Bruce's Hypothermia Final prep Flashcards
4 Physiologic impacts of Hypothermia.
↓ metabolic rate
↓oxygen consumption
↓ enzymatic activity
– prolonged reaction rates
Reduction of 1 degree C =
metabolic rate reduction of 5%
Describes the relationship between biochemical reaction rates and and temperature
Q10
Total body oxygen consumption has a rate of
2
If you lower the temperature by 10 deg you will reduce oxygen consumption by ?
50%
5 Technical advantages of Hypothermia
↓blood flow ↓ flow through collaterals – Improved operating conditions ↓ fewer passes through circuit = Less trauma to blood ↓ 3rd Spacing
Mild Hypothermia
32-34 °C
Moderate Hypothermia
28-32 °
Profound Hypothermia
< 28 °C
Deep Hypothermia for circulatory arrest
~18°C
4 reasons to conduct deep hypothermic circulatory arrest?
• Repair of complex congenital cardiac lesions • Aortic arch reconstruction / type 1 Aortic dissections. • Uncontrollable hemorrhage • When ever exsanguinous surgical field is essential
Pathophysiology of Hypothermia
• Blood flow redistribution
• Electrolyte imbalances
• Catecholamine release
– increased SVR
Gradient based on gas solubility to reduce bubble formation ?
6°C
Hyperthermia (temps > 37) linked to
poor cerebral outcomes
Blood Gas Strategies during Hypothermia.
Alpha Stat :
Maintain the PCO2 at 40 at 37°C
Blood Gas Strategies during Hypothermia.
Ph Stat:
Maintain the PCO2 at 40 mmHg at the actual temperature.
Temperature sensor in the human body?
- Anterior hypothalamus
- skin
- spinal cord
Receptors in the skin, spinal cord, and abdomen stimulate what ?
Posterior hypothalamus to cause heat conservation by:
- Peripheral vasoconstriction
- Pilo Errection
- Vasodilation of the muscle bed > Shivering
1 °C decrease in temp =
DO2 decrease by 5%
Core temp has reached 32°C. what is the DO2
DO2 reduced by 25%
Core temp has reached 28°C. what is the DO2
DO2 reduced by 50%
5 ways to minimize cerebral damage?
- < 60 min circ arrest
- Slow uniform cooling
- Control of hyperglycemia
- Control of acid base management
- Use of cerebral perfusion techniques in prolonged arrest
As temperature decreases what 3 things happen?
- CO2 becomes more soluble.
- PaCO2 decreases
- Ph increases
Why might you observe an increase in reservoir volume after initiating CPB with cold arterial blood being pumped?
Hypothalamus orders the release of Epi & Nor-epi > peripheral vasoconstriction > Increased bloow flow into the deep arteries > increased volume in the reservoir.
Deep hypothermia 18-28°C to Profound Hypothermia 0-18°C may lead to what ?
3rd spacing throughout the entire body
Decreased core temp causes what to the kidneys?
-Increased urine production “Cold induced diuresis”
Decreased core temp causes what to the electrolyte metabolism?
- Decreased effectiveness of the Na+ / K+ pump
- changes in cell membrane permeability
Decreased core temp causes what to the Endocrine system?
Insulin secretion is blocked > decreased movement of glucose into the cell > Hyperglycemia for the duration of hypothermia.
During rewarming, the brain rewarms much faster than any other tissue bed. This creates a risk for cerebral hyperthermia while other tissue beds are still rewarming. Monitor the following ?
Bladder temp &
Esophageal temp to 37°C
Hypothalamus exerts ____ times as much influence on vasoactivity as does the skins thermoreceptors.
10 - 20
