Capnography screening for sleep apnea in patients with acute stroke

Sleep apnea syndrome (SAS) is a prominent clinical feature in acute stroke patients. Diagnosis is usually established by polysomnography or cardio-respiratory polygraphy (CRP). Both diagnostic procedures produce high costs, are dependent on the access to a specialized sleep laboratory, and are poorly tolerated by patients with acute stroke. In this study we therefore investigated whether capnography may work as a simple screening tool in this context. In addition to conventional CRP, 27 patients with acute stroke were studied with capnography provided by our standard monitoring system. The trend graphs of the end-tidal CO2 values (EtCO2) were used to determine the capnography-based estimate of the apnea-hypopnea index (AHI(CO2)). Index events were scored when the Et-CO2 value dropped for > 50% of the previous baseline value. We found that the AHI(CO2) correlated significantly with the apnea-hypopnea index measured with conventional CRP(AHI(CRP))(r=0.94;p<0.001). An AHI(CO2) >5 turned out to be highly predictive of an AHICRP > 10. According to our findings, routinely acquired capnography may provide a reliable estimate of the AHI(CRP). The equipment needed for this screening procedure is provided by the monitoring systems of most intensive care units and stroke units where stroke patients are regularly treated during the first days of their illness. Therefore, early diagnosis of SAS in these patients is made substantially easier.