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Sumit Das
MB BS BSc FRCA
Consultant
Anaesthetist
John Radcliffe Hospital
Oxford
UK
Sean Neill
MB ChB FRCA
Resource Editor
Anaesthesia UK
Salisbury
UK
The use of ultrasound (US) by anaesthetists has increased markedly in recent times. Apart from imaging vessels for safe cannulation and guiding nerve blocks, it is also used in ITU to locate pleural effusions or ascites and to guide drainage. US may be used to assist the cannulation of arteries and both peripheral and central veins.
Ultrasound imaging uses the transmission and reflection of high-frequency longitudinal mechanical (“ultrasonic sound”) waves in tissues. These are created using the piezoelectric effect: using crystals to convert electrical to mechanical energy, and vice versa. Image information is provided by the energy from these waves as they are reflected from surfaces between different tissues. The reflections are due to differences in the mechanical properties of the tissues. Using wave propagation speed in tissues, time of reflection information can be converted into distance of reflection information. Image resolution and tissue penetration are functions of the ultrasound frequency. A 12 MHz scanhead has very good resolution but cannot penetrate very deeply into the body. A 3 MHz scanhead can penetrate deeply into the body, but the resolution is not as good as with the 12 MHz scanhead.
Central venous catheters (CVCs) are frequently utilised in anaesthesia and intensive care.(1) Approximately 200,000 central venous cannulation procedures are performed in the NHS each year.(2) CVCs have many uses, including haemodynamic monitoring; blood sampling; haemofiltration; and administering fluids, vasopressors, inotropes, antibiotics, cytotoxic drugs, parenteral nutrition and concentrated electrolyte solutions.(3)
CVCs are produced in many forms, but the insertion technique remains similar. Most systems require the Seldinger insertion technique: a guidewire is passed through a small needle into a central vein and the catheter threaded over this. Previously, the standard method for locating the vein was using anatomical landmarks, but failure to cannulate the vessel using this technique may occur in more than 19 % of patients. Success using the landmark technique depends on many variables, including access site chosen, operator’s level of experience, condition of the patient (including coagulation status), presence of atypical vascular anatomy and previous catheterisations or scarring in the area.
Continued failure to cannulate a central vein may lead to repeated attempts by multiple operators, increasing complication rates. This carries risks in terms of patient safety and costs in terms of patients’ discomfort, clinicians’ time and healthcare resources. Complications of CVC insertion can add to patient morbidity – and some may be life-threatening. The latter may include bleeding, infection, arterial puncture, venous tears, nerve damage, air embolism, thromboembolism, pneumothorax, incorrect positioning, arrhythmias, damage to valves or myocardium, and cardiac tamponade.
For more than 20 years, authors have recommended ultrasound guidance to improve cannulation success rates and minimise complications.(4) In 2002, the UK’s National Institute for Health and Clinical Excellence (NICE) stated that 2D imaging ultrasound guidance should be the preferred method when inserting a CVC into the internal jugular vein in adults and children in “elective situations”.(5) The guidelines on this topic support the routine use of this technology for the internal jugular route, but there is insufficient evidence to make recommendations on other sites of access.
In 2004, a survey of anaesthetists showed that only 36% agreed with the recommendation that 2D imaging ultrasound should be considered in clinical circumstances where CVC insertion is necessary (electively or in an emergency). Closer analysis of the data showed that 67% of those who disagreed with the main recommendation had not changed their use of this technology. This compared with 73% of those who had agreed with guidance having increased their use (35% had significantly increased use). The authors of this study concluded that concurrence with guidance recommendations was a driver of implementation and change.(6)
In infants, central venous cannulation remains challenging even for experienced paediatric anaesthetists. Ultrasound-guided techniques are proven to be safer for internal jugular vein catheterisation. But the subclavian vein (SCV) is often the preferred site for long-term central venous catheterisation in children. A recent study demonstrated that US-guided approach of the SCV offers a new possibility for central venous catheterisation in children of less than 10 kg and probably also for older children.(7) It allows checking the vessel patency before puncture and provides good-quality needle guidance.
As with any new device or technique, there are cost implications with regard to equipment, consumables and training. A systematic review of randomised controlled trials and an economic evaluation concluded that ultrasound guidance used in central venous cannulation procedures saves healthcare resources even with conservative modelling assumptions.(2)
With ongoing resource issues and budget restrictions, departments may be reluctant to approve large capital expenses. However, there has been much interest in the use of US to assist the placement of nerve blocks, and some think this may represent the gold standard in regional anaesthesia.(8) These high-resolution machines can also be used to assist with cannulation, and this will also make them more readily available. Over the next few years we can expect to see an increase in the use of US in
anaesthesia.
References
1. Muhm M. Ultrasound guided central venous access. BMJ 2002;325:1373-4.
2. Calvert N, et al. Ultrasound for central venous cannulation: economic evaluation of cost-effectiveness. Anaesthesia 2004;59(11):1116.
3. Rosen M, Latto P, Ng S. Percutaneous central venous catheterisation. London: Saunders; 1992.
4. Legler D, Nugent M. Doppler localization of the internal jugular vein facilitates central venous cannulation.
Anesthesiology 1984;60(5):481-2.
5. National Institute for Health and Clinical Excellence. Guidance on the use of ultrasound locating devices for
placing central venous catheters. NICE
technology appraisal 49. London: NICE; 2002.
6. National Institute for Health and Clinical Excellence. A survey measuring the impact of NICE technology appraisal 49. London: NICE; 2004.
7. Pirotte T, Veyckemans F. Ultrasound-guided subclavian vein cannulation in infants and children: a novel approach. Br J Anaesth 2007;98(4):509-14.
8. Hopkins PM.
Ultrasound guidance as a gold standard in regional anaesthesia. Br J Anaesth 2007;98(3):299-301.
Resource
European Society of Anaesthesiology
W: www.euroanesthesia.org
