Physiological dead space/tidal volume ratio during face mask, laryngeal mask, and cuffed oropharyngeal airway spontaneous ventilation.
OBJECTIVE
To compare the physiological dead space/tidal volume ratio and arterial to end-tidal carbon dioxide tension (ETCO2) difference during spontaneous ventilation through a face mask, a laryngeal mask (LMA), or a cuffed oropharyngeal airway.


METHODS
Prospective, randomized, cross-over study.


METHODS
Inpatient anesthesia at a university department of orthopedic surgery.


METHODS
20 ASA physical status I and II patients, without respiratory disease, who underwent ankle and foot surgery.


METHODS
After a peripheral nerve block was performed, propofol anesthesia was induced and then maintained with a continuous intravenous (i.v.) infusion (4 to 6 mg/kg/h). A face mask, a cuffed oropharyngeal airway, or an LMA were placed in each patient in a random sequence. After 15 minutes of spontaneous breathing through each of the airways, ventilatory variables, as well as arterial, end-tidal, and mixed expired CO2 partial pressure, were measured, and physiological dead space/tidal volume ratio was calculated.


RESULTS
Expired minute volume and respiratory rate (RR) were lower with LMA (5.6 +/- 1.2 L/min and 18 +/- 3 breaths/min) and the cuffed oropharyngeal airway (5.7 +/- 1 L/min and 18 +/- 3 breaths/min) than the face mask (7.1 +/- 0.9 L/min and 21 +/- 3 breaths/min) (p = 0.0002 and p = 0.013, respectively). Physiological dead space/tidal volume ratio and arterial to end tidal CO2 tension difference were similar with the cuffed oropharyngeal airway (3 +/- 0.4 mmHg and 4.4 +/- 1.4 mmHg) and LMA (3 +/- 0.6 mmHg and 3.7 +/- 1 mmHg) and lower than with the face mask (4 +/- 0.5 mmHg and 6.7 +/- 2 mmHg) (p = 0.0001 and p = 0.001, respectively).


CONCLUSIONS
Because of the increased dead space/tidal volume ratio, breathing through a face mask required higher RR and expired minute volume than either the cuffed oropharyngeal airway or LMA, which, in contrast, showed similar effects on the quality of ventilation in spontaneously breathing anesthetized patients.
Casati
A
A
Department of Anesthesiology, University of Milan, Italy.
Fanelli
G
G
Torri
G
G
D000704:Analysis of Variance; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D000842:Ankle / Q000601:surgery; D002245:Carbon Dioxide / Q000097:blood / Q000378:metabolism; D018592:Cross-Over Studies; D005260:Female; D005528:Foot / Q000601:surgery; D006801:Humans; D007440:Intubation / Q000295:instrumentation*; D017214:Laryngeal Masks; D008297:Male; D008397:Masks; D008875:Middle Aged; D009407:Nerve Block; D009960:Oropharynx; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D015742:Propofol / Q000008:administration & dosage; D011446:Prospective Studies; D012119:Respiration; D012126:Respiratory Dead Space / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology*
D018686:Anesthetics, Intravenous; D002245:Carbon Dioxide; D010100:Oxygen; D015742:Propofol