Evaluation of 2 Weight-Based Protocols: RESULTS

20 Dec
2010

Charts were reviewed for a total of 153 consecutive patients who had a prescription for heparin infusion. Fifty- three patients were excluded for the following reasons: total infusion time less than 24 h (n = 23), heparin protocol not used (n = 9), older version of protocol used (n = 5), heparin infusion started at another hospital (n = 4), protocol modified by physician (n = 4), incorrect initial infusion rate (n = 2), switch in protocols during therapy (n = 2), interruption in heparin therapy before first PTT sample was drawn (n = 1), and inadvertent exclusion (n = 3). This left a total of 100 patients with 50 patients in each group.

In the 1996 study, almost all patients received a full bolus dose of heparin; however, in the current study, only two-thirds of patients in the standard 2006 protocol group and only about half of those in the lower-target protocol group received a full bolus (Table 1). The standard protocol was ordered appropri­ately for the majority of patients in the current study (88%) (Table 1); the exceptions were 6 patients who received heparin according to this protocol for treatment of acute coronary syndrome. These 6 patients were receiving care on a nursing unit that did not have preprinted orders for the lower-target protocol; the forms have since been made available on this nursing unit. The lower-target protocol was ordered inappropriately for 5 patients, 3 with active venous throm­boembolic disease and 2 with peripheral arterial thrombosis.

Table 1. Demographic Characteristics of Patients at Baseline

Protocol; No. (%) of Patients or Mean ±

SD

Characteristic 2006 Standard Protoco

l* 2006 Lower-Target Protocolt

1996 Study1*

No. of patients

50 (100)

50 (100)

50 (100)


Full bolus


33 (66)


26 (52)


47 (94)


Half bolus


0


4 (8)


Unknown§


No bolus


17 (34)


20 (40)


Unknown§


Age (years)



66.3

±

15.0



70.1

±

13.4



58.0

±

17.2


Weight (kg)



77.7

±

21.7



73.6

±

17.0



76.1

±

17.9


Sex, males


29 (58)


29 (58)


24 (48)


Indication


Acute coronary syndrome


6 (12)


32 (64)


0


DVT or PE


34 (68)


3 (6)


50 (100)


Peripheral arterial thrombosis


4 (8)


2 (4)


0


Bridging for warfarin therapy


4 (8)


2 (4)


0


Atrial fibrillation


2 (4)


6 (12)


0


Transient ischemic attack or stroke


0


4 (8)


0


Thrombophlebitis


0


1 (2)


0


Protocol appropriate


44 (88)


45 (90)


NA


Baseline PTT (s)


40 ± 9


39 ± 8


25.3 ± 2.7


Baseline
platelet count x 10
9/L


258 ±114


216 ±125


289 ±142


Duration of heparin therapy (days)


5.5 ± 7.2


6.3 ± 9.1


6.2 ± 4.2


DVT = deep vein thrombosis, NA
= not app


licable, PE = pulmo


nary embolism, PTT
= partial thrombopl;


stin time,

Overall, there were no statistically significant differences between the two 2006 protocols with respect to times to achieve PTT above the lower limit and within the therapeutic range (Table 2). The times to achieve these outcomes appeared shorter for the current protocols than for the original 1996 protocol (Table 2). Two values for patients treated with the standard protocol were excluded from the analysis of time to achieve PTT value above the lower limit of the target range. The samples for these initial PTTs were drawn late, at 12 and 14 h after initiation of heparin, respectively. Similarly, 3 values for patients treated with the lower-target protocol were excluded because the PTT samples were drawn too early, at less than 4 h after initiation. Of note, for one patient who was receiving heparin via the standard protocol, the PTT remained slightly above the therapeutic range (134 s) at 48 h after initiation, and an arbitrary time of 54 h was assigned to achieve the target. This extension was applied because the heparin dose had been reduced per protocol at 48 h, but the infusion was then discontinued before the next scheduled PTT measurement could be obtained, 6 h later. It was anticipated that if the heparin infusion had been continued, the PTT would have been within target range by the next measurement.

Table 2. Comparison of Selected Outcomes



Parameter



2006

Standard
Protocol

(n


= 50)



2006


Lower-Target Protocol

(n

= 50)



1996

Study1

(n

= 50)



Primary outcomes


Time to achieve PTT
> lower limit of
therapeutic range i


Median (range) Mean ± SD


h)



6.0 (4.0-40.8)* 8.3

±

6.8



6.3 (4.5-53.0)*

9.7 ± 9.2



10.7

±

11.1


Time to achieve PTT within therapeutic
range (h)


Median (range) Mean ± SD



14.4 (4.0-40.8)+ 17.2

±

12.5



14.3 (4.5-53.0)+ 16.1

±

10.5



22.3

±

14.0


Other
outcomes


Time to first PTT measurement (h)

Median (range) Mean ± SD



6.0 (3.0-14.3)+ 6.2

±

1.6



6.0 (1.8-8)+ 6.0

±

1.5



6.3

±

1.1


Value of
first PTT (s)

Median
(range) Mean ± SD


First PTT
therapeutic (no. and


%

of
patients) First PTT subtherapeutic (no. and


%

of
patients) First PTT supratherapeutic (no. and


%

of
patients)



128 (53-200) 88 (43-200) 137

±

56 106

±

49

18 (36)

7 (14) 25 (50)


NA



18 (36) 10 (20)

22 (44)


NA NA


31 (62)


Value of first supratherapeutic PTT (s)


Median (range)§ Mean ± SD



200 (132-200) 188

±

23



150 (101-200) 152

±

37



118.9

±

28.9


PTT
within


24
h (no. and % of patients)
Patients with PTT
> lower limit of therapeutic range Patients with PTT within therapeutic range


48 (96)

40 (80)


47 (94) 40 (80)


NA (80.9) NA


Patients with rate adjustments to
therapeutic range if initial PTT
> 200
s


  1. adjustment


  2. adjustments

> 2 adjustments


3/16 7/16 6/16


3/6 3/6 0


NA NA NA

There was no statistically significant difference between the standard and lower-target protocol groups for time to the first PTT measurement, and for both of these groups the value for this outcome appeared similar to that in the 1996 study (Table 2). About one-third of patients in both of the 2006 protocol groups had achieved therapeutic PTT levels by the time of the first measurement, and about half of the initial PTT values in both groups were supratherapeutic. In the 1996 study, about two-thirds of initial PTT values were supratherapeutic. The majority of patients in the current study had at least one PTT value above the lower limit of the therapeutic range and within the target range by 24 h. Of the 16 patients in the standard protocol group with an initial PTT value above 200 s (the upper limit of detection), most required at least 2 adjust­ments of the heparin infusion rate to reach PTT values within the therapeutic range (range 1 to 3). Patients in the lower- target protocol group required fewer rate adjustments: 3 of the 6 patients with initial PTTs above 200 s required only 1 rate adjustment, and 3 required 2 rate adjustments.

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