Classic Laryngeal Mask Airway (CLMA) has been used as a substitute for the Endotracheal Tube (ETT) during elective and emergency anesthesia and as a lifesaving airway conduit in patients with difficult intubations in various branches of surgery and critical care [1-8].

The most common induction technique to place CLMA is administering propofol in a fixed dose of 1-3 mg/kg. Unfortunately, administering propofol alone can be insufficient or at times in excess resulting in hazardous airway complications (coughing, laryngospasm) and hemodynamic disturbances [9-10].

Various combinations of propofol with either etomidate [11] or sevoflurane [12] have been used to reduce the incidence of hypotension while using propofol.  Induction with 8% sevoflurane to the point of loss of eyelash reflex followed by the administration of 1.5mg/kg propofol resulted in most successful CLMA placement as compared to propofol or sevoflurane alone [12]. However, the fall of blood pressure in their study was no different when induction was done with 3mg/kg propofol. In our experience, getting the patient deeper with the sevoflurane after IV induction with propofol but before CLMA insertion gives the propofol a chance to circulate and peak in the brain before CLMA insertion resulting in smooth CLMA placement without undue hemodynamic disturbances. To validate our technique, we undertook a prospective trial comparing the placement characteristics of CLMA and hemodynamic variations with 3 mg/kg propofol alone or with 1.5 mg/kg propofol followed by one minute of 6% sevoflurane in 50% oxygen+50% N2O with patient breathing spontaneously. Our research hypothesis was that propofol 1.5 mg/kg followed by 6% sevoflurane in 50% each of oxygen and N2O shall provide a better characteristic of CLMA placement with lesser hemodynamic disturbances than with 3mg/kg propofol alone.

After obtaining ethical committee approval from the Ministry of Health (Oman) and written informed consent from patients, this prospective randomised study was carried out on fifty-one adult American Society of Anesthesiologists Physical Status I–II patients aged 18–60 years undergoing elective surgical procedure under general anesthesia were studied over a period of 1 year from the date of ethical approval. Randomization was done by allocating patients with even hospital number to Propofol Group and odd hospital number to Sevoflurane-Propofol Group. 

The following patients were excluded from participating in this study:

• Patients with a history of difficult intubation or anticipated difficult intubation

• Allergy or sensitivity to propofol

• Body mass index>1.5 times normal

• Heavy smokers (>20 cigarettes/day)

• Patients with diabetes, hypertension, cardiovascular disease, and ischemic heart disease

The initial sample size that was set for this study was 150 which would have given power of the study as 90. Unfortunately, elective anesthetic procedures were curtailed due to Covid-19 pandemic and hence the sample size was restricted to 51 patients. The patients were randomly allocated to either Propofol Group (p Group, n = 26) or Sevoflurane-Propofol Group (SP Group, n = 25) on the basis of odd or even hospital registration number respectively.

p Group patients were induced with 3 mg/kg of propofol IV. This was followed by administration of 50% oxygen-50% N2O with patient breathing spontaneously for 60s before attempting to place CLMA.

SP Group Patients were induced with 1.5 mg/kg of propofol IV followed by 6% sevoflurane in 50% oxygen-50% N2O with patient breathing spontaneously for 60s before attempting to place CLMA. An anesthesiologist who was well conversant with its placement technique placed the CLMA.

In case of apnea during induction, assisted ventilation was provided at rate of 12/min using 6-8 ml/kg tidal volume. Additional propofol (0.5mg/kg) was administered if there was any adverse response such as movement, gagging, coughing, or laryngospasm. If CLMA placement failed in the first attempt or was inadequate, 2 further attempts were made every 30 seconds, each time preceded by ventilation with oxygen and N2O as above.

Table 1: In Addition, the Following Parameters Were Also Recorded (Lund and Stovner Grading System)

The following parameters were recorded:

• Time to successfully place CLMA. This included time in seconds from picking up the CLMA to first capnographic curve

• Number of attempts needed to successfully place CLMA

• Failures, if any

• Changes in BP and HR 2, 4, and 6 min after completion of induction and CLMA placement as compared to immediate pre induction values

Statistics

Data analysis has been done with the help of SPSS Software Version 18 (IBM, Chicago, USA). Quantitative data in tables have been presented as mean and standard deviation. Comparison among the groups has been done using unpaired t-test and Mann–Whitney test as per the results of normality test. p<0.05 has been considered statistically significant in this study.

Table 1 shows no statistical significant difference in the two groups in respect to jaw relaxation during CLMA insertion (p = 0.263). However, there were two patients in p Group whose jaws were not adequately relaxed and needed further dose of propofol to allow jaw relaxation and permit CLMA placement in the second attempt. 

As may be seen from Table 2, there were no failures (impossible placements) of CLMA insertion in either group. In addition, there was no significant difference noted in ease of insertion of CLMA in both groups (p 0.789). 

Patients of both the groups showed no significant difference in body movement during CLMA insertion as shown in Table 3. Majority of the patients in either group showed no movement during CLMA placement. 

There was no incidence of coughing upon CLMA insertion in either group as shown in Table 4. As can be seen from Table 5, except for one patient in the propofol group who was noted to have minor gagging during CLMA placement, all other patients remained gag free (p = 0.322). There was no patient who had developed laryngospasm while CLMA insertion in both groups (Table 6).

Failure to place CLMA was not encountered in any of the patients of either group. However, there were two patients in propofol group who needed a second attempt to successfully place the CLMA. This was secondary to poor jaw relaxation. 

As can be seen from Table 7 that a significant fall in systolic blood pressure is noted in both the groups at 4 min time interval as compared to control value. The fall remains significantly low till the 6th minutes after CLMA placement in either group. Effect of sevoflurane cannot be ruled out as it was started in both the groups at 2-3% concentration after CLMA placement. A similar effect can be seen on the diastolic blood pressure but unlike systolic blood pressure, diastolic blood pressure was noted to rise above the control value at 6 min time interval in both the groups. These changes were statistically significant (Table 8).

Table 1: Showing the Incidence of Jaw Relaxation in the Two Groups

Table 2: Showing Incidence of Ease of CLMA Placement

Table 3: Showing Incidence of Body Movement during CLMA Placement

Table 4: Showing Incidence of Coughing During CLMA Placement

Table 5: Showing Incidence of Gagging During CLMA Placement

Table 6: Showing Incidence of Laryngospasm in the Two Groups

Table 7: Showing Systolic Blood Pressure Changes at 2, 4 and 6 Minutes Post CLMA Placement As Compared To Control Values within the Two Groups

p-value: Comparison within the group as compared to control value

Table 8: Showing Diastolic Blood Pressure Changes at 2, 4 and 6 Minutes Post CLMA Placement as Compared To Control Values within the Two Groups

Table 9: Showing HR Changes At 2, 4 and 6 Minutes Post CLMA Placement as Compared To Control Values In the Two Groups

p-value: Comparison within the group as compared to control value

As is evident from Table 9 that a significant fall in heart rate is noted in both the groups at 4 min time interval as compared to control value.   The   fall   remains significantly low till the 6th minutes after CLMA placement in either group.

Table10: Shows Number of Attempts Required For CLMA Placement

p-value: Comparison within the group as compared to control value

Table 10 shows that number of attempts for CLMA placement is statically insignificant between the two groups. There were no patients who required more than 2 attempts for CLMA placement in either group.

We did not observe any statistical difference in the time of insertion required for CLMA placement in p and sp groups (p = 0.711). The mean placement time of CLMA was 38.81 and 37.56 seconds in the p-Group and SP-Group respectively.

The most commonly used induction agent for CLMA insertion continues to be propofol as this agent is known to obtund oropharyngeal reflexes. Propofol (2.5-3mg/kg) has been the induction agent of choice for CLMA insertion [13]. However, there are also conflicting reports regarding insertion of CLMA with propofol. Studies have shown an incidence of poor insertion condition in 38-60% patients with standard induction doses (2- 3 mg/kg) of propofol [14]. To overcome these shortcomings, there have been reports of the successful use of a combination of sevoflurane and propofol that resulted in higher frequency of CLMA placement in the first attempt as compared with induction of anesthesia with either sevoflurane or propofol alone [12]. In contrast, [15] observed that anesthetic induction with sevoflurane requires longer time to jaw relaxation and even causes jaw tightness.

In this study, we observed that there is no significant difference in using propofol as single induction agent for CLMA insertion or combination of propofol-sevoflurane. This difference in finding from earlier studies may be attributed to difference in methodology. We had administered a smaller dose of 1.5 mg/kg propofol followed by 6% sevoflurane for 60s in 50% oxygen and nitrous oxide prior to CLMA placement. 

In the present study the hemodynamic responses were nearly identical in both groups though significant changes were observed in blood pressure and heart rate between 4-6 min in the combination and propofol group alone. 

Insertion of CLMA was achieved in all patients in both groups with no failure. In contrast, in an earlier study there were four failures in LMA insertion in the propofol group [16]. This could be attributed to our restriction of CLMA placement by experienced anesthesiologist who had over 3 years of experience. 

However, although few more attempts at insertion were required in the P group, but overall they remained statistically indifferent in the two groups. In addition, all reported adverse events in this study were minor, and the consequences were not detrimental to patient safety. 

In our study, we did not encounter laryngospasm but in the study done by Molloy, M.E., Buggy, D.J. and Scanion, P.F. [15], laryngospasm was encountered in 10% of patients who received propofol and in 20% of patients who received sevoflurane, although we used the same sevoflurane concentration (6%) used by by Molloy, M.E., Buggy, D.J. and Scanion, P.F. [15]. This could be a chance finding.

Similarly, we did not encounter any patient who coughed during CLMA insertion. In the study done by Molloy, M.E., Buggy, D.J. and Scanion, P.F. [15], cough was encountered in 13% of patients who received propofol and in 25% of patients receiving sevoflurane. However, we had one patient in the propofol group who was noted to have minor gagging during CLMA placement. Patients of both the groups showed no significant difference in body movement during CLMA insertion. In addition, there was no significant difference in ease of insertion of CLMA in either groups (p = 0.789). 

As regard the degree of jaw opening, [17] in 1999 encountered difficulty in jaw opening in 30% of patients induced by sevoflurane. [16], encountered difficulty in jaw opening in 45% with sevoflurane and in 21% of patients induced by propofol. In our study there were two patients in propofol group whose jaws were not adequately relaxed and needed further dose of propofol to allow jaw relaxation and permit CLMA placement in the second attempt. Complete failure to place CLMA was not encountered in any of the patients of either group in this trial. 

This trial had its own share of limitations. First, we had to curtail sample size due to the closure of several operation theatres due to covid-19 pandemic for over a year. Second, we did not follow-up our patients for any evidence of laryngo-pharyngeal morbidity over next couple of days. 

In conclusion, this study observed that essentially there is no major difference in the speed, success of CLMA placement or unwanted complications when it was placed under propofol alone or a combination of sevoflurane and propofol.

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