Post-spinal shivering is a common problem during anesthesia and surgery. Thus, the prevention of post-anesthesia shivering is relevant clinical practice. Ketamine and tramadol are among the prophylactic agents used for intraoperative shivering. Different evidence depicts the effectiveness of pharmacological drugs like ketamine, pethidine, and tramadol in preventing post-spinal shivering. Pethidine has a better outcome in preventing PSS but is mostly associated with adverse events like respiratory depression and arterial oxygen desaturation, nausea, vomiting, and sedation in some patients [19, 23, 29]. Low-dose ketamine and tramadol, on the other hand, have fewer or no adverse effects like mild sedation and hallucinations [17, 30]. However, certain studies have shown contradictory views on the effectiveness of prophylactic low-dose ketamine and tramadol in preventing post-spinal shivering [6]. Furthermore, despite the fact that high doses of ketamine and tramadol were effective in controlling post-spinal shivering, their side effects limited their use [31, 32]. In our study, the effectiveness of low-dose ketamine versus tramadol in reducing intraoperative shivering among orthopedic surgical patients under spinal anesthesia was compared.

The overall incidence of post-spinal shivering in the current study was 36.2%. That is higher than the study done in North West Ethiopia, with a prevalence of 25.6% [7]. Our finding is much higher than studies conducted elsewhere, with a range of 8–14.4% [10, 33]. On the other hand, our finding is lower than the study conducted in Khyber Teaching Hospital, Pakistan. The difference could be due to pre-warmed intravenous fluid (IV) and controlling the operation room temperature between 24 and 26 oC [34].

In the current study, the incidence of post-spinal shivering was significantly lower among patients taking low-dose ketamine as compared to the tramadol group. This finding was corroborated with a study conducted on the effectiveness of ketamine in Abubakar Tafawa Balewa Teaching Hospital, Bauchi, Nigeria [35]. In contrast to this, no significant difference was observed between the two prophylactic drugs, according to the study conducted in India. This could be due to PSS being recorded for only 30 min after the surgery, where prolonged follow-up is used in the current study [36].

The incidence of intraoperative shivering was 28.7% in the ketamine group and 43.8% in the tramadol group. This is in line with the study conducted in a combined military hospital and medical college in Lahore, Pakistan, which revealed that the incidence of intraoperative shivering was 18.75% in the ketamine group and 46.88% in the tramadol group [37]. Our study result is lower than the study finding reported in Gondar, with an incidence of 41.5% and 53.7% among ketamine and tramadol groups, respectively [18]. In contrast, the study conducted in Jinnah Hospital Lahore showed that the incidence of shivering was 6% in the tramadol group and 32% in the ketamine group, which may be due to the infusion of the prophylactive agent and pre-warmed intravenous fluid used for the load [38].

In the current study, the severity of shivering scores 1, 2, and 3 was higher in the tramadol group than in the ketamine group. This is in line with the study conducted in Mustasharak hospital, Egypt [39]. Our result shows that the severity of shivering in the ketamine group was 27.9% in score 2, whereas in the tramadol group it was 35.3%. This finding is comparable with the 22% and 31.7% documented in Gondar and the study findings reported in Indonesia, with a severity score in ketamine of 23.3% whereas in the tramadol group it is 26.7%. The difference between our study and the previous one could be due to more than one-hour of follow-up in the current study and the study that included the high block. According to the study conducted in India, the severity of shivering was higher in the ketamine group than in the tramadol group. This could be due to premedication of Midazolam and Fentanyl [40].

Concerning grade 3 score shivering in our study, it is less than 1% in ketamine and 8.5% in tramadol. This finding is much lower than the finding in North West Ethiopia, where shivering scores greater than 19% are reported after both drugs. This could be due to the small sample size and a pregnant mother with an age less than 39 years [18].

In the present study, there was a significant change in intraoperative hemodynamic parameters between the two groups, and mean arterial blood pressure was higher in the ketamine group. This result is in line with a comparative study conducted in India which showed that mean arterial blood pressure was higher in patients who received ketamine as compared to the placebo group [17]. According to the studies documented in India, intraoperative hemodynamic parameters in the ketamine and tramadol groups did not show significant changes in hemodynamic parameters [41] This could possibly be due to a preload with pre-warmed IV fluid to 37 oC and ketamine being a sympathomimetic agent that increases the mean arterial blood pressure.

Our study results showed the incidence of intraoperative nausea and vomiting was significantly higher in the tramadol group when compared to the ketamine group, which is in line with a comparative study conducted in Nishutar Medical College and Hospital, Multan, which reveals the incidence of nausea and vomiting is low in the ketamine group [42]. In another study that was conducted in Calcutta National Medical College and Hospital, India, there was an increased incidence of nausea and vomiting in the tramadol and pethidine groups [43]. In contrast, the study conducted in Songklanagarind hospital, Thailand reveals that there is no statistically significant difference in the incidence of nausea and vomiting in between ketamine and placebo groups, which may be due to general anesthesia started by giving propofol and narcotics [6].

The incidence of low levels of sedation was higher in the ketamine group when compared to the tramadol group. One comparative study also investigated the incidence of sedation scores and found that it was significantly higher in the ketamine group as compared with the tramadol group [16]. In contrast, the study conducted at Siddhardha Medical College, India revealed that sedation scores of ketamine and tramadol were statistically significantly higher than those of dexamethasone. This may be due to premedication of Midazolam and Fentanyl [40].

In the previous study conducted in Safdarjung hospital, India, there was a greater fall in core temperature in the placebo group as compared with the ketamine, tramadol, and clonidine groups. In our study, there was a significant decrease in mean temperatures after spinal anesthesia with respect to baseline value and changes over time in the ketamine and tramadol groups. This result is in line with a study conducted in the Faculty of Medicine et al.-Azhar University, Egypt [39]. Another study conducted in the institute civil hospital, Aizawl, Mizoram, showed that the decrease in core temperature was statistically significant in ketamine compared to the baseline level. This could be due to the vasodilation effect of spinal anesthetic agents [44]. In contrast, the study conducted in the faculty of medicine, Tanta University, Egypt, showed the change in the mean temperature in the tramadol group was not statistically significant at any time of the post-anesthesia period. That may be because they measured tympanic membrane temperature [45].

The result of our study shows that the aged group has a strong association with a reduced risk of post-spinal shivering, which is in line with a study conducted at the University of Gondar, in 2015 [7]. That may be due to diminished thermoregulatory response to changes in body temperature in old age or it could be due to the atrophy of skeletal muscles [10].

Our study results showed that those patients with a duration of surgery greater than 1 h were strongly associated with post-spinal shivering, which is in line with a comparative study conducted at the University of Gondar, Ethiopia [7]. However, according to the study conducted at the University of Marburg, Germany in 2005, there was no strong association. This could be because of the general anesthesia and the patient's assessment at the post-anesthesia care unit [10].

Our study results showed that patients who had taken low-dose ketamine had a statistically significant association with the prevention of PSS. This finding is supported by similar studies conducted in Pakistan, Turkey, and Iran [26, 46, 47].

In this study, hypothermia was not associated with post-spinal shivering. In contrast to our finding, a study conducted in Gondar showed that hypothermia was associated with PSS [7]. This may be due to the type of anesthesia used during surgery.

The limitation of this study was the failure to measure core temperature, which is the more accurate way to assess intraoperative temperature.

Patients were followed for one hour during the surgery to observe the incidence of shivering, which is higher than most of the literature in the country and elsewhere.