 Detection of Blood Oxygen

The task force did not find evidence to change the 2007 recommended sensor for estimation of arterial oxygen saturation which is pulse oximetry (SpO₂) with an appropriate averaging time (Table 2) [Recommended] (Consensus). It was noted that the presence of carboxyhemoglobin (e.g., in heavy smokers) may result in the SpO₂ being higher than the true fraction of total hemoglobin bound to oxygen.49 Accurate measurement of the amount of carboxyhemoglobin requires use of a co-oximeter that uses the absorption of four or more wavelengths of light (compared to two wavelengths in routine oximetry). The presence of carboxyhemoglobin also shifts the oxygen hemoglobin saturation curve to the left causing a given SpO₂ to be associated with a lower than expected partial pressure of oxygen.

Because of the sigmoid shape of the oxyhemoglobin dissociation curve, a much greater drop in arterial partial pressure of oxygen (PaO₂) occurs in the setting of a drop of 4% from a baseline saturation of 96% to 92% (PaO₂ change ~18 mm Hg) compared to the same drop of 4% from a baseline saturation of 92% to 88% (PaO₂ change ~ 9 mm Hg). Therefore, linking respiratory event definitions to a specific change in saturation for event detection requires a greater fall in the PaO₂ for patients with a high baseline saturation (e.g., 98%) than those with lower baseline saturations. The desaturation associated with a respiratory event is defined as a drop from a baseline SpO₂ preceding the event to the nadir in the SpO₂ following the event. While identification of the nadir in the SpO₂ following a respiratory events is usually straightforward, selecting a “baseline” SpO₂ in a patient with back-to-back respiratory events is more difficult. The highest SpO₂ following a respiratory event can exceed values present during stable breathing. Defining a “baseline SpO₂” during sleep may be difficult in such patients. While the above ambiguities in SpO₂ measurement were recognized, the task force did not recommend changes in terminology or measurement.

3.1.6 Detection of Snoring

The 2007 AASM scoring manual did not recommend a sensor for snoring. There is a paucity of published data on snoring sensors. Optimal visualization of snoring requires a high frequency filter setting that permits recording/display of rapid oscillations (100 Hz recommended in the 2007 scoring manual).1 Snoring may be visualized in the nasal pressure signal as high-frequency oscillations32 superimposed on the slower varying flow signal but is not seen in the PAP device flow signal which is either filtered or too under-sampled to show the high-frequency vibrations. Snore sensors are typically piezoelectric sensors that detect vibration of the neck or microphones that record the sound of snoring. The AASM guidelines for continuous positive airway pressure (CPAP) and for NPPV titration14,15 both listed a snore signal as an option for recording. Based on limited information, the task force recommends several sensors as options for snore detection: the unfiltered nasal pressure signal, piezoelectric sensors to detect vibration, or acoustic sensors (e.g., microphone) to record sound (Table 4) [Recommended] (Consensus). The ability of the sensor to detect simulated snoring should be demonstrated before sleep recording. The task force concurs with the 2007 manual that whether or not to monitor snoring is at the discretion of the clinician or investigator [Optional] (Consensus).

3.1.7 Detection of Hypoventilation

The gold standard method for documenting hypoventilation is the processing of an arterial sample for determination of the arterial partial pressure of carbon dioxide (PaCO₂). Given the difficulty of drawing an arterial sample during sleep, the 2007 scoring manual states that finding an elevated PaCO₂ obtained immediately after waking would provide evidence of hypoventilation during sleep. Regardless of whether this value underestimates the sleeping PaCO₂, the ability to draw or process an arterial blood gas sample is rarely available in sleep centers. In neonates and some research studies, capillary blood samples have been used to provide an estimate of the PaCO₂ when sampling of arterial blood is difficult.50 Although capillary sampling requires less expertise than obtaining an arterial blood gas, processing of the sample still requires equipment rarely available in most sleep centers.

Given the difficulties in obtaining a direct measurement of PaCO₂, surrogate measures such as end-tidal PCO₂ (P_ETCO₂) and transcutaneous PCO₂ (P_TCCO₂) are commonly used during PSG. A 2007 scoring manual note for the hypoventilation rule in adults states that there is insufficient evidence to allow specification of sensors for direct or surrogate measures of PaCO₂. It goes on to clarify that “both end-tidal CO₂ and transcutaneous CO₂ may be used as surrogate measures of PaCO₂ if there is demonstration of reliability and validity within laboratory practices.”1 In contrast, the pediatric hypoventilation scoring rules state “acceptable methods for assessing alveolar hypoventilation are either transcutaneous or end-tidal PCO₂ monitoring.”1 The task force examined the literature to see if the recommendations for hypoventilation sensors in adults and children could be brought into closer concordance.

Monitoring of exhaled CO₂ (capnography) is widely used in pediatric PSG. In children, respiratory events are often associated with increases in P_ETCO₂ with minimal changes in the SpO₂.51 In most sleep centers, a bedside device containing the CO₂ measuring sensor continuously suctions gas through a nasal cannula worn by the patient (side stream method). During inhalation, room air is suctioned (PCO₂ = 0), and during exhalation, the PCO₂ in the exhaled gas is measured. The end-tidal PCO₂ provides an estimate of the arterial value (usually PaCO₂ > P_ETCO₂). The PaCO₂ – P_ETCO₂ difference is usually 2 to 7 mm Hg, and the difference is higher in patients with lung disease.52 The P_ETCO₂ is not an accurate estimate of the PaCO₂ during mouth breathing or with low tidal volume and fast respiratory rates. Some manufacturers make a sampling nasal cannula with a “mouth guide” to allow sampling of gas exhaled through the mouth. To be considered accurate, a definite plateau in the exhaled P_ETCO₂ versus time waveform should be observed.1,9,51,52 End-tidal PCO₂ measurements are often inaccurate during application of supplemental oxygen or during mask ventilation.53 The exhaled gas sample is diluted by supplemental oxygen flow or PAP device flow. Some clinicians use a small nasal cannula under the mask to sample exhaled gas at the nares in order to minimize dilution during PAP titration. However, the accuracy of measurements using this approach has not been documented.

Transcutaneous CO₂ monitoring (P_TCCO₂)54 is also used during PSG to estimate the PaCO₂, but the signal has a longer response time than the P_ETCO₂ to acute changes in ventilation. In adults, one study using an earlobe sensor found that the P_TCCO₂ lagged behind PaCO₂ by about 2 minutes.55 Newer transcutaneous device technology has allowed more rapid response time and enabled the devices to work at a lower skin temperature. The advantage of P_TCCO₂ monitoring compared to P_ETCO₂ is that the accuracy of transcutaneous measurements is not degraded by mouth breathing, supplemental oxygen, or mask ventilation. However, P_TCCO₂ will not provide data for breath-by-breath changes, e.g., changes in the first few breaths after an apnea.

The task force considered the literature on the accuracy of end-tidal CO₂ and transcutaneous PCO₂ as surrogates for determination of arterial PCO₂. Sanders et al. found that both P_ETCO₂ and P_TCCO₂ monitoring did not provide an accurate estimation of PaCO₂ during sleep53; however, this study was limited by the technology used, i.e., P_ETCO₂ was measured using a loose-fitting mask, which would be unlikely to result in an adequate waveform. A study of P_ETCO₂ during the awake postoperative state in both non-obese and obese patients found the average P_ETCO₂ values to differ from the PaCO₂ by around 8 mm Hg (nasal cannula) or 6 mm Hg (nasal cannula + oral guide).56 Another study evaluated the utility of P_ETCO₂ for determining daytime hypoventilation in a group of patients with neuromuscular disease. Although fairly accurate in some patients, in others there was a large difference between the P_ETCO₂ and PaCO₂.57

A number of studies54–59 have evaluated the accuracy of P_TCCO₂ compared to PaCO₂ or capillary PCO₂. Maniscalco et al. found the average PaCO₂ – P_TCCO₂ difference to be −1.4 mm Hg (95% confidence interval −1.7 to 7.5 mm Hg) in a group of obese adult patients with various disease processes.58 In a recent study, Storre et al.59 compared capillary blood gas PCO₂ and P_TCCO₂ from 3 different devices in a group of patients being started on nocturnal noninvasive ventilation. The bias (PaCO₂ – P_TCCO₂ drift uncorrected) for one device was as low as 0.8 mm Hg, with the limits of agreement extending from −4.9 to 6.5 mm Hg. Pavia and coworkers60 used P_TCCO₂ monitoring during sleep in 50 children receiving chronic NPPV. Twenty-one patients had nocturnal hypoventilation (without desaturation on oximetry). Of these 21 patients, 18 did not have daytime hypoventilation (capillary blood gas). The authors concluded that P_TCCO₂ monitoring was useful for detection of unsuspected nocturnal hypoventilation. Senn and coworkers61 compared transcutaneous and arterial PCO₂ measurement in a group of patients undergoing mechanical ventilation. The mean difference ± 2 SDs between P_TCCO₂ and PaCO₂ during stable ventilation was 3 ± 7 mm Hg.

A number of investigations compared values obtained from simultaneous measurements of P_ETCO₂ and P_TCCO₂. Kirk et al.62 analyzed the findings of PSG with simultaneous monitoring of P_ETCO₂ and P_TCCO₂ in 609 children. In 437 patients, the difference between the mean nocturnal P_ETCO₂ and P_TCCO₂ was between −4 and +4 mm Hg. Of note, interpretable results were found in 61% of PSGs for P_ETCO₂ and 71.5% for P_TCCO₂. Thus, obtaining interpretable data using either P_ETCO₂ or P_TCCO₂ is often challenging. Hirabayashi and coworkers63 studied awake, spontaneously breathing adults and found the bias ± 2 SD of end-tidal and transcutaneous PCO₂ measurements compared to PaCO₂ to be 0.48 ± 8.2 for P_TCCO₂ and −6.3 ± 9.8 mm Hg for P_ETCO₂. The authors concluded that transcutaneous monitoring was more accurate. Casati and colleagues compared P_ETCO₂ and P_TCCO₂ to PaCO₂ in a group of anesthetized mechanically ventilated patients. The exhaled CO₂ was sampled between the endotracheal tube and the ventilator circuit. The P_TCCO₂ was within 3 mm Hg of the PaCO₂ in 21 of 45 pairs sampled, and the P_ETCO₂ was within 3 mm Hg of the PaCO₂ in 7 of 45 pairs sampled. The authors concluded that P_TCCO₂ was more accurate than P_ETCO₂.64

In summary, it appears that both P_TCCO₂ and P_ETCO₂ have clinical utility as surrogates of PaCO₂ during diagnostic studies. At least in some settings, these surrogates may be more useful for following trends in the PaCO₂ than providing a highly accurate estimate of the exact PaCO₂ value_. Use of both methodologies requires careful review of tracings to determine if artifacts are present. P_TCCO₂ is the preferred technology in patients with lung disease, significant mouth breathing, or those who are using supplemental oxygen or mask ventilation. The clinician should recognize that P_TCCO₂ values can occasionally be quite spurious and clinical judgment is needed. When readings do not match the clinical setting, a change in sensor site or recalibration may be needed. P_ETCO₂ is preferred where breath-to-breath changes in PaCO₂ need to be detected. In this setting, the ability to detect an increase in PCO₂ associated with a respiratory event is clinically useful.

The task force concurred with the 2007 manual that whether or not to monitor hypoventilation in adults during diagnostic study or PAP titration is at the discretion of the clinician or investigator [Optional] (Consensus). Monitoring hypoventilation in children during diagnostic study is [Recommended] (Consensus) and during PAP titration is [Optional] (Consensus). The task force recommends that arterial PCO₂, transcutaneous PCO₂, or end-tidal PCO₂ be used for detecting hypoventilation during diagnostic study in both adults and children (Table 4) [Recommended] (Consensus). During PAP titration in both adults and children, either arterial PCO₂ or transcutaneous PCO₂ is the recommended method to detect hypoventilation (Table 4) [Recommended] (Consensus). There are a number of caveats that accompany these recommendations: (1) Sensors should be properly calibrated according to manufacturer specifications. (2) Clinical judgment is essential when assessing the accuracy of end-tidal PCO₂ and transcutaneous PCO₂ readings. The values should NOT be assumed to be accurate surrogates of the arterial PCO₂ when the values do not fit the clinical picture. (3) Transcutaneous PCO₂ should be calibrated with a reference gas according to the manufacturer's recommendations and when the accuracy of the reading is doubtful. (4) End-tidal PCO₂, to be accurate, a plateau in the PCO₂ versus time wave form should be present. Validation of the surrogate PCO₂ with a simultaneous PaCO₂ or capillary gas is ideal but not required.

3.1.8 Summary of Sensor Recommendations

As a reminder, sensors noted here as recommended have corresponding alternative sensors that may only be used if the recommended fails or is inaccurate. At this time alternative sensors are only named for identifying apneas and hypopneas in diagnostic studies. For monitoring of airflow during diagnostic studies, both an oronasal thermal sensor and a nasal pressure transducer should be used [Recommended] (Table 2). For apnea detection, the oronasal sensor is the recommended sensor and the nasal pressure can serve as an alternative sensor [Recommended]. Other alternative apnea sensors include use of RIPsum, RIPflow [both Recommended] and PVDFsum (adults only) or end-tidal PCO₂ (children only) [both Acceptable] (Table 3). During PAP titration studies, the PAP device flow is the signal that should be used for apnea detection [Recommended]. For hypopnea monitoring during diagnostic studies, nasal pressure is the recommended sensor [Recommended]. Alternative hypopnea sensors include an oronasal thermal sensor, RIPsum, RIPflow, dual thoracoabdominal RIP belts [all Recommended], or PVDFsum (adults only) [Acceptable]. During PAP titration studies, the PAP device flow is the sensor to be used for hypopnea detection [Recommended]. For respiratory effort monitoring (Table 2), use esophageal manometry or thoracoabdominal RIP belts (adults and children) [both Recommended] or thoracoabdominal PVDF effort belts (adults only) [Acceptable]. Pulse oximetry is the sensor to be used for oxygen saturation [Recommended]. Detecting snoring is [Optional], and a nasal pressure transducer, piezoelectric sensor, or acoustic sensor (e.g., microphone) should be used [Recommended] (Table 4). Detection of hypoventilation is [Optional] in adults, [Recommended] in children during diagnostic study only, and the following may be used for diagnostic studies: arterial PCO₂, transcutaneous PCO₂, or end-tidal PCO₂ [Recommended] (Table 4). For PAP titration studies, arterial PCO₂ or transcutaneous PCO₂ may be used [Recommended].

4.1.1 Classification of Apnea

The classification of apnea as obstructive, mixed, or central in the 2007 scoring manual is based on respiratory effort. The definitions are consistent with those appearing in previous literature. The Chicago consensus paper did not specifically define mixed apnea because of the lack of reliability in scoring these events. The task force considered combining obstructive and mixed events as well as a revision of the definition of central and mixed apneas to address events where there are only 1 or 2 obstructive breaths (see Figure 4). If one changes the central apnea definitions to allow 1 or 2 obstructed breaths, then a change in the mixed apnea definition must follow. The choice of how many obstructive breaths to allow and still consider an event to be central seems entirely arbitrary. After discussion, the task force recommended that the definitions of obstructive, central, and mixed apnea in the 2007 scoring manual not be revised (Consensus).

3% Versus 4% Oxygen Desaturation

The recommended hypopnea definition requires a 30% or greater drop in nasal pressure excursions for 10 seconds or longer associated with ≥ 4% oxygen desaturation. At the time that the 2007 scoring manual task force examined the literature (pre 2006) there was considerable evidence that respiratory events linked to arterial oxygen desaturation of either ≥ 3 or 4% identified individuals at increased risk of cardiovascular consequences.8,9,70 The current task force found further evidence to support this conclusion. For example, Punjabi et al.71 found respiratory events based on a desaturation of at least 4% were associated with an increased risk of cardiovascular consequences. Further analysis of Wisconsin cohort data and Sleep Heart Health study data suggests that the use of ≥ 3% desaturation criterion yields an AHI that is as predictive of adverse outcomes as an AHI based on ≥ 4% oxygen desaturation criterion.8,9 This is to be expected, given the very high correlation of > 0.95 between the AHIs determined using 3% versus 4% oxygen desaturation.66 Mehra et al. used a definition of hypopnea based on ≥ 3% desaturation and found significant associations between AHI and the risk of atrial fibrillation or complex ventricular ectopy in older men without self-reported heart failure.72 A study by Stamatakis et al. found that levels of desaturation of 2% or 3% were associated with fasting hyperglycemia.73 A recent study using a hypopnea definition requiring ' 3% oxygen desaturation found an association between incident stroke and obstructive sleep apnea.74 Recognizing the apparent equivalence of hypopnea definitions requiring ≥ 3% or ≥ 4% desaturation, the task force has recommended adoption of the 3% criterion. However, it should be noted that using ' 3% instead of ≥ 4% desaturation requirement for defining hypopnea does increase the AHI substantially (Table 6), with median AHI in a general community sample being almost twice as great using a 3% as a 4% criterion.66,75 Therefore, thresholds for identification of the presence and severity of OSA, and for inferring health-related consequences of OSA, must be calibrated to the hypopnea definition employed.

Table 6 Scoring reliability of different respiratory indices (N = 20)

Inclusion of Arousal in Hypopnea Definition

The alternative definition of hypopnea for adults in the 2007 scoring manual requires a 50% or greater drop in nasal pressure excursions for 10 seconds or longer associated with either ' 3% desaturation or an arousal. Whether or not to include arousal as part of the hypopnea definition remains controversial. Opponents of inclusion of arousal in the hypopnea definition cite the fact that the majority of studies have not found an association between arousal frequency and adverse cardiovascular outcomes (independent of arterial oxygen desaturation). Another argument against inclusion of arousal in the hypopnea definition is that the scoring of arousals is said to be less reliable and would consequently reduce the reliability of scoring respiratory events.75 Opponents of inclusion of arousal criteria in the hypopnea definition also argue that the current Medicare/Medicaid hypopnea definition does not consider arousals and that a hypopnea definition based only on flow and oxygen saturation would be applicable to limited channel sleep testing (i.e., out-of-center sleep testing). One can also argue that milder sleep apnea patients would not be excluded if diagnosis of obstructive sleep apnea syndrome was based on the number of apnea, hypopneas, and respiratory effort related arousals (RERAs) per hour of sleep. The ICSD-2 diagnostic criteria for OSA are based on this metric (≥ 15/hour or ≥ 5/hour with symptoms).10

Proponents of inclusion of arousal in the hypopnea definition cite evidence that sleep fragmentation without arterial oxygen desaturation can be associated with symptoms76,77 (e.g., daytime sleepiness) and that treatment with CPAP can improve symptoms and objective sleepiness.5,76 For symptomatic patients with milder OSA and a significant proportion of events associated with arousal but not ≥ 3% desaturation, the AHI may be ≥ 5/hour using the alternative hypopnea definition but not the recommended definition. While a metric based on the AHI + RERA index may be greater than 5/hour in such patients, RERAs are not scored in many sleep centers and not recognized by Medicare. Of interest, if one uses a hypopnea definition based on desaturation or arousal there are relatively few RERA events.78,79 There is a paucity of data concerning symptomatic patients with an AHI < 5/hour using the recommended hypopnea definition. Guilleminault et al.5 analyzed a cohort of 35 lean subjects diagnosed with OSA based on the Chicago consensus paper definition of hypopnea (50% drop in flow OR discernible drop in flow + ≥ 3% desaturation or arousal). The cohort was selected based on demonstrated improvement of OSA after treatment with CPAP or surgery (based on repeat sleep study) and improvement in subjective sleepiness. The original diagnostic studies were rescored, and 40% of the patients had an AHI < 5/hour using a hypopnea definition based only on flow and ≥ 4% oxygen desaturation. Therefore, in the admittedly carefully selected cohort, a significant number of patients (40%) who benefited from treatment would NOT meet diagnostic criteria for OSA based on the recommended hypopnea definition and therefore not qualify for CPAP treatment. There is a paucity of data demonstrating a relationship between increased arousals and adverse cardiovascular outcomes. Supporters of the inclusion of arousal in the hypopnea definition cite biological plausibility of arousals leading to sympathetic nervous system activation and data showing sympathetic activation related to arousals with increased chin EMG activity (movement arousals).80 Cortical arousal stimuli sufficient to induce a K complex have been shown to elicit sympathetic activity.81 Of interest, an analysis of the Cleveland Family Study by Sulit et al.82 did find the arousal index correlated with the risk of hypertension whereas desaturation did not. This study did not evaluate if an AHI definition including arousal or desaturation had a higher association with the presence of hypertension than a hypopnea definition based solely on desaturation. Another study found an association between the arousal index and white matter disease in older adults.83 Using a hypopnea definition that included arousal criteria, a recent study found that the combination of an elevated AHI and daytime sleepiness was predictive of increased mortality in older adults.84 No analyses using a hypopnea definition based on oxygen desaturation alone were reported.

Regarding the issue of hypopnea definition and portable monitoring, proponents of the alternative hypopnea definition point out that this would simply underscore that PSG is more sensitive for detection of significant respiratory events than limited channel testing. PSG would permit scoring of hypopneas based on arousal as well as arterial oxygen saturation. Respiratory events that cause arousal but are associated with relatively minor drops in the arterial oxygen saturation could be identified as hypopneas. This would allow identification and treatment of a wider spectrum of symptomatic patients.

Concerning the scoring reliability of hypopneas, proponents of a hypopnea definition based on arousal as well as desaturation present several arguments. First, a 2007 AASM review concluded that the scoring of arousals when scorers were trained had moderate reliability.77 The review found evidence that visualization of information other than the EEG and EMG during scoring (e.g., respiratory channels) can improve the reliability of arousal scoring. The frequently quoted study of Whitney et al.75 provides information on the reliability of hypopneas associated with arousal. Twenty randomly chosen studies of good quality were scored by each of 3 scorers. The scorers first identified candidate apnea and hypopnea based only on flow (although oximetry tracings were visible) and then combined events with the presence or absence of arousals (based on a single EEG derivation) and various degrees of arterial oxygen desaturation (Table 6). Arousals were scored based on EEG without regard to respiration. The intraclass correlation (ICC) was highest when respiratory events were linked to oxygen desaturation. The ICC correlation was much lower for the scoring of arousals. However, respiratory events based on flow and the presence of arousal had a better ICC (0.77). Moreover, the reliability of events based on flow, oxygen desaturation, or arousal was even higher (Table 6). Of note, arousal scoring was based on a single EEG derivation from data acquired during an unattended study. In the discussion section of the paper, the authors stated that when the two most experienced scorers performed the analysis, the arousal scoring ICC correlation was much higher (0.72). Indeed, subsequent tracking of reliability showed that, over the course of the Sleep Heart Health Study, the ICC for arousal scoring varied between 0.72 and 0.78.83,84 A recent analysis of the data from the Osteoporotic Fractures in Men Sleep Study85 found the interscorer reliability (intraclass correlations coefficients [ICC]) for the arousal index based on central derivations to be 0.80. Of note, in current practice arousals are scored based on frontal, central, and occipital derivations with montages typically showing respiratory channels. The above considerations suggest that adding arousals to the hypopnea definition will not significantly reduce scoring reliability of hypopneas.

30% Versus 50% Drop in Flow

The task force considered the use of different flow criteria in hypopnea definitions. The 2007 scoring manual definitions of hypopnea for adults use either a 30% drop in flow (recommended definition) or 50% drop (alternative definition). The single pediatric definition requires a 50% drop in flow. Given the difficulty of accurately measuring flow or tidal volume in clinical settings, linking a change in flow or tidal volume to a physiological consequence would help identify an event as physiologically relevant. The degree of oxygen desaturation for a given reduction in airflow varies widely between individuals and depends on baseline arterial oxygen desaturation, oxygen stores (lung volumes), obesity, and the presence or absence of lung disease.86,87 Therefore a less than 50% drop in flow could result in significant oxygen desaturations in some individuals, while in others a desaturation may not occur.

Proponents of using the 30% drop argued that a 30% drop should identify a clear change in breathing from baseline. Furthermore, they argue that the associated consequences (desaturation or arousal) are more important for estimation of an event's physiological significance than the magnitude of drop in flow (as a percentage of baseline). That is, a 30% drop in flow associated with 4% desaturation likely has physiological significance but would not be scored if one required a 50% drop in flow. Proponents of a 50% drop cite the current use of this value in the adult alternative definition and the pediatric hypopnea definition.

Hypopnea Summary

The above discussion outlines the difficulties in choosing a single definition for hypopnea. Although there were dissenters, the task force reached consensus on a definition of a hypopnea rule in adults using a 30% drop in the nasal pressure excursion for 10 seconds or greater associated with ≥ 3% desaturation OR an arousal. The majority of the task force felt that a hypopnea definition based only on desaturation would result in misdiagnosis of some patients in whom respiratory events fragment sleep but result in minor drops in the SpO₂. While there seems little doubt that cardiovascular morbidity is associated with oxygen desaturation, the goals of OSA treatment address a much wider range of symptoms including daytime sleepiness, insomnia, and non-restorative sleep. The task force also recognizes that the proposed definition of hypopnea is not currently accepted by the Centers for Medicare and Medicaid Services (CMS) reimbursement. For Medicaid and Medicare patients the use of a hypopnea definition based on a 30% drop in flow and 4% or greater desaturation will need to be used to ensure reimbursement until reimbursement policies are changed to reflect the new hypopnea definition. Following the logic of the proposed revised apnea definition, the requirement that the qualifying drop in flow must occupy > 90% of the event duration was removed from the hypopnea definition.

Hypopnea Rule for Adults [Recommended] (Consensus)

Score a respiratory event as a hypopnea if all of the following are met:

1. The peak signal excursions drop by ≥ 30% of pre-event baseline using nasal pressure (diagnostic study), PAP device flow (titration study), or an alternative hypopnea sensor.

2. The duration of the ≥ 30% drop in signal excursions is ≥ 10 seconds.

3. There is ≥ 3% oxygen desaturation from pre-event baseline or the event is associated with an arousal.

   Note: If necessary, the number of hypopneas using a definition requiring ≥ 30% drop in flow for ≥ 10 seconds that is associated with ≥ 4% desaturation may additionally be reported to qualify a patient for PAP reimbursement (e.g., Medicaid or Medicare patients).

4.2.1 Classification of Hypopnea

The task force discussed the clinical utility of scoring hypopneas as either obstructive or central events. In the 2007 scoring manual, the definition of Cheyne-Stokes breathing (CSB) does mention central hypopnea. The CMS criteria for reimbursement of a PAP device with a backup rate requires that 50% of events be central in nature.88 Some patients with CSB or complex sleep apnea have a large proportion of central hypopneas. Scoring central hypopneas would allow them to qualify for a device with a backup rate. In addition, as will be discussed below, many of the publications on CSB in heart failure include central hypopneas in computing an AHI.89–93 As the scoring of hypopneas as central or obstructive is clinically useful, the task force sought to define these two events, taking note of the definitions used in other publications. The Chicago consensus paper9 defined central apnea/hypopnea events as those events with a reduction in airflow and a clear reduction in esophageal pressure swings from baseline that parallels chronologically the reduction in airflow. The 2007 scoring manual only states that “classification of a hypopnea as obstructive, central, or mixed should not be performed without a quantitative assessment of ventilatory effort (esophageal manometry, calibrated RIP, or diaphragmatic/intercostal EMG).”1 This presents a problem as calibrated RIP excursions do not always reflect the magnitude of respiratory effort (as measured by esophageal pressure excursions) and esophageal manometry is rarely used.

In general, an obstructive hypopnea is one in which the reduction in airflow is mainly due to increased upper airway resistance, and a central hypopnea is one in which the reduction in flow is mainly due to a reduction in ventilatory effort. The fact that there can be some overlap should be noted as obstructive hypopneas may be characterized by an initial reduction in effort followed by a progressive increase until the event is terminated (Figure 5). Obstructive hypopneas are usually associated with flattening of the inspiratory portion of the nasal pressure (or PAP device flow) waveform, often associated with snoring, and sometimes associated with thoracoabdominal paradox (Figure 6). Central hypopneas are typically characterized by absence of flattening of the inspiratory portion of the nasal pressure or PAP flow wave form (or flattening is present but unchanged from baseline breathing) and absence of thoracoabdominal paradox in the thoracic and abdominal RIP band excursions (Figure 7).

The task force reviewed definitions of central and obstructive hypopnea in the literature with an emphasis on articles discussing CSB.89–93 One study defined a hypopnea as obstructive versus central if paradoxical thoracoabdominal excursions were noted or when the reduction in flow was out of proportion to the decrease in thoracoabdominal excursions (e.g., in central hypopnea the decrease in flow was proportional to the decrease in effort).90 Most articles have defined a central hypopnea on the basis of a lack of paradox in thoracoabdominal RIP belts and/or absence of flattening in the nasal pressure signal.89,91 Of note, in some studies hypopnea was defined based on a 50% drop in tidal volume (using RIP) without a requirement for associated desaturation or arousal.91 Lanfranchi et al. defined central hypopnea as ≥ 50% decrease in RIPsum lasting 10 seconds or longer followed by ≥ 2% desaturation.92 In this study, subjects with an obstructive AHI ≥ 5/hour were excluded. Ryan and coworkers defined central hypopnea as ≥ 50% decrease in RIPsum lasting 10 seconds or longer with in-phase thoracoabdominal motion and absence of flow limitation on the nasal pressure signal.93 In a study of CPAP and heart failure, Javaheri classified hypopnea as obstructive if paradoxical thoracoabdominal excursions occurred or if the airflow decreased out of proportion to the reduction in the thoracoabdominal excursions; otherwise hypopneas were classified as central.90

Some members of the task force felt that some mention of respiratory effort should be made in the definitions of central and obstructive hypopnea. Others noted that thoracoabdominal movements (RIP excursions) are not a direct measure of the amount of respiratory effort (e.g., esophageal pressure excursions). Task force members pointed out that a decrease in RIP excursions cannot differentiate obstructive and central hypopneas because the excursions may decrease in both types of hypopneas (see Figures 6 and 7). Although a disproportionate increase in effort when compared to flow can be indicative of obstruction, this is difficult to operationalize. The task force recommended the following definitions for scoring hypopneas as obstructive or central [Recommended] (Consensus) but also recommended that performing such scoring be [Optional] (Consensus). Such a separation of hypopneas into central or obstructive is not clinically indicated in the majority of patients.

Classifying Hypopnea in Adults [Recommended] (Consensus)

If electing to score obstructive hypopneas, score a hypopnea as obstructive if ANY of the following criteria are met:

1. Snoring during the event

2. Increased inspiratory flattening of the nasal pressure or PAP device flow signal compared to baseline breathing

3. Associated thoracoabdominal paradox occurs during the event but not during pre-event breathing

If electing to score central hypopneas, score a hypopnea as central if NONE of the following criteria are met:

1. Snoring during the event

2. Increased inspiratory flattening of the nasal pressure or PAP device flow signal compared to baseline breathing

3. Associated thoracoabdominal paradox occurs during the event but not during pre-event breathing

5.2.1 Classification of Pediatric Apnea

The proposed revised obstructive apnea definition is similar to the one recommended for adults. The central apnea definition differs from adults as normal infants and children may have a considerable number of short central pauses in respiration not associated with desaturation or arousal. Such events are felt to be within normal variation limits.51,113,114 The central apnea definition is similar to the 2007 scoring manual central apnea definition except that a provision for children less than 1 year of age has been added. In these individuals, a central apnea is believed to be significant if followed by significant bradycardia (a decrease in heart rate to < 50 beats per minute for at least 5 seconds or < 60 beats per minute for 15 seconds).113,114 In one study of normal infants, none had a heart rate less than 55 beats per minute for more than 10 seconds.113 The proposed pediatric mixed apnea definition differs from the adult definition in that the central portion may be present before or after the obstructive portion of the event. This option was added at the request of pediatric task force members who thought this was a common clinical occurrence. An example of a mixed apnea with the central portion following the obstructive portion in a 3-year-old child is shown in Figure 11.

Classification of Pediatric Apnea [Recommended] (Consensus)

Score a respiratory event as an obstructive apnea if it meets apnea criteria for at least the duration of 2 breaths during baseline breathing and is associated with the presence of respiratory effort throughout the entire period of absent airflow.

Score a respiratory event as a central apnea if it meets apnea criteria, is associated with absent inspiratory effort throughout the entire duration of the event, and at least one of the following is met:

1. The event lasts 20 seconds or longer.

2. The event lasts at least the duration of two breaths during baseline breathing and is associated with an arousal or ≥ 3% oxygen desaturation.

3. For infants younger than 1 year of age, the event lasts at least the duration of two breaths during baseline breathing and is associated with a decrease in heart rate to less than 50 beats per minute for at least 5 seconds or less than 60 beats per minute for 15 seconds.

Score a respiratory event as a mixed apnea if it meets apnea criteria for at least the duration of 2 breaths during baseline breathing and is associated with absent respiratory effort during one portion of the event and the presence of inspiratory effort in another portion, regardless of which portion comes first.

5.3.1 Classification of Pediatric Hypopnea

The recommended scoring rules for scoring pediatric hypopneas as either central or obstructive are the same as for adults [Recommended] (Consensus), and classifying hypopneas in pediatric patients should be considered as [Optional] (Consensus).