G. Conti et al., EVALUATION OF RESPIRATORY SYSTEM RESISTANCE IN MECHANICALLY VENTILATED PATIENTS - THE ROLE OF THE ENDOTRACHEAL-TUBE, Intensive care medicine, 20(6), 1994, pp. 421-424
Objective: To investigate the role played by the endotracheal tube (ET
T) in the correct evaluation of respiratory system mechanics with the
end inflation occlusion method during constant flow controlled mechani
cal ventilation. Setting: General ICU, university of Rome ''La Sapienz
a''. Patients: 12 consecutive patients undergoing controlled mechanica
l ventilation. Methods: We compared the values of minimal resistance o
f the respiratory system (i.e. airway resistance) (RRS min) obtained:
i) subtracting the theoretical value of ETT resistance from the differ
ence between P max and P1, measured on airway pressure tracings obtain
ed from the distal end of the ETT, ii) directly measuring airway press
ure 2 cm below the ETT, thus automatically excluding ETT resistance fr
om the data. Results. The values of RRS min obtained by measuring airw
ay pressure below the ETT were significantly lower than those obtained
by measuring airway pressure at the distal end of the ETT and subtrac
ting the theoretical ETT resistance (4.5+/-2.8 versus 2.5+/-1.6 cm H2O
/1/s, p < 0.01). Conclusion: When precise measurements of ohmic resist
ances are required in mechanically ventilated patients, the measuremen
ts must be obtained from airways pressure data obtained at tracheal le
vel. The ''in vivo'' positioning of ETT significantly increases the ai
rflow resistance of the ETT.