EFFICACY OF THE SELF-INFLATING BULB IN CONFIRMING TRACHEAL INTUBATIONIN THE MORBIDLY OBESE

Background: This study was designed to determine the incidence of fals e-negative and false-positive results when the self-inflating bulb (SI B) is used to differentiate tracheal from esophageal intubation in mor bidly obese patients using two techniques. In technique 1, the SIB is compressed before it is connected to the tube; in technique 2, the SIB is compressed after connection to the tube. Methods: With institution al review board approval, 54 consenting adult morbidly obese patients (body mass index > 35) undergoing elective surgical procedures were in cluded in the study. After anesthetic induction and muscle relaxation, both the trachea and esophagus were intubated under direct vision wit h identical cuffed tubes. The efficacy of the sip in verifying the pos ition of both tubes was tested by a second anesthesiologist. The speed of reinflation was graded as rapid (<4 s) or none (>4 s), using both techniques. In the case of tracheal intubation, the absence of reinfla tion was recorded as a false-negative, whereas in cases of esophageal intubation, rapid reinflation was recorded as a false-positive. Identi fication of tube location by the second anesthesiologist was based on SIB reinflation results from techniques 1 and 2, as well as the presen ce of a flatuslike sound elicited by technique 2 in esophageally place d tubes. All patients were retested by the SIB after receiving three b reaths of 400-500 ml each. In all patients exhibiting false-negative r esults, six obese patients exhibiting true-positive results, and four nonobese patients exhibiting true-positive results, tracheal responses to the SIB maneuvers were observed directly by a flexible fiberoptic bronchoscope incorporating an airtight system, 15-20 min after mechani cal ventilation was instituted. Results: The incidence of false-negati ve results was initially 30% with technique 1 and 11% with technique 2 , but decreased to 4% when technique 2 was used after the delivery of three breaths. The second anesthesiologist initially identified tube l ocation in 92.5% of patients correctly. After the delivery of three br eaths, tube location was correctly identified in 96.3% of patients. Fi beroptic bronchoscopic examination of the patients exhibiting false-ne gative results revealed exaggerated inward bulging of the posterior tr acheal membrane during reinflation of the SIB when technique 1 was use d. Conclusions: Contrary to previous investigations in healthy patient s, the current study demonstrates a high incidence of false-negative r esults when the SIB is used to confirm tracheal intubation in morbidly obese patients. If the SIB is used, the technique should include comp ression of the SIB after connection to the tube and should be used in conjunction with other clinical signs and technical aids. The mechanis m of false-negative results in these patients seems to be related to r eduction of caliber of airways secondary to a marked decrease in funct ional residual capacity, and collapse of large airways due to invagina tion of the posterior tracheal wall when subatmospheric pressure is ge nerated by the SIB.