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Flow increases with an enlarging intravenous catheter
Flow Increa~s with an Enlarging Intravenous Catheter Brian R. Jones, MD, * Mark S. Scheller, MD-f Department Diego,
of Anesthesiology,
University
of California
School
of Medicine,
San
CA.
Study Objective: To determine the increase inflow of a hydratable enlarging intravenous (IV) catheter in anesthetized patients. Design: A randomized, nonblinded study, with standard Teflon IV catheters used as controls. Setting: Operating room at a university medical center. Patients: Thirty adult patients receiving general anesthesiafor lower extremity surgery. Interventions: An IV catheter wu placed in the upper extremity, and flow measurements were made b measuring the time for infusion of 250 ml of normal saline within Z minute after placement and at I hour after placement. Measurements and Main Results: The enlarging catheters had a statistically sig@cant auerage flow increase of 26% after 1 hour indwelling time. The standard Teflon catheters had no statistically significant change in flow after 1 hour. The percentage increase in flow for the enlarging catheters was not as
0 1992 Butterworth-Heinemann J. Clin. Anesth. 4:120-122,
120
J. Clin. Anesth.,
1992.
vol. 4, March/April
and equipment,
catheter;
fluids, intravenous.
Introduction Rapid intravenous (IV) fluid administration is frequently limited by the resistance of the IV catheter.’ When possible, large-gauge catheters are inserted to facilitate fluid administration. However, placement of a large-gauge cathIV catheter (Menlo Care, Inc., eter is not always possible. 2-6 A Streamline Menlo Park, CA) made of an elastomeric hydrogel (Aquavene) that is of standard size when inserted and then enlarges after hydration is now commercially available (Figure 1). In vitro study of this catheter has demonstrated improved flow characteristics after hydration. Initial studies showed a 100% increase in flow after 1 hour of hydratiom7 Because of the possible effects of human tissues on the expansion of the catheter in vivo, we tested it to see whether it had the same increase in flow when placed in patients.
Materials and Methods This
study
San Diego
1992
was performed Human
Subjects
with the approval Committee
and
of the University the consent
of California-
of 30 adult
patients
Enlarging IV catheters: Jones and Scheller
??
P <,001
??time0 ? ?time60
20 Teflon
20 Streamline
18 Teflon
Figure 1. The upper IV catheter is a new 20-gauge Streamline IV catheter. The lower catheter is a 20-gauge Streamline catheter after hydration. It has increased in size so that it is approximately equal to an l&gauge catheter.
Figure 2. Mean flow within 1 minute and at 1 hour. The error bars represent standard deviation of the mean flows.
undergoing lower extremity surgery. After induction of general anesthesia, a second IV catheter was placed in the opposite upper extremity. The patients were randomized to one of three groups: those receiving a 20gauge Streamline catheter (Menlo Care, Menlo Park, CA), an 1%gauge Jelco Teflon catheter (Criticon, Tampa, FL), or a 20-gauge Jelco Teflon catheter. All catheters were 1.25 inches long. The study catheter was placed in the forearm, no drugs were given through this IV, and all blood pressure (BP) measurements were done on the opposite arm. A standard IV set (Travenol 2COOOS, Deerfield, IL) was connected to a 250 ml bag of normal saline and directly to the IV catheter. No IV tubing extension sets were used. Flow measurements were made by measuring the time for infusion of 250 ml of normal saline. Fluid pressure was held constant for all tests by maintaining the fluid at 100 cm above the IV catheter. The patient’s arm was maintained by his or her side at all times. Flow was measured within 1 minute after placing the IV catheter and again at 1 hour after placement. The IV rate was maintained at approximately 50 mVhr during the interval between flow measurements. Study catheters were removed and examined after the I-hour study period. A paired Student’s t-test was used to compare study catheter flows before and after the l-hour test period.
Figure 3. Enlarged photograph of a Streamline IV catheter after removal from a patient. Note the segment of the catheter shaft that has not completely expanded.
Results All patients completed the study. In the ten patients who had a 20-gauge Streamline catheter, flow increased by 26% after 1 hour of hydration @ < 0.001; Figure 2. The percent increase in flow for the Streamline catheter ranged from 19% to 35%. There was no statistically significant change in flow for either the 18-gauge or the 20-gauge standard Teflon catheters. After hydration, the flow from the 20-gauge Streamline catheters exceeded the flow of the IB-gauge Teflon catheters. Several Streamline catheters that were removed after the study
appeared to have incomplete the shaft (Figure 3).
expansion
in segments along
Discussion Traditionally, large IV catheters are used when rapid fluid administration is required. The majority of commonly used IV catheters are made of Teflon or other nonexpandable material that does not change in size or shape with time. The Streamline catheter tested expands with hydration and has been shown to have improved flow in vitro.7 The elastomeric hydrogel IV catheters tested in vivo had significantly greater flow after hydration than immediately after placement. Although the flow did increase with hydration, our results show a smaller percentage increase than previously demonstrated in vitro. When removed, several of the Streamline catheters appeared to have incomplete expansion (Figure 3). This may explain why the flow increases were not as large as those seen in the previous laboratory studies.’ Because the limitation in expansion appears to be limited to a short section on the shaft of the catheter at approxi.J. Clin. Anesth.,
vol. 4, March/April
1992
121
Original Contributions
mately the point at which the catheter enters the vein, it is most likely that the vein is preventing the catheter from complete expansion. This bottlenecking effect--&., expansion of the catheter within the interior of the vein and in the surrounding subcutaneous tissues but not where the catheter enters the vein-may explain why this catheter has been found to have a lower frequency of infiltration.8 We speculate that this custom fitting of catheter to the vein wall forms a tight seal and subsequently decreases the extravasation of fluid out of the vein. After hydration, both the diameter and length of the Streamline catheter increased, as seen in Figure 1. Fluid flow is a function of catheter diameter and, to a lesser degree, of length. Flow is proportional to radius (r) to the fourth power and inversely related to length (L): Flow = K; The change in diameter of the catheter is the major factor in the increase in flow, and the slight increase in length decreases flow only slightly. In an in vitro study, Cooke and Walker’ showed that 50% of the maximum flow was obtained by 30 minutes and the maximum flow was obtained by 1 hour. In our study, we chose to measure the flow at two times, within 1 minute and at I hour after placement, as we assumed that maximum flow would be realized by 1 hour. If we had waited for a longer period, the catheter may have expanded more, possibly resulting in a greater increase in flow. During the initial measurement period, the time required for 250 ml of fluid to flow varied from 5 to 7 minutes, and the catheter was probably expanding during that time. This expansion and presumed increase in flow during the initial measurement period would yield a higher initial flow than if a true zero time measurement had been obtainable. Subsequently, the percentage increase in flow we obtained would be lower than if a true zero to 1 hour indwelling period were tested. McKlveen et ~1.~evaluated the Streamline catheter in obstetric patients and found a similar increase in flow after hydration. In their study, there was significant patient variability (2% to 54%), possibly because the patients were awake and movement may have affected the
122
J. Clin.
Anesth.,
vol. 4, March/April
1992
flow. It is reassuring to note that the mean flow increase they measured was similar to the mean flow increase seen in our study. Although the Streamline catheter does not demonstrate an in vivo improvement in flow as great as that initially seen in laboratory testing, it does appear to have substantial benefits. The Streamline catheter also has been shown to have a “lower kink potential” than Teflon catheters.’ This benefit may be important for IV catheters that are in situ for prolonged periods. This aspect was not evaluated in our study, although this characteristic could help maintain the maximum flow, as once a standard catheter has been kinked, the flow decreases. This catheter also may have a use in the neonatal intensive care unit or home health care settings, as improvements in indwelling time and lower extravasation rates could be cost-effective. In summary, the Streamline IV catheter had an average flow increase of 26% after 1 hour. This was not as large an increase as seen in laboratory testing, which may be due to physiologic factors preventing complete expansion.
References Philip BK, Philip JH: Characterization of flow in intravenous infusion systems. IEEE Trans Biomed Eng 1983;30:702-7. Knight RJ: Flow rates through disposable intravenous cannulae. Lancet 1968;2:665-7. Dula DJ, Muller HA, Donovan JW: Flow rate variance of commonly used IV infusion techniques. J Trauma 198 1;2 1:480-2. Kestin IG: Flow through intravenous cannulae. Anaesthesia 1987;42:67-70. Dailey RH: Flow rate variance of commonly used IV units. J Am Co11Emerg Physicians 1973;2:341-2. Rosen KR, Rosen DA: Comparative flow rates for small bore peripheral intravenous catheters. Pediatr Emerg Care 1986;2: 153-6. Cooke JE, Walker JM: Evaluation of a unique hydratable I.V. Anesthesiology 1987;67:A208. catheter [Abstract]. Hickey RF, Cason BA, Charles R: Lower incidence of intravenous catheter complication with an elastomeric hydrogel catheter [Abstract]. Anesth Analg 1989;68:Sl21. McKlveen RE, Cooke JE, Loftus JR: Increased fluid flow through the Streamfine intravenous catheter. Anesth Analg 1990;70:32830.
of Anesthesiology,
University
of California
School
of Medicine,
San
CA.
Study Objective: To determine the increase inflow of a hydratable enlarging intravenous (IV) catheter in anesthetized patients. Design: A randomized, nonblinded study, with standard Teflon IV catheters used as controls. Setting: Operating room at a university medical center. Patients: Thirty adult patients receiving general anesthesiafor lower extremity surgery. Interventions: An IV catheter wu placed in the upper extremity, and flow measurements were made b measuring the time for infusion of 250 ml of normal saline within Z minute after placement and at I hour after placement. Measurements and Main Results: The enlarging catheters had a statistically sig@cant auerage flow increase of 26% after 1 hour indwelling time. The standard Teflon catheters had no statistically significant change in flow after 1 hour. The percentage increase in flow for the enlarging catheters was not as
0 1992 Butterworth-Heinemann J. Clin. Anesth. 4:120-122,
120
J. Clin. Anesth.,
1992.
vol. 4, March/April
and equipment,
catheter;
fluids, intravenous.
Introduction Rapid intravenous (IV) fluid administration is frequently limited by the resistance of the IV catheter.’ When possible, large-gauge catheters are inserted to facilitate fluid administration. However, placement of a large-gauge cathIV catheter (Menlo Care, Inc., eter is not always possible. 2-6 A Streamline Menlo Park, CA) made of an elastomeric hydrogel (Aquavene) that is of standard size when inserted and then enlarges after hydration is now commercially available (Figure 1). In vitro study of this catheter has demonstrated improved flow characteristics after hydration. Initial studies showed a 100% increase in flow after 1 hour of hydratiom7 Because of the possible effects of human tissues on the expansion of the catheter in vivo, we tested it to see whether it had the same increase in flow when placed in patients.
Materials and Methods This
study
San Diego
1992
was performed Human
Subjects
with the approval Committee
and
of the University the consent
of California-
of 30 adult
patients
Enlarging IV catheters: Jones and Scheller
??
P <,001
??time0 ? ?time60
20 Teflon
20 Streamline
18 Teflon
Figure 1. The upper IV catheter is a new 20-gauge Streamline IV catheter. The lower catheter is a 20-gauge Streamline catheter after hydration. It has increased in size so that it is approximately equal to an l&gauge catheter.
Figure 2. Mean flow within 1 minute and at 1 hour. The error bars represent standard deviation of the mean flows.
undergoing lower extremity surgery. After induction of general anesthesia, a second IV catheter was placed in the opposite upper extremity. The patients were randomized to one of three groups: those receiving a 20gauge Streamline catheter (Menlo Care, Menlo Park, CA), an 1%gauge Jelco Teflon catheter (Criticon, Tampa, FL), or a 20-gauge Jelco Teflon catheter. All catheters were 1.25 inches long. The study catheter was placed in the forearm, no drugs were given through this IV, and all blood pressure (BP) measurements were done on the opposite arm. A standard IV set (Travenol 2COOOS, Deerfield, IL) was connected to a 250 ml bag of normal saline and directly to the IV catheter. No IV tubing extension sets were used. Flow measurements were made by measuring the time for infusion of 250 ml of normal saline. Fluid pressure was held constant for all tests by maintaining the fluid at 100 cm above the IV catheter. The patient’s arm was maintained by his or her side at all times. Flow was measured within 1 minute after placing the IV catheter and again at 1 hour after placement. The IV rate was maintained at approximately 50 mVhr during the interval between flow measurements. Study catheters were removed and examined after the I-hour study period. A paired Student’s t-test was used to compare study catheter flows before and after the l-hour test period.
Figure 3. Enlarged photograph of a Streamline IV catheter after removal from a patient. Note the segment of the catheter shaft that has not completely expanded.
Results All patients completed the study. In the ten patients who had a 20-gauge Streamline catheter, flow increased by 26% after 1 hour of hydration @ < 0.001; Figure 2. The percent increase in flow for the Streamline catheter ranged from 19% to 35%. There was no statistically significant change in flow for either the 18-gauge or the 20-gauge standard Teflon catheters. After hydration, the flow from the 20-gauge Streamline catheters exceeded the flow of the IB-gauge Teflon catheters. Several Streamline catheters that were removed after the study
appeared to have incomplete the shaft (Figure 3).
expansion
in segments along
Discussion Traditionally, large IV catheters are used when rapid fluid administration is required. The majority of commonly used IV catheters are made of Teflon or other nonexpandable material that does not change in size or shape with time. The Streamline catheter tested expands with hydration and has been shown to have improved flow in vitro.7 The elastomeric hydrogel IV catheters tested in vivo had significantly greater flow after hydration than immediately after placement. Although the flow did increase with hydration, our results show a smaller percentage increase than previously demonstrated in vitro. When removed, several of the Streamline catheters appeared to have incomplete expansion (Figure 3). This may explain why the flow increases were not as large as those seen in the previous laboratory studies.’ Because the limitation in expansion appears to be limited to a short section on the shaft of the catheter at approxi.J. Clin. Anesth.,
vol. 4, March/April
1992
121
Original Contributions
mately the point at which the catheter enters the vein, it is most likely that the vein is preventing the catheter from complete expansion. This bottlenecking effect--&., expansion of the catheter within the interior of the vein and in the surrounding subcutaneous tissues but not where the catheter enters the vein-may explain why this catheter has been found to have a lower frequency of infiltration.8 We speculate that this custom fitting of catheter to the vein wall forms a tight seal and subsequently decreases the extravasation of fluid out of the vein. After hydration, both the diameter and length of the Streamline catheter increased, as seen in Figure 1. Fluid flow is a function of catheter diameter and, to a lesser degree, of length. Flow is proportional to radius (r) to the fourth power and inversely related to length (L): Flow = K; The change in diameter of the catheter is the major factor in the increase in flow, and the slight increase in length decreases flow only slightly. In an in vitro study, Cooke and Walker’ showed that 50% of the maximum flow was obtained by 30 minutes and the maximum flow was obtained by 1 hour. In our study, we chose to measure the flow at two times, within 1 minute and at I hour after placement, as we assumed that maximum flow would be realized by 1 hour. If we had waited for a longer period, the catheter may have expanded more, possibly resulting in a greater increase in flow. During the initial measurement period, the time required for 250 ml of fluid to flow varied from 5 to 7 minutes, and the catheter was probably expanding during that time. This expansion and presumed increase in flow during the initial measurement period would yield a higher initial flow than if a true zero time measurement had been obtainable. Subsequently, the percentage increase in flow we obtained would be lower than if a true zero to 1 hour indwelling period were tested. McKlveen et ~1.~evaluated the Streamline catheter in obstetric patients and found a similar increase in flow after hydration. In their study, there was significant patient variability (2% to 54%), possibly because the patients were awake and movement may have affected the
122
J. Clin.
Anesth.,
vol. 4, March/April
1992
flow. It is reassuring to note that the mean flow increase they measured was similar to the mean flow increase seen in our study. Although the Streamline catheter does not demonstrate an in vivo improvement in flow as great as that initially seen in laboratory testing, it does appear to have substantial benefits. The Streamline catheter also has been shown to have a “lower kink potential” than Teflon catheters.’ This benefit may be important for IV catheters that are in situ for prolonged periods. This aspect was not evaluated in our study, although this characteristic could help maintain the maximum flow, as once a standard catheter has been kinked, the flow decreases. This catheter also may have a use in the neonatal intensive care unit or home health care settings, as improvements in indwelling time and lower extravasation rates could be cost-effective. In summary, the Streamline IV catheter had an average flow increase of 26% after 1 hour. This was not as large an increase as seen in laboratory testing, which may be due to physiologic factors preventing complete expansion.
References Philip BK, Philip JH: Characterization of flow in intravenous infusion systems. IEEE Trans Biomed Eng 1983;30:702-7. Knight RJ: Flow rates through disposable intravenous cannulae. Lancet 1968;2:665-7. Dula DJ, Muller HA, Donovan JW: Flow rate variance of commonly used IV infusion techniques. J Trauma 198 1;2 1:480-2. Kestin IG: Flow through intravenous cannulae. Anaesthesia 1987;42:67-70. Dailey RH: Flow rate variance of commonly used IV units. J Am Co11Emerg Physicians 1973;2:341-2. Rosen KR, Rosen DA: Comparative flow rates for small bore peripheral intravenous catheters. Pediatr Emerg Care 1986;2: 153-6. Cooke JE, Walker JM: Evaluation of a unique hydratable I.V. Anesthesiology 1987;67:A208. catheter [Abstract]. Hickey RF, Cason BA, Charles R: Lower incidence of intravenous catheter complication with an elastomeric hydrogel catheter [Abstract]. Anesth Analg 1989;68:Sl21. McKlveen RE, Cooke JE, Loftus JR: Increased fluid flow through the Streamfine intravenous catheter. Anesth Analg 1990;70:32830.