AI-Assisted Evaluation of Anatomical Success of Fascial Plane Blocks Applied in Open Heart Surgery and Investigation of Its Relationship With Postoperative Pain Scores: A Prospective Observational Study

This single-centre prospective observational cohort included 120 consenting adults undergoing elective isolated coronary artery bypass grafting through median sternotomy. At the end of surgery, after complete sternal and skin closure, 115 participants received bilateral ultrasound-guided pecto-intercostal fascial plane block with 20 mL of 0.25% bupivacaine on each side (40 mL and 100 mg in total). Five participants declined the block but consented to Ethics Committee-authorised standardised ultrasound imaging, storage and subsequent de-identified human/AI assessment; no needle was inserted and no local anaesthetic was administered in this group.

Ultrasound videos were acquired from the left side with an M5 portable ultrasound system and a 7L4s linear-array transducer at a nominal frequency of 7.5 MHz using standardised settings. Eight to ten representative frames were selected from each video across the pre-block view, needle advancement, local-anaesthetic spread and final post-injection view, as applicable. The same frame set and fixed participant order were shown to every reader.

After participant follow-up had ended, five general-purpose multimodal AI configurations, three expert anaesthesiologists and one separate senior reference anaesthesiologist independently classified each image set as successful, patchy/inadequate or failed/no local anaesthetic. The evaluated configurations were Gemini 3.5 Flash, Claude Sonnet 4.6, GPT-5.5 Instant in ChatGPT, Grok 4.3 and Kimi K2.6. They were accessed through free, non-subscription consumer accounts using their standard web interfaces and default response and data-use settings. For each system-participant pair, a new conversation was opened, the same fixed prompt and image set were submitted, and the first response was recorded without regeneration or re-prompting. The visible conversation was deleted before the next assessment, although this did not establish provider-side deletion. Each configuration assessed each participant once; within-system repeatability was not evaluated. The number and identities of the five consumer configurations were fixed before any reader output was observed; no bespoke AI model was developed or trained. The separate senior anaesthesiologist was a pragmatic single-expert reference and not an objective gold standard. The study was not designed as an equivalence or non-inferiority analysis.

Postoperative Numerical Rating Scale pain at rest and during coughing was scheduled at 6, 12, 24 and 48 hours. The 6-hour assessment was applicable only to participants who had already been extubated at that time. Rescue analgesic administration during the first 48 hours, intensive-care and hospital length of stay, complications and mortality were also recorded. Pain associations were secondary, observational and non-causal.

The ClinicalTrials.gov record was first submitted on 6 May 2026 and first posted on 12 May 2026, after the study had begun but while recruitment, image acquisition and clinical follow-up were still ongoing. Registration was therefore retrospective relative to study start. Image acquisition ended on 27 May 2026 and participant clinical follow-up ended on 1 June 2026.