Machine Learning Prediction of Spinal Anaesthesia Block Duration

Artificial Intelligence-Based Prediction of Sensory and Motor Block Duration Following Spinal Anaesthesia: A Prospective Observational Prediction Model Development Study

The duration of sensory and motor block after spinal anaesthesia varies widely between patients given the same dose of local anaesthetic. Much of this variability is explained by differences in lumbosacral cerebrospinal fluid volume, which cannot be measured routinely in clinical practice but is related to simple body measurements such as abdominal circumference and vertebral column length. This prospective observational study will develop and internally validate prediction models for the duration of sensory and motor block following spinal anaesthesia in adults undergoing elective surgery. Preoperative clinical and anthropometric variables will be recorded, and block regression will be assessed serially after intrathecal injection. Machine learning methods (lasso regression, ridge regression, random forest, extreme gradient boosting, and support vector regression) will be developed and compared against multivariable linear regression as the reference model. The aim is a practical tool that helps anaesthetists anticipate how long a spinal block will last in an individual patient, supporting decisions about case scheduling, supplementation, and discharge planning.

Study Overview

• Status: Not yet recruiting
• Conditions: Nerve Block; Anesthesia, Spinal; Anesthesia Recovery Period

Detailed Description

Background. Spinal anaesthesia produces block of unpredictable duration. Cerebrospinal fluid volume in the lumbosacral region is the dominant determinant of block spread and regression, and correlates inversely with abdominal circumference and directly with vertebral column length. Existing single-variable rules perform poorly, and no validated multivariable model is in routine clinical use. Objectives. The primary objective is to develop and internally validate models predicting the duration of sensory block and the duration of motor block after single-shot spinal anaesthesia. The secondary objective is to compare the predictive performance of machine learning approaches with conventional multivariable linear regression. Design. Single-centre prospective observational cohort study. No study-directed intervention is applied; anaesthetic technique, drug, and dose are determined by the attending anaesthetist according to routine practice and are recorded as candidate predictors. Assessments. Sensory block level is assessed bilaterally by pinprick with a 25-gauge needle along the mid-clavicular line, over dermatomes T4 to S1. Motor block is assessed using the modified Bromage scale (0-3). Assessments are performed at fixed intervals from intrathecal injection until complete regression of sensory and motor block. Candidate predictors. Age, sex, height, weight, body mass index, abdominal circumference, vertebral column length, ASA physical status, local anaesthetic dose and baricity, and adjuvant use. Sample size. A target of 255 participants was derived using the Riley criteria for continuous-outcome prediction models (pmsampsize), assuming 9 candidate predictors, an outcome standard deviation of 40 minutes, anticipated R-squared of 0.35, shrinkage of at least 0.90, and a multiplicative margin of error of 1.10. The four criteria yielded 183, 183, 234, and 246; the largest requirement of 246 was inflated by approximately 4 per cent for attrition. Analysis. Model development will use nested repeated 10-fold cross-validation with bootstrap optimism correction. Performance will be reported as R-squared, root mean squared error, and mean absolute error, with calibration plots. SHAP values will be used to describe predictor contributions. Reporting will follow TRIPOD+AI.

• Study Type: Observational
• Enrollment (Estimated): 255

Contacts and Locations

• Study Contact: Name: Salaheldin A Abdelaziz Ahmed; Phone Number: +966508818713; Email: saladin28.sa@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Consecutive adults scheduled for elective surgery under single-shot spinal anaesthesia at Specialized Medical Center, King Fahad campus, Riyadh.

Description

Inclusion Criteria:

• Adults scheduled for elective surgery under single-shot spinal anaesthesia ASA physical status I to III Written informed consent obtained

Exclusion Criteria:

• Contraindication to neuraxial anaesthesia (coagulopathy, local or systemic infection, raised intracranial pressure, patient refusal) Failed or incomplete block requiring conversion to general anaesthesia Repeated or top-up intrathecal injection Pregnancy Known spinal deformity or previous spine surgery Pre-existing neurological or neuromuscular disease affecting sensory or motor assessment Inability to cooperate with sensory and motor assessment

Study Plan

How is the study designed?

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Duration of sensory block	Time from completion of intrathecal injection to regression of sensory block to the S1 dermatome, assessed bilaterally by pinprick with a 25-gauge needle along the mid-clavicular line	Up to 8 hours after intrathecal injection
Duration of motor block	Time from completion of intrathecal injection to return to modified Bromage score 0 (full ability to flex knee and ankle)	Up to 8 hours after intrathecal injection

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Predictive performance of machine learning models	R-squared, root mean squared error, mean absolute error, and calibration slope for lasso regression, ridge regression, random forest, extreme gradient boosting, and support vector regression, each compared with multivariable linear regression as the reference model	Through study completion, an average of 20 months
Time to peak sensory block level	Time from intrathecal injection to the highest dermatomal level of sensory block, assessed by pinprick	Up to 30 minutes after intrathecal injection

Collaborators and Investigators

• Sponsor: Specialized Medical Center (SMC)
• Investigators: Principal Investigator: Salaheldin A abdelaziz Ahmed, Specialized Medical Center

Study record dates

Study Major Dates

• Study Start (Estimated): December 1, 2026
• Primary Completion (Estimated): July 1, 2028
• Study Completion (Estimated): September 1, 2028

Study Registration Dates

• First Submitted: September 7, 2026
• First Submitted That Met QC Criteria: September 7, 2026
• First Posted (Actual): September 11, 2026

Study Record Updates

• Last Update Posted (Actual): September 11, 2026
• Last Update Submitted That Met QC Criteria: September 7, 2026
• Last Verified: September 1, 2026

More Information

Terms related to this study

• Keywords: machine learning; spinal anaesthesia; prediction model; sensory block duration; motor block duration; abdominal circumference; TRIPOD+AI; vertebral column length
• Other Study ID Numbers: IRBSMC1-2026-0001

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data underlying published results, together with the data dictionary and model code, will be made available to researchers whose proposed use has been approved by an independent review committee. Requests should be directed to the principal investigator. Data will be available from 6 months to 36 months after publication of the primary results.
• IPD Sharing Time Frame: Data will become available 6 months after publication of the primary results and will remain available for 36 months
• IPD Sharing Access Criteria: Requests should be directed to the principal investigator. Proposals will be reviewed by the principal investigator and the Specialized Medical Center Institutional Review Board. Requesters must provide a methodologically sound proposal and sign a data access agreement.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ICF; ANALYTIC_CODE

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No