Medical Accuracy Analysis of Metabolic Acidosis Cheat Sheet
Overall Assessment
The cheat sheet is largely medically accurate and provides a clinically useful framework for recognizing and managing metabolic acidosis in skilled nursing facilities, with several key thresholds and formulas correctly stated, though some nuances require clarification.
Section-by-Section Analysis
1) Quick Steps – Accurate with Minor Clarifications
The HCO₃⁻ threshold of <22 mmol/L for metabolic acidosis is correct and aligns with established definitions, where metabolic acidosis is characterized by primary reduction in serum bicarbonate below 22 mmol/L 1, 2.
The anion gap formula (AG = Na⁺ − [Cl⁻ + HCO₃⁻]) is accurate, and the normal range of 8-12 mEq/L is standard 3, 4.
The albumin correction formula (AGcorr = AG + 2.5 × [4.0 − albumin]) is correct and essential, as low albumin can mask an elevated anion gap 3.
The classification thresholds are appropriate: AGMA when AG >12 and NAGMA when AG 8-12 with elevated chloride accurately divides metabolic acidoses into clinically useful categories 3, 4.
The Delta Ratio calculation ([AG − 12] / [24 − HCO₃⁻]) is correctly stated and is a validated method for detecting mixed acid-base disorders 3, 4.
2) Thresholds & Severity – Accurate
The normal HCO₃⁻/CO₂ range of 22-29 mmol/L is correct, though some sources suggest 22-26 mmol/L as the tighter normal range 1, 2.
The severity classification (Mild ≥19, Moderate-Severe <19) is clinically reasonable, though formal severity grading varies by clinical context and underlying etiology 4.
The normal AG range of 8-12 mEq/L is standard, and the emphasis on using corrected AG when albumin is low is appropriate 3.
Respiratory compensation clues (RR >25/min, Kussmaul breathing) are accurate clinical signs of severe metabolic acidosis, particularly in high anion gap acidosis 4, 2.
3) Delta Ratio – Accurate and Clinically Useful
The Delta Ratio interpretation is correct: a ratio ≈1 indicates simple AGMA, <1 suggests AGMA + NAGMA (additional bicarbonate loss), and >1 suggests AGMA + metabolic alkalosis 3, 4.
This calculation is essential for identifying mixed acid-base disorders that would otherwise be missed 3.
4) Pick a Lane & Do Something – Largely Appropriate for SNF Setting
NAGMA Management:
The recommendation for balanced crystalloid and consideration of oral NaHCO₃ 650 mg BID-TID is reasonable for stable patients with hyperchloremic acidosis, with the target of maintaining bicarbonate ≥22 mmol/L supported by guidelines 1, 5.
The 24-48 hour recheck interval for CO₂/K⁺ is appropriate for stable outpatients 1, 5.
AGMA Management:
DKA transfer recommendation is appropriate, as SNFs typically lack the monitoring and insulin infusion capabilities required for DKA management 4.
The lactic/sepsis management approach (cultures, antibiotics, fluids) is standard and aligns with sepsis management protocols 4.
Uremia/renal failure transfer consideration is appropriate, particularly when bicarbonate <18 mmol/L or when dialysis may be needed 1, 5.
5) Causes by Pattern – Accurate
AGMA causes listed are correct:
- DKA, lactic acidosis, renal failure (uremia), and toxins (salicylates, methanol, ethylene glycol, metformin) are the classic causes of high anion gap metabolic acidosis 3, 4.
NAGMA causes listed are accurate:
- RTAs (with appropriate potassium patterns), diarrhea/GI losses, carbonic anhydrase inhibitors, and early renal failure are established causes of non-gap acidosis 4, 2.
6) Pitfalls – Accurate and Important
The albumin correction warning is critical, as hypoalbuminemia can mask an elevated anion gap, leading to missed diagnoses of AGMA 3.
The emphasis on calculating Delta Ratio in all AGMA cases is appropriate to detect mixed disorders 3, 4.
The osmolal gap formula (Measured Osm − [2Na + Glu/18 + BUN/2.8]) is correct and useful for detecting toxic alcohols 3.
The CKD monitoring recommendation (bicarbonate q3 months when GFR <30) is supported by guidelines recommending monthly monitoring in CKD stages 3-5 1, 5.
The caution about early acidosis at 22-23 mmol/L is clinically astute, as trends and context matter when bicarbonate is at the lower limit of normal 1.
7) Red Flags – Appropriate Transfer Criteria
- The listed red flags (severe tachypnea, MAP <60, K⁺ ≥6.0 with ECG changes, toxic ingestion, stage 3 AKI/anuria, hypoxemia, shock) are all appropriate indications for immediate transfer from an SNF to acute care 4.
CO₂ vs. HCO₃⁻ Explanation – Accurate
The statement that "CO₂" on CMP equals total CO₂ content and essentially equals serum bicarbonate is correct, as >95% of total CO₂ is bicarbonate in routine chemistry 1.
The formulas provided (AG, corrected AG, Delta ratio, calculated osmolality) are all accurate and can be computed directly from CMP values 3, 4.
Key Caveats and Clinical Considerations
Treatment Thresholds
The cheat sheet appropriately emphasizes maintaining bicarbonate ≥22 mmol/L, which aligns with guidelines for CKD patients to prevent protein catabolism, bone disease, and CKD progression 1, 5.
For severe acidosis (bicarbonate <18 mmol/L), the recommendation for transfer/escalation is appropriate, as this threshold indicates need for pharmacological treatment and close monitoring 1, 5.
Bicarbonate Therapy Controversy
The cheat sheet appropriately avoids recommending routine bicarbonate therapy for acute AGMA, as the evidence for benefit is controversial and treatment should focus on the underlying cause 5, 4, 2.
For DKA specifically, bicarbonate therapy is generally not needed unless pH <7.0, which the cheat sheet correctly implies by recommending transfer rather than SNF-based bicarbonate administration 5.
Mixed Disorders
- The emphasis on Delta Ratio calculation is essential, as mixed disorders are common in critically ill patients and can be easily missed without systematic evaluation 3, 4.
Common Pitfalls to Avoid (Beyond Those Listed)
Do not assume normal anion gap excludes AGMA when albumin is low – always correct for hypoalbuminemia 3.
Do not overlook the possibility of multiple simultaneous acid-base disorders – Delta Ratio helps identify these 3, 4.
In CKD patients, do not restrict protein during acute illness or hospitalization, as the catabolic state requires increased protein intake despite metabolic acidosis 1.
Avoid citrate-containing alkali in CKD patients exposed to aluminum, as citrate increases aluminum absorption 1.
Summary of Accuracy
The cheat sheet demonstrates strong medical accuracy across all major components, with appropriate thresholds, formulas, classifications, and management recommendations for an SNF setting. The emphasis on escalation to higher levels of care for unstable patients is appropriate and prioritizes patient safety. The systematic approach using anion gap, Delta Ratio, and clinical context provides a sound framework for recognizing and initially managing metabolic acidosis before transfer when indicated.