Comparison between Classic Laryngeal Mask and Cobra Perilaryngeal Airway during Mechanical Ventilation

Selection of an optimal method for the safe preoperative airway management is the base of a successful general anaesthesia. To achieve this goal various methods and devices are used including endotracheal tube and laryngeal mask airway, each has its own advantages and disadvantages. In this study, we compared a new supraglottic instrument (cobra perilaryngeal airway) with laryngeal mask airway (LMA), considering each one''s abilities specially their role in preventing intraocular pressure rise during insertion. In a prospective randomized clinical trial 200 ASA class I, II patients with no history of glaucoma, cardiovascular or respiratory diseases and susceptibility to difficult intubation were randomly divided into two similar groups (100 subjects each). None of them (age range 6-70 yrs) received premedication after preoxygenation and induction with sodium thiopental, fentanyl and atracurium. The patient was ventilated manually then one of the devices was inserted. After assurance of the correct position, its cuff was filled with air. In this study various factors including intraocular pressure (IOP), systolic blood pressure (SBP), SPO2, end tidal CO2 (ETCO2), heart rate, peak airway pressure and end expiratory tidal volume were recorded exactly before the induction (time 1), after the induction (time 2), 5 minutes after the induction (time 3), 15 minutes after the induction (time 4), and 5 minutes after releasing the device (time 5). Cuff pressure was measured immediately after insertion and at the end of operation. Quality of insertion (1: simple 2: relatively simple 3: difficult 4: unsuccessful), their complications (bleeding, no bleeding) and sore throat 2 and 24 hours after the operation were detected by interview. Fitness of LMA or Cobra PLA on airway for prevention of air leakage were recorded as well. Qualitative data with chi-square and quantitative data with t-test and SPSS software (version 11) were analyzed. There was no clinical significant difference between the two groups regarding age, sex, ASA class, weight, duration of surgery, SPO2, heart rate and blood pressure. Cobra PLA offered advantages in regard to easy insertion (p=0.005), sore throat (p<0.0001) and bleeding (p<0.0001). Mean rise of intraocular pressure and mean increase of systolic blood pressure (at the time 3) was higher in LMA (p=0.02). Regarding ETCO2 (p=0.0001), peak airway pressure (p<0.0001), ability to fitness on airway (p=0.01) and cuff pressure (p<0.0001) cobra significantly offered advantages over LMA. Cobra PLA is a useful device for airway management in general anaesthesia during mechanical ventilation with minimal post-up complication and simplicity of usage offering high potential ventilation. More studies are required in regard to use of Cobra tube in different ages. (Tanaffos 2006; 5(2): 13-19)