Update on Anaesthetic Management of Pulmonary Arterial Hypertension in Children

Abstract

Pulmonary arterial hypertension (PAH) refers to a group of diseases that have in common narrowing of the small pulmonary arteries and arterioles resulting in progressive elevation of pulmonary vascular resistance and potential development of right ventricular failure and death. Pulmonary arterial hypertension is defined as a resting mean pulmonary artery pressure of more than 25 mmHg, often seen with a regurgitation velocity across the tricuspid valve of more than 2.8 m/s on Doppler echocardiography. However, this must be put into the context of the patient, especially in pediatrics where systemic mean arterial pressure may be 50 mmHg. Therefore, pulmonary hypertension is also recognized when the systolic pulmonary to systemic pressure ratio exceeds 0.5. Pulmonary arterial hypertension can occur idiopathically or associated with underlying conditions. The clinical classification of pulmonary hypertension (PH) categorizes PAH into idiopathic PAH, heritable PAH and PAH associated with various underlying conditions, including congenital heart defects with systemic-to-pulmonary shunt, connective tissue disease, HIV infection, portal hypertension and certain drug and toxin use. Pulmonary arterial hypertension is associated with significant perioperative risk for major complications, including pulmonary hypertensive crisis and cardiac arrest. Several mechanisms of hemodynamic deterioration, including acute increases in pulmonary vascular resistance (PVR), alterations of ventricular contractility and function and coronary hypoperfusion can contribute to morbidity. The goals of balanced and cautious anaesthetic management are to provide adequate anaesthesia and analgesia for the surgical procedure while minimizing increases in pulmonary vascular resistance and depression of myocardial function. A variety of anaesthetic induction drugs have been safely employed in patients with PH. One technique would be to use a combination of midazolam and fentanyl. Etomidate has been described as an ideal agent in PH. Propofol and thiopentone have also been used without problems. Concern has been raised that ketamine may raise PVR; however it too has been utilized safely in humans with PH. Non-depolarising and depolarising muscle relaxants can be used safely, and should be chosen based on airway management issues. A balanced anaesthetic of volatile agent and opioids can be used as maintenance. All of the commonly used modern volatile agents have been safely used in PH, and there is no evidence to recommend one over the other. Nitrous oxide should be used with caution as it may raise PVR. A systemic vasoconstrictor such as phenylephrine or noradrenaline should be on hand to treat reductions in systemic blood pressure. A carefully titrated infusion may be commenced at induction. Inotropes can be employed to improve right heart contractility but they are often more beneficial to the left heart than the right heart. The development of specific pulmonary vasodilators (Agents such as nitric oxide and prostacyclin) has led to significant advances in medical therapy of PAH that can be incorporated in anaesthetic management.It is important that anaesthesiologists caring for children with PAH be aware of the increased risk, understand the pathophysiology of PAH, form an appropriate anaesthetic management plan and be prepared to treat a pulmonary hypertensive crisis. Children with PAH are at increased risk of adverse events following anesthesia.Possible causes include increased pulmonary vascular tone, pulmonary hypertensive crisis and pulmonary thromboembolism. All precautions should be taken to avoid hypoxemia, hypotension, and hypovolemia. Postoperativecontrol of pain should be effective. Any therapy to decrease PVR, such as iNO, should be weaned with caution so as to avoid rebound increases in PVR.It may be necessary to admit the child overnight to a unit where monitoring is available and immediate medical response is possible.