Pulse oximetry is an extremely useful monitor during the perioperative period and in a number of other clinical situations (1,2). Although pulse oximeter readings, particularly when using finger probes, can be erroneous during hypoperfusion and severe hypoxemia, pulse oximetry has been recommended for use during cardiopulmonary resuscitation (CPR) (3). We would like to emphasize that pulse oximetry cannot replace monitors such as electrocardiograms, the blood pressure cuff, and arterial pulse palpation during CPR.The following acute events, one in the recovery room and one in the operating room, demonstrate our point. A 64-yr-old man with a history of myocardial infarction of indeterminate duration underwent an uneventful left thoracotomy and left upper lobectomy for carcinoma of the lung. Ninety minutes after surgery the patient complained of left-sided chest pain, abruptly sat up, and lost consciousness. At that time, when the electrocardiogram showed asystole, the pulse oximeter indicated 94% arterial oxygen saturation and a pulse rate of 72 beatslmin. Clinically, asystole was suspected and immediate CPR was started. Although CPR was prolonged, it was, unfortunately, not successful. The second patient was a 58-yr-old man scheduled for resection of a lung carcinoma. After induction of anesthesia with thiopental and muscle relaxation with vecuronium the patient's trachea was intubated without difficulty. Soon after tracheal intubation ventilation became difficult because of a malfunctioning PEEP valve. Although the pulse oximeter registered a saturation of 92% and a pulse rate of 72 beats/min, the carotid pulse could not be palpated. A right tension pneumothorax was detected and a tube thoracostomy was performed. The patient had an uneventful recovery.Most pulse oximeters require 8-10 s of asystole to indicate absence of the pulse and to initiate the alarm.Noise signals and movement of the patient's hands and fingers during CPR can, however, give erroneous indicators of hemoglobin saturation and pulse rate. The "signal alarm" should alert the anesthesiologist to check the electrocardiogram and pulse.We evaluated two pulse oximeters with finger probes by using acute arterial occlusion with a blood pressure cuff. The results were similar for both pulse oximeters: movement of the fingers or hand with the finger probe in place during acute arterial occlusion produced false but physio-logically acceptable readings and pulse wave patterns. The resultant misinterpretation can, under clinical conditions, lead both to incorrect judgment as to when CPR should be initiated and to the adequacy of CPR once it is initiated. We conclude that there is a finite lag time between cardiac arrest and the indication of arrest by the pulse oximeter. Furthermore, noise signals and limb movement during CPR produce spurious results. Pulse oximeter data must be interpreted in conjunction with the electrocardiographic and blood pressure data during CPR. References 1. Alexander CM, Teller LE, Gross JB. Principles of pulse oxirnetq. Anesth 2...
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