Urinary electrolytes and the urinary anion gap Urinary anion gap The urinary anion gap is extensively explored in the chapter on the diagnosis of renal tubular acidosis. Its role in the SAQs has been limited to the diagnosis of renal tubular acidosis (i.e where it is used to discriminate between renal and non-renal causes of a normal anion gap acidosis, such as in Question 3.4  from the second paperof 2013). In brief: Urinary anion gap...

The delta gap and delta ratio, advantages and disadvantages The delta ratio (or the equivalent delta gap) are diagnostic and analytical tools used to determine the contribution from extra anions to the acidaemia of any given acidosis. A much more detailed overview of the delta ratio is available in a dedicated chapter from the Acid-Base Disturbances series. Even though the calculation of a delta ratio is expected in every ABG interpretation que...

Can we measure Plateau pressure during pressure support? And what does it indicate? Alice Grassi, M.D.Department of Anesthesia and Pain Management, University Health Network, Toronto School of Medicine, University of Milan Bicocca, Monza, Italy from https://coemv.ca/can-we-measure-plateau-pressure-during-pressure-support-and-what-does-it-indicate/ Pressure Support Ventilation is one of the most commonly used modes of assisted ventilation during the weaning phase....

The anion gap, advantages and disadvantages A calculation of the anion gap is an essential part of practically every ABG interpretation question in the CICM fellowship exam. A profound understanding of the anion gap as a diagnostic tool is not an essential part of answering those questions. Only a crude workmanlike grasp is called for. In brief: The anion gap is (Na+ + K+) - (Cl- + HCO3-).The use of potassium in the calculation is thought...

Base excess and standard base excess Trainees were called upon to define these basic terms in Question 9 from the second paper of 2006. Since then, this topic has remained submerged for almost ten years, reappearing again in Question 4.3 from the first paper of 2016. It may now be lost again for another ten years. However, the issue remains interesting. The "Base Excess" is the amount of acid or base required to titrate a blood sample (of whole...

Stewart's physicochemical approach to acid-base analysis Stewart's approach is a mathematically coherent explanation of acid-base balance, which allows one to make precise predictions regarding the interactions of the numerous interacting variables which affect pH. Laws governing the behaviour of aqueous solutions can be used to create equations which describe these interactions.  In their model answer for Question 24 f...

PulmCrit- Liberating the patient with no cuff leak May 22, 2017 by Josh Farkas Prior to extubation, the cuff leak is usually checked.  This consists of deflating the cuff of the endotracheal tube to verify that gas is able to move around the tube.  Absence of a cuff leak suggests the presence of airway edema, increasing the risks of post-extubation stridor and reintubation.  However, the test isn't that great.  Absence of cuff leak can ...

ABG interpretation in the context of hypothermia The interpretation of blood gas data relies on certain standard variables being in place. Apart from atmospheric pressure (which everybody always assumes is 760 mmHg), theother  most important variable is temperature. Temperature changes the physicochemical properties of water, influencing solubility of gases and the autoionisation of water into H3O+ and OH-. Influence of temperature on pH and gas solub...

ABG interpretation in the context of normal pregnancy The college examiners seem to love nothing more than to throw seemingly normal-looking ABG results at the candidates, with the respiratory acidosis disguised by the effects of pregnancy. There are several such examples: Question 6.2 from the first paper of 2013Question 6.1 from the second paper of 2012Question 9.2 from the second paper of 2011Question 7.3 from the first paper of 2009 These ...

A systematic approach to ABG interpretation For blood gas interpretation, there is an official "Diagnostic Sequence" available in Oh's Manual. It is presented in T.J. Morgan's chapter for Oh's Manual (Chapter 92, "Acid base balance and disorders"); an owner of the Manual may find it on page 943 of the 7th edition. One expects that the college examiners, being the authors of the Manual, expect their exam candidates to use this ritualised approach. Therefo...