Delayed Abdominal Closure in the Management of Ruptured Abdominal Aortic Aneurysm

Methods

After obtaining permission from the Institutional Review Board, we performed analysis of a retrospective database, which included 122 consecutive patients who underwent open repair of an rAAA between April 1989 and June 2005 at the University of Utah. This tertiary care facility is a centrally located hospital that receives patients from five surrounding states in the intermountain west.

Demographic data collected included age, gender, and travel distance to this hospital. Preoperative clinical data included blood pressure and heart rate, as well as need for cardiopulmonary resuscitation. Preoperative hypotension was defined as any recorded systolic blood pressure (SBP) prior to the OR < 90 mm Hg. Intraoperative clinical data included operative time; estimated blood loss (EBL); use of a supraceliac cross-clamp; units of blood products transfused; volume of cell-saver, crystalloid, and colloid fluid given; and use of a tube or bifurcated graft. Lowest intraoperative pH and Acute Physiology and Chronic Health Evaluation (APACHE) II scores from the initial 24 hours in the surgical intensive care unit (SICU) were also recorded.

In a review of the literature focused on IAH and ACS in rAAA and trauma patients, predictive clinical factors for the development of IAH and ACS consistently included a shock or ischemic state followed by reperfusion with large-volume resuscitation using crystalloid and/or colloids. ^{1,2,8,10,13,15,16} In our data set, preoperative hypotension, ≥ 6 L blood loss, and resuscitation with ≥ 12 L crystalloid or colloid were each predictive of an increased mortality rate. We used these three ischemia-reperfusion (IR) criteria as surrogate markers of clinical risk for the development of IAH and ACS.

The review period was broken into two management eras: era 1 included April 1989 through May 2000, in which most abdomens were primarily closed in the OR, and era 2 beginning June 2000, at which time, the first rAAA at this institution had delayed abdominal closure, through to June 2005. All rAAA repairs during the study period were accomplished by open repair. Endovascular repair is now used but was not available in the study institution during the time frame of this analysis. All patients managed with an open abdomen during era 2 used a noncommercial vacuum-pack technique.

Patients treated in the two eras were used as comparative groups. Within each group, we identified patients who were at high risk for IR injury and IAH and ACS. These IR subgroups were then compared by treatment era and type of abdominal management. Initial 24-hour, 30-day, and in-hospital mortality were examined as outcome measures. Fisher exact test and t-test were used to compare groups, and the threshold for statistical significance was set at a two-tailed p value of < .05.

Results

Between April 1989 and June 2005, 122 patients were diagnosed with an rAAA and emergently taken to the OR; of these, 108 survived through surgical repair and were admitted to the SICU (11% intraoperative mortality). Five patients who underwent abdominal closure with Dexon mesh at the time of their initial AAA repair were excluded from analysis because their management was not directly comparable to either the fully open or the primarily closed abdomen group. Fifty-eight of the patients underwent surgery in era 1 and 45 patients in era 2. No patients in era 1 underwent decompression laparotomy after their initial AAA repair.

Comparing the two eras, there were no significant differences in age, gender, OR time, total OR fluid, incidence of preoperative hypotension, EBL, APACHE II score, use of a supraceliac cross-clamp, or lowest intraoperative pH. Demographic results are shown in Table 1.

Over this time span, the in-hospital mortality among these 103 patients was 27% (28 of 103), the 30-day mortality was 22% (23 of 103), and the initial 24-hour mortality was 7% (7 of 103). The in-hospital mortality rates were not significantly different between eras 1 and 2, at 28% (16 of 58) versus 27% (12 of 45), respectively. Although there was a trend toward improved initial 24-hour mortality in era 2 (2% vs 10% in era 1), this was not significant (p = .13). The mortality rate for this entire time period, including intraoperative deaths, was 39% (47 of 122). Mortality results are shown in Table 2.

Most importantly, within each era, we evaluated the subgroups who were at high risk for IAH and ACS owing to IR injury as a result of one or more of the following three criteria: the occurrence of preoperative hypotension, EBL ≥ 6 L, or intraoperative fluid resuscitation with ≥ 12 L of crystalloid and/or colloid. Our results demonstrated that the in-hospital mortality rate among patients from either era with at least one IR criterion was 43% (23 of 54) compared with 10% (5 of 49) of patients without IR criteria (p = .0003). Twenty-nine of the patients treated during era 1 and 25 patients in era II had at least one of these criteria, for a total of 54 patients (Table 3).

Comparing patients who had at least one IR criterion between eras, there was no statistical difference in age, APACHE II score, fluids given in the OR, operative EBL, incidence of preoperative hypotension, or operative time (see Table 3). However, there was a significant reduction in initial 24-hour mortality in era 2 versus era 1 (0 vs 21%, respectively, p = .03). As most patients in era II who met at least one IR criterion also had delayed abdominal closure, it is possible that this reduction in early postoperative mortality was secondary to management with an open abdomen. Among the 25 patients treated in era 2 who had at least one IR criterion, 18 were treated with delayed abdominal closure and 7 had primary abdominal closure. Only three patients during era 2 with delayed abdominal closure did not have any IR risk factors.

We analyzed the outcome for all patients who met at least one IR criterion by abdominal management, open versus closed, irrespective of surgical era, and found that both the initial 24-hour and 30-day mortality rates were lower in the open management group (initial 24 hours: 0 vs 17% and 30 days: 22 vs 42%, respectively). These results demonstrate a strong trend in favor of open management but did not reach statistical significance (p = .20 for both). There was no difference between the two groups in regard to mean age, APACHE II score, crystalloid and colloid given in the OR, incidence of preoperative hypotension, incidence of ≥ 6 L EBL, or operative time. The results are shown in Table 4.

Of the patients who were treated with an open abdomen, 33% (7 of 21) died before hospital discharge without a known graft infection. One patient was diagnosed with a pseudoaneurysm and graft infection 10 months after rAAA repair. This patient had Dexon mesh placed after removal of the vacuum pack and required repeated skin grafting; with the patient later developing a colocutaneous fistula. The remaining 13 patients have had no evidence of graft infection on long-term follow-up.

Discussion

Rasmussen and colleagues proposed an algorithm to guide the decision regarding delayed abdominal closure following rAAA repair. ¹³ In that algorithm, the operating surgeon should consider open management whenever there is obvious compromise of the abdominal domain or all six of the following criteria are present: preoperative anemia (hemoglobin < 10 g/dL), prolonged shock (more than 18 minutes of SBP < 90 mm Hg), preoperative cardiac arrest, massive intraoperative resuscitation (greater than 3.5 L per hour), hypothermia (< 33°C), or severe acidosis (base deficit > 13 mmol/L).

In our study, we introduced the importance of acute mortality (initial 24 hours) after rAAA surgery for two reasons. First, rAAA patients at risk for significant IR injury had a high (21%) mortality in the first 24 hours. It is important to recognize that ACS can cause MOF through at least two pathways. ¹⁷ The first and most acutely lethal pathophysiology is caused by direct mechanical pressure from a rapid rise in IAP during aggressive resuscitation, resulting in direct compression of blood flow to multiple organ systems. In particular, compromised venous return to the heart can result in hemodynamic collapse and cardiac arrest, and increased IAP can compromise respiratory function resulting in an inability to adequately ventilate or oxygenate. This acute rise in IAP can be a result of both fluid resuscitation and bleeding. Mehta and colleagues reported that five of six of their patients who developed ACS did so in the first 24 hours (four of six immediately at the end of operative repair) and reported extreme bladder pressures greater than 40 mm Hg in these patients. ¹⁶ In addition, the two patients who died in this study were reported as having a “delayed diagnosis” of ACS. This delay was a mere 9 and 36 hours postsurgery. Fietsam and colleagues also reported the multiorgan effects of acute IAP elevation in rAAA patients with primary closure in the form of increased ventilator pressures, decreased urine output, and massive abdominal distention. ¹² In this study, all ACS patients developed the syndrome within 24 hours of their primary operation. A second overlapping pathway is described by Bown and colleagues as a triggering of the systemic inflammatory response owing to IR injury, with its concomitant cytokine cascade resulting in MOF. ^18–21 This response can present subtly with mild capillary leak and minimal organ dysfunction or very acutely as a result of severe IR injury and shock, with rapid onset of visceral edema and significant elevation in IAP. This can occur with or without acute bleeding. Combined with acute bleeding, it can compound the effects of pressure-induced obstruction to blood flow described above.

Our study verified that the presence of one of three clinical criteria, preoperative hypotension, EBL ≥ 6 L, or ≥ 12 L fluid resuscitation in the OR, was predictive of increased mortality among patients who survive operative repair of an rAAA. Additionally, these results suggest that initial 24-hour mortality may be improved by managing these patients with an open abdomen. This study also suggests a trend for improved in-hospital mortality in high-risk rAAA patients managed with an open abdomen. We therefore recommend that patients with preoperative and intraoperative risk factors of preoperative hypotension, EBL ≥ 6 L, or ≥ 12 L of OR fluid resuscitation be considered for open abdominal management.

IAH and ACS are well documented within the trauma and general surgical literature. ^15,22–24 Recent literature supports the existence of this syndrome in other critically ill patients, including medical patients without any primary intra-abdominal pathology or surgery. ^6,25,26

Keeping the abdominal fascia open in the early postoperative period may avert this cascade of events, prevent acute postoperative death, and potentially reduce long-term morbidity and mortality. ^27–29 Once the patient has recovered from the early period of ischemia and reperfusion, edema should be expected to resolve and the fascia can often be closed in a short period of time. The challenges involved with managing an open abdomen have led to a number of surgical techniques. The vacuum-pack technique is a simple, inexpensive method that maintains sterility within the abdomen, allows for easy management of peritoneal fluid, and can quickly be changed at the bedside if necessary. Injury to the fascia is avoided because there are no fascial sutures, allowing for healthier fascia at the time of closure. ^30–32

Previous studies have discussed the possibility of graft infection with open management of the abdomen, and among our 21 patients managed with an open abdomen, a single patient developed a late graft infection. Endovascular repair of rAAA may potentially minimize the risk for IAH and ACS and the postoperative complication of the open abdomen. However, Mehta and colleagues demonstrated a concerning incidence of ACS (18%) with endovascular aneurysm repair of rAAA. ³³ Larger, prospective studies will clarify the actual risks for IAH and ACS with endovascular repair.

Based on the results of this study and review of the current literature, we would recommend that patients with pre- and intraoperative risk factors should be considered for open abdomen management. Ruptured AAA intraoperative risk factors for postoperative development of IAH and ACS may include prolonged preoperative and intraoperative shock; prolonged operative ischemic time; and large-volume resuscitation with crystalloids, colloids, and/or blood and blood products. Prospective studies will help further refine the positive predictive value of such risk factors. Until such a prospective evaluation is complete, we recommend that all rAAA patients with intraoperative risk factors for IAH and ACS should be considered for delayed abdominal closure on a case-by-case basis. In addition, IAP should be monitored on closure and closely followed during the postoperative period, whether or not the patient is left open or primarily closed. ³⁴

The main limitation of this study is the retrospective nature of the review. Specifically, a retrospective analysis cannot prove that open abdominal management alone reduced the mortality among these critically ill patients. As the study reviews two sequential eras, advances in ICU care may also contribute to improved outcomes in the second era. Also, given the small number of study patients, the power of this study to detect differences was limited. This retrospective study cannot show whether mortality was directly related to increases in IAP as measurement was not routine at this institution until much later in this study. Our institution now uses both intraoperative and postoperative serial measurement of IAP to better identify all patients at risk for IAH and ACS. Further, a postoperative SICU protocol for the diagnosis and management of IAH and ACS was instituted in 2005. Analysis of the impact of this protocol has demonstrated a relative risk reduction in mortality of 18% for patients at risk for IAH and ACS since this protocol was implemented.

Future directions of investigation in this study population would include prospectively confirming the predictive value of the IR criteria used in this study for the development of IAH and ACS and their relationship to mortality. The utility of delayed abdominal closure should also be prospectively evaluated in high-risk rAAA patients, although treatment randomization, given the current literature, may be difficult. In addition, evaluation of the routine use of IAP measurement to help identify those at risk for ACS early in their course will likely prove to be a valuable tool in the postoperative care of rAAA cases.

Conclusion

This study reports a long-term, single-center experience with repair of rAAA. Three simple IR risk factors were identified as being associated with increased mortality in this population. Patients with at least one of these risk factors who were treated with delayed abdominal closure were found to have a significant improvement in acute postoperative survival and a trend toward improved long-term survival. Delayed abdominal closure attenuates IAP in rAAA patients at high risk for developing ACS. Prospective evaluation will be required to establish the efficacy and risks of this management strategy.