Author(s): John B. Chambers , Nadia Short , Luna Gargani
Emergency ultrasonography is useful for the presentations in Table 114.1.
- It is more accurate than a chest X-ray for the detection of pleural fluid. It can be used to guide chest drain insertion for those who have approved British Thoracic Society training (Chapter 122).
- A bladder scan as part of the abdominal examination can assess the amount of urine in the bladder pre- and post-voiding.
- Ultrasonography can also be used to identify peripheral veins for venepuncture or cannulation, or central veins for the insertion of central lines (Chapter 116).
- Practical aspects are summarized in Table 114.2.
Surgical applications (e.g. diagnosis of ruptured abdominal aortic aneurysms or traumatic intraperitoneal bleeds) are not described in this chapter.
- The ALS mnemonic ‘4Hs and 4Ts’ (Table 114.3) summarizes the potentially reversible causes of hypotension, shock and cardiac arrest (Chapters 2 and 6). The findings in these conditions are shown in Table 114.4.
- In a cardiac arrest the cardiac scan can be performed in the 5s pulse check of the Advanced Life Support Resuscitation Council algorithm of ‘non-shockable’ rhythms.
- A motionless, asystolic heart at CPR is associated with a positive predictive value of 97% death.
- Cardiac ultrasonography at the time of chest pain may help to exclude myocardial ischaemia and to differentiate between an acute coronary syndrome and pericarditis (Chapter 7). Note that:
- Left ventricular wall-motion analysis can be difficult and should be performed by an accredited echocardiographer.
- The cardiac scan should be interpreted within the clinical context, including troponin levels.
- In suspected pulmonary embolism (Chapter 57):
- The signs in Table 114.4 can be used to prove the working diagnosis sufficient to give immediate thrombolysis in a critically ill patient.
- Sometimes the presence of RV dilatation can suggest the need for inpatient care in patients apparently suitable for outpatient care using clinical scoring systems.
- In hypotension (Chapter 2), a cardiac scan is useful to detect hypovolaemia (flat IVC) and cardiac dysfunction.
- In patients with suspected exacerbation of COPD (Chapter 61), LV systolic dysfunction is either the correct diagnosis or an associated diagnosis in up to 20% of cases.
- A thoracic emergency scan does not substitute for a standard thoracic ultrasound scan for pleural diseases as defined by British Thoracic Society (BTS) guidelines.
- A BTS approved ultrasound course is mandated before performing interventions such as chest drain insertion under real-time ultrasound.
- A thoracic scan can aid management by the detection of:
- Normal aerated lung reflects ultrasound poorly and is characterized by A lines (Table 114.5) (Figure 114.1 (a)). The scatter of ultrasound causes a ‘snow-storm’ appearance.
- A wet lung reflects ultrasound and is characterized by ‘B-lines’ (Table 114.5, Figure 114.1 (b)):
- Identifying whether A or B lines are present helps differentiating between COPD and heart failure with pulmonary oedema.
- The absence of multiple bilateral B lines excludes cardiogenic pulmonary oedema with negative predictive value of 100%.
- Acute respiratory distress syndrome/acute lung injury (Table 47.1) are characterized by non-homogeneously distributed B-lines and lung consolidations.
- In a tense distended abdomen ultrasound can confirm the presence of ascites immediately.
- Points on the examination are given in Table 114.6.
- Unless there is marked splenomegaly, the left lateral flank is the preferred site for a diagnostic ascitic tap or paracentesis, aiming for an area between the anterior abdominal wall and the dark hypoechogenic fluid, and having confirmed that there is no bowel or other organ in the proposed track.
- The bladder produces a posterior acoustic shadow. Scan suprapubically in midline both longitudinally and transversely.
- A bladder scan is useful for:
- Obese elderly males where clinical assessment for urinary retention due to prostatic hypertrophy can be difficult.
- Post-voiding volumes when uncertainty about incomplete bladder emptying exists.
- Confused patients who cannot tell you when they were last able to pass urine.
- In acute kidney injury (Chapter 25).