Blood gases
pH, pCO₂ (kPa), HCO₃⁻, base excess, pO₂/saturation, lactate, sampling time and specimen type.
VÝUKOVÁ APLIKACE PRO ACIDOBAZICKOU ROVNOVÁHU · DATA SE NEUKLÁDAJÍ
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PŘEHLED CELÉHO ROZHODOVACÍHO POSTUPU
Souhrnná mapa vstupních dat, určení primární poruchy, kontroly kompenzace a navazujících větví.
Stewart: pH = f(pCO₂, SID, Atot); SID = strong cations − strong anions; Atot ≈ albumin + phosphate
pH, pCO₂ (kPa), HCO₃⁻, base excess, pO₂/saturation, lactate, sampling time and specimen type.
Na⁺, K⁺, Cl⁻, glucose, urea, creatinine, albumin and measured osmolality.
pH, Na⁺, K⁺, Cl⁻, ketones, glucose, protein, osmolality, urea; use a paired pretreatment spot sample.
β-hydroxybutyrate, salicylate, ethanol, methanol, ethylene glycol, CK, liver tests and toxicology.
pH < 7.35 → acidemia
pH > 7.45 → alkalemia
Normal pH with abnormal pCO₂/HCO₃⁻ → consider a mixed disorder.
Winter equation in kPa:
expected pCO₂ = 0.20 × HCO₃⁻ + 1.07
tolerance ±0.27 kPa.
Expected pCO₂ (kPa) = 5.33 + 0.093 × (HCO₃⁻ − 24)
approximate tolerance ±0.67 kPa.
For each 1.33 kPa change in pCO₂, compare the expected acute or chronic change in HCO₃⁻. A deviation suggests a mixed disorder.
HCO₃⁻ = 0.225 × pCO₂(kPa) × 10(pH−6.1)
AG = Na⁺ − Cl⁻ − HCO₃⁻. Use the local reference interval.
Corrected AG = AG + 0.25 × (40 − albumin in g/L).
(corrected AG − 12) / (24 − HCO₃⁻). Values <0.8 suggest additional NAGMA; values >2 suggest an alkalinizing process or chronic respiratory acidosis.
Calculated osmolality = 2Na⁺ + glucose + urea (+ ethanol, all in mmol/L). OG = measured − calculated osmolality.
Assess lactate, β-hydroxybutyrate, renal function, salicylate and the osmolal gap. If unexplained and clinically suspected, test for methanol, ethylene glycol and other toxic alcohols.
UAG = U-Na⁺ + U-K⁺ − U-Cl⁻. If unreliable, use the urine osmolal gap or directly measured U-NH₄⁺. Then distinguish gastrointestinal bicarbonate loss, chloride-rich fluid exposure, distal/proximal RTA and type 4 RTA using serum K⁺, urine pH and the clinical context.
Urine Cl⁻ <20 mmol/L suggests a chloride-responsive process; ≥20 mmol/L suggests ongoing renal chloride loss or a chloride-resistant process.
Elevated pCO₂: determine whether acute or chronic and compare HCO₃⁻ with the expected compensation.
Reduced pCO₂: determine whether acute or chronic and compare HCO₃⁻ with the expected compensation.
An increased OG with a normal AG may occur early; an increased OG and AG may indicate ongoing metabolism. A normal OG or AG does not exclude late exposure.
LG = POC lactate − laboratory lactate. Some POC methods may read glycolate/glyoxylate as lactate, providing a method-dependent clue to ethylene glycol exposure.
No universal cut-off exists. Verify both analyzer methods. A normal lactate gap does not exclude poisoning and treatment must not be delayed for this result.
Educational algorithm. Always verify reference intervals, analytical interference and treatment pathways with the local laboratory and current clinical guidance.