Use of Noninvasive Ventilation to Improve Pre-oxygenation Before Intubation of Hypoxemic Patients

Abstract

Critically ill patients are predisposed to severe oxyhemoglobin desaturation during intubation due to many factors, including the limited physiologic oxygen reserve and the high complexity of intubation. In the intensive care unit, the usual preoxygenation is marginally effective especially in hypoxemic patients. In this short review, we discuss controversies surrounding preoxygenation in hypoxemic critically ill patients. Noninvasive ventilation (NIV), as a preoxygenation method, increases both the contents (FAO 2 ) and the container (functional residual capacity) and could be viewed as one of the best ways to enhance the oxygen stores before apnea. A short application (3 min) of NIV is more effective at reducing arterial oxyhemoglobin desaturation than using a non-rebreather bag-valve mask with reservoir in hypoxemic patients. The impact of NIV on morbidity or mortality is currently being investigated. Careful analysis of the risks and benefits on individual basis should hence be made until further studies are available for the intensivist dealing with hypoxemic critically ill patients. (Clin Pulm Med 2009;16: 270 -274) P reoxygenation allows patient to tolerate longer periods of apnea during the intubation procedure performed under anesthesia. When a difficult airway management occurs, preoxygenation protects against hypoxemia and its potential deleterious consequences. The rate of oxyhemoglobin desaturation mainly depends on the amount of the oxygen stored at the onset of the apnea. Usual preoxygenation (3 minutes of spontaneous ventilation with bag and mask with 100% O 2 ) is recommended in delaying arterial desaturation during the apnea related to endotracheal intubation (ETI) procedures. 1 In healthy apneic adult patient, the time course to reach SpO 2 Ͻ90% after 3 minutes preoxygenation is about 8 minutes. Numerous factors are involved in the oxygen loading process during the preoxygenation such as those able to interfere with alveolar, arterial, tissue, and venous compartments and those interacting with the delivered FiO 2 . The extent of oxyhemoglobin desaturation also depends on the duration of apnea which correspond to the time elapsed between the onset of apnea and successful intubation with the subsequent oxygen provision. The difficulties encountered during airway management prolong the duration of apnea. Finally, the capacity for oxygen loading and the condition of intubation will be the determinants of the efficiency of preoxygenation. PREOXYGENATION IN CRITICALLY ILL PATIENTS: WHAT IS THE MATTER?To consider the factors affecting the rate of oxyhemoglobin desaturation during apnea, Farmery and Roe developed a model. 2 Of note, this model was adapted to a postoperative scenario to predict the consequences of such a nonphysiological condition on the time course of arterial oxyhemoglobin desaturation. The authors stated that it represented to some extent a worst-case scenario in which the combined effect of hypovolemia (4 L), reduced cardiac output (4 L/min), anemia (10 g/dL), increased V/Q misma...