Real-time monitoring of breath ammonia during haemodialysis: use of ion mobility spectrometry (IMS) and cavity ring-down spectroscopy (CRDS) techniques.

BACKGROUND The diffusion of high-performance analytical technology has opened prospects for breath diagnosis as a non-invasive diagnostic tool. In this study, ion mobility spectrometry (IMS) and cavity ring-down spectroscopy (CRDS) techniques were used to analyse ammonia gas (NH3) in real-time in breath from patients undergoing haemodialysis (HD) treatment and any correlation with blood urea nitrogen (BUN) levels and Kt/V were investigated. METHODS We studied 20 patients on intermittent HD treatment. The first breath samples were taken before the start of dialysis and further breath samples were taken every hour during the treatment and after the end of the session. An evaluation was also made of 20 healthy volunteers, acting as controls [healthy subjects (HS)]. RESULTS Breath ammonia concentrations were higher in CRDS-HD (914.5±301.4 versus 280±120 parts per billion (p.p.b.), P<0.0001) and IMS-HD patients (964.4±402.4 versus 280±120 p.p.b., P<0.0001) than in HS. We assessed real-time variations in the levels of NH(3) and showed a continuous decrease in the levels of NH3. Expired NH3 correlated directly with BUN levels, both in the IMS-HD (P=0.002; r=0.84; P=0.009; r=0.76) and in the CRDS-HD group (P=0.005; r=0.80; P=0.008; r=0.77), respectively, both before and at the end of dialysis. A direct correlation with Kt/V was found in both groups studied (IMS-HD: P=0.003; r=0.82; CRDS-HD: P=0.006; r=0.79). CONCLUSIONS Breath monitoring of NH3 with IMS and CRDS techniques could be useful to assess the real-time clinical status of patients during HD. By using pre-dialysis ammonia values, an approximate calculation of the Kt/Vurea ratio can be established.