Comparison of isoflurane and sevoflurane in anaesthesia for day care surgeries using classical laryngeal mask airway.

BACKGROUND: In the present study, we compared isoflurane with sevoflurane in day care surgeries in order to determine the suitability of each agent for anaesthesia with Classical laryngeal mask airway (LMA). AIMS: The aim of this study has been to compare isoflurane and sevoflurane as maintenance anaesthetic agents in day care surgeries with respect to intraoperative haemodynamics, recovery profile, time of first postoperative analgesia and pain score, adverse effects when used with classical LMA. SETTINGS AND
DESIGN: This open - level, prospective randomized study was carried out on 60 patients who were admitted on a day care basis for elective short surgical procedures.
METHODS: The patients were randomly assigned to one of the two study groups of 30 patients each. First group was maintained on isoflurane and second on sevoflurane as inhalational agent. STATISTICAL ANALYSIS: The observations obtained in both the groups were recorded and tabulated. Statistical analysis was carried out using the Student t test, Chi-square test, Mann-Whitney test.
RESULTS: Emergence from Sevoflurane was significantly quicker as compared to isoflurane. Sevoflurane group also showed earlier discharge time from the post anaesthesia care unit (PACU)-1 as compared to isoflurane group, but discharge time was same from the PACU-1. Isoflurane has more incidences of mild airway hyper reactivity when compared to sevoflurane.
CONCLUSIONS: It can be concluded that both isoflurane and sevoflurane are suitable for day care anaesthesia. Sevoflurane has little advantages of less airway hyper reactivity and quicker emergence and discharge from PACU-1.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Day care surgery is a planned surgery wherein the patients, requiring early recovery and discharge, are admitted for short stay for surgery on a non-resident basis. Advances in anaesthetic induction agents and airway management have contributed to the success of day care surgeries. An ideal day-care anaesthetic agent should have rapid smooth induction; provide optimum surgical conditions with rapid recovery and minimal side effects. One should be able to rapidly alter the effect site concentration, allowing the anaesthetic depth to be altered easily. Although no single anaesthetic agent completely satisfies all these requirements, pharmacological developments over the past decades have brought us considerably closer.[1] In recent times, inhalational agents like isoflurane[2] and sevoflurane[134] have shown a promising result. This study was conducted to compare isoflurane and sevoflurane, when used as maintenance anaesthetic agents for anaesthesia using classical Laryngeal mask airway (LMA) in day care surgery. The study was designed to determine if these agents offered advantages in terms of intraoperative haemodynamics, cardio respiratory effects, recovery profile, emergence times and adverse effects including severity of airway hyper reactivity associated with LMA removal.

METHODS

Approval from the ethical committee of the hospital and informed consent from each patient were taken. The study was an open level, prospective, randomized clinical trial. The study was done on 60 patients of American Society of Anaesthesiologist (ASA) grade I or II undergoing elective day care surgeries with an anticipated length of hospitalisation of less than 24 h post anaesthesia. The patients were randomly selected and divided into two group of 30 patients to receive either isoflurane or sevoflurane as a maintenance agent. The groups were:

Group I: Patients who were maintained on isoflurane anaesthesia

Group S: Patients who were maintained on sevoflurane anaesthesia

Upon arrival in the operation theatre, the patients were made to lie supine on the operating table, a peripheral vein was cannulated and an intravenous ringer lactate drip was started. The patients were connected to non invasive syphgmomanometer, Electrocardiogram (ECG) monitor and pulse oximeter.

A uniform premedication with Inj. Glycopyrrolate 0.2 mg, Inj. Ondansetron 4 mg and Inj. Fentanyl 1.5 mg/kg intravenous (IV) was given on the operating table 5 min before induction of anaesthesia. The patients were pre oxygenated with 100% oxygen for 3 min.

Induction was done with Inj. Propofol 2.5 mg/kg iv and classical LMA was inserted. Anaesthesia was maintained with oxygen (40%), nitrous oxide (60%) with isoflurane or sevoflurane on spontaneous ventilation with closed circuit. The volatile agent was administered at approximately one ‘minimal alveolar concentration’ (MAC) for 3 min i.e. 1.2% for isoflurane and 2% for sevoflurane. Then it was continued at 0.75 MAC i.e. 0.8% for isoflurane and 1.5% for sevoflurane, further increasing or decreasing by 0.5% for sevoflurane and 0.2% for isoflurane (0.5 MAC) according to the clinical assessment of the depth of anaesthesia and to maintain blood pressure at ±20% of base line values in response to surgical stimulation.

At the end of surgery, administration of isoflurane or sevoflurane was discontinued without tapering and then after 3 min nitrous oxide was discontinued. The LMA was removed after eye opening and mouth opening to command. The haemodynamic variables heart rate (HR), blood pressures, saturation percentage of oxygen (SpO2), respiratory rate (RR) was monitored initially every 2 min for the first 10 min and then every 5 min up to the end of the surgery. Then shifted to post anaesthesia care units (PACU); PACU-1 i.e. recovery room and then to PACU-2 i. e. surgical intensive care unit in our setup. Time of emergence from the inhalational anaesthetic (time of stopping inhalational agent to time of extubation) and recovery criteria (modified Aldrete score)[56] observed, the patient is shifted to PACU-1, when the score is 8 or more. Discharge criteria[3] were used for assessment and discharge from PACU-1 and 2. Time of discharge from PACU-1 and 2 and the duration from extubation were noted. Airway hyper reactivity score,[7] nausea score,[2] visual analogue score (VAS) for pain and any adverse effect were also noted.

Recovery criteria (modified Aldrete score)

Oxygenation

SPO2 more than 92% on room air - 2

SPO2 more than 90% on room air - 1

SPO2 less than 90% on oxygen - 0

Respiration

Breathes deeply and coughs freely - 2

Dyspnoeic, shallow or limited breathing - 1

Apnoea - 0

Circulation

B.P ± 20 mmHg of normal - 2

B.P ± 20 to 50 mmHg of normal - 1

B.P change more than 50 mmHg of normal - 0

Consciousness

Fully awake - 2

Arousable on calling - 1

Not responsive - 0

Activity

Moves all extremities - 2

Moves two extremities - 1

No movement - 0

Airway hyper reactivity score

Nausea score

None - 0

Mild (nausea and no vomiting) - 1

Moderate (nausea and occasional vomiting)-2

Severe (nausea and frequent vomiting) - 3

Pain score

VAS on a scale of 1 to 10

Discharge readiness from PACU-1

Alert and oriented to time and place

Conversant and cooperative

Stable vital signs for at least 0.5 h

Able to sit up without nausea and or dizziness

Pain is tolerable

Aldrete score is >/ = 8

Discharge readiness (home readiness) from PACU-2

Stable vital signs for at least 1 h

Pain controllable by oral analgesics

Nausea or emesis mild if present

Able to walk without dizziness, and able to retain oral fluids

The observations obtained in both the groups were recorded and tabulated. After the study, analysis of the data done by Chi-square test and t-test for parametric data and Mann-Whitney for non parametric data. A probability value (P value) of <0.05 was considered as statistically significant. The software used was stat 32 (Systat software, inc.)

RESULTS

The groups were comparable (P value >0.05) in terms of demographic data, ASA grading, type of surgeries and duration of anaesthesia [Table 1].

Table 1

Demographic and relevant data

In our study after LMA placement, the inhalational agent (isoflurane or sevoflurane) was started at 1 MAC (i. e.2% for sevoflurane and 1.2 for isoflurane) for 3 min and then maintained between 0.75 MAC (i. e. 1.5% for sevoflurane and 0.8 for isoflurane) and 0.5 MAC (i. e. 1.0% for sevoflurane and 0.6 for isoflurane) in both the groups. The mean concentration against time interval is plotted in the graph [Figure 1].

Figure 1

Graphical representation of inhalational agent concentration at various intervals in isoflurane and sevoflurane groups. LMA: Laryngeal mask airway

The blood pressures between the two groups were compared by the Mann-Whitney test. Systolic blood pressure (SBP) reveals lower values in Group S which were statistically significant to Group I, from start to the first 20 min [Figure 2]. Diastolic blood pressures (DBP) between the two groups reveal lower values in the Group S which were statistically significant when compared to Group I, from start to the first 40 min [Figure 2]. Mean arterial pressures (MAP) between the two groups reveal lower values in Group S which were statistically significant when compared to Group I, from start to the first 40 min. Statistical analysis indicated that both isoflurane and sevoflurane decrease SBP, DBP and MAP, although the fall was significantly more in the sevoflurane group. However we have reduced the MAC to keep these values within 20% of the baseline values in any group. HR and RR were comparable in both the groups and also did not change from the baseline values in any group. There were no episodes of hypotension (SBP less than 90 mmHg) or bradycardia (HR less than 60/ min).

Figure 2

Graphical comparison of diastolic BP and systolic BP at various intervals. (DBP I-Mean diastolic BP of Group-I, DBP S-Mean diastolic BP of Group-S, SBP I-Mean systolic BP of Group-I, SBP S-Mean systolic BP of Group-S)

Comparison of respiratory rate between the two groups did not reveal a statistically significant difference except for three isolated readings. Comparison of respiratory rates in the respective groups also did not reveal any significant change from the baseline values, P value >0.05. All the patients in both the groups maintained SpO2 above 96% throughout.

Analysis reveals quicker extubation in the sevoflurane group as compared to isoflurane group. Median (inter quarantile range [IQR]) in Group S was 4 (1.25) min ad thatin Group I it was 10 (1) min, with P values=2.22 E-11 as analysed by the Mann-Whitney test, which is significant. Discharge from the PACU-1 was significantly early in sevoflurane anaesthesia as compared to isoflurane anaesthesia, median±IQR in Group I was 47±7.25 min and that in Group S was 35±3 min. Mann-Whitney test revealed a P value=1.35×10–10, which is significant . There was a minor difference in the discharge times from PACU 2 between the isoflurane and sevoflurane groups, median±IQR in Group I was 136.00±20.50 while in Group S it was 132.00±21.25, this difference is not statistically significant as analysed by the Mann-Whitney test (P value=0.08).

In our study, the time of requirement of first post op analgesia after extubation is similar in both the sevoflurane and isoflurane groups; median±IQR in Group I was 53.0±19 min while in Group S it was 54.5±15 min. Analysis by the Mann-Whitney test revealed a P value=0.094 which is not significant.

In the present study, only one patient in the sevoflurane group and five patients in the isoflurane group complained of mild nausea in the PACU-1. Comparison by Mann-Whitney test revealed a P value of 0.08 which is statistically not significant; hence the incidence of nausea was comparable in the two groups. None of the patients in either group complained of nausea in PACU-2. There was no episode of emesis in any patient. Airway hypersensitivity score was higher in Group I in PACU-1 (P value=0.001). No other adverse effects were seen in the two groups.

DISCUSSION

In our study after LMA placement, the inhalational agent (isoflurane or sevoflurane) was started at 1 MAC for 3 min and then maintained between 0.75 MAC and 0.5 MAC in both the groups. Our study cannot draw any conclusions regarding equianaesthetic concentration effects of the anaesthetics as our clinical protocol like most other clinical protocols allowed us to titrate the anaesthetic concentration to maintain stable blood pressure within 20% of baseline values during the surgical case and fluid administration was not a controlled variable. Moreover, the use of other anaesthetic adjuvants was included as a part of the routine management of these patients like narcotics and nitrous oxide (N2O). Therefore, measurement of actual differences in blood pressure between the two groups could be difficult to detect due to routine clinical management that was guided by blood pressure. Smith et al.,[8] reported that the end tidal concentration of sevoflurane required to maintain a stable level of anaesthesia, as indicated by clinical and haemodynamic signs was 0.86±0.35 MAC and that of isoflurane was 0.69±0.17 MAC, which is correlating to our study.

In our study, we found that the SBP, DBP, MAP were all lower in the sevoflurane group when compared to isoflurane group. Within group comparisons also revealed a significant fall in the SBP, DBP and MAP in both the groups when these were compared to the baseline values. However, in both the groups, SBP, DBP as well as MAP did not change more than 20% from the baseline values. No episodes of hypotension, bradycardia, or arrythmias were recorded.

Frink et al.,[9] in their comparison of sevoflurane and isoflurane in healthy subjects found that compared to baseline values, sevoflurane anaesthesia decreased systolic and diastolic arterial blood pressures 3-5 min before surgical incision, whereas in the isoflurane group, systolic and diastolic arterial blood pressures did not differ from baseline values at this time. Arterial blood pressures did not differ from baseline values after incision or during maintainance anaesthesia with sevoflurane and isoflurane but increased in both groups during emergence from anaesthesia.

Bachani and Kothari[10] in their comparison of sevoflurane and isoflurane in paediatric patients observed that complications like bradycardia and hypotension were more with sevoflurane.

There was no episode of oxygen desaturation nor any differences in respiratory rate. Sevoflurane and isoflurane maintained adequate depth of anaesthesia in the spontaneously breathing patients in our study.

In our study, the time from the stopping of inhalational agent to the time of extubation was recorded and it was found to be significantly less in the sevoflurane group as compared to isoflurane group. Smith I et al.[8] in the comparison between sevoflurane and isoflurane found that for operations lasting 1-4 h (with a mean of 135 min), sevoflurane permitted emergence within 4.1±2.2 min after the end of anaesthesia compared with 6.7±2.2 min with isoflurane.

In our study there is a statistically significant difference in the discharge time from PACU-1 between the isoflurane and sevoflurane groups with earlier discharge from PACU-1 in the sevoflurane group compared to isoflurane group, However, this earlier discharge from PACU-1 did not translate into earlier discharge from PACU-2 (home readiness) for the sevoflurane group. Gupta et al.[11] concluded that recovery was faster with sevoflurane compared to isoflurane. They found a minor difference of 5 min in home readiness between sevoflurane and isoflurane.

The time of requirement of first postoperative analgesia was similar in the two groups; however patients in Group I had higher pain score (VAS-score) than Group S in PACU-1 (P value=0.03). The airway hypersensitivity scores were higher in the isoflurane group; however only mild coughing or bucking was seen, there were no critical airway events. Airway hyperreactivity during maintainence and emergence from anaesthesia can be attributed to several factors as the depth of anaesthesia, the choice of volatile anaesthetic drug, use of opioid analgesics, and history of upper respiratory infection. To specifically examine the impact of choice of volatile anaesthetic agent on airway hyperreactivity, this study attempted to control several factors that could contribute to airway hyperreactivity during maintainence and emergence from anaesthesia.

Pappas et al.[7] in their study found that the depth of anaesthesia during LMA removal does not appear to affect the incidence or severity of airway hyperreactivity when sevoflurane is the maintainence anaesthetic. Awake LMA removal during isoflurane anaesthesia however resulted in a higher incidence of adverse events and carried a high risk of severe airway hyperreactivity and critical events. So although our study showed a higher incidence of airway hyperreactivity in the isoflurane group as corroborated by the above discussed studies as well, no adverse airway events were seen in our study, only mild to moderate cough or bucking was reported in the isoflurane group at emergence.

The incidence of nausea was low and comparable (P value=0.08) in the present study. Frink EJ et al.[9] in their clinical comparison of sevoflurane and isoflurane in healthy patients reported that the incidence of postoperative nausea did not differ between the sevoflurane and isoflurane groups, with an incidence of 10 and 12% respectively, occurring in the PACU immediately after anaesthesia.

CONCLUSION

Hence it can be concluded that both sevoflurane and isoflurane are suitable for day care anaesthesia. Sevoflurane has advantages of quicker emergence, early discharge from PACU I and less airway hypersensitivity. Isoflurane has more incidence of airway hyper reactivity though milder level, when compared to sevoflurane. Incidence of nausea and vomiting and requirement of postoperative analgesia are comparable in both the groups. Isoflurane is less costly in comparison to sevoflurane.