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561 - Perfusion Technology > Exam 9 - Hypothermia & Bypass > Flashcards

Exam 9 - Hypothermia & Bypass Flashcards

1
Q

Bigelow

A
  • First to introduce idea of hypothermia
  • 1950
  • Used animals
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2
Q

Lewis

A
  • First application of hypothermia in cardiac surgery
  • Closed ASD
  • Used surface cooling
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3
Q

Sealy

A
  • Used hypothermia with CPB circuit
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4
Q

Thermoregulation

A
  • Thermoreceptors in skin
  • Causes hypothalamus to trigger sympathetic
  • Vasoconstrict skin vessels
  • Vasodilate skeletal muscles
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5
Q

Endocrine affect on thermoregulation

A
  • Increase O2 consumption
  • Increase HR
  • Increase CO
  • Increase BP
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6
Q

Induced hypothermia

A
  • can be global or localized
  • buys time in case something fails on CPB
  • decreases metabolic demand
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7
Q

Why do we induce hypothermia

A
  • reduce ALL metabolic rate
    - especially enzyme reactions / clotting
  • reduce O2 consumption
  • Preserve high energy phosphate stores
  • Reduces excitatory neurotransmitter release
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8
Q

Benefits of hypothermia on CPB

A 
- Allows lower pump flows
   ~ lower the temp -> lower the flow (because lower O2 used)
- better myocardial protection
- less blood trauma
- better organ protection
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9
Q

Mild Hypothermia

A
  • 32-35

- Most common level

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10
Q

Tepid Hypothermia

A
  • 35-37
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11
Q

Moderate Hypothermia

A
  • 28-31
  • Bigger cases like CABG, DaVinci, AAA
  • Peds
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12
Q

Deep Hypothermia

A
  • 18-27
  • More complex cases
  • Peds
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13
Q

Profound Hypothermia

A
  • <18
  • Circulatory arrest
  • Peds
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14
Q

Affect of hypothermia on blood flow

A
  • biggest decrease to skeletal muscles/extremities
  • also decreases:
    - kidneys
    - splanchnic beds
    - heart
    - brain
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15
Q

Hypothermia on the heart

A
  • Decreased HR
  • Same or Increased contractility (tries to maintain CO)
  • Dysrhythmias common but cause unknown
    ~ electrolytes? Uneven cooling? ANS?
  • Coronary blood flow well preserved
    ~ this means dysrhythmias not due to ischemia/hypoxia
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16
Q

Hypothermia on Lungs

A
  • Decrease ventilation
  • Gas exchange unaffected
  • Doe snot matter if on CPB
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17
Q

Hypothermia on kidneys

A
  • Largest PROPORTIONAL decrease in blood flow
  • Increases renal vascular resistance
  • decrease blood flow to inner/outer cortex
  • decrease O2 delivery
  • Na/H2O/Cl transport decreased (slow active transport)
  • Impaired ability to concentrate/reabsorb (slow active transport)
  • Impaired glucose handling (shows in urine)
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18
Q

Hemodilution and hypothermia after bypass

A
  • Hemodilution/hypothermic bypass improves renal blood flow and protects renal tubules post-op
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19
Q

Hypothermia on Liver

A
  • Blood flow reduced in proportion to reduction in CO
  • decrease in metabolic and excretory function
  • changes drug actions/requirements
    - need to adjust drug dosages
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20
Q

Hyperglycemia

A
  • Happens on hypothermic CPB
  • Decreased insulin production
  • Patient does not respond to insulin if given on cold CPB
  • Also caused by giving dextrose in cardioplegia
21
Q

Blood viscosity and hypothermia

A
  • Water moves from plasma into the cells
  • increases Hct
  • increase in viscosity
    - need to hemodilute patient…especially if circ. arrest
22
Q

O2 carrying capacity

A
  • reduced if on hypothermia
  • BUT blood/oxygen is actually getting to microcirculation
  • If temp decreases….gas is more soluble in blood
23
Q

SVR and hypothermia

A
  • SVR/PVR increases
  • Big effect if < 26
  • increase in viscosity/ epi and NE/ hemoconcentration/ cell swell
  • Thoroughfare channels form…decrease O2 to tissues
  • Thrombocytopenia…less platelets
24
Q

Clinical use of Hypothermia

A
  • Mild to moderate (> 25)
  • Profound selective myocardial hypothermia
    • used during aortic x-clamp
    • topical ice
    • cold cardioplegia
    • get to 2-4 but NOT freezing….freezing kills cells
25
Q

Methods of hypothermic induction

A
  • Surface cooling….ice
  • Core cooling…using CPB
  • Deep hypothermic circ. arrest (drain all blood into VR)
  • Low/Intermittent flow deep hypothermic circ. arrest
    - circ arrest for so long need to flush out metabolic waste
26
Q

Surface cooling uses

A
  • Small infants less than 2.5 kg

- Myocardial protection on adults and peds

27
Q

Profound hypothermia with arrest uses

A
  • Repair complex congenital heart defects (infants/children)
  • Aortic arch operations
  • venous drainage difficulties
  • surgeon has trouble seeing
  • If arrest > 60 min…use intermittent arrest…low flow…is safer
28
Q

Biochemical reactions and hypothermia

A
  • all rxns decrease in rate
  • metabolic / humoral / coag cascades decrease
  • cellular functions decrease
    - communication / receptor mechanisms / membrane proteins
29
Q

Q10 principle

A
  • relates increase/decrease in rxn rates/metabolic processes to a temperature change of 10 degrees
  • Example: Q10=2
    - rxn will double with a 10 degree increase in temp.
    - rxn will be cut in half for a 10 degree decrease in temp.
  • Q10 range in humans: 1.9-4.2 (mean = 2)
    - most rxns are 2-3
  • Q10 bigger at lower temps
30
Q

7 degree principle

A
  • deals with O2 demand
  • reduced by 50% for every 7 degree drop in temp
  • @30: VO2 is 50% of normal
  • @20: VO2 is 25% of normal
  • Anesthesia and muscle relaxers will decrease further
31
Q

Hypothermia and gas solubility

A
  • Solubility increase if decrease in temp
  • Partial pressure down if decrease in temp
  • SO….total content does not change
    - just the proportions of components change
32
Q

Henry’s law

A

I. Pressure increase -> solubility of gas in liquid increases
II. Temp increase -> solubility of gas in liquid decrease

  • Content = partial pressure x solubility
  • Temp is DIRECTLY related to partial pressure
  • Temp is INVERSE to solubility
33
Q

PO2 / PCO2 and Temp

A
  • Increase temp -> decrease solubility -> increase partial press.
  • decrease temp -> increase solubility -> decrease partial press
  • NO CHANGE in total gas content w/ change in temp
34
Q

Profound hypothermia concerns

A
  • Homogeneity of cooling:
    • if cool unevenly…hurt tissues
    • rate of cooling / temp gradients
  • Homogeneity of warming:
    • if warm unevenly…. bubbles
    • need to warm much slower than cool…bubbles
    • exposure to hyperthermia…protein denature
35
Q

Rate of cooling/warming

A
  • Cool at 1 degree/min
  • Warm at 1 degree/ 3-5 min
  • If too fast:
    • build temp gradients / body cooling after CPB (gradients) / hyperthermia (cook brain)
36
Q

Rate of cooling/warming limitations

A
  • Water temp in heat exchanger
  • BP and SVR
  • Flow rate
37
Q

Temp gradients

A
  • Keep at 6 degrees
    • reduce GME generation / too fast cool or rewarm
  • Keep pO2 less than 200 mmHg
  • Gradient between:
    • HE / venous blood
    • patient / arterial blood
38
Q

Hyperthermia causes

A
  • Warm too fast
  • Efficiency of HE (more/less than expected)
  • High water temps
  • Not paying attention
  • Causes cerebral injury
39
Q

DHCA

A
  • Deep hypothermic circ arrest
  • 18-20 degrees
  • turn off pump for 30-60 min
  • Brain at greatest risk
  • Optimal depth of cooling?
    - multiple temp site monitoring / EEG cessation
40
Q

Normal way to DHCA

A
  • On CPB
  • Cool
  • XC and CPG
  • Off CPB (arrest)
  • On CPB and warm
41
Q

Alternative way to DHCA

A
  • On CPB
  • Cool
  • Off CPB (arrest)
  • XC and CPG
  • On CPB and Warm
  • sometimes on peds
  • if cant give CPG right away
  • have to turn on pump before giving CPG
42
Q

DHCA benefits

A
  • allows exposure
  • reduces metabolic rate and molecular movement
  • cessation of circulation
  • excitatory neurotransmitter reduction
43
Q

DHCA negatives

A
  • neurological injury / morbidity
  • brain is at risk
  • > 60 min is detrimental
  • > 40 min increases risk
44
Q

HLFB / HILFB

A
  • Safer than just DHCA
  • lower rates of neural dysfunction
  • getting more common
45
Q

How to increase brain tolerance to ischemic insult

A
  • Thiopental: short acting barbituate (slows brain metabolic)
  • Solumedrol: anti-inflammatory / stabilize cell membranes
46
Q

How to achieve homogenous temp

A
  • rate of warming/cooling
  • hemodilution
  • acid/base management
  • head on ice
47
Q

Better recovery - reprofusion conditions

A
  • Perfusate temp
  • Perfusate composition: mannitol / bicarb / etc
  • Rewarming tools:
    • bear hugger
    • warming blanket
48
Q

Sequence of CPB

A
  • Patient brought in
  • ECG leads placed by anesthesia
  • IVs placed
  • Art line placed in radial/femoral
  • Baseline ABG and ACT
  • Swan cath placed / central line placed / CO recorded
  • Patient put under
  • Patient intubated
  • Foley cath placed
  • Temp probes placed (bladder/nasopharyngeal/rectal)
  • Patient prepped
  • Patient draped
  • Lines to table
  • Incision made
  • Sternum split
  • LIMA taken down
  • Saph vein harvested
  • Heparin given and post-Hep ACT from anesthesia
  • Purse strings
  • Arterial cannula inserted
  • Pump sucker on
  • Venous cannula inserted
  • Check ACT and ON CPB
  • Monitor Temp
  • Fill CPG line
  • Flow down for XC (1L)
  • XC on and flow up (watch pressures)
  • CPG (vent off for antegrade)
  • Vent on
  • Draw ABG/VBG/ACT
  • More CPG
  • Rewarm
  • Hotshot
  • Check ECG
  • Flow down and XC
  • Flow up (watch pressure)
  • ABG/VBG/ACT draw
  • Wean off CPB / Fill heart / flow down
  • STOP CPB
  • Calculate protamine dose
  • Give protamine (suck and vent off)
  • Post protamine ACT
  • Wires in and stop bleeders
  • Close chest and twist wires
  • Close skin
  • Lines from table
  • Transport patient

561 - Perfusion Technology (12 decks)

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