14.4.1 Preoperative assessment and premedication

The equilibrium of patients with congenital heart disease depends on a delicate compromise between the haemodynamic disorder and any compensation mechanisms. Such mechanisms deplete the heart and lungs’ functional reserve, thus reducing the safety margin. This is a particularly significant issue with neonates, since, compared to older children, they exhibit higher cardiac index, alveolar ventilation and oxygen requirement. Although their pharmacokinetic volume of distribution is larger, substance metabolism is slower.

Surgery entails the following major risk factors:
 

Echocardiography and catheterisation are the main factors used to determine anaesthetic strategy. It is essential to fully understand the results of these examinations, be aware of previous palliative or corrective operations, and observe patients’ response to any initiated treatments. It is possible to determine a child's general condition and ascertain how she/he is affected by her/his disease based on medical history, physical examinations and laboratory results.
 

The aim of premedication is to calm children in order to reduce oxygen demand without making them hypoxic or hypercapnic through hypoventilation. Cyanotic children exhibit reduced response to hypoxia, but continue to respond normally to hypercapnia. While neonates are happy in a warm, dry environment, older children require more personalised contact. Any premedication for children (aged one year and above) should be chosen based mainly on whether they present with cardiac failure or a dynamic obstruction – any depressants of myocardial function are dangerous for the former, but beneficial for the latter. If in doubt, mask induction in a calm environment is preferable. Children are particularly averse to the intramuscular route, although this is the only possible route of administration for ketamine in premedication (3 mg/kg). The dilemma lies in determining whether heavier premedication would increase a child's safety without impairing his/her haemodynamics or respiratory reflexes or provide him/her with greater protection from stress and anxiety. The most commonly adopted approach is to use midazolam (0.5 mg/kg oral or rectal, 0.2 mg/kg intranasal, 0.1 mg/kg IM) and/or fentanyl transmucosal (10-15 mcg/kg). Infants < 6 months are not premedicated.

Cardiovascular medicines should not be discontinued preoperatively. This includes aspirin, which interruption could cause catastrophic thrombosis in delicate conduits. Angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB) should not be discontinued as they have little impact on hypotension incidence on induction in children [5]. Although preoperative fasting provides a guarantee of safety, steps should be taken to avoid the risk of dehydration or hypoglycaemia in young children with cyanosis or haemoconcentration. If required, a venous line is fitted the day before the operation. Under current recommendations, timings are determined by age:
 

Prophylaxis against endocarditis

Endocarditis incidence is approximately 30 times higher among children with congenital heart diseases than among normal children. The risk is highest among patients who are carriers of prosthetic equipment (patches, valves, conduits), those with lesions involving high-velocity jets (VSD, valvular insufficiency), and cyanotic subjects (tetralogy of Fallot). The risk is reduced if lesions involve low-velocity flows (ASD, PFO) [6]. Once implanted equipment has been completely endothelialised (i.e. on average after 6 months), bacterial risk is very low. Besides cardiac surgery procedures, prophylaxis against endocarditis is also recommended in the following situations [2,4].
 

These recommendations only apply to septic surgery and dental procedures involving opening the gums or periapical region. Antibiotic prophylaxis is not routinely recommended for digestive, respiratory, neurological, genitourinary, dermatological or orthopaedic procedures, unless such action is necessary due to the patient's infectious state or local contamination [1]. A single dose of amoxicillin (50 mg/kg) is routinely administered orally one hour prior to surgery. In the event of allergies, cefazolin (50 mg/kg), ceftriaxone (50 mg/kg) or clyndamycin (20 mg/kg) are used. Antibiotic prophylaxis is recommended for all operations in cardiac surgery.

 

 

 

© BETTEX D, BOEGLI Y, CHASSOT PG, June 2008, last update February 2020