Blood Gases & Hypothermia: Topic 3 Flashcards
What do the major differences between adult and pediatric CPB stem from?
Anatomic Differences
Metabolic differences
Physiologic Differences
Myocytes/Myofibrils in Peds
Increase in size
Number of Mitochondria in Peds
Increases as the oxygen requirements of the heart rises
Amt of Sarcoplasmic Reticulum in Peds
Amount of Sarcoplasmic reticulum and its ability to sequester calcium increase in early development
Activity of Na+/K+ Adenosine Triphosphate (ATPase) in Peds
Increases with maturation and affects the sodium-calcium exchange
What happens when kids don’t have adequate pulmonary blood flow?
Won’t grow (also blue babies….)
What structure is response for SR storing calcium? (Affects ability to release too)
Terminal Cisternae
Ca++ handling in the immature myocardium _________(increases/decreases) intracellular Ca++ concentrations post ischemia/reperfusion.
Increases
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
What leads to cellular damage after CPB?
Abnormal and uncontrolled activation of these enzymes
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
Immature myocardium uses what substrates?
Carbs Glucose Medium and long chain fatty acids Ketones Amino acids
What is considered the “mature” heart?
3-12 months
What are the primary substrates in the mature heart?
Long-chain fatty acids
What happens when the long-chain fatty acids become primary substrates in the mature heart?
Enzymes and an increased number of mitochondria are needed
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
What are premature infants prone to?
Hypocalcemia
What can hypocalcemia result in?
Hypoxia, infection, stress, diabetes
What are the effects of hemodilution in neonates?
Decreased plasma proteins, coagulation factors and Hgb
Reduction increases organ edema, coagulopathy and transfusion requirements
Infants/neonates have a ______ (high/low) oxygen-consumption rate
High
What flow rates to infants/neonates require?
200 ml/kg/min at normal temperature (kg based flow rates)
What are unique anatomic and physiologic findings in patients with congenital cardiac disease?
Intra-cardiac and extra-cardiac shunts and the reactive pulmonary vasculature
How does glucose management on CPB differ between adults/pediatrics?
Adults: control high blood sugar
Peds: control low blood sugar
Why do peds get hypoglycemia?
Decrease in glycogen stores
Why do adults get hyperglycemia?
CPB –> stress response –> hyperglycemia
How does hematologic management differ between adults and pediatrics?
Adults: Inflammatory response
Pediatrics: exaggerated response; inflammatory response inversely proportional to age
What is the relationship between inflammatory response and age?
Inversely proportion; younger children have a higher inflammatory response
What are the events that trigger stress?
Ischemia
Hypothermia
Anesthesia
Surgery
CPB causes hormone release and also releases what?
Catecholamines Cortisol ACTH TSH Endorphins
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
What is the cost of pediatric patients tolerating ischemia?
Higher lactates seen
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%)
How much do neurological problems in peds in crease with routine CPB?
Increase 25%
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
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
What is the normal urine output of a 70kg adult?
35-70 mL/hr
What is the normal urine output of a 5kg child?
5 mL/hour
What are two pediatric CPB techniques?
Hypothermia
DHCA
Children are often brought to colder temperatures _______ (more/less) frequently than adults.
More
Smaller Children cool _______ (more/less) rapidly than adults.
More rapidly
Warm Temperature Range
36-37
Mild Hypothermia
32-35
Moderate Hypothermia
28-31
Deep Hypothermia
18-27
Profound Hypothermia
<18
Temperature Monitoring Locations
Core (Central)
Shell (peripheral)
Core Temperature Monitoring Locations
Bladder (not on small children) Nasopharyngeal Tympanic Esophageal Venous
Shell (Peripheral) Monitoring Locations
Rectal
Skin
What’s probably the most accurate temp monitored?
Venous; last available temp coming directly back from the patient
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
What is metabolic rate determined by?
Enzymatic activity which, in turn, depends on temperature
The safe period of hypothermic cardiopulmonary bypass is ________ (longer/shorter) than the period predicted on the basis of reduced metabolic activity alone.
Longer
PHCA/DHCA Safe Period Durations
> 32 = <18 = 45-60 minutes
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
How is cooling started in DHCA?
Before CPB by simply cooling the room
CPB is started and cooling begins for at least how long in DHCA?
20- 30 minutes
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
Cannulation for PHCA/DHCA is usually a what?
SAC; the heart is not opened until circ arrest
When is the heart opened in bicaval cannulation for PHCA/DHCA?
opened before circ arrest
DHCA Pros
Allows exposure
Reduces metabolic rate and molecule movement
Allow cessation of circulation
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
Art to Venous gradient shouldn’t be greater than what?
> 8 C
Trials show lowered rates of _________ in patients undergoing HLFB compared to DHCA.
Neural dysfunction
What is intermittent low flow bypass (ILFB)?
1-2 minutes every 15-20 min
Antegrate Cerebral Perfusion
Perfusing the head vessels in an antegrade fashion to perfuse the brain during DHCA
via head vessels/ shunt
Retrograte Cerebral Perfusion
Perfusing the head vessels in a retrograde fashion to perfuse the brain during DHCA
via SVC
The concept of RCP originated from what?
Tx of massive air embolism during CPB
Superior maintained at what pressure in RCP
15-20 mmHg
Incidents of cerebral edema after retrograde cerebral perfsuion, particularly when the perfusion pressure exceeds what?
25 mmHg
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
What’s more common: RCP or ACP?
ACP more common in pediatric population
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
What is an example of a procedure requiring arch reconstruction?
Norwood operation
The perfusate temp is usually set to what in ACP?
18 C
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
What flows are recommended for neonates while doing ACP?
30-40 mL/kg/min
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
Incidents of cerebral edema ACP, particularly when the perfusion pressure exceeds what?
25 mmHg
During hypothermia, the solubility of carbon dioxide __________ (increases/decreases) in blood, pCO2 _________ (increases/decreases), and the blood becomes ____________(acidotic/alkalotic).
Increases, decreases, alkalotic
During pH-state acid-base management, the patient’s pH is managed at what temperature?
At the patient’s temperature.
pH-stat is __________(temperature corrected/temperature non-corrected)
Temperature corrected
pH stat aims for what pCO2 and what pH?
pCO2 of 40
pH of 7.40
(at the patient’s actual temperature)
pH stat leads to __________ (higher/lower pCO2).
Higher (adding CO2)
What two conditions does pH stat management lead to?
Respiratory acidosis
Increased cerebral blood flow
How do you maintain a pCO2 of 40mmHg during hypothermia in pH stat?
CO2 is deliberately added
Where is carbon dioxide added in pH stat?
Added to the gas mixture in the oxygenator to maintain pH and pCO2
In pH stat, when blood samples are warmed to room temp, blood gases are _________ (hypercapnic/hypocapnic) and __________ (acidotic/alkalotic)
Hypercapnic, acidotic
On the CDI, which values do you read in pH stat management?
At the perfusate temperature
Which acid-base strategy is best for the pediatric population?
pH-stat strategy
What are the findings with pH stat management?
Improved neurologic outcome
hastened EEG recovery times
reduced number of postop seizures.
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
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
What happens when the body loses autoregulation during pH stat management?
Perfusion pressure rules, pressure-dependent
What happens during alpha stat management?
Ionization state of histidine is maintained by managing a standardized pH, measured at 37C
Alpha-Stat is _________ temeperature corrected/non-temperature corrected
Not temperature corrected
During alpha-stat management, as the patient’s temperature falls, what happens to the partial pressure of CO2? Solubility?
Decreases; solubility increases
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
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
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.
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.
Where do you read ABGs with alpha-stat management?
at 37C
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
Most studies on alpha-stat managements have been performed on what patient population?
Adults
What are the cons of alpha-stat?
Vasoconstriction
Poor cooling, which potentiates problems at the cellular level
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)
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)
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
