Positive fluid balance is associated with earlier acute kidney injury in COVID-19 patients

Variables	M (SD) or n (%)
Net input and output average [mean]	612.2 (747.38)
Age (years) [mean]	58.1 (16.54)
Sex (female)	159 (39.5)
Race/ethnicity
White	85 (21.1)
Black	79 (19.6)
Hispanic	214 (53.1)
Other	25 (6.2)
Insurance
Private	105 (26.1)
Uninsured/emergency Medicaid	105 (26.1)
Regular Medicaid	132 (32.8)
Medicare	61 (15.1)
Body mass index (kg/m²) [mean]	29.8 (7.11)
Charlson comorbidity index [mean]	2.2 (2.11)
Chronic kidney disease (yes)	7 (1.7)
Intensive care unit (yes)	190 (47.1)
Mechanical ventilation (yes)	97 (24.1)
Nephrotoxin (yes)	359 (89.1)
Vasopressor (yes)	56 (13.9)
Loop diuretic (yes)	63 (15.6)
Outcomes
Acute kidney injury (yes)	92 (22.8)
Mortality (yes)	106 (26.3)
Days to acute kidney injury [mean]	7.7 (6.27)
Length of stay (days) [mean]	11.5 (13.17)

[i] Note: M=mean, SD=standard deviation

Table 2.

Fluid Net Input and Output Missing Data for Each Day While In-Hospital

Variable	Whole Sample Frequency (%) (n=403)	No AKI Frequency (%) (n=311)	Yes AKI Frequency (%) (n=92)	No Mortality Frequency (%) (n=297)	Yes Mortality Frequency (%) (n=106)
On day 1	84 (20.8)	65 (20.9)	19 (20.7)	54 (18.2)	30 (28.3)
On day 2	103 (25.6)	81 (26.0)	22 (23.9)	78 (26.3)	25 (23.6)
On day 3	156 (38.7)	123 (39.5)	33 (35.9)	119 (40.1)	37 (34.9)
On day 4	189 (46.9)	149 (47.9)	40 (43.5)	145 (48.8)	44 (41.5)
On day 5	239 (59.3)	194 (62.4)	45 (48.9)	183 (61.6)	56 (52.8)
On day 6	270 (67.0)	216 (69.5)	54 (58.7)	206 (69.4)	64 (60.4)
On day 7	295 (73.2)	238 (76.5)	57 (62.0)	223 (75.1)	72 (67.9)
On day 8	320 (79.4)	252 (81.0)	68 (73.9)	238 (80.1)	82 (77.4)
On day 9	335 (83.1)	263 (84.6)	72 (78.3)	247 (83.2)	88 (83.0)
On day 10	349 (86.6)	275 (88.4)	74 (80.4)	256 (86.2)	93 (87.7)

[i] Note: AKI=acute kidney injury

Table 3.

Fluid Net Input and Output Total Number of Days Performed While In-Hospital

Variable	Frequency (%) (n=403)
1 day	80 (19.9)
2 days	89 (22.1)
3 days	41 (10.2)
4 days	46 (11.4)
5 days	23 (5.7)
6 days	30 (7.4)
7 days	22 (5.5)
8 days	13 (3.2)
9 days	18 (4.5)
10 days	41 (10.2)

Table 4.

Multivariate Logistic Regression Analyses for Acute Kidney Injury

Variables	Whole sample OR (95% CI) (n=403)	p-value	No ICU OR (95% CI) (n=213)	p-value	Yes ICU OR (95% CI) (n=190)	p-value
Net input and output average	1.00 (1.00, 1.00)	0.76	1.00 (1.00, 1.00)	0.48	1.00 (1.00, 1.00)	1.00
Age (years)	0.99 (0.96, 1.02)	0.39	0.97 (0.92, 1.02)	0.22	1.01 (0.97, 1.04)	0.76
Sex (female)	0.89 (0.44, 1.79)	0.74	2.15 (0.63, 7.37)	0.22	0.56 (0.22, 1.42)	0.22
Race/ethnicity
White	1.00		1.00		1.00
Black	2.99 (1.05, 8.51)	0.04	9.98 (0.97, 102.57)	0.053	1.62 (0.41, 6.49)	0.50
Hispanic	1.75 (0.68, 4.54)	0.25	4.44 (0.39, 50.95)	0.23	1.59 (0.50, 5.01)	0.43
Other	1.65 (0.41, 6.67)	0.48	<0.001 (<0.001,---)	1.00	1.80 (0.33, 9.65)	0.50
Insurance
Private	1.00		1.00		1.00
Uninsured/emergency Medicaid	0.63 (0.25, 1.57	0.32	1.01 (0.21, 4.93	1.00	0.43 (0.13, 1.42)	0.16
Regular Medicaid	0.58 (0.25, 1.35)	0.20	0.56 (0.12, 2.60)	0.46	0.62(0.21, 1.85)	0.39
Medicare	0.45 (0.15, 1.36)	0.16	1.33 (0.16, 11.08)	0.79	0.39 (0.10, 1.54)	0.18
Body mass index (kg/m²)	1.00 (0.96, 1.05)	0.88	1.02 (0.94, 1.10)	0.71	1.00 (0.95, 1.06)	0.99
Charlson comorbidity index	1.17 (0.94, 1.45)	0.15	1.39 (1.02, 1.91)	0.04	0.97 (0.71, 1.32)	0.84
Chronic kidney disease (yes)	1.55 (0.10, 22.02)	0.75	<0.001 (<0.001,---)	1.00	5.24 (0.17, 161.05)	0.34
Intensive care unit (yes)	1.54 (0.61, 3.91)	0.36	---	---	---	---
Mechanical ventilation (yes)	28.43 (11.77, 68.68)	<0.001	---	---	25.27 (10.33, 61.83)	<0.001
Nephrotoxin (yes)	1.16 (0.33, 4.15)	0.81	1.00 (0.23, 4.32)	1.00	4.78 (0.33, 69.01)	0.25
Vasopressor (yes)	1.20 (0.16, 8.96)	0.86	---	---	1.37 (0.20, 9.51)	0.75
Loop diuretic (yes)	1.09 (0.48, 2.51)	0.84	<0.001 (<0.001,---)	1.00	1.53 (0.60, 3.91)	0.37

[i] Note: OR=odds ratio, CI=confidence interval, ICU=intensive care unit. In the model of no ICU, there were no patients with mechanical ventilation or vasopressor. Nagelkerke R Square: whole sample=0.51, no ICU=0.20, yes ICU=0.51.

Table 5.

Multivariate Logistic Regression Analyses for Mortality

Variables	Whole sample OR (95% CI) (n=403)	p-value	No ICU OR (95% CI) (n=213)	p-value	Yes ICU OR (95% CI) (n=190)	p-value
Net input and output average	1.001 (1.0001, 1.0011)	0.02	1.00 (1.00, 1.00)	0.79	1.001 (1.0002, 1.0013)	0.01
Age (years)	1.05 (1.02, 1.08)	0.001	1.07 (0.99, 1.15)	0.09	1.04 (1.01, 1.08)	0.01
Sex (female)	1.48 (0.66, 3.35)	0.34	1.14 (0.19, 6.92)	0.89	1.61 (0.62, 4.24)	0.33
Race/ethnicity
White	1.00		1.00		1.00
Black	0.61 (0.19, 1.92)	0.39	0.85 (0.13, 5.58)	0.86	0.44 (0.10, 1.84)	0.26
Hispanic	0.62 (0.22, 1.74)	0.36	0.22 (0.02, 3.19)	0.27	0.85 (0.25, 2.90)	0.79
Other	0.50 (0.10, 2.56)	0.40	<0.001 (<0.001,---)	1.00	0.85 (0.14, 5.32)	0.86
Insurance
Private	1.00		1.00		1.00
Uninsured/emergency Medicaid	0.80 (0.25, 2.62)	0.72	1.77*10⁷ (<0.001,---)	1.00	0.70 (0.19, 2.57)	0.59
Regular Medicaid	2.57 (0.90, 7.35)	0.08	4.50*10⁷ (<0.001,---)	1.00	2.88 (0.88, 9.38)	0.08
Medicare	3.00 (0.85, 10.60)	0.09	3.23*10⁷ (<0.001,---)	1.00	2.50 (0.60, 10.45)	0.21
Body mass index (kg/m²)	1.00 (0.95, 1.06)	0.95	0.80 (0.61, 1.04)	0.09	1.04 (0.98, 1.10)	0.23
Charlson comorbidity index	1.06 (0.84, 1.34)	0.62	0.86 (0.53, 1.42)	0.56	1.15 (0.87, 1.51)	0.34
Chronic kidney disease (yes)	1.30 (0.10, 17.93)	0.84	3.11 (<0.001,---)	1.00	1.41 (0.07, 27.23)	0.82
Intensive care unit (yes)	10.18 (3.67, 28.22)	<0.001	---	---	---	---
Mechanical ventilation (yes)	23.46 (9.24, 59.57)	<0.001	---	---	23.16 (8.91, 60.19)	<0.001
Nephrotoxin (yes)	0.49 (0.12, 1.92)	0.30	0.50 (0.05, 5.08)	0.56	0.64 (0.08, 4.80)	0.66
Vasopressor (yes)	17.58 (1.23, 250.55)	0.03	---	---	17.24 (1.21, 245.50)	0.04
Loop diuretic (yes)	0.60 (0.22, 1.63)	0.32	<0.001 (<0.001,---)	1.00	0.67 (0.24, 1.89)	0.45

[i] Note: OR=odds ratio, CI=confidence interval, ICU=intensive care unit. In the model of no ICU, there were no patients with mechanical ventilation or vasopressor. In the model of no ICU, the Box-Tidwell test suggested that the assumption of linearity of the logit for the Charlson comorbidity index was not met. An analytical model excluding the Charlson comorbidity index as a predictor variable had the same significance pattern as the model including the Charlson comorbidity index as a predictor variable. Data shown in the table is for the analytical model including the Charlson comorbidity index. Nagelkerke R Square: whole sample=0.69, no ICU=0.41, yes ICU=0.59.

Table 6.

Multivariate Linear Regression Analyses for Days to Acute Kidney Injury

Variables	Whole sample B (SE) (n=403)	p-value	No ICU B (SE) (n=213)	p-value	Yes ICU B (SE) (n=190)	p-value
Net input and output average	−6.63*10⁻⁵ (<0.001)	0.003	1.52*10⁻⁵ (<0.001)	0.65	<0.001 (<0.001)	<0.001
Age (years)	0.001 (0.001)	0.33	−0.001 (0.002)	0.78	0.002 (0.002)	0.22
Sex (female)	0.01 (0.03)	0.89	−0.05 (0.04)	0.29	0.07 (0.06)	0.26
Race/ethnicity
White	Reference		Reference		Reference
Black	−0.12 (0.05)	0.02	−0.15 (0.06)	0.02	−0.10 (0.09)	0.25
Hispanic	−0.07 (0.05)	0.12	−0.13 (0.06)	0.03	−0.04 (0.07)	0.61
Other	−0.04 (0.08)	0.57	−0.12 (0.10)	0.23	0.01 (0.11)	0.96
Insurance
Private	Reference		Reference		Reference
Uninsured/emergency Medicaid	0.06 (0.05)	0.23	0.05 (0.06)	0.39	0.07 (0.08)	0.34
Regular Medicaid	0.03 (0.04)	0.51	0.06 (0.06)	0.27	−0.01 (0.07)	0.86
Medicare	−0.03 (0.06)	0.59	0.02 (0.08)	0.77	−0.10 (0.09)	0.23
Body mass index (kg/m²)	−0.001 (0.002)	0.73	−0.002 (0.003)	0.58	−0.001 (0.003)	0.82
Charlson comorbidity index	0.004 (0.01)	0.71	0.02 (0.01)	0.19	−0.001 (0.02)	0.95
Chronic kidney disease (yes)	−0.21 (0.13)	0.11	−0.07 (0.22)	0.74	−0.23 (0.18)	0.20
Intensive care unit (yes)	0.23 (0.04)	<0.001	---	---	---	---
Mechanical ventilation (yes)	−0.21 (0.05)	<0.001	---	---	−0.18 (0.05)	<0.001
Nephrotoxin (yes)	0.18 (0.05)	<0.001	0.20 (0.06)	<0.001	0.07 (0.14)	0.62
Vasopressor (yes)	−0.01 (0.12)	0.95	---	---	−0.01 (0.13)	0.91
Loop diuretic (yes)	0.07 (0.05)	0.14	0.17 (0.08)	0.03	0.01 (0.06)	0.92
Constant	0.56 (0.12)	<0.001	0.63 (0.15)	<0.001	0.84 (0.23)	<0.001

[i] Note: B=unstandardized beta, SE=standard error, ICU=intensive care unit. In the model of no ICU, there were no patients with mechanical ventilation or vasopressor. Adjusted R Square: whole sample=0.15, no ICU=0.09, yes ICU=0.13.

Table 7.

Multivariate Linear Regression Analyses for Length of Stay in Hospital

Variables	Whole sample B (SE) (n=403)	p-value	No ICU B (SE) (n=213)	p-value	Yes ICU B (SE) (n=190)	p-value
Net input and output average	−1.90*10⁻⁵ (<0.001)	0.39	1.83*10⁻⁵ (<0.001)	0.57	−2.97*10⁻⁵ (<0.001)	0.33
Age (years)	−0.001 (0.001)	0.70	0.001 (0.002)	0.79	−0.001 (0.002)	0.66
Sex (female)	−0.04 (0.03)	0.31	−0.04 (0.04)	0.32	−0.02 (0.06)	0.80
Race/ethnicity
White	Reference		Reference		Reference
Black	−0.03 (0.05)	0.62	−0.09 (0.06)	0.12	0.05 (0.09)	0.58
Hispanic	−0.01 (0.05)	0.77	−0.12 (0.06)	0.04	0.09 (0.07)	0.24
Other	−0.02 (0.08)	0.85	−0.12 (0.10)	0.22	0.11 (0.12)	0.32
Insurance
Private	Reference		Reference		Reference
Uninsured/emergency Medicaid	0.07 (0.05)	0.11	0.05 (0.06)	0.35	0.09 (0.08)	0.26
Regular Medicaid	−0.02 (0.04)	0.72	0.05 (0.05)	0.40	−0.08 (0.07)	0.23
Medicare	−0.05 (0.06)	0.44	0.02 (0.08)	0.77	−0.11 (0.09)	0.22
Body mass index (kg/m²)	−0.001 (0.002)	0.73	−0.001 (0.003)	0.81	−0.01 (0.004)	0.07
Charlson comorbidity index	−0.004 (0.02)	0.10	0.02 (0.01)	0.12	−0.01 (0.02)	0.75
Chronic kidney disease (yes)	−0.09 (0.13)	0.50	−0.11 (0.22)	0.61	−0.03 (0.18)	0.87
Intensive care unit (yes)	0.27 (0.04)	<0.001	---	---	---	---
Mechanical ventilation (yes)	0.14 (0.05)	0.003	---	---	0.16 (0.05)	0.004
Nephrotoxin (yes)	0.18 (0.05)	<0.001	0.17 (0.05)	0.002	0.18 (0.14)	0.23
Vasopressor (yes)	−0.24 (0.12)	0.051	---	---	−0.27 (0.13)	0.04
Loop diuretic (yes)	0.10 (0.05)	0.03	0.17 (0.08)	0.03	0.09 (0.06)	0.13
Constant	0.71 (0.12)	<0.001	0.16 (0.08)	0.04	1.07 (0.23)	<0.001

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DOI: https://doi.org/10.62838/jccm-2026-0006 | Journal eISSN: 2393-1817 | Journal ISSN: 2393-1809

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Language: English

Page range: 186 - 198

Submitted on: Dec 16, 2024

Accepted on: Jan 21, 2026

Published on: Apr 30, 2026

Published by: University of Medicine, Pharmacy, Science and Technology of Targu Mures

In partnership with: Paradigm Publishing Services

Publication frequency: 4 issues per year

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Internal medicine, other,

Surgery,

Surgery, other,

Anaesthesiology,

Emergency medicine and intensive-care medicine

© 2026 Rezwan Munshi, Sandra Gomez-Paz, Salman Bhutta, Joshua Fogel, James Pellegrini, Narois Nehru, Eric Lam, Sofia Rubinstein, published by University of Medicine, Pharmacy, Science and Technology of Targu Mures
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 12 (2026): Issue 2 (April 2026)