Study protocol
In the preoperative moment, all patients were functionally assessed
using the FIM, six-minute walk test and peripheral muscle strength
through the Medical Research Council (MRC).
The next day the patients were referred to the operating room. The
surgery took place with the same surgical team, being performed via
median sternotomy and cardiopulmonary bypass, using the graft of the
external thoracic artery or bypass. All patients left the operating room
with a subxiphoid and intercostal drain and were referred to the ICU
with full analgesia. Upon arriving at this unit, they were conducted
according to routine, with no influence from the researchers. In
accordance with the weaning criteria, the patients were guided and,
subsequently extubated, oxygen support at low flow was started, with a
percentage sufficient to maintain saturation between 94 and 97%.
In the hospital where the research was carried out, NIV is routinely
performed on the first postoperative day. Shortly after extubation,
eligible patients were randomized using the electronic system:
http://randomizer.org/form.htm, performed by a professional not
belonging to the research group, and this procedure was kept
confidential from other members of the search. Sealed, opaque and
sequentially numbered envelopes were used to hide the allocation
sequence until interventions were designated. The researchers
responsible for the evaluations were blinded to the intervention and
control groups.
Patients were divided into two groups: immediate NIV group (NIVI) and
conventional NIV group (NIVC). The NIVI group performed noninvasive
ventilation immediately after orotracheal extubation, whereas the NIVC
group performed NIV on the first postoperative day around 24 hours after
extubation.
NIV was performed on the Servo-S ventilator (Dräger Medical, Lübeck,
Germany) in ventilation mode with support pressure, the pressure being
sufficient to maintain the tidal volume between 6 to 8 ml/kg, positive
pressure at the end of expiration starting at 5 cmH2O, reaching 12 cmH2O
and inspired oxygen fraction of 30%. A face mask was used and the
increase in PEEP was protocol, occurring in all patients. This therapy
was maintained for 40 minutes in both groups and performed only once. An
arterial blood gas analysis was collected before and after NIV for
analysis of gas behavior. A day later, a new blood gas analysis was
collected for late verification of oxygenation.
On the day of discharge from the ICU, patients were again evaluated for
MIF, MRC and analyzed for pulmonary complications, deaths and length of
stay in that unit. These assessments were repeated on the day of
hospital discharge, adding up to the repetition of the six-minute walk
test. All patients received standard assistance from the physiotherapy
service, which consisted of kinesiotherapy, cycle ergometry and walking.
The outcomes related to postoperative complications were assessed by a
radiologist who was blind. Gasometric and functional evaluation were
performed one by a blind doctor and physiotherapist, respectively.