Effect of Obesity Phenotype on Intraabdominal Pressure and Bleeding in Major Lumbar Spinal Surgery (OBESPINE)

Effect of Obesity Phenotype on Intraabdominal Pressure, Intraoperative Bleeding, and Perioperative Complications in Patients Undergoing Major Lumbar Spinal Surgery: A Prospective Observational Study

Obesity is prevalent among patients with lumbar degenerative disease and is a known risk factor for perioperative complications in spinal surgery. However, most existing evidence relies solely on body mass index (BMI) without distinguishing between central and peripheral obesity phenotypes. Central and peripheral fat distribution may have distinct biomechanical and hemodynamic consequences, particularly with respect to intraabdominal pressure (IAP) changes during prone positioning and intraoperative blood loss.

This prospective single-center observational study aims to evaluate the effect of obesity phenotype - classified as non-obese, centrally obese, or peripherally obese based on BMI and waist-to-hip ratio - on intraabdominal pressure, intraoperative blood loss, and other perioperative outcomes in adult patients undergoing major lumbar spinal surgery (decompression and/or instrumentation)

Study Overview

• Status: Not yet recruiting
• Conditions: Obesity; Lumbar Spinal Stenosis; Intraabdominal Hypertension; Intraoperative Blood Loss; Perioperative Complications; Lumbar Degenerative Disease
• Intervention / Treatment: Other: Intraabdominal Pressure Measurement via Urinary Bladder Catheter; Other: Total Intravenous Anesthesia (TIVA)

Detailed Description

Major lumbar spinal surgery, including lumbar canal stenosis decompression and instrumented fusion, is associated with substantial intraoperative blood loss and notable perioperative morbidity. Obesity is highly prevalent in this patient population due to its role in lumbar degenerative disease pathogenesis. Prone positioning during surgery significantly increases intraabdominal pressure, which in turn may impair venous drainage from the spinal epidural plexus, thereby augmenting operative blood loss. While BMI has been studied as a predictor of spinal surgical outcomes, the differential impact of fat distribution pattern (central vs. peripheral obesity) on IAP dynamics and bleeding has not been adequately characterized.

Study Design:

Prospective, single-center, observational cohort study conducted at Marmara University Pendik Training and Research Hospital and Asaf Ataseven Hospital, Istanbul, Turkey. No interventions beyond routine clinical anesthesia practice will be performed.

Patient Groups:

Patients will be categorized into three groups based on BMI and waist-to-hip ratio (WHR):

• Group NO (Non-obese): BMI <30 kg/m² (n=30)
• Group PO (Peripheral obese): BMI ≥30 kg/m² and WHR <0.85 (n=30)
• Group CO (Central obese): BMI ≥30 kg/m² and WHR ≥0.85 (n=30)

Anesthetic Protocol:

All patients will receive standard intraoperative monitoring (ECG, non-invasive blood pressure, pulse oximetry, end-tidal CO₂, BIS). Anesthesia will be induced with propofol 2 mg/kg, fentanyl 2 µg/kg, and rocuronium 0.6 mg/kg, and maintained with total intravenous anesthesia (TIVA) using propofol and remifentanil infusion, consistent with the institutional protocol for neuromonitoring-guided spinal surgery. Adjusted body weight will be used for drug dosing in obese patients.

Intraabdominal Pressure Measurement:

IAP will be measured via urinary bladder catheter (standard intravesical technique) at three time points: (1) supine position after intubation, (2) prone position, and (3) supine position at the end of surgery.

Data Collection:

Preoperative: age, sex, BMI, weight, height, waist and hip circumferences, WHR, ASA classification, comorbidities, baseline hemogram, BUN, creatinine, INR, aPTT, anticoagulant/antiplatelet use.

Intraoperative: surgical procedure type and level, revision status, anesthesia and surgery duration, neuromonitoring use, hemodynamic parameters at standardized time points, estimated blood loss, fluid and blood product administration, vasopressor/inotrope use, urine output, cell saver use.

Postoperative: hemoglobin and hematocrit drop, BUN, creatinine at 24 hours, Aldrete score, VAS score, ICU admission and indication, postoperative complications (surgical and medical), transfusion requirements, and total hospital length of stay.

Statistical Analysis:

SPSS 21.0 will be used. Continuous variables will be reported as mean ± SD or median (IQR) depending on normality (Kolmogorov-Smirnov/Shapiro-Wilk). Categorical variables will be reported as n (%). Between-group comparisons will employ one-way ANOVA or Kruskal-Wallis test for continuous variables and chi-square or Fisher's exact test for categorical variables. Post-hoc pairwise comparisons will be performed with appropriate correction. Significance threshold: p<0.05.

Sample Size:

Based on published BMI-stratified spinal surgery data, a minimum of 90 patients (30 per group) is required to achieve 80% power at α=0.05 (G*Power 3.1).

• Study Type: Observational
• Enrollment (Estimated): 90

Contacts and Locations

• Study Contact: Name: Dilara Göçmen, asst prof; Phone Number: +90 216 625 45 45; Email: dilara.gocmen@marmara.edu.tr
• Study Contact Backup: Name: Seniyye Ülgen Zengin, Assoc Prof; Email: szengin@marmara.edu.tr

Participation Criteria

Eligibility Criteria

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

• Sampling Method: Probability Sample

Study Population

Adult patients aged 18-80 years with ASA physical status I-III scheduled for elective major lumbar spinal surgery (decompression and/or instrumentation) at Marmara University Pendik Training and Research Hospital and Asaf Ataseven Hospital, Istanbul, Turkey. Patients are classified by obesity phenotype based on BMI and waist-to-hip ratio. Patients with renal failure, coagulation disorders, anemia, pregnancy, prior lumbar surgery, or emergency procedures are excluded.

Description

Inclusion Criteria:

• Age 18-80 years
• ASA Physical Status Classification I-III
• Scheduled for elective major lumbar spinal surgery (canal stenosis decompression and/or instrumented fusion)
• No prior lumbar spinal surgery
• Written informed consent obtained

Exclusion Criteria:

• - Pediatric patients (<18 years)
• Pregnancy
• Emergency surgical procedures
• Pre-existing renal failure
• Coagulation disorder
• Pre-existing anemia
• Known drug allergy relevant to study medications
• Inability to obtain written informed consent

Study Plan

How is the study designed?

Number of groups / cohorts

3

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Group 1 - Non-Obese (NO); BMI <30 kg/m². Adult patients undergoing major lumbar spinal surgery without obesity. Target n=30.	Other: Intraabdominal Pressure Measurement via Urinary Bladder Catheter; Intravesical intraabdominal pressure measurement performed via indwelling urinary catheter at three standardized time points: supine position after intubation, prone position during surgery, and supine position at end of surgery. This measurement is performed as part of observational data collection within the scope of routine catheterization; no additional invasive procedure is applied.; Other: Total Intravenous Anesthesia (TIVA); Standardized TIVA protocol applied uniformly to all patients per institutional neuromonitoring-guided spinal surgery protocol. Induction with propofol 2 mg/kg, fentanyl 2 µg/kg, and rocuronium 0.6 mg/kg; maintenance with propofol and remifentanil infusion. Adjusted body weight used for drug dosing in obese patients. No study-specific modification to routine anesthetic management is performed. Arm Label: All Groups (NO, PO, CO)
Group 2 - Peripheral Obese (PO); BMI ≥30 kg/m² and waist-to-hip ratio <0.85. Patients with predominantly peripheral (gynoid) fat distribution. Target n=30.	Other: Intraabdominal Pressure Measurement via Urinary Bladder Catheter; Intravesical intraabdominal pressure measurement performed via indwelling urinary catheter at three standardized time points: supine position after intubation, prone position during surgery, and supine position at end of surgery. This measurement is performed as part of observational data collection within the scope of routine catheterization; no additional invasive procedure is applied.; Other: Total Intravenous Anesthesia (TIVA); Standardized TIVA protocol applied uniformly to all patients per institutional neuromonitoring-guided spinal surgery protocol. Induction with propofol 2 mg/kg, fentanyl 2 µg/kg, and rocuronium 0.6 mg/kg; maintenance with propofol and remifentanil infusion. Adjusted body weight used for drug dosing in obese patients. No study-specific modification to routine anesthetic management is performed. Arm Label: All Groups (NO, PO, CO)
Group 3 - Central Obese (CO); BMI ≥30 kg/m² and waist-to-hip ratio ≥0.85. Patients with predominantly central (android) fat distribution. Target n=30	Other: Intraabdominal Pressure Measurement via Urinary Bladder Catheter; Intravesical intraabdominal pressure measurement performed via indwelling urinary catheter at three standardized time points: supine position after intubation, prone position during surgery, and supine position at end of surgery. This measurement is performed as part of observational data collection within the scope of routine catheterization; no additional invasive procedure is applied.; Other: Total Intravenous Anesthesia (TIVA); Standardized TIVA protocol applied uniformly to all patients per institutional neuromonitoring-guided spinal surgery protocol. Induction with propofol 2 mg/kg, fentanyl 2 µg/kg, and rocuronium 0.6 mg/kg; maintenance with propofol and remifentanil infusion. Adjusted body weight used for drug dosing in obese patients. No study-specific modification to routine anesthetic management is performed. Arm Label: All Groups (NO, PO, CO)

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Intraoperative Blood Loss	Total estimated blood loss (mL) calculated from suction canister volume and surgical sponge weight.	Intraoperative
Intraabdominal Pressure (IAP)	Intravesical IAP measurement (mmHg) via urinary bladder catheter at positional transitions during surgery	Three intraoperative time points from beginning to end: 1.supine after intubation, 2.prone position, and 3.supine at end of surgery

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Intraoperative Transfusion Requirement	Number of units of packed red blood cells, fresh frozen plasma, and platelet concentrate administered intraoperatively	Intraoperative
Postoperative Hemoglobin Drop	Difference between preoperative and postoperative hemoglobin levels (g/dL).	Within 24 hours postoperatively
Vasopressor/Inotrope Requirement	Type and cumulative dose of vasopressor or inotropic agents administered intraoperatively.	Intraoperative
Postoperative Transfusion Requirement	Postoperative blood product transfusion rate and indication (Hb <7 g/dL, hemodynamic instability, ongoing bleeding).	up to 7 days postoperatively
Postoperative ICU Admission Rate	Proportion of patients requiring ICU admission and primary indication (hemodynamic instability, respiratory failure, excessive bleeding, neurological complication).	postoperative day 1
Postoperative Surgical Complications	Wound infection, deep infection, seroma/hematoma, CSF fistula, neurological deficit, revision surgery requirement	Up to 30 days postoperatively
Postoperative Medical Complications	Acute kidney injury, deep vein thrombosis, pulmonary embolism, pneumonia, atelectasis, cardiac events, delirium, urinary tract infection.	Up to 30 days postoperatively
Hospital Length of Stay	Total duration of hospital stay in days(up to 30 days postoperatively),	From surgery to hospital discharge, assessed up to 30 days
Acute Kidney Injury Incidence	Presence of acute kidney injury assessed according to KDIGO (Kidney Disease: Improving Global Outcomes) criteria.	Time Frame: Within 24 hours postoperatively

Collaborators and Investigators

• Sponsor: Marmara University Pendik Training and Research Hospital

Study record dates

Study Major Dates

• Study Start (Estimated): June 15, 2026
• Primary Completion (Estimated): May 1, 2027
• Study Completion (Estimated): June 1, 2027

Study Registration Dates

• First Submitted: May 2, 2026
• First Submitted That Met QC Criteria: July 5, 2026
• First Posted (Actual): July 7, 2026

Study Record Updates

• Last Update Posted (Actual): July 7, 2026
• Last Update Submitted That Met QC Criteria: July 5, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: perioperative hemorrhage; intraoperative blood loss; intraabdominal pressure; major spinal surgery; obesity phenotype
• Additional Relevant MeSH Terms: Bone Diseases; Musculoskeletal Diseases; Vascular Diseases; Cardiovascular Diseases; Muscular Diseases; Nutrition Disorders; Overnutrition; Body Weight; Spinal Diseases; Overweight; Compartment Syndromes; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity; Spinal Stenosis; Intra-Abdominal Hypertension
• Other Study ID Numbers: mu anesth

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

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