Objective To investigate the efficacy and significance of Rox index, lymphocyte count and blood glucose in predicting retracheal intubation after high-flow nasal cannula(HFNC) oxygen therapy for severe pneumonia.

Methods A total of 180 patients with severe pneumonia were selected as the study subjects, and all patients were treated with invasive and high-flow oxygen therapy sequentially. According to whether mechanical ventilation with re-intubation occurred after HFNC oxygen therapy, the patients were divided into re-intubation group (n=31) and non-re-intubation group (n=149). The ROX index, lymphocyte index lymphocyte (LYM) count, helper/inducer T lymphocyte (CD4⁺T) count and suppressor/cytotoxic T lymphocyte (CD8⁺T) count and blood glucose levels between the two groups before and at 6 hours and 12 hours after high-flow nasal cannula (HFNC) oxygen therapy were compared. The random forest algorithm was used to sort and screen the characteristic variables affecting retracheal intubation. Receiver operating characteristic (ROC) curve was used to analyze the predictive value of ROX index, lymphocyte index and blood glucose for retracheal intubation.

Results The ROX index of the reintubation group was significantly lower at 6 and 12 h after HFNC oxygen therapy, and the blood glucose was significantly higher than that of the non-reintubation group (P < 0.05). Random forest algorithm showed that the top 3 variables in importance ranking were ROX index, CD4⁺T count and blood glucose. ROX index, CD4⁺T count combined with blood glucose at 6 and 12 h after HFNC oxygen therapy predicted the area under the curve (AUC) of retracheal intubation was greater than that of the single index, and the AUC of the three combined to predict retracheal intubation at 12 h after HFNC oxygen therapy was greater than that at 6 h after HFNC oxygen therapy (P < 0.05).

Conclusion The combined evaluation of ROX index, CD4⁺T count and blood glucose has certain predictive efficacy for retracheal intubation mechanical ventilation after HFNC oxygen therapy in patients with severe pneumonia.