heat stroke is defined clinically as a core body temperature above 40c and accompanied by central nervous system ( cns ) abnormalities such as delirium , convulsions , or coma . heat stroke , the extreme form of hri is associated with significant mortality and morbidity , mortality in these patients range between 10% to 50% . heat stroke is often associated with multiple organ system involvement and survivors may sustain permanent neurologic damage . heat stroke may be divided into exertional and non - exertional ( classical ) heat stroke . while exertional heat stroke is associated with exercise , classic heat stroke is typically seen in debilitated patients during high ambient temperature and humidity . risk factors for classical heat stroke include - old age , alcoholics , antihypertensive or psychiatric medications , neurological disease and dehydrating illness . the year 2012 recorded the highest temperatures in last 10 years in chennai [ figure 1 ] . due to the unusually high temperatures recorded in the summer of 2012 , there was spurt in such patients admitted to our intensive care unit ( icu ) . arrow indicates admission time frame of patients to intensive care unit with heat - related illness the aim of the study was to identify the profile of patients admitted to our multidisciplinary icu with clinical features of hri and analyse their clinical outcomes . this was a retrospective case series , of patients admitted with features of hri during the period from april to june 2012 in our 25 bedded multidisciplinary icu . after obtaining institutional ethics committee approval , we included all patients admitted with complaints of fever with cns abnormalities such as delirium , convulsions , acute alteration of consciousness , or coma and absence of any other evident cause for the fever or acute onset of cns dysfunction . we excluded patients showing features of cns infection , stroke and other causes of encephalopathy . all the patients were managed in the icu in a similar manner as mandated by their severity of illness which included appropriate organ support , fluid resuscitation , electrolyte management and active cooling as required . patients also received other supportive measures such as , stress ulcer , deep vein thrombosis prophylaxis , glycaemic control , nutritional support and analgesia / sedation . the patients were evaluated to rule out any underlying infections including cns infection , stroke or encephalopathy as deemed necessary . data collected from patient 's medical records , included demographics , co - existing illness , current medications , admission vitals and glasgow coma scale ( gcs ) score . other laboratory parameters required to calculate acute physiology and chronic health evaluation ii ( apache ii ) and sequential organ failure assessment ( sofa ) scores were also captured . these two scores were calculated using the worst parameters recorded during the first 24h of icu admission . details regarding cerebrospinal fluid analysis , echocardiography and neuroimaging studies obtained wherever indicated were also captured . outcome data on mortality , icu length of stay ( los ) , number of ventilator days , discharge gcs and sofa score were recorded . continuous variables with normal distribution were compared using student 's t - test whereas those not normally distributed were analysed using mann - whitney u - test . categorical data were analysed using pearson chi - square test or fischer 's exact test . during the study period , 30 patients presented with features of hri as described above , of whom two patients had features suggestive of cns infection and another two patients had features of acute stroke in neuroimaging studies . excluding these patients , data from the remaining 26 patients were analysed . demographic characteristics of patients are presented in [ table 1 ] . 20 patients ( 77% ) had at least one co - existing illness , of which hypertension and diabetes mellitus were the most common [ table 1 ] . 18 ( 69.2% ) demographics , pre - existing medical conditions and prior medications of patients with hri patients admitted to icu with hri were critically ill as indicated by high admission apache ii ( 19.62  7.7 , mean  sd ) and sofa ( 7.5  2.64 , mean  sd ) scores [ table 2 ] . organ system involvement includes cns ( 100% ) , renal ( 57% ) , liver ( 34% ) , coagulation ( 26% ) , respiratory ( 26% ) and heart ( 23% ) . characteristics of patients with hri in line with our inclusion criteria , all our patients were febrile ( temperature 102.7  2.7 f , mean  sd ) . more than 30% of patients presented with seizures and more than a third were comatose on admission [ figure 2 ] . apart from cns involvement , 30% of patients also had gastrointestinal ( gi ) symptoms such as nausea , vomiting ( 8/26 ) and diarrhoea ( 4/26 ) . spectrum of neurological involvement in heat - related illness seventy - three percentage ( 19/26 ) of our patients had hyponatraemia ( serum sodium < 135 meq / l ) on admission ( mean serum sodium 124.38  13.33 meq / l [ sd ] ) and most responded to resuscitation with normal saline [ figure 3 ] . however , hypertonic saline ( 3% ) was used in seven patients who had persistent neurological symptoms ( gcs 11.2  1.79 , mean  sd ) and hyponatraemia ( serum sodium 111  4.0 meq / l , mean  sd ) . meq / l ) ( mean serum potassium 3.5  0.9 meq / l [ sd ] ) . creatinine phosphokinase ( cpk ) levels were elevated in all patients ( 1856  2372 iu / l , mean  sd ) . l on admission ; this patient had a previous history of heat stroke , had myoglobinuria and renal failure requiring haemodialysis . 15 ( 57% ) patients had elevated serum creatinine ; five of these patients had progressively worsening renal function requiring haemodialysis . liver enzymes were raised in 50%(13/26 ) patients ( aspartate aminotransferase [ ast ] 198.50  395.6 iu / l and alanine aminotransferase [ alt ] 97.5  110 iu / l , mean  sd ) with mildly deranged coagulation profile ( international normalised ratio 1.40  0.55 ) with no obvious bleeding tendencies . serum sodium levels in patients with heat stroke neuroimaging was performed in patients who were comatose or had focal neurological deficit post - resuscitation and stabilisation . computerised tomography scan of brain was done in 11 ( 11/26 ) patients , while magnetic resonance imaging ( mri ) of brain was done in 12 ( 12/26 ) patients . diffusion - weighted mri features suggestive of heat stroke [ figure 4 ] were seen in five patients . these included diffusion restriction involving cerebellum ( 4/5 ) , basal ganglia and thalamus ( 3/5 ) , hippocampus ( 2/5 ) , cerebral cortex and subcortical white matter ( 2/5 ) . there were corresponding increased t2/t2 fluid - attenuated inversion recovery signal intensities in these regions . features of diffuse cerebral oedema ( 3/5 ) and diffuse cerebellar oedema ( 4/5 ) were also seen in these patients . diffusion - weighted magnetic resonance imaging showing restricted diffusion involving ( a ) cerebellum ( b ) thalamus ( c ) basal ganglia and ( d ) hippocampus sixteen patients ( 61.5% ) required mechanical ventilation to protect airway due to low gcs . six patients ( 23% ) who remained in shock ( mean arterial pressure < 70 mmhg ) despite adequate fluid resuscitation required vasopressor support . mean icu los was 16.0  17.05 days ( sd)(range 2 - 60 days ) . mean ventilator days were 10.16  12.46 days ( sd ) [ table 2 ] . the mean discharge gcs of our patients was 13.17  1.8 , ( sd ) . nine out of 17 patients were discharged with normal gcs . of the remaining eight patients , these four patients had a prolonged icu stay ( 28  5 days , mean  sd ) . the remaining four patients had a discharge gcs of 14 , of whom two had pre - existing , parkinsonism , one had dementia and another had previous stroke . raised serum lactate , high admission sofa scores and prolonged ventilator days were risk factors for mortality in univariate analysis ; however , multivariate analysis by logistic regression did not identify any risk factors of mortality . hri following periods of sustained heat wave have been reported previously ; however , in our study , we had cases admitted over a period of 2 months corresponding to high ambient temperature . risk factors for hri include old age , alcohol abuse , neurological disease , psychiatric illness and patients on long - term medications . in our study , this was a strikingly younger group as compared to the patients in the studies by argaud et al . nearly 30 - 50% of patients had significant functional limitations and in our study , most of the patients were functionally active prior to admission . hence , our patients may have been exposed to high ambient temperatures in an open environment making them more prone to hri . exposure to high temperatures lead to elevation of body temperature , which causes activation of various physiological compensatory mechanisms which include increased cutaneous circulation and concomitant vasoconstriction of the renal and splanchnic circulation . heat stress causes cell damage by apoptosis , release of inflammatory mediators and endothelial damage leading to multi organ failure . . most common sites of cns involvement of heat stroke include cerebellum , basal ganglia , thalamus , hippocampus and fronto - parietal cortex all our patients had neurological involvement of varying degrees . mri features were due to cerebral ischaemia ( uk english ) resulting from auto regulatory mechanisms that divert blood flow towards periphery to dissipate excessive heat . apart from cns symptoms , 30% of patients also presented with gi symptoms such as nausea , vomiting and diarrhoea . studies have shown that even though thermal stress results in an increased cardiac output , splanchnic flow is reduced because of increased splanchnic vascular resistance , resulting in gut ischaemia with focal necrosis , resulting in gi symptoms . a high prevalence of elevated liver aminotransferase levels has been reported in exertional heat stroke and has been attributed to ischaemia and direct thermal injury . the primary event seems to be related to direct thermal injury of vascular endothelium , initiating platelet aggregation and activation of the clotting cascade along with increased fibrinolysis and disseminated intravascular coagulation . even though our patients had mildly elevated liver enzymes and slightly deranged coagulation parameters , they did n't show any obvious bleeding tendencies . the french heat wave reported 40% incidence of raised alt levels in their study compared to the 50% in our study . all but 5 of the 15 patients with elevated serum creatinine improved their renal function with fluid resuscitation , this points to volume depletion as a cause for renal involvement . three of the five patients requiring haemodialysis had myoglobinuria . suggested mechanisms of renal injury in patients with heat stroke include direct thermal injury , renal hypoperfusion secondary to compensatory renal artery vasoconstriction and rhabdomyolysis . haemodynamic failure requiring vasopressor support was seen in 23% of our patients compared to 43% reported by argaud et al . shock in heat stroke is due to the inability of the cardiovascular system to increase cardiac output in the context of heat - related dehydration and vasoplegia enhanced by proinflammatory response . cardiovascular dysfunction could be exacerbated in patients with pre - existing cardiovascular disease and patients on long - term antihypertensive medications . reported a mortality rate of 62% in 345 patients following 2003 heat stroke in france . compared to ours , their patients were elderly ( 67.2  14.1 vs. 53.11  20.59 years ) , were sicker as reflected by lower gcs ( 5.7 vs. 8.6 ) and higher rate of mechanical ventilation ( 99% vs. 64% ) . various predictors of mortality have been previously described in heat stroke which includes long - term use of antihypertensive medication , anuria at admission , coma , cardiovascular failure , high simplified acute physiology score ( saps ii ) , high body temperature and prolonged prothrombin time . described 33% of their survivors having moderate to severe neurological impairment which was higher than the rate of 23.52% ( 4 of 17 with gcs < 10 ) observed in our study . this difference may be due to the greater sickness of their patients ( apache ii 28  6 vs. 19.62  7.7 mean  sd ) as compared to our patients . however , survivors regained normal function of other organ systems in our study . due to the retrospective nature of our study we faced certain limitations . history of intensity of heat exposure , or exertion prior to admission and information regarding cooling methods employed were not reliable . similarly there was a lack of clarity on the degree of neurological involvement in patients with pre - existing neurological disease . we also did not have information on long - term follow - up of patients after hospital discharge . patients admitted to icus with heat related illness had multiple organ system dysfunction and were associated with significant neurological morbidity , and mortality .
background and aims : heat - related illness ( hri ) due to high ambient temperatures is a common feature during the indian summer . 
 hri often results in intensive care unit ( icu ) admissions and are associated with significant morbidity and mortality . 
 however , published report on the effects of hri among the indian population is lacking . 
 this study was undertaken to identify the profile of patients admitted to icu with clinical features of hri and study their clinical outcomes.methods:this was a retrospective case series of patients admitted with features of hri during the summer of 2012 in our multidisciplinary icu . 
 data on demographics , co - morbid illness , admission severity of illness ( acute physiology and chronic health evaluation ii [ apache ii ] ) , organ failure scores ( sequential organ failure assessment [ sofa ] ) and neuroimaging studies were collected . 
 outcome data studied included mortality , icu length of stay ( los ) , ventilator days and hospital los . 
 statistical analysis was performed using student 's t - test , chi - square test and multivariate analysis.results:twenty-six patients met the diagnostic criteria for hri . 
 fifteen were males . 
 the mean age was 53.12  18.6 years . 
 mean apache ii score was 19.6  7.7 and mean sofa score was 7.5  2.6 . 
 the common presenting symptoms were fever with neurological impairment ( 100% ) and gastrointestinal symptoms ( 30% ) . 
 major organ systems involvement include neurological ( 100% ) , renal ( 57% ) , hepatic ( 34% ) and coagulation abnormalities ( 26% ) . most common metabolic abnormality noted was hyponatraemia ( 73% ) . 
 magnetic resonance imaging findings suggestive of heat stroke were seen in 5 of 26 patients . 
 mortality rate was 34% . 
 8 of 17 survivors had residual neurological impairment.conclusion:hri carries a high mortality and significant neurological morbidity .