Hospital Pharmacy - February 2020 - 28

Hospital Pharmacy 55(1)

Figure 1. Study design.

Note. IRB = institutional review board; ICU = intensive care unit.

The study conducted by Bauer et al showed that there was
about a 4-day difference in ICU length of stay between the 2
groups; however, this difference was not significant.10 Based
on this study, we estimated that to find a 4-day difference in
ICU length of stay with predicted 80% power to detect an α
of 0.05, approximately 160 patients in each group would be
needed. Categorical variables were analyzed using chisquare tests and continuous variables were analyzed using
independent-sample t tests or Mann-Whitney U tests. A multiple linear regression was also conducted to see whether any
variables potentially contributed to an increase in ICU length
of stay. The multiple linear regression was controlled for
when vasopressin was discontinued first, and then underwent
log transformation due to outliers. P values of less than .05
were considered to indicate statistical significance.

Results
From October 1, 2013, through August 31, 2016, 1192
patients were screened for inclusion in the study. Of these
1192 patients, a total of 86 were deemed appropriate to be
included in the study. The most common reason for exclusion was that the patient did not receive norepinephrine and
vasopressin in combination. Of the 86 included patients, 34
were grouped into the NDF group and the remaining 52 were
grouped into the VDF group. The full breakdown of the
inclusion and exclusion reasons can be found in Figure 1.

The baseline characteristics between the groups were
fairly well matched (Table 1); however, there was a significant difference in the rates of mechanical ventilation between
the NDF and the VDF group (21% vs 47%, P = .001).
Patients in the VDF group also had higher APACHE II scores
compared with the NDF group at both the initiation of vasoactive therapy and the discontinuation of the first agent (22
vs 19, P = .016, 16 vs 13, P = .014). The patients in the VDF
group also had SOFA scores that were higher at the discontinuation of the first agent compared with the NDF group (7
vs 6, P = .025). These differences suggest that the patients in
the VDF group likely had a greater severity of illness compared with those in the NDF group.
There was no statistical difference in the primary endpoint of ICU length of stay between the NDF group and the
VDF group (9.4 days vs 11.1 days, P = .313). There was also
no difference in the dose of norepinephrine at which vasopressin was initiated between the groups, 27 µg/min in the
NDF group versus 31 µg/min in the VDF group (P = .11). In
addition, there was no difference in the rates of hypotension
within 24 hours of discontinuation of the first agent, with
50% in the NDF group versus 60% in the VDF group (P =
.38). Finally, the mean dose of norepinephrine at which vasopressin was discontinued was 11.9 µg/min ± 13.5. Complete
results of endpoints can be found in Table 2.
Although there were no statistically significant differences in outcomes, a multiple linear regression was

Hospital Pharmacy - February 2020

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