[Evaluation of postoperative hypoxemia after spinal anesthesia with a pulse oximeter]

We investigated postoperative hypoxemia after spinal anesthesia in 24 adult patients by monitoring SPO2 with a pulse oximeter for 5 hours in the ward. The patients received spinal anesthesia with 0.5% hyperbaric tetracaine and sedated with midazolam during operation. Twelve patients inhaled 3 l.min-1 oxygen via a mask for initial 3 hours, and the other breathed room air all the time. In two of the patients breathing room air, SPO2 decreased to less than 94%. In patients inhaling oxygen, SPO2 was maintained above 98% but decreased significantly after stopping oxygen inhalation (below 94% in five patients). The postoperative SPO2 value correlated significantly with BMI (body mass index) and preanesthetic SPO2, but not with the dose of midazolam or supplemental pentazocine, and postoperative conscious states. In conclusion, there are some incidences of postoperative hypoxemia after spinal anesthesia irrespectively of the dose of midazolam used intraoperatively. Inhalation of 3 l.min-1 oxygen via a mask is sufficient to prevent such postoperative hypoxemia.