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!
How to assess my patient:
- Determine if it is an acid or base disorder (using pH, HCO3 and pCO2 levels)
- Is it respiratory or metabolic?
- Has the body compensated?
- 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.
- 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