Title: Agitated Saline Contrast Injection in Patients with Severe Hypoxemia<br/>Author: Caleb Chan<br/><a href='http://umem.org/profiles/alumni/1583/'>[Click to email author]</a><hr/><p>
<span font-size:="" helvetica="" style="font-family: ">Hypoxemic respiratory failure is a common presentation of critically ill patients. If the degree of hypoxemia is severe and </span><span font-size:="" helvetica="" style="font-family: " text-decoration:="">disproportionate </span><span font-size:="" helvetica="" style="font-family: ">to the patient's radiographic findings and not responding to increasing FiO2, a right-to-left shunt should be considered. To evaluate for an anatomic shunt, an intravenous agitated saline contrast (ASC) echocardiographic evaluation can be conducted by an ED provider at the bedside.</span></p>
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Technique:</p>
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Use two operators, nursing can perform the ASC with the physician obtaining the echo views</li>
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Set-up:
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20 gauge (or larger) PIV in the AC fossa or more proximal is sufficient (does not have to be a CVC)</li>
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Flush PIV aggressively prior to attempt to make sure it won't blow</li>
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Obtain 3-way stopcock and 2 10 cc syringes</li>
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One port is connected to the PIV, and a second port to an empty 10cc syringe with the plunger fully depressed </li>
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Third port connected to a syringe filled with 9ccs of saline and 1cc of air (eject 1cc of saline from the syringe of normal saline (NS) and replace it with air)</li>
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Echo technique:
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Any view where the RA, LA, and IAS can be seen will suffice</li>
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Apical 4-chamber view is favored, with a focus on the bilateral atria (can also do sub-xiphoid)</li>
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Procedure:
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With the equipment connected to the PIV, bubbles are created by turning the stopcock valve to “off” toward the patient and alternately depressing the plungers on the 2 syringes to send the air/NS mixture back-and-forth between them (should be done forcefully)</li>
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Push ASC completely into one of the syringes and quickly turn the stopcock “off” toward the other, and inject the ASC into patient while maintaining echo view and actively recording</li>
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Interpretation:</p>
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Quality control check:
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A vigorous injection should result in <span style="text-decoration: underline">dense </span>opacification of the RA
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If the chamber is not densely opacified, likely technique issue and the exam should not be interpreted</li>
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The LA should be examined for a period of at least 10 full beats</li>
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Timing when microbubbles are seen in the LA:
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<span style="text-decoration: underline">Immediately </span>(within 3-6 beats is a typically used cutoff): likely to be intracardiac (most likely PFO)
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Under ideal circumstances, bubbles can be seen to transit across the septum in real time</li>
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<span style="text-decoration: underline">After the 3-6 beat cutoff</span>: more likely to be due to a transpulmonary shunt, either an AVM or hepatopulmonary syndrome, depending on the clinical circumstances
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Further workup might include a CT angiogram of the chest or workup for cirrhosis</li>
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Rough qualitative interpretation
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no bubbles</li>
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a small number (roughly <10)</li>
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a large number (roughly >10)</li>
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enough to completely opacify the LA</li>
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(Significant continuous hypoxemia requires significant continuous right-to-left shunting, and thus the ongoing passage of many ASC bubbles)</li>
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<fieldset><legend>References</legend>
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Millington SJ, Mayo-Malasky H, Koenig S. Agitated saline contrast injection in patients with severe hypoxemia. J Intensive Care Med. 2023;38(5):479-486.</p>
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