CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 3, May/June 2011
AFRICA
129
Committees of Guiyang Medical College and Huaxi Medical
School of Sichuan University.
Surgical preparation and cardiopulmonary bypass
The studies were performed in 12 adult mongrel dogs weigh-
ing 10–18 kg. The animals were anaesthetised with intravenous
pentobarbital sodium (25 mg/kg as an initial bolus and then 4
mg/kg/h), paralysed with intravenous vecuronium (0.1 mg/kg as
an initial bolus and then 50 µg/kg every 30–40 min during the
experiment). They were endotracheally intubated and ventilated
on a volume-controlled mode with a tidal volume (TV) of 12 ml/
kg, an inspiratory:expiratory ratio (I:E) of 1:2, extrinsic positive
end-expiratory pressure (PEEP
e
) of 0 cm H
2
O, and an inspired
O
2
fraction (FiO
2
) of 1.0. Respiratory rate (RR) was adjusted to
maintain normocapnia as guided by end-tidal CO
2
monitoring
and intermittent arterial blood gas analyses. Peak inspiratory
pressure (PIP), intrinsic positive end-expiratory pressure (PEEP
i
)
and mean airway pressure (MPaw) were continually measured
by the airway monitor system of the anaesthesia machine
(Narkomed GS; Dräger Medical Inc, Telford, PA).
The femoral vein and artery were cannulated to admin-
ister drugs and fluids, monitor arterial pressure and collect
blood samples. A 7-French Swan–Ganz catheter (CritiCath
TM
SP107H-14 TD Catheter; Becton Dickinson Critical Care
Systems, Singapore) was inserted through the right external
jugular vein and placed in the main pulmonary artery to record
central venous pressure (CVP), pulmonary artery pressure (PAP),
and cardiac output (CO) by thermodilution technique (Spacelabs
Monitor model 90369; Spacelabs Medical Inc, Redmond, WA).
Nasopharyngeal temperature was continuously recorded.
For CPB, the bypass circuit consisted of a heat exchanger,
cardiotomy reservoir, roller pump, bubble oxygenator, and
microfilter primed with Ringer lactate solution (30 ml/kg),
6% HAES-steril (HES 200/0.5; 20 ml/kg), 30 ml 5% sodium
bicarbonate, and heparin (150 U/kg). Gas flow to the oxygen-
ator was 100% oxygen at 1 l/min. After median sternotomy
and heparinisation (300 U/kg, IV), the ascending aorta and the
right atrium were cannulated for initiation of bypass, and the
left atrium for left atrial pressure (LAP) monitoring. The time
between commencement of CPB and cardiac plegia arrest was
standardised at 10 min. The aorta was clamped in combination
with the pulmonary artery for 60 min to prevent any antegrade
flow to the lungs and therefore make the ischaemic degree of the
lungs comparable.
Ventilation was terminated during the period from cross
clamping to declamping. The heart was arrested via the aortic
root with cold (4°C) crystalloid St Thomas’ solution (20 ml/kg)
at a pressure of 70 mmHg immediately and 30 min after cross
clamping. During total CPB, the pump flow was maintained
between 80 and 100 ml/kg/min
at a mean perfusion pressure
of 40–80 mmHg and each animal was cooled to a nasopharyn-
geal temperature of 28–30°C. Alpha-stat pH management was
observed during CPB. Twenty minutes before declamping,
rewarming was initiated until the nasopharyngeal temperature of
each animal was rewarmed to 38°C before termination of CPB.
The heart was defibrillated with 20 J if necessary after cross
clamp removal.
At the end of total CPB, the lungs were inflated manually for
15 s to 40 cm H
2
O, according to a technique by Magnusson,
et
al
.
18
Thirty minutes after declamping, all animals were weaned
from CPB using dopamine, starting at 3 µg/kg/min and up to
8
µ
g/kg/min. Following cessation of CPB, the blood in the
oxygenator was transfused back into the circulation and all the
dogs without heart decannulation and chest closure were closely
observed for 150 min. Then lung tissue samples were taken
after administration of an overdose of pentobarbital sodium
(50 mg/kg, IV). Twelve lung tissue samples of approximately 1
cm
×
1 cm
×
1 cm were harvested from the non-dependent and
dependent portions of the upper, middle and lower lobes of each
animal’s left and right lungs, with the excised lungs were inflated
to a constant pressure of 20 cm H
2
O. Harvested lung tissue
samples were used for PMN counts.
Experimental protocol
Twelve adult mongrel dogs were randomly divided into two
groups (
n
=
6 each). Measurable variables recorded after 15-min
stabilisation following heart cannulation served as baseline.
During the 40-min period from recording the baseline to initiat-
ing CPB, the animals in the control group received no treatment,
while the other six dogs received 30 min 1.0 MAC isoflurane
(Abbott Laboratories, North Chicago, IL; 1.39% for 1.0 MAC
in dogs;
19
Spacelabs). The pre-treatment time of the clinically
frequent applied concentration (1.0 MAC) of isoflurane was
based on previous
in vivo
studies concerning myocardial protec-
tive preconditioning in dogs.
20
Dynamic lung compliance (DLC), measured at baseline and
5, 31, 60, 120 and 180 min after declamping, was calculated
using the following formula:
DLC (ml/cm H
2
O)
=
TV (ml)
_______________________
PIP (cm H
2
O) – PEEP (cm H
2
O)
Pulmonary vascular resistance, measured at baseline and 31,
60, 120 and 180 min after declamping, was calculated using the
following formula:
PVR (dynes/s/cm
5
)
=
[mean PAP (mm Hg) – mean LAP (mm
Hg)]
×
79.92/CO (l/min)
Arterial blood samples, taken at baseline and 5, 31 and 180 min
after declamping, were examined in a blood gas analyser (i-Stat;
Abbott Laboratories Inc., East Windsor, NJ). Alveolar arterial
oxygen difference (AaDO
2
) was calculated using the following
formula:
AaDO
2
(mmHg)
=
PiO
2
– PaCO
2
__________
R – PaO
2
PiO
2
=
(P
B
– P
H2O
)
×
FiO
2
Where PiO
2
is inspired oxygen pressure, R is respiratory quotient
with an assumed value of 0.8, P
B
is barometric pressure with an
assumed value of 760, P
H2O
is the pressure of the water vapour
at body temperature with an assumed value of 47, and PaO
2
is
arterial oxygen tension.
The excised lung tissue samples were immediately fixed in
10% formol, then dehydrated, embedded in paraffin, cut into
4-
µ
m slices along a coronal plane from apex to base and stained
with haematoxylin and eosin. The slices were coded and exam-
ined in a blinded manner by a single examiner. Interstitial and
intra-alveolar PMNs were identified and counted in 10 different
fields, excluding airways and pulmonary vessels, under 400
×
magnification (Model CH30RF200, Olympus, Tokyo, Japan).
The data were expressed as number of PMNs per high-power
lung field.
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