Peri -operative Management of Pulmonary Hypertension

1. Peri-operative Management of Pulmonary Hypertension DR SP MACHAWIRA University of Wits

2. Introduction • Pulmonary hypertension complicates 2% of patients undergoing congenital cardiac surgery(Adatia I et al 2009) • In India 60% of post operative deaths due to PHT crises(Choudhary SK et al Ann ThoracSurg 1999) • The functional and structural status of the pulmonary bed important • Immediate post-operative period the most vulnerable time • Pulmonary endothelium dysfunction the most important factor but pathophysiology incompletely understood

3. Introduction • The outcome of patients has improved due to better understanding of peri-operative management • PHT is an independent risk factor in morbidity and mortality in patients undergoing congenital cardiac surgery • Pulmonary hypertensive crisis is the extreme end and a feared complication associated with increased morbidity and mortality

4. Hypertensive Pulmonary Crisis • Complicates 0.75% of congenital cardiac surgery and has a mortality of 20% • Pathophysiology incompletely understood and complex • Increased post operative vasoreactivity to sympathetic stimuli • Vasospastic stimuli result in sudden increase of pulmonary artery pressure and resistance • Right heart failure with TR • Systemic hypotension and MI • Increased airway resistance

5. Management • Complex and unpredictable • Prevention is the best • Identifying patients at risk • Pre-operative care • Intra-operative care • Post-operative care

6. General • Early surgery prevents the development of pulmonary vascular obstructive disease • Sedation with fentanyl and paralysis first 24 hours • Prevent acidosis: pH and not pCO2 increases pulmonary vascular resistance • Correct hypothermia • Maintain adequate oxygenation but avoid baro and volutrauma • Correct polycythaemia to reduce PVR

7. Patients At Risk • Difficult to predict influenced by age, lesion & pre-existing endothelial cell dysfuction • Usually affects patients with reactive pulmonary vascular beds • Patients with pulmonary venous hypertension(TAPVC) have extremely reactive beds • Extra-cardiac syndromes eg Trisomy 21, omphalocele

8. Patients at risk • PA arising from the aorta, Truncus arteriosus, AP window • Single ventricle physiology with unrestricted pulmonary blood flow • mPAP >25mmHg or 50-60% of systemic on coming off bypass with signs of low cardiac output • Patients with residual lesions

9. Pre-operative Care • Severe CCF needs significant resuscitation • Intubation and ventilation may be necessary to correct metabolic derangements • Control and treat sepsis • Avoid hypotension at induction may cause cardiac ischaemia • Need to maintain Qp:Qs at 1:1 to ensure adequate organ perfusion as pulmonary overcirculation implies systemic hypoperfusion • Hypercapnia and low FiO2 increase PVR to ensure adequate systemic blood flow • Research on pre-op iNO, sildenafil and endothelin inhibitors

10. Intra-operative Strategies • Smaller tidal volumes once sternum open • Cardiopulmonary bypass, hypothermia and circulatory arrest enhances pulmonary vaso-reactivity • Complete repair where possible • PFO may be a life saving procedure allowing for pop-off valve • Use of PAP lines debatable increased risk of bleeding, overreacting to changes, considered mandatory in research on new drugs

11. Effect of Bypass on Haemodynamicc

12. Post-operative • ICU care plays a critical role in the patient outcome • Anticipate and treat PHT crises aggressively • Sedation with Fentanyl and paralysis in the first 24 hours especially when suctioning to avoid pain and anxiety • Adequate oxygenation without barotrauma or hyperoxygenation • Avoid hypercapnia however pH control more important • pH> 7.4 or pH>7.5 when patient has had a crisis: • HCO3 and hyperventilation may be necessary

13. III. INOTROPIC SUPPORT IN THE PERI-OP PERIOD Effect of pH and CO2 on PVR

14. Post-operative Strategies • Use of inodilators eg milrinone, dobutamine, low dose adrenaline with nitroglycerin • Specific pulmonary vasodilators iNO, prostacyclin, sildenafil • Investigate surgical accuracy ie residual lesions • ECMO • RVAD

16. Inhaled Nitric Oxide • Nitric oxide produced by endothelial cell final pathway to vasodilation • Accepted mode of treatment for post-operative pulmonary hypertension • Easy to administer, minimal side effects and specific for pulmonary vascular bed • Dose 2-80ppm, however no clinical benefits of doses>10-20ppm • Rebound PHT wean slowly from 5ppm at 0.5ppm/2hours- prolongs ventilation • Side effect methaemoglobinaemia(>5%) negligible

17. iNOvs Placebo on PVRI

18. Sildenafil • Type 5 phosphodiesterase inhibitor • Can be used to assist with weaning off iNO hence earlier extubation • At doses of 0.3-0.5mg/kg/6hourly can be used to prevent rebound PHT on weaning iNO • Can be used in conjuction with iNO, and inhaled Illoprost in patients who are in refractory PHT • May be useful in transition to chronic therapy

19. Illoprost • Prostacyclin analogue, inhibits thrombocyte aggregation and brings about vasodilation • Can be inhaled or intravenous • Inhaled has half life 30 minutes • No toxic effects • Effect comparable to iNO • Can be used in PHT resistant iNO • Can be used intermittently thus allows for weaning off from ventilation

20. Other Strategies • ECMO used much less often due to general improvement in peri-operative care • RVAD • Prophylactic therapy citrulline, sildenafil and endothelin receptor inhibitors • Combination therapy in refractory cases