[The arterial blood gas change in anesthetized patients with apnea: disadvantage of hyperventilation before intubation].

We studied the arterial blood gas changes during 4 minute apnea period without using constant oxygen flow under anesthesia. Fifteen adult surgical patients (ASA PS 1 or 2, 21-49 years of age) were randomly divided into 3 groups by ETCO2 before the start of apnea (group I: 40 mmHg, group II: 30 mmHg, group III: 20 mmHg). In addition, each patient was monitored with pulse oximetry, ECG, blood pressure, FIO2 and ETCO2. The rate of rise of PaCO2 during the apnea showed no significant difference among these 3 groups. In the first minute of apnea, PaCO2 increased 9.8 +/- 1.9 mmHg, and then increased at a rate of 3.4-4.4 mmHg.min-1 thereafter. In conclusion, the rate of rise of PaCO2 in anesthetized patients with apnea was logarithmic and there was no correlation with pre-apnea ETCO2. The rate of SpO2 decrease was significant in hyperventilated group (III). Thus, hyperventilation applied before the endotracheal intubation is not of benefit to the oxygenation of healthy humans.