The investigators will monitor the pressure generated inside the abdomen in a patient in whom the surgeon, for whatever reason, felt that the abdomen could not be closed at the initial operation. The investigators will aggressively treat rises in intra-abdominal pressure and see what changes, if any are found when the abdomen finally is closed.

The detrimental effects of elevated intra-abdominal compartment pressure have been known for some time and are actively managed by most surgical critical care physicians. Similarly, it is well known that occasionally the abdomen cannot be immediately closed in some patients due to concern of elevated intra-abdominal pressure or ongoing contamination; these patients typically stay in hospital, often in expensive ICU's until final closure - and even then, some patients do not get definitive reconstruction of the abdominal wall until many months later, again adding to the expense of their care. Thus, there has been a move to give these patients early, aggressive closure of the abdomen, often using a combination of negative pressure wound therapy and biologic mesh. Currently these groups of patients who have early aggressive closure are incompletely studied; although abdominal compartment pressure measurements are routinely made on them, this is not commonly done intra-operatively when closure is being performed; nor have these patients been studied with continuous monitoring. This is especially striking considering the occlusive nature of negative wound therapy dressings: anecdotal increases in abdominal pressures have been noted in these patients, sometimes to dangerous levels. As there is accumulating evidence that diligent management of intra-abdominal pressure can improve outcomes in a variety of patients, there is an opportunity to apply accurate monitoring to a patient group that is also likely to benefit.

The investigators propose a prospective observational study on patients who are unable to be definitively closed at the time of surgery and are candidates for early aggressive abdominal closure. The investigators will monitor abdominal pressure using the AbViser continuous abdominal pressure monitoring device to ascertain whether there are episodes if intra-abdominal hypertension in these patients, and whether this improves or not after definitive closure. The research team will then attempt to correlate abdominal pressure measurements to outcomes. Finally the team will compare patients to historical controls using propensity scoring to explore differences in outcome.

Intra-abdominal pressure monitoring will be initiated when a patient has been identified as requiring an open abdomen. The monitoring will be done until the patient's abdominal wound has been closed and there are no elevated measurements. Once the patient has been discharged from the intensive care unit, the AbViser system will be discontinued. Patients will continue to be followed for the duration of their hospital stay and outcome measures will be assessed until discharge from the hospital, an expected average of 2 - 3 weeks.

Inclusion Criteria:

• Postoperative Surgical Patients who have not undergone abdominal closure, irrespective of the type of dressing used to protect the viscera

Exclusion Criteria:

• Age less than 18 years
• Coagulopathy
• Moribund/not expected to survive 48 hrs
• Patients in whom there is not a commitment to life supporting therapy
• Patients who have had definitive closure at the time of operation
• Patients in whom abdominal closure is not planned or not feasible

Cohort of patients in ICU with open abdomen