Monitoring of arterial oxygen saturation with pulse oximetry or by arterial blood gases is essential. Blood gas determination will allow monitoring of acid-base balance. Goals of management should be maintenance of PaO2 between 70-100 torr and O2 saturation of 95% with appropriate FiO2. Hypoxemia may be due to cardiac causes, neurogenic pulmonary edema or pulmonary problems such as pneumonia, atelectasis or fluid overload. Careful review of the chest X-ray to exclude pneumothorax is important. Diagnosis of pneumothorax in a supine chest film is difficult. Consultation with a radiologist is therefore required if there is a suspicion of pneumothorax.
Treatment of hypoxemia requires careful attention to fluid status and correction of contributing factors such as atelectasis and pneumothorax. Pulmonary edema should respond to diuresis. Atelectasis may be secondary to poor pulmonary toilet. Bronchoscopy may be required to diagnose and treat bronchial mucus plugs. Finally, positive end expiratory pressure (PEEP) should be instituted. PEEP should be instituted carefully and should not exceed 5-10 cm H2O because of potential adverse hemodynamic causes. These include reduced venous return from increased intrathoracic pressure and/or a direct effect on cardiac output with resultant decreased poor perfusion. PEEP should be increased in 2.0-2.5 cm H2O increments.
Minute ventilation and tidal volume need to be adjusted to maintain an arterial pH of 7.4. Hyperoxia may predispose to atelectasis. If the lungs have been excluded however, maintenance of arterial saturation by increasing FiO2 is preferred to increasing levels of PEEP.
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