DISORDERS OF TEMPERATURE REGULATION

Normal body temperature is 36.5-37.5°C and is controlled by temperature-sensitive cells within the hypothalamus which control heat generation and loss. Fever during an infection is due to cytokines, particularly interleukin-1, released from inflammatory cells acting in the hypothalamus affecting the thermoregulatory set-point.

Hypothermia

Hypothermia is defined as a drop in core (i.e. rectal) temperature to below 35°C. It is frequently fatal when the temperature falls below 28°C.

Aetiology

Very young and elderly individuals are particularly prone to hypothermia, the latter having a reduced ability to feel the cold. Hypothyroidism, hypnotics, alcohol or intercurrent illness may contribute. In healthy individuals, pro-longed exposure to extremes of temperature or prolonged immersion in cold water is the most common underlying cause.

Clinical features

Mild hypothermia (32-35°C) causes shivering and a feeling of intense cold. More severe hypothermia leads progressively to altered consciousness and coma. This is usually associated with a fall in pulse rate and blood pressure, muscle stiffness and depressed reflexes. As coma ensues, the pupillary and other brainstem reflexes are lost. Ventricular arrhythmias or asystole is the usual cause of death.

Diagnosis

Measurement of core temperature with a low-reading thermometer makes the diagnosis. Alteration in consciousness usually indicates a core temperature of below 32°C; this is a medical emergency. With severe hypothermia there are ECG changes, including an increase in the PR interval, widening of the QRS complex and ‘J' waves (prominent convex deflections at the junction of the QRS complex and ST segment, best seen in the precordial leads).

Management

The principles of treatment are to rewarm the patient gradually while cor-recting metabolic abnormalities (if severe) and treating cardiac arrhythmias (Emergency Box 14.4). Hypothyroidism occurs and if suspected should be treated with i.v. triiodothyronine.

Clues to the presence of hypothyroidism include previous radioiodine treatment or surgery for thyrotoxicosis, and preceding symptoms of hypo-thyroidism (p. 620). Hypothermia may protect organs from ischaemia in patients with prolonged hypothermia-induced cardiopulmonary arrest. There-fore, resuscitation should be continued (maybe for some hours) until arrest persists after rewarming or until attempts to raise the core temperature have failed. Drugs used in the usual arrest situation, e.g. adrenaline (epinephrine), have reduced efficacy at low temperatures and are withheld until the tem-perature is greater than 30°C.

Emergency Box 14.4

Management of hypothermia
Investigations
• Arterial blood gases
• Full blood count, urea and electrolytes, blood glucose, thyroid function tests, blood cultures
• Chest X-ray, ECG

Management

• Give oxygen by face mask and attach an ECG monitor
• Search for and treat infection, pneumonia is common
• Intubate and ventilate patients who are comatose or in respiratory failure
• Warmed (37°C) intravenous fluids to achieve urine output 30–40 mL/h

• Passive external warming if core temperature >32°C
• Place patient in a warm room (27–29°C)
• ‘Space’ blankets
• Warm bath water
• Active external rewarming if core temperature 28–32°C
• Warm blankets, heating pads or forced warm air
• Rewarm trunk before extremities to minimize peripheral vasodilatation
• Warm bath water
• Active internal rewarming if core temperature <28°C
• Humidified and warmed (40–46°C) oxygen
• Lavage (gastric, peritoneal, bladder) with warm fluids (40°C)
• Extracorporeal shunt (haemodialysis, arteriovenous or venovenous) rewarming
• Cardiopulmonary bypass – treatment of choice for arrested hypothermic patients
• Monitor core temperature, oxygen saturation by pulse oximetry, urine output and central venous pressure

Hyperthermia (hyperpyrexia)

Hyperpyrexia is a body temperature above 41°C. Causes include:

■ Injury to the hypothalamus (trauma, surgery, infection)

■ Malignant hyperpyrexia- rare autosomal dominant condition in which skeletal muscle generates heat in the presence of certain anaesthetic drugs, e.g. suxamethonium

■ Ingestion of 3,4-methylenedioxy-methamfetamine (ecstasy)

■ Neuroleptic malignant syndrome: idiosyncratic reaction to therapeutic dose of neuroleptic medication, e.g. phenothiazines.

Treatment includes stopping the offending drug, cooling and the administra-tion of dantrolene sodium.

Ebook Essentials of Kumar and Clark's Clinical Medicine, 5e

1. Ethics and communication

Ethics and communication

2. Infectious diseases

Infectious diseases

3. Gastroenterology and nutrition

Gastroenterology and nutrition

4. Liver, biliary tract and pancreatic disease

Liver, biliary tract and pancreatic disease
LIVER BIOCHEMISTRY AND LIVER FUNCTION TESTS
SYMPTOMS AND SIGNS OF LIVER DISEASE
JAUNDICE
HEPATITIS
NON - ALCOHOLIC FATTY LIVER DISEASE (NAFLD)
CIRRHOSIS
COMPLICATIONS AND EFFECTS OF CIRRHOSIS
LIVER TRANSPLANTATION
TYPES OF CHRONIC LIVER DISEASE AND CIRRHOSIS
PRIMARY SCLEROSING CHOLANGITIS
BUDD - CHIARI SYNDROME
LIVER ABSCESS
LIVER DISEASE IN PREGNANCY
LIVER TUMOURS
GALLSTONES
THE PANCREAS
CARCINOMA OF THE PANCREAS
NEUROENDOCRINE TUMOURS OF THE PANCREAS

5. Haematological disease

Haematological disease
ANAEMIA
Assessment and treatment of suspected neutropenic sepsis
HAEMOLYTIC ANAEMIA
INHERITED HAEMOLYTIC ANAEMIAS
ACQUIRED HAEMOLYTIC ANAEMIA
MYELOPROLIFERATIVE DISORDERS
THE SPLEEN
BLOOD TRANSFUSION
THE WHITE CELL
HAEMOSTASIS AND THROMBOSIS
THROMBOSIS
THERAPEUTICS

6. Malignant disease

Malignant disease
MYELOABLATIVE THERAPY AND HAEMOPOIETIC STEM CELL TRANSPLANTATION
THE LYMPHOMAS
THE PARAPROTEINAEMIAS
PALLIATIVE MEDICINE AND SYMPTOM CONTROL

7. Rheumatology

Rheumatology
COMMON INVESTIGATIONS IN MUSCULOSKELETAL DISEASE
COMMON REGIONAL MUSCULOSKELETAL PROBLEMS
BACK PAIN
OSTEOARTHRITIS
INFLAMMATORY ARTHRITIS
THE SERONEGATIVE SPONDYLOARTHROPATHIES
Clinical features, Investigations
INFECTION OF JOINTS AND BONES
AUTOIMMUNE RHEUMATIC DISEASES
SYSTEMIC INFLAMMATORY VASCULITIS
DISEASES OF BONE
THERAPEUTICS

8. Water, electrolytes and acid–base balance

WATER AND ELECTROLYTE REQUIREMENTS
BODY FLUID COMPARTMENTS
REGULATION OF BODY FLUID HOMEOSTASIS
PLASMA OSMOLALITY AND DISORDERS OF SODIUM REGULATION
DISORDERS OF POTASSIUM REGULATION
DISORDERS OF MAGNESIUM REGULATION
DISORDERS OF ACID - BASE BALANCE
THERAPEUTICS

9. Renal disease

Renal disease
INVESTIGATION OF RENAL DISEASE
GLOMERULAR DISEASES
NEPHROTIC SYNDROME
URINARY TRACT INFECTION
TUBULOINTERSTITIAL NEPHRITIS
HYPERTENSION AND THE KIDNEY
RENAL CALCULI AND NEPHROCALCINOSIS
URINARY TRACT OBSTRUCTION
ACUTE RENAL FAILURE/ACUTE KIDNEY INJURY
CHRONIC KIDNEY DISEASE
RENAL REPLACEMENT THERAPY
CYSTIC RENAL DISEASE
TUMOURS OF THE KIDNEY AND GENITOURINARY TRACT
DISEASES OF THE PROSTATE GLAND
TESTICULAR TUMOUR
URINARY INCONTINENCE

10. Cardiovascular disease

COMMON PRESENTING SYMPTOMS OF HEART DISEASE
INVESTIGATIONS IN CARDIAC DISEASE
CARDIAC ARRHYTHMIAS
HEART FAILURE
ISCHAEMIC HEART DISEASE
RHEUMATIC FEVER
VALVULAR HEART DISEASE
PULMONARY HEART DISEASE
MYOCARDIAL DISEASE
CARDIOMYOPATHY
PERICARDIAL DISEASE
SYSTEMIC HYPERTENSION
ARTERIAL AND VENOUS DISEASE
ELECTRICAL CARDIOVERSION
DRUGS FOR ARRHYTHMIAS
DRUGS FOR HEART FAILURE
DRUGS AFFECTING THE RENIN - ANGIOTENSIN SYSTEM
NITRATES, CALCIUM - CHANNEL BLOCKERS AND POTASSIUM - CHANNEL ACTIVATORS

11. Respiratory disease


Respiratory disease
TUBERCULOSISnd
DIFFUSE DISEASES OF THE LUNG PARENCHYMA
OCCUPATIONAL LUNG DISEASE
CARCINOMA OF THE LUNG
DISEASES OF THE CHEST WALL AND PLEURA
DISORDERS OF THE DIAPHRAGM

12. Intensive care medicine

Intensive care medicine

13. Drug therapy, poisoning, and alcohol misuse

Drug therapy, poisoning, and alcohol misuse

14. Endocrine disease

Endocrine disease
PITUITARY HYPERSECRETION SYNDROMES
THE THYROID AXIS
MALE REPRODUCTION AND SEX
FEMALE REPRODUCTION AND SEX
THE GLUCOCORTICOID AXIS
THE THIRST AXIS
DISORDERS OF CALCIUM METABOLISM
DISORDERS OF PHOSPHATE CONCENTRATION
ENDOCRINOLOGY OF BLOOD PRESSURE CONTROL
DISORDERS OF TEMPERATURE REGULATION
THERAPEUTICS

15. Diabetes mellitus and other disorders of metabolism

DIABETES MELLITUS
DIABETIC METABOLIC EMERGENCIES
COMPLICATIONS OF DIABETES
SPECIAL SITUATIONS
HYPOGLYCAEMIA IN THE NON - DIABETIC
DISORDERS OF LIPID METABOLISM
THE PORPHYRIAS

16. The special senses

THE EAR
THE NOSE AND NASAL CAVITY
THE THROAT
THE EYE

17. Neurology

COMMON NEUROLOGICAL SYMPTOMS
COORDINATION OF MOVEMENT
THE CRANIAL NERVES
COMMON INVESTIGATIONS IN NEUROLOGICAL DISEASE
UNCONSCIOUSNESS AND COMA
STROKE AND CEREBROVASCULAR DISEASE
EPILEPSY AND LOSS OF CONSCIOUSNESS
NERVOUS SYSTEM INFECTION AND INFLAMMATION
HYDROCEPHALUS
HEADACHE, MIGRAINE AND FACIAL PAIN
SPINAL CORD DISEASE
DEGENERATIVE NEURONAL DISEASES
DISEASES OF THE PERIPHERAL NERVES
MUSCLE DISEASES
MYOTONIAS
DELIRIUM
THERAPEUTICS

18. Dermatology

Dermatology

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