Hypoxia Clinical Trial
Official title:
The Influence of Prolonged Inspiratory Time on Respiratory Mechanics and Oxygenation in Obese Patients Undergoing Spine Surgery in the Prone Position
The area of aesthesia-induced atelectasis is much larger in the obese compared with the
non-obese, but there may also be more airway closure and impaired matching of ventilation and
lung blood flow.
When an anesthetized patient is turned to the prone position, dynamic compliance (Cdyn)
decreases and peak airway pressure increases unless the abdomen hangs freely to prevent the
abdominal viscera from compromising the diaphragm movement. Although the Wilson frame is
designed to allow the abdomen to hang, it partially compresses the anterior abdominal wall
and therefore does not allow the abdomen to hang completely, especially in obese patients.
This in turn increases peak airway pressure and decreases Cdyn, oxygenation. This study aimed
to investigate the effects of a prolonged I:E ratio (i.e., 1:1) compared with the
conventional I:E ratio of 1:2 on respiratory mechanics and hemodynamics during spine surgery
in the prone position in obese patients.
We hypothesized that, compared with an I:E ratio of 1:2, a ratio of 1:1 improve oxygenation
without hemodynamic instability .
After written informed consent was obtained from all patients, 50 adult patients were
enrolled in the study.
The patients met the following inclusion criteria: (1) body mass index (BMI, weight in
kilograms divided by the square of height in metres) > 25 kg/m2; (2) American Society of
Anesthesiology (ASA) physical status classification grade I or II (BMI by itself was not used
as the basis for the ASA classification); (3) aged 20 - 65 years; and (4) scheduled for
elective spine surgery in prone position.
Exclusion Criteria:
- Patients who have severe pulmonary disease:
history of chronic obstructive pulmonary disease (COPD), asthma, or pneumothorax. Patients
with haemodynamic instability, hypovolaemia, bronchopleural fistula, The enrolled patients
were randomly allocated according to a predetermined allocation sequence to receive an I:E
ratio of either 1:1 (group 1:1) or 1:2 (group 1:2).
The allocation sequence with no blocking was generated in an Internet website Standard
monitoring techniques, including electrocardiography, pulse oximetry, and noninvasive
arterial blood pressure measurement, are applied upon arrival at the operating room.
Anesthesia was induced with intravenous propofol 1.5 mg_kg-1 and rocuronium 0.8 mg_kg-1 was
administered intravenously.
After tracheal intubation, volume-controlled ventilation was initiated with an I:E ratio of
1:2 or 1:1, no positive end-expiratory pressure, and a tidal volume of 10 mL per ideal body
weight (kg). A respiratory rate was adjusted in order to end-tidal carbon dioxide (EtCO2) of
33 - 36 mmHg during surgery. Anesthesia was maintained with an end-tidal concentration of
2-2.5 vol% sevoflurane in 40% oxygen/air. The bispectral index score was monitored
continuously in order to maintain an adequate anesthetic depth and was targeted at a range of
40-60 during surgery.
Radial artery cannulation was conducted for monitoring continuous arterial blood pressure and
blood sampling.
Respiratory, hemodynamic, and arterial blood gas data were assessed and recorded at three
time points: ten minutes after tracheal intubation in the supine position (T1), 30 min after
prone positioning (T2), 90 min after prone positioning(T3). Respiratory data consisted of
peak airway pressure, plateau airway pressure, mean airway pressure, static compliance,
EtCO2, respiratory rate, and minute volume. Arterial pH, arterial oxygen tension (PaO2),
arterial carbon dioxide tension (PaCO2), and lactate level were obtained from arterial blood
gas analysis.
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