An association between the use of epidural analgesia during labor and an elevation in maternal temperature was first noted in 1989, when Fusi (1) reported that the vaginal temperatures of 18 parturients receiving epidural analgesia increased by about 1 degree Centigrade over 7 hours when compared to women receiving intramuscular narcotics. Since detrimental fetaI effects had been demonstrated in animals warmed to a temperature of about 42 degrees Centigrade (2), Fusi's article raised concern regarding the effects of epidural anesthesia on maternal temperature. Perhaps decreases in sweating and hyperventilation contribute to the association between epidural analgesia and increasing temperature in the parturient. However, increased lower extremity blood flow during epidural analgesia renders vaginal or rectal temperatures unreliable, and tympanic membrane temperature will more accurately reflect core temperature.
Camann et al (3) studied tympanic temperature measurements in laboring parturients in a controlled temperature environment and found no difference in temperature in the groups receiving either epidural or intravenous analgesia up to four hours after epidural placement. At five hours, the parturients receiving epidural analgesia with either plain bupivacaine or bupivacaine plus fentanyl showed a small but significant increase in temperature from 36.6 degrees C to 37.1 degrees C (3). These authors felt that this degree of temperature increase was not sufficient to result in an adverse intrauterine environment and fetal compromise. Macaulay then studied intrauterine fetal skin temperature directly and noted a maximum fetal skin temperature greater than 38.0 degrees C in 10 of 33 parturients in the epidural group but in none of those not receiving epidurals (4). There were no differences in neonatal acid base measurements or Apgar scores (Table 35.1). The ambient room temperatures in this study, however, ranged as high as 29.0 degrees C. These authors suggested maintaining cooler ambient temperatures and frequent sponging in women receiving epidural analgesia for prolonged periods of time.
In conclusion, although epidural anesthesia maintained for longer than five hours is associated with an increase in maternal temperature, it is unlikely that epidural anesthesia causes increases in temperature of sufficient severity to cause fetal compromise. There is no evidence of adverse fetal effects based on Apgar scores and acid base status. Altered thermoregulatory transmission from the periphery to the hypothalamus may be postulated as a possible mechanism for the increase in temperature seen during epidural analgesia.
References:
1. Fusi et al, Lancet 1989;1:1250-1252.
2. Morishima et al, Am J Obstet Gynecol 1970; 121:531-8
3. Camann et al, Br J Anaesth 1991;67:565-568
4. Macaulay et al, Obstet Gynecol 1992;80:665-669