EFFECT OF HALOTHANE, ENFLURANE AND ISOFLURANE ON BODY TEMPERATURE DURING AND AFTER SURGERY

Br. J. Anaesth. (1989), 62, 409-414

EFFECT OF HALOTHANE, ENFLURANE AND ISOFLURANE ON BODY TEMPERATURE DURING AND AFTER SURGERY V. RAMACHANDRA, C. MOORE, N. KAUR AND F. CARLI

PATIENTS AND METHODS

SUMMARY The superficial and deep body temperatures of 40 healthy females undergoing total abdominal hysterectomy were measured during surgery and for 4 h afterwards. The patients were allocated randomly to one of five groups and anaesthetized to produce an end-tidal concentration of 1 % halothane, 1 % enflurane, 2 % enflurane, 1 % isoflurane or 2% isoflurane. The patients received also 70% nitrous oxide in oxygen and neuromuscu/ar blockade. The theatre temperature was maintained at 22.0 °C. There were significant body temperature changes during operation in all groups. The mean (SD) decrease in core temperature over 85 min was approximately 1.1 (0.3) °C in the 1% halothane, 2% enflurane and 2% isoflurane groups, and 0.6 (0.4) °C in the 1 % enflurane and 1% isoflurane groups (? < 0.05). During the recovery period the 1% halothane, 2% enflurane and 2% isoflurane groups took 2 hto rewarm to preoperative temperatures, and the rate of rewarming during this time was similar for all groups.

Forty healthy female patients were studied during total abdominal hysterectomy for menorrhagia. Informed consent was obtained from each patient, and the study was approved by the Hospital Ethics Committee. Patients who were grossly obese or who had endocrine diseases or pyrexia were not included. None of the patients had previously been exposed supplemented with halothane, enflurane or isoflurane. The inspired concentration was adjusted to halothane anaesthesia. Patients were allocated randomly to one of five to produce end-tidal concentrations of 1 % haloequal groups. Premedication comprised papaver- thane, 1% enflurane, 2% enflurane, 1% isoetum and hyoscine i.m. 60 min before surgery. flurane or 2 % isoflurane respectively, in the five General anaesthesia was induced with thio- groups, as measured by an anaesthetic gas analyser pentone. Following the administration of pancuro- (Engstrom, Emma). The calibration of the EMMA nium, the trachea was intubated and the lungs was checked regularly against known concenwere ventilated to maintain normocapnia with trations of certified test gases. The end-tidal 70% nitrous oxide in oxygen. Anaesthesia was anaesthetic concentration was assumed to correlate with the depth of anaesthesia. All patients received an i.v. infusion of HartV. RAMACHANDRA, M.B., B.S., F.F.A.R.C.S.; C. MOORE, M.B., B.S.; N . KAUR, M.B., B.S., M.D., F.F.A.R.C.S.; F. CARLI, mann's solution 4 ml kg"1 h"1 during operation F.F.A.R.C.S.; Department of Anaesthesia, Northwick Park and, after surgery, a mixture of 4 % Dextrose in Hospital and Clinical Research Centre, Watford Road, Harrow HA1 3UJ. Accepted for Publication: August 3, 1988. 0.18% sodium chloride 40 ml kg"V24 h. All i.v. fluids were at room temperature. Skin preparation Correspondence to F. C.

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Heat loss occurs during anaesthesia and surgery. The factors responsible for this are related, not only to the patient, environment or type and duration of surgery, but also to anaesthetic regimen [1]. General anaesthetic agents have central and peripheral effects on body temperature regulation, the alterations being related to the depth of anaesthesia [2]. In this study we have measured the extent of change in body temperature that occurs with different concentrations of halothane, enflurane and isoflurane. In addition, the rate of rewarming during the first 4 h after surgery was measured. We attempted to standardize the operative procedure, the type of patient studied and the environment.

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Statistical analysis The temperatures at each time interval studied were grouped and the mean values and standard

deviations calculated for each anaesthetic regimen. Student's t test was used to compare observations in the same groups of patients, and the unpaired t test, and Welch's test where appropriate, for comparison among different groups. For each patient, the rewarming rate after surgery was calculated as the slope of the regression line of temperature on the time (every 30 min from 0 to 4 h). P < 0.05 was considered significant. RESULTS

There were no significant differences between the five groups with regard to the patients' physical characteristics, duration of surgery and theatre temperature (table I). The operating theatre relative humidity was maintained at a mean value of 53 % (range 49-58 %), with 20 air changes per hour. Mean recovery room temperature was 25.0 °C (range 24.0-26.5 °C) and mean relative humidity 54% (range 50-59%). Mean blood loss during surgery was 235 ml (range 205-375 ml), and no blood transfusion was required. During the first 4 h after operation, all patients received one i.m. injection of papaveretum. Aural canal temperature decreased in all groups by the end of surgery (table II). However, the decrease was significantly greater in those patients with an end-tidal concentration of 1 % halothane, 2 % enflurane or 2 % isoflurane than in those with end-tidal concentrations of 1 % enflurane or 1 % isoflurane. There was a significant difference between the changes in core temperature in the 2% enflurane and 2% isoflurane groups compared with the 1 % enflurane and 1 % isoflurane groups. No significant difference was shown between 1 % enflurane and 1 % isoflurane. The Minimal Alveolar Concentration (MAC) for thefiveanaesthetic regimens used in this study and the corresponding core temperature changes are shown in figure 1. At MAC values of 1.3 and 1.5, corresponding to 1 % enflurane and 1% isoflurane, respectively, the decrease in aural canal temperature was 0.6 (0.4) °C. At higher MAC, 1.9 for 2 % enflurane, 2.0 for 1 % halothane and 2.35 for 2 % isoflurane, there was a temperature decrease of 1.1 (0.6) °C. Mean skin temperature decreased in all groups during surgery, with the largest change in the halothane group. However, there was no significant difference between the five groups (table II).

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comprised 0.5% chlorhexidine in spirit, and drapings of double thickness material were spread over the patient except for the abdomen. No active warming devices were used during surgery. At the end of surgery, each patient was covered with a single sheet and blanket, and transferred to the recovery room, where she remained for 4 h at a mean ambient temperature of 25.0 °C. Postoperative pain relief comprised an i.m. injection of papaveretum 0.25 mg kg"1 when required. Before induction of anaesthesia, temperature probes were placed against the skin over the lateral aspect of the upper arm, the nipple, the ventral surface of the mid thigh and the lateral aspect of the calf. The temperature was recorded at these sites. Immediately after induction of anaesthesia, a thermocouple probe was inserted under direct vision in the aural canal and well secured with cotton wool to eliminate air currents. Skin and aural canal temperature measurements were repeated at the end of surgery, and subsequently at 30-min intervals for 4 h. The thermocouple probes and the recording thermometer (manufactured by Comark Electronics) were calibrated against a National Physics Laboratory standardized mecury-in-glass total immersion thermometer in a stirred water bath. The probes were accurate to 0.05 °C over the temperature range studied. Mean skin temperature was calculated using the four-points formula proposed by Ramanathan [3]: mean skin temperature = 0.3 (nipple + arm)+ 0.2 (thigh + calf). Mean body temperature was calculated by averaging mean skin and core (aural canal) temperatures (T) according to the equation of Colin and others [4]: mean body temperature = 0.66 Tcore + 0.34 Tmean skin. Body heat content (kj) was calculated and corrected for body weight [5]: mean body heat = mean body temperature x 0.83 x body weight x 4.18, where 0.83 represents specific heat. The presence or absence of shivering was recorded. The ambient temperature and the relative humidity in the operating theatre and the recovery room were measured with a mercury-in-glass thermometer and a hair hygrometer, respectively.

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ANAESTHETICS AND BODY TEMPERATURE

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TABLE I. Mean (range) group characteristics

1 % Enflurane (n = 8)

2 % Enflurane (» = 8)

1 % Isoflurane (« = 8)

2% Isoflurane (n = 8)

43 (40-51) 64.3 (56-75) 25.4(21.9-29.3) 86 (60-120)

43 (32-61) 64.6 (55-77) 26.9(22.1-33.5) 89 (45-115)

46 (30-70) 68 (53-80) 26.5 (19.1-32.4) 81 (55-95)

40 (30-47) 75.5 (63-94) 28.6(24.1-31.1) 94 (60-135)

43 (30-51) 61.4(49-80) 24.9 (22.6-30.5) 96 (45-135)

21.9(20.2-22.8)

22.0 (20.3-22.5)

22.2 (20.9-22.8)

22.0(20.5-23.1)

22.0(21.5-22.5)

3

1

2

2

1

TABLE II. Mean (SD) intraoperattve decrease in aural canal and mean skin temperature (°C). Significant differences (P<0.05): *v. halothane; fv. 1% isoflurane; $v. 1% enflurane

Aural canal Mean skin

1 % Halothane („ = 8)

1 % Enflurane (n = 8)

2 % Enflurane (n = 8)

1.1 (0.3) 1.2(0.8)

0.6 (0.4)* 0.9 (0.7)

1.1 (0.3)$ 1.0(1.0)

Body heat loss (calculated from mean skin and core temperatures) in the halothane group was significantly greater than in the 1 % enflurane (P < 0.05). No significant difference was found between isoflurane and halothane (fig. 2). Aural canal temperature (fig. 3) at the end of surgery was significantly lower in the 1 % halothane, 2% enflurane and 2% isoflurane groups than in the 1 % enflurane and 1 % isoflurane groups (P < 0.01). During the first 2 h after operation, all groups 1.5-1

1 % Isoflurane (n = 8)

2 % Isoflurane (n = 8)

0.6 (0.4)* 0.5 (0.9)

1.2(0.4)t 0.8 (0.9)

had a similar slope of change in temperature (figs 3, 4, table III), but significantly different intercepts (P < 0.05). The patients in the 1 % halothane, 2% enflurane and 2% isoflurane groups started with lower temperatures and 300^

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FIG. 2. Intraoperative and postoperative change in body heat content (mean (SD)). Significant differences (P<0.05): * 1 % enflurane v. 1% halothane; \2% enflurane v. 1% enflurane.

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Age (yr) Body weight (kg) Body Mass Index Duration of surgery (min) Theatre temp. (°C) Shivering (No. patients)

1 % Halothane (» = 8)

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Time (h)

FIG. 4. Postoperative rate of change in mean skin temperature in the five study groups (mean values).

after operation varied with end-tidal concentration and not with the particular inhalation reached preoperative core temperature values anaesthetic agent used. within 2 h of the end of surgery, while the 1 % It is well established that body heat is lost enflurane and 1 % isoflurane groups rewarmed in during anaesthesia and surgery as a result of low 1 h. During the last 2 h of recovery, the rate of environmental temperature [6], use of cold i.v. change in body temperature was similar for all fluids, ventilation of the lungs with cold and dry groups (fig. 4). gases, absence of musle movement [7] and use of Mean heat gain during the recovery period was drugs [8]. Therefore, it is essential to standardize in the range 101-150 kj h"1 with no significant the operative procedure, the anthropometric characteristics of the subjects, the age group and the differences between the groups. The incidence of post-anaesthetic shivering environment in order to demonstrate the effect of was greater in the halothane group than the other inhalation anaesthetic agents on body temperagroups (table I). No correlation was found ture. We chose to study total abdominal hysterbetween shivering and the skin and core tempera- ectomy because the subjects were relatively young, healthy and fairly lean. In addition, this tures at admission to the recovery room. surgery causes minimal blood loss, and has an average duration of 90 min—sufficient time for DISCUSSION major changes in body temperature to occur [9]. Core temperature changes occurring during anaes- The environments in the operating theatre and thesia and surgery and in the period immediately recovery area were also maintained constant. TABLE III. Mean (SD) aural canal temperatures after operation (°C) Time after surgery (h)

1 % Halothane 1 % Enflurane 2% Enflurane 1 °,o Isoflurane 2% Isoflurane

End of surgery

1

34.8 (0.6) 35.2 (0.6) 34.7 (0.4) 35.2 (0.7) 34.6 (0.7)

35.7 (0.5) 36.0 (0.5) 35.4 (0.7) 36.0 (0.5) 35.6 (0.5)

36.0 (0.5) 36.2 (0.5) 35.9 (0.6) 35.8 (0.7) 36.1 (0.5)

36.4 36.4 35.8 36.2 36.2

(0.5) (0.6) (0.6) (0.4) (0.4)

36.7 36.7 36.6 36.4 36.6

(0.3) (0.4) (0.6) (0.4) (0.3)

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ANAESTHETICS AND BODY TEMPERATURE

mechanism these anaesthetic agents cause different temperature gradients from core to skin. While the effect of halothane on muscle blood flow seems variable [16], with isoflurane there is a great increase in muscle blood flow which appears to be dose dependent [14]. With enflurane there is a decrease in resistance without a change in muscle blood flow [15]. Nevertheless, halothane, enflurane and isoflurane decrease resistance to blood flow in cutaneous vessels, causing heat loss. During the postoperative period the rate of change in core temperature was similar for 1 % halothane, 2 % enflurane and 2 % isoflurane, and significantly different from 1 % enflurane and 1 % isoflurane groups. While the last two groups reached a core temperature of 36.0 °C within 1 h from the end of surgery, the other three groups rewarmed to preoperative values after 2 h of recovery, with a large heat gain occurring during the first 1 h after operation. The clinical implications of these findings are that, by using 1 % halothane, 2 % enflurane or 2 % isoflurane during anaesthesia, body temperature decreases during operation and the postoperative rewarming can be delayed. Previous studies have shown that the majority of patients who leave the recovery room are still hypothermic [17]. In young healthy patients this might not cause serious clinical problems, but in the elderly and in patients with a poor cardiovascular and respiratory reserve, the high metabolic rate required during rewarming can increase tissue oxygen demand by as much as 400-500 % [18]. The rate of change in mean skin temperature during recovery was similar for all groups. They all rewarmed by approximately 1.2 °C during the first 1 h of recovery. This change contributed to a mean heat gain of 200 kj during this period. However, throughout the recovery period, mean skin temperature in the halothane group was greater by 0.6 °C than that of isoflurane. Shivering occurred in all groups within the first 1 h, and the greatest incidence occurred in the halothane group. These data are in agreement with earlier findings for halothane [19], while a low incidence of shivering with isoflurane has been reported [20]. More recent work has shown that post-anaesthetic shivering appears not to differ, in character and aetiology, from that occuring with exposure to cold [21].

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Anaesthetic agents alter body temperature either by depressing heat production or by increasing heat loss. There have been few studies comparing the effect of individual anaesthetic agents on body temperature. Morris [9] did not find any difference between the effect of ether, halothane or methoxyflurane on body temperature during anaesthesia. Engleman and Lockart [10] found in children, that halothane in a nitrous oxide in oxygen mixture produced a greater decrease in rectal temperature than did ketamine. Unfortunately, in that study, the ambient temperature was not controlled well. Holdcroft and Hall [11] failed to shown any significant difference in heat loss when patients's lungs were ventilated artificially with nitrous oxide in oxygen and supplemented with 0.5 % halothane or 1 % halothane, or with a moderate dose of fentanyl (10ugkg~l) for up to 3 h of anaesthesia under standardized conditions. In a study comparing high dose fentanyl (50 ug kg"1) and 1 % halothane in non-cardiac patients, the same authors found that fentanyl produced a greater redistribution of body heat from core to periphery than did halothane, and that it caused a greater reduction in aural canal temperature [12]. However, a subsequent study comparing halothane and fentanyl failed to show a different pattern of temperature distribution [13]. The effects on body temperature of enflurane and isoflurane at anaesthetic concentrations have been investigated in volunteers by Stevens and others [14] and by Calverley and others [15]. These authors observed an increase in skin temperature with higher concentrations of the anaesthetic agents. This conflicts with the present study, which showed a reduction in body temperature during surgery with increasing alveolar concentrations. However, in the present study, surgical stimuli, neuromuscular blockade and the exposure of the peritoneal cavity were all important factors which were not present in the other studies. The reduction in mean skin temperature during surgery showed a wide variation between patients in each group, and did not depend on the drug and the concentration used. It was interesting to observe that halothane caused the largest decrease in mean skin temperature amongst the five groups studied, and this contributed to the greatest loss of body heat. This is in agreement with the observations of Holdcroft and Hall [11]. It is not clear from this study by what

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6. 7. 8.

9. 10. 11. 12.

body heat during anaesthesia. Anaesthesia 1979; 34: 758-764. 13. Nieminen MT, Rosow CE, Triantafillou A, Schneider RC, Lowenstein E, Philbin DM. Temperature gradients in cardiac surgery patients. A comparison of halothane and fentanyl. Anesthesia and Analgesia 1983; 62: 1002-1005. 14. Stevens WC, Cromwell TH, Halsey MJ, Eger El, Shakespeare TF, Bahlman SH. The cardiovascular effect of a new inhalation anesthetic, Forane, in human volunteers at constant arterial carbon dioxide tension. Anesthesiology 1971; 35: 8-16. 15. Calverley RK, TySmith N, Prys-Roberts C, Eger El, Jones CW. Cardiovascular effects of enflurane anesthesia during controlled ventilation in man. Anesthesia and Analgesia 1978; 57: 619-628. 16. Eger El, TySmith N, Stoelting RK, Cullen DJ, Kadis LB, Whitcher CE. Cardiovacular effects of halothane in man. Anesthesiology 1970; 32: 396-409. 17. Carli F, Gabrielczyk M, Clark MM, Aber VR. An investigation of factors affecting postoperative rewarming of adult patients. Anaesthesia 1986; 41: 363-369. 18. Bay J, Nunn JF, Prys-Roberts C. Factors influencing arterial Po2 during recovery from anaesthesia. British Journal of Anaesthesia 1968; 40: 398-406. 19. Jones HD, McLaren AB. Postoperative shivering and hypoxaemia after halothane, nitrous oxide and oxygen anaesthesia. British Journal of Anaesthesia 1965; 37: 35-41. 20. Eger El. Isoflurane. A compendium and reference. Airco Inc. 1982; 108-109. 21. Lipton JM, Giesecke AH. Body temperature and shivering in the perioperative patient. Seminars in Anaesthesia 1988; 1: 3-10.

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5.

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