• F Colò, M Girardis, A Pasqualucci, U Da Broi, and A Pasetto.
• Cattedra di Anestesia e Rianimazione, Università degli Studi di Udine.
• Minerva Anestesiol. 1994 Jul 1;60(7-8):367-74.

ObjectiveTo evaluate the effects of physiological ventilatory patterns on P(a-ET)CO2 gradient and on the alveolar dead space production during controlled mechanical ventilation.DesignProspective and experimental comparison among three different ventilatory settings in three different groups of subjects.SettingGeneral surgery's operating-theatre in university hospital.PatientsTwenty-eight patients subdivided randomly in 3 groups differing for ventilatory setting. I group: constant tidal volume (VC = 8 ml.kg-1) and 3 different respiratory frequencies (f = 10, 12 and 14 breaths.min-1); II group: constant ventilation (112 ml.kg-1) but VC and f modified in three different ways; III group: inspiratory volume was set to give an end-tidal PCO2 (PETCO2) of about 35 mmHg. The cases were subdivided, on the basis of P(a-ET)CO2 distribution, in three groups: group with values larger than mean plus 1 standard deviation, group with values between +/- 1 standard deviation and group with values lower than mean minus 1 standard deviation. Moreover in two homogeneous groups for age.InterventionsGeneral surgery but not important because measures were performed before surgical manoeuvres.Measurements And Main ResultsAnthropometrical data (age and body weight), PaCO2, PETCO2, heart rate, invasive arterial pressure, ventilatory parameters and airway pressure were collected for every subject and ventilatory setting; arterial to end-tidal difference P(a-ET)CO2 and P(a-ET)CO2.PaCO2(-1) were calculated during data analysis. The P(a-ETFCO2 and P(a-ET)CO2.PaCO2(-1) values were not significantly different among the three different ventilatory patterns both in the first and in the second group. P(a-ET)CO2 values were significantly correlated with age, body weight and airway pressure. These parameters were correlated significantly also with P(a-ET)CO2.PaCO2(-1) values.ConclusionsVentilatory setting, used in a normal physiological range, don't affect P(a-ET)CO2 difference during mechanical ventilation. Age, body weight and airway pressure of the patient must be considered to obtain a correct value of PaCO2 by the measure of PETCO2.

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