Airway pressure monitoring as an aid in the diagnosis of air embolism.

We designed a prospective study to compare the validity of airway pressure (AWP) monitoring with that of end-tidal CO2 (ETCO2) monitoring for early detection of air embolism. Subjects included 76 patients of both sexes who underwent neurosurgery in the sitting position. Anesthesia was maintained with O2, N2O, narcotics, pancuronium, and intermittent positive pressure ventilation (IPPV). Continuous monitoring was done of HR, ECG, intraarterial pressure, AWP, and ETCO2. A sudden and sustained decrease in ETCO2 during anesthesia in a hemodynamically stable patient was considered as a sign of air embolism. Concomitant changes in AWP and cardiovascular parameters were also recorded simultaneously. Onset time, stage of surgery, and duration of disturbances were recorded. At the same time, the chest was auscultated for any murmur. Aspiration of air through the CVP catheter was attempted for diagnosis and management of air embolism. ETCO2 monitoring detected 24 episodes (31.5%) of air embolism in 16 patients. We observed 10 episodes (13.1%) of tachycardia in nine patients and nine episodes (11.8%) of hypotension in eight of the 16 patients. Murmur was noted in four patients and air aspiration in six patients. Only six patients of the 16 had an increase in AWP along with the decrease in ETCO2. We conclude that AWP monitoring is neither a sensitive nor reliable indicator of air embolism.