Ped perfusion blood gases and hypothermia

Question 1

Why Pediatrics are NOT Small Adults

Answer 1

Major differences exist between adult and pediatric cardiopulmonary bypass, stemming from:
Anatomic differences Metabolic differences Physiologic differences

Question 2

myocytes and myofibrils are ______ in peds

Answer 2

larger

Question 3

the # of mitochondria in peds

Answer 3

increases as the oxygen requirements of the heart rises.

Question 4

The amount of sarcoplasmic reticulum and its ability

Answer 4

to sequester calcium similarly increase in early development.

Question 5

Activity of Na+/K+ adenosine triphosphatase (ATPase)

Answer 5

increases with maturation, and affects the sodium-calcium exchange.

Question 6

what factors affect the way in which the immature heart handles calcium (monitor calcium closely)

Answer 6

The amount of SR and ability to sequester calcium increase. Na+, K+ and Ca++ movement have increased activity

Question 7

Ca++ handling in immature myocardium

Answer 7

↑’s intracellular Ca ++ concentrations post ischemia/reperfusion.

Question 8

↑’s intracellular Ca ++ concentrations causes

Answer 8

Activates energy-consuming processesdecreased levels of adenosine triphosphatase (ATPase)lack of energy sources for cardiac function
Contributes to dysfunction observed after CPB
Abnormal and uncontrolled activation of these enzymes leads to cellular damage after CPB

Question 9

Increased myocardial oxygen demands  associated with

Answer 9

a switch from anaerobic metabolism after birth to

a more aerobic metabolism

Question 10

The immature myocardium uses

Answer 10

several substrates

carbohydrates, glucose, medium, and long-chain fatty acids, ketones, and amino acids.

Question 11

In the mature (3-12 mo) heart,

Answer 11

ong-chain fatty acids are the primary substrates

enzymes and an increased number of mitochondria are needed.

Question 12

Bottom Line:

Because of the increased ability of the immature myocardium to rely on anaerobic glycolysis,

Answer 12

it can withstand ischemic injury better than an adult myocardium can.

Question 13

Premature infants prone to

Answer 13

hypocalcemia hypoxia, infection, stress, diabetes (mom)

Question 14

Effects of hemodilution is

Answer 14

enhanced in neonates decreased plasma proteins, coagulation factors, and
Hgb
reduction increases organ edema, coagulopathy, and transfusion requirements

Question 15

Infants/neonates have high

Answer 15

oxygen-consumption rates

Question 16

require flow rates

Answer 16

as high as 200 mL/kg/min at normal temperature (kg based flow rates)

Question 17

unique anatomic and physiologic findings in patients with congenital cardiac disease

Answer 17

Intra-cardiac and extra-cardiac shunts and the reactive pulmonary vasculature

Question 18

glucose in adults

Answer 18

ontrol high blood sugar CPB => stress response => hyperglycemia Studies link hyperglycemia with adverse outcomes

Question 19

glucose in peds

Answer 19

control low blood sugar Hyperglycemia has not been linked to adverse
outcomes in pediatric CPB more common on pediatric CPB is hypoglycemia
( ↓ glycogen stores)

Question 20

Hematologic

 Adult:

Answer 20

Inflammatory response upon surgery/CPB

Question 21

Hematologic Peds

Answer 21

Exaggerated response to surgery/CPB

Inflammatory response inversely proportional to age

Question 22

The events that trigger stress:

Answer 22

Ischemia

Hypothermia Anesthesia Surgery

Question 23

CPB causes hormone release and also releases:

Answer 23

Catecholamines
Cortisol ACTH TSH Endorphins
Immature organs affect the release

Question 24

Cardiac

Adult

Answer 24

Less ischemia tolerance May/may not be preconditioned to ischemia More tolerant of overfilling

Question 25

cardiac Peds

Answer 25

Tolerate ischemia Higher lactates seen (cost of tolerating | ischemia) Prone to stretch injury (overfilling)

Question 26

CNS | Adult

Answer 26

More neurological injuries Multifaceted etiology Stem from disease processes

Question 27

CNS Peds

Answer 27

Neuro problems rare with routine CPB Increased with DHCA (?25%)

Question 28

Pulmonary | Adult

Answer 28

Lungs fully developed Less reactive vasculature May have preexisting disease

Question 29

Pulmonary Peds

Answer 29

Lungs not fully developed More reactive vasculature Usually without existing disease

Question 30

Renal | Adults

Answer 30

The normal urine output for adults can be 0.5 to 1 ml/min, regardless of weight. That translates to 60 ml/hr. Average 70kg adult would be expected to produce 35-70 mL/hour of urine.

Question 31

Renal Peds

Answer 31

For children, the expected urine output is closer to 1ml/kg/hour of urine. Average 5 kg child would be expected to produce 5 mL/hour

Question 32

Pediatric CPB Techniques

Answer 32

Hypothermia | Deep Hypothermic Circulatory Arrest (DHCA)

Question 33

Hypothermia in Children: What can you expect?

Answer 33

Due to the complex nature of congenital heart repairs you will see that children are often brought to colder temperatures more frequently than adults Different temperature monitoring sites in pediatrics Smaller children cool more rapidly than adults DHCA is more often utilize

Question 34

hypothermia definitions

Answer 34

“The importance of the preservation of tissue viability can not be overstated”  Warm 36-37°C Mild Hypothermia 32-35°C Moderate Hypothermia 28-31°C Deep Hypothermia 18-27°C Profound Hypothermia < 18°C

Question 35

Q10 Principle (temperature coefficient)

Answer 35

The temperature coefficient (Q10) represents the factor by which the rate (R) of a reaction increases for every 10-degree rise in the temperature (T) Remember: Oxygen consumption is a reaction

Question 36

Q10 factor (a unitless quantity) How is it obtained?

Answer 36

``` R1 = reaction rate at temperature T1 (where T1 < T2) R2 = reaction rate at temperature T2 (where T2 > T1) T1 = temperature at which the reaction rate R1 is measured (where T1 < T2) T2 = temperature at which the reaction rate R2 is measured (where T2 > T1) Temps = C0 or K, R1 and R2 units must be the same ```

Question 37

7° C Principle

Answer 37

• This reduction in metabolic rates can be summarized as follows: • Every 7°C drop in temperature will result in a 50% decrease in oxygen consumption 37°C Normothermic 34°C 25% decrease 30°C 50% decrease 23°C 75% decrease 16°C 87.5% decrease 9°C 94% decrease

Question 38

Temperature monitoring locations: | I. Core (central)

Answer 38

 Bladder (not on small children)  Nasopharyngeal  Tympanic  Esophageal  Venous

Question 39

Pediatric Monitoring of Temperature during Hypothermia: | II. Shell (peripheral)

Answer 39

 Rectal  Skin

Question 40

Protective effects of hypothermia

Answer 40

* Excitatory neurotransmitter release is reduced with hypothermia * Hypothermia helps to protect organs against injury caused by the compromised substrate supply to tissues resulting from reduced flow.

Question 41

why Protective effects of hypothermia occur

Answer 41

This protection occurs because of a reduced metabolic rate and decreased oxygen consumption. The metabolic rate is determined by enzymatic activity, which, in turn, depends on temperature. The safe period of hypothermic cardiopulmonary bypass (CPB) is longer than the period predicted on the basis of reduced metabolic activity alone

Question 42

PHCA/DHCA “Safe period durations”

Answer 42

> 320C= < 18 0 C =45-60 minutes

Question 43

Negative effects of hypothermia

Answer 43

brain blood flow loses autoregulation at extreme temperatures which makes blood flow highly dependent on extracorporeal perfusion. As we will later see, this uncoupling of autoregulation is a serious issue and is the basis for the Alpha stat/pH stat debate

Question 44

DHCA provides

Answer 44

excellent surgical exposure by eliminating the need for several cannulas in the surgical field and by providing a motionless and bloodless field.

Question 45

Cooling is started before

Answer 45

CPB by simply cooling room

Question 46

CPB is started and cooling is begins for at least

Answer 46

20-30 minutes. The patient's body temperature is monitored. After adequate cooling is achieved, the circulation is arrested. The desired duration of DHCA is limited to the shortest time possible.

Question 47

After circulation is resumed,

Answer 47

the final repairs are done on warming

Question 48

Cannulation for PHCA/DHCA is usually

Answer 48

a SAC  The heart is not opened until circulatory arrest

Question 49

Cannulation for PHCA/DHCA can and will be done with

Answer 49

BICAVAL also |  The heart is can be opened before circulatory arrest

Question 50

DHCA the good

Answer 50

Allows exposure Reduces metabolic rate and Allows cessation of circulation

Question 51

DHCA the Bad

Answer 51

Neurologic injury & morbidity Brain is at the most risk >60 min arrest is detrimental >40 min increases risk MUST monitor temp gradients closely

Question 52

he finding that DHCA was associated with neurologi morbidity led researchers to investigate the

Answer 52

HLFB

Question 53

Trials to compare the 2 methods (DHCA vs. HLFB) ha demonstrated lowered rates of neural dysfunction in patients undergoing

Answer 53

HLFB

Question 54

Finally, some groups have combined the 2 approaches mentioned above by using

Answer 54

approaches mentioned above by using DHCA with INTERMITTENT LOW FLOW BYPASS (ILFB) for 1-2 minutes every 15-20 minutes

Question 55

Cerebral Perfusion | Antegrade

Answer 55

Perfusing the head vessels in an antegrade fashion to perfuse the brain during DHCA Via head vessels/shunt

Question 56

Cerebral Perfusion Retrograde

Answer 56

Perfusing the head vessels in an retrograde fashion to perfuse the brain during DHCA Via SVC

Question 57

The concept of RCP originated in

Answer 57

the treatment of massive air embolism during CPB.

Question 58

When RCP is started, the superior vena cava

Answer 58

is snared, antegrade arterial flow is terminated, and the arterial cannula is connected to the arterial return line to the SVC cannula pressure in the superior vena cava is maintained at 15-20 mm Hg

Question 59

Mechanisms with which retrograde cerebral perfusion may accomplish neuroprotection include

Answer 59

the flushing of air and atheromatous embolic material from the cerebral circulation the maintenance of cerebral hypothermia, and the provision of nutritive cerebral flow RCP can be given continuously or intermittently However, incidents of cerebral edema after retrograde cerebral perfusion, particularly when the perfusion pressure exceeds 25 mm Hg, are reported.`

Question 60

Despite signs of oxygen uptake observed in several studies, the amount of perfusate that provides cerebral nutrition IS

Answer 60

ow, corresponding to only about 5% of total retrograde flow. Most of this flow is drained from the SVC into the inferior vena cava given the rich network of collaterals between the veins. This technique is used less commonly than ACP used in the pediatric population.

Question 61

Antegrade cerebral perfusion can be achieved by using an

Answer 61

open end of a modified Blalock-Taussig (BTT) shunt after the proximal anastomosis is constructed in neonates who require arch reconstruction (i.e Norwood operation).

Question 62

The perfusate temperature, flow, and pressure is usually set at for ACP

Answer 62

18°C, and the flow is set at 10-20 mL/kg/min or adjusted to maintain a pressure of 40-50 mm Hg in the right radial artery. Higher flows of 30-40 mL/kg/min are recommended for neonates.

Question 63

Several drawbacks are associated with those various cannulation techniques and are mainly related to complications of direct cannulation of arch vessels such as

Answer 63

dissection of the arterial wall air atheromatous plaque embolization malposition of the cannula overcrowding of the operative field with cannulas ACP can be given continuously or intermittently

Question 64

However, incidents of cerebral edema antegrade cerebral perfusion, particularly when the perfusion pressure exceeds

Answer 64

25 mm Hg, are reported

Question 65

During hypothermia, the solubility of carbon dioxide in blood increases and

Answer 65

for a given concentration of carbon dioxide in blood, PCO2 decreases and the blood becomes alkalotic.

Question 66

During pH-stat acid-base management, the patient's pH is managed

Answer 66

at the patient's temperature.

Question 67

Compared to alpha-stat, pH stat (which aims for a pCO2 of 40 and pH of 7.40 at the patient's actual temperature) leads to

Answer 67

``` higher pCO2 (respiratory acidosis), and increased cerebral blood flow. CO2 is deliberately added to maintain a pCO2 of 40 mm Hg during hypothermia. ```

Question 68

In pH-stat , to compensate for increased carbon dioxide solubility,

Answer 68

carbon dioxide is added to the gas mixture in the oxygenator to maintain the hypothermic pH at 7.40 and the PCO2 at 40 mm Hg.

Question 69

When blood samples are warmed to room temperature, blood gases are

Answer 69

hypercapnic and acidotic. | CDI: READ ABG’s AT PERFUSATE TEMPERATURE

Question 70

Ph stat - GOOD

Answer 70

Improved neurologic outcome, hastened EEG recovery times, and reduced number of postop seizures.

Question 71

reasons for better neuro outcomes

Answer 71

Increased cortical oxygen saturation before arrest, Decreased cortical oxygen metabolic rates during arrest Increased brain-cooling rates. CBF during reperfusion increases by using a pH- stat management strategy.

Question 72

Ph stat -BAD

Answer 72

 increased CBF that can increase embolic events, high CBFs during reperfusion, and reperfusion injury Acid load induced by pH-stat strategy may impair enzymatic function and metabolic recovery. To retain the benefits of the pH- stat method on cooling and to eliminate its negative effect on enzymatic function Lose autoregulation.

Question 73

During alpha-stat acid-base management, the ionization state of histidine is perfusion pressure then rules

Answer 73

maintained by managing a standardized pH (measured at 37C) Alpha-stat pH management is not temperature-corrected as the patient's temperature falls, the partial pressure of CO2 decreases (and solubility increases)

Question 74

The alpha-stat method allows blood pH

Answer 74

increase during cooling, which leads to hypocapnic and alkalotic blood in vivo.

Question 75

alpha stat Blood samples warmed to room temperature have a pH

Answer 75

7.4 and a PCO2 of 40 mm Hg. These conditions allow the alpha- imidazole group of the histidine moiety on blood/cellular proteins to maintain a constant buffering capacity, which enhances enzyme function and metabolic activity.

Question 76

Furthermore, the increase in pH parallels

Answer 76

the increase in the hydrogen ion dissociation constant of water during cooling, which can maintain a constant ratio of OH- ions to H+ ions. READ ABG’s AT 37°C

Question 77

Alpha- stat: good

Answer 77

With the alpha-stat approach: • Cerebral Blood Flow (CBF) autoregulation is maintained, which allows for metabolism and blood flow coupling. CBF can be adjusted depending on the patient's cerebral metabolic activity and oxygen needs. • Autoregulation is intact • Normal enzyme function  Most studies of this approach have been performed in adults.

Question 78

Alpha–stat: bad

Answer 78

With the alpha-stat approach: • Vasoconstriction | • Poor Cooling, which potentiates problems at the cellular level

Question 79

initial cooling is accomplished with

Answer 79

the pH- stat method, which is then switched to alpha-stat method to normalize the pH in the brain before ischemic arrest is induced (some do it on the last gas before arrest)