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).
Ventriject uses seismocardiography (SCG) signals generated by the vibrations from a
beating heart, picked up by a small accelerometer placed on the chest. SCG is an
alternative method of assessing cardiac function (Sorensen et al). V02Max is estimated
from the SCG signal and patient demographics including gender, age, height and weight,
using machine learning. Ventriject has been tested against CEPT in over 400 healthy
subjects and has been found to closely correlate with V02Max measurements (0.80,
p<0.001). This is the closest correlation to ergometer testing when compared to
alternative methods.
It is estimated that each Ventriject assessment costs approximately £15 and takes a total
of 120 seconds to complete. It requires no physical exercise and may be more acceptable
in certain clinical situations and patient groups. Currently, Ventriject has been used in
non-clinical settings and lacks evidence as to its usability in the clinical environment.
Given the advantages of a cheap, rapid, and accessible method of measuring V02Max,
Ventriject would be an appropriate method for measuring CRF in the emergency setting and
may compliment the current risk stratification tools to aid in the clinical decision
making around emergency surgery.
The aim of this study is to assess whether Ventriject V02Max can provide values in a
clinical setting and whether this value correlates with clinical outcome in patients
admitted to the emergency general surgery department in a single centre. We will also be
assessing the acceptability of the device to patients and clinicians.