After obtaining approval from the Hospital Ethics Committee, 60 patients were studied. A randomized prospective study was planned to compare size 2.5 i-gel with ProSeal LMA (PLMA) of the same size.
The children included in the study were 5-10 years of age, ASA physical status I-II, they weighed 20-30 kg, and were posted for elective surgeries of less than one hour duration in the supine position, including lower abdominal, inguinal, and orthopedic procedures. The following were excluded from the study: (i) Patients with upper respiratory tract symptoms, (ii) those with risk of gastroesophageal regurgitation, and (iii) those with airway related conditions such a trismus, limited mouth opening, trauma, or mass. Sixty patients were equally randomized to any of the two groups (i-gel and PLMA) of 30 each, for airway management, using a computer-generated randomization program.
Written informed consent was taken from the parents prior to intervention and a standardized protocol for anesthesia was maintained for all cases. All the children were kept nil per mouth, as per the standard guidelines. They were premedicated with 0.3 mg. kg-1 of midazolam syrup, one hour prior to induction of anesthesia. Induction of anesthesia included sevoflurane in oxygen with standard monitors placed. Anesthesia was maintained with 1-2 vol% sevoflurane and 60% nitrous oxide in oxygen.
Once an adequate depth of anesthesia was achieved, the supraglottic device was inserted by the standard technique recommended by the manufacturer. We considered easy up-and-down movements of the lower jaw, no reaction to pressure applied to both angles of the mandible, and end-tidal sevoflurane concentration (EtSev) of 2.5 vol%, to indicate the adequate depth of anesthesia, for insertion of the device. Each device was inserted by an experienced anesthesiologist who had performed at least 75, size 2.5 PLMA, and 20, size 2.5 i-gel placements.
The ease of insertion was graded as very easy, easy, or difficult by the attending anesthesiologist. The device was inserted in the ‘sniffing’ position. The following maneuvres were included, (i) chin lift, (ii) jaw thrust, (iii) head extension, and (iv) neck flexion. If the device could be inserted without any manipulation, it was graded as ‘very easy’. If there was only one manipulation required, it was called ‘easy,’ and any difficulty more than that was graded as ‘difficult’. The number of attempts was noted, and it was considered a failure if the insertion was not successful in three attempts. The patient was then excluded from the study, and either a different size of the same device was inserted or the child was intubated with an endotracheal tube.
The device was fixed from maxilla to maxilla, and the cuff was inflated in the PLMA group using a cuff pressure monitor (Mallinckrodt Medical Gmbh, Hennef, Germany) to achieve a pressure of 60 cm H2O. This pressure was maintained throughout the surgery by continuous cuff pressure monitoring. A lubricated gastric tube was passed through the gastric channel. The device was connected to a closed circle breathing system (Fabius® plus anesthesia work station, Draeger, Germany) and an effective airway was defined by a square wave capnograph trace, normal chest movements, stable oxygen saturation (SpO2), not less than 95%, and bilateral auscultation of the chest.
Any coughing, breath holding, or laryngospasm were noted. Non-invasive systolic blood pressure (SBP), heart rate (HR), and oxygen saturation (SpO2) were recorded just before and one and five minutes after insertion. A 20% increase or decrease in SBP and HR between, before, and after insertion was considered clinically significant. The ease of insertion was graded by the attending anesthesiologist, but the rest of the data were recorded by an independent observer who was blinded to the study.
The oropharyngeal sealing pressure (OSP) was measured by closing the expiratory valve of the circle system at a fixed gas flow of 3 L. min-1, observing the airway pressure at which equilibrium was reached. At this point, gas leakage was heard at the mouth, at the epigastrium (epigastric auscultation), or coming out of the drainage tube. The Manometric stability test was supposed to be the most reliable test.
Statistical analysis was done using the SPSS software version 17.0;(SPSS Inc. Chicago, USA). Sample size was based on a crossover pilot study of 10 patients, and was selected to detect a projected difference of 30% between the groups for airway sealing pressure, for a type 1 error 0.05 and a power of 0.8. The demographic data (age, weight, and height) and complications were analyzed using the Chi-square test. The OSP and hemodynamic data were compared using the unpaired t-test. The Fisher's exact test was used to analyze the insertion characteristics and insertion attempts of the gastric tube. Unless otherwise stated, data are presented as mean (SD). A ‘P value’ of <0.05 was considered statistically significant.