Hypothermia in Injury Care
Outline
HYPOTHERMIA IN INJURY CARE
HYPOTHERMIA
Neuroprotective
Cold cardioplegia
Pediatric heart anomalies
Environmental exposure: prolonged survival (drowning)
Trauma
Randomized, prospective
392 patients from 7 level I centers
Isolated major brain injury
Clifton, Miller, Sung, et al. Lack of Effect of
Induction of Hypothermia after Acute Brain Injury NEJM 2001
Hypothermia:
reduces intracranial pressure
diminishes harmful biochemical cascade
NEUROPROTECTION after CARDIAC ARREST
Induction of hypothermia within one hour
in survivors of cardiac arrest resulted in
significantly improved neurologic outcomes.
Bernard, Gray, Buist, et al. NEJM 2002
Holzer. NEJM 2002
We need a study of hypothermia as a neuroprotectant in
traumatic brain injury with induction beginning < 1 hour of injury.
GRADES OF HYPOTHERMIA
Mild -tachycardia, tachypnea, diuresis,
apathy, vasoconstriction, shivering
Moderate -cardiac conduction disturbances, hypo- ventilation, hallucinations
Severe -severe dysrrhythmias, renal bl. flow
decreased metabolism, areflexia
shivering stops
Profound - asystole
4 MECHANISMS OF HEAT LOSS
radiation: heat loss to surrounding objects
evaporation: heat loss to vaporization of water
conduction: direct contact with cold surface
convection: heat loss to overlying air currents
CARDIAC OUTPUT & BLOOD PRESSSURE
dec myocardial compliance = inc filling pressures required
MYOCARDIUM
slowing of depolarization
QRS widening
PR prolongation
T inversion
J waves
a-fibrillation, bradycardia
low threshold for V-fib
asystole
HYPOTHERMIA AND COAGULATION
Hypothermia impairs:
1. intrinsic pathway, ( APTT )
2. extrinsic pathway, as measured by the (PT)
3. common pathway as measured by the Thrombin Time
4. platelet function as measured by the Bleeding Time
Clotting times performed at 37 C per lab protocol
NL. LAB CLOTTING STUDY NL. IN VIVO CLOTTING
TEMPERATURE EFFECTS on PLATELET FUNCTION
Wolberg, et al, J Trauma, June 2004
RECOMBINANT FACTOR VIIa
Will rFVIIa work in cold trauma patients?
Decreasing the pH of the reactions decreased the rate
of FXa formation by the FVIIa/TF complex.
Rate of FX activation by rFVII was actually increased
by falling temperature
“RFVIIa should be effective in enhancing
hemostasis in hypothermic patients…however..
its efficacy may be reduced in acidotic patients.”
Meng et al, J Trauma, Nov 2003
HEMATOLOGIC EFFECTS OF HYPOTHERMIA
1. Increased blood viscosity
microcirculatory flow
O2 delivery
2. Hgb P50 : shift to left
3. Diminished clotting function
platelets
clotting factors
LETHAL TRIAD
Acidosis
Hypothermia
Coagulopathy
HYPOTHERMIA IN TRAUMA: PREDICTOR OF SURVIVAL?
ISS CORE TEMP (C) MORTALITY (%)
> 50 < 32 100
32-33 40
> 33 25
25-29 < 32 100
> 32 3
Jurkovich GJ, et al
J. Trauma 27:1019,1987
PREVENTION
1. Avoid cold fluids
2. Avoid cold rooms
3. Avoid wet surfaces
4. Cover the patient
5. Treat shock well and quickly
Minimize exposure heat loss
Control Your Thermostat
REWARMING TECHNIQUES
ACTIVE CORE REWARMING
1. warm intravenous fluids
2. airway rewarming
3. warm peritoneal / pleural lavage
4. continuos arteriovenous rewarming
5. continuos venovenous rewarming
6. cardiopulmonary bypass
Standard Rewarming vs. CAVR
Randomized, prospective
57 hypothermic patients
85% blunt trauma
CAVR
Faster rewarming
Less fluid requirements (24 vs. 32 L)
Lower early mortality
But no overall mortality advantage
or differences in complication rates
Gentilello, et al, J Trauma, 1997
Forced air convection blankets aka: BAIR Hugger
IV Fluid warmers
HOW HOT IS TOO HOT?
Anaesthetized beagles cooled to 30 C and
shocked to MAP of 40 mm Hg
Ringer’s Lact. Soln via central vein
60 °C vs. 40 °C
No difference in:
RBC destruction (as measured
by osmotic fragility or plasma free hb)
endothelia cell damage
Faster warming (3.6 °C / hr. vs. 1.9 °C / hr)
Hyperthermic crystalloid is safe and faster
Wiley, et al. J Trauma 2000
|
Ministry of Health
