It is interesting to know on what parameters you want to measure this quality (outcome, process, other).
You can measure this on outcome level. A possible thing to choose in this situation can be incidence op pneumonia (or other postoperative complications, more broad perspective). You probably are able to compare this with the incidence numbers from a previous year.
You can also measure the quality of your care to compare te delivered care with (international) guidelines (interventions up to date). How is the comparability accordinig to these up-to-date guidelines.
You can contact me If you need more input / advice / discussion.