Ventilation‐Perfusion Relationships During Halothane Anaesthesia and Mechanical Ventilation. Effects of Varying Inspired Oxygen Concentration

Abstract

Ventilation-perfusion relationships (VA/Q), assessed by a multiple inert-gas elimination technique, were studied during halothane anaesthesia and mechanical ventilation at different inspiratory oxygen fractions (FIO2). All nine patients (mean age 65 years, five smokers) displayed unaltered VA/Q distributions with increasing FIO2 from a mean of 29% to 53%. A further increase in FIO2 to a mean of 85% caused an increase in true shunt (VA/Q = 0) from 7 to 10% of cardiac output (P less than 0.01), but no increase in "low" VA/Q (VA/Q less than 0.1). On the return to FIO2 of 29%, true shunt was reduced to the initial level. The findings may fit in with release of hypoxic vasoconstriction when FIO2 is increased to 85%, or the opening up of a certain population of shunt vessels.

Can Mathematical Modeling Explain the Measured Magnitude of the Second Gas Effect?

“…A further advantage of this method is that it facilitates equilibration of gas and blood over the whole range of V̇/Q̇ values, particularly at the extremities of each log-normal distribution. Log-normal distributions are not the only distributions seen clinically, 16–20 but we believe the choice is not particularly relevant to the conclusions reached here, which depend primarily on the application of the Fick principle.…”

“…Worsening of V̇/Q̇ matching is known to occur soon after induction of anesthesia and has been well documented experimentally, with typical values for σ of 0.75 to 1.5. 16–20 Further information regarding this way of presenting a log-normal distribution of ventilation and blood flow is provided in appendix 1.…”

Influence of Positioning on Ventilation-Perfusion Relationships in Severe Adult Respiratory Distress Syndrome

“…Ventilation to unperfused lung units (VA/Q) >100) was defined as dead space ventilation. 10 As an index of VA/O inequality, LOgSDQ, was defined as the square root of the value for the second moment of blood-flow distribution.…”

Mechanical ventilation and management of botulism secondary to an injection abscess in an adult horse

“…Increasing the FIO, increases Pa02 if the problem is either a diffusional disturbance or a ventilation-perfusion imbalance. Alveolar hyrmxia, ('hvpoxic lung iniurv') results in atelectasis' associated with decrease lung volumes and alveolar collapse (Lundh and Hedenstiema 1984). Probably both these mechanisms were present in this filly.…”