Z-score vs percentage of predicted value: how they perform in preoperative functional assessment?

<bold>Introduction:</bold> According to the 2009 ERS guidelines for preoperative assessment of lung resection candidates, spirometry (FEV1) and diffusing capacity of the lungs for carbon monoxide (DLCO) represent key parameters of patients´ functional status. In 2022, new interpretation of lung functions, using the Z-score instead of percentage of predicted value (% p.v.) has been proposed. This was yet not adopted in the preoperative functional assessment algorithms. <bold>Aim:</bold> To compare the diagnostic utility of Z-scores and % p.v. of both FEV1 and DLCO to predict postoperative pulmonary complications (PPC). <bold>Methods:</bold> This was a post-hoc analysis of data from two prospective multicentre studies conducted between 2017 and 2023. We compared demographic parameters, lung function data, surgical data and ICU and hospital LOS for subgroups of patients with and without PPC. A separate analysis on performance of Z-scores and % p.v. was performed for the age subgroup >70 years. Spearman correlation coefficients between Z-scores and % p.v. were calculated for FEV1, FVC, DLCO and FEV1/FVC ratio. Differences were considered statistically significant with p values <0.05. <bold>Results:</bold> PPC were observed in 40 out of the 131 included patients. Both % p.v. and Z-scores performed comparably in the non-selected population as well as in the subgroup of patients aged >70 years. Correlation analyses showed significant and almost perfect correlation between % p.v. and Z-scores of FEV1, FVC, DLCO (R=0.99 and p˂0.01 for all) and moderate correlation for the FEV1/FVC ratio (R=0.67; p˂0.01). <bold>Conclusion:</bold> We demonstrated that Z-scores can be used equally to % p.v. in preoperative functional assessment. Supported by grant No MH CZ NU21-06-00086.