Chapter 11 Intensive Care Unit

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CHAPTER 11 • Intensive Care Unit Imaging

distal to a PAC tip or in a patient with hemoptysis) is likely to represent pulmonary infarction.

angulation of the imaging table or gantry is often a limiting factor for patients who are not intubated and receiving mechanical support. If the patient is to undergo a sedation-based procedure such as drain placement, then a prior coagulation profile and NPO status are prerequisites. With elective procedures, the clinician must plan ahead or defer transport in order to comply with these require- ments and imaging suite schedules. It is wise to check verbally with the technical staff whenever there is doubt regarding the demands and timing of Establish urgency of exam ( stat vs. routine). The exam is usually protocoled by the radiologist, and the selected protocol then helps determine the appropriate prep. Depending on the exam, the patient may need oral contrast (e.g., CT abdomen), which can be administered via enteric tube, if nec- essary. Establish appropriate IV access for IV con- trast administration provided that it both indicated and not prohibited by allergy or renal insufficiency. If CTA is ordered, then the type (and patency) of IV access catheter may need to be approved by CT staff, as this study requires a relatively high injec- tion rate of the contrast with elevated risk of IV contrast extravasation/infiltration. Communication with the radiology staff prior to transport is usually advisable. Magnetic Resonance Imaging Because it invariably takes a relatively long time to complete, MRI is generally avoided in ICU patients unless both clinician and radiology team believe it to be absolutely necessary. Unstable and tenuous patients are placed at particular risk because of the relative separation of patient from caregivers. Confer with the MR tech and/or radiologist to dis- cuss how best to proceed. Individual patients may pose unique limitations. Ultrasound Ultrasound imposes very few limitations other than physical restricted access to appropriate acoustic windows from binders, wounds, and dressings. For many purposes, high-quality ultrasonic examina- tions are acquired by technicians at the bedside. Abdominal and pelvic imaging are preferably done in an NPO state to limit bowel gas from interfering with the imaging. the study or procedure. Computed Tomography

Intra-abdominal Conditions The upright CXR can also help diagnose acute intra-abdominal problems. Midline or paraesopha- geal hiatal hernias usually pose little diagnostic problem. Diaphragmatic disruption may allow abdominal contents to herniate into the chest fol- lowing abdominal trauma, often displacing a gas- containing viscus into the left chest. When safe to administer, oral contrast aids in the diagnosis dur- ing the CT scan. Short of a trip to the CT scanner, the upright CXR also provides the most sensitive method of detecting free air within the abdominal cavity. (A cross-table film of the abdomen taken at least 5 minutes after decubitus positioning may serve a similar purpose.) Intubated patients fre- quently swallow air, producing gastric dilation. In the appropriate setting, massive gastric dilation can suggest the possibility of esophageal intubation or a tracheoesophageal fistula. CT AND MRI Scanning and digital analysis have undergone an important transformation over the most recent decade. Using data from a single acquisition of CT data, images obtained without or preferably with contrast can be reconstructed to view multiple planes—not only the traditional axial plane but also the coronal and sagittal ones, allowing improved diagnostic accuracy (Fig. 11-11). Moreover, subtrac- tion techniques may highlight the vasculature (Fig. 11-12). Three-dimensional reconstructions may be developed from the CT database that proves of high value in detailing the anatomy of difficult cases. Such helpful innovations were unavailable before the accelerated development of digital radiography. Expanding Imaging Potential— Reconstruction, Multiplanar, and Subtraction Views General Preparing of the Patient for Imaging Studies Radiology staff performing these exams will facili- tate and help implement their preparation, depend- ing on the study being performed. Restricted