Background: The proper positioning of patients before direct laryngoscopy is a key step that facilitates tracheal intubation. In obese patients, the 25 degree back-up or head-elevated laryngoscopic position, which is better than the supine position for tracheal intubation, is usually achieved by placing blankets or other devices under the patient's head and shoulders. This position can also be achieved by reconfiguring the normally flat operating room (OR) table by flexing the table at the trunk-thigh hinge and raising the back (trunk) portion of the table (OR table ramp). This table-ramp method can be used without the added expense of positioning devices, and it reduces the possibility of injury to the patient or providers that can occur during removal of such devices once tracheal intubation is achieved. In this study, we sought to determine if the table-ramp method of patient positioning was equivalent to the blanket method with regard to the time required for tracheal intubation.
Methods: Eighty-five adults with a Body Mass Index >30 kg/m(2), scheduled for elective surgery, consented to participate in this prospective randomized equivalence study conducted in a teaching hospital. The randomization scheme used permuted blocks with subjects equally allocated to be positioned using either the blanket method or the table-ramp method. The end-point in either case was to achieve a head-elevated position, where the patient's external auditory meatus and sternal notch were in the same horizontal plane. Although all patients were positioned by the same anesthesiologist, laryngoscopy and tracheal intubation were performed by trainees with various levels of expertise. Standard i.v. induction and tracheal intubation techniques were used. The time from loss of consciousness to the time after tracheal intubation when end-tidal CO(2) was detected was recorded. The effectiveness of mask ventilation and quality of laryngeal exposure were also noted.
Results: The mean time (SD) to tracheal intubation was 175 (66) s in the blanket group, as compared to 163 (71) s in the table-ramp group. Assuming the bounds for equivalence are -55,55 s, our study found a 95% confidence interval of -36.22, 13.52 s using two one-sided tests for equivalence corresponding to a significance level of 0.05. There was no difference in the number of attempts at laryngoscopy (P = 0.21) and tracheal intubation (P = 0.76) required to secure the airway between the two groups.
Conclusions: Before induction of anesthesia, obese patients can be positioned with their head elevated above their shoulders on the operating table, on a ramp created by placing blankets under their upper body or by reconfiguring the OR table. For the purpose of direct laryngoscopy and tracheal intubation, these two methods are equivalent.