الفهرس 
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Abstract
Hypothermia during regional anaesthesia is common and can be nearly as severe as that observed during general anaesthesia. There are three principal reasons for hypothermia under spinal anaesthesia. First, spinal anesthesia produces vasodilatation, which leads to an internal redistribution of heat from the core to the peripheral compartment. Secondly, with loss of thermoregulatory vasoconstriction below the level of the spinal block, there is increased heat loss from body surfaces. Lastly, there is altered thermoregulation under spinal anaesthesia characterized by a 0.5°C decrease in vasoconstriction and shivering thresholds.
Shivering consists of muscular tremor and rigidity. It is often associated with body heat loss, although hypothermia alone does not fully explain the occurrence of shivering. Shivering is self-limiting, never becomes chronic, and is rarely associated with major morbidity. However, it affects the comfort of the patients, and may sometimes lead to more serious complications. Up to a 57% incidence of shivering during regional anesthesia has been reported.
Ketamine, which is a competitive receptor antagonist of N-methyl-d-aspartic acid (NMDA), has a role in thermoregulation at various levels. In rats, application of NMDA agonist increases the firing rate of neurones in the preoptic-anterior hypothalamus. Ketamine probably controls shivering by non-shivering thermogenesis either by action on the hypothalamus or by the b-adrenergic effect of norepinephrine.
Ketamine increases arterial pressure, heart rate and cardiac output because of direct sympathetic stimulation and inhibition of norepinephrine uptake into postganglionic sympathetic nerve endings, and may decrease core-to-peripheral redistribution of heat . Thus, it may be logical to use ketamine in patients who are at risk of hypothermia.
Among benzodiazepines, diazepam has been found to be effective in the prevention of postoperative shivering. Midazolam, even in plasma concentrations far exceeding those used routinely, produces minimal impairment of thermoregulatory control .
Benzodiazepines have been found to reduce repetitive firing in response to depolarizing pulses in mouse spinal cord neurons. Such inhibitory functions of midazolam in the spinal cord may be responsible for inhibiting the conduction of afferent impulses from muscle spindles and cutaneous receptors for cold to the higher centres, thereby and so suppressing shivering.
Our study was conducted on 60 adult patients undergoing elective surgery under spinal anesthesia divided into 4 groups 15 patients each. Patients received either midazolam 75 ug/kg, ketamine 0.5 mg/kg, combination of midazolam 37.5mg/kg and ketamine 0.25mg/kg or normal saline after commencement of spinal anesthesia. The incidence of shivering was lower in patients receiving midazolam and ketamine as demonstrated by lower shivering grades and less requirement for pethidine for the treatment of shivering as compared to the other three groups. The degree of sedation was also lower in the combined group. We conclude that prophylactic use of ketamine 0.25 mg kg−1 and midazolam 37.5 µg kg−1 i.v. is better than ketamine 0.5 mg kg−1 i.v. or midazolam 75 µg kg−1 i.v. in preventing shivering related to regional anaesthesia while producing less complications than a higher dose of either drug alone.