Prophylactic Mirtazapine or Dexamethasone for Post-spinal Anesthesia Shivering in Patients Undergoing Gynecological Surgeries: a Randomized Controlled Trial

Enrollment After approval by the institute ethics committee, this study was conducted at Ain-Shams university hospitals, from the 1st of March 2018 till the 31st of August 2018, on 300 patients aged 18-60 years of the American Society of Anesthesiologists (ASA) physical status I or II and underwent gynecological surgeries under spinal anesthesia. A written informed consent was obtained from all patients to participate in the study.

Patient's refusal, duration of surgery more than 120 min, obesity with body mass index (BMI) >35 kg/m2, generalized infection or localized infection at level of blockade, neurologic disease, coagulation disorder, patients with hypo- or hyperthyroidism, cardiopulmonary disease, psychological disorders, a need for blood transfusion during surgery, an initial body temperature >38.0C or <36.0C, a known history of alcohol or substance abuse, or receiving vasodilators, or medications likely to alter thermoregulation excluded the patient from the study.

Randomization and Blinding This study was designed to be a randomized, placebo-controlled, double-blinded parallel study. Following enrollment, patients were randomized into 3 equal groups;

1. The M (Mirtazapine) (Merta) group:(n=100) each patient received 30 mg Mirta tablet orally with sips of water and 100 ml 0.9% sodium chloride (normal saline [NS]) (IVI) over 15 min as a placebo for Dex 2 h preoperatively.
2. The D (Dexamethasone) (Dex) group: (n=100) each patient received a placebo tablet identical to Mirta tablet orally with sips of water and Dex 8 mg ampoule diluted in 100 ml 0.9% NS IVI over 15 min, 2 h preoperatively.
3. The C (Control) group: (n=100) each patient received the same placebo tablet identical to Mirta tablet orally with sips of water and 100 ml 0.9% NS IVI over 15 minas a placebo for Dex 2 h preoperatively.

Randomization was done using computer-generated table of random numbers in a 1:1 ratio in opaque and sealed envelope (SNOSE). The assigned treatment was written on a card and sealed in opaque envelopes consecutively numbered. These envelopes were opened just immediately before infusing the medication in the patient's room. The study drugs were prepared by the hospital pharmacy and follow-up of patients were conducted by anesthesia residents not involved in any other part of the study.