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Technical Innovation |
1 All authors: Department of Radiology, Shands Hospital, University of Florida College of Medicine, 1600 S.W. Archer Rd., Gainesville, FL 32610-0374
Received May 15, 2000;
accepted after revision June 27, 2000.
Address correspondence to I. F. Hawkins, Jr.
Introduction
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On the contrary, hand delivery of CO2 is fraught with several potential dangers: delivery of unknown and possibly excessive volumes, explosive delivery, and air contamination [4]. In 1995, we introduced a plastic bag delivery system, which applied the principles learned during the development of the dedicated injector [5]. This system, currently used by many, has effectively eliminated the possibility of injecting excessive volumes and has reduced explosive delivery. Unfortunately, the complexity of the five-port system has been confusing for some operators. A few operators have incorrectly placed the delivery syringe and have injected room air. Others have added additional stopcocks and connecting tubing, which could result in delivering excessive volumes and air contamination. As a result, the previously published delivery system has recently been modified to reduce these problems.
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The commercially available hand-delivery set comprises a CO2 reservoir and delivery system with multiple check valves. A 1500-mL flexible plastic bag with a single port is attached to low-pressure tubing and a two-way distal stopcock with a special gas fitting (Angioflush III fluid collection bag; AngioDynamics). The delivery system itself consists of a standard three-way stopcock to which the angiographic catheter is connected, a check-flow valve attached to the port of the three-way stopcock, a 100-cm connecting tube, a dual check-flow valve with a port for the delivery syringe, and a port with a special O-ring fitting for connection to the CO2 plastic bag reservoir (Angioflush III fluid management system; AngioDynamics). The system differs from the previous system in that the distal purge valve and syringe have been eliminated, and a gas O-ring connector that attaches the bag to the delivery system has been added (Fig. 1).
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The bag is filled and emptied three times from a pure CO2 source (laboratory-grade 99.99% CO2; Custom Medical Devices, Gainesville, FL). A submicron filter is attached to the Luer-Lok fitting on the CO2 cylinder. This filter increases the sterility of the gas and provides a sterile device to prevent contamination while attaching the plastic bag's connecting tube to the CO2 cylinder. After each inflation, the CO2 is emptied from the bag by manual compression. The filled bag system is connected to the dual check-flow valve fitting and is purged five times by aspiration and injection with the delivery syringe (20-60 mL). The system is connected to the angiographic catheter, and the blood is cleared from the catheter using the side port of the three-way stopcock. Any residual air in the fitting can be purged by closing the stopcock to the patient and injecting CO2 through the open port. The port is closed, and the fluid is purged from the catheter by making a small forceful CO2 injection (3-5 mL) completely emptying the delivery syringe (Fig. 2). The delivery syringe is then filled with the desired amount of CO2, and the plunger is advanced at the desired rate. To refill the syringe, the one-way valve system allows the plunger to simply be retracted, and injections can be made at variable rates and volumes without any stopcock manipulation.
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Previously, we have flushed the catheter with saline solution after each injection. Since 1995, we have flushed the catheter every 2-3 min with 1-3 mL of CO2. This obviates the 3-mL injection of CO2 before each bolus injection, which is required to reduce explosive delivery.
For interventional procedures, the system is attached to a Tuohy-Borst fitting (Cook, Bloomington, IN), which permits injection between a needle and a guidewire or between a guidewire and a catheter (Fig. 3). Before injection, the air can be purged by loosening the Tuohy-Borst fitting and purging the CO2 through the fitting. The CO2 will preferentially exit this fitting because the resistance is greater between the guidewire and the catheter. Because of the compressibility of the CO2, at least a 20-mL syringe should be used for interventional procedures. During the first injection, because of the close tolerances between the needle and the guidewire, or between a 0.035-inch guidewire and a 4- or 5-French catheter, there will be a delay of 7-10 sec before the CO2 exits the catheter tip. Also, a very forceful injection will be required. With subsequent injections, the delay is considerably less and less force is required to deliver the CO2 because the saline solution has been removed during the initial injection.
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The most dangerous potential complication can occur when connecting the CO2 cylinder directly to the delivery system [4]. If a stopcock is inadvertently opened, large volumes of CO2 can be delivered in a short time period. Reports of several potentially dangerous delivery systems, which also connect the CO2 cylinder directly to the angiographic catheter, have recently been published [6,7,8].
The plastic bag, which is not connected to the CO2 cylinder, eliminates any possibility of delivering excessive volumes. Because the bag is flaccid, the gas is subjected only to atmospheric pressure. Whatever volume is aspirated from the bag represents an accurate measurement of the CO2 delivered. If a syringe is simply filled via the cylinder, there is usually an unknown amount of compressed CO2 in the syringe. If a liquid angiographic injector is used, unless the system is vented before injection, the syringe could be loaded with large volumes.
With the previous bag system, some operators interposed a three-way stopcock to quickly refill the plastic bag. In several cases, this has resulted in aspiration of room air and inadvertent injection of very large volumes of CO2. The present system uses a special gas fitting with an O-ring, which not only creates a much better seal to prevent aspiration of room air, but also prevents addition of three-way stopcocks, connecting tubing, and so forth. Additional three-way stopcocks are superfluous because more than 1500 mL of CO2 would not be required in any patient.
The next issue is the explosive delivery of CO2. Many of the published CO2 delivery systems do not clear the catheter of saline solution before CO2 is delivered [7, 8]. This results in an explosive delivery, which we have found to be associated with discomfort, reflux in unwanted areas, breakup of the gas into small bubbles, and possible vascular injury. We believe that explosive delivery is caused by compression of gas behind the liquid as the liquid is forced from the catheter. At the instant the liquid exits the catheter, the compressed gas expands, resulting in an explosive, unreliable delivery. If the saline solution is removed from the catheter, the CO2 can be delivered evenly in a controlled manner.
The previous CO2 system used a 3-mL purge syringe adjacent to the distal three-way connector. This method effectively purged the saline solution or blood from the catheter. However, several novice operators have used this port as the delivery port and have not closed the port that is normally used for delivery. This procedure resulted in aspiration and inadvertent injection of significant volumes of room air. For the last year and a half in several hundred patients, using both the current and previously published plastic bag system, we have purged the saline solution from the catheter by filling the delivery syringe with 3-5 mL and forcefully injecting the total volume to completely empty the syringe. If a large syringe is filled and only a small amount of CO2 is injected, then the CO2 may simply compress and not clear the fluid from the catheter (Fig. 2). After the purge injection, the distal one-way check valve prevents reflux of blood into the catheter.
Because of the potential for ischemia in non-dependent areas [4], we have decreased our injection rates and volumes and have waited longer between injections. For abdominal aortography, we have recently been injecting only 30 mL of CO2 per injection with good filling of the abdominal vasculature in most patients. The more posteriorly located left renal artery may not fill with low volumes but will always fill if the patient is placed in the right lateral decubitus position even when injecting as little as 10 mL. For runoff studies, a low injection rate (10 mL/sec) and higher injection volumes (30-50 mL) with the addition of an intraarterial vasodilator (100-150 g nitroglycerin) will usually produce good distal filling even to the feet. Also, for runoff studies, if the inferior mesenteric artery is well filled, we advance the catheter into the contralateral external iliac or common femoral artery and perform a single leg runoff. We retract the catheter into the ipsilateral iliac artery for the ipsilateral leg study. Avoiding inferior mesenteric artery filling is most important in patients with distal abdominal aortic aneurysms, because trapping frequently occurs.
The modification of the plastic bag delivery system decreases the possibility of inadvertent air aspiration with the use of the gas O-ring fitting, and there is less chance of operator error. However, it is important to deliver the CO2 via the port adjacent to the CO2 source. The operator should be sure that the connection between the CO2 source and the delivery system is secure to eliminate any possibility of air aspiration.
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