The Cost in Oxygen of Surgical Trauma

The Cost in Oxygen of Surgical Trauma (CO2ST) - a Feasibility Study of the Non-invasive Measurement of Oxygen Delivery and Consumption After Major Abdominal Surgery

The investigators will examine the relationship between post-operative oxygen consumption (using non-invasive measurement technology ) and complications in patients having contemporary major abdominal surgery. The investigators hypothesis is that major surgery may trigger a physiological stress response that results in an increase in post-operative metabolic demand and oxygen consumption (V̇O2) which must be met by an increased oxygen delivery (DO2).

1. To determine the feasibility of non-invasive measurement of oxygen consumption (V̇O2) using indirect calorimetry in a cohort of patients
2. To determine the feasibility of non-invasive measurement of oxygen delivery (DO2) in the same cohort using non-invasive measures of cardiac output, oxygen saturation and haemoglobin (pulse wave transit time and co-oximetry techniques)

Prospective observational study of non-invasive measurements of V̇O2 and DO2 pre-operatively and at 8 time points in the 48 hours postoperatively in a cohort of 40 patients undergoing elective major abdominal surgery (both open and laparoscopic) with a pre-operative cardiopulmonary exercise testing (CPET).

As pilot work examining the relationship between post-operative oxygen consumption and complications in patients having contemporary major abdominal surgery , the investigators need to define and grade the severity of complications. The Post-Operative Morbidity Survey (POMS) is a simple outcome scale designed to record the incidence of clinically important complications - specifically complications likely to keep a patient in hospital. A POMS score performed on Day 5 is likely to be discriminative between patients who are recovering well, and those who are developing complications. POMS is easily performed, has good internal validity and is predictive of a prolonged length of stay. POMS is not a simple additive scale; however patients with POMS score of 1 or greater are highly likely to remain in hospital, whereas those with a score of 0 are likely to be able to go home.

Inclusion Criteria:

• Male and female patients aged 18 or over.
• Undergoing elective major open or laparoscopic abdominal surgery.

Exclusion Criteria:

• Refusal to participate
• Requirement for post-operative ventilation
• Requirement of inspired oxygen concentrations (FiO2) > 28% to maintain oxygen saturations ≥ 90%.