◊ 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.
◊ Reviewed by M. Van de Velde MD. PhD.
Department of Anaesthesiology, UZLeuven, Leuven, Belgium
The present paper is about a prospective, observational study to evaluate risk factors for neuraxial anesthesia difficulty in obstetric patients.
The practitioner’s ability to palpate the bony landmarks and the ability of the patient to flex her back were independent risk factors for neuraxial anesthetic difficulty whereas obesity was not. However, obesity was associated with both risk factors. So indirectly in some patients obesity was a risk factor, but not in all!
The study has been well performed, uses adequate statistical techniques and evaluates several potential risk factors. Unfortunately, the study population is small and this may have influenced results. It is also unfortunate that operator experience was only briefly mentioned as authors plan to publish these results separately. Personally, I am looking to learn whether operator experience has an effect in this patient population.
The authors clearly describe the limitations and weaknesses of their study. I would like to add that they could have evaluated if ultrasound makes the anesthetic easier or not. However, two important lessons can be learned from this publication:
- Neuraxial anesthesia is complicate in some cases of obese patients, but remarkably simple in others.
- More important factors to predict neuraxial anesthesia difficulty are the ease to palpate landmarks and the ability of patients to flex their back.
So from a clinical perspective, the initial patient evaluation and especially the patient’s back is what we should focus on as anesthesiologists!
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