tcome, two died without requiring dialysis, and their uNGAL levels decreased within 48 h (details in Table [3](#Tab3){ref-type="table"} and Supplemental Table [7](#MOESM2){ref-type="media"}).Table 3Association between tracheotomy and discharge modality with regard to patients suffering from AKI with and without required dialysis.Discharge modality depending on tracheotomy and AKI req. dialysisAKI req. dialysis andNo AKI andTracheotomyTracheotomyYesNoTotalYesNoTotaldischarge mortalityfavorable13403939adverse707202Total831123941p (Fisher Test)P = 0.0242\*P = 0.0012\*Data listed in each of the combination cell corresponds to absolute frequency. \**p* \< 0.05.

Repeated measures analysis of uNGAL {#Sec10}
-----------------------------------

In a longitudinal analysis, a significant impact of the baseline value of uNGAL on the post-surgical measured levels of uNGAL within the first 48 h after admission to ICU (Table [4](#Tab4){ref-type="table"}; base: *p* = 0.0011) was observed. Overall, uNGAL did not change significantly over time (base: *p* = 0.6935). The repeated factors urea, urine, and serum creatinine were also identified as significantly related to uNGAL (Table [4](#Tab4){ref-type="table"}; urea: *p* = 0.0462; urine: *p* = 0.0044; serum creatinine: *p* = 0.0018). Nevertheless, the slope estimate of urine was close to zero.Table 4Repeated measures analysis of uNGAL in a single parameter and Multivariable analysis of the longitudinal model.Linear mixed model for log(uNGAL)CovariablesEstimateSEM (Estimate)DF resp Num DF/Den DFt- resp. F-valuep-valueBase model   Intercept0.96060.222871.54.31\<0.0001\*   Baseline (uNGAL)0.10310.029750.13.470.0011\*   Time Point (overall)3/1130.480.6935   ICU (Reference)0\....   12 h after ICU0.11540.14871270.780.4390   24 h after ICU−0.01520.1496118−0.100.9192   48 h after ICU−0.06080.1568122−0.390.6989**Single parameter analysis of the longitudinal model**Continuous covariables   Age0.015830.0143548.71.1