Evaluation of the use of a heparin dose-response test in dogs to determine the optimal heparin dose during intravascular procedures and assessment of the in vitro heparin response in healthy dogs

BACKGROUND

No guidelines for administering and monitoring anticoagulants intraprocedurally are currently available in dogs, despite the prevalence of procedures necessitating systemic anticoagulation with heparin.

OBJECTIVES

To evaluate an activated clotting time (ACT)-based heparin dose-response (HDR) test to predict the individual required heparin dose in dogs during intravascular procedures, and to investigate both the in vitro heparin - ACT and in vitro heparin - factor anti-Xa activity (anti-Xa) relationships in dogs.

METHODS

Blood was collected from eight healthy beagles undergoing a cardiac procedure and utilised to establish baseline ACT and for in vitro evaluation. Subsequently, 100 IU/kg heparin was administered intravenously (IV) and ACT was remeasured (HDR test). The required heparin dose for an ACT target response ≥300 s was calculated for each individual and ACT was remeasured after administration of this dose. For in vitro testing, a serial heparin blood dilution (0-0.5-1-2-4 international unit (IU)/mL) was prepared and ACT and anti-Xa were determined using whole blood and frozen plasma, respectively.

RESULTS

The HDR test overestimated the required heparin dose in 3/7 dogs. In vitro, ACT and anti-Xa increased significantly with increasing blood heparin concentration. Heparin - ACT was nonlinear in 4/8 dogs at heparin concentrations >2 IU/mL, whereas heparin - anti-Xa remained linear throughout the tested range.

CONCLUSIONS

The HDR test poorly estimated the required heparin dose in dogs. This is most likely attributed to a nonlinear heparin - ACT relationship, as observed in vitro. Anti-Xa is a promising alternative for ACT; however, unavailability as a point-of-care test and lack of in vivo target values restrict its current use.

Surgical correction of an infundibular pulmonic stenosis and ventricular septal defect in a Shetland Sheepdog

A four-month-old male Shetland Sheepdog presented with exercise intolerance. Physical examination revealed an IV/VI left cranial systolic heart murmur. Echocardiography showed a severe infundibular pulmonic stenosis and a concomitant restrictive ventricular septal defect. As clinical signs of congestive right-sided heart failure worsened and were refractory to medical treatment, surgical correction was advised. Via sternotomy, with cardiopulmonary bypass and cardioplegic cardiac arrest, ventricular septal defect closure and resection of the stenotic infundibular band were performed through right ventriculotomy, followed by patch enlargement. Postoperative recovery was uneventful and echocardiography showed complete resolution of the stenosis and successful closure of the ventricular septal defect. Follow-up echocardiography revealed restenosis after seven weeks and recurrence of right-sided heart failure three months postoperatively. Stenting of the restenosis was attempted via a hybrid procedure with sternotomy and direct transventricular approach. The dog developed fatal ventricular fibrillation during stent deployment. This is the first dog in which surgical right ventricular patch enlargement under cardiopulmonary bypass is reported for the treatment of a primary infundibular pulmonic stenosis.

Use of a right ventricular continuous flow pump to validate the distensible model of the pulmonary vasculature

In the pulmonary circulation, resistive and compliant properties overlap in the same vessels. Resistance varies nonlinearly with pressure and flow; this relationship is driven by the elastic properties of the vessels. Linehan et al. correlated the mean pulmonary arterial pressure and mean flow with resistance using an original equation incorporating the distensibility of the pulmonary arteries. The goal of this study was to validate this equation in an in vivo porcine model. In vivo measurements were acquired in 6 pigs. The distensibility coefficient (DC) was measured by placing piezo-electric crystals around the pulmonary artery (PA). In addition to experiments under pulsatile conditions, a right ventricular (RV) bypass system was used to induce a continuous pulmonary flow state. The Linehan et al. equation was then used to predict the pressure from the flow under continuous flow conditions. The diameter-derived DC was 2.4%/mmHg (+/-0.4%), whereas the surface area-based DC was 4.1 %/mmHg (+/-0.1%). An increase in continuous flow was associated with a constant decrease in resistance, which correlated with the diameter-based DC (r=-0.8407, p=0.044) and the surface area-based DC (r=-0.8986, p=0.028). In contrast to the Linehan et al. equation, our results showed constant or even decreasing pressure as flow increased. Using a model of continuous pulmonary flow induced by an RV assist system, pulmonary pressure could not be predicted based on the flow using the Linehan et al. equation. Measurements of distensibility based on the diameter of the PA were inversely correlated with the resistance.

Evaluation of different paediatric venous cannulae using gravity drainage and VAVD: an in vitro study

Six different commercially available paediatric venous cannulae, together with a specially constructed cannula, were tested in vitro for their pressure-flow relationship. With the cannulae placed in an open reservoir, flow increased with larger diameters and higher pressures. At a pressure of 30 cm H2O, flows were 219± 20, 285± 13, 422± 11 and 728± 4 ml/min for the 12, 13.2, 14 and 16 French, respectively. No differences were found between angled and straight cannulae. When the cannulae were tested in a latex model simulating the right atrium and vena cavae, the highest flow obtained by gravity was 164 ml/min using an angled 14-French cannula. When vacuum was applied to augment venous return, a maximum flow of 179 ml/min was measured using an angled 14-French cannula. Collapse can occur when the pressure difference becomes too high in the test system. This is important, since most children are selectively cannulated in both major veins. Monitoring of the intravascular pressure might help to prevent collapse. A larger-diameter venous cannula does not always produce the highest flow when placed in a vein. This is most obvious when augmenting venous return. The design of the cannula tip, in combination with VAVD, can affect the venous return.

Postmortem pump-driven reperfusion of the vascular system of porcine lungs: towards a new model for surgical training

PURPOSE

The objective of this experiment is to establish a continuous postmortem circulation in the vascular system of porcine lungs and to evaluate the pulmonary distribution of the perfusate. This research is performed in the bigger scope of a revascularization project of Thiel embalmed specimens. This technique enables teaching anatomy, practicing surgical procedures and doing research under lifelike circumstances.

METHODS

After cannulation of the pulmonary trunk and the left atrium, the vascular system was flushed with paraffinum perliquidum (PP) through a heart-lung machine. A continuous circulation was then established using red PP, during which perfusion parameters were measured. The distribution of contrast-containing PP in the pulmonary circulation was visualized on computed tomography. Finally, the amount of leak from the vascular system was calculated.

RESULTS

A reperfusion of the vascular system was initiated for 37 min. The flow rate ranged between 80 and 130 ml/min throughout the experiment with acceptable perfusion pressures (range: 37-78 mm Hg). Computed tomography imaging and 3D reconstruction revealed a diffuse vascular distribution of PP and a decreasing vascularization ratio in cranial direction. A self-limiting leak (i.e. 66.8% of the circulating volume) towards the tracheobronchial tree due to vessel rupture was also measured.

CONCLUSIONS

PP enables circulation in an isolated porcine lung model with an acceptable pressure-flow relationship resulting in an excellent recruitment of the vascular system. Despite these promising results, rupture of vessel walls may cause leaks. Further exploration of the perfusion capacities of PP in other organs is necessary. Eventually, this could lead to the development of reperfused Thiel embalmed human bodies, which have several applications.

Does contemporary oxygenator design influence haemolysis?

Based on their design, all membrane oxygenators generate a certain resistance to flow. In clinical practice, this resistance is calculated by measuring both blood flow and the pressure drop over the oxygenator. Historically, some designs, such as the Kolobow spiral coil oxygenator and the Cobe flat sheet oxygenator, had quite a high pressure drop, but were, nevertheless, considered very haemocompatible. Today, both medium and low pressure drop oxygenators are commercially available. Based on physics and the existing literature, this review aims to investigate whether pressure drop by itself can be considered an independent factor of haemolysis.

End-organ protection in cardiac surgery

Mortality and morbidity postcardiac surgery with cardiopulmonary bypass (CPB) remain relative stable over the last decades, while the number of patients with increased comorbidity and more complex cardiac disease increases. Nevertheless, end-organ dysfunction and/or failure remain an issue. Multiple perioperative variables, such as non-optimal oxygen delivery, manipulation of the aorta, hyperlactatemia, type of anesthesia, surgical procedure and myocardial protection can be hold responsible for end-organ failure postcardiac surgery. However, it becomes more and more evident that also pre-existing factors, such as metabolic syndrome, renal insufficiency, hypertension, stroke and infection exacerbate mortality and morbidity. Unfortunately, these predisposing risk factors cannot be influenced perioperatively. Therefore, therapy should focus on controlling perioperative variables that, in combination with the predisposing factors, will further exacerbate organ dysfunction. In order to achieve this, more emphasis should be given to a patient-specific, goal-directed perfusion approach. This review will mainly focus on the impact of perioperative variables.

Platelet gel supernatant as a potential tool to repopulate acellular heart valves

OBJECTIVE

The aim of this study was to repopulate decellularized heart valve matrices with ovine mesenchymal stem cells (oMSCs) by the use of platelet gel (PG) supernatant, a storage vehicle for growth factors.

METHODS

oMSCs were exposed to different concentrations of PG-released supernatant and cell proliferation was evaluated using the MTS assay. oMSC motility and invasiveness were assayed using a Boyden chamber. A quantitative sandwich enzyme immunoassay was used to examine amounts of bFGF and TGF-β1 in the PG supernatant. Repopulation of acellular heart valve matrices was stimulated by seeding matrices with oMSCs supplemented with the PG supernatant.

RESULTS

The most significant increase in proliferation induced by PG supernatant appeared at 1 × 10(5) plts/ml concentration. Higher concentrations evoked reduction of the stimulatory process. oMSC motility was most significantly stimulated at 1 × 10(6) plts/ml. Stimulating invasiveness of oMSCs needed the much higher concentration of 2 × 10(6) plts/ml. Immunoassays revealed that sheep PG supernatant contains 184.8 pg/ml bFGF and 60.5 ng/ml TGF-β1. Moreover, repopulation of acellular heart valve matrices was significantly enhanced by PG supernatant addition and resulted in upregulation of the myofibroblast marker alpha-smooth muscle actin.

CONCLUSIONS

Growth factors released from platelets had the potential to induce cell repopulation in a heart valve tissue engineering procedure, through stimulation of mesenchymal stem-cell migration and invasion.

Venous drainage--gravity or assisted?

Since the early start of cardiopulmonary bypass, vascular access has been recognized as a main variable for obtaining optimal blood flow during cardiopulmonary bypass. In particular, venous drainage can limit the maximum flow as the wide, low-resistance, collapsible veins are connected with smaller stiff cannulas and tubing. Due to the introduction of long venous cannulas for minimally invasive cardiac surgery and the desire to limit hemodilution during cardiopulmonary bypass, more and more centers have started using assisted venous drainage techniques. This article gives an overview of these techniques, with their respective advantages and disadvantages.

Active or passive bio-coating: does it matters in extracorporeal circulation?

Background: Two types of surface coating for cardiopulmonary bypass (CPB) are used: bioactive (heparin, nitric oxide) and biopassive (albumin, polyethyleneoxide (PEO), phosphorylcholine). When haemocompatible coatings are combined with the separation of pleuro-pericardial aspiration, attenuation of both the coagulation and complement cascades, as well as better platelet preservation, has been demonstrated. This study wants to investigate if the combination of a bioactive with a biopassive coating (unfractionated heparin embedded in a phosphorylcholine matrix) combines the beneficial effects of both approaches.

Materials and methods: Thirty patients undergoing elective CABG were prospectively randomized into two groups of 15 patients. The sole exclusion criterion was an ejection fraction of less than 40%. In the control group (PC), the whole CPB circuit was coated with phosphorylcholine (PC). In the study group (XPC), unfractionated heparin was embedded in the PC matrix of the oxygenator and arterial line filter.

Results: No differences were found for haemolytic index, thrombin-anti-thrombin complex (TAT), IL-6, IL-10 and blood loss. PF4 plasma concentration increased from 27.6±22.0 IU/mL to 165.7±43.9 IU/mL (p<0.001) at 15 minutes of CPB in the PC and from 16.0±9.7 IU/mL to 150.9 ± 61.3 IU/mL (p<0.001) in the XPC group. Terminal complement complex (TCC) increased over time in both groups until the end of CPB (Figure 2A). Within each group, TCC generation was statistically significantly higher after the release of the aortic cross-clamp (p<0.001) and at the end of CPB (p<0.001). Total TCC generation was statistically significantly higher in the XPC group compared to the PC group (p=0.026). The difference was statistically significant after the release of the aortic cross-clamp (p=0.005) and at the end of CPB (p=0.001).

Conclusions: Based on our results, there is no additional benefit in combining phosphorylcholine with unfractionated heparin in elective patients undergoing coronary artery bypass grafting (CABG). Massive haemodilution leads to enhanced complement activation.

Haemostasis monitoring during sequential aortic valve replacement and liver transplantation

Despite advances in anaesthesiological and surgical techniques, cardiac surgery in cirrhotic patients remains hazardous. This report outlines our experience with haemostasis monitoring in two consecutive cases of sequential aortic valve replacement and liver transplantation. Clotting disturbances proved to have fatal consequences since one of these patients died following massive lung embolism. The second patient underwent successfully this combined procedure and is in good clinical state 14 months postoperatively. Evaluation and discussion of the coagulation monitoring by the Sonoclot Analyzer in both patients and related therapeutic suggestions for the prevention of thrombotic events are discussed.

Optimal Versus Suboptimal Perfusion During Cardiopulmonary Bypass and the Inflammatory Response

Despite major improvements in perfusion techniques over the past 50 years, it is still not possible to formulate a clear definition of what is meant by optimal perfusion. In part this is due to the lack of sufficient evidence-based data and in part because of the complex pathophysiology that takes place during cardiac surgery with cardiopulmonary bypass. To find an answer we need to understand the exact mechanism of the inflammatory reaction triggered by the cardiopulmonary bypass. However, it is clear that further improvement of the cardiopulmonary bypass components alone will be sufficient. Only a combined strategy can further improve cardiopulmonary bypass—related morbidity and mortality. Such a combined strategy will embrace perfusion techniques as well as a pharmacological approach. It will also require a continuous monitoring of the microcirculation. The latter will not only allow to rapidly sense changes in the quality of perfusion but, even more important, also make it possible to intervene at the moment of deterioration. Recent research shows that such an approach has positive an impact on cardiopulmonary bypass—related morbidity postoperatively.

Interaction of plasma proteins with commercial protein repellent polyvinyl chloride (PVC): a word of caution

Protein adsorption onto polymers remains a problem. In recent years, several protein-repellent PVC tubings have been developed. Although several studies report the interaction between plasma coagulation proteins and PVC, few address the interaction with other plasma proteins. Two commercial brands of untreated medical grade PVC tubing, phosphorylcholine-coated PVC tubing, triblock-copolymer (polycaprolactone-polydimethylsiloxane-polycaprolactone)-treated PVC tubing and poly-2-methoxyethylacrylate (PMEA)-coated tubing were exposed for 60 minutes to human plasma. A broad spectrum of plasma proteins was found on all tubing. The adsorbed albumin to total protein ratio is lower than the similar ratio in plasma while alpha1 and alpha2 globulins are over-represented in the protein spectrum. On PMEA tubing, not only alpha globulins, but also beta and gamma globulins, are found in high concentrations in the adsorbed protein. PMEA tubing and uncoated PVC tubing of brand B had a higher amount of protein adsorbed compared against all other tubing (p < 0.05). There were no statistical differences in protein adsorption between the triblock-copolymer-treated tubing, the phosphorylcholine-coated tubing and the uncoated PVC tubing of brand A. The average thickness of the protein layer was 23 nm. Plasma protein adsorption still exists on uncoated and protein-repellent tubing and can initiate a systemic inflammatory reaction.

Cytoreductive surgery with hyperthermic intraperitoneal chemoperfusion (HIPEC): Toxicity, survival, and prognostic variables in 130 patients with peritoneal carcinomatosis

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Background: Peritoneal carcinomatosis (PC) has a dismal prognosis. Cytoreductive surgery with HIPEC has been introduced in the management of PC with biologically favourable features. Methods: In an eight year period, 130 patients were treated (53% female, mean age 56±1 years). The origin of PC was colorectal cancer (CRC, 58%), pseudomyxoma peritonei (PMP, 9%), ovarian cancer (17%), primary peritoneal mesothelioma (10%) and gastric cancer (6%). Surgery was followed by HIPEC with mitomycin C (90 min, 35 mg/m2), oxaliplatin (30 min, 460 mg/m2) or cisplatin (90 min, 100–250 mg /m2) depending on tumour histology and previous systemic chemotherapy. The extent of disease was scored using a scale ranging from 0–9, while completeness of cytoreduction (CC) was scored as complete (CC0), nearly complete (CC1, miliary residual disease) or incomplete (CC2, gross residual disease). Target intraperitoneal temperature was 41°C-42°C. Actuarial survival was calculated using the Kaplan Meier method and univariate analysis performed using the log rank method. Results: Open perfusion (coliseum technique) was used in 41% of procedures. Macroscopically complete resection was achieved in 41%. Postoperative 30 day mortality was 1.5% while major morbidity developed in 18% of patients. Morbidity was mainly related to the extent of surgery. Median overall survival (months) was as follows: CRC, 20; PMP, 38; ovarian cancer, 19; gastric cancer, 10; mesothelioma, 9. Median survival was significantly better in CC0 patients (40 months) compared to CC1 (17 months) or CC2 (12 months). Survival was significantly worse in patients with ascites at surgery (p<0.02) and in patients who did not receive adjuvant systemic chemotherapy (p<0.001). The extent of disease score before surgery (p=0.29), performance of a splenectomy (p=0.65), and timing of PC (metachronous or synchronous, p=0.25) were not significantly related to overall survival. Conclusions: Cytoreduction followed by HIPEC offers a significant survival advantage in selected patients with PC with acceptable early toxicity. Survival is significantly associated with disease histology, CC, presence of ascites and adjuvant chemotherapy.

No significant financial relationships to disclose.

Hemodynamic comparison of two different pediatric aortic cannulas

Any extracorporeal blood treatment requires an adequate and safe connection to the circulation. For cardiopulmonary bypass procedures, aortic and venous cannulas are utilized. However, the performance of these cannulas is not only dependent on their size (diameter), but also on their complete geometric design. In this paper two aortic cannula designs are evaluated hemodynamically for two different sizes (8, 10 Fr) both with aqueous fluids and with blood. Using the novel concept of equivalent diameter, a new performance parameter, and the theory of dynamic similarity the results obtained with different fluids can be compared. Data points of one cannula can be fitted to a parabolic equation. There is a significant performance difference between the two 8 Fr cannulas. The 10 Fr cannulas differ non-significantly except when water is used. Equivalent diameters obtained with water in the turbulent region are significantly higher than those obtained with fluids that have a higher viscosity (blood and aqueous glycerine mixture). The latter fluids have comparable viscosities and render an equal equivalent diameter. The coefficients of their proper parabolic fit lines can easily be recalculated into each other. This provides a simple method to quickly determine pressure drops in cannulas in the operating room.

Tissue factor as the main activator of the coagulation system during cardiopulmonary bypass

OBJECTIVE

This study investigates the influence of foreign material and blood aspirated from nonvascular structures on activation of coagulation, hemolysis, and blood loss.

METHODS

The series comprises 3 randomized groups (groups C, S, and S+P) of 10 patients undergoing routine coronary artery bypass grafting with cardiopulmonary bypass. In group C, the control group, all aspirated blood was returned into the circulation. In group S suction blood was discarded, whereas group S+P was identical to group S, with surfaces coated with phosphorylcholine. Plasma concentrations of beta-thromboglobulin, thrombin generation, haptoglobin, and free hemoglobin, as well as blood loss, were measured.

RESULTS

A steady increase in free plasma hemoglobin, as well as an increased generation of thrombin, was noticed in group C. Moreover, a close correlation (r = 0.916) between the generation of thrombin and its inhibition (thrombin-antithrombin complexes) was observed. Platelets were clearly activated in group C and, to a lesser extent, in group S. In contrast, platelet activation in group S+P was negligible, resulting in a 30% decrease in blood loss (P =.05).

CONCLUSIONS

Aspirated blood contaminated by tissue contact is the most important activator of the coagulation system and the principal cause of hemolysis during cardiopulmonary bypass. Contact with a foreign surface is not a main variable in the procoagulant effect of bypass. Mimicking the outer cell membrane structure resulted in decreased platelet activation and decreased blood loss.

Mass transfer characteristics of artificial lungs

An artificial lung is used during cardiopulmonary bypass to oxygenate blood and control blood temperature. The oxygen transfer rate-flow rate characteristics of three hollow fiber membrane artificial lungs (Sarns Turbo 440, Cobe Optima, Dideco Compactflo) were determined in vitro to characterize design features. Results are presented as a unique dimensionless relationship between Sherwood number, NSh (ratio of convective to diffusive mass transfer), Schmidt number, NSc (ratio of momentum to diffusive transport), and Reynolds number, NRe (ratio of inertial to viscous forces). This relationship is a function of device porosity, epsilon, and characteristic device length, xi, defined as the ratio of the mean blood path and manifold length: Nsh/NSc(1/3) x xi(1/2) = phi x (epsilon(1/m) x NRe)(m) where phi = 0.26 and m = 1.00 for NPe < 3,200 and phi = 0.47 and m = 0.64 for NPe > 3,200 where NPe is the dimensionless Péclet number defined as NRe x NSc. We found good correspondence between the model predictions and in vitro blood oxygen transfer rates. We conclude that this dimensionless approach allows us (1) to compare artificial lungs independently, (2) to relate water tests to blood, and (3) to predict the oxygen transfer rate of a new artificial lung design.

Phosphorylcholine coating of extracorporeal circuits provides natural protection against blood activation by the material surface

OBJECTIVE

The aim of this study is to evaluate the use of a new coating, mimicking the outer cell membrane, in paediatric cardiac surgery.

METHODS

Two groups of ten patients with a body weight below 8 kg, undergoing elective cardiac operations for different congenital anomalies, were prospectively enrolled in this study. In one group the whole extracorporeal circuit, including the cannulas, was coated with phosphorylcholine (PC). In the second group the same circuit was used without coating. Platelet activation (thromboxane B2 (TXB2), beta-thromboglobulin (betaTG)), activation of the coagulation system (F1+2), leukocyte activation (CD11b/CD18) and terminal complement activation (TCC) were analyzed pre-cardiopulmonary bypass (CPB), at 15, 60 min of CPB, at the end of CPB, 20 min post CPB and at postoperative day 1 and 6.

RESULTS

No statistical differences were found for F1+2 and CD11b/CD18. After onset of CPB mean levels of TCC remained stable in the PC group whereas an increase was observed in the control group. During CPB betaTG values in both groups increased to a maximum at the end of CPB. Within groups the increase in betaTG levels during CPB was statistically significant (P<0.05) from baseline in the control group starting from 60 min of CPB whereas no statistical difference was observed in the PC group. After the start of CPB TXB2 mean levels increased to 405+/-249 pg/ml in the PC group vs. 535+/-224 pg/ml in the control group. After this initial increase there was a small decline in the PC group with further increase. This was in contrast to the control group were TXB2 levels further increased up to a mean of 718+/-333 pg/ml at the end of CPB (P=0.016).

CONCLUSIONS

Phosphorylcholine coating had a favourable effect on blood platelets, which is most obvious after studying the changes during cardiopulmonary bypass. A steady increase of TXB2 and betaTG was observed in the control group, whereas plateau formation was observed in the phosphorylcholine group. Clinically, this effect may contribute to reduced blood loss and less thromboembolic complications. Complement activation is lower in the coated group.

Hydrodynamic characteristics of artificial lungs

An artificial lung is used during cardiopulmonary bypass to oxygenate blood and to control blood temperature. The pressure drop-flow rate characteristics of the membrane compartment in three hollow fiber membrane oxygenators were determined in vitro to characterize design features. Results are presented in a unique dimensionless relationship between Euler number, N(Eu) (ratio of pressure drop to kinetic energy), and Reynolds number, N(Re) (ratio of inertial to viscous forces), and are a function of the device porosity, epsilon, and a characteristic device length, xi, defined as the ratio of the mean blood path and manifold length: [equation in text]. This dimensionless approach allows us (1) to compare oxygenators independently, and (2) to relate water tests to blood.

Chondrosarcoma of the hyoid bone

The CT and MRI findings in a case of chondrosarcoma of the hyoid bone are reported. Although chondrosarcoma is the second most common primary malignant bone tumor, only 10 % of chondrosarcomas occur in the head and neck region. The hyoid bone is a rare site of involvement with only seven cases reported previously.

Feasibility of a pumpless extracorporeal respiratory assist device

BACKGROUND

Our study evaluated the efficacy and feasibility of a pumpless respiratory assist device and determined its capacity for carbon dioxide removal.

METHODS

In five adult pigs the left femoral vein and artery were cannulated with a 20F cannula and connected to a low-pressure hollow-fiber artificial lung. After we had obtained baseline values of mean arterial pressure, cardiac output, and blood flow across the artificial lung, the mean arterial pressure was reduced 20% and 40% relative to baseline; in a second phase, it was raised 20% and 40. Cardiac output and artificial lung flow were simultaneously recorded. We determined the carbon dioxide removal capacity of the artificial lung by gradually increasing the arterial partial carbon dioxide tension of the animal.

RESULTS

An increase of 10 mm Hg in mean arterial pressure resulted in an increase of flow of 0.14 L/min. The mean pressure drop across the artificial lung was measured at 17 +/- 9 mm Hg. The shunt flow over the artificial lung varied between 14 and 25% of the cardiac output of the animal. Depending on inlet conditions, carbon dioxide removal by the artificial lung was between 62 +/- 22 mL/L/min and 104 +/- 25 mL/L/min.

CONCLUSIONS

A pumpless respiratory assist device can remove a significant proportion of the metabolic carbon dioxide production. However, adequate mean arterial pressure is mandatory to maintain sufficient flow across the device. The technique seems attractive because of its simplicity and can be used in acute lung injury in conjunction of apneic oxygenation for prolonged respiratory support.

Nitric oxide donors attenuate increase in pressure drop across membrane oxygenators

We have evaluated the effect of nitric oxide (NO) on the pressure drop across a membrane oxygenator in one in vitro model and two in vivo models (using four dogs and five pigs). In all the experiments sodium nitroprusside (SNP) was used as a NO source, whereas gaseous NO was only used in the in vitro model. The drugs were given when the pressure drop or resistance across the device increased to at least twice the baseline values. In the in vitro model, both SNP and gaseous NO decreased the pressure drop to 75% of its peak value after 10 min and to 67% after 20 min. In the dog model, resistance decreased from 390 to 153 mmHg/l/min after 5 min and to 85 mmHg/l/min after 20 min for a baseline value of 75 mmHg/l/min. The initial resistance across the membrane oxygenator in the pig model increased from 6.6+/-1.3 to 74+/-38 mmHg/l/min. An infusion of 10 microg/kg/min SNP reduced the resistance to 16+/-5 mmHg/l/min.

In vivo evaluation of a phosphorylcholine coated cardiopulmonary bypass circuit

A complete phosphorylcholine coated cardiopulmonary bypass circuit, including the Dideco D901 oxygenator, was tested for gas transfer, blood path resistance, and biocompatibility in a standardized setting. Blood compatibility was tested by measuring complement and platelet activation. Three dogs (mean body weight 28 +/- 3 kg) were placed on cardiopulmonary bypass at a flow rate of 600 mL/min during 6 hours. The animals were weaned from cardiopulmonary bypass and sacrificed electively after 7 days. Oxygen and carbon dioxide transfer were 26.6 +/- 2.4 mL/min and 33.0 +/- 1.9 mL/min, respectively. Mean pressure drop across the oxygenator was 52.6 +/- 0.2 mmHg. The respective baseline values for thromboxane B2, prostaglandin E2 and platelet factor 4 were 1817 +/- 283 pg/mL, 12783 +/- 2109 pg/mL, and 0.35 +/- 0.08 IU/mL. Thromboxane B2 and prostaglandin E2 increased slightly to 2881 +/- 868 pg/mL and 18083 +/- 3144 pg/mL at 30 minutes of bypass, whereas platelet factor 4 values remained stable curing the procedure. Concentrations of complement split products C5a were only mildly increased. After use scanning electron microscopy was performed on the inner housing, heat exchanger, and outer surface of the hollow fibers. No thrombi nor organized cellular deposits were found on any of the components. Phosphorylcholine coating of CPB seems to be very promising regarding platelet activation and complement activation.

Hydrodynamical comparison of aortic arch cannulae

The high velocity of blood flow exiting aortic arch cannulae may erode atherosclerotic material from the aortic intima causing non-cardiac complications such as stroke, multiple organ failure and death. Five 24 Fr cannulae from the Sarns product line (straight open tip, angled open tip with and without round side holes, straight and angled closed tip with four rectangular, lateral side holes), and a flexible cannula used at the University Hospital of Gent (straight open tip) are compared in an in vitro steady flow setup, to study the spatial velocity distribution inside the jet. The setup consists of an ultrasound Doppler velocimeter, mounted opposite to the cannula tip in an outflow reservoir. An elevated supply tank supplies steady flow of 1.3 L/min of water. Exit forces at various distances from the tip are calculated by integrating the assessed velocity profiles. The pressure drop across the cannula tip is measured using fluid filled pressure transducers. The four sidehole design provides the lowest exit velocity (0.85 versus 1.08 m/s) and force per jet (0.03 vs 0.15-0.20 N). The round sideholes are useless as less than 1% of the flow is directed through them. Furthermore, the use of angled tip cannulae is suggested because the force exerted on the aortic wall decreases the more the angle of incidence of the jet deviates from 90 degrees. Pressure drop is the lowest for the 4 side hole design and highest for the open tip and increases when an angled tip is used.

Can an oxygenator design potentially contribute to air embolism in cardiopulmonary bypass? A novel method for the determination of the air removal capabilities of neonatal membrane oxygenators

At present, air handling of a membrane oxygenator is generally studied by using an ultrasonic sound bubble counter. However, this is not a quantitative method and it does not give any information on where air was entrapped in the oxygenator and if it eventually was removed through the membrane for gas exchange. The study presented here gives a novel technique for the determination of the air-handling characteristics of a membrane oxygenator. The study aimed at defining not only the amount of air released by the oxygenator, but also the amount of air trapped within the oxygenator and/or removed through the gas exchange membrane. Two neonatal membrane oxygenators without the use of an arterial filter were investigated: the Polystan Microsafe and the Dideco Lilliput. Although the air trap function of both oxygenators when challenged with a bolus of air was similar, the Microsafe obtained this effect mainly by capturing the air in the heat exchanger compartment while the Lilliput did remove a large amount of air through the membrane. In conclusion, the difference in trap function was most striking during continuous infusion of air. Immediate contact with a microporous membrane, avoidance of high velocities within the oxygenator, pressure drop, transit time and construction of the fibre mat all contribute to the air-handling characteristics of a membrane oxygenator.

Low extracorporeal priming volumes for infants: a benefit?

An extracorporeal circuit consisting of an oxygenator especially designed for neonatal use and appropriately sized tubing, with an average total priming volume of 205 ml, was used on 80 infants undergoing cardiac surgery for congenital heart-disease. The priming volume and foreign surface area of the circuit were determined. The influence of low priming volumes on the use of blood products and the management of cardiopulmonary bypass was studied. No whole blood or platelets were used in this study. The mean volume of packed red blood cells used over the hospital stay was 202 +/- 67 ml. The mean volume of fresh frozen plasma (FFP) used until the second postoperative day was 62 +/- 72 ml. The mean total blood loss until the second postoperative day was 15.8 +/- 9.2 ml/kg. The priming volume of the extracorporeal circuit was 62% lower than values commonly reported in the literature. The low priming volume had a strong influence on the use of platelets and FFP and to a lesser extent on the use of packed red blood cells.

D-901 neonatal oxygenator: a new perspective

Five infants with congenital heart disease were perfused with the D-901 neonatal oxygenator at the time of their cardiac surgery. The ability to reduce the prime volume below the blood volume as well as the blood handling and gas transfer characteristics were studied. In all cases the prime volume was less than or equal to the blood volume of the patient. This resulted in a reduction in the use of homologous blood products. Due to the concept of the D-901 it was possible to adapt the tubing in such a way that a complete prime of 220 ml was obtained. The device had a maximum oxygen transfer of 45 ml/min. The maximum carbon dioxide removal was 50 ml/min at a blood gas ratio of one. The mean platelet count post bypass decreased to 91% of the baseline value. Mean free haemoglobin levels increased to 86 mg/100 ml at 120 minutes of bypass. We conclude that the D-901 oxygenator opens new perspectives for perfusion in small babies in terms of priming volume and use of homologous blood products while maintaining good gas transfer characteristics. However, larger series are necessary to expand our experience with this device and its limitations. No specific problems related to the device were encountered and all infants had an uneventful postoperative course.

Clinical evaluation of a new hollow fibre membrane oxygenator

Twelve consecutive patients undergoing elective cardiac surgery were perfused with the Cobe Optima hollow fibre oxygenator. Gas transfer characteristics and blood handling were studied. The device had a maximum oxygen transfer of 315 ml/minute. The average shunt fraction was 4.5%, and was not influenced by blood-flow rate. Mean platelet count declined slightly to 91% of the baseline at the end of the study period. Haemolysis was evaluated by monitoring serum-free haemoglobin, serum haptoglobin and serum haemopexin. The evolution was as follows: free haemoglobin increased from 14 +/- 5 mg/100 ml to 85 +/- 0.8/100 ml (p = 0.01) at the end of bypass; haptoglobin decreased from 1.33 +/- 0.90 g/l to 0.89 +/- 0.15 g/l (p = 0.01); and haemopexin decreased from 0.84 +/- 0.13 g/l to 0.74 +/- 0.15 g/l (p = nonsignificant). In all patients the residual capacity of serum haptoglobin to protect against haemolysis was satisfactory. All patients had an uneventful postoperative course.

Cervical intervertebral disc calcification in children: case report

We present the case of an 8-year-old male with intervertebral disc calcification at C2-C3. This uncommon entity has a very striking clinical and radiographic appearance. The course is mostly benign and therefore only needs conservative treatment.

[Digital intravenous subtraction angiography as a screening method in patients suspected of having renovascular hypertension]

Since January 1982 we combine urography in hypertensive patients with intravenous angiography of the renal arteries. In the first 20 patients examined by this new method, we also performed conventional intra-arterial angiography to evaluate the accuracy of the intravenous examination. In more than 80% of 104 patients the examination was of good diagnostic quality and both renal arteries were well visualized. I.V.D.S.A. has a lower morbidity and cost than conventional angiography. It is more accurate than urography and therefore gives us the possibility of a better screening of hypertensive patients.

Transluminal angioplasty: late results sustained by digital intravenous subtraction angiography

Digital intravenous subtraction angiography (DIVSA) appears to be a technique of minimal invasiveness and high accuracy in the follow-up of patients after percutaneous angioplasty (PTA) allowing correct angiographic evaluation in more than 96% of the cases. Correlation between clinical and angiographic findings seems to be excellent. Of the controlled intravenous examinations performed in 54 successful PTA procedures 75% appeared patent after 10 to 30 months, constituting 52% of the original attempts.

[Intravenous digital subtraction angiography following surgical vascular interventions and percutaneous transluminal angioplasty]

I.V.D.S.A. was performed as a follow-up after a surgical vascular procedure or a percutaneous transluminal angioplasty in 157 patients. The quality of the intravenous angiography was excellent in 91% of the patients. In 6,6% the examination was sub-optimal with possible error and in 2.4% the examination was not diagnostic. The inherent limitations of the technique are less important in these follow-up examinations because a limited region only has to be examined. A more accurate follow-up of vascular procedures is possible with I.V.D.S.A.

Digital intravenous and intraarterial subtraction angiography. Applications to the intracranial vascular system

Digital intravenous subtraction angiography (DIVSA) appears a promising and not highly invasive technique in the study of intracranial tumors and vascular lesions. In combination with computed tomography it should be sufficient in future for determining a preoperative tumourovascular balance. Already now it can be a valuable method in the screening for vascular malformation, in the postoperative evaluation of vascular intracranial lesions or after embolization of those lesions. In the study of the dural venous sinuses, DIVSA appears largely superior to conventional angiography. Advantages of the intravenous approach are the outpatient base, the low risk and low cost.--Low contrast dose and low pressure intraarterial subtraction technique is equivalent to conventional angiography with less risk and discomfort to the patient and resulting in considerable saving in cost.

Contrast enhancement by bolus technique in the CT examination of the kidney

Clinical results of contrast enhancement by bolus technique in the CT study of the kidney, performed with a two second scanner, are presented. The value of the method is discussed in relation with congenital abnormalities and more extensively in the evaluation of mass lesions of the kidney. In comparison with the widely used contrast infusion technique for CT examination, early scans after contrast enhancement by bolus technique allow better study of anatomical details of the normal kidney and variants. Furthermore in mass lesions assessment of vascularity leads to better differential diagnosis.