Academic Day Seminars

ADS – Acid Base

Prior to this session I had the most undeniably basic (pun intended) understanding of acid base disorders! I had a patient during my OEE rotation who had a congenital metabolic disorder with some acid/base implications, but at the time I only had begun to explore the topic. After this ADS I feel more adequately prepared to tackle an acute or chronic acid/base patient!

Notes:

How to assess my patient:

  1. Determine if it is an acid or base disorder (using pH, HCO3 and pCO2 levels)
  2. Is it respiratory or metabolic?
  3. Has the body compensated?
  4. Is there an anion gap more than normal? (10 = normal gap)
    • Calculate an anion gap = Na+ – (Cl- + HCO3-)
    • If hypoalbumenia (albumin has neg charge, it’ll change the gap. Normal alb ~ 45g/L, for every 10g/L drop in alb, the anion gap shrinks by 2.
  5. Is there an osmolar gap?
    • Calculate an osmolar gap = 2*[Na+] + [BUN] + [Glu]
    • Normal ~ v290 (gap +/-10)
    • High osmolar gap >350 indicates ethanol overdose

Why do we care? the body’s enzymes do not work well at pH <7.0 –> medical emergency!

Gap acidosis can be due to: ingestion, generation of acid or failure to excrete acid

Non-gap acidosis can be due to a loss of bicarbonate: due to renal tubular acidosis, GI losses (e.g. diarrhea), or a huge blood loss and subsequent replacement with NS (would lack the replacement of HCO3)

Causes of metabolic acidosis (gap dx) MUDPILES

  • Methanol (can be broken down to ketones), metformin (=lactic acidosis)
  • Uremia (unable to get rid of waste products – e.g. PO4, SO4)
  • Diabetic ketoacidosis
  • Propofol (& paraldehyde – a seizure tx rarely used – only peds)
  • Isoniazide, Iron (due to mitochondrial toxins)
  • Lactic acidosis (could be secondary to septic shock –> inadequate perfusion)
  • Ethylene glycol
  • Salicylates (b/c of mitochondrial toxicity ->lactic or other acidosis) & starvation

Causes of respiratory acidosis (think what is causing the decreased ventilation)

  • CNS – cerebrovascular accident, trauma, CNS depressants
  • Spinal cord – high spinal cord trauma, abscess on spinal cord, hematoma
  • Nerve – polio, demyelinating nerve issues
  • Neuromuscular junction – myasthenia gravis, botox, succinylCoA, rocuronium
  • Musculature – intercoastal and diaphragm: myopathy, muscular dystrophy
  • Obstructive causes: e.g. choking, asthma, COPD
  • Restrictive causes: e.g. pleural effusion, pneumothorax, hemathorax
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