Sleep apnea may speed-up kidney decline

Jun 12 2012

By Laura Cowen

Patients with chronic kidney disease (CKD) are commonly exposed to nocturnal hypoxia that may increase the rate of decline in kidney function, Canadian researchers report.

The nocturnal hypoxia occurs as a result of unrecognized sleep apnea, which was detected in over 40% of patients with CKD, report Patrick Hanley and colleagues from the University of Calgary in Alberta.

The researchers recruited 254 patients from outpatient nephrology clinics and hemodialysis units, all of whom completed an overnight cardiopulmonary monitoring test to determine the prevalence of sleep apnea (respiratory disturbance index ≥15) and nocturnal hypoxia (oxygen saturation <90% for ≥12% of monitoring).

The patients were stratified into those with an estimated glomerular filtration rate (eGFR) at or above 60 mL/min per 1.73 m²(n=55), those with CKD (eGFR<60 mL/min per 1.73 m²not on dialysis; n=124), and those with end-stage renal disease (ESRD; on hemodialysis; n=75).

As reported in Chest, the prevalence of sleep apnea increased significantly as eGFR declined, from 27% in patients with an eGFR ≥ 60 mL/min per 1.73 m²to 41% in those with CKD, and 57% in those with ESRD).

Of note, the prevalence of nocturnal hypoxia was similar between patients with CKD and ESRD (47% and 48%, respectively), and was significantly higher than among those with an eGFR ≥60 mL/min per 1.73 m²(16%).

The researchers described this similarity as "striking" because nocturnal hypoxia has previously been demonstrated to be associated with an increased loss of kidney function.

"The chronic hypoxia hypothesis suggests that chronic ischemic damage in the tubulointerstitium of the kidney is the final common pathway for the development of ESRD," explain Hanley et al.

"If such a process is already under way in patients with CKD, it is possible that ongoing nocturnal hypoxia will amplify the effect and accelerate the decline in kidney function," they add.

This means that identification and treatment of nocturnal hypoxia may provide a potential disease-modifying intervention that could delay or halt the progression of CKD to ESRD.

However, the researchers note that a history of snoring and unrefreshing sleep were equally common among the three patient groups, indicating that objective cardiopulmonary evaluation may be required to identify respiratory abnormalities.

Hanley and team also point out that by examining patients with the full spectrum of kidney function, rather than just patients with ESRD, the study addresses limitations of those conducted previously. It shows that "further studies are required to determine whether treatment of sleep apnea and nocturnal hypoxia improves these clinical outcomes in patients with CKD," they conclude.

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