Tracheobronchial consequences of the use of heat and moisture exchangers in dogs

Comparison of the temperature and humidity in the anesthetic breathing circuit among different anesthetic workstations: Updated guidelines for reporting parallel group randomized trials

BACKGROUND

For patients undergoing general anesthesia, adequate warming and humidification of the inspired gases is very important. The aim of this study was to evaluate the differences in the heat and moisture content of the inspired gases with low-flow anesthesia using 4 different anesthesia machines.

METHODS

The patients were divided into 11 groups according to the anesthesia machine used (Ohmeda, Excel; Avance; Dräger, Cato; and Primus) and the fresh gas flow (FGF) rate (0.5, 1, and 4 L/min). The temperature and absolute humidity of the inspired gas in the inspiratory limbs were measured at 5, 10, 15, 30, 45, 60, 75, 90, 105, and 120 minutes in 9 patients scheduled for total thyroidectomy or cervical spine operation in each group.

RESULTS

The anesthesia machines of Excel, Avance, Cato, and Primus did not show statistically significant changes in the inspired gas temperatures over time within each group with various FGFs. They, however, showed statistically significant changes in the absolute humidity of the inspired gas over time within each group with low FGF anesthesia (P < .05). The anesthesia machines of Cato and Primus showed statistically significant changes in the absolute humidity of the inspired gas over time within each group with an FGF of 4 L/min (P < .05). However, even with low-flow anesthesia, the temperatures and absolute humidities of the inspired gas for all anesthesia machines were lower than the recommended values.

CONCLUSION

There were statistical differences in the provision of humidity among different anesthesia workstations. The Cato and Primus workstations were superior to Excel and Avance. However, even these were unsatisfactory in humans. Therefore, additional devices that provide inspired gases with adequate heat and humidity are needed for those undergoing general anesthetic procedures.

The Humidity in a Low-Flow Dräger Fabius Anesthesia Workstation with or without Thermal Insulation or a Heat and Moisture Exchanger: A Prospective Randomized Clinical Trial

Background

During anesthesia, as compared with intensive care, the time of the tracheal intubation is much shorter. An inhaled gas minimum humidity of 20 mgH₂O.L^-1 is recommended to reduce the deleterious effects of dry gas on the airways during anesthesia with tracheal intubation. The Fabius GS Premium® anesthesia workstation (Dräger Medical, Lübeck, Germany) has a built-in hotplate to heat gases in the breathing circuit. A heat and moisture exchanger (HME) is used to further heat and humidify the inhaled gas. The humidity of the gases in the breathing circuit is influenced by the ambient temperature. We compared the humidity of the inhaled gases from a low-flow Fabius anesthesia workstation with or without thermal insulation (TI) of the breathing circuit and with or without an HME.

Methods

We conducted a prospective randomized trial in 41 adult female patients who underwent elective abdominal surgery. The patients were allocated into four groups according to the devices used to ventilate their lungs using a Dräger Fabius anesthesia workstation with a low gas flow (1 L.min^-1): control, with TI, with an HME or with TI and an HME (TIHME). The mean temperature and humidity of the inhaled gases were measured during 2-h after connecting the patients to the breathing circuit.

Results

The mean inhaled gas temperature and absolute humidity were higher in the HME (29.2±1.3°C; 28.1±2.3 mgH₂O·L^-1) and TIHME (30.1±1.2°C; 29.4±2.0 mgH₂O·L^-1) groups compared with the control (27.5±1.0°C; 25.0±1.8 mgH₂O·L^-1) and TI (27.2±1.1°C; 24.9±1.8 mgH₂O·L^-1) groups (P = 0.003 and P<0.001, respectively).

Conclusions

The low-flow Fabius GS Premium breathing circuit provides the minimum humidity level of inhaled gases to avoid damage to the tracheobronchial epithelia during anesthesia. TI of the breathing circuit does not increase the humidity of the inhaled gases, whereas inserting an HME increases the moisture of the inhaled gases closer to physiological values.

Larynx and Cervical Trachea in Humidification and Heating of Inhaled Gases

To evaluate the participation of the larynx and cervical trachea in conditioning inspired gases, we randomly allocated 16 mixed-breed dogs to two groups: group TT (tracheal tube; n = 8) and group LMA (laryngeal mask airway; n = 8). The dogs were anesthetized with pentobarbital sodium and mechanically ventilated for 3 hours. The parameters studied were temperature and absolute humidities of ambient, inhaled, and tracheal air. There was a small increase in tracheal air temperature compared to inhaled air temperature, but no significant difference between groups. The absolute humidity of tracheal air was greater in group LMA than in group TT (23 mg H2O • L–1 and 14 mg H2O • L–1, respectively; p < .0001). The difference in absolute humidity between the tracheal air and the inhaled air was higher in group LMA at all times (p < .0001). We conclude that the larynx and cervical trachea of the dog participate in humidification and heating of inhaled air by means of air contact with mucosa in this airway segment.

The humidity in a Dräger Primus anesthesia workstation using low or high fresh gas flow and with or without a heat and moisture exchanger in pediatric patients

BACKGROUND

An inhaled gas absolute humidity of 20 mg H2O·L is the value most considered as the threshold necessary for preventing the deleterious effects of dry gas on the epithelium of the airways during anesthesia. Because children have small minute ventilation, we hypothesized that the humidification of a circle breathing system is lower in children compared with adults. The Primus anesthesia workstation (Dräger Medical, Lübeck, Germany) has a built-in hotplate to heat the patient's exhaled gases. A heat and moisture exchanger (HME) is a device that can be used to further humidify and heat the inhaled gases during anesthesia. To evaluate the humidifying properties of this circle breathing system during pediatric anesthesia, we compared the temperature and humidity of inhaled gases under low or high fresh gas flow (FGF) conditions and with or without an HME.

METHODS

Forty children were randomly allocated into 4 groups according to the ventilation of their lungs by a circle breathing system in a Dräger Primus anesthesia workstation with low (1 L·min) or high (3 L·min) FGF without an HME (1L and 3L groups) or with an HME (Pall BB25FS, Pall Biomedical, East Hills, NY; HME1L and HME3L groups). The temperature and absolute humidity of inhaled gases were measured at 10, 20, 40, 60, and 80 minutes after connecting the patient to the breathing circuit.

RESULTS

The mean inhaled gas temperature was higher in HME groups (HME1L: 30.3°C ± 1.1°C; HME3L: 29.3°C ± 1.2°C) compared with no-HME groups (1L: 27.0°C ± 1.2°C; 3L: 27.1°C ± 1.5°C; P < 0.0001). The mean inhaled gas absolute humidity was higher in HME than no-HME groups and higher in low-flow than high-flow groups ([HME1L: 25 ± 1 mg H2O·L] > [HME3L: 23 ± 2 mg H2O·L] > [1L: 17 ± 1 mg H2O·L] > [3L: 14 ± 1 mg H2O·L]; P < 0.0001).

CONCLUSIONS

In a pediatric circle breathing system, the use of neither high nor low FGF provides the minimum humidity level of the inhaled gases thought to reduce the risk of dehydration of airways. Insertion of an HME increases the humidity and temperature of the inhaled gases, bringing them closer to physiological values. The use of a low FGF enhances the HME efficiency and consequently increases the inhaled gas humidity values. Therefore, the association of an HME with low FGF in the breathing circuit is the most efficient way to conserve the heat and the moisture of the inhaled gas during pediatric anesthesia.

Morphological findings in the tracheal epithelium of dogs exposed to the inhalation of poorly conditioned gases under use of an endotracheal tube or laryngeal mask airway

PURPOSE

To study morphological findings in the tracheal epithelium of dogs exposed to the inhalation of poorly conditioned gases under use of an endotracheal tube (ET) or laryngeal mask airway (LMA).

METHODS

Twelve dogs randomly were allocated to two groups: ET group (n-6) and LMA group (n-6), anaesthetized and mechanically ventilated, without CO(2) reabsorption. Haemodynamic and ventilatory parameters, tympanic temperature, temperature, relative and absolute humidity of the ambient and inhaled gases were analyzed during three hours. The animals were submitted to euthanasia and biopsies were carried out along the tracheal segment to morphological study. Three healthy dogs were used to morphological control.

RESULTS

Inhaled gas temperature was maintained between 24ºC and 26ºC, relative humidity between 10% and 12%, and absolute humidity between 2 - 3 mg H(2)O.L(-1) with no significant differences between groups. In both groups, histological analysis showed epithelial inflammation and congestion in the corion and scanning electron microscopy showed ciliary grouping and disorganization. Transmission electron microscopy showed higher alterations in ET group than LMA group as widening of cell junctions, ciliary disorientation, cytoplasmic vacuolization, nuclear abnormalities, picnosis and chromatin condensation.

CONCLUSION

LMA determined less pronounced changes in the tracheal epithelium in dogs exposed to the inhalation of poorly conditioned gases.

The temperature and humidity in a low-flow anesthesia workstation with and without a heat and moisture exchanger

BACKGROUND

The Dräger Primus anesthesia workstation has a built-in hotplate to heat the patient's exhaled gas. The fresh gas flow is mixed with the heated exhaled gas as they pass through the soda lime canister. A heat and moisture exchanger (HME) may also be used to further heat and humidify the inhaled gas. In this study we measured the temperature and humidity of the inhaled gas coming from the Dräger Primus with or without a HME.

METHODS

Thirty female patients were randomly divided into 2 groups and their lungs ventilated by the Primus Dräger anesthesia workstation with or without a HME. The humidity and temperature of the inhaled gas were measured 15, 30, 60, 90, and 120 minutes after connecting the patient to the breathing circuit.

RESULTS

After 120 minutes of ventilation with a low-flow breathing circuit, the temperatures of inhaled gas were 25°C ± 1°C and 30°C ± 2°C without and with HME, respectively, with a statistically significant difference between groups (P < 0.001) with 95% confidence interval (CI) of 3.80°C to 6.40°C; and the absolute humidity values of the inhaled gas were 20.5 ± 3.6 mgH(2)O · L(-1) and 30 ± 2 mgH(2)O · L(-1) without and with HME, respectively, with a statistically significant difference between groups (P < 0.001) with 95% CI of 7.37°C to 13.03°C.

CONCLUSIONS

The Primus anesthesia workstation partially humidifies the inspired gas when a low fresh gas flow is used. Insertion of an HME increases the humidity in inhaled gas, bringing it close to physiological values.

The effect of heat-moisture exchanger and closed-circuit technique on airway climate during desflurane anesthesia

PURPOSE

We assessed whether closed-circuit anesthesia (CCA) could provide a more favorable airway climate than semi-closed anesthesia (SCA), and we also determined the beneficial effect of heat moisture exchangers (HMEs) on the preservation of airway climate during desflurane anesthesia.

METHODS

Forty patients scheduled for colorectal surgery (n = 10 for each group) were randomized to receive a fresh gas flow of 250 or 3000 ml.min(-1) with or without HMEs. Anesthesia was maintained by adjusting the inspired concentration of 6% desflurane. Absolute moisture and temperature of inspired gases were measured as the baseline value first at 5 min after tracheal intubation, and then at 10, 20, 45, 60, 90, and 120 min after the induction of anesthesia.

RESULTS

At 120 min, the inspiratory humidity and temperature were higher in CCA than in SCA. The HME led to major improvements of the humidity (from 22.1 to 35.7 mg H(2)O.l(-1)) and temperature (from 23.6 degrees C to 31.5 degrees C) of anesthetic gases in the CCA group.

CONCLUSION

CCA was much more advantageous than SCA for maintaining the patient's airway climate during the 2-h study. The beneficial effect of HME on the airway climate should be emphasized, especially in patients undergoing general anesthesia.

Influence of passive humidification on nasal conditioning

BACKGROUND

Passive humidifiers (PH) have been beneficial to upper and lower airway humidity, especially in patients who are in a long-time ventilated intensive care unit. The goal of this pilot study was to provide nasal conditioning data and measure the benefit of a nasal PH to spontaneously breathing, conscious subjects.

METHODS

Eleven healthy volunteers had to wear a PH for 1 hour, which was introduced into both nasal vestibules. The PH had a heat and moisture restoring body of polyurethane foam with an open-pore structure. Before and after application of the nasal PH, nasal conditioning was measured and nasal symptoms were assessed by the participants.

RESULTS

Ten minutes after removal of the PH a significant increase was observed for the scores for nasal patency and nasal humidity.

CONCLUSION

We hypothesize that the nasal PH could provide a valuable contribution to the supportive therapy of diseases that accompany nasal mucosal dryness.

Effect of heat and moisture exchanger (HME) positioning on inspiratory gas humidification

Background

In mechanically ventilated patients, we investigated how positioning the heat and moisture exchanger (HME) at different places on the ventilator circuit affected inspiratory gas humidification.

Methods

Absolute humidity (AH) and temperature (TEMP) at the proximal end of endotracheal tube (ETT) were measured in ten mechanically ventilated patients. The HME was connected either directly proximal to the ETT (Site 1) or at before the circuit Y-piece (Site 2: distance from proximal end of ETT and Site 2 was about 19 cm) (Figure. 1). Two devices, Hygrobac S (Mallinckrodt Dar, Mirandola, Italy) and Thermovent HEPA (Smiths Medical International Ltd., Kent, UK) were tested. AH and TEMP were measured with a hygrometer (Moiscope, MERA Co., Ltd., Tokyo, Japan).

Results

Hygrobac S provided significantly higher AH and TEMP at both sites than Thermovent HEPA. Both Hygrobac S and with Thermovent HEPA provided significantly higher AH and TEMP when placed proximally to the ETT.

Conclusion

Although placement proximal to the ETT improved both AH and TEMP in both HMEs tested, one HME performed better in the distal position than the other HME in the proximal position. We conclude the both the type and placement of HME can make a significant difference in maintaining AH and TEMP during adult ventilation.

The Lanz® endotracheal tube decreases tracheal injury in dogs

PURPOSE

To determine, in dogs anesthetized with nitrous oxide (N2O), (whether the endotracheal tube (ETT) cuffed with a Lanz pressure regulating valve decreases the tracheal consequences of tracheal intubation.

METHODS

Sixteen mixed-breed dogs were allocated to two groups according to the ETT used: Control group (n = 8) - Rüsch ETT, and Lanz group (n = 8) - ETT with Lanz pressure regulating valve. The ETT cuffs in both groups were inflated with air to an intracuff pressure of 30 cm H2O. Anesthesia was induced and maintained with pentobarbitone and N2O (1.5 L x min(-1)) and O2 (1 L x min(-1)). ETT cuff pressures were measured before (control) and 60, 120, and 180 min during N2O administration. The dogs were sacrificed, and biopsy specimens from four predetermined areas of the tracheal mucosa in contact with the ETT were collected for light and scanning electron microscopy (SM) examination.

RESULTS

Cuff pressures in the Control group were higher than in the Lanz group at all time points studied (P < 0.001), with an increase over time only in the Control group (P < 0.001). Median neutrophilic inflammatory infiltration values of the epithelial surface, and in the subepithelial layer in contact with the cuff, were higher in the Control group as compared to the Lanz group (3.0 vs 1.0 and 3.0 vs 1.5 respectively) (P < 0.05). On SM examination, median histological grades were higher in the Control group compared to Lanz group (2.9 vs 1.9 respectively), (P < 0.05).

CONCLUSIONS

The Lanz ETT decreases tracheal mucosal injury in dogs.

Complicações das vias aéreas relacionadas à intubação endotraqueal

Descrevemos as principais complicações das vias aéreas relacionadas à intubação endotraqueal, por meio de revisão da literatura e apresentação dos resultados de pesquisas clínicas e experimentais realizadas pelo nosso grupo de estudo. Procuramos alertar os profissionais de saúde quanto à alta incidência de complicações secundárias à intubação, as quais podem ser reduzidas com a adoção de medidas profiláticas simples e de cunho prático, estabelecidas após a compreensão da fisiopatologia das lesões.