Comparison of the effects of two humidifier systems on endotracheal tube resistance

Humidification during mechanical ventilation to prevent endotracheal tube occlusion in critically ill patients: A case control study

BACKGROUND:

Endotracheal tube (ETT) occlusion is a potentially life-threatening event. This study describes a quality improvement project to prevent ETT occlusion in critically ill patients.

METHODS:

After a cluster of clinically significant ETT occlusion incidents at a tertiary-care intensive care unit (ICU), the root cause analysis suggested that the universal use of heat moisture exchangers (HMEs) was a major cause. Then, we prospectively audited new ETT occlusion incidents after changing our practices to evidence-based active and passive humidification during mechanical ventilation (MV). We also compared the outcomes of affected patients with matched controls.

RESULTS:

During 100 weeks, 18 incidents of clinically significant ETT occlusion occurred on a median of 7 days after intubation (interquartile range, 4.8–9.5): 8 in the 10 weeks before and 10 in the 90 weeks after changing humidification practices (8.1 vs. 1.0 incidents per 1000 ventilator days, respectively). The incidents were not suspected in 94.4%, the peak airway pressure was >30 cm H₂O in only 25%, and 55.6% were being treated for pneumonia when ETT occlusion occurred. Compared with 51 matched controls, ETT occlusion cases had significantly longer MV duration (median of 13.5 vs. 4.0 days; P = 0.002) and ICU stay (median of 26.5 vs. 11.0 days; P = 0.006) and more tracheostomy (55.6% vs. 9.8%; P < 0.001). The hospital mortality was similar in cases and controls.

CONCLUSIONS:

The rate of ETT occlusion decreased after changing humidification practices from universal HME use to evidence-based active and passive humidification. ETT occlusion was associated with more tracheostomy and a longer duration of MV and ICU stay.

Heat and moisture exchangers (HMEs) and heated humidifiers (HHs) in adult critically ill patients: a systematic review, meta-analysis and meta-regression of randomized controlled trials

BACKGROUND

The aims of this systematic review and meta-analysis of randomized controlled trials are to evaluate the effects of active heated humidifiers (HHs) and moisture exchangers (HMEs) in preventing artificial airway occlusion and pneumonia, and on mortality in adult critically ill patients. In addition, we planned to perform a meta-regression analysis to evaluate the relationship between the incidence of artificial airway occlusion, pneumonia and mortality and clinical features of adult critically ill patients.

METHODS

Computerized databases were searched for randomized controlled trials (RCTs) comparing HHs and HMEs and reporting artificial airway occlusion, pneumonia and mortality as predefined outcomes. Relative risk (RR), 95% confidence interval for each outcome and I ² were estimated for each outcome. Furthermore, weighted random-effect meta-regression analysis was performed to test the relationship between the effect size on each considered outcome and covariates.

RESULTS

Eighteen RCTs and 2442 adult critically ill patients were included in the analysis. The incidence of artificial airway occlusion (RR = 1.853; 95% CI 0.792-4.338), pneumonia (RR = 932; 95% CI 0.730-1.190) and mortality (RR = 1.023; 95% CI 0.878-1.192) were not different in patients treated with HMEs and HHs. However, in the subgroup analyses the incidence of airway occlusion was higher in HMEs compared with HHs with non-heated wire (RR = 3.776; 95% CI 1.560-9.143). According to the meta-regression, the effect size in the treatment group on artificial airway occlusion was influenced by the percentage of patients with pneumonia (β = -0.058; p = 0.027; favors HMEs in studies with high prevalence of pneumonia), and a trend was observed for an effect of the duration of mechanical ventilation (MV) (β = -0.108; p = 0.054; favors HMEs in studies with longer MV time).

CONCLUSIONS

In this meta-analysis we found no superiority of HMEs and HHs, in terms of artificial airway occlusion, pneumonia and mortality. A trend favoring HMEs was observed in studies including a high percentage of patients with pneumonia diagnosis at admission and those with prolonged MV. However, the choice of humidifiers should be made according to the clinical context, trying to avoid possible complications and reaching the appropriate performance at lower costs.

Relationship between pre-anesthetic and intra-anesthetic airway resistance in patients undergoing general anesthesia: A prospective observational study

Surgery patients in Japan undergo routine spirometry testing prior to general anesthesia. The use of a flow sensor during general anesthesia has recently become common. However, it is not certain whether the information derived from flow-volume curves is being adequately used for mechanical ventilation management during general anesthesia. So far, there have been no attempts to calculate airway resistance using flow-volume curves. Therefore, we performed a prospective, observational study to investigate the relationship between pre-anesthetic and intra-anesthetic airway resistance in patients scheduled for surgery under general anesthesia. We calculated pre-anesthetic and intra-anesthetic airway resistance in each patient, based on the slopes of flow-volume curves obtained prior to and during general anesthesia. We also calculated endotracheal tube resistance to correct the intra-anesthetic airway resistance values calculated. A total of 526 patients were included in the study, and 98 patients had a forced expiratory volume in the first second/forced vital capacity ratio of < 70%. Pre-anesthetic airway resistance was significantly higher in patients with airflow obstruction than in those without airflow obstruction (p < 0.001), whereas no significant difference in intra-anesthetic airway resistance was found between patients with and without airflow obstruction during mechanical ventilation (p = 0.48). Pre-anesthetic and intra-anesthetic airway resistance values were closer to each other in patients without airflow obstruction, with a mean difference < 1.0 cmH2O L-1s-1, than in those with airflow obstruction, although these respiratory parameters were significantly different (p < 0.001). Intra-anesthetic airway resistance was not related to the FEV1/FVC ratio, regardless of the degree to which the FEV1/FVC ratio reflected pre-anesthetic airway resistance. As compared with patients with airflow obstruction, the mean difference between pre-anesthetic and intra-anesthetic airway resistance was small in patients without airflow obstruction.

[Non-invasive and invasive out of hospital ventilation in chronic respiratory failure : Consensus report of the working group on ventilation and intensive care medicine of the Austrian Society of Pneumology]

The current consensus report was compiled under the patronage of the Austrian Society of Pneumology (Österreichischen Gesellschaft für Pneumologie, ÖGP) with the intention of providing practical guidelines for out-of-hospital ventilation that are in accordance with specific Austrian framework parameters and legal foundations. The guidelines are oriented toward a 2004 consensus ÖGP recommendation concerning the setup of long-term ventilated patients and the 2010 German Respiratory Society S2 guidelines on noninvasive and invasive ventilation of chronic respiratory insufficiency, adapted to national experiences and updated according to recent literature. In 11 chapters, the initiation, adjustment, and monitoring of out-of-hospital ventilation is described, as is the technical equipment and airway access. Additionally, the different indications-such as chronic obstructive pulmonary diseases, thoracic restrictive and neuromuscular diseases, obesity hypoventilation syndrome, and pediatric diseases-are discussed. Furthermore, the respiratory physiotherapy of adults and children on invasive and noninvasive long-term ventilation is addressed in detail.

End-inspiratory pause prolongation in acute respiratory distress syndrome patients: effects on gas exchange and mechanics

Background

End-inspiratory pause (EIP) prolongation decreases dead space-to-tidal volume ratio (Vd/Vt) and PaCO₂. We do not know the physiological benefits of this approach to improve respiratory system mechanics in acute respiratory distress syndrome (ARDS) patients when mild hypercapnia is of no concern.

Methods

The investigation was conducted in an intensive care unit of a university hospital, and 13 ARDS patients were included. The study was designed in three phases. First phase, baseline measurements were taken. Second phase, the EIP was prolonged until one of the following was achieved: (1) EIP of 0.7 s; (2) intrinsic positive end-expiratory pressure ≥1 cmH₂O; or (3) inspiratory–expiratory ratio 1:1. Third phase, the Vt was decreased (30 mL every 30 min) until PaCO₂ equal to baseline was reached. FiO₂, PEEP, airflow and respiratory rate were kept constant.

Results

EIP was prolonged from 0.12 ± 0.04 to 0.7 s in all patients. This decreased the Vd/Vt and PaCO₂ (0.70 ± 0.07 to 0.64 ± 0.08, p < 0.001 and 54 ± 9 to 50 ± 8 mmHg, p = 0.001, respectively). In the third phase, the decrease in Vt (from 6.3 ± 0.8 to 5.6 ± 0.8 mL/Kg PBW, p < 0.001) allowed to decrease plateau pressure and driving pressure (24 ± 3 to 22 ± 3 cmH₂O, p < 0.001 and 13.4 ± 3.6 to 10.9 ± 3.1 cmH₂O, p < 0.001, respectively) and increased respiratory system compliance from 29 ± 9 to 32 ± 11 mL/cmH₂O (p = 0.001). PaO₂ did not significantly change.

Conclusions

Prolonging EIP allowed a significant decrease in Vt without changes in PaCO₂ in passively ventilated ARDS patients. This produced a significant decrease in plateau pressure and driving pressure and significantly increased respiratory system compliance, which suggests less overdistension and less dynamic strain.