Diagnostic Tests

• A CT scan is the most commonly used test to diagnose PE but some institutions still use a ventilation/perfusion (V/Q) scan. Spiral CT scans can detect emboli in the pulmonary arteries. A V/Q scan measures the distribution of blood and air flow in the lungs. When there is a large mismatch between blood and air flow in one area of the lung, there is a high probability that the patient has a PE.

• Pulmonary angiography is the gold standard for the diagnosis of PE. However, it is an invasive test that involves injection of radiopaque contrast dye into the pulmonary artery. The test is expensive and associated with a significant risk of mortality.

Table 10-2 Risk Classification and Consensus Guidelines for VTE Prevention

Lewi of Risk

Risk of VTE

Pinrffllwn Strategies

Low

Minor surgeiy, In mobilepalienti

Less than l-Dfe

tarly And aggressAwamhulalon

MidiCJl (jJCifnCi ivho iie fully mcftih.'

Modtme

Major sunjmy, and no clinical rivk: factors

10-«*

UFH 5,<XK> units SC every fl-[2 hours

AiuKty ill mi«litJl cordis («S, fryKirijidl

[HlRpaft ?,SX?-SJMI U«ili K 2* IXKjri.

infiicrkja Ut hemic mofce, heart failure

fnonapjiiin HI ring every hourt

(¡iacwbaiionf at laid rust

FomJapai mux 2.5 SC every 24 Imurs 1 idMlMr in units it fvei y l*Si*4 IPC- iCS^

HI9I1

Major l&ner exiieniViy orthopedic lurgeiy

-lO-SOTo

Lunepan 5i«X) untti iC evety 2i houii

Hipirjcruni

Eno*ipjrin JO my 5C rvny '2 flours t» iny 5C (.vwy 24 Injurs

Major trauma

Fciidapawiu* 2£ nrg SC every 24 hours fmrapai in 75 units/kg 5£ every M hours Warfarin (targel INR = 2-il IPC*GCS<

GCSv graduated compression stocking INR. International Normalized Ratio: IPC, ¡rtamittert pneumatic compression; SC, sirtxulaneouK UFH, ..■iIm: llonifed hrii'ir n; '/if. vfYUUt Ihipmixirminjlmir

WiiN.iniT.il meihodiofpop^tli iri Uied in pitteffti .SI liiuh ink oi i/ffilirKj i I;rri|:!'■ LitinriS From Ref. I.

GCSv graduated compression stocking INR. International Normalized Ratio: IPC, ¡rtamittert pneumatic compression; SC, sirtxulaneouK UFH, ..■iIm: llonifed hrii'ir n; '/if. vfYUUt Ihipmixirminjlmir

WiiN.iniT.il meihodiofpop^tli iri Uied in pitteffti .SI liiuh ink oi i/ffilirKj i I;rri|:!'■ LitinriS From Ref. I.

Inferior vena cava (IVC) filters, also known as Greenfield filters, provide short-term protection against PE in very-high-risk patients by preventing the embolization of a thrombus formed in the lower extremities into the pulmonary circulation. Insertion of a filter into the IVC is a minimally invasive procedure. Despite the widespread use of IVC filters, there are very limited data regarding their effectiveness and long-term safety. The evidence suggests that IVC filters, particularly in the absence of effective antithrombotic therapy, increase the long-term risk of recurrent DVT. In the only randomized clinical trial examining the short-and long-term effectiveness of the filters in patients with a documented proximal DVT, treatment with IVC filters reduced the risk of PE by more than 75% during the first 12 days following inser-21

tion. However, this benefit was not sustained during 2 years of follow-up and the long-term risk of recurrent DVT was nearly two-fold higher in those who received a filter. Although IVC filters can reduce the short-term risk of PE in patients at highest risk, they should be reserved for patients in whom other prophylactic strategies cannot be used. To further reduce the long-term risk of VTE in association with IVC filters, pharmacologic prophylaxis is necessary and warfarin therapy should begin as soon as

the patient is able to tolerate it. Pharmacologic Therapy

Numerous randomized clinical trials have extensively evaluated pharmacologic

strategies for VTE prophylaxis. Appropriately selected drug therapies can dramatic ally reduce the incidence of VTE following hip replacement, knee replacement, general surgery, myocardial infarction, and ischemic stroke (Table 10-2). The choice of medication and dose to use for VTE prevention must be based on the patient's level of risk for thrombosis and bleeding complications, as well as the cost and availability of an adequate drug therapy monitoring system.

The ACCP Conference on Antithrombotic Therapy recommends against the use of aspirin as the primary method of VTE prophylaxis. Antiplatelet drugs clearly reduce the risk of coronary artery and cerebrovascular events in patients with arterial disease, but aspirin produces a very modest reduction in VTE following orthopedic surgeries of the lower extremities. The relative contribution of venous stasis in the pathogenes-is of venous thrombosis compared with that of platelets in arterial thrombosis likely explains the reason for this difference.

The most extensively studied drugs for the prevention of VTE are unfractionated heparin (UFH), the low-molecular weight heparins (LMWHs; dalteparin, enoxaparin, and tinzaparin), fondaparinux, and warfarin. The LMWHs and fondaparinux provide superior protection against VTE when compared to low-dose UFH after hip and knee replacement surgery and in other high-risk populations. Even so, UFH remains an effective, cost-conscious choice for moderate-risk patient populations, provided that it is given in the appropriate dose (Table 10-2). Low-dose UFH (5,000 units every 12 or 8 hours) given subcutaneously (SC) has been shown to significantly reduce the risk of VTE in patients undergoing a wide range of general surgical procedures as well as following a myocardial infarction or stroke. For patients who are hospitalized with an acute medical illness, the available evidence supports the use of UFH (5,000 units every 12 or 8 hours), enoxaparin 40 mg SC daily, dalteparin 5,000 units SC daily, or fondaparinux 2.5 mg SC daily.

For the prevention of VTE following hip and knee replacement surgery, the effectiveness of low-dose UFH is considerably lower. Adjusted-dose UFH therapy provided SC, which requires dose adjustments to maintain the activated partial thromboplastin time (aPTT) at the high end of the normal range, may be used in the highest-risk patient populations. However, adjusted-dose UFH has been studied in only a few, relatively small clinical trials and requires frequent laboratory monitoring. The LMWHs and fondaparinux appear to provide a high degree of protection against VTE in most high-risk populations. The appropriate prophylactic dose for each LMWH product is indication-specific (Table 10-2). There is no evidence that one LMWH is superior to another for the prevention of VTE. Fondaparinux was significantly more effective than enoxaparin in several clinical trials that enrolled patients undergoing high-risk orthopedic procedures, but has not been shown to reduce the incidence of

symptomatic PE or mortality, and heightened the risk of bleeding. To provide optimal protection, some experts believe that the LMWHs should be initiated prior to surgery.2

Warfarin is another commonly used option for the prevention of VTE following orthopedic surgeries of the lower extremities.2 Warfarin appears to be as effective as the LMWHs for the prevention of symptomatic VTE events in the highest-risk populations. When used to prevent VTE, the dose of warfarin must be adjusted to maintain an International Normalized Ratio (INR) between 2 and 3. Oral administration and low drug cost give warfarin some advantages over the LMWHs and fondaparinux. However, warfarin does not achieve its full antithrombotic effect for several days and requires frequent monitoring and periodic dosage adjustments, making therapy cumbersome. Warfarin should only be used when a systematic patient monitoring system is available.

The optimal duration for VTE prophylaxis is not well established. Prophylaxis should be given throughout the period of risk. For general surgical procedures and medical conditions, once the patient is able to ambulate regularly and other risk factors are no longer present, prophylaxis can be discontinued. The risk of VTE in the first month following hospital discharge among patients who have undergone total knee replacement, total hip replacement or hip fracture repair is very high. Therefore, extended prophylaxis for 21 to 35 days following hospital discharge with an LMWH, fondaparinux, or warfarin is recommended.

Blood Pressure Health

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