The Use of Ventriject to Assess V02Max in Patients Admitted to Hospital in the Emergency Surgery Setting

Pre-operative risk stratification is an important aspect of clinical decision-making in patients undergoing surgery. Thorough pre-operative assessment aids in the evaluation of mortality and morbidity on an individual basis and enhances the process of shared decision-making. This is particularly important in emergency surgery, which is associated with higher morbidity and mortality than elective surgery. Emergency general surgery accounts for approximately 11% of surgical cases but represents 47% of all surgical related deaths and 28% of complications. Colorectal cancer surgery has demonstrated a 90-day mortality rate of 3.2% (NBOCA 2017) and is associated with complication rates of up to 30% (Luca et al 2014). In the emergency setting, the 90-day mortality after bowel cancer surgery rises to 8.7% (NBOCA 2021).

Cardiorespiratory fitness (CRF) is an independent risk factor for mortality and morbidity for individuals undergoing surgery (Older et al, Wilson et al). Cardiorespiratory complications are the leading cause of death in non-cardiac surgery (Devereaux et al 2015, Gupta et al 2011). The insult of surgery can cause a 40% reduction in CRF for individuals with a hospital stay of up to 9 days and only half of patients regain their CRF after 6 months (Jensen et al 2011).

Cardiopulmonary exercise testing (CPET) is an exercise stress test used before planned surgery to aid risk stratification of individual patients. The CPET test involves a treadmill exercise or cycle ergometry to assess anaerobic threshold (AT) and the peak oxygen uptake (V02 peak) (Older et al 2017. CPET is a method of quantifying CRF. CPET testing is limited in certain patient populations, such as those with a physical disability or arthritis. It is time-consuming, taking approximately 40-60 minutes per assessment. A survey of patients' experiences of CPET testing was conducted by Boyd in 2016. Several aspects of CPET were described as a "serious problem" and these included dryness in mouth (11%), muscle soreness (10%), being uncomfortable (8-9%) and coughing (9%). Generally, patients requiring emergency surgery will be too unwell to preform CPET testing, but also the combination of access to facilities and the time constraints of emergency surgery make CPET testing in an emergency scenario inappropriate.

Currently there are several scoring tools used to assess a patient's risk of surgery in the emergency setting, which include PPOSSUM and NELA. These scoring tools aid in the risk stratification of mortality and morbidity to aid in the decision making for clinicians and patients. Patient characteristics integrated in these scoring tools include evidence of cardiorespiratory dysfunction assessed on ECG and clinical evidence, blood pressure, heart rate and blood test results. However, there currently is no established method of measuring CRF in the emergency setting.

Ventriject is a non-exercise method for estimating V02Max. V02Max is defined as the metabolic rate at which oxygen uptake plateaus despite further increases in work rate and this maximum end point is rarely reached during CPET examinations. V02Max has been shown to relate to post operative outcomes (Scholes et al 2009).