THE OXIMETER—A TECHNICAL AID FOR THE ANESTHESIOLOGIST

Abstract

The use of the oximeter for the determination of hypoxia during anesthesia is discussed. The apparatus used consists of a Milliken earpiece which transmits illumination through the pinna. This illumination then falls upon a filter which transmits red light and a filter which transmits infrared light. These light values are then picked up by photoelectric cells which are in circuit with a galvanometer. The galvanometric readings and the patient''s hemoglobin concn. make absolute values of arterial oxygen saturation calculable. Oximeter values, when compared with values detd. by the Van Slyke and Niell apparatus, agreed within 2.5% on patients with normal circulation and within 5% on patients with cardiovascular anomalies with marked arterial unsaturation and varying degrees of polycythemia. 89 children were followed during anesthesia with this oximeter and the following observations recorded. Hypoxia due to low O2 concn. in an anesthetic mixture can be relieved in a few seconds by 100% O2, but takes several minutes to be relieved by room air (20% O2). Moderate obstruction will cause hypoxia rapidly and will lengthen recovery period even in presence of 100% O2. Gradually increasing hypoxia can be expected during open drop ether anesthesia unless a constant flow of O2 is provided under the ether mask. Breathholding can cause serious oxygen deficit. Reflex bronchospasm, laryngospasm and apnea associated with entro-tracheal intubation were shown by oximetry to produce hypoxia. Suction catheters remaining too long in tracheobronchial tree for aspiration of secretions cause a severe fall in oxygen saturation. In thoracic operations adequate oxygenation is maintained by one lung only when high O2 concns. and assisted respirations are employed. The oximeter is of value in deter-mining the benefit of O2 therapy in the wards. Limitations of the oximeter are the delicacy of the instrument, the technical assistance needed for operation and maintenance, and the possibility of burns of the pinna.