Impact of Airway Humidification Strategy in Mechanically Ventilated COVID-19 Patients

Hygrometric Performance of 113 Passive Humidifiers: ISO Standard Method Versus Psychrometry

Background: Passive humidifiers, also known as heat-and-moisture exchangers (HMEs) are used to warm and humidify inspired gases delivered during mechanical ventilation. Recent data demonstrate that the evaluation and selection of these devices is not optimal, leading to severe complications, such as endotracheal tube occlusions. The aim of the study was to assess the humidification performances of a large number of commercially available devices, with the psychrometric method, and to compare the results with manufacturer's data. Methods: We assessed 113 devices using a bench test that simulated physiological ventilation conditions. Seventy-one devices were described by the manufacturers as HME without or with filtration properties (HMEF) and 42 as antimicrobial filters. Among the 71 HME/HMEF, 60% were foam-based, 32% were paper-based, 6% were fiber-based, and 1 had carbon media (HMEF with inhaled sedation function). Three hygrometric measurements using the psychrometric method for each device were performed after reaching a steady state and compared with manufacturers' data (based on the International Organization for Standardization [ISO] method). Results: Among the 71 HME/HMEF tested, only 24 (34%) delivered absolute humidity above 28 mg H2O/L. Nineteen percent of the foam-based and 57% of the paper-based HME/HMEF delivered desired levels of humidity. Humidification data provided by manufacturers were available for 59 HME/HMEFs. In all but one device, humidity output was overestimated using the ISO method. The median (interquartile) difference between our measurements and the manufacturers' data were 6.0 (3.8-8.7) mg H2O/L for devices described as HMEs (P < .001). Poor performing devices were detected only with the psychrometric method. Conclusions: Several HME/HMEFs performed poorly and should not be used for prolonged mechanical ventilation. The values determined by independent assessments were lower than values reported by manufacturers. Evaluation of a passive humidifier using the current ISO method does not guarantee provision of adequate humidification.

Impact of Humidification Modality on Incidence of Endotracheal Tube Occlusion in COVID-19 Patients

Background: Endotracheal tube (ETT) occlusion is reported at a higher frequency among coronavirus disease-2019 (COVID-19) patients. Prior to the COVID-19 pandemic, literature examining patient and ventilator characteristics, including humidification, as etiologies of ETT occlusion yielded mixed results. Our study examines the relationship of humidification modality with ETT occlusion in COVID-19 patients undergoing invasive mechanical ventilation (IMV). Methods: We conducted a retrospective chart review of COVID-19 patients requiring IMV at a tertiary care center in New York from April 2020 to April 2021. Teleflex Neptune heated wire heated humidification (HH) and hygroscopic Intersurgical FiltaTherm and Sunmed Ballard 1500 heat and moisture exchangers (HME) were used. Episodes of ETT occlusion were recorded. Univariate and multivariable logistic regression models were used to investigate the relationship between humidification modality and the occurrence of ETT occlusion. Findings: A total of 201 eligible patients were identified. Teleflex HH was utilized in 50.2% of the population and the others Intersurgical and Sunmed HME devices. Median age was 62 years and 78.6% of patients had at least one medical comorbidity. Precisely, 24% of patients experienced an ETT occlusion after a median of 12 days. The HME group was younger (58.5 vs 64 years), predominantly male (75% vs 59.4%), and experienced more total ventilator days than the HH group (24 vs 12). Those using the studied HME devices had significantly higher odds of ETT occlusion (OR 4.4, 95% CI 1.8-10.6, P = .0011). Three patients (6.1%) experienced cardiac arrest as a consequence of their occlusion. There were no deaths directly attributed to ETT occlusion. Conclusions: The studied HME devices were significantly associated with higher odds of ETT occlusion in COVID-19 patients requiring invasive mechanical ventilation. These events are not without significant clinical consequences. Prolonged use of under-performing HME devices remains suspect in the occurrence of ETT occlusions.

Validity and Reliability of a Short Form of the Questionnaire for the Reflective Practice of Nursing Involving Invasive Mechanical Ventilation: A Cross-Sectional Study

The number of patients on ventilators is rapidly increasing owing to the coronavirus pandemic. The previously developed Questionnaire for the Reflective Practice of Nursing Involving Invasive Mechanical Ventilation (Q-RPN-IMV) for the care of patients on ventilators includes nurses' thought processes as items. This study aims to develop a short form of the Q-RPN-IMV for immediate use in practice and to test its reliability and validity. A convenience sample of 629 participants was used to explore the factor structure using factor analysis. The test-retest reliability was assessed using the intraclass correlation coefficient (ICC). The study was a cross-sectional design instrument development study and was reported according to GRRAS guidelines. Q-RPN-IMV short form was divided into ventilator management and patient management. The ventilator management comprised 31 items organized into six factors. Cronbach's alpha ranged from 0.82 to 0.91, and the ICC ranged from 0.82 to 0.89. The patient management comprised 27 items organized into five factors. Cronbach's alpha ranged from 0.75 to 0.97, and ICC ranged from 0.75 to 0.97. The Q-RPN-IMV short form is a reliable and validated instrument for assessing care for patients on ventilators. This study was not registered.

Monitoring of Heated Wire Humidifier Hygrometric Performances With Heater Plate Temperature

BACKGROUND

Under-humidification and associated complications may occur with heated humidifiers. Hygrometric performances of heated wire humidifiers are reduced by high ambient and high outlet ventilator temperatures. Currently, there is no reliable monitoring tool to evaluate humidification performances of heated wire humidifiers in the daily practice. We sought to demonstrate the relation between humidity delivered by heated wire humidifiers and different parameters that could be used to monitor humidity of gas delivered to subjects.

METHODS

On a bench test, we measured heater plate temperature, inlet chamber temperature, and delivered humidity with MR850 system. Temperature displayed on the humidifier was also recorded. The measurements were performed at different ambient temperatures and five minute ventilation levels (5, 7.5, 10, 12.5, 15 L/min). Inlet chamber temperatures varied from 20-40°C. In each condition, hygrometric measurements with the psychrometric method were performed at steady state.

RESULTS

We performed 279 measurements at steady state including all conditions. We found a good correlation between heater plate temperature and absolute humidity delivered (R² = 0.82). This relationship was hardly affected by ambient temperature, but minute ventilation had more effect. For different minute ventilations, the correlation between heater plate temperature and absolute humidity delivered was very good with coefficient of determination R² from 0.87-0.98. Heater plate temperature > 62°C was a good predictor of absolute humidity delivered > 30 mg H₂O/L (area under the curve = 0.96, sensibility 79%, specificity 94%). No correlation existed between humidity delivered and the outlet chamber temperature (displayed on the humidifier).

CONCLUSIONS

In this bench study, we have shown a good correlation between heater plate temperature and humidity delivered with a heated wire humidifier. This means that a "hidden" hygrometer is built into the heated wire humidifier. Heater plate temperature should be used as a surrogate of humidity to improve the humidification monitoring.