Delayed detection of hypoxic events by pulse oximeters: computer simulations.

There is a variable delay between a reduction in alveolar PO2 and the decrease in arterial oxygen saturation recorded on a pulse oximeter. The decrease in arterial oxygen saturation in response to disconnexion of a paralysed patient from the breathing system, oxygen supply failure with continued mechanical ventilation and disconnexion of the fresh gas supply to Mapleson D and circle absorption breathing systems were studied by simulations on the MacPuf computer model of the cardiorespiratory system. The simulations revealed that there were marked differences between the rate of arterial desaturation which resulted from each of the three types of oxygen supply failure and that arterial oxygen saturation may reach dangerous levels before a pulse oximeter alarm is activated.