Heparin: Improving Treatment and Reducing Risk of ... - CareFusion

HEPARIN SAFETY
changes its thromboplastin reagent and can go in either direction.
Failure to account for such change by updating heparin
dosing schemes would have resulted in systematic underdosing
of the vast majority of patients. For this reason, it is important
that each institution adjust heparin dosing guidelines as necessary
to the aPTT assay reagent currently in use.
patients with lower UFH infusion rates can lead to underestimation
of UFH anticoagulation. The presence of a heparin
effect may not be appreciated because the ACT test is not
designed to measure effects in the lower target range. Thus,
while POC testing devices provide rapid results, such devices
may sacrifice accuracy and precision.
Pre-analytical Variables
Pre-analytical variables that adversely affect aPTT test results
include poor phlebotomy technique, incorrect or improperly
filled blood collection tubes, delays in sample testing, temperature,
and inadequate sample centrifugation prior to testing.
Some drugs and disease states can also affect test results (Table
2). Increased levels of fibrinogen and factor VIII (both acute
phase reactants) may also reduce the aPTT result, leading to
“heparin resistance.”
Impact of Bolus Dosing
Depending on the size of a heparin bolus, it can affect aPTT values
for more than 6 hours. For example, 4 hours after a 5,000-
unit bolus the aPTT result may suggest adequate heparinization,
but a subsequent aPTT result may show that the continuous
infusion is subtherapeutic. Earlier determination of aPTT value
may be of benefit to determine if a rate increase should occur if
the value is low.
Point-of-Care (POC) Testing
Test results will vary among POC devices and typically do not
match laboratory aPTT results, because of differences in the
sample type, clot-detection method, and incubation period.
There are also differences between ACT manufacturers and cartridge
types. A different ACT test may be used depending on the
desired degree of heparin effect is being followed, which can
vary between methods. Use of high-dose ACT cartridges in
• Preanalytical
• Poor phlebotomy technique!!!!
• Time and temperature (for UFH monitoring, sample should be tested
within 2 hours of collection)
• Centrifugation-platelet poor (300 reagent—Instrument combinations
• No standardization of reagents (despite attempts)
• Reagent variability
• Phospholipid concentration
• Activator type
• Influences on test
• Increases in factor levels-acute phase ( aPTT)
• Decreases in factor levels ( aPTT)
• Drug effect ( or aPTT)
• Lupus anticoagulant (may aPTT)
Table 2. aPTT Test Variables
Anti-Xa monitoring of UFH treatment
Most institutions that measure anti-Xa activity use either a clot
based or a chromogenic method. While this test is more robust
than the aPTT and may be less adversely affected by pre-analytical
variables, test calibration variability and methodology differences
can result in a wide range of anti-Xa levels reported,
(CAP, 2008).
Administration
The most common type of heparin-related error is also the type
most likely to be associated with patient harm—administration
of an improper dose or quantity (Santell, 2008). Pooled data
from 54 hospitals using smart IV pumps revealed that heparin
was the number one drug associated with averted errors, i.e.,
smart pump alerts that resulted in reprogramming. Some
errors, if not averted, would have infused dosages 50- to 100-
times above or below the pre-established drug-library
limits.(Cardinal Health, 2008) Analysis of smart-pump data at a
regional healthcare system showed that 93% of high-risk heparin
errors averted by smart pump use occurred in non-criticalcare
settings (Williams et al., 2006).
A frequent, potentially dangerous practice involves administering
bolus doses from continuous infusions, rather than
preparing a loading dose or subsequent bolus dose in a separate
container such as a syringe or mini-bag. Serious errors can also
occur in calculating dosage changes from an initial loading dose
in units/kg to continuous infusion in units/kg/hr or units/hr.
Unnecessary variability in heparin
concentrations, nomenclature and dosing
units further increases opportunities
for error. A review of smart-pump
drug libraries in 207 hospitals identified
14 different heparin concentrations
being used in various facilities.
Heparin nomenclature also varied
widely, with 191 different namedescriptors
(Bates et al., 2005). Data
from a 54-hospital sample showed that
48% of hospitals had standardized dosing
units on units/kg/hr, 22% used only
units/hr and 30% allowed either
weight-based or non-weight-based
dosing units. When both dosing units
were available, there was a four-fold
increase in smart pump alerts that led
to infusion reprogramming, i.e., averted
errors (Cardinal Health, 2008).
To reduce opportunities for such
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Patient Safety & Quality Healthcare ■ January/February 2009 www.psqh.com