Physicochemical Interpretation of Acid‐Base Abnormalities in 54 Adult Horses with Acute Severe Colitis and Diarrhea

Background

The quantitative effect of strong electrolytes, pCO₂, and plasma protein concentration in determining plasma pH and bicarbonate concentrations can be demonstrated with the physicochemical approach. Plasma anion gap (AG) and strong ion gap (SIG) are used to assess the presence or absence of unmeasured anions.

Hypotheses

The physicochemical approach is useful for detection and explanation of acid‐base disorders in horses with colitis. AG and SIG accurately predict hyperlactatemia in horses with colitis.

Animals

Fifty‐four horses with acute colitis and diarrhea.

Methods

Retrospective study . Physicochemical variables were calculated for each patient. ROC curves were generated to analyze sensitivity and specificity of AG and SIG for predicting hyperlactatemia.

Results

Physicochemical interpretation of acid‐base events indicated that strong ion metabolic acidosis was present in 39 (72%) horses. Mixed strong ion acidosis and decreased weak acid (hypoproteinemia) alkalosis was concomitantly present in 17 (30%) patients. The sensitivity and specificity of AG and SIG to predict hyperlactatemia (L‐lactate > 5 mEq/L) were 100% (95% CI, 66.4–100; P < .0001) and 84.4% (95% CI, 70.5–93.5 P < .0001). Area under the ROC curve for AG and SIG for predicting hyperlactatemia was 0.95 (95% CI, 0.86–0.99) and 0.93 (95% CI, 0.83–0.99), respectively.

Conclusion and Clinical relevance

These results emphasize the importance of strong ions and proteins in the maintenance of the acid‐base equilibria. AG and SIG were considered good predictors of clinically relevant hyperlactatemia.     

Physicochemical Approach to Determine the Mechanism for Acid–Base Disorders in 793 Hospitalized Foals

Background

The quantitative effect of strong electrolytes, unmeasured strong anions (UAs), pCO ₂, and plasma protein concentrations in determining plasma pH can be demonstrated using the physicochemical approach. Plasma anion gap (AG) and strong ion gap (SIG) are used to assess UAs in different species.

Hypotheses

Strong ions are a major factor influencing changes in plasma pH of hospitalized foals. AG and SIG accurately predict severe hyper‐l‐lactatemia ([l‐lac⁻] > 7 mmol/L).

Animals

Seven hundred and ninety three hospitalized foals < 7 days old.

Methods

Retrospective study. The relationship between measured pH and physicochemical variables, and the relationship between plasma [l‐lac⁻] and AG and SIG, were determined using regression analyses. Optimal AG and SIG cut points to predict hyper‐l‐lactatemia were identified using an ROC curve analysis.

Results

Combined, the measured strong ion difference and SIG accounted for 54–69% of the changes in the measured arterial pH of hospitalized foals. AG and SIG were significantly associated with plasma [l‐lac⁻] (P < .0001). The receiver operator characteristics (ROC) AUC of AG and SIG for prediction of severe hyper‐l‐lactatemia were 0.89 (95%CI, 0.8–0.95; P < .0001) and 0.90 (95%CI, 0.81–0.96; P < .0001), respectively. Severe hyper‐l‐lactatemia was best predicted by AG > 27 mmol/L (sensitivity 80%, 95%CI, 56–94, specificity 85%, 95%CI, 73–93; P < .0001) and SIG <−15 mmol/L (sensitivity 90%, 95%CI, 68–98; specificity 80%; 95%CI, 68–90; P < .0001).

Conclusion and clinical relevance

Altered concentrations of strong ions (Na⁺, K⁺, Cl⁻) and UAs were the primary cause of acidemia of hospitalized foals. AG and SIG were good predictors of hyper‐l‐lactatemia and could be used as surrogate tests.     

Experimental determination of net protein charge and A(tot) and K(a) of nonvolatile buffers in canine plasma

Acid-base abnormalities frequently are present in sick dogs. The mechanism for an acid-base disturbance can be determined with the simplified strong ion approach, which requires accurate values for the total concentration of plasma nonvolatile buffers (A(tot)) and the effective dissociation constant for plasma weak acids (K(a)). The aims of this study were to experimentally determine A(tot) and K(a) values for canine plasma. Plasma was harvested from 10 healthy dogs; the concentrations of quantitatively important strong ions (Na+, K+, Ca2+, Mg2+, Cl-, L-lactate) and nonvolatile buffer ions (total protein, albumin, phosphate) were determined; and the plasma was tonometered with CO2 at 37 degrees C. Strong ion difference (SID) was calculated from the measured strong ion concentrations, and nonlinear regression was used to estimate values for A(tot) and K(a), which were validated with data from an in vitro and in vivo study. Mean (+/- SD) values for canine plasma were A(tot) = (17.4 +/- 8.6) mM (equivalent to 0.273 mmol/g of total protein or 0.469 mmol/g of albumin); K(a) = (0.17 +/- 0.11) x 10(-7); pK(a) = 7.77. The calculated SID for normal canine plasma (pH = 7.40; P(CO2) = 37 mm Hg; [total protein] = 64 g/L) was 27 mEq/L. The net protein charge for normal canine plasma was 0.25 mEq/g of total protein or 0.42 mEq/g of albumin. Application of the experimentally determined values for A(tot), K(a), and net protein charge should improve understanding of the mechanism for complex acid-base disturbances in dogs.     

Quantitative Physicochemical Analysis of Acid‐Base Balance and Clinical Utility of Anion Gap and Strong Ion Gap in 806 Neonatal Calves with Diarrhea

Background

Acid‐base abnormalities in neonatal diarrheic calves can be assessed by using the Henderson‐Hasselbalch equation or the simplified strong ion approach which use the anion gap (AG) or the strong ion gap (SIG) to quantify the concentration of unmeasured strong anions such as d‐lactate.

Hypothesis/Objectives

To determine and compare the clinical utility of AG and SIG in quantifying the unmeasured strong anion charge in neonatal diarrheic calves, and to examine the associations between biochemical findings and acid‐base variables by using the simplified strong ion approach. We hypothesized that the SIG provides a more accurate prediction of unmeasured strong anions than the AG.

Animals

Eight hundred and six neonatal diarrheic calves admitted to a veterinary teaching hospital.

Methods

Retrospective study utilizing clinicopathologic findings extracted from medical records.

Results

Hyperphosphatemia was an important predictor of venous blood pH. Serum inorganic phosphorus and plasma d‐lactate concentrations accounted for 58% of the variation in venous blood pH and 77% of the variation in AG and SIG. Plasma d‐ and total lactate concentrations were slightly better correlated with SIG (r _s  = −0.69; −0.78) than to AG (r _s = 0.63; 0.74).

Conclusions and Clinical Importance

Strong ion gap is slightly better at quantifying the unmeasured strong anion concentration in neonatal diarrheic calves than AG. Phosphorus concentrations should be included as part of the calculation of A _tot when applying the simplified strong ion approach to acid‐base balance to critically ill animals with hyperphosphatemia.     

Blood acid-base and plasma electrolyte values in healthy ostriches: The effect of age and sex

The effect of age and sex on blood acid-base and plasma electrolyte values was determined in venous blood samples from 45 clinically healthy ostriches (Struthio camelus) from 26 days to 6 years of age. Animals were divided by age into four groups and the group of adults was divided by sex into two subgroups. Blood samples were collected without sedation. There was a significant (P < 0.05) age difference in blood values of base excess (BE), plasma , total CO₂ (TCO₂), Na⁺, K⁺, Cl⁻ and anion gap (AG). The highest plasma concentrations of Na⁺, Cl⁻ and value of AG were found in adult ostriches with a steady decrease to chicks. A significant (P < 0.05) sex difference in adult animals with higher blood pH, lower blood values of pCO₂, BE, plasma concentrations of , TCO₂ and K⁺ was found in females. We concluded that blood acid-base values and plasma electrolyte concentrations in ostriches are affected by age and sex.     

Quantitative Accuracy of the Simplified Strong Ion Equation to Predict Serum pH in Dogs

Background

Electrochemical approach to the assessment of acid‐base states should provide a better mechanistic explanation of the metabolic component than methods that consider only pH and carbon dioxide.

Hypothesis/Objectives

Simplified strong ion equation (SSIE), using published dog‐specific values, would predict the measured serum pH of diseased dogs.

Animals

Ten dogs, hospitalized for various reasons.

Methods

Prospective study of a convenience sample of a consecutive series of dogs admitted to the Massey University Veterinary Teaching Hospital (MUVTH), from which serum biochemistry and blood gas analyses were performed at the same time. Serum pH was calculated (Hcal+) using the SSIE, and published values for the concentration and dissociation constant for the nonvolatile weak acids (A_tot and K _a), and subsequently Hcal+ was compared with the dog''s actual pH (Hmeasured+). To determine the source of discordance between Hcal+ and Hmeasured+, the calculations were repeated using a series of substituted values for A_tot and K _a.

Results

The Hcal+ did not approximate the Hmeasured+ for any dog (P = 0.499, r ² = 0.068), and was consistently more basic. Substituted values A_tot and K _a did not significantly improve the accuracy (r ² = 0.169 to <0.001). Substituting the effective SID (Atot−[HCO3−]) produced a strong association between Hcal+ and Hmeasured+ (r ² = 0.977).

Conclusions and clinical importance

Using the simplified strong ion equation and the published values for A_tot and K _a does not appear to provide a quantitative explanation for the acid‐base status of dogs. Efficacy of substituting the effective SID in the simplified strong ion equation suggests the error lies in calculating the SID.     

Effects of intravenous hyperosmotic sodium bicarbonate on arterial and cerebrospinal fluid acid-base status and cardiovascular function in calves with experimentally induced respiratory and strong ion acidosis

The objectives of this study were to determine the effects of hyperosmotic sodium bicarbonate (HSB) administration on arterial and cerebrospinal fluid (CSF) acid-base balance and cardiovascular function in calves with experimentally induced respiratory and strong ion (metabolic) acidosis. Ten healthy male Holstein calves (30-47 kg body weight) were instrumented under halothane anesthesia to permit cardiovascular monitoring and collection of blood samples and CSE Respiratory acidosis was induced by allowing the calves to spontaneously ventilate, and strong ion acidosis was subsequently induced by i.v. administration of L-lactic acid. Calves were then randomly assigned to receive either HSB (8.4% NaHCO3; 5 ml/kg over 5 minutes, i.v.; n=5) or no treatment (controls, n=5) and monitored for 1 hour. Mixed respiratory and strong ion acidosis was accompanied by increased heart rate, cardiac index, mean arterial pressure, cardiac contractility (maximal rate of change of left ventricular pressure), and mean pulmonary artery pressure. Rapid administration of HSB immediately corrected the strong ion acidosis, transiently increased arterial partial pressure of carbon dioxide (P(CO2)), and expanded the plasma volume. The transient increase in arterial P(CO2) did not alter CSF P(CO2) or induce paradoxical CSF acidosis. Compared to untreated control calves, HSB-treated calves had higher cardiac index and contractility and a faster rate of left ventricular relaxation for 1 hour after treatment, indicating that HSB administration improved myocardial systolic function. We conclude that rapid i.v. administration of HSB provided an effective and safe method for treating strong ion acidosis in normovolemic halothane-anesthetized calves with experimentally induced respiratory and strong ion acidosis. Fear of inducing paradoxical CSF acidosis is not a valid reason for withholding HSB administration in calves with mixed respiratory and strong ion acidosis.     

Effects of Alkalinization and Rehydration on Plasma Potassium Concentrations in Neonatal Calves with Diarrhea

Background

Increased plasma potassium concentrations (K⁺) in neonatal calves with diarrhea are associated with acidemia and severe clinical dehydration and are therefore usually corrected by intravenous administration of fluids containing sodium bicarbonate.

Objectives

To identify clinical and laboratory variables that are associated with changes of plasma K⁺ during the course of treatment and to document the plasma potassium‐lowering effect of hypertonic (8.4%) sodium bicarbonate solutions.

Animals

Seventy‐one neonatal diarrheic calves.

Methods

Prospective cohort study. Calves were treated according to a clinical protocol using an oral electrolyte solution and commercially available packages of 8.4% sodium bicarbonate (250–750 mmol), 0.9% saline (5–10 L), and 40% dextrose (0.5 L) infusion solutions.

Results

Infusions with 8.4% sodium bicarbonate solutions in an amount of 250–750 mmol had an immediate and sustained plasma potassium‐lowering effect. One hour after the end of such infusions or the start of a sodium bicarbonate containing constant drip infusion, changes of plasma K⁺ were most closely correlated to changes of venous blood pH, plasma sodium concentrations and plasma volume (r = −0.73, −0.57, −0.53; P < .001). Changes of plasma K⁺ during the subsequent 23 hours were associated with changes of venous blood pH, clinical hydration status (enophthalmos) and serum creatinine concentrations (r = −0.71, 0.63, 0.62; P < .001).

Conclusions and Clinical Importance

This study emphasizes the importance of alkalinization and the correction of dehydration in the treatment of hyperkalemia in neonatal calves with diarrhea.