Our study demonstrated that the L-1 system is as efficient as the RIS at transfusing crystalloid rapidly when used in conjunction with a 20- or 18-gauge catheter. However, as catheter size is increased >18 gauge, the infusion rates provided by the RIS become progressively greater than those of the L-1. We compared the systems by using only one arm of the RIS infusion set. It is likely that the RIS is capable of even more rapid fluid delivery if both arms of the infusion set are used. Conversely, two L-1 systems could be used at less of a cost than the RIS. This may be adequate in pediatric patients who are not of adult size.
Another difference was that the end temperature achieved with the L-1 was inversely proportional to flow rate whereas end temperatures using the RIS were more consistent over a wide range of flow rates. The end temperatures achieved with the RIS were consistently >36°C for all flow rates. The end temperature obtained with the L-1 was >36°C only for flows <400 mL/min. The end temperatures achieved by the RIS using the smallest catheters (i.e., longest infusion times) (20- and 18-gauge) were lower than with many of the larger catheters. This probably occurred secondary to cooling of the fluid as it traversed the nonheated extension tubing to the graduated cylinder (1). Because blood products are often cold when being infused, the end temperatures achieved with either device when infusing blood would likely be lower than what we measured using room-temperature crystalloid.
An additional observation that may be clinically relevant was the incremental increase in infusion capacity of successively larger IV catheters. Of the catheters tested, a 16-versus an 18-gauge catheter provided the largest incremental increase in maximal flow (with both the L-1 and RIS) than any other sequential increase in catheter size. This is a function of the increase in the radius of the catheter lumen; the radius of the 16-gauge catheter is 37% larger than the 18-gauge catheter. As dictated by Poiseuille’s Law, the radius is the most important factor determining maximal flow of a given fluid. Flow = π(P1 − P2) r 4/8ηL describes this relationship where P1 and P2 are pressures at the proximal and distal ends of the tubing, r is the radius of the tubing, η is viscosity of the fluid, and L is length of tubing (2). The additional importance of catheter length is demonstrated when comparing the flows through the 14-gauge and 5F catheters. Although the radius of the 5F is smaller than that of the 14 gauge, its flows are faster with both the L-1 and the RIS (the length of the 5F is 52% less than the 14-gauge catheter). Although Poiseuille’s Law demonstrates important factors, the actual flow of fluid under pressure is described as a quadratic equation because of the development of turbulence (3). This explains in part why even larger-bore catheters are not capable of delivering the flows predicted using only Poiseuille’s Law (4).
In the United States, peripheral IV catheters are conventionally sized in terms of “gauge” whereas central venous catheters are described in F sizes. The gauge system was designed in the 19th century for use in wire manufacturing and uses arbitrary multiples of 0.0010 in. in inverse rank ordering of sizes (5). The F system, also developed in the 19th century, is based on uniform incremental measurements of 0.333 mm and was originally used for sizing urologic and other medical devices (6). Differences in wall thickness and rounding of the sizes account for the actual measurements not being strict multiples of the above-stated increments. The overlap between these measurement systems is demonstrated in Table 1. The catheters for which this overlap occurs are the larger-gauge IV catheters and smaller-size F catheters (16- and 14-gauge and 4 and 5F). Central lines of this caliber are more likely to be placed in children than adults. These internal-diameter measurements may provide some guidance as to which catheters (i.e., larger peripheral versus smaller central lines) should allow more flow in a given patient regardless of which type of infusion system is being used in conjunction with them.
Our study also found that the RIS allows a constant rate of infusion over a large volume whereas the L-1 flows slow down as the IV bags empty. Despite using both L-1 pressure chambers simultaneously, it consistently took longer to infuse the second liter of fluid than the first. Although a constant amount of pressure (300 mm Hg) is applied to the bag within the pressure chamber, the additional hydrostatic pressure exerted by the column of fluid within the bag may have some effect. As the bag empties, the smaller column of fluid exerts less force upon the infusion and thus it slows. It may also relate in part to changes in the configuration of applied pressure as the bags empty. This phenomenon does not occur when using the RIS because it uses a roller pump mechanism and does not depend at all on gravity or compression of the bag. Although a consistent observation, this is likely of minimal clinical importance.
When caring for infants and toddlers in the perioperative setting, neither the L-1 nor RIS is typically necessary to meet transfusion requirements unless massive hemorrhage occurs. Manual methods for delivering fluids have traditionally been used for these small patients. For small-bore IV catheters (22- and 24-gauge), rapid withdrawal and injection of fluids with a syringe and stopcock is more efficient than pressure pump chamber compression and is most efficient when performed with a 10-mL syringe (7). Inflatable pressure bags can also deliver fluids more rapidly than manual compression of drip chambers, but will be rate limited if used with conventional blood warmers that require fluids to traverse coiled tubing within a heating plate (8,9). This additional length of coiled tubing provides considerable resistance and requires a long contact time with the heating plate to allow adequate warming. Conversely, the L-1 and RIS provide superior heating and flow of fluids by using counter-current heat exchangers and heated water baths to avoid the increased resistance of coiled tubing used in heating-plate-type blood warmers (10,11). They provide superior flow rates to manual methods and help to free anesthesiologists’ hands during times of rapid transfusion. Because of these advantages, their use should be considered in situations of massive transfusion in patients of all sizes.
The differences in capabilities of the L-1 and the RIS found in this study may be partially explained by differences in their design. The L-1 is smaller and less technically complex. It consists of a simple disposable infusion set of large-bore IV tubing which can be connected to two infusion bags (i.e., crystalloid or blood product). Each infusion bag may be placed within a pressure chamber and infused under 300 mm Hg of pressure or may simply flow by gravity. Fluid is warmed in the heat exchanger as described above. A single air filter and vent are located distal to the heat exchanger. The L-1 disposable infusion set is easy to install, and costs approximately 20 times less than that of the RIS (approximately $20 United States dollars [USD] for L-1 versus approximately $440 for RIS). The initial purchase cost of the L-1 infusion device is also much less than the RIS (approximately $5500 versus approximately $51,700 USD). Disadvantages of the L-1 system are its lack of low-fluid indicator and its inferior air-removal capabilities. Despite its air filter, fatal air embolism has been reported with the use of the L-1, and thus all air must be removed from fluid bags before placing them into the pressure chamber for infusion (12,13). The necessity for manual removal of air adds time to the changeover of fluid bags. This may be suboptimal during an emergent situation.
The RIS uses a similar strategy for warming as the L-1. However, the RIS also uses the principles of cardiopulmonary bypass, allowing rapid transfusion of fluids and increasing safety. It uses a 3-L reservoir and a roller-pump mechanism for transfusing fluids. Low reservoir alarms with automatic flow shut-off, two air detectors, as well as a debubbling filter are incorporated to help prevent air embolism and increase the safety of rapid transfusion. The RIS also has an over-pressure alarm to prohibit high-pressure delivery of fluid into a nonvascular space or to alert the clinician of an obstruction or kink in the catheter or tubing. The amount of fluid given, the current flow rate, temperature, and infusate pressures are provided by digital display. The anesthesiologist has the capability of changing the flow rate to a precise amount between 0 and 1500 mL/min. A one-step mechanism by which to deliver a 100- or 500-mL fluid bolus may aid the operator in fluid management as well. These features demonstrate how the RIS is more technically advanced than the L-1. The main disadvantages of the RIS are its expensive cost, the complexity of the set-up, and its larger footprint. Another theoretical disadvantage is that the large reservoir requires priming with multiple units of blood products that may result in unnecessary exposure of the patient, i.e., partial infusion of multiple combined units. The RIS set-up requires a series of specific steps that may be time consuming for the occasional user.
In our pediatric institution, in situations of potential massive blood loss, it is common practice to use 1 or 2 L-1 devices for children under 30 kg. We consider using the RIS for children larger than 30 kg in whom surgical pathology, coagulopathy, or “re-do” surgery places the patient at additional risk. Our data regarding flow rates confirm that this is likely to be a reasonable transition point because peripheral IV catheters ≥16 gauge and central venous catheters ≥5F are likely to be placed in patients of this size. Although a 10% (16 gauge) to 25% (5F) advantage in flow with the use of the RIS compared with the L-1 may not seem clinically important, considering RIS use in these larger pediatric patients has allowed us to maintain our skills and familiarity with the device.
The findings of our study are somewhat limited because, in clinical situations, the rates achieved with either system would probably be less because of venous resistance and increased turbulence (14). Additionally, in massive transfusion situations, crystalloids are only part of the resuscitation process. Transfusion of blood products would be slower because of their increased viscosity (15). We chose to study crystalloids rather than blood products because of the ease of obtaining large quantities and as a means of establishing some of the differences between the two transfusion systems.
The RIS has proven life-saving in situations of adult-sized pediatric patients with massive hemorrhage, e.g., liver transplantation, trauma, and liver tumor resection. We recently cared for a 12-yr-old, 60-kg patient undergoing hepatoma resection in which the advantages of the RIS were clearly demonstrated. The patient suddenly developed massive, rapid intraoperative hemorrhage, which 4 anesthesiologists and 2 L-1 devices could not match. The patient became hemodynamically unstable and the hemoglobin level decreased to 1 g/dL. Switching to the RIS enabled us to transfuse >50 L of blood products and crystalloid through 2 7F introducers in 1 hour while surgical control over bleeding was obtained and the patient was stabilized. The total transfusion for the case was 46 L of crystalloid, 55 U of packed red blood cells, 30 U of fresh frozen plasma, and multiple pheresis units of platelets. Despite all of this, the child’s core temperature never decreased to <34.5°C. According to our data for crystalloid, the RIS is capable of delivering 25 L more fluid than the L-1 with these size catheters over 60 minutes. Although the increased viscosity of blood products and patient’s venous resistance may limit the in vivo amount of fluid able to be given, the difference between the devices’ capabilities as demonstrated in our patient can be clinically important.
In conclusion, both devices offer advantages and disadvantages and each clinician and each hospital must decide which equipment is most appropriate for their surgical population. In infants and smaller pediatric patients, the added cost and complexity of the RIS cannot be justified. Nor can its use be justified for use with catheters smaller than 16 gauge. Although the RIS has superior warming capabilities, other methods of warming the patient, e.g., forced-air warming blankets, must be considered. However, larger pediatric patients, like adults, may benefit from the use of the RIS. The decision to use the RIS instead of the L-1 is based on the rate and duration of massive bleeding. For example, even though there may only be a 20% difference in flow per minute through a 14-gauge IV catheter, this means double the transfused volume every 5 minutes. The differences become even greater with catheters ≥5F, and the RIS also offers the advantage of not having to vent air from bags of crystalloid or blood products before infusion. When deciding which device may be most useful in a particular pediatric patient, one must consider the size of the patient, the size of available venous access, the potential for rapid bleeding, and likelihood of hypothermia.
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© 2003 International Anesthesia Research Society
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