Colorectal cancer is the third most commonly diagnosed malignancy worldwide, accounting for \~10% of all cancers and ranking as the fourth leading cause of cancer death, with 1.9 million new cases and \~930,000 deaths in 2020. Surgical resection remains the mainstay of treatment for nonmetastatic cases and plays a crucial role in managing metastatic disease. Outcomes depend on preoperative staging, surgical quality, complication rates, and multidisciplinary care. Since Jacobs' 1991 report of 20 laparoscopic resections, minimally invasive techniques have reduced local and systemic complications. However, anastomotic dehiscence (AD) remains the most significant local complication, increasing hospital stays, costs, morbidity, mortality, and negatively affecting overall prognosis.
The International Study Group of Rectal Cancer defines AD as a breach in the anastomotic integrity creating a communication between intra- and extra-luminal compartments. Mortality rates vary widely, from 1.7% in an Australian cohort to as high as 29% in other reports, with AD accounting for roughly one-third of postoperative colorectal surgery deaths. Incidence is site-dependent: 1-20% in colo-rectal, 0-2% in colo-colic, and 0.02-4% in ileo-colic anastomoses.
Risk factors are categorized as local or systemic. Local factors include anastomotic level, technique (mechanical vs. manual), surgeon experience, bowel prep, use of laparoscopy, diverting stomas, drains, radiotherapy, chemotherapy, and gut microbiota. Systemic factors include male sex, malnutrition, hypoalbuminemia, anemia, comorbidities, American Society of Anesthesiologists (ASA) score, nonsteroidal anti-inflammatory drug (NSAID) use, smoking, alcohol, peripheral vascular disease, obesity, and diabetes. Reduced oxygen delivery-pre-, intra-, or post-operatively-can contribute to AD, while adequate oxygenation improves healing. Supplemental O₂ (FiO₂ 80%) has been shown to reduce AD risk after gastric surgery.
Tissue oxygen delivery can be quantified by indexed oxygen delivery (DO2I), defined as ml/min/m² and determined by cardiac output, hemoglobin, and saturation. A DO2I \< 400 ml/min/m² is associated with increased AD risk; normal values range from 450-550 ml/min/m². Below this, compensation through increased extraction fails beyond a critical threshold, leading to anaerobic metabolism and lactic acidosis. Accurate DO2I calculation requires cardiac output monitoring.
While the esophageal Doppler is the standard for cardiac output measurement, its invasiveness and operator dependence limit use. Less invasive alternatives, like pulse-contouring (e.g., PiCCO, Vigileo) or fully non-invasive methods like ClearSight®, offer continuous hemodynamic data. ClearSight® uses the volume-clamp method via a finger cuff and photoplethysmography to measure real-time arterial pressure and advanced parameters such as cardiac output and stroke volume.
DO2I calculation also requires hemoglobin levels, which fluctuate intraoperatively due to blood loss and fluid shifts. Reliable measurement would ideally involve repeated blood sampling, which adds invasiveness and cost. Advances in pulse oximetry, like the Rad-97 Pulse CO-Oximeter® (Masimo), allow continuous non-invasive monitoring of O₂ saturation, Hb, carboxyhemoglobin, methemoglobin, perfusion index, and more, even under low perfusion or motion conditions.
This prospective observational cohort study aims to explore the correlation between intraoperative DO2I and the risk of postoperative anastomotic dehiscence, using the non-invasive technologies described.
