External validation of the CARDOT score for predicting respiratory complications after thoracic surgery

Abstract Background Respiratory complications after thoracic surgery are common and can lead to increased perioperative morbidity and mortality. Although several clinical risk scores for the prediction of respiratory complications have been proposed, these scores are not specific for thoracic surgery. In addition, few clinical risk scores have been adopted in clinical practice due to the lack of external validation. Our thoracic-specific risk score, the CARDOT score, showed good predictive performance for postoperative respiratory complications during score development. This study aimed to validate the CARDOT score in an external dataset and determine the score performance after including the neutrophil-lymphocyte ratio (NLR) to the score as an additive predictor. Methods A retrospective cohort study of consecutive thoracic surgical patients at a single tertiary hospital in northern Thailand was conducted. The development and validation datasets were collected between 2006 and 2012 and from 2015 to 2021, respectively. Six prespecified predictive factors were identified, and formed a predictive score, the CARDOT score (chronic obstructive pulmonary disease, American Society of Anesthesiologists physical status, right-sided operation, duration of surgery, oxygen saturation, thoracotomy), was calculated. The external performance of the CARDOT score was evaluated in terms of discrimination by using the area under the receiver operating characteristic (AuROC) curve and calibration. Results The incidence of respiratory complications was 15.7% (171 of 1088) in the development dataset and 24.6% (370 of 1642), in the validation dataset. The CARDOT score had good discriminative ability for both the development and validation datasets (AuROC 0.789 (95% CI 0.753–0.827) and 0.758 (95% CI 0.730–0.787), respectively). The CARDOT score showed good calibration in both datasets. A high NLR (≥ 4.5) significantly increased the risk of respiratory complications after thoracic surgery (P < 0.001). The AuROC of the CARDOT score with the NLR showed significantly greater discrimination power than that of the CARDOT score alone (P = 0.008). Conclusions The CARDOT score had consistent discriminative performance in the external validation dataset. This tool may be beneficial in settings where preoperative pulmonary function tests are not routinely performed.