Background
Accidental hypothermia: an update- part 1 definitions, diagnosis, prehospital management and triage
Introduction
Methods
Cooling: implications for drowning and avalanche rescue
Staging
Stage | Clinical findings | Core temperature (°C) (if available) |
---|---|---|
Hypothermia I (mild) | Conscious, shiveringa
| 35–32 °C |
Hypothermia II (moderate) | Impaired consciousnessa; may or may not be shivering | <32–28 °C |
Hypothermia III (severe) | Unconsciousa; vital signs present | <28 °C |
Hypothermia IV (severe) | Apparent death; Vital signs absent | Variableb
|
Temperature measurement
Prehospital insulation, rewarming, rescue collapse and afterdrop
Triage and prognostication of accidental hypothermic patients in cardiac arrest
Longest no flow time | 42-year-old male, found in crevasse, 7 m under snow, no vital signs, CPR started only after 70 min in hospital when patient was asystolic, 19 °C core temperature, ECLS rewarming, full recovery [211]. |
Longest manual CPR | 42-year-old male, found outdoors. Developed asystole just after discovery, CPR started, 23.2 °C, 6 h and 30 min CPR. Rewarmed with non-ECLS methods until ROSC. Full recovery [143]. |
Longest mechanical CPR | 42-year-old female, found unconscious in her apartment. VF arrest during evacuation to hospital. Manual CPR started and this was changed to mechanical CPR on arrival at hospital. Minimal temperature 24 °C. 80 min mechanical CPR while the patient was rewarmed noninvasively [153]. |
Longest total resuscitation | 65-year-old female went missing and was found on a snow-covered riverbank. Initially 28 °C (rectal) but dropped to 20.8 °C. Asystole. Resuscitation was CPR (4 h 48 m) and ECLS (3 h 52 m). Total resuscitation time was 8 h 40 min [142]. |
Lowest survived body core temperature | 29-year-old female, fell into water fall gully, flooded by icy water but able to breathe. Lifeless for approx. 45 min, CPR started after rescue, at hospital admission 13.7 °C and K+ of 4.3 mmol L-1, ECLS rewarming, full recovery [11]. |
Longest persisting VF | 42-year-old male, found outdoor, CPR started, repeated shocks, hospital transfer, 22 °C, ECLS rewarming started at 130 min CPR and after 38 shocks, successful shock at 30 °C, full recovery [234]. 25-year-old female, buried by and avalanche in Tatra mountains, Poland. Witnessed VF cardiac arrest (17.0 °C) after extrication, 3 unsuccessful shocks. CPR until ECMO rewarming (6 h, 45 min), and successful 4th shock at 24.8 °C. Full recovery [235]. |
Longest intermittent CPR | 57-year-old female, witnessed cardiac arrest in French Alps at 2000 m altitude in a snowstorm; transport distance to EMS vehicle of 1.1 km, 122 m difference in height; 1 min CPR alternating with 1 min walking for 25 min, 5 h CPR, ECLS rewarming, full recovery [69]. |
Longest submersion | |
Longest survival in an avalanche | |
Longest time in an avalanche indoor | Thirteen days entrapped in a house which in part collapsed after being hit by an avalanche, Heiligenblut, Austria [238]. |
Lowest temperature with vital signs | Male age 3 years. ECG showed very irregular rhythm 8–10/min. Rectal temperature recorded about 20 min after arrival at the hospital was 17 °C [232]. Female age 37 years. Rectal temperature 17.2 °C. ECG showed atrial fibrillation 28–40/min with PVCs [233]. |
Highest survived potassium in an avalanche victim | Avalanche victim, 6.4 mmol L-1, survived; core temperature and neurological outcome are not reported [130]. |
Highest survived potassium in an adult | 34 year old female, 20 °C, cold environment exposure, asystole, 7.9 mmol L-1, ECLS rewarming, survived. Neurologic outcome not reported [239]. |
Highest potassium in an accidentally hypothermic patient | |
Longest time in a crevasse | 27 -year-old male, 8 days, good outcome, no temperature or other specific details reported [240] 70 year male, moderate fractures of skull, vertebral column, pelvis, and femur, 6 days, 33.5 °C, cold injuries to toes, otherwise good outcome [241]. |
Largest number of simultaneous cases of accidental hypothermia with cardiac arrest | 15 healthy subjects age 15–45 years were immersed in 2 °C salt water. Seven victims were recovered in circulatory arrest with a median temperature of 18.4 °C. They were rewarmed with ECMO and were subsequently evaluated with advanced neuroradiological and functional testing. All were successfully resuscitated [41]. |
Oxygenation, anaesthesia induction and airway management
Cardiopulmonary resuscitation
Dispatching and transport decisions
Conclusions
Accidental hypothermia: an update- part 2 in-hospital management
In-hospital management of hypothermic patients
Rewarming technique | Rewarming rate | Notes & controversies | Rewarming complications |
---|---|---|---|
PASSIVE REWARMING [79] | |||
Passive rewarming | Protect from further heat loss and allow patient to self-rewarm. Minimal controversy for mild hypothermia if the patient is able to self-rewarm. | Negligible in isolated mild hypothermia. For colder patients and those with secondary hypothermia or comorbid illness, there may be morbidity associated with a prolonged rewarming process if the patient has poor tolerance for the hypothermia-induced organ dysfunction (i.e. hypotension, coagulopathy, arrhythmias, impaired cellular function etc.). | |
Passive rewarming with active movement | 1–5 °C hr-1
| Exercise has been shown to increase afterdrop in physiology studies from ~0.3 °C in controls to ~1 °C in exercised subjects, however the exercised subjects rewarmed more quickly [243]. | No reported complications. Some authors highlight the theoretical risk that the slightly increased afterdrop could contribute to morbidity and mortality. No adverse events were noted [243]. |
ACTIVE EXTERNAL REWARMING | |||
0.5-4 °C hr-1
| Protect from further heat loss, deliver external heat and (if required) warmed IV fluids. Minimal controversies. | Similar to passive rewarming. | |
ACTIVE INTERNAL REWARMING | |||
Bladder lavage | Variable. Adds ~0.5–1 °C hr-1
| Negligible unless difficult catheterization. | |
Gastric lavage | Adds ~0.5–1 °C hr-1
| Not commonly used due to risk vs. benefit ratio [249]. | Potential for aspiration, fluid & electrolyte shifts. |
Device specific (adds ~0.5–2.5 °C hr-1) | Uncertain indication for use, potential for benefit exists in colder and sicker co-morbid patients with stable circulation. | Potential for haemorrhage or thrombosis, potentially worsening hypotension in unstable patients. | |
Adds ~1–2 °C hr-1
| Not commonly used unless patient is unstable and ECLS rewarming is not available. | Potential for haemorrhage, lung or bowel trauma, fluid & electrolyte shifts. Thoracic lavage has the potential to impair CPR quality. | |
Adds ~1.5–3 °C hr-1
| Not commonly used unless ECLS rewarming not available. Requires adequate blood pressure. Heparinisation required. | Problems rare. Local vascular complications. Air embolism. Hypotension. | |
Adds ~2–3 °C hr-1
| Not commonly used, patient must be able to increase cardiac output to perfuse the external circuit. Heparinisation required. | Potential for hypotension, haemorrhage, thrombosis, haemolysis, etc. | |
Veno-venous rewarming (usually with an ECMO circuit) [248] | ~4–10 °C hr-1
| Not commonly used. Provides no circulatory or ventilatory support in case of cardiac arrest. Patient must be able to increase cardiac output to provide circuit perfusion. | Potential for hypotension, haemorrhage, thrombosis, haemolysis, etc. |
Extra-corporeal life support (VA-ECMO or CPB) | ~4–10 °C hr-1
| Potential for haemorrhage, thrombosis, haemolysis, etc. (as with all intravascular devices). |
Interpreting arterial blood gases in severe hypothermia
System | Parameter | Clinical implications |
---|---|---|
• Initial vasoconstriction (effect blocked by ethanol). Vasoconstriction fails <24 °C [268]. | • Failed vasoconstriction means the patient becomes poikilothermic i.e. dependent on ambient temperature. | |
• Cardiac conduction is affected by cold and changes in pH and PaO2 [79]. Initial tachycardia due to shivering [79] subsides as temperature drops due to decreased spontaneous depolarization of pacemaker cells leading to linear fall in pulse rate (~50 % at 28 °C) [79]. Any ECG rhythm is possible. Commonly at <32 °C, sinus bradycardia, prolonged QTc. J waves (not pathognomonic for hypothermia) best seen in leads I & V6 [79, 269‐272]. Likelihood of VF is high <28 °C [267]. | • Bradycardia is atropine unresponsive [79]. • A “relative” tachycardia inconsistent with patient’s temperature means something else is going on e.g. occult trauma. • Be prepared for any rhythm but expect it to be resistant to treatment until the heart rewarms. • Normal rhythm resumes on rewarming. | |
• Cardiac output falls to 45 % at 25 °C [79]. | • Hypotension is the norm. | |
• After rewarming, mean arterial pressure, contractility, and cardiac output are decreased, especially if alcohol ingested before cooling [273]. | • More prolonged depression of cardiac function after rewarming | |
CENTRAL NERVOUS SYSTEM | • Reflexes become increasingly sluggish as body temperature falls and become absent ≈ 28–30 °C [230, 274]. • Pupils become dilated and cease reacting to light at ≈ 28 °C [230]. | • The level of consciousness should be consistent with the core temperature. A significant discrepancy suggests an alternative diagnosis. • All the effects of hypothermia make it very hard to diagnose death by the usual criteria while the patient is still cold |
RESPIRATORY | • Tidal volume, respiratory rate, pulmonary compliance and thoracic elasticity decrease [230]. The respiratory rate may only be five breaths per minute when the body temperature is <30 °C [79]. Sensitivity to CO2 is attenuated, although the hypoxic drive is maintained to deeper levels of hypothermia [230]. Cough reflex is obtunded, ciliary activity is reduced and secretions are more viscous. | • An irregular respiratory pattern can be mistaken for agonal breathing leading to premature institution of CPR. • The likelihood of a chest infection is increased. |
• Oxygen consumption and carbon dioxide production fall by about 50 % at 30 °C [230] | • Reduced CO2 production means it is easy to inadvertently hyperventilate hypothermic patients. Hyperoxia is also possible. | |
RENAL & METABOLIC | • Severely hypothermic patients are dehydrated. This becomes particularly important during rewarming as the consequent opening up of the peripheral circulation will lead to a rapid fall in BP. | |
• Hyperglycaemia can exacerbate the diuresis. | ||
• This makes the interpretation of acid-base more complex. | ||
• Hypokalaemia commonly occurs with hypothermia [230]. | • If potassium replacement is given excess to the losses, hyperkalaemia may occur on rewarming [276, 277]. • Severe initial hyperkalaemia is a marker of acidosis and cell death and is therefore a sign of poor prognosis [8] | |
HAEMATOLOGY | • Haematocrit increases by about 2 % for every 1 °C decline in temperature [250]. | • A normal haematocrit in a moderately or severely hypothermic patient suggests pre-existing anaemia or blood loss [230]. |
COAGULATION | • Platelet function and coagulation enzyme activity are reduced [278]. | • Coagulopathy is likely and increases with decreasing core temperature. At temperatures below 33 °C coagulopathy significantly increases mortality in patients with concomitant trauma [279]. |