Flow reduction and cessation in infant and pediatric cardiac surgery / Pedi Test 2 Flashcards by JR Gallegos

Ground squirrel

– Respiratory rate drops from 200 per min to

4 to 5 per min, HR from

150 to 5.

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Wood Chuck Drops its body temperature more than ?

30°

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Jumping Mouse

– Reduce heart rate from 500 to 600 BPM to

30 BPM

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O2 Consumption Vs. Temperature
y axis = O2 comsumption
x axis = Perfusion flow rate

What is the summary of this graph?

The colder we make he patient, the less requirements for oxygen, which allows us to decrease our flow rate.

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Myocardial oxygen uptake of the
Beating heart at 37° celcius?

Beating heart:
Fibrillating heart:
Arrested heart:

Beating heart: 5.5 L/m
Fibrillating heart: 6.5 L/m
Arrested heart: 1 L /m

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Myocardial oxygen uptake of the
Beating heart at 32° celcius?

Beating heart:
Fibrillating heart:
Arrested heart:

Beating heart: 5.0 L/m
Fibrillating heart: 4 L/m
Arrested heart: .75 L /m

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Myocardial oxygen uptake of the
Beating heart at 28° celcius?

Beating heart:
Fibrillating heart:
Arrested heart:

Beating heart: 4 L/m
Fibrillating heart: 3 L/m
Arrested heart: .50 L/m

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Myocardial oxygen uptake of the
Beating heart at 22° celcius?

Beating heart:
Fibrillating heart:
Arrested heart:

Beating heart: 3 L/m
Fibrillating heart: 2 L/m
Arrested heart: .25 L/m

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What does CMRO2 stand for ?

Cerebral Metabolic Rate of O2

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CMRO2 drops as the temperature drops from 37 to 14 degrees. What is the drop of CMRO2

from 100% to 10%

then goes back up to 100% as we return to 37 degrees.

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The fundamental effects of hypothermia is

the progressive reduction of molecular movement through, passive transport and active transport.

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Q10

reaction rate changes for every 10°C change in temperature

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Simple diffusion

Through solution, down the gradient

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Facilitated diffusion:

across a membrane, down the gradient, via membrane carriers

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Active Transport :

Transport across membranes, up concentration gradient, via pumps and ATP

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Hypothermia reduces metabolic rate and facilitates:

– Reduced blood flow
– Reduced blood trauma
– Reduced surface contact (blood to circuit)
– Safety buffer

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Hypothermia reduces metabolic rate and facilitates a safety buffer that could be caused by :

Accident

* Regional perfusion deficits

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The virtues of hypothermia come at a cost, Disruptions may occur due to differential
reduction of transport mechanisms such as ?

Electrochemical gradients

* Osmotic gradients

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A technical reason for reducing flow is the presence of collateral blood flow caused by ?

– Wash out cardioplegia

– Increase tissue temperature – Cerebral steal

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A technical reason for reducing flow is a small playing field ?

Tiny hearts with big
cannulas make for poor visualization and
unsuccessful surgeries

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Congenital Heart Defects with reduced pulmonary blood flow ?

Tricuspid Atresia 
Tetralogy of Fallot
TAPVR
Pulmonary Stenosis
Ebstein's Malformation

2 Technical approaches to reducing flow ?

Low Flow Cardiopulmonary Bypass (LFCPB)

Deep Hypothermic Circulatory Arrest (DHCA)

During the clinical testing of LFCPB vs. DHCA, what were the findings:

DHCA had a significantly higher incidence of seizure

The estimated probabilities of definite seizures in infants following repair of transposition of the great arteries with VSD or intact ventricular septum (IVS). Which group had a higher incidence for seizures post circulatory arrest ?

Patients with VSDs

Ictal definition ?

relating to or caused by a stroke or a seizure

In regards to our biochemical parameters, we can expect an increased Lactate release during?

Rewarming

In regards to our biochemical parameters, we can expect an increased release of isoenzyme ______ 6 degrees s/p surgery.

CK an enzyme marker of myocellular injury

CMVO2 definition ?

Cerebral mixed venous oxygen saturation.

CMVO2 returns to normal in ?

2-4 hours after profound hypothermia

Cerebral vascular resistance (CVR) Remains elevated for ?

6-8 hour after | profound hypothermia

What where the outcomes for Children randomized to DHCA (especially with VSD) ?

lower developmental scores at 1 year and 2.5 years

During LFCPB with flows less than 30 ml/kg, what can we expect ?

``` – Undetectable flow using Trans Cranial Doppler – Reduced cerebral oxygen consumption – Development of Oxygen debt in the brain ```

During LFCPB with flows less than 30 ml/kg, why can we expect a development of Oxygen debt in the brain?

results from anaerobic metabolism

4 Proper techniques for LFCPB ?

``` • Even Cool (long time) • Use appropriate blood gas strategy • Pack head in ice ? • Maintain blood flow greater the 30 ml/kg ```

If blood flow is creating a real problem for the surgeon what can we do ?

DHCA may be better than a sub-par surgical repair

Proper techniques for LFCPB maintains continuous blood flow but may expose brain to ?

increased embolic load (bad)

In an attempt to avoid DHCA and try to palliate a CHD patient, what will delaying the surgery lead to ?

• Increased collateral vessel development • the patient continues to suffer from secondary effects on the central nervous system, the pulmonary arteries, the airways, and the heart itself.

In the safe circulatory arrest times vs. temperatures graph, we can assume that ?

The colder we get down to 18 degrees, the longer the duration of total circulatory arrest. At 18 degrees = 45 min of safe total circulatory arrest with 70% probability.

The predicted safe duration of HCA at 15 degrees C is only

29 min

Subjects were reperfused for 20 minutes at 20°C and then rewarmed with (cold reperfusion). This study resulted in what?

↓ cerebral edema & ↓ Intracranial pressures Diastolic flow velocity returns after 20 min

With DHACA we may reduce the embolic load on the brain (good), but ?!?!?

DHCA interrupts cerebral blood flow (bad)

7 proper techniques for DHCA?

``` • Even cooling • Pack head in ice • Appropriate blood gas management • Pharmacology – steroids and/or barbiturates • Minimize arrest time (periodic reperfusion?) • Cold reperfusion • Respect the 6 degree temperature gradients when warming. ```

HCT vs. Cerebral blood flow graph conclusion ?

Hgb concentration of 7 to 9 produced a higher cerebral blood flow.

During Hypothermia Blood viscosity increases (capillary sludging), Therefore CBF would ?

↓ CBF | ↓ CDO2 (O2 delivery)

During Hypothermia, how can we Counteract temperature mediated increased viscosity ?

By decreasing HCT to | Maintain CBF which would lead to ↑ CDO2.

Cerebral ischemia does not result from

low Hct perfusion

Severe hemodilution (10%) results in what?

inadequate cerebral tissue oxygenation during cooling

Higher Hcts greatly reduced priming of

leukocytes

Higher Hct does not impair CBF

( 10,20, and 30% Hct) Greater Oxygen delivery is good

During Hct. Vs. Temp the Difference between 15 and 25 degrees was ?

Important

Blood is appropriate solution for

buffering ischemic environment

Cerebral ischemia has been shown, following what?

low hct perfusion