Effects of Temperatureon Amnioinfusion
Abstract & Commentary
By John C. Hobbins, MD, Professor of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora, CO, is Associate Editor for OB/GYN Clinical Alert.
Dr. Hobbins reports no financial relationships relevant to this field of study.
Synopsis: A recent study suggests that it may be possible to lower the chances of neurological injury in fetuses vulnerable to hypoxia by dropping intrauterine temperatures through
Source: Tomlinson TM, et al. Intrauterine temperature during intrapartum amnioinfusion: A prospective observational study. BJOG 2012;119:958-963.
Every so often, one runs across a paper that is somewhat offbeat, but could have some beneficial clinical implications. One such article appeared recently in the British Journal of Obstetrics and Gynecology that dealt with a way to possibly counter the fetal effects of maternal hyperthermia and even protect the brains of fetuses/infants against potential hypoxic insult during labor.
Tomlinson et al recruited 20 laboring women who had had intrauterine catheters inserted to assess uterine contractions (controls).1 Another 14 patients having amnioinfusion (AI) for repetitive variable decelerations were recruited (the AI group). Every patient had a temperature probe inserted into the uterine cavity through the already-inserted catheter so that continuous intrauterine temperatures could be monitored. The patients having AI had room temperature sterile saline infused at a rate of 10 mL/minute for the first hour and 3 mL/minute thereafter. Ambient temperatures in the patients' rooms were recorded during the infusion and maternal oral temperatures were taken every 15 minutes. Neonatal rectal temperatures were assessed as soon as possible after delivery (within 90 seconds). All but three patients in the study had epidurals in place.
The authors' null hypothesis was that infusion of room temperature saline would not lower intrauterine temperatures, and, as the authors hoped, it was rejected. The mean average intrauterine temperatures were 0.5°C warmer than the maternal oral temps in the control group. However, the infused group had mean intrauterine temperatures that were 0.2°C cooler than mean maternal temperatures. When comparing average intrauterine temperatures between AI and controls in the total populations studied, AI mean temperature was 36.4°C vs 37.4°C in controls, representing a 1°C difference. In a subgroup of patients who were afebrile throughout the study, the AI lowered intrauterine temperatures by 1.5°C (35.8°C vs 37.3°C), and if an epidural was in place for 3 hours or less, the AI group's average intrauterine temperature was 1.7°C cooler (35.5°C vs 37.2°C). The above results were statistically significant.
Regarding neonatal temperatures, the infants tested had rectal temperatures immediately after birth that were, on average, 1.0°C higher than their moms' oral temperatures, and there was a non-significant trend toward lower rectal temperatures in the AI group (0. 4°C lower than the control neonates).
Commentary
This is one of the most convoluted published papers I have recently read, and it was very difficult to sort out the most meaningful nuggets of information. Nevertheless, the idea that emerges is very interesting. By doing AI with room temperature fluid, one might cool down the fetus enough to potentially protect against the effects of hypoxia in those with signs of compromise. The benefits of cooling asphyxic neonates has been well-documented,2 and dropping the temperature by 1°C can result in a 5-6% reduction in brain energy utilization.3 Another study has shown that if neonatal core temperatures can be dropped by 2°C, a delayed adverse neurological effect can be avoided.4 It is encouraging that in some patients in the AI study intrauterine temperatures were lowered into that range. This obviously brings up the possibility of initiating therapy at the time of hypoxic insult since it has been demonstrated in animals that cooling during the primary phase of injury provided the best protection against neurological damage.5
Actually, I am surprised that the authors did not mention the concept of infusing even cooler saline solutions to coax the intrauterine temperatures down even further.
Epidurals possibly can raise the maternal temperatures to a level where the fetal brain is more susceptible to hypoxic injury. It is interesting that when an epidural was in place for more than 3 hours, AI had little effect on maternal temperature, suggesting that after a while the infusion could not neutralize elevated intrauterine temperatures.
The greatest benefit might be in clinical situations where the fetus is most vulnerable to hypoxia such as fetal growth restriction, fetal tracing with late decelerations, fetal tracing with decreased beat-to-beat variability, or any fetal tracing with non-reassuring fetal heart rate pattern. This could perhaps be done even while preparing for an emergency cesarean section.
This paper can act as a springboard to further study, which obviously is necessary since this intriguing concept is great for chin stroking, but, as of now, is simply conjecture.
References
- Tomlinson TM, et al. Intrauterine temperature during intrapartum amnioinfusion: A prospective observational study. BJOG 2012;119:958-963.
- Shah PS, et al. Hypothermia to treat neonatal hypoxic ischemic encephalopathy: Systematic review. Arch Pediatr Adolesc Med 2007;161:951-958.
- Laptook AR, et al. Modest hypothermia provides partial protection when used for an immediate resuscitation after brain ischemia. Pediatr Res1997;42:17-23.
- Busto R, et al. Small differences in intraischemic brain termperature critically determine the extent of ischemic neuronal injury. J Cereb Blood Flow Metab 1987;7:729-738.
- Dietrich WD, et al. Intraischemic but not postischemic brain hypothermia protects chronically flowing global forebrain ischemia in rats. J Cereb Blood Flow Metab 1993;171:541-549.
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