Heatstroke

Overview

Definition

Heatstroke is a temperature-related illness caused by the body’s failure to maintain temperature homeostasis Homeostasis The processes whereby the internal environment of an organism tends to remain balanced and stable. Cell Injury and Death. Heatstroke is characterized by body temperatures approaching and exceeding 40ºC (104ºF) and neurological symptoms including seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures, delirium Delirium Delirium is a medical condition characterized by acute disturbances in attention and awareness. Symptoms may fluctuate during the course of a day and involve memory deficits and disorientation. Delirium, and ataxia Ataxia Impairment of the ability to perform smoothly coordinated voluntary movements. This condition may affect the limbs, trunk, eyes, pharynx, larynx, and other structures. Ataxia may result from impaired sensory or motor function. Sensory ataxia may result from posterior column injury or peripheral nerve diseases. Motor ataxia may be associated with cerebellar diseases; cerebral cortex diseases; thalamic diseases; basal ganglia diseases; injury to the red nucleus; and other conditions. Ataxia-telangiectasia.

Epidemiology

Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency in the United States is difficult to determine due to lack of reporting:

• Estimated annual incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 1.34 ED visits per 100,000 
• Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency increases with age.
• Male > female
• More common in spring and summer months
• More common in southern states
• Approximately 3,332 deaths from 2006–2010

Risk factors for heatstroke:

• Advanced age or immobility 
• Psychiatric disease
• Dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders 
• Physical exercise in a hot, humid environment
• Medications that impair heat Heat Inflammation response:
  • Anticholinergics Anticholinergics Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs
  • Antihistamines Antihistamines Antihistamines are drugs that target histamine receptors, particularly H1 and H2 receptors. H1 antagonists are competitive and reversible inhibitors of H1 receptors. First-generation antihistamines cross the blood-brain barrier and can cause sedation. Antihistamines
  • Diuretics Diuretics Agents that promote the excretion of urine through their effects on kidney function. Heart Failure and Angina Medication 
  • Neuroleptics 
  • Antihypertensives Antihypertensives The 1st-line medication classes for hypertension include thiazide-like diuretics, angiotensin-converting enzyme inhibitors (ACEis), angiotensin II receptor blockers (ARBs), and calcium channel blockers (CCBS). Contraindications, adverse effects, and drug-to-drug interactions are agent specific. Hypertension Drugs
  • Phenothiazines
  • Tricyclic antidepressants Tricyclic antidepressants Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. Tricyclic Antidepressants

Etiology

Heatstroke can be divided based on its etiology as classic or exertional.

• Classic (non-exertional) heatstroke affects patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship who, due to illness or situation, cannot thermoregulate or act to remedy exposure to excessive environmental heat Heat Inflammation:
  • Elderly
  • Disabled
  • Neurological disorders
  • Psychiatric disorder
  • Recreational drug use
• Exertional heatstroke affects patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship who perform strenuous activities in exceedingly hot or humid conditions, such as:
  • Athletes
  • Military personnel

Pathophysiology

Under normal conditions, the body can thermoregulate extremely efficiently (undergoing a 1°C (1.8°F) change in core temperature for every 25–30°C (45–54°F) change in environmental temperature). Heatstroke is the product of a failure to thermoregulate.

• Normal temperature regulation:
  • Body temperature is regulated by the CNS.
  • Hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus monitors body temperature and activates mechanisms to dissipate heat Heat Inflammation:
    • Increased cardiac output Cardiac output The volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat). Cardiac Mechanics
    • Vasoconstriction Vasoconstriction The physiological narrowing of blood vessels by contraction of the vascular smooth muscle. Vascular Resistance, Flow, and Mean Arterial Pressure of splanchnic circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment
    • Sweating
• Situations in which heat Heat Inflammation dissipation fails:
  • Existing pathology disrupts hemostasis Hemostasis Hemostasis refers to the innate, stepwise body processes that occur following vessel injury, resulting in clot formation and cessation of bleeding. Hemostasis occurs in 2 phases, namely, primary and secondary. Primary hemostasis involves forming a plug that stops the bleeding temporarily. Secondary hemostasis involves the activation of the coagulation cascade. Hemostasis mechanisms.
  • Inadequate hydration to produce sweat
  • Ambient humidity > 75% disrupts evaporation of sweat
• Sequelae of heatstroke arise:
  • Severe dehydration Severe Dehydration Fluid Replacement Therapy in Children:
    • Hypernatremia Hypernatremia Hypernatremia is an elevated serum sodium concentration > 145 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled by the hypothalamus via the thirst mechanism and antidiuretic hormone (ADH) release. Hypernatremia occurs either from a lack of access to water or an excessive intake of sodium. Hypernatremia
    • Hyperkalemia Hyperkalemia Hyperkalemia is defined as a serum potassium (K+) concentration >5.2 mEq/L. Homeostatic mechanisms maintain the serum K+ concentration between 3.5 and 5.2 mEq/L, despite marked variation in dietary intake. Hyperkalemia can be due to a variety of causes, which include transcellular shifts, tissue breakdown, inadequate renal excretion, and drugs. Hyperkalemia
    • Brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis (muscle breakdown):
    • Weakness
    • Kidney damage
  • Coagulopathies Coagulopathies Hemothorax:
    • Strokes
    • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures

Diagnosis

History and physical exam

• History of exposure to elevated temperatures in high humidity
• Symptoms:
  • Lethargy Lethargy A general state of sluggishness, listless, or uninterested, with being tired, and having difficulty concentrating and doing simple tasks. It may be related to depression or drug addiction. Hyponatremia
  • Weakness
  • Nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics/ vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia
  • Dizziness Dizziness An imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness. Lateral Medullary Syndrome (Wallenberg Syndrome)
• Signs:
  • Vital signs:
    • Elevated body temperature
    • Low blood pressure
    • Tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children
    • Tachypnea Tachypnea Increased respiratory rate. Pulmonary Examination
    • Widened pulse pressure
  • Cutaneous findings:
    • Anhydrosis: classic heat Heat Inflammation stroke
    • Diaphoresis: exertional heat Heat Inflammation stroke
  • Neurological findings:
    • Delirium Delirium Delirium is a medical condition characterized by acute disturbances in attention and awareness. Symptoms may fluctuate during the course of a day and involve memory deficits and disorientation. Delirium 
    • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
    • Diffuse weakness

Workup

Lab testing is for monitoring of progression of symptoms and cure.

• Continuous core temperature monitoring (rectal probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography) or Foley catheter)
• Lab testing:
  • CBC
  • CMP
  • Blood glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance
  • Clotting studies
  • Blood gasses 
  • Serum creatine Creatine An amino acid that occurs in vertebrate tissues and in urine. In muscle tissue, creatine generally occurs as phosphocreatine. Creatine is excreted as creatinine in the urine. Acute Kidney Injury phosphokinase (CPK)
  • Urine myoglobin Myoglobin A conjugated protein which is the oxygen-transporting pigment of muscle. It is made up of one globin polypeptide chain and one heme group. Rhabdomyolysis
• ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG): in setting of electrolyte imbalance

Management

Morbidity Morbidity The proportion of patients with a particular disease during a given year per given unit of population. Measures of Health Status and mortality Mortality All deaths reported in a given population. Measures of Health Status are directly related to the duration of core temperature elevation.

Classic heatstroke

• Rapid cooling (evaporative methods are preferred):
  • Ice-water immersion may be used.
  • Stop when core temperature reaches 39°C (102.2°F).
• Volume resuscitation Resuscitation The restoration to life or consciousness of one apparently dead. . Neonatal Respiratory Distress Syndrome: careful monitoring of electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes
• Avoid vasoconstrictors (treat dysrhythmia with cooling, not drugs).
• Antipyretics are not indicated and may be harmful.

Exertional heatstroke

• Rapid cooling (cold-water immersion, misting with fan)
• Repletion of glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance and electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes 
• Maintain high-volume urine output for rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis.

Differential Diagnosis

• Fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever: elevation of core body temperature induced by cytokine (mainly prostaglandin E Prostaglandin E Three of the six naturally occurring prostaglandins. They are considered primary in that no one is derived from another in living organisms. Originally isolated from sheep seminal fluid and vesicles, they are found in many organs and tissues and play a major role in mediating various physiological activities. Eicosanoids₂) activation during inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation. Regulation occurs at level of hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus. Usually occurs in response to infection and resolves with treatment of same.
• Thyroid storm Thyroid Storm Thyrotoxicosis and Hyperthyroidism: an acute exacerbation of hyperthyroidism Hyperthyroidism Hypersecretion of thyroid hormones from the thyroid gland. Elevated levels of thyroid hormones increase basal metabolic rate. Thyrotoxicosis and Hyperthyroidism marked by fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, profuse sweating, tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children and/or arrhythmia ( atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation), hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, agitation Agitation A feeling of restlessness associated with increased motor activity. This may occur as a manifestation of nervous system drug toxicity or other conditions. St. Louis Encephalitis Virus, nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics, vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, confusion, seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures, delirium Delirium Delirium is a medical condition characterized by acute disturbances in attention and awareness. Symptoms may fluctuate during the course of a day and involve memory deficits and disorientation. Delirium, and coma Coma Coma is defined as a deep state of unarousable unresponsiveness, characterized by a score of 3 points on the GCS. A comatose state can be caused by a multitude of conditions, making the precise epidemiology and prognosis of coma difficult to determine. Coma. Treatment involves rehydration Rehydration Dengue Virus, beta-blockers Beta-blockers Drugs that bind to but do not activate beta-adrenergic receptors thereby blocking the actions of beta-adrenergic agonists. Adrenergic beta-antagonists are used for treatment of hypertension, cardiac arrhythmias, angina pectoris, glaucoma, migraine headaches, and anxiety. Class 2 Antiarrhythmic Drugs (Beta Blockers), iodide Iodide Inorganic binary compounds of iodine or the i- ion. Thyroid Hormones, antithyroid drugs, sedatives for agitation Agitation A feeling of restlessness associated with increased motor activity. This may occur as a manifestation of nervous system drug toxicity or other conditions. St. Louis Encephalitis Virus, antipyretic Antipyretic Acetaminophen medication, and cooling blankets.
• Serotonin Serotonin A biochemical messenger and regulator, synthesized from the essential amino acid l-tryptophan. In humans it is found primarily in the central nervous system, gastrointestinal tract, and blood platelets. Serotonin mediates several important physiological functions including neurotransmission, gastrointestinal motility, hemostasis, and cardiovascular integrity. Receptors and Neurotransmitters of the CNS syndrome: a group of symptoms that may occur if certain serotonergic medications are combined. Marked by autonomic instability Autonomic instability Rabies Virus, muscle rigidity Muscle rigidity Continuous involuntary sustained muscle contraction which is often a manifestation of basal ganglia diseases. When an affected muscle is passively stretched, the degree of resistance remains constant regardless of the rate at which the muscle is stretched. This feature helps to distinguish rigidity from muscle spasticity. Motor Neuron Lesions, and altered mental status Altered Mental Status Sepsis in Children. 
• Neuroleptic malignant syndrome Neuroleptic malignant syndrome Neuroleptic malignant syndrome (NMS) is a rare, idiosyncratic, and potentially life-threatening reaction to antipsychotic drugs. Neuroleptic malignant syndrome presents with ≥ 2 of the following cardinal symptoms: fever, altered mental status, muscle rigidity, and autonomic dysfunction. Neuroleptic Malignant Syndrome: a rare, idiosyncratic, and potentially life-threatening reaction to a neuroleptic (i.e., antipsychotic Antipsychotic Antipsychotics, also called neuroleptics, are used to treat psychotic disorders and alleviate agitation, mania, and aggression. Antipsychotics are notable for their use in treating schizophrenia and bipolar disorder and are divided into 1st-generation antipsychotics (FGAs) and atypical or 2nd-generation antipsychotics. First-Generation Antipsychotics) drug. Marked by high temperature (above 38°C (100.4°F)), alteration in level of consciousness, autonomic dysregulation Autonomic Dysregulation Neuroleptic Malignant Syndrome, and severe muscular rigidity Severe muscular rigidity Neuroleptic Malignant Syndrome (typically, lead-pipe rigidity Rigidity Continuous involuntary sustained muscle contraction which is often a manifestation of basal ganglia diseases. When an affected muscle is passively stretched, the degree of resistance remains constant regardless of the rate at which the muscle is stretched. This feature helps to distinguish rigidity from muscle spasticity. Megacolon).
• Malignant hyperthermia Malignant hyperthermia An important complication of anesthesia is malignant hyperthermia, an autosomal dominant disorder of the regulation of calcium transport in the skeletal muscles resulting in a hypermetabolic crisis. Malignant hyperthermia is marked by high fever, muscle rigidity, rhabdomyolysis, and respiratory and metabolic acidosis. Malignant Hyperthermia: a rare complication triggered by certain anesthetics Anesthetics Agents that are capable of inducing a total or partial loss of sensation, especially tactile sensation and pain. They may act to induce general anesthesia, in which an unconscious state is achieved, or may act locally to induce numbness or lack of sensation at a targeted site. Anesthesiology: History and Basic Concepts and, if not treated, lethal in 70%–80% of cases. Characterized by a rapid increase in body temperature, tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children, dysrhythmia, hypercapnia Hypercapnia A clinical manifestation of abnormal increase in the amount of carbon dioxide in arterial blood. Neonatal Respiratory Distress Syndrome, and rigid or painful muscles.