Preoxygenation: Physiologic Basis, Benefits, and Potential Risks

Abstract

Preoxygenation before anesthetic induction and tracheal intubation is a widely accepted maneuver, designed to increase the body oxygen stores and thereby delay the onset of arterial hemoglobin desaturation during apnea. Because difficulties with ventilation and intubation are unpredictable, the need for preoxygenation is desirable in all patients. During emergence from anesthesia, residual effects of anesthetics and inadequate reversal of neuromuscular blockade can lead to hypoventilation, hypoxemia, and loss of airway patency. In accordance, routine preoxygenation before the tracheal extubation has also been recommended. The objective of this article is to discuss the physiologic basis, clinical benefits, and potential concerns about the use of preoxygenation. The effectiveness of preoxygenation is assessed by its efficacy and efficiency. Indices of efficacy include increases in the fraction of alveolar oxygen, increases in arterial oxygen tension, and decreases in the fraction of alveolar nitrogen. End points of maximal preoxygenation (efficacy) are an end-tidal oxygen concentration of 90% or an end-tidal nitrogen concentration of 5%. Efficiency of preoxygenation is reflected in the rate of decline in oxyhemoglobin desaturation during apnea. All investigations have demonstrated that maximal preoxygenation markedly delays arterial hemoglobin desaturation during apnea. This advantage may be blunted in high-risk patients. Various maneuvers have been introduced to extend the effect of preoxygenation. These include elevation of the head, apneic diffusion oxygenation, continuous positive airway pressure (CPAP) and/or positive end-expiratory pressure (PEEP), bilevel positive airway pressure, and transnasal humidified rapid insufflation ventilatory exchange. The benefit of apneic diffusion oxygenation is dependent on achieving maximal preoxygenation, maintaining airway patency, and the existence of a high functional residual capacity to body weight ratio. Potential risks of preoxygenation include delayed detection of esophageal intubation, absorption atelectasis, production of reactive oxygen species, and undesirable hemodynamic effects. Because the duration of preoxygenation is short, the hemodynamic effects and the accumulation of reactive oxygen species are insufficient to negate its benefits. Absorption atelectasis is a consequence of preoxygenation. Two approaches have been proposed to reduce the absorption atelectasis during preoxygenation: a modest decrease in the fraction of inspired oxygen to 0.8, and the use of recruitment maneuvers, such as CPAP, PEEP, and/or a vital capacity maneuver (all of which are commonly performed during the administration of anesthesia). Although a slight decrease in the fraction of inspired oxygen reduces atelectasis, it does so at the expense of a reduction in the protection afforded during apnea.

Modified Anesthesia Protocol for Electroconvulsive Therapy Permits Reduction in Aerosol-Generating Bag-Mask Ventilation during the COVID-19 Pandemic

“…Preoxygenation with 100% oxygen replaces nitrogen in the lungs and tissue and greatly increases total body oxygen stores, which effectively creates a reservoir that can be drawn down during the apneic period from anesthesia induction through paralysis and until resumption of spontaneous ventilation [23]. Preoxygenation is routinely used to prolong time to hypoxemia in procedures such as rapid sequence intubation (RSI), with randomized trials finding non-inferiority for non-rebreather masks relative to bag-valve masks for this purpose [24].…”

Preoxygenation in the elderly: Comparison of three minutes and four deep breath tecniques

“…In the elderly, this condition disturbs distribution of ventilation and alveolar gas exchange. This is accompanied by respiratory muscle weakness and physiological reduction in all lung volumes of the elderly patient, and consequently, the pulmonary reservoir decreases [18] .…”

Efficiency and efficacy of two techniques of preoxygenation during modified rapid sequence intubation

“…[ 1 ] The benefit of apneic diffusion oxygenation is dependent on achieving maximal preoxygenation, maintaining airway patency, and the existence of a high functional residual capacity–to-body weight ratio. [ 2 ]…”

“…Preoxygenation is practiced commonly to increase the safety during periods of apnea, which is attained by denitrogenation of the functional residual capacity to provide a reservoir of oxygen during apnea. [ 1 2 3 ] Administration of oxygen during the apneic period leads to mass movement of oxygen down a concentration gradient into the alveolus and helps in maintaining the oxygen reservoir in the lungs. This apneic mass movement of oxygen is possible only when the airway is kept patent.…”