Post on 11-Apr-2017
Heat Emergencies
Dr .Shabbir2nd year PG
MD Emergency Medicine
Introduction
• Heat emergencies represent a spectrum of disorders, including heat cramps, heat syncope, heat exhaustion and heat stroke.
• patients can progress rapidly from relatively benign to life-threatening disease.
• The male-to-female ratio for heat emergencies is essentially equal, and people of any age can be affected.
• The incidence of heat-related emergencies varies with the weather.
• During heat waves and severe droughts, fatality rates may spike.
PATHOPHYSIOLOGY
• MECHANISMS OF HEAT TRANSFER
• RESPONSE TO HEAT STRESS
• ACCLIMATIZATION
• PATH TO HEAT INJURY
MECHANISMS OF HEAT TRANSFER
Radiation- transfer of heat by electromagnetic waves from a warmer object to a colder object.Conduction—heat exchange between two surfaces in direct contact.Convection—heat transfer by air or liquid moving across the surface of an object.Evaporation—heat loss by vaporization of water (sweat). <35°C (<95°F)-radiation , >35°C (>95°F)-evaporation.
RESPONSE TO HEAT STRESS
• The body tends to maintain its core temperature between 36°C and 38°C(96.8°F and 100.4°F).
• dilatation of blood vessels, particularly in the skin;
• increased sweat production; • decreased heat production; • behavioural heat control.
• As the core temperature of the body rises Sympathetic flow from the anterior hypothalamus decreased vascular tone dilatation of cutaneous blood vessels.
• cardiac output increases about 3 L/min for each 1°C (1.8°F) elevation of core temperature.
• The heart rate increases to compensate for the decrease in stroke volume.
• Heat stress may also result in arrhythmias, myocardial ischemia and exacerbation of congestive heart failure.
ACCLIMATIZATION
• Acclimatization is the adaptation of the body’s heat stress mechanisms to increase the efficiency of heat loss in a hot climate.
• Acclimatization involves a number of physiologic and biochemical adjustments that allow an individual to withstand heat stresses that would otherwise result in substantial morbidity and mortality.
• primary methods of acclimatization-sweating, improvement in cutaneous vascular flow and
overall cardiovascular function, and alterations of the thermoregulatory set point.
• In most individuals, acclimatization can be achieved over 7 days to several weeks.
• Once removed from the hot environment, the body will de-acclimate to the original physiologic parameters within 1 to 2 weeks.
PATH TO HEAT INJURY• Heat production rapidly increases during
physical activity due to skeletal muscle contraction.
• The increase in core temperature seen in high environment is often slow, occurring over a period of hours to days. Because of this volume and electrolyte abnormalities are common.
• Excessive heat is directly toxic to cells, causes an acute-phase reaction with release of inflammatory cytokines, and damages vascular endothelium
• Dehydration and hyperpyrexia-cardiovascular and metabolic failure.
CLINICAL FEATURES AND TREATMENT
• Minor- (heat edema, prickly heat, heat syncope, heat cramps, and heat exhaustion).
• Major- (heat stroke).
HEAT EDEMA
• self-limited process manifested by mild swelling of the feet, ankles, and hands that appears within the first few day.
• cutaneous vasodilatation and orthostatic pooling of interstitial fluid in gravity-dependent extremities
• increase in the secretion of aldosterone and antidiuretic hormone in response to the heat stress contributes to the mild edema.
• heat edema does not progress to the pretibial region.
• differentiated from early congestive heart failure or deep venous thrombosis.
• No special treatment is necessary.
• Diuretics are not effective.
PRICKLY HEAT
• Prickly heat is a pruritic, maculopapular, erythematous rash over normally clothed areas of the body.
• Also known as lichen tropicus, miliaria rubra, or heat rash.
PRICKLY HEAT (heat rash)
• acute inflammation of the sweat ducts causedby blockage of the sweat pores by macerated stratum corneum.
• Itching is the predominant clinical feature during this phase and can be treated successfully with antihistamines.
• Chlorhexidinein a light cream or lotion base may provide some relief.
HEAT CRAMPS
• Heat cramps are painful, involuntary, spasmodic contractions of skeletal muscles, usually those of the calves, although they may involve the thighs and shoulders.
• individuals who are sweating profusely and replace fluid losses with water or other hypotonic solutions.
• occur during exercise or, more commonly, during a rest period after several hours of vigorous physical activity.
• heat cramps are short in duration, are limited to a definitive group of muscles.
• hyponatremia and hypochloremia
• Treatment consists of fluid and salt replacement (PO or IV) and rest in a cool environment.
• Salt tablets should be taken with sufficient water to replace volume.
HEAT TETANY
• Heat tetany consists of typical hyperventilation resulting in respiratory alkalosis, paresthesia of the extremities, circumoral paresthesia and carpopedal spasm.
• Heat tetany can be differentiated from heat cramps -little pain or cramping in the muscle compartments, and paresthesias of the extremities and perioral region are more prominent.
HEAT SYNCOPE
• Heat syncope is a variant of postural hypotension resulting from the cumulative effect of relative volume depletion, peripheral vasodilatation and decreased vasomotor tone.
• It occurs most commonly in nonacclimatized individuals during the early stages of heat exposure.
• highest incidence – elderly.
• Evaluation of patients requires exclusion of metabolic, cardiovascular, and neurologic disorders .
• Treatment consists of removal from the heat source, PO or IV rehydration and rest.
HEAT EXHAUSTION
• water depletion & sodium depletion.
• Water depletion heat exhaustion tends to occur in the elderly and in persons working in hot environments with inadequate water replacement.
• Salt depletion heat exhaustion tends to occur in unacclimatized individuals who replace fluid losses with large amounts of hypotonic solutions.
• presents with symptoms that include headache, nausea, vomiting, malaise, dizziness, and muscle cramps as well as signs of dehydration, such as tachycardia and orthostatic hypotension.
• On physical examination, the temperature may be normal or elevated.
• Not manifest signs of central nervous system impairment.
• Laboratory studies- hemoconcentration electrolyte abnormalities.
• Heat exhaustion is treated with volume and electrolyte replacement and rest.
• mild heat exhaustion- ORS
• who demonstrate significant tissue hypo perfusion-IV fluids (1 to 2 L of saline solution).
• patients with heat exhaustion who do not respond to 30 minutes of fluid replacement and removal from the heat-stressed environment be aggressively cooled until their core temperatures drop to 39°C (102°F)
HEAT STROKE
• Heat stroke is an acute life-threatening emergency with mortality rates as high as 30% to 80% and is universally fatal if left untreated.
• The cardinal features of heat stroke are hyperthermia [>40°C />104°F)] and altered mental status.
• central nervous system-cerebellum is highly sensitive to heat.
• neurologic abnormality-ataxia can be an early neurologic finding, irritability, confusion, bizarre behavior, combativeness, hallucinations, plantar responses, decorticate and decerebrate posturing, hemiplegia, status epilepticus, and coma.
• Seizures are quite common, especially during cooling.
• A delay in cooling increases the mortality rate.
• Laboratory Evaluation- GRBS,ABG, CBC , metabolic panel, coagulation profile, creatine phosphokinase level, myoglobin level, urinalysis, ECG, and chest radiograph.
• Lumbar puncture and CT of the head.
Treatment
• The goals of therapy are immediate cooling and support of organ system function.
• Pre-hospital Care• ED Management
Pre-hospital Care
• Immediately patient must be removed from the environment.
• Cooling should be initiated by removing Clothing and placing wet towels or sheets over the patient’s body, or placing ice packs over the neck, groin, and axillae.
• transported by air-conditioned vehicle to the closest hospital.
ED Management
• Initial ResuscitationStandard resuscitation measures Cooling Techniques• Treatment of Complications
Initial Resuscitation
• ABC CARE…
• administration of high-flow oxygen;
• initiation of continuous cardiac monitoring and pulse oxymetry; and establishment of IV access.
• Glucose levels should be evaluated on arrival.
• IV fluids should be initiated at a rate that ensures adequate urine output, beginning with 250 mL/h NS.
• In elderly patients, fluid therapy should be monitored using a central venous pressure line or pulmonary artery catheter, if possible.
Cooling Techniques
• only physical methods of cooling are recommended.
• Antipyretics have no role.
• Dantrolene is ineffective in heat stroke.
• The choice of cooling method depends on the setting and the condition of the patient
• With all cooling methods, the goal is to reduce the core temperature to 39°C (102.2°F) and then stop to avoid overshoot hypothermia.
Evaporative Cooling
• Patient clothing is removed and cool water [15°C (59°F)] is sprayed on most of the patient’s body surface.
• Directing a fan over the patient facilitates evaporation.
• To prevent hypothermic overshoot, some recommend using either tepid water warmed to 40°C (104°F).
• This method is the foundation of several cooling units such as the Makkah cooling unit.
• The Makkah cooling unit is composed of a large hammock with built-in sprinklers that spray cool water [15°C (59°F)] over the patient’s body and powerful fans that blow warm air [45°C (113°F)] over the patient.
Makkah cooling unit
• The two main difficulties—shivering and the inability of cardiac electrodes to adhere to the skin.
• Shivering is treated primarily with short-acting benzodiazepines.
• Electrodes can be applied to the patient’s back.
Immersion Cooling
• placing the undressed patient into a tub of ice water deep enough to cover the trunk and extremities, while keeping the patient’s head out of the water.
• shivering, displacement of monitoring leads, and inability to perform defibrillation or resuscitative procedures.
Other Methods
• The most rapid method of cooling a heat stroke victim is cardiopulmonary bypass.
• Cold water gastric lavage, cold water urinary bladder lavage, and cold water rectal lavage.
• Cold water peritoneal lavage but not effective.
• IV infusion of cold fluids is not considered effective treatment.
Treatment of Complications
• Hypotension is a common. small fluid bolus (500 mL NS) and body cooling.
• low cardiac output and elevated CVP warrants the use of dopamine or dobutamine.
• severe vasoconstriction by norepinephrine.
• Hypokalemia due to total-body depletion of potassium may be noted.
• Hypernatremia seen in severely dehydrated patients.
• hyponatremia occurs in patients who hydrate with oral hypotonic solutions
• Coagulation studies may show thrombocytopenia, hypoprothrombinemia, and hypofibrinogenemia.
• Thermal injury to the liver is a common, always reversible, with a full recovery.
• Renal failure, Adult respiratory distress syndrome may also occur.
• The presence of hypotension, low cardiac output, and a falling cardiac index is associated with a poor prognosis.
• Seizures may occur during cooling and can be controlled with benzodiazepines.
• Persistent neurologic deficits occur in approximately 20% of patients and are associated with high mortality
DISPOSITION AND FOLLOW-UP
• Patients with minor heat emergency syndromes require only ED treatment along with clear discharge instructions.
• congestive heart failure or renal failure, and patients with severe electrolyte imbalance may require hospital admission.
• Heat stroke is a true medical emergency, and all patients require admission.
• Patients who are intubated- require invasive hemodynamic monitoring.
SPECIAL POPULATIONS
• Elderly (>75 years of age), young children (<4 years).
• Limited mobility, alcoholic and people taking antipsychotics, major tranquilizers, anticholinergics, antiparkinsonian agents, cardiovascular medications.
• Teenagers and preadolescents.
• Athletes, soldiers, and laborers.
•Thank you