Effect of low dose phenylephrine infusion on shivering and hypothermia in patients undergoing cesarean section under spinal anesthesia: a randomized clinical trial.

BACKGROUND: Shivering is a common complication of spinal anesthesia. Phenylephrine, due to its peripheral vasoconstrictive effect, may limit the core to periphery redistribution of body temperature following spinal anesthesia, and reduce hypothermia and shivering. We hypothesized that prophylactic phenylephrine infusion would reduce shivering and hypothermia in women undergoing cesarean section under spinal anesthesia. METHODS: A two-arm randomized, double-blind, placebo-controlled trial in term pregnant patients undergoing cesarean section. In the phenylephrine group (n=75) prophylactic phenylephrine infusion was administered at 25 µg/min immediately after initiation of spinal anesthesia and continued until the end of the operative period. In the placebo group (n=75) a normal saline infusion was administered during the same period. The primary outcome was the incidence of shivering; secondary outcomes were severity of shivering, changes in nasopharyngeal (core) temperature, and incidence of hypotension and bradycardia. RESULTS: The incidence of shivering in the phenylephrine and control groups was 24.0% (95% CI 14.3% to 33.7%) and 53.3% (95% CI 42.0% to 64.6%), respectively. The severity of shivering was greater in the control group (P=0.002) and the mean (±SD) end of surgery core temperature was significantly higher in the phenylephrine group (35.84°C ±â€¯0.60) compared with controls (35.61°C ±â€¯0.48) (P=0.009). The incidence of hypotension was higher in controls (53.4% vs. 2.7%; P <0.001) but bradycardia more frequent in group P (P=0.023). CONCLUSION: The incidence of shivering and degree of hypothermia were significantly reduced by a prophylactic phenylephrine infusion during cesarean section under spinal anesthesia.

The effect of spinal hyperbaric bupivacaine-fentanyl or hyperbaric bupivacaine on uterine tone and fetal heart rate in labouring women: a randomised controlled study.

The mechanism for fetal heart rate abnormalities following spinal opioids remains controversial. We evaluated uterine tone, using an intra-uterine pressure catheter, and fetal heart rate abnormalities in 30 women in spontaneous labour with cervical dilation of 3-5 cm having combined spinal-epidural analgesia. Women were randomly assigned to receive a spinal with 2.0 mg hyperbaric bupivacaine plus 15 µg fentanyl, or 2.5 mg hyperbaric bupivacaine. The primary outcome measure was an increase > 10 mmHg in baseline uterine tone in the 30-min period following spinal injection. Only three (20%) women who had a bupivacaine-fentanyl spinal showed a > 10 mmHg increase in baseline tone vs. none who had bupivacaine (p = 0.63). The mean (SD) baseline uterine tone after the spinal injection was 13.3 (7.0) mmHg in the bupivacaine-fentanyl group and 7.7 (2.5) mmHg in the bupivacaine group (p = 0.01). Seven (47%) in the bupivacaine-fentanyl group showed new onset fetal heart rate changes during the 30-min period after the spinal, compared with two (13%) in the bupivacaine group (p = 0.04); however, these were transient and responded to intra-uterine resuscitation. Pain scores, sensory and motor block as well as neonatal outcomes were comparable between the groups. We found that raised baseline uterine tone was not more frequent when using bupivacaine-fentanyl rather than bupivacaine in the spinal component of combined spinal-epidural, although absolute values of baseline tone were higher, and fetal heart rate changes more frequent, in the former group.