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The effect of obesity on neuraxial technique difficulty in pregnant patients: a prospective, observational study. Anesth Analg 2009 Oct;109(4):1225-31



Pubmed ID




Scopus ID

2-s2.0-70349569213 (requires institutional sign-in at Scopus site)   69 Citations


BACKGROUND: Practitioners often presuppose that obesity will increase neuraxial technique difficulty in pregnant patients, but few investigators have systematically examined this population for risk factors associated with difficult epidural or spinal needle placement. We designed this study to prospectively identify factors that predict neuraxial technique difficulty in pregnant patients.

METHODS: Using a prospective, observational format, pregnant patients were examined for multiple potential risk factors for neuraxial technique difficulty, including current body mass index, ability to palpate spinous processes, maximum back flexion, scoliosis, and experience of the practitioner. Neuraxial technique difficulty was then assessed using two measures: 1) the number of needle passes needed to reach the desired space, and 2) the placement time from skin infiltration to either spinal injection or epidural catheter threading. Predictors of total needle passes were determined by fitting the data to a generalized linear model with negative binomial error. Predictors of neuraxial anesthetic time were determined by fitting a linear model to the log of neuraxial anesthetic placement time. A survival model was used to account for bias introduced when attending physicians intervened in resident physician procedures.

RESULTS: Neuraxial procedures in 427 pregnant patients were studied. For both the number of needle passes and the neuraxial anesthetic placement time, the significant predictors of difficulty were the practitioner's ability to palpate the patient's bony landmarks and the patient's ability to flex her back. Obesity, as measured by body mass index, was not an independent predictor of either end point. Obesity did, however, strongly predict both the ability to palpate landmarks and flex the back.

CONCLUSIONS: Despite concerns that obesity may cause difficulty with neuraxial technique, some obese patients have surprisingly easy neuraxial block placements. When approaching any neuraxial anesthetic in a pregnant patient, and especially in the obese parturient, back flexion and landmark palpation predict neuraxial technique difficulty.

Author List

Ellinas EH, Eastwood DC, Patel SN, Maitra-D'Cruze AM, Ebert TJ


Thomas J. Ebert MD, PhD Vice Chair, Professor in the Anesthesiology department at Medical College of Wisconsin
Elizabeth H. Ellinas MD Associate Dean, Professor in the Anesthesiology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Body Mass Index
Clinical Competence
Injections, Epidural
Injections, Spinal
Internship and Residency
Linear Models
Logistic Models
Medical Staff, Hospital
Muscle Contraction
Muscle, Skeletal
Proportional Hazards Models
Prospective Studies
Risk Assessment
Risk Factors
Time Factors