High-Flow Oxygen Therapy in Tracheostomized Subjects With Prolonged Mechanical Ventilation: A Randomized Crossover Physiologic Study.

BACKGROUND: High-flow oxygen therapy via tracheostomy (HFT) can be used in tracheostomized patients during ventilator disconnection. The physiologic effects of this technique are unknown. We hypothesized that HFT would reduce inspiratory effort and improve breathing pattern compared to conventional oxygen therapy via T-tube. This study aimed to evaluate the physiologic effects of HFT compared to conventional O2 in patients with prolonged mechanical ventilation. METHODS: A randomized crossover physiologic study was conducted in adult tracheostomized patients who experienced temporary periods of ventilator disconnection. Subjects were ventilated with pressure support ventilation (PSV) for 15 min and were then randomly assigned to HFT or conventional O2 via T-tube for 30 min. After a washout period, subjects were switched to the other system. Esophageal pressure (Pes), breathing frequency, blood pressure, heart rate, [Formula: see text], and transcutaneously measured pressure of carbon dioxide ([Formula: see text]) were recorded. The primary outcome was inspiratory effort as determined by the simplified esophageal pressure-time product (sPTPes). Secondary outcomes were Pes swing, breathing frequency, heart rate, mean arterial pressure, [Formula: see text], and [Formula: see text] between groups. RESULTS: Twenty-two subjects were enrolled: sPTPes per minute was significantly higher with HFT and conventional O2 compared to PSV (153.5 ± 97.9, 163.5 ± 111.3, and 86.8 ± 51.1 cm H2O × s/min, respectively, P = .001), but it was not different between HFT and conventional O2 (P = .72). Breathing frequency increased significantly after switching from PSV to HFT and conventional O2 (23 ± 4 vs 26 ± 6 and 23 ± 4 vs 27 ± 5 breaths/min, respectively, P = .001). [Formula: see text] was higher with conventional O2 compared to HFT (P = .02). No differences in [Formula: see text], mean arterial pressure, or heart rate were observed between HFT and conventional O2. CONCLUSIONS: Inspiratory effort and breathing frequency increased significantly during unassisted breathing compared to PSV in tracheostomized subjects, but HFT via tracheostomy provided no measurable additional physiologic benefit compared to O2 therapy via T-tube.

Intrathoracic Airway Closure Impacts CO2 Signal and Delivered Ventilation during Cardiopulmonary Resuscitation.

RATIONALE: End-tidal CO2 (EtCO2) is used to monitor cardiopulmonary resuscitation (CPR), but it can be affected by intrathoracic airway closure. Chest compressions induce oscillations in expired CO2, and this could reflect variable degrees of airway patency. OBJECTIVES: To understand the impact of airway closure during CPR, and the relationship between the capnogram shape, airway closure, and delivered ventilation. METHODS: This study had three parts: 1) a clinical study analyzing capnograms after intubation in patients with out-of-hospital cardiac arrest receiving continuous chest compressions, 2) a bench model, and 3) experiments with human cadavers. For 2 and 3, a constant CO2 flow was added in the lung to simulate CO2 production. Capnograms similar to clinical recordings were obtained and different ventilator settings tested. EtCO2 was compared with alveolar CO2 (bench). An airway opening index was used to quantify chest compression-induced expired CO2 oscillations in all three clinical and experimental settings. MEASUREMENTS AND MAIN RESULTS: A total of 89 patients were analyzed (mean age, 69 ± 15 yr; 23% female; 12% of hospital admission survival): capnograms exhibited various degrees of oscillations, quantified by the opening index. CO2 value varied considerably across oscillations related to consecutive chest compressions. In bench and cadavers, similar capnograms were reproduced with different degrees of airway closure. Differences in airway patency were associated with huge changes in delivered ventilation. The opening index and delivered ventilation increased with positive end-expiratory pressure, without affecting intrathoracic pressure. Maximal EtCO2 recorded between ventilator breaths reflected alveolar CO2 (bench). CONCLUSIONS: During chest compressions, intrathoracic airway patency greatly affects the delivered ventilation. The expired CO2 signal can reflect CPR effectiveness but is also dependent on airway patency. The maximal EtCO2 recorded between consecutive ventilator breaths best reflects alveolar CO2.