Mannitol Shower: The Artefactual Air Embolism!

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To JNA Readers:
Intraoperative venous air embolism (VAE) is one of the most dreaded anesthetic emergencies. We report a case of artefactual air embolism visualized by transesophageal echocardiography (TEE) which was in fact a shower caused by mannitol infusion.
A 35-year-old man presenting for surgical excision of para-sagittal meningioma underwent standard induction and maintenance of anesthesia with routine monitoring. The patient was placed in sitting position, and TEE monitoring was instituted to screen for intraoperative air embolism. The tumor being large with associated subfalcine herniation, decision was taken to initiate osmotherapy with 20% mannitol. As we interrogated the mid-esophageal bicaval view to screen for patent foramen ovale and superior vena cava diameter, we observed a dense shower of bubbles as observed in active air embolism. (Fig. 1) Immediately, the surgical team was alerted about the possible air embolism, but they responded in negative as there were no exposed venous spaces and the shower continued despite flooding the surgical field with saline. Other evidences to clinch the diagnosis of VAE, such as a fall in tidal carbon dioxide (ETCO2), tachycardia, hypotension, desaturation, and an arterial blood gas sample proved to be negative for the same. The shower phenomenon continued despite this, and as we verified the intravenous (IV) infusion sets, connectors, and the IV bottles to rule out any iatrogenic sources of air, we stopped the mannitol infusion, after which there was a simultaneous disappearance of the bubble shower noted on TEE, which again reappeared on restarting the infusion. Immediately the mannitol infusion was stopped and suspicion of mannitol crystals was considered. The diagnosis of “Mannitol shower” was confirmed when no shower was visualized on the TEE when mannitol infusion was restarted after replacing the regular IV set with the IV infusion set with a filter. Mannitol solutions with concentrations >15% have a tendency to crystallize when exposed to lower temperatures.1,2 With the ambient temperature of operating rooms being 18°C to 22°C, there is propensity of mannitol to crystallize. As opined by the pharmaceutical companies, the container should be inspected for crystals before administration and if observed, the container should be warmed to not >60°C, shaken, and then cooled to body temperature before administering. Crystals can also be avoided by using an IV set with filter. Although there is no evidence in literature about potential risks of infusion of mannitol crystals, there is a theoretical possibility of causing micro particulate embolism in the pulmonary circulation.
In neurosurgical patients, the use of TEE aids in determining the hemodynamic and volume status, screening for structural pathologies of heart, such as patent foramen ovale in addition to diagnosing critical events like air embolism. The neuroanesthesiologist should be prepared to differentiate this “Mannitol shower” from actual VAE, as they have an identical presentation on TEE imaging. The diagnosis of “Mannitol shower” can be determined by eliminating the plausible causes of air embolism and applying clinical assessment as this phenomenon will not have any hemodynamic instability nor drop in ETCO2.3 Confirmation can be achieved by stopping the mannitol infusion. Keeping in mind that TEE is the gold standard for diagnosis of air embolism with detection levels as low as 0.02 mL/kg which will not be associated with any hemodynamic instability or clinical manifestations, this phenomenon of “Mannitol shower” should not add to a false positive diagnosis of VAE.

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