|Year : 2012 | Volume
| Issue : 1 | Page : 1-6
Truncus arteriosus ( perioperative management)
Department of Anesthesia and Critical Care, Aswan Heart Center, Aswan, Egypt
|Date of Submission||26-Mar-2012|
|Date of Acceptance||26-Apr-2012|
|Date of Web Publication||30-Jun-2014|
MB, ChB, MMed Anes (SA) CESR (UK), Cardiac Anesthetist at Christiaan Barnard Memorial Hospital, Cape Town, South Africa
Source of Support: None, Conflict of Interest: None
Truncus arteriosus is a congenital cardiovascular anomaly characterized by a single arterial vessel (truncus) with one valve arising from the heart. The truncus overrides a large perimembranous ventricular septal defect and receives mixed blood from both ventricles and supplies blood to the pulmonary, systemic, and coronary circulation, the ratio of the bloodflow vary according to the different vascular resistances. The anomaly is divided into four types according to Collett and Edwards classification on the basis of the origin of the pulmonary arteries from the truncal artery. In truncus, the goal is to balance the circulation to obtain QP:QS = 1 to maintain reasonable oxygen saturation as well as adequate organ perfusion. Careful titration of anesthetic agents and careful monitoring of their hemodynamic effects and appropriate measures to adjust pulmonary (PVR) and systemic vascular (SVR) resistances and cardiac performance are probably more important than the selection of a particular anesthetic agent. Postoperatively, low cardiac output can be expected because of high PVR and right ventricular failure. High PVR, both sustained and paroxysmal, should be anticipated. Pulmonary hypertensive crisis presents as low cardiac output and right ventricular failure. Avoidance of these potentially fatal events is essential to decrease the mortality and morbidity associated with repair. Events that trigger a hypertensive crisis, such as hypoxia, hypercapnia, acidosis, pain, airway stimulation, and left ventricular failure, must be avoided.
Keywords: Anaesthesia, congenital heart disease, pediatric anesthesia, truncus arteriosus
|How to cite this article:|
Bosman M. Truncus arteriosus ( perioperative management). Egypt J Cardiothorac Anesth 2012;6:1-6
Truncus arteriosus is a congenital cardiovascular anomaly characterized by a single arterial vessel (truncus) with one valve arising from the heart. The truncus overrides a large perimembranous ventricular septal defect (VSD) and receives mixed blood from both ventricles and supplies blood to the pulmonary, systemic, and coronary circulations 1–3. The anomaly is divided into four types according to Collett and Edwards classification 4 on the basis of the origin of the pulmonary arteries (PAs) from the truncal artery.
In type I, a common trunk arises and immediately bifurcates into a PA and an ascending aorta.
In type II, the PAs arise from the posterior aspect of the truncus.
In type III, the PAs arise from the lateral aspects of the truncus.
In type IV, or pseudotruncus, the main PA is absent and the lung blood supply comes from arteries arising from the descending aorta. This type is not a true truncus arteriosus, but rather a pulmonary atresia with a VSD with blood supply from aortopulmonary collaterals.
The Collet and Edwards classification is useful to describe pulmonary blood flow (PBF) in the truncus: PBF is increased in type I, almost normal in types II and III, and decreased in type IV. Types I and II constitute 85% of cases 5.
The second classification, Van Praagh and Van Praagh 6, classifies truncus arteriosus on the basis of the presence or absence of the conotruncal septum. This classification allows a clearer anatomic description of the defect and planning for surgery 1. When the conal septum fails to form, a conal-type VSD results. The system uses the designation to represent the presence of a VSD and for the absence of a VSD. The variable development of the truncal septum defines their specific category.
In Van Praagh type 1, the truncal septum is partially developed, so that a PA and an aorta coexist.
In type 2, there is complete absence of the truncal septum, with the main PAs originating from the truncal artery separately.
Type 3 is characterized by the absence of one PA originating from the truncal artery.
Type 4 describes any type of truncus associated with an interrupted arch defect. The arch anomaly is usually a type B interruption with the descending aorta receiving its blood supply from a large patent ductus arteriosus and the PAs originating from the truncal artery 1.
| Associated anomalies: cardiac and other|| |
The truncal valve is usually tricuspid, but may have multiple cusps and is often incompetent 2. Coronary artery abnormalities are quite common and may contribute toward the high surgical mortality 5.
The PA branches are usually of normal caliber 1. The pulmonary vasculature is subject to changes similar to those observed in conditions in which a high pressure, left-to-right shunt is found. This can cause pulmonary vascular obstructive disease, as described by Heath and Edwards 7.
Other cardiac anomalies are an interrupted aortic arch, patent ductus arteriosus, persistent left superior vena cava, an atrial septal defect and anomalous subclavian artery, and a right aortic arch 1.
DiGeorge syndrome is present in 30% of patients 8, and there may be associated thymus abnormalities (T-cell immune deficiency), parathyroid abnormalities (hypocalcemia), thrombocytopenia, cleft palate, and renal agenesis 9,10.
| Natural history|| |
Most infants present with congestive heart failure (CHF) 5 that can be severe, and decreased systemic oxygen delivery and cyanosis during the first 2 weeks of life 1,5.
As pulmonary vascular resistance (PVR) decreases during the first few weeks of life, PBF becomes torrential and severe CHF develops. The left ventricle is subjected to a significant volume overload. The increase in the left ventricular end-diastolic volume results in an increase in the pulmonary vascular hydrostatic pressure and severe pulmonary edema. This pulmonary overflow occurs at the cost of systemic and coronary perfusion and leads to progressive metabolic acidosis. If truncal valve insufficiency is present, this will place an additional volume load on the ventricles. The valvular insufficiency worsens with time, and if surgical correction is not performed, mortality during the first year of life is higher than 80%, with half succumbing during the neonatal period 1.
PVRs in infants who survive the neonatal period will increase as a result of increased flows. Due to the transmission of systemic arterial pressures to the pulmonary vasculature, irreversible pulmonary vascular disease develops rapidly, usually by the end of the second year, with the infant dying of the effects of chronic, progressive hypoxemia, and cyanosis. Surgical repair at this age should be approached with caution and may be contraindicated in individuals older than 2 years with PVR greater than 8 Woods units 1,11.
The elevated pulmonary flow maintains aortic saturation greater than 85%. When arterial oxygen saturation is less than 85%, significant pulmonary vascular disease limiting PBF is usually the cause, and the child may not tolerate correction 1.
Operative mortality approaches 100% in these children, with the majority of deaths because of acute right ventricular failure. A small percentage of children will survive past the third year of life with large left-to-right shunts and protected pulmonary circulation 1. Prenatal death often occurs when the truncus is complicated by severe valve regurgitation or an interrupted aortic arch 12.
| Hemodynamics|| |
Truncus arteriosus is an example of single-ventricle physiology in the presence of two well-formed ventricles. This physiology describes the situation wherein complete mixing of pulmonary venous and systemic venous blood occurs at the atrial or the ventricular level and the ventricle then distribute output to both the systemic and the pulmonary beds. The amount of PBF to the amount of systemic blood flow is determined by the ratio of resistance to flow in the pulmonary vascular bed and the resistance to flow in the systemic vascular bed 2.
In truncus, the large nonrestrictive ventricular spetal defect (VSD) allows the equalization of pressures in the right and the left ventricles. There is bidirectional shunting and complete mixing of systemic and pulmonary venous blood in a functionally common ventricular chamber 13. This mix is ejected into the truncal root and thus the oxygen saturation is the same in the aorta and the PAs. Aortic diastolic pressure, which is normally low in neonates and infants, is further compromised in single-ventricle physiology lesions because these lesions induce diastolic runoff of aortic blood into the lower resistance pulmonary circuit 2,14.
| Balancing the circulation|| |
- Three important points should be considered.
- The systemic arterial oxygen saturation depends on the amount (volume and ratio) of PBF. However, as with all single-ventricle lesions, a low PBF to systemic blood flow ratio (QP : QS) will reduce arterial saturation, whereas a high QP : QS will produce ventricular volume overload without a marked increase in arterial saturation 2,15.
- As the pulmonary and systemic circulations are supplied in parallel from a single vessel in truncus arteriosus, it means that for a given ventricular output, an increase in flow to one circulatory system will produce a reduction in flow to the other 15.
- To balance the circulation, the ideal QP : QS is 1.
The following equation can be used to determine the ratio, derived from the Fick principle:
Where SaO2 is the arterial oxygen saturation (as measured from the arterial blood gas); SsvcO2 is the superior vena cava saturation (as measured from the central venous line); SpvO2 is the pulmonary vein saturation; and SpaO2 is the PA saturation.
In a parallel circulation, SaO2=SpaO2 and during normal metabolic demands, SpvO2 can be assumed to be 95–100%.
| Clinical manifestations|| |
Cyanosis may be seen immediately after birth. Signs of CHF develop within several days to weeks after birth. Dyspnea with feeding, failure to thrive, and frequent respiratory infections will often be present in infants. Coronary ischemia can occur secondary to a relatively low diastolic pressure (as a result of pulmonary circulation runoff) 5,18.
Echocardiography is the diagnostic procedure of choice 5; diagnostic findings are:
- A large VSD is imaged straddled by the truncal valve.
- A large, single great artery arises from the heart (i.e. truncus arteriosus).
- Only one semilunar valve (i.e. truncal valve) is imaged.
- Color flow and Doppler flow across the truncal valve will indicate the truncal valve of regurgitation or stenosis.
- Biventricular hypertrophy is frequently seen. The left atrium may be dilated.
- A right-sided aortic arch is frequently present. Interruption of the aortic arch is occasionally present.
- Coronary artery anatomy can be assessed.
Cardiac catheterization is reserved for those cases in which the anatomy is unclear, further information is required in terms of the truncal valve, or when the status of the pulmonary vasculature is unclear. Systemic pressure is detected in both ventricles. The left atrial pressure is frequently elevated because of the increased pulmonary venous return. PVR is usually only mildly elevated (2–4 Wood units/m2) in infants younger than 3 months 1.
| Management|| |
Truncus arteriosus is an example of single-ventricle physiology that is amenable to two-ventricle repair, and unlike the staged repair of the hypoplastic single ventricle, truncus repair is usually performed during a single procedure.
Please note that the following is a very basic description of the surgery, with the sole aim of highlighting the effect of surgery on the postoperative course.
Ideally, surgery should be performed within the first week of life. When the diagnosis is delayed, surgery should be performed on an urgent basis and medical stabilization may be necessary. Surgery is similar to the Rastelli procedure, during which the PAs are separated from the truncus, which becomes the neoaorta. The truncal valve can usually be repaired and becomes the aortic valve. If there is significant truncal valve insufficiency, it may have to be replaced. Care is taken to protect the coronary arteries. The VSD is closed with a dacron patch through a right ventriculotomy with or without deep hypothermic arrest in such a way that the left ventricle (LV) ejects into the truncus. The right ventricle (RV) and PAs are connected with a valved homograft 1,5.
| Anesthesia management|| |
When planning an anesthetic for any type of congenital cardiac disease, it is essential to have a clear understanding of the physiology and pathophysiology of the lesion and to be aware of the pharmacological effects of different anesthetic drugs, and the salient points of surgery. Mixing lesions present a distinct set of challenges to the anesthesiologist.
In truncus, the goal is to balance the circulation to obtain QP : QS=1 to maintain reasonable oxygen saturation as well as adequate organ perfusion. Careful titration of anesthetic agents and careful monitoring of their hemodynamic effects and appropriate measures to adjust (particularly) pulmonary vascular resistance (PVR), systemic vascular resistance (SVR), and cardiac performance are probably more important than the selection of a particular anesthetic agent 18.
Depending on the timing of surgery, the hemodynamics will vary and anesthesia must be adapted 3,18.
- If the operation is in the first 2 weeks of life, there is likely to be pulmonary overflow preoperatively and measures to increase the PVR and maintain cardiac output are important. Exposure to a high inspired oxygen fraction (FiO2) at induction may lower PVR. Hypotension associated with a relatively high SaO2, lactic acidosis, or ischemic changes on ECG suggests that lung blood flow is excessive.
PVR may be increased by decreasing FiO2 even to room air. Increasing the PaCO2 to 45–55 mmHg (6.5–7.8 kPa) may result in a further increase in PVR. Lung blood flow may be restricted by ventilation strategies that increase the mean airway pressure, such as positive end-expiratory pressure. If surgical access is available, mechanical restriction of the PAs with temporary partially occlusive vascular snares may establish hemodynamic stability in the prebypass phase. All these techniques increase PVR and decrease SaO2. An SaO2 of about 70% may be required for optimal systemic perfusion 18.
- If the surgery is after 3–4 months, the PVR may be high and labile or still low.
- After 1 year, PVR would be increased and the patient may benefit from lowering PVR at induction, by administration of premedication, the use of higher concentrations of oxygen, and careful hyperventilation [Table 1].
The functional anatomy should be identified and the degree of heart failure, failure to thrive, pulmonary hypertension and cyanosis should be assessed and evidence for coronary ischemia should be searched for. The PBF should be assessed and a decision should be made as to whether the patient will benefit from a change in PVR 18.
Due to the frequent association of DiGeorge syndrome serum calcium and magnesium levels should be checked; and their supplementation may be indicated. Only irradiated blood products should be used for an urgent surgery (because of insufficient time for an accurate evaluation of immune status). Due to the thymus-based immune deficiency, treatment, and prophylaxis against pneumococcal and streptococcal infections are important. The possibility of cooling should be discussed with the surgeon; nitric oxide (NO) should be considered for use after surgery. The patients may benefit from premedication 18.
In the operating room:
- The saturation and blood pressure on room air should be checked, and near infrared spectral monitoring of tissue oxygenation (NIRS) should be placed if available.
- Heart rate should be maintained at an age-appropriate value.
- Before induction, preoxygenation should be performed, whilst taking care not to cause pulmonary overflow.
- After a careful gas induction, a small amount of opioids can be administered, keeping in mind that the circulation of patients with truncus arteriosus may be subject to significant sympathetic drive. This may be a response to heart failure, pulmonary hypertension, or relative hypovolemia linked to fluid restriction or diuretics. Although opioids are generally associated with cardiovascular stability, bolus doses at induction are likely to decrease the sympathetic drive and cause hypotension in these patients. Intravenous fluids or sympathomimetics may be required to treat hypotension. Other anesthetic agents can depress the sympathetic drive, with similar hemodynamic effects 18.
- Once ensured that ventilation is possible, a muscle relaxant may be given, and after tracheal intubation, recheck the QP:QS and balance again by adjusting ventilation or inotropes. An arterial line and a central venous line should be placed.
Post-cardiopulmonary bypass management 1,15:
- The heart rate (preferably sinus rhythm) should be maintained at an age-appropriate rate.
- The PVR should be reduced when necessary using ventilatory interventions.
- Inotropic support of the left ventricle and right ventricle (RV) may be necessary. Dobutamine (5–10 μg/kg/min) or dopamine (5–10 μg/kg/min) is useful in this instance as they provide inotropic support without increasing PVR. Milrinone (0.5–1.0 μg/kg/min started during rewarming instead of administering a bolus) should be considered for its inotropic and lusitropic effects as well as its ability to reduce PVR.
- Some degree of right ventricular (RV) dysfunction is likely to exist due to the presence of a ventriculotomy and a large VSD patch. This will be particularly problematic in patients with high PVR preoperatively or early pulmonary vascular obstructive disease.
- Left ventricular volume overload may occur secondary to truncal valve insufficiency.
- Intraoperative placement of PA and left atrial catheters will aid in the postoperative management of potentially fatal pulmonary hypertensive crises.
- Because of limited space in the mediastinum secondary to the placement of an RV-to-PA conduit, adequate drainage is critical to prevent tamponade. It is often useful to leave the sternum open until the pulmonary compliance recovers, as closure of the chest can create ‘pulmonary tamponade’ with compression of the conduit and decreased filling of the right heart 1.
Mild-to-moderate truncul regurgitation is often well tolerated and will improve postoperatively. Severe truncal regurgitation is a poor prognostic indicator for long-term survival. The patients should be monitored for residual VSD and patient foramen ovale (PFO), and coronary artery flow and PA flow should be checked 1,15.
| Intensive care management|| |
Postoperatively, low cardiac output can be expected due to high PVR and right ventricular failure. High PVR, both sustained and paroxysmal, should be anticipated. This is possible whether PVR was high or low preoperatively. A high PVR will almost always be present in infants with preoperative elevation of PA pressures and those who undergo delayed repair 1. Pulmonary hypertensive crisis presents as low cardiac output and right ventricular failure. Avoidance of these potentially fatal events is essential to decrease the mortality and morbidity associated with repair 13. Events that trigger a hypertensive crisis, such as hypoxia, hypercapnia, acidosis, pain, airway stimulation, and left ventricular failure, must be avoided 1. Patients should be kept sedated and paralyzed for the first 24–48 h after repair. In addition to avoiding triggering conditions, analgesia and sedation in the ICU play a large role in the avoidance of or treatment of a pulmonary hypertensive crises. High-dose fentanyl boluses do not affect the baseline hemodynamics significantly after cardiac surgery, but can blunt the response to noxious stimuli such as tracheal suctioning. A continuous infusion of opioids such as fentanyl (2–4 mcg/kg/h) alone or in combination with a benzodiazepine (50–100 mcg/kg/h) is generally administered in the first 24–48 h postoperatively for infants with pulmonary hypertension. A bolus dose of narcotics or benzodiazepines is used for ‘break-through’ episodes. If significant difficulties with pulmonary hypertensive crises continue, the period of deep sedation should be prolonged.
Keeping an infant well oxygenated and somewhat hypocapneic (pCO2 30–35 mmHg) is considered ideal 2. Metabolic acidosis must be cautiously corrected with sodium bicarbonate. Correction with sodium bicarbonate with inappropriate minute ventilation will result in an increase in plasma CO2. Excessive CO2 will not only increase PVR but may also result in depressed myocardial function. An initial dose of 1 mEq/kg can be used, with an additional dose tailored to the arterial blood gas 1.
Episodes of pulmonary hypertension are treated in a standard manner. The infants are hyperventilated with 100% oxygen and a fentanyl bolus (1–3 mcg/kg) with or without paralysis can be given. They may need inotropic support 1. Intermittent or continuous neuromuscular blockade is often used for a more precise control of ventilation, pH, and systemic carbon dioxide tension (PaCO2) and to prevent increases in alveolar pressure and a subsequent decrease in pulmonary perfusion caused by coughing or ventilator dyssynchrony.
Nitric Oxide (19) and Sildenafil have been shown to reduce the mortality associated with these episodes, although recent reports question the effectiveness of nitric oxide in reducing the incidence of pulmonary hypertensive episodes 19. For infants refractory to conventional attempts to reduce pulmonary resistance, extracorporeal membrane oxygenation may be initiated during the immediate postoperative period in infants who are hemodynamically uns[Table 1]3.
It should be kept in mind that many of these patients will have elevated PA pressures for a prolonged period of time, and if the increased pressures do not compromise cardiac output, they can be tolerated.
Right ventricular dysfunction may result from ventriculotomy, elevated pulmonary pressures, insufficient preload relative to a stiff RV, metabolic derangements, volume overload secondary to residual left-to-right shunting, or compression of coronary arteries because of the RV-to-PA conduit 1.
Irrespective of the etiology, right heart failure will result in inadequate systemic perfusion, exacerbating the original problem. Low cardiac output will result in persistent acidosis with elevated lactate levels, low mixed venous saturation, elevated arterial–venous gradient, low urine output, and cool extremities. Measures to optimize preload, contractility, and afterload must immediately be initiated. In cases where the cardiac output remains limited, extracorporeal membrane oxygenation is justified 18.
Central venous pressure (CVP) should be maintained at relatively high levels because of the decreased compliance of the RV. CVP of 13–18 mmHg or a left atrial pressure of 8–12 mmHg should be maintained. The patients must be ventilated at the lowest airway pressure possible. Increased intrathoracic pressure will have a detrimental effect on ventricular filling and output. Because of the stiffness of the ventricle, only moderate increases in stroke volume can be achieved at any given preload 1.
To optimize cardiac output, pacing (atrial or sequential) at heart rates of 140–160 beats/min can be performed with epicardial pacing leads placed at the time of repair. The use of a high-dose α-agonist must be avoided. Most infants will require some degree of inotropic support for the first 24–48 h. Low-dose dopamine, dobutamine, or epinephrine is commonly used to augment myocardial contractility. Care must be taken to prevent undue effects on the pulmonary vasculature. A right bundle branch block is almost always present postoperatively. Other common dysrhythmias include junctional ectopic tachycardia, atrial tachycardias, and atrioventricular block. Complete heart block occurs in 3–5% of patients 1.
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