Filling the (strong ion) gap

SERIAL CHANGES IN METABOLIC ACID-BASE STATUS IN THREE SPECIES OF ANESTHETIZED CAPTIVE LARGE FELID

Determination of acid-base status contributes important information about patient health, including for patients under anesthesia. There is a paucity of information about the determinants of acid-base status of large felids managed under anesthesia, and advancement of such knowledge may contribute to patient safety. This study serially monitored the individual metabolic acid-base status of 11 large felids, including lions (Panthera leo), tigers (Panthera tigris), and cheetahs (Acinonyx jubatus), under general anesthesia. We analyzed the contributions of measured strong ions (sodium, chloride, potassium, lactate), weak acids and buffers (albumin, phosphate and bicarbonate), and unmeasured anions to standardized extracellular base excess (SBE). A general linear model assessed for species differences in these parameters, with time since immobilization, SBE, and mean arterial pressure as covariates. By employing a Stewart-based analytical approach, it was possible to separate chloremic and unmeasured anion contributions to metabolic acid base status. This provided a basis for identifying mixed metabolic processes, generating differentials for underlying causes. Using normal acid base parameters for domestic felids, metabolic acidosis was found to be prevalent. Frequent evidence of unmeasured anion accumulation was also found, with unmeasured anions occasionally exceeding 5mmol/L. These findings warrant further inquiry into the drivers and clinical significance of metabolic acidosis and unmeasured anion accumulations in anesthetized large felids, encouraging further anion identity studies to elucidate possible causes. Reference ranges need to be established for acid-base parameters in large felids as a foundation for interpreting more controlled, prospective research into determinants of metabolic acid-base status in these animals under anesthesia.

Advanced arterial blood gas analysis in septic shock: a Singaporean nursing case review

INTRODUCTION

The admission to the intensive care unit with a diagnosis of sepsis and/or septic shock is not uncommon. The aim of this article is to present a nursing case review of a patient admitted to the intensive care unit with a diagnosis of septic shock and the use of bedside acid-base formulae to inform clinical decision making.

METHOD

We chose to use a case review. This method is useful in reporting unusual or rare cases and is typically seen more in medicine than in nursing.

DISCUSSION

The gentleman in question was a self-presentation with a short history of fever and worsening shortness of breath. His condition worsened where he required admission to the intensive care unit. The use of 'advanced' acid-base interpretation to guide his nursing care provided a platform from which to advance a deeper understanding of the intricacies the critically ill patient often presents.

CONCLUSION

The use of case review is enlightening in understanding the disease process and the decision-making that accompanies this. The lessons learnt are applicable to a wider nursing audience because understanding acid-base physiology is beneficial in supporting and advancing critical care nursing practice.

An assessment of the population variance of the strong ion gap using Monte Carlo simulation

The strong ion gap is a derived parameter used to quantify clinically significant but unmeasured charged species in human plasma. In the general population the strong ion gap has a mean value of approximately 0.0 mEq/l, but at present no reference range exists. This severely limits its clinical application. In order to establish a reference range, a 95% confidence interval around the population mean must be calculated. As each of the variables that make up the strong ion gap have their own unique and different means and standard deviations, simple methods of pooled variance can not be used to calculate this interval. In place of a direct solution, Monte Carlo methodology was employed using known reference standard deviations to construct a large sample of a simulated population. In addition, the partial correlation between the plasma concentrations of sodium and chloride was included in the calculations. Sample sets of 20,000 were simulated, each giving a normally distributed strong ion gap. A 95% confidence interval of 3.9+/-6.4 mEq/l was derived. Depending on the degree of strong ion correlation, minima and maxima for this reference range were calculated as 3.9+/-5.1 mEq/l and 3.9+/-7.6 mEq/l respectively. Reasons for the positive bias in the mean strong ion gap result are examined briefly.