Blood Gases & Hypothermia: Topic 3 Flashcards Preview

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Flashcards in Blood Gases & Hypothermia: Topic 3 Deck (107):
1

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

Anatomic Differences
Metabolic differences
Physiologic Differences

2

Myocytes/Myofibrils in Peds

Increase in size

3

Number of Mitochondria in Peds

Increases as the oxygen requirements of the heart rises

4

Amt of Sarcoplasmic Reticulum in Peds

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

5

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

Increases with maturation and affects the sodium-calcium exchange

6

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

Won't grow (also blue babies....)

7

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

Terminal Cisternae

8

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

Increases

9

What does an increase in intracellular calcium concentration activate?

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

10

What leads to cellular damage after CPB?

Abnormal and uncontrolled activation of these enzymes

11

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

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

12

Immature myocardium uses what substrates?

Carbs
Glucose
Medium and long chain fatty acids
Ketones
Amino acids

13

What is considered the "mature" heart?

3-12 months

14

What are the primary substrates in the mature heart?

Long-chain fatty acids

15

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

Enzymes and an increased number of mitochondria are needed

16

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

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

17

What are premature infants prone to?

Hypocalcemia

18

What can hypocalcemia result in?

Hypoxia, infection, stress, diabetes

19

What are the effects of hemodilution in neonates?

Decreased plasma proteins, coagulation factors and Hgb
Reduction increases organ edema, coagulopathy and transfusion requirements

20

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

High

21

What flow rates to infants/neonates require?

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

22

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

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

23

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

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

24

Why do peds get hypoglycemia?

Decrease in glycogen stores

25

Why do adults get hyperglycemia?

CPB --> stress response --> hyperglycemia

26

How does hematologic management differ between adults and pediatrics?

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

27

What is the relationship between inflammatory response and age?

Inversely proportion; younger children have a higher inflammatory response

28

What are the events that trigger stress?

Ischemia
Hypothermia
Anesthesia
Surgery

29

CPB causes hormone release and also releases what?

Catecholamines
Cortisol
ACTH
TSH
Endorphins

30

Cardiac Differences btw adults and peds

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

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

31

What is the cost of pediatric patients tolerating ischemia?

Higher lactates seen

32

CNS Differences in Adults/Peds

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

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

33

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

Increase 25%

34

Pulmonary Differences Between Adults/Peds

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

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

35

Renal Differences Between Adults/peds

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

36

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

35-70 mL/hr

37

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

5 mL/hour

38

What are two pediatric CPB techniques?

Hypothermia
DHCA

39

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

More

40

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

More rapidly

41

Warm Temperature Range

36-37

42

Mild Hypothermia

32-35

43

Moderate Hypothermia

28-31

44

Deep Hypothermia

18-27

45

Profound Hypothermia

<18

46

Temperature Monitoring Locations

Core (Central)
Shell (peripheral)

47

Core Temperature Monitoring Locations

Bladder (not on small children)
Nasopharyngeal
Tympanic
Esophageal
Venous

48

Shell (Peripheral) Monitoring Locations

Rectal
Skin

49

What's probably the most accurate temp monitored?

Venous; last available temp coming directly back from the patient

50

What are the protective effects of hypothermia?

Excitatory neurotransmitter release is reduced with hypothermia

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

51

What is metabolic rate determined by?

Enzymatic activity which, in turn, depends on temperature

52

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

Longer

53

PHCA/DHCA Safe Period Durations

>32 = <18 = 45-60 minutes

54

What are the negative effects of hypothermia?

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

How is cooling started in DHCA?

Before CPB by simply cooling the room

56

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

20- 30 minutes

57

What occurs after adequate cooling is achieved in DHCA?

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

58

Cannulation for PHCA/DHCA is usually a what?

SAC; the heart is not opened until circ arrest

59

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

opened before circ arrest

60

DHCA Pros

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

61

DHCA Cons

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

62

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

>8 C

63

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

Neural dysfunction

64

What is intermittent low flow bypass (ILFB)?

1-2 minutes every 15-20 min

65

Antegrate Cerebral Perfusion

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

via head vessels/ shunt

66

Retrograte Cerebral Perfusion

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

via SVC

67

The concept of RCP originated from what?

Tx of massive air embolism during CPB

68

Superior maintained at what pressure in RCP

15-20 mmHg

69

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

25 mmHg

70

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

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

71

What's more common: RCP or ACP?

ACP more common in pediatric population

72

How can antegrade cerebral perfusion be achieved?

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

73

What is an example of a procedure requiring arch reconstruction?

Norwood operation

74

The perfusate temp is usually set to what in ACP?

18 C

75

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

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

76

What flows are recommended for neonates while doing ACP?

30-40 mL/kg/min

77

Complications of direct cannulation of arch vessels in ACP

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

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

25 mmHg

79

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

Increases, decreases, alkalotic

80

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

At the patient's temperature.

81

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

Temperature corrected

82

pH stat aims for what pCO2 and what pH?

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

83

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

Higher (adding CO2)

84

What two conditions does pH stat management lead to?

Respiratory acidosis
Increased cerebral blood flow

85

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

CO2 is deliberately added

86

Where is carbon dioxide added in pH stat?

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

87

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

Hypercapnic, acidotic

88

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

At the perfusate temperature

89

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

pH-stat strategy

90

What are the findings with pH stat management?

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

91

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

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

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

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

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

Perfusion pressure rules, pressure-dependent

94

What happens during alpha stat management?

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

95

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

Not temperature corrected

96

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

Decreases; solubility increases

97

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

Increase, hypocapnic, alkalotic

98

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

pH of 7.4
pCO2 of 40 mmHg

99

Alpha-stat conditions allow what?

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

In alpha stat, the increase in pH parallels what?

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

101

Where do you read ABGs with alpha-stat management?

at 37C

102

What are the pros to alpha-stat?

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

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

Adults

104

What are the cons of alpha-stat?

Vasoconstriction
Poor cooling, which potentiates problems at the cellular level

105

Combined Acid-Base Management Strategy

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

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

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

107

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

Limit crystalloid
have room for drugs
have room for blood