• G Conti, R A De Blasi, A Lappa, A Ferretti, M Antonelli, M Bufi, and A Gasparetto.
• Istituto di Anestesiologia e Rianizmazione, University of Rome La Sapienza, Italy.
• Intensive Care Med. 1994 Jul 1;20(6):421-4.

ObjectiveTo investigate the role played by the endotracheal tube (ETT) in the correct evaluation of respiratory system mechanics with the end inflation occlusion method during constant flow controlled mechanical ventilation.SettingGeneral ICU, university of Rome "La Sapienza".Patients12 consecutive patients undergoing controlled mechanical ventilation.MethodsWe compared the values of minimal resistance of the respiratory system (i.e. airway resistance) (RRS min) obtained: i) subtracting the theoretical value of ETT resistance from the difference between P max and P1, measured on airway pressure tracings obtained from the distal end of the ETT; ii) directly measuring airway pressure 2 cm below the ETT, thus automatically excluding ETT resistance from the data. RESULTS. The values of RRS min obtained by measuring airway pressure below the ETT were significantly lower than those obtained by measuring airway pressure at the distal end of the ETT and subtracting the theoretical ETT resistance (4.5 +/- 2.8 versus 2.5 +/- 1.6 cm H2O/l/s, p < 0.01).ConclusionWhen precise measurements of ohmic resistances are required in mechanically ventilated patients, the measurements must be obtained from airways pressure data obtained at tracheal level. The "in vivo" positioning of ETT significantly increases the airflow resistance of the ETT.

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