Sub-Tenon Block with Bolus-Free Dexmedetomidine Sedation for Penetrating Keratoplasty: A Retrospective Clinical Case Series of 50 High-Risk Patients

Background: Penetrating keratoplasty (PK) is a technically demanding corneal transplant procedure frequently performed in elderly patients with substantial systemic comorbidities. In this population, an anesthetic strategy that ensures hemodynamic stability, cooperative sedation, adequate analgesia, and preserved spontaneous ventilation is highly desirable. Dexmedetomidine, a highly selective alpha2-adrenergic agonist, provides “cooperative” sedation with minimal risk of respiratory depression and additional sympatholytic benefits. Methods: This single-center retrospective observational case series included 50 consecutive patients (American Society of Anesthesiologists [ASA] II–III, age 50–90 years) undergoing PK under sub-Tenon block combined with continuous dexmedetomidine infusion. Dexmedetomidine was administered without a loading bolus at 0.7 mcg/kg/h for 10–15 min, then reduced to 0.5 mcg/kg/h, targeting a Ramsay Sedation Scale (RSS) score of 2–3. The sub-Tenon block was performed using a mixture of levobupivacaine 0.5% and lidocaine 2% (3–5 mL). Heart rate (HR), mean arterial pressure (MAP), oxygen saturation (SpO2) and RSS were recorded in nine predefined perioperative phases. Data were analyzed descriptively. Results: The mean age was 72 ± 9 years; 52% of patients were ASA III. Hypertension was present in all patients; 30% had cardiovascular disease, 28% diabetes mellitus type II, and 30% chronic obstructive pulmonary disease. Progressive, controlled bradycardia was observed (mean HR decreased from 76 to 57 beats/min during graft transplantation), while MAP gradually decreased from hypertensive baseline values (150–160 mmHg) to an optimal intraoperative range of 115–130 mmHg, without episodes of clinically significant hypotension. SpO2 remained stable at 98–99% throughout all phases, with no episodes of desaturation or need for airway intervention or supplemental oxygen. Target sedation (RSS 2–3) was achieved in all patients (median RSS 3), with preserved spontaneous breathing and cooperation. Sub-Tenon block-related bulging occurred in 6% of cases. No episodes of clinically significant bradycardia, malignant arrhythmia, respiratory compromise, or need to discontinue dexmedetomidine were recorded. No opioids or non-steroidal analgesics were required intraoperatively or in the early postoperative period. Conclusions: The combination of sub-Tenon block and continuous dexmedetomidine sedation without a loading bolus represents a hemodynamically stable and respiratory-safe anesthetic strategy for PK in elderly, high-risk patients. These preliminary, hypothesis-generating findings suggest that the protocol provides stable surgical conditions and a favorable safety profile, justifying future prospective randomized controlled trials to establish its comparative efficacy against general anesthesia or standard sedative regimens.