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Acid Base

Acid base info from July

5 steps to acid-base (1-3) 1. Check numbers (pH, bicarb, pCO2, lytes), has PCO2 moved in same or diff direction as bicarb? 2. AG (>15 = wide) 3. Rule of 15 to eval respiratory compensation in acidosis (bicarb + 15 = expected PCO2 & last 2 of pH)
5 steps to acid base (steps 4-5) 4. Delta-delta (delta-gap) if acidosis 5. Osmolar gap if unexplained AG acidosis
Relationship of pH, PCO2, bicarb 1. pH = acidosis or alkalosis 2. PCO2 & bicarb in same direction = metabolic, different direction = respiratory
Causes of AG acidosis MUDPILES Methanol, Uremia, DKA (starvation & alcoholic ketosis), Paraldehyde (anti-sz drug of 70's) & Paracetamol (metabolite of tylenol), INH & Iron, Lactic acidosis, Ethylene glycol, Salicylates
Causes of non-AG (hyperchloremic) acidosis HAARD-UPS Hyperventilation (chronic, compensation), Adrenal insufficiency, Acetazolamide, RTA, Diarrhea, Uretero-enteric diversion (urine through small bowel), Pancreatic fistula, Saline over-infusion
Rule of 15 interpretation Use buffer of +/- 2 1) PCO2 = expected PCO2 --> appropriate secondary respiratory alkalosis 2) PCO2 > expected PCO2 --> additional primary respiratory acidosis 3) PCO2 < expected PCO2 --> additional primary respiratory alkalosis
When does the rule of 15 fail? What numbers to know? Other strategy? As HCO3 falls below 10 and approaches 5 --> PCO2 bottoms out at 15 (max hyperventilation), but pH drops precipitously HCO3 = 5 --> PCO2 = 15 --> pH = 7.12 HCO3 = 2.5 --> PCO2 = 15 --> pH = 6.88 Can revert to Winter's formula: pCO2 = 1.5*Bicarb + 8 +/-
How do you eval delta-gap Change in AG (gap - 14) should = change in HCO3 (24-bicarb) for single metabolic disturbance (+/- 4)
Examples of eval delta gap 1. HCO3 = expected HCO3 --> no other primary metabolic disturbance 2. HCO3 > expected HCO3 --> additional primary metabolic alkalosis 3. HCO3 < expected HCO3 --> additional primary non-gap metabolic acidosis
How to calculate osmolar gap (OG) & what is a nl osmolar gap 1. Send lab to check Osmolality 2. Calc osmolality = 2*Na + Glu/20 + BUN/3 + EtOH/4 3. OG = lab value - calc value (nl = 10)
Methanol intoxication --> AG & OG To determine methanol level: 1. Determine OG 2. Determine osmolal contribution from EtOH ( = EtOH level / 4) 3. Determine osmolal forces of methanol ( = OG - EtOH contribution) 4. Methanol level = osmolal forces of methanol x 3
How do alcohols cause AG acidosis Metabolism by EtOH dehydrogenase --> formaldehyde and formic acid
Uremia BUN > 60 (usually > 100) & Cr > 5 (usually > 10) Acidosis due to accumulation of sulfates & phosphates
INH = GABA inhibitor --> refractory seizures --> lactic acidosis
Iron Seen in kids, preg women, postpartum women, GIB Fe2+ --> Fe3+ & lactic acidosis
What poisonings can result in Lactic acidosis… CO, cyanide
Ethylene glycol level Each mosm of OG = 6 mg % ethylene glycol
ASA Primary resp alkalosis + Primary AG acidosis May look like DKA or hypoglycemia
AG met acidosis + resp alkalosis 1. R/o ASA OD & sepsis 2. Most common = AKA + EtOH w/d (hyperventilation), hypotension/bleeding (lactate) + pain (hyperventilation)
AG met acidosis + resp acidosis Respiratory failure disguised as hyperventilation R/o: 1. Resp muscle weakness or fatigue 2. Sedative hypnotic OD 3. HypoPO4, HypoK 4. Cardiac arrest and hypoventilation 5. Hypotension & pulm edema
AG met acidosis & hyperchloremic met acidosis (Fall in bicarb is more than inc in AG) 1. Diabetic with RTA who develops DKA 2. DKA tx with NaCl 3. Any AG ds with RTA 4. Any AG ds with diarrhea
Met acidosis & met alkalosis 1. DKA and vomiting 2. Wide AG but pH and HCO3 may be nl 3. Wide AG due to ketoacids 4. Normal HCO3 b/c HCl is lost (vomiting)
Met acidosis & resp acidosis Hallmark = pH lower than predicted based on HCO3 fall 1. Resp failure in acidotic pt 2. Relative resp failure in acidotic pt (r/o hypoK & hypoPO4) 3. Cardiac arrest 4. Pulm edema 5. CO & CN poisoning
Created by: wamberge