Secretion Buildup in Closed System Catheters: A Risk Factor?

Abstract & Commentary

Glass and colleagues examined the extent, prevalence, and distribution of narrowing related to secretion buildup in endotracheal tubes (ETT) following removal from 40 patients (18 males, 22 females) who had been intubated for an average of 6.6 days (range, 3-20 days) in a medical-respiratory ICU. The ETT were examined within four hours following extubation. Each tube was weighed on a gram scale (accurate to 0.1 mg) and then cut longitudinally on the lesser curvature. Areas containing debris were recorded at the closest 1-cm mark throughout the entire tube for each of 28 centimeter markings. Depth of debris was measured using a periodontal dental probe marked in 1-mm increments. The ETT were then cleaned, dried, and weighed again to determine weight of the debris.

Two ETT (5%) had no measurable debris. In the remaining tubes, the mean overall depth of debris was 0.64 mm (range, 0-2.36 mm). The entire length of the ETT was affected, with the greatest depth of debris at the 6-9 cm and 13-14 cm markings. The greatest depth of debris of each ETT was also calculated; this ranged from 0-5 mm (mean, 2.0 mm). The mean weight of debris was 1.16 g. A significant positive correlation was found between the duration of intubation and mean overall depth of debris (r = 0.48; P < 0.01), mean greatest depth of debris (r = 0.37; P < 0.05), and mean weight of debris (r = 0.38; P < 0.05). No significant relationship was found among these variables and patient age, size of the ETT, ventilator humidification temperature, a secretion score that considered consistency, and amount of secretions, fluid balance, number of suctioning episodes, or rhonchi on chest auscultation. Stepwise multiple regression resulted in a model that included only duration of intubation, with this model predicting 23% of the variance in overall depth of debris. (Glass C, et al. Am J Crit Care 1999;8:93-100.)

COMMENT BY LESLIE A. HOFFMAN, RN, PhD

In this study, most ETT had a substantial buildup of debris. With a mean depth of 0.64 mm, this buildup was sufficient to, in essence, reduce the internal diameter of the tube to the next smaller size (e.g., from 8.0 to 7.5), assuming an eccentric buildup. To determine if the buildup was eccentric or concentric, Glass et al examined five additional ETT, which they cut in a cross-sectional manner. Of six cuts on each of five tubes (30 observations), only two observations in the same ETT showed a concentric distribution. Thus, for the majority of ETT, secretion buildup appeared to be eccentric.

The findings from this study have several important clinical implications. Patients who are intubated for longer intervals are typically more difficult to wean from mechanical ventilation. Any factor that decreases airway diameter will increase work of breathing, making weaning more difficult. In this study, a longer duration of intubation was associated with a greater buildup of debris. When patients require suctioning, this debris and any bacteria it contains will be dislodged into the lungs, increasing the risks of ventilator-associated pneumonia (VAP).

Numerous studies have examined potential risk factors for VAP, including oral colonization, gastric pH, and adequate cuff pressures. Findings of this study suggest that secretion buildup inside the ETT may be an additional risk factor. Early tracheotomy, if indicated, may avert or minimize this problem, as a tracheostomy tube is shorter and an inner cannula can be used if secretion buildup is a concern. Since all patients in this study were suctioned using a closed suctioning system, the findings may not apply to patients suctioned with an open system. Ventilator humidification temperature was maintained at 34.8 ± 1.04°C (range, 33-36°C), but no information was provided regarding the type of system. The number of suctioning episodes per day (6.98 ± 2.31) was reported, but not the type of ETT. The methodology used in this study is simple to replicate.

Further studies are indicated to assess risk factors for secretion buildup and interventions to minimize this problem. It would be interesting to examine ETT in patients who extubate themselves, but do not require intubation, to determine the extent of secretion buildup.

The extent of buildup of debris in endotracheal tubes was related to:

    a. size of the endotracheal tube.
    b. duration of intubation.
    c. number of suctioning passes.
    d. volume and tenacity of secretions.
    e. All of the above