Different modes of assisted ventilation in patients with acute respiratory failure

The aim of the present study was to verify that the patient/ventilator interaction is similar, regardless of the mode of assisted mechanical ventilation (i.e. pressure- or volume-limited) used, if tidal volume (VT) and peak inspiratory flow (PIF) are matched. Therefore, the authors compared the effects of three different modes of assisted ventilation on the work of breathing (WOB) and gas exchange in patients with acute respiratory failure. For Protocol 1, in seven patients, the authors compared pressure support, assist pressure control and assist control (with square and decelerating wave inspiratory flow pattern) set to deliver the same VT and PIF. For Protocol 2, in another 10 patients, the authors compared pressure support and assist control with high (0.8 L x s(-1)) and low (0.6 L x s(-1)) PIFs set to deliver the same VT. In Protocol 1, there was no difference in WOB and gas exchange between the three modes of assisted ventilation tested. In Protocol 2, the decrease of PIFs during assist control significantly increased WOB. In conclusion, different modes of assisted ventilation similarly reduce work of breathing and provide adequate gas exchange at fixed tidal volume and peak inspiratory flow only. During assist control, tidal volume and peak inspiratory flow (set by the physician) are the main determinants of the patient/ventilator interaction

Sigh in supine and prone position during acute respiratory distress syndrome

Interventions aimed at recruiting the lung of patients with acute respiratory distress syndrome (ARDS) are not uniformly effective. Because the prone position increases homogeneity of inflation of the lung, we reasoned that it might enhance its potential for recruitment. We ventilated 10 patients with early ARDS (PaO2/FIO2, 121 +/- 46 mm Hg; positive end-expiratory pressure, 14 +/- 3 cm H2O) in supine and prone, with and without the addition of three consecutive "sighs" per minute to recruit the lung. Inspired oxygen fraction, positive end-expiratory pressure, and minute ventilation were kept constant. Sighs increased PaO2 in both supine and prone (p < 0.01). The highest values of PaO2 (192 +/- 41 mm Hg) and end-expiratory lung volume (1840 +/- 790 ml) occurred with the addition of sighs in prone and remained significantly elevated 1 hour after discontinuation of the sighs. The increase in PaO2 associated with the sighs, both in supine and prone, correlated linearly with the respective increase of end-expiratory lung volume (r = 0.82, p < 0.001). We conclude that adding a recruitment maneuver such as cyclical sighs during ventilation in the prone position may provide optimal lung recruitment in the early stage of ARDS

Continuous positive airway pressure delivered with a "helmet" : effects on carbon dioxide rebreathing

OBJECTIVE: The "helmet" has been used as a novel interface to deliver noninvasive ventilation without applying direct pressure on the face. However, due to its large volume, the helmet may predispose to CO2 rebreathing. We hypothesized that breathing with the helmet is similar to breathing in a semiclosed environment, and therefore the PCO2 inside the helmet is primarily a function of the subject's CO2 production and the flow of fresh gas through the helmet. DESIGN: Human volunteer study. SETTING: Laboratory in a university teaching hospital. SUBJECTS: Eight healthy volunteers. INTERVENTIONS: We delivered continuous positive airway pressure (CPAP) with the helmet under a variety of ventilatory conditions in a lung model and in volunteers. MEASUREMENTS AND MAIN RESULTS: Gas flow and CO2 concentration at the airway were measured continuously. End-tidal PCO2, CO2 production, and ventilatory variables were subsequently computed. We found that a) when CPAP was delivered with a ventilator, the inspired CO2 of the volunteers was high (12.4 +/- 3.2 torr [1.7 +/- 0.4 kPa]); b) when CPAP was delivered with a continuous high flow system, inspired CO2 of the volunteers was low (2.5 +/- 1.2 torr [0.3 +/- 0.2 kPa]); and c) the inspired CO2 calculated mathematically for a semiclosed system model of CO2 rebreathing was highly correlated with the values measured in a lung model (r = .97, slope = 0.92, intercept = -1.17, p < .001) and in the volunteers (r = .94, slope = 0.96, intercept = 0.90, p < .001). CONCLUSIONS: a) The helmet predisposes to CO2 rebreathing and should not be used to deliver CPAP with a ventilator; b) continuous high flow minimizes CO2 rebreathing during CPAP with the helmet; and c) minute ventilation and Pco2 should be monitored during CPAP with the helmet

Lateral-horizontal patient position and horizontal orientation of the endotracheal tube to prevent aspiration in adult surgical intensive care unit patients : a feasibility study

BACKGROUND: Recent data suggest that during mechanical ventilation the lateral-horizontal patient position (in which the endotracheal tube is horizontal) decreases the risk of ventilator-associated pneumonia, compared to the recommended semi-recumbent position (in which the endotracheal tube slopes downward into the trachea). We tested the feasibility of the lateral-horizontal patient position, measured the incidence of aspiration of gastric contents, and watched for any adverse effects related to the lateral-horizontal position. METHODS: Ten adult intensive care unit patients were ventilated for 64 hours in the standard semi-recumbent position, and ten for 12 24 hours in the lateral-horizontal position. Tracheal secretions were collected every 8 hours and every 4 hours, respectively, and tested for pepsin, which is a marker of gastric contents. We also recorded clinical, physiologic, and outcome variables. RESULTS: The patients remained stable during ventilation in the lateral-horizontal position, and no adverse events occurred. Pepsin was detected in the trachea of 7 semi-recumbent patients and in five of the lateral-horizontal patients (P = .32). The number of ventilator-free days was 8 days (range 0-21 days) in the semi-recumbent patients, versus 24 days (range 12-25 days) in the lateral-horizontal patients (P = .04). CONCLUSIONS: Implementing the lateral-horizontal position for 12-24 hours in adult intubated intensive care unit patients is feasible, and our patients had no adverse events. The incidence of aspiration of gastric contents in the lateral-horizontal position seems to be similar to that in the semi-recumbent position