Abstract
Postoperative complications in major elective surgery are common, occurring in up to 40% of patients. Many complication risk factors including age, the surgery complexity and the characteristics of the underlying pathology are non-modifiable, and most modifiable risk factors only apply in a subset of the surgical population. Furthermore, there can be as little as three weeks between the decision to operate and the proposed surgical date. Cardiorespiratory fitness (CRF) is a predictor of surgical outcome which can be modified rapidly in the majority of surgical patients. This can be accomplished through a preoperative high-intensity interval training (HIIT) protocol.
Heterogeneity in study design and patient populations has contributed to conflicting results in the literature, hindering our ability to individualise HIIT protocols specific to the patient's preoperative timeframe and pathologies. This thesis aims to address this gap through a meta-analysis and a prospective observational study.
The meta-analysis aimed to see if HIIT is capable of improving CRF and surgical outcomes versus standard care in major elective surgical patients not undergoing neo-adjuvant chemo-radiotherapy. A systematic search of the literature identified 1,846 studies. Fourteen prospective controlled studies were included. CRF was improved by a clinically relevant margin in patients undergoing HIIT versus standard care over the preoperative period (mean difference [95% CI] = 2.21 mL.min-1.kg-1 [0.9 - 3.51] in peak oxygen consumption (𝑉̇ O2Peak); mean difference = 30.29 m [24.10 - 39.01], for change in six-minute walk test (6MWT)). This improvement was translated to a reduction in the number of patients experiencing complications (mean difference = 0.65 patients [0.45 - 0.92]). Non-significant reductions in the number of complications per patient and length of stay was observed.
Having established the efficacy of preoperative HIIT, the prospective observational study aimed to optimise HIIT by developing a dose-response curve between the number of HIIT sessions and change in CRF (quantified as 𝑉̇ O2Peak), using patients aged 55-85 years, either referred to us or identified from surgical waitlists. These patients undertook 24 HIIT sessions, aiming to achieve 90% of their maximum heart rate (MHR) per session. CRF was measured using cardiopulmonary exercise testing (CPET) at four different time points in the protocol.
Thirty-eight patients were enrolled, with 22 completing all four CPET’s. There was a statistically- and clinically significant improvement in 𝑉̇ O2Peak that occurred after 14 sessions (+1.54 ± 1.60 mL.min-1.kg-1 (p < .0001)). However, in our per-protocol analysis this change occurred after eight sessions (n = 18; +1.92 ± 1.67 mL.min-1.kg-1, p = .0021), and continued through to session 14 (+2.34 ± 1.27 mL.min-1.kg-1, p < .0001). No further changes occurred between 14 and 24 sessions of HIIT. After stratifying populations according to sex, BMI, risk status, and the presence of cardiovascular and respiratory disease, some variable responses to HIIT were observed.
These two studies provide evidence of the benefit HIIT has compared to standard care across a range of clinical populations, while demonstrating time-efficient changes to CRF. This data allows us to adapt protocols specific to time frames and pathologies, which has implications on patient wellbeing, surgical outcome and hospital costs.