After obtaining the Institutional Ethical committee's approval, 48 adults attending hospital during March 2009 till December 2010 were enrolled constituting both sexes, ASA-I and ASA-II, aged 16-50 years, weighing 35-75 kgs undergoing various surgical procedures like release of post burn contracture, debridement, split skin graft (SSG) and change of dressing for post burn neck contracture in whom laryngeal mask airway was considered appropriate.
With a type I error 0.05 and power of 80% we calculated that the sample size required was at least 21 in each group, based on a parallel group design.[8
] Data were entered and statistical analysis was performed using SPSS software (version 16, SPSS Inc.., Chicago, IL, USA). The significance level was set at 0.05.
All the patients underwent pre-operative fasting according to the hospital guideline. The size of device used was decided by the anaesthetists based on the patient's bodyweight and manufactures’ recommendation. For the cLMA size 3 was used when the patients’ weight was <50 kg, size 4 for the patients weighing between 50-90 kg and size 5 for patients weighing more than 90 kgs. The i-gel size 3 was used for patients weighing between 30-60 kgs, size 4 between 50-90 kgs and size 5 for patients weighing >90 kgs. Both the devices were soaked with normal saline before use. In this crossover trial, both airways were inserted in each patient in random order. Patients were allocated randomly into one of the two groups using sequentially numbered sealed opaque envelop naming the airway device to be evaluated first, group I i-gel group and group II cLMA group. Randomization was performed by an envelop method. The insertions were performed by a single user who had experience of more than 1000 insertions of cLMA and at least 20 insertions for the i-gel.
A thorough pre anesthetic evaluation was done a day before the procedure. All patients with co-exiting disease were excluded from the study. All elective patients as per the study protocol were enrolled. The induction procedures were explained to them and informed consent was taken. All the patients in both the groups were pre-medicated with oral Midazolam 7.5 mg one hour prior to induction of anesthesia. Both the groups received intra-venous injection midazolam 0.02 mg/kg, glycopyrrolate 0.2 mg and fentanyl 2 mcg/kg as premedication. Induction of anesthesia was done by propofol titrated to loss of verbal contact with the patient, loss of eyelash reflex and relaxation of jaw. If coughing, gagging, or body movement occurred during insertion of device, propofol 1 mg/kg was added to achieve an adequate level of anesthesia. For the safety reason of the patients before the insertion of any of the devices after loss of verbal contact, the anesthetist checked that hand-ventilation with a facemask was possible.
Adequate placement of the airway device was assessed by gentle squeezing the reservoir bag and observing the end-tidal CO2 waveform and movement of the chest wall. If ventilation was deemed inadequate, the following manipulations were allowed: gentle pushing or pulling the device, chin lift, jaw thrust, head extension, or neck flexion. The number of attempts required for insertion was recorded. A “failed attempt” was defined as removal of the device from the mouth before re-insertion. Two attempts were allowed for placement of each device with mask ventilation with oxygen between attempts. If second attempt also failed then the device was changed into other study device. The airway was manipulated after each attempt if a secure airway was not achieved. Intervention required on the airway was graded as either minor [changing neck position/adjusting head (changing depth of inspiration)] or major (requiring jaw thrust, re-insertion/change of device).
Effective ventilation was defined as proper chest expansion or square wave capnograph trace, absence of audible leak and lack of gastric insufflations. The total time of placement from grasping of the device to observing a square wave capnograph trace (the insertion time) and the numbers of attempts were recorded. Airway leak pressure tests were then performed. The oropharyngeal leak pressure was measured by closing the expiratory valve of the circle system at a fixed gas flow of 3 litters per minute and noting the airway pressure (maximum allowed 40 cm H2O). The position of the device was assessed and graded by the investigators using a fiberoptic bronchoscope (2.8 mm: Olympus, Tokyo, Japan) for the view of glottis.
Pre insertion complications were defined as minor (coughing or gagging on insertion, hiccough, gastric insufflations); or major (bronchospasm or airway obstruction). If both the devices failed then fiberoptic bronchoscope was kept as backup plan for intubation and the patients were excluded from the study.