DURATION OF APNEA IN ANESTHETIZED CHILDREN REQUIRED FOR DESATURATION OF HEMOGLOBIN TO 95-PERCENT - COMPARISON OF 3 DIFFERENT BREATHING GASES

In this study, we compared three gas compositions to determine if the duration of apnoea for Spot to decrease is proportionate to the oxygen fraction of the gas prior to apnoea. Twenty-five patients ASA physica l status 1-2 aged two months to 12 years were included in the study. A naesthesia was induced via a mask with 5% sevoflurane and 66% N2O in o xygen. After paralysis with vecuronium (0.12 mg . kg(-1), i.v.) the tr achea was intubated and anaesthesia was maintained with sevoflurane an d N2O in oxygen. When cardiovascular stability was obtained, the patie nt was randomly set to breathe one of three gas compositions: 1. oxyge n (Fio(2) 1.0), 2. N2O/O-2 (Fio(2) 0.4), and 3. air/O-2 (Fio(2) 0.4). All three gas compositions included 2-4% of sevoflurane to maintain an aesthesia. After more than eight min of each gas breathing, apnoea was begun by disconnecting the breathing circuit from the tracheal tube. The time from the start of apnoea (Spo(2) 100%) to Spo(2) of 95% (T-95 ) was measured. T-95 measured after breathing N2O/O-2 and air/O-2 were 34.6 +/- 5.7 and 28.8 +/- 4.7% of that measured after oxygen breathin g (P < 0.001 vs oxygen breathing, P < 0.001 vs oxygen and N2O/O-2 brea thing), respectively. Preoxygenation before intubation was validated t o delay the haemoglobin desaturation brought about by apnoea. An induc tion technique using a low Fio(2) will allow rapid haemoglobin desatur ation.