American Society of Regional Anesthesia and Pain Medicine February 2018 - 11

Diaphragm Ultrasonography for Regional Anesthesiologists

R

egional anesthesiologists
frequently perform interscalene
and supraclavicular brachial plexus
blocks to manage postoperative pain after
shoulder surgery, with some patients
developing respiratory distress from
hemidiaphragm paralysis caused by
simultaneous phrenic nerve blocks.
Although chest radiographic findings of an
elevated hemidiaphragm suggests phrenic
nerve paralysis, sonographic assessment
of the diaphragm provides a more accurate
and quantitative analysis (movement
and contractility) that anesthesiologists
can perform at the bedside before or
after those nerve blocks. Preoperative
diagnosis of diaphragm dysfunction on
the surgical site's contralateral side may
warrant suprascapular and axillary nerve
blocks or other alternate techniques in
patients with pre-existing
respiratory dysfunction.
Additionally, when dyspnea
occurs after an interscalene
block, chest sonography can
be used to identify iatrogenic
pneumothorax.

Peter H. Cheng, DO
Partner Emeritus
Kaiser Permanente Medical Center
Moreno Valley, California

Andrea J. Boon, MD
Professor of Physical Medicine
and Rehabilitation
Professor of Neurology
Mayo Clinic
Rochester, Minnesota

Stephen Haskins, MD
Assistant Attending Anesthesiologist
Hospital for Special Surgery
Clinical Assistant Professor of
Anesthesiology
Weill Cornell Medical College
New York, New York

Section Editor: Kristopher Schroeder, MD

"Could a perioperative ultrasound
examination be used to assess diaphragm
function and reversal of phrenic nerve
blockade prior to extubation?"

In this article, we will
describe sonographic evaluation of the diaphragm at the zone of
apposition (ZOA) pertinent to the practice of anesthesia. Unlike
sonography of diaphragm excursion, which is influenced by the
accessory muscles of respiration, diaphragm thickening more
accurately quantifies diaphragmatic contraction.

CLINICAL SCENARIO
A 58-year-old American Society of Anesthesiologists class III
male patient presented for a right rotator cuff repair. He had a
history of smoking, well-controlled chronic obstructive pulmonary
disease, obstructive sleep apnea, obesity, difficult airway, diabetes
mellitus, and hypertension. He denied dyspnea at rest. After a
right interscalene nerve block, rotator cuff repair was performed
under general anesthesia. At the conclusion of surgery and after
reversal of neuromuscular blockade, he was fully responsive to
command. Because he had mild respiratory dysfunction, he was
extubated. Following extubation, he required reintubation because
of worsening dyspnea. He was admitted to the intensive care unit,
where he was successfully extubated the following day.
Did the interscalene nerve block and associated phrenic
nerve block cause diaphragm paralysis? Could a preoperative

ultrasound examination
have identified diaphragm
dysfunction that would
warrant phrenic nervesparing blocks? Could a
perioperative ultrasound
examination be used to
assess diaphragm function
and reversal of phrenic nerve blockade prior to extubation?
ULTRASOUND EQUIPMENT AND SETTINGS
Correct probe selection is essential when insonating the diaphragm,
and it depends on the location of the diaphragmatic evaluation.
When assessing the diaphragm through the liver and spleen as
acoustic windows using M-mode sonography, a low-frequency
curvilinear array (2-5 MHz) or narrower cardiac phased array
transducer (1-5 MHz) is recommended to provide the penetration
needed for abdominal sonography. When assessing the diaphragm
at the zone of apposition (ZOA), a high-frequency linear array
transducer (10-13 MHz) is recommended.
DIAPHRAGMATIC EVALUATION AT THE ZOA: ABCDE
Zone of Apposition. Sonographic assessment of diaphragm
motion and contractility is performed at the ZOA, which is best
seen in the coronal plane at the level of the eighth and ninth
ribs in the region of the axillary or anterior axillary line (Figure
1A). The diaphragm appears as a thin hypoechoic or isoechoic
structure located between two hyperechoic layers: peritoneum and
diaphragmatic pleura (Figure 1B). During inspiration, the diaphragm
normally thickens more than 20% (Figure 2).

American Society of Regional Anesthesia and Pain Medicine
2018

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