23 CONGENITAL HEART DISEASE Flashcards
1
Q
- When does shunting occur in congenital heart disease?
A
- Under normal physiologic conditions, pulmonary blood flow and systemic blood
flow do not mix, and the entire cardiac output flows in one direction. Shunting
occurs when a portion of the venous return is redirected back to the arterial
outflow of the same circulation. The shunt occurs when there is an abnormal
communication between the pulmonary blood flow and systemic blood flow.
2
Q
- What is the usual limitation to the direction and amount of shunt flow?
A
- A shunt occurs when there is an abnormal communication, or defect, between
the pulmonary and systemic circulations. The direction of the shunt flow is dictated
by the relative pressures between the communicating structures. The amount of
shunting is limited by the size of the defect
3
Q
- When does a left-to-right shunt occur?
A
- A left-to-right shunt occurs when part of the pulmonary venous return is redirected
toward the pulmonary arterial system. This can occur through anomalies in the
pulmonary veins, atrial septum, ventricular septum, or at the great vessels
4
Q
- What is the physiologic effect of a left-to-right shunt on the pulmonary blood flow
(Qp) relative to the systemic blood flow (Qs)?
A
- The physiologic effect of a left-to-right shunt is that the total pulmonary blood flow
(Qp) is greater than the systemic blood flow (Qs); that is Qp becomes greater than Qs.
This can result in hypotension and pulmonary edema.
5
Q
- What are the long-term effects of increased pulmonary blood flow that occurs in a
left-to-right shunt?
A
- Long-term effects of an increase in pulmonary blood flow, as occurs in a
left-to-right shunt, are an increase in pulmonary vascular resistance and abnormal
cardiac chamber dilation. In addition, prolonged hypotension can lead to
circulatory shock and multiple organ failure
6
Q
- Give an example of a congenital heart defect that results in a left-to-right shunt.
A
- An example of a left-to-right shunt congenital heart lesion would be an atrial septal
defect (ASD).
7
Q
- When does a right-to-left shunt occur? What is the physiologic effect of this?
A
- A right-to-left shunt occurs when a portion of the systemic venous return is
redirected to the systemic arterial outflow without first circulating through the lung.
Physiologically this would result in desaturated blood returning to the systemic
circulation, and potentially arterial hypoxemia. The degree of hypoxemia would be
dictated by the magnitude of the shunt.
8
Q
- Give an example of a congenital heart defect that results in a right-to-left shunt
A
- An example of a right-to-left shunt congenital heart lesion would be tetralogy
of Fallot.
9
Q
- What are mixing lesions in congenital heart disease? How do mixing lesions affect
the systemic arterial oxygen saturation?
A
- Mixing lesions in congenital heart disease describes a complete blending of the
pulmonary and systemic circulations such that there is identical or nearly identical
oxygen saturations in both circulatory systems. In mixing lesions the systemic
arterial oxygen saturation decreases.
10
Q
- What determines the Qp:Qs ratio in mixing lesions?
A
- In mixing lesions, the Qp:Qs ratio is determined by the relative resistance of
blood flow in the pulmonary and systemic circulatory systems. That is, in mixing
lesions, the ratio of blood flow is determined by pulmonary vascular resistance and
systemic vascular resistance
11
Q
- What is the ideal Qp:Qs ratio in mixing lesions? Why?
A
- The ideal Qp:Qs ratio in mixing lesions is 1. Any preferential flow toward the
systemic circulation would be at the expense of greater desaturation and therefore
less oxygen delivery. Conversely, any preferential flow toward the pulmonary
circulation would be at the expense of cardiac output, and therefore less oxygen
delivery to the tissues. (
12
Q
- What are some factors that can increase systemic vascular resistance?
A
- Factors that can increase systemic vascular resistance are light anesthesia,
systemic nervous system activation, administration of a agonists, and physical
manipulations such as flexing the hips of infants and small children.
13
Q
- What are some factors that can decrease systemic vascular resistance?
A
- Factors that can decrease systemic vascular resistance are deep anesthesia and
the administration of vasodilating drugs, such as nitrates and inhaled anesthetics.
14
Q
- What are five factors that increase pulmonary vascular resistance
A
- Five factors that increase pulmonary vascular resistance are alveolar hypoxemia,
hypercapnia, acidosis, light anesthesia, and hypothermia. Other factors include high
lung volumes and pressures, or low lung volumes with atelectasis.
15
Q
- What are five factors that decrease pulmonary vascular resistance?
A
- Five factors that decrease pulmonary vascular resistance are hyperventilation with
resultant hypocarbia, alkalosis, oxygenation, pulmonary vasodilators such as
inhaled nitric oxide, warmth, and bronchodilators such as albuterol.
16
Q
- What is Eisenmenger syndrome?
A
- Eisenmenger syndrome is a condition that can develop when pulmonary blood
flow is increased over a long period of time, and the direction of the shunt flow
becomes irreversibly left-to-right. This syndrome occurs due to a remodeling of
pulmonary vasculature, an increase in pulmonary vascular resistance, and
ultimately pulmonary hypertension yielding a pulmonary systolic blood pressure
that is higher than systemic systolic blood pressure.
17
Q
- What are some ways an anesthesiologist can prepare for a patient requiring surgery
for congenital heart disease?
A
- An anesthesiologist should prepare by understanding the physiology of the
congenital heart lesion and the subsequent effects of the planned surgery.
Aspects of the patient’s condition that can be improved prior to surgery should
be identified. (
18
Q
- What preexisting conditions might be important to the care of patients with
congenital heart disease?
A
- Preexisting conditions that might be important to the care of patients with
congenital heart disease include a history of prematurity, trisomy 21, DiGeorge
syndrome, and chronic illness such as renal dysfunction, pulmonary edema, and
electrolyte abnormalities. In addition, the preoperative evaluation of morning
admission patients scheduled for congenital heart surgery should include the usual
preoperative evaluation of pediatric patients, such as evaluation for new upper
respiratory tract infections.
19
Q
- What information might be gained from preoperative echocardiograms or magnetic
resonance imaging (MRI)?
A
- Important preoperative information that could be derived from the magnetic
resonance imaging (MRI) and echocardiograms would be anatomic manifestations
of disease, such as an existing ventricular septal defect and concomitant right
ventricular hypertrophy. (
20
Q
- What is a risk factor from a previous sternotomy?
A
- Risk factors from previous sternotomy include increased operative blood loss and
cardiac trauma during dissection secondary to adhesions that may have formed
adherent to the sternum and chest wall.
21
Q
- What are the fasting recommendations for infants and children scheduled for
congenital heart surgery?
A
- Fasting recommendations for infants and children scheduled for congenital heart
surgery should follow the standard American Society of Anesthesiologist
guidelines. (
22
Q
- What is the most important feature of the intravenous administration set up for the
patient scheduled for congenital heart surgery?
A
- The most important feature of intravenous administration set up for patients
scheduled for congenital heart surgery is to meticulously de-air the system.
The inadvertent introduction of an air bubble into the patient’s vascular system
via the intravenous tubing can result in an air embolus entering the systemic
circulation in a patient with a left-to-right shunt. Although the risk is greater in
patients with right-to-left shunts, patients with left-to-right shunts may have
reversal of their shunt during certain phases of the cardiac cycle, during
cardiopulmonary interventions as during manual manipulation of the heart during
surgery, or with coughing in the awake patient.
23
Q
- What are some common side effects of the induction of anesthesia using inhaled
agents, such as sevoflurane or halothane?
A
- Some common side effects of induction of anesthesia with inhaled agents, such
as sevoflurane or halothane, include myocardial depression, decreased heart
rate and myocardial contractility, and decreased systemic vascular resistance.
A halothane induction may also have associated myocardial dysrhythmia and
ventricular irritability
24
Q
- What are some side effects of an intravenous induction of anesthesia using opioids
such as fentanyl?
A
- Some side effects of an intravenous induction of anesthesia using opioids
such as fentanyl would include bradycardia and loss of sympathetic tone.
25
Q
- What are some side effects of an intravenous induction of anesthesia using
ketamine, a drug that preserves sympathetic nervous system tone?
A
- Some side effects of an intravenous induction of anesthesia using ketamine might
include increases in heart rate and myocardial depression
26
Q
- What are some general principles for the induction of anesthesia that might apply to
all patients with congenital heart disease?
A
- Some general principles for the induction of anesthesia that might apply to all
patients with congenital heart disease would include the avoidance of dehydration,
maintaining the patient in sinus rhythm, avoiding myocardial depression, and
avoiding air entrapment in the intravenous and pressure tubings.