Nocturnal haemoglobin oxygen desaturation in urban and rural East African paediatric cohorts with and without sickle cell anaemia: a cross-sectional study.

Low haemoglobin oxygen saturation (SpO2) predicts complications in children with sickle cell anaemia (SCA) in the North but there are few data from Africa, where the majority of the patients reside. We measured daytime and overnight SpO2 in children with SCA in routine follow-up clinic, and controls without symptoms of SCA, comparing rural (Kilifi, Kenya) and urban (Dar-es-Salaam, Tanzania) cohorts. Daytime SpO2 was lower in 65 Tanzanian children with SCA (TS; median 97 (IQR 94-100)%); p<0.0001) than in 113 Kenyan children with SCA (KS; 99 (98-100)%) and 20 Tanzanian controls (TC; 100 (98-100)%). Compared with 95 Kenyan children with SCA, in 54 Tanzanian children with SCA and 19 TC who returned for overnight oximetry, mean (KS 99.0 (96.7-99.8)%; TS 97.9 (95.4-99.3)%; TC 98.4 (97.5-99.1)%; p=0.01) and minimum nocturnal SpO2 (92 (86-95)%; 87 (78.5-91)%; 90 (83.5-93)% p=0.0001) were lower. The difference between children with SCA persisted after adjustment for haemoglobin (p=0.004). Urban Tanzanian children, with and without SCA, experience greater exposure to low daytime and night-time SpO2 compared with rural Kenyan children with SCA. Possible explanations include differences in the prevalence of obstructive sleep apnoea or asthma, alterations in the oxyhaemoglobin desaturation curve or cardiovascular compromise, for example, to shunting at atrial or pulmonary level secondary to increased pulmonary artery pressure. The fact that non-SCA siblings in the urban area are also affected suggests that environmental exposures, for example, air pollution, nutrition or physical exercise, may play a role. Further studies should determine aetiology and clinical relevance for the SCA phenotype in children resident in Africa.

Nocturnal haemoglobin oxygen saturation variability is associated with vitamin C deficiency in Tanzanian children with sickle cell anaemia.

AIM: To compare pulse oximetry in children with sickle cell anaemia (SCA) and controls and test the hypothesis that vitamin C deficiency (VCD; <11.4 µmol/L) is associated with nocturnal haemoglobin oxygen desaturation in SCA. METHODS: We undertook nocturnal and daytime pulse oximetry in 23 children with SCA (median age 8 years) with known steady-state plasma vitamin C concentrations and 18 siblings (median 7 years). RESULTS: Median nocturnal delta 12 s index (delta12 s), a measure of haemoglobin oxygen saturation (SpO(2)) variability, was 0.38 (interquartile range 0.28-0.51) in SCA and 0.35 (0.23-0.48) in controls, with 9/23 and 6/18, respectively, having a delta12 s >0.4, compatible with obstructive sleep apnoea (OSA). Eleven of twenty-three with SCA had VCD; logged vitamin C concentrations showed a 66% decrease per 0.1 unit increase in delta12 s ([95% CI -86%, -15%]; p=0.023) and delta12 s >0.4 was associated with VCD (odds ratio 8.75 [1.24-61.7], p=0.029). Daytime and mean nocturnal SpO(2) were lower in SCA but there was no association with vitamin C. CONCLUSION: Obstructive sleep apnoea (OSA), detected from nocturnal haemoglobin oxygen saturation variability, is common in Tanzanian children and associated with vitamin C Deficiency in SCA. The direction of causality could be determined by comparing OSA treatment with vitamin C supplementation.