(J-374) Comparison of Humidifier Performance when Paired with the Puritan Bennett 980 Ventilator: A Comparative Manufacturer Bench Study

Introduction: Artificial humidification is essential to the health of patients using invasive and non-invasive ventilation to avoid potential damage to the airway structure and function (1). Optimal physiological conditions during ventilation include delivery of 34 - 37°C air with 100% relative humidity (2). The objective of this bench testing was to measure humidity and temperature of mixed gas delivered from a mechanical ventilator, through patient circuits to an artificial lung, using active heated humidifiers from different manufacturers.

Materials and Methods: This research was completed using a bench test to represent a clinical scenario in which an adult, 75kg patient is ventilated with a Puritan Bennett™ 980 Ventilator (Medtronic, Carlsbad, CA). The ventilator was connected to a patient circuit to deliver air to an artificial lung via an active heated humidifier (Figure 1). Sensirion chips (SHT35, Switzerland) were placed within the system to measure temperature and humidity at the ventilatory inspiratory port, the patient wye, inside the artificial lung, inside the heated artificial lung chamber, at the ventilator expiratory port, and at the ventilator exhalation valve outlet. The humidifiers tested included Fisher & Paykel MR850, Fisher & Paykel MR950, Vincent Medical VHB20, Hamilton H900, and Medline RCI Neptune 425-00, each paired with a matching patient circuit (Table 1). The performance of each humidifier/circuit pair was measured three independent times using, with room temperature set to 23°C±3˚C, 40-70% relative humidity, for 8 hours, using the following ventilator parameters: Assist Control/Volume Control breath mode and type, flow 65L/min, TV 450mL (6mL/Kg), PEEP 5cmH₂O and FiO₂ 21%. The artificial lung and lung chamber were heated to 37°C, and the humidifier was set to default settings to deliver 37°C with 100% relative humidity. Performance was evaluated by measuring the humidity and temperature of air delivered to the patient wye after the system had fully stabilized, as well as quantifying the volume of rainout within the system. Two sample t-tests were used to compare humidifier performance for humidity and temperature, with p<0.05 considered statistically significant.

Results: Across repeat measurements, the mean temperature of the air delivered was 34.3°C ± 0.2, 34.1°C ± 0.2, 35.3°C ± 0.2, 31.8°C ± 0.2, and 34.0°C ± 0.2, for the MR850, MR950, VHB20, H900, and Neptune humidifiers, respectively (Figure 2). In addition, the relative humidity was 100% ± 0.0, 98.9% ± 1.6, 100% ± 0.0, 88.7% ± 1.4, and 98.2% ± 2.5 for the same humidifiers (Figure 2). Together, these indicate an absolute humidity of 38.1mg H₂0/L ± 0.5, 37.4mg H₂0/L ± 0.4, 40.1mg H₂0/L ± 0.4, 29.6mg H₂0/L ± 0.4, and 36.9mg H₂0/L ±0.7 for the MR850, MR950, VHB20, H900, and Neptune humidifiers, respectively, compared to the target of 44mg H₂0/L absolute humidity. Statistical comparisons between humidifiers found that each pair of humidifiers and patient circuit had significant differences in performance, with respect to the temperature and absolute humidity (p<0.001). The rainout observed when using the MR850, MR950, VHB20, or H900 humidifiers was negligible, but the Neptune averaged 19mL ± 8 in the inspiratory circuit, 6mL ± 3 in the expiratory circuit, and 5mL ± 4 in the ventilator expiratory filter (Table 2).

Discussion: Across 5 humidifiers, the VHB20 achieved the closest temperature and relative humidity to the ideal settings of 37°C and 100% relative humidity. The absolute humidity of air delivered by the VHB20 was significantly higher than the MR850, MR950, H900, and Neptune humidifiers. Only the Neptune humidifier generated measurable rainout during the 8hr bench test.

Conclusions: The findings of this bench study demonstrate that active heated humidifiers differ in ability to achieve set temperature and relative humidity. Delivering an accurate absolute humidity is essential to maintaining the health of the respiratory tract during mechanical ventilation.

Acknowledgements: Miguel Sanchez, Alex Honeycutt, Tom Rachlin

References

1. Plotnikow GA, Accoce M, Navarro E, Tiribelli N. Humidification and heating of inhaled gas in patients with artificial airway. A narrative review. Revista Brasileira de terapia intensiva. 2018;30:86-97.


2. Williams R, Rankin N, Smith T, Galler D, Seakins P. Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa. Critical care medicine. 1996;24(11):1920-9.