Download Hypothermia - St. Mary Medical Center Langhorne PA

Systemic Hypothermia
Philip Wry, MD, FACS
St. Mary Regional Trauma Center Annual Conference
May 5, 2011
Systemic Hypothermia
 Human physiology functions within a relatively
narrow core temperature range
 The effects of hypothermia on military
campaigns has been noted for thousands of
years
 Napoleon’s chief surgeon noted injured
patients farthest from the fire were most likely
to die
 German’s (WW II) recognized the absolute
lethality of immersion hypothermia with
U-boat crews in the North Atlantic
Pathogenesis Hypothermia
 Altered Central thermoregulation
 Inability to Produce sufficient metabolic heat
 Unalterability of heat Losses
 Primary hypothermia: Excessive exposure to cold,
wind, snow ,water, or altitude
 Secondary hypothermia: patient becomes cold in
normal environmental temperature, secondary to
underlying condition such as trauma, myxedema,
sepsis; higher mortality than primary
Pathogenesis of Hypothermia
 Exercise and Shivering are the only
effective compensatory methods for
raising heat production
 At rest, most heat is generated by
energy-consuming processes within the
viscera
Pathogenesis Hypothermia
 Elderly, alcoholic, and chronically ill have
impaired heat generation owing to reduced
lean body mass, impaired mobility,
inadequate nutrition, reduced shivering;
also, impaired vasoregulatory responses
and ability to sense temp extremes
 Children are more susceptible due to
increased BSA and limited energy sources
Pathogenesis Hypothermia
 Altered Central Thermoregulation:
 Medications altering central dopaminergic tone
(phenothiazines, barbiturates, lithium, α-blockers)
 CNS disease states (Parkinson's disease, stroke,
multiple sclerosis)
 Chronic illness (hypothyroidism, hypopituitarism,
hypoadrenalism, diabetes, uremia)
Classification Hypothermia
 Defined as a core temp below 35ºC
 Mild: 35oC to 32oC (95oF to 89.6oF)
 Moderate: 32oC to 28oC (89.6oF to 82.4oF)
 Severe: below 28oC (82.4ºF)
 With Trauma:
 Below 36oC (98.6oF),
Severe below 32oC (89.6oF)
Signs of Hypothermia
 Depends on degree of hypothermia
 Depressed level of consciousness most
common finding
 Vital signs are variable
 Absence of respiratory and cardiac
activity can be absent in patients who
eventually recover
 Severe cases: patient is cold to touch and
appears gray and cyanotic
Mild Hypothermia (32º to 35º C)
 Patients are not usually seriously ill and present with





stable vital signs
Heart rate, blood pressure, and respiratory rate are
typically increased with the metabolic demands of
increased themogenesis
Shivering should be seen unless thermoregulation is
impaired (can be mistaken for rigors)
Mental status is generally intact, some patients
present with mild to moderate lethargy to
confusion
Screening labs are normal
Findings are nonspecific and easily missed
Moderate Hypothermia (28º to 32º C)




Hypotension is common
Shivering is notably absent
Muscle tone is rigid
Arrhythmias such as atrial fibrillation,
reentrant SVT, and ventricular ectopy are
common
 Patients often obtunded or incoherent
 Pupillary dilation present below 30º (86ºF)
 Diagnosis of hypothermia can be mistaken for
intoxication
Severe Hypothermia (below 28ºC)
 Patient may appear dead
 Vital signs usually not present
 Demonstrable neurological function is
absent including deep tendon, oculocephalic,
and corneal reflexes
 Ventricular fibrillation present in more than
50 % patients
 Laboratory abnormalities such as
hemoconcentration become more profound
End-Organ Effects
Central Nervous System Effects
 At mild levels dysarthria, bradykinesia, confusion and




impaired memory and judgement can be seen
CNS vascular autoregulation is lost at 25ºC causing
concomitant decrease in cerebral blood flow
Ischemic threshold is higher due to decreased
cerebral metabolism
Below 32ºC patients stop complaining about cold and
shivering stops
Delayed autonomic nervous system conduction
velocities can cause profound orthostasis,
transport in head down position
Central Nervous System Effects
 Below 25ºC EEG is typically silent and brain
stem reflexes may be lost
 Brain Death even after CPR should not be
diagnosed until core temp restored
 Complete recovery from full cardiac arrest at
25ºC without CNS sequelae has been
documented
Cardiovascular Effects
 Initial tachyarrhythmias and vasoconstriction
of mild hypothermia progresses to atropinerefractory bradycardia
 Below 32ºC cardiac output , myocardial
compliance, cardiac contractions, and stroke
volume decrease
 SVR may remain elevated from
vasoconstriction, hemoconcentration and
increased blood viscosity
Cardiovascular Effects
 33oC (91.4oF): Cardiac irritability
 28oC (82.4oF): Ventricular Fibrillation
 25oC (77oF): Asystole
Cardiovascular Effects
 Oxygen Consumption and Metabolic Rate
decrease
 V Fib more common below 28ºC precipitated
by movement, procedures, changes in acidbase, Pco2, and O2
 Asystole occurs below 25ºC
Pulmonary Effects
 Depression of ventilatory drive and
decreased pulmonary compliance
 Below 32ºC: CO2 sensitivity attenuated
 Bronchorrhea, bronchspasm, and blunted
cough reflex lead to atelectasis and gastric
aspiration
 Noncardiogenic pulmonary edema due solely
to hypothermia is controversial
 O2-Hgb dissociation curve shifts Left
Renal Effects
 ADH resistance and tubular dysfunction
cause a Cold Diuresis
 Renal perfusion and glomerular filtration are
decreased
 Tubular secretion of hydrogen leads to
acidosis
 Oliguria occurs after intravascular volume
depletion
 40% incidence of Acute Renal Failure
GI and Hepatic Effects
 Pancreatitis 20% to 30%,
decreased insulin secretion
 Hyperamylasemia 50%
 Gastric hypomotility and shallow punctate
ulcers (Wischnevsky’s ulcers)
 Hepatic clearance of meds decreased,
glycogen stores depleted (shivering)
 Avoid Lactated Ringer’s, reduced lactate
conversion by liver may worsen metabolic
acidosis
Hematologic Effects
 Hemoconcentration induced by plasma
extravasation, Hematocrtit increases 2% for
every one-degree (ºC) decline in temp
 Bone Marrow Suppression results in
thrombocytopenia, granulocytopenia, and
erythroid dysplasia
Hematologic Effects
 Coagulopathy due to cold inactivation of
coagulation enzymes
 Thrombocytopenia compounded by splenic
sequestration
 Qualitative platelet dysfunction from
decrease in thromboxane B2
 Classic DIC and hypofibrinogenemia in
severe cases
Immune Response
 Immune Response Impaired
 Reduced enzymatic function of WBCs
 Reduced reactive oxygen intermediates produced
by PMN leukocytes
 Reversible inhibition of the transcription and
expression of E-selectin
 Bacteria are at an advantage not being
homeothermic
 Clinical studies show increased risk for surgical
site infection, pneumonia, and other infectious
complications with mild hypothermia
Hypothermia in Trauma
 Hypothermia and Trauma exponentially
increase each others physiologic and metabolic
derangements
 Hypothermic trauma patients are at increased
risk of metabolic exhaustion evidenced by a
significant drop in ATP levels
 Hypothermia serves no clinical protective role
(by virtue of reduced cellular oxygen consumption
requirements), therein every attempt should
be made to aggressively prevent and
treat it
Laboratory Findings
 PH falsely Low, O2 and CO2 falsely high
on temp corrected ABGs
(avoid hyperventilation and bicarb)
 Elevated liver enzymes and
amylase
 No prototypical laboratory pattern
may have hypo or hyperkalemia
Electrocardiographic Findings
 Osborne J wave seen in hypothermia, SAH,
and myocardial ischemia so
not patholgnomic
 Notch and deflection at QRS-ST
 T wave inversion, prolongation
of PR, QRS, QT intervals,
ventricular and extraventricular ectopic
rhythms, and bradycardia (late)
 V Fib most common nonperfusing rhythm
Management of Hypothermia
Temperature Measurement
 Measure core temperature with a full range
rectal, bladder, or esophageal measurement
probe
 Intravenous electronic thermocoupling
temperature monitoring devises such as
pulmonary artery catheters are accurate but
may precipitate arrhythmias
 Infrared-sensing ear canal probes are now
quite accurate, not useful due
to vasoconstriction
Management of Hypothermia
 ABCs, airway-protective reflexes
commonly absent
 Endotracheal intubation secures airway and
provides a means to limit heat loss via the
airway, not a risk factor for arrhythmias
 Metabolic processes and reperfusion
accelerate as rewarming continues
 Intravascular volume restoration is
important, cold diuresis
 Assessment of volume status difficult
Management of Hypothermia
Pharmacologic Agents
 Bretylium: drug of choice for augmentation of
electrical defibrillation
 Dopamine may be only effective vasopressor
 ADH and Epinephrine may improve coronary
perfusion
 Magnesium has been used successfully with
arrhythmias
 Levothyroxine and Hydrocortisone useful
 Procanamide contraindicated (increases
incidence of V- fib)
Rewarming
 Passive external rewarming for mild to
moderate exposure, warming room, using warm
blankets, removing wet clothing (rise 0.5 to
2ºC/hr)
 Active external rewarming primarily forced air
warming devices (rise 2.5ºC/ hr), immersion
impractical, afterdrop
 Active core rewarming for severe exposure,
includes warmed IVFs (level I rewarmer),
warmed vent gases, peritoneal, pleural, gastric,
rectal lavage, hemodialysis, or cardiopulmonary
bypass
Rewarming
 Afterdrop drop in core temp seen with active
external rewarming, as patient warms and
vasodilates cold ,acidotic blood returns to heart
from periphery, lethal arrhythmias
 Pleural lavage warm fluid flows by gravity
through anterior chest tube out posterior chest
tube (rise 2ºC to 4ºC/hr)
 Peritoneal lavage use peritoneal dialysis or
DPL catheter and dialysate at 40ºC
 Gastric and rectal lavage small surface area, risk
of perforation
Extracorporeal Rewarming
 Cardiopulmonary Bypass standard of care
for rewarming a potential survivor without a
perfusing cardiac rhythm, arterial and venous
femoral catheters needed (rise 7ºC - 10ºC/hr)
 Hemodialysis use a standard venous
Hemodialysis catheter (Quinton)
Management of Hypothermia
 Care must be taken to identify an organized
cardiac rhythm; chest compression may
convert a perfusing rhythm to fibrillation
 Anoxic event and /or potassium >
10mmol/L should discourage CPR
Role of CPR in Hypothermia
 There are multiple yearly documented
reports of patients with hypothermic
cardiac arrest, and no signs of life
successfully resuscitated, after many hour
of CPR, without neurologic injury
 14ºC lowest survival core temp reported
 Should warm to 29ºC to 32ºC before declaration of
death
 Complete neurological recovery is possible following
an hour or more of asystolic cardiac resuscitation
QUESTIONS ?