Abstract
Objective
To compare F-shunt and oxygen content indices in sheep ventilated with a positive
end-expiratory pressure (PEEP) of 5 cmH2O alone or preceded by a stepwise alveolar recruitment manoeuvre (ARM).
Study design
Randomized crossover design.
Animals
A total of six nonpregnant Brogna ewes weighing 34–47 kg, undergoing thoracolumbar
magnetic resonance scan.
Methods
In medetomidine-sedated sheep, anaesthesia was induced with propofol and maintained
with isoflurane 1.1% ± 0.1% and an inspired oxygen fraction (FiO2) of 0.4. Animals were placed in left lateral recumbency and, after 10 minutes of
spontaneous breathing, mechanically ventilated with 5 cmH2O of PEEP with (group ARM) or without (group PEEP) a stepwise recruitment manoeuvre.
Maintaining a fixed driving pressure of 15 cmH2O, PEEP was increased from 0 to 20 cmH2O every 3 minutes in 5 cmH2O increments. In each sheep, arterial blood samples were collected to measure arterial
gases and to calculate F-shunt, PaO2/alveolar oxygen partial pressure (PAO2) and PaO2/FIO2 during spontaneous breathing before mechanical ventilation (T0), after 20 minutes of ventilation (T20) and during spontaneous breathing at extubation (Text).
Results
Both ventilatory strategies improved the arterial oxygen content although four animals
in group PEEP showed oxygen content compatible with hypoxia compared with group ARM.
F-shunt values were not statistically different at any time point in sheep that underwent
only PEEP ventilation while they decreased at T20 and Text compared with T0 in group ARM. At extubation F-shunt was statistically lower in sheep that underwent
an ARM. Mechanical ventilation improved PaO2/PAO2 and PaO2/FIO2 but they did not differ between groups.
Conclusions
and clinical relevance The stepwise ARM evaluated in this study improved oxygenation indices and decreased
F-shunt. This effect was maintained at extubation compared with sheep that were ventilated
with only PEEP 5 cmH2O.
Keywords
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Article info
Publication history
Published online: April 16, 2020
Accepted:
February 12,
2020
Received:
September 30,
2019
Identification
Copyright
© 2020 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.
