Anesth Analg 2002;95:635-638
© 2002 International Anesthesia Research Society
AMBULATORY ANESTHESIA
A Novel Ambulatory Intravenous Holder: Preliminary Findings
Moeen K. Panni, MD PhD*,
Mark Fernandes, BS ,
Nazif Mohdazhar, BS,
Todd Taylor, BS,
Anthony Tomasi, BS, and
Stephen B. Corn, MD*
*Department of Anesthesiology, Perioperative, and Pain Medicine, Brigham and Women’s Hospital, and Department of Anesthesiology, Children’s Hospital, Harvard Medical School; and Department of Engineering, Northeastern University, Boston, Massachusetts
Address correspondence and reprint requests to Stephen B. Corn, MD, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, 75 Francis St., Boston, MA 02115. Address e-mail to corn{at}zeus bwh.harvard.edu.
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Abstract
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IMPLICATIONS: Many devices serve as portable systems for IV equipment but are expensive and use complex electronic controls. We present a novel device to facilitate safe ambulation of IV-dependent patients. This device was effective in delivering required therapeutic flow rates over time periods desired for unattended operation.
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Introduction
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IV administration of fluids and drugs is an important aspect of routine clinical care. In the United States, at least 20 million patients receive IV fluids (1,2). For hospital patients, unnecessary bed rest may contribute to patient morbidity with its resultant increases in muscle loss and weakness, impairment of pulmonary function, and predisposition to venous stasis and thromboembolism (3). Cumbersome IV equipment (e.g., wheeled-pole assemblies) can frequently interfere with encountered obstacles in the hospital environment, which may limit patient mobility and be potentially hazardous. Falls among hospital inpatients are common, especially among those with increasing age (4). These concerns further prompt the need for safer ambulatory IV equipment.
The health care industry has responded by providing clinicians with a variety of sophisticated fluid delivery devices. Devices include controllers and pumps with accurate flow rates (5), alarm systems, in-line pressure sensors, and other features. However, many of these devices are not portable for the ambulatory patient, and those that are, are cumbersome, complicated, and do not interface with standard hospital IV tubing and equipment. The Ambulatory IV Holder (AIVH) (6) presented in this report overcomes many of these difficulties. Further testing of the flow characteristics of this device was performed using a modification of a clinically applicable model to understand the physics and physiology of fluid flow (7).
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Methods
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The design concept was chosen based on concerns of safety, ergonomics, compatibility with existing equipment, and cost. Additionally, only nonferromagnetic components were used in the device construction to allow close proximity to magnetic resonance imaging units. A prototype of this harness was designed and fabricated and can be seen in Figure 1.
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Figure 1. Schematic drawing of proposed Ambulatory IV Holder (AIVH) orientation on the patient. 1. Pressure-infuser bag. 2. Waist strap. 3. Inelastic fabric layer. 4 Fabric pouch. 5. Compressible bulb. 6. Conduit tubing. 7. Drip chamber and proprietary fixation device to maintain drip chamber alignment. 9. IV fluid bag.
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To assess the control of flow rate of the AIVH, simulation of venous pressure was achieved by an appropriate column height of saline in a hollow metal tube. The function of the pressure-infuser bag (Vital Signs IN-8000 or 9000, Vital Signs Inc, Totowa, NJ) was to provide the pressure gradient required to overcome IV pressure, substituting for the height-induced pressure gradient used in standard gravity-based IV equipment.
To address the issue of accidental air infusion, a worst-case scenario was used where maximal flow rate and a minimally filled drip chamber were used and maximum inversion of the drip chamber was performed. The experimental paradigm involved a set fluid infusion rate of 125 mL/h, after which the drip chamber was rotated 180 degrees so that air communicated with the tubing at the exit of the drip chamber during continuous flow of the system. The drip rate was continually monitored as the air moved through the line, with the pressure-infuser bag being pumped when required to maintain this higher flow rate (125 mL/h).
To assess the time period for unattended operation of the AIVH, the test was conducted in the same manner as previously described flow tests. The large (1000 mL) pressure-infuser bag was pumped to the desired level to achieve a 125 mL/h fluid flow however no pumps were given to increase the pressure-infuser bag pressure. The test was run until the flow rate slowed to 25 mL/h, our lower limit chosen to maintain IV patency.
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Results
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In the first experimental model (20-gauge IV; 1000 mL pressure-infuser bag), it was found that one pump given to the pressure-infuser bulb would increase the drip rate by approximately four drips per minute. It was seen that the relationship between time, drip rate, and pressure-infuser bag pumps could be predicted for all acceptable flow rates (from 25–125 mL/h). Figure 2A represents the total volume of fluid flow over time for this test. The relationship is linear, with a constant range of flow rates being maintained throughout.
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Figure 2. (A) Graph showing fluid volume over time using the Ambulatory IV Holder (AIVH) setup through a 20-gauge IV catheter. The fluid flow rate was set at 125 mL/h using a 1000 mL pressure-infuser bag.
(B) Graph showing fluid volume over time using the AIVH setup through an 18-gauge IV catheter. The fluid flow rate was set at 125 mL/h using a 500 mL pressure-infuser bag.
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In the second experimental model (18-gauge IV; 500 mL pressure-infuser bag), a linear relationship with the volume of IV fluid infused over time was also seen (Fig. 2B). In addition, one pump in the smaller pressure-infuser bag (500 mL) increased its drip rate by a larger percentage than one pump in the larger bag (1000 mL).
The time taken for air to travel with a maximum flow rate of 125 mL/h in five experimental runs performed was 481 s (+29.5; equal to 8 min and 1 s), which is a calculated velocity of 29 cm/min. The mass of air measured in the IV bag was 0.0118 g at atmospheric pressure and room temperature. Under normal body conditions, the equivalent volume of air would be 9.92 mL. Similarly, the amount of air that occupies the nonfluid-filled drip chamber was equal to 8.43 mL under body conditions (percent error for the volume measurements, +5.76%).
With unattended operation of the AIVH set at 125 mL/h without additional infuser bag pumps, 2 test runs confirmed the time elapsed to be more than 40 min before the flow rate decreased to less than <25 mL/h, a value consistent with maintaining IV patency (Fig. 3).
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Figure 3. Graph displaying drip rate (per minute) versus time (minutes) with the small (500 mL) pressure-infuser bag and 20-gauge IV catheter experiment, with a fluid flow rate of approximately 125 mL/h to start the study and no additional pumps given to the pressure-infuser bag throughout the experiment.
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Discussion
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Ambulation of patients after surgery contributes to faster recovery, reduced frequency of deep venous thrombosis formation with its associated complications, and earlier discharge from both the intensive care units and hospital wards (8). The AIVH presented in this report is a novel design that facilitates convenient patient ambulation for patients with indwelling gravity-based IV infusions.
A complete value analysis was not performed, however the AIVH incorporates current hospital equipment and will likely be cost-effective. The pressure-infuser bag would have a retail cost of approximately $15–$20 US. The prototype version was produced for only $45 US. Of note, an IV pole costs approximately $95 US (#WEL14042, Medical Resources®, Welch Allyn, Skaneateles Falls, NY) and requires storage, cleansing, and maintenance. The costs of tubing assemblies and IV fluid bags would not be relevant to the unit cost because they are required regardless of the transport method used.
Air infusion is always a concern where an indwelling IV catheter is connected to an external supply source. The morbidity and mortality rates from venous air embolism are determined by the volume of air entrained, the rate of entrainment, the patient’s position, and cardiac status. As early as 1809, Nysten (9) estimated the lethal dose of air to be 40–50 mL in a small dog and 100–120 mL in a large dog. The lethal volume of air in an adult human is unknown but is estimated to range from 200 to 300 mL. These numbers are derived from the cases of fatalities (reported by Martland (10), Yeakel (11), and Flanagan et al. (12)). One recent report (13) actually quantified the lethal volume of air to be 200 mL, albeit in a patient with congestive heart failure. This compares with previous retrospective estimates in studies that follow incidents of fatal venous air embolism.
Through use of the AIVH, air could possibly enter the IV line through two sources: the drip chamber and the IV bag. First, in terms of the drip chamber, it was calculated that the maximum amount of air that could be infused into the patient would be approximately 8.43 mL, which would take approximately eight minutes to reach the patient. The proprietary drip-chamber securement device is designed to prevent the drip chamber from being inverted and therefore reduces the chance of air entering the IV line. With the drip-chamber three-quarters filled with fluid, even a reclining patient would not risk air entry into the IV tubing. Second, air entry from the IV bag is extremely unlikely because well before the fluid level becomes so low as to have the air interface approach the IV tubing line entry point, pressure in the pressure-infuser bag would be insufficient to maintain forward flow.
Regarding infectious disease considerations, the AIVH is the only ambulatory IV system that allows the use of standard IV fluid bags and tubing without the need to break the integrity of the infusion line to adapt the system for use. Infectious disease transmission is an important risk factor for both the patient and health care worker when dealing with the need to initiate and maintain intravascular access. An estimated 200,000 nosocomial blood stream infections occur each year (14). Most nosocomial blood stream infections are related to the use of intravascular devices (15). The incidence of and potential risk factors for intravascular-device–related infections vary considerably with the type of device and therapy used. Short-term temporary vascular access catheters do have fewer incidences of these infections (16,17), however their frequency increases with conditions such as phlebitis (16,18) and are not trivial considerations.
With regard to health care worker exposure to blood borne infection such as human immunodeficiency virus, hepatitis B virus, and hepatitis C virus, the main goal in prevention is to reduce the amount of exposure to blood and bodily fluids. Studies of intravascular-related percutaneous injuries have shown reductions in incidence ranging from 70% to 100% temporally associated with the introduction of needleless systems (19). The AIVH addresses this specifically with a simple conversion to the ambulatory IV system without the need for disconnecting and reconnecting the IV bag from the sharp IV tubing spike. In summary, the AIVH design was effective in delivering IV fluid at a flow rate of 125 mL/h.
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Acknowledgments
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We would like to express our gratitude to Jim Philip, MD, for his contribution in this area of medicine and for his guidance in our study. We would like to thank Stephane Wadjas for his contribution towards studying the flow characteristics of the AIVH.
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Footnotes
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Stephen B. Corn, MD, is the inventor of the Ambulatory IV Holder (AIVH) and has voluntarily assigned the technology to Children’s Medical Center Corporation, Boston, MA.
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References
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- Green JS. On the air in the veins as a cause of death. Am J Med Sci 1864; 24: 38–65.
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- Jarvis WR, Edwards JR, Culver DH, et al. Nosocomial infection rates in adult and pediatric intensive care units in the United States: National Nosocomial Infections Surveillance System. Am J Med 1991; 91: S185-91.[Medline]
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- Maki DG, Ringer M. Risk factors for infusion-related phlebitis with small peripheral venous catheters: a randomized controlled trial. Ann Intern Med 1991; 114: 845–54.
- Adams KS, Zehrer CL, Thomas W. Comparison of a needleless system with conventional heparin locks. Am J Infect Control 1993; 21: 263–9.[Web of Science][Medline]
Accepted for publication May 14, 2002.
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Abstract
Introduction
