In addition to its well-known advantages, SA has an additional advantage in uroscopic surgeries, especially procedures that require intraluminal fluid irrigation such as TURP, as it allows the early detection of complications such as TURP syndrome in conscious patients (1). However, SA is not a complication-free technique; shivering is a common complication of SA, with an incidence of 40-60% in patients who undergo SA (5). Though shivering is a protective mechanism to preserve body heat, it causes patient discomfort and pain and may be dangerous in patients with impaired cardiovascular reserves or limited respiratory capacity, as shivering increases the circulating catecholamine, HR, cardiac output, minute ventilation, oxygen consumption, metabolic CO2 production and lactic acid level. It also increases intraocular and intracranial pressure and postoperative pain due to surgical incision stretching. Shivering may also interfere with the monitoring of patients by causing artefacts on the ECG or disrupting BP and pulse oximetry readings (4). Additionally, shivering in patients with ASA grades III and IV may cause challenges for the surgeon and increase the operative time.
Hypothermia is a major risk for shivering, but there is no definite linear relationship between body temperature and the occurrence of shivering. Other major risk factors include age, sensory block level, temperature of the operating room and temperatures of the IV solutions (23).
The exact mechanisms to explain the occurrence of shivering during SA have not yet been elucidated. Possible mechanisms include central thermoregulation disturbance, internal body heat redistribution, and body heat loss to the environment (24). Regional and general anaesthesia are known to impair the efficiency of the hypothalamic thermoregulatory centre, causing different grades of hypothermia (25). Under regional anaesthesia, vasodilatation and redistribution of the core temperature are restricted to the lower body below the block, while vasoconstriction and shivering are restricted to the upper body, as they are inhibited below the level of the block due to sympathetic and somatic nerve blocks (26).
The neurotransmitter pathways responsible for shivering are complex, and different receptors patients, such as opioid, α-2 adrenergic, serotonergic, and anti-cholinergic receptors, are involved patients. Different drugs that act on these receptors have been examined in different trials for the prevention or treatment of shivering after SA (4). The studied drugs include meperidine, fentanyl, clonidine, ketamine, and tramadol; they have resulted in different degrees of efficacy and many associated side effects, such as haemodynamic instability, respiratory depression, nausea and vomiting (27).
Dexmedetomidine (5-15) and magnesium sulfate (2, 3, 17-20) have been demonstrated to be effective and safe for the prevention and treatment of shivering following SA; their efficacy and safety are equal or superior to other adjuvants, with fewer adverse effects. Few trials (3, 5, 15, 17) have examined intrathecal administration to prevent SA-related shivering.
Dexmedetomidine is a highly selective alpha-2 adrenergic agonist, known for its sedative effect in anaesthesia and intensive care practice; its affinity for alpha-2 adrenoreceptors is ten times higher than that of clonidine (28). The response to activation of these alpha-2- receptors includes a decreased sympathetic tone, resulting in a decreased BP and HR. Dexmedetomidine has been effectively examined in several studies for the prevention and treatment of shivering following general anaesthesia or SA at a dose that does not induce major sedation or haemodynamic instability, respiratory depression, nausea or vomiting (11). The exact mechanism of dexmedetomidine in the control of shivering is unclear and complex. One suggested mechanism is as follows: dexmedetomidine and other alpha-2 agonists reduce shivering by inhibiting central thermoregulatory control by restraining neuronal conductance and suppressing vasoconstriction and shivering thresholds. Drugs that inhibit thermoregulatory vasoconstriction prevent shivering (29).
Magnesium (Mg+2) is a naturally occurring non-competitive antagonist of N-methyl-D aspartate (NMDA) receptors with a good safety profile and neuroprotective properties under the condition of hypothermia (30). There are many theories regarding the anti-shivering effect of MgSO4; it has been reported to reduce shivering through a central effect by reducing the shivering threshold (16, 31). Additionally, it blocks NMDA receptors and decreases norepinephrine and 5-HT, which both play a role in thermoregulation (32). As a calcium antagonist, Mg+2 has a peripheral mild muscle relaxation effect that may reduce the intensity of shivering (incremental shivering intensity with progressing hypothermia) (33). Mg+2 also cause peripheral vasodilation, which increases cutaneous circulation, leading to a decrease in the incidence of shivering (34, 35).
Based on previous studies, we compared the effect of subarachnoid injections of dexmedetomidine and MgSO4 on the prevention of shivering after SA in patients who underwent uroscopic surgery. The current study demonstrated that post-SA injection of both dexmedetomidine (5 μg) and MgSO4 (25 mg) significantly reduced the incidence of post-SA shivering. Five patients (14.3%) in group D, 8 patients (22.8%) in group M, and 21 patients (60%) in group C developed shivering. The number of patients who developed shivering and required meperidine administration in group D group was 5 (14.3%), in group M was 6 (17.4%), and in group C was 21 (60.0%).
Similar to our study, Ellakany et al (15) administered the same intrathecal dexmedetomidine dose (5 μg) and concluded that both intrathecal dexmedetomidine and meperidine effectively lowered the incidence of shivering following SA in patients who underwent lower abdominal surgery, but meperidine was associated with more side effects, such as pruritus, nausea and vomiting, than dexmedetomidine. In sixty patients who underwent lower abdominal surgery, Abdel Hamid et al. (36) concluded that adding 5 μg of dexmedetomidine to intrathecal bupivacaine improved the characteristics of the spinal block, with less postoperative analgesic requirements and a lower incidence of shivering than the placebo with no sedation or other complications.
Moawad et al (5) studied the effect of adding dexmedetomidine to intrathecal bupivacaine at a higher dose (10 μg) than that in our study (5 μg). They found that it significantly decreased the incidence and degree of shivering in patients undergoing TURP.
Usta et al (12) and Bajwa et al (23) studied the prophylactic effect of IV dexmedetomidine on shivering in patients who received SA and general anaesthesia, respectively. They found that perioperative dexmedetomidine infusion significantly decreased the incidence and intensity of shivering, with no major adverse effects.
Botros et al. (14) compared the prophylactic effects of an intravenously infused placebo, 1 μg/kg of dexmedetomidine and 8 mg of ondansetron on the prevention of post-SA shivering in 120 patients undergoing different lower body surgeries and found that IV dexmedetomidine and ondansetron were equally as effective in reducing the incidence of post-SA shivering as the placebo.
Abdel-Ghaffar et al. (37) compared the clinical efficacy and side effects of three different doses of IV dexmedetomidine (0.5, 0.3 and 0.2 µg/kg) and IV meperidine 0.4 mg/kg for the treatment of post-SA shivering in 120 patients. They found that 0.3 µg/kg of dexmedetomidine was the most appropriate dose for the effective treatment of shivering after SA, with modest effects on haemodynamic characteristics and sedation.
Faiz et al (3) concluded that an intrathecal injection of MgSO4 (25 mg) improved perioperative shivering in female patients who underwent an elective caesarean section.
Ibrahim et al (19) studied the prophylactic and therapeutic effects of IV MgSO4 on SA-induced shivering and proved that it was effective.
Gozdemir et al. (2) found that following SA, an IV infusion of 80 kg/mg of MgSO4 over 30 minutes, followed by IV infusion at a rate of 2 g/hr until the end of surgery had a significant effect on preventing post-SA shivering in patients undergoing TURP.
In a study by Sachidananda et al (20), a prophylactic IV infusion of MgSO4 and tramadol effectively reduced shivering during caesarean section under SA and the shivering intensity.
There was no difference between the three groups in terms of intraoperative haemodynamics. Regarding the sensory and motor block onset times, group D had the fastest sensory and motor blocks onset times, while group M had delayed sensory and motor block onset times compared to group D. This may be due to changes in the pH and baricity of bupivacaine due to the addition of MgSO4. The durations of both the sensory and motor blocks in group D were longer than those in group M, which were longer than those in group C. Similar results were observed in two studies (38, 39) that compared the effects of 10 μg of intrathecal dexmedetomidine and 50 mg of intrathecal MgSO4 when added to bupivacaine, considering the characteristics of the spinal block as the primary outcomes.
Limitations and recommendations:
The limitation to this study was that we did not estimate the mean volumes of the irrigating fluids in each group. We recommend conducting further studies on both drugs with increased sample sizes and different doses.