Total knee arthroplasty (TKA) and total hip arthroplasty (THA) are among the most frequently performed elective surgical procedures and are highly effective treatments for advanced joint disease, most commonly osteoarthritis. Over the past decade, improvements in surgical techniques, perioperative care pathways, anaesthetic management, and postoperative rehabilitation have enabled an increasing proportion of these procedures to be performed as outpatient surgery, allowing patients to return home on the day of surgery. Outpatient arthroplasty has the potential to improve patient satisfaction, reduce hospital length of stay, lower healthcare costs, and decrease the risk of hospital-acquired complications. However, achieving safe and successful same-day discharge requires carefully optimized perioperative care.
Anaesthetic management is a central component of outpatient arthroplasty pathways. Both general anaesthesia (GA) and spinal anaesthesia (SA) are routinely used for TKA and THA, and both techniques are well established with extensive safety data. Neuraxial anaesthesia has traditionally been associated with reduced intraoperative blood loss and certain postoperative complications, and it is commonly recommended in clinical guidelines for hip and knee arthroplasty. In contrast, modern general anaesthesia using short-acting intravenous agents may offer advantages in the outpatient setting, including predictable onset and offset, rapid recovery of motor function, and reduced postoperative nausea and vomiting when volatile agents are avoided.
Despite widespread clinical use of both techniques, the optimal choice of anaesthesia for outpatient TKA and THA remains uncertain. Much of the existing evidence comparing GA and SA is derived from retrospective observational studies and registry-based analyses. These studies often include mixed inpatient and outpatient populations and are subject to confounding by indication, as patients receiving GA frequently differ from those receiving SA with respect to comorbidity, functional status, or anticipated surgical complexity. As a result, it is difficult to determine whether observed differences in outcomes are attributable to the anaesthetic technique itself or to underlying patient characteristics. Randomized clinical trials specifically designed to compare GA and SA in the outpatient arthroplasty setting are scarce.
The GASPS (General Anaesthesia vs Spinal Anaesthesia: Patient Outcomes and Success in Outpatient Primary Total Knee and Hip Arthroplasty) trial was designed to address this evidence gap. GASPS is a multicentre, randomized, phase IV clinical trial comparing GA and SA in adults undergoing outpatient primary TKA or THA. The overarching aim of the trial is to generate high-quality randomized evidence on whether the choice of anaesthetic technique influences the likelihood of successful same-day discharge and postoperative recovery in outpatient arthroplasty.
A total of 600 participants will be enrolled across multiple orthopaedic centres in Sweden. Eligible patients scheduled for outpatient primary TKA or THA are randomized on the day of surgery to receive either GA or SA. Randomization is performed using a stratified permuted block design, with stratification by type of surgery (knee or hip arthroplasty) and study site, to ensure balanced allocation across groups. Allocation concealment is maintained until shortly before surgery. Due to the nature of the interventions, blinding of patients and clinical staff is not feasible; however, data analysts remain blinded during analysis.
Both anaesthetic techniques are delivered according to standardized protocols that reflect contemporary routine clinical practice. General anaesthesia is provided using total intravenous anaesthesia with short-acting agents, primarily propofol and remifentanil, administered by trained anaesthesiologists. Spinal anaesthesia is administered as a single-shot intrathecal block with bupivacaine, with optional intrathecal opioid adjuncts and light sedation as clinically indicated. No experimental drugs or procedures are introduced, and all perioperative care apart from the assigned anaesthetic technique follows local standard practice.
The primary outcome of the trial is successful same-day discharge, defined as discharge from hospital on the day of surgery without readmission within 48 hours. This outcome was chosen as a clinically meaningful and patient-relevant measure of perioperative success in outpatient arthroplasty, integrating both recovery efficiency and short-term safety. Successful same-day discharge reflects the combined effects of anaesthetic technique, surgical care, postoperative recovery, and early complication rates.
Secondary outcomes are designed to capture multiple dimensions of perioperative and postoperative recovery. These include perioperative time metrics related to anaesthesia induction, surgery, and recovery; early postoperative outcomes such as pain, nausea and vomiting, opioid consumption, mobilisation, and adverse events; and patient-reported outcomes assessing quality of recovery, function, and health-related quality of life. Recovery is conceptualized as a multi-phase process, ranging from early recovery in the postoperative care unit to longer-term recovery at home. Validated instruments such as the Quality of Recovery-15 (QoR-15), Knee injury and Osteoarthritis Outcome Score (KOOS), Hip disability and Osteoarthritis Outcome Score (HOOS), and EQ-5D-5L are used to assess these domains over time.
In addition to quantitative outcomes, the GASPS trial incorporates a qualitative component to explore patient experiences of anaesthesia and postoperative recovery. Semi-structured interviews are conducted with a subset of participants several weeks after surgery. This mixed-methods approach allows for a deeper understanding of patient perceptions, expectations, and experiences that may not be fully captured by standardized questionnaires, and provides important contextual information to complement clinical and patient-reported outcome data.
Participants are followed from the day of surgery up to 12 months postoperatively using a combination of medical record review and patient-completed questionnaires. Safety monitoring focuses on adverse events occurring in the immediate perioperative period, while longer-term follow-up captures functional outcomes, quality of life, healthcare utilization, and productivity losses. A health economic evaluation is embedded within the trial to compare GA and SA in terms of costs and quality-adjusted life years, with the aim of informing resource-efficient anaesthetic strategies for outpatient arthroplasty.
By integrating randomized clinical data, patient-reported outcomes, qualitative insights, and health economic analyses, the GASPS trial aims to provide a evaluation of the role of anaesthetic technique in outpatient total knee and hip arthroplasty.
