HE’s the One

Hepatic encephalopathy (HE) is a spectrum of neuropsychiatric signs or symptoms attributable to hepatic dysfunction after ruling out other brain diseases. In human patients, identifying known precipitating factors (eg, GI bleeding, constipation, diarrhea, infection, hypokalemia, hyponatremia, excessive dietary protein) is important for management and prognosis to understand the relationship between plasma ammonia concentrations and HE severity, and to assess the association between common human HE precipitating factors and clinical signs at admission. The purpose was to uncover any relationship between common precipitating factors for human HE and the presence of HE clinical signs at hospital admission in dogs previously treated for HE. The most common clinical signs in dogs were lethargy, altered behavior, obtundation, ataxia, seizures, head pressing, ptyalism, vomiting, blindness, circling, shaking or twitching, and anorexia or hyporexia. Dogs treated for HE before hospitalization were significantly less likely to have clinical signs at time of hospitalization than untreated dogs; this indicates successful application of common treatment strategies. Putative precipitating factors for HE at admission included systemic inflammatory response syndrome, hyponatremia, alkalosis, hypokalemia, dietary changes or indiscretion, furosemide treatment, azotemia, GI hemorrhage, and constipation. None of these were significantly associated with clinical signs on hospitalization. Hyperammonemia (≥ 50 µg/mL) was present in 78/83 (94%) dogs with HE measured within 24 hours of hospitalization. Severity of HE at time of hospitalization was not significantly correlated with plasma ammonia concentration.

As clinicians, we commonly expect that blood ammonia concentrations will be markedly elevated when a patient presents with severe signs of HE. A surprising finding of this study was that severity of hyperammonemia was not significantly correlated with the severity of clinical signs of HE. Treatment for HE (typically involving antimicrobial therapy, diet change, and lactulose) before referral appeared to be associated with fewer clinical signs on admission to the referral hospital. Although the study was not able to assess efficacy of different therapies, it appears that this general treatment approach helps alleviate clinical signs associated with HE. Despite having an incomplete understanding of precipitating factors and all of the chemical mediators contributing to HE, it appears that general treatment concepts taught during veterinary training are effective. Further research may elucidate the most effective treatments.—Julie Walker, DVM, DACVECC