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Blood-flow augmentation of intermittent pneumatic compression systems used for the prevention of deep vein thrombosis prior to surgery
BloodZlow Augmentation of Intermittent Pneumatic Compression Systems Used for the Prevention of Deep Vein Thrombosis Prior to Surgery Eric Flam, PhD, Piscataway, Silvia Berry, MSc, RVT, Amy Coyle, VT, Herbert Dardik, MD, Englewood, Loretta Raab, RPh, East Brunswick, New Jersey
PURPOSE: To compare, using Duplex ultrasonography, diierent intermittent pneumatic compression (IPC) systems to augment venous blood flow for deep venous thrombosis (DVT) prevention during and after surgery and during periods of immobility. MOODS This cross-over study randomly assigned 26 young, healthy, adult subjects, without history of DVT, hypertension, diabetes, stroke, vascular or cardiac pathologies, to an order of knee-high, foam, single-pulse IPC device and thigh-high, vinyl, sequential-pulse pneumatic compression systems. Prior to making the flow measurement, the girth of the calf and thigh and length of the leg of each subject were determined. The right leg was used in this evaluation. RESULTS: The average flow augmentation, which is a direct measure of the amount of femoral vein blood flow velocity increase over the base, was 107% f 49% with the knee-high system, and 77% f 35% with the thigh-high IPC system (P <0.002). Augmentation was higher for 62% of the subjects with knee-high IPC, and for 23% of the subjects with the thigh-high system. Overall, the blood was actively moving through the vein during the decompression phase. On occasion, the velocity during the decompression phase viould fall to zero for short intervals with both systems, indicating complete emptying of the vessel. Variation in limb anatomy did not significantly affect blood-flow augmentation with the kneehigh IPC, but augmentation decreased with increase in girth with the thigh-high IPC. CONCLUSIONS: The study indicates that the kneehigh, foam, single-pulse IPC device produces a
From UMDNJ-Robert Wood Johnson Medical School, Piscataway (EF); Englewood Hospital, Englewood (33, AC, HD), and NTL Associates, Inc., East Brunswick (LR), New Jersey. All work was done at Englewood Hospital Vascular Lab. Requests for reprints should be addressed to Dr. Eric Flam, PhD, 29 Ainsworth Avenue, East Brunswick, New Jersey 08816. This project was funded by a grant from HNE Healthcare. Manuscript submitted December 12, 1994 and accepted in revised form June 14, 1995.
312
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significantly higher venous blood-flow augmentation than the thigh-high, vinyl, sequentialpulse system. Am J Surg. 1996;171:312-315.
I
ntermittent pneumatic compression (IPC) is used to augment venous blood flow in the prevention of deep vein thrombosis (DVT) during and after surgery and during periods of immobility. L* The mechanism of action is stated to be a combination of relief of venous stasis due to increased motion of the blood, and induction of fibrinolytic activity in the veins.3a8 Much of the documentation for IPC effectnreness has come from clinical studies where the incidence of DVT and pulmonary emboli were determined with and without IPC.1*9S26 Most of these studies evaluated either one IPC system,1~9~‘0~‘2~‘4~‘7~‘9~25 an IPC device versus other physical devices,13,27 an IPC device versus pharmaceuticals,‘*~20~22 or IPC device versus pharmaceuticals and other physical devices.23 Only two other studies24,26 compared more than one IPC system. There have not, to date, been any studl.es that directly compare the effect of IPC systems on venous blood flow and DVT prevention in orthopedic surgery. However, it is the current consensus that an important perfomrance indicator of the effectiveness of IPC modalities in DVT prevention is the peak venous blood velocity augmentation occurring during the compression phase.26’32 There are several IPC systems currently available to the surgeon. For the surgeon to decide on the most effective system for DVT prophylaxis, it is important to have some performance-oriented method for accurately evaluating these systems. One of the first such performance-oriented evaluations was reported by Nicolaides et a126 in 1980. The study sought to describe the performance of IPC systems in terms of venous blood flow measured with Doppler ultrasonography. Only 10 subjects were evaluated, and since no data on individual venous flows were provided, the ‘effectiveness of the systems on the individual participants could not be ascertained. The instrumentation available to these investigators was quite technician dependent, and did not allow simultaneous observation of the vein location. Currently, because of its capability of simultaneous realtime observation of the vein location and blood velocity, high resolution, instantaneous display, and greater controllability by the technician, state-of-the-art Duplex ultrasonography is used for quantitative venous blood-flow measurements. This would make it an ideal modality to measure MARCH
1996
INTERMITrENT
PNEUMATIC
COMPRESSION
TO PREVENT
DVT/FLAM
ET AL
TABLE Femoral Vein Blood in 26 Healthy Subjects During Peak
Compression
Kne+High Mean Standard
deviation
39.5 10.2
Velocity Thigh-High
(cm/s)
Velocities Pneumatic Maximum
and Flow External Decompression
Knee-High
34.2+ 10.8
Velocity
of the (cm/s)
Thigh-High
19.8 5.3
‘Two intermittent pneumatic compression systems were used, in random 10, Polyfoam caif sleeve with the Now&on AC 500 Pump [HNE Healfhcare vice (SCD Sequential Compression Device Model 5320, Thhlgb-ffi Sleeve +P cO.002 versus knee-high values.
Augmentations Compression*
19.8 6.5
Leg Flow
Augmentation
Knee-High
(%) I Thigh-High
107.0 49.3
77.3+ 35.4
order, on each subject: a knee-high, foam, single-pulse device (Flow&on Inc , Manaiapan, New Jersey]), and a thigh-high, viny/, sequential-p&a 5330 {Kendall Company, Mansfield, Massachuseitsj)
and compare the peak venous blood flows and augmentations produced with different IPC systems. The purpose of this study was to measure peak venous blood velocity and flow augmentation with different IPC devices using Duplex ultrasonography, and to determine which subject-related factors influence these measurements. This paper presents the results of a comparative study with a knee-high and a thighhigh IPC system.
METHODS Subject Selection The purpose of this study was to evaluate the performance of the IPC systems with a minimum of other study or subject variables. Therefore, young, healthy, adult subjects, without history of DVT, hypertension, diabetes, stroke, vascular or cardiac pathologies, were recruited into the study. All patients gave informed consent. As they entered the study, the subjects were randomly assigned to an order of products to be used. There were 18 women and 8 men, aged (mean ? standard deviation) 33.8 c 9.3 years, with a mean calf girth of 36.2 + 3.6 cm, thigh girth of 54.1 k 6.2 cm, and leg length of 74.8 * 7.4 cm. IPC Systems Two types of IPC systems were evaluated in this study. One employed a knee-high foam sleeve with a single-pulse compression (Flowtron DVT-10, Polyfoam calf sleeve with the Flowtron AC 500 Pump [HNE Healthcare, Inc., Manalapan, New Jersey]). The other used a thigh-high vinyl sleeve with a sequential-pulse compression (SCD Sequential Compression Device Model 5320, Thigh-Hi Sleeve 5330 [Kendall Company, Mansfield, Massachusetts]). The cycles for the devices were similar; the knee-high system used 10 seconds of compression followed by 50 seconds of decompression, and the thigh-high system used 11 seconds of compression followed by 66 seconds of decompression. The IPC sleeves were applied to the right leg of each subject. The subject was semirecumbent (45” to horizontal), with legs horizontal. Prior to making the flow measurements, the girth of the calf and thigh and the length of the leg of each subject were determined. The IPC sleeves were placed on the leg and operated according to the manufacturers’ instructions. The femoral vein blood velocity (FVBV) in that leg was measured noninvasively using Duplex ultrasonography (ATL Ultramark 9-HDI, Bothell, Washington). The setting at the distal positioning of the Kendall unit was adTHE AMERICAN
DVTde-
justed to 40 mm Hg. Since this is a gradient, sequential-compression system, the actual pressures proximal to the maximum pressure were lower than the maximum pressure. The FVBV was measured continuously during the ‘compression and decompression phases for 10 cycles. At the conclusion of each test, the FVBV was measured with the sleeve on and the pump turned off. The subject was allowed to rest for 5 minutes between tests before conducting the evaluation on the second system. The FVBV was measured at that time and the evaluation of the second system was irntiated when the velocity returned to its initial baseline value. Earlier investigators’6 developed the analytic procedure for comparing the performance of IPC systems. This consisted of determining the difference between the FVBV at peak compression and the maximum FVBV in the decompression phase. This difference is the velocity increase produced by the IPC system. This velocity increase, divided by the maximum FVBV in the decompression phase, is the venous blood-flow augmentation. Thi:: augmentation is a ditect measure of the amount of femoral vein blood-flow increase over the base, and is defined by the following equation: Flow Augmentation = [(peak compression - maximum decompression FVBV)/maximum decompression E\IBV] X 100. The Figure displays the typical velocity profiles for the two IPC systems evaluated in this study, and shows the FVBV at peak compression and the maximum FVBV in the decompression phase. Influence
of Limb Anatomy this evaluation, the calf girth, thigh girth, and leg length of each participant were measured. Regression analyses of the venous blood-flow augmentations and these anatomic variables were conducted to discover if there were any correlations between augmentation and limb anatomy. The coefficients of determination (COD) based on a linear regression analysis were determined. The COD is the square of the correlation coefficient, and indicates how much of the variation of the augmentation can be accounted for by the variation in leg anatomy. During
Statistical Analysis A nonparametric statistical treatment, th.e Wilcoxon matched-pair, signed-rank test was used in analyzing the findings. A risk of 0.05 was selected for determining statistical significance. JOURNAL
OF SURGERY”
VOLUME
171
MARCH
1996
313
1
,
Peak Compression
Velocity
Maximum Decompression
Velocity Augmentation
Velc
Time Peak Compression t
Velocity \
Maximum Decombression
Vel
Figure. Typical compression and decompression femoral vein blood velocity profiles for A. knee-high and B. thigh-high intermittent pneumatic compression (IPC) systems.
FlESULTS The Table presents the averaged, measured venous blood elocities and calculated venous blood-flow augmentations )r this study. Overall, the blood was actively moving through the vein uring the decompression phase. However, on occasion, the elocity during the decompression phase would fall to zero )r short intervals with both systems, indicating complete mptying of the vessel.16 F‘emoral Vein Blood Velocity at Peak Compression The peak compression FVBV was highest with the kneerigh, single-pulse system for 17 of the 26 subjects (65.40/o), md with the thigh-high, sequential-pulse system for 4 subects (15%); peak compression FVBV was similar with )oth systems for 5 of the 26 subjects (19%). The average ralue of the peak compression FVBV for all 26 particiIants with the knee-high, single-pulse system was 39.5 + 10.2 cm/s. The average value of the peak compression ‘VBV with the thigh-high, sequential-pulse system was 14.2 + 10.7 cm/s. This difference was statistically signifiC:ant (P cO.002). I ?emoral Vein Blood Velocity at Maximum Decompression The maximum decompression FVBV was highest with the mee-high, single-pulse system for I3 subjects (50%), and vith the thigh-high, sequential-pulse system for 7 (27%) of he 26 subjects; it was similar with both systems for 6 subects (23%). The average value of the maximum decomlression FVBV for all 26 participants with the knee-high, 314
single-pulse system was 19.8 f 5.3 cm/s. The average value of the maximum decompression FVBV with the thigh-high, sequential-pulse system was 19.8 f 6.5 cm/s. This difference was not statistically significant. Flow Augmentation Blood-flow augmentation was greatest with the knee-high, single-pulse system for 16 of the 26 subjects (62%), and with the thigh-high, sequential-pulse system for 6 subjects (23%); flow augmentation was similar with both systems for 4 subjects (15%). The average value of the flow augmentation for all 26 participants with the knee-high, single-pulse system was 107% f 49%. The average value of the flow augmentation with the thigh-high, sequential-pulse system was 77% f 35%. This difference was statistically significant (P ~0.002). The power of the test for flow augmentation was calculated. The experiment had a probability of 0.887 of correctly rejecting the null hypothesis when the true difference between the augmentations with the knee-high and thigh-high IPC systems was 7.71. Influence of Limb Anatomy For the knee-high IPC device, the variation in calf girth, thigh girth, or leg length accounted for only 0.6% to 7.3% of the variation in augmentation. The findings .with the thighhigh IPC indicated that the variation in leg length accounted for only 8.0% of the variation in augmentation, while the variation in calf girth and thigh girth accounted for 20.1% to 28.0% of the variation in augmentation. The augmentation decreased with increase in girth for both locations.
THE AMERICAN JOURNAL OF SURGERY@ VOLUME 171 MARCH 1996
TERMI-ITENT
COMMENTS A randomized study involving 26 young, healthy, adult subjects, without a history of DVT, hypertension, diabetes, stroke, or vascular or cardiac abnormalities, compared different IPC systems to augment venous blood flow for DVT prevention. This study employed state-of-the-art duplex ultrasonography for comparative measurement of venous blood flow augmentation with a knee-high, foam, single-pulse IPC device and a thigh-high, vinyl, sequential-pulse system. Regression anaylsis of the relationship between augmentation and limb anatomy indicates that there is virtually no correlation between flow augmentation with the knee-high IFC and any of the anatomic measurements, and suggests that variation in limb anatomy does not significantly affect augmentation with this device. Findings for the thigh-high IPC system indicate that there is virtually no correlation between the flow augmentation and leg length, suggesting that variation in leg length does not significantly affect augmentation with this device. However, the slight correlation between the flow aug mentation and the calf and thigh girths suggests that variation in limb girth does affect augmentation with the thigh-high IPC. The overall conclusion from the study was that the kneehigh, foam, single-pulse IPC device produced a significantly higher venous blood-flow augmentation than did the thighhigh, vinyl, sequential-pulse system. This study assesses the physiologic walue and significance of below-knee versus above-knee intermittent compression therapy of tk lowerextremity. While only a few patientswereincluded,tk findings appear quite objective. Tk paper describes an apparent efjectiwe prophylaxis for deep vein thrombosis.
REFERENCES 1. Inada K, Shigefumi K, Skirai N, et al. Effects of intermittent pneumatic leg compression for prevention of postoperative deep venous thrombosis with special reference to fibrinolytic activity. Am J Surg. 1988;155:602-605. 2. Kamm RD. Bioengineering studies of periodic external compression asprophylaxis against deep vein thrombosis-part 1: numerical studies.J BtomechEng. 1982;104:87-95. 3. Salzman EW, McManama GP, Shapiro AH, et al. Effect of optimization of hemodynamics on fibrinolytic activity and antithrombotic efficacy of external pneumatic calf compression. Ann Surg. 1987;206: 636-641. 4. Hartman JT, Pugh JL, Smith RD, et al. Cyclic sequential compression of the lower limb in prevention of deep venous thrombosis. J Bone Joint Surg. 1982;64:1059-1062. 5. Borow M, Goldson H. Postoperative venous thrombosis. Am J Surg. 1981;2:246-250. 6. Tamay rJ, Rohr PR, Davidson AC, et al. Pneumatic calf compression, fibrinolysis, and the prevention of deep venous thrombosis. Surgery. 1980;88:489-496. 7. O’Brien TE, Woodford M, Irving MH. The effect of intermittent compression of the calf on the fibrinolytic responses in the blood during a surgical operation. Surg, Gyn &? Obst. 1979;149:38@384. 8. Pidala MJ, Donovan DL, Kepley RF. A prospective study on intermittent pneumatic compression in the prevention of deep vein thrombasis in patients undergoing total hip or total knee replacement. Surg Gynecot Obstet. 1992;175:47-51. 9. Hull RD, Raskob GE, Gent M, et al. Effectivenessof intermittent pneumatic leg compression for preventing deep vein thrombosis after total hip replacement. JAMA. 1990;263:2213-2217. 10. Scurr JH, Coleridge-Smith PD, Hasty JH. Regimen for improved effectiveness of intermittent pneumatic compression in deep venous thrombosis prophylaxis. Surgery. 1987;102:816-820.
PNEUMATIC
COMPRESSION
TO PREVENT
DVT/FLAM
ET AL
11. Pogson GW, Reed W, Weinstein GS. Prevention of deep vein thrombosis. MO Med. 1985;82:133-136. 12. Nicolaides AN, Miles C, Hoare M, et al. Intermittent sequential pneumatic compression of the legs and thromboembdism-deterrent stockings in the prevention of postoperative deep venous thrombosis. Surgery. 1983;94:21-25. 13.Caprini JA, Chucker JL, Zuckerman L, et al. Thrombosis prophylaxis using external compression. Swg Gywol Obslet. 1953;156:5 99-604. 14. Lee BY, Trainor FS, Thoden WR, et al. Prevention of deep venous thrombosis: intermittent pneumatic compression. Comp~ Ther. 1979;5: 6%75. 15. Blackshear WM Jr., Prescott C, LePain F, et al. Influence of sequential pneumatic compression on postoperative venous function. J Var;c Surg. 1987;3:432-436. 16. Clark WB, Prescott RJ, MacGregor AB, Ruckley CV. Pneumatic compression of the calf and postoperative deep-vein thmmbosis. Lmcet. 1974;7:5-15. 17. Hull R, Delmore TJ, Hirsh J, et al. Effectivenessof intermittent pulsatile elastic stockings for the prevention of calf and thigh vein thrombosis in patients undergoing elective knee surgery Tkromb Res. 1979;16:1-2. 18. Hirsh J. Prevention of venous thrombosis in patients undergoing major orthopaedic surgical procedures. Acta Chir SC& .%@I. 1990;556: 30-35. 19. Hills NH, Pflug JJ,Jeyasingh K, et al. Prevention of deep vein rhromb&s by intermittent pneumatic compression of calf. Bw. 1972;l: 131-135. 20. Haas SB, Insall JN, Scuderi GR, et al. Pneumatic sequential-compression boots compared with aspirin prophylaxis of deep-vein thrombosis after total knee arthroplasty. J Bone Joint Sur,. 1990;72:27-31. 21. Moser G, Krahenbuhl B, Barroussel R, et al. Mechanical versuspharmacologic prevention of deep venous thrombosis. Surg Gynecol O&t. 1981;152:448-450. 22. Mellbring G, Palmer K. Prophylaxis of deep vein thrombosis after major abdominal surgery. Acta Chir Sumd. 1986;152:597-600. 23. Lynch JA, Baker PL, Polly RE, et al. Mechanical measures in the prophylaxis of postoperative rhromboembolism in total knee arrhroplasty. C&n Onhop. 1990;26024-29. 24. Ljungner H, Bergqvist D, Nilsson IM. Effect of intermittent pneumatic and graduated static compression on factor VIII and the fibrinolytic system.Acta Chir Stand. 1981;147:657-661. 25. Lee BY, Trainor FS, Kavner D, et al. Noninvasivat prevention of deep vein thrombosis. AFI’. 1976;14:12&134. 26. Nicolaides AN, Femandes E, Femandes J, Pollock AV. Intermittent sequential pneumatic compression of the legs in the prevention of venous stasis and postoperative deep venous thrombosis. Surgerjr 1980;87:69-76. 27. Keith SL, McLaughlin DJ, Anderson FA Jr., et al. Do graduated compression stockings and pneumatic boots have an aclditive effect on the peak velocity of venous blood flow? Arch Surg. 1992;127:727-730. 28. Caprini JA, Scurr JH, Hasty JH. Role of compression modalities in a prophylactic program for deep vein thrombosis. Semin Thwmh Hemost. 1988;14:77-87. 29. Paiement G, Wessinger SJ, Waltman AC, Harris WH. Low-dose warfti versusexternal pneumatic compression for prophylaxis against venous thromboembolism following total hip replacement. J Arthropkwy. 1987;2:23-26. 30. Olson DA, Kamm RD, Shapiro AH. Bioengineering studies of pe riodic external compression as prophylaxis against deep vein thrombosis-part ii: experimental studies on a simulated leg. J Biomech Eng. 1982;104:96-104. 31. Sigel B, Edelstein AL, Savitch L, et al. Type of compression for reducing venous stasis.Arch Surg. 1975;110:171-175. 32. Roberts VC, Sabri S, Beeley AH, Cotton LT. The effect of intermittently applied external pressure on the haemcdynarnics of the lower limb in man. Br J Surg. 1972;59:223-226. J
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1996
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PURPOSE: To compare, using Duplex ultrasonography, diierent intermittent pneumatic compression (IPC) systems to augment venous blood flow for deep venous thrombosis (DVT) prevention during and after surgery and during periods of immobility. MOODS This cross-over study randomly assigned 26 young, healthy, adult subjects, without history of DVT, hypertension, diabetes, stroke, vascular or cardiac pathologies, to an order of knee-high, foam, single-pulse IPC device and thigh-high, vinyl, sequential-pulse pneumatic compression systems. Prior to making the flow measurement, the girth of the calf and thigh and length of the leg of each subject were determined. The right leg was used in this evaluation. RESULTS: The average flow augmentation, which is a direct measure of the amount of femoral vein blood flow velocity increase over the base, was 107% f 49% with the knee-high system, and 77% f 35% with the thigh-high IPC system (P <0.002). Augmentation was higher for 62% of the subjects with knee-high IPC, and for 23% of the subjects with the thigh-high system. Overall, the blood was actively moving through the vein during the decompression phase. On occasion, the velocity during the decompression phase viould fall to zero for short intervals with both systems, indicating complete emptying of the vessel. Variation in limb anatomy did not significantly affect blood-flow augmentation with the kneehigh IPC, but augmentation decreased with increase in girth with the thigh-high IPC. CONCLUSIONS: The study indicates that the kneehigh, foam, single-pulse IPC device produces a
From UMDNJ-Robert Wood Johnson Medical School, Piscataway (EF); Englewood Hospital, Englewood (33, AC, HD), and NTL Associates, Inc., East Brunswick (LR), New Jersey. All work was done at Englewood Hospital Vascular Lab. Requests for reprints should be addressed to Dr. Eric Flam, PhD, 29 Ainsworth Avenue, East Brunswick, New Jersey 08816. This project was funded by a grant from HNE Healthcare. Manuscript submitted December 12, 1994 and accepted in revised form June 14, 1995.
312
THE AMERICAN
JOURNAL
OF SURGERYa
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significantly higher venous blood-flow augmentation than the thigh-high, vinyl, sequentialpulse system. Am J Surg. 1996;171:312-315.
I
ntermittent pneumatic compression (IPC) is used to augment venous blood flow in the prevention of deep vein thrombosis (DVT) during and after surgery and during periods of immobility. L* The mechanism of action is stated to be a combination of relief of venous stasis due to increased motion of the blood, and induction of fibrinolytic activity in the veins.3a8 Much of the documentation for IPC effectnreness has come from clinical studies where the incidence of DVT and pulmonary emboli were determined with and without IPC.1*9S26 Most of these studies evaluated either one IPC system,1~9~‘0~‘2~‘4~‘7~‘9~25 an IPC device versus other physical devices,13,27 an IPC device versus pharmaceuticals,‘*~20~22 or IPC device versus pharmaceuticals and other physical devices.23 Only two other studies24,26 compared more than one IPC system. There have not, to date, been any studl.es that directly compare the effect of IPC systems on venous blood flow and DVT prevention in orthopedic surgery. However, it is the current consensus that an important perfomrance indicator of the effectiveness of IPC modalities in DVT prevention is the peak venous blood velocity augmentation occurring during the compression phase.26’32 There are several IPC systems currently available to the surgeon. For the surgeon to decide on the most effective system for DVT prophylaxis, it is important to have some performance-oriented method for accurately evaluating these systems. One of the first such performance-oriented evaluations was reported by Nicolaides et a126 in 1980. The study sought to describe the performance of IPC systems in terms of venous blood flow measured with Doppler ultrasonography. Only 10 subjects were evaluated, and since no data on individual venous flows were provided, the ‘effectiveness of the systems on the individual participants could not be ascertained. The instrumentation available to these investigators was quite technician dependent, and did not allow simultaneous observation of the vein location. Currently, because of its capability of simultaneous realtime observation of the vein location and blood velocity, high resolution, instantaneous display, and greater controllability by the technician, state-of-the-art Duplex ultrasonography is used for quantitative venous blood-flow measurements. This would make it an ideal modality to measure MARCH
1996
INTERMITrENT
PNEUMATIC
COMPRESSION
TO PREVENT
DVT/FLAM
ET AL
TABLE Femoral Vein Blood in 26 Healthy Subjects During Peak
Compression
Kne+High Mean Standard
deviation
39.5 10.2
Velocity Thigh-High
(cm/s)
Velocities Pneumatic Maximum
and Flow External Decompression
Knee-High
34.2+ 10.8
Velocity
of the (cm/s)
Thigh-High
19.8 5.3
‘Two intermittent pneumatic compression systems were used, in random 10, Polyfoam caif sleeve with the Now&on AC 500 Pump [HNE Healfhcare vice (SCD Sequential Compression Device Model 5320, Thhlgb-ffi Sleeve +P cO.002 versus knee-high values.
Augmentations Compression*
19.8 6.5
Leg Flow
Augmentation
Knee-High
(%) I Thigh-High
107.0 49.3
77.3+ 35.4
order, on each subject: a knee-high, foam, single-pulse device (Flow&on Inc , Manaiapan, New Jersey]), and a thigh-high, viny/, sequential-p&a 5330 {Kendall Company, Mansfield, Massachuseitsj)
and compare the peak venous blood flows and augmentations produced with different IPC systems. The purpose of this study was to measure peak venous blood velocity and flow augmentation with different IPC devices using Duplex ultrasonography, and to determine which subject-related factors influence these measurements. This paper presents the results of a comparative study with a knee-high and a thighhigh IPC system.
METHODS Subject Selection The purpose of this study was to evaluate the performance of the IPC systems with a minimum of other study or subject variables. Therefore, young, healthy, adult subjects, without history of DVT, hypertension, diabetes, stroke, vascular or cardiac pathologies, were recruited into the study. All patients gave informed consent. As they entered the study, the subjects were randomly assigned to an order of products to be used. There were 18 women and 8 men, aged (mean ? standard deviation) 33.8 c 9.3 years, with a mean calf girth of 36.2 + 3.6 cm, thigh girth of 54.1 k 6.2 cm, and leg length of 74.8 * 7.4 cm. IPC Systems Two types of IPC systems were evaluated in this study. One employed a knee-high foam sleeve with a single-pulse compression (Flowtron DVT-10, Polyfoam calf sleeve with the Flowtron AC 500 Pump [HNE Healthcare, Inc., Manalapan, New Jersey]). The other used a thigh-high vinyl sleeve with a sequential-pulse compression (SCD Sequential Compression Device Model 5320, Thigh-Hi Sleeve 5330 [Kendall Company, Mansfield, Massachusetts]). The cycles for the devices were similar; the knee-high system used 10 seconds of compression followed by 50 seconds of decompression, and the thigh-high system used 11 seconds of compression followed by 66 seconds of decompression. The IPC sleeves were applied to the right leg of each subject. The subject was semirecumbent (45” to horizontal), with legs horizontal. Prior to making the flow measurements, the girth of the calf and thigh and the length of the leg of each subject were determined. The IPC sleeves were placed on the leg and operated according to the manufacturers’ instructions. The femoral vein blood velocity (FVBV) in that leg was measured noninvasively using Duplex ultrasonography (ATL Ultramark 9-HDI, Bothell, Washington). The setting at the distal positioning of the Kendall unit was adTHE AMERICAN
DVTde-
justed to 40 mm Hg. Since this is a gradient, sequential-compression system, the actual pressures proximal to the maximum pressure were lower than the maximum pressure. The FVBV was measured continuously during the ‘compression and decompression phases for 10 cycles. At the conclusion of each test, the FVBV was measured with the sleeve on and the pump turned off. The subject was allowed to rest for 5 minutes between tests before conducting the evaluation on the second system. The FVBV was measured at that time and the evaluation of the second system was irntiated when the velocity returned to its initial baseline value. Earlier investigators’6 developed the analytic procedure for comparing the performance of IPC systems. This consisted of determining the difference between the FVBV at peak compression and the maximum FVBV in the decompression phase. This difference is the velocity increase produced by the IPC system. This velocity increase, divided by the maximum FVBV in the decompression phase, is the venous blood-flow augmentation. Thi:: augmentation is a ditect measure of the amount of femoral vein blood-flow increase over the base, and is defined by the following equation: Flow Augmentation = [(peak compression - maximum decompression FVBV)/maximum decompression E\IBV] X 100. The Figure displays the typical velocity profiles for the two IPC systems evaluated in this study, and shows the FVBV at peak compression and the maximum FVBV in the decompression phase. Influence
of Limb Anatomy this evaluation, the calf girth, thigh girth, and leg length of each participant were measured. Regression analyses of the venous blood-flow augmentations and these anatomic variables were conducted to discover if there were any correlations between augmentation and limb anatomy. The coefficients of determination (COD) based on a linear regression analysis were determined. The COD is the square of the correlation coefficient, and indicates how much of the variation of the augmentation can be accounted for by the variation in leg anatomy. During
Statistical Analysis A nonparametric statistical treatment, th.e Wilcoxon matched-pair, signed-rank test was used in analyzing the findings. A risk of 0.05 was selected for determining statistical significance. JOURNAL
OF SURGERY”
VOLUME
171
MARCH
1996
313
1
,
Peak Compression
Velocity
Maximum Decompression
Velocity Augmentation
Velc
Time Peak Compression t
Velocity \
Maximum Decombression
Vel
Figure. Typical compression and decompression femoral vein blood velocity profiles for A. knee-high and B. thigh-high intermittent pneumatic compression (IPC) systems.
FlESULTS The Table presents the averaged, measured venous blood elocities and calculated venous blood-flow augmentations )r this study. Overall, the blood was actively moving through the vein uring the decompression phase. However, on occasion, the elocity during the decompression phase would fall to zero )r short intervals with both systems, indicating complete mptying of the vessel.16 F‘emoral Vein Blood Velocity at Peak Compression The peak compression FVBV was highest with the kneerigh, single-pulse system for 17 of the 26 subjects (65.40/o), md with the thigh-high, sequential-pulse system for 4 subects (15%); peak compression FVBV was similar with )oth systems for 5 of the 26 subjects (19%). The average ralue of the peak compression FVBV for all 26 particiIants with the knee-high, single-pulse system was 39.5 + 10.2 cm/s. The average value of the peak compression ‘VBV with the thigh-high, sequential-pulse system was 14.2 + 10.7 cm/s. This difference was statistically signifiC:ant (P cO.002). I ?emoral Vein Blood Velocity at Maximum Decompression The maximum decompression FVBV was highest with the mee-high, single-pulse system for I3 subjects (50%), and vith the thigh-high, sequential-pulse system for 7 (27%) of he 26 subjects; it was similar with both systems for 6 subects (23%). The average value of the maximum decomlression FVBV for all 26 participants with the knee-high, 314
single-pulse system was 19.8 f 5.3 cm/s. The average value of the maximum decompression FVBV with the thigh-high, sequential-pulse system was 19.8 f 6.5 cm/s. This difference was not statistically significant. Flow Augmentation Blood-flow augmentation was greatest with the knee-high, single-pulse system for 16 of the 26 subjects (62%), and with the thigh-high, sequential-pulse system for 6 subjects (23%); flow augmentation was similar with both systems for 4 subjects (15%). The average value of the flow augmentation for all 26 participants with the knee-high, single-pulse system was 107% f 49%. The average value of the flow augmentation with the thigh-high, sequential-pulse system was 77% f 35%. This difference was statistically significant (P ~0.002). The power of the test for flow augmentation was calculated. The experiment had a probability of 0.887 of correctly rejecting the null hypothesis when the true difference between the augmentations with the knee-high and thigh-high IPC systems was 7.71. Influence of Limb Anatomy For the knee-high IPC device, the variation in calf girth, thigh girth, or leg length accounted for only 0.6% to 7.3% of the variation in augmentation. The findings .with the thighhigh IPC indicated that the variation in leg length accounted for only 8.0% of the variation in augmentation, while the variation in calf girth and thigh girth accounted for 20.1% to 28.0% of the variation in augmentation. The augmentation decreased with increase in girth for both locations.
THE AMERICAN JOURNAL OF SURGERY@ VOLUME 171 MARCH 1996
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COMMENTS A randomized study involving 26 young, healthy, adult subjects, without a history of DVT, hypertension, diabetes, stroke, or vascular or cardiac abnormalities, compared different IPC systems to augment venous blood flow for DVT prevention. This study employed state-of-the-art duplex ultrasonography for comparative measurement of venous blood flow augmentation with a knee-high, foam, single-pulse IPC device and a thigh-high, vinyl, sequential-pulse system. Regression anaylsis of the relationship between augmentation and limb anatomy indicates that there is virtually no correlation between flow augmentation with the knee-high IFC and any of the anatomic measurements, and suggests that variation in limb anatomy does not significantly affect augmentation with this device. Findings for the thigh-high IPC system indicate that there is virtually no correlation between the flow augmentation and leg length, suggesting that variation in leg length does not significantly affect augmentation with this device. However, the slight correlation between the flow aug mentation and the calf and thigh girths suggests that variation in limb girth does affect augmentation with the thigh-high IPC. The overall conclusion from the study was that the kneehigh, foam, single-pulse IPC device produced a significantly higher venous blood-flow augmentation than did the thighhigh, vinyl, sequential-pulse system. This study assesses the physiologic walue and significance of below-knee versus above-knee intermittent compression therapy of tk lowerextremity. While only a few patientswereincluded,tk findings appear quite objective. Tk paper describes an apparent efjectiwe prophylaxis for deep vein thrombosis.
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