This study improves upon previous observational research10–12 on the effects of clinical PR as a measure to improve the quality of care in intensive care medicine. Neither the main results nor the subgroup and sensitivity analyses provided evidence for a beneficial effect of clinical PR regarding ventilation on mortality in patients ventilated for more than 24 hours. In line with these results, the hospital survey indicated that many of the recommendations made to improve the quality of care had been implemented, but that these measures were not considered to have a direct impact on the mortality rates in patients ventilated for more than 24 hours.

The survey results showed that clinical PR was perceived positively by the participating hospitals and many measures recommended during clinical PR were implemented in intervention group hospitals. The expert rating indicated that most of these measures were not seen as directly related to mortality in ventilated patients. This reflects that many potentials for improvement were identified which did not directly affect mortality but may have had other beneficial effects. If the above-average baseline mortality in the participating hospitals was driven by deficits in quality of care, clinical PR may not, therefore, have adequately identified these deficits.

This study used a randomised design to prevent regression to the mean, unmeasured confounding and selection biases, and to ensure a high degree of generalisability. A limitation of the study is that, due to the study design, the effectiveness of clinical PR as a complex intervention could only be assessed as a whole and its impacts on outcomes other than mortality were not captured. The high number of measures recommended during clinical PR may primarily affect process quality, which was not considered as an outcome. However, in line with the value-based healthcare framework,19 patients are mainly interested in health outcomes rather than the structural or procedural quality of care.

The reliability of judgements by reviewers and the adequacy of recommended measures for improvement of inpatient care are crucial if clinical PR is to be effective. The IQM clinical PR is strictly standardised regarding both training and implementation. The IQM clinical PR report addresses specific topics related to the quality of care, including structures and especially processes. The clinical PR team represents different professions (physicians, nurses), specialties (eg, anaesthesiology, pulmonology) and hierarchical positions (eg, senior physicians, resident physicians). We believe that the high degree of standardisation and the interdisciplinary and interprofessional nature of the IQM clinical PR are likely to facilitate adequate judgements of potentials and flaws and facilitate the derivation of suitable measures for improvement. However, all these advantages did not translate into mortality benefit for patients.

Due to its focus on clinical structures and processes, the IQM clinical PR does not consider external drivers of poor quality and patient outcomes, including characteristics of the healthcare system. Therefore, identifying those external potentials for improvement requires different complementary approaches.

Another limitation of our study is the possibility that intervention effects may have evolved over time and that longer follow-up may have been valuable. However, sensitivity analyses did not provide support for time-varying intervention effects (see online supplemental material).

Despite the robustness of our findings against adjustment for multiple patient characteristics in sensitivity analyses (see online supplemental material), the persistence of above-average mortality in both intervention and control hospitals may be due to patient-associated risk not captured by our data. While our data provide information on patient-specific risk factors for mortality, for example, in terms of Elixhauser comorbidities, some clinical indicators of disease severity (eg, laboratory and imaging findings) could not be operationalised. However, since our study relies on a randomised design, we do not expect systematic differences between intervention and control groups regarding those characteristics.

In line with IQM methodology, the selection of intervention and control hospitals was based on the assumption that hospitals with the highest mortality rates in specific patient groups have the largest potential for improvement in terms of quality of care. Although previous observational studies on IQM clinical PR seemed to support this assumption, we cannot exclude that modifiable mortality in the participating hospitals was actually too low to induce a significant intervention effect.

This study did not investigate differences between hospitals with low and high mortality rates in patients ventilated for more than 24 hours in terms of care characteristics (eg, use of lung-protective ventilation or measures aimed at preventing ventilator-associated pneumonia). Investigating such differences could shed more light on mortality-relevant potentials for improvement and could be used to derive suitable quality standards for future clinical PRs.

Finally, this study examined the effectiveness of IQM clinical PR. The extent to which our results are generalisable to other variants of clinical PR may depend on specific methodological aspects, including the degree to which the considered clinical PR procedure focuses on measures related to mortality.

The COVID-19 pandemic has highlighted the role of long-term ventilation as a key element in the care of critically ill patients.1 Ensuring and improving the quality of care of ventilation patients is the main objective of this study. The lack of outcome improvements indicated by our analysis has major implications for the conceptualisation of clinical PR. Potential modifications of the clinical PR procedure include a more specific focus on outcome quality and stricter monitoring of changes in structures and procedures after clinical PR. Those modifications would require enhanced identification of mortality-relevant care processes and targeted measurement of mortality related to these processes.

Alternatively, the focus of future clinical PR may be shifted from outcome quality towards process quality. The latter would require measurement of process-related outcomes to assess effectiveness and different triggers for clinical PR. Modification of clinical PR may also require improved training of clinical PR teams, better documentation in lists of recommendations for improvement and more emphasis on implementation of sustainable measures. These issues have been recognised by the IQM steering group, which defined an action plan regarding the IQM clinical PR method. IQM clinical PR reports and trainings have been restructured with stronger focus on potentials to reduce mortality.

A general implication of this study is that the effectiveness of the clinical PR is under scrutiny. As with all complex interventions, reliable evidence on the effective components of clinical PR is required to improve the method and justify its continued use.