The aim of our study was to develop and validate a LOS more than 14 days risk prediction model for TKA patients. The risk factors were Age, ASA status, type of anesthesia, operation duration, procedure description, DM, IHD, CHF, day of operation and blood transfusion.Ultimately, We built the nomogram using the above risk factors for LOS more than 14 days in TKA patients. The Nomogram transforms the complex regression equation into a visual graph, which makes the results of the prediction model more readable and convenient for patient evaluation. Because of the intuitive and easy to understand characteristic of nomogram, it has gradually been paid more and more attention and applied in medical research and clinical practice.
In the risk prediction nomogram with LOS more than 14 days in this study, the highest independent predictor score was blood transfusion, many studies have come to the same conclusion, and the transfusion rate was directly related to LOS13-15. Autologous blood transfusion is often required when the blood loss is between 1000-1500 ml. research shows that the total blood loss after TKA may be as high as 2000 ml, and the proportion of blood transfusion may be as high as 67%16,17. In a cohort of 228,316 TKA patients at 922 hospitals, the mean predicted probability of TKA transfusion was 7.9%, with 60% (95% CI, 36%-87%) patients with LOS more than 3 days13. In a cross-sectional study of 4,544,999 patients who received TKA between January 2000 and December 2009, blood transfusion were associated in-hospital mortality, LOS increased by 0.71±0.01 days 14. In addition, Danninger et al.15showed a significantly higher rate of major complications in patients receiving transfusion (19.1% vs 11.2%, P<0.0001), the mean length of hospital stay was significantly increased.
Our study found that the date of operation was a major factor in predicting the risk of LOS more than 14 days after blood transfusion. Similarly, studies demonstrated that operation procedure or factors related to doctors-nurses provide clinically relevant improvement in explaining length of stay in addition to patient-related risk factors8. In a prospective cohort study of 4,509 patients who underwent initial TKA at four hospitals between January 1, 2016 and September 30, 2017, surgery later in the day predicted a longer hospital stay, with patients who had surgery on Friday having a significantly longer LOS than patients who had surgery on Monday8. Our study showed that the risk prediction scores of operations on Monday, Tuesday and Friday were much higher than those on Thursday. The length of hospital stay was related to the date of operation. Possible reasons for this result include patients from different countries, surgical hospital system, doctors' mood and doctors' preferences.
This study found that the greater the variety of comorbid diseases, that is, the higher the comorbidity index, and the longer the hospital stay. Swain et al. 18showed that 67% of patients with osteoarthritis had at least one other chronic condition, 20% more than those without osteoarthritis. The results of this study suggest that co-morbidity CHF, DM, and IHD are independent predictors of LOS more than 14 days. Similarly, some previous studies suggested that the TKA patients with comorbidities had prolonged LOS19-23. Higuera et al.22 showed that chronic heart failure was associated with longer hospital stays and increased rates of major postoperative complications in TKA patients. In a study of 15,321 TKA patients, 18.2% had a medical comorbidity DM, with a 300% increase in overall mortality. Belmont et al.23found that DM was an independent predictor of hospitalization of 4 days or more.
ASA status was also particularly important for predicting LOS more than 14 days of risk. Consistent with previous literature, ASA-status more than 3 is an independent risk factor for prolonged LOS and increased postoperative complications23,24.The predicted risk score of bilateral total knee arthroplasty is higher than that of unilateral TKA, probably because bilateral patients suffer more blood loss, more severe hypotension, and more cardiac, respiratory, and neurological complications than unilateral patients25,26. In this study, it was suggested that patients undergoing knee revision were also predictors of LOS more than 14 days of risk, and that revision arthroplasty was associated with longer hospital stays and higher rates of complications and mortality, similar to results confirmed in previous studies27,28.
The type of anesthesia also played an important role in predicting the risk of LOS more than 14 days. In both primary and revised TKA patients, general anesthesia was associated with an increased risk of postoperative complications, such as thromboembolism and surgical incision infection, as well as increased the LOS, blood transfusion rates, postoperative opioid consumption, and surgical time, compared with epidural or spinal anesthesia29-33.In addition, age and operation duration were independent predictors of LOS more than 14 days risk, similar to previous finding23,34.Limitations of this study include: as the included cases excluded patients with GA combined with RA and other anesthesia methods, the results of this study cannot be used to predict the risk of this population.
There are still some limitations in our study. Firstly, this study is a retrospective study, using clinical data from a single center. Therefore, there may be differences in treatment strategies, race, and so on. Second, because of differences in healthcare Settings and practices, predictive models developed in one country are unlikely to be directly applicable in another country, requiring external validation and updating of the predictive performance of models in other new patient. Finally, there may be some influencing factors not included in this paper, including patient income, medical expenses, medical insurance, hospital location, etc. Potential factors not included may also have some influence on the results.