BiPAP is being more frequently used for acute postoperative respiratory failure as it provides several advantages over traditional invasive mechanical ventilation. BiPAP is a form of noninvasive ventilatory support that minimizes the risks of ventilator-induced lung injuries, reduces the need for excessive sedation, and preserves the upper airways’ reflexes and functions for better protection against aspiration and for better humidification of inspired gas. Two separately adjusted pressure levels, EPAP and IPAP, allow the clinician to independently maintain upper-airway patency and prevent airway/alveolar collapse/derecruitment during exhalation, thereby preventing atelectasis and increasing the FRC that is the main oxygen store as well as augmenting tidal volume and alveolar ventilation and subsequently alveolar oxygenation [7]. BiPAP as a preoxygenation method has been shown to be more effective at reducing arterial oxyhemoglobin desaturation than conventional preoxygenation techniques during intubation in hypoxemic patients [8]. Furthermore, the levels of oxygenation achieved with BiPAP are usually sustained for longer duration after intubation than conventional preoxygenation techniques with a non-rebreather bag-valve mask [8]. This reflects the possible significant linear correlation between oxyhemoglobin saturation at the end of the preoxygenation period with BiPAP and the minimal oxyhemoglobin saturation during endotracheal intubation.

In a prospective randomized study, Delay et al. [9] showed, in morbidly obese patients, that a larger proportion of patients achieved a 95 % end-tidal oxygen concentration (ETO₂) at 5 min with BiPAP than in spontaneously breathing patients. Several reports confirmed that oxygen administration via BiPAP is safe, feasible, and efficient in morbidly obese patients in the operating room and provides a faster preoxygenation than normal spontaneous breathing of high fraction of inspired oxygen [9, 10].

The tonic increase in the baseline pressure that is usually achieved with EPAP during BiPAP tends to reverse atelectasis and reduce the shunt that could have developed during the administration of anesthesia and subsequently led to the acute postoperative respiratory failure. This can significantly increase the non-hypoxic apnea duration by more than 2 min compared with when no EPAP or BiPAP therapy is applied during acute postoperative respiratory failure [11].

Following anesthesia, patients with obstructive sleep apnea should be extubated in a semirecumbent position after they are fully awake and confirmation of airway patency and after verification of complete reversal of neuromuscular blockade. Otherwise, there will be a high risk of post-extubation airway obstruction and severe postoperative oxyhemoglobin desaturation. BiPAP should be applied as soon as possible after surgery to patients with obstructive sleep apnea who exhibit mild to severe postoperative oxygen desaturation. Its immediate use after tracheal extubation may prevent oxygen desaturation and eliminate the need for reintubation [11].

BiPAP has also been used for management of hypoxemia associated with unilateral phrenic nerve palsy following surgery for thoracic outlet syndrome. The unilateral phrenic nerve palsy that may mimic one-lung ventilation that creates an obligatory right-to-left transpulmonary shunt flow through the nonventilated lung and resulting in severe hypoxemia might not be reversed with simple face mask oxygenation. The use of BiPAP and supplemental oxygen can significantly improve oxygenation and reverse signs and symptoms of respiratory distress in these patients [12]. Under these clinical circumstances, BiPAP with adequate adjustments of EPAP and IPAP can improve V/Q mismatch, decrease the shunt, and improve alveolar ventilation.

Noninvasive BiPAP is usually provided using a standard pressure-cycled positive pressure ventilator (whether a stand-alone ICU or an anesthesia-machine incorporated ventilator) or a specialized BiPAP machine [13]. The therapy can be delivered to the patient using either a full face mask or a nasal mask. Despite the several clinical benefits, reported adverse effects related to BiPAP have been relatively mild and most commonly include skin breakdown over the bridge of the nose due to pressure from the mask (Table 35.1). The use of a bio-occlusive dressing, soft mask cushions, and intermittent repositioning of the mask can significantly limit these problems. Additional concerns of BiPAP therapy, particularly with full face masks, are the risk of gastric insufflation, distention, and aspiration [7]. Gastric distention has been noted previously with the application of BiPAP, however, to date, no reports document the occurrence of aspiration. In the event of excessive gastric dilation, it may be necessary to decompress the stomach with a naso/orogastric tube or decrease the level of IPAP.