14.3.8 Treatment options for neonates

Palliative procedures

Due to neonates’ extreme frailty, practitioners have traditionally settled for palliative procedures aimed at ensuring babies' survival until they are of an age and weight at which total correction is less risky. The aim of palliation is to control pulmonary blood flow sufficiently for achieving a balance  between pulmonary and systemic blood flow (Qp/Qs = 1:1), for maintaining sufficient SaO2 (approximately 85%), and thus enabling growth [8]. For example:
 
  • Banding of the pulmonary artery to reduce blood flow in patients with an L-to-R shunt and high pulmonary blood flow. The target values are SaO2 of 85% while breathing ambient air, a 20% increase in systemic pressure, and a 50% reduction in PAP. Bandings with ultrasound-adjustable diameters are available, enabling pulmonary blood flow to be adapted to children's postoperative status.
  • Systemic-pulmonary anastomosis (Potts or Waterston central shunt, Blalock-Taussig shunt) to increase pulmonary blood flow if this is too low. The target SaO2 is 80-85%.
  • Stage 1 Norwood procedure or hybrid procedure in cases of hypoplastic left heart syndrome (see Ventricular Hypoplasia).

The degree of PA stenosis or the size of the shunt are difficult to assess since children's needs change as they grow and PVR falls during the first weeks of life. There is a risk of being too restrictive or too liberal. Moreover, as a result of palliation, children are faced with severe cyanosis or relative pulmonary hypertension and inadequate afterload for the ventricles. Remodelling of the heart chambers and pulmonary vessels may jeopardise the chances of future correction.

Uni- or biventricular correction

If one ventricle is so hypoplastic that reconstruction of two functional chambers is impossible, the only option is to perform palliative procedures based on univentricular reconstruction. The single functional ventricle is used to ensure high-pressure systemic circulation. The challenge is then to create an arrangement capable of ensuring low-pressure pulmonary circulation: staged Norwood procedures, hybrid procedure, partial cavopulmonary connection (Glenn procedure) or total cavopulmonary connection (Fontan procedure) (see Ventricular Hypoplasia).

Primary total correction

The current preference is to perform total corrections of biventricular congenital heart defects very soon after birth, and to only conduct palliative procedures on patients with univentricular pathologies. This involves operating on children weighing 4 kg or less with CPB and sometimes deep hypothermia in the first weeks of life [12,13,16]. Pending a curative procedure, neonates may be stabilised with targeted therapies.
  • Prostaglandin (PGE1) infusion to maintain ductus arteriosus patency;
  • Atrial septostomy by catheterisation to improve the mixture of pulmonary and systemic venous blood (Rashkind procedure);
  • Lowering PVR by hyperventilation and NO.;
  • Lowering SVR (vasodilator) to improve LV blood flow and reduce an L-to-R shunt.
When anaesthetising neonates with congenital heart diseases, a number of problems are added to the list of factors involved in paediatric cardiac anaesthesia.
 
  • Immature heart function, low contractility, excessive ventricular interdependence, fixed and heart rate-dependent systolic volume [1]
  • High metabolic requirements (100-150 kcal/kg/24 hr) but immature vital organs:
    • Low pulmonary compliance and increased work of breathing, low functional residual capacity, closing volume attained at tidal volume; 
    • Increased total water and fragile capillary membranes (risk of interstitial leakage);
    • Kidneys unable to concentrate urine normally and excrete water and Na+.
  • Very severe systemic inflammatory reaction after CPB with exacerbation of interstitial leakage and multiple organ failure requiring haemofiltration.
  • Major neurological risks: convulsions and neurological deficiencies linked to CPB duration, temperature, cerebral blood flow, pH regulation mode, Ht reduction, and the duration of any hypothermic arrests [4].
  • Postductal systemic hypoperfusion may result in mesenteric ischaemia. The incidence of postoperative necrotising enterocolitis is 3.5% and the mortality rate is 25% [7].
  • Premature infants are more likely to suffer a brain haemorrhage.
  • Surgeons and anaesthesiologists are faced with considerable technical difficulties due to small structures and tissue fragility.
A high-dose fentanyl anaesthetic (50-75 mcg/kg) supplemented with midazolam should be appropriate for limiting subjects’ reaction to stress and pulmonary hypertensive crises [8]. The outcomes of corrective surgery on very young infants (< 2.5 kg) are rather encouraging, since the mortality rate is 2-5% [2,11,12,13]. The post-palliation survival rate for subjects with a single ventricle in the early stages of life (Norwood stage I, Giessen) is currently almost 95% with long-term life expectancy of 85% [9,10,14].

Circulatory support for children

Although a miniature version of the intra-aortic balloon pump (IABP) exists (2.5 mL balloon, for subjects weighing 2 kg and above), it is not widely used for children for several reasons.
 
  • The dysfunction is often right-sided or biventricular, whereas an IABP only supports the LV.
  • It is difficult to control the balloon due to excessively rapid heart rate.
  • The flexibility of children's aortas considerably diminishes the balloon's haemodynamic effect.
  • Any aortopulmonary collaterals or systemic-pulmonary shunts present divert blood from the aorta to the PA.
ECMO (extracorporeal membrane oxygenation) is a venoarterial circulatory and respiratory support system combining a pump and an oxygenator. Blood is taken from the RA or a vena cava and returned to the aorta or a great artery. Young children’s femoral arteries are too narrow to accommodate cannulas. The circuit volume ranges from 350 mL (neonates) to 2 L (adults). The flow rate is similar to CPB: 100-150 mL/kg/min for subjects under 10 kg, 2.4 L/min/m2 for subjects above this weight. Ht must be between 35% and 45% and platelets > 105/mL. Inotropic agents are discontinued to prevent down-regulation of beta receptors and ventilation is reduced to prevent atelectasis. The system requires aggressive anticoagulation (heparin 10-20 U/kg/hour) for ACT > 250 seconds. To that end, the optimal means of monitoring is to track heparinaemia by measuring the anti-Xa effect (target: 0.25-0.35). ECMO requires constant supervision and strict monitoring of anti-Xa, antithrombin (AT-III) and platelets. The effects of heparin are diminished in cases of AT-III deficiency [17].

ECMO is preferable for short-term assistance (1-3 weeks) and in cases of PAH or respiratory failure, while ventricular assist devices are superior for long-term and for univentricular support. Although outcomes for respiratory distress syndrome in neonates are satisfactory (90% survival), the mean survival rate after cardiac surgery is only 45% [6]. Postoperatively, it is higher (approximately 70%) in cases where cardiorespiratory failure develops after a period of haemodynamic stability than in instances where withdrawal from CPB is impossible (approximately 35%) [3]. The prognosis is poor if the ventricle does not demonstrate any functional recovery within 48-72 hours [15]. The duration of ECMO ranges from 24-48 hours to 2-4 weeks. Outcomes are disastrous beyond this period [5]. Its main complications are haemorrhage combined with blood dyscrasia, kidney failure, neurological lesions of haemorrhagic or embolic origin, arrhythmia and sepsis.

Ventricular assist devices are used to provide longer term support, in most cases for the LV (acute myocarditis, ischaemia related to ALCAPA syndrome, failure following arterial switch, etc.). With univentricular systems, the RV must be capable of ensuring pulmonary blood flow, which in most cases requires pharmacological assistance (milrinone, NO, possibly temporary right-side assist). The RV develops failure in 25% of cases (see Section 12 - Ventricular Assist Devices) [2]. The potential imbalance between the two circulations may reverse an L-to-R shunt and induce arterial desaturation by switching to R-to-L, this is the reason why such shunts must be closed before installing an assist device. Although the survival rate to transplantation is currently 79%, the rate of stroke is up to 45% depending on the publication quoted [2]. Several devices may be used in paediatrics.
 
  • The Thoratec™ system is a paracorporeal pulsatile univentricular chamber. It is intended for children aged 7 years and above (body surface area > 0.7 m2) (see Figure 12.22).
  • The BerlinHeart EXCOR™ (uni- or biventricular) is designed to operate at pump volumes of 10 to 80 mL. It can be used in children weighing 4 kg and above (body surface area > 0.2 m2). The pulsatile ventricular chamber is also paracorporeal.
  • Implantable non-pulsatile systems that can be used with children aged 12 years and above (see Figures 12.24 and 12.25A).
System performance is dependent on adequate preload and satisfactory RV function. Indeed, the RV must ensure increased blood flow since the flow from the pump is higher than that of the deficient LV and it also loses any support from the LV through septum contraction since the LV is decompressed. Right-side decompensation and severe TI are common [17]. This must be managed with a specific treatment for right-side failure – respiratory alkalosis, NO, epinephrin + milrinone. Anaesthetists should ensure that they use non-cardiodepressant agents, maintain blood volume (the pump flow rate is preload-dependent) and ventilate patients at a low intrathoracic pressure.
 
Therapeutic options for children
Total correction in the first weeks of life: ideal solution if feasible.

Palliative procedure: ensure that the pulmonary and systemic blood flow are as close as possible (Qp/Qs = 1), maintain SaO2 at 80-90% in cases of cyanosis, and prepare the ventricles for definitive reconstruction.

Some complex defects require reconstructions based on a univentricular system.

In cases of ventricular failure, ECMO and ventricular assist devices can be used with children weighing 4 kg and above. ECMO is the preferred option for PAH or respiratory failure. Assist devices enable long-term treatment, preferably of the LV. The main complications are right-side decompensation, haemorrhages, infections and strokes.
 
 
© BETTEX D, BOEGLI Y, CHASSOT PG, June 2008, last update February 2020


References
 
  1. BAUM VC, PALMISANO BW. The immature heart and anesthesia. Anesthesiology 1997; 87:1529-48
  2. CLARK JB, PAULIKS LB, MYERS JL, et al. Mechanical circulatory support for end-stage heart failure in repaired and palliated congenital heart disease. Curr Cardiol Rev 2011 ; 7 :102-9
  3. DUNCAN BW. Mechanical circulatory support for infants and children with cardiac disease. Ann Thorac Surg 2002 ; 73 :1670-7
  4. DU PLESSIS AJ. Neurologic complications of cardiac disease in the newborn. Clin Perinatol 1997; 24:807-26
  5. GUPTA P, McDONALD R, CHIPMAN CW, et al. 20-year experience of prolonged extracorporeal membrane oxygenation in critically ill children with cardiac or pulmonary failure. Ann Thorac Surg 2012 ; 93 :1584-90
  6. JOFFE AR, LEQUIER L, ROBERTSON CM. Pediatric outcomes after extracorporeal membrane oxygenation for cardiac disease and for cardiac arrest : a review. ASAIO J 2012 ; 58 :297-310
  7. McELHINNEY DB, HEDRICK HL, BUSH DM, et al. Necrotizing enterocolitis in neonates with congenital heart disease: Risk factors and outcomes. Pediatrics 2000; 106:1080-7
  8. ODEGARD KC, LAUSSEN PC. Approach to premature and full-term infant. In: ANDROPOULOS DA, et al, eds. Anesthesia for congenital heart disease. Oxford: Blackwell-Futura, 2005, 197-209
  9. OHYE RG, SCHRANZ D, D'UDEKEM Y. Current therapy for hypoplastic left heart syndrome and related single ventricle lesions. Circulation 2016; 134:1265-79
  10. PETIT CJ. Staged single-ventricle palliation in 2011 : outcomes and expectations. Congenit Heart Dis 2011 ;  6:406-16
  11. REDDY VM, HANLEY FL. Cardiac surgery in infants with very low birth weight. Semin Pediatr Surg 2000; 9:91-5
  12. REDDY VM, McELHINNEY DB, SAGRADO T, et al. Results of 102 cases of complete repair of congenital heart defects in patients weighing 700 to 2500 grams. J Thorac Cardiovasc Surg 1999; 117:324-31
  13. ROSSI AF, SEIDEN HS, SADEGHI AM, et al. The outcome of cardiac operations in infants weighing two kilograms or less. J Thorac Cardiovasc Surg 1998; 116:28-35
  14. SCHILLING C, DALZIEL K, NUNN R, et al. The Fontan epidemic: population projections from the Australia and New Zealand Fontan Registry. Int J Cardiol 2016; 219:14-9
  15. SCHURRE AY, LAUSSEN PC, McGOWAN FX. Mechanical cardioplmonary support in infants and children with congenital heart disease. Semin Cardiothorac Vasc Anesth 2001 ; 5 :45-54
  16. WERNOVSKY G, RUBENSTEIN SD, SPRAY TL. Cardiac surgery in the low-birth weight neonate. New approaches. Clin Perinatol 2001; 28:249-64
  17. YUKI K, SHARMA R, DINARDO J. Ventricular-assist device therapy in children. Best Pract Res Clin Anaesthesiol 2012 ; 26 :247-64