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