Augmentation of abdominal organ perfusion during cardiopulmonary bypass with a novel intra-aortic pulsatile catheter pump.

BACKGROUND: Current pulsatile pumps for cardiopulmonary bypass (CPB) are far from satisfactory because of the poor pulsatility. This study was undertaken to examine the efficiency of a novel pulsatile catheter pump on pulsatility and its effect on abdominal organ perfusion during CPB. METHODS: Twelve pigs weighing 89+/-11 kg were randomly divided into a pulsatile group (n=6) and a non-pulsatile group (n=6). All animals had a CPB for 120 min, aorta clamped for 60 min, temperature down to 32 degrees C, and a perfusion flow of 60 ml/kg/min. In the pulsatile group, a 21 Fr intra-aortic pulsatile catheter, which was connected to a 40 mL membrane pump, was placed in the descending aorta and activated by a balloon pump driver during the first 90 minutes of CPB until aortic declamping. Hemodynamics, organ blood flow, body metabolism, and blood trauma were studied during experiments. RESULTS: Compared with the non-pulsatile group during CPB, the pulsatile group had a higher systolic blood pressure (p<0.01), higher mean arterial pressure (p<0.05), and higher blood flow to the superior mesenteric artery (p<0.05). The hemodynamic energy, indicated by the energy equivalent pressure (EEP) was higher in the gastrointestinal tract and kidney in the pulsatile group (p<0.01, p<0.01). Abdominal organ perfusion status, as indicated by SvO 2 in the inferior vena cava, was higher in the pulsatile group (p<0.05) 30 min after cessation of CPB. Hemolysis indicated by release of free hemoglobin during CPB was similar in the two groups. CONCLUSION: Applying the pulsatile catheter pump in the descending aorta is effective in supplying the pulsatile flow to the abdominal organs and results in improved abdominal organ perfusion during the ischemic phase of CPB.

Instrument-independent flux units for laser Doppler perfusion monitoring assessed in a multi-device study on the renal cortex.

To investigate the feasibility of instrument-independent perfusion units for laser Doppler flowmetry, a comparison was performed of two commercial fiberoptic laser Doppler perfusion monitors measuring the same flux situation for two different types of probes. In vivo measurements were performed on the cortex of pig's kidney, with an ultrasonic arterial flow meter as reference. The flow was mainly varied by internal arterial constriction using a balloon catheter. For each probe, instruments are compared in terms of the ratio of laser Doppler flux and arterial flow. For a given probe, the flux-to-flow ratios of the two instruments show a linear mutual relationship for a wide variety of arterial flows and laser Doppler fluxes. In vitro measurements were performed on an aqueous suspension of polystyrene microspheres. For the probe with interfiber distance 500 microm the ratio of the in vivo fluxes appears to agree within 16% to the value found in vitro, while for the 250-microm probe a difference of 28% was found. For a wide range of fluxes, the in vivo flux values of one instrument can be translated into flux values for the other instrument, in spite of the instrumental differences. This enables the user to render experimental results independent of the specific instrument, thus facilitating multi-center studies.

Blood interaction with a Bioline heparin coated HIA-VAD: a study on calves.

The blood compatibility of ventricular assist devices developed by the Helmholtz Institute Aachen (HA-VAD's) was tested on calves. Seven calves received a non-coated HIA-VAD (control) and three a Bioline heparin coated device. The circulatory support of these HIA-VAD's lasted one week. Mechanical blood cell trauma estimated by hematocrit (Hct), hemoglobin (total Hb) and free plasma hemoglobin (free Hb) levels did not differ in either group. All HIA-VAD's in the control group remained thrombus free, except on one occasion when an inflow cannula was obstructed by a thrombus located in the tip. After circulatory support, the animals in this group seemed clinically healthy. However, thrombus formation was observed in the three heparin coated HIA-VAD's. One animal in this group died from complications after re-operation for pneumothorax on the fifth day of support, whereas the other two animals seemed clinically healthy. In these three animals, a strong decrease in platelet numbers was measured even after 24 hours of support which recovered after 72 hours. This decrease in platelet numbers was associated with a lower degree of platelet aggregation ability stimulated by ADP (p < 0.05). Fibrin(ogen) degradation products (FDP) increased significantly immediately after the implantation procedure (p < 0.05). Fibrinogen levels initially decreased during the implantation procedure, but increased thereafter in both groups. The FDP levels remained high in this group, although the FDP levels in both groups were decreased after the implantation procedure. The ex vivo measured circulating heparin levels were lower in the heparin coated HIV-VAD group despite the equally administrated heparin doses in both animal groups. No differences were measured in either group with regard to white blood cell (WBC) numbers and complement hemolytic activity (CH50). Despite these hemostatic changes, no mechanical trauma could be demonstrated after seven days of circulatory support.

Ex vivo design evaluation of an implantable blood port system.

A prototype of a totally implantable vascular catheter-port system was evaluated on its design using three animals of different species. The catheter was placed either intravenously or intra-arterially, and connected to the port which was retained outside the body. Parameters used for design evaluation or functionality testing were focused on the use and handling of the port-catheter system such as easiness of flushing, injection, blood sampling, septum stiffness to prevent blood reflux after pushing the septum, and possible diffusion of blood into the saline present in the port-catheter system. This pilot experiment showed that the septum of the prototype port system was too flexible, and that the distance between septum and base of the port was too short. These findings have led to a major improvement of the catheter-port system, currently successfully used in cancer chemotherapy.

Reflectance pulse oximetry in fetal lambs.

Transmission pulse oximetry is used for monitoring in many clinical settings. However, for fetal monitoring during labor and in situations with poor peripheral perfusion, transmission pulse oximetry cannot be used. Therefore, we developed a reflectance pulse oximeter, which uses the relative intensity changes of the reflected red and infrared light (red/infrared ratio) to measure the arterial oxygen saturation. The performance of the reflectance pulse oximeter was studied in acute experiments in fetal lambs. By stepwise reduction of the inspired oxygen concentration of the ewe, measurements were done at the fetal scalp at various arterial oxygen saturation levels (17-82%). Reflectance pulse oximeter readings were averaged over periods of 15 s and compared with simultaneously taken fetal arterial blood samples. A calibration curve for the relationship between red/infrared ratio and arterial oxygen saturation was obtained from 53 measurements in four fetal lambs, by linear regression analysis [red/infrared = 4.088-(0.038.SaO2), r = 0.96]. In these experiments, the pulse oximeter showed a precision of 4.7% oxygen saturation around the calibration curve, with a 95% confidence interval of +/- 9.4%.

Clear prime for infant cardiopulmonary bypass: a miniaturized circuit.

The extracorporeal circuit used clinically to perform cardiopulmonary bypass (CPB) in small infants is relatively large requiring blood to prime the circuit to reduce hemodilution. To study the merits of clear prime also in infants, we did experiments in rabbits with two extracorporeal circuits: one employing traditional venous gravity drainage (priming volume 330 ml) and the other employing vacuum drainage (priming volume 90 ml). The first circuit still had to be primed with blood, whereas the second circuit could be primed with a clear solution. Both circuits were automatically controlled to lighten the task of the perfusionist to operate the CPB safely and accurately. We demonstrated that the clear priming solution in the second circuit eliminates the hemodynamic deterioration caused by blood prime in the first circuit. Studying the effect of various modes of regulation, we showed that automatic control of CPB based on venous return is similar to autoregulation of the heart according to Starling's law, and maintains not only normal hemodynamics, but also an optimal microcirculation.

Airborne contamination during cardiopulmonary bypass: the role of cardiotomy suction.

Airborne contamination of the wound area and the cardiopulmonary bypass circuit during sham open-heart operations on dogs was studied. The air of the operating room (OR) was contaminated with two typeable bacterial strains. It was found that the number of wounds, blood specimens, oxygenators, and cardiotomy reservoirs contaminated with Staphylococcus aureus was related to the number of S. aureus present in the air of the OR, but that contamination with Serratia marcescens was related to the type of suction used. This form of contamination was considerably higher when air was aspirated together with blood into the suction line (p less than 0.05). The oxygenator and cardiotomy reservoir were contaminated mainly by aspirating wound fluid from the airborne-contaminated wound area. The low number of sample sites positive for S. marcescens may be due to a better preserved host defense mechanism if only wound fluid is sucked. A rather high incidence of postoperative infections occurred even in dogs operated on in an OR with a low level of airborne contamination.

Isolated hindlimb perfusion in dogs: the effect of perfusion pressures on the oxygen supply (ptO2 histogram) to the skeletal muscle.

During regional isolated perfusion, neoplasms in extremities are treated with high doses of chemotherapeutic drugs by means of an extracorporeal circuit. The question is whether optimal tissue perfusion, which is essential for the therapy, is obtained by regulation of the extracorporeal circuit on an adequate perfusion flow or on an adequate perfusion pressure. To determine which perfusion pressure is needed to maintain adequate tissue perfusion, hindlimbs of six dogs were perfused at perfusion pressures 0, 15, 25, and 50 mm Hg below systemic mean arterial pressure. A multiwire polarographic oxygen electrode placed on the sartorius muscle permitted quantitative evaluation of tissue oxygenation by means of ptO2 histograms. Our results indicated that the perfusion pressure must be equal to or within 15 mm Hg below systemic mean arterial pressure to obtain optimal tissue perfusion. To maintain this perfusion pressure, high perfusion flows of about five to 10 times control femoral flows were needed. At a perfusion pressure 50 mm Hg below systemic mean arterial pressure, perfusion flow was normal, but tissue perfusion was severely impaired.

Effects of acute bleeding on oxygen supply to the skeletal muscle in dogs.

To study the effect of acute bleeding on the oxygen supply to the skeletal muscle, heparinized dogs were bled via an arterial cannula until mean arterial pressures of 25 and 50 mm Hg below initial value were reached. The shed blood was retransfused in reverse (50, 25 mm Hg) after correction of the acid-base imbalance in the dogs. Oxygen supply to the skeletal muscle was measured by means of a multiwire polarographic electrode placed on the sartorius muscle and was evaluated by means of ptO2 histograms. The ptO2 histograms showed that the oxygen supply to the skeletal muscle is severely impaired after a decrease in mean arterial pressure of 25 mm Hg. Further impairment was seen after a decrease in pressure of 50 mm Hg. During retransfusion tissue oxygenation was normalized only after all shed blood was retransfused and the initial mean arterial pressure was reached.

Improved tissue perfusion during pressure-regulated hyperthermic regional isolated perfusion in dogs.

To achieve adequate tissue perfusion during regional isolated perfusion, hind limbs of dogs were perfused for 60 min, regulating the extracorporeal circuit on pressure. The dogs were divided into three groups. In groups I and II perfusions were performed at a delta pressure (systemic mean arterial pressure minus hind limb mean arterial pressure) of respectively 50 and 15 mm Hg; in group III delta pressure was also 15 mm Hg but the cytostatic drug Melphalan was added. Tissue perfusion was determined by means of a multiwire polarographic oxygen electrode. Adequate tissue perfusion was obtained only at subnormal perfusion pressures (groups II and III), although in all groups perfusion flow was higher than preoperative flow. At low perfusion pressures (group I), tissue perfusion was severely impaired. In all groups leakage remained less than 10%. During regional isolated perfusion the extracorporeal circuit must be regulated at a delta pressure of 15 mm Hg to achieve adequate tissue perfusion.

A new hollow fiber membrane oxygenator with an integral heat exchanger: a hematological evaluation in dogs.

A recently developed hollow fiber membrane oxygenator, made of microporous polypropylene (Capiox, Terumo, 1.6 m2) was tested to evaluate the hemocompatibility and the ease and safety of operation. Two types of this oxygenator were tested: one with and one without an integral heat exchanger. Each type was tested in 6 dogs during a partial bypass of 2 hours at a flow rate of 2 l/min. In addition, gas transfer measurements were carried out. The Terumo oxygenator preserved the blood cells and the platelet function very well. In addition, neither the Wu-Hoak index, a method to measure platelet aggregates, nor inspection of the oxygenator revealed platelet aggregates. Operation and debubbling procedure were easy and safe. The estimated rated blood flow for O2 was 1.5 l/min with a corresponding CO2 removal of 90 ml/min. The integral heat exchanger did not affect the results significantly. Our data show that this oxygenator is easy and safe to use. Clinical evaluation is recommended.