test 9 Flashcards
Thermoreceptors in the skin
Causes hypothalamus to trigger sympathetic nervous
system response
Vasoconstriction of the skin vessels which decreases loss of heat by convection (move it all to core)
Vasodilation of skeletal muscle vascular beds (shiver)
Endocrine
Oxygen consumption increases
HR Increases
CO Increases
BP Increases
why use hypothermia
- buys time in case you need to stop blood flow
2. safety mechanism if something fails
why does hypothermia protect
Reduces metabolic rate (enzyme rxn slowed)
Reduces oxygen consumption
Helps preserve high energy phosphate stores
Reduces excitatory neurotransmitter release
general affects of hypothermia
Allows lower pump flows
Better myocardial protection
Less blood trauma
Better organ protection
mild hypothermia temp range
32-35°
moderate hypothermia temp range
28-31°
Deep Hypothermia temp range
18-27°
Profound Hypothermia temp range
< 18°
Alteration to Organ Function
Decreased blood flow to all organs: Greatest: Skeletal Muscle / Extremities Kidneys Splanchnic Beds Heart Brain
Heart function due to hypothermia
Heart rate – Decreased
Contractility – same or increased
Dysrhythmias
Lung function due to hypothermia
Decrease in ventilation
Gas exchange is unaffected
tepid hypothermia
35-37°
surgeries using mild hypothermia
- Aortic valve replacement
- most CABG
surgeries using moderate hypothermia
- valve and a CABG
- Mitral valve
- Davinci
- ascending aortic annurysms
surgeries from moderate down
-surgeries for kids
Kidney function due to hypothermia
Largest proportional decrease in blood flow
Decrease in active transport
Won’t reabsorb water
Hemodilution and hypothermic bypass improves renal blood flow and protects renal tubules post operatively
Liver function due to hypothermia
Blood flow is reduced in proportion to the reduction in cardiac output
⬇ in metabolic and excretory function of the liver
Drug actions / requirements
Hyperglycemia
Feature of hypothermic CPB
Decreased insulin production (decrease metabolic function of pancreas)
Give dextrose to increase glucose levels
SVR increases
Increase in viscocity Increase in catecholamines (Epi, NE) Hemoconcentration Cell Swelling Thoroughfare channel Further decrease in oxygen delivery to the tissues Thrombocytopenia
Methods of Hypothermia
Induction
Surface Cooling
Core Cooling
Deep Hypothermic Total Circulatory Arrest
When to use Surface Cooling
Small infants less than 2.5 to 3.0kg
Myocardial protection on adults and peds
when to use Profound hypothermia with arrest
Repair complex congenital heart defects – small infants
and children
Operations involving the aortic arch
If arrest period longer than 60 minutes
Use intermittent arrest with brief periods of hypothermic
flow
Low-flow hypothermic perfusion is safer than total arrest
Q10 Principle
Q10 = relates the increase or decrease in reaction
rates or metabolic processes to a temperature
change of 10˚C.
Reduction in Metabolic Rate
reduced oxygen demand by 50% for every 7°C drop in temperature
as pressure increases what happens to solubility of gas
increases
as temperature increases what happens to the solubility of gases
decreases
as temp increases, what happens to solubility and partial pressure
- Decreased solubility
- Increased partial pressure
Rate of cooling
Cool at 1°C per minute
rate of warming
Warm at 1°C per 3-5 minutes
Consequences of Cooling / Warming too fast
Development of temperature gradients within tissues
Body cooling after bypass
Exposure to hyperthermia
Rate of Cooling / Warming Limitations
Water temperature in heat exchanger
Blood pressure and systemic vascular resistance
Flow Rate
Rewarming
-rewarm slowly so that the peripheral vascular beds open up
Use tools to help you rewarm (after AoXC removal)
Bair Hugger
Warming Blanket
