Centrifugal pump failures

Centrifugal pumps will not pass gross quantities of gaseous emboli due to the nonocclusive nature of the pump. However, retrograde flow can occur under circumstances that include: product malfunctions, low flows, and human errors. Negative pressure created by falling arterial perfusate can draw air into the cannula. Food and Drug Administration (FDA) records about centrifugal pump malfunctions were obtained. Out of 350,000 cases completed with centrifugal pumps over a 23 month period, the FDA received reports of 68 malfunctions, 22 electrical burning smells, and three speed surges, yielding a failure rate of 1 in 3,763 cases. FDA records revealed five death reports and three serious injury reports. A survey was sent to 2,424 Society of Thoracic Surgeons' members to obtain more information; 285 who use centrifugal pumps responded. Sixty surgeons (21%) reported 108 malfunctions, including 46 complete pump failures. Fifty-one of 243 surgeons (21%) who use centrifugal pumps for bypass reported that perfusionists have forgotten to clamp the pump line, resulting in backflow. We conclude centrifugal pumps are generally safe, but malfunctions, low flows, and human errors can lead to retrograde flow and occasionally air embolization. There are valves that can be added to the bypass circuitry to prevent this risk.     

An under-occluded roller pump is less hemolytic than a centrifugal pump

The purpose of this study is to measure and compare the hemolysis produced by roller pumps with varied occlusion settings and a centrifugal pump. The null hypothesis is that there is no difference in the Index of Hemolysis (IH = gm Hb/100 L pumped) produced by a roller pump (RP) at four different occlusion settings and a centrifugal pump (CP) at the same blood flow rate (4.5 L/min) and afterload (250 mmHg, +/-10 mmHg) over three hours. Five identical closed-loop circuits were assembled and primed with saline. The pumps were then calibrated and occlusions were set. In three circuits, the occlusion for the RP was opened at 5 RPMs to support 150, 225, or 300 mmHg (+/-10 mmHg) against a clamped line. In one circuit, a RP was adjusted to a barely non-occlusive setting (1 cm drop/30 inch gradient). The fifth circuit employed a CP. Prior to testing, the saline in each circuit was replaced with one liter of fresh bovine blood (Hct = 22 +/- 2%). The IH for each treatment was compared in six trials yielding a statistical power > 0.80. Analysis of variance with multiple comparison (p < or = 0.05) demonstrated that compared to the barely non-occlusive setting, the IH in the centrifugal pump was not significantly greater. Under-occluded RP settings yielded IHs significantly less than the CP. It appears that opening the occlusion on a roller pump allows a lower IH compared to traditional RP occlusion setting or centrifugal pumping.     

Aquaflo pump vs FMS 4 pump for shoulder arthroscopic surgery.

A prospective controlled trial was carried out to compare two different fluid delivery systems used for shoulder arthroscopy. One an advanced pump system that controls both pressure and flow of fluid delivered, the other an air-driven diaphragm pump that only controls fluid pressure. Blood loss, presence of bleeding vessels and visual clarity were parameters used to assess the pump systems. There was no difference between the pumps in straightforward shoulder procedures. However, complicated and prolonged procedures benefited from the use of the advanced pump system.     

The intra-aortic balloon pump

The intra-aortic balloon pump (IABP) is a mechanical device designed to support the failing or ischaemic myocardium. It is usually inserted percutaneously through the femoral arteries, with the tip just distal to the left subclavian artery. The principle lies in diastolic counterpulsation (augmentation) that inflates at the start of diastole and deflates just before systole. This allows increased coronary perfusion during diastole and also reduces the impedance to forward flow during systole. This scenario of reduced cardiac workload and increased supply of oxygen results in increased cardiac output. Indications include mechanical complications of myocardial infarction, refractory unstable angina, high-risk cardiac surgery, and support of the failing myocardium before transplantation. Contraindications include aortic dissection, aortic regurgitation and severe peripheral vascular disease.     

A magnetically levitated centrifugal blood pump with a simple-structured disposable pump head

Abstract:  A magnetically levitated centrifugal blood pump (MedTech Dispo) has been developed for use in a disposable extracorporeal system. The design of the pump is intended to eliminate mechanical contact with the impeller, to facilitate a simple disposable mechanism, and to reduce the blood-heating effects that are caused by motors and magnetic bearings. The bearing rotor attached to the impeller is suspended by a two degrees-of-freedom controlled radial magnetic bearing stator, which is situated outside the rotor. In the space inside the ringlike rotor, a magnetic coupling disk is placed to rotate the rotor and to ensure that the pump head is thermally isolated from the motor. In this system, the rotor can exhibit high passive stiffness due to the novel design of the closed magnetic circuits. The disposable pump head, which has a priming volume of 23 mL, consists of top and bottom housings, an impeller, and a rotor with a diameter of 50 mm. The pump can provide a head pressure of more than 300 mm Hg against a flow of 5 L/min. The normalized index of hemolysis of the MedTech Dispo is 0.0025 ± 0.0005 g/100 L at 5 L/min against 250 mm Hg. This is one-seventh of the equivalent figure for a Bio Pump BPX-80 (Medtronic, Inc., Minneapolis, MN, USA), which has a value of 0.0170 ± 0.0096 g/100 L. These results show that the MedTech Dispo offers high pumping performance and low blood trauma.     

Off pump versus conventional on pump coronary artery bypass: a review

Despite many years of clinical and experimental research, the contribution of Cardiopulmonary Bypass (CPB) and cardioplegic arrest to morbidity and mortality following cardiac surgery remains unclear. In the last few years, Off-Pump Coronary Artery Bypass grafting (OPCAB) has gained widespread attention as an alternative technique to conventional On-Pump Coronary Artery Bypass grafting (ONCAB). It has provided an opportunity to compare the operations, in similar patient groups, with or without CPB and cardioplegic arrest. Although initial studies performed on low risk patients preferably with single vessel disease showed favorable outcome, we currently lack larger properly randomized high quality studies which show definite benefit. Proponents of off-pump surgery state that the avoidance of the CPB leads to significantly reduced myocardial ischemia-reperfusion injury, post-operative systemic inflammatory response, postoperative pulmonary complications, hospital stay and cost, a feature that may improve the clinical and economical outcomes. However, perfection in surgical technique, completeness of revascularization and whether the off pump method leads to improved outcome are still burning issues. In this review, OPCAB is found to be significantly better than the ONCAB in reducing cost, hospital stay, blood transfusion requirements, incidence of post-operative pulmonary complications, systemic inflammation and post-operative atrial fibrillations in most of the studies. The comparison show almost equivocal results regarding mortality, survival, quality of life, re-intervention rate, risk of stroke, cognitive decline and GI complication.