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2019308695055Assessment00Assessment14605008695055Heat exhaustion: no neurological symptoms; as per heat stroke but less severe; may be ? Na if dehydrated; ? Na if voluntary overhydrationHeat stroke symptoms: neurological abnormalities + hot dry skin; look for cause; symptoms more transient in exertional heat stroke; consider in any patient with exposure to heat and altered LOC, athlete with change in personalityInvestigations: U+E (? Na / Cl / K); use oesophageal / rectal thermometer (T >40°C; but may be lower initially); urate (high), BSL (? in 70%), LFT (? AST, LDH; almost always in exertional; LDH >1000 indicates severe; due to centrilobular hepatic necrosis), CK (10,000-1000,000 in rhabdomyolysis), urine (myoglobin), ECG (prolonged QT, arrhythmia, intraventricular conduction delay, ST segment changes), FBC (WCC 30-40), coagulation (DIC), ABG (lactic acidosis, respiratory alkalosis metabolic acidosis), CXR (ARDS)00Heat exhaustion: no neurological symptoms; as per heat stroke but less severe; may be ? Na if dehydrated; ? Na if voluntary overhydrationHeat stroke symptoms: neurological abnormalities + hot dry skin; look for cause; symptoms more transient in exertional heat stroke; consider in any patient with exposure to heat and altered LOC, athlete with change in personalityInvestigations: U+E (? Na / Cl / K); use oesophageal / rectal thermometer (T >40°C; but may be lower initially); urate (high), BSL (? in 70%), LFT (? AST, LDH; almost always in exertional; LDH >1000 indicates severe; due to centrilobular hepatic necrosis), CK (10,000-1000,000 in rhabdomyolysis), urine (myoglobin), ECG (prolonged QT, arrhythmia, intraventricular conduction delay, ST segment changes), FBC (WCC 30-40), coagulation (DIC), ABG (lactic acidosis, respiratory alkalosis metabolic acidosis), CXR (ARDS)2019307734935Differential Diagnosis00Differential Diagnosis14605007734936InfectiousEndocrine (thyroid, pheochromocytoma)Neurological (CVA, status, dystonia, akathesia, tardive dyskinesia, Parkinsons)Toxiological (withdrawal, syndromes, rapid withdrawal of Parkinson meds)Tetanus00InfectiousEndocrine (thyroid, pheochromocytoma)Neurological (CVA, status, dystonia, akathesia, tardive dyskinesia, Parkinsons)Toxiological (withdrawal, syndromes, rapid withdrawal of Parkinson meds)Tetanus2019305690235Risk Factors00Risk Factors14605005690235Environmental: ? T, ? humidity, exerciseAge: infant / elderlyPhysical: fat, dehydration, ETOH, unusual exertion, inappropriate clothing, febrile illness, lack of sleep/food/water/acclimitisation/fitness, PMH sameMedical: cystic fibrosis, diabetes, hyperthyroidism, Parkinsons, spinal injury, infection, IHD, delirium tremens, epilepsy, dermatological problems (eg. Scleroderma), CCFMedication: anticholinergics (? sweating; atropine, lithium, TCAD); serotonin syndrome; neuroleptic malignant syndrome; malignant hyperthermia altered oxidative phosphorylation (aspirin, lithium), inhibited CO (Ca channel, beta-blockers), disrupted thermoregulation (LSD) ? muscle activity (amphetamines, coke) dehydration (diuretics)00Environmental: ? T, ? humidity, exerciseAge: infant / elderlyPhysical: fat, dehydration, ETOH, unusual exertion, inappropriate clothing, febrile illness, lack of sleep/food/water/acclimitisation/fitness, PMH sameMedical: cystic fibrosis, diabetes, hyperthyroidism, Parkinsons, spinal injury, infection, IHD, delirium tremens, epilepsy, dermatological problems (eg. Scleroderma), CCFMedication: anticholinergics (? sweating; atropine, lithium, TCAD); serotonin syndrome; neuroleptic malignant syndrome; malignant hyperthermia altered oxidative phosphorylation (aspirin, lithium), inhibited CO (Ca channel, beta-blockers), disrupted thermoregulation (LSD) ? muscle activity (amphetamines, coke) dehydration (diuretics)2019304166870Patho-physiology00Patho-physiology14605004166871Heat dissipation: conduction, convection, radiation (accounts for 65% heat loss, stops >35°C), evaporation (accounts for 30% heat loss, from skin and lungs, stops at humidity >75%)Heat acclimitisation: gradual increase in heat changes in body thermoregulation (? sweat rate, sweat at lower skin T, lower sweat Na concentration, ? skin circulation, change in thermoregulatory set point, ? plasma volume, ? exercise HR, ? aldosterone levels, ? Na loss in urine, ? ability to resist rhabdomyolysis); takes 8-14/7 (faster if fit), max at 2-3/12, need to exercise in heat for 60-90mins/dayHeat stroke: >42°C uncoupling of cellular oxidative phosphorylation direct cellular damage, failure of thermoregulatory mechanisms, physiological changes, inflammatory and coagulopathic responses00Heat dissipation: conduction, convection, radiation (accounts for 65% heat loss, stops >35°C), evaporation (accounts for 30% heat loss, from skin and lungs, stops at humidity >75%)Heat acclimitisation: gradual increase in heat changes in body thermoregulation (? sweat rate, sweat at lower skin T, lower sweat Na concentration, ? skin circulation, change in thermoregulatory set point, ? plasma volume, ? exercise HR, ? aldosterone levels, ? Na loss in urine, ? ability to resist rhabdomyolysis); takes 8-14/7 (faster if fit), max at 2-3/12, need to exercise in heat for 60-90mins/dayHeat stroke: >42°C uncoupling of cellular oxidative phosphorylation direct cellular damage, failure of thermoregulatory mechanisms, physiological changes, inflammatory and coagulopathic responses201930963930Definition00Definition1460500962660Heat exhaustion: less severe form of heat stroke; most due to volume and electrolye loss as sweat, but with inadequate replacement ( dehydration); heat regulatory mechanisms remain; CNS unaffectedHeat cramps: painful involuntary spasms of major muscles; usually heavily exercised muscles, during or after exercise; due to body water loss and large sweat Na loss; if doesn’t appear dehydrated, suspect hyponatraemiaHeat tetany: due to hyperventilationHeat oedema: mild swelling of extremities; due to vasodilation and orthostatic pooling of fluids during 1st few daysPrickly heat: pruritic, maculopapular, erythematous rash with superficial vesicles due to inflammation of sweat ductsHeat stroke: life threatening condition with core T >40°C + altered LOC (delirium, seizures, coma) +/- anhydrosis, multi-organ failure; medical emergency; failure of hypothalamic thermostat; CNS dysfunction; mortality 10-50% (approaches 80% if not promptly treated, <10% if promptly treated); 33% mortality if hypotensionClassical heat stroke: high environmental T; young and elderly vulnerable; skin hot and dryExertional heat stroke: strenous exercise; occurs if heat exhaustion not properly treated; usually young athletes / military; skin hot and sweating (50%); dehydration more common; results in severe lactic acidosis, rhabdomyolysis, DIC more often00Heat exhaustion: less severe form of heat stroke; most due to volume and electrolye loss as sweat, but with inadequate replacement ( dehydration); heat regulatory mechanisms remain; CNS unaffectedHeat cramps: painful involuntary spasms of major muscles; usually heavily exercised muscles, during or after exercise; due to body water loss and large sweat Na loss; if doesn’t appear dehydrated, suspect hyponatraemiaHeat tetany: due to hyperventilationHeat oedema: mild swelling of extremities; due to vasodilation and orthostatic pooling of fluids during 1st few daysPrickly heat: pruritic, maculopapular, erythematous rash with superficial vesicles due to inflammation of sweat ductsHeat stroke: life threatening condition with core T >40°C + altered LOC (delirium, seizures, coma) +/- anhydrosis, multi-organ failure; medical emergency; failure of hypothalamic thermostat; CNS dysfunction; mortality 10-50% (approaches 80% if not promptly treated, <10% if promptly treated); 33% mortality if hypotensionClassical heat stroke: high environmental T; young and elderly vulnerable; skin hot and dryExertional heat stroke: strenous exercise; occurs if heat exhaustion not properly treated; usually young athletes / military; skin hot and sweating (50%); dehydration more common; results in severe lactic acidosis, rhabdomyolysis, DIC more often201930330200Hyperthermia00Hyperthermia2908308281670Prognosis00Prognosis15182858281671Up to 80% mortalityHeat exhaustion: usually recover over 2-3 hours; hospital if: failure of initial treatment significant dehydration, ? Na, altered LOCHeat stroke: Most recover without sequelaePoor prognosis: duration and degree of hyperthermia most important; core T >41.1°C; AST >1000 in 1st 24 hours; prolonged coma; hypotension not responsive to cooling and IV fluid; oliguria; need for ETT; ARF / hyperkalaemia; altered coagulation00Up to 80% mortalityHeat exhaustion: usually recover over 2-3 hours; hospital if: failure of initial treatment significant dehydration, ? Na, altered LOCHeat stroke: Most recover without sequelaePoor prognosis: duration and degree of hyperthermia most important; core T >41.1°C; AST >1000 in 1st 24 hours; prolonged coma; hypotension not responsive to cooling and IV fluid; oliguria; need for ETT; ARF / hyperkalaemia; altered coagulation53701957646035Invasive; not readily available; labour intensive; requires anticoagulation00Invasive; not readily available; labour intensive; requires anticoagulation290830485775Management00Management15182857641590CPB00CPB25660357641590?00?37096707646035Fast; effective00Fast; effective15182856506210Ice water immersion00Ice water immersion256603565062100.15-0.25°C/min000.15-0.25°C/min37096706506210Effective; easy at events; widely available; fast; safe00Effective; easy at events; widely available; fast; safe53701956506210Shivering; peri vasoC if T <30°C; poorly tolerated; not compatible with resus; impractical; electrodes fall off; may ? mortality and morbidity in elderly00Shivering; peri vasoC if T <30°C; poorly tolerated; not compatible with resus; impractical; electrodes fall off; may ? mortality and morbidity in elderly37096705960110?00?15170155960110Gastric lavage00Gastric lavage256603559601100.5°C/min000.5°C/min53701955969635Invasive; labour intensive; may lead to water intoxication00Invasive; labour intensive; may lead to water intoxication53701955413375Limited efficacy; poorly tolerated00Limited efficacy; poorly tolerated15170155406390Ice packs00Ice packs256413054063900.04-0.08°C/min000.04-0.08°C/min37103055406390Practical; can be added to other measures00Practical; can be added to other measures25647654572000?00?37103054549775Easy00Easy53701954864100Limited efficacy; impedes use of other cooling methods00Limited efficacy; impedes use of other cooling methods15170154895215Cooling blankets00Cooling blankets53689254572000Unjustified complication rate00Unjustified complication rate15176504572000Cool IV fluids00Cool IV fluids15170154004310Evaporative00Evaporative256476540093900.3°C/min000.3°C/min53689254009390Shivering; less effect if humid; hard to maintain electrodes00Shivering; less effect if humid; hard to maintain electrodes53689253635375Cons00Cons37096703635375Pros00Pros37103054008755Effective, readily available, practical, well tolerated00Effective, readily available, practical, well tolerated25660353639820Cooling Speed00Cooling Speed1517015486410Heat exhaustion: stop exertion, move to cool shaded area, supine with legs elevated; replace fluid and electrolytes (avoid hypotonic fluids), treat hypogylcaemia; active cooling if T >40°C; aim to ? Na by no more than 2.5mmol/hrHeat cramps: rest; prolonged stretch of muscles; ORT 0.1-0.2% solution (eg. 1/8-1/4 tsp salt + 300-500ml water) or IVFA: consider early ETT; avoid suxC: avoid vigorous IVF unless severe dehydration (aim to restore BP and tissue perfusion; fluid deficit 1-2L in severe, 1.5-2.5L in marathon runner; use N saline; avoid K/lactate containing fluids; aim urine output 50- 100ml/hr if renal damage or rhabdomyolysis; may be high output failure; beware pulmonary oedema; pressor agents if ongoing hypotension (avoid NE+E as cause peripheral vasoconstriction and prevent heat dissipation; use dopamine 2.5mcg/kg/min); treatment coagulopathy (FFP, platelets)D: monitor T, HR, BP, urine output; consider invasive monitoring; can use sedatives to ? shivering; can paralyseSupport circulation and organ function; prevent irreversible tissue damage and death; can use mannitol / frusemide to ? urine output in rhabdomyolysis; consider urinary alkalinisation in rhabdomyolysis (1mmol/kg NaHCO3 IV bolus to maintain urine pH >6) Cooling: see below; aim rapid cooling to <39°C then stop to avoid overshoot but monitor closely; remove from heat source, remove all clothing00Heat exhaustion: stop exertion, move to cool shaded area, supine with legs elevated; replace fluid and electrolytes (avoid hypotonic fluids), treat hypogylcaemia; active cooling if T >40°C; aim to ? Na by no more than 2.5mmol/hrHeat cramps: rest; prolonged stretch of muscles; ORT 0.1-0.2% solution (eg. 1/8-1/4 tsp salt + 300-500ml water) or IVFA: consider early ETT; avoid suxC: avoid vigorous IVF unless severe dehydration (aim to restore BP and tissue perfusion; fluid deficit 1-2L in severe, 1.5-2.5L in marathon runner; use N saline; avoid K/lactate containing fluids; aim urine output 50- 100ml/hr if renal damage or rhabdomyolysis; may be high output failure; beware pulmonary oedema; pressor agents if ongoing hypotension (avoid NE+E as cause peripheral vasoconstriction and prevent heat dissipation; use dopamine 2.5mcg/kg/min); treatment coagulopathy (FFP, platelets)D: monitor T, HR, BP, urine output; consider invasive monitoring; can use sedatives to ? shivering; can paralyseSupport circulation and organ function; prevent irreversible tissue damage and death; can use mannitol / frusemide to ? urine output in rhabdomyolysis; consider urinary alkalinisation in rhabdomyolysis (1mmol/kg NaHCO3 IV bolus to maintain urine pH >6) Cooling: see below; aim rapid cooling to <39°C then stop to avoid overshoot but monitor closely; remove from heat source, remove all clothing666755448303473458637270Haema-tological 00Haema-tological 46780458637905Coagulopathy, DIC; urinary myoglobin; WBC 30-40; haemorrhagic complications in exertional00Coagulopathy, DIC; urinary myoglobin; WBC 30-40; haemorrhagic complications in exertional16154408637270Haemoconcentration and intravascular thrombosis due to hypovolaemia (? Hct 2% for every 1°C ? temp, worsened by cold-induced diuresis)Coagulopathy, DIC, thrombocytopenia00Haemoconcentration and intravascular thrombosis due to hypovolaemia (? Hct 2% for every 1°C ? temp, worsened by cold-induced diuresis)Coagulopathy, DIC, thrombocytopenia3473456899910Metabolic00Metabolic16154406899275Hyperglycaemia if rapid onset; hypoglycaemia if slow onset (glycogen depleted by shivering)HypoK (intracellular shift) hyperK (marker of acidosis and cell death, sign of poor prognosis)Metabolic acidosis; ? CK, rhabdomyolysis; 3rd spacing00Hyperglycaemia if rapid onset; hypoglycaemia if slow onset (glycogen depleted by shivering)HypoK (intracellular shift) hyperK (marker of acidosis and cell death, sign of poor prognosis)Metabolic acidosis; ? CK, rhabdomyolysis; 3rd spacing3473458085455Gastro-intestinal00Gastro-intestinal16154408084185? intestinal motility; hepatic impairment (due to ? CO and lactic acidosis); pancreatitis; mesenteric venous thrombosis00? intestinal motility; hepatic impairment (due to ? CO and lactic acidosis); pancreatitis; mesenteric venous thrombosis46780458085455Deranged LFT’s (AST, LDH)Pancreatic injury00Deranged LFT’s (AST, LDH)Pancreatic injury46780456899275Hyperglycaemia (70%)HypoK early (due to catecholamine effect, hyperventilation, respiratory alkalosis, sweat l losses, renal wasting, physiological hyperaldosteronism) hyperKHyperCa early hypoCaHyperP, hyperaldosteronism, hyperuricaemia; rhabdomyolysis (CK >10,000); Lactic acidosis00Hyperglycaemia (70%)HypoK early (due to catecholamine effect, hyperventilation, respiratory alkalosis, sweat l losses, renal wasting, physiological hyperaldosteronism) hyperKHyperCa early hypoCaHyperP, hyperaldosteronism, hyperuricaemia; rhabdomyolysis (CK >10,000); Lactic acidosis3473456326505Renal00Renal16154406326505Early: cold-induced diuresis (urine output is unreliable indicator)Late: ? GFR due to ? renal blood flow ARF (in 40% admitted to ICU)00Early: cold-induced diuresis (urine output is unreliable indicator)Late: ? GFR due to ? renal blood flow ARF (in 40% admitted to ICU)46780456326505ARF in 30%, ? Ur (direct thermal injury to kidneys, volume depletion, renal hypoperfusion, rhabdomyolysis, DIC)00ARF in 30%, ? Ur (direct thermal injury to kidneys, volume depletion, renal hypoperfusion, rhabdomyolysis, DIC)3473455300345Respiratory00Respiratory46780455300345? RR (in 100%) respiratory alkalosisARDS00? RR (in 100%) respiratory alkalosisARDS16154405299710Early: ? RR respiratory alkalosis; initial L shift in curve tissue hypoxiaLate: ? RR, CO2 retention, respiratory acidosis; apnoea; R shift in curve better delivery; disturbance of normal respiratory regulatory responses? O2 consumption and CO2 production; Pulmonary oedema00Early: ? RR respiratory alkalosis; initial L shift in curve tissue hypoxiaLate: ? RR, CO2 retention, respiratory acidosis; apnoea; R shift in curve better delivery; disturbance of normal respiratory regulatory responses? O2 consumption and CO2 production; Pulmonary oedema3473454310380Neurological00Neurological16154404310380Loss of fine motor gross motor skills; ? LOC; Loss of cerebrovascular autoregulation; Rigidity, pupil dilatation, areflexia; EEG flattening00Loss of fine motor gross motor skills; ? LOC; Loss of cerebrovascular autoregulation; Rigidity, pupil dilatation, areflexia; EEG flattening46780454310380Delirium, lethargy, coma; Seizures (especially during cooling); Ataxia occurs early (cerebellum most susceptible); Permanent in 20%; Due to metabolic problems, cerebral oedema and cerebral ischaemia; Encephalopathy, cerebral oedema, intracerebral haemorrhage, seizures00Delirium, lethargy, coma; Seizures (especially during cooling); Ataxia occurs early (cerebellum most susceptible); Permanent in 20%; Due to metabolic problems, cerebral oedema and cerebral ischaemia; Encephalopathy, cerebral oedema, intracerebral haemorrhage, seizures347345852170Cardio-vascular00Cardio-vascular4678045852170Hyperdynamic (80%): ? HR, ? CO (3L/min for every 1°C ?)Hypodynamic (20%): ? CO, ? PVRCirculatory failure in 20-65%? BP (25%) – due to vasodilation, hypovolaemia, cardiac dysfunctionMyocardial injuryHypovolaemia (due to sweating and ? fluid intake), distributive shock (peripheral vasodilation), cardiac dysfunction ? BPArrhythmia, cardiac arrestECG: prolonged QTc, AF, SVT, RBBB00Hyperdynamic (80%): ? HR, ? CO (3L/min for every 1°C ?)Hypodynamic (20%): ? CO, ? PVRCirculatory failure in 20-65%? BP (25%) – due to vasodilation, hypovolaemia, cardiac dysfunctionMyocardial injuryHypovolaemia (due to sweating and ? fluid intake), distributive shock (peripheral vasodilation), cardiac dysfunction ? BPArrhythmia, cardiac arrestECG: prolonged QTc, AF, SVT, RBBB23660102679065001617345851535Early: tachycardia, peripheral vasoconstriction, ? COLate: bradycadia (refractory to atropine), vasodilation, ? CO Intravascular volume depletion? chest wall elasticity and myocardial compliance less effective CPRECG: wave size proportional to degree of hypothermia; Osborn / J wave (best seen in inferior and precordial leads); 2nd and 3rd degree heart block; AF, VF, asystole; prolonged PR, QRS and QT; ST and T wave changes may mimic MI (eg. ST elevation, delayed depolarisation); systole prolonged > diastole, ? conduction time; slow AF common (in 50% patients with mod hypothermia), ECG changes of hyperK may be bluntedDD of ECG: SAH, cerebral injust, MI, hyperCa, Brugada, Chagas diseaseEarly: tachycardia, peripheral vasoconstriction, ? COLate: bradycadia (refractory to atropine), vasodilation, ? CO Intravascular volume depletion? chest wall elasticity and myocardial compliance less effective CPRECG: wave size proportional to degree of hypothermia; Osborn / J wave (best seen in inferior and precordial leads); 2nd and 3rd degree heart block; AF, VF, asystole; prolonged PR, QRS and QT; ST and T wave changes may mimic MI (eg. ST elevation, delayed depolarisation); systole prolonged > diastole, ? conduction time; slow AF common (in 50% patients with mod hypothermia), ECG changes of hyperK may be bluntedDD of ECG: SAH, cerebral injust, MI, hyperCa, Brugada, Chagas disease1615440500380Hypothermia00Hypothermia4678045497205Hyperthermia00Hyperthermia1873254895840017278357076440Asystole00Asystole499745707644018001817278356645910EEG flat, appears dead00EEG flat, appears dead499745664591019001917278356232525HR 2000HR 20499745623252520002017278355787390Maximum risk of VF00Maximum risk of VF499745578739022002217278355346700Absent corneal and oculocephalic reflex00Absent corneal and oculocephalic reflex499745534670023002317278354884420Loss of vascular tone and cerebrovascular autoregulation00Loss of vascular tone and cerebrovascular autoregulation499745488442024002417278354455160Risk of asystole; CO 45% normal; cerebral blood flow 1/3 normal00Risk of asystole; CO 45% normal; cerebral blood flow 1/3 normal499745445516025002517272004028440Severe hypothermia; areflexia00Severe hypothermia; areflexia499745402844026002617272003594735HR 30-40; rigidity; BMR ? by 55-65%; major acidosis00HR 30-40; rigidity; BMR ? by 55-65%; major acidosis499745359473528002817278353164841Pupils dilated; VF may occur00Pupils dilated; VF may occur4997453164840290029499745243332030003017278352433955O2 consumption and CO2 production ? by 50%; ? myocardial irritability, ectopics; threshold for spontaneous bad arrhythmias; defibrillation and antiarrhythmics become ineffective; Double intervals between drug doses00O2 consumption and CO2 production ? by 50%; ? myocardial irritability, ectopics; threshold for spontaneous bad arrhythmias; defibrillation and antiarrhythmics become ineffective; Double intervals between drug doses17278352000885Shivering stops (24-35°C, very variable)00Shivering stops (24-35°C, very variable)4997452000885310031499745140208032003217278351402080Mod hypothermia; AF and other arrhythmias; 2/3 ? HR and CO; Osborn waves common; ? RR; ? LOC; insulin resistance00Mod hypothermia; AF and other arrhythmias; 2/3 ? HR and CO; Osborn waves common; ? RR; ? LOC; insulin resistance4997459366253500351727200936625Mild hypothermia00Mild hypothermia1727834502285Heat stroke00Heat stroke499745502285400040 ................
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