Among the range of patients cared for by anaesthetists are those who are high risk of complications and mortality. Some of these patients are critically ill before surgery, while some become critically ill during, or soon after surgery. One sign that patients are becoming or have become critically ill is when their blood becomes acidic. However, many clinicians struggle with the complexity of analysing why patients are acidic and the importance of the causes of the acidity.
Building on the work of others, Professor Story and the Critical Care group from the University of Melbourne have developed the Bedside Stewart, a simplified approach to analysing acidity in patients that is designed to help clinicians, particularly anaesthetists, while they are caring for patients.
The aim of the MOIRA study was to determine the prognostic value for mortality of the base-excess effect parameters derived from the Bedside Stewart approach to analyse the metabolic component of clinical acid-base changes. The hypothesis is that elements of the Bedside Stewart approach, particularly the base-excess effects of unmeasured and lactate ions, would have prognostic value in a multivariate model for in-hospital mortality for patients with metabolic acidosis at the time of ICU admission.
In this study, the investigators used data routinely collected from thousands of patients admitted to ICU to examine how well these indirect Bedside Stewart measures of abnormal acids can predict the mortality outcome of patients with high levels of theses acids.
The significance of this study is that currently the Bedside Stewart approach has clinical diagnostic utility but would have added value if the elements of the analysis also had important prognostic utility. That is, the Bedside Stewart approach could provide a detailed quantitative diagnostic analysis of a patient’s acid-base status with added important prognostic information. Knowing this would help to plan care for patients and help inform them and their families about potential risks.
Professor David Story, Melbourne Medical School, The University of Melbourne
The project was awarded $A66,358 through the ANZCA research grants program for 2022.
Using analysis methods developed by ANZCA experts, researchers looked at the causes of blood acidity in thousands of patients admitted to ICU at the Austin Hospital. It was found that lactic acidosis is associated with increased mortality in hospital as is acidity due to other acids not found in the blood of healthy people. These abnormal acids were more important in patients admitted after surgery than in those who had not had surgery.
It was confirmed that the value of estimating the associated mortality risk with base-excess effects of different types of acidosis.
The study reinforces the clinical value of the very practical Bedside Stewart approach to acid-base disorders, particularly for surgical patients admitted to ICU.
The results were presented at the 2023 ANZCA ASM in Sydney as part of many activities associated with the Douglas Joseph Professorship. A manuscript is underway awaiting publication in Anesthesiology of a supporting review article.
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