Correspondence  |   December 2008
Minimizing the Risk of Intravascular Injection during Ultrasound-guided Peripheral Nerve Blockade
Author Affiliations & Notes
  • Richard Brull, M.D., F.R.C.P.C.
  • *Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada.
Article Information
Correspondence   |   December 2008
Minimizing the Risk of Intravascular Injection during Ultrasound-guided Peripheral Nerve Blockade
Anesthesiology 12 2008, Vol.109, 1142. doi:10.1097/ALN.0b013e31818dd8aa
Anesthesiology 12 2008, Vol.109, 1142. doi:10.1097/ALN.0b013e31818dd8aa
To the Editor:  —We read with interest the recently published case reports by Loubert et al.  1 and Zetlaoui et al.  2 regarding suspected inadvertent intravascular injection of local anesthetic (LA) and LA toxicity during ultrasound-guided axillary brachial plexus blockade. While ultrasound likely reduces the risk of accidental vascular puncture compared with “blind” peripheral nerve stimulation,3 these two case reports demonstrate that the risk of intravascular injection persists despite ultrasound guidance.1,2 In 2006 and 2007 at the Toronto Western Hospital, we performed 1,797 ultrasound-guided brachial plexus blocks without any sign or symptom of LA toxicity. Good fortune notwithstanding, there are several important principles that merit thoughtful consideration to improve detection of accidental intravascular injection and possibly prevent LA toxicity during ultrasound-guided peripheral nerve blockade. We believe that the most reliable feature during real-time ultrasound imaging indicative of intravascular injection is the failure to visualize a hypoechoic fluid bolus on the ultrasound monitor during and/or after injection of as little as 1 ml of injectate. Indeed, we customarily initiate LA injection with a 1-ml bolus to exclude intravascular or intraneural4,5 needle tip placement before proceeding with 5-ml increments of injectate. Visualization of the needle tip does not preclude intravascular injection per se  ; it is the real-time observation of hypoechoic fluid causing tissue dispersion that most consistently excludes intravascular injection. The absence of a discernible extraneural hypoechoic fluid bolus on the ultrasound monitor means that either the needle tip is intravascular or the plane of imaging is inaccurate.
We are also hesitant to recommend the use of ultrasound for perivascular block techniques as described by Loubert et al.  1 Rather, we contend that perineural LA deposition is the safest application of ultrasound technology. There can be multiple veins traveling alongside landmark pulsatile arteries, especially in the axilla. Veins are exquisitely collapsible with even the slightest amount of pressure applied by the transducer to the skin, and can therefore vanish from sonographic view, fooling even the most experienced providers, as demonstrated by these two recent case reports.1,2 We therefore use systematic scanning of the intended block site before needle insertion. Our systematic sonographic survey includes sliding the transducer distally and proximally to trace the target nerve along its expected course and examine the surrounding vasculature and tissues. Scanning is performed with varying degrees of pressure, with and without the use of color Doppler, to identify any hazards that may cross the planned trajectory of the needle. In addition, applying pulse wave Doppler over a nearby vessel during perineural injection may help to detect inadvertent intravascular injection by the characteristic high-pitch sound of turbulent flow associated with a sudden rush of fluid. Finally, however contentious,6 we strongly believe that patients undergoing ultrasound-guided peripheral nerve blockade should remain awake with judicious sedation so that signs and symptoms of LA toxicity can be recognized, communicated, and treated immediately upon onset.
*Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada.
Loubert C, Williams SR, Helie F, Arcand G: Complication during ultrasound-guided regional block: Accidental intravascular injection of local anesthetic. Anesthesiology 2008; 108:759–60Loubert, C Williams, SR Helie, F Arcand, G
Zetlaoui PJ, Labbe JP, Benhamou D: Ultrasound guidance for axillary plexus block does not prevent intravascular injection. Anesthesiology 2008; 108:761Zetlaoui, PJ Labbe, JP Benhamou, D
Maalouf D, Gordon M, Paroli L, Tong-Ngork S: Ultrasound-guidance versus  nerve stimulation for the infraclavicular blockade of the brachial plexus: A comparison of the vascular puncture rate. Reg Anesth Pain Med 2006; 30:A46Maalouf, D Gordon, M Paroli, L Tong-Ngork, S
Brull R, Chan VW, McCartney CJ, Perlas A, Xu D: Ultrasound detects intraneural injection (letter). Anesthesiology 2007; 106:1244Brull, R Chan, VW McCartney, CJ Perlas, A Xu, D
Chan VW, Brull R, McCartney CJ, Xu D, Abbas S, Shannon P: An ultrasonographic and histological study of intraneural injection and electrical stimulation in pigs. Anesth Analg 2007; 104:1281–4Chan, VW Brull, R McCartney, CJ Xu, D Abbas, S Shannon, P
Lee M, Howell K: Regional anesthesia may be performed in adult patients under general anesthesia: Pro/Con. Am Soc Reg Anesth Pain Med Newsletter 2008; February:6–8