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Congenital Defects & Pediatrics IA > Blood Gases & Hypothermia: Topic 3 > Flashcards

Blood Gases & Hypothermia: Topic 3 Flashcards

1
Q

What do the major differences between adult and pediatric CPB stem from?

A

Anatomic Differences
Metabolic differences
Physiologic Differences

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2
Q

Myocytes/Myofibrils in Peds

A

Increase in size

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3
Q

Number of Mitochondria in Peds

A

Increases as the oxygen requirements of the heart rises

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4
Q

Amt of Sarcoplasmic Reticulum in Peds

A

Amount of Sarcoplasmic reticulum and its ability to sequester calcium increase in early development

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5
Q

Activity of Na+/K+ Adenosine Triphosphate (ATPase) in Peds

A

Increases with maturation and affects the sodium-calcium exchange

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6
Q

What happens when kids don’t have adequate pulmonary blood flow?

A

Won’t grow (also blue babies….)

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7
Q

What structure is response for SR storing calcium? (Affects ability to release too)

A

Terminal Cisternae

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8
Q

Ca++ handling in the immature myocardium _________(increases/decreases) intracellular Ca++ concentrations post ischemia/reperfusion.

A

Increases

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9
Q

What does an increase in intracellular calcium concentration activate?

A

Energy-consuming processes –> decreased levels of ATPase–> lack of energy sources for cardiac function–> dysfunction observed after CPB

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10
Q

What leads to cellular damage after CPB?

A

Abnormal and uncontrolled activation of these enzymes

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11
Q

What is the pediatric increase in myocardial oxygen demands attributed to?

A

Associated with a switch from anaerobic metabolism after birth to a more aerobic metabolism

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12
Q

Immature myocardium uses what substrates?

A 
Carbs
Glucose
Medium and long chain fatty acids
Ketones
Amino acids
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13
Q

What is considered the “mature” heart?

A

3-12 months

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14
Q

What are the primary substrates in the mature heart?

A

Long-chain fatty acids

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15
Q

What happens when the long-chain fatty acids become primary substrates in the mature heart?

A

Enzymes and an increased number of mitochondria are needed

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16
Q

Why can the immature heart withstand ischemic injury better than adult myocardium?

A

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

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17
Q

What are premature infants prone to?

A

Hypocalcemia

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18
Q

What can hypocalcemia result in?

A

Hypoxia, infection, stress, diabetes

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19
Q

What are the effects of hemodilution in neonates?

A

Decreased plasma proteins, coagulation factors and Hgb

Reduction increases organ edema, coagulopathy and transfusion requirements

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20
Q

Infants/neonates have a ______ (high/low) oxygen-consumption rate

A

High

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21
Q

What flow rates to infants/neonates require?

A

200 ml/kg/min at normal temperature (kg based flow rates)

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22
Q

What are unique anatomic and physiologic findings in patients with congenital cardiac disease?

A

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

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23
Q

How does glucose management on CPB differ between adults/pediatrics?

A

Adults: control high blood sugar
Peds: control low blood sugar

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24
Q

Why do peds get hypoglycemia?

A

Decrease in glycogen stores

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25
Q

Why do adults get hyperglycemia?

A

CPB –> stress response –> hyperglycemia

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26
Q

How does hematologic management differ between adults and pediatrics?

A

Adults: Inflammatory response
Pediatrics: exaggerated response; inflammatory response inversely proportional to age

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27
Q

What is the relationship between inflammatory response and age?

A

Inversely proportion; younger children have a higher inflammatory response

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28
Q

What are the events that trigger stress?

A

Ischemia
Hypothermia
Anesthesia
Surgery

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29
Q

CPB causes hormone release and also releases what?

A 
Catecholamines
Cortisol
ACTH
TSH
Endorphins
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30
Q

Cardiac Differences btw adults and peds

A

Adult: Less ischemia tolerance, potentially preconditioned to ischemia, more tolerant of overfilling

Pediatrics: tolerate ischemia, higher lactates seen, prone to stretch injury

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31
Q

What is the cost of pediatric patients tolerating ischemia?

A

Higher lactates seen

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32
Q

CNS Differences in Adults/Peds

A

Adult: more neurological injuries, multifaceted etiology, stem from disease processes

Peds: Neuro problems rare with routine CPB, increased with DHCA (25%)

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33
Q

How much do neurological problems in peds in crease with routine CPB?

A

Increase 25%

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34
Q

Pulmonary Differences Between Adults/Peds

A

Adult: lungs fully developed, less reactive vasculature, may have preexisting disease

Pediatrics: lungs not fully developed, more reactive vasculature, usually without existing disease

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35
Q

Renal Differences Between Adults/peds

A

Adults: normal U/o 0.5-1 ml/min, regardless of weight. 60 ml/hr.

Peds: the expected urine output is closer to 1 ml/kg/hour

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36
Q

What is the normal urine output of a 70kg adult?

A

35-70 mL/hr

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37
Q

What is the normal urine output of a 5kg child?

A

5 mL/hour

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38
Q

What are two pediatric CPB techniques?

A

Hypothermia

DHCA

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39
Q

Children are often brought to colder temperatures _______ (more/less) frequently than adults.

A

More

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40
Q

Smaller Children cool _______ (more/less) rapidly than adults.

A

More rapidly

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41
Q

Warm Temperature Range

A

36-37

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42
Q

Mild Hypothermia

A

32-35

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43
Q

Moderate Hypothermia

A

28-31

44
Q

Deep Hypothermia

A

18-27

45
Q

Profound Hypothermia

A

<18

46
Q

Temperature Monitoring Locations

A

Core (Central)

Shell (peripheral)

47
Q

Core Temperature Monitoring Locations

A 
Bladder (not on small children)
Nasopharyngeal
Tympanic
Esophageal
Venous
48
Q

Shell (Peripheral) Monitoring Locations

A

Rectal

Skin

49
Q

What’s probably the most accurate temp monitored?

A

Venous; last available temp coming directly back from the patient

50
Q

What are the protective effects of hypothermia?

A

Excitatory neurotransmitter release is reduced with hypothermia

Protects organs against injury caused by the compromised substrate supply to tissues resulting from reduced flow

51
Q

What is metabolic rate determined by?

A

Enzymatic activity which, in turn, depends on temperature

52
Q

The safe period of hypothermic cardiopulmonary bypass is ________ (longer/shorter) than the period predicted on the basis of reduced metabolic activity alone.

A

Longer

53
Q

PHCA/DHCA Safe Period Durations

A

> 32 = <18 = 45-60 minutes

54
Q

What are the negative effects of hypothermia?

A

Brain blood flow loses autoregulation at extreme temperatures which makes blood flow highly dependent on extracorporeal perfusion

Uncoupling of autoregulation is a serious issue and is the basis for Alpha Stat/pH stat debate

55
Q

How is cooling started in DHCA?

A

Before CPB by simply cooling the room

56
Q

CPB is started and cooling begins for at least how long in DHCA?

A

20- 30 minutes

57
Q

What occurs after adequate cooling is achieved in DHCA?

A

The circulation is arrested; the desired duration of DHCA is limited to the shortest time possible

58
Q

Cannulation for PHCA/DHCA is usually a what?

A

SAC; the heart is not opened until circ arrest

59
Q

When is the heart opened in bicaval cannulation for PHCA/DHCA?

A

opened before circ arrest

60
Q

DHCA Pros

A

Allows exposure
Reduces metabolic rate and molecule movement
Allow cessation of circulation

61
Q

DHCA Cons

A 
Neurologic Injury and Morbidity
Brain is the most risk
>60 min arrest is detrimental
>40 min increases risk
Must monitor temp gradients closely
62
Q

Art to Venous gradient shouldn’t be greater than what?

A

> 8 C

63
Q

Trials show lowered rates of _________ in patients undergoing HLFB compared to DHCA.

A

Neural dysfunction

64
Q

What is intermittent low flow bypass (ILFB)?

A

1-2 minutes every 15-20 min

65
Q

Antegrate Cerebral Perfusion

A

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

via head vessels/ shunt

66
Q

Retrograte Cerebral Perfusion

A

Perfusing the head vessels in a retrograde fashion to perfuse the brain during DHCA

via SVC

67
Q

The concept of RCP originated from what?

A

Tx of massive air embolism during CPB

68
Q

Superior maintained at what pressure in RCP

A

15-20 mmHg

69
Q

Incidents of cerebral edema after retrograde cerebral perfsuion, particularly when the perfusion pressure exceeds what?

A

25 mmHg

70
Q

The amount of perfusate that provides cerebral nutrition is what percent? Where is most of this flow drained?

A

5%; most of this flow drained form SVC into IVC given rich network of collaterals between the veins

71
Q

What’s more common: RCP or ACP?

A

ACP more common in pediatric population

72
Q

How can antegrade cerebral perfusion be achieved?

A

Using an open end of a modified Blalock-Taussig (BTT) shunt after the proximal anastomosis is constructed in neonates who require arch reconstruction

73
Q

What is an example of a procedure requiring arch reconstruction?

A

Norwood operation

74
Q

The perfusate temp is usually set to what in ACP?

A

18 C

75
Q

The flow is set to what in ACP? or adjusted to maintain what pressure?

A

10-20 mL/kg/min or adjusted to maintain pressure of 40-50 mmHg in the right radial artery

76
Q

What flows are recommended for neonates while doing ACP?

A

30-40 mL/kg/min

77
Q

Complications of direct cannulation of arch vessels in ACP

A

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

78
Q

Incidents of cerebral edema ACP, particularly when the perfusion pressure exceeds what?

A

25 mmHg

79
Q

During hypothermia, the solubility of carbon dioxide __________ (increases/decreases) in blood, pCO2 _________ (increases/decreases), and the blood becomes ____________(acidotic/alkalotic).

A

Increases, decreases, alkalotic

80
Q

During pH-state acid-base management, the patient’s pH is managed at what temperature?

A

At the patient’s temperature.

81
Q

pH-stat is __________(temperature corrected/temperature non-corrected)

A

Temperature corrected

82
Q

pH stat aims for what pCO2 and what pH?

A

pCO2 of 40
pH of 7.40
(at the patient’s actual temperature)

83
Q

pH stat leads to __________ (higher/lower pCO2).

A

Higher (adding CO2)

84
Q

What two conditions does pH stat management lead to?

A

Respiratory acidosis

Increased cerebral blood flow

85
Q

How do you maintain a pCO2 of 40mmHg during hypothermia in pH stat?

A

CO2 is deliberately added

86
Q

Where is carbon dioxide added in pH stat?

A

Added to the gas mixture in the oxygenator to maintain pH and pCO2

87
Q

In pH stat, when blood samples are warmed to room temp, blood gases are _________ (hypercapnic/hypocapnic) and __________ (acidotic/alkalotic)

A

Hypercapnic, acidotic

88
Q

On the CDI, which values do you read in pH stat management?

A

At the perfusate temperature

89
Q

Which acid-base strategy is best for the pediatric population?

A

pH-stat strategy

90
Q

What are the findings with pH stat management?

A

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

91
Q

What are the reasons for the findings of pH stat managment?

A

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

92
Q

What are the potential harmful effects of the pH-stat method?

A

Increased CBF that can increase embolic events, high CBFs during reperfusion, reperfusion injury

Acid load may impair enzymatic function and metabolic recovery

Lose autoregulation

93
Q

What happens when the body loses autoregulation during pH stat management?

A

Perfusion pressure rules, pressure-dependent

94
Q

What happens during alpha stat management?

A

Ionization state of histidine is maintained by managing a standardized pH, measured at 37C

95
Q

Alpha-Stat is _________ temeperature corrected/non-temperature corrected

A

Not temperature corrected

96
Q

During alpha-stat management, as the patient’s temperature falls, what happens to the partial pressure of CO2? Solubility?

A

Decreases; solubility increases

97
Q

Alpha-stat method allows blood pH to ___________ (increase/decrease) during cooling, which leads to ___________ (hypocapnic, hypercapnic) and ___________(acidotic/alkalotic) blood in vivo.

A

Increase, hypocapnic, alkalotic

98
Q

In alpha stat, blood samples warmed to room temperature have a pH of ______ and a pCO2 of ______.

A

pH of 7.4

pCO2 of 40 mmHg

99
Q

Alpha-stat conditions allow what?

A

Alpha-imidazole group of the histidine moiety on blood/cellular proteins to maintain a constant buffering capacity, which enhances enzyme function and metabolic activity.

100
Q

In alpha stat, the increase in pH parallels what?

A

The increase in the hydrogen ion dissociation constant of water during recooling, which can maintain a costant ratio of OH- and H+ ions.

101
Q

Where do you read ABGs with alpha-stat management?

A

at 37C

102
Q

What are the pros to alpha-stat?

A 
CBF maintained
Allows metabolism/BF coupling
CBF can be adjusted depending on patients' cerebral metabolic activity and oxygen needs
Autoregulation is intact
Normal enzyme function
103
Q

Most studies on alpha-stat managements have been performed on what patient population?

A

Adults

104
Q

What are the cons of alpha-stat?

A

Vasoconstriction

Poor cooling, which potentiates problems at the cellular level

105
Q

Combined Acid-Base Management Strategy

A

Initial cooling accomplished with pH-stat
Switch to alpha-stat to normalize pH in brain before ischemic arrest is induced (some do it on the last gas before arrest)

106
Q

What are the three cerebral oximeters the FDA has approved in the US for infants?

A

INVOS (System by Somanetics Corp)
NONIN EQUINOX (Regional, nonin medical inc)
FORE-SIGHT (CASMED medical systems)

107
Q

What are some things you want to keep in mind when priming the pediatric circuit?

A

Limit crystalloid
have room for drugs
have room for blood

Congenital Defects & Pediatrics IA (17 decks)

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