Mitochondrial Function in the Peri-operative Setting: an Observational Study

Postoperative mortality is the third highest cause of death globally. Postoperative morbidity is up to 17 times higher than mortality. As well as being a burden for patients, postoperative complications result in excess costs of tens of thousands of dollars (USA) per patient. Complications are also strongly correlated with overall cost in European studies. Increasing evidence suggests that common but essential parts of general anaesthetic techniques, such as administration of supplemental oxygen, may be related to these postoperative outcomes. Work from our group has shown that changes in mitochondrial activity are central to altered oxygen handling seen at high altitude and indirectly suggested this may change during major abdominal surgery. Changes in mitochondrial activity have also already been shown to be distinct between survivors and non-survivors in critical care cohorts. Early unpublished data has also shown there may be some change in mitochondrial signal in skeletal muscle in surgical patients at end of surgery with an average of around 6 hours duration. Therefore, our hypothesis is that mitochondrial function/ activity changes during and in recovery from major abdominal surgery in trajectories associated with different rates of postoperative complications. Establishing this may enable us to predict patient susceptibility to postoperative complications. This would be extremely powerful to enable optimisation of patient selection, preparation and prognostication. It may also lead to changes in intra- and postoperative management. All of these factors could reduce postoperative complications and their associated morbidity and mortality.

A two-stage prospective observational cohort study has been designed to test this hypothesis. The first phase will be a pilot, including up to 10 adult patients scheduled for elective major open abdominal surgery, requiring siting of arterial and central venous lines and admission the day before surgery. This will focus on examining the feasibility of performing multi-modal mitochondrial analysis in surgical patients and charting the trajectory of change in mitochondrial markers through the perioperative period. Blood will be taken around the start of surgery and on postoperative days 1 and 7. Muscle biopsies will be taken around the start of surgery and at end of surgery or 12 hours after start, whichever is soonest. Exhaled breath samples will be taken the day before surgery and on postoperative day 7. High-resolution respirometry will be used for skeletal muscle and platelet analysis ex-vivo with saturating quantities of substrate and oxygen. 13C-ketoisocaproate (13C-KICA) breath tests (BT) will be carried out to measure hepatic and skeletal muscle mitochondrial function representing in-vivo substrate concentrations and intercurrent oxygenation levels. Clinical data and results of routine blood tests and blood gas analysis will also be collected.

Following the pilot phase of up to 10 patients there will be an interim data analysis. This is to allow optimisation of the process following the feasibility phase. It may also provide the opportunity to reduce sampling burden for the patient. For example if it is established that either fewer sampling points are needed, or if muscle and platelet respirometry data correlate it may be possible to remove the need for muscle biopsy in the second phase.

The second phase will include a cohort of up to 40 patients recruited in the same manner and sampled in the same scheme as the pilot, unless it has been possible to reduce the sample burden as a result of the pilot phase data. This phase will aim to establish if changes in mitochondrial activity are related to clinical outcomes.

The primary objective of the pilot phase is: To examine the feasibility of multi-modal mitochondrial analysis in patients undergoing major elective abdominal surgery. This will include the number of eligible patients screened and consented, the optimisation of sampling timepoints and clinical data collection.

Secondary objectives will include:

• Establishing if and how mitochondrial activity measured in platelets and in skeletal muscle relates to each other in surgical patients.
• Relation of postoperative complication rate as measured by day 7 Postoperative Morbidity Survey (POMS), to change in platelet mitochondrial activity from start of surgery to day 1 postoperatively, as measured by high resolution respirometry.
• Description of the trajectories of change in respiratory capacity/ mitochondrial function through the perioperative period as measured by respirometry in platelets and skeletal muscle, and by 13C-KICA breath test.
• Relation of postoperative complication rate to change in skeletal muscle mitochondrial activity and respiratory capacity, as measured by high resolution respirometry, from start of surgery to 12 hours into surgery/ end of surgery.
• Relation of postoperative complication rate to change in platelet mitochondrial activity and respiratory capacity, as measured by high resolution respirometry, from start of surgery to 7 days postoperatively.
• Relation of postoperative complication rate to change in hepatic and skeletal muscle mitochondrial function as measured by 13C-KICA breath test from baseline to 7 days postoperatively.
• Change in the following criteria in relation to mitochondrial function/ activity as measured by any of the above:
• Oxygenation parameters (eg. Fraction of inspired oxygen (FiO2), Partial pressure of oxygen in arterial blood (PaO2))
• Length of stay in ICU/HDU environment prior to ward step-down
• Duration of postoperative invasive mechanical ventilation
• Postoperative delirium on day 7 as measured by Confusion Assessment Method (CAM) score
• Patient reported postoperative pain (score out of 10)
• Charleston Comorbidity Index

Following the pilot phase of up to 10 patients there will be an interim data analysis. This is to allow optimisation of the process following the feasibility phase. It may also provide the opportunity to reduce sampling burden for the patient. For example if it is established that either fewer sampling points are needed, or if muscle and platelet respirometry data correlate it may be possible to remove the need for muscle biopsy in the second phase.

The second phase will include a cohort of up to 40 patients recruited in the same manner and sampled in the same scheme as the pilot, unless it has been possible to reduce the sample burden as a result of the pilot phase data. This phase will aim to establish if changes in mitochondrial activity are related to clinical outcomes.

The primary objective of the second phase is: to establish any relation of postoperative complication rate as measured by day 7 Postoperative Morbidity Survey (POMS), to change in mitochondrial activity through the perioperative period, as measured by high resolution respirometry.

The secondary objectives will include a subset of those of the pilot phase, established following the interim analysis.

Blood/ muscle/ breath sampling and data collection will be performed by Good Clinical Practice (GCP) -trained researchers or members of the treating clinical team. The definition of the study end is once all analysis has been completed on the final sample. We anticipate the results of this study will be disseminated by publication in a peer-reviewed journal and through conference presentations. Published results will be made available to participants on request.