regional anaesthesia ( spinal anaesthesia ) is widely used as a safe anaesthetic technique for both elective and emergency operations . shivering is known to be a frequent complication , reported in 40 to 70% of patients undergoing surgery under regional anaesthesia shivering is a potentially serious complication , resulting in increased metabolic rate ; increased oxygen consumption ( up to 100 - 600% ) along with raised carbon dioxide ( co2 ) production ; ventilation and cardiac output ; adverse postoperative outcomes , such as wound infection ; increased surgical bleeding ; and morbid cardiac events . it causes arterial hypoxemia , lactic acidosis , increased intraocular pressure ( iop ) , increased intracranial pressure ( icp ) ; and interferes with pulse rate , blood pressure ( bp ) and electrocardiographic ( ecg ) monitoring.[35 ] shivering is very unpleasant , physiologically stressful for the patient undergoing surgery , and some patients find the accompanying cold sensation to be worse than the surgical pain . though the mechanism of origin of shivering is not clear , various hypotheses have been proposed to explain its occurrence . perioperative hypothermia is the primary cause , which occurs due to neuraxial anaesthesia - induced inhibition of thermoregulatory mechanism . shivering occurs as a thermoregulatory response to hypothermia or muscle activity with tonic or clonic patterns , and various frequencies have been noticed . however , in the postoperative period , muscle activity may be increased even with normothermia , suggesting that mechanisms other than heat loss with subsequent decrease in the core temperature contribute to the origin of shivering . these may be uninhibited spinal reflexes , sympathetic over - activity , postoperative pain , adrenal suppression , pyrogen release and respiratory alkalosis . moreover , shivering per se may aggravate postoperative pain , simply by stretching of surgical incision . there are various methods available to control shivering during anaesthesia , which include non - pharmacological methods and pharmacological methods using drugs which have anti - shivering properties . non - pharmacological methods using equipment to maintain normal temperature of the body are effective but expensive and lack practicality , while the pharmacological methods using drugs like pethedine , tramadol , clonidine , doxapram , katenserin , nefopam , etc . , are simple , cost - effective and easy to implement . the aim of this prospective double - blind randomized clinically controlled study was to clinically compare the efficacy , potency , haemodynamic effects , complications and side effects of clonidine with those of tramadol for control of shivering . after obtaining approval of the ethics committee and written informed consent , 80 american society of anaesthesiologists grade - l ( asai ) patients ( power of study , 70% ) of either sex aged 18 to 40 years scheduled for elective abdominal , orthopaedic and gynaecological surgeries , e.g. , inguinal herniorraphy , abdominal and vaginal hysterectomy , k - nailing , dynamic hip screw ( dhs ) , under spinal anaesthesia with no prior pre - medication , were included in this prospective double - blind randomized clinically controlled study . patients with known hypersensitivity to clonidine and tramadol , known history of alcohol or substance abuse , hyperthyroidism , cardiovascular diseases , psychological disorder , severe diabetes or autonomic neuropathies and urinary tract infection ( uti ) were excluded . all patients who developed post - spinal anaesthesia intraoperative shivering were randomly allocated to two groups : group c ( n=40 ) received clonidine 0.5 g / kg ( intravenously ) iv , and group t ( n=40 ) received tramadol 0.5 mg / kg iv . anaesthesiology personnel who were not involved in the study made the trial preparations and recorded group randomization separately . the anaesthesiologists conducting the case and recording the data were unaware of the preparation administered . bupivacaine 0.5% ( 10 - 15 mg ) at l3 - 4 or l4 - 5 interspace using 25 gauge quincke 's needle , and blockage up to t9 - 10 dermatome was achieved . all operation theatres in which the operations were performed maintained constant humidity ( 70% ) and an ambient temperature of around 21c to 23c . oxygen was administered to all the patients of both groups at a rate of 5 l / min with face mask , and patients were covered with drapes but not actively warmed . preloading was not done in both the groups as we did not want intravenous fluid to influence the onset of shivering mechanism . standard monitoring of pulse rate was done , and non - invasive blood pressure ( nibp ) , oxygen saturation ( spo2 ) , body temperature ( axillary ) were recorded before the commencement of surgery and thereafter at every 5 minutes from the baseline ie subarachnoid block ( sab ) , for 1 hour ; and every 15 minutes , for the rest of the observation period . grading of shivering was done as per wrench , which is as follows : grade 0 : no shivering grade 1 : one or more of the following : piloerection , peripheral vasoconstriction , peripheral cyanosis with , but without visible muscle activity grade 2 : visible muscle activity confined to one muscle group grade 3 : visible muscle activity in more than one muscle group grade 4 : gross muscle activity involving the whole body patients who developed either grade 3 or grade 4 of shivering were included in the study . the attending anaesthetist recorded the time in minutes at which shivering started after spinal anaesthesia ( onset of shivering ) , severity of the shivering , time to disappearance of shivering ( in minutes ) and response rate ( shivering ceased after treatment in 15 minutes ) . duration of surgery was noted , and duration of spinal anaesthesia was recorded by assessing spontaneous recovery of sensory block using pin - prick method and observing spontaneous movements of limbs in the postoperative period . if the shivering did not subside by 15 minutes , the treatment was considered to be not effective . patients who did not respond or in whom recurrence of shivering occurred were treated with additional dose of clonidine ( 0.5 g / kg iv ) or tramadol ( 0.5 mg / kg iv ) in the respective groups , if required . side effects like nausea , vomiting , bradycardia ( < 50/min ) , hypotension ( > 20% of baseline ) , dizziness ; and sedation score were recorded . sedation score was assessed with a four - point scale as per filos : 
 1:awake and alert2:drowsy , responsive to verbal stimuli3:drowsy , arousable to physical stimuli4:unarousable 
  drowsy , responsive to verbal stimuli drowsy , arousable to physical stimuli bradycardia , hypotension and vomiting were treated with atropine , mephenteramine and metaclopramide , respectively , in titrated doses when required . statistical analysis was done using suitable statistical software , and student t test and chi - square test were applied for the interpretation of results . a total of 80 patients were enrolled in the present study and were randomized into two groups of 40 each ( n=40 ) , 57 of whom were male and 23 were female [ table 1 ] . both the groups were comparable with respect to age , sex , weight , duration of surgery , type of surgery , volume of intravenous fluid administered and the duration of spinal block . the mean age of the patients in group c was 30.03  3.80 years ; and patients in group t , 28.8  3.47 years ( p=.137 ) [ table 1 ] . demographic data of patients in the two groups shivering disappeared in 39 ( 97.5% ) patients who received clonidine and 37 ( 92.5% ) who received tramadol [ table 2 ] . both the drugs were found to be effective in reducing shivering . however , severity of shivering was unchanged in 1 ( 2.5% ) patient of group c and 3 ( 7.5% ) patients of group t. one patient in group c ( severity of shivering unchanged ) and 5 patients ( 3- severity of shivering unchanged ; 2- recurrence of shivering ) in group t were given rescue doses of clonidine or tramadol , respectively . six ( 7.5% ) patients out of a total of 80 patients received rescue doses . post - spinal anaesthesia shivering and responses the mean interval between the injection of drug ( clonidine and tramadol ) and the complete cessation of shivering was 2.540.76 and 5.011.02 minutes , respectively ( p=.0000001 ) . time for onset of shivering and severity of shivering were not statistically significantly different between the two groups . however , the time interval between administration of drug after onset of shivering and disappearance of shivering was significantly shorter in the clonidine group [ table 2](p=.0000001 ) . there was no statistically significant difference with respect to heart rate , mean blood pressure , axillary temperature and oxygen saturation between the two groups . complication rates were significantly higher in group t than in group c [ table 3 ] . nausea , vomiting and dizziness were higher in group t [ nausea - 31 ; vomiting - 8 ; and dizziness - 22 ) than in group c. more patients of group c ( 10 patients ) were sedated than of group t ( 5 patients ) . complications in both groups bradycardia occurred in 2 patients of group c and 1 patient of group t. in group c , 3 patients suffered from hypotension , and 1 patient complained of dry mouth , both of which were not present in group t [ table 3 ] . regional anaesthesia , either central neuraxial block or peripheral nerve block , is a safe and very popular technique used for various surgeries . however , 40% to 70% of patients undergoing regional anaesthesia develop shivering , though it is also found to occur after general anaesthesia . the mechanism which leads to shivering after regional anaesthesia is not very clear , but the probable mechanisms could be decrease in core body temperature secondary to sympathetic block ; peripheral vasodilatation ; increased cutaneous blood flow , which leads to increased heat loss through skin ; cold temperature of operation theatre ; rapid infusion of cold iv fluids ; and effect of cold anaesthetic drugs upon the thermosensitive receptors in the spinal cord . there are many non - pharmacological and pharmacological methods used to prevent heat loss and decrease shivering . non - pharmacological methods include radiant heat warmers , warming the operation theatre , blankets , warm iv fluids and using anaesthetic drugs at body temperature . the present study was designed to standardise these possible compounding factors , while reflecting the common practice in our institution . the factors that influence the occurrence of shivering , like temperature of iv fluids and drugs , were not tightly controlled , but this should not affect the validity of our study because the present study is focused on response to treatment used rather than incidence of shivering ; and by randomization , both groups were subjected to similar degrees of influence of these factors . pharmacological methods to treat shivering include pethedine , tramadol , doxapram , ketanserin , nefopam , alfentanyl , doxapram , etc . a limitation of this study is that we could not measure the core body temperature . for measurement of core body temperature , the probe needs to be put in the oesophagus or near the tympanic membrane . rectal temperature monitoring was a possibility but was not tried . in the present study , we compared the efficacy of clonidine and tramadol for treatment of shivering after spinal anaesthesia in patients undergoing various elective surgeries . clonidine exerts its anti - shivering effects at three levels : hypothalamus , locus coeruleus and spinal cord . at the hypothalamic level , it decreases thermoregulatory threshold for vasoconstriction and shivering , because hypothalamus has high density of 2 adenoceptors and hence is effective in treating the established post - anaesthetic shivering . it also reduces spontaneous firing in locus coeruleus  a pro - shivering centre in pons . at the spinal cord level clonidine is highly lipid - soluble and easily crosses the blood - brain barrier . due to these merits , interaction at the 2 adrenoreceptors at spinal and supraspinal sites tramadol is an opioid analgesic with opioid action preferably mediated via  ( mu ) receptor with minimal effect on kappa and delta binding sites . the anti - shivering action of tramadol is probably mediated via its opioid or serotonergic and noradrenergic activity or both.[1820 ] in the present study , we found that clonidine is as effective as tramadol in treating post  spinal anaesthesia shivering , but the time interval from the commencement of treatment to cessation of shivering is quite less with clonidine ( 2.540.76 minutes ) than with tramadol ( 5.031.02 minutes ) ( p=.0000001 ) . the response rate was also higher in the clonidine group than in tramadol group , but the difference was not statistically significant ( p=.03 ) . the complications were found to be higher in case of tramadol compared to clonidine . in the present study , similar differences were noted between the two groups in relation to vomiting and dizziness . in case of group c , 10 ( 25% ) patients had sedation of grade 2 ; while in group t , it was 5 ( 12.5% ) patients who had sedation . one patient of group c had dry mouth , which was not present in group t. two patients of group t had recurrence of shivering in postoperative period , while no patient in clonidine group suffered recurrence of shivering . these findings were similar to the findings of other researchers who compared clonidine with other drugs having anti - shivering properties.[2123 ] bradycardia occurred in 2 patients of group c , while 1 patient of group t suffered from bradycardia . hypotension occurred in 3 patients of group c. on overall analysis , higher complication rates were noted in group t patients compared to group c patients . it was noted in the present study that clonidine was quicker than tramadol in providing relief in shivering . zavaherforoush et al . compared clonidine with pethedine and fentanyl for treating post  spinal anaesthesia shivering in elective lower segment caesarean section ( lscs ) and also found it to be offering better thermodynamics than pethedine . the present study also found that the patients who received clonidine were more sedated than the patients in the other group . in conclusion , both clonidine ( 0.5 g / kg ) and tramadol ( 0.5 mg / kg ) effectively treated patients with post  spinal anaesthesia shivering , but tramadol took longer time to achieve complete cessation of shivering than clonidine , the difference being statistically significant . so we conclude that clonidine offers better thermodynamics than tramadol , with fewer side effects . the more frequent incidence of side effects of tramadol , like nausea , vomiting and dizziness , may limit it 's use as an anti - shivering drug . further studies are needed to compare the effectiveness of various drugs in the treatment of shivering in patients undergoing surgery under spinal anaesthesia .
the aim of this study was to evaluate the efficacy , potency and side effects of clonidine as compared to tramadol in post  spinal anaesthesia shivering . in this prospective double - blind randomized controlled clinical trial , 80 american society of anaesthesiologists grade - l ( asai ) patients aged between 18 and 45 years scheduled for various surgical procedures under spinal anaesthesia , who developed shivering were selected.the patients were divided into two groups : group c ( n=40 ) comprised of patients who received clonidine 0.5mg / kg intravenously ( iv ) and group patients who received tramadol 0.5 mg / kg iv . grade of shivering , disappearance of shivering , haemodynamics and side effects were observed at scheduled intervals . 
 disappearance of shivering was significantly earlier in group c ( 2.540.76 ) than in group t ( 5.011.02 ) ( p=.0000001 ) . 
 response rate to treatment in group c was higher ( 97.5% ) than in group t ( 92.5% ) , but the difference was not significant . 
 nausea , vomiting and dizziness were found to be higher in group t ( p=0.001 , 0.005 , 0.001 , respectively ) , while the patients in group c were comparatively more sedated ( sedation level , 2 ; group c , 25% ) . 
 we conclude that clonidine gives better thermodynamics than tramadol , with fewer side effects .