Paediatric sickle cell disease: pulmonary hypertension but normal vascular resistance

Adults with sickle cell disease (SCD) and pulmonary hypertension have high mortality but death in SCD children with pulmonary hypertension is rare. The authors hypothesised that pulmonary hypertension in SCD children may be secondary to anaemia-induced high cardiac output rather than pulmonary vascular disease.

Two independent, validated techniques were used to estimate pulmonary vascular resistance (PVR) in 50 SCD children and 50 matched controls. Tricuspid regurgitant jet velocity (TRV) and right ventricular outflow tract velocity time integral were measured using Doppler echocardiography; PVR was calculated from their ratio. Acetylene rebreathing technique using respiratory mass spectrometry was also performed to calculate pulmonary blood flow and stroke index, an estimate of PVR.

TRV was higher in SCD children compared with controls (2.28 vs 2.14 m/s, p=0.02). Fifteen of 34 (44%) children with haemoglobin of the SS genotype (HbSS) versus 1/16 (6%) children with haemoglobin of the SC genotype (HbSC) had pulmonary hypertension (TRV≥2.5 m/s) (p=0.009). Right ventricular stroke volume was higher (p<0.05) and Doppler PVR lower (1.20 (0.19) vs 1.31 (0.20) Wood units, p=0.04) in SCD children with pulmonary hypertension compared with controls. Qpeff and stroke index were higher in SCD children compared with controls (p<0.001 for both) and correlated with anaemia (p<0.001) and TRV (p=0.03). There was no correlation between TRV and history of asthma or acute chest syndrome.

Pulmonary hypertension due to raised cardiac output is common in HbSS SCD children and is associated with normal PVR. PVR should be measured before therapy with agents such as sildenafil or bosentan is contemplated.