Hyperchloremia and postoperative acute kidney injury: a retrospective analysis of data from the surgical intensive care unit

Table 4 Multivariable logistic regression analyses for postoperative AKI stage ≥ 2 according to Cl⁻ increase

Group	Variable	Multivariable model 4
Group	Variable	Odds ratio (95% CI)	P value
Entire sample (n = 8157)	Increase in Cl⁻, mmol L^− 1*
	Q1: ≤1 mmol L^− 1	1	(0.802)
	Q2: 1–3 mmol L^− 1	1.22 (0.65, 2.28)	0.542
	Q3: 3–6 mmol L^− 1	0.86 (0.46, 1.62)	0.642
	Q4: > 6 mmol L^− 1	1.00 (0.53, 1.89)	0.992
	Interaction of Cl⁻ increase with eGFR^a
	Increase in Cl⁻: Q1 * eGFR: ≥ 90	1	(0.960)
	Increase in Cl⁻: Q2 * eGFR: 60–89	0.62 (0.23, 1.67)	0.348
	Increase in Cl⁻: Q2 * eGFR: 30–60	1.01 (0.31, 3.30)	0.990
	Increase in Cl⁻: Q2 * eGFR: < 30	0.00 (0.00)	0.996
	Increase in Cl⁻: Q3 * eGFR: 60–89	1.14 (0.46, 2.79)	0.780
	Increase in Cl⁻: Q3 * eGFR: 30–60	1.44 (0.48, 4.37)	0.518
	Increase in Cl⁻: Q3 * eGFR: < 30	2.52 (0.38, 16.95)	0.342
	Increase in Cl⁻: Q4 * eGFR: 60–89	0.96 (0.38, 2.44)	0.937
	Increase in Cl⁻: Q4 * eGFR: 30–60	1.52 (0.50, 4.62)	0.460
	Increase in Cl⁻: Q4 * eGFR: < 30	2.53 (0.38, 17.01)	0.341

Covariates with P < 0.2 on univariable analysis (see also Additional file 4) were included in the final multivariable model to adjust for potential confounders. Covariates for multivariable model 4 included preoperative American Society of Anesthesiologists (ASA) score, preoperative estimated glomerular filtration rate (eGFR), cardiovascular surgery, NaCl 0.45% and hydroxyethyl starch infused
*The increase in Cl⁻ was calculated as the difference between the preoperative value and the maximum value noted during postoperative days (PODs) 0–3. The following quartiles were obtained: Q1, 2535 patients (31.7%); Q2, 1593 patients (20.0%); Q3, 2075 patients (26.0%); and Q4, 1788 patients (22.4%). The Hosmer-Lemeshow goodness-of-fit test was performed to investigate the fitness of the multivariable logistic regression models, and revealed no indication of lack of fit. For the entire sample, the Hosmer-Lemeshow statistic was 5.76 and the P value was 0.674
AKI acute kidney injury, CI confidence interval, Cl⁻ serum chloride levels
^aPreoperative eGFR (mL·min^− 1·1.73·m^− 2) was calculated using the Modification of Diet in Renal Disease formula: 186 × (preoperative serum Creatinine)^-1.154 × (Age)^-0.203 (× 0.742 if female)

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