Micropatterned Endotracheal Tubes Reduce Secretion-Related Lumen Occlusion

Abstract

Tracheal intubation disrupts physiological homeostasis of secretion production and clearance, resulting in secretion accumulation within endotracheal tubes (ETTs). Novel in vitro and in vivo models were developed to specifically recapitulate the clinical manifestations of ETT occlusion. The novel Sharklet™ micropatterned ETT was evaluated, using these models, for the ability to reduce the accumulation of both bacterial biofilm and airway mucus compared to a standard care ETT. Novel ETTs with micropattern on the inner and outer surfaces were placed adjacent to standard care ETTs in in vitro biofilm and airway patency (AP) models. The primary outcome for the biofilm model was to compare commercially-available ETTs (standard care and silver-coated) to micropatterned for quantity of biofilm accumulation. The AP model's primary outcome was to evaluate accumulation of artificial airway mucus. A 24-h ovine mechanical ventilation model evaluated the primary outcome of relative quantity of airway secretion accumulation in the ETTs tested. The secondary outcome was measuring the effect of secretion accumulation in the ETTs on airway resistance. Micropatterned ETTs significantly reduced biofilm by 71% (p = 0.016) compared to smooth ETTs. Moreover, micropatterned ETTs reduced lumen occlusion, in the AP model, as measured by cross-sectional area, in distal (85%, p = 0.005), middle (84%, p = 0.001) and proximal (81%, p = 0.002) sections compared to standard care ETTs. Micropatterned ETTs reduced the volume of secretion accumulation in a sheep model of occlusion by 61% (p < 0.001) after 24 h of mechanical ventilation. Importantly, micropatterned ETTs reduced the rise in ventilation peak inspiratory pressures over time by as much as 49% (p = 0.005) compared to standard care ETTs. Micropatterned ETTs, demonstrated here to reduce bacterial contamination and mucus occlusion, will have the capacity to limit complications occurring during mechanical ventilation and ultimately improve patient care.

Keywords: Airway patency model; Biofilm; Endotracheal tube; Mechanical ventilation; Micropattern; Occlusion.

FIGURE 1.

Micropattern incorporated on an endotracheal tube. These first-generation devices were injection-molded to imprint the micropattern on the ETT lumen and outer surface. Confocal microscopy demonstrates that the micropattern is oriented such that the long axis of individual features aligns with the longitudinal direction of the tube, i.e., along the direction of secretion flow. Scale bar, 20 μm.

FIGURE 2.

Airway patency model using artificial mucus. The adjustable supports allowed investigators to bend ETTs to match tracheal anatomy and head-of-bed position. Four ETTs were simultaneously connected to an air splitter and a breathing circuit that ultimately attached to a ventilator. The distal ends of ETTs were placed inside the breathing reservoir filled with artificial mucus. A test lung connected to the reservoir returned air to the ventilator simulating expiration. A liquid level sensor, peristaltic pump, and mucus supply reservoir provided a constant supply of artificial mucus to counteract evaporation over long experimental durations. As breathing proceeded through the AP model, simulated airway secretions were pulled into tubes to mimic the interaction of respiratory secretions with airway devices.

FIGURE 3.

The micropattern reduces artificial mucus accumulation. Artificial mucus weight (g) in the ETTs grouped by section along the tube length. Micropatterned ETTs significantly reduced weight of accumulated material in every section compared to standard care ETTs. Error bars indicate standard error of the mean of three individual experiments.

FIGURE 4.

The micropattern prevents airway narrowing. (a) Representative images of reductions in cross-sectional area due to secretion accumulation in standard care ETTs (top) and micropatterned ETTs (bottom). Standard care ETTs show an increase in accumulated material compared to the micropatterned ETTs in all sections. The black areas inside the luminal portion of each tube are accumulated artificial mucus. (b) The graph shows that micropatterned ETTs have significantly less reduction in cross-sectional area compared to standard care ETTs in all three sections along the tubes. Error bars represent standard of the mean from three individual experiments.

FIGURE 5.

Preclinical sheep model of ETT occlusion. (a) Volume of accumulated airway secretions was reduced by 61% (p<0.001, *) in micropatterned ETTs compared to standard care ETTs. (b) Micropatterned ETTs had 45% (p = 0.103) less mucus weight compared to standard care ETTs. (c) Representative images of mucus in cross-sectioned ETTs following extubation.

FIGURE 6.

In vivo Airway Patency Model. Five sheep (2 with standard care and 3 with micropatterned ETTs) were evaluated. Total mechanical ventilation time was divided into two intervals: 0–8 and 8–24 h (indicated in the graph). Data were collected continually during each interval for each device type to produce a linear regression determination of average peak inspiratory pressure over time. Standard care and micropatterned regression graphs are presented independent from each other for clarity. The solid lines in the graphs represent the average peak inspiratory pressure over time for each ETT type while the broken lines represent the 95% prediction intervals for each surface type. The change in peak inspiratory pressure over time for each surface is indicated in the table along with the percent reduction comparing micropatterned to standard care ETTs. A 49% (p = 0.005) reduction in peak inspiratory pressure increase over time was measured on micropatterned ETTs after raising the animal head between 8 and 24 h of ventilation compared to standard care ETTs. (nd refers to no difference).