Biology Reference
In-Depth Information
surgery is usually associated with an increased intra-abdominal pressure that
interferes with the diaphragmatic function, promoting alveolar collapse (Lundh
and Hedenstierna
1983
). The aim of this study was to evaluate the influence of the
abdominal surgery on pulmonary atelectasis formation in healthy dogs undergoing
ovariohysterectomy.
24.2 Materials and Methods
Twenty healthy female dogs scheduled for elective ovariohysterectomy were
included in this study. Dogs were premedicated with acepromazine (30
g/kg)
and morphine (0.3 mg/kg) administered intramuscularly (IM). General anesthesia
was induced with intravenous (IV) thiopental (10 mg/kg) and maintained with
inhalation of isoflurane in 100% oxygen. After intubation, all patients were
mechanically ventilated (Aliseo, Datex Ohmeda, Helsinki). During premedication,
induction, and intubation, all dogs were restrained in sternal recumbency, and when
an adequate level of anesthesia was achieved, dogs were positioned in dorsal
recumbency and maintained in this position until the end of the study. Heart rate
(HR beats/minute) systolic, mean, and diastolic noninvasive arterial pressures
(mm Hg), respiratory rate (RR, breaths/minute), hemoglobin oxygen saturation
(SpO
2
, %), and the end-tidal partial pressure of carbon dioxide (EtCO
2
, mmHg)
were continuously monitored and recorded every 5 min during the study. All dogs
were ventilated in a volume-controlled mode with a tidal volume (
V
T
) of 12 ml/kg,
an inspiratory to expiratory ratio (I:E) of 1:2, a positive end expiratory pressure
(PEEP) of 0, and an inspired oxygen fraction (FiO
2
) greater than 0.9. Randomly,
10 dogs underwent surgery immediately after the stabilization of the general
anesthesia (S Group), and the other 10 dogs underwent surgery after the execution
of the thoracic computed tomography (CT; NS Group). In all dogs, 60 min after
positioning in dorsal recumbency, a thoracic spiral CT was performed, and an
arterial blood sample was collected. Dogs of the S group were excluded from the
study if, after 60 min from positioning in dorsal recumbency, they were still
undergoing surgery. For the execution of the thoracic CT, each dog was positioned
in the scanner in dorsal recumbency, and a dorsal plane scout image was obtained.
Spiral CT of the thorax was then performed during end-expiration apnea. All
images were obtained at a setting of 120 kVp and 160 mA using a lung algorithm;
matrix size was 512
m
512, field of view was 35, and pitch was 1.5. Images of 10-
mm slice thickness were reconstructed. All CT images were analyzed for lung
abnormalities; if pathologic changes were observed, the dog was excluded from the
study. Lung densities were analyzed in all CT images with specific software
(Dicom Works v 1.2.5) as previously described (Staffieri et al.
2007
,
2009
,
2010
).
The total area (mm
2
) of the entire lung was calculated by including pixels with
density values between
1,000 and +100 Hounsfield units (HUs). In accordance
with previous studies, the following lung compartments were identified: hyperin-
flated (
1,000 to
901 HUs), normally aerated (
900 to
501 HUs), poorly
