Two-Lung and One-Lung Ventilation in Patients - Anesthesia ...

36 CARDIOVASCULAR ANESTHESIA BARDOCZKY ET AL. ANESTH ANALG
POSITION AND Fio 2 DURING OLV 2000;90:35–41
1.0 eight patients) throughout the study. The patients
had mild pulmonary hyperinflation (functional
residual capacity 120%). All patients were premedicated
with midazolam 3 to 5 mg IM, approximately
30 min before the induction of anesthesia. In the operating
room, all patients had an epidural catheter
inserted around the T7 level, and after the administration
of a test dose, an epidural anesthesia was started
with 8 mL of 2% lidocaine with 100 g fentanyl and
was maintained with a continuous infusion of epidural
bupivacaine 0.5% (2–5 mL/h). The patients
were anesthetized with a variable-rate (3–6 mg
kg 1 min 1 ) continuous infusion of propofol and inhaled
isoflurane (0.4%–0.6%) in 40% or 60% oxygen in
air or pure oxygen. Muscle relaxation was achieved
with pancuronium. In all patients, the bronchus of the
dependent lung was intubated with a double-lumen
endotracheal tube (DLT) (Broncho-cath tm ; Mallinckrodt
Laboratories, Athlone, Ireland) of an appropriate
size determined by the height of the patient (10). The
correct position of the DLT was determined with fiberoptic
bronchoscopy in both the supine and the
lateral positions.
The electrocardiogram, heart rate, systemic arterial
blood pressure, noninvasive arterial oxygen saturation,
and end-tidal CO 2 were continuously monitored.
Constant tidal volume of 10 mL/kg was delivered
with a Siemens 900C ventilator (Siemens ® Elema tm ,
Solna, Sweden) throughout the study. The ventilatory
pattern consisted of a volume-controlled, square-wave
flow pattern, at a rate of 10 breaths/min. Inspiratory
time (T I/T TOT) was 0.33 and end-inspiratory pause
was 10% of the total respiratory cycle. All measurements
were performed with zero applied endexpiratory
pressure. Ventilatory variables were kept
constant during the study, both during TLV and OLV.
This investigation was performed with the chest
closed and before the surgical procedure.
After intubation in the supine position and fiberoptic
control of the correct DLT position, the two lungs
were ventilated with the above-described ventilatory
pattern for 15 min. End-inspiratory and end-expiratory
occlusions were performed to determine the mechanical
characteristics of the respiratory system (peak inspiratory
airway pressure, end-inspiratory plateau pressure,
and intrinsic positive end-expiratory pressure) and arterial
blood gas samples were drawn. Then, the tracheal
lumen of the DLT was clamped, and the would-be operated
nondependent lung was allowed to deflate to
atmospheric pressure. After 15 min of OLV and data
collection, TLV was restored with unaltered ventilatory
settings, and the patient was turned to the lateral decubitus
position. TLV and turning and positioning of the
patients generally lasted approximately 30 min. At the
end of this period, ventilatory data were recorded, an
arterial blood gas sample drawn, and the nondependent
lung collapsed again, now with the patient in the lateral
decubitus position. After 15 min, respiratory mechanics
and gas exchange data were collected again. Pao 2,
alveolar-arterial oxygen tensions difference [P(A-a)o 2]
were calculated by using standard equations.
Demographic data and preoperative pulmonary
functions of the three groups were comparable
(Kruskall-Wallis test). The data obtained in the two
positions were compared with the Wilcoxon matched
pair test. The data caused by Fio 2 differences were
analyzed with the Kruskall-Wallis test. Values of P
0.05 were considered as statistically significant. Data
were presented as median (range).
Results
Demographic characteristics, preoperative pulmonary
function tests, and the values of the preoperative arterial
oxygen and carbon dioxide tensions of the 24
patients are shown in Table 1. The differences were
not statistically significant among the three groups.
Right- and left-sided thoracotomies were comparable
in the three groups and among the groups (Kruskall-
Wallis test). Initiating OLV with unaltered ventilatory
settings increased peak inspiratory pressures significantly
in all three groups (Tables 2–4).
Effects of the Position
During the period of TLV, the position of the patient
(supine versus lateral) did not significantly influence
the variables related to gas exchange in the three
groups of patients (Tables 2–4).
In contrast, in the OLV assessment stages, the Pao 2
values in the lateral position were always significantly
higher than in the supine position: Group 0.4, 63 (57–
144) vs 101(72–201) mm Hg (P 0.02); Group 0.6, 155
(114–235) vs 268 (162–311) mm Hg (P 0.02); Group
1.0, 301 (216–422) vs 486 (288–563) mm Hg (P 0.02)
(Wilcoxon’s matched pair test). The values of P(A-a)o 2
showed similarly significant changes, but in the opposite
direction (Tables 2–4 and Figure 1).
While turning the patients from the supine into the
lateral position, no changes were observed regarding
the variables related to the mechanical properties of
the respiratory system (peak inspiratory airway pressure,
end-inspiratory airway pressure, and intrinsic
positive end-expiratory pressure), during neither TLV,
nor OLV (not significant, Wilcoxon matched-pair test).
Effects of FIO 2
In the three groups of patients ventilated with different
Fio 2 values, the differences of Pao 2 values observed
between the supine and lateral TLV periods
were not significant. In contrast, the increases of Pao 2