Two Types of Anaesthesia and Length of Hospital Stay in Patients Undergoing Unilateral Total Knee Arthroplasty (TKA)

A Secondary Analysis Based on a Single-centre Retrospective Cohort Study in Singapore

Xuan JI; Weiqi KE


BMC Anesthesiol. 2021;21(242) 

In This Article

Abstract and Introduction


Background: Evidence regarding the relationship between the type of anaesthesia and length of hospital stay is controversial. Therefore, the objective of this research was to investigate whether the type of anaesthesia was independently related to the length of hospital stay in patients undergoing unilateral total knee arthroplasty (TKA) after adjusting for other covariates.

Methods: The present study was a cohort study. A total of 2622 participants underwent total knee arthroplasty (TKA) at a hospital in Singapore from 2013 to 1–1 to 2014-6-30. The target independent variable and the dependent variable were two types of anaesthesia and length of hospital stay, respectively. The covariates included age, BMI, hemoglobin (Hb), length of stay (LOS), duration of surgery, sex, ethnicity, American Society of Anesthesiologist (ASA) Status, smoking, obstructive sleep apnea (OSA), diabetes mellitus (DM), DM on insulin, ischemic heart disease (IHD), congestive cardiac failure (CCF), cerebrovascular accident (CVA), creatinine > 2 mg/dl, day of week of operation. Multivariate linear and logistic regression analyses were performed on the variables that might influence the choice of the two types of anaesthesia and the LOS. This association was then tested by subgroup analysis using hierarchical variables.

Results: The average age of 2366 selected participants was 66.57 ± 8.23 years old, and approximately 24.18% of them were male. The average LOS of all enrolled patients was 5.37 ± 4.87 days, 5.92 ± 6.20 days for patients receiving general anaesthesia (GA) and 5.09 ± 3.98 days for patients receiving regional anaesthesia (RA), P < 0.05. The results of fully adjusted linear regression showed that GA lasted 0.93 days longer than RA (β = 0.93, 95% CI (0.54, 1.32)), P < 0.05. The results of fully adjusted logistic regression showed that LOS > 6 days was 45% higher for GA than for RA (OR = 1.45, 95% CI (1.15, 1.84)), P < 0.05. Through the subgroup analysis, the results were basically stable and reliable.

Conclusion: Our study showed that GA increased the length of stay during unilateral TKA compared with RA. This finding needs to be validated in future studies.


Total knee arthroplasty (TKA) is a radical surgery for the treatment of pain, movement limitation and joint deformity caused by osteoarthritis, rheumatoid arthritis and knee joint trauma. With the continuous development of TKA and the application of the concept of accelerated rehabilitation surgery in TKA, patients who undergo TKA now have less trauma, less bleeding, faster recovery and a significantly shorter length of stay (LOS), and some patients can even be discharged the day of surgery. Shortening the LOS can increase the turnover of inpatients, reduce the waste of medical resources, reduce medical expenses and lighten the social burden of medical treatment.[1] The LOS after TKA is closely related to prognosis; however, there are many factors that affect LOS,[2] and there have been some studies linking the type of anaesthesia to the LOS.[3] At present, the two most commonly used types of anaesthesia by broad category are general anaesthesia (GA) and regional anaesthesia (RA). In this study, GA includes endotracheal intubation anaesthesia and RA includes spinal anaesthesia and epidural anaesthesia. Previous research has established that both types of anaesthesia can be used in TKA. However, findings from previous studies regarding the relationship between type of anaesthesia and LOS are controversial. In some studies, no association between the type of anaesthesia and LOS was found in multivariable analyses.[4] In contrast, some other studies suggested that the type of anaesthesia was related to the LOS.[5,6] Given the differences in research design, target population, and data analysis of these studies, the performance of additional studies remains important. Previous studies have shown that different types of anaesthesia can increase or decrease the LOS; therefore, this study investigated whether different types of anaesthesia are associated with longer LOS. This study conducted a secondary analysis based on previously published data to investigate whether the two most commonly used types of anaesthesia were independently associated with LOS in patients undergoing unilateral TKA.[7]

Participants and Methods

Study Design. A retrospective cohort study was conducted to compare the LOS in patients who underwent unilateral TKA under the two most common types of anaesthesia. The objective independent variable was the type of anaesthesia, and the dependent variable was the LOS.

Study Population. This was a retrospective cohort study conducted at the Singapore General Hospital. All patients who underwent TKA from January 2013 to June 2014 (n = 2622). Patients who underwent bilateral TKA (n = 206) and those who underwent revision TKA (n = 22) were excluded. Patients who received GA combined with RA and other methods of anaesthesia were excluded (n = 28). The final number of qualifying cases was 2366. This study was approved by the Institutional Review Board prior to its initiation (SingHealth Centralized Institutional Review Board (CIRB) 2014/651/D).[7] (Figure 1) The informed consent of the participants was not required for this study because it was a retrospective cohort study. Written informed consent was waived by the SingHealth CIRB because our study did not involve the privacy or treatment of patients.

Figure 1.

Flowchart of patient selection

Abdullah et al. uploaded the raw data of their research to the Datadryad website ( and granted the Datadryad site ownership of the original data.[7] Therefore, we were able use these data for secondary analyses of different hypotheses without infringing on the rights of the authors.

Variables. We obtained the data of patients who underwent unilateral TKA, including the variables we needed, from the clinical information system of Singapore General Hospital. We considered the two types of anaesthesia as categorical variables, and unilateral TKA anaesthesia was divided into GA and RA.

We considered LOS a continuous variable, and then we generated the categorical variable based on a cut-off point of 6, defining an LOS longer than 6 days as an extended LOS. This cut-off was selected because it represents the >75th percentile LOS of the whole sample. The use of the 75th percentile to define prolonged LOS is consistent with other studies.[7]

In this study, we obtained the following types of covariates from the database: (1) demographic data; (2) variables that can affect the type of anaesthesia or LOS; and (3) other diseases. The following variables were used to construct the fully adjusted model: (1) continuous variables: Age, BMI, Hb, LOS, duration of surgery; (2) categorical variables: Sex, ethnicity, American Society of Anesthesiologists (ASA) status, smoking, obstructive sleep apnea (OSA), diabetes mellitus (DM), ischemic heart disease (IHD), congestive cardiac failure (CCF), cerebrovascular accident (CVA), creatinine > 2 mg/dl, DM on insulin, day of week of operation.

The study protocol was performed in accordance with the relevant guidelines.

Statistical Analysis

The baseline characteristics of the participants are expressed as the mean ± standard deviation (Gaussian distribution) or median (range) (skewed distribution) for continuous variables and as percentages for categorical variables. We used χ2 (categorical variables), Student's t test (normal distribution), or the Mann-Whitney U test (skewed distribution) to test for differences among the anaesthesia groups (bisected). The data analysis process of this study was based on three questions: (1) what is the relationship between anaesthesia and LOS?; (2) which factors modify or interfere with the relationship between anaesthesia and LOS?; and (3) after adjustment for interference factors or after the stratified analysis, what is the true relationship between anaesthesia and LOS? Therefore, data analysis can be summarized in three steps. Step 1: We used univariate and multivariate linear regression models to test the link between the two types of anaesthesia and LOS (days) with three distinct models, as presented in Table 3, and we used univariate and multivariate binary logistic regression models to test the connection between the two types of anaesthesia and LOS > 6 days with three distinct models, as presented in Table 4. The three models were a crude model, in which no covariates were adjusted; model 1, which was adjusted only for sociodemographic data (age, sex, ethnicity); model 2, which included the adjustments in model 1+ the other covariates presented in Table 1.[8] Step 2: Subgroup analyses were performed using stratified linear regression models. For continuous variables, we first converted the variables to categorical variables according to the clinical cut-off point or tertile and then performed an interaction test. Tests for the effect modification of subgroup indicators were followed by the likelihood ratio test.[9] To ensure the robustness of the data analysis, we performed a sensitivity analysis. All analyses were performed with the statistical software packages R (, The R Foundation) and EmpowerStats (, X&Y Solutions, Inc., Boston, MA). P values less than 0.05 (two-sided) were considered statistically significant.[10]