Chapter 11 Intensive Care Unit

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SECTION 1 • Techniques and Methods in Critical Care

equipment and personnel are immediately available to cope with any catastrophic event (e.g., accidental extubation or extraction of venous or arterial cath- eters or chest tubes, interruption of critical infu- sions, unanticipated cardiac arrest). Patients with bronchopleural fistula needing continual pleural drainage and those requiring vasopressors or high inspired oxygen concentrations or PEEP are at par- ticular risk. It is important to be sure that the intu- bated patient is able to be adequately oxygenated and ventilated on the transport set-up for several minutes before departure. Although now rarely used in transportable patients, interruption of inhaled nitric oxide or nebulized prostacyclin infusions during transport can precipitate calamitous physi- ological deterioration. Metallic appliances create artifact on CT scans and may preclude use of MRI because of the powerful magnetic fields involved. Furthermore, MRI studies are especially time con- suming, and the inability of critically ill patients to remain adequately immobile may produce unac- ceptable motion artifact unless neuromuscular blocking agents are used. CT scanning often requires use of nephro- toxic contrast material. (Enteral contrast used for abdominal scanning does not carry this risk.) Prophylaxis of the patient with marginal renal func- tion is highly variable but should include at least adequate hydration; from this standpoint, sodium bicarbonate may be preferable to the chloride load of saline. Acetylcysteine may be effective, but evi- dence is conflicting. In years past, MRI was used in place of CT for patients with marginal renal func- tion in an attempt to avoid contrast nephrotoxicity. Unfortunately, the use of some gadolinium-based MRI contrast media may be even more dangerous. Gadolinium has been associated with a progres- sive often devastating scleroderma-like syndrome known as progressive nephrogenic sclerosis. Many features of this syndrome remain uncertain; there- fore, until this condition is better understood, it is probably prudent to use gadolinium contrast spar- ingly and attempt to avoid it in patients with renal insufficiency. The financial aspects of imaging should not be overlooked. A chest CT scan typically costs three to four times as much as a portable CXR in addi- tion to the costs of transport, which can be sub- stantial. Because patients are placed at higher risk during travel and there are significant financial and manpower costs involved, it is logical to plan ahead

by bundling studies together when feasible. For example, if an elective head CT is planned tomor- row but an urgent chest CT must be done today, it may make sense to perform both studies today, avoiding the second trip. As a corollary, if an imag- ing study is likely to yield results that will prompt a radiology-based intervention (e.g., needle or cath- eter aspiration), it is common sense to confer with the radiologist in advance of the transport, so as to arrange rapid interpretation of the diagnostic study and subsequent intervention in a single trip. Simple preplanning can also avoid wasteful, redundant studies. For example, if a chest CT is to be per- formed today, there is little reason to do a “routine” morning CXR. In neurocritical care applications, the noncon- trasted CT excels for diagnosis of acute intracra- nial bleeding. It is also helpful when determining if there is an intracranial mass prior to a lumbar punc- ture and for detecting sinus cavity opacification. However, detailed anatomical imaging of the brain, spinal cord, and other soft tissues is best performed by MRI (Fig. 11-15). Moreover, detection of acute ischemic strokes by CT is not reliable until many hours have passed after the event (Fig. 11-16A), and inflammation of the meninges may evade notice. For these selected problems, the MRI is better adapted, as it is immediately sensitive to both (Fig. 11-16B). With different radio frequency stimulation and puls- ing sequences (so-called “weighting,” Fig. 11-17),

FIGURE 11-15. Sagittal MRI imaging of brain and spinal cord. Note the fine anatomic detail provided by T1 weighting.