Simple blood and urinary parameters measured at ICU admission may sign for AKI development in the early postoperative period: a retrospective, exploratory study

Figures & data

Table 1. General characteristics of the 112 surgical patients included in the analysis.

	No-AKI (n = 84)	AKI (n = 28)	p-Values
Age (years)	57 [41,69]	73 [67,83]	<0.001
Gender (male)	39 (46.4%)	13 (46.4%)	0.827
SAPS 3 predicted risk of mortality	1.6% [0.6,4.5]	4.0% [2.2,16.6]	<0.001
Baseline creatinine (mg/dL)	0.8 [0.7,1.1]	1.1 [0.8,1.5]	<0.001
Day of AKI diagnosis
0	–	3
1	–	13
2	–	9
3	–	3
Maximum AKIN reached
1	–	23
2	–	2
3	–	3
Associated diseases:
Arterial hypertension	32 (38.1%)	18 (64.3%)	0.028
Diabetes mellitus	14 (16.7%)	11 (39.3%)	0.026
Congestive heart failure	2 (2.4%)	0 (0%)	1.000
COPD	4 (4.8%)	1 (3.6%)	0.792
cirrhosis	2 (2.4%)	0 (0%)	1.000
ICU support*
Diuretic	15 (17.9%)	9 (32.1%)	0.184
Vasopressor	7 (8.3%)	10 (35.7%)	0.001
Mechanical ventilation**	4 (4.8%)	7 (25%)	0.006
RRT	0	2 (7.1%)	0.099
Elective surgery	71 (84.5%)	23 (82.1%)	1.000
Type of surgery:
Neurosurgery	27 (32.1%)	4 (14.3%)
Gastrointestinal	22 (26.2%)	7 (25.0%)
Genitourinary	13 (15.5%)	7 (25.0%)
Orthopedic	10 (11.9%)	5 (17.9%)
Vascular	5 (5.9%)	3 (10.7%)
Head and Neck	4 (4.8%)	0
Cardiac	1 (1.2%)	2 (7.1%)
Thoracic	1 (1.2%)	0
Plastic	1 (1.2%)	0
Mortality
ICU	1 (1.2%)	3 (10.7%)	0.078
Hospital	3 (3.6%)	5 (17.9%)	0.034

Abbreviations: AKI: acute kidney injury; SAPS: Simplified Acute Physiology Score; AKIN: Acute Kidney Injury Network; COPD: chronic obstructive pulmonary disease; ICU: intensive care unit; RRT: renal replacement therapy.

*During the first three postoperative days.

**Need of mechanical ventilation beyond the day of ICU admission.

Table 2. Traditional acid-base and renal parameters according to acute kidney injury status in the early postoperative period.

		D0 (63/23)Φ	D1 (84/27)	D2 (57/23)	D3 (28/19)
pH	No AKI	7.33 [7.28,7.36]*	7.34 [7.31,7.38]**	7.36 [7.34,7.39]***	7.37 [7.34,7.41]*
	AKI	7.30 [7.27,7.32]	7.31 [7.26,7.35]	7.32 [7.30,7.35]	7.34 [7.32,7.38]
SBE (mEq/L)	No AKI	−1.5 [−3.5,0.1]	−1.5 [−3.7,0.1]*	−0.2 [−1.6,1.8]***	0.0 [−1.8,1.9]*
	AKI	−2.6 [−4.0,0.1]	−2.8 [−5.1,−1.5]	−2.4 [−3.5,−1.0]	−2.2 [−4.0,−0.1]
PCO2 (mmHg)	No AKI	47.2 [42.5,52.9]	44.0 [41.9,47.9]	44.8 [41.8,48.2]	41.7 [37.3,50.7]
	AKI	50.7 [44.5,56.4]	46.6 [42.9,51.0]	46.5 [41.0,49.2]	44.3 [38.5,49.8]
Lactate (mEq/L)	No AKI	2.7 [2.1,3.5]	2.4 [1.6,3.4]	1.3 [0.9,1.9]	1.1 [0.8,1.8]
	AKI	2.4 [2.0,3.2]	2.3 [1.5,3.8]	1.7 [1.2,2.8]	1.1 [0.7,1.8]
Anion gap (mEq/L)	No AKI	12.3 [10.6,13.6]	11.4 [10.0,13.0]	10.2 [8.9,11.8]***	10.8 [9.4,12.6]**
	AKI	11.5 [9.1,13.6]	12.4 [10.5,14.0]	12.3 [10.9,15.5]	12.1 [11.6,15.8]
Urea (mg/dL)	No AKI	30 [22,40]***	28 [21,40]***	27 [21,40]***	30 [20,42]***
	AKI	47 [32,63]	51 [30,67]	55 [32,90]	59 [39,95]
Creatinine (mg/dL)	No AKI	0.8 [0.7,1.0]**	0.8 [0.7,1.0]***	0.8 [0.7,0.9]***	0.7 [0.6,0.9]***
	AKI	1.1 [0.8,1.5]	1.3 [1.0,1.7]	1.7 [1.2,2.3]	1.7 [1.2,2.1]
24h-diuresis (mL)	No AKI	–	1550 [1120,2450]	2040 [1178,3590]	1835 [978,2550]
	AKI	–	1413 [569,2413]	1900 [790,2780]	1400 [850,2185]
24h-fluid input (mL)	No AKI	–	2426 [1942,3219]	2207 [1721,2931]	2160 [1057,2752]
	AKI	–	2621 [1409,3327]	1980 [1720,3162]	1984 [1293,2275]

Notes: Φnumber of patients in the no-AKI and AKI group, respectively, at that specific day.

*p< 0.05, **p< 0.01, ***p< 0.001 in comparison to AKI.

SBE: standard base excess; AKI: acute kidney injury; D0: Day of ICU admission.

Figure 1. Differences in serum leukocytes count (A) and C-reactive protein (B) evolution in the first three postoperative days between patients who developed or not AKI during this period. Notes: ICU: intensive care unit. AKI: acute kidney injury. *p < 0.05; **p = 0.01.

Figure 2. Differences in strong ion gap evolution in the first three postoperative days between patients who developed or not AKI during this period. Notes: ICU: intensive care unit. AKI: acute kidney injury. *p < 0.05; **p < 0.01; ***p < 0.001.

Table 3. Blood physicochemical parameters according to acute kidney injury status in the early postoperative period.

		D0 (63/23)Φ	D1 (84/27)	D2 (57/23)	D3 (28/19)
SIDa (mEq/L)	No AKI	37.0 [34.0,39.3]	36.6 [34.3,38.5]	37.2 [35.0,39.0]	38.1 [36.3,39.3]
	AKI	37.0 [33.3,38.4]	36.6 [32.4,38.5]	38.1 [36.8,41.1]	38.8 [36.5,40.6]
SIDe (mEq/L)	No AKI	35.3 [32.2,37.2]	35.1 [32.6,36.6]*	35.1 [32.8,37.5]*	34.9 [30.7,37.9]
	AKI	33.9 [30.9,37.3]	33.3 [30.4,34.6]	33.1 [32.0,35.2]	32.7 [30.6,36.3]
Albumin (g/dL)	No AKI	3.3 [2.9,3.6]**	3.1 [2.7,3.4]	2.8 [2.5,3.2]	2.7 [2.5,3.2]
	AKI	2.8 [2.5,3.1]	2.9 [2.7,3.1]	2.8 [2.4,3.0]	2.9 [2.4,3.1]
Phosphorus (mg/dL)	No AKI	3.4 [2.9,3.9]	3.4 [3.0,4.1]	2.8 [2.2,3.2]***	2.6 [2.4,3.4]**
	AKI	3.5 [2.5,4.6]	3.7 [3.1,4.4]	3.8 [3.1,4.5]	3.6 [3.3,4.8]

Notes: Φnumber of patients in the no-AKI and AKI group, respectively, at that specific day.

*p< 0.05, **p< 0.01, ***p< 0.001 in comparison to AKI.

SIDa: apparent strong ion difference; SIDe: effective strong ion difference; AKI: acute kidney injury; D0: Day of ICU admission.

Table 4. Urinary biochemical parameters and indices according to acute kidney injury status in the early postoperative period.

		D0 (63/23)Φ	D1 (84/27)	D2 (57/23)	D3 (28/19)
NaU (mEq/L)	No AKI	119 [89,167]*	126 [66,167]*	108 [59,172]**	126 [82,146]*
	AKI	81 [56,133]	82 [45,120]	61 [32,113]	79 [37,96]
KU (mEq/L)	No AKI	47 [26,75]	69 [42,109]	47 [28,78]	32 [20,58]*
	AKI	58 [31,89]	57 [33,92]	63 [27,97]	53 [38,89]
ClU (mEq/L)	No AKI	131 [97,161]	141 [77,184]**	116 [81,164]***	127 [88,151]**
	AKI	115 [57,138]	88 [29,142]	63 [22,106]	66 [27,111]
UrU (mg/dL)	No AKI	774 [375,1078]	1212 [702,1751]**	1290 [976,2005]**	956 [664,1844]
	AKI	795 [577,965]	750 [465,1216]	805 [508,1332]	1272 [687,1542]
CrU (mg/dL)	No AKI	50.5 [29.1,100.0]	89.5 [55.9,137.8]	108.3 [65.3,151.1]	71.2 [41.8,128.6]
	AKI	87.5 [31.3,110.1]	70.6 [34.0,116.2]	119.3 [42.6,149.2]	106.9 [75.1,126.2]
SIDu (mEq/L)	No AKI	41 [25,68]	54 [31,89]	36 [16,82]	35 [12,57]**
	AKI	46 [22,61]	52 [18,74]	51 [31,107]	63 [45,92]
FENa (%)	No AKI	1.4 [0.4,3.0]	0.9 [0.3,1.6]	0.7 [0.3,1.0]	0.8 [0.4,1.4]
	AKI	1.0 [0.5,2.3]	1.1 [0.2,3.1]	0.8 [0.2,2.6]	0.8 [0.3,1.9]
FEUr (%)	No AKI	39 [31,57]**	43 [32,54]	41 [30,49]	37 [31,54]
	AKI	33 [24,36]	35 [26,51]	36 [25,44]	37 [25,48]
FEK (%)	No AKI	18 [14,25]	15 [11,20]***	9 [7,14]***	9 [6,13]***
	AKI	21 [15,30]	27 [18,36]	24 [14,46]	25 [15,50]

Notes: Φnumber of patients in the no-AKI and AKI group, respectively, at that specific day.

*p < 0.05, **p < 0.01, ***p < 0.001.

NaU: urinary sodium; KU: urinary potassium; ClU: urinary chloride; UrU: urinary urea; CrU: urinary creatinine; SIDu: urinary strong ion difference; FENa: fractional excretion of sodium; FEUr: fractional excretion of urea; FEK: fractional excretion of potassium; AKI: acute kidney injury; D0: Day of ICU admission.

Figure 3. Correlation between serum creatinine and fractional excretion of sodium (A), urea (B) and potassium (C). Horizontal lines represent the usual cutoffs for the fractional excretions (1%, 35% and 10%, respectively); vertical lines represent the cutoff for normal serum creatinine levels (considered less than 1.2 mg/dL). The gray zone highlights the almost absence of samples with increased serum creatinine and simultaneous normal fractional excretion of potassium.

Table 5. Diagnostic accuracy, sensitivity, specificity, positive and negative predictive values for AKI diagnosis in the early postoperative period of distinct urinary and blood parameters measured at ICU admission.

	AUC (CI 95%, p-value)	Youdeńs best cutoff value	Sensitivity	Specificity	PPV	NPV
C-reactive protein (mg/dL)	0.687 (0.560-0.814, p = 0.009)	0.83	64%	69%	41%	85%
Serum albumin (g/dL)	0.727 (0.609-0.844, p = 0.002)	3.3	86%	58%	41%	93%
Urinary sodium (mEq/L)	0.679 (0.556-0.803, p = 0.012)	84	59%	78%	46%	84%
FEUr (%)	0.685 (0.557-0.812, p = 0.011)	35	73%	62%	41%	86%
ΔFEK (%)	0.774 (0.640-0.907, p < 0.001)	6.1	52%	97%	85%	86%

Notes: AKI: acute kidney injury; ICU: intensive care unit; AUC: area under the curve; CI: confidence interval; PPV: positive predictive value; NPV: negative predictive value; FEUr: fractional excretion of urea; ΔFEK: fractional excretion of potassium at D1 minus fractional excretion of potassium at D0.