Pulmonary hypertension

Definition: systolic PAP >35 mmHg or mean PAP >25 mmHg, clinically if systolic PAP:systolic BP <0.5

WHO Classification
I.	Pulmonary arterial hypertension
I.1	Idiopathic
I.2	Familial
I.3	Associated with collagen vascular disease, portal hypertension, HIV, drugs & toxins, congenital systemic-pulmonary shunts, others
I.4	Persistent PHT in the Newborn
I.5	Pulmonary veno-occlusive disease
II.	Pulmonary hypertension w/ left heart disease:left sided atrial, valvular or ventricular disease (TAPVR, MS, AS, Coarctation)
III.	PHT associated with disorders of the respiratory system: COPD, sleep apnea, central hypoventilation Syndrome, high altitude, CLD
IV.	PHT due to chronic thrombotic or embolic events
V.	Miscs: sarcoidosis, histiocytosis, others

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Diagnosis:

• PA pressure: most reliable, invasive line
• LA pressure: differential diagnosis – LV dysfunction
• Echocardiography: measurement of TR jet velocity (modified Bernoulli equation: RVSP = 4 * v2 + RAP), movement of the interventricular septum, identify anatomical problems
• Cardiac catheterisation: right heart catheter (mPAP >25 mmHg or PVR >3 Wood units/m2) → vasodilator therapy challenge to guide further therapy
• Cardiac MRI: RV structure and function (limited in neonates)
• High resolution chest CT with contrast: parenchymal lung disease, thromboembolism, others

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Physiology:

Increase in RV afterload → RV volume and pressure increase → RV systolic dysfunction (→ TR) and diastolic dysfunction (→ RV diastolic HTN → increased right to left shunt if exists → hypoxia) → reduced RV output → reduced LV filling → reduced CO and reduced coronary artery perfusion pressure → RV ischemia and ventricular interdependence → RV systolic dysfunction

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Neonatal PHT:

Incidence 2:1000, most common due to MAS, RDS, pneumonia, also idiopathic or in congenital diaphragmatic hernia

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Postoperative PHT:

• Preoperative predisposition: increased PVR, increased PBF, increased PVR and PBF, increased pulmonary venous pressure, lesion related (TAPVD, AVSD, VSD, IAA, truncus, shunt ops)
• Cardiopulmonary bypass: decreased NO production, ischaemia-reperfusion injury, attendant inflammatory response (thromboxane, microemboli, leucosequestration, HPV)
• Standard cardiovascular monitoring: early signs are tachycardia and hypotension; hypoxia occurs early only due to intracardiac shunts or as a late sign

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Prophylaxis for postoperative PHT:

Maintain adequate analgesia and sedation (fentanyl 1 mcg/kg IV before painful stimuli), consider paralysis, normothermia, normal pH, aim paCO2 30-35 mmHg, paO2>75 mmHg in non-cyanotic lesion, prevent hyper- and hypoinflation, minimise intrathoracic pressures, consider milrinone infusion, consider iNO

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Therapy for acute PHT crisis:

• Increase FiO2 to 1.0: O2 is the best pulmonary vasodilator
• Support cardiac output:resuscitation if required, dopamine (5-10 mcg/kg/min), dobutamine (5-10 mcg/kg/min), adrenaline (0.02-0.1 mcg/kg/min), milrinone (0.25-0.75 mcg/kg/min) as a PDE3 inhibitor increases cAMP → PVR vasodilation
• NO donator: increased cGMP → vasodilation: commence NO 20 ppm, SNP (0.5-4 mcg/kg/min), GTN (0.5-5 mcg/kg/min)
• Prostacyclin (= prostaglandin I2 = epoprostenol): increased cAMP → vasodilation, commence infusion (5-15 ng/kg/min), or nebulised; half-life: 3 min., can increase PBF and promote pulmonary oedema
• Surfactant in neonates: promotes lung expansion, commence stat dose of poractant alpha (200 mg/kg)
• Consider HFO: promotes lung expansion, avoid hyperinflation
• Consider ECMO

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Therapy for chronic PHT:

• Sildenafil: (PDE5 inhibitor → increased cGMP), test dose 0.1 mg/kg, then increase slowly to maximum 2 mg/kg q4hr. FDA recommends against the use in sildenafil in chronic PHT in children, as lower doses were not effective, higher doses increased mortality. The implication its use in PICU is unclear.
• Prostacyclin
• Bosentan (1 mg/kg BD, increase to 2 mg/kg BD after 4 weeks)
• Lung transplantation

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References:

[1] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S79-84: Steinhorn: Neonatal pulmonary hypertension

[2] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S27-9: Taylor et al: Fundamentals of management of acute postoperative pulmonary hypertension

[3] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S23-6: Mullen: Diagnostic strategies for acute presentation of pulmonary hypertension in children: particular focus on use of echocardiography, cardiac catheterization, magnetic resonance imaging, chest computed tomography, and lung biopsy

[4] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S15-22: Bronicki et al: Pathophysiology of right ventricular failure in pulmonary hypertension

[5] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S30-6: Barr et al: Inhaled nitric oxide and related therapies

[6] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S41-5: Ivy: Prostacyclin in the intensive care setting

[7] Pharmacotherapy. 2010 Jul;30(7):728-40: Buckley et al: Inhaled epoprostenol for the treatment of pulmonary arterial hypertension in critically ill adults

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