Transcript REWARMING THERAPIES IN HYPOTHERMIA

HYPOTHERMIA
BERNARD FOLEY
EMERGENCY DEPARTMENT
AUCKLAND CITY HOSPITAL
16/07/2015
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Environment
NZ climate temperate
Urban water temperatures relatively warm
Greater extremes in mountainous areas
Generally population aware of dangers
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Hypothermia - aetiology
Healthy people in
unhealthy
environments
Cold
Wet
Wind-chill
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Hypothermia – aetiology 2
Predisposing illness in a “safe” environment
- Trauma
- Drugs
- Elderly/Young
- Endocrine/ metabolic
- Neurological
- Dermatological
- Iatrogenic
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Heat balance in a given patient
Heat gain
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chemical energy from
metabolism
physical energy from
exertion
heat transfer from the
environment
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Heat loss
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inhibition of
metabolism
decreased work
heat transfer to
environment or other
parts of body
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Gaining Heat
Autonomic nervous system
Increased skeletal muscle tone
Shivering
Endocrine
Behavioural
Assisted warming
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Losing Heat
Radiation
Conduction
Convection
Evaporation
Respiration
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Hypothermia - classification
MILD 32 - 35degrees C
- thermogenesis still possible
MODERATE 28 - 32degrees C
- progressive failure of thermogenesis
SEVERE less than 28degrees C
- spontaneous cardiac arrest
poikilothermic
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MILD HYPOTHERMIA
Alert and active
Shivering
Increased BP, HR, RR
diuresis
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MODERATE HYPOTHERMIA
Progressive reduction in vital organ
function
Failure of compensatory homeostatic
mechanisms begins
Reduced L.O.C./ stupor
Reduced BP, HR, RR
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SEVERE HYPOTHERMIA
Coma (fixed dilated pupils)
Very low cardiac outputs
Minimal/ no respiratory movement
Increasingly significant arrhythmias
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LABORATORY CHANGES
Early respiratory alkalosis
But usually acidosis in hospital
admissions
Raised haematocrit (@2% per degree
temp drop)
Electrolytes little effected unless extensive
tissue necrosis
Glucose usually elevated in acute
hypothermia (decrease in chronic)
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ECG changes
Bradyarrythmias predominate
T wave abnormalities common
Usual arrest rhythms
J-wave (Osborn wave)
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Highly suggestive of hypothermia
May appear at any temp < 32 C
Commonest in lead 2 or V6
V3 and V4 in severe
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Osborn wave
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CASE 1
38-year-old woman
Found collapsed on front lawn 0600 hrs
? Drug overdose
Palpable pulse, no recordable BP
On ED arrival no palpable pulses
No discernable chest movement
Pupils fixed and dilated
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Continued
Rectal temp 23.4 C
No signs of external trauma
BM glucose normal
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ASSESSMENT
Accurate temperature measurement
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Rectal (low reading)
Tympanic (debate over probe accuracy)
? Underlying cause
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BM glucose
? Associated injuries
Cardio respiratory status
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MANAGEMENT
Mild : will self correct unless
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Underlying problem
Ongoing hypothermia favourable conditions
Usually discharge home when recovered
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SUPPORTIVE CARE
Gentle handling
Removal of wet clothing
Monitoring
? CPR
IV access
Oxygen
Disposition?
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CPR ?
CONTROVERSIAL
ARE THEY REALLY IN ARREST ?
myocardium much less compliant
perfusion <50% cf. normothermic
metabolic rate decreased
? increased risk of injury
DEFIBRILLATION?
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Pharmacology
Most drug activity temperature dependent
Toxic doses required for effect
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Leading to problems when rewarmed
Most arrhythmias revert with rewarming
VF treatment controversial
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Bretylium
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CASE 1
Resuscitation
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Intubation and ventilation
CPR
ACLS algorithm for PEA
Investigation
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BM glucose 8.4
ECG junctional bradycardia rate 30
Rewarming
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Humidified warmed oxygen
Warm air blanket
Warm IV fluids
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REWARMING
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Rewarming therapies What to measure ?
absolute rewarming rate
afterdrop - magnitude+/- duration
clinical variables
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survival rates
complication rates, either due to the
hypothermia or due to the treatment
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Core afterdrop
A paradoxical ongoing drop in core
temperature with rewarming
May matter if shivering inhibited or
arrhythmia's occur
Theories
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“Convective” - return of cold blood from
periphery to core
“Conductive” - simple temperature
equilibration
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Is afterdrop a real clinical issue
?
a traditional concern
should be most likely with active external
rewarming techniques
may depend on measurement site
in practice generally less than 0.60C
small with more sophisticated therapies
Seldom a problem in practice
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Rewarming research in general
Paucity of RCTs esp in humans
Volunteer studies predominate, usually in
shivering mild hypothermics
Methodological variations with same Rx
Questionable external validity
Limited clinical trials with small numbers
Many therapies ethically hard to study
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Rewarming therapy
classification
Passive rewarming
Active external rewarming
Active core rewarming
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Passive rewarming
Dry, insulate and allow to rewarm by
endogenous heat production (largely by
shivering)
often the control arm in rewarming studies
an integral part of most rewarming
modalities
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Passive rewarming - results
typically small but sustained afterdrop
afterdrop usually ~ 0.5 degrees
rewarming rate ~ 0.75 degrees/hr
no RCTs have studied space blankets
compared to wool or cotton blankets
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Exercise
a special case of passive rewarming
possible down to 310C in healthy, non
exhausted hypothermics
increased rewarming rates ~50C/hr
larger afterdrop
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Field rewarming techniques
body to body rewarming blunts shivering
thermogenesis so net effect is no greater
than passive rewarming
heat pads risk local burns or inhibiting
shivering
portable burners are a CO risk
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Methods of active rewarming
External
Hot bath immersion
Forced air
Heat packs
Plumbed garments
Body to body
Radiant Heat
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Internal
Warm inhalation
Radiofrequency
Very hot IV fluids
Body cavity lavage
e.g. pleural, gastric
peritoneal
Extracorporeal
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Hot bath immersion
water temps up to 430C
theoretical risk of greater afterdrop not
born out by the clinical trials
rewarm at ~20C/hr with afterdrop usually
less than 0.30C
no advantage to trunk only immersion
practical problems in clinical use
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AV anastomosis rewarming
based on the anatomy and physiology of
the blood supply of the hands, and to a
lesser extent the feet
theoretically attractive but no more
effective than passive rewarming in
practice
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Forced air rewarming
heat sources that direct a constant hot air
flow over the patient through a disposable
blanket
widely available and often used
high initial purchase cost but disposable
blankets are cheap
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Forced air rewarming - results
supported by best clinical RCT to date
no afterdrop in clinical trials
rewarming rate of 2.50C/hr in patients with
moderate to severe hypothermia
no apparent complications in use
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Other external rewarming
therapies
Radiant heat
Plumbed garments
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both used clinically in various settings
probably effective but evidence hard to find like all therapies the heat delivered must
outweigh the inhibition of the usual heat
generating mechanisms
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Inhalation rewarming
the subject of considerable debate in the
literature
only delivers a small amount of heat esp if
not humidified
proponents claim added benefits of
decreased heat loss, heat delivery to
brainstem and core, improved mucociliary
function
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Inhalation rewarming - results
field devices no better than passive
rewarming
in hospital warmed, humidified devices
show no afterdrop and rewarming rates of
~1.50C/hr
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Radio frequency rewarming
using electromagnetic radiation to warm
structures deep to the skin esp torso
RF (13.56MHz) doesn't cause the
superficial burns assoc. with microwave
volunteer human studies only with variable
results
await dose finding studies
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Body cavity lavage
strong anecdotal evidence in humans
possible sites
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pleural
gastric
peritoneal
Bladder
mediastinal
rewarming rates of ~50C/hr in pleural
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Very hot IV fluids
dog studies only
fluids at 650C as IV tubing melts at higher
temps
delivered centrally
significantly higher rewarming rates
venous injury or haemolysis rare
role in humans undefined
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Extracorporeal
no RCT’s
strong anecdotal evidence
~20C/hr with VV or AV
~70C/hr with full cardiopulmonary bypass
(CPB)
risk of haemolysis and coagulopathy
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Does rewarming rate matter ?
rewarming rate tends to increase as
rewarming therapy becomes more
sophisticated
no evidence that this improves outcome
largest series to date used only passive
and inhalation rewarming in all but 2 of
620 cases
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The practical issues in choice
bath rewarming limits patient access
no commercial RF devices
extracorporeal has limited availability
forced air and inhalation are widely
available and apparently without
complication
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CASE 1
REWARMING
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Warm oxygen
Warm fluids
Warm air blanket
Bladder lavage
Gastric lavage
Pleural lavage
Temperature raised to 33 C over 5 hours
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OUTCOME
3 cycles of ACLS universal algorithm for
PEA/ asystole once warmed
No return of circulation so resuscitation
terminated.
DIED
Subsequent toxicology all negative
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Prognostic factors 1
Individual/environmental
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rate of cooling
underlying medical illness
duration of exposure
additional injuries
Vital signs
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presence of vital function
initial core temperature (<15 C)
initial heart rhythm and rate
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Prognostic factors 2
Laboratory values predictive of poor
outcome
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low paO2
serum potassium (>10mmol/L)
serum fibrinogen (<0.5g/L)
serum ammonia (>250μmol/L)
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Rewarming recommendations
measure core temperature
treat underlying cause
is rewarming indicated
>320C - passive rewarming
<320C or not shivering
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if arrested - CPB if possible, left pleural lavage
if not
non arrested - warmed humidified O2 +/forced air rewarming
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GUINNESS BOOK OF RECORDS
TYPE STUFF
Coldest survivors with
intact CNS
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Adult 16 C
Child 14.8C
Longest CPR in intact
survivor
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6.5 hours
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