Dr Neena Sharma
Heat wave is the period of abnormal high temperature, more than normal maximum temperature during summer in the North-western parts of India. Heat wave occurs between March and June and rarely extends till July. The guidelines to declare heat wave by the Indian Meteorological Department (IMD) combine temperature, relative humidity, pressure, altitude, wind speed and direction.
Criterion for declaring Heat Wave
Heat Wave is declared when maximum temperature of a place reaches at least 40 degree C or more for plains and at least 30 degree C or more for hilly regions. The IMD has given two criterias for declaring heat wave based on departure from normal or maximum actual temperature.
Based on departure from normal-
Moderate heat wave- departure from normal is 4.5 degree C to 6.4 degree C
Severe heat wave- departure from normal is > 6.4 degree C
Based on maximum actual temperature-
Moderate heat wave- maximum actual temperature degree 45 degree C
Severe heat wave- maximum actual temperature degree 47 C
If the above criteria is met in two stations, in a meteorological subdivision for two consecutive days, the heat wave is declared on the second day.
Do’s during Heat wave
Stay hydrated- Drink sufficient water even if not thirsty, carry drinking water, use oral rehydration solution and homemade drinks like lemon water, buttermilk, fruit juices, eat seasonal fruits and vegetables with high water content like watermelon, muskmelon, orange , grapes, pineapple, cucumber, lettuce.
Stay covered- Wear thin loose, light coloured cotton garments. Cover head with umbrella and traditional head gears and wear shoes while going out in sun.
Stay alert- Listen to radio, watch TV or read newspaper for local weather forecast. Get the latest update of weather on IMD website at https://mausam.imd.gov.in
Stay indoors- Stay in cool places, block direct sunlight by keeping windows and curtains closed during the day, limit the outdoor activity during cooler part of the day.
Stay in shady areas – To reduce direct exposure of sun, seek shelter or shade.
Additional attention to vulnerable groups- Infants, children, pregnant women, people working outdoors, elderly, physically ill and travellers from colder climate to hot climate need special attention. Travellers from colder area should avoid overexertion and drink plenty of water. Labour contractors to provide cold drinking water, fans, shady areas for the labourers. To organize an event or sports activity, follow the weather forecast and heatstroke prevention plan by providing adequate ventilation and cold water.
Don’ts during heat wave
Avoid getting out in the sun between 12:00 noon and 3:00pm
Avoid going out barefoot.
Avoid alcohol, tea, coffee, and carbonated drinks or drinks with large amount of sugar as they lead to loss of more body fluids.
Avoid eating high protein and stale food.
Avoid keeping children, elderly or pets in parked vehicles.
Avoid cooking in peak summer hours and ventilate the cooking area.
Role of Government, IMD and Hospitals in Prevention
Warning by IMD- Weather information can be received on All India weather forecast bulletin and special heat wave guidance bulletins by IMD.
Mass Education – Spread advance information to the public on preparedness and prevention of heat waves through Radio, television, social media, newspapers, NGOs and community groups.
Health Services – Preparedness by the hospitals to adopt safe practices, early diagnosis and treatment of heat-related conditions.
Government authorities should ensure provision of drinking water supply, temporary shelters/ shades/ screens at public places, and the recommendation to close schools, colleges, and offices during heat wave.
Impact of Heat Wave
Normal body temperature ranges between 36.4 degree C to 37.2 degree C. Exposure to high temperature lead to heat related illnesses that include-
Heat rash / Prickly heat
Heat cramps- Painful and spasmodic skeletal muscle contraction with excessive loss of sodium and chloride in sweat.
Heat Exhaustion- Headache, nausea, vomiting, fatigue, dizziness, heavy sweating, dehydration, hypotension, and tachycardia with temperature varying from 37 – 39 degree C.
Heat Syncope – Prolonged standing in the sun leads to pooling of blood in the lower limbs and simultaneous decrease in blood pumped by the heart.
Heat Stroke – Body temperature of 40 degree C or more along with delirium, seizure or coma in adults. Refusal to feed, irritability, dry oral mucosa, altered sensorium and seizures in children.
Heat stroke is a medical emergency, and every second delay in cooling the person leads to multiorgan dysfunction and irreversible Brain Injury.
Note: Antipyretics such as paracetamol and aspirin do not have role in lowering the temperature in heat stroke.
Heat related illness are preventable
Shift to cool area and drink liquids.
Measure body temperature and remove clothes.
Get medical attention.
Hospital Management in Heat Stroke –
Heat Stroke is fatal if not managed aggressively.
Diagnosis –
Hyperpyrexia- It is diagnosed when the Core temperature is > 40 degree C with altered sensorium. It is mild when there is associated abnormal behaviour like delirium and severe when encephalopathy, convulsions, and coma occur.
High ambient temperature
Rule out the conditions with impaired sweating- Conditions that impair sweating are alcohol abuse, fever, skin diseases & cardiac illness.
Management
ABC- Stabilize the patient by maintaining airway, breathing and circulation. Supportive treatment includes iv fluids, oxygen, and intubation if there is low sensorium level.
Therapeutic Cooling- at 1 degree C every 10 minutes until a temperature of 38 degree C is achieved.
* Conductive Cooling
* External Cooling – It is done by sponge cooling, cool water bath, Ice cold water packs.
* Internal Cooling – It is done by parenteral refrigerated fluids through nasogastric tube
* Evaporative Cooling –
* Remove clothing and apply wet sheets
* Spray Cooling with cool water at 15 degree C with simultaneous blowing of cool air from fans or cooler.
* Manage the Complications
Note: Once the temperature is reached 38 degree C, monitor the patient for hypothermia or rebound hyperthermia
(The author is Associate Professor, Department of Physiology, AIIMS Jammu)
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