We have previously observed that endotracheal tubes (ETT) in sheep on mechanical ventilation (MV), combined with ITPV, invariably remained free of mucus; and never required suctioning. This study attempts to elucidate its mechanism. In ITPV, all fresh gas is introduced through a small reverse thrust catheter (RTC), which is advanced through the ETT to the distal level of the ETT, close to the carina. The distal tip of the RTC is closed, with all gas exiting at a high velocity in a direction away from the carina, forming a venturi. Methods: 14 young female sheep (27.79±3.29kg) were anaestethized, paralyzed, and intubated with a #8 ETT of known weight. The carotid artery and the jugular vein were cannulated for hemodynamic measurements and blood sampling. Sheep were ventilated in the prone position, without suctioning. Animals were randomly assigned to two groups: Group A: seven sheep were ventilated with ITPV; 6ml/h of normal saline was added to the ITPV gas flow, delivered by a roller pump; VE 9.5 to 14 l/min, VT 10 ml/kg, RR 15 to 20 bpm, FiO2 0.3, I:E 1:2, PEEP 6 to 8 cm H2O, with CO2 added to sustain normocapnia. Group B: seven sheep were ventilated with volume controlled ventilation (VC), VT 10 ml/kg, RR 10 to 18 pbm, FiO2 0.3, I:E 1:2, PEEP 6 cm H2O. Standard Concha humidifiers were used in all studies. Following 72h of MV, the animals were sacrificed, the tracheae were exposed and inspected. The ETTs were weighed after wiping off any adhering saliva from the outer surface. Air flow pressure drop along the ETTs (▵Pres) was measured in vitro at a flow of 60 l/min. Results: Blood gases and circulatory status did not change in either group. The weight of the ETTs increased by 0.7± 0.141 g in group A, and 2.443±0.812 g in group B (P<0.001). ▵Pres were 6.157 ± 0.535, and 15.343±5.282, and 5.22 cm H2O/l/sec in groups A, B, and in a new 8mm ETT, respectively. Layers of yellowish or greenish mucus were found in the ETTs of group B; those of group A appeared clean. Gross appearance of tracheae and lungs were normal in both groups. Conclusion: sheep ventilated with ITPV, with saline added to the RTC, prevented gross mucous depositions within the ETTs, without suctioning, with no rise in airway resistance over the 3 d duration of this study.
