Total knee arthroplasty (TKA) and total hip arthroplasty (THA) are common operations used to treat severe joint disease, most often caused by osteoarthritis. An increasing number of these procedures are now performed as outpatient surgery, meaning that patients can go home on the same day as the operation. This can be beneficial for both patients and healthcare systems, but it requires safe and efficient anaesthetic care.

Two different types of anaesthesia are commonly used for these operations: general anaesthesia (where the patient is asleep) and spinal anaesthesia (where the lower part of the body is numbed). Both methods are well established and widely used. Previous studies suggest that the choice of anaesthesia may affect how quickly patients recover, how comfortable they feel after surgery, and whether they can be safely discharged on the day of surgery. However, most existing studies are based on retrospective data, and there is limited randomized evidence comparing these anaesthetic techniques in the outpatient setting.

The GASPS trial is a multicentre, randomized, phase IV clinical study that compares general anaesthesia and spinal anaesthesia in adults undergoing outpatient primary total knee or hip arthroplasty. A total of 600 participants will be included and randomly assigned to receive one of the two anaesthetic methods on the day of surgery. All participants will receive standard surgical and perioperative care, and both anaesthetic techniques are part of routine clinical practice.

The main aim of the study is to investigate whether the type of anaesthesia influences the chance of successful same-day discharge, defined as going home on the day of surgery without needing to be readmitted within 48 hours. The study will also examine recovery time, pain, nausea and vomiting, use of pain medication, complications, patient-reported recovery and function, and healthcare costs. In addition, patient experiences of anaesthesia and postoperative recovery will be explored through interviews in a smaller group of participants.

Participants will be followed using questionnaires and medical records from the day of surgery up to 12 months after the operation. The results of this study are expected to provide clear and reliable information to help guide anaesthetic care for patients undergoing outpatient hip and knee replacement surgery.

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.

Inclusion Criteria:

1. The participant has given their written consent to participate in the trial.
2. Planned for primary TKA or THA.
3. Adults aged 18 to 80 years at time of written consent.
4. ASA (American Society of Anaesthesiologists) classification 1 or 2, or 3 without significant functional impairment.
5. Scheduled start of surgery before 13:00.
6. Ability to communicate in Swedish, ensuring understanding of informed consent and follow-up procedures.

Exclusion Criteria:

1. Indication for surgery other than degenerative or inflammatory joint diseases (e.g. fracture).

2. Body mass index (BMI) > 35 kg/m.

3. Preoperative opioid use exceeding 20 mg oral morphine equivalents daily.

4. Haemoglobin < 120 g/L (sample no older than 3 months).

5. Known bleeding disorders, including coagulopathies.

6. Known allergies to investigational anaesthetic drugs (e.g., bupivacaine, remifentanil, or propofol).

7. Neurological conditions with persistent motor or sensory deficits.

8. Localised infections at the spinal injection site.

9. Determined by the surgical or anaesthesia team to be unsuitable for trial participation and/or outpatient surgery.

10. Women of childbearing potential (i.e., those who are fertile, following menarche and until becoming post-menopausal, unless permanently sterile)

    1. Who are not willing to use a highly effective method of contraception judged by the investigator, from the time of signing the informed consent, OR
    2. Who has a positive pregnancy test at enrolment

This trial uses a partial blinding strategy to minimise bias while accommodating the practical requirements of the interventions. Participants and clinical staff involved in preoperative care will be blinded to the assigned anaesthesia method until a few hours prior to surgery.

The anaesthesia team responsible for administering the allocated intervention will not be blinded, as they must deliver the specific anaesthetic technique (GA or SA). Outcome assessors will not be blinded, as their interactions with participants and the nature of the postoperative evaluations (e.g., assessing sensory or motor blockade) may reveal the anaesthetic technique. To reduce potential bias, all assessors will follow standardised assessment protocols.

Data analysts will remain blinded to the treatment allocation during the analysis phase.