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The potential benefits of intermittent pneumatic compression in the prevention of deep venous thrombosis
ORIGINAL
ARTICLE
The potential benefits of intermittent pneumatic compression in the prevention of deep venous thrombosis Peter Davis and Cathy O'Neill Deep Venous Thrombosis (DVT) is a common condition, which can lead to Pulmonary Embolism (PE) with fatal consequences. Patients who have developed DVT may also suffer a long-term complication known as post-thrombotic syndrome, resulting in chronic conditions such as leg ulcers. The article presents a basic review of the incidence and clinical significance of DVT with a brief description of aetiology and prevention. Interventions are reviewed and intermittent pneumatic compression specifically evaluated. The essence of risk assessment and patient education to successful patient outcomes is emphasised. © 2002 Elsevier Science Ltd. All rights reserved.
Associate Editor's comment Choices in DVT prevention continue to be a debatable and confusing area of practice. This article clearly presents the risks and issues relevant to any preventative method with a focus on one mechanical method used internationally.
PO KEY WORDS: Deep venous thrombosis, pulmonary embolism, intermittent pneumatic compression, post-thrombotic syndrome, risk assessment
INTRODUCTION
Peter Davis MBE, MA, BEd, RN, ONe. Health Lecturer - University of Nottingham
Cathy O'Neill PhD, BSc, FRSM, Clinical Manager, Huntlelgh Healthcare Ltd, Luton Correspondence to' Cathy O'Neill, Huntlelgh Healthcare, 310-312 Dallow Road, Luton, Bedfordshlre, LU I ITO, UK Tel. 01582 745736, Email cathyoneill@ huntlelgh-healthcare com
DVT usually occurs as a result of a combination of venous stasis, vein injury and blood chemistry changes. These factors occur frequently in surgical patients and in many specialities, particularly orthopaedics and trauma. Intermittent Pneumatic Compression (IPC) is an established non-invasive method of DVT prevention. Inflatable garments are wrapped around the leg, or the foot and the garments are inflated with air using a pump. IPC has a dual effect, preventing venous stasis by mechanically simulating the pumping action of muscle groups and addressing the blood chemistry changes, by enhancing fibrinolytic activity. The latter is achieved without the surgical bleeding complications associated with anticoagulants.
journal of OrthopaedIc Nursmg (2002) 6. 95-100
l~)
2002 ElseVier SCience Ltd All r12'hts reserved
dOL 10 1054/\00n 2002.0231. aVailable online http.llwww,deallbrary.com on
IDE ~l®
All medical and surgical patients should be assessed for DVT risk. Guidelines on appropriate prevention based on low, moderate and high-risk categories should be used in conjunction with clinicaljudgement particularly where prophylactic intervention itself may carry risk. There remains considerable variation in prevention strategies between and even within hospitals and further research is required to optimise DVT prophylaxis for orthopaedic and other patients. Clearer guidelines on venous thromboembolism (VTE) are beginning to emerge. The Scottish Intercollegiate Guidelines Network (2002, p 13) in their latest guidelines covering management of hip fracture in older people recommend: • Mechanical prophylaxis (IPC or foot pumps) should be considered to reduce the risk of
96 Journal
of Orthopaedic Nursing
asymptomatic DVT after hip fracture. There is no evidence for efficacy of graded elastic compression stockings in hip fracture patients. • All patients with hip fracture should receive aspirin (150mg orally, started on admission and continued for 35 days) unless contraindicated. • Heparin should be reserved for selected patients at high risk of VTE after hip fracture due to; -multiple risk factors -contraindications to routine mechanical prophylaxis and/or aspirin DVT has recently commanded more media interest than at any other time in the past. Interestingly, this is not as a response to the large number of hospital patients who die as a result of this problem but due to the relatively low number of long-haul flight passengers who succumb. The International Consensus Statement (1997) reports that patients who have developed a DVT may also suffer a long-term complication known as post-thrombotic syndrome affecting the blood supply of the lower limb and leading to possible leg ulcers. They report the incidence of post-thrombotic syndrome as being 35-69% at 3 years after DVT and 49-100% at 5-10 years. In addition, venous ulcers develop in at least 300 per 100 000 of the population and the proportion due to DVT is approximately 25%. Despite the known effects of DVT, less than half of high-risk surgical patients receive any form of prophylaxis (Griffin 1996). In 1997,790,000 major elective surgical procedures were carried out in the UK; this constitutes over 390,000 who did not receive DVT prophylaxis (Griffin 1996). It is estimated that post surgical DVT and PE cost the NHS between £204.7 and £222.8 million in 1992 (Griffin 1996). If all patients at high-risk post surgery had received adequate prophylaxis there would have been a cost saving of £33.4 to £81.8 million and the number of deaths from PE reduced by more than 400.
INCIDENCE OF DVT Obtaining accurate data on the incidence of DVT is difficult; on the one hand, due to the inability to make a diagnosis by clinical signs alone, and on the other, as it is often asymptomatic (Griffin 1996). In the general population DVT of the lower limbs presents with clinical signs in approximately 1 per 1000 annually (Nicolaides et al. 1997). Incidence rates in the hospital population are much higher than this, due to a combination of acute injury, surgery and immobilisation. For example, the incidence of clinical DVT in orthopaedic surgery is thought to be in the region of 4% (THRiFT II 1998), although DVT rates as high as 60% have
been reported in patients undergoing knee replacement surgery (Warwick and Whitehouse 1997). Prevalence rates of DVT in cases of major trauma of 58% have been documented (Geerts et al. 1994).
AETIOLOGY OF DVT There are three factors responsible for the development of DVT; venous stasis, vein injury and blood chemistry changes. These factors were first described by Rudolph Virchow, a German pathologist in 1856, and are commonly referred to as Virchow's Triad. It is now generally accepted that it is usually a combination of these factors that causes a thrombosis, rather than one factor in isolation. A combination of these factors occur in some patients in virtually all hospital specialties, including all types of surgery, trauma, obstetrics, oncology, medical and even paediatrics (THRiFT II 1998, Donnelly 1999). For example, blood chemistry changes due to surgery occur as a protective mechanism to prevent wounds bleeding excessively, venous stasis occurs due to anaesthesia and inactivity in the postoperative period, and vein injury may occur as a direct result of certain surgical procedures.
PREVENTION OF DVT Methods of DVT prophylaxis include; early mobilisation, the use of pharmacological agents, most commonly the parenteral anticoagulants (low dose heparin, low molecular weight heparin (LMWH» and mechanical methods, such as graduated compression stockings and intermittent pneumatic compression (lPe) (THRiFT II 1998). There has been a growing interest in the latter as a noninvasive method of prophylaxis. Unlike the other methods of prophylaxis mentioned, which address one element of Virchow's Triad, IPC affects two components of the Triad (Figure 1), namely venous stasis and the blood chemistry changes. Most importantly it does not carry the risk of excessive surgical bleeding associated with anticoagulants (Griffin 1996, THRiFT II 1998, Salvati et al. 2000). A prospective study by Hooker et al. in 1999, showed that the use of intraoperative and postoperative thigh-high intermittent pneumatic compression was effective for prophylaxis against thromboembolism in 425 patients undergoing total hip arthroplasty. The low prevalence of DVT (4.6%) and pulmonary embolism (0.6%) reported in the study is comparable with that associated with pharmacological prophylaxis. A smaller study by Stone et al. (1996) directly compared IPC with LMWH for thromboprophylaxis in total hip replacement. This study concluded that both methods of prophylaxis decreased the incidence of DVT but that
Prevention of deep venous thrombosis
97
Vein lI1Jury
~_.,.
I Venous stasis Fig. I
Vichow's Triad.
IPC has fewer complications and contraindications than LMWH. Indeed, they found the operative field to be drier and easier to work when patients received IPC compared with that ofpatients receiving LMWH and fewer patients in the IPC group required blood transfusion.
PRINCIPLES OF IPC FOR DVT PROPHYLAXIS Most venous thrombi originate in regions of slow blood flow, such as the large venous sinuses of the calf and thigh or in valve cusp pockets (Mammen 1992). Decreased blood flow or even stasis due to lack of the pump action of large muscle groups is a major factor in the development of DVT. It seems logical to compensate for this by simulating this pumping action mechanically. IPC is applied by wrapping an inflatable garment around the leg, or foot and a section of the garment is inflated with air via a pump. The garment is deflated after a few seconds. This sequence of inflation and deflation of the garments continues for the duration of therapy, providing cyclic mechanical compression to the venous system of the leg or foot. Calf garments (Figure 2) operate at low pressures, for example 40 mmHg, with a short inflation period, 12 seconds, and a long deflation period, 48 seconds, to allow venous refilling to occur (Huntleigh Healthcare 1998). The inflation forces blood in the superficial veins into the deep veins of the leg, increasing venous blood velocity and preventing venous stasis. Foot garments (Figure 3) utilise the venous foot pump in the sole of the foot, which consists of the
venae comites of the lateral plantar artery (Binns and Pho 1988). Applying IPC to the foot causes a flattening of the plantar arch similar to that caused by weight bearing (Gardner and Fox 1993). This causes emptying of the lateral plantar veins, into the deep veins of the leg. Foot pump systems operate at higher pressures than calf/thigh systems with shorter inflation and deflation periods. It is recommended that the garments should be applied and worn continuously during the pre, intra, and post-operative phases of surgery for a minimum of 72 hours post-operatively. or until the patient is fully mobile (Huntleigh Healthcare 1998). The use ofIPC as a prophylactic strategy for the prevention of DVT is far from new. More than 30 years ago it was demonstrated in an animal model that the application of IPC to muscles of the calf altered venous blood flow in the leg rhythmically in a similar manner to that of the normal calf-muscle pump (Calnan et al. 1970). Researchers at the Hammersmith Hospital demonstrated the effect of IPC on the blood constituent part of Virchow's Triad (Allenby et al. 1973). They showed that IPC applied to the legs of patients undergoing surgery stimulated fibrinolysis post-operatively, when fibrinolysis would normally be depressed. The importance of this biochemical effect to the overall action of IPC was confirmed by the work of Knight and Dawson in 1976 (Knight and Dawson 1976). They showed IPC was still able to reduce the incidence of DVT without increasing blood flow in the legs, although to a lesser extent. They achieved this by applying IPC to patient's arms rather than to their legs during surgery. It is now thought that IPC enhances fibrinolytic activity by reducing the amount of plasminogen
98 Journal of Orthopaedic Nursing
." -.r- •• -
.'
,,~J~"
t
"
Fig. 2
Intermittent pneumatic compression of the calf (with permission of Huntleigh Healthcare).
,
\.
..
Fig. 3
Intermittent pneumatic compression of the foot (with permission of Huntleigh Healthcare).
activator inhibitor and thereby reducing the risk of clot formation by inactivating fibrin (Comerota et al. 1997). This works in a different way to chemical methods ofprophylaxis, such as heparin, which actively prevent fibrin formation.
RISK ASSESSMENT In 1998 the THRiFf II Consensus Group reviewed published data on DVT prophylaxis
and recommended that all medical and surgical patients should be assessed for the risk of DVT with respect to medical/family history, clinical signs, existing conditions and results of specific blood tests. Based on these assessments patients could be categorised into three groups; low (risk <10%), moderate (risk 10-40%) and high risk (40-80%). Unlike the use of risk assessment tools in pressure ulcer risk assessment, no specific scoring system or weighting for different factors were provided within the Consensus document, but
Prevention of deep venous thrombosis
Table 1 Recommendations for, prophylaxis against DVT (THRiFT II 1998) Recommendations for DVT prophylaxis
Risk level Low Moderate & High
• • • • • •
Early mobilisation Graduated compression stockings Early mobilisation Graduated compression stockings UFH/LMWH Foot impulse technology or intermittent pneumatic compression • Development of specific prophylaxis protocol
99
episode (Bergquist et al. 1997) makes the identification of at risk patients and the implementation of preventative strategies vital. The evidence base for interventions to prevent DVT and PE is still comparatively poor and often contradictory in nature. This means that action is highly variable from hospital to hospital and sometimes even within the same hospital. Clarification is still needed on which interventions are best for which circumstances and with which patients.
REFERENCES
examples of patient groups covered within each category were listed, including orthopaedics. The Consensus Group provided guidelines (Table 1) on which methods of prophylaxis were suitable for patients based on the low, moderate and high-risk categorisation. IPC was recommended for moderate and high-risk patients. Recently the benefit of categorising patients by risk level has been questioned. Orthopaedic surgeons in particular have been reluctant to implement risk categorisation. The concept of categories may overemphasis prophylaxis so that patients, particularly those at medium to low risk, may be put at more risk due to the prophylactic intervention than due to venous thromboembolism without intervention. For example, there is concern about the possible risks of pharmacological prophylaxis in total hip replacement patients (Francis and Brenkel 1997). Also there is the possible risk of low molecular weight heparin causing vertebral canal haematoma after a spinal epidural block (Checketts and Wildsmith 1999). Recent reluctance to categorise patients into risk groups does not imply that identifying risk is unnecessary. Rather, this position indicates the complexities of risk assessment and the need to individualise interventions for the patient and the specifics of the situation.
CONCLUSION IPC offers a non-invasive method of prophylaxis that can be used for: moderate or high-risk patients, or for patients contraindicated for pharmacological prophylaxis, or in conjunction with pharmacological agents as a complementary intervention (THRiFT II 1998). It is recommended for patients following hip fracture (SIGN 2002). IPC has a dual benefit reducing venous stasis and enhancing fibrinolytic activity. Further large randomised controlled trials are needed comparing the efficacy of IPC with LMWH, particularly in trauma and orthopaedic patients (THRiFT II 1998). The need for DVT prophylaxis spans all areas of the hospital. The potential complications and the recurrent nature of DVT following an initial
Allenby F, Pflug n, Boardman L, Calnan JS (1973) Effects of external pneumatic intennittent compression on fibrinolysis in man. The Lancet 2: 1412-1414 Bergquist D, Jendteg S, Johansten L, Persson D, Odegaard K (1997) Costs of long-tenn complications of deep venous thrombosis of the lower extremities: an analysis of a defined patient population in Sweden. Annuals of Internal Medicine 126: 454--457 Binns M, Pho WH (1988) Anatomy ofthe venous foot pump. Injury 19: 443-445 Calnan JS, Pflug n, Mills CJ (1970) Pneumatic Intennittent compression legging simulating calf-muscle pump. The Lancet 2: 502-503 Checketts MR, Wildsmith JW (1999) Central nerve block and thromboprophylaxis - is there a problem? British Journal of Anaesthesia 82: 164-167 Comerota AJ, Chouhan V, Harada R, Sun L, Hosking J, Veennansunemi R, Comerota A, Schlappy D, Koneti Rao A (1997) The fibrinolytic effects of Intennittent Pneumatic Compression. mechanism of enhanced fibrinolysis. Annals of Surgery 226(3): 306-314 Donnelly KM (1999) Venous thromboembolic disease in the paediatric intensive care unit. Current Opinion in Pediatrics 11(3)' 213-217 Francis RM, Brenkel IJ (1997) Survey of the use thromboprophylaxis for routine total hip replacement by British orthopaedic surgeons. British Journal of Hospital Medicine 57: 427-431 Gardner AMN, Fox RH (1993) The Return of Blood to the Heart. Venous Pumps in Health and Disease Second Edition. London: John Libbey and Company Ltd. Geerts WHo Code KI, Jay RM. Chen E. Szalai JP (1994) A prospective study of venous thromoembolism after major trauma. New England Journal of Medicine 331: 1601-1606 Griffin J (1996) Deep Vein Thrombosis and Pulmonary Embolism. London: Office of Health Economics Hooker JA, Lachiewlcz PF, Kelley SS (1999) Efficacy of prophylaxis against thromboembolism with intennittent pneumatic compression after primary and revision total hlp arthroplasty. The Journal of Bone and Joint Surgery 81A' 690-96 International Consensus Statement (1997) Prevention of Venous Thromboembolism, London: Med-Orion Pubhshmg Huntleigh Healthcare (1998) Flowtron Excel Protocol for use of external intennittent pneumatic compression for deep vein thrombosis prophylaxis. Huntleigh Healthcare: Lit 282. Knight MTH, Dawson R (1976) Effects of intennittent compression of the arms on deep venous thrombosis in the leg" The Lancet 2: 1265-1268 Mammen EF (1992) Pathogenesis of venous thrombosis. Chest 102(supplement 6): 640S-644S Nicolaides AN. BergqUIst D, Hull R (J 997) Consensus statement on prophylaxis of venous thromboembolism. International AngIology 16: 3-38
100 Journal
of Orthopaedic Nursing
Salvati EA, Pellegrini Jr VD, Sharrock NE, Lotke PA, Murray DW, Potter H, Westrich GH (2000) Symposium: Recent advances in venous thromboembolic prophylaxis during and after total hip replacement. The Journal of Bone and Jomt Surgery 82-A (2): 251-270 Scottish Intercollegiate Guidelines Network (2002) Prevention and management of hip fracture in older people Edinburgh: SIGN Stone MH, Limb D, Campbell P, Stead D, Culleton G (1996) A comparison of intermittent calf compression and
enoxaparin for thromboprophylaxis in total hlP replacement. International Orthopaedics 20: 367-369 THRiFT II (1998) Risk of and prophylaxis for venous thromboembolism in hospital patients. Phlebology 13 87-97 Warwick OJ, Whitehouse S (1997) Symptomatic thromboembolism after total knee replacement. Journal of Bone and Joint Surgery 78B: 780-786
ARTICLE
The potential benefits of intermittent pneumatic compression in the prevention of deep venous thrombosis Peter Davis and Cathy O'Neill Deep Venous Thrombosis (DVT) is a common condition, which can lead to Pulmonary Embolism (PE) with fatal consequences. Patients who have developed DVT may also suffer a long-term complication known as post-thrombotic syndrome, resulting in chronic conditions such as leg ulcers. The article presents a basic review of the incidence and clinical significance of DVT with a brief description of aetiology and prevention. Interventions are reviewed and intermittent pneumatic compression specifically evaluated. The essence of risk assessment and patient education to successful patient outcomes is emphasised. © 2002 Elsevier Science Ltd. All rights reserved.
Associate Editor's comment Choices in DVT prevention continue to be a debatable and confusing area of practice. This article clearly presents the risks and issues relevant to any preventative method with a focus on one mechanical method used internationally.
PO KEY WORDS: Deep venous thrombosis, pulmonary embolism, intermittent pneumatic compression, post-thrombotic syndrome, risk assessment
INTRODUCTION
Peter Davis MBE, MA, BEd, RN, ONe. Health Lecturer - University of Nottingham
Cathy O'Neill PhD, BSc, FRSM, Clinical Manager, Huntlelgh Healthcare Ltd, Luton Correspondence to' Cathy O'Neill, Huntlelgh Healthcare, 310-312 Dallow Road, Luton, Bedfordshlre, LU I ITO, UK Tel. 01582 745736, Email cathyoneill@ huntlelgh-healthcare com
DVT usually occurs as a result of a combination of venous stasis, vein injury and blood chemistry changes. These factors occur frequently in surgical patients and in many specialities, particularly orthopaedics and trauma. Intermittent Pneumatic Compression (IPC) is an established non-invasive method of DVT prevention. Inflatable garments are wrapped around the leg, or the foot and the garments are inflated with air using a pump. IPC has a dual effect, preventing venous stasis by mechanically simulating the pumping action of muscle groups and addressing the blood chemistry changes, by enhancing fibrinolytic activity. The latter is achieved without the surgical bleeding complications associated with anticoagulants.
journal of OrthopaedIc Nursmg (2002) 6. 95-100
l~)
2002 ElseVier SCience Ltd All r12'hts reserved
dOL 10 1054/\00n 2002.0231. aVailable online http.llwww,deallbrary.com on
IDE ~l®
All medical and surgical patients should be assessed for DVT risk. Guidelines on appropriate prevention based on low, moderate and high-risk categories should be used in conjunction with clinicaljudgement particularly where prophylactic intervention itself may carry risk. There remains considerable variation in prevention strategies between and even within hospitals and further research is required to optimise DVT prophylaxis for orthopaedic and other patients. Clearer guidelines on venous thromboembolism (VTE) are beginning to emerge. The Scottish Intercollegiate Guidelines Network (2002, p 13) in their latest guidelines covering management of hip fracture in older people recommend: • Mechanical prophylaxis (IPC or foot pumps) should be considered to reduce the risk of
96 Journal
of Orthopaedic Nursing
asymptomatic DVT after hip fracture. There is no evidence for efficacy of graded elastic compression stockings in hip fracture patients. • All patients with hip fracture should receive aspirin (150mg orally, started on admission and continued for 35 days) unless contraindicated. • Heparin should be reserved for selected patients at high risk of VTE after hip fracture due to; -multiple risk factors -contraindications to routine mechanical prophylaxis and/or aspirin DVT has recently commanded more media interest than at any other time in the past. Interestingly, this is not as a response to the large number of hospital patients who die as a result of this problem but due to the relatively low number of long-haul flight passengers who succumb. The International Consensus Statement (1997) reports that patients who have developed a DVT may also suffer a long-term complication known as post-thrombotic syndrome affecting the blood supply of the lower limb and leading to possible leg ulcers. They report the incidence of post-thrombotic syndrome as being 35-69% at 3 years after DVT and 49-100% at 5-10 years. In addition, venous ulcers develop in at least 300 per 100 000 of the population and the proportion due to DVT is approximately 25%. Despite the known effects of DVT, less than half of high-risk surgical patients receive any form of prophylaxis (Griffin 1996). In 1997,790,000 major elective surgical procedures were carried out in the UK; this constitutes over 390,000 who did not receive DVT prophylaxis (Griffin 1996). It is estimated that post surgical DVT and PE cost the NHS between £204.7 and £222.8 million in 1992 (Griffin 1996). If all patients at high-risk post surgery had received adequate prophylaxis there would have been a cost saving of £33.4 to £81.8 million and the number of deaths from PE reduced by more than 400.
INCIDENCE OF DVT Obtaining accurate data on the incidence of DVT is difficult; on the one hand, due to the inability to make a diagnosis by clinical signs alone, and on the other, as it is often asymptomatic (Griffin 1996). In the general population DVT of the lower limbs presents with clinical signs in approximately 1 per 1000 annually (Nicolaides et al. 1997). Incidence rates in the hospital population are much higher than this, due to a combination of acute injury, surgery and immobilisation. For example, the incidence of clinical DVT in orthopaedic surgery is thought to be in the region of 4% (THRiFT II 1998), although DVT rates as high as 60% have
been reported in patients undergoing knee replacement surgery (Warwick and Whitehouse 1997). Prevalence rates of DVT in cases of major trauma of 58% have been documented (Geerts et al. 1994).
AETIOLOGY OF DVT There are three factors responsible for the development of DVT; venous stasis, vein injury and blood chemistry changes. These factors were first described by Rudolph Virchow, a German pathologist in 1856, and are commonly referred to as Virchow's Triad. It is now generally accepted that it is usually a combination of these factors that causes a thrombosis, rather than one factor in isolation. A combination of these factors occur in some patients in virtually all hospital specialties, including all types of surgery, trauma, obstetrics, oncology, medical and even paediatrics (THRiFT II 1998, Donnelly 1999). For example, blood chemistry changes due to surgery occur as a protective mechanism to prevent wounds bleeding excessively, venous stasis occurs due to anaesthesia and inactivity in the postoperative period, and vein injury may occur as a direct result of certain surgical procedures.
PREVENTION OF DVT Methods of DVT prophylaxis include; early mobilisation, the use of pharmacological agents, most commonly the parenteral anticoagulants (low dose heparin, low molecular weight heparin (LMWH» and mechanical methods, such as graduated compression stockings and intermittent pneumatic compression (lPe) (THRiFT II 1998). There has been a growing interest in the latter as a noninvasive method of prophylaxis. Unlike the other methods of prophylaxis mentioned, which address one element of Virchow's Triad, IPC affects two components of the Triad (Figure 1), namely venous stasis and the blood chemistry changes. Most importantly it does not carry the risk of excessive surgical bleeding associated with anticoagulants (Griffin 1996, THRiFT II 1998, Salvati et al. 2000). A prospective study by Hooker et al. in 1999, showed that the use of intraoperative and postoperative thigh-high intermittent pneumatic compression was effective for prophylaxis against thromboembolism in 425 patients undergoing total hip arthroplasty. The low prevalence of DVT (4.6%) and pulmonary embolism (0.6%) reported in the study is comparable with that associated with pharmacological prophylaxis. A smaller study by Stone et al. (1996) directly compared IPC with LMWH for thromboprophylaxis in total hip replacement. This study concluded that both methods of prophylaxis decreased the incidence of DVT but that
Prevention of deep venous thrombosis
97
Vein lI1Jury
~_.,.
I Venous stasis Fig. I
Vichow's Triad.
IPC has fewer complications and contraindications than LMWH. Indeed, they found the operative field to be drier and easier to work when patients received IPC compared with that ofpatients receiving LMWH and fewer patients in the IPC group required blood transfusion.
PRINCIPLES OF IPC FOR DVT PROPHYLAXIS Most venous thrombi originate in regions of slow blood flow, such as the large venous sinuses of the calf and thigh or in valve cusp pockets (Mammen 1992). Decreased blood flow or even stasis due to lack of the pump action of large muscle groups is a major factor in the development of DVT. It seems logical to compensate for this by simulating this pumping action mechanically. IPC is applied by wrapping an inflatable garment around the leg, or foot and a section of the garment is inflated with air via a pump. The garment is deflated after a few seconds. This sequence of inflation and deflation of the garments continues for the duration of therapy, providing cyclic mechanical compression to the venous system of the leg or foot. Calf garments (Figure 2) operate at low pressures, for example 40 mmHg, with a short inflation period, 12 seconds, and a long deflation period, 48 seconds, to allow venous refilling to occur (Huntleigh Healthcare 1998). The inflation forces blood in the superficial veins into the deep veins of the leg, increasing venous blood velocity and preventing venous stasis. Foot garments (Figure 3) utilise the venous foot pump in the sole of the foot, which consists of the
venae comites of the lateral plantar artery (Binns and Pho 1988). Applying IPC to the foot causes a flattening of the plantar arch similar to that caused by weight bearing (Gardner and Fox 1993). This causes emptying of the lateral plantar veins, into the deep veins of the leg. Foot pump systems operate at higher pressures than calf/thigh systems with shorter inflation and deflation periods. It is recommended that the garments should be applied and worn continuously during the pre, intra, and post-operative phases of surgery for a minimum of 72 hours post-operatively. or until the patient is fully mobile (Huntleigh Healthcare 1998). The use ofIPC as a prophylactic strategy for the prevention of DVT is far from new. More than 30 years ago it was demonstrated in an animal model that the application of IPC to muscles of the calf altered venous blood flow in the leg rhythmically in a similar manner to that of the normal calf-muscle pump (Calnan et al. 1970). Researchers at the Hammersmith Hospital demonstrated the effect of IPC on the blood constituent part of Virchow's Triad (Allenby et al. 1973). They showed that IPC applied to the legs of patients undergoing surgery stimulated fibrinolysis post-operatively, when fibrinolysis would normally be depressed. The importance of this biochemical effect to the overall action of IPC was confirmed by the work of Knight and Dawson in 1976 (Knight and Dawson 1976). They showed IPC was still able to reduce the incidence of DVT without increasing blood flow in the legs, although to a lesser extent. They achieved this by applying IPC to patient's arms rather than to their legs during surgery. It is now thought that IPC enhances fibrinolytic activity by reducing the amount of plasminogen
98 Journal of Orthopaedic Nursing
." -.r- •• -
.'
,,~J~"
t
"
Fig. 2
Intermittent pneumatic compression of the calf (with permission of Huntleigh Healthcare).
,
\.
..
Fig. 3
Intermittent pneumatic compression of the foot (with permission of Huntleigh Healthcare).
activator inhibitor and thereby reducing the risk of clot formation by inactivating fibrin (Comerota et al. 1997). This works in a different way to chemical methods ofprophylaxis, such as heparin, which actively prevent fibrin formation.
RISK ASSESSMENT In 1998 the THRiFf II Consensus Group reviewed published data on DVT prophylaxis
and recommended that all medical and surgical patients should be assessed for the risk of DVT with respect to medical/family history, clinical signs, existing conditions and results of specific blood tests. Based on these assessments patients could be categorised into three groups; low (risk <10%), moderate (risk 10-40%) and high risk (40-80%). Unlike the use of risk assessment tools in pressure ulcer risk assessment, no specific scoring system or weighting for different factors were provided within the Consensus document, but
Prevention of deep venous thrombosis
Table 1 Recommendations for, prophylaxis against DVT (THRiFT II 1998) Recommendations for DVT prophylaxis
Risk level Low Moderate & High
• • • • • •
Early mobilisation Graduated compression stockings Early mobilisation Graduated compression stockings UFH/LMWH Foot impulse technology or intermittent pneumatic compression • Development of specific prophylaxis protocol
99
episode (Bergquist et al. 1997) makes the identification of at risk patients and the implementation of preventative strategies vital. The evidence base for interventions to prevent DVT and PE is still comparatively poor and often contradictory in nature. This means that action is highly variable from hospital to hospital and sometimes even within the same hospital. Clarification is still needed on which interventions are best for which circumstances and with which patients.
REFERENCES
examples of patient groups covered within each category were listed, including orthopaedics. The Consensus Group provided guidelines (Table 1) on which methods of prophylaxis were suitable for patients based on the low, moderate and high-risk categorisation. IPC was recommended for moderate and high-risk patients. Recently the benefit of categorising patients by risk level has been questioned. Orthopaedic surgeons in particular have been reluctant to implement risk categorisation. The concept of categories may overemphasis prophylaxis so that patients, particularly those at medium to low risk, may be put at more risk due to the prophylactic intervention than due to venous thromboembolism without intervention. For example, there is concern about the possible risks of pharmacological prophylaxis in total hip replacement patients (Francis and Brenkel 1997). Also there is the possible risk of low molecular weight heparin causing vertebral canal haematoma after a spinal epidural block (Checketts and Wildsmith 1999). Recent reluctance to categorise patients into risk groups does not imply that identifying risk is unnecessary. Rather, this position indicates the complexities of risk assessment and the need to individualise interventions for the patient and the specifics of the situation.
CONCLUSION IPC offers a non-invasive method of prophylaxis that can be used for: moderate or high-risk patients, or for patients contraindicated for pharmacological prophylaxis, or in conjunction with pharmacological agents as a complementary intervention (THRiFT II 1998). It is recommended for patients following hip fracture (SIGN 2002). IPC has a dual benefit reducing venous stasis and enhancing fibrinolytic activity. Further large randomised controlled trials are needed comparing the efficacy of IPC with LMWH, particularly in trauma and orthopaedic patients (THRiFT II 1998). The need for DVT prophylaxis spans all areas of the hospital. The potential complications and the recurrent nature of DVT following an initial
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