Bubbles and bypass: an update

Abstract

Bubbles in the bloodstream are not a normal condition--yet they remain a fact of cardiopulmonary bypass (CPB), having been extensively studied and documented since its inception some 50 years ago. While detectable levels of gaseous microemboli (GME) have decreased significantly in recent years and gross air embolism has been nearly eliminated due to increased awareness of etiologies and technological advances, methods of use of current perfusion systems continue to elicit concerns over how best to totally eliminate GME during open-heart procedures. A few studies have correlated adverse neurocognitive manifestations associated with excessive quantities of GME. Newer techniques currently in vogue, such as vacuum-assisted venous drainage, low-prime perfusion circuits, and carbon dioxide flooding of the operative field, have, in some instances, exacerbated the problem of gas embolism or engendered secondary complications in the safe conduct of CPB. Doppler monitoring (circuit or transcranial) primarily remains a research tool to detect GME emanating from the circuit or passing into the patients' cerebral vasculature. Newer developments not yet widely available, such as multiple-frequency harmonics, may finally provide a tool to distinguish particulate microemboli from GME and further delineate the clinical significance of GME.

Detection and Classification of Gaseous Microemboli During Pulsatile and Nonpulsatile Perfusion in a Simulated Neonatal CPB Model

“…11 Numerous sources of gaseous microemboli have been reported during CPB procedure in vivo and in vitro models. 17 Although, traditionally, removing gaseous microemboli from the CPB circuit has been assumed by using arterial line filters and improving design of oxygenator and venous reservoir, introduction of air into the venous line still resulted in the detection of gaseous microemboli in the arterial line prior to the arterial cannula, particularly when using vacuum assisted venous drainage during CPB procedure. 6,7 In our simulated neonatal CPB model, the results showed that, regardless of the type of perfusion mode, increasing the pump flow rate and introducing 5 ml air into venous line resulted in more microemboli detected by the EDAC TM system at postpump site; this result was in agreement with Beckley and DeSomer's that higher blood flow rates were associated with a higher release of air, 8,9 because higher flow rates generated higher blood flow velocities, which shorten the contact time between gaseous microemboli and the venous reservoir filter; however, microemboli were rarely detected at postoxygenator site and almost never at postfilter site, which means the majority of microemboli were removed by the oxygenator.…”

In vivo microvascular mosaics show air embolism reduction after perfluorocarbon emulsion treatment

“…Clinical effects of microbubbles reflect phenomena that take place at the level of the microcirculation (Barak and Katz, 2005) and there is a dynamic, constant process of small bubbles fusing to create large bubbles, and large bubbles splitting into small ones. Both massive air bubbles and gaseous microemboli have been the subject of numerous studies, and efforts have been directed at elimination of both types (Kurusz and Butler, 2004).…”

“…The observation of air bubbles in microvessels is relatively trivial and several reports document microvascular embolism (Barak and Katz, 2005;Helps et al, 1990;Kurusz and Butler, 2004;Muth and Shank, 2000). In many cases, pictures are produced but a number of technical issues related to image quality and acquisition of the angiograms prevent accurate measurements of bubble dimensions (Herren et al, 1998;Parsons et al, 2009;Soga et al, 1999).…”

Evaluation of the Quadrox-I neonatal oxygenator with an integrated arterial filter

“…While it has been reported that keeping an arterial filter purge line open in a CPB circuit can improve microemboli trapping by reducing total volume and size of microemboli delivered to the patient 4,5,11,13 , an open purge line also shunts significant amounts blood away from the patient, resulting in hypoperfusion, particularly at low flow rates 8,14 . Blood flow and pressure measurements across a CPB circuit are significant parameters in that a significant decrease in blood flow to the patient ("stolen" blood flow) 14 or pressure drop can result in hypoperfusion of the patient, thus, increasing the potential for post-operative morbidity.…”