TSRA Content:
Author: Hannah McMullen MD
This is a revision and update from the previous edition of the TSRA Primer in Cardiothoracic Surgery written by Osama El Tayeb, MD, and Hyde Russell, MD.
Perioperative Care
Introduction:
The perioperative care of an infant or child with critical congenital heart disease can differ substantially from the adult with acquired heart disease. Although the goals of maintaining adequate cardiac output and oxygen delivery are similar, the unique cardiac lesions that are encountered in the pediatric cardiac ICU create physiology that is quite different than what is typically seen in the adult. Understanding fundamental cardiac physiology is paramount. This chapter will highlight aspects of pediatric cardiac ICU care that are distinct from adult practice.
Pediatric cardiac surgeons are generally intimately involved with the care of these critical patients on a day to day and hour to hour basis. As a resident, keeping the attending surgeon appropriately informed is always the most important priority. Be honest, work hard, and good luck!
Key Pearls:
- Fluid boluses are given in 10 cc/kg amounts. The surgeon should be notified if a patient's hemodynamics fail to respond to 2-3 boluses of fluid
- Blood transfusions are given generally as 10 cc/kg to raise the hemoglobin by 1-2g/dL
- Urine output is expected to be 0.5 cc/kg/hr or greater
- Chest tube output of >5 cc/kg in one hour or >2-3 cc/kg/hr for three hours is considered significant and should prompt a call to the surgeon for possible re-exploration
- The surgeon should be notified if the patient requires an escalation of inotropic support of >30%
- Patients with shunts (e.g., after Norwood) may benefit from a hemoglobin of 15 g/dl or hematocrit of 40-45% for improved oxygen carrying capacity
Preoperative Management
Congenital heart defects are complex, varied, and often difficult to categorize. Rather than trying to determine the management of each individual anatomic defect, a physiologic approach can be taken. The following questions are important in determining management prior to corrective or palliative surgery:
Is pulmonary blood flow adequate?
Patients with Tetralogy of Fallot, pulmonary atresia, and other "right sided" lesions may have insufficient pulmonary blood flow resulting in cyanosis.
Is systemic blood flow adequate?
Patients with critical "left sided" obstructive lesions such as critical aortic stenosis and aortic coarctation may have insufficient systemic blood flow and may present with renal insufficiency, acidosis, or shock.
If the answer to either of these two questions is no, then intervention is necessary. Prostaglandin El (PGE1) relaxes smooth muscle and can open and maintain patency of the ductus arteriosus. This duct can then provide pulmonary blood flow via a left-to-right shunt from the aorta in cases of pulmonary stenosis. Conversely, it can provide systemic blood flow to the descending aorta via a right-to-left shunt from the pulmonary artery in cases of aortic coarctation. These are "ductal dependent" lesions because the presence of the patent duct is necessary to permit oxygenated blood to reach the systemic circulation. PGE1 is incorporated for medical management of these patients to allow resuscitation while awaiting surgery. Apnea is a known side effect of PGE1, so infants must be monitored closely in a TCU while on the infusion.
Importantly, a patent ductus arteriosus (PDA) can be problematic if it supplies too much pulmonary blood flow. While adults generally develop congestive heart failure from left sided problems (LV failure, mitral regurgitation, aortic insufficiency, or stenosis), the etiology of congestive heart failure in an infant is usually pulmonary over-circulation secondary to a left-to-right shunt (often a large PDA or a ventricular septal defect (VSD). This manifests as tachypnea with characteristic pulmonary edema on chest Xray. Diuretics are the mainstay of medical management, but if the infant fails to gain appropriate weight because of the excessive calories spent on work of breathing, or worse, requires mechanical ventilation for respiratory distress, then medical therapy has failed, and the timing of surgical intervention is reconsidered.
Two other lesions deserve mention in regard to pre-operative management. Babies born with transposition of the great arteries may be persistently cyanotic despite medical management with PGE1. In this case, a balloon atrial septostomy can be performed in the cath lab to allow additional mixing at the atrial level. This allows the patient to be stabilized and corrective surgery to be scheduled electively. Total anomalous pulmonary venous return with obstructed pulmonary veins is a life-threatening cardiac emergency for which there is no medical management; there is no patent path for oxygenated blood to reach systemic circulation. Neonates with this condition are typically identified during pregnancy ultrasound screenings, and delivery is ideally adjacent to an operating room to allow immediate surgery to repair the defect.
Cardiovascular Support:
The goal of cardiopulmonary hemodynamic management is to provide enough oxygen delivery to the tissues to meet metabolic demands. An assessment of preload, afterload, and contractility is essential. Swan-Ganz catheters are generally not used in the pediatric patient. Adequacy of cardiac output is assessed by vital signs (heart rate and blood pressure), physical exam (warmth and perfusion of extremities), acid-base balance, lactic acid production, and end-organ function (urine output).
The functional status of the right ventricle is especially important when considering inotropic management. As in adults, the right ventricle is weaker than the left ventricle and less well protected during cardioplegic arrest. It is also often exposed to greater stresses related to the complexity of the operation and immaturity of the ventricle. Heart rates are often kept higher to avoid right ventricular distention, and inotropes (e.g. milrinone) are used longer postoperatively when compared with routine adult cardiac surgery. Residual shunts and obstructive or regurgitant lesions also need to be considered in the cardiac assessment and management of the postoperative patient.
Mechanical Ventilation:
Infants and children are generally ventilated in a pressure-cycled mode as opposed to the routine volume-cycled mode commonly seen in the adult ICU. Pressures of 16-20 mmHg typically achieve tidal volumes of 5-10 cc/kg in compliant lungs. Early extubation is favored for less complex cases. When needed, ventilatory maneuvers to maintain proper ventilation and oxygenation are similar to those used in adults and include altering the rate, tidal volume, FiO2, and PEEP. However, the goals for arterial blood gas values are often quite different. A few examples best illustrate this point:
- A reasonable blood gas following stage I Norwood palliation would be pH 7,4/pCO2 40/ pO2 40/ saO2 75%. This suggests adequate mixing through the ASD and adequate flow from the shunt to the pulmonary circulation.
- In cases of perioperative pulmonary hypertension (pHTN), keeping the pH normal by avoiding hypercapnia and hypoxia is paramount. Full ventilatory support, sedation, paralysis, and nitric oxide are helpful in cases of severe pHTN.
- In cases of excessive pulmonary blood flow via a natural or surgically created shunt, reducing FiO2 and allowing the pCO2 to drift up to 45-50 mmHg promotes pulmonary vasoconstriction to limit over circulation.
- Following a bi-directional Glenn, mild hypoventilation (pCO2 48-55 mm Hg) promotes cerebral vasodilation and increases blood flow through the SVC to the pulmonary arteries.
Sedation is an important aspect of ventilator management in critically ill pediatric patients. Pulmonary hypertensive crises, which can acutely stress a weak right ventricle or limit tenuous pulmonary blood flow, and thus cardiac output, can lead to cardiac arrest. Paralytics, rarely used in the adult ICU, are frequently seen in the pediatric ICU in the early post-operative phase to help avoid such catastrophic events.
Postoperative Care
Lines and Tubes:
A Swan-Ganz catheter is rarely used in pediatric cardiac patients. Central venous pressure (CVP) catheters are typically placed following induction and intubation by anesthesia in the internal jugular (IJ) or subclavian vein. Two 20-gauge peripheral IVs suffice both for induction and for postoperative management. If a central line is required, it can be placed in the IJ, subclavian, or femoral vein. Typical universal precautions are taken when placing these lines; central-line associated infections can be particularly devastating for congenital patients. For single ventricle patients or any patient with difficulty oxygenating, it is extremely important to avoid a pneumothorax and to be prepared to decompress one if it occurs.
A distal greater saphenous vein cut down is an excellent option for central access in infants and children with difficult peripheral access. A 2 cm incision is made over the vein below the inguinal crease and the fat is bluntly dissected with a hemostat until the vein is identified. The vein is partially transected, ligated distally, and the catheter is inserted, flushed, and secured.
Arterial lines can also be challenging and may require a femoral line or a radial cutdown. The radial cutdown involves a 1 cm incision over the radial artery and blunt dissection of the adipose tissue with a hemostat. The artery is identified and encircled with a fine PDS suture proximally and distally. Under direct visualization, an angiocath is inserted and advanced. Sometimes a guidewire is necessary. The distal suture is tied, and the proximal tie is secured around the catheter within the vessel.
For larger teenagers or adult congenital patients, chest tubes are inserted just as they are for typical adults. For infants or neonates, a pigtail catheter can be placed at the bedside. Most units have a pigtail set that includes the prep, towels, finder needle, wire, dilator, and pigtail catheter. The child is sedated and adequately anesthetized. The desired location is identified. It is safer to be higher (i.e. 4th intercostal space) but direct the catheter posteriorly for effusions. There is no need to tunnel. Advance the finder needle over the interspace until air or fluid is retrieved, advance the wire, dilate, and insert the pigtail over the wire. It is helpful to measure the pigtail outside of the body first. Secure it as usual and connect it to the chest tube drainage set.
Cardiac Arrhythmias:
Atrial arrhythmias are commonly seen in postoperative pediatric patients. While atrial fibrillation is seen frequently in adults, pediatric patients are prone to supraventricular atrial tachycardia (SVT) and junctional ectopic tachycardia (JET).
SVT is generally well tolerated and self-limited. It can be terminated by over-pacing with pacing wires or a trans-esophageal pacing probe. Recurrent episodes may prompt additional medical management but often the SVT resolves after the early post-operative period.
JET, however, is a more serious arrhythmia. Although uncommon, it is usually associated with surgery near the atrioventricular (AV) node (e.g., VSD closure in tetralogy patients). This arrhythmia results in loss of AV synchrony, which reduces pre-load to stiff right ventricles and can lead to hemodynamic deterioration. Treatment involves systemic sedation and cooling to lower the junctional rate. If the rate fails to respond to these measures, antiarrhythmics such as amiodarone can be initiated. After stabilization, atrial pacing above the junctional rate is often effective in restoring AV synchrony and improving hemodynamics. JET episodes are often complicated by low cardiac output syndrome and the team needs to be prepared for escalating circulatory support.
Ventricular arrhythmias are a dangerous complication after cardiac surgery in congenital patients, just as in the adult population. Telemetry monitoring is standard after operations to detect these morbid arrhythmias, and episodes of sustained ventricular tachycardia should be discussed with the surgeon.
Single Ventricle Management:
Unique to the congenital surgery population are patients with palliated single ventricle physiology. Although there are many important single ventricle lesions, hypoplastic left heart syndrome is a useful and common example. These patients require staged palliation beginning with the Norwood operation as a neonate.
During this first stage, patients have complete mixing of pulmonary and systemic venous return at the atrial level. In the early postoperative period, patients may benefit from transfusion to a goal hemoglobin level of 15g/dL (hematocrit 40-45%). This helps to raise the systemic venous oxygen content that is being mixed with pulmonary venous return. Pulmonary blood flow is provided by a shunt from the innominate artery (Blalock-Taussig shunt) or the right ventricle (Sano shunt).
Balancing the pulmonary blood flow with the systemic flow through the neoaorta is an important goal. It is necessary to understand the concept of the Qp:Qs (pulmonary flow:systemic flow) ratio and know how to calculate it. Achieving a balanced circulation involves manipulating systemic vascular resistance with vasoactive drugs and pulmonary vascular resistance with ventilator maneuvers.
Norwood Tips:
- Keep H/H at 15/45 initially
- Goal ABG values: pH 7.4 / pCO2 40 / pO2 40 / SpO2 75%
- Do not reflexively put any single ventricle on 100% Fi02. This can result in excessive pulmonary blood flow and inadequate systemic blood flow
- Desaturation is often effectively treated by transfusion to a Hct of 45 while raising cardiac output and blood pressure. This will provide more pulmonary blood flow through the shunt
- Atelectasis and pleural effusions need to be addressed when identified - these can be a source of important V:Q mismatch which can be critical in a single ventricle patient
The second stage of palliation is the bi-directional superior cavopulmonary anastomosis (bi-directional Glenn). The BT-shunt is removed, and the SVC is connected to the pulmonary artery. These patients are no longer complete "mixers" as they were following the Norwood, but control of pulmonary vascular resistance is still important.
Glenn Tips:
- Keep H/H at 15/45. These patients still mix their IVC blood and pulmonary venous return in the common atrium and thus systemic venous saturation dilutes the initial arterial saturation
- Goal pCO2 is 50 initially. This will allow for cerebral vasodilation and promote more SVC blood flow to the pulmonary arteries. The net increase in pulmonary blood flow more than compensates for the pulmonary vasoconstriction caused by the mildly increased pCO2
- Expect the Glenn pressure (CVP if upper extremity catheter) to be in the 12-15 range initially
- Keep the head of the bed elevated to aid in venous return and decrease cerebral pressure
The final palliative step for single ventricle patients is the Fontan operation, which connects the IVC to the pulmonary artery. Thus, all systemic venous return is directly to the pulmonary arteries. These patients are dependent on preload for adequate pulmonary blood flow. Fluid balance and diuretics need to be considered with care. Chest tube drainage can be high early on, and it is important that chest tubes are not removed prematurely. Atelectasis and pleural effusions need to be identified and treated promptly as these patients have markedly decreased reserve to compensate for this problem.