Role of determination of partial pressure of ammonia in cirrhotic patients with and without hepatic encephalopathy

Background/Aims: To compare venous, arterial and partial pressure of ammonia (pNH 3) in 27 consecutive cirrhotics with hepatic encephalopathy, 15 cirrhotics without hepatic encephalopathy and nine controls; to reevaluate all parameters after the improvement of encephalopathy. Methods: Patients were studied by clinical examination and psychometric testing. pNH 3 was calculated from arterial ammonia and pH. Results: In patients with encephalopathy, each form of ammonia was higher than in both controls and patients without encephalopathy. The correlation with the severity of hepatic encephalopathy was similar for venous ( r=0.72), arterial ammonia ( r=0.76) and pNH 3 ( r=0.75). The sensitivity and specificity of each variable in correctly classifying the patients as having or not having hepatic encephalopathy was also similar. Each form of ammonia decreased after the resolution or amelioration of symptoms. However, even in the 17 patients with complete resolution of hepatic encephalopathy, all three ammonia determinations resulted unchanged or increased in some patients. Conclusions: Despite the significant correlation between pNH 3 and hepatic encephalopathy, our study suggests that neither pNH 3 nor arterial ammonia are, from a clinical point of view, more useful than venous ammonia: all three determinations being limited both for the diagnosis of hepatic encephalopathy and for the clinical management of the patients.