Duration of apnoea in anaesthetized children required for desaturation of haemoglobin to 95%: comparison of three different breathing gases

Summary In this study, we compared three gas compositions to determine if the duration of apnoea for Spo2 to decrease is proportionate to the oxygen fraction of the gas prior to apnoea. Twenty‐five patients ASA physical status 1–2 aged two months to 12 years were included in the study. Anaesthesia was induced via a mask with 5% sevoflurane and 66% N2O in oxygen. After paralysis with vecuronium (0.12 mg·kg−1, i.v.) the trachea was intubated and anaesthesia was maintained with sevoflurane and N2O in oxygen. When cardiovascular stability was obtained, the patient was randomly set to breathe one of three gas compositions: 1. oxygen (Fio2 1.0), 2. N2O/O2 (Fio2 0.4), and 3. air/O2 (Fio2 0.4). All three gas compositions included 2–4% of sevoflurane to maintain anaesthesia. 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 (Spo2 100%) to Spo2 of 95% (T95) was measured. T95 measured after breathing N2O/O2 and air/O2 were 34.6 ± 5.7 and 28.8 ± 4.7% of that measured after oxygen breathing (P < 0.001 vs oxygen breathing, P < 0.001 vs oxygen and N2O/O2 breathing), respectively. Preoxygenation before intubation was validated to delay the haemoglobin desaturation brought about by apnoea. An induction technique using a low Fio2 will allow rapid haemoglobin desaturation.