In the past few decades, there has been increasing in the rate of cesarean section (C/S) in both developed and developing countries due to maternal, fetal, medico-legal, and social factor. Because of the rising in the rate of C/S more attention should be paid for its outcome due to the high rate of mortality and morbidity. This complication is not occur due to surgical procedure only it can be attributed to preferred anesthetic technique as well as physiological changes which occur during pregnancy and medical condition of the mother (1–7).

The choice of anesthetic technique depends on obstetrics indication, experience of anesthetist, and choice of the mother. The spinal anesthesia (SA) become popular due to its simplicity, fast onset, good sensory & motor block with avoidance of airway obstruction, and risk of aspiration as well as reduced occurrence of deep vein thrombosis (1, 8–10).

Even if SA is considered to be safe it is not complication-free. Shivering is the most common and unpleasant complication of anesthesia which reaches incidence of 40–70% after SA which is associated with deleterious sequela (11).

Shivering is defined as a spontaneous and involuntary rhythmic oscillatory contraction of muscles with a frequency of 4–8 hertz (12, 13). It will occur as a physiologic response to hypothermia and muscular hyperactivity which increases basal metabolic heat production up to 600%; even though muscular activity may be increased in normothermic patients during the perioperative period. This suggests that shivering may be caused by other mechanism rather than heat loss such as pain, uninhibited spinal reflex, reduction in sympathetic activity, adrenal suppression, discharge of fever-causing agents, and respiratory alkalosis (12–19).

Even if the exact cause of SA-induced shivering is unknown; its vasodilatation effect, increased cutaneous heat loss, decreases the threshold of shivering and redistributes the heat from the core to periphery will predispose the patient to shivering (20).

Shivering will be prevented or managed with non-pharmacological and pharmacological treatments. The non-pharmacological method includes forced-air warmers, active & passive cutaneous counter warming, blankets, body core warming, electro-acupuncture, fluid warming, and increasing operating room temperature prevents shivering (21, 22).

From pharmacological agent, Pethidine is gold standard drug that has been used for the long period of time for the prevention and treatment of shivering during surgery and emergence (23).

Pethidine is a synthetic phenylpiperidine derivative opioid that acts on μ and k opioid receptors. It has several structural features which mimic local anesthetics including tertiary amine, an ester group, and lipophilic phenyl group. The administration of pethidine intrathecally blocks sodium channel as blocked by lidocaine (24).

Antishivering effect of meperidine is mediated by its effect on k opioid receptors (15, 25).

The study aimed to assess the effect of Intrathecal Pethidine on the Incidence and Severity of Shivering during Cesarean section under Spinal anesthesia.

An institutional-based randomized controlled trial (RCT) was employed in 86 pregnant mothers who undergo C/S under SA from September 2021 to January 2022 in Dilla University Referral Hospital.

The ethical clearance was obtained from the institutional review board (IRB) of Dilla University before the beginning of the study. The written informed consent was obtained from each study participant. This study was prospectively registered by October 2021 on pan African clinical trial registry¹ with the Trial number of PACTR202110617970132. The study was reported in line with the 2010 CONSORT guideline for clinical trial http://www.consort-statement.org. In addition, we registered our study on research registry with unique identification number of research registry 7357 https://www.researchregistry.com/browse-the-registry#home

All elective ASA II pregnant mothers scheduled for C/S were included in this study. Patients whose initial axillary temperature < 36 and > 38°C, the one with allergy history to pethidine & LA agent, Patient who received thermoregulatory medication or antipsychotic medication, a patient who has a history of alcohol or substance abuse, cardiovascular disease, preeclampsia, and patient with antepartum hemorrhage were excluded from the study.

As the pregnant mother arrived at to operating room standard monitoring was applied; axillary temperature and vital signs were recorded. The parturient was resuscitated with 20 ml/kg crystalloid which was warmed to 37°. After preparing equipment for SA, the anesthetist opens the envelope and SA was performed with 12.5 mg of 0.5% bupivacaine which was standard approach of the hospital for group C while for group T SA was performed by adding 1 ml of 10 mg preservative-free pethidine to 12.5% mg of 0.5% bupivacaine. The medication was prepared by investigators, coded and the responsible anesthetist gives SA based on the code he/she get inside envelope. In all parturient, SA was performed in sitting position between L3/L4 and L4/L5 through midline approach. After a performance of SA parturient was positioned, the exposed body area was covered with non-warmed drapes & put on nasal oxygen with a flow of 4l/min. A block was assessed by pinprick for sensory & Bromage scale for a motor block. The procedure was started with a sensory level of T6 & Bromage scale > 3 blocks. Axillary temperature and vital signs were monitored every 10 min to the end of surgery. The patient was maintained by warmed fluid throughout the procedure to post anesthesia care unit (PACU). If the systolic BP is reduced by more than 20% & HR drops to less than 50 beats per min IV adrenaline 1 μg/kg and atropine 0.02 mg/kg was given, respectively. Incidence of shivering was recorded intraoperatively & in PACU continuously. Its intensity was determined by using a validated 5 scale of Crossly and Mahajan which defined as 0 no shivering, I piloerection or peripheral vasoconstriction but no visible shivering, II muscular activity observed only in one muscle group, III muscular activity observed in more than one muscle group without generalized shivering, and IV all body shivering (26) and followed for 1 h in PACU. In PACU, all patients were covered with warmed cloth up to they were discharged. The patient who develops shivering grade ≥ 3 was given 25 mg of IV pethidine. As secondary outcome, incidence of postoperative nausea & vomiting (PONV) as well as pruritus were recorded & followed intraoperatively & for the first 6 h every 2 h in PACU & ward. Those complications were scored by validated 11 scales of numeric rating scale (NRS). If nausea & vomiting score is ≥ 4, 10 mg metoclopramide was given and if pruritus NRS score is ≥ 4, 25 mg of IV Diphenhydramine was given. Data were collected using pretested and structured checklist by two trained BSc anesthetists who had no any role in the patient management.

For this study, the following descriptions were used:

Incidence of shivering occurrence of spontaneous & involuntary rhythmic oscillatory contraction of muscles during intraoperative time and in PACU and full-fill Crossly and Mahajan scale.

The postoperative nausea and vomiting sensation of urgent to vomit and actual oral passage of GI content once or more than one times within 6 h of postoperative time.

The postoperative pruritus-unpleasant sensation of skin which lead to the desire to scratch within 6 h postoperatively.

Shivering is troublesome side effect of SA for parturient, anesthetists, and surgeon because of its interference of monitoring and surgery as well as it disturbs patient comfort.

Many classes of substance are responsible to regulation of thermoregulatory center such as biogenic monoamines, cholinomimetics, endogenous peptides, and N methyl D aspartate receptor antagonist. From peptides, antishivering effect of pethidine is mediated by its effect on reducing shivering threshold by two times & its effect on kappa receptors (15, 17, 18).

Our finding demonstrated that the demographic and perioperative characteristic of patients who were enrolled in treatment and control group was comparable with p > 0.05. The commonest indication of surgery was previous cesarean section and the mean time for the performance of surgery was 44.1 ± 8.5 min in treatment group and 44.9 ± 7.6 min which was not statistical different with p = 0.640. The mean total amount of blood loss in treatment group was 545 and 523 ml in control group with p = 0.127 which was comparable. Intraoperative axillary temperature was significantly reduced through time in control group and it became significantly different after 20 min of surgery with p < 0.005.

Our study revealed that the administration of 10 mg of pethidine with bupivacaine intrathecally will reduce incidence and intensity of shivering without increasing incidence of postoperative nausea and vomiting. But there was a significant effect on incidence of pruritus.

Our study revealed that the incidence of shivering was 20.9% in treatment group while 53.5% in control group which was statistical significant with p = 0.002. The risk of developing shivering was reduced by 61% in treatment group with [RR = 0.39 CI, (0.205, 0.745)]. Our result is comparable with study done by Shami et al. on 150 parturient had cesarean section. Their finding showed that the incidence of shivering was 50% in control group and 3.6% in pethidine group with p < 0.001 (23). In addition, our finding is in line with RCT conducted by J.-Y. Hong and I. H. Lee, Anaraki et al., Abdulzera Sotoodeh Joharmi, and others (25–30).

In our finding, it was clearly seen that the severity of shivering was different between the groups. From 23 patients who developed shivering in the control group 4 (9.3%) patients developed grade IV 9 (20.9%) grade III, and 10 (23.3%) of them grade II while none of them develop grade I shivering. In treatment group 7 (16.3%) of patients developed grade I and 2 (4.7%) patients got grade II which was statistically significant with p = 0.004. In agreement to our finding, RCT conducted by savafi et al. showed that the control group develops the higher intensity of shivering than the intrathecal pethidine group with p < 0.001 (30). The result of shami et al., Roy et al., J.-Y. Hong, and I. H. Lee, Chun et al., Rastegarian et al., Safavi et al., Nasseri K et al., and Nada and Ezz also comparable to our study and showed that the intensity of shivering was significantly higher in the treatment group (23, 26, 28, 29, 31–34).

In our study incidence of postoperative nausea and vomiting was followed for the 1^st 6 h post operatively. The finding showed that the incidence of PONV was not significantly different between treatment and control group p = 0.632. In addition, the severity of PONV was also had no statistical significant difference with p = 0.635; this finding is in line with result of Rastegarian et al., Nasseri K et al., Shami et al., Roy et al., J.-Y. Hong, and I. H. Lee and others (23, 26, 28, 31, 33).

In contrast to our finding, RCT conducted by Anaraki et al. and Khan et al. showed that the incidence of PONV was significantly higher in the pethidine group than the control group. The possible explanation for this contrary result is those authors used high dose of pethidine 0.4 mg/kg and 12.5–25 mg, respectively, which is higher than the one we used 10 mg of pethidine (27, 35).

The incidence of pruritus was 18.6% in treatment but none of patients in control group develop pruritus. This finding has statistically significant difference with p = 0.003. This finding is in agreement with result of study conducted by Chun et al. which showed the incidence of pruritus was 16% in the pethidine group while it was 0% in the control group (29).

In contrast to our result study done by J.-Y Hong and I. H. Lee indicated that there was no significant difference in the incidence of pruritus between treatment and control group. The possible explanation for this divergence is duration of follow up. We followed the patients for the 1st 6th postoperative hours but they follow them only in intraoperative time (26).

Administering 10 mg of pethidine intrathecally during spinal anesthesia is effective in reducing the incidence, and severity of shivering in addition without increasing risk of PONV, while it increases mild incidence of pruritus.

The original contributions presented in this study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

This study was approved by the Dilla University College of Health Science and Medicine Institutional Review Board with protocol unique number of 005/21-03. The written informed consent for participation in the study was obtained from all patients. All methods were carried out under the Declaration of Helsinki.

TG had made substantial contributions to conception, design, analysis, and interpretation of data, acquisition of data, preparing the manuscript of this study, the critical review, and editing of the manuscript drafts for scientific merit and depth. WA and SA made contributions to the interpretation of data, acquisition of data, preparing the manuscript of this study, and the critical review. All authors have read and approved the final version of the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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