Portable Respiratory Monitor Research Articles

Sleep Apnea Treatment After Stroke (SATS) Trial: Is It Feasible?

Sleep apnea affects more than half of patients with acute ischemic stroke and is associated with poor stroke outcome. This pilot study assessed the feasibility of a randomized, sham-controlled continuous positive airway pressure (CPAP) trial in subjects with acute ischemic stroke. Subjects identified with sleep apnea based on an apnea-hypopnea index≥5 on overnight polysomnography or portable respiratory monitoring within 7 days of onset of stroke symptoms were randomized to receive active or sham CPAP for a 3-month period. Objective usage was ascertained by compliance data cards. Subjects, treating physicians, and outcome assessors were masked to intervention allocation. Among 87 subjects who provided consent, 74 were able to complete sleep apnea screening, 54 (73%) of whom had sleep apnea. Thirty-two subjects agreed to randomization. Of the 15 subjects who commenced active titration, 11 (73%) took the device home, and 8 (53%) completed the 3-month follow-up. Of the 17 subjects who commenced sham titration, 11 (65%) took the sham device home and completed the 3-month follow-up. The median cumulative usage hours over the 90 days were similar in the active group (53 hours; interquartile range, 22-173 hours) and the sham group (74 hours; interquartile range, 17-94 hours), and blinding to subject condition was successfully maintained. This first-ever randomized, sham-controlled trial of CPAP in patients with recent stroke and sleep apnea demonstrates that sham treatment can be an effective placebo.

Positional therapy in ischemic stroke patients with obstructive sleep apnea

Background Obstructive sleep apnea (OSA) is common in stroke patients and is associated with poor functional outcome. The effects of positional therapy in ischemic stroke patients with OSA have not been investigated. We tested the hypothesis that ischemic stroke patients have less severe OSA during positional therapy that promotes nonsupine positioning. Methods We conducted a randomized, controlled, cross-over study. Sleep apnea screening studies were performed on two consecutive nights, using a portable respiratory monitoring system, on 18 subjects within the first 14 days of ischemic stroke. An apnea–hypopnea index (AHI) ⩾5 established the diagnosis of OSA. Subjects were randomized to positional therapy that included the use of a therapeutic pillow on either the first or second night. On the control night, subjects used the hospital pillow and were positioned ad lib. Treatment effect on AHI was estimated using a repeated measures model. Results All ischemic stroke subjects studied had OSA. The predominantly male group had a median age of 58 years, BMI of 29 kg/m 2, NIH Stroke Scale score of 3, and a median AHI on the nontherapeutic night of 39 (interquartile range: 21–54). Positional therapy reduced the amount of supine positioning by 36% (95% CI: 18–55% ( P < 0.001)). The AHI was reduced by 19.5% (95% CI: 4.9–31.9% ( P = 0.011)), when using positional therapy compared to sleeping ad lib. Conclusions Positional therapy to avoid supine positioning modestly reduces sleep apnea severity after ischemic stroke, and may therefore improve outcomes.

Diagnosis of Obstructive Sleep Apnea Syndrome and Its Outcomes With Home Portable Monitoring

The use of portable respiratory monitoring (PM) has been proposed for the diagnosis of obstructive sleep apnea syndrome (OSAS), but most studies that validate PM accuracy have not followed the best standards for diagnostic test validation. The objective of the present study was to evaluate the accuracy of PM performed at home to diagnose OSAS and its outcomes after first validating PM in the laboratory setting by comparing it to polysomnography (PSG). Patients with suspected OSAS were submitted, in random order, to PM at the sleep laboratory concurrently with PSG (lab-PM) or at home-PM. The diagnostic performance was assessed by sensitivity, specificity, positive and negative predictive values, positive likelihood ratio (+LR), negative likelihood ratio (-LR), intraclass correlation coefficients, kappa statistic, and Bland-Altman plot. One hundred fifty-seven subjects (73% men, mean age +/- SD, 45 +/- 12 yr) with an apnea-hypopnea index (AHI) of 31 (SD +/- 29) events/h were studied. Excluding inadequate recordings, 149 valid comparisons with lab-PM and 121 with unattended home-PM were obtained. Compared to PSG for detecting AHI > 5, the lab-PM demonstrated sensitivity of 95.3%, specificity of 75%, +LR of 3.8, and -LR of 0.11; the home-PM exhibited sensitivity of 96%, specificity of 64%, +LR of 2.7, and -LR of 0.05. Kappa statistics indicated substantial correlation between PSG and PM results. Bland-Altman plot showed smaller dispersion for lab-PM than for home-PM. Pearson product moment correlation coefficients among the three AHIs and clinical outcomes were similar, denoting comparable diagnostic ability. This study used all available comparison methods to demonstrate accuracy of PM in-home recordings similar to that of repeated PSGs. PM increases the possibility of correctly diagnosing and effectively treating OSAS in populations worldwide.

Comparison of the work of breathing imposed by three anaesthetic breathing systems in children

Introduction There is concern that the resistance of the valves in circle systems may impose an unacceptable respiratory load in children (1). In this study we compared the work of breathing imposed by the Bain, Jackson Rees and the circle systems in anaesthetised spontaneously breathing children.Methods Following local ethics committee approval and the written informed consent of a parent, 12 children, aged 2–6 years, ASA grades I–II scheduled for routine genital surgery (e.g. circumcision) were recruited [Weight 14.4 ± 2.9 kg and age 3.02 ± 1.3 years (meant SD)]. Patients were premedicated with midazolam 0.5 mg·kg−1. Anaesthesia was induced by inhalation of 66% N2O in O2 and sevoflurane 8%, and the trachea was intubated. Caudal analgesia was provided using bupivacaine 0.25% in a dose of 0.5 mg·kg−1. Anaesthesia with spontaneous ventilation was maintained with 66% N2O in O2, and sevoflurane 2–4%. Routine monitoring consisted of ECG, pulse oximetry, capnography and non‐invasive blood pressure.When anaesthesia had been stable for at least 15 min, the patients were attached to three different breathing systems in random succession for 10 min: 1, a Circle (Draeger Julian); 2, a Bain; 3, a Jackson Rees system. At the end of these 10 min periods, work of breathing was measured using a computerised, portable respiratory monitor (CP‐100 Pulmonary Monitor, Bear Medical). Work of breathing (W) was calculated by measuring the area enclosed in the oesophageal pressure‐volume loop (2). Oesophageal pressure was measured using a disposable balloon catheter (Smartcath, Bear Medical) and flow was measured using a disposable flow transducer (Varflex, Bear Medical). All equipment was calibrated in accordance with the manufacturers instructions prior to use.The total work of breathing (W) was expressed as Joules per litre of ventilation (J·l−1). This was compared between breathing systems using anova. P &lt; 0.05 was considered statistically significant.Results The results are presented in Table 1. Direct measurements and calculated variables (mean ± SD) Circle Bain Jackson – Rees Work of breathing (J·l−1) 0.34 ± 0.1 0.36 ± 0.07 0.34 ± 0.09 Peak inspiratory flow rate (l·s−1) 0.19 ± 0.03 0.20 ± 0.04 0.20 ± 0.04 Peak expiratory flow rate (l·s−1) 0.16 ± 0.03 0.14 ± 0.03 0.16 ± 0.03 Δ Poes(cmH2O) 5.5 ± 2.71 6.3 ± 1.49 5.9 ± 1.83 Minute ventilation (l·min−1) 2.9 ± 0.6 2.8 ± 0.7 2.9 ± 0.6 End‐tidal CO2 (kPa) 7.8 ± 0.9 7.7 ± 0.9 7.0 ± 2.4 Δ Poes = difference between end‐expiratory oesophageal pressure and lowest oesophageal pressure. Conclusions Our results indicate that there was no difference in the total work of breathing in children attached to a circle system compared to a Bain or Jackson Rees systems.Acknowledgements This work was supported by a grant from Draeger UK Ltd.

Using Tracheal Pressure to Trigger the Ventilator and Control Airway Pressure During Continuous Positive Airway Pressure Decreases Work of Breathing

We evaluated the difference in work of breathing (WOB) during spontaneous ventilation with continuous positive airway pressure (CPAP) among three methods of triggering the ventilator: conventional pressure triggering, tracheal pressure triggering, and flow-by triggering. In an in vitro model of the respiratory system consisting of a bellows (lungs) in a plastic canister (chest wall), spontaneous ventilation was simulated with a piston-driven pump (respiratory muscles). Data were recorded during CPAP of 5 cm H2O (model 7200ae ventilator, Puritan-Bennett, Overland Park, Kan) at peak sinusoidal inspiratory flow rate demands of 60 and 80 L/min and airway resistances of 5 and 20 cm H2O/L/s, with the demand flow system triggered by conventional pressure, tracheal pressure, or flow. Under each condition, tidal volume, pressure-time product (PTP), WOB, and changes in intrapleural pressure (Ppl) and airway pressure were recorded in real time by means of a computerized portable respiratory monitor (model CP-100, Bicore, Irvine, Calif). The Ppl was measured from within the canister, tidal volume by positioning a flow sensor between the Y-piece of the breathing circuit and the endotracheal tube (ETT), and airway pressure from a catheter attached to the flow sensor. The WOB was calculated by the monitor in real time. Changes in Ppl were greatest with conventional pressure triggering, less with flow-by triggering, and least with tracheal pressure triggering. The WOB was significantly lower (approximately 50%) with tracheal pressure triggering than with the other two methods. With tracheal pressure triggering only, an effect similar to that of pressure support ventilation (PSV) occurred, which accounted in part for the significant decrease in WOB. The PTP/breath ratio correlated strongly and was a good predictor of WOB (r2 = 0.95). Compared with conventional pressure and flow-by methods, triggering with tracheal pressure decreased WOB significantly. This method of triggering may improve patient-ventilator interaction.

Decreasing imposed work of the breathing apparatus to zero using pressure-support ventilation.

To apply pressure-support ventilation with the goal of decreasing the imposed work of the breathing apparatus (endotracheal tube, breathing circuit tubing, and the ventilator's demand-flow system) to zero and to evaluate a clinical method of measuring the imposed work of breathing. A prospective evaluation of adult and pediatric patients receiving mechanical ventilatory support. A surgical and a pediatric intensive care unit in a university hospital. Fifteen patients (11 adult and four pediatric), who were diagnosed with acute respiratory failure from various etiologies, and who were intubated and spontaneously breathing, received continuous positive airway pressure and pressure-support ventilation. Imposed work of the breathing apparatus was calculated by integrating pressure measured at the tracheal end of the endotracheal tube from a narrow air-filled catheter and the change in volume from a miniature pneumotachograph (flow sensor) positioned between the "Y" piece of the breathing circuit and the endotracheal tube. Pressure and volume signals were directed to a computerized, portable respiratory monitor (Bicore Monitoring Systems) that provides real-time display of the pressure-volume (work) loops and calculation of the imposed work. Imposed work was measured at 0 cm H2O pressure-support ventilation, and then incremental levels of pressure-support ventilation were applied until the imposed work decreased to zero. Imposed work decreased in a quadratic fashion after incremental levels of pressure-support ventilation (r = -.83 [r2 = .69]; p < .001). At pressure-support ventilation level of 0 cm H2O, the imposed work was 0.60 +/- 0.17 joule/L. At mean pressure-support ventilation levels of 13.5 +/- 4.8 cm H2O, imposed work decreased to 0 joule/L. Ideally, the imposed work of the breathing apparatus should be zero to decrease the afterload on the ventilatory muscles and, thus, the patient's work of breathing. Eliminating the imposed work is achieved using appropriate levels of pressure-support ventilation. We describe an easily applied, practical method of measuring imposed work using a commercially available, portable, bedside respiratory monitor. We recommend that all patients diagnosed with respiratory failure and compromised pulmonary mechanics and who are intubated and breathing spontaneously, receive at least a minimal level of pressure-support ventilation that results in zero breathing apparatus-imposed work of breathing.