End-tidal carbon dioxide in the early phase of cardiopulmonary exercise testing prior to major colorectal cancer surgery associates with postoperative outcome.

BACKGROUND: Cardiopulmonary exercise testing (CPET) objectively informs preoperative risk stratification prior to major surgery. CPET facilities are resource intensive and therefore more cost-effective triage methods are desirable for scalability. We tested two dynamic CPET parameters (end-tidal CO2 (PetCO2) and heart rate (HR)) to early phase exercise and resting diffusion capacity (DLCO) as potential point of care assessments that could be used outside of formal CPET testing facilities. METHODS: We conducted a retrospective cohort study including 84 patients who underwent CPET prior to elective major abdominal cancer surgery. Data were analyzed for PetCO2 and HR in response to early phase (2 minutes) exercise as well as resting DLCO against postoperative complications and two-year survival. Complications were classified according to Clavien-Dindo classification into less severe and severe (CD>IIIb) grades. Optimal cut points for predicting outcomes were determined using the Youden Index of receiver operating characteristic (ROC) curves. Multivariate regression modeling including both logistic and Cox proportional-hazards model adjusted to age and comorbidity burden was used to analyse the association between the selected parameters and postoperative outcomes. RESULTS: PetCO2, in response to two minutes of loaded exercise was higher in survivors than in non-survivors (median (IQR) 40.0 (4.2) mmHg vs. 34.5 (5.2) mmHg, P<0.001). There was no association between chronotropic response and postoperative outcome. The optimal cut point for predicting postoperative complications and survival was 38 mmHg and 37.1 mmHg for PetCO2, respectively. Low PetCO2 was associated with considerably lower odds of survival (OR 0.12; 95% CI 0.03, 0.47; P=0.003) and additionally increased odds of severe postoperative complications (OR 6.77; 95% CI 1.45, 38.4; P=0.019). Reduced age-predicted DLCO% <80% was associated with increased mortality (HR 5.27; 95% CI 1.09, 25.5; P=0.039). CONCLUSIONS: Assessment of DLCO at rest and dynamic assessment of PetCO2 during the early phase of exercise may potentially be developed as inexpensive point-of-care triage tools to scale objective preoperative risk assessment.

Clinical covariates that improve surgical risk prediction and guide targeted prehabilitation: an exploratory, retrospective cohort study of major colorectal cancer surgery patients evaluated with preoperative cardiopulmonary exercise testing.

BACKGROUND: Preoperative risk stratification is used to derive an optimal treatment plan for patients requiring cancer surgery. Patients with reversible risk factors are candidates for prehabilitation programmes. This pilot study explores the impact of preoperative covariates of comorbid disease (Charlson Co-morbidity Index), preoperative serum biomarkers, and traditional cardiopulmonary exercise testing (CPET)-derived parameters of functional capacity on postoperative outcomes after major colorectal cancer surgery. METHODS: Consecutive patients who underwent CPET prior to colorectal cancer surgery over a 2-year period were identified and a minimum of 2-year postoperative follow-up was performed. Postoperative assessment included: Clavien-Dindo complication score, Comprehensive Complication Index, Days at Home within 90 days (DAH-90) after surgery, and overall survival. RESULTS: The Charlson Co-morbidity Index did not discriminate postoperative complications, or overall survival. In contrast, low preoperative haemoglobin, low albumin, or high neutrophil count were associated with postoperative complications and reduced overall survival. CPET-derived parameters predictive of postoperative complications, DAH-90, and reduced overall survival included measures of VCO2 kinetics at anaerobic threshold (AT), peakVO2 (corrected to body surface area), and VO2 kinetics during the post-exercise recovery phase. Inflammatory parameters and CO2 kinetics added significant predictive value to peakVO2 within bi-variable models for postoperative complications and overall survival (P < 0.0001). CONCLUSION: Consideration of modifiable 'triple low' preoperative risk (anaemia, malnutrition, deconditioning) factors and inflammation will improve surgical risk prediction and guide prehabilitation. Gas exchange parameters that focus on VCO2 kinetics at AT and correcting peakVO2 to body surface area (rather than absolute weight) may improve CPET-derived preoperative risk assessment.

Real-world estimate of the value of one metabolic equivalent in a population of patients planning major surgery.

BACKGROUND: One metabolic equivalent (MET) is equal to resting oxygen consumption. The average value for one MET in humans is widely quoted as 3.5 mL/kg/min. However, this value was derived from a single male participant at the end of the 19th century and has become canonical. Several small studies have identified varied estimates of one MET from widely varying populations. The ability of a patient to complete 4 MET (or 14 mL/kg/min) is considered an indicator of their fitness to proceed to surgery. AIMS: To define a typical value of one MET from a real-world patient population, as well as determine factors that influenced the value. METHODS: A database of cardiopulmonary exercise testing (CPET) was interrogated to find a total of 1847 adult patients who had undergone CPET testing in the previous 10 years. From this database, estimates of oxygen consumption (VO2 ) at rest and at the anaerobic threshold and several other variables were obtained. The influence of age, body mass index (BMI), sex and the use of beta-blockers was tested. RESULTS: The median resting VO2 at rest was 3.6 mL/kg/min (interquartile range (IQR): 3.0-4.2). Neither sex, age >65 years or the use of beta-blockers produced a significant difference in resting VO2 , while those with a BMI >25 kg/m2 had a significantly lower VO2 at rest (3.4 mL/kg/min vs 4.0 mL/kg/min; P < 0.001). CONCLUSIONS: The estimate of 3.6 mL/kg/min for resting VO2 presented here is consistent with the previous literature, despite this being the first large study of its kind. This estimate can be safely used for pre-operative risk stratification.

Time-driven activity-based costing to model the utility of parallel induction redesign in high-turnover operating lists.

BACKGROUND: Value-based healthcare is strongly advocated to reduce the spiralling rise in healthcare expenditure. Operating room efficiency is an important focus of value-based healthcare delivery due to high costs and associated hospital revenue derived from procedural streams of care. A parallel induction design, utilising induction rooms for anesthetising patients, may improve operating room efficiency and optimise revenue. We used time-driven activity-based costing (TDABC) to model personnel costs for a high-turnover operating list to assess value of parallel induction redesign. METHODS: We prospectively captured activity data from high-turnover surgery allocated to induction of anesthesia within the operating room (serial design) or within induction rooms prior to completion of preceding surgery (parallel design). Personnel costs were constructed using TDABC following assignment of a case-mix that integrated our activity data. This was contrasted against procedural revenue to assess value of projected case throughput. RESULTS: Under a parallel induction design, projected operating list duration was reduced by 55 min at marginal increase (1.6%) in personnel costs as assessed by TDABC. This could facilitate an additional short duration surgical case (e.g. Wide Local Excision, with potential additional revenue of $2818 per day and $0.73 M per annum per operating room. CONCLUSIONS: Parallel induction design reduces non-operative time at minimal increase in personnel costs for all-day, high turnover surgery. An additional short duration surgical case is likely feasible under this model and represents a value investment with minimal requirement for additional personnel resources. IMPLICATIONS: A parallel induction design, within the constraints of finite healthcare funding, may help alleviate some of the global increase in demand for surgical capacity that accompanies an expanding and aging population.