Severe hypoxemia secondary to pulmonary embolization treated successfully with the use of a CPAP (continuous positive airway pressure) mask

Continuous Positive Airway Pressure in Acute Respiratory Failure: The Importance of the Valve

Continuous positive airway pressure (CPAP) is known to improve oxygenation and although the exact mechanism is uncertain, the literature suggests that the positive pressure may have a significant role. There may be other mechanisms. In this study, a lung model was used to investigate the mean fractional inspired oxygen at different respiratory rates delivered by CPAP, a venturi mask with 15 L/min flow and a Hudson mask at 6 L/min flow. In each, the fractional inspired oxygen was set at 0.6. An observational study was then undertaken to determine the effect of CPAP at pressures of 0 cm H2O, 5 cm H2O and 10 cm H2O on oxygenation in patients with acute respiratory failure. The model demonstrated that while the CPAP delivered a fractional inspired oxygen of 0.6 at all respiratory rates and at all pressures, the venturi and Hudson masks both become less efficient as the respiratory rate rose. In patients with acute respiratory failure, there is an initial and immediate rise in the partial pressure of oxygen when the patient changes from a venturi mask to a CPAP system at a pressure of 0 cm H2O but there is no further increase in oxygenation at 5 or even 10 cm H2O. The respiratory rate does, however, decrease with time. The initial effects of CPAP on oxygenation are immediate but do not appear to be significantly influenced by pressure, at least within the first two hours.

Noninvasive positive-pressure ventilation in patients with acute respiratory failure

This article provides a systematic review of the literature on the application of noninvasive ventilation in various forms of hypercapnic and hypoxemic respiratory failures. A description of the underlying pathophysiology is followed by a review of physiologic data explaining the mechanisms of action of noninvasive ventilation. A critical review of clinical studies is presented with specific suggestions. The methodology of correctly implementing and monitoring noninvasive ventilation in patients with acute respiratory failure, critical to success, is detailed.

Efficacy of continuous positive airway pressure administered by face mask

The efficacy of administering continuous positive airway pressure (CPAP) by face mask was evaluated in 40 consecutive patients treated with 10 cm of water pressure or greater. Thirty-five patients were treated for progressive hypoxemia with all patients improving their PaO2/FIO2 ratio within the first hour of therapy. Oxygen delivery, when measured, also improved in each patient, although five patients ultimately required endotracheal intubation and higher CPAP levels to further improve their arterial hypoxemia. Five other patients were treated for atelectasis unresponsive to the usual therapeutic measures, with three patients demonstrating roentgenographic improvement. Face mask CPAP proved to be a safe and effective method for treating hypoxemia associated with early progressive respiratory distress in alert, spontaneously breathing patients.

Central haemodynamics and oxygen transport during CPAP with and without mandatory ventilations

Ten patients, subjected 16 h earlier to open-heart surgery (aortocoronary bypass and/or aortic valve replacement), were studied during the weaning period after postoperative mechanical ventilation. Central haemodynamics and oxygen transport were assessed along with total oxygen consumption during continuous positive airway pressure with four mandatory ventilations per minute (mode CPAP + IMV) and, subsequently, during CPAP alone. During the two modes of ventilation, airway pressure was adjusted to be equal during the spontaneous inspiratory phases. All parameters of haemodynamics, oxygenation and oxygen consumption were found to be essentially satisfactory and unchanged during both modes of ventilation. Our observations suggest that, as the parameters studied were unaltered with the change from CPAP + IMV to CPAP, the use of ventilatory support for these patients during the weaning period (in the form of four mandatory ventilations per minute) appears, in terms of central haemodynamics and oxygen transport, to be well tolerated in cases where adequate spontaneous ventilation is in doubt.