Automatic CPAP compared with conventional treatment for episodic hypoxemia and sleep disturbance after major abdominal surgery

After major abdominal surgery, patients have repeated episodes of upper airway obstruction, hypoxemia, and sleep disruption. These episodes have been associated with heart rate and ischemic electrocardiographic changes. Although oxygen therapy reduces the incidence and severity of hypoxemia, oxygen therapy probably does not affect the incidence or severity of episodes of obstruction. Episodes of obstruction in the postoperative patient resemble the episodes seen in the sleep apnea–hypopnea syndrome (SAHS). SAHS can be effectively treated with nasal continuous positive airway pressure (nCPAP), which reduces obstructive episodes, reduces the incidence and severity of hypoxemic episodes during sleep, and relieves daytime drowsiness. In patients with SAHS, obstructive episodes disturb sleep, activate the sympathetic system, and may cause hypertension. These effects are reduced by nCPAP. We considered the possibility that if nCPAP could prevent episodic airway obstruction, it would reduce hypoxemia and improve sleep for patients after surgery. Although oxygen therapy is widely recommended for the prevention of postoperative hypoxemia, it may not be entirely without adverse effects. If an episode of obstruction causes less hypoxemia when oxygen is given, the stimulus to arousal will be less, and the duration of obstruction can become longer. A possible advantage of oxygen treatment is that prevention of hypoxemia could limit hyperventilation and consequent hypocapnia after relief of the obstruction and hence reduce the tendency to cyclical episodes of obstruction. Therefore, we also tested the possibility that oxygen therapy might alter the frequency of sleep disturbance.