| Partâ… Development of Modified Femoral Arteriovenous Cannulae for Children1. Design of modified femoral arterial cannulae for childrenModified femoral arterial cannulae consist of bodies and guidewires. These cannulae feature elongated, one piece, kink resistant wirewound bodies. Modified femoral arterial cannulae have multi-port tips. This construction allows for higher flow rates with minimal pressure differential. An introducer along with depth markings permit precise positioning of the cannulae. All cannulae are available with the Bio-Active coating.2. Design of modified bi-caval femoral venous cannulae for childrenModified bi-caval femoral venous cannulae consist of bodies and guidewires. These cannulae have a unique wirewound, kink resistant, two stage design which more efficiently drains the heart by meeting the 3:1 IVC/SVC drainage requirements. By simultaneously draining the IVC and SVC, superior flow rates are obtained. This design eliminates the need for two cannulae ( one in the IVC and one in the SVC ) which occupy a large portion of a very limited space, making these cannulae ideal for use during mitral valve, ASD and small incision heart cases. Depth markings permit precise positioning of the cannulae.3. Design of Minimally Invasive Intra-aortic Balloon Cannulae for children Minimally invasive intra-aortic balloon cannulae consist of bodies and guidewires and manual inflate balloons with pressure monitoring. These cannulae feature kink resistant, wirewound body with an inflatable balloon. This design eliminates the need for aortic root cannulae and aortic clamp which occupy a large portion of a very limited space, making these cannulae ideal for use during pediatric thoracoscopic cadiac surgery. A variety of balloon and guidewire are available. All cannulae come with a syringe for balloon inflation.4. ResultsUsing polyvinyl chloride ( PVC ) metarial, femoral arteriovenous cannulae were developed. They include modified femoral arterial cannulae, modified bi-caval femoral venous cannulae and minimally invasive intra-aortic balloon cannulae. Modified femoral arteriovenous cannulae overcome shortcoming of traditional arteriovenous cannulae and enlarge their function in pediatric thoracoscopic cardiac surgery. Modified cannulae with Bio-Active coated surface may relieve trauma and operative risk. Simple performance can obtain better operative effect.Partâ…¡Biocompatibility Evaluation of Modified Femoral Arteriovenous Cannulae for Children1. Method Including in vivo experiments and in vitro experiments。1.1 In vivo experiments1.1.1 Hemolysis testRabbit blood ( 20 ml ) was achieved by cardiac puncture and mixed with 2 % potassium oxalate. Modified femoral arteriovenous cannulae were soaked in the prepared fresh anticoagulated blood. Then absorbed optical density (OD) was measured. The haemolysis rate of these modified arteriovenous cannulae was calculated by determination of absorbed OD in vitro experiments.1.1.2 Platelet adhension testBy Sysmex K-4500 autokinetic blood analysator, normal platelet were diluted 1.0×109 L-1 fluid. These cannulae were made test specimens ( 0.5 mm×0.5 mm ) and soaked 2 h in diluted platelet fluid. Then test specimens were fixed by 3 % glutaric dialdehyde. Condition and quantity of platelet on material surface were observed through scanning electron microscope ( SEM ).1.1.3 Skin irritative testThe leaching liquor of these cannulae was prepared according to the national evaluation standards of medical biomaterials, and then prepared leaching liquor was injected subcutaneously in rabbits to observe the histological responses of skin 72 h after injection.1.1.4 Systemic acute toxic test in miceThe leaching liquor of these cannulae was prepared according to the national evaluation standards of medical biomaterials, and prepared leaching liquor was injected intravenously into mice to observe the systemic responses 72 h after injection.1.2 In vitro experiments1.2.1 Grouping 20 dogs were divided into 2 groups at random. In experimental group, CPB was established through modified femoral arteriovenous cannulation, whereas control group adopted DLP femoral arteriovenous cannulation.1.2.2 Establishment of CPB40 dogs were anesthetized with an intravenous injection of sodium pentobarbital and maintained with mechanical ventilation. All dogs were placed in a supine position. The right groin was exposed. After heparinization (300U/kg), by femoral arteriovenous cannulation, CPB was established. Then the venous and arterial lines were connected to heart-lung machine. At different time to stop CBP, cannulae were put out.1.2.3 Measure of optical density (OD)Femoral arteriovenous cannulae were made test specimen (0.5 mm×0.5 mm). By euzymelinked immunosorbent assay, fibrinogen and albumin of superficial adsorption were measured on cannulae. Optical density was obtained by spectrophotometer.2. Results2.1 Hemolysis testHemolysis test showed that the hemolysis rate of the modified arteriovenous cannulae was 1.58 %, which was much lower than the international standard (5 %).2.2 Platelet adhension testThe number of platelet on modified femoral arteriovenous cannulae was (12.7±2.5) (5.1±1.2) / field of view; the number of platelet on DLP femoral arteriovenous cannulae was (18.5±3.4) (7.1±1.6) / field of view. There was significant statistical meaning ( P<0.05 ).2.3 Skin irritative test and systemic acute toxic test Primary skin test in rabbit showed no erythema, necrosis or edema in skin. Furthermore, acute systemic toxic test in mice showed no death and no loss of body weight, and no obvious abnormal response was observed 72h after injection.2.4 Fibrinogen and albumin of superficial adsorptionWith temporal lasting of CPB, fibrinogen and albumin of superficial adsorption were increasing. Fibrinogen on modified femoral arteriovenous cannulae was lower than on DLP femoral arteriovenous cannulae ( P<0.05 ), whereas albumin was higher than control groups ( P<0.05 ) at different time.Partâ…¢The Hydrodynamic Study of Modified Femoral Arteriovenous Cannulae for Children1. MethodHydrodynamic experimental table was established in vitro. At different flow rate, pressure gradients of the modified femoral arteriovenous cannulae were tested, and compared with DLP femoral arterial cannulae. But modified bi-caval femoral venous cannulae were compared with former bi-caval femoral venous cannulae. Intra-aortic Balloon pressures of minimally invasive intra-aortic balloon cannulae were measured on the in vitro experiment table.2. ResultsThe hydrodynamic experiments showed that pressure gradient is increasing with adding of flow rate. The less sizes were, the bigger pressure gradients were at same flow rate.2.1 Modified femoral arterial cannulaeThe pressure gradients of modified femoral arterial cannulae were much lower than DLP femoral arterial cannulae, the difference has statistical meaning at the flow rate 2 to 5 L /min ( P < 0.05 ) and significant statistical meaning at the flow rate 6 L /min ( P < 0.01 ). At the pressure gradient 200 mmHg,8 Fr,10 Fr modified femoral arterial cannulae flow rate was 2.45 L/min, 3.24 L/min respectively, whreras 12 Fr, 14 Fr and 16 Fr all was at 4.0 L/min above.2.2 Modified bi-caval femoral venous cannulaeCompared with the pressure gradient, modified femoral venous cannulae were much lower than former bi-caval femoral venous cannulae. The difference has statistical meaning at the flow rate 2 to 5 L/min (P<0.05) and significant statistical meaning at the flow rate 6 L /min (P<0.01). At pressure gradient 20 mmHg,16/21Fr,20/25Fr,24/29Fr modified bi-caval femoral venous cannulae flow rate was 3.08L/min, 3.79L/min and 4.50L/min respectively. Hydrodynamics of experimental groups was better than of control groups.2.3 Minimal invasive intra-aortic balloon cannulaeWith the increasing of flow rate, the pressure gradients of minimally invasive intra-aortic balloon cannulae were raising. The difference has statistical meaning at the flow rate 3 to 5 L /min ( P<0. 05 ) and significant statistical meaning at the flow rate 6L /min ( P < 0.01 ). Maximal flow rate was 6 L /min, and pressure gradient was much lower than 220 mmHg. The ratio of balloon pressure to endovascular pressure was 3 to 4:1.Partâ…£Animal Experiment of Modified Femoral Arteriovenous Cannulae for Children1. Method1.1 Test animal and grouping 40 dogs were divided into 2 groups at random. In experimental group, CPB was established through 18 Fr minimally invasive intra-aortic balloon cannulae and 16/21 Fr modified bi-caval femoral venous cannulae. Whereas CBP adopted 16 Fr DLP femoral arterial cannulae, 20 Fr DLP femoral venous cannulae and 22 Fr DLP SVC cannulae in control group. ASD repair was performed in both groups.1.2 Operation40 dogs were anesthetized with an intravenous injection of sodium pentobarbital and maintained with mechanical ventilation. All dogs were placed in a supine position and set up transesophageal echocardiography ( TEE ). The right groin was exposed. After heparinization, by the guidance of TEE, the tips of bi-caval femoral venous cannulae were placed in the SVC and the tips of the intra-aortic balloon cannulae were positioned in the ascending aortae. Intra-aortic balloon was inflated about 2 cm above the aortic valve. A balloon pressure was about 350 mmHg. The venous and arterial lines were connected to heart-lung machine. These dogs were performed totally endoscopic repair of ASD in both groups. Intra-aortic balloon position was checked with contrast injection before deflation. These dogs were sacrificed after operation.1.3 Preparation of sampleSimples of heart, lungs, kidneys and aortae were obtained and fixed by 3 % glutaric dialdehyde. These samples was made 70 to 80 mm ultrathin section, and observed pathological change by light microscope and electron microscope.2. ResultsAll dogs were successfully maintained on cardiopulmonary bypass. In experimental groups, the operative duration was 56.1±5.8 min, duration of the establishment of CPB was 10.1±2.8 min and occlusion time was 14.7±2.9 min. However, the operative duration was 71.3±4.5 min, duration of the establishment of CPB was 18.1±3.5 min, occlusion time was 16.7±3.2 min in control groups. The duration of experimental groups was less than the duration of control groups. In addition, experimental groups'flow rate on CPB was 1.28 to 2.97 L/min and pump pressure 61 to 178 mmHg, whereas control groups'flow rate was 1.35 to 3.05 L/min and pump pressure 60 to 175 mmHg. The difference did not reach statistical significance between both groups ( P>0.05 ). Visualization showed that there was no migration toward the aortic valve and no evidence of loss of aortic occlusion. At postmortem examination, aortae, myocardium, lungs and kidneys were histologically normal in all dogs. There were no significantly differences in both groups. Observed through electron microscope, aortae had not obvious tissue damage using minimally invasive intra-aortic balloon cannulae.Conclusions1. Modified femoral arteriovenous cannulae for children include modified femoral arterial cannulae, modified bi-caval femoral venous cannulae and minimally invasive intra-aortic balloon cannulae.2. Modified femoral arteriovenous cannulae for children have better blood compatibility. Primary skin irritation test showed no erythema, eschar and edema. Toxicity was not found. The biologic compatibility can meet requirements of medical demand.3. Modified femoral arteriovenous cannulae for children showed good hydrodynamic characteristics in vitro experiment. They can meet the requirements in thoracoscopic pediatric cardiac surgery and can be further applied to clinical use.4. Animal experiment showed that establishing of CPB using femoral arterial cannulation and femoral venous cannulation is feasible, and can save time and reduce trauma.5. Modified femoral arteriovenous cannulae are suitable for children weighing less than 30kg in thoracoscopic cardiac surgery. They will be used extensively in the near future. |
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