|Year : 2008 | Volume
| Issue : 2 | Page : 170-174
Comparison of Clinical Performance of the LMA Classic with Disposable Soft Seal LMA in Spontaneously Breathing Patients for Elective Surgical Procedures
Dipasri Bhattacharya1, BM Bhalotia2, Sudev Saha3
1 Associate Professor, Dept.of Anaesthesiology, B.S. Medical College, Bankura, West Bengal, India
2 P.G.Student, Department of Surgery, N. R. S. Medical College, Kolkata, West Bengal, India
3 Associate Prof., Department of Surgery, N. R. S. Medical College, Kolkata, West Bengal, India
|Date of Acceptance||16-Mar-2008|
|Date of Web Publication||19-Mar-2010|
B-26/10, E.K.T.P. Phase IV, Abhyudoy Cooperative, P.O. E.K.T, Kolkata - 700107
Source of Support: None, Conflict of Interest: None
The laryngeal mask airway - LMA classic has been widely used in clinical practice. A new disposable supraglottic airway device, the soft seal LMA has been introduced recently. We have compared the LMA classic with the disposable soft seal LMA in terms of various clinical parameters.
Two hundred patients aged 20-50 years, body weight 50 to 70 kg, ASA I and II were randomly assigned into two equal groups for airway management during surgery with size 4 LMA, Group A (n=100) for classic LMA and Group B (n=100) for disposable soft seal LMA. Anaesthesia was induced with fentanyl 2mcg.kg-1 + propofol 3mg.kg-1, maintained with nitrous oxide 66%, oxygen 33% and halothane 2 to 3%. The variables studied were ease of insertion and insertion time, cuff pressure changes during nitrous oxide anaesthesia, presence of blood on the LMA on withdrawal and postoperative sore throat at 2 and 24 hours.
LMA classic and disposable LMA showed similar clinical performance as shown by their insertion time, successful insertion at first attempt achieved within 15 seconds in 98% of Group A and in 97% of Group B. LMA cuff pressure increased from 45.01 ± 8.0 mm of Hg to 68.40+ 10 mm of Hg in Group A and from 45.02 ± 2.0 to 48.10±6.0 mm of Hg in Group B (P<0.05). Macroscopic blood was seen on 8 occasions in Group A and never in Group B. Incidence of sore throat at 2 hours post operatively was 30% in Group A and 10% in Group B (P< 0.05). However, there was no such difference at 24 hours postoperatively.
So LMA disposable soft seal is a useful alternative to LMA classic, there is less trauma and less incidence of sore throat in the postoperative period.
Keywords: Disposable soft seal LMA; LMA classic; Clinical performance
|How to cite this article:|
Bhattacharya D, Bhalotia B M, Saha S. Comparison of Clinical Performance of the LMA Classic with Disposable Soft Seal LMA in Spontaneously Breathing Patients for Elective Surgical Procedures. Indian J Anaesth 2008;52:170-4
|How to cite this URL:|
Bhattacharya D, Bhalotia B M, Saha S. Comparison of Clinical Performance of the LMA Classic with Disposable Soft Seal LMA in Spontaneously Breathing Patients for Elective Surgical Procedures. Indian J Anaesth [serial online] 2008 [cited 2020 Nov 27];52:170-4. Available from: https://www.ijaweb.org/text.asp?2008/52/2/170/60616
| Introduction|| |
The reusable laryngeal mask airway, LMA classic is widely being used for securing airway in patients undergoing elective surgery under general anaesthesia  . Recently a new disposable soft seal variety made up of latex free thermo sensitive plasticized polyvinyl chloride has been introduced. These are preferred for a number of reasons , . First the silicon-based classic LMA is too expensive , . Secondly reusable devices require time and effort for maintenance and there is always some risk of contamination if the sterilization process is not proper ,,,, . The disposable LMA made of polyvinyl chloride avoids this complication. They are available in presterilized packs ,,,, . It has been documented by many authors that disposable LMA can be used successfully in patients with less side effects ,, . Particularly the disposable soft seal variety causes less trauma during insertion and minimize the incidence of postoperative sore throat  . The aim of this study was to evaluate the clinical acceptability of the new soft seal disposable LMA as an alternative to the LMA classic. We have compared them in terms of ease of insertion, insertion time, cuff pressure changes during nitrous oxide anaesthesia and postoperative complications like sore throat, at 2 and 24 hours following surgery. Since the disposable LMA is now available in India, this study is all the more relevant and worthwhile.
| Methods|| |
After obtaining approval from the institutional ethical committee and informed written consent from the patients 200 patients (ASA I& II), aged 20 to 50 years, body weight 50 to 70 kg of both sexes undergoing elective surgery under general anaesthesia with spontaneous ventilation using LMA (no 4 size) were randomly allocated into two equal groups. Patients of ASA III& IV predicted difficult airway management, requiring surgery in nonsupine position, undergoing oral or nasal surgery and patients having history of preoperative sore throat were excluded from the study. Patients were randomly allocated according to computer - generated random number sequences and sealed opaque envelopes, to placement of either the LMA Classic followed by the Soft seal or vice versa. Group A (n=100) had LMA classic insertion and Group B (n=100) had soft seal disposable LMA insertion for a wide range of surgery (general, gynaecological, urological, orthopaedic and plastic surgery of one and half to two hours duration).As the patients of average body weight 50-70 kg were chosen for the study, size 4 LMA was used  .Patients were unaware of the type of airway device used. The same anaesthesiologist inserted all laryngeal masks in both the groups. Routine pre insertion test of the cuff for leaks was done immediately before use. The tip of LMA and posterior aspect of the mask was coated with watersoluble lubricant, which is the normal practice in our institution. The cuff was inflated before insertion with ambient room air at 10mm of Hg (15 cm of H2O) above atmospheric pressure, which is the standard practice of our institution and advocated by many authors who believe insertion of laryngeal mask with cuff partially inflated is equally successful to insert the laryngeal mask and results in a lower incidence of sore throat and pharyngeal mucosal bleeding , . No premeditation was used and all patients were preoxygenated for 3 minutes before intravenous induction which consisted of 2 mcg.kg -1 of fentanyl and 3 mg.kg -1 of propofol. The laryngeal mask was inserted after loss of eyelash reflex and the relaxation of the jaw  . The LMA was held at the masktube junction in pen holding fashion and was inserted in sniffing position to facilitate passage around the back of the mouth in the line of palatopharyngeal curve. The mask was introduced till a definite resistance was felt as the tip entered the hypopharynx and backline of the airway tube faced upper lip. The mask was then inflated with the recommended volume and the position was secured with tape and bite block. An unsuccessful attempt at insertion was defined as placement of the mask into the mouth and withdrawal from the mouth. Successful placement and adequate ventilation was confirmed by clinical observation of the clear airway, observing chest wall movement with manual ventilation, listening to escape of gas from the mouth, observing the square wave tracing of capnograph and satisfactory movement of the reservoir bag on spontaneous ventilation. Mapleson A circuit was used. Anaesthesia was maintained with N2O + O2 (2:1) and halothane 2 to 3%. Intra operative analgesia was maintained with intravenous infusion of diclofenac sodium 75 mg in 100 ml normal saline. The insertion time was noted i.e. the time (in secs) taken from loss of eyelash reflex to successful LMA insertion was recorded in both the groups.
The ease of insertion of laryngeal mask was graded as:
After proper positioning of LMA the pilot balloon cuff pressure was adjusted to 45 mm of Hg (60 cm of H2O) as recommended , using a cuff pressure monitor. Cuff pressure was recorded every half hourly. Time 0 sec was the moment the cuff was inflated to a pressure of 45 mm of Hg and monitored half hourly until the administration of N2O was switched off. The monitors used were SpO2, NIBP, continuous ECG and capnography. At the end of surgery nitrous oxide and halothane were discontinued to allow the patient to resume full recovery and cuff pressure was recorded. When the protective reflexes had returned to normal, the LMA was removed after deflation of the cuff and presence of blood if any was noted. Presence of sore throat was enquired and the patients were requested to grade the sore throat (none, mild, moderate and severe) at 2 and 24 hours after surgery by another anaesthesiologist. The following parameters were recorded: patient's demographic data (sex, age, body weight, duration of surgery - from the time of skin incision to skin closure, duration of anesthesia - from the time of induction to removal of LMA), time to insert LMA, number of insertions, laryngeal mask cuff pressure every ½ hour intraoperatively.
- very easy insertion at first attempt with no resistance,
- easy at first attempt with little resistance,
- some difficulty, but successful at second attempt and
- not successful.
Two groups were chosen. Statistical analysis was done. Sample size calculation was performed using Sampsize version 2.0 (Sample size tables for clinical studies ; Blackwell Science Ltd., Oxford, United Kingdom). The study had a power of 90% ((3 =10%, a=0.05 ) and the standardized difference was 0.35 (SD, 0.86).The estimated sample size was 88 patients per group. Two groups each of 100 patients were chosen. Comparison were performed using Mann - Whitney and Wilconsin tests as appropriate for paired and independent observations and Chi-square test for comparison of categorical outcomes. All data were presented as mean+SD and P<0.05 was considered to be significant
| Results|| |
The two groups were similar with respect to age, sex, body weight, height, duration of surgery and anaesthesia [Table 1]. [Table 2] indicates the type of surgeries in both the groups. The overall laryngeal mask insertion time was within 15 seconds and successful insertion at first attempt was performed in 98% of Group A (LMA classic) whereas it was 97% in Group B (LMA disposable) [Table 3]. In none of the cases there were laryngospasm, retching or any haemodynamic or respiratory side effects. The laryngeal mask cuff pressure increased from 45.01±8.0 to 68.40±10 mm of Hg in Group A and from 45.02±2.0 to 48.10±6.0 mm of Hg in Group B, P<0.05, [Table 4].
Macroscopic blood was seen on 8 occasions in Group A whereas none in Group B, P< 0.05, [Table 5]. The incidence of sore throat at 2 hour was 30% in Group A, 24% mild to moderate grade and 6% severe grade whereas it was 10% in Group B of only mild to moderate grade, p<0.05.[Table 5].
| Discussion|| |
LMA is the most important milestone in the development of airway devices in the past 20 years. It was originally developed for airway management of routine cases with spontaneous ventilation  .LMA classic is a reusable device. It is made up of medical grade silicone and is latex free  . It is to be discarded after 40 autoclaving. LMA is specially designed to conform to the contours of the hypo pharynx. LMA classic is currently available in 8 sizes: 1, 1½, 2, 2½, 3, 4, 5 and 6.
Recently the new variety of soft seal disposable LMA which is made primarily of medical grade polyvinyl chloride is available in the market  . Three sizes of this variety are available ,,, . They are used once and thereby contamination can be avoided in contrast to LMA classic  . First reports on the use of a new disposable soft seal laryngeal mask were compared with LMA classic proved that both LMA provided an adequate airway and similar clinical performance in spontaneously breathing patients  . Brain opposed the idea of a PVC based equivalent of LMA classic because adequate softness could never be achieved and there would be many instances where the disposable LMA would be sterilized and reused  .Ultimately disposable LMA became commercially available in late 1997  . Its clinical performance appears to be similar to the LMA classic  . Of late, the disposable LMAs are being made of a plastic material that closely mimic silicone to achieve the softness of classic LMA  . In our study the clinical performance as evidenced by ease of insertion at first attempt and LMA insertion time was almost similar in both the groups. During N 2 O anaesthesia a significant increase in cuff pressure was seen in LMA classic because of the diffusion of N 2 O used for the maintenance of anaesthesia. A study was undertaken in 2000 by Brimacombe and Keller comparing intracuff pressure changes with and without N 2 O in the anaesthesia gas mixture. They found that intracuff pressure remained stable without N 2 O but increased from 45 to 92 mm of Hg in 30 minutes with N 2 O  . Brimacombe et al in 1998 studied 60 adult patients breathing 66% N 2 O in oxygen and found that intracuff pressure was increased for classic LMA but remained unchanged for the disposable LMA because polyvinyl chloride based LMA cuff is relatively impermeable to N 2 O  . In our study the cuff pressure was increased from 45.01±8.0 to 68.40 ±10 mm of Hg in Group A (LMA classic) but remained almost unchanged in Group B (disposable soft seal LMA). The incidence of sore throat using the LMA classic was 30% at 2 h postoperatively identical to the finding of Dirgley et al, Brimacombe et al and Molt et al ,, when the cuff was partially inflated compared to 42% if the cuff was fully inflated after insertion. Our incidence of sore throat was only 10% in disposable soft seal LMA group which was similar to the studies using disposable LMA by Dingley et al, and Molt et al , . The incidence of sore throat is less with disposable soft seal LMA because there is practically no change in cuff pressure and no evidence of soft tissue trauma by the presence of blood on LMA during removal, which is the probable explanation for increased incidence of sore throat in LMA classic , .
To conclude, disposable soft seal laryngeal mask is an acceptable device and is a useful alternative to LMA classic with no change of intracuff pressure during N 2 O anaesthesia and less incidence of sore throat in the postoperative period.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]