GRADUAL REDUCTION OF ENDOTRACHEAL-TUBE DIAMETER DURING MECHANICAL VENTILATION VIA DIFFERENT HUMIDIFICATION DEVICES

Background: Limited data suggest that increased resistance to flow wit hin endotracheal tubes (ETT) may occur in patients whose lungs are mec hanically ventilated for more than 48 h, especially when airway humidi fication is inadequate, This could lead to sudden ETT obstruction or i nduce excessive loading during spontaneous breathing. Methods: Twenty- three such patients were randomly assigned to three types of airway hu midifier based on three different working principles: a Fisher Paykell hot water system (n = 7), a Pall BB2215 heat and moisture exchanger ( HME) hydrophobic filter (n = 8), and a Dar Hygrobac 35254111 HME hygro scopic filter (n = 8), The decrease in internal pressure along the ETT and the flow rate were measured in each patient every 2 days, An ''ef fective inner diameter'' was derived from these measurements and allow ed the inner ETT configuration to be monitored. Results: On the first day of intubation, the mean diameter was similar in the three groups, and was slightly smaller than the in vitro diameter (mean +/- SD: 7.6 +/- 0.6 mm for Fisher-Paykell, 7.7 +/- 0.4 for Pall, and 7.5 +/- 0.4 f or Dar). The mean diameter tended to decrease from day to day. At the end of the study, the overall reduction in mean diameter was significa ntly greater with the hydrophobic HME (Pall) than with the two other s ystems (Pall: -6.5 +/- 4% vs. -2.5 +/- 2.5% for Dar and -1.5 +/- 3% fo r Fisher-Paykell; P < 0.01 with analysis of variance), The same was tr ue of the mean reduction in effective inner ETT diameter expressed per day of ventilation (-1.6 +/- 1.5% per day for Pall vs. -0.5 +/- 0.4% for Dar and -0.2 +/- 0.4% for Fisher-Paykell; P < 0.01), In four patie nts, the ETT became obstructed and emergency repeated tracheal intubat ion was required, The Pall HME and the Fisher-Paykell system were bein g used in three and one patient, respectively. Before obstruction, the reduction in ETT diameter was significantly greater for these four pa tients than for the remaining 23 patients (7.8 +/- 1.4% vs. 3.1 +/- 4. 1%; P < 0.01). Conclusions: During prolonged mechanical ventilation, s ignificant alterations in inner ETT configuration occur frequently and are influenced by the type of humidification device used, In vivo mon itoring of ETT mechanical properties might be clinically useful.