Structural equation modelling exploration of the key pathophysiological processes involved in cardiac surgery-related acute kidney injury in infants

Table 2 Exploratory factor analysis with varimax rotation: results of the 4-factor solution

Variable	Factor 1	Factor 2	Factor 3	Factor 4
Variable	Outcome	CPB	LCOS	AKI
Age, days			−0.773
Duration of cardiopulmonary bypass, minutes	0.305	0.907		0.242
Duration of aortic cross-clamping, minutes		0.817
Conventional ultrafiltration on bypass, ml		0.695
Blood transfusions on day 0, ml	0.251	0.215	0.627
Lactacidemia, AUC		0.280	0.680
Systolic arterial pressure, AUC^a	0.209		0.610	0.214
Urine output <0.5 ml kg⁻¹ h⁻¹, AUC	0.188			0.420
Increase in serum creatinine >50 % relative to baseline, AUC				0.538
Urine creatinine normalized NGAL, AUC^b		0.393		0.494
Duration of mechanical ventilation, days	0.946	0.202	0.227
Length of intensive care unit stay, days	0.910		0.227
In-hospital mortality	0.613			0.236
Eigenvalue	5.11	1.71	1.55	1.01
Proportion of the explained variance	0.198	0.183	0.158	0.071

NGAL neutrophil gelatinase-associated lipocalin, AKI acute kidney injury, CPB cardiopulmonary bypass, LCOS low cardiac output syndrome
The table shows the estimated factor loadings. The factor loading value is equivalent to the correlation coefficient between the variable and the factor. Only factor loading values greater than ±0.200 are shown. Factor loading values greater than ±0.400 (considered significant for a sample size of 200) are shown in boldface type; they allowed for identification of the variables further used to model the latent constructs Outcome, CPB, LCOS and AKI. Together, the four factors explained 0.610 of the total variance in the dataset, a proportion considered acceptable. AUC accounts for the magnitude and the duration of the parameter variation
^aWithin 24 h of surgery
^bWithin 12 h of surgery. All the other parameters were monitored within 48 h of surgery