Hemolytic potential of hydrodynamic cavitation

Cavitation phenomenon in mechanical prosthetic valves: Not only microbubbles

INTRODUCTION

Microbubbles (MBs) or cavitation is high-velocity, echo-bright findings present during the closing or opening of a mechanical valve (MVP). Cavitation bubble growth or gas emboli are less frequently described. We evaluated the hemodynamic parameters involved in the formation of gas emboli and the impact of gas emboli on requests for additional investigations.

METHODS AND RESULTS

Transthoracic echocardiographic studies (TTE) of 57 patients (31 males, mean age 46.8 ± 13.8 years) with gas emboli were evaluated after heart valve replacement surgery. The majority (72%, n = 42) had a mitral or combined mitral/aortic MVP, with 28% (n = 16) an aortic MVP. The last TTE with and without gas emboli were considered for the same patient and the no emboli group was the control group (42 patients). The patient's blood pressure (BP) and heart rate (HR) were available for each TTE. Comparing the two TTEs, the systolic and diastolic BP, transmitral and aortic gradients, and left ventricular ejection fraction were similar but the HR (80.9 ± 18.7 vs 72.5 ± 13.9 bpm, P = .02) was significantly higher in the group with gas emboli. A TEE was performed 52 times in 27 patients, due to gas emboli, with one case positive for thrombus/vegetation. For 19 patients, a brain CT was requested. In two patients, the indication for the brain CT was gas emboli but the result was negative.

CONCLUSION

Gas emboli are frequently present and associated to an increased HR. They can cause the misdiagnosis of endocarditis or thrombus formation with significant additional requests for diagnostic examinations.

High Hemoglobin Is an Independent Risk Factor for the Development of Hemolysis During Pediatric Extracorporeal Life Support

OBJECTIVE

To evaluate risk factors for hemolysis in pediatric extracorporeal life support.

DESIGN

Retrospective, single-center study.

SETTING

Pediatric intensive care unit.

PATIENTS

Two hundred thirty-six children who received extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Risk factors for hemolysis were retrospectively analyzed from a single center in a total of 236 neonatal and pediatric patients who received extracorporeal membrane oxygenation support (ECMO). There was no difference in the incidence of hemolysis between centrifugal (127 patients) and roller head (109 patients) pump type or between venoarterial and venovenous ECMO. High hemoglobin (Hb) was found to be an independent risk factor for hemolysis in both pump types. The Hb level >12 g/dL was significant in the roller group and the Hb level >13 g/dL was significant in the centrifugal group for the development of hemolysis for the cumulative ECMO run. The presence of high Hb levels on any given day increased the risk of hemolysis for that day of the ECMO run regardless of ECMO pump type. Higher revolutions per minute (RPMs) and higher inlet pressures on any given day increased the risk for the development of hemolysis in the centrifugal pump. Lower inlet venous pressures and RPMs were not associated with hemolysis in the roller group.

CONCLUSIONS

An Hb level greater than 13 g/dL was associated with an increased risk of hemolysis, and a high Hb on a given day was associated with a significantly higher risk of hemolysis on the same day. Higher RPMs and lower inlet venous pressures were associated with an increased risk of hemolysis in the centrifugal pump only.

The relationships between air exposure, negative pressure, and hemolysis

The purpose of this study was to describe the hemolytic effects of both negative pressure and an air-blood interface independently and in combination in an in vitro static blood model. Samples of fresh ovine or human blood (5 ml) were subjected to a bubbling air interface (0-100 ml/min) or negative pressure (0-600 mm Hg) separately, or in combination, for controlled periods of time and analyzed for hemolysis. Neither negative pressure nor an air interface alone increased hemolysis. However, when air and negative pressure were combined, hemolysis increased as a function of negative pressure, the air interface, and time. Moreover, when blood samples were exposed to air before initiating the test, hemolysis was four to five times greater than samples not preexposed to air. When these experiments were repeated using freshly drawn human blood, the same phenomena were observed, but the hemolysis was significantly higher than that observed in sheep blood. In this model, hemolysis is caused by combined air and negative pressure and is unrelated to either factor alone.