Predictors of Unilateral Spinal Block Success (UNISS)

Determination of Factors Affecting Success in Unilateral Spinal Anesthesia: A Prospective Observational Study

This prospective observational study aims to determine the factors affecting the success of unilateral spinal anesthesia in patients undergoing orthopedic lower extremity surgery. Unilateral spinal anesthesia is preferred to minimize unwanted effects such as hypotension and to provide more stable hemodynamic conditions, especially in vulnerable patient populations.

Unilateral spinal anesthesia is defined as achieving sensory and motor block predominantly on the operated side without significant contralateral spread. However, the factors influencing the success of this technique have not been fully clarified.

This study will evaluate various patient-related and procedure-related factors, including age, sex, body mass index, patient positioning, needle type and orientation, injection technique and local anesthetic dose. The primary outcome is the success of unilateral spinal anesthesia, defined as the absence of contralateral block.

The results of this study are expected to contribute to improving clinical practice by identifying major and minor factors affecting block success and optimizing anesthesia techniques.

Study Overview

• Status: Completed
• Conditions: Regional Anaesthesia; Spinal Aneshtesia; Unilateral Spinal Anesthesia

Detailed Description

This prospective observational study is designed to investigate the factors influencing the success of unilateral spinal anesthesia in patients undergoing lower extremity orthopedic surgery.

Spinal anesthesia is widely used in lower extremity procedures; however, it may be associated with hemodynamic instability such as hypotension. Unilateral spinal anesthesia has been proposed as a technique to limit sympathetic blockade and maintain more stable hemodynamic conditions. Despite its advantages, the determinants of successful unilateral block remain unclear.

Patients aged between 18 and 65 years with American Society of Anesthesiologists (ASA) physical status I-III who are scheduled for elective lower extremity surgery will be included in the study after providing written informed consent. This study will be conducted in a single tertiary care center.

No intervention will be performed by the investigator. All anesthesia procedures will be carried out according to routine clinical practice. The investigator will record patient demographics, including age, sex, height, weight, and body mass index.

Procedure-related variables such as patient positioning, spinal needle type, needle orientation, injection speed, level of injection, local anesthetic type and dose will be recorded.

Block characteristics will be assessed intraoperatively, including sensory and motor block distribution. The primary outcome is defined as successful unilateral spinal anesthesia, characterized by the absence of contralateral sensory block. Secondary outcomes include factors associated with block success and variability in block characteristics.

Data will be collected using standardized case report forms and analyzed to identify factors influencing the success of unilateral spinal anesthesia. The results of this study are expected to contribute to optimizing anesthesia techniques and improving patient safety.

• Study Type: Observational
• Enrollment (Actual): 318

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Izmir, Turkey (Türkiye)
    • İzmir City Hospital

Participation Criteria

Eligibility Criteria

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

• Sampling Method: Non-Probability Sample

Study Population

Adult patients aged 18-65 years with ASA physical status I-III undergoing elective unilateral lower extremity surgery under spinal anesthesia in a single tertiary care center.

Description

Inclusion Criteria:

• Patients aged 18-65 years
• ASA physical status I-III
• Undergoing elective unilateral lower extremity surgery under spinal anesthesia
• Provided written informed consent

Exclusion Criteria:

• ASA IV patients
• Known allergy to local anesthetics
• Contraindications to spinal anesthesia
• Decompensated congestive heart failure
• Hemodynamic instability (including sepsis, septic shock, or need for inotropic support)
• Pregnancy
• Patients with vertebral anomalies (e.g., scoliosis, vertebral fractures) preventing proper positioning

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort
patients undergoing unilateral spinal anesthesia; Patients aged 18-65 years with ASA physical status I-III undergoing elective unilateral lower extremity surgery under spinal anesthesia.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Unilateral Spinal Block Success Rate	Successful unilateral spinal anesthesia defined as the absence of contralateral sensory block, assessed by pinprick test and bromage scale within the first 20 minutes after spinal anesthesia.	Intraoperative period (within first 30 minutes after spinal anesthesia

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Rate of unilateral spinal anesthesia success by age	Proportion (%) of patients achieving unilateral spinal anesthesia success across age groups.	Intraoperative period
Rate of unilateral spinal anesthesia success by BMI	Proportion (%) of patients achieving unilateral spinal anesthesia success across age groups.	Intraoperative period
Rate of unilateral spinal anesthesia success by position	Proportion (%) of unilateral spinal anesthesia success by patient positioning during injection (lateral vs sitting).	Intraoperative period
Rate of unilateral spinal anesthesia success by needle type	Proportion (%) of unilateral spinal anesthesia success by spinal needle type (Quincke vs pencil-point).	Intraoperative period
Rate of unilateral spinal anesthesia success by needle gauge	Proportion (%) of unilateral spinal anesthesia success by needle gauge.	Intraoperative period
Rate of unilateral spinal anesthesia success by local aneshtetic dose	Proportion (%) of unilateral spinal anesthesia success by administered local anesthetic dose (mg).	Intraoperative period
Rate of unilateral spinal anesthesia success by injection speed	Proportion (%) of unilateral spinal anesthesia success by injection speed category (faster vs ≤1 mL/5 s).	Intraoperative period
Sensory Block Level and Distribution	Assessment of sensory block level (dermatomal level) and comparison between operated and non-operated sides.	Intraoperative period
Rate of unilateral spinal anesthesia success by intervertebral level of spinal injection	Proportion (%) of unilateral spinal anesthesia success by intervertebral level (L1-2,L2-3,L3-L4 ,L4-L5).	Intraoperative period

Collaborators and Investigators

• Sponsor: Izmir City Hospital
• Investigators: Principal Investigator: Derya Arslan Yurtlu, MD, İzmir City Hospital

Study record dates

Study Major Dates

• Study Start (Actual): August 10, 2025
• Primary Completion (Actual): February 1, 2026
• Study Completion (Actual): February 1, 2026

Study Registration Dates

• First Submitted: April 9, 2026
• First Submitted That Met QC Criteria: May 6, 2026
• First Posted (Actual): May 12, 2026

Study Record Updates

• Last Update Posted (Actual): May 12, 2026
• Last Update Submitted That Met QC Criteria: May 6, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: regional anesthesia; lower extremity surgery; unilateral spinal anesthesia; spinal block success; anesthesia technique; block distribution
• Other Study ID Numbers: UNISS-2025

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared due to patient confidentiality and institutional data protection policies