Time to hemoglobin desaturation with initial fractional alveolar oxygen concentration = 0.87

This graph shows the SaO₂ versus time of apnea after maximal preoxygenation in an obese adult, a 10 kg child (low functional residual capacity [FRC] and high oxygen consumption [VO₂]), and a moderately ill adult, compared with a healthy adult. The graph also shows the mean time to recovery from paralysis after a dose of succinylcholine that might be used for intubation. Critical oxygen desaturation occurs before functional recovery in most patients, even after maximal preoxygenation.