title: The effect of obesity on neuraxial technique difficulty in pregnant patients: a prospective, observational study.
abstract: 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.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA. libby@mcw.edu
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Ellinas
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Eastwood
authors.forename: Smita N
authors.initials: SN
authors.lastname: Patel
authors.forename: Anita M
authors.initials: AM
authors.lastname: Maitra-D'Cruze
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Ebert
mesh_terms: D000328:Adult; D015992:Body Mass Index; D002983:Clinical Competence; D005260:Female; D006801:Humans; D007268:Injections, Epidural / Q000009:adverse effects*; D007278:Injections, Spinal / Q000009:adverse effects*; D007396:Internship and Residency; D016014:Linear Models; D016015:Logistic Models; D008505:Medical Staff, Hospital; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology; D009765:Obesity / Q000150:complications* / Q000503:physiopathology; D010173:Palpation; D011247:Pregnancy; D016016:Proportional Hazards Models; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012600:Scoliosis / Q000209:etiology / Q000503:physiopathology; D013997:Time Factors