7 Management of Cardiac Surgical Patients

Mehrdad Salamat, MD, FAAP, FACC

The current trend is to carry out total repair of congenital heart defects (CHDs) at an early age whenever such repair is technically possible. Early total repair may obviate the need for palliative procedures. It may also prevent pulmonary vascular disease or permanent damage to the cardiovascular system, which is known to develop in certain CHDs. However, recommendations for the timing and type of operation vary from institution to institution. The improved results currently seen with pediatric cardiac surgery are in part attributed to improved operative technique and cardiopulmonary bypass (CPB) methods. In addition, a coordinated multidisciplinary approach has contributed to a significant decrease in perioperative morbidity and mortality.

Open heart procedures use CPB with some degree of hypothermia and a varying duration of low flow or circulatory arrest. Open procedures are required for repair of intracardiac anomalies (e.g., ventricular septal defect [VSD], tetralogy of Fallot [TOF], transposition of the great arteries [TGA]). Closed procedures do not require CPB; they are performed for repair of extracardiac anomalies (e.g., coarctation of the aorta [COA], patent ductus arteriosus [PDA]) or palliative procedures (e.g., S-P shunt procedures or pulmonary artery [PA] banding). The following sections outline some basic aspects of preoperative and postoperative management of cardiac patients for pediatricians.

I. PREOPERATIVE MANAGEMENT

Good preoperative preparation, including complete delineation of cardiac anatomy and assessment of hemodynamics, is mandatory for a smooth operative and postoperative course. Some infants require preoperative stabilization with prostaglandin E₁ (continuous IV drip at 0.01 to 0.1 mcg/kg/min) to maintain ductus arteriosus patency while others may need inotropic and lusiotropic support. Patients with TGA and restrictive patent foramen ovale (PFO) may require balloon atrial septostomy.

1. All children should have a careful history and physical examination within a few days before the procedure. This is to gain full understanding of chronic medical problems (e.g., renal dysfunction, asthma) and to uncover acute medical problems (e.g., upper and lower respiratory and urinary tract infections) that would mandate rescheduling of elective surgeries.

2. Laboratory evaluation

a. Complete blood count, urinalysis, serum electrolytes and glucose, blood urea nitrogen (BUN), and serum creatinine of all cardiac patients are routinely obtained.

b. Chest x-ray (CXR) film and ECG of all patients are obtained.

c. Head and renal ultrasound is performed in all neonates with significant congenital heart defects.

d. For open heart procedures, blood coagulation studies—prothrombin time (PT), activated partial thromboplastin time (aPTT), and platelet count—are obtained.

e. If necessary, blood should be collected for chromosome studies (karyotyping and fluorescence in situ hybridization).

3. Patients undergoing CPB whose weight is more than 3.5 kg are cross-matched for four units of packed red blood cells (PRBCs) and those weighing less for two units of whole blood. One to two units of PRBCs are cross-matched for those undergoing closed procedures. In addition, one to four units of platelets are needed for the procedure. Irradiated blood products will be required for immunocompromised patients (e.g., patients with suspected or confirmed chromosome 22 microdeletion).

4. Medications

a. Digoxin is discontinued after the evening dose.

b. Diuretics are discontinued 8 to 12 hours preoperatively (or this may be individualized).

c. Antiarrhythmics are continued at the same dosage until immediately before the surgery.

d. Nonsteroidal antiinflammatory drugs (e.g., aspirin, ibuprofen) and antiplatelet drugs (e.g., dipyridamole) are discontinued 7 to 10 days prior to surgery.

e. Warfarin is discontinued 4 days prior to the planned operation. If the patient is at high risk for thromboembolism, a continuous heparin drip is started 2 days prior to the operation and the infusion rate is adjusted to maintain an aPTT of 60 to 85 seconds.

5. Prevention of infection: Broad-spectrum antibiotics are used to decrease the risk of perioperative infection. These are continued until all chest tubes and intracardiac and vascular monitoring lines are removed.

a. Clindamycin, 10 mg/kg/dose (adolescents/adults: 600 mg/dose) IV every 6 to 8 hours, starting immediately prior to surgery, is the recommended regimen at some institutions.

b. Vancomycin, 10 to 15 mg/kg/dose IV every 6 to 8 hours (maximum dose 4 g/day), and ceftazidime, 40 mg/kg/dose IV every 8 hours (maximum dose 6 g/day), or another third-generation cephalosporin, or gentamicin, 2.5 mg/kg/dose IV every 8 to 12 hours, is used for patients with open chest.

c. A thin layer of mupirocin 2% ointment is applied to both nostrils to prevent methicillin-resistant Staphylococcus aureus (MRSA) colonization.

6. For older children the emotional preparation for surgery is as important as the physical preparation.

II. POSTOPERATIVE CARE OF CARDIAC PATIENTS

A high level of vigilance for signs of complications should be maintained during the postoperative period so that appropriate therapy can be initiated early.

A. NORMAL CONVALESCENCE

Physicians should be familiar with the postoperative course of normally recovering patients in order to recognize abnormal convalescence.

1. General care: Successful postoperative management requires accurate monitoring and documentation of the patient’s vital signs, medication administration, and laboratory results. Vital signs, including heart rate, arterial or noninvasive blood pressure, oxygen saturation, and respiratory rate, are monitored closely (e.g., every 15 to 60 minutes). Urine and chest tube outputs, end-tidal or transcutaneous CO₂, central venous pressure, and at times, right and left atrial, and pulmonary arterial pressures are recorded meticulously. All administered medications, enteral or parenteral fluids, and blood products are documented. Fluid balance is monitored continuously. Laboratory results and their trends are charted for review.

2. Pulmonary system

a. Arterial blood gases are in the acceptable normal range.

b. CXR films show no evidence of pneumothorax, atelectasis, pleural effusion, or elevation of hemidiaphragm.

3. Cardiovascular system

a. Warm skin, full peripheral pulses with brisk capillary refill, normal blood pressure (BP), and an adequate urine output (at least 1 mL/kg/hr) are clinical evidence of good cardiac output. Decrease in expected systemic venous saturation is a sensitive predictor of low cardiac output. A normal systemic arterial-to-venous oxygen saturation difference of less than 30% is indicative of good cardiac output.

b. Mild arterial hypertension is present in the early postoperative period following CPB (due to increased levels of catecholamines, plasma renin, or angiotensin II).

c. Cardiac rhythm should be sinus and the heart rate relatively high. Ranges of heart rate (beats/min) in normally convalescing postoperative patients are as follows:

(1) Less than 6 months: 110 to 190

(2) 6 to 12 months: 100 to 170

(3) 1 to 3 years: 90 to 160

(4) Over 3 years: 80 to 150

4. Renal system: Adequate urine output (i.e., above 1 mL/kg/hr) and evidence of adequate solute excretion (e.g., serum K⁺ below 5 mEq/L; BUN below 40 mg/dL; creatinine below 1 mg/dL) are signs of normal renal function.

5. Metabolic system

a. Retention of water and sodium and depletion of whole-body potassium are commonly seen following open heart surgery. They result in mild hyponatremia and hypokalemia and a 5% weight gain. In anticipation of fluid overload, mechanical ultrafiltration is performed in selected cases intraoperatively.

b. Mild metabolic acidosis (with a base deficit of −4 mEq/L) associated with mild lactic acidemia is common in the first few hours after CPB and does not usually require treatment.

c. Varying degrees of fever are nearly always present during the first few days, and extensive workup for infection is not indicated. Causes of fever include reaction to CPB, reaction to homologous blood, atelectasis, pleural effusion, low cardiac output, infection, and brainstem damage.

6. Gastrointestinal system: As the splanchnic circulation receives over 25% of total cardiac output, avoidance of low cardiac output syndrome is the principal strategy to prevent gastrointestinal (GI) dysfunction. Feedings are started after the patient becomes hemodynamically stable and are advanced as tolerated. Daily caloric count and its adjustment are crucial. H₂-receptor antagonists (e.g., ranitidine, 1 mg/kg/dose IV every 6 to 8 hours) are initiated for gastric protection.

7. Hematologic system: Clotting studies should be normal, and hemoglobin should be at least 9.5 g/dL or higher depending on the patient’s age, cardiac anatomy, and surgical procedure.

8. Neurologic system: The patient should respond appropriately for the level of sedation without evidence of neurologic defects (e.g., hemiplegia, visual field defects) or seizures. Near infrared spectroscopy (NIRS) for transcranial cerebral oximetry is a noninvasive method to monitor frontal lobe oxygen metabolism. Cerebral oxygen saturation, measured by NIRS, is a composite of the oxygen saturation in combined cerebral arterial and venous vascular bed (arterial and venous blood flow ratio of approximately 25:75, with negligible capillary blood). It is a helpful method to detect cerebral hypoxia during low cardiac output states.

B. CARE FOLLOWING AN UNCOMPLICATED OPERATION

Postoperative care in congenital cardiac surgery is extremely unique due to the complexity and heterogeneity of cardiac defects and the wide age range of patient population. Furthermore, the guidelines for postoperative management differ from institution to institution, making this task even more complicated. Although the following recommendations are only one set of these guidelines, one aspect of successful management remains the same: anticipation of possible complications (e.g., decrease of cardiac index 6 to 12 hours postoperatively, pulmonary hypertension in association with particular defects, arrhythmias after specific surgeries, etc.).

1. General care

a. Fluid replacement: Because of the tendency to retain sodium and water, a minimal amount of dextrose in water without sodium (D₁₀W in infants, D₅W in children) or with only a small amount of sodium (D₁₀ ¼ NS, D₅ ¼ NS) is administered for approximately 48 hours after surgery. A modest amount of potassium (e.g., KCl, 4 mEq/100 mL IV fluids) is given on the first day of surgery. Recommended fluid volume in the first 24 hours after open procedures is 50% of maintenance volume with a gradual increase over the following postoperative days to 60% and then to 75%.

b. The patient should receive medications for adequate analgesia and sedation. For pain relief, fentanyl (IV drip at 1 to 3 mcg/kg/hr or 1 to 2 mcg/kg/dose IV every 30 to 60 minutes) or morphine sulfate (IV drip at 0.01 to 0.05 mg/kg/hr or 0.1 to 0.2 mg/kg/dose IV every 2 to 4 hours, maximum dose 15 mg/dose) is commonly used. Sedation is achieved by administration of midazolam (0.05 to 0.15 mg/kg/dose IV every 1 to 2 hours or IV drip at 1 to 2 mcg/kg/min) or other benzodiazepams.

2. Pulmonary system

a. Extubated patients should show no signs of respiratory distress (grunting, nasal flaring, and retraction). Good chest expansion and evidence of good air exchange to both lungs should be present. Depending on the hemodynamics or cardiopulmonary pathophysiology, patients may be administered supplemental oxygen via nasal cannula or face mask. Pulmonary physiotherapy (consisting of incentive spirometry, coughing and deep breathing exercise, and chest percussion with postural drainage) is administered as necessary.

b. In intubated patients, CXR films are obtained to check the position of chest tubes and central and arterial lines and to check for evidence of pneumothorax, atelectasis, pleural effusion, or main-stem bronchus intubation. Significant degrees of pneumothorax or pleural effusion may require treatment. Widening of the mediastinal shadow suggests accumulation of blood and requires investigation of the function of the mediastinal chest tube.

(1) In the first postoperative days the goal of ventilation is to maintain adequate arterial partial pressure of oxygen (Pao₂), and mild respiratory alkalosis along with an arterial partial pressure of carbon dioxide (Paco₂) between 28 and 35 mm Hg (all to decrease pulmonary vascular resistance [PVR]). Hyperventilation (Paco₂ below 28 mm Hg) is corrected by decreasing the ventilator rate, decreasing the tidal volume, and adding dead space (5 to 10 mL at a time) to the airway. Hypoventilation is corrected by the opposite maneuvers. Low Pao₂ is corrected by raising the Fio₂, adding positive-end expiratory pressure (PEEP), or increasing tidal volume. Physiologic PEEP of 3 to 5 cm H₂O is used in children. The use of high mean airway pressure or high levels of PEEP may increase PVR and decrease cardiac output; both should be avoided in a patient who has had a Senning procedure or cavopulmonary anastomosis (e.g., Glenn or Fontan operation).

(2) Tracheal toilet is carried out through the endotracheal tube every 2 hours or more often if necessary. It consists of instillation of 0.5 to 5 mL of saline and suctioning of both main-stem bronchi and bag ventilation for 1 to 2 minutes with oxygen (Fio₂ 1) immediately before and after suctioning.

c. Extubation is performed as soon as possible, usually in the operating room in children undergoing closed procedures, within 4 to 8 hours after uncomplicated open heart procedures, and the day after complex open procedures. Criteria for extubation include the following:

(1) The patient should be awake and alert and should have a favorable nutritional status.

(2) The patient should be breathing well, with a satisfactory spontaneous respiratory rate for age and no use of accessory respiratory muscles. Ideally, vital capacity should be more than 15 mL/kg. On minimal ventilatory support (Fio₂ no more than 0.4, tidal volume at 8 to 10 mL/kg, and PEEP no more than 5 cm H₂O), there should be adequate Pao₂ and no evidence of acidosis or hypercapnia.

(3) The patient should be in a reasonable and stable hemodynamic state (normal BP, adequate cardiac output, no significant arrhythmias). There should be no significant pneumothoraces or pleural effusions. The patient should not have important bleeding and should have minimal chest tube drainage.

(4) Postextubation laryngeal edema is treated with racemic epinephrine (2.25% solution; 0.125 to 0.5 mL diluted with 3 mL of water or normal saline given via nebulizer).

d. Postoperative pulmonary hypertensive crisis leads to decreased cardiac output and, if untreated, may be fatal. The best strategy is prevention. Measures to prevent pulmonary hypertensive crisis are important for patients who had severe pulmonary arterial hypertension preoperatively. The following are recommended.

(1) Adequate analgesia and sedation.

(2) Paralysis by vecuronium bromide (continuous IV drip at 0.05 to 0.15 mg/kg/hr or intermittent IV infusion of 0.05 to 0.1 mg/kg/dose every 60 minutes) or pancuronium bromide (continuous IV drip at 0.02 to 0.1 mg/kg/hr or intermittent IV infusion of 0.05 to 0.1 mg/kg/dose every 30 to 60 minutes).

(3) Supplemental oxygen.

(4) Low PEEP.

(5) Maintaining alkalotic pH.

(6) Avoidance of deep and vigorous tracheal aspiration.

(7) Administration of inhaled nitric oxide (selective pulmonary vasodilator) at 5 to 40 parts per million (usual range 5 to 20 parts per million).

(8) Intravenous vasodilators (α-adrenergic antagonists, phosphodiesterase inhibitors, nitrovasodilators, and prostaglandins) may be considered. However, it should be noted that essentially all these agents dilate the systemic vasculature as well, leading to systemic hypotension.

3. Cardiovascular system: Complete correction of the intracardiac defect and adequate intraoperative myocardial protection generally will result in good cardiac function. Signs of reduced cardiac output, abnormal blood pressures, abnormal heart rate, and abnormal rhythm should be monitored continuously.

a. Low cardiac output syndrome

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