In the current study, the concentration of CO in the exhaled air (COexh) and the concentration of carboxihemoglobin in venous blood (COHb), as indexes of the systemic production of CO, were assessed in 16 healthy subjects, and 32 patients with cirrhosis (12 without ascites and 20 with ascites). Smokers and patients with lung diseases were excluded; COexh and COHb were significantly higher in patients with ascites than values in healthy subjects (p < 0.005 for both). In 19 patients with spontaneous bacterial peritonitis (SBP), values of COexh and COHb were even higher than those in patients with ascites without SBP (P < 0.01 for both). Resolution of SBP was associated with a significant reduction in both parameters, which reached values similar to those of patients without SBP one month after resolution on infection. In patients with SBP, high levels of COexh correlated with Child-Pugh score, plasma renin activity and serum levels of norepinephrine.

In conclusion, these results support the presence of an increased systemic production of CO in cirrhosis with ascites and SBP, which could participate in the pathogenesis of arterial vasodilation present in advanced cirrhosis.