A method to determine the P50 of whole blood is described using a modified American Optical reflectance oximeter, pump, and membrane tonometer, together with PO2, PCO2, and pH measurements in a standard blood gas machine. Determinations of P50 were made in 66 patients and normal subjects and in two situations where P50 was very low and very high. The results were compared to oxygen saturations calculated from measured oxygen content. The directly determined oxygen saturation agreed with the assumed saturation of 50 per cent in the oximeter within 0.5 per cent. The apparatus appears to be a simple and relatively inexpensive method to obtain P50 as long as blood carboxyhemoglobin or methemoglobin contents are not elevated.

Carbon Dioxide↗

PubMedDate not supplied

Cardiac electrodes and safe voltage limits.

The 5-mV safe voltage limit that has been proposed for hospital safety codes is shown to be based on incorrect assumptions. The actual voltage threshold for 60-Hz current is of the order of 100 mV or greater, because of the effects of electrode interface impedance and cell membrane characteristics. AK value of 50 mV is proposed as the safe voltage limit for 60 Hz current for the purposes of safety standards. The medical community is requested to consider this value.

Accident Prevention↗