Randomization was performed in computer-generated,
permuted blocks of 6 to 10, stratified according
to the participating ICU. Treatment assignments
and a five-digit reference number were
placed in sealed, opaque envelopes, which were
opened by the person responsible for the preparation
of the trial-drug solutions. The solutions of
norepinephrine or dopamine were prepared in vials
or syringes according to the preference of the
local ICU. Each vial or syringe was then labeled
with its randomly allocated number. The doctors
and nurses administering the drugs, as well as the
local investigators and research personnel who
collected data, were unaware of the treatment assignments.
The trial was approved by the ethics
committee at each participating center. Written informed
consent was obtained from all patients or
next of kin