Relationship between tidal volume and deadspace during high frequency ventilation.
Physiological (VDphys) and anatomical (VDanat) deadspaces were measured in seven anaesthetized, paralysed and intubated adult patients ventilated at normal and high frequencies. To maintain a constant PaCO2 while increasing the ventilation frequency from 15 to 120 b.p.m., the mean VT was decreased from 454 +/- 62 ml (mean +/- SD) to 117 +/- 9 ml. The mean VDanat and VDphys decreased from 130 +/- 11 ml to 74 +/- 12 ml and 165 +/- 24 ml to 92 +/- 3 ml, respectively, by 80 b.p.m., above which frequency there was no further significant reduction in either. The mean VD/VT ratio increased from 0.36 +/- 0.04 to 0.76 +/- 0.05. This study showed that the deadspace volume measured conventionally was not a constant factor, was mainly a function of VT and was a determinant of tidal and minute volume requirement even during high frequency ventilation. The variable VDphys showed a wide variation between subjects, and appeared to have a mean minimal value of approximately 1.1 ml kg-1 at 80 b.p.m. in adult human subjects with a tracheal tube in situ--a value about half the VDphys measured at conventional normal tidal volumes and ventilation frequencies.
Chakrabarti
M K
MK
Gordon
G
G
Whitwam
J G
JG
D002245:Carbon Dioxide / Q000097:blood; D006801:Humans; D007442:Intubation, Intratracheal; D008176:Lung Volume Measurements; D008875:Middle Aged; D012121:Respiration, Artificial; D012126:Respiratory Dead Space; D013990:Tidal Volume
D002245:Carbon Dioxide