Morbid obesity (body mass index ≥35 kg/m2) is associated with a 2-fold increase in overall mortality, a 7-fold increase in cardiopulmonary mortality, and a 40 times more frequent incidence of sudden death than the general population (1). The interference of anesthesia with cardiopulmonary compensatory mechanisms in the already-compromised obese increases the propensity for perioperative complications in this population (2). In addition, laparoscopic surgeries present special problems, such as systemic CO2 embolization and cardiopulmonary derangements caused by increased intraabdominal pressure and sudden changes in the patient’s position (3). Banded gastroplasty for weight reduction carries a reported overall mortality rate of 0.1%–0.5% and a morbidity rate of 10.3%–15%(4). The intraoperative surgery-related complication rate for laparoscopic gastric banding is 0.8%(5).
Correct positioning of the tip of the endotracheal tube (ETT) is essential to avoid an additional untoward endobronchial intubation or accidental extubation. This would prevent the morbidity/mortality rate from increasing in any population, especially in the obese. For safe positioning, the tip of the ETT should lie approximately 3–5 cm above the carina (6) or, on chest radiograph, at the level of the clavicle (mid trachea) (7). The classic clinical way to assess the ETT’s correct position is to pass the tube’s cuff 1 cm below the vocal cords (6). This, however, may not guarantee that the correct position will be maintained throughout the procedure.
This study investigated the incidence of ETT tip movement within the trachea in morbidly obese patients undergoing gastroplasty by a laparoscopic route and in matched controls who underwent the same procedure by open laparotomy.
The Institutional Ethics Committee approved the study, and all participating patients gave their written, informed consent. Sixty morbidly obese patients, aged 18–70 yr, weighing 90–160 kg, ASA physical status I–III, were enrolled in this double-blinded, prospective, controlled study. Excluded were patients with past bronchial, airway, or lung surgery or with concurrent lung disease. The participants were consecutively and equally allocated to two groups: the study group (Group 1) included patients who underwent laparoscopic LapBand gastroplasty, whereas the control group (Group 2) consisted of patients who underwent gastroplasty through open laparotomy. The same surgical team operated on both groups of patients. All patients underwent standardized general anesthesia by the same anesthesiologist and received propofol 2 mg/kg and midazolam 1 mg for induction; oral endotracheal intubation was facilitated by suxamethonium 1.5 mg/kg. The presence of a capnography trace and bilateral breath sounds were confirmed by the anesthesiologist who performed the intubation. Anesthesia was maintained by N2O/oxygen, isoflurane, rocuronium, and aliquots of fentanyl, 50 μg each, as deemed necessary by the anesthesiologist. The ETT was secured in every patient in a similar manner, with adhesive tape, according to a standard technique (8). All tubes (Portex®; SIMS Portex Ltd., Hythe, Kent, UK) were uncut, with inner diameter 8.5 mm for men and 7.5 mm for women. The cuff pressure was maintained between 20 and 25 cm H2O (9) and was constantly monitored by a manometer (Control-Inflator™; VBM®, Sulz am Neckar, Germany). The position of the ETT tip in reference to the carina was confirmed in all patients with the Rapiscope™ (Cook® Critical Care, Bloomington, IN) (Fig. 1; 1.6-mm external diameter, 70-cm-long fiber), which was inserted by a second anesthesiologist into the ETT through a special fiberoptic swivel connector. A scale (in millimeters) on a band was printed onto the fiber of the Rapiscope™ to indicate the distance of the tip of the ETT to the carina. The first anesthesiologist who was in charge of the case and performed the intubation was blinded to the Rapiscope™ findings by leaving the operating room during the Rapiscope™ assessments performed by the second anesthesiologist. The second anesthesiologist changed the ETT’s position according to the Rapiscope™ findings if clinically advisable. If the tip was found to have migrated within the bronchial lumen during surgery, it was pulled out and repositioned in the original position. All measurements were performed at designated times during the procedure. The second anesthesiologist repeated the Rapiscope™ evaluations at the following time points:
- After intubation (5 min): baseline values in both groups.
- Five minutes before starting the peritoneal inflation with CO2 (Group 1) and 10 min postintubation (Group 2).
- At maximal abdominal inflation pressure in Group 1 (a peak intraabdominal pressure of 12 mm Hg was maintained in all study group patients) and at 20 min into the procedure in Group 2.
- Five minutes before and 5 min after changing the patient’s body position from neutral to a 10° head-up position and a 10° head-down position for patients in Group 1 and at 30 and 40 min for patients in Group 2.
- Two minutes after abdominal gas deflation and table repositioning in Group 1 and at 50 min in Group 2.
- Just before extubation in both groups.
The first anesthesiologist recorded the Spo2 and ETco2 values continuously from a CS3™ (Datex-Ohmeda®, Helsinki, Finland); any sudden changes in ETco2 tracings or in peak inspiratory pressure values were also noted.
All data are reported as mean ± sd. The prestudy power table, which included α = 0.05, δ = 20 mm, and power = 0.9, indicated that each group had to include ≥15 patients. The analyses were performed with SPSS for Windows, Version 9 (SPSS Inc., Chicago, IL). The background characteristics of the two groups were compared by using the nonpaired Student’s t-test. The incidence of ETT movement between the groups was compared by using the Pearson χ2 test. The paired Student’s t-test was used to evaluate changes in Spo2 before and after intubation, as well as before and after extubation. Analysis of variance with repeated measures was used to compare trends obtained at each time point between the two groups (ETT position, Spo2, ETco2, and peak inspiratory pressure). A P value of ≤0.05 indicated a significant difference.
All patients underwent the procedures uneventfully. There were no statistical differences with regard to the patients’ mean age, sex distribution, or duration of surgery (data not presented), and none of these variables proved to be a risk factor for the tip’s migration. The body mass index was 43 ± 5 kg/m2 and 45 ± 3 kg/m2 for the study and the control groups, respectively (P = not significant). In no patient was there a failed intubation. The duration of the surgical procedures ranged between 45 and 65 min. The thyromandibular and sternomandibular distances were also similar among all the patients of both groups (data not presented). In no case did baseline inspection, immediately after intubation, reveal an endobronchial positioning of the tube’s tip. Baseline assessments of the distances between the ETT tip and the carina were similar in both groups with use of the Rapiscope™: the mean distance was 28 ± 3 mm in the study group and 31 ± 5 mm in the control group (P = not significant).
Oxyhemoglobin saturation, peak inspiratory pressures, and end-tidal CO2 values did not differ significantly among the patients in each group or between the groups at any time point throughout the procedures (data not presented). The changes in the ETT tip’s position between the two groups were significantly (P = 0.02, time × type of procedure effect) more frequent in the study group than in the control group. Indeed, migration of the tip occurred in 15 (50%) of the study group patients, compared with 6 (20%) patients in the control group. In Group 1, 12 (80%) of these events were downward movements that occurred after the maximal abdominal inflation or in association with the head-down positioning of the table (Fig. 2). The polynomial regression for each group’s data indicated a different and distinct data distribution between the two groups (r2 = 0.25 in the study group and r2 = 0.75 in the control group;P < 0.05) (Figs. 2 and 3).
Continuing assessments of the locations of the tips relative to the carina and in comparison to the baseline positions indicated a significant (P = 0.001, main effect of time) downward migration of the ETT tip in the control group. A mean advancement of 7 ± 3 mm was observed in 5 control patients (17%), all occurring at the first 10-min measurements. A 5-mm upward migration of the tip occurred 40 min after intubation in one additional patient (3%) (Fig. 3). In none of the control patients was an endobronchial migration of the tip ever diagnosed. In contrast, the tube advanced into the right bronchus in five patients (17%) in Group 1: three events occurred at the point of maximal abdominal inflation, and the other 2 occurred after changing the table position from neutral to head down. There were seven additional events of downward movements (but without entering the bronchus) in Group 1; this occurred at the time of maximal abdominal inflation in four patients and after the head-up positioning of the table was canceled in the other 3 (Fig. 2). The remaining three events in Group 1 involved upward migrations of the tip of 10 and 18 mm; this occurred in association with the head-up changes in position.
This double-blinded, prospective study demonstrated that morbidly obese patients who underwent a procedure that required peritoneal insufflation with gas, as well as head-up or head-down changes in the operating table position, were more prone to ETT tip migration than matched patients who underwent the same operation by an open route (gastroplasty via laparotomy). Most importantly, the tip’s downward movement, even when advancing into the main right bronchus, did not cause significant changes in Spo2, ETco2, or peak inspiratory pressure. It is indeed possible that the larger right lung is more compliant than the left one and that changes, especially in the latter variable, would appear only when the tube’s cuff occludes the right upper lobe. We believe that the fact that these clinical variables failed to monitor changes in the tip’s position is rather alarming, and a specific method or device to recognize such events is desirable.
Factors such as changes in the operating table position and abdominal gas insufflation during laparoscopy (10,11), as well as flexion of the head (12,13), were shown to cause endobronchial movement of the ETT. Three of our patients experienced endobronchial intubation in the Trendelenburg (head-down) position, thus reconfirming previous data (10). A movement of the lungs cephalically may cause the bronchi to move upward toward the tip of the ETT (10). However, Mendonca et al. (14) claimed that a 10° Trendelenburg position had no influence on the ETT position. Because movement during the endobronchial intubation in Group 1 occurred twice at the point of maximal abdominal gas insufflation, we suggest that the abdominal gas inflation might have amplified the effect of the Trendelenburg position (11,15,16). A shift of the diaphragm toward the trachea may be exaggerated in obese patients (17). However, obesity per se may be less hazardous than the combination of obesity with changing table positioning and abdominal inflation, as demonstrated by the increased incidence of ETT movements in our study group compared with the controls.
The range of change in the ETT position may also depend on the method of taping the ETT to the patient’s face (7). We did not analyze this variable, but we did use a standardized method of tube fixation, type of tube, and cuff pressure monitoring. It was suggested that women might present a more frequent incidence of ETT migration than men, for unexplained reasons (18): in our study, both sexes were evenly distributed with regard to the incidence of ETT migration.
Interestingly, the tip of the ETT migrated downward into the trachea in several patients in both groups at a similar time point after intubation (i.e., approximately five minutes) and before there had been any change in the table position and abdominal gas insufflation in the study group. This may be related to an upward movement of the lungs toward the tube, probably pushed by the abdominal content when muscle was relaxed. Our literature search failed to reveal any reports on this finding, and we suggest that it warrants more in-depth investigation.
In conclusion, we demonstrated that downward movements of the ETT tip occur in the obese during abdominal surgeries, more often in association with changes in the operating table position and/or abdominal gas insufflation specific to laparoscopic procedures than in the open abdominal surgery. Furthermore, the tip’s movement into the main right bronchus may cause no changes in the ventilation/perfusion ratio and no significant changes in Spo2 or ETco2 values or in peak inspiratory pressure. The Rapiscope™ may provide critical assistance for early detection of similar movement of the tube’s tip, particularly in morbidly obese patients undergoing laparoscopic procedures, and we suggest that such a device be available to the anesthesiologist in such occurrences.
Thanks to Esther Eshkol for editorial assistance.
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© 2003 International Anesthesia Research Society
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