Incidence, Outcomes, and Factors Associated with Intra-Abdominal Hypertension and Primary Abdominal Compartment Syndrome in Abdominopelvic Injury Patients

Background The primary aim was to identify the incidence of intra-abdominal hypertension (IAH) and primary abdominal compartment syndrome (1oACS) of abdominopelvic injury patients at Thammasat University Hospital (TUH), Thailand, and the secondary objective was to evaluate those factors that contributed to developing these conditions. Methods The retrospective cohort of 38 abdominopelvic injury cases was admitted to the intensive care unit at Thammasat University Hospital, from January 1st to December 31st, 2018. The bladder pressure was recorded every 4 hours until the urethral catheter was removed. Data of age, gender, weight, height, body mass index, injury mechanisms, initial vital signs, imaging, laboratory data, blood component requirements, abdominal organs involved, treatments including surgery and intervention radiology, abbreviated injury scale (AIS) and injury severity score (ISS), length of ICU stays, and results of treatment were all analyzed. Results The patients were mostly young (mean age 31.5 years), male (68.4%), and suffering from blunt trauma (89.5%). The mean maximum bladder pressure was 8.3 ± 5.2 mmHg. Six patients (15.8%) developed IAH, and one patient (2.6%) was diagnosed with 1oACS. Two patients expired. The multivariate analysis showed the patient who had initial Cr ≥ 1.5 g/dL, lower extremity including pelvis AIS ≥3, and ISS >15 was significantly associated with the developing of IAH. Conclusions The incidence of IAH and 1oACS was 15.8% and 2.6%. Predicted factors to find developing IAH were initial Cr ≥ 1.5 g/dL, lower extremity AIS ≥3, and ISS >15. We should consider awareness of IAH and 1oACS in abdominopelvic injury patients.


Introduction
Intra-abdominal hypertension (IAH) is defined as a sustained elevated level of intra-abdominal pressure (IAP) more than 12 mmHg. Abdominal compartment syndrome (ACS) is defined as a sustained raised level of IAP more than 20 mmHg with or without abdominal perfusion pressure (APP) less than 60 mmHg and developing of new end-organ failure. Primary ACS (1 o ACS) is defined as ACS developing from intra-abdominal pathologies. Secondary ACS (2 o ACS) means ACS following from extra-abdominal pathologies.
And recurrent ACS is defined as redeveloped ACS following medical or surgical treatments of 1 o or 2 o ACS [1].
ACS is caused by persistent increase in IAP leading to a decrease in venous return and cardiac output, and then, endorgan damage occurs [2]. Many reports define both IAH and ACS as significantly associated with morbidity and mortality in critically ill patients [3][4][5]. e incidence of IAH and ACS varies by the population group; the overall incidence is 30-70% and 10-35%, respectively [6]. If focusing on a trauma patient group, the incidence of IAH is 2-50%, and the incidence of ACS is 0.6-36% [7]. e indirect intra-abdominal pressure measurement uses a catheter inserted into the intraluminal cavity of an intra-abdominal organ and measures the intraluminal pressure [8]. Nowadays, intravesicular pressure measurement has become the gold standard in the analysis of IAP; it has shown strong correlations to the direct IAP measurement and is reliable [2,9]. e standard recommendations to evaluate IAP mostly use the World Society of the Abdominal Compartment Syndrome (WSACS) recommendation 2013. ey recommend measuring IAP at least every 4 hours in an injured patient with any known risk factors for IAH/ACS [1].
is study focuses on IAH and 1 o ACS from abdominopelvic injury etiology. We want to know precisely the incidence of these conditions in our institute and which factors contribute to development of IAH/1 o ACS and also what is the clinical result of these conditions. ese data may represent the incidence in specific population and guide us to improve the accuracy of protocol.

Materials and Methods
is retrospective cohort study was conducted at ammasat University Hospital (TUH), Pathumthani, a tertiary care center located in the central region of ailand. e study protocol was approved by the Human Ethics Committee of ammasat University No. 1 (Faculty of Medicine), ailand, which also waived the requirement for informed consent due to the retrospective nature of the study.
All adult abdominopelvic injury patients (age ≥ 18 years old) admitted to the intensive care unit (ICU) from January 1 st to December 31 st , 2018, were included. e exclusion criteria were the patient who could not insert a urethral catheter for any reason and the patient who had a history of pelvic mass bringing compression to the bladder or previous bladder surgery. Data regarding age, gender, weight, height, body mass index (BMI), injury mechanisms, initial vital signs, clinical presentations, imaging, laboratory data, blood component requirements in the first 24 hours, abdominal organs involved, all recorded intravesicular pressure, urethral catheter complications, treatments including surgery and intervention radiology, regional abbreviated injury scale (AIS), injury severity score (ISS), length of ICU stays, and results of treatment (death or alive until discharged) were all collected and analyzed.
Abdominopelvic injury is defined as any injury to internal organ of abdomen and abdominal wall. e boundary of the abdominopelvic region is below the diaphragm to the pelvic outlet. e injury includes intraperitoneal organs, extraperitoneal organs, pelvic bone, or pelvic viscera. e patient may or may not have had any combined injuries.
All of the patients were initially evaluated at the emergency room (ER) and fitted with a urethral catheter to evaluate the initial intravesicular pressure. e patient who had indication for immediate surgery needed to proceed to the operating room (OR). If the patient did not have indication for surgery, the patient was admitted to ICU for nonoperative management and to intermittent measurement and recording of intravesicular pressure in mmHg every 4 hours. e measurement of IAP is defined by first emptying the bladder and then filling by a maximum of 25 ml of sterile saline solution via the catheter. e zero is referenced at the midaxillary line, and then, the catheter is held vertically above the patient. e end-expiration fluid level was measured in cmH 2 O and converted to mmHg by using this formula: 1 mmHg � 1 cmH 2 O x 0.735. e patient who had intravesicular pressure more than 12 mmHg was treated by turning the patient into a supine position and then giving adequate pain control medication. We optimized the organ perfusion and avoided excessive fluid resuscitation. If intravesicular pressure was more than 20 mmHg, we defined the patient as IAH grade III and considered evaluating endorgan failure for diagnosis of 1 o ACS. e patients diagnosed with 1 o ACS were treated with decompressive laparotomy. e primary end point of this study was the patient had abdominopelvic operation which was the end of 1 o ACS definition, or the urethral catheter was removed. e secondary end point was the length of ICU stays, total blood components required, total operations required, the need for intervention radiology, and mortality. e statistical analysis tools used were IBM® and SPSS®, Version 20 for Mac® (SPSS, Chicago, Illinois, USA). Values were reported as percentages for categorical variables and mean (range) or mean with standard deviation (SD) for continuous variables. Comparison data, such as demographic and clinical characteristics, were evaluated using bivariable analysis. Correlation analysis of qualitative variables to developing IAH/1 o ACS was using the Pearson Chisquare test and unpaired t-test for quantitative variables. Independent risk factors associated with developing IAH/ 1 o ACS were measured using a stepwise logistic regression method. Statistical significance was set at p < 0.050.

Results
A total of 38 consecutive abdominopelvic injury cases were identified in the one year. e mean age was 31.5 years (18-67). Most of the patients were male (68.4%). irty-four patients (89.5%) were suffering from a blunt mechanism. e mean patient weight, height, and BMI were 61.2 ± 11.3 kg, 1.67 ± 0.09 m, and 21.7 ± 2.8 kg/m 2 , respectively. On primary surveys, seven patients (18.4%) had airway problems. Six cases (15.8%) had ventilation problems, and ten patients (26.3%) were suffering from hemorrhagic shock.
Six cases (15.8%) developed IAP ≥ 12 mmHg and were defined as the IAH group. Only one patient (2.6%) from the IAH grade III group developed renal failure after admission and was defined as 1 o ACS. Seventeen cases (43.7%) required the operative treatment; 11 cases (28.9%) needed abdominal operations, and 5 patients (13.2%) required orthopedic surgeries (included pelvic bone fixation). Six patients (15.8%) required the angiography with embolization. ere were no complications of urethral catheterized and IAP measurement in this study. e mean ICU stay was 4.5 ± 3.3 days. e mean of blood components required in the first 24 hours was 1.2 ± 1.1 unit of packed red cells (PRC), 0.7 ± 1.4 unit of fresh frozen plasma (FFP), and 0.5 ± 1.5 unit of platelets concentration. Two patients (5.3%) died: one from a severe head injury, and the other was multiorgan failure syndrome. e result of treatments is listed in Table 2. e incidence of IAH and 1 o ACS from this study was 15.8% and 2.6%, respectively. One patient from the IAH grade III group was diagnosed with blunt abdominal injury and lateral compression-type pelvic fracture. e patient had hemodynamic stability on admission (WSES grade II) and received pelvic angiography with embolization as a primary treatment.
e patient subsequently developed oliguria concomitant with gradually increased IAP and serum creatinine in the first day of ICU admission. e maximum IAP was 23 mmHg. e patient was diagnosed with 1 o ACS and proceeded to decompressive celiotomy. e operative finding was 200 ml of hemoperitoneum, a serosal tear of the transverse colon, and a large zone III retroperitoneal hematoma with a fractured pelvis. Preperitoneal packing with primary repair of the colon was conducted, and then, temporary abdominal closure with negative pressure wound therapy and external pelvic fixation was performed. Unfortunately, the patient expired after this operation with multiorgan failure syndrome. IAH and 1 o ACS cases are listed in Table 3.
Many variables had a significant difference between the patient who developed IAH and not as shown in Table 1. Some of the variables were selected for a statistical calculation for which factors are associated with developing IAH. e multivariate analysis with stepwise regression analysis was performed, and we found the patient who had initial Cr ≥ 1.5 g/dL, lower extremity including pelvis AIS ≥3, and ISS >15 were statistically significantly associated with developing IAH at p < 0.050. e relative risk (RR), 95% confidence interval (95% CI), and the result of multivariate analysis are listed in Table 4. We failed to demonstrate which factors are associated with developing 1 o ACS because only 1 case developed this condition.

Discussion
e incidence of IAH in our study was 15.8% (6 cases/year). In past studies [7,10], the incidence of IAH in mixed trauma populations was 2-50%. Balogh et al. [11] reported the incidence of IAP > 12 mmHg shock/trauma cases who were admitted to ICU was 75%. A study focusing on pelvic fracture patients [12] reported the incidence of IAH was 9.7%. e data of the IAH incidence in our study focus only on abdominopelvic injury patients who were admitted to ICU. is finding of this is more concise coming from a unique population.
Some studies have reported the prevalence and incidence of ACS in trauma patients. One study [13] said the rate of ACS in severe trauma patients was 0-28%, and subgroup analysis in trauma patients admitted to ICU and patients who had visceral injury was 0-5.3% and 1-20%, respectively. Ivatury et al. [14] reported 32% incidence of ACS in severe abdominal trauma, and Balogh et al. [15] reported the incidence of 1 o ACS in major torso trauma who required shock resuscitation was 6%. Compared to our result, the incidence of 1 o ACS is 2.6%. e result is different from previous data because of the difference in ACS definitions. In our study, we defined 1 o ACS as the sustained increase IAP >20 mmHg with new organ dysfunction/failure developing from abdominopelvic injury, but Ivatury et al. [14] defined ACS as a clinical syndrome characterized by increased intra-abdominal pressure (IAP > 25 cmH 2 O) and improvement after abdominal decompression, and they included all type of ACS. Balogh et al. [15] defined 1 o ACS as the patient having intraperitoneal injuries with IAP > 25 mmHg and progressive organ dysfunction despite resuscitation, which improved after decompression. e true incidence of 1 o ACS in abdominopelvic injury is still not established although this study may be the first report in this specific population and using the exact 1 o ACS definitions according WSACS recommendations 2013 [1]. e multivariate analysis shows initial Cr ≥ 1.5 g/dL, lower extremity including pelvis AIS ≥ 3, and ISS > 15 can predict the development of IAH in this study. Many investigators have identified factors contributing to the development of IAH. In the latest prospective multicenter study in mixed critically ill patients with IAH [16], they found BMI ≥ 27 kg/m 2 , APACHE II ≥ 18 points, abdominal distension, and absence of bowel sounds, and PEEP ≥ 7 cmH 2 O was associated with IAH. Mahmood et al. [17] found increased base deficit level, and frequent blood transfusion could predict the developing IAP > 20 mmHg. He L et al. [12] Anesthesiology Research and Practice reported only fluid resuscitation over 24 hours was a significant association with IAP > 12 mmHg, and each 1 L increment fluid over 24 hours was significantly associated with an increased 5 mmHg of IAP in fractured pelvis patients. Vatankhah et al. [18] reported risk factors contributed to developing of IAH and ACS in blunt abdominal trauma patients (mixed all age groups). ey found the amount of fluid received and pelvis fracture was associated with IAH and ACS but did not evaluate the cut-off point of these factors. From our perspective, we cannot conclude from previous studies which factors contribute to the development of IAH due to variation and mixed population data. is is the strong  point of our study because we focus on a unique population, and we make the cut-off points for parameters. ese significant parameters correspond with the severity of injuries that means the patient who suffers from severe abdominopelvic injuries has a high risk to develop IAH. e initial Cr ≥ 1.5 g/dL can occur in severe trauma that may develop after exsanguinating, suboptimal fluid resuscitations, renal injuries, or in case of the patient's preexisting conditions. However, a high level of initial Cr in this series mostly associates with severely injured cases. is means that our findings may answer the question of which factors contributed to the development of IAH in adult abdominopelvic injury patients.
About the clinical result of IAH, we found statistically significant differences between both groups in the requirement of blood components in first 24 hours, the need for overall procedures, the need for abdominopelvic operations, orthopedic surgeries, the need for intervention radiology, and ICU stays. Many literatures such as Malbrain et al.' study demonstrated poor clinical outcomes followed IAH [4] and found that the patients who developed IAP > 12 mmHg decreased 30-day survival time. Reintam et al. [16] who studied mixed critically ill patients concluded that a higher IAH grade was associated with a higher mortality. Murphy et al. [19] studied mixed ICU patients and found the patients who developed IAH recorded increased ventilation days, vasoactive medication days, ICU length of stay, death in ICU, and death in hospital and also reported IAH was an independent risk factor of ICU mortality (odds ratio 3.33, 95% CI 1.46-7.57). We cannot conclude which one is the real clinical result of IAH in abdominopelvic injury patients due to the mixed populations of the previous studies. Our study may answer this question.

Conclusions
e incidence of IAH and 1 o ACS in our study was 15.8% and 2.6%, respectively. We found that initial Cr ≥ 1.5 g/dL, lower extremity including pelvis AIS ≥3, and ISS >15 are the predictors of developing IAH in abdominopelvic injury patients. Further investigation about the actual clinical outcomes of IAH and 1 o ACS and strengthening of a useful protocol are our next step. Data Availability e data that support the findings of this study are available from ammasat University Hospital, but restrictions apply to the availability of these data, which were used under license for the current study and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of the Faculty of Medicine, ammasat University, and the ammasat University Hospital.

Ethical Approval
is project was ethically approved by the Human Ethics Committee of ammasat University No. 1 (Faculty of Medicine), ailand (MTU-EC-SU-1-068/60), and waived the requirement for inform consent due to the retrospective nature of the study.

Disclosure
is research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflicts of Interest
e authors declare that they have no conflicts of interest.

Authors' Contributions
KA contributed to literature search, study design, data interpretation, draft writing, critical revision, and final approval of the final version for submitted. NK made contributions to literature search, data collection, data analysis, and interpretation. AK made contributions to draft writing, critical revision, and faculty collaborations. WW made contributions to data collection and data analysis.