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Review

Physical and social causes of hypothermia

National and local strategies aim to reduce the risk of hypothermia. Nurses have a vital role in identifying and supporting patients at risk of hypothermia

In this article…

  • Risk factors for hypothermia
  • National and local prevention strategies
  • Role of the nurse in identifying risk, signs and symptoms

 

Author

Julie Dalphinis is lead nurse for safeguarding adults and mental capacity act and lecturer practitioner at Central London, West London, Hammersmith and Fulham and Hounslow Clinical Commissioning Groups Collaborative and Buckinghamshire New University.

Abstract

Dalphinis J (2013) Physical and social causes of hypothermia. Nursing Times; 109: 49/50, 12-15.

Hypothermia has a number of physical and social causes, particularly among older people. It is vital that nurses are aware of these risk factors. This article explores the causes of hypothermia, preventive measures, clinical signs and immediate treatment in the community.

 

5 key points

  1. Hypothermia is defined as a core temperature of 35oC or less
  2. It is difficult to estimate the role of hypothermia in excess winter mortality figures
  3. Hypothermia has multiple causes including environmental issues, physical ill health and drug therapies
  4. Thorough health and social assessment is needed to identify those at risk
  5. Patients diagnosed with hypothermia need immediate emergency care

 

With winter here and energy prices increasing, it is a sobering thought that the risk of hypothermia among older people is likely to rise sharply.

The charity Age UK has been monitoring this closely for some years and compiled a compelling evidence paper for the Age UK campaign to end loneliness last year (Age UK, 2012). This showed a direct relationship between loneliness and the risk of hypothermia due to poor living environments and highlighted that a growing number of isolated older people were becoming at risk of loneliness.

There are physical and social reasons why hypothermia occurs (Marini and Wheeler, 2006). Physical causes include exposure to low environmental temperature, hypoglycaemia and depressant drugs including alcohol; social causes include abuse, poverty and self-neglect. A diagnosis of hypothermia is normally given when core temperature drops to 35°C or below (Trim, 2005); however, it is frequently misdiagnosed. The International Classification of Diseases (2010) defines hypothermia as a failure to deal with exposure to excessive cold. It provides three further divisions:

  • Hypothermia not associated with low environmental temperature;
  • Exposure to excessive natural cold;
  • Exposure to excessive cold of man-made origin.

The Office for National Statistics (2013) bulletin, covering England and Wales mortality tables, measures excess winter mortality by comparing the difference between the number of deaths during the winter months (December to March) and the average number of deaths during the previous four months (August to November) and the following four months (April to July). They estimate 31,100 excess winter deaths occurred in England and Wales in 2012-13, which is a 29% increase compared with the tally of winter deaths in England and Wales during the previous winter. Most of these deaths occurred among those aged 75 years and over and were linked to respiratory and circulatory diseases, dementia and Alzheimer’s disease. The ONS notes when episodes of severe winter weather hit the UK and temperatures fall below 5°C, there is a marked rise in general practitioner consultations, acute admissions, and cardiovascular deaths among those aged over 75 (ONS, 2012).

Hypothermia is not always recorded as a cause of death on its own in England and Wales and death certificates may not make it clear whether hypothermia was due to a cold environment or the direct result of another illness. In Scotland and Northern Ireland these figures are based on death registrations. This makes it difficult to identify the role hypothermia plays in winter deaths accurately or to compare figures between the four countries in the UK.

Hypothermia is an emotive subject because those at increased risk include older people and the vulnerable in our society. It is interesting that excess deaths among older people are higher in European countries such as the UK and Ireland, which have relatively mild winter temperatures compared with the Scandinavian countries, which have much lower winter temperatures (Healy, 2003).

Causes of hypothermia

The body needs to keep a stable temperature of between 36°C and 37.5°C to maintain cellular function (Dougherty and Lister, 2011). It is kept in balance by the thermoregulatory centre of the hypothalamus (Fig 1) (Tortora and Derickson, 2008); it is thought increasing age can affect the body’s ability to regulate temperature (McClafferty, 2009; Neno, 2005; Nakamura et al, 1997).

Heat is gained through movement and cellular metabolism and lost through the skin by radiation, convection, conduction and evaporation (Marieb and Hoehn, 2007). Hypothermia results in decreased oxygen release from haemoglobin into the tissues leading to increased blood viscosity, peripheral vasoconstriction and tissue hypoxia.

Although hypothermia can be a single cause of death, excess winter deaths seem to be related to older people’s incomes, attitudes to heating and insulating their homes, winter clothing, mobility as well as respiratory and cardiovascular problems (Lloyd, 2013).

Some underlying medical conditions increase the risk of hypothermia (Marini and Wheeler, 2006). These include endocrine diseases, such as adrenal insufficiency, hypopituitarism and hypothyroidism, which can cause a metabolic decrease in body heat production and a reduction in glycogen, an important source of energy. Shivering, a normal response to decreased body temperature, may be suppressed by drugs, such as benzodiazepines, phenothiazine, tricyclic antidepressants and alcohol. Shivering is also dependent on glycogen stores and will stop when stores are exhausted. Alcohol can increase vasodilation of the small capillary beds in the dermis, leading to increased heat loss.

Impaired, burnt or inflamed skin can also cause the body to lose heat. Diabetic neuropathy and spinal cord injury can result in poor control of peripheral circulation, which impairs vasodilation and constriction. Central nervous system dysfunction from a stroke or intracerebral haemorrhage may result in a loss of hypothalamic temperature regulation. Other systemic causes include multisystem trauma, shock, acidosis, pancreatitis, uraemia, systemic infections, and cancer. Cold intravenous fluids and exposure during resuscitations or operative procedures are also known to carry a risk of hypothermia (Edwards, 1997).

Signs and symptoms

Hypothermia can be categorised as mild, moderate or severe (Table 1). Mild hypothermia occurs between 32°C and 35°C, when increased muscle tone and shivering are employed to increase heat production (Cuddy, 2004). Peripheral vasoconstriction helps to minimise heat loss from the skin. Moderate hypothermia is defined as having a temperature of 28°C-32°C and shivering stopping. In severe hypothermia, where the temperature is less than 28°C, the endocrine and autonomic nervous systems become inactive and there is a decline in cerebral blood flow and oxygen use.

Preventing hypothermia

One of the problems with identifying hypothermia in older people is they may not be able to tell you they feel cold. They may have long-term conditions such as heart disease, arthritis, cerebral vascular disease or be prone to falls, all of which increase the risk of hypothermia. In addition, financial problems may prevent them from heating their home adequately. Gascoigne et al (2010) found that concern about heating bills was a barrier to reducing the risk of hypothermia.

To reduce the likelihood of hypothermia, any predisposing risk factors must be considered as part of patients’ holistic health and social assessment. Tips for prevention are outlined in Table 2 and Table 3 provides an assessment checklist.

Available support

There are many sources of advice for the public and the prevention of cold deaths is part of the public health outcomes framework (tinyurl.com/PH-outcome-FW).

Community nurses should be aware of local support for vulnerable patients and what benefits they may be entitled to. Local councils and social services will have advice about housing and benefits and can follow up assessments and refer vulnerable people. Voluntary agencies, such as Age UK and the Red Cross, are campaigning in this area and can also offer support and advice. It is useful to create a directory of local contacts to use with potentially vulnerable patients.

Those in receipt of certain benefits may be eligible for a cold weather payment. These are made when local temperature is either recorded as or forecast to be an average of 0°C or below over seven consecutive days. Adults aged over 60 can receive between £100 and £300 tax free to help pay heating bills. This is paid to people receiving a state pension or other social security benefit (excluding housing benefit, council tax reduction or child benefit).

Multiple government departments have implemented policies to reduce winter deaths (Table 4) and there have been notable policy successes. For example, Gascoigne et al (2010) used scientific literature to plan practical advice for older people for episodes of severe winter weather, and this was used by the UK Met Office to develop a severe winter weather early warning system. An advice booklet was also produced based on a systematic review, consensus development and focus group discussions with older people. In a subsequent field trial, a combination of the Met Office’s early warning system and the advice booklet, was seen to change behaviour among older people and reduce risks.

Treating hypothermia in the community

If you suspect a patient has hypothermia in their own home, emergency services should be called. As in any emergency, a systematic assessment of the acutely ill patient using the ABCDE approach including airway, breathing, circulation, disability, exposure/examination should be performed (tinyurl.com/ABCDE-assess). Crucially, their temperature should be measured using a thermometer capable of registering below 30°C.

A cold heart is resistant to pharmacotherapeutic measures, pacing and defibrillation. Chest compressions, if required, may need to be performed for an extended period of time until the core temperature is high enough for the heart to respond (Marini and Wheeler, 2006). Pulse oximeters, used to measure oxygen saturation, are not accurate with hypothermic patients because of peripheral vasoconstriction (Marini and Wheeler, 2006).

If the patient does not need immediate resuscitation, they should be kept warm, dry and alcohol free until help arrives. De Witte et al (2010) evaluated the efficacy of warming in hypothermia and suggest physical methods for rewarming patients (Table 5).

Drug therapies should not be given during the hypothermia episode because the liver metabolism decreases and the body becomes less responsive to medications as the core temperature drops.

Safeguarding

Following an episode of hypothermia, it may be appropriate to call a safeguarding strategy meeting to discuss options as there may have been neglect leading up to the episode of hypothermia. This could include ignoring medical or physical care needs, failing to provide access to appropriate healthcare, social care, education services, adequate nutrition and/or heating.

Conclusion

Hypothermia is likely to impact on the quality of life and health of many vulnerable older people. It is important that nurses know how to recognise, assess, and manage this challenging condition as well as being able to advise on measures and sources of advice to prevent it.

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