Perfusion Related Evaluation of Systemic and Renal Vulnerability to Events in CABG

This is a prospective, observational pilot study designed to investigate the relationship between elevated intra-abdominal pressure (IAP), impaired perfusion pressures, and the development of acute kidney injury (AKI) in adult patients undergoing cardiac surgery. The study will focus on whether continuous intra-abdominal pressure (CIAP) monitoring can provide early warning signs for AKI and other postoperative complications.

Intra-abdominal pressure (IAP) refers to the steady-state pressure within the abdominal cavity. In healthy individuals, IAP typically ranges between 5 and 7 millimeters of mercury (mmHg), while values may rise to around 10 mmHg in critically ill patients. Sustained IAP values at or above 12 mmHg define intra-abdominal hypertension (IAH). More severe elevations above 20 mmHg can result in abdominal compartment syndrome (ACS), which is associated with new organ dysfunction or failure. IAH can negatively impact multiple organ systems, including the kidneys, lungs, cardiovascular system, gastrointestinal tract, liver, and brain, through both mechanical and biochemical mechanisms.

Traditional IAP monitoring methods rely on intermittent measurement via the urinary bladder using a Foley catheter and saline instillation, performed at end-expiration with the patient in the supine position. Although this method is widely accepted, it is labor-intensive, operator-dependent, and cannot provide real-time pressure trends. As a result, diagnosis and management of IAH may be delayed.

Advancements in monitoring technology now allow for continuous IAP measurement using devices such as the TraumaGuard catheter. This dual-balloon Foley catheter provides real-time data on both IAP and core body temperature. It connects to standard intensive care unit (ICU) bedside monitors and allows continuous data capture and analysis.

This study will use continuous measurements of IAP, mean arterial pressure (MAP), central venous pressure (CVP), and mean alveolar pressure (Palv) to calculate key perfusion pressures:

Abdominal perfusion pressure (APP) = MAP - IAP

Mean perfusion pressure (MPP) = MAP - CVP

Renal perfusion pressure (RPP):

* In patients not receiving mechanical ventilation: RPP = MAP - IAP - CVP * In mechanically ventilated patients: RPP = MAP - IAP - CVP - Palv

Continuous monitoring will also allow for the calculation of area under the curve (AUC) and time above threshold (TAT), providing a dynamic view of the pressure-time burden and potentially offering earlier insight into evolving complications. These data will be analyzed to assess whether sustained periods of low APP, MPP, or RPP are associated with higher rates of AKI and other adverse outcomes.

Cardiac surgery patients are considered at high risk for IAH due to fluid shifts, systemic inflammation, positive pressure ventilation, and reduced abdominal wall compliance. This study will capture multiple IAH risk factors, including patient demographics (e.g., obesity, body mass index, age), surgical variables (e.g., cardiopulmonary bypass duration, transfusion volume), and clinical factors (e.g., presence of sepsis, acidosis, or coagulopathy).

All participants will receive standard-of-care monitoring, including urinary catheters and arterial lines. The TraumaGuard catheter will be used only for data collection purposes and will not influence clinical management. No deviation from routine practice is required, and the study is entirely observational in nature.

The primary outcome is the incidence of acute kidney injury (AKI), diagnosed using Kidney Disease: Improving Global Outcomes (KDIGO) criteria. AKI will be identified by changes in serum creatinine levels and reductions in urine output during the first seven postoperative days. Secondary outcomes include myocardial injury, intensive care unit (ICU) and hospital length of stay, 30-day mortality, and hospital readmission.

Perfusion pressures (MAP, APP, MPP, RPP) will be analyzed to determine the duration and depth of hypotension relative to specific thresholds. All data will be collected continuously from bedside monitors and synchronized using timestamps to ensure accuracy. The TraumaGuard data will be integrated with beat-to-beat electronic medical record data (e.g., CapsuleTech or equivalent systems).

A total of 45 adult patients undergoing elective cardiac surgery (CABG or valve surgery) will be enrolled at two academic centers. This sample size is based on previous feasibility data and is expected to generate at least 12 AKI events, sufficient to explore statistical associations, estimate variance, and refine methodology for a larger follow-up study.

Descriptive statistics will be used to summarize perfusion pressures, with group comparisons between patients who develop AKI and those who do not. Receiver operating characteristic (ROC) curve analysis will be conducted to identify thresholds of IAP, APP, MPP, and RPP that predict AKI and other complications. A Kaplan-Meier survival analysis will be used to compare outcomes based on the presence of IAH and low perfusion pressures.

Due to the limited sample size, multivariable regression analysis will not be performed in this pilot phase.

This study aims to determine whether continuous intra-abdominal pressure monitoring can serve as a clinically valuable, noninvasive method for early detection of hemodynamic deterioration and AKI after cardiac surgery. The results may inform the design of larger-scale studies and help evaluate the potential role of IAP monitoring as a new vital sign in critical care.

• Association between abdominal perfusion pressure (APP) and incidence of acute kidney injury (AKI) [Time frame: Postoperative Days 0 through 7]
• Association between mean perfusion pressure (MPP) and incidence of acute kidney injury (AKI) [Time frame: Postoperative Days 0 through 7]
• Association between renal perfusion pressure (RPP) and incidence of acute kidney injury (AKI) [Time frame: Postoperative Days 0 through 7]
• Association between intra-abdominal hypertension (IAH) and postoperative myocardial injury [Time frame: Postoperative Days 0 through 7]
• Agreement between intra-abdominal pressure (IAP) measurements using the TraumaGuard device and standard intermittent bladder pressure measurements [Time frame: Up to 48 hours post-surgery (duration of Foley catheter placement in ICU)]