Besides its well-known advantages, SA has an additional one in uroscopic surgeries especially procedures that need intralumnal fluids irrigation such as TURP, as it allows early detection of complications as TURP syndrome in conscious patients (1). However, SA is not a complication free technique; Shivering is one of the common complications of spinal anesthesia with an incidence reach 40-60% of patients undergoing spinal anesthesia (5). Though, shivering is a protective mechanism to preserve body heat but it causes patient discomfort and pain and it may be dangerous in patients with impaired cardiovascular reserve or a limited respiratory capacity as shivering increases circulating catecholamine, heart rate, cardiac output, minute ventilation, patient’s oxygen consumption, metabolic CO2 production and lactic acid level. It also increases intraocular and intra cranial pressure, postoperative pain from surgical incision stretching. Shivering also may interfere with the monitoring of patients by causing artifacts of the ECG, blood pressure, and pulse oximetry (4). Also shivering in high grades -III & IV- may cause some difficulties to 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 appearance of shivering. Other major risk factors include aging, level of sensory block, and temperatures of the operating room and intravenous solutions (23).
The exact mechanisms that explains occurrence of shivering during SA haven’t been established yet. The possible mechanisms include disturbance of central thermoregulation, internal body heat redistribution, and loss of body heat to the environment (24). Regional and general anesthesia are known to impair the efficiency of hypothalamic thermoregulatory center causing different grades of hypothermia (25). During regional anesthesia, vasodilatation and redistribution of the core temperature is 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 block due to sympathetic and somatic nerve block (26).
The neurotransmitter pathways of shivering are complex and different receptors are involved like opioids, α-2 adrenergic, serotonergic, and anti-cholinergic receptors. Different drugs that act on these receptors have been examined in different trials for the prevention or treatment of shivering that occurs after SA (4). These drugs include meperidine, fentanyl, clonidine, ketamine, and tramadol, and they have resulted in different degrees of efficacy and many associated side effects like hemodynamic instability, respiratory depression, nausea and vomiting (27).
Dexmedetomidine (5-15) and magnesium sulphate (2, 3, 17-20) proved efficacy and safety in preventing and treating shivering following spinal anesthesia as equal as, or sometimes superior than, other adjuvants with less adverse effects. Few of these trials (3, 5, 15, 17) examined them intrathecally to prevent related shivering.
Dexmedetomidine is a highly selective alpha-2 adrenergic agonist known with its sedative effect in anesthesia &intensive care practice and it has ten times higher affinity for alpha-2 adrenoreceptor than clonidine (28). The response to activation of this alpha-2- receptors includes decrease sympathetic tone resulting in decrease in blood pressure and heart rate. Dexmedetomidine has been effectively examined in several studies for prevention and treatment of shivering following general or spinal anesthesia in a dose that doesn’t cause major sedation or hemodynamic instability, no respiratory depression, less nausia and vomiting (11). The exact mechanism of dexmedetomidine in shivering control is not clear and complex. The suggested mechanism is that dexmedetomidine and other alpha-2 agonists reduce shivering through inhibiting the central thermoregulatory control by restraining the neuronal conductance and through suppressing the vasoconstriction and shivering thresholds. These drugs which 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 during hypothermia (30). Anti-shivering effect of Mg SO4 has many theories, as it has been reported to reduce shivering through a central effect by reducing shivering threshold (16,31). Also blocking NMDA receptors decreases norepinephrine and 5-HT, which both play a role in thermoregulation control (32). Being a calcium antagonist, magnesium has a peripheral mild muscle relaxation effect which may reduce the gain of shivering (incremental shivering intensity with progressing hypothermia) (33). Magnesium also causes peripheral vasodilation that increases the cutaneous circulation leading to decreasing the incidence of shivering (34,35).
Based on those previous studies, we compared the effect of subarachnoid injection of dexmedetomidine and magnesium sulfate in prevention of shivering after spinal anesthesia in patients with uroscopic surgeries. The current study showed that both SA injection of dexmedetomidine 5μg and magnesium sulfate 25 mg have significantly reduced the incidence of post spinal shivering. (5 patients (14.3%) developed shivering in D group, 8 patients (22.8%) in M group, and 21 patients (60%) in C group). Number of patients who develop shivering and needed meperdine administration was 5 patients (14.3%) in D group, 6 patients (17.4%) in M group, and 21 patients (60.0%) in C group.
Similar to our study using the same intrathecal dexmedetomidine dose (5 μg), Ellakany et al (15) concluded that both intrathecal dexmedetomidine and meperidine effectively lowered the incidence of shivering following spinal anesthesia in patients undergoing lower abdominal surgeries, but meperdine was associated with more side effects like pruritus, nausea and vomiting. On sixty patients undergoing lower abdominal surgeries, Abdel Hamid et al. (36) concluded that adding dexmedetomidine 5 μg to intrathecal bupivacaine improved the characters of the spinal block with less postoperative analgesic requirements and less shivering incidence when compared to placebo with no sedation or other complications.
Moawad et al (5) studied the effect adding dexmedetomidine to intrathecal bupivacaine but in a larger dose, 10 μg, than that of our study 5 μg, and 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 intravenous dexmedetomidine on shivering in patients who had spinal and general anesthesia respectively. They found that perioperative dexmedetomidine infusion significantly decreased the incidence and intenisty of shivering with no major adverse effects.
Botros et al. (14) compared the prophylactic effect of intravenously infused placebo, 1μg/kg of dexmedetomidine and 8 mg ondansetron on preventing postspinal shivereing on 120 patients undergoing different lower body surgeries, and they found that both iv dexmedetomidine and ondansetron are equally effective in reducing the incidence of postspinal shivering compared to 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 meperdine 0.4 mg/kg on treating postspinal shivering in 120 patients. They found that dexmedetomidine 0.3µg/kg was the most appropriate in treating shivering after spinal anesthesia effectively with the modest effect on hemodynamics and sedation.
Faiz et al study (3) concluded that Intrathecal injection of MgSO4 (25 mg) improved perioperative shivering in female patients undergoing elective caesarean section.
Ibrahim et al (19) studied the iv prophylactic and therapeutic effects of MgSO4 on spinal anesthesia induced shivering and proved it effective.
Gozdemir et al. (2) found that following spinal anesthesia, iv infusion of 80/kg mg Mg So4 over 30 minutes, followed by iv infusion at a rate of 2g/hr till the end of surgery is significantly effective in prevention of postspinal anesthesia shivering in patients undergoing TURP.
In Sachidananda et al study (20), prophylactic iv infusion of MgSO4 and tramadol effectively reduced shivering incidence during cesarean section under SA with a reduced shivering intensity with MgSO4
There is no difference between the three groups in intraoperative hemodynamics. Regarding onset of sensory and motor block, D group had the fastest onset of sensory and motor block while M group had a delayed onset of sensory and motor block than D and M groups. This may be due to change in ph and baricity of bupivacaine due to addition of magnesium sulfate. Duration of both sensory and motor blocks of D group were longer than those of M group which were longer than those of C group. Similar results were observed in two studies (38,39) which compared the intrathecal effect 10 μg dexmedetomidine and 50 mg Mg SO4 when added to bupivacaine targeting the characteristics of spinal block as primary out comes.
Limitations and recommendations:
The limitation was that we didn’t estimate the mean volume of the irrigating fluids in each group. Besides, we recommend conducting further studies on both drugs with larger sample size and different doses.