This prospective, randomized, comparative study was conducted at a tertiary care hospital after obtaining approval from Institutional Ethics Committee. This study was registered in the Clinical Trials Registry India (CTRI/2010/091/000355). Two hundred patients scheduled for elective surgery were enrolled. The inclusion criteria were: a) patients of either gender, aged between 18 and 65 years, scheduled for surgery with anticipated duration <2 h and (b) American Society of Anesthesiologists physical status 1 and 2. The exclusion criteria were: (a) patients at risk of regurgitation and aspiration; (b) surgeries where use of LMA would be inappropriate; (c) body mass index > 35 kg/m2; (d) predicted airway difficulty; and (e) emergency surgery. Written informed consent was obtained from all the patients included. Preoperative nil per oral instructions were 6 h for solids and 2 h for clear fluids. Patients were premedicated with oral diazepam, 5 mg (if body weight ≤ 50 kg) or 10 mg (if body weight > 50 kg), on the night prior to surgery.
Patients were randomized to two groups: standard technique group (standard insertion technique with digital intraoral manipulation) or modified technique group (modified insertion technique without digital intraoral manipulation) using computer generated random number table and the allocation was concealed in a sealed envelope. The sealed envelope was opened before shifting the patient to the operating room. Stratified randomization into five strata was done for LMA Classic™ to be inserted by five designated anesthesiologists (two consultant and three resident anesthesiologists). The consultant/resident anesthesiologist who inserted the LMA had an experience of at least 100 insertions with the standard technique. They were briefed about the modified technique of insertion before the start of the study and were given the opportunity to practice this technique on a manikin.
In the operating room, standard monitoring included ECG, pulse oximetry, non-invasive blood pressure, and end-tidal carbon dioxide. Intravenous (IV) access was secured. Glycopyrrolate 10 mcg/kg and fentanyl 2 mcg/kg were administered IV. After 3 min of preoxygenation, anesthesia was induced with propofol 3 mg/kg IV. Loss of verbal contact was considered as the end point of induction. If required, additional boluses of 10 mg propofol were administered. Ventilation was then assisted with 2% isoflurane in 100% oxygen for 1 min. After ensuring adequate jaw relaxation, LMA Classic™ was inserted either by the standard technique or by the modified technique, depending on the randomization. If the jaw was not adequately relaxed or the patient moved during insertion, further boluses of 10 mg propofol were injected. The total dose of propofol injected was recorded. In either group, LMA Classic™ of appropriate size was used based on the patient's weight. Pre-use test was performed before LMA Classic™ insertion.[3
] Number of repetitive use of LMA Classic™ was restricted to 40 as recommended by the manufacturer, in both the groups.[3
] The LMA Classic™ was deflated completely and the posterior aspect lubricated with water-soluble jelly prior to insertion. In the standard technique group, LMA Classic™ was inserted as recommended by the manufacturer. (The patient was positioned supine with head and neck in sniffing position. LMA Classic™ was held like a pen, with the index finger placed at the junction of the cuff and the airway tube. Under direct vision, the tip of the cuff was pressed upward against the hard palate and the cuff was flattened against it. Using the index finger, the cuff was pressed backward toward the occiput and the device was advanced into the hypopharynx. The index finger was inserted to its fullest extent into oral cavity before resistance was encountered. Before removing the index finger, the non-dominant hand was used to stabilize the shaft of the LMA, to prevent the LMA from being displaced, when the index finger of the dominant hand was removed.) In the modified technique group, the patient was positioned supine with head and neck in sniffing position. After opening the mouth, LMA Classic™ was held at the junction of the proximal one-third and distal two-thirds of the shaft, between the index finger and the thumb of the dominant hand. LMA Classic™ was introduced into the mouth, flattening the cuff against the hard palate and pushing it down into the pharynx until resistance was encountered. When the index finger and the thumb reached the mouth of the patient as the LMA was introduced, these fingers were readjusted to the proximal end of the LMA. No undue force was exerted on the LMA during these steps.
If the anesthesiologist felt that the tongue was hampering the advancement of LMA, then the assistant was asked to provide jaw thrust externally, by lifting the angle of the mandible. Such maneuvers were recorded, if used.
After insertion of LMA Classic™, the cuff was inflated with maximum recommended volume of air for that particular size. Ventilation was assisted to check whether an effective airway was secured (as defined by square wave capnogram trace, without audible leak at peak inspiratory pressure 20 cm H2O and normal chest movements). Subsequently, the intracuff pressure was measured with an aneroid cuff pressure manometer. The cuff was inflated or deflated to achieve an intracuff pressure of 60 cm H2O.
A maximum of 90 s was allowed for successful insertion. A maximum of two attempts within this 90 s duration was allowed. An attempt was defined as inserting the LMA into patient's mouth and removing it from the patient's mouth. If both the attempts failed with one technique, then crossover to the other technique was tried with only one attempt. If this too failed, then the concerned anesthesiologist was free to decide on further airway management. If there was desaturation to 95% or below during an attempt to insert, the attempt was aborted and mask ventilation with 100% oxygen was resumed.
The time taken to achieve an effective airway was defined as the time from picking up of LMA Classic™ till achievement of square wave capnogram trace without audible leak at 20 cm H2O and normal chest movements.
Ease of insertion was graded as follows: grade 1 – easy, no resistance; grade 2 – some difficulty, some resistance; and grade 3 – impossible to insert.
Number of attempts taken to insert LMA Classic™ successfully was recorded. If the LMA could not be inserted in two attempts, it was considered as failed insertion.
A blinded observer (blinded to insertion technique) assessed the final position of LMA Classic™ after successful insertion and its fixation. The glottic view obtained by fiberoptic scope through LMA Classic™ was recorded, keeping the tip of the fiberoptic scope at the aperture bar in neutral position. Glottic view was graded as follows: grade 1 – vocal cords entirely visible, grade 2 – vocal cords or arytenoids partially visible, grade 3 – epiglottis only visible, and grade 4 – no laryngeal structure visible. The patient was blinded to the technique of insertion.
Any blood stain on LMA Classic™ at the end of the procedure was noted. Patients were interviewed for the presence of sore throat after 1 h and then 24 h after the procedure. The modified Mallampati class of every patient was recorded preoperatively to analyze whether the relative size of the tongue in the oral cavity influenced the success rate of insertion.
Assuming α = 0.05 and β = 0.20, with success rate at first attempt for standard technique and modified technique of insertion at 97%, the hypothesized difference of ≤0.1 considered as equivalence, it was calculated that this study would require a total of 192 patients. To account for any dropouts, we included 200 patients in this study. Data were analyzed using SPSS 13.0 for Windows. Duration of surgery, dose of propofol injected, and time to achieve an effective airway were compared with independent samples t-test. Modified Mallampati class of patients, number of attempts taken to achieve an effective airway, success rate of LMA insertion, ease of LMA insertion, and the glottis view through the fiberoptic bronchoscope were compared with Chi-square test. P value <0.05 was considered significant.