In this single-group longitudinal study that was confirmed in the Ethics Committee of Mashhad University of Medical Sciences, Mashhad Iran. (IR.MUMS.NURSE.REC.1397.081) and adhered to the STARD guidelines for diagnostic accuracy studies, Patients, who were admitted to two kidney transplant centers of Iran and Afghanistan., and were undergone kidney transplantation, from February 2019 to the end of October 2019, participated in the study as the sample group after obtaining written informed consent.
The sample size was considered to be 135 with the help of STATA 14 statistical software and according to papers (9).
Patients who received kidney transplantation entered the study in coordination with the related physician, based on inclusion criteria, including age range of 13-65 years, willingness to participate in the study, not being afflicted by urinary tract or neurogenic bladder disorders, and not undergone bladder transplantation. They were excluded from the study under some circumstances, such as refusal to continue participating in the study, death. The patients would be also excluded if the researcher was not able to control IAP because of conditions, including the patient’s intolerance of testing, incidence of respiratory distress, hemodynamic changes, non-authorization by the physician, and suprapubic catheter placement.
Among the transplanted patients at the research period, two patients due to neurogenic bladder, and one patient due to urethral stricture and suprapubic catheter insertion were excluded. Finally, 135 patients were included in the study and their data were analyzed (figure1).
IAP measurement through bladder was made every 6 hours after transplantation for 24 hours. Afterwards, it was done 48 and 72 hours after transplantation if IAP was higher than and equal to 12.
Data collection instruments
For each patient, a form containing information related to the patient’s demography, diseases, 24-hour urine volume, type of dialysis (hemodialysis or peritoneal), and history of the previous transplantation were recorded. Each patient’s postoperative information were recorded and examined in a checklist including: vital signs (pulse, blood pressure), the rate of intake and output within the first 24, IAP scores every 6 hour up to 24 hours, laboratory parameters ( urea, and creatinine) during 24h, 72h and a week after surgery. The need for dialysis and Thymoglobulin, and also the results of renal artery Doppler ultrasound were also checked.
In the present study, IAP measurement through the bladder catheter was utilized considering the constraints in two countries , and the existence of simple urinary catheters, not equipped with culture aspiration port from each patient's urinary tube ─as a route of water elevation along the scale of centimeter of water .
Here, the capillary effect (i.e., the tendency of liquid to rise in low-diameter tubes) was used. This study was initiated by putting the patient in a supine position, so that the abdominal muscles were in a relaxed state. It was proceeded by entering 50 cc normal saline slowly into bladder through the path connected to urine bag, and the path was then clamped. At this time, the urinary bag tube was emptied. After that, the scale zero point was placed at the joining point of iliac spine and armpit midline, and at the same level or Pubic symphysis of patient; the tube of urinary bag was also fixed from the junction to the catheter at zero point, and the rest of urinary tube was held at the zero level of the scale. After 30 to 50 seconds, the patient was asked to hold his breath, and then the clamp was opened for urine to move along the path of the urinary bag tube and rise through the scale level; the number indicated IAP at the point, where urine stopped and fluctuated with the patient's breath (figure2).
The most important point in IAP measurement is the zero point of the scale or transducer that should be placed in the mid axillary and iliac lines, and parallel to the pubic symphysis. An appropriate volume of bladder as well as a minimum time of 30 seconds are necessary to relax the bladder muscles. Entering an excessive volume of fluid or allowing the bladder to relax too much result in a false high number for IAP. Body position can contribute to an accurate IAP number, so that bed height above 10 to 20 degrees can lead to a false high number for IAP. (10,7)
According to Abdominal Compartment Syndrome Association, there are three grades for IAP : grade (1) IAP range of12-15 mmHg, grade (2) IAP range of 16-20 mmHg, and grade (3) IAP range of 21-25 mm Hg. (7).
The indices used to predict renal dysfunction included the urinary output less than 100 cc/hr, lack of creatinine depletion of less than 25% of baseline, Delayed Graft Function (dialysis requirement in the first week of transplantation), and Doppler sonographic changes (increase in vascular resistance).
The statistical analysis was performed after collecting and encoding data by using STATA software version 14. Descriptive statistics, including the distribution of relative frequency, mean and standard deviation were used to describe the characteristics of research sample. To decide on an appropriate test for examining the correlation between variables, the compatibility of variables distribution with normal distribution was examined by means of the Shapiro-Wilk test. Since the distribution of quantitative variables did not follow normal distribution, the Mann-Whitney test was employed and the significance level was considered to be 5% in all tests.
The statistical tests were used in a way that, first, the correlation between IAP variables or their conversions with dichotomous variables, indicating renal dysfunction (i.e., decrease of urine volume lower than 100 cc/h, creatinine decrease less than 25% of preoperative baseline, and delayed function of the transplanted kidney) was examined by the Mann-Whitney test. Then, the predictive power of IAP variables for renal dysfunction was evaluated by using the System Performance a Receiver Operating Characteristic (ROC) curve; the sensitivity, specificity , as well as positive and negative predictive values were calculated by considering the area under the curve for each of their values (cut-off point). Next, a combination of tests with maximum sensitivity, specificity and predictive values was administered in series or sequential, and parallel forms by employing the Multiple Testing approach. The basis for comparing the cut-off points was the predictive or diagnostic power of Youden's and d2 indices; ultimately, a final cut-off points with the highest Youden's index and the lowest d2 index was recorded. Finally, the sensitivity and specificity identified in the Youden's and d2 indices were determined in IAP differences of 1-4 and 1-3; multiple sequential and parallel testing methods were used and sensitivity and specificity were determined by combining these tests in a parallel-sequential multiple test (11, 12).
Given the low incidence of renal dysfunction among the patients under study, sensitivity, which indicated the ability of a test to detect cases of disease was proved to be more important in this study. On the other hand, the low incidence of renal dysfunction among the patients under study caused the negative predictive value of the test to be important since this index showed the ratio of healthy cases to all the cases with negative test reports. Therefore, determining the negative predictive value of the test was more emphasized in the study, and on this account a combination of parallel statistical test was used with the highest sensitivity and negative predictive value.
 Youden's= (Sensitivity + specificity) -1
 d2= (1-sensitivity)2 + (1- specificity)2