Neonatal calves with severe diarrhea can develop dangerously high blood potassium concentrations, a condition that disrupts the electrical activity of the heart and can quickly become life-threatening. A new randomized clinical trial now shows that a small intravenous volume of hypertonic sodium solution can reverse the characteristic electrocardiographic signs of hyperkalemia within minutes, and that the choice of infusion solution matters for how long the benefit lasts. The study, conducted on 22 diarrheic calves admitted to a university hospital, compared three rapidly infused fluids: 8.4% sodium bicarbonate, 7.5% sodium chloride, and 46.2% glucose.
Hyperkalemia is common in severely affected neonatal diarrheic calves, with reported prevalence figures of 28% to 34% in study populations of severely ill animals. Earlier thinking attributed the problem largely to acidemia driving potassium ions out of cells, but more recent work indicates that the type of acidosis present is the decisive factor and that acidemia itself is not associated with depletion of intracellular potassium stores. Plasma potassium concentrations in these calves correlate most strongly with clinical and laboratory indicators of dehydration, pointing to a reduced glomerular filtration rate as the central mechanism behind potassium accumulation.
The clinical consequences stem primarily from impaired neuromuscular excitability. Rising plasma potassium first increases the voltages of the P, Ta, S, and T waves on the electrocardiogram. As hyperkalemia worsens, P waves may disappear entirely, a sign of atrial standstill, and the QRS complex widens as ventricular conduction slows. ST segment elevation, ventricular escape rhythms, and frank arrhythmias can follow. These cardiac effects are exacerbated by the concurrent hyponatremia and strong ion acidosis that frequently coexist in hyperkalemic diarrheic calves, which often present with severe dehydration, cyanosis, an inability to stand, and signs of shock.
Standard treatment logic for hyperkalemia proceeds in chronological order: first antagonize the effects of potassium on excitable tissues, then redistribute extracellular potassium into cells, and finally enhance elimination from the body. In neonatal calves, the first two goals can theoretically be achieved with a rapid intravenous injection of a small volume of hypertonic sodium salt solution, because such infusions expand plasma volume quickly and can drive potassium back into cells. The resulting sodium load is itself therapeutic, since raising plasma sodium concentrations has been shown in humans, dogs, and a single diarrheic calf to rapidly reverse the cardiotoxic effects of hyperkalemia.
In the new trial, calves no more than 21 days old with plasma potassium above 5.8 mmol/L were randomly assigned to one of three groups. Seven calves received 8.4% sodium bicarbonate at 6.4 mL/kg over 5 minutes, delivering the same sodium load as the saline regimen given to eight calves, which received 7.5% sodium chloride at 5 mL/kg over 5 minutes. Seven calves received 46.2% glucose at 5 mL/kg over 5 minutes, prepared to match the osmolarity of the hypertonic saline. Twenty minutes after the infusion began, all calves were offered 2 L of an oral electrolyte solution. Electrocardiograms were recorded at baseline, during the infusion, and at 7, 15, 30, 60, 90, and 120 minutes after its start, using bipolar limb lead II from 32-second averaged recordings.
The electrocardiographic results were striking for the two sodium-containing solutions. At baseline, irregular heart rhythm was evident in three calves in the bicarbonate group and four in the saline group, four of which showed an irregular rhythm with missing P waves and increased QRS duration; no arrhythmias were present in any calf in the glucose group. Administration of the hypertonic sodium solutions restored regular heart rhythm and produced a significant decrease in heart rate variability measures. P waves returned as early as 7 minutes in one bicarbonate-treated calf and two saline-treated calves, and QRS duration shortened significantly in both sodium groups during the first 30 minutes, with S and T wave amplitudes falling in parallel. These changes occurred during or immediately after the infusions.
The glucose group told a different story. Plasma potassium remained essentially unchanged in these calves until 30 minutes, and the expected immediate improvement in conduction variables did not appear. Instead, the dynamics of the ratio between plasma potassium and plasma sodium were associated with an increase in QRS duration in the glucose group, while the sodium groups showed shortening. In the single glucose-treated calf that initially presented with absent P waves, return of P waves, decreased QRS duration, ST segment flattening, and reduced T wave amplitudes were observed only at 30 minutes, consistent with the delayed potassium-lowering effect of endogenous insulin release that hypertonic glucose triggers.
Statistical modeling reinforced the mechanistic interpretation. In generalized linear mixed models predicting changes in heart rate, P, Ta, S, and T wave amplitudes, QRS duration, and ST segment variables, the interaction between plasma potassium and plasma sodium was a significant predictor in nearly all models and added explanatory value beyond potassium alone for QRS duration and the amplitudes of the P wave, T wave, and ST segment. The regression coefficients indicated that calves with similar potassium concentrations showed less severe electrocardiographic changes when sodium was higher. Segmented regression analyses identified breakpoints at which electrocardiographic variables changed slope, although the previously reported threshold values from an earlier study of 130 calves were not confirmed here, likely because treatment-related changes in the potassium-to-sodium ratio added variability to the data.
The potassium-lowering trajectories themselves differed between solutions. Plasma potassium decreased similarly in the bicarbonate and saline groups until 15 minutes, but then rebounded in the saline group while continuing to fall in the bicarbonate group through the end of the 120-minute observation period. This difference had clinical consequences: in individual saline-treated calves, loss of P waves, ventricular escape rhythms, and tachycardia reappeared at 60, 90, and 120 minutes, associated with a renewed rise in potassium. In one of these calves, ventricular tachycardia was observed. The authors note that the absence of P waves reflects severe impairment of atrial depolarization that may compromise ventricular filling and predispose to hemodynamic instability, and that ventricular escape rhythms are generally considered signs of myocardial electrical instability, findings that underscore the importance of a rapid and sustained decrease in plasma potassium.
The study has important limitations that the authors themselves emphasize. It was exploratory, the sample size was small, and baseline imbalances existed across treatment groups, with arrhythmias absent from the glucose group but present in several calves in the sodium groups; a sensitivity analysis excluding calves with baseline arrhythmias preserved the significant effects of time and the group-by-time interaction. Electrocardiograms were evaluated with dedicated software but the assessment was not blinded, and bipolar limb lead II was used rather than a base-apex configuration, although a previous comparison in calves found no major differences between the two approaches. The 120-minute observation window was short, and all calves required further intravenous fluid therapy afterward because the oral rehydration protocol was insufficient to correct their existing fluid deficits. The authors also caution that the significant treatment-group effects detected in some models should not necessarily be interpreted as a clinically meaningful advantage of any single intervention.
Nevertheless, the central conclusion stands: small-volume intravenous administration of hypertonic sodium solutions can rapidly reverse the cardiotoxic effects of hyperkalemia in neonatal diarrheic calves, restoring normal heart rhythm and atrial activity, shortening QRS duration, and reducing S and T wave amplitudes. Because of its alkalinizing capacity and more sustained potassium-lowering effect compared with hypertonic saline, hypertonic sodium bicarbonate emerges as a promising option for the rapid stabilization of affected animals. The authors point out that hypertonic sodium bicarbonate is already routinely administered to severely acidemic diarrheic calves regardless of potassium concentration, so the principal contribution of the work is not a new therapy but a better understanding of the mechanisms underlying the rapid reversal of hyperkalemia-associated conduction abnormalities. They call for adequately powered future studies, including an evaluation of whether combined administration of sodium bicarbonate and glucose offers additional clinical benefit. Of the 22 calves enrolled, 21 were discharged in a healthy state after a mean hospitalization of 12 days; one calf in the saline group was euthanized because of advanced pneumonia that progressed during hospitalization.
Subject of Research: Rapid reversal of hyperkalemia-induced electrocardiographic abnormalities in neonatal diarrheic calves treated with small-volume hypertonic sodium bicarbonate, sodium chloride, or glucose infusions
Article Title: Ability of intravenous small-volume hypertonic sodium bicarbonate, sodium chloride, and glucose solutions to rapidly reverse electrocardiographic abnormalities in hyperkalemic calves with neonatal diarrhea
Article References: Trefz, F. M., Lorenz, I., & Constable, P. D. (2026). Ability of intravenous small-volume hypertonic sodium bicarbonate, sodium chloride, and glucose solutions to rapidly reverse electrocardiographic abnormalities in hyperkalemic calves with neonatal diarrhea. Journal of Veterinary Internal Medicine, 40(5), Article aalag215. https://doi.org/10.1093/jvimsj/aalag215
Image Credits: AI Generated
Keywords: hyperkalemia, neonatal diarrhea, calves, electrocardiography, hypertonic sodium bicarbonate, hypertonic saline, glucose infusion, QRS duration, atrial standstill, potassium-sodium ratio, veterinary emergency, randomized clinical trial
News Source: Drew Townsend. (October 26, 2026). Hypertonic sodium infusions rapidly reverse heart rhythm dangers in hyperkalemic diarrheic calves. Scienmag.
