Breath Gas, or “Exhalome,” Analysis of Volatile Organic Compounds Could Help Gauge AKI Severity

Dozens of volatile organic compounds (VOCs) are found at elevated concentrations in expired gas from critically ill patients with acute kidney injury (AKI), reports a study in Critical Care Medicine.

The study included 20 mechanically ventilated patients with AKI, along with a control group of critically ill patients without AKI. The mechanically ventilated patients also had indications for dialysis.

Intensities of VOCs in breath samples were measured using multicapillary column ion-mobility spectrometry. Each patient’s “exhalome” was evaluated from 30 minutes before they started continuous venovenous hemodialysis through 7 hours after the start of dialysis.

The researchers hypothesized that AKI would be associated with a characteristic alteration of the VOC pattern, and that the changes would be reversed during hemodialysis.

Their analysis included 719 samples of expired air. Of the 60 signals they observed, 44 compounds were identified. During hemodialysis, 34 signals decreased while 26 signals were unchanged. Among the VOCs that decreased with dialysis were cyclohexanol, 3-hydroxy-2-butanone, 3-methylbutanal, and dimer of isoprene.

The hemodialysis-associated decreases in VOC signals included 30 of the 45 signals that were increased in the AKI group.

Many critically ill patients develop AKI requiring dialysis. Breath gas analysis might help to meet the need for real-time bedside assessment of kidney function in this group of patients, the authors of the study noted.

The study documents higher exhaled concentrations of 45 different VOCs that were greater in critically ill patients with AKI than in those with normal kidney function and finds that most of these VOCs decrease during continuous dialysis.

“Exhalome analysis may help to quantify the severity of acute kidney injury and to gauge the efficacy of dialysis,” the authors said.

March 2019 (Vol. 11, Number 3)


1. Hüppe T, et al. Volatile organic compounds in patients with acute kidney injury and changes during dialysis. Crit Care Med 2019; 47:239–246.