Nocturnal monitoring of home non-invasive ventilation: the contribution of simple tools such as pulse oximetry, capnography, built-in ventilator software and autonomic markers of sleep fragmentation

Complex respiratory events, which may have a detrimental effect on both quality of sleep and control of nocturnal hypoventilation, occur during sleep in patients treated with non-invasive ventilation (NIV). Among these events are patient-ventilator asynchrony, increases in upper airway resistance (with or without increased respiratory drive) and leaks. Detection of these events is important in order to select the most appropriate ventilator settings and interface. Simple tools can provide important information when monitoring NIV. Pulse oximetry is important to ensure that adequate oxygen saturation is provided and to detect either prolonged or short and recurrent desaturations. However, the specificity of pulse oximetry tracings during NIV is low. Transcutaneous capnography helps discriminate between hypoxaemia related to ventilation/ perfusion mismatch and hypoventilation, documents correction of nocturnal hypoventilation and may detect ventilator-induced hyperventilation, a possible cause for central apnoea/hypopnoea and glottic closure. Data provided by ventilator software help the clinician by estimating ventilation, tidal volume, leaks and the rate of inspiratory or expiratory triggering by the patient, although further validation of these signals by independent studies is indicated. Finally, autonomic markers of sympathetic tone using signals such as pulse wave amplitude of the pulse oximetry signal can provide reliable information of sleep fragmentation. INTRODUCTION Home non-invasive ventilation (NIV) aims to correct daytime and nocturnal hypoventilation and associated symptoms and to ensure adequate nocturnal oxygen saturation measured by pulse oximetry (SpO2). During sleep, specific respiratory events may occur resulting both from sleep-related physiological changes and use of NIV. Among these events, described in another article in this series, are repetitive leaks, upper airway instability and residual obstructive events, recurrent decreases in ventilatory command with or without glottic closure, or patient-ventilator asynchrony. An appropriate strategy for monitoring these respiratory events is necessary. Monitoring tools can be limited to the recognition of their consequences such as oxygen desaturation or increases in transcutaneous carbon dioxide tension (PtcCO2). The latest generation of home ventilators are often equipped with sophisticated built-in software capable of recording a wide range of parameters over several months, and thus offering information to the clinician on items such as compliance and leaks, among many other respiratory parameters. This review describes the contributions, limits and caveats of non-invasive assessment of NIV during sleep through simple techniques such as pulse oximetry, combined capnography and pulse oximetry, built-in ventilator software and autonomic markers of sleep fragmentation. More complex and complete evaluations can be performed by polygraphic or polysomnographic recordings which will be discussed in a later article in this series. PULSE OXIMETRY AND NON-INVASIVE VENTILATION Nocturnal oxygen desaturation is considered as one of the major determinants of adverse neurocognitive and cardiovascular consequences occurring during chronic respiratory failure and sleep apnoea syndrome. Pulse oximetry has the advantages of simplicity, short set-up time and short time response (seconds); disadvantages are motion artefacts and sensitivity to perfusion. Information provided by pulse oximetry also depends on the device used and its settings, particularly signal averaging time; the magnitude of desaturations decreases when averaging time increases and this influences the sensitivity of the technique. In the field of sleep apnoea it has been shown that the number of hypopnoeas associated with desaturations of $4% could change significantly according to the device used and this could affect clinical decisions. Sampling frequency (on average 25 times/s) and signal averaging time may vary considerably between devices (reported range 2e21/s). New generation pulse oximeters usually average SpO2 signals over <10 s; high speed signal averaging also improves detection of motion artefacts, which can be quite frequent in subjects with sleep-disordered breathing. 9 The accuracy of SpO2 measurements reported in sleep studies is 2e6% compared with arterial blood-derived determinations of haemoglobin saturation which are in the Division of Pulmonary Diseases, Geneva University Hospital, Geneva, Switzerland Pole Rééducation et Physiologie et Laboratoire HP2, INSERM ERI 0017, Université Joseph Fourier, Grenoble, France Association médico-technique AGIR à dom, Meylan, France Correspondence to Jean Paul Janssens, Centre Antituberculeux, Division of Pulmonary Diseases, Geneva University Hospital, Rue Gabrielle Perret-Gentil 4, 1211 Geneva 14, Switzerland; [email protected] Received 1 April 2010 Accepted 19 August 2010 Published Online First 22 October 2010 438 Thorax 2011;66:438e445. doi:10.1136/thx.2010.139782 Review series group.bmj.com on July 6, 2017 Published by http://thorax.bmj.com/ Downloaded from