Getting ready for Winter

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Although Sydney is currently enjoying an extended summer, last week’s education day had a frosty feel to it as we were treated to two presentations on the perils of cold weather. This is currently being typed as it’s 34 degrees outside, but it is worth remembering that temperatures in both the Blue Mountians and the Snowy Mountains can hover around zero in winter time and catch some unprepared hikers (and medics!) unaware.

(Photo Credit: Bob Lisle)

Critical care paramedic Bob Lisle discussed how best to look after ourselves and our patients in cold weather and gave us these survival tips:

  • Weather can change quickly and dramatically – be prepared
  • Cotton clothing is dangerous and can get wet and cold very quickly
  • Ensure you are wearing correct clothing; merino underlayer, wet weather gear, good boots, thick socks, and a beanie.
  • When arriving by helo, try not to blow away the patient’s tent if they have managed to erect one as this will provide shelter for the entire team.
  • Do not expose the patient to assess injuries unless absolutely necessary; try and do as much examination as possible through their clothes.

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(Photo Credit: Bob Lisle)

A reminder on the medical aspects of hypothermia is below.

Severity:

Hypothermia occurs when core body temperature is < 35 C

  • Mild: 32-35 C
  • Moderate: 28-32 C
  • Severe: < 28 C

Effects of Hypothermia:

Central nervous system effects

  • Fixed dilated pupil at < 30degrees – mimics brain death.
  • Confusion and decreased level of consciousness
  • Increased seizure threshold
Acid-base changes:

  • Rise of pH with falling body temperature
  • Fall of PCO2 with falling body temperature
  • Increased oxygen solubility and O2-haemoglobin affinity
Cardiovascular consequences

  • Decreased cardiac output and bradycardia
  • ECG: QT prolongation and the J wave, increased PR and QT
  • Arrhythmias – classically AF and VF (<28 deg)
  • Resistance to defibrillation
  • Vasoconstriction
  • Increased viscosity of blood & myocardial work
Endocrine and metabolic consequences

  • Decreased metabolism and oxygen consumption
  • Decreased carbohydrate metabolism and hyperglycaemia
  • Decreased drug metabolism and clearance
  • Essentially unchanged electrolytes
  • Shivering

 

Respiratory consequences

  • Decreased CO2 production
  • Decreased gas solubility >> decreased PAO2 & PaCO2
  • Decreased respiratory rate and medullary sensitivity to CO2
  • Increased dead space
  • Diaphragmatic fatigue
Renal consequences

·       Decreased GFR and RBF.

·       Reduced vasopressin >> “Cold diuresis”

GIT consequences

  • Decreased hepatic blood flow and metabolism
Haematological consequences

  • Increased haematocrit and blood viscosity
  • Neutropenia and thrombocytopenia
  • Coagulopathy and platelet dysfunction
Immunological consequences

  • Decreased granulocyte and monocyte activity

Management:

Resuscitation

  • Pulse check – palpate for up to 1 minute (consider Echo / Doppler as hard to find – do not delay CPR)
  • Move patient gently if <32 degrees due to risk of triggering VF (risk is overstated)
  • No adrenaline or other drugs until >30C
  • Between 30-35C double the dose intervals of ACLS drugs
  • Shock VF up to 3 times if necessary, then no further shocks until T>30C
  • ‘Not dead until warm and dead’ (30-32C)

Passive warming – useful in conscious patients who are able to shiver  (1.5C per hour)

  • Keep dry
  • Keep in a warm environment
  • Provide insulation with blankets (e.g. aluminium foil) and hat
  • Allow to mobilise if conscious (beware of hypotension on cessation of exercise)

Active warming:

  • Peripheral active warming
    • Chemical heat pads
    • Radiant methods
    • Forced air warming blankets (1-2C/h)
  • Central active warming
    • Warmed (40-46C) humidified inspired gases (1 C/h; 1.5°C/h ET tube)
    • Warm IV fluids (42C)  (only give if need fluids, prevents cooling rather than promotes warming) – use Level 1 fluid warmer
    • Body cavity lavage with 40C fluid e.g. peritoneal (3C/h), gastric, bladder, right-sided thoracic lavage (3-6C/h – use 2 ICCs for continuous flow)
    • Dialysis
    • ECMO/ bypass (9-18C/h)
  • Afterdrop, a drop in core body temperature during rewarming may occur a consequence of peripheral vasodilation and release of cold peripheral blood to the body core. It is not usually significant.

Supportive care and monitoring

  • Use oesophageal probe preferentially (core temperature, minimal lag time)
  • Use low reading thermometer
  • ABG measurements at 37C (temperature uncorrected values) to allow serial monitoring

What is in our packs?: Buddy lite fluid warmer, space blankets, EasyWarm Active Self-Warming Blanket

Our second speaker was Dr Andrew Peacock, a part time emergency medicine physician and part time expedition doctor. In the course of his travels around the world he has also developed incredible skill as an award winning photographer. We heard about his recent trip to Denali (Mt McKinley) which, at 6190m above sea level, poses the dual challenge of freezing temperatures and altitude. The main issues Andrew faced on Denali were altitude sickness, frostbite and hypothermia.

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(Photo credit: CNN, Andrew Peacock)

Altitude related medical issues can occur at altitudes above 2500m but this isn’t the only risk factor; rate of ascent and previous medical issues at altitude are more relevant predictors.

Altitude sickness comprises a spectrum ranging from AMS (Acute Mountain Sickness) through to HAPE (High Altitude Pulmonary Oedema) and HACE (High Altitude Cerebral Oedema).

Symptoms

AMS: headache, nausea, anorexia, dizziness, general malaise

HAPE: dry cough, decreased exercise tolerance, shortness of breath

HACE: headache, nausea, vomiting, truncal ataxia, altered mental status

Treatment

Mild AMS can be treated by stopping the ascent, acetazolamide (125mg bd) and simple analgesia. However both HAPE and HACE (and severe AMS) warrant descent and supplemental oxygen. In addition HACE can be treated with dexamethasone (8mg stat dose then 4mg q6h) and HAPE with nifedipine (30mg slow release bd)

Andrew also provided a broader classification for hypothermia which is easier to apply in the field and is a helpful guide to treatment

Mild: Shivering and normal mental function (temp 32-35 degrees)

Severe: Absence of shivering and abnormal mental function (temp <32 degrees)

Andrew’s top tip for managing frostbite was to avoid rewarming the affected digits until you can guarantee that further frost bite will not occur. Then, rewarm in a bath of 37-39 degrees. This is a painful process and requires liberal analgesia. Finally, splint, elevate and protect.

Andrew’s beautiful travel photographs can be seen on his website   www.footloosefotography.com and on his instagram page https://www.instagram.com/footloosefotography/?hl=en.

If they dont give you an acute case of wanderlust, then nothing will.

References and resources

  1. https://lifeinthefastlane.com/ccc/hypothermia/
  2. https://coreem.net/core/acute-mountain-sickness/
  3. CNN – The expedition doctor who photographs his extreme travels
  4. Wilderness Medicine Society
  5. expeditionmedicine.com.au
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