Accidental hypothermia and cold injuries are rare but consistent occurrences within health care (Brändström et al, 2014; Kieboom et al, 2015). In a letter to the BMJ (Cronin de Chavez at al, 2013) highlighted the importance of considering hypothermia as an indicator of the severity of illness in children and young people; furthermore, the World Health Organization (WHO) (1997) has been highlighting the importance of hypothermia in the care of infants for a quarter of a century.
According to Zafren et al (2014), accidental hypothermia is the unintentional reduction in core body temperature below 35.00C. This is higher in neonates, with WHO (1997) defining neonatal hypothermia as a drop below 36.40C. The hypothalamus and integumentary system are responsible for the regulation and maintenance of body temperature; peripheral stimuli send messages to the hypothalamus, which in turn reacts to regulate heat—for example, vasodilation and activation of the sweat glands, which cools the body, or vasoconstriction and shivering, which assist in warming the body (Colbert et al, 2012; Peate, 2017). Hypothermia may be categorised as mild with temperatures between 32.00C and 34.90C; moderate with temperatures between 28.00C and 31.90C or severe, with temperatures below 280C, but as these definitions may vary and each has a range, ensuring documentation of precise numeric value remains important (Brändström et al, 2014). It is important to note that standard clinical thermometers may not read below 34.00C, therefore specialist thermometers may be necessary in emergency care settings.
Risk factors and symptoms
Although often associated with extreme conditions and environments such as during military combat, natural disaster or arctic exploration, hypothermia and cold injuries can also occur in more familiar circumstances eg during homelessness or accidental cold exposure (Brändström et al, 2014; Zafren et al, 2014; Petrone et al, 2014; Boles et al, 2018). Evidence suggests that infants sleeping in cold bedrooms and young people under the influence of a psychoactive substance may also be at increased risk of hypothermia or a cold-related injury (Brändström et al, 2014; Boles et al, 2018; Centers for Disease Control and Prevention (CDC), 2019). In the latter case, this is potentially due to altered perceptions of temperature and pain while under the influence of psychoactive substances coupled with their physiological effects (such as vasodilation and muscle relaxation). Whereas in infants, particularly neonates, thermoregulation mechanisms may not be adequately developed, fat stores used to generate heat are very limited, and their increased ratio of surface area to body mass increases heat loss through the skin, all of which lead to the infant being more vulnerable to hypothermia. Accidental hypothermia can also be associated with a range of acute and chronic medical conditions such as sepsis, cancer, hypoendocrine disorders such as Addison's or Gull's disease, stroke or trauma where thermoregulation is disrupted (Zafren et al, 2014).
Newborn and preterm babies are at particular risk of hypothermia and this should be actively avoided. WHO (1997) set out 10 steps for avoiding hypothermia immediately after a baby is born, many of which continue in contemporary practice (Lyon, 2008; Unicef, 2018; Fawke et al, 2021) including those mentioned in Box 1.
Box 1.Ten steps for avoiding hypothermia in newborns
- A warm delivery room: World Health Organization (1997) recommends 25–280C, Resuscitation Council UK (RCUK) (Fawke et al, 2021) recommends 23–250C for the most infants with a minimum of 25 C for premature infants born at or before 28 weeks' gestation
- Immediate drying; RCUK (Fawke et al, 2021) also suggests using plastic wrapping for infants of 32 weeks' or less gestation (without wrapping the face) with a thermal mattress and potentially warmed humidified respiratory gases
- Skin-to-skin contact, which promotes temperature regulation and breastfeeding, although in pre-term infants less able to temperature regulate this needs to be managed carefully to avoid hypothermia
- Breastfeeding, recommended within the first hour to give the infant the energy needed to keep warm, early initiation continues to be supported (Unicef, 2018)
- Postponing bathing and weighing due to the potential for conductive heat loss
- Appropriate bedding and clothing
- Keeping parent and baby together
- Warm transportation
- Warm resuscitation
- Raising awareness and training – consider the use of checklists and a quality improvement programme (Fawke et al, 2021)
Symptoms in infants may include bright red, cold skin and fatigue, whereas older children and young people may show confusion, irritability, shivering, exhaustion, slurred speech, drowsiness and memory loss, which are the result of acidosis, electrolyte disturbances, hypoglycaemia, dehydration, hypoxia, respiratory failure, intense vasoconstriction and cardiac dysfunction, all of which should be considered and monitored during and after rewarming (Petrone et al, 2014; Zafren et al, 2014; CDC, 2019). Initially during cold stress the body attempts to compensate with vasoconstriction, tachycardia and increased respiratory rate; however, as the hypothermia progresses patients may experience a bradycardia and respiratory depression. Patients may also have disordered clotting and diuresis throughout caused by fluctuations to blood flow, hormone production, renal function and platelet function (Petrone et al, 2014).
Management of hypothermia and potential risks of rewarming
The primary concern during management of hypothermia is rewarming of the patient, which may include a combination of passive and active strategies, internal and external rewarming. Strategies include drying the skin, warmed infusion, forced warm air, fluid filled garments, warm water immersion, peritoneal dialysis, radiant rewarming all while caring for the patient in a warm environment above 210C (Brändström et al, 2014; Petrone et al, 2014). However, some studies and guidelines warn that submersion in warm water (such as in a bath) may be dangerous, promoting a rapid vasodilation and resulting in hypotension (Zafren et al, 2014), and others question how effective warmed infusions are (Petrone et al, 2014). Skin-to-skin contact is also considered appropriate for newborn rewarming (WHO, 1997).
To understand the different potential strategies for rewarming a patient, it may be pertinent to consider the methods of heat gain and loss: through electromagnetic transfer of energy from warm to cold (radiation), gas or liquid passing over the body (convection), direct contact between two objects (conduction) and energy lost via water being evaporated from the skin (evaporation) (WHO, 1997; Petrone et al, 2014). It may help to take a minute to think about going for a walk on a cold, wet and windy winter day: you might wear layers to trap warm air, simultaneously reducing radiation (the surfaces next to your skin are warm) and stopping the convection of cold wind travelling over your skin; you might ensure outer layers are waterproof to ensure your skin underneath does not get wet, reducing evaporation and (unless it has been snowing) you are unlikely to actively seek out contact with a cold surface. However, consider a patient who is not wearing weather-resistant clothes and has prolonged exposure, or a patient who is submerged in cold water, or is born from a warm body into a colder delivery room.
Rewarming a severely hypothermic patient has the potential for complications. Petrone et al (2014) listed core temperature after-drop, rewarming-related hypotension, hypoglycaemia, bladder atony, paralytic ileus, bleeding diathesis, rhabdomyolysis, changes in electrolytes, ventricular fibrillation, hyperkalaemia and hypophosphatemia as potential post-rewarming complications.
Literature continues to guide that hypothermic patients should be rewarmed even in circumstances where they do not appear to be alive (Petrone et al, 2014), specifically in paediatric patients where hypothermia is coupled with cardiac arrest following drowning, prolonged resuscitation is advocated (Kieboom et al, 2015; Chen et al, 2016; Dragann et al, 2016) although others have questioned the efficacy of this practice due to poor outcomes (Maconochie and Deakin, 2015), where possible monitoring with an ECG is recommended for hypothermic patients, including during rewarming (Zafren et al, 2014).
Management of cold injuries
Cold injuries such as frostbite can cause significant tissue damage and may require surgical intervention (Brändström et al, 2014; Salloum et al, 2017; Boles et al, 2018), with the most severe injuries associated with exposure to temperatures of 23°C or below and most commonly occurring in the extremities (Boles et al, 2018). Limb extremity damage is unsurprising during cold exposure, due to the body's natural regulatory mechanisms, which will cause vasoconstriction in an effort to maintain core temperature (Colbert et al, 2012), preserving vital organ function and increasing survival.
Boles et al (2018) found that when frostbite occurred in children and young people, over half of cases were associated with walking or other recreational activities outdoors but there were significant proportions of young people whose cold exposures occurred during a loss of consciousness, during abuse or via a road traffic accident, although as these were reported as percentages it is not clear to what extent these factors were co-occurring. These correlate with the some of the risk factors for frostbite, which are similar to those for hypothermia: prolonged exposure to cold, wet conditions and windchill, alcohol and use of other psychoactive substances, malnutrition and pre-existing medical conditions such as Raynaud's disease, vasculitis and diabetes (Petrone et al, 2014; Basit et al, 2021).
During frostbite, the blood flow to the area reduces by between 80% and 90% causing direct and indirect damage to the blood vessels and surrounding tissues, electrolyte disturbances and potentially reperfusion injury (Basit et al, 2021). There are four grades in the classification of frostbite with grade 1 and grade 2 being mostly superficial and grade 3 and grade 4 affecting deeper tissue, similar to the grading of burns (Petrone et al, 2014; Basit et al, 2021). Frostbite is considered as three zones, those of coagulation, stasis and hyperaemia (Basit et al, 2021), which radiate away from the zone of coagulation at the site of injury away. In circumstances where the patient is also hypothermic, rewarming of the core temperature should take precedence over the frostbite injury. Otherwise, and if there is no risk of refreezing, rewarming the area of injury through the removal of wet clothing, drying without vigorously rubbing and covering with dry clothing or blankets, in-hospital submersion in warm water (approximately 400 C) can aid rewarming; pain management and intra-arterial thrombolytic therapy should also be considered (Salloum et al, 2017; Basit et al, 2021).
Management of drowning with cardiac arrest
Hypothermia is often a pathological consequence of drowning (Evans et al, 2021). Drowning is defined as the process of primary respiratory distress caused by immersion or submersion in a liquid medium, where breathing is prevented; the event is classified as a drowning even if the incident does not result in fatality (Idris et al, 2003). In the UK, in 2019, drowning accounted for 19 fatalities in young people under 19 years, with an increase to 32 fatalities in 2020 (National Water Safety Forum (NWSF), 2020; 2021). In 2020, the largest proportion of drownings occurred in the 15-19 age range, with 22 reported deaths (NWSF, 2021). Although drowning is uncommon in the UK, drowning is one of the top 5 causes of death in children aged 1-14 years globally (WHO, 2014).
Following extraction from the water, advanced paediatric life support (APLS) actions should commence as soon as possible (Evans et al, 2021). Neurological deficits are more common when return of spontaneous circulation (ROSC) does not take place within 30 minutes (Kieboom et al, 2015); however, there are case reports of good neurological outcomes when ROSC has been greater than 30 minutes when victims have been severely hypothermic (Chen et al, 2016; Dragann et al, 2016). Hypothermia can have a protective effect on the body, drowning in temperatures above 33°C is an indicator for poorer outcomes, such as bathtub drownings (Macintosh and Austin, 2017). Hypothermia usually occurs early in drowning, other early consequences include electrolyte imbalance, cardiac arrest, and pulmonary and cerebral oedema (Evans et al, 2021).
During APLS, temperature should be recorded, and warming should begin to aim for normothermia. The APLS algorithm changes when the child is hypothermic: when temperature is less than 30°C, defibrillation should be limited to three shocks and inotropic and antiarrhythmic drugs should not be given. When temperature is between 30°C and 35°C inotropic and antiarrhythmic drug doses should be doubled (Evans et al, 2020). Rewarming techniques vary depending on circumstances but typically warm intravenous fluids, forced-air warming system and increased room temperatures are useful (Macintosh and Austin, 2017). The European Resuscitation Council (Lott et al, 2021) recommends extracorporeal membrane oxygenation (ECMO) as the preferred rewarming method in hypothermic cardiac arrests. There are case studies that suggest good neurological outcomes when hypothermia is prolonged during ECMO for 12-24 hours after resuscitation in patients who remain unconscious (Guenther et al, 2009; Chen et al, 2016). ECMO should quickly be considered in drowned hypothermic children, early contact with paediatric intensive care units should be made to decide whether this should be facilitated, or whether resuscitation should be stopped (Evans et al, 2021).
Therapeutic hypothermia
Therapeutic hypothermia has been used to protect brain tissue and function by slowing metabolism in a range of circumstances with the potential for neurological hypoxia, these have included patients post cardiac arrest, in neonates (following specific birth circumstances) and during status epilepticus (National Institute for Health and Care Excellence (NICE), 2011; Mancera and DeCou, 2012; Guilliams et al, 2013; Azzopardi et al, 2014; Zafren et al, 2014; Kieboom et al, 2015). This is most commonly seen in the neonatal intensive care unit (NICU) and features throughout the Royal College of Nursing (2015) guidance for nurses working in NICU. Although evidence has been deemed sufficient for a standard in neonates it is mixed and thus more research could be helpful (NICE, 2011; Mancera and DeCou, 2012; Guilliams et al, 2013; Azzopardi et al, 2014; Zafren et al, 2014; Scholefield et al, 2014; Kieboom et al, 2015).
In neonates, therapeutic hypothermia may include 72 hours of whole-body cooling and subsequent rewarming, during this time the baby requires intensive support and monitoring, which may include ventilation, electroencephalography (EEG), vital signs, venous access via a central line and more (Bäcke et al, 2021). This intensive intervention has been explored from the parental perspective, with Bäcke et al (2021) reporting three key themes of the parental role, support in a chaotic situation and the environment. Although the experience of having a child undergo therapeutic hypothermia is a unique event similar themes, needs and areas for development have been reported in parenting children and young people who are technology dependent, who have complex needs, who are undergoing cancer treatment or who require admission to paediatric intensive care units (Williams et al, 2013; Woodgate et al, 2015; McCann et al, 2016; Dahav and Sjöström-Strand, 2018; Camara and Callum, 2020). Therefore, although evidence for the specific support needs of parents during therapeutic hypothermia is limited the requirements for clear, timely information, emotional support, a confusion or blurring between the roles of nurse and parent and difficulty balancing their own needs with the needs of their child are not new or unique concepts and nurses in a range of settings should be able to support and guide parents through these issues.
Conclusion
Although hypothermia is a rare occurrence in the UK, recognition and early intervention can make a significant difference for patients. Ensuring vulnerable patients in our care (including neonates and those under anaesthetic) avoid the additional physical stress of hypothermia may improve outcomes and circumvent potential harm. This prevention could extend to public health messaging, initially in vulnerable groups; this may extend to the wider population with the rising interest in open water swimming and cold water immersion.
KEY POINTS
- Prevention of accidental hypothermia in vulnerable groups such as newborns and neonates is important and should be considered in care planning: think conduction, convection, evaporation and radiation
- Rewarming is a priority but has potential complications and continued monitoring throughout is essential
- Clinical thermometers may not read below 34.00C, specialist thermometers may be necessary in emergency care settings
- Educating young people around the dangers of prolonged exposure in context of their recreational choices may help reduce risk
CPD reflective questions
- What does your area do to manage patient thermal regulation?
- How could you reduce the risk of hypothermia in your area of practice?
- How do thermal regulation measures put in place for patients affect staff in those areas?
- Are there opportunities to raise awareness of avoiding hypothermia in your role?