Chapter 11 Intensive Care Unit

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CHAPTER 11 • Intensive Care Unit Imaging

hazardous misadventures. Because answers usually come quickly, US saves valuable time and guides the path through the diagnostic decision tree, avoiding unnecessary delays and costly tests. For patients who are difficult or risky to transport, the portability and capability of US may obviate moving them outside the emergency suite or ICU environments. As US has become more generally deployed, the library of sonographic findings associated with key pathologic findings has been expanded and detailed. Stepwise bedside US examination sequences, or “protocols,” have been developed that use these signatures to logically and comprehensively assess a number of urgent ICU problems. US for the acutely ill patient is usually categorized into these broad headings: thoracic, abdominal, cardiac, and vascular. Despite its high value and negligible hazard, acute care ultrasound (ACUS) is not the ultimate diag- nostic tool. The inherent limitations of US itself have been apparent ever since consultant-provided echocardiography was first introduced to clinical practice. An adequate ultrasonic window may be obscured or degraded by massive obesity, bone, dressings, or hyperinflated lung. The penetration depth of US is restricted, and although the probe is easily repositioned, access points and acoustic windows are limited. Furthermore, only confined sectors and tissue “chunks” are imaged at a given site. Detailed and three-dimensional imaging in the Limitations of Clinician-Applied US at the Bedside

critically ill remains the province of CT, fluoroscopy and, to a lesser extent, MRI. Thus, although US often serves to rule in and rule out certain broad possibilities, there are a more restricted number of situations for which it provides the incontrovertibly precise diagnosis. Bedside US, then, often serves as an initial probe for (or complement to) more established and often more precise diagnostic tools, rather than a replacement for them. Nonetheless, US speeds and facilitates the diagnostic process. For many purposes (e.g., chest tube insertion), US precludes the need for radiation or contrast, pro- motes early intervention, and encourages repeated cost-effective monitoring of progress. Operator pro- ficiency at performing and interpreting bedside US ultimately determines the value or interpretive error of this methodology. Although these skills cannot be acquired without successful “hands on” train- ing and practical clinical experience, the potential and technical backgrounds for US are important to understand.

Problem Categories and Protocols Cardiovascular ACUS

Detailed ultrasonic examination of the stable patient with heart disease continues to be best assigned to consulting cardiologists who formally evaluate detailed echocardiograms acquired with high capa- bility equipment (Fig. 11-19). In emergency settings and for targeted critical care purposes, however, provider-implemented ACUS can be of high value to direct further steps in management. A fundamental

Base

Long axis

Short axis

Apex

FIGURE 11-19.  Long and short axes of the heart used in cardiac ultrasound (echocardiography).