Today, we discussed the case of a middle-aged man with history of CKD who presented with abdominal pain/diarrhea, altered mental status, AKI, and numerous metabolic derangements (AG metabolic acidosis + metabolic alkalosis + respiratory acidosis). His AKI and AMS improved with IV hydration.
- See below for a step-wise approach to acid-base evaluation.
- When a patient has an anion-gap metabolic acidosis, calculate the delta gap to assess for evidence of other concomitant metabolic abnormalities (such as metabolic alkalosis or non-gap metabolic acidosis).
- ESRD patients are predisposed to unique colonic pathology, including uremic colitis (more below).
Acid-Base evaluation (Flashback to our pearls from earlier this year):
- What is the primary disorder? Primary acidosis if pH <7.4, alkalosis if >7.4
- Is it metabolic or respiratory?
- If acidosis, high CO2 implies respiratory, low bicarb implies metabolic à If elevated anion gap, a metabolic acidosis is present (but may not be primary)
- If alkalosis, low CO2 implies respiratory, high bicarb implies metabolic
- Is there a 2nd disorder too? Compensation formulas:
a. Metabolic acidosis Expected pCO2 = 1.5 x bicarb + 8 +/- 2 (Winter’s formula)
b. Metabolic alkalosis Expected pCO2 = 0.7 x bicarb + 20 +/- 5 c. There are also compensation formulas for acute and chronic respiratory acid-base disorders: http://www.anaesthesiamcq.com/AcidBaseBook/ab9_3.php If calculated value does not match expected value, there is a 2nd disorder.
- Is anion gap elevated (*corrected for albumin)? Calculate the “delta gap” or “delta ratio.”
- Normal anion gap = 12, Normal HCO3 = 24
- Delta gap = (AG – 12) – (24 – HCO3) If Delta gap >6, superimposed metabolic alkalosis If Delta gap <-6, superimposed non-gap metabolic acidosis
- Delta ratio = (AG – 12)/(24 – HCO3) If Delta ratio >1, superimposed metabolic alkalosis If Delta ratio <1, superimposed non-gap metabolic acidosis
Colonic Manifestations of ESRD or Dialysis Patients
- Uremic colitis: Harry’s pearl from report. Long-standing, untreated uremia leading to colonic ulcerations and pseudomembranes.
- Colonic ischemia: vascular disease is accelerated in ESRD, increasing risk for ischemic colitis.
- Spontaneous colonic perforation: etiology is largely unknown in ESRD patients, but some identified causes include aluminum-containing antacids, barium studies, or dehydration.
- Colonic necrosis: Sodium polystyrene sulfonate (used to treat hyperkalemia in patients with renal failure) can lead to colonic necrosis.
- Fecal impaction: complication of usage of phos binders, analgesic, iron, etc.
- Dialysis-related amyloidosis: causes dysmotility, intestinal necrosis, perforation.