Ultrasound Guided Procedures
Dr Peter Hebbard
Wangaratta and St Vincent’s Hospitals Victoria
For most anaesthetists, procedures assisted with ultrasound will mean vascular access and nerve blocks. There is a range of other potential ultrasound applications including detection of pneumothorax, drainage of pericardial, plural and ascetic fluid and location of foreign bodies.
The evidence demonstrating the advantages of ultrasound assisted CVC placement is extensive particularly in the Emergency Medicine literature. Both the UK National Institute of Clinical Excellence (NICE) in 2002 and the USA Agency for Healthcare Research and Quality (AHRQ) in 2001 recommended the use of real-time ultrasound guidance during central line insertion via the internal jugular route. Although this recommendation has been challenged particularly for experienced operators, there is an increasing evidence base showing faster access, less failure, lower numbers of needle passes and fewer complications. Training in the landmark technique can occur while also using ultrasound, as the approach is the same and such a critical technique should not be dependent on the availability of technology. Other routes of CVC insertion under ultrasound have been described, however there is currently no evidence base supporting their superiority over conventional techniques.
Performing nerve blocks under ultrasound guidance is becoming routine in many institutions. There is evidence for improved onset and block quality for many approaches including the supraclavicular, infraclavicular, axillary, ilioinguinal and femoral block. Potential safety advantages include avoidance and early detection of intravascular or intraneural injection along with the ability to image the needle tip during the insertion to avoid major blood vessels, pleura and to image the spread of the local anaesthetic. Improved safety is currently unproven and as nerve blocks by conventional techniques have a very good safety record that data may never be proven by randomized controlled trial evidence. There is a trend in many studies to reduced complications such as paraesthesias, vascular and peritoneal puncture.
The range of nerve blocks that can be achieved under ultrasound guidance is extensive. Many more approaches are possible than with anatomical landmark techniques. Limitations occur with deep nerves and those behind bones including the central neuraxis, lumbar plexus and the sciatic nerve above the greater trochanter. The practice of ultrasound guided blocks extends past the visualization of blockable nerves to the identification of tissue planes in which to infuse local anaesthetics.
Ultrasound guided nerve blockade requires knowledge of the physics and limitations of ultrasound, detailed knowledge of the anatomy, the ultrasound appearance of structures and eye/hand coordination skills. Starting from a position of experience in conventional nerve blockade ultrasound skills can be added on incrementally once basic instruction and a knowledge base is obtained. It is important to not forget the basic skills and precautions of nerve blockade when applying ultrasound. Loss of imaging of the needle tip with blind advancement has been shown to be the greatest hazard when learning ultrasound techniques.
Training and credentialing in ultrasound is being considered by both anaesthetists and administrators. Many good short courses are becoming available which provide the basic knowledge and skill however considerable practice and machine familiarity may be still required.
Nerves maybe imaged in transversely (short axis) or longitudinally (long axis). Short axis imaging of nerves is preferred for placing nerve blocks. The needle may be introduced either in the plane or across the plane of the ultrasound beam. Although each approach has strengths I strongly favour the in plane approach if possible due to the superior needle imaging possible particularly if the needle is introduced perpendicular to the beam, (Often possible by moving the needle insertion site a few cm away around the natural curve of the body surface). Block needles may be poorly imaged by ultrasound, larger size and a more perpendicular orientation to the ultrasound beam will enhance the image.
Nerve stimulators help to confirm nerve identity particularly during learning or teaching. One recent series found no advantage in block effectiveness using a nerve stimulator. The use of nerve stimulators as a reliable way of assessing whether the needle is intra-neural before injection is poorly supported by objective evidence. Paraesthesia and ultrasound studies have shown a 10 to 20% incidence of lack of stimulation at high currents (>0.9mA) when needles are in apparent contact with nerves. Ultrasound offers alternative means of assessing the position of the needle tip and the absence of intra-neural injection through direct visualization of needle, nerve and spread of injectate. The use of ultrasound to avoid direct nerve damage and intra-neural injection is however also unsupported by objective evidence.
The most exciting part of ultrasound guided regional anaesthesia is the ability to perform new blocks which extend the therapeutic options. There are probably no blocks possible with ultrasound that have not been done by the conventional regional enthusiast equipped with a long needle, stout heart and lots of local. There are however a number of new approaches that are difficult or unreliable (at least in my hands) performed by the conventional approach which are very straightforward with ultrasound. These include the precise localization and blockade of the major peripheral nerves in the arm and forearm as well as blockade of the sciatic nerve between the buttock and the popliteal fossa.
Precise localization of the anatomical planes of the abdominal wall is possible making major regional blockade of the somatic anterior abdominal wall an effective option for many types of abdominal surgery. The recently described Transversus Abdominis Plane (TAP) block for post operative analgesia is the outstanding example of this. Placement through an anterior ultrasound guided approach is simple and can be performed bilaterally without the operator changing sides. Catheters for continuous infusion may also be placed. In my practice this has become the most commonly placed regional block and is suitable for analgesia for any lower to mid abdominal incision including laparotomy, caesarean section, hernia repair and appendicetomy. Sub costal positioning of the block may extend the effectiveness to upper abdominal incisions.
References and Further Reading
1. The Agency for Healthcare Research and Quality Evidence Report/Technology Assessment, No. 43 Making Health Care Safer A Critical Analysis of Patient Safety Practices Chapter 21. Ultrasound Guidance of Central Vein Catheterization www.ahrq.gov/clinic/ptsafety/chap21.htm
2. National Institute for Clinical Excellence TA49 Central venous catheters - ultrasound locating devices: Guidance http://www.nice.org.uk/page.aspx?o=TA049guidance
3. Sabbaj A, Hedges JR.
Ultrasonographic guidance for internal jugular vein cannulation: an educational imperative, a desirable practice alternative.
Ann Emerg Med. 2006 Nov;48(5):548-50.
4. Marhofer P, Greher M, Kapral S. Ultrasound guidance in regional anaesthesia. Br J Anaesth2005;94:7-17.
5. Gray AT. Ultrasound-guided regional anesthesia: current state of the art. Anesthesiology. 2006 Feb;104(2):368-73
6. Schafhalter-Zoppoth I, McCulloch CE, Gray AT. Ultrasound visibility of needles used for regional nerve block: an in vitro study. Reg Anesth Pain Med. 2004 Sep-Oct;29(5):480-8.
7. Beach ML, Sites BD, Gallagher JD.Use of a nerve stimulator does not improve the efficacy of ultrasound-guided supraclavicular nerve blocks.J Clin Anesth. 2006 Dec;18(8):580-4.
8. Hebbard P, Barrington M, Royse C, Ultrasound Guided Procedures in Anaesthesia www.Heartweb.com.au
9. Sites BD, Spence BC, Gallagher JD, Wiley CW, Bertrand ML, Blike GT.Characterizing novice behavior associated with learning ultrasound-guided peripheral regional anesthesia.Reg Anesth Pain Med. 2007 Mar-Apr;32(2):107-15.
10. McDonnell JG, O'Donnell B, Curley G, Heffernan A, Power C, Laffey JG.The analgesic efficacy of transversus abdominis plane block after abdominal surgery: a prospective randomized controlled trial.Anesth Analg. 2007 Jan;104(1):193-7.
