There is now much emphasis placed on dynamic and appropriate triage, with evidence clearly suggesting better outcomes when certain injuries are triaged directly to specialist centres (Sampalis et al, 1997; Sampalis et al. 1999). The ability to enhance decision-making skills at the scene will therefore be a welcome addition to the skills base of prehospital care practitioners. The use of a focused scanning approach means that training and initial competence are easy to accomplish and within a framework of audit and governance are easy to review and monitor.
In addition, prehospital ultrasound can guide the practitioner to make better, more informed decisions as to the feasibility and merits of further on–scene care. This means that findings of on– scene ultrasound can be used in an algorithmic approach as to the functional endpoint of on-scene care—thus avoiding unnecessary delay in reaching definitive care.
Ultrasound technology is relatively inexpensive and portable due to the now large number of competing providers in the marketplace.
Potential applications of ultrasound in prehospital care
In the prehospital setting, there are a number of important applications of medical ultrasound, both to aid in treatment and to make informed decisions regarding destination hospital. This second area requires impacts on how emergency services will interface with other primary and secondary care services.
In addition to the usage in trauma, paramedics and emergency care practitioners can bring ultrasound into a range of other scenarios. For example, detection of deep vein thrombosis by simple vascular assessment or recognition of certain fractures can allow referral to the appropriate specialist teams in secondary care.
In cases of resuscitation attempts, prehospital ultrasound can be used to guide effective fluid resuscitation, detect cardiac tamponade and to confirm myocardial standstill. The latter of these has, in the authors experience, empowered prehospital care physicians and paramedics to have more confidence in making what can be a difficult decision to discontinue a resuscitation attempt.
Indeed, emergency echocardiography may well become a ‘definitive’ test of cardiac resuscitation futility. The usefulness of ultrasound has been shown to be a sensitive indicator of prognosis (Volpicelli, 2010).
The training and accreditation of UK paramedics in emergency on scene ultrasound is innovative but well within the scope, abilities and remit of that profession. It does, however, need to be part of a physician–led service with a clear programme of training and clinical supervision.
There is, at present, an opportunity to develop an accreditation framework which is both efficient and yet appropriately rigorous. The authors suggest that a portfolio approach be used—this facilitates recognition of the experiential learning which has taken place in the workplace. In building a portfolio, the learner can avail of the guidance of any number of appropriately skilled mentors.
It is clear that progression of quality prehospital care lies not only in the ability to deliver additional critical care skills but is also reliant on the ability to make graduated and informed decisions related to a reproducible, reliable and sensible assessment modality. Ultrasound fulfils this and its role in prehospital care in the UK is now in its birthing phase. The following sections will now describe some of the areas that are covered in the emergency and prehospital ultrasound introductory course held at Imperial College, London.
‘In addition to the usage in trauma, paramedics and emergency care practitioners can bring ultrasound into a range of other scenarios’
Focused assessment with sonography in trauma (FAST)
The FAST scan has over the last few years become almost ubiquitous in emergency departments in the UK. A UK study reported that it is a good ‘rule in’ test which can effectively be used by medical personnel with a brief training period (Brenchley et al, 2006). More recently, FAST scan performed by non-medically qualified healthcare professionals have been shown to have similar sensitivity and specificity to that performed by their medical colleagues (Bowra et al, 2010). The basic premise of the FAST scan is that intra-abdominal bleeding will gravitate to the lowest points in the abdomen of a supine patient. Hence, the examiner follows a specific sequence of steps to interrogate these ‘usual suspect’ areas with the ultrasound scanner. Fluid including blood shows up as a dark homogenous area on ultrasound.
The scan also includes a view of the heart from the abdomen to evaluate for cardiac tamponade. This article will describe the extended FAST scan including assessment for pneumothorax in a subsequent section. Figure 1 shows a sub-xiphoid view—this facilitates a ‘four chamber view’ of the heart. Cardiac tamponade is noted as a dark rim around the heart. Following this, there are two upper abdominal views which assess for blood between the liver and kidney on the right (hepato-renal/Rutherford’s pouch) and the spleen and kidney on the left.
Emergency echocardiography in cardiac arrest and peri-arrest scenarios
This year, the Resuscitation Council UK has included in its guidance on adult resuscitation the statement: ‘There is no doubt that ultrasound imaging provides information that may help to identify reversible causes..’ (of cardiac arrest). The major issue with the introduction of ultrasound is that it should be done in an Advanced Life Support (ALS) compliant manner i.e. without interruption of chest compressions.
A prospective study in the prehospital setting reported that using an ALS compliant emergency echocardiography protocol alters management in 78% of cases (Breitkreutz et al, 2010). Emergency echocardiography can, in the very short 10 second ‘rhythm check’ window, offer an opportunity to evaluate whether the heart is generating co-ordinated contractions, fibrillating, which might not necessarily be detected on ECG, or whether there is no contractile activity at all.
Additionally, ultrasound diagnosis of cardiac tamponade and pulmonary embolus early on in resuscitative efforts may instigate appropriate treatment earlier than otherwise (Hernandez et al, 2008).
Pneumothorax
The sensitivity of ultrasound scan for detecting pneumothorax varies between 58.9% and 100%, and specificity varies between 94% and 100%. However, the study with the lowest sensitivity used CT as part of the gold standard—which may be a comment on CT finding very small pneumothoraces not seen on CXR of debatable relevance ( Jaffer and McAuley, 2005).
There are two main ultrasound ‘signs’ which have been employed in the detection of pneumothorax with ultrasound:
These signs are present in the normal lung. In a pneumothorax, air is present between the two pleural layers and hence the lung sliding and the comet tails cannot be visualized.
Abdominal aortic aneurysm (AAA)
The normal aorta has a diameter of 3 cm in men and 2.5 cm in women. The widely accepted rupture risk for an AAA over 7 cm in antero-posterior (AP) diameter is 75%.
A validation study found that Duplex ultrasound for AP measurement of the abdominal aorta estimated sensitivity of 98.9% and specificity of 99.9% for the distal aorta. For the proximal aorta, sensitivity was found to be slightly less at 87.4% and specificity of 99.9% (Lindholt et al, 1999).
The prehospital identification of an aneurysm of size greater than 5 cm in a patient with abdominal pain would be of great advantage in terms of choice of destination hospital. The need for this skill has become particularly acute in this age of centralisation of services where vascular surgery is frequently not available on an emergency basis in all hospitals.
Deep vein thrombosis (DVT)
Grey scale or B mode ultrasound is readily used to image veins. The technique of compression ultrasonography for DVT assessment relies on patent veins being compressible with probe pressure applied by the operator to the vein. Complete compression will not be possible of a vein in which thrombosis has occurred.
The rapidly performed technique of compression ultrasonography of just the femoral and popliteal segments has been evaluated in an emergency department setting.
Compared to a full Duplex ultrasound assessment, it had a sensitivity of 88.9% and specificity of 75.9%. negative predictive value was 95.7% (Frazee et al. 2001). This technique could readily be applied by prehospital practitioners and may be very interesting in terms of potentially purely primary care based management.
Limb tourniquet application
Tourniquets can be vital for haemorrhage control in a variety of trauma conditions. Vascular injury to the arms and legs is quite common in combat injury and is not uncommon in civilian blunt and penetrating trauma.
Tourniquet application to prevent haemorrhage in the prehospital care setting is of particular interest. Accuracy and efficacy of application are crucial to improvement in outcome—this may be an issue in the occasional user as there is some degree of subjectivity in tourniquet application. Better and more effective tourniquet application may result using ultrasound to visualize the target artery which needs to be occluded.
The course at Imperial College teaches a simple technique of tourniquet application based upon obliteration of Doppler ultrasound detected flow in the superficial femoral artery of the thigh.
Confirmation of arterial occlusion can be achieved by visualizing the artery in transverse section distal to the site of tourniquet application. Appropriate ultrasound-guided tourniquet adjustment will ensure that the artery is occluded without excess compression to the injured limb.
Training in medical ultrasound
There has been much discussion recently regarding the dissemination of diagnostic ultrasound into professions with little previous experience in its performance. The majority of responsible bodies who have made recommendations on this subject have advocated structured training involving both theoretical knowledge of ultrasound physics and image acquisition, as well as practical training in scanning. Due to the way we work as medical professionals today, we believe that a work based model should be adopted, potentially relying of multiple and opportunistic mentoring should be employed.
Some work has been done in defining how much practical experience is required to attain competence in ultrasound scanning (Eiberg et al, 2008). A clear learning curve can be demonstrated during which time the learner should be mentored and reliance not placed on the results obtained without confirmation by an experienced practitioner.
The Royal College of Radiology and the British Medical Ultrasound Society have agreed minimum standards of training following those of the European federation of societies for ultrasound in medicine and biology (EFSUMB). Clear importance has been given to both theoretical training, incorporating the physics of ultrasound and instrumentation as well as practical training (Board of the faculty of clinical radiology, 2005).
Emergency and prehospital ultrasound course
It must be remembered that ultrasound enhances the decision-making process—it does not replace it. The adage ‘There is no such thing as a negative’ ultrasound prehospital holds good and reinforces the need for it to be used in the hands of a clinical decision-maker rather than a technical user. Notwithstanding this, it is also important to realize that the basic skills required to use an ultrasound device for focused scanning are easy to learn and are well within the scope of the average paramedic and ECP. Its development into practice is somewhat reliant on trials and evaluation, but this is achievable with a sensible approach.
A short multidisciplinary course has been established to be run at the Hammersmith hospital in conjunction with other healthcare professionals to introduce the concepts outlined above.
An introduction to medical physics related to ultrasound is relevant and important in understanding the images one acquires from an ultrasound scan, hence these are introduced in a didactic manner for the sake of efficiency.
The remainder of the course is hands on practice in recognition of normal findings and practising protocols. We feel this is a good way to begins ones journey in diagnostic medical ultrasound. Learners are encouraged to maintain a portfolio of evidence and reflective practice both to facilitate their learning and also to serve as an assessment tool.
Conclusion
Emergency ultrasound has the potential to improve service delivery in the prehospital setting. The introduction of this new tool to the matrix of skills that already exist in the prehospital care requires adequate training and quality control. However, equally important is the integration of these techniques into service wide decision-making algorithms with the ultimate aim to improve quality outcomes.
We hope this approach will go some way to ensuring that this important assessment modality establishes itself properly into the UK in the prehospital setting. For further information and course availability, please go to: www.axiomultrasound.com
