Acetazolamide-mediated decrease in strong ion difference accounts for the correction of metabolic alkalosis in critically ill patients

Table 2 Acid–base and electrolyte data

Acid–base and electrolyte data	Baseline	t = 24
PH	7.49 (7.48–7.51)	7.46 (7.44–7.48)
PaCO₂ (kPa)	5.7 (5.1–6.1)	5.3 (4.9–5.9)
Bicarbonate (mmol/l)	31.5 (29.5–33.7)	28.6 (26.3–30.3)
Sodium (mmol/l)	141 (139–145)	142 (139–145)
Potassium (mmol/l)	3.7 (3.7–4)	3.8 (3.4–3.9)
Chloride (mmol/l)	106 (102–107)	108 (107–110)
Creatinine (μmol/l)	64 (49–95)	65 (49–101)
Lactate (mmol/l)	1.4 (1.2–1.8)	1.5 (1.2–1.7)
Albumin (g/l)	16 (14–20)	17 (15–20)
Apparent SID (mEq/l)	41.7 (39.1–44.0)	39.4 (36.4–41.4)
Effective SID (mEq/l)	39.0 (37.3–40.3)	35.6 (32.9–37.7)
SIG (mEq/l)	2.4 (1.5–4.4)	3.1 (2.1–4.8)
Sodium–chloride effect (mEq/l)	-2.0 (-3.5 to +0.5)	-3.0 (-7.5 to -1.5)

Shown are baseline acid–base and electrolyte data (median [interquartile range]) for 15 patients before administration of 500 mg acetazolamide (baseline) and after 24 hours (t = 24). The serum apparent SID (SID_app) was calculated using the following equation: SID_app = [Na⁺] + [K⁺] + [Ca²⁺] + [Mg²⁺] - [Cl^-] - [lactate^-]. The serum effective SID (SID_eff) was calculated using the following equation: SID_eff = 12.2 × PCO₂/(10^-pH) + [albumin] × (0.123 × pH - 0.631) + [PO₄^-] × (0.309 × pH - 0.469). The SIG was calculated using the following equation: SIG = SID_app - SID_eff. The sodium–chloride effect was calculated using the formula [Na⁺] - [Cl^-] - 38. PaCO₂, arterial carbon dioxide tension; SID, strong ion difference; SIG, strong ion gap.

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