Introduction There are few effective therapies available for the long-term management of the cardiac and renal sequelae of SCD. Identifying reversible factors, which exacerbate disease severity, would facilitate development of new therapies or novel applications of established treatments. Nocturnal hypoxia (NH) merits investigation as a disease modulating factor as it is established that hypoxia promotes polymerisation of sickle haemoglobin and this is reversible with oxygen therapy (Noguchi et al, 1993). Although NH is common in children with SCD and is associated with poor outcome, similar data for adults with SCD are lacking. This is the first study to determine the prevalence of OSA and NH and quantify the severity of NH in adults with SCD. In addition, we investigated the correlation between the degree of NH and organ dysfunction.
Method Patients attending SCD clinic had an Epworth sleepiness score performed. Patients with either an ESS ≥10 or symptoms suggestive of SDB were offered nocturnal oximetry. Nocturnal oximetry findings were objectively scored and compared with the detailed clinical datasets collected at regular clinic attendances. OSA was defined as 4% oxygen desaturation index (4% ODI) of >10 events/h and NH was defined as >30% total sleep time (TST) with SpO2 <90%.
Results 93 patients were screened. 34 had ESS ≥10 or clinical symptoms suggestive of SDB. 22 underwent nocturnal oximetry; mean ESS 12±4, clinic SpO2 96±4%, 4% ODI 8±6 events/h, nocturnal SpO2 91±4%, %TST SpO2 <90% 43±41%. Prevalence of OSA and NH was 59%. The degree of nocturnal hypoxia was correlated with urine protein:creatinine (r=−0.35, p=0.02), elevated pulmonary artery systolic pressure (r=−0.71; p=0.0001) and prevalence of priapism (p=0.004). There was no difference detected in frequency of painful crises or hospital admission in patients with significant NH compared to those without NH.
Conclusion This small pilot study showed that OSA and NH had a prevalence of 59% in symptomatic adult SCD patients. These data have demonstrated a correlation between the severity of nocturnal hypoxia and pulmonary hypertension, renal impairment and priapism. These observations have not previously been reported. The strength of these correlations could suggest a causal relationship, although this needs to be confirmed in a larger prospective trial. Future studies should investigate the relationship between OSA, nocturnal hypoxia and organ dysfunction and need to be focussed on interventions such as nocturnal oxygen and continuous positive airway pressure.