Effects of gas composition on the delivered tidal volume of the Avance Carestation

Abstract

These results support our hypothesis and suggest that changing gas composition may alter delivered tidal volume of anesthesia machines with built-in ventilators that are feedback-controlled by uncorrected flowmeters due to changes in gas mixture density.

Influence of Respiratory Gas Density on Tidal Volume During Pressure-Controlled Ventilation: A Laboratory Investigation and Observational Study in Children.

“…However, the degree of the impact of this phenomenon in clinical settings remained unclear. The results of our study were generally consistent with those of previous studies [5,6]. Additionally, our results indicate two important findings: First, the true TV of the lung decreased with an increase in respiratory gas density during PCV as expected, in both laboratory and clinical settings.…”

“…Moreover, some studies have reported that changes in the respiratory gas composition affect the accuracy of respiratory flow measurements [2,5,6], In this regard, with the progress of anesthesia machines, some anesthesia workstations have integrated gas analyzers and use the information of gas compositions to improve flow and volume monitoring so that TV measured by a built-in pneumotachometer is a closer approximation of the delivered TV. External pneumotachometers with gas 4 analyzers have also been widely used.…”

Comparison of pneumotachography and anemometery for flow measurement during mechanical ventilation with volatile anesthetics

“…Following these principal findings, Miyaji et al [4] demonstrated that ventilation with sevoflurane and desflurane altered delivered V T for feedback-control conditions determined using a variable orifice flow sensor. Their findings are similar to our observations that increasing concentrations of less potent anesthetic agents yield considerable differences in estimated V T between the PNT and HWA (Fig.…”

“…By contrast, a more complicated relationship exists between V̇ HWA and several other properties of the gas [9, 10]. Based on previous findings [4, 12], we assumed that changes in gas density were primarily responsible for changes in V̇ HWA during measurement with anesthetic gas mixtures. Thus we adjusted V̇ HWA using a compensation factor accounting for changes in gas mixture density ( ρ mix ) relative to the density of the gas used for the calibration of the HWA ( ρ cal ): $${{\dot{V}}^{\prime }}_{\mathrm{italicHWA}}=\left(\frac{{\rho }_{\mathrm{cal}}}{{\rho }_{\mathrm{mix}}}\right){\dot{V}}_{\mathrm{HWA}}$$where ${{\dot{V}}^{\prime }}_{\mathrm{italicHWA}}$ is the compensated estimate of HWA flow.…”

“…Consequently such changes can bias estimates of airway flow ( V̇ ), as well as flow-derived parameters such as tidal volume ( V T ), respiratory resistance, and respiratory compliance. A recent study [4] demonstrated that variations in ρ , due to changes in carrier gas composition or volatile anesthetic concentration, will alter delivered V T during feedback-controlled ventilation due to inaccuracies in measured V̇ . These findings were observed using a variable-orifice flowmeter, implying that other flow measuring devices may similarly be influenced by changes in gas mixture.…”