By what percentage is tissue metabolic rate reduced during cardiopulmonary bypass at 30 degrees Celsius?

By what percentage is tissue metabolic rate reduced during cardiopulmonary bypass at 30 degrees Celsius?

• A. 10%
• B. 25%
• C. 50%
• D. 75%

Answer: (C)

Cooling tissues on cardiopulmonary bypass slows biochemical reactions, so their metabolic rate and oxygen demand fall as temperature drops. At 30°C, the body’s tissue metabolic rate is about half of what it is at normal body temperature, roughly a 50% reduction. This 50% decrease is a commonly used approximation in practice, reflecting how hypothermia protects organs during CPB by lowering their oxygen needs and allowing the circuit to sustain perfusion with reduced flow. Other options would imply different levels of suppression not consistent with 30°C: a 10% reduction would be far too small for this temperature, a 25% reduction suggests deeper cooling (around the 18°C range), and a 75% reduction would indicate even more profound hypothermia than is typical at 30°C.

Cooling tissues on cardiopulmonary bypass slows biochemical reactions, so their metabolic rate and oxygen demand fall as temperature drops. At 30°C, the body’s tissue metabolic rate is about half of what it is at normal body temperature, roughly a 50% reduction. This 50% decrease is a commonly used approximation in practice, reflecting how hypothermia protects organs during CPB by lowering their oxygen needs and allowing the circuit to sustain perfusion with reduced flow.

Other options would imply different levels of suppression not consistent with 30°C: a 10% reduction would be far too small for this temperature, a 25% reduction suggests deeper cooling (around the 18°C range), and a 75% reduction would indicate even more profound hypothermia than is typical at 30°C.