In vitro and in vivo evaluation of a new active heat moisture exchanger

Fiber Bragg Grating Measuring System for Simultaneous Monitoring of Temperature and Humidity in Mechanical Ventilation

During mechanical ventilation, the humidification of the dry air delivered by the mechanical ventilator is recommended. Among several solutions, heated wire humidifiers (HWHs) have gained large acceptance to be used in this field. The aim of this work is to fabricate a measuring system based on fiber Bragg grating (FBG) for the simultaneous monitoring of gas relative humidity (RH) and temperature, intended to be used for providing feedback to the HWHs' control. This solution can be implemented using an array of two FBGs having a different center wavelength. Regarding RH monitoring, three sensors have been fabricated by coating an FBG with two different moisture-sensitive and biocompatible materials: the first two sensors were fabricated by coating the grating with a 3 mm × 3 mm layer of agar and agarose; to investigate the influence of the coating thickness to the sensor response, a third sensor was developed with a 5 mm × 5 mm layer of agar. The sensors have been assessed in a wide range of RH (up to 95%) during both an ascending and a subsequent descending phase. Only the response of the 3 mm × 3 mm-coated sensors were fast enough to follow the RH changes, showing a mean sensitivity of about 0.14 nm/% (agar-coated) and 0.12 nm/% (agarose-coated). The hysteresis error was about <10% in the two sensors. The contribution of temperature changes on these RH sensors was negligible. The temperature measurement was performed by a commercial FBG insensitive to RH changes. The small size of these FBG-based sensors, the use of biocompatible polymers, and the possibility to measure both temperature and RH by using the same fiber optic embedding an array of two FBGs make intriguing the use of this solution for application in the control of HWHs.

Humidification during mechanical ventilation in the adult patient

Humidification of inhaled gases has been standard of care in mechanical ventilation for a long period of time. More than a century ago, a variety of reports described important airway damage by applying dry gases during artificial ventilation. Consequently, respiratory care providers have been utilizing external humidifiers to compensate for the lack of natural humidification mechanisms when the upper airway is bypassed. Particularly, active and passive humidification devices have rapidly evolved. Sophisticated systems composed of reservoirs, wires, heating devices, and other elements have become part of our usual armamentarium in the intensive care unit. Therefore, basic knowledge of the mechanisms of action of each of these devices, as well as their advantages and disadvantages, becomes a necessity for the respiratory care and intensive care practitioner. In this paper, we review current methods of airway humidification during invasive mechanical ventilation of adult patients. We describe a variety of devices and describe the eventual applications according to specific clinical conditions.

Trocador de calor e umidade: proteção contra infecções pulmonares? Estudo piloto

O objetivo deste trabalho foi realizar um estudo bacteriológico comparativo entre os sistemas de umidificação aquoso aquecido (UAA) e filtro trocador de calor e umidade (FTCU) quanto à colonização bacteriana e a incidência de infecção respiratória em pacientes submetidos à ventilação mecânica (VM). Trata-se de uma pesquisa prospectiva, controlada e randomizada, na qual 15 pacientes internados na Unidade de Terapia Intensiva (UTI) foram distribuídos em dois grupos. O primeiro fez uso de UAA (n=7) e o outro de FTCU (n=8). Foram coletadas amostras da secreção traqueal, condensado do circuito e FTCU na admissão do paciente, no quarto e oitavo dias, e realizada análise bacteriológica dos mesmos. Quanto às características antropométricas, não observou-se diferenças entre os grupos estudados. A prevalência de pneumonia associada à ventilação (PAV) foi de 57,1% no UAA e 62,5% no FTCU. Ao realizar a análise bacteriológica quantitativa entre eles, não foram observadas variações, sugerindo não haver diferença na prevenção de PAV entre os sistemas de umidificação; porém a presença das mesmas bactérias na secreção traqueal e no condensado e ausência destas na membrana do FTCU podem indicar que a principal fonte de contaminação é o próprio paciente.

Discomfort associated with underhumidified high-flow oxygen therapy in critically ill patients

OBJECTIVE

To measure (1) the discomfort in non-intubated patients under high-flow oxygen therapy (HFOT) humidified with bubble (BH) or heated humidifiers (HH), and (2) the hygrometric properties of oxygen with a BH and an HH.

DESIGN AND SETTING

This was a randomized cross-over study in critically ill patients during a 3-day period. The humidification device used at days 1 and 3 was changed for the other at day 2. (2) It was also an experimental bench study using the psychrometric method with five randomized flows (3, 6, 9, 12 and 15 l/min) and different humidification techniques.

METHODS

Discomfort, particularly dryness of the mouth and throat, was measured for two humidification conditions (BH and HH) using a 0-10 numerical rating scale (NRS) by patients requiring HFOT with a face mask at a flow >/=5 l/min, in a double-blinded condition.

RESULTS

(1) In this clinical study, 30 patients treated by HFOT at a median flow of 7.8 l/min (5.1-10.9) were included. The global incidence of moderate (NRS = 4-6) and severe discomfort (NRS = 7-10) was 25 and 29%, respectively. The median intensities of both mouth and throat dryness were significantly lower with the HH than with the BH [7.8 (5.0-9.4) vs. 5.0 (3.1-7.0), P = 0.001 and 5.8 (2.3-8.5) vs. 4.3 (2.0-5.0), P = 0.005, respectively]. (2) In the bench study, the mean absolute humidity measured at an ambient temperature of 26 degrees C with the HH was two times greater than with the BH (30 +/- 1 vs. 16 +/- 2 mg/l, P < 0.05) regardless of the flow rate.

CONCLUSIONS

Compared to bubble humidifiers, the use of a heated-humidifier in patients with high-flow oxygen therapy is associated with a decrease of dryness symptoms mediated by increased humidity delivered to the patient.

Discomfort associated with underhumidified high-flow oxygen therapy in critically ill patients

OBJECTIVE

To measure (1) the discomfort in non-intubated patients under high-flow oxygen therapy (HFOT) humidified with bubble (BH) or heated humidifiers (HH), and (2) the hygrometric properties of oxygen with a BH and an HH.

DESIGN AND SETTING

This was a randomized cross-over study in critically ill patients during a 3-day period. The humidification device used at days 1 and 3 was changed for the other at day 2. (2) It was also an experimental bench study using the psychrometric method with five randomized flows (3, 6, 9, 12 and 15 l/min) and different humidification techniques.

METHODS

Discomfort, particularly dryness of the mouth and throat, was measured for two humidification conditions (BH and HH) using a 0-10 numerical rating scale (NRS) by patients requiring HFOT with a face mask at a flow >/=5 l/min, in a double-blinded condition.

RESULTS

(1) In this clinical study, 30 patients treated by HFOT at a median flow of 7.8 l/min (5.1-10.9) were included. The global incidence of moderate (NRS = 4-6) and severe discomfort (NRS = 7-10) was 25 and 29%, respectively. The median intensities of both mouth and throat dryness were significantly lower with the HH than with the BH [7.8 (5.0-9.4) vs. 5.0 (3.1-7.0), P = 0.001 and 5.8 (2.3-8.5) vs. 4.3 (2.0-5.0), P = 0.005, respectively]. (2) In the bench study, the mean absolute humidity measured at an ambient temperature of 26 degrees C with the HH was two times greater than with the BH (30 +/- 1 vs. 16 +/- 2 mg/l, P < 0.05) regardless of the flow rate.

CONCLUSIONS

Compared to bubble humidifiers, the use of a heated-humidifier in patients with high-flow oxygen therapy is associated with a decrease of dryness symptoms mediated by increased humidity delivered to the patient.

Performance of heated wire humidifiers: an in vitro study

PURPOSE

We assessed the performance of heated wire humidifiers (HWHs), which should avoid water condensation in the circuit.

METHODS

We evaluated the efficiency of 3 HWHs, MR850 (Fisher & Paykel, Auckland, New Zealand), CONCHATHERM IV (Hudson RCI, Temecula, Calif), and DAR HC 2000 (Mallinckrodt DAR, Mirandola, Italy), in comparison with that of the MR730 heated humidifier (HH), which has a standard circuit. We measured gas temperature and absolute humidity (AH) at the Y piece of the ventilatory circuit using a test lung ventilated at 2 minute ventilation volumes (5 and 15 L/min). Temperature levels at the Y piece of the ventilatory circuit of the HHs were set at 35 degrees C, 37 degrees C, and 39 degrees C with different gradients (-2 degrees C, 0 degrees C, and +2 degrees C) between the outlet chamber and the Y piece of the ventilatory circuit.

RESULTS

At the set temperature levels of 35 degrees C, 37 degrees C, and 39 degrees C with a gradient of 0 degrees C, the MR850 and CONCHATHERM IV had lower gas temperature and AH levels as compared with the DAR HC 2000 and MR730 HH. With increasing temperature gradient, gas temperature increased only with the CONCHATHERM IV but AH increased with all the HWHs. The MR850 showed lower gas temperature and AH levels as compared with CONCHATHERM IV. The condensate was abolished inside the inspiratory circuit with the HWHs.

CONCLUSIONS

Heated wire humidifiers eliminate water condensation but present significant differences in gas temperature and AH levels that are lower than the expected settings.

Year in review in Critical Care, 2003 and 2004: respirology and critical care

We summarize all original research in the field of respirology and critical care published in 2003 and 2004 in Critical Care. Articles were grouped into the following categories to facilitate a rapid overview: pathophysiology, therapeutic approaches, and outcome in acute lung injury and acute respiratory distress syndrome; hypoxic pulmonary arterial hypertension; mechanical ventilation; liberation from mechanical ventilation and tracheostomy; ventilator-associated pneumonia; multidrug-resistant infections; pleural effusion; sedation and analgesia; asthma; and techniques and monitoring.