Page 299 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 29: ICU Ultrasonography 203

When combined with the Competence Statement, it serves to guide other qualities are important to consider in making a purchase decision.
intensivists in planning their training for which there are three inter- Durability, reliability, ease of operation, and the manufacturer’s repu-
related parts. tation for service-related matters are important considerations when
making a purchase decision.
1. Mastery of image acquisition: This includes knowledge of ultrasound
physics, machine controls, transducer manipulation, ultrasound ana-
tomy, and scanning tactics that are specific to each organ system. Skill APPLICATIONS OF CRITICAL CARE
in image acquisition is a mandatory component of competence, as the ULTRASONOGRAPHY
only be achieved with hands-on training. It best starts with deliberate ■ GUIDANCE OF VASCULAR ACCESS
intensivist personally performs the scan. Skill in image acquisition can
practice on normal human subjects followed by supervised scanning Vascular access is a common procedure for the intensivist. Central
of patients. The training process may be supervised by a local expert venous access, arterial line insertion, and challenging peripheral venous
who is responsible for ensuring the quality of training. It is recom- access are routine in the ICU. Considerations such as unusual body habi-
mended that the trainee keeps a logbook of scanning activity and tus, obesity, or bleeding risk may present special challenges. Peripheral
develops an image portfolio for review. venous access may be difficult in patients due to intravenous drug use,
2. Mastery of image interpretation: This includes the ability to iden- obesity, or repeated hospitalization. Ultrasound is very useful for guid-
tify the wide variety of normal variants of ultrasound anatomy, as ance of all forms of vascular access.
well as to recognize a wide range of pathology. This may be achieved Ultrasonography allows the clinician to identify contraindications to
by scanning of actual patients, but primarily through review of a access that are not apparent on physical examination. A thrombus in
comprehensive image collection. the internal jugular vein will not be detected on physical examination. It
3. Mastery of the cognitive elements: These are required to integrate contraindicates venous access at that site, and it is readily detected with
ultrasonography with clinical management. This may be achieved ultrasonography. The volume depleted patient with respiratory distress
in blended fashion using textbook, articles, lecture material, and may have marked intrathoracic pressure swings that completely obliter-
Internet-based learning programs. Cognitive training includes ate the lumen of the internal jugular or subclavian vein during inspira-
review of the limitations of intensivist performed ultrasonography, in tion. This precludes safe venous access, and yet can only be detected
particular when to ask for review of the results by an advanced-level with ultrasonography. The intensivist who uses landmark technique
ultrasonographer, and when to use alternative imaging modalities. assumes that the carotid artery lies medial to the internal jugular vein,
and that the vein is of normal caliber. In fact, there is risk of variant
Training in advanced critical care echocardiography requires a major position of the vein relative to the artery, as well as of a narrowed venous
time commitment, a large number of scans both performed and inter- caliber. Ultrasonography is able to identify variant anatomy, which is
5,6
preted, and comprehensive knowledge of the cognitive elements of the not detectable with physical examination. In addition to identification of
field. Most intensivists neither need nor are interested in this level of dangerous anatomy, ultrasonographic guidance of central venous access
training for typical ICU function. For those who seek this type of train- improves success rate and decreases complication rate at the internal
ing, the American Heart Association/American College of Cardiology jugular, subclavian, and femoral site. Ultrasonographic guidance of
8
7
9
has applicable recommendations that can be combined with the optional arterial access has benefit, and in difficult peripheral venous access
10
requirement of taking the echocardiography boards. La Société de cases, ultrasound improves success rate as well. 11
3
Réanimation de Langue Française in France has very specific guide- The evidence so favors ultrasound guidance for vascular access that
lines for training for advanced-level critical care echocardiography that major quality organizations recommend its use, 12,13 and is now a require-
include a board-type examination. Training in critical care echocardiog- ment for critical care fellowship training in the United States (USA) as
raphy includes mastery of transesophageal echocardiography. of July 1, 2012. 14
From the point of view of a pragmatic frontline intensivist, it is hard
EQUIPMENT REQUIREMENTS to argue against the evident advantage of being able to see the target
vessel, as opposed to guessing where it is. An argument against ultra-
The ICU must be equipped with a fully capable ultrasound machine sonography is that it might degrade the practitioner’s ability to perform
on site 24/7 that is under the complete control of the intensivist staff. access using landmark technique when ultrasonography is not available.
The machine should be equipped with both a standard cardiac trans- The counter argument is that it may actually improve the landmark
ducer and an additional probe that is designed specifically for vascular approach, as the clinician learns the anatomy from ultrasonographic
ultrasonography. A separate abdominal transducer, while desirable, examination. Another argument is that it complicates setup for line
adds significant cost to the machine. It is not required as the cardiac insertion. Compared to the complexity of setup required for prevention
probe has multipurpose utility and is capable of good-quality thoracic, of central-line infection, the addition of a transducer with sterile probe
abdominal, and cardiac imaging. There are many types of machines on cover is inconsequential. A benefit of ultrasonography is that it greatly
the market. The size and portability of the machine has major implica- decreases the number of attempts required for successful insertion in
tion for ICU use. A large high-end machine used for cardiology-type difficult cases; while this decreases the risk of mechanical complication,
echocardiography is impractical in a busy ICU. The industry has it may also reduce the risk of disrupting the sterile field.
designed portable machines they may be easily positioned, by virtue of
their small footprint, around the crowded ICU bed. The machine may ■ GENERAL PRINCIPLES
be rapidly detached from the cart to become a handheld unit that is ideal
to carry to cardiac arrest or rapid response events outside of the ICU. 1. Ultrasonographic guidance of vascular access is performed with a
These modern units have excellent image quality as well as the manda- transducer of higher frequency (typically 7.5 MHz) than that used
tory memory capability that is required to capture image clips in digital for general body ultrasonography. Most transducers are of linear
format. For those interested in advanced echocardiography, they may be design. Microconvex types are available as well, and are useful for
configured with full Doppler and TEE capability. While a recent gen- small area scanning. Compared to a cardiac transducer of lower fre-
eration portable machine is desirable, many older generation machines quency, the vascular transducer has superior resolution but reduced
have excellent imaging capability. In fact, many of the key elements of penetration. Most major vessels of interest are close to the surface of
critical care ultrasonography were fully defined using a machine built the body, so are within the depth range of a vascular transducer.
in 1990. Use of a capable older machine results in substantial cost sav- 2. The ultrasound machine should be positioned for maximal ergo-
4
ings. Because modern portable machines have excellent image quality, metric efficiency. This may require repositioning ICU equipment

section02.indd 203 1/13/2015 2:05:44 PM