Hemodynamic studies on cholera. Effects of hypovolemia and acidosis

Issues and Controversies in the Evolution of Oral Rehydration Therapy (ORT)

The original studies demonstrating the efficacy of oral glucose-electrolytes solutions in reducing or eliminating the need for intravenous therapy to correct dehydration caused by acute watery diarrheas (AWD) were focused chiefly on cholera patients. Later research adapted the oral therapy (ORT) methodology for treatment of non-cholera AWDs including for pediatric patients. These adaptations included the 2:1 regimen using 2 parts of the original WHO oral rehydration solution (ORS) formulation followed by 1 part additional plain water, and a “low sodium” packet formulation with similar average electrolyte and glucose concentrations when dissolved in the recommended volume of water. The programmatic desire for a single ORS packet formulation has led to controversy over use of the “low sodium” formulations to treat cholera patients. This is the subject of the current review, with the conclusion that use of the low-sodium ORS to treat cholera patients leads to negative sodium balance, leading to hyponatremia and, in severe cases, particularly in pediatric cholera, to seizures and other complications of sodium depletion. Therefore it is recommended that two separate ORS packet formulations be used, one for cholera therapy and the other for non-cholera pediatric AWD.

Acidosis in a patient with cholera: a need to redefine concepts

A patient presented with cholera and a severe degree of ECF volume contraction. Despite large losses of bicarbonate (HCO3-)-containing diarrhoeal fluid, laboratory acid-base values were remarkably close to normal. A detailed analysis emphasizing principles of physiology and a quantitative approach provided new insights and eventually better definitions of metabolic and respiratory acidosis. A shift in focus from HCO3- concentration to HCO3- content in the extracellular fluid (ECF) compartment revealed the presence of metabolic acidosis. Central to this analysis was an emphasis on the haematocrit to enable a more accurate estimate of the degree of ECF volume contraction. The latter also revealed 'contraction' metabolic alkalosis, which masked the underlying metabolic acidosis. The presence of a respiratory acidosis of the tissue type was evident from the raised venous PCO2, which was not surprising once the magnitude of the ECF contraction had been appreciated. 'Bad buffering', as defined by Professor McCance, was the immediate danger and prompted swift action to restore an effective circulation. The haematocrit and the venous PCO2 also contribute valuable information to monitor the response to therapy. Nevertheless, there were still dangers to be discovered when an in-depth analysis suggested that the administration of isotonic saline would introduce an unanticipated danger for the patient.

Pathogenic vibrios in the natural aquatic environment

In recent years, members belonging to the genus Vibrio of the family Vibrionaceae have acquired increasing importance because of the association of several of its members with human disease. The most feared of the Vibrio species is Vibrio cholerae, the causative agent of cholera, a devastating disease of global significance. Other important vibrios of medical importance are V. parahemolyticus, V. vulnificus, V. mimicus, and to a lesser extent V. fluvialis, V. furnissii, V. hollisae, and V. damsela. Recent studies have also implicated V. alginolyticus and V. metschnikovii in human disease, although their complete significance has not yet been established. The virulence of all medically important vibrios is aided by a variety of traits that help breach human defenses. In this review, we provide an overview of the environmental distribution of the pathogenic vibrios and the important virulence traits that enable them to cause disease.