Extended focused assessment by sonography for trauma (EFAST) [3–6]

Descriptions of the use of ultrasound by clinicians to evaluate trauma patients appeared in the European literature in the 1970s. Reports have subsequently appeared from countries around the world and the technique is now well established. Initially limited to the abdomen and pericardium (FAST), the examination is now routinely extended to include the chest (EFAST). With relatively brief training and experience, non-radiologists are able to diagnose haemoperitoneum, pericardial effusions, pleural effusions and pneumothorax with a high degree of sensitivity and specificity, although accuracy does improve with experience.

Clinical examination in abdominal trauma can be difficult and unreliable. Diagnostic peritoneal lavage (DPL), ultrasound (FAST) and computed tomography (CT) have been used to evaluate further this group of patients. In most cases, FAST has replaced diagnostic peritoneal lavage as it is non-invasive and does not interfere with subsequent interpretation of CT images. CT scanning is highly accurate for diagnosing both free fluid and solid organ injury and is slightly less accurate for hollow viscus and diaphragmatic injury.

Studies of ultrasound scanning in trauma have reported varying sensitivity. Much of this variation is due to differences in the gold standard used for comparison and definition of ‘true positive’. Haemoperitoneum (on further imaging, surgical or post-mortem examination), organ injury and clinical stability have all been used in different studies. It must be remembered that the primary role of a FAST scan is to detect free fluid in the peritoneal or pericardial spaces, for which it has high sensitivity and specificity. Solid organ or retroperitoneal haemorrhage may be detected but, even in expert hands, the accuracy is much lower (with as many as two-thirds of injuries being missed). FAST has been shown to be reliable and useful in both pregnant and paediatric patients.

Technique

FAST scanning evaluates four regions for the presence of free fluid: (1) pericardial; (2) perihepatic; (3) perisplenic; and (4) pelvic (Fig. 23.1.4). The chest is then scanned to examine the pleural spaces posterolaterally for fluid and anteriorly to exclude pneumothorax. The technique is rapid, generally being completed in under 5 minutes.

Free fluid appears as an echolucent area (i.e. black) which is generally linear or triangular in shape in the most dependent area of the peritoneal or pericardial space, although blood clots may be seen as echogenic (grey) collections (Figs 23.1.5–23.1.7). While fluid is most commonly seen in the perihepatic space, all spaces should be examined before the result can be considered negative. Small amounts of fluid (<500 mL) may not to be detected.

When scanning the chest, the presence of lung sliding or lung pulse is an indication that the visceral and parietal pleura are in contact, excluding a pneumothorax at that point. The presence of a moving transition point between areas of lung sliding and absent lung sliding (the ‘lung point’ sign) is diagnostic of pneumothorax.

Clinical implications and utility

The limitations of ultrasound in excluding all intra-abdominal injuries requiring laparotomy and the increasing use of conservative management of some injuries, even in the setting of intra-abdominal free fluid, has resulted in there being no universally accepted clinical algorithm based upon EFAST scan results. However, in this regard, EFAST scanning is no different to any other clinical, laboratory or imaging information of the trauma patient, the results of which are routinely used in combination to determine the management plan. Various algorithms incorporating EFAST scanning have been proposed, which generally incorporate haemodynamic stability and EFAST scan result, such as in Figure 23.1.8. Some algorithms incorporate a semiquantitative scoring system to estimate the amount of free fluid, with an increased volume of free fluid associated with greater need for therapeutic laparotomy. A positive abdominal EFAST scan is highly predictive of significant intra-abdominal injury and, based upon the clinical condition of the patient, generally indicates the need for CT or surgical exploration. A negative EFAST scan, stable haemodynamics and clinical observation have been shown to be highly accurate in excluding significant intra- abdominal injury. Some authors advocate serial EFAST examinations in stable patients, suggesting this can reduce the requirement for CT.

Similarly, for pneumothorax, the integration of EFAST findings with other clinical, laboratory and imaging findings will determine patient management. Conservative management of small pneumothoraces, even in the setting of positive pressure ventilation means that the ultrasound findings must be considered in the setting of the individual patient when management decisions are made.

In the Australasian setting, EFAST is generally accepted as fulfilling a complementary role to CT. Its portability and speed allow it to be used early in the evaluation of trauma patients (e.g. immediately after the primary survey) and this information is then incorporated with other clinical information to risk stratify the trauma patient to help to determine the requirement and timing for either laparotomy, thoracotomy or CT. Repeated examinations, particularly if the patient’s condition changes, can be valuable. Providing the limitations of the technique are not ignored, it can rapidly provide vital information to assist with patient management.

Technique

The aorta should be identified anterior to the vertebral body and to the left of the inferior vena cava (IVC). It should be followed from the epigastric region to its bifurcation, just above the umbilicus, remembering that, in elderly patients, it may follow an ectactic course rather than following a strictly cranial–caudal course. It must be distinguished from both the superior mesenteric artery (SMA) (which runs anterior to the aorta) and the IVC (ensuring that the venous pulsation of the IVC is not mistaken for the arterial pulse of the aorta). Measurements should be taken both proximally and distally and, if an aneurysm is present, at the widest point. Measurements from both transverse and longitudinal planes should be taken. Measurements are taken from the outer wall to outer wall, including any mural thrombus (Fig. 23.1.9). If the renal arteries or SMA origin are identifiable then the relation to the aneurysm should be noted although, in the ED setting, this may not be possible. Any retroperitoneal haematoma or peritoneal free fluid should be noted.

Technique

TAS is performed initially, preferably when the patient has a full bladder, as the pelvic organs will be better visualized. The uterus is identified and examined in both longitudinal and transverse planes (recognizing that the longitudinal axis of the uterus may not necessarily be in a strictly sagittal plane). The endometrial thickness is noted and any fluid collections or gestational sac noted. The adnexa are examined to identify the ovaries and any masses. The pelvis is scanned for free fluid. The upper abdomen can be examined to estimate the volume of free fluid if seen. The kidneys can also be examined to identify any alternate diagnoses.

TVS is performed after the procedure is explained and consent is obtained. A chaperone should be present if the sonographer is male. The patient is asked to empty their bladder and the pelvis is elevated slightly off the bed using a foam wedge or similar. The probe is covered with a sterile sheath (e.g. condom) with gel placed inside and outside the sheath. The probe is gently inserted into the vagina and advanced. The uterus and adnexa are then examined in both longitudinal and transverse planes as in TAS. After the scan is complete the probe must be cleaned and disinfected.

Limitations and pitfalls

If an intrauterine pregnancy is confirmed, the risk of ectopic pregnancy is very low in spontaneously conceived pregnancies. Heterotopic pregnancy is where both an intrauterine and extrauterine pregnancy coexist and occurs in up to 1:7000 pregnancies in spontaneous conceived pregnancies, but over 1:100 pregnancies in the setting of fertility treatment. Failure to visualize an intrauterine pregnancy may be due to early dates in a normal pregnancy, failed intrauterine pregnancy (including complete miscarriage) or ectopic pregnancy. Other ultrasound findings in ectopic pregnancy include non-specific findings, such as pelvic blood and adnexal mass (Table 23.1.2) [12]. Visualization of a gestational sac (with yolk sac or embryo) outside the uterus is diagnostic, but seen only in 8–26% of ectopic pregnancies (Fig. 23.1.10).

Distinguishing between miscarriage and ectopic pregnancy when no adnexal mass has been identified can be difficult on ultrasound. However, if the clinical symptoms have settled, no free fluid is identified on ultrasound and no adnexal masses have been identified, then it is safe to observe or discharge the patient for formal ultrasound review the following day and subsequent follow up with repeat ultrasound and quantitative HCG (see Chapter 19.2).

If an intrauterine pregnancy is confirmed, the gestational age can be estimated by measuring the size of the embryo. Most machines will automatically calculate gestational age based upon this measurement. Cardiac activity can usually be identified by TVS once the embryo is approximately 5 mm (9 mm by TAS). Absent cardiac activity when the embryo is 7 mm or above suggests embryonic demise. Absent yolk sac or embryo on TVS when the gestational sac is 25 mm suggests an empty sac miscarriage (also referred to as a blighted ovum) [13]. Other sonographic signs of poor prognosis for continued pregnancy exist, but they are generally beyond the scope of emergency ultrasound.

Technique

Ultrasound is the imaging modality of choice for assessing for DVT. The technique relies primarily on B-mode imaging with intermittent venous compression, with the main diagnostic criteria used to exclude a DVT being complete collapse of the vein with apposition of the anterior and posterior walls of the vessel.

A broadband linear array transducer with a centre frequency of about 5 MHz is used to examine the femoral, popliteal and sometimes the calf veins. In larger patients, the curved linear array transducer with a centre frequency of 3.5 MHz (as used for abdominal studies) may be substituted. The curved linear array transducer is also used to examine the iliac veins. The machine should be configured to use the lower limb venous preset and the use of harmonic imaging may improve the contrast resolution between the vessel and surrounding tissue. Transducer compression of the interrogated vessel should be in the transverse imaging plane. Starting at the level of the groin, with the patient in a supine position, the common femoral vein is identified lying medial to the common femoral artery and the vein is compressed to demonstrate collapsibility extending distally in a stepwise fashion with the vein compressed every 2–3 cm (Fig. 23.1.14). Where thrombus is present in the vein, pressure with the transducer will not result in its collapse. The popliteal vein is best examined with the patient in a lateral or prone position with the knee slightly flexed. Colour and spectral Doppler may be used to supplement the findings of intermittent compression. Emergency physicians who had undergone standardized training to identify clot in the femoral or popliteal veins have shown an accuracy comparable to formal vascular studies [20].

The accuracy of compression ultrasonography is highest in symptomatic patients, with studies comparing venography with compression ultrasound demonstrating an average sensitivity of 95% and specificity of 98% [21]. For proximal lower limb DVT, this technique has demonstrated sensitivity of up to 100% [22]. The use of colour and spectral Doppler to assess for vessel filling defects and flow patterns has not been shown to increase significantly the sensitivity for proximal DVT detection in the lower limb [22–25]. It has also been suggested that an abbreviated technique, using only two compression points (the saphenofemoral junction and the lower popliteal vein) has adequate sensitivity, provided repeat examination is performed in 5–7 days [24,26,27]. The accuracy of ultrasound in detecting isolated calf DVT, especially when applied to bedside emergency ultrasound, is low with success rates as low as 40% reported [28].

Thus, the aim of focused emergency department ultrasound in the assessment of DVT is generally to confirm or exclude the presence of clot in the proximal deep veins of the lower limb. A negative compression ultrasound study of the proximal lower limb significantly reduces the likelihood of DVT and discharge from the emergency department without anticoagulation, with outpatient follow up for a definitive study can be considered [21,29–31].

Technique

Modern general ultrasound machines can provide good quality transthoracic echocardiography capability. A broadband phased array transducer with a centre frequency of 2 MHz and a small footprint to improve access between the ribs should be used. Ideally, the patient should be positioned on their left side.

The full, standard echocardiographic examination includes parasternal long and short axis views obtained at the left sternal edge in the 2nd to 4th rib spaces, the apical 4-, 5-, 3- and 2- chamber views that are obtained at the cardiac apex and the subcostal views obtained from a subxiphoid position. The standard examination would involve 2-D assessment of cardiac structure and function using B-mode, supplemented by the use of colour and spectral Doppler to assess valvular function and measure chamber pressures using the windows described above.

Where an abbreviated, emergency bedside echocardiographic examination is being used to screen for the presence of tamponade, right ventricular dysfunction, left ventricular dysfunction and hypovolaemia alone, simply using B-mode and attaining the parasternal short and long axis views, the apical 4-chamber view and the subcostal view is generally enough.

In cardiac arrest, the subcostal view is used with the patient in the supine position. All preparations are made while CPR continues. During the 10-second pulse check, a loop is recorded and reviewed once CPR recommences. It is imperative that the time without CPR is minimized and echocardiography should not interfere with this.

Emergency physicians have been shown to assess accurately left ventricular function in the hypotensive patient [35].

Limitations and pitfalls