Hypothermia/DHCA

What happens to all organs during hypothermia & examples of the important ones

• ↓BF to all organs

• Greatest: skeletal muscle/extremities

• kidneys

• splanchnic beds

• heart

• brain

Hypothermia to Heart

• HR ↓ (bradycardia)

• Contractility → or ↑ (body might try to compensate)

• dysrhythmias are common with cooling

• coronary BF is well preserved

Hypothermia to lungs

• ↓ventilation (in general since we are lungs w/ oxy)

• gas exchange is unaffected

Hypothermia to Kidneys

• Largest proportional ↓ in BF

• ↑ in renal vascular resistance (↓ urine output)

• ↓O2 delivery

• ↓transport of Na, H2O, Cl

• impaired ability to concentrate

• tubular reabsorption ↓

• impaired glucose handling

  • May show up in urine

Hypothermia to Liver

• BF ↓ in proportion to ↓CO

• ↓ in metabolic & excretory functions of liver

• might need to adjust drug dosages

  • (drugs might not get broken down by liver, so ↑ conc in bloodstream/↑ half life)

Hyperglycemia

• Often present during CPB

• d/t ↓ insulin production

• keep BS levels <180 mEq/L w/ insulin drip or bolus

How to treat viscosity?

hemodilute the pt by ↓ Hct to b/w 20-30%

• O2 carrying capacity may be reduced

• but blood/O2 is actually getting to the microcirculation

Hypothermia on SVR & PVR

• SVR & PVR both ↑ d/t vasoconstriction

What appears in capillaries at low temps

arteriovenous shunts appear (anastamoses)

• thoroughfare channel b/w arterioles & venules where no gas exchange occurs so further ↓O2 delivery to tissues

Why does thrombocytopenia occur at hypothermia

d/t reversible sequestration of platelets in the portal circulation

• A) L coronary artery

• B)R coronary artery

• C)Brachiocephalic artery

• D)R subclavian artery

• E)R common carotid artery

• F)L common carotid artery

• G)L subclavian artery

Retrograde cerebral perfusion

• Hypothermic oxygenated blood perfusing brain retrogradely via SVC

• deoxygenated blood returning via carotids to aortic arch

Antegrade cerebral perfusion

• Hypothermic oxygenated blood perfusing brain via right subclavian artery (clamped off to aorta)

• deoxygenated blood returning thru contralateral carotid artery & IVC