Normal response of the heart to hypothermia

 

BENEFITS

 

1) Reduction in metabolic rate & O2 demands of the myocardium

i) MVO2 (myocardial oxygen consumption) decreases by 50% for  every 10oC reduction in temperature [assuming heart is arrested; not VF]

ii) greatest reduction in MVO2 in a quiescent heart is between 37o & 25oC; only small decrease in energy requirements achieved when cool below 25 oC

 

2) Retards progression of ischemic injury

i) Due to a reduction in O2 deficit during elective ischemia —> increases the tolerable period of ischemia

 

3) Reduces K+ necessary to accomplish arrest

 

4) Prolongs arrest

 

 

DETRIMENTS

 

1) Oedema

            i) complex etiology

            ii) usually transient and reversible after  reperfusion

 

2) Impair O2 dissociation

 

3) Impairs autoregulation

 

4) May induce VF

 

 

It must be emphasized that the benefits of diastolic arrest and hypothermia are additive, each component contributing to the total protection of the heart

 

 

K. C. Potger
Copyright © 2001