Journal club cover on low dose phenylephrine

Anaesthesia implications

1. Moderator: Dr Monika Presentor : Dr Joshva

2. Introduction Spinal anesthesia is the preferred anesthetic technique in parturients undergoing cesarean section for various maternal and fetal reasons. The high sensory level of subarachnoid block required results in systemic vasodilation, with a subsequent redistribution of blood from the core to the periphery causing maternal hypothermia. The compensatory activation of the thermoregulatory center results in maternal shivering, with the reported incidence up to 56.7%.

3. Introduction Phenylephrine is the recommended vasopressor for prevention and treatment of spinal anesthesia ‐induced hypotension. Due to the peripheral vasoconstrictive effect of phenylephrine, the core to peripheral redistribution of blood volume is expected to be minimized, which may maintain the core temperature, and reduce shivering during spinal anesthesia .

4. Aim: To study the effect of Low dose phenylephrine infusion on shivering and hypothermia in patients undergoing cesarean section under spinal Aneasthesia .

5. Objectives: Primary: Incidence of shivering Secondary: Severity of shivering Temperature changes Incidence of hypotension and bradycardia.

6. Inclusion Criteria: Pregnant women ≥18 years of age ASA physical status 2, planning to undergo elective or emergency cesarean section under spinal anesthesia .

7. Exclusion criteria Fever (axillary temperature >37°C) Shivering Hypertensive disorders of pregnancy Cardiac diseases Antepartum hemorrhage Known allergy to drugs

8. Methodology: Study design: Randomized double blinded placebo-control trial Sampling technique: Convenience sampling Total patients recruited: 150 Phenylephrine Group (n=75) Placebo group (n=75) Prophylactic phenylephrine infusion was administered at 25 μg /min immediately after initiation of spinal anaesthesia and continued until the end of the operative period Normal saline infusion was administered during the same period Core temperature: soft nasopharyngeal temperature probe Peripheral temperature: Thermistor based skin temperature probe taped in axilla Baseline line parameters were monitored

9. Hemodynamic parameters were manually recorded every 3min for 15mins following SA In the case of hypertension, the study drug infusion was discontinued and restarted once the MAP returned to below the hypertension threshold value. Hypotension: S ystolic blood pressure (SBP) <90 mmHg. ( Treated with an IV bolus of mephentermine 3 mg) Hypertension: M ean arterial pressure (MAP) greater than a 20% increase from the baseline. B radycardia: Heart rate <60 beats/min

10. Shivering : P resence of fasciculations on the face, chest, and limbs for 15 s. Graded using a four‐point scale proposed by Vanderstappen et al. N one: no perceptible tension of muscles observed. M ild: slight muscle tonus of masseter muscle. M oderate: Real shivering of proximal muscles. S evere: Generalized shivering of the whole body Vanderstappen I, Vandermeersch E, Vanacker B, et al. The effect of prophylactic clonidine on postoperative shivering. Anaesthesia . 1996;51:351 – 355. https://doi. org/10.1111/j.1365-2044.1996.tb07747.x .

11. Statistical Analysis Data was analyzed using Stata 14 software (Stata Corp 2015, Stata Statistical Software Release 14; StataCorp LLC, College Station, TX, USA). Categorical variables were analyzed using Chi- squared test and Fishcer exact test The comparison of continuous and discrete variables was made using unpaired Student’s t‐test or Mann Whitney U test for. parametric and nonparametric data, respectively.

12. Results Demography

13. Results 2. Intraoperative shivering, hypothermia and hemodynamic events

14. Results 3. Nasopharyngeal temperature at different time interval following SA The nasopharyngeal temperature showed a decreasing trend over time in both groups, but to a greater degree in the control group.

15. Results 3. Nasopharyngeal temperature The fall in nasopharyngeal temperature from the baseline to the end recording P henylephrine group: 0.49°C (95% CI 0.61 to 0.37) and Control group: 0.65°C (95% CI 0.54 to 0.76) ( P =0.054) Final nasopharyngeal temperature was significantly different between two groups Parameter Phenylephrine Control P value Nasopharyngeal temperature at the end of surgery ( o C ) 35.8 + 0.6 35.6 + 0.5 <0.009

16. Results The incidence of hypotension was higher in controls (53.4% vs. 2.7%; P <0.001) but bradycardia was more frequent in placebo group ( P =0.023). The total volume of intravenous fl uids did not differ between groups. The mean time for shivering from the spinal block, total duration of surgery and APGAR scores were not significantly different between two groups.

17. Discussion Incidence of shivering was significantly lower in patients who received phenylephrine compared to placebo. Probable reason being better preservation of core body temperature in phenylephrine group. Hypothermia was noted in both the groups, but the extent was significantly lesser in phenylephrine group. Phenylephrine reduces vasodilation and likely reduces hypothermia and shivering by redistribution of blood from the centre to periphery following spinal block.

18. Limitations The duration of labor and use of oxytocin supplementation was not measured in laboring parturients so could have influenced the thermal parameters. Anxiety, another risk factor for shivering, was not assessed. Lack of use of intrathecal opioids, a factor which has been found to influence the extent of hypothermia. The use of nasopharyngeal temperature probe for core temperature monitoring can cause discomfort and alter values due to air movement in spontaneously breathing patients.

19. Conclusion T he use of prophylactic phenylephrine infusion at 25 μ g /min reduces shivering and the extent of hypothermia after the induction of spinal anaesthesia, and has the additional advantage of improved hemodynamic stability in the obstetric population undergoing cesarean section.