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Volume 15 No. 09
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Accepted Papers

Letters to the Editor

Autocycling During Noninvasive Positive Pressure Ventilation as a Factor for Severe Syncope: Exciting Observation, But Needs More Scrutiny

Habib Md Reazaul Karim, MD, DNB, IDCCM1; Antonio M. Esquinas, MD, PhD, FCCP2
1Department of Anaesthesiology and Critical Care All India Institute of Medical Sciences, Raipur, India; 2International School of Non-invasive Ventilation, Hospital General Universitario Morales Meseguer, Murcia, Spain


Karim HMR, Esquinas AM. Autocycling during noninvasive positive pressure ventilation as a factor for severe syncope: exciting observation, but needs more scrutiny. J Clin Sleep Med. 2019;15(9):1377.

We read the case report by Mu et al with great interest and want to congratulate the authors on the original observation to explain how autocycling could induce a clinical major adverse complication.1 However, there are some interesting aspects that could help provide a clear vision of this relationship.

The authors have monitored oxygenation during syncope, but it is to be noted that the monitoring by finger probe pulse oximetry poorly correlates with saturation during apnea- induced hypoxemia.2

Chronic hypoventilation and sleep apnea are often associated with pulmonary hypertension and cardiac rhythm alterations. Although the authors indicate that there was no rhythm disturbance during the event, it is essential to know whether the patient had pulmonary artery hypertension, which is reported to be associated with nocturnal events.3

The modern ventilators are capable of leak compensation to a great extent, and autotriggering could be influenced by leak-compensating capabilities, set triggering sensitivity, etc.4 The effect of high inspiratory positive airway pressure that can induce low cardiac output and hypotension also needs to be considered.5 These can act as a potential mechanism of inadequate perfusion and syncope, leading to low peripheral oxygen saturation reading and carbon dioxide production.

We believe that the aforementioned information will help the readers to better accept the authors’ exciting and new observation.


The authors have seen and approved the final manuscript. The authors report no conflicts of interest.



Mu S, Rautela L, Howard ME, Hannan L. Autocycling during noninvasive positive pressure ventilation producing a prolonged severe apnea and syncope. J Clin Sleep Med. 2019;15(4):663–665. [PubMed]


Lindholm P, Blogg SL, Gennser M. Pulse oximetry to detect hypoxemia during apnea: comparison of finger and ear probes. Aviat Space Environ Med. 2007;78(8):770–773. [PubMed]


Izzo A, McSweeney J, Kulik T, Khatwa U, Kothare SV. “Nocturnal seizures” in idiopathic pulmonary arterial hypertension. J Clin Sleep Med. 2013;9(10):1091–1092. [PubMed Central][PubMed]


Mehta S, McCool FD, Hill NS. Leak compensation in positive pressure ventilators: a lung model study. Eur Respir J. 2001;17(2):259–267. [PubMed]


Marini JJ, Culver BH, Butler J. Mechanical effect of lung distention with positive pressure on cardiac function. Am Rev Respir Dis. 1981;124(4):382–386. [PubMed]