Introduction

Congenital heart diseases are classified into:

Cyanotic Heart Disease

Acyanotic Heart Disease

Congenital Heart Diseases with Left-to-Right Shunts

Congenital Heart Diseases with Right-to-Left Shunts

There are 6 common types of congenital heart diseases with right-to-left lesions: tetralogy of Fallot (TOF), transposition of the great arteries (TGA), truncus arteriosus (TA), tricuspid atresia, total anomalous pulmonary venous return (TAPVR), and pulmonary atresia with intact ventricular septum (PAIVS).

TOF is the most common intrinsic cyanotic congenital heart disease, which accounts for 5% to 10% of all congenital heart disease and has a prevalence of about 1 out of 2,000 live births ₁₁ .

TGA is congenital heart lesion characterized by ventriculoarterial discordance. It accounts for 5% to 7% of all congenital cardiac malformations.

TA accounts for 1% to 2% of congenital heart disease ₁₂ . There is a single semilunar valve and annulus with a common outflow trunk arising from the ventricles. It may be associated with DiGeorge syndrome ₁₃ (Figure 8). Tricuspid Atresia accounts for 1% to 3% of congenital heart defects. It is congenital heart lesion characterized by agenesis of the tricuspid valve ₁₄ .

TAPVR accounts for 1% of all congenital heart lesions. The pulmonary veins connect to the systemic venous system instead of to the left atrium.

PAIVS accounts for less than 1% of all congenital heart defects. The prevalence of this disorder is 4.1 per 100, 000 live births ₁₅ .

In our institute >600 cardiac surgery procedures in adults and pediatrics are operated annually. Table 1 show the different pathology encountered.

Figure 1

Table 1: Pediatric cardiac anesthesia in prince sultan cardiac center for 2007(n=625).

Anesthesia technique for pediatric cardiac surgery

The stress response to major cardiac surgery in infants and children is a subject that continues to evoke considerable interest. In their landmark study, published in 1992, Amand and Hickey ₁₆ reported the use of sufentanil at a total mean dose of 37µ/kg, and an infusion that continued for 24 hours postoperatively, as a sole anesthetic for complex neonatal cardiac surgery. This technique was compared with halothane with morphine (mean dose of 0.35 mg/kg) intra-operatively, followed by intermittent intravenous doses of morphine and diazepam postoperatively. Stress response was evaluated by measuring changes in levels of adrenal hormones, cortisol, glucose, and lactate. This response was significantly decreased in the sufentanil group, and mortality and major complications such as sepsis and necrotizing enterocolitis were also significantly reduced. Duncan et al. ₁₇ reported a dose response study of 2, 25, 50, 100, and 150µg/kg fentanyl before bypass in 40 children (average age 13 months). The patients who received 2µg/kg had significant increases in pre-bypass nor-epinephrine, glucose, and cortisol, and significantly higher heart rate and blood pressure than all other groups. Fentanyl doses of 25µg/kg or higher eliminated changes in all measured parameters for the duration of the surgery. Remifentanil is a synthetic, ultra-short-acting narcotic with a half-life of 3-5 minutes, independent of the duration of infusion, which is metabolized by nonspecific plasma esterases ₁₈ . Donmez ₁₉ reported a series of 55 children who underwent cardiac catheterization using a remifentanil infusion of 0.1µg/kg/min, with spontaneous respiration maintained. This technique provided cardiovascular stability, with minimal changes in heart rate, blood pressure or oxygen saturation. About half of the patients required additional sedation with midazolam. Apnea was infrequent, and time to recovery after discontinuation of remifentanil was only 2-4 minutes. Patients undergoing long cardiac catheterization procedures could thus potentially benefit from this agent. Its use has also been reported during surgical repair of atrial septal defects, with patients subsequently extubated in the operating room during switch operation the left ventricle is acutely converted from the pulmonary to the systemic ventricle. This imposes a significant increase in after load on the left ventricle and may predispose the patient to acute left ventricle dysfunction in the immediate post-operative period. Milrinone improves myocardial contractility, diastolic relaxation and decrease in after load due to vasodilatation. We conduct a study to determine the effect of milrinone infusion on hemodynamic profile in pediatric cardiac surgery. We found that milrinone infusion was shown to be more effective on a post-bypass course of hemodynamic profile by decreasing the LAP ₄₀ .

Echocardiography

Recently, echocardiographic techniques have been used to evaluate the ventricular function response to anesthetics in patients with congenital heart disease. A study comparing halothane, isoflurane, and sevoflurane ₂₀ in 54 biventricular children, aged 1 month to 13 years and who underwent cardiac surgery, demonstrated that at both 1 and 1.5 minimum alveolar concentration {MAC) halothane, significant myocardial depression occurred. Sevoflurane preserved both CO and heart rate (HR), with fewer hypotensive and negative inotropic effects seen compared with halothane. The effects of these anesthetic agents on pulmonary (Qp) and systemic (Qs) blood flow in 30 biventricular patients with left-to-right shunts was also assessed echocardiographically ₂₁ . Recently, the myocardial performance index (MPI) has been validated as an accurate assessment of ventricular function for all ventricular configurations, including functional single ventricle ₂₂ . MPI is a useful new tool to assess ventricular function in response to anesthetics and other agents in this important and enlarging patient population ²². In the near future three-dimensional echocardiography may also provide new insights into ventricular function in response to anesthetics in patients with congenital heart disease ₂₃ . In a study by Ogletree and coworkers ₂₄ , etomidate at therapeutic levels was shown to have negative inotropic effects in right ventricular muscle resected from patients with tetralogy of Fallot, and reversal of these effects with isoproterenol also appeared to be attenuated.

Antifibrinolytic agents

Cardiopulmonary bypass results in significant fibrinolysis and several agents are commonly used to attempt to limit this effect and reduce bleeding. E-aminocaproic acid (EACA) and tranexamic acid (TA) are both carboxylic acid derivatives that are structurally related to the amino acid lysine ₂₅ . Previous studies have determined that both EACA and TA are effective at reducing bleeding and transfusion requirements in infants and children undergoing cardiac surgery with bypass, particularly those who are either undergoing repeat stemotomy or who are cyanotic ₂₆,₂₇ . Aprotinin is a serine protease inhibitor isolated from bovine lung. Its ability to inhibit trypsin, plasmin, and kallikrein has been recognized since the 1930s, with clinical use first reported in 1953 for the treatment of acute pancreatitis ₂₈,₂₉ . At plasma levels of only 50 kallikrein inhibitor units (KIU)/mL, aprotinin is able to inhibit plasmin. At higher plasma levels (200 KIU/mL), aprotinin inhibits kallikrein formation, thus attenuating its central role in the production of post CPB coagulopathies and the activation of the inflammatory response ₃₀ .

Recombinant factor VIIa

Recombinant factor VIIa (rFVIIA) was originally approved for use in hemophilia patients who had developed inhibitors to factors VIII or IX. In doses of 90µg/kg it was shown to be effective at treating bleeding in these patients ₃₁ .

Fresh versus reconstituted whole blood

Debate continues as to whether fresh whole blood (< 48 hr) reduces bleeding and transfusion requirements, particularly in infants. The classic study by Manno and coworkers ₃₂ demonstrated that either very fresh whole blood (< 6 hr), or fresh whole blood (24-48 hr) reduced blood loss by 85% in patients less than 2 yr of age who were undergoing cardiac surgery with bypass, when compared with reconstituted whole blood. A recent prospective, randomized, controlled study of 48 hr old whole blood versus reconstituted whole blood in 200 infants under 1 yr of age, demonstrated similar blood loss, blood transfusion requirements, and serum levels of inflammatory mediators and troponin I in both groups. The group received 48 hr old whole blood averaged a longer intensive care unit stay by one day, and postoperatively had a larger positive fluid balance ₃₃ .

Brain monitoring

Currently the following brain monitors are in common use during cardiac surgery: processed electroencephalogram (EEG), transcranial Doppler ultrasound (TCD), and near-infrared cerebral oximetry (NIRS).

EEG

The Bispectral Index (BIS) monitor uses a proprietary algorithm based on the normal adult EEG; Fourier transformation and bispectral analysis of a one-channel processed EEG pattern compute a single number, the BIS. This index ranges from 0 (isoelectric EEG) to 100 (awake). Mean awake values in are the 90 – 100 range in adults, infants and children. The real-time unprocessed EEG waveform of the BIS can be used to recognize EEG burst suppression, or electrical silence.

TCD

TCD is sensitive, real-time monitor of cerebral blood flow velocity and emboli during congenital heart surgery. Currently available instruments use pulsed-wave ultrasound at 2 MHz frequency, which is range-gated, emits a power of 100 mW, and has a sample volume length of up to 15 mm. a display of the frequency spectrum of Doppler signals is easily interpreted, and peak systolic and mean flow velocities, in cm/sec, are displayed. The temporal or anterior fontanelle windows (in infants) are insonated at a depth sufficient to obtain a signal from the middle or anterior cerebral arteries on the side of interest.

NIRS

NIRS is a non-invasive optical technique used to monitor brain tissue oxygenation. Most devises use 2 – 4 wavelengths of near-infrared light at 700 – 1000 nm, where the iron-porphyrin complexes of oxygenated and deoxygenated hemoglobin have distinct absorption spectra. Commercially available devices measure the concentration of oxy – and deoxyhemoglobin, thereby determining cerebral oxygen saturation. The INVOS 5100 is FDA approved for use in children, is compact, simple to use, and requires no warm up. It uses two near-infrared wavelengths of 730 and 810 nm. The INVOS processor displays a numerical value, the regional cerebral oxygen saturation index (rSO₂i), which is the ratio of oxygemoglobin to total hemoglobin in the light path. The rSO₂i is reported as a percentage on a scale ranging from 15% to 95%. Clinical evidence suggests a correlation between low cerebral saturation and adverse neurological outcome.