This multicenter, prospective, randomized clinical trial aims to compare the effects of spinal (neuraxial) anesthesia with spontaneous ventilation versus general anesthesia with mechanical ventilation on the incidence of postoperative pulmonary complications in adult patients undergoing elective lower limb revascularization surgery. A total of 594 patients with symptomatic peripheral arterial disease will be randomly assigned to receive either spinal anesthesia with sedation or general anesthesia with mechanical ventilation. The primary outcome is the incidence of postoperative pulmonary complications within 30 days or until hospital discharge, including pneumonia, respiratory failure, pleural effusion, atelectasis, and other defined respiratory events. Secondary outcomes include cardiovascular events, hemodynamic instability, renal injury, delirium, extrapulmonary complications, adverse events in the operated limb, ICU and hospital length of stay, and mortality. The study will be conducted at Hospital de Clínicas de Porto Alegre, Hospital Nossa Senhora da Conceição, and other participating Brazilian centers, with an expected start date in July 2025 and completion in December 2029.

This is a prospective, randomized, multicenter clinical trial designed to evaluate the impact of the anesthetic technique-general anesthesia with mechanical ventilation versus spinal (neuraxial) anesthesia with spontaneous ventilation-on the incidence of postoperative pulmonary complications in patients undergoing elective peripheral arterial revascularization surgery. The study population will include 594 adult patients (ASA II-IV) with symptomatic critical limb ischemia, scheduled for elective lower limb revascularization at tertiary hospitals in Brazil. Patients will be randomized into two groups: Group 1 will receive spinal anesthesia with intravenous sedation and supplemental nasal oxygen; Group 2 will receive general anesthesia with controlled mechanical ventilation using lung-protective strategies (tidal volume 6-8 mL/kg and PEEP 5 cmH₂O).

The primary outcome is the incidence of postoperative pulmonary complications within 30 days after surgery or until hospital discharge. These include pneumonia, respiratory failure, pleural effusion, atelectasis, pneumothorax, aspiration pneumonitis, bronchospasm, ARDS, pulmonary embolism, and exacerbation of preexisting respiratory disease, defined according to internationally recognized criteria.

Secondary outcomes include:

1. major cardiovascular complications (nonfatal myocardial infarction, acute coronary syndrome, cardiogenic shock);
2. hemodynamic complications (prolonged hypotension or distributive shock requiring vasopressors);
3. other extrapulmonary complications such as acute kidney injury, stroke, delirium, sepsis, surgical limb complications (e.g., graft thrombosis, amputation), and thromboembolic events (e.g., DVT, PE);
4. ICU and hospital length of stay, PACU time, and 30-day or in-hospital mortality.

Data collection will include perioperative gasometric evaluation, detailed intraoperative hemodynamic and ventilatory monitoring, analgesia and antiemetic usage, and adverse events tracking through predefined time points (intraoperative, immediate postoperative, and up to 30 days after surgery). Sample size calculation is based on detecting a reduction in pulmonary complications from 25% in the general anesthesia group to 15% in the spinal anesthesia group, with a power of 80% and a two-tailed alpha of 0.05. Randomization will be performed using computer-generated block sequences, and outcome assessors and statisticians will be blinded. The statistical analysis will follow the intention-to-treat principle and include regression modeling to control for potential confounders such as comorbidities and operative duration.

The study will begin in July 2025 and is expected to be completed by December 2029. Results will be published in peer-reviewed journals and used to inform perioperative management strategies in vascular surgery.

Inclusion Criteria:

• Adults aged ≥18 years
• ASA physical status II to IV
• Scheduled for elective peripheral arterial revascularization of the lower limbs
• Diagnosis of symptomatic peripheral arterial disease with critical limb ischemia
• Able and willing to provide informed consent

Exclusion Criteria:

• Body mass index (BMI) > 40 kg/m²
• Emergency vascular surgery
• History of lung resection surgery
• Persistent hemodynamic instability preoperatively
• History of bronchial asthma or chronic corticosteroid therapy
• History of neuromuscular disorders
• Current use of anticoagulants or antiplatelet agents contraindicating spinal anesthesia
• Contraindications to spinal anesthesia (e.g., patient refusal, infection at puncture site, increased intracranial pressure, inability to cooperate due to agitation or cognitive impairment)
• Acute vascular obstruction or other vascular complications not consistent with elective revascularization

Plan to Share Individual Participant Data (IPD)? - No

IPD Sharing Description:

• The individual participant data (IPD) collected during the study will not be made publicly available due to ethical considerations and patient confidentiality.
• Plan to Share IPD with Other Researchers? No
• Available Supporting Information:

Not applicable

- Time Frame and Access Criteria: Not applicable

Single-blinded (Outcomes Assessor)

Participants and anesthesiologists will not be blinded due to the nature of the interventions (general vs. spinal anesthesia).

However, postoperative outcome assessors and statisticians performing data analysis will be blinded to group allocation to reduce detection and assessment bias.

Randomization will be performed using a computer-generated block sequence and managed via the REDCap platform. Allocation concealment will be maintained using sealed envelopes.