Generation of microbubbles in extracorporeal life support and assessment of new elimination strategies

Veno-arterial extracorporeal membrane oxygenation for the treatment of obstructive shock caused by venous air embolism: A case report

BACKGROUND

Venous air embolism (VAE) is a potentially lethal condition, with a reported incidence rate of about 0.13%, and the true incidence may be higher since many VAE are asymptomatic. The current treatments for VAE include Durant's maneuver, aspiration and removal of air through venous catheters, and hyperbaric oxygen therapy. For critically ill patients, use of cardiotonic drugs and chest compressions remain useful strategies. The wider availability of extracorporeal membrane oxygenation (ECMO) has brought a new option for VAE patients.

CASE SUMMARY

A 53-year-old female patient with VAE presented to the emergency clinic due to abdominal pain with fever for 1 d and unconsciousness for 2 h. One day ago, the patient suffered from abdominal pain, fever, and diarrhea. She suddenly became unconscious after going to the toilet during the intravenous infusion of ciprofloxacin 2 h ago, accompanied by nausea and vomiting, during which a small amount of gastric contents were discharged. She was immediately sent to a local hospital, where cranial and chest computed tomography showed bilateral pneumonia as well as accumulated air visible in the right ventricle and pulmonary artery. The condition deteriorated despite endotracheal intubation, rehydration, and other treatments, and the patient was then transferred to our hospital. Veno-arterial ECMO was applied in our hospital, and the patient's condition gradually improved. The patient was successfully weaned from ECMO and extubated after two days.

CONCLUSION

ECMO may be an important treatment for patients with VAE in critical condition.

Ultrasonic Traveling Waves for Near-Wall Positioning of Single Microbubbles in a Flowing Channel

Although microbubbles are used primarily in the medical industry as ultrasonic contrast agents, they can also be manipulated by acoustic waves for targeted drug delivery, sonothrombolysis and sonoporation. Acoustic waves can also potentially remove microbubbles from tubing systems (e.g., in hemodialysis) to prevent the negative effects associated with circulating microbubbles. A deeper understanding of the interactions between the acoustic radiation force, the microbubble and the channel wall could greatly benefit these applications. In this study, single air-filled microbubbles were injected into a flowing (polydimethylsiloxane) channel and monitored by a high-speed camera while passing through a pulsed ultrasonic wave zone (0.5 MHz). This study compared various bubble sizes, flow rates and acoustic pressure amplitudes to better understand the three physical regimes observed: free bubble translation (away from the wall); on-wall translation; and bubble-wall attachment. Comparison with a theoretical model revealed that the acoustic radiation force needs to exceed the combined repulsive forces (shear lift, wall lubrication and repulsive Van der Waal forces) for the dead state of bubble-wall attachment. The bubble dynamics revealed through this investigation provide an opportunity for efficient positioning of microbubbles in a channel flow, for either in vivo manipulation or removal in biological applications.

Pulsatility protects the endothelial glycocalyx during extracorporeal membrane oxygenation

BACKGROUND

Pulsatile flow protects vital organ function and improves microcirculatory perfusion during extracorporeal membrane oxygenation (ECMO). Studies revealed that pulsatile shear stress plays a vital role in microcirculatory function and integrity. The objective of this study was to investigate how pulsatility affects wall shear stress and endothelial glycocalyx components during ECMO.

METHODS

Using the i-Cor system, sixteen canine ECMO models were randomly allocated into the pulsatile or the non-pulsatile group (eight canines for each). Hemodynamic parameters, peak wall shear stress (PWSS), serum concentration of syndecan-1, and heparan sulfate were measured at different time points during ECMO. Pulsatile shear stress experiments were also performed in endothelial cells exposed to different magnitudes of pulsatility (five plates for each condition), with cell viability, the expressions of syndecan-1, and endothelial-to-mesenchymal transformation (EndMT) markers analyzed.

RESULTS

The pulsatile flow generated more surplus hemodynamic energy and preserved higher PWSS during ECMO. Serum concentrations of both syndecan-1 and heparan sulfate were negatively correlated with PWSS, and significantly lower levels were observed in the pulsatile group. Besides, non-pulsatility triggered EndMT and endothelial cells exposed to low pulsatility had the lowest possibility of EndMT.

CONCLUSION

The maintenance of the PWSS by pulsatility during ECMO possesses beneficial effects on glycocalyx integrity. Moreover, pulsatility prevents EndMT in endothelial cells, and low pulsatility exhibits the best protective effects. The augmentation of pulsatility may be a plausible future direction to improve the clinical outcome in ECMO.