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...

Sources of error in blood gas analysis Essentially, this chapter is a short list of reasons as to why your ABG (or venous biochemistry)  measurement may be wrong, i.e. not reflective of what is happening in the patient. In 99% of cases, it is a problem with the collection storage and transport of the sample, because these are factors which are subject to human input and thus human error. The self-calibrating blood gas analyser is a dutiful and dependable serv...

How the blood gas analyser measures ABG variables Question 9.1 from the second paper of 2008 asks of the bewildered candidates: "Outline  how pH, PCO2 and PO2  are measured in a blood gas analyser and briefly state the underlying principle behind  each of those measurements." The pass rate of 47% was pleasantly surprising, suggesting that many (if not all) of the candidates arose from an intellectually robust anaesthetic background. Judgi...

CLINICAL PICTURE| VOLUME 395, ISSUE 10235, P1516, MAY 09, 2020 Myocarditis in a patient with COVID-19: a cause of raised troponin and ECG changes Denis Doyen, Pamela Moceri, Dorothée Ducreux, et al Lancet 2020; 395: 1516 A 69-year old man, from Lombardy, Italy, was admitted to our unit because of acute respiratory distress syndrome that required mechanical ventilation; he was in Nice, France, on holiday. He had previously been fit and well; he had a history of...

Massive Splenomegaly from Disseminated Mycobacterium avium–intracellulare Infection Lucas R. Massoth, Abner Louissaint, Jr. N Engl J Med 2020; 382:1041DOI: 10.1056/NEJMicm1905550 A 29-year-old man with HIV infection presented with abdominal pain and drenching nights sweats. Computed tomography of the abdomen revealed massive splenomegaly caused by disseminated Mycobacterium avium–intracellulare infection.