Heat-induced illness

Published on 23/06/2015 by admin

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22.3 Heat-induced illness

1 Most heat-induced illness in children is due to overheating from exogenous sources

2 Children are particularly susceptible to heat related illness due to their unique physiology

3 Certain genetic and dermatological disorders in children put them at high risk of heat related illness

4 Genuine heat stroke is a true medical emergency. It is characterised by a core body temperature above 40.5 Celsius in association with acute mental state changes.

5 Immediate aggressive cooling methods should be instituted for heatstroke

6 Children account for almost one fifth of all cases of malignant hyperthermia. Dantrolene should be given early for suspected cases. Approximately 50% of cases have a gene defect of the ryanodine receptor.

Introduction

Hyperthermia in the paediatric patient differs physiologically from fever. Fever is caused by an elevation of body temperature secondary to regulation by the hypothalamus. High body temperature not caused by hypothalamic thermoregulatory mechanisms is usually caused in children by one of the following: prolonged exposure to high ambient temperature (overheating), increased heat production or reduced heat loss. In the neonate and small infant, overheating is almost always the cause.

In children, heat related illness is the second most common cause of non-traumatic death after heart disease.¹ Children are particularly at risk because of the following:

• Children have a greater body surface area relative to mass and therefore are more susceptible to radiant heat.

• Children have less cardiovascular compensatory mechanisms to deal with heat insult

• Young children particularly produce less sweat which limits their ability to lose heat through evaporation.

• Children depend on parents or adult caregivers to protect them from exogenous heat sources and cannot manipulate their environment to cool themselves. ²

Certain genetic disorders such as ectodermal dysplasia and Fabry’s disease also put children at risk of heat-related illness.³ In these conditions, there is an impaired ability to dissipate heat through sweating.

Rising temperatures and more extreme weather events due to climate change has the potential to increase the incidence of heat related illness in children.

Causes of heat-related illness

Usually seen in setting of high ambient temperature and humidity. Examples are athletics, summertime sporting events and during heat waves. Young children left in cars are also particularly at risk. A review of 171 cases of heat related car deaths found that in approximately 25% of cases the child gained access to an unlocked vehicle and in 75% of cases, the child was left by an adult.⁴

Increased heat production

Metabolic (e.g. hyperthyroidism)

Drugs (e.g. anticholinergics such as atropine, sympathomimetics, aspirin, neuroleptic agents, selective serotonin reuptake inhibitor drugs)

Decreased heat loss

Over-wrapped babies

Excess clothing on hot/humid days

Disease states (e.g. cystic fibrosis)

Drugs (e.g. phenothiazines, anticholinergics)

Clinical syndromes

The neonate/infant

Overheating is the most common cause in the neonate and infant. It is important to distinguish the healthy infant who is overheated from the febrile infant (Table 22.3.1).⁵

Overheated infant Febrile infant High rectal temp High rectal temperature Warm hands and feet Cool hands and feet Pink skin Pale skin Extended posture Lethargic Healthy appearance Looks unwell Abdomen temperature > hand temperature by <2 degrees Abdomen exceeds hand skin temperature by >3 degrees

Mild overheating is usually not dangerous to infants though there may be some association with apnoeic episodes in premature babies.⁵ Hyperthermia from overheating, with sudden death,⁶ particularly in families with a history of malignant hyperthermia.

Babies with heat-related illness may present like any seriously ill infant. Hewson’s work has summarised this as A,B,C, fluids in and out approach.⁷

Heat syncope

Heat syncope commonly involves children who have been standing for prolonged periods in hot/humid weather or who have undergone strenuous exertion.

Heat cramps

Heat cramps occur in the setting of strenuous exercise in hot/humid conditions. A relative lack of body salt plays a part. Heat cramps can be very painful; however, most last for less than 1 minute. Abdominal muscle cramps have been known to simulate an acute abdomen.⁸

Heat exhaustion

Heat exhaustion in children presents as hyperpyrexia, vomiting, headache, lethargy and weakness with a normal mental state. The major problem is body water depletion; however, in some paediatric patients (e.g. cystic fibrosis where greater amounts of salt are lost in their sweat), heat exhaustion may occur predominantly due to salt depletion.⁸

Heat stroke

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Textbook of Paediatric Emergency Medicine