Comparison of ProSeal laryngeal mask airway size 2 and 2½ in anesthetized and paralyzed pediatric patients with same weight group: A prospective randomized clinical study.

CONTEXT: ProSeal laryngeal mask airway (PLMA) efficacy in pediatric anesthesia. AIMS: The aim of this study was to compare PLMA size 2 and 2½ in anesthetized paralyzed pediatric patients weighing 20-30 kg undergoing elective surgery. SETTINGS AND
DESIGN: A prospective randomized study was conducted in a tertiary care teaching hospital.
MATERIALS AND METHODS: A total of 60 American Society of Anesthesiologists I pediatric patients of either sex having body weight between 20 and 30 kg undergoing elective surgeries were randomly allocated to PLMA of either size 2 or 2½. Standardized anesthetic technique with propofol, sevoflurane, vecuronium bromide, nitrous oxide was used in all patients. Parameters such as number of attempts, time to achieve an effective airway, hemodynamic parameters, drain tube test, oropharyngeal leak pressure (OPL), gastric tube placement, and postoperative adverse events were noted. Statistical analysis by Kolmogorov-Smirnov analysis, Mann-Whitney U-test, Student's t-test, Wilk's lambda test and power analysis was done.
RESULTS: There were no significant differences in demographic variables, ease of insertion and ventilation, number of insertion attempts, hemodynamics, and postoperative complications. OPLs were slightly higher in PLMA size 2½ (27.38 ± 6.36 vs. 22.62 ± 2.85 cm H2O, respectively; P = 0.001) than size 2.
CONCLUSIONS: Both PLMA size 2 and 2½ provided adequate seal pressures that would allow positive pressure ventilation in healthy children. Thus PLMA of either size 2 or 2½ can be used as a reliable airway device in children weighing 20-30 kg.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Optimal size selection is critical to the safe and effective use of laryngeal mask airway (LMA).[1] A fundamental difficulty in predicting optimal LMA size is that relationship between sex, weight, height, and pharyngeal geometry is inconsistent.[2] Ideally the optimal LMA should be easy to insert, have an oropharyngeal leak pressure (OPL) sufficient for positive pressure ventilation (PPV), and pharyngeal mucosal pressure less than capillary perfusion pressure.[3] One method of studying this is to compare the incidence of air leak from the gap between mask and pharynx for different sizes of LMAs during PPV. LMA associated with lower incidence of air leak may be appropriate. Another method is to identify, which size of mask exerts lower pressure on pharynx. When pressure exerted on pharynx is greater than mucosal capillary perfusion pressure, there is theoretical possibility of mucosal ischemia. This problem may be minimized when the cuff is inflated with minimum volume of air that effectively prevents air leak around the mask.[4] However, there are very few studies in which an attempt was made to determine the appropriate size of LMA. Voyagis, et al.[5] and Brimacombe et al.[6] showed that a sex based formula was more successful strategy than manufacturer weight based recommendations in adults. The instruction manual of the ProSeal LMA (PLMA) indicates that size 2 should be used in children weighing 10-20 kg and 2½ in 20-30 kg.[7] In this study, we have investigated if there are any differences between PLMA size 2 and 2½ for pediatric patients weighing 20-30 kg in terms of ease of insertion, OPL, gastric tube placement and postoperative complications.

MATERIALS AND METHODS

After obtaining approval from the local Ethical Committee and parental consent, 60 American Society of Anesthesiologists (ASA) I children weighing 20-30 kg undergoing general anesthesia for elective surgery were included. Patients having upper respiratory tract infection, known airway problems, ASA status more than one, having risk of aspiration and undergoing laparoscopic surgeries were excluded from the study.

In this randomized trial, patients were randomly allocated to either Group I (n = 30) where PLMA size 2 was used or Group II (n = 30) where PLMA size 2½ was used by drawing slips from a sealed envelope before induction of anesthesia. 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 of 0.05 and a power of 0.8.

Patients were kept fasting for 6 h for solids and 4 h for clear liquids prior to surgery and written informed consent was obtained from parents of all patients. In all patients intravenous (i.v.) access was obtained when child was with parents in preoperative room and premedicated with i.v. midazolam 0.03 mg/kg. Routine monitoring such as pulse rate (PR), blood pressure, respiratory rate and electrocardiography were done in operation theatre. Anesthesia in all patients was induced using propofol 2 mg/kg and fentanyl 2 mcg/kg and maintained by sevoflurane 2% along with 50% nitrous oxide in oxygen followed by injection vecuronium bromide 0.06-0.08 mg/kg intravenously. After ventilating for 3 min via face mask using pediatric circuit, the PLMA either size 2 or 2½ was introduced by using standard introducer tool technique with head and neck in neutral position and intra-cuff pressure was set at 60 cm H2O using cuff pressure manometer. Further anesthesia was maintained with 66% nitrous oxide in oxygen along with 2% sevoflurane on PPV. Intra-cuff pressure was rechecked intermittently and set at exactly 60 cm H2O using the hand held mechanical cuff inflator (Portex Ltd., Hythe, UK). Each device was inserted when fully deflated. Parameters such as airway leak pressure, ease of insertion, drain tube test, gastric tube placement, hemodynamic parameters, and postoperative adverse events were measured and recorded by an independent unblinded observer.

Hemodynamic parameters including basal values of PR, systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and peripheral oxygen saturation (SpO2) were recorded prior to induction, after induction, and 1, 2 and 5 min after device placement. The number of insertion attempts was recorded. Manipulating the LMA in oral cavity was not considered as an attempt. If device was removed from the mouth, it was considered as one attempt. Two attempts were allowed before labeling the device used as failure. The time between picking up PLMA (T1) and successful placement (T2) was recorded. A successful placement was defined as normal thoraco-abdominal movements with gentle manual squeeze of reservoir bag. OPL was determined at 60 cm H2O cuff pressure. Airway sealing was determined by closing the expiratory valve of breathing system at a fixed gas flow of 3 L/min, ventilator support off and noting the airway pressure at which equilibrium was reached and by auscultation of air leak on the trachea. Maximum allowed airway pressure was 40 cm H2O. A drain tube test was conducted to confirm correct position of PLMA. A small amount of lubricant jelly was placed on proximal end of drainage tube. A slight up and down movement of lubricant conus was judged as positive drain tube test. A well lubricated gastric tube 10F for size 2 and 12F for size 2½ PLMA was inserted through the drain tube. Correct placement was judged by auscultation on stomach with injection of small amount of air and/or gastric fluid aspiration.

At the end of surgery, anesthesia was discontinued, neuromuscular blockade reversed and PLMA was removed once the child was fully awake. Any adverse event such as hoarseness, coughing, laryngospasm, sore throat, evidence of trauma or problem with the device was noted.

Statistical analysis

The distribution of data was determined by Kolmogorov-Smirnov analysis and it was found that data was normally distributed for almost all the characteristics and wherever normal distribution was not found, appropriate nonparametric tests (like Mann–Whitney U-test) were applied. Statistical analysis was performed with Student's t-test. Percent relative changes were also determined and compared between two groups. To detect changes occurring over a period of time in hemodynamic characteristics, multivariate analysis (Wilk's lambda test) was used.

RESULTS

There was no statistically difference between two groups with regard to demographics [Table 1]. The changes in PR, SBP, DBP and MAP were comparable in both groups [Table 2]. There was no desaturation in any patient in any group. PLMA size 2 was inserted in first attempt in 90% (27/30) cases and in second attempt in 10% (3/30) cases. Size 2½ PLMA was inserted in first attempt in 83.3% (25/30) cases and in second attempt in 16.6% (5/30) cases.

Table 1

Demographic data

Table 2

Hemodynamic parameters

Mean time of insertion in Group I was 8.31 ± 2.77 s and in Group II was 11.66 ± 7.25 s (P = 0.026) which is significant by using Student's t-test. Mean OPL for Group I was 22.62 ± 2.85 cm H2O and for Group II was 27.38 ± 6.36 cm H2O (P = 0.001). Student's t-test was used and the result was highly significant. Mann-Whitney test was also applied and similar results were found. Drain tube test and gastric tube placement were similar in both the groups [Table 3]. In Group I, after removal of PLMA, there were blood stained secretions on PLMA cuff in one patient. One patient in Group II had episode of mild dry cough in the postoperative period.

Table 3

Comparison of insertion attempts, OPL, time of insertion, drain tube test and gastric tube placement between PLMA size 2 and 2½

DISCUSSION

In our study, in both groups, we did not find any significant hemodynamic response to PLMA placement. Similar hemodynamic response during PLMA insertion were found by Lopez-Gil et al.[8] and Agrawal et al.[9] In our study, PLMA size 2 was inserted in first attempt in 90% (27/30) cases and in second attempt in 10% (3/30) cases. Size 2½ PLMA was inserted in first attempt in 83.3% (25/30) cases and in second attempt in 16.6% (5/30) cases. Both groups were comparable (P = 0.670) statistically. Goldmann and Jakob[10] in their study found that first attempt insertion success rate for PLMA 2½ was 86.67%, which is comparable to our study.

The average insertion time of PLMA size 2 in our study was less (8.31 ± 2.77) s when compared to PLMA size 2½ (11.66 ± 7.25) s. The difference was statistically significant (P < 0.05). Brimacombe et al.[11] found that in anesthetized nonparalyzed adult patients insertion time for PLMA was 41 ± 49 s. We found shorter time for insertion when compared to Brimacombe et al. because of paralyzed state and pediatric age group of our patients. In our study, mean OPL for PLMA size 2 was 22.62 ± 2.85 cm H2O and for PLMA size 2½ was 27.38 ± 6.36 cm H2O (P = 0.001) with head in neutral position. The result was highly significant. Goldmann and Jakob[12] found OPL for PLMA size 2 was 18.8 ± 4.8 m bar in neutral position, in maximum flexion was 33.8 ± 6.8 m bar and in maximum extension was 13.3 ± 5.7 m bar. Similar results were found by Kuppusamy and Azhar.[13] Arslan et al.[14] found OPL 26.4 ± 5.5 cm H2O for PLMA size 2 in spontaneously breathing patient. Lardner et al.[15] reported same OLP but Lopez-Gil et al.[16] in their study reported higher OPL in children receiving neuromuscular blocking agent.

In our study, drain tube test was positive in 93.3% (28/30) patients in both PLMA size 2 and 2½. In 6.7% patients for PLMA both sizes it was negative, which is similar to study by Goldmann and Jakob.[12] Lubricated 10 F gastric tube was placed through PLMA size 2 in 86.6% (26/30) patients and 12F through PLMA size 2½ in 93.3% (28/30) patients because we took only one attempt at gastric tube placement but the airway seal was adequate in all the four patients. Lopez-Gil et al.[8] placed gastric tube in first attempt in 57 patients in digital technique; and in 52 patients by bougie guided technique. In Group I, after removal of PLMA, there were blood stained secretions on the cuff in one patient, but the PLMA bowel was free of secretions. This might be due to trauma caused by manipulations in the oral cavity, although the device was placed in first attempt. One patient in Group II had episode of mild dry cough in the postoperative period. Similar findings have been shown by previous studies by Kihara et al.[17] and Lopez-Gil et al.[8]

The important finding in our study is that there was no significant difference between two sizes of PLMA in terms of hemodynamics, OPL, ease of insertion, and drain tube test when used in same weight based groups. Our study was limited by its small sample size as a large sample will be required to confirm the findings. Similar studies were done by Berry et al.[18] and Asai et al.[4] but in adult patients. Voyagis et al.[5] concluded that airway is improved by applying gender related formula for selection of size of LMA. In our study we found that both sizes were suitable for weight groups 20–30 kg as both were easy to insert, had nearly similar OPL (though size 2½ had slightly higher OPL than size 2). This may have implications for provision of LMA outside the operation theater such as in wards, in recovery rooms, accident and emergency, ambulances and helicopters where availability of a variety of sizes may be not be possible because of lack of space and cost. A literature search failed to reveal published data on weight based parameter in pediatric patients. Our study is based on Indian children population and we did not found any literature about pharyngeal variation between children of UK and India.

CONCLUSION

As ProSeal size 2½ (Group II) had higher OPL, it is still the best size for weight group 20-30 kg as recommended by manufacturer, but in this study we observed that in case size 2½ is not available, size 2 could also be used as it has also provided the good conditions to ventilate the children having this weight range. Hence, PLMA size 2 and 2½ both can be safely used in children weighing 20-30 kg undergoing elective surgery. However, we consider that further conclusive trials are required for manufacturer's weight based recommendations.