Preoxygenation: Physiologic Basis, Benefits, and Potential Risks.

Area of Science:

• Anesthesiology
• Respiratory Physiology

Background:

• Preoxygenation is standard before anesthetic induction and tracheal intubation to maximize oxygen stores.
• It aims to delay arterial hemoglobin desaturation during apnea.
• Routine preoxygenation is also recommended before tracheal extubation due to potential hypoventilation post-anesthesia.

Purpose of the Study:

• To discuss the physiologic basis of preoxygenation.
• To review clinical benefits and potential concerns associated with preoxygenation.
• To assess the effectiveness, efficacy, and efficiency of preoxygenation strategies.

Main Methods:

• Efficacy assessed by increases in alveolar oxygen and arterial oxygen tension, and decreases in alveolar nitrogen.
• Maximal preoxygenation defined by end-tidal oxygen ≥90% or end-tidal nitrogen ≤5%.
• Efficiency measured by the rate of oxyhemoglobin desaturation decline during apnea.

Main Results:

• Maximal preoxygenation significantly delays arterial hemoglobin desaturation during apnea.
• Effectiveness may be reduced in high-risk patients.
• Various maneuvers (e.g., CPAP, PEEP) can extend preoxygenation effects.

Conclusions:

• Preoxygenation is a critical maneuver with proven benefits in delaying desaturation.
• Potential risks such as absorption atelectasis and reactive oxygen species are generally outweighed by benefits.
• Strategies exist to mitigate risks and enhance preoxygenation effectiveness.