Reduction in Resting End-Expiratory Position of the Respiratory System with Induction of Anesthesia and Neuromuscular Paralysis

The effect of propofol on airway pressures generated by magnetic stimulation of the phrenic nerves

“…Bergman found a fall in resting end expiratory volume 30 s after induction, stabilising at a lower level after another 1545 s [8]. Some of this volume change may also be due to other factors [25], such as movement of blood into the thorax during spontaneous breathing or out during mechanical ventilation [26,27].…”

“…In the case of the patients with balloon catheters, pressures were measured using identical transducers. The change in lung volumes with anaesthesia was recorded using an 8-l dry spirometer (SensorMedics, Calif., USA) substituted for the breathing bag in an anaesthetic circle system, which contained a CO 2 absorber [8].…”

“…The 8-l volume of the spirometer bellows was sufficient to ensure that the inspired oxygen remained adequate throughout the recording. Changes in REEP with induction of anaesthesia were later estimated from the spirometer tracings, to the nearest 100 ml, using the method described by Bergman [8]. After adequate spirometer recordings had been made fresh oxygen was introduced from the common gas outlet of the anaesthetic machine.…”

Perioperative functional residual capacity

“…There is no significant change on changing from spontaneous to controlled ventilation. An initial reduction of approximately 200 ml occurs during the injection of thiopentone, coincident 20 with the loss of consciousness. With ketamine, however, no change in FRC occurs in either adults, 24 reduction, whereas FRC will be reduced by about 20% if methohexitone induction is followed by tracheal intubadon, 27 particularly if coughing occurs during intubation.…”

“…5~'52 However, muscle paralysis, which abolishes this activity, does not restore FRC. t~ , 18,20 An increase in abdominal blood volume, which can displace the diaphragm cranially, has been suggested as the cause of reduced FRC. 53 A small ( 150 ml) reduction in the volume of the four limbs occurs during thiopentoneneuroleptanaesthesia but not during inhalational or regional anaesthesia.…”