Ultrasound and the Femoral Three-in-One Nerve Block

To the Editor: I wish to make a few comments regarding Marhofer et al.'s interesting and novel article on the ultrasonic performance of the femoral 3-in-1 nerve block [1]. First, I would suggest that the anesthesia community find some politically correct way to reflect the controversy that exists regarding the existence of the femoral 3-in-1 block [2]. I use a portable Doppler device to facilitate the performance of nerve blocks in difficult patients-the concept of localizing the neural structures by virtue of their proximity to vascular structures is not new. I would define difficult patients as those in whom there are anatomical challenges, such as morbid obesity. I agree with the authors that the use of ultrasound technology (or Doppler) can improve success rates in this subpopulation. However, I disagree with the conclusion that the use of ultrasound can shorten latencies, improve the quality of sensory block, and increase the overall success rate of any nerve block! The single most important factor in the success or failure of any nerve block is where the local anesthetic is injected [3]. The authors provide insufficient information for the reader to know whether the nerve stimulator was used properly. In addition, the study was not blind, which adds an element of bias to the results. For example, the authors could have performed both techniques in rapid serial fashion, using either saline or local anesthetic in a double-blind manner-nerve stimulator followed by ultrasound-in all patients, and the assessments could have been performed by an individual blinded to the technique. The authors suggest that the use of ultrasound will decrease the volume of local anesthetic required for the successful performance of femoral 3-in-1 nerve blocks [1]. The proper use of a nerve stimulator can also achieve that goal [4,5]. The authors use inadequate methodology when assessing blockade of the obturator nerve. Investigators must learn to use assessment of adductor motor power (or a surrogate end point such as motor evoked potentials) to assess the occurrence of successful conduction blockade of the obturator nerve [2]. Subsequently, the authors' conclusions about the relative frequency of blocking the obturator nerve are in error-conduction block of the parent trunk of the obturator nerve cannot be ascertained by cutaneous sensory assessment. Contrary to popular belief, the obturator nerve has no consistent cutaneous sensory contribution to the thigh [6]. In summary, I agree that the use of ultrasound may be useful in cases in which the anatomical landmarks are difficult to identify. However, the allegations that ultrasound will shorten onset time and improve the quality of sensory block are unfounded. Scott A. Lang, FRCPC Department of Anaesthesia; Foothills Hospital; Calgary, Alberta, Canada T2N 2T9