Comparison of three oxygen monitors in detecting endobronchial intubation

Rapid and reliable detection of inadvertent endobronchial intubation is an essential function of oxygen monitoring. We have studied the detection of this event by using three oxygen monitoring techniques: pulse oximetry, transcutaneous measurement of oxygen tension, and intraarterial fiberoptic measurement of oxygen tension. Four dogs were anesthetized, intubated, and monitored with these three techniques and with arterial and central venous cannulas. Endotracheal tubes were moved from the trachea into the right mainstem bronchi at several inspired oxygen fraction (FIO2) values for each dog, and the responses of the oxygen monitors were recorded for 20 minutes thereafter. The pulse oximeter showed little change in oxygen saturation (SpO2) during endobronchial intubation at FIO2 values above 0.3. SpO2 decreased by an average of 1.3 +/- 2.1% at an FIO2 of 1.0 and by 4.0 +/- 4.1% at an FIO2 of 0.5. Simultaneously measured transcutaneous oxygen tensions decreased by 42 to 64% and the optode reading decreased by 64 to 79%. At lower FIO2 values, the changes in SpO2 were more significant: a decrease of 6.0 +/- 6.3% at an FIO2 of 0.3 and of 9.8 +/- 6.1% at an FIO2 of 0.2. The transcutaneous oxygen and optode readings decreased by 31 to 45% under these conditions. Endobronchial intubations at FIO2 values greater than 0.3 may not yield immediate decreases in arterial saturation and hence may go undetected by pulse oximetry. Transcutaneous oxygen tension decreases significantly with endobronchial intubation at any FIO2. The experimental, intraarterial optode consistently yielded the greatest changes with the fastest time response.