Metabolic Alkalosis Evaluation
OVERVIEW
- Evaluation of causes of metabolic alkalosis requires a systematic approach involving history, examination and some specific investigations.
CAUSES
Initiating Process
- gain of HCO3- — endogenous: metabolism of ketoacids — exogenous: citrate, NaHCO3, lactate, antacid
- loss of H+ — Renal: diuretics — GI: vomiting, nasogastric losses
Maintenance Process
- hypochloraemia
- hypokalaemia
- hypomagnasaemia
- volume contraction
- increased adrenocorticoids (endogenous or exogenous)
Stewart approach
- elevation in SID: plasmalyte or NaHCO3 use
- reduction in ATOT: hypoalbuminaemia
HISTORY AND EXAMINATION
- vomiting & gastric losses, laxative induced diarrhoea
- signs of volume depletion (loss of bicarbonate free fluids)
- administered drugs (mineralocorticoids, diuretics and antacids in renal failure)
- administration of alkali (bicarbonate, lactate, citrate etc)
- recent hypercapnia
INVESTIGATIONS
Plasma
- hypokalemia (with hydrogen shifting into cells)
- hypochloremia
- hypomagnesaemia
Urinary
- high potassium excretion (reabsorbing hydrogen)
- alkaline pH (increased bicarbonate)
- high chloride excretion (diuretic therapy, hypokalaemia)
MANAGEMENT
- treat cause!
- K+ and Mg2+ replacement
- correct hypovolaemia with 0.9% NaCl
- consider acetazolamide
- consider spinolactone to antagonize hyperaldosteronism
- consider drugs to reduce GI acid secretion – H2-blockers, PPIs, octreotide
- consider administration of acid – lysine or arginine HCl or HCl (CVL and monitor K+)
- if the diagnosis is not obvious, spot urine chloride is useful: low levels suggest Cl- depletion and need for replacement; high levels suggest adrenocortical excess and need for K+ replacement
References and Links
- Acid-Base: ABG analysis – Anion Gap – SID – NAGMA
- Metabolic acidosis: Overview – Evaluation – DDx
- Metabolic alkalosis: Overview – Evaluation – DDx
- Respiratory acidosis: Overview – DDx
- Respiratory alkalosis: Overview – DDx
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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