Advanced Hemodynamic and Cardiopulmonary Ultrasound for Critically Ill Patients in the Emergency Department

In many cases, ultrasound has been shown to be superior to traditional chest radiography to assess critically ill patients. ^2-8 Although there are several protocols that utilize thoracic ultrasound in evaluating the critical patient, this review focuses solely on the components of thoracic ultrasound, rather than specific protocols.

Pneumothorax

Ultrasound imaging with a high-frequency probe is highly sensitive and specific in assessing for pneumothorax in a supine patient. ⁹ In the normal lung, the visceral and parietal pleura are visualized as sliding with each breath. In this examination, the transducer is placed on the chest wall to visualize two ribs and the pleura between them ( Figures 2a and 2b ).

Figure 2.

When lung sliding is present, the appearance in M-mode is that of the “seashore” or “sandy beach.” The hyperechoic white pleura is seen as moving with the respiratory cycle. Additionally, lung artifacts such as A-lines, horizontal reverberation artifacts; and B-lines (also referred to as “comet-tails”), vertical lines arising from distended subpleural alveoli, will be seen in a normal lung. If pneumothorax is present, no sliding or comet-tail artifacts will be present at the pleural surface. Although A-lines may also be absent in pneumothorax, studies have shown that the absence of lung sliding and the presence of A-lines are associated with increased specificity (94% vs 78% with absent lung sliding alone) for diagnosing occult pneumothorax. ⁹

Figure 3.

While the lack of pleural sliding is highly sensitive for pneumothorax, the clinician must place this finding within the clinical context of the patient. For example, an intubated patient may not have left-sided sliding in the case of a right main-stem intubation. Moreover, patients who have an underlying obstructive lung disease (eg, chronic obstructive pulmonary disease [COPD]) and/or emphysema may present a more challenging examination because pleural sliding is often absent, especially in the apical segments, and can mimic pneumothorax in these patients. ¹⁰

In addition to pleural sliding, presence or absence of a lung pulse also assists in assessing patients for pneumothorax. The detection of a lung pulse on M-mode ultrasound indicates subtle cardiac pulsation at the periphery of the lung; this finding only appears in the nonventilated lung in the absence of a pneumothorax. The presence of lung pulse is therefore useful in distinguishing other causes of nonventilated lung from pneumothorax. ¹¹

Pleural Fluid

The low-frequency curvilinear or phased array probes are used to assess for pleural fluid. In this study, the clinician fans the probe cephalad from Morison’s pouch on the patient’s right side, or from the splenorenal recess on the left side, to visualize the bright, hyperechoic diaphragm. If pleural fluid is present, there will be loss of the mirroring artifact, and the fluid will appear as an anechoic collection cephalad to the diaphragm. In addition, when fluid is present, the normal lung may be visualized moving within the effusion, evoking a quad or sinusoid sign with M-mode imaging. ^12,13 In the setting of complicated parapneumonic effusion, the echogenicity may be mixed or difficult to detect.