Download The recognition and management of body temperature

259
Clinical
The recognition and management
of body temperature disturbances in
Royal Navy personnel
Surg Lt Cdr DJC Angus, Dr EHN Oakley
Abstract
This article discusses hypothermia and hyperthermia, described together as thermal illness. These conditions are seen
within the United Kingdom (UK) Armed Forces population at home and abroad and may endanger life, with significant
implications for both the individual and the chain of command. Recognition and management from initial presentation to
return to duty is discussed and guidance given on occupational considerations.
Introduction
In the summer of 2013, three Service personnel died
from heat illness during a training exercise in Wales (1).
This highly publicised event on UK soil reminds us of
the risk to Service personnel from thermal illness, even
in relatively benign conditions. In the United States of
America (USA), heat illness claims an average of 448
lives a year and contributes to the deaths of a further 240
individuals, whilst hypothermia results in 1,301 deaths per
year (the USA has around 2.5 million deaths per year) (2).
Review of the Naval Service Incident Notification Cell
database reveals that between June 2012 and June 2013,
there were ten reported thermal illness cases in the Royal
Navy (RN) alone, distributed evenly between hypothermia
and hyperthermia. These occurred on board ships and
submarines, and in the field.
Extremes of heat and cold can be fatal, but survivors can also
suffer significant long-term problems, even from a single
incident and despite optimal management. Prevention is
therefore preferable and the chain of command must be
given robust advice from the medical branch, which has
a key role. Individuals can also help protect themselves
both by preparation and discipline in the field. Detailed
advice on prevention is beyond the scope of this article, but
is available in Joint Service Publication (JSP) 539 (3).
While thermal illness may result in mortality, it has
arguably a greater impact on operations through associated
morbidity. Extremes of temperature cause impairment in
the ability to reason and perform, and irrational decisions
in the field may endanger the individual and colleagues.
Additionally, others may follow one case of thermal illness
and operations may have to be delayed or altered in order
to maintain the health of those at risk. While on board
a ship or submarine, sailors are generally protected by a
controlled climate. However, emergencies including fire,
man overboard or failure of heating or air-conditioning
units can cause thermal problems. More routine activities
can also pose a risk: fitness test candidates, upper deck
sentries and weapons aimers, for example, can be at risk.
The early recognition and management of thermal illness
maintains our fighting effectiveness, reduces or prevents
long-term illness, and saves lives.
Clinical picture and diagnosis
Hypothermia
Environmental hypothermia follows exposure to cold, but
individuals are affected differently by the same exposure.
The unwell, poorly fed, or dehydrated sailor will be
much less able to stay warm than his or her colleagues.
Hypothermia should always be suspected when there is a
suggestive history of circumstances such as:
• Immersion. Exposure to cold or cool water,
classically following a man overboard. The initial
overwhelming cold stimulus to the peripheral
thermoreceptors will produce immediate ‘cold
shock’ with difficulty controlling breathing and
keeping the airway clear of water. Following this,
rapid heat loss to the water can cause early signs of
hypothermia within minutes and unprotected lean
individuals may be unconscious after as little as half
an hour.
• Exposure. Typically outdoors in wet, windy, cool
or cold environments. Symptoms may even develop
J Royal Naval Medical Service 2014, Vol 100.3
in still air temperatures above 5 degrees C, especially
in wet clothing. While possible on ship, this would
most likely be seen in a land-based operation or
exercise, particularly within the UK, when clothing,
shelter and physical activity may be insufficient to
stay warm. Evaporating water from skin and clothing
can be an even more potent means of heat loss than
immersion, so cases are common in those who have
become drenched from immersion or precipitation.
Other scenarios include disaster relief operations,
Pre-hypothermia
Mild hypothermia
temperature between 32˚C and 35˚C) Moderate hypothermia
(core temperature <32˚C) and severe (<30˚C) 260
both in survivors and those rendering assistance.
• Urban. Typically a gradual onset in compromised
people such as the elderly in poorly heated houses.
The formal diagnosis of hypothermia requires a
core temperature below 35 degrees C as measured
with a rectal thermometer. Several other forms
of temperature measurement (including aural,
particularly infra-red tympanic membrane, axillary
and oral thermometers) are not reliable in this
These subtle symptoms occur in individuals at high risk of developing
hypothermia. Their mood may change, they may lose coordination or feel
overly tired, and they are often slow and the last in a moving group. Spotting
these symptoms in someone exposed to cold should raise suspicion and prompt
core temperature assessment.
This patient will probably be conscious and feeling very cold, shivering
uncontrollably and have cold hands and feet. They may have a rapid heart
rate and a cold diuresis can result in dehydration and other changes in
fluid balance. While this helps the body preserve warmth, it sacrifices the
extremities and should be borne in mind during re-warming.
Distinguishing these clinically is difficult and rather unhelpful. Both are lifethreatening emergencies and generally develop as shivering wanes with falling
core temperature. Patients are likely to have stiff limbs (increased muscle
tone which changes to flaccidity as death approaches) with reduced
consciousness, vital signs that are difficult to detect (including pupillary
reflexes) and have ‘marbled’ skin. This means they may appear dead even
on careful examination, so all profoundly hypothermic casualties should be
assumed to be revivable until attempts to re-warm them (preferably in hospital)
have proven unsuccessful.
Table 1. Stages of hypothermia.
Investigation(s)
Blood sugar level
Electro-Cardiogram (ECG) blood pressure Full Blood Count (FBC)
Urea and Electrolytes (U&Es).
Coagulation screen
Amylase
Blood cultures
Arterial Blood Gas (ABG)
Explanation
Hypoglycaemia may present with very similar symptoms to early
hypothermia and is treated by replacing sugar either orally or intravenously.
A Boehringer-Mannheim (BM)TM device will suffice pre-hospital.
Hypothermia may trigger changes that can be life threatening: immersion and
casualties can be in profound hypothermic bradycardia, asystole, or
ventricular fibrillation, and there are characteristic changes seen in many
hypothermic casualties including J waves, prolonged PR and QT segments
and a widened QRS complex.
Anaemia and infection predispose to hypothermia.
Exclude acute kidney injury secondary to dehydration.
Hypothermia can produce clotting disorders, which may need careful
correction.
Pancreatitis is more common in hypothermic patients and sub-acute
fulminating pancreatitis does sometimes cause unexpected death in those
who may not have appeared to be particularly hypothermic.
To exclude sepsis as a cause of the hypothermia.
Monitoring of the effectiveness of gas exchange, particularly in those who
may have aspirated water, and in differential diagnosis.
Table 2. Suggested investigations for the hypothermic patient.
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Clinical
scenario and should never be used for diagnosis (3,
4). Although most commonly associated with cold
and wet environments, patients may present with
hypothermia from the same event that has rendered
other participants hyperthermic, and they can be
hard to distinguish from symptoms alone. A reliable
estimate of core body temperature is therefore
important and it may be helpful to consider three
levels or stages of progression (Table 1).
Symptoms and signs may appear in any order and
inconsistently (Box 1).
Pulse, respiratory rate and level of consciousness should
always be recorded. When able, perform a standard panel
of investigations (Table 2).
Pulse, respiratory rate and level of consciousness should
always be recorded and investigations performed if possible
(Box 2).
Hyperthermia
Similarly, raised core temperature may cause a wide variety
of illness of varying severity. Classification and terminology
can be confusing, but effective early management is essential
in all cases. As the symptoms are often non-specific, the
history is important and should prompt formal assessment.
Commonly, symptoms will develop in individuals after a
period of exercise in a warm environment while wearing
excessive clothing.
Acclimatisation is an important
protective factor, but raised environmental heat stress or
additional occlusive clothing, which challenges individuals
beyond their acclimatised condition, are frequent causes of
hyperthermia (3, 5). Cases are also common in those required
to undertake physical work shortly after arriving in a warm
theatre of operations, before any effective acclimatisation
can take place (3, 5). Dehydration may be evident from the
history, perhaps the result of prior alcohol consumption, and
there are strong associations with drug use, both prescribed
and illegal (5, 6).
Neurological
Headache,
Weakness,
Confusion,
Loss of co-ordination and/or dizziness,
Disturbed vision,
Collapse,
Loss of consciousness,
Agitation, which may progress to aggression
and violence.
Other systems
Feeling hot, tired, exhausted,
Hyperventilation, which often results in further
symptoms including tetany,
Cramps,
Diarrhoea, nausea or vomiting, resulting in
dehydration and worsening illness if untreated.
Box 1. Symptoms of hyperthermia.
Individual variation is an important consideration.
Differences in body mass index, clothing, physical
exertion, hydration, and microclimate, can produce both
hypothermic and hyperthermic casualties on the same day.
This means that reliable measurement of core temperature
is crucial.
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Rectal temperature. Temperature measured in other
areas may be misleading.
Blood pressure. Low pressure is a late sign of suboptimal hydration and imminent circulatory
collapse.
Arterial oxygenation using a pulse oximeter. Give
supplemental oxygen if <94% in an otherwise
healthy individual.
Blood sugar level. Give sugar by an appropriate
route if low.
Urine dip. Look for protein as a sign of renal
failure, specific gravity to monitor hydration and
“blood” which may indicate myoglobinuria, a sign
of extensive muscle damage.
Fluid balance monitoring on an In/Out chart such as
the FMed 100.
Box 2. Observations suggested for hyperthermic patients.
With such vague symptoms there is a very broad differential
diagnosis. Paradoxically, consumption of excessive fluid
may cause overload with similar symptoms to hyperthermia,
but rectal temperature may appear normal, and in hot
environments some individuals may become profoundly
hyponatraemic. Although this may resolve spontaneously,
the risk of pulmonary oedema and serious sequelae of
hyponatraemia should promote hospital admission during
which other potential causes may be excluded (3). Infection
commonly causes pyrexia (which may be apparent from the
history) and this independently predisposes to heat illness
(5). Acute neurological events such as stroke or epilepsy
should be considered, especially if rectal temperature is
normal. Other, non-environmental causes of hyperthermia
include thyroid storm, phaeochromocytoma, malignant
hyperthermia, neuroleptic malignant syndrome, and
hypothalamic haemorrhage.
Clinical management
Confused patients may temporarily lack capacity and be
unable to consent to, or refuse, treatment. There is detailed
J Royal Naval Medical Service 2014, Vol 100.3
guidance available from the General Medical Council but
in short, when a patient cannot “…understand, retain, use
and weigh up the information needed to make a decision,
and communicate their wishes”, then healthcare workers
must act in the best interests of the patient (7).
Hypothermia
The aim of management is to restore the core temperature
to normal as safely as possible. Importantly, this does not
necessarily require the fastest re-warming possible because
rapid heating of a profoundly hypothermic patient risks
arrhythmia, collapse and rapid changes in fluid balance,
making successful management more difficult. Passive
methods are normally used in the field to avoid these
problems, and generally, the rate of warming should not
exceed the original rate of cooling (5).
While at the site, assess for catastrophic haemorrhage,
a patent airway, effective breathing and adequate
circulation (<C>ABC). The normal rules of first aid
apply, and serious injuries should be treated before, or
ideally while, rewarming the patient. Cardio-Pulmonary
Resuscitation (CPR), however, should only be started if
it can be maintained effectively until delivery to a place
of definitive care. JSP 539 Chapter 5 includes a modified
algorithm (Figure 5.1) which considers the actions required
for patients in whom signs of life are absent in remote
locations where maintaining effective life support may not
be feasible (Figure 1) (5).
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incorporating metallic sheeting seldom seal the internal
environment properly, meaning additional insulation is
beneficial, particularly if a water-tight layer is included
(9). Those who are only very mildly hypothermic and fully
conscious can be offered hot and sweet, but non-alcoholic,
drinks. Continue to monitor the patient (Figure 1).
Once inside shelter, a patient who has been rapidly cooled
but has remained conscious (typically seen in immersion
incidents) can be rapidly re-warmed in a warm bath at no
more than 40 degrees C. However, this must be avoided
where hypothermia is profound or prolonged, and is
inadvisable if there is a concomitant risk of non-freezing
cold injury, which would be worsened by rapid re-warming
(3). Once in hospital, further interventions and monitoring
may be appropriate (Box 3).
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Humidified oxygen warmed to 42-46˚C.
ECG monitoring to detect arrhythmias.
Continuous monitoring of rectal temperature until
>36˚C.
Where available, extra-corporeal rewarming using
cardio-pulmonary bypass may be the method of
choice for rewarming the profoundly hypothermic,
and those apparently dead.
Avoid giving any drugs until core temperature is
>30˚C and then prolong the intervals between doses.
Consider a Central Venous Pressure (CVP) line and
urinary catheterisation for monitoring fluid balance.
Record an ECG as high core temperature can cause
cardiac damage and metabolic disturbances can
cause dysrhythmias.
Continuous rectal temperature monitoring.
Consider intubation or ventilation to reduce effort
and therefore heat generation by the patient.
Blood tests including FBC, U&Es, Liver Function
Tests (LFT), calcium, magnesium, creatinine kinase
(CK), coagulation screen, myoglobin clearance,
lactate and serum osmolality.
Arterial blood gases if indicated.
Consider a urinary catheter, giving fluids by
nasogastric tube, central venous pressure line or
arterial line for accurate fluid balance monitoring.
Consider Dantrolene (2.5-3 mg/kg) in exertional
illness administered by an anaesthetist/intensivist (3).
At 24 hours, repeat at least the U&Es, CK, LFT and
coagulation to monitor for deterioration.
Seek shelter where available. This would ideally be
indoors or within the ship’s superstructure, but in the field
a cave or tent would suffice. Because of the risk of circumrescue collapse, anyone suspected of being hypothermic
should rest in a recumbent position until thoroughly rewarmed (8). This is most important in immersion casualties
as the pressure of the water around the legs and a roughly
horizontal position helps return blood to the heart. If
removed from the water in an upright posture, the loss of
this pressure along with the increased circulatory demand
of this position may cause excessive cardiac strain upon
an already ‘irritable’ heart and may precipitate atrial and
ventricular arrhythmias. In an attempt to avoid this postimmersion collapse, the Royal Navy now uses two strops
to rescue a casualty, one under the arms and one behind
the knees to keep the patient close to a horizontal position
(Figure 2).
Box 3. In-hospital monitoring and treatment of hypothermia.
Dry clothes, if available, should be worn by an otherwise
well casualty. Otherwise, a wind- and water-proof bag
will stop evaporative heat loss and make wet clothing less
thermally disadvantageous. Specialist re-warming and
recovery bags are available, although their most important
property is stopping evaporative heat loss; thin, flimsy bags
Significant heat illness may result in cardiac arrest,
convulsions and other central nervous damage,
hypoglycaemia, hyperkalemia, renal failure, and
rhabdomyolysis. The most severe cases may have overt
evidence of single or multi-organ failure, which can also
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Figure 1. Management of hypothermia (5).
Clinical
J Royal Naval Medical Service 2014, Vol 100.3
Figure 2. Taken during a man overboard exercise, a rescuer is lifted with one strop (left) and a dummy casualty with two (right).
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Figure 3. Management of hyperthermia (3).
Clinical
J Royal Naval Medical Service 2014, Vol 100.3
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result in cardiac muscle damage, liver failure and clotting
disorders. If present, these conditions should be treated
while continuing to cool the patient concomitantly.
Occupational considerations in the RN/UK Armed Forces
At the site, stop physical activity as soon as possible and
consider stopping and cooling other personnel if present,
in order to prevent further casualties. Assess <C>ABC and
treat any life-threatening injuries or illnesses, then lie the
patient down in the shade or, ideally, in an air-conditioned
space. If conscious, raise the patient’s legs, or place
them in the recovery position if unconscious. The patient
should be stripped to their underwear and then sponged or
sprayed with cool (not cold) water and their skin fanned.
Commercially available garden sprays with a capacity
of several litres are ideal. This should be stopped if the
patient starts to shiver and can be restarted when shivering
stops. Keep a careful temporal record of their level of
consciousness using a recognised scoring system such as
Alert, Voice, Pain, Unresponsive (AVPU) or the Glasgow
Coma Scale (GCS). Give sips of water if conscious and
arrange urgent medical evacuation (3).
Following complete recovery from hypothermia, potential
causes or contributing factors such as hypothyroidism
should be considered. In the absence of these, and
assuming there were no significant sequelae such as
pancreatitis, a patient can be returned to full duties when
fit. Even relatively brief periods of mild hypothermia can
leave personnel feeling physically exhausted for some
days. Patients who have been hypothermic may have also
sustained local cold injury, so it is important to question or
examine them for possible symptoms including numbness,
discolouration or swelling of an exposed body part.
In a pre-hospital setting, administer 100% inspired oxygen
if this is available. Continue to give oral fluids if the
patient is conscious; oral fluid may be supplemented with
intravenous fluids. A suggested regimen is to give one
litre of crystalloid fluid over 30 minutes, followed by 2.5
ml/kg/hr (i.e. the second litre over four to six hours). If
hospital admission is not indicated, the patient should
be removed from duties and rested for 24 to 48 hours.
Blood investigations should be performed after 24 hours
if available (Box 4) and Medical Officer review arranged
on at least days three, five and seven (4). The individual
should then re-undertake the local acclimatisation protocol
as if newly arrived from the UK.
Patients who do not respond within 30 minutes of treatment
or who suffer seizures, have a GCS<8 at any stage or have a
rectal temperature persistently >40C despite active cooling
should be evacuated to a Role 2 or 3 facility where they
should be comprehensively re-assessed (Box4) (3).
JSP 539 Chapter 4 Annex A details management strategies
of such patients in this setting (Figure 3).
Reporting
There are statutory and single Service requirements to report
thermal illness. Cases should also prompt a Significant
Event report where appropriate, and a Defence Lessons
Implementation and Management System (DLIMS)
submission (3). All moderate and severe cases should be
reported, but even milder cases should be reported when
the risk assessment had deemed them unlikely. Instructions
for reporting are in JSP 539 paragraphs 106-114 (3).
Hypothermia
Hyperthermia
Any significant central nervous system (CNS) derangement,
seizures, or significant biochemical disturbance should
prompt referral for follow-up in the Heat Illness Clinic at the
Institute of Naval Medicine (INM) (3). The occupational
impact will depend on severity and may be ultimately
determined by the Heat Illness Clinic. As a guide:
• Mild heat illness. Where there was no need for
hospital admission and no evidence of biochemical
abnormality, patients may be restricted to light
physical exercise only for seven days followed by
gradual supervised return to activity over the next
seven days (3).
• Moderate heat illness. These patients will probably
have required hospital admission and should be
restricted from exposure to excessive heat and made
unfit for any physical training until INM review.
Using the current UK Joint Medical Standards
(JMES), this is P7 Medically Non Deployable
(MND) L4, 214 (Unfit exposure to excessive heat),
103 (Unfit physical training). They can, however,
start a gradual, supervised return to exercise before
attending INM, starting no sooner than fourteen
days after biochemical recovery (3). Recurrence of
a mild heat illness should be managed similarly.
• Severe heat illness. Patients who require intensive
care admission should all be discussed with INM and
referred for review. The likely recommendation is for
restricted duties as for moderate illness (above) for at
least three months, and until INM review. Gradual,
supervised return to exercise is recommended from
at least one month after biochemical recovery and
resolution of any complications (3).
Return to exercise should be part of a structured regime
developed with an Exercise Rehabilitation Instructor (ERI)
in a Primary Care Rehabilitation Facility (PCRF). This
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should start before an INM appointment, if needed. If the
creatinine kinase (CK) was markedly raised, a baseline and
8-24 hour post-exercise CK should be compared after the
first fifteen-minute treadmill session. Significant elevation
requires a further two weeks of rest, and this should be
repeated until the CK is normal (3). Water-based exercise
is ideal, otherwise only Physical Training (PT) kit should be
worn and intensity should not exceed 60% of the patient’s
maximum heart rate. Initially limited to fifteen minutes,
sessions should be gradually extended to 30 minutes,
twice daily, with the aim of avoiding delayed onset muscle
soreness, which contraindicates further exercise until
resolved (3).
Clinical
Conclusion
Thermal illness poses a significant threat to RN personnel
and other members of the Armed Forces both during
training and while on deployed operations. While these
conditions would ideally be prevented by preparation and
protection, early recognition and management will reduce
the risk to the individual and facilitate a prompt return to
duty. Unfortunately, these conditions tend to develop in
remote and environmentally adverse areas, which may
make management more difficult. Adhering to the advice
in this article as far as practicable will help provide the best
available care for the patient.
References
1. http://www.bbc.co.uk/news/uk-wales-23311651 accessed Apr 14.
2. www.cdc.gov accessed Apr 14.
3. Headquarters of the Surgeon General, Head of Strategic Medical Policy. Joint Services Publication 539: Climatic illness and injury
in the Armed Forces: force protection and initial medical treatment. London: Ministry of Defence; 2012.
4. Lt Col R Russell RAMC, Miss A Bess MIPA, editors. Joint Service Publication 999: Clinical Guidelines for Operations [Internet].
Royal Centre for Defence Medicine; Sep 2012 [cited 2014 Jan 4]. Available from: https://www.gov.uk/government/uploads/system
uploads/attachment_data/file/79106/20121204-8-AVB-CGO_Online_2012.pdf accessed Jan 14.
5. Pandolf KB & Burr RE. Medical Aspects of Harsh Environments, Vol 1. Virgina: Office of the Surgeon General US Army 2001.
Available from: www.cs.amedd.army.mil/borden/Portlet.aspx?ID=eebb9338-2027-46d5-a5f2-f245e2019b6c accessed Jun 14.
6. Seedat YK, Aboo N, Naicker S et al. Acute renal failure in the “Comrades Marathon” runners. Renal Failure 1990;11(4):209-12.
7. http://www.gmc-uk.org/guidance/ethical_guidance/consent_guidance_endnotes.asp accessed Apr 14.
8. Golden FStC, Hervey GR, Tipton MJ. Circum-rescue collapse: collapse, sometimes fatal, associated with rescue of immersion
victims. J R Nav Med Serv 1991;77:139-149.
9. Light IM, Dingwall RHM, Norman JN. The thermal protection offered by lightweight survival systems. Aviat Space Environ Med
1980;51(10):1100.
Authors
Surgeon Lieutenant Commander DJC Angus, MB ChB RN
General Practice Specialty Trainee Year 2
Dr EHN Oakley
Physician
Former Head of Survival and Thermal Medicine
Institute of Naval Medicine
Gosport ,Hampshire
PO12 2DL