Monitored arterial and end-tidal carbon dioxide during in-flight mechanical ventilation

Abstract

Introduction: Mechanical ventilation with monitored arterial carbon dioxide tension is necessary for optimum pulmonary support and hemodynamic stability. Ongoing monitoring is necessary to ensure adequate ventilation parameters. The prospective study purpose was to (1) compare mechanical ventilation to historic manual ventilation, (2) evaluate the effectiveness of institutional tidal volume parameters, (3) determine the effect of institutional tidal volume manipulation on end-tidal carbon dioxide tension, and (4) explore the relationship between in-flight end-tidal carbon dioxide tension and arterial carbon dioxide tension. Methods: Randomized groups were mechanically ventilated (tidal volume = 12 cc/kg, rate = 14/min) with a target arterial carbon dioxide tension between 30 and 35 torr. Group I was monitored with in-line end-tidal carbon dioxide tension, and group II was monitored with arterial carbon dioxide tension by means of inflight arterial blood gas. Results: Arterial carbon dioxide tension varied less with monitored mechanical than with manual ventilation ( p = 0.001). The gradient between arterial and end-tidal carbon dioxide tension was 5.3 ± 4.4 (mean ± standard deviation [SD]). End-tidal and arterial carbon dioxide tension positively correlated ( r = 0.76, p = 0.001), yet end-tidal carbon dioxide tension accounted for only 58% variation of arterial carbon dioxide tension ( r 2 = 0.58). Conclusion: Mechanical ventilation is more precise but inconsistent in achieving a target arterial carbon dioxide tension with current ventilation parameters. End-tidal carbon dioxide tension is a reasonable estimate of, but cannot exclusively replace, arterial carbon dioxide tension in critically ill patients.