Impact of Different Inspiratory Flow Patterns on Arterial CO₂-tension

Abstract

Ventilation with decelerating inspiratory flow is known to reduce the dead space fraction and to decrease PaCO2 . Constant inspiratory flow with an end-inspiratory pause (EIP) is also known to increase the removal of CO,.The aim of the study was to elucidate the effect of the pauseho-flow period while both the pattern and rate of inspiratory flow was unchanged, and when the lung was ventilated with sufficient PEEP to prevent end-expiratory collapse.Surfactant depleted piglets were assigned to decelerating or constant inspiratory flow with 24 breaths per minute (bpm) or12 bpm, or to constant flow, without and with an end-inspiratory pause of 25%. By adding an EIP the total time without active inspiratory flow of the respiratory cycle was kept unchanged. Gas exchange, airway pressures, functional residual capacity (using sulfurhexafluoride) and haemodynamics (thermo-dye indicator dilution technique) were measured.Irrespective of ventilatory frequency, PaCOz was lower and serial dead space reduced with decelerating flow, compared with constant inspiratory flow. With an end-inspiratory pause added to constant inspiratory flow, serial dead space was reduced but did not decrease PaCO, .The results of this study corroborate the assumption that total time without active inspiratory flow is important for arterial C0,-tension.

A prolonged postinspiratory pause enhances CO2 elimination by reducing airway dead space

“…Notably, a decelerating or accelerating inspiratory flow pattern will have longer and shorter MDT, respectively, compared to symmetrical flow waveforms. Different waveforms have been studied in humans with indistinct results (Johansson, 1975;Johansson & Lo¨fstro¨m, 1975;Dammann et al, 1978;Al-Saady & Bennett, 1985;Markstro¨m et al, 2000). Such studies merit to be repeated with modern technique.…”

“…Several studies in health or in disease show a decrease in dead space or PaCO 2 when using a postinspiratory pause (Fuleihan et al, 1976;Dammann et al, 1978;Lachmann et al, 1982;Wolff et al, 1989a;Mercat et al, 2001). However, positive effects of inspiratory patterns intended to improve gas exchange have not always been observed (Johansson, 1975;Johansson & Lo¨fstro¨m, 1975;Dammann et al, 1978;Al-Saady & Bennett, 1985;Markstro¨m et al, 2000). Partly diverging results may reflect methodological limitations.…”

“…However, positive effects of inspiratory patterns intended to improve gas exchange have not always been observed (Johansson, 1975; Johansson & Löfström, 1975; Dammann et al. , 1978; Al‐Saady & Bennett, 1985; Markström et al. , 2000).…”

Pattern of inspiratory gas delivery affects CO2 elimination in health and after acute lung injury

“…Such positive effects have not always been observed, however [9,[12][13][14]. Diverging results may reflect methodological limitations.…”