3. Blood Gas/Hypothermia- Exam 1 Flashcards
what are the 3 Major differences that exist between adult and pediatric cardiopulmonary bypass
Anatomic differences
Metabolic differences
Physiologic differences
Anatomic Differences Structural and Functional for Myocytes, myofibrils, mitochondria, sarcoplasmic reticulum, and Activity of Na+/K+ ATPase
-Myocytes and myofibrils: increase in size
-mitochondria: number increases as the oxygen requirements of the heart rises.
-sarcoplasmic reticulum: The amount and its ability
to sequester calcium increase in early development.
-Activity of Na+/K+ ATPase: increases with maturation, and affects the sodium-calcium exchange
How do anatomic differences effect Ca++ handling?
Ca++ handling in immature myocardium ↑’s intracellular Ca ++ concentrations post ischemia/reperfusion.
How do anatomic differences effect energy consuming processes?
Activates energy-consuming processes–> decreased
levels of adenosine triphosphatase (ATPase)–> lack of
energy sources for cardiac function
Anatomic differences contribute to what on bypass?
Contributes to dysfunction observed after CPB
_____ and _____ activation of these enzymes leads to cellular damage after CPB
Abnormal and uncontrolled
Increased myocardial oxygen demands is associated with a switch from _______ after birth to a more _________
anaerobic metabolism
aerobic metabolism
The immature myocardium uses several substrates such as (5)
carbohydrates glucose medium, and long-chain fatty acids ketones amino acids
What is the primary substrate In the mature (3-12 mo) heart?
long-chain fatty acids are the primary substrates
–enzymes and an increased number of mitochondria are needed
Because of the increased ability of the immature myocardium to rely on anaerobic glycolysis, it can withstand ___ better than an adult myocardium can.
ischemic injury
Premature infants prone to what?
hypocalcemia
–hypoxia, infection, stress, diabetes (mom)
Effects of hemodilution is enhanced in what group?
neonates
what are the Effects of hemodilution that is enhanced in neonates
–decreased plasma proteins, coagulation factors, and
Hgb
–reduction increases organ edema, coagulopathy,
and transfusion requirements
Infants/neonates have high ________ rates
oxygen-consumption
Infants/neonates have high oxygen-consumption
rates… this requires what kind of flow rates?
require flow rates as high as 200 mL/kg/min at normal temperature (kg based flow rates)
______/______ and ______ are unique anatomic and physiologic findings in patients with congenital cardiac disease
Intra-cardiac and extra-cardiac shunts and the
reactive pulmonary vasculature
Adult vs Ped glucose control
Adult= control high blood sugar Ped= control low blood sugar
describe adults response to hyperglycemia
CPB => stress response => hyperglycemia
Studies link hyperglycemia with adverse outcomes
describe peds response to hyperglycemia
–Hyperglycemia has not been linked to adverse
outcomes in pediatric CPB
–more common on pediatric CPB is hypoglycemia
( ↓ glycogen stores)
Adult vs Ped hematologic response to CPB
–Adult: Inflammatory response upon surgery/CPB
–Pediatric: Exaggerated response to surgery/CPB. Inflammatory response inversely proportional to
age
Name 4 events that trigger stress
Ischemia
Hypothermia
Anesthesia
Surgery
CPB causes hormone release and also releases what 5 things
Catecholamines Cortisol ACTH TSH Endorphins
What affects the release of hormone release
immature organs
describe adult cardiac characteristics
Less ischemia tolerance
May/may not be preconditioned to ischemia
More tolerant of overfilling
describe ped cardiac characteristics
Tolerate ischemia
Higher lactates seen (cost of tolerating ischemia)
Prone to stretch injury (overfilling)
describe adult CNS characteristics
More neurological injuries
Multifaceted etiology
Stem from disease processes
describe ped CNS characteristics
Neuro problems rare with routine CPB
Increased with DHCA (?25%)
describe adult pulmonary characteristics
Lungs fully developed
Less reactive vasculature
May have preexisting disease
describe ped pulmonary characteristics
Lungs not fully developed
More reactive vasculature
Usually without existing disease
describe adult renal characteristics
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
describe ped renal characteristics
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
Due to the complex nature of congenital heart
repairs you will see that children are often brought to
__________ more frequently than adults
colder temperatures
Smaller children ____more rapidly than adults
cool
what method of hypothermia is most often used for peds
DHCA
Warm temp=
36-37 C
Mild Hypothermia temp=
32-35 C
Moderate Hypothermia temp=
28-31 C
Deep Hypothermia temp=
18-27 C
Profound Hypothermia temp=
below 18 C
define Q10
Reaction Rates: factor by which the rate of a reaction increases or decreases by 50% for every 10-degree increase/decrease in the temperature
is Oxygen consumption is a reaction
yes
Q10= [formula]
(R2/R1)^(10/[T2-T1])
define Q7
Oxygen consumption: Every 7°C drop in temperature will result in a 50% decrease in oxygen consumption
Q7: at 37C (normothermic) what the %decrease of oxygen consumption and what is the temp in F?
0%
98.6F
Q7: at 34C (mild) what the %decrease of oxygen consumption and what is the temp in F?
25%
93.2F
Q7: at 30C (moderate) what the %decrease of oxygen consumption and what is the temp in F?
50%
86.0F
Q7: at 23C (deep) what the %decrease of oxygen consumption and what is the temp in F?
75%
73.4F
Q7: at 16C (profound) what the %decrease of oxygen consumption and what is the temp in F?
- 5%
60. 8F
Q7: at 9C (almost frozen) what the %decrease of oxygen consumption and what is the temp in F?
94%
48.2F
Q7: at 0C (frozen) what the %decrease of oxygen consumption and what is the temp in F?
100%
32.0F
Name 5 central/core temperature monitoring locations
Bladder (not on small children) Nasopharyngeal Tympanic Esophageal Venous
Name 2 shell/peripheral temperature monitoring locations
Rectal
Skin
What temperatures do you feel are the most accurate indicator of being cold or warm?
venous
Excitatory neurotransmitter release is _____ with hypothermia
reduced
Hypothermia helps to protect organs against injury caused by what?
the compromised substrate supply to tissues resulting from reduced flow.
why does hypothermia work?
because of a reduced metabolic rate and decreased oxygen consumption.
The metabolic rate is determined by what?
enzymatic activity, which, in turn, depends on temperature
The safe period of hypothermic CPB is _____ than the period predicted on the basis of reduced metabolic activity alone
longer
safe period for DHCA above 32C
less than 10 min
safe period for DHCA at 28C
10-20 min
safe period for DHCA at 18C
20-45 min
safe period for DHCA below 18C
45-60min
brain blood flow loses _______ at extreme temperatures which makes blood flow highly dependent on extracorporeal perfusion
autoregulation
DHCA provides excellent surgical exposure by doing what
eliminating the need for several cannulas in the surgical
field and by providing a motionless and bloodless field
how is Cooling is started before CPB
cooling the room
describe the process for how DHCA is carried out
- CPB is started and cooling is begins for at least 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. - After circulation is resumed, the final repairs are done
on warming
with DHCA, when you turn the pump off during arrest- what do you have to do
recirculate through oxygenator recirc line to prevent blood from clotting
Cannulation for PHCA/DHCA is usually a?
SAC
-The heart is NOT opened until circulatory arrest
Cannulation for PHCA/DHCA can and will be done with BICAVAL also, here the heart _____?
is/can be opened before circulatory arrest
name 3 DHCA benefits
Allows exposure
Reduces metabolic rate and molecular movement
Allows cessation of circulation
name 5 DHCA disadvantages
Neurologic injury & morbidity Brain is at the most risk >60 min arrest is detrimental >40 min increases risk MUST monitor temp gradients closely
what should the arterial to venous temp gradient for DHCA not exceed
NOT > 8°C
Trials to compare the 2 methods (DHCA vs. HLFB) have demonstrated what?
lowered rates of neural dysfunction in patients undergoing HLFB.
some groups have combined the 2 approaches mentioned above by using DHCA with INTERMITTENT LOW FLOW BYPASS (ILFB) for ____ min every ____ min
1-2 minutes every 15-20 minutes
There is __ specific consensus on what is the best method to allow complex repairs in neonates. The use of DHCA, PHCA, HLFB, ILFB, antegrade and retrograde cerebral perfusion are all used to varying extents
NO
The secret formula may very well lie in the _____ of these techniques and not the ______
mixture
techniques alone
how is antegrade cerebral perfusion performed
Via head vessels/shunt
how is retrograde cerebral perfusion performed
Via SVC
The concept of RCP originated in the treatment of what?
massive air embolism during CPB
describe the RCP procedure
When RCP is started, the SVC 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 SVC is maintained at 15-20 mm Hg
Mechanisms with which retrograde cerebral perfusion may accomplish neuroprotection include (3)
- 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 __ mm Hg, are reported
25 mmHg
Despite signs of oxygen uptake observed in several studies, the amount of perfusate that provides cerebral nutrition is low, corresponding to only about _% of total retrograde flow
5%
RCP is used ___ commonly than ACP used in the pediatric population.
less
Antegrade cerebral perfusion can be achieved by using?
an 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).
what is the perfusate temp and pressure for ACP
- -The perfusate temperature is usually set at 18°C
- -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*
what ACP flows are recommended for neonates
Higher flows of 30-40 mL/kg/min
Several drawbacks are associated with those various cannulation techniques and are mainly related to complications of direct cannulation of arch vessels. Give 6 examples
- 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
However, incidents of cerebral edema antegrade cerebral perfusion, particularly when the perfusion pressure exceeds __ mm Hg, are reported
25 mmHg
During hypothermia, the solubility of carbon dioxide in blood _____, and for a given concentration of carbon dioxide in blood, PCO2 ______ and the blood becomes _____
increases
decreases
alkalotic
During pH-stat acid-base management, the patient’s
pH is managed at the patient’s?
temperature
–pH-stat pH management is temperature-corrected
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 what?
higher pCO2 (respiratory acidosis), and increased cerebral blood flow
with pH stat- ___ is deliberately added to maintain a pCO2 of 40 mm Hg during hypothermia
CO2
In pH-stat , to compensate for increased carbon dioxide solubility, carbon dioxide is added to the gas mixture in the ______ to maintain the hypothermic pH at 7.40 and the PCO2 at 40 mm Hg
oxygenator
with pH-stat, When blood samples are warmed to room temperature, blood gases are ______ and _______
hypercapnic and acidotic
with pH-stat, CDI: READ ABG’s AT _________
PERFUSATE TEMPERATURE
Data have suggested that the pH-stat strategy is best for the
pediatric population
name 3 things that pH-stat cause as a final result
Improved neurologic outcome
hastened EEG recovery times
reduced number of postop seizures
physiologically, when using pH stat- what 3 things increase and what 1 thing decreases
- -increases= cortical oxygen saturation before arrest, brain-cooling rates, and CBF during reperfusion
- -decreases= cortical oxygen metabolic rates during arrest
when using pH stat- increased CBF can potentially cause what
can increase embolic events, high CBFs during reperfusion, and reperfusion injury
Acid load induced by pH-stat strategy may impair what?
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
pH stat can do what to autoregualtion
Lose autoregulation-perfusion pressure then rules
During alpha-stat acid-base management, the ionization state of histidine is 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)
The alpha-stat method allows blood pH to increase during cooling, which leads to what?
hypocapnic and alkalotic blood in vivo
with alpha-stat, Blood samples warmed to room temperature have a pH of 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 what?
a constant buffering capacity, which enhances enzyme function and metabolic activity.
with alpha-stat, the increase in pH parallels the increase in the …?
hydrogen ion dissociation constant of water during cooling, which can maintain a constant ratio of OH- ions to H+ ions
with alpha stat, you read the ABGs at?
37C
with alpha stat, Cerebral Blood Flow (CBF) autoregulation is maintained, which allows for what?
metabolism and blood flow coupling.
with alpha stat, CBF can be adjusted depending on what?
the patient’s cerebral metabolic activity and oxygen needs.
with alpha stat, how is autoregulation and enzyme function handled
Autoregulation is intact
Normal enzyme function
with alpha stat, Most studies of this approach have been performed in ____
adults
with alpha stat, name 2 disadvantages
- Vasoconstriction
- Poor Cooling, which potentiates problems at the cellular level
combined ph/alpha management=
initial cooling is accomplished with 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)
what 3 cerebral oximeters FDA approved in the United States for use in the infant population
INVOS
NONIN EQUINOX
FORE-SIGHT
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