A drop in gas temperature in the external part of the endotracheal tube is problematic during neonatal respiratory support

The Effect of 2 Humidifier Temperature Settings on Inspired Gas Temperatures and the Physiological Parameters of Preterm Infants Receiving Mechanical Ventilation Therapy

BACKGROUND

The use of heated and humidified gas during mechanical ventilation is routine care in neonatal intensive care units. Giving gas at inadequate heat and humidity levels can affect neonatal morbidity and mortality.

PURPOSE

To compare the effects of 2 humidifier temperature settings on the temperature and humidity of the inspired gas and the physiologic parameters in preterm newborns receiving mechanical ventilation.

METHODS

The research was conducted in a single-group quasi-experimental design. Proximal temperature was measured using a humidity heat transmitter. The humidifier temperature was set at 38°C (temperature I) and then at 39°C (temperature II).

RESULTS

The mean proximal temperatures were significantly lower than the values set in the humidifier (33.8 ± 1.20°C at temperature I, and 34.06 ± 1.30°C at temperature II, P < .001). However, the difference between the 2 proximal temperatures was not significant (P = .162). The incubator temperature was found to be effective on the proximal gas temperature (P < .05). It was found that only preterm infants in the temperature II group had a higher mean heart rate (P < .05).

IMPLICATIONS FOR PRACTICE

Incubator temperatures may have an effect on inspired gas temperature in preterm infants who are mechanically ventilated and caregivers should be aware of these potentially negative effects.

IMPLICATIONS FOR RESEARCH

Future studies should focus on how to measure the temperature and humidity of gas reaching infants in order to prevent heat and humidity losses.

Airway gas temperature within endotracheal tube can be monitored using rapid response thermometer

Inappropriate preparation of respiratory gases is associated with serious complications during mechanical ventilation. To develop a temperature monitoring system of respiratory gases within the endotracheal tube, four newborn piglets were studied using an ultra-rapid-response thermometer attached to the closed endotracheal tube suction system. Respiratory gas temperatures were monitored at the mouth-corner level of the endotracheal tube using three thermocouples (T_airway, inserted into the endotracheal tube via the closed suction system; T_{tube_centre} and T_{tube_wall}, embedded within the endotracheal tube 0.5 mm and 1.6 mm from the tube wall, respectively). Univariate analysis showed that inspiratory T_{tube_centre} and inspiratory T_{tube_wall} were positively correlated with inspiratory T_airway (both p < 0.001). Multivariate analysis showed the dependence of inspiratory T_airway on inspiratory T_{tube_centre} and T_{tube_wall} and deflation of endotracheal tube cuff (p < 0.001, p = 0.001 and p = 0.046, respectively). Inspiratory gas temperature within the endotracheal tube can be monitored using a thermometer attached to the closed endotracheal tube suction system. Our system, with further validation, might help optimise respiratory gas humidification during mechanical ventilation.

Temperature and Humidity Associated With Artificial Ventilation in the Premature Infant: An Integrative Review of the Literature

BACKGROUND

Approximately half of the 55,000 very low birth-weight infants (<1500 g) born in the United States each year develop bronchopulmonary dysplasia (BPD). Many etiologies have been associated with the development of BPD, including aberrant temperature/humidity levels of artificial ventilation.

PURPOSE

The purpose of this literature review is to explore what is known regarding inspired air temperature/humidity levels from artificial ventilation in very premature infants, focusing on what levels these infants actually receive, and what factors impact these levels.

METHODS/SEARCH STRATEGY

PubMed, CINAHL, Scopus, and Web of Science were searched. Of the 830 articles retrieved, 23 were synthesized for study purpose, sample/study design, and temperature/humidity findings.

FINDINGS/RESULTS

Heating and humidification practices studied in neonatal ventilation did not maintain recommended levels. In addition, human neonatal studies and noninvasive neonatal ventilation research were limited. Furthermore, ventilation settings, environmental temperatures, and mouth position (in noninvasive ventilation) were found to impact temperature/humidity levels.

IMPLICATIONS FOR PRACTICE

Environmental temperatures and ventilatory settings merit consideration during artificial ventilation. In addition, aberrant temperature/humidity levels may impact infant body temperature stability; thus, employing measures to ensure adequate thermoregulation while receiving artificial ventilation must be a priority.

IMPLICATIONS FOR RESEARCH

This review underscores the need for further research into current warming and humidification techniques for invasive and noninvasive neonatal ventilation. A focus on human studies and the impact of aberrant levels on infant body temperature are needed. Future research may provide management options for achieving and maintaining target temperature/humidity parameters, thus preventing the aberrant levels associated with BPD.

A case of pulmonary artery sling where onset Was induced by therapeutic hypothermia

A neonate with severe neonatal asphyxia was treated with therapeutic hypothermia. He developed hypothermia-induced respiratory deterioration, after which congenital tracheal stenosis and pulmonary artery sling were diagnosed. Even low-grade hypothermia is likely to induce bronchial narrowing in neonates, especially in neonates with congenital respiratory tract anomalies. Congenital tracheal stenosis represents a potential pitfall in differential diagnosis and should be carefully ruled out in cases of bronchial narrowing episode induced by therapeutic hypothermia. Pediatr Pulmonol. 2017;52:E7-E10. © 2016 Wiley Periodicals, Inc.

Influence of mouth opening on oropharyngeal humidification and temperature in a bench model of neonatal continuous positive airway pressure

Clinical studies show that non-invasive respiratory support by continuous positive airway pressure (CPAP) affects gas conditioning in the upper airways, especially in the presence of mouth leaks. Using a new bench model of neonatal CPAP, we investigated the influence of mouth opening on oropharyngeal temperature and humidity. The model features the insertion of a heated humidifier between an active model lung and an oropharyngeal head model to simulate the recurrent expiration of heated, humidified air. During unsupported breathing, physiological temperature and humidity were attained inside the model oropharynx, and mouth opening had no significant effect on oropharyngeal temperature and humidity. During binasal CPAP, the impact of mouth opening was investigated using three different scenarios: no conditioning in the CPAP circuit, heating only, and heated humidification. Mouth opening had a strong negative impact on oropharyngeal humidification in all tested scenarios, but heated humidification in the CPAP circuit maintained clinically acceptable humidity levels regardless of closed or open mouths. The model can be used to test new equipment for use with CPAP, and to investigate the effects of other methods of non-invasive respiratory support on gas conditioning in the presence of leaks.

Use of Normothermic Default Humidifier Settings Causes Excessive Humidification of Respiratory Gases During Therapeutic Hypothermia

Adult patients frequently suffer from serious respiratory complications during therapeutic hypothermia. During therapeutic hypothermia, respiratory gases are humidified close to saturated vapor at 37°C (44 mg/L) despite that saturated vapor reduces considerably depending on temperature reduction. Condensation may cause serious adverse events, such as bronchial edema, mucosal dysfunction, and ventilator-associated pneumonia during cooling. To determine clinical variables associated with inadequate humidification of respiratory gases during cooling, humidity of inspiratory gases was measured in 42 cumulative newborn infants who underwent therapeutic hypothermia. Three humidifier settings of 37-default (chamber outlet, 37°C; distal circuit, 40°C), 33.5-theoretical (chamber outlet, 33.5°C; distal circuit, 36.5°C), and 33.5-adjusted (optimized setting to achieve 36.6 mg/L using feedback from a hygrometer) were tested to identify independent variables of excessively high humidity >40.7 mg/L and low humidity <32.9 mg/L. The mean (SD) humidity at the Y-piece was 39.2 (5.2), 33.3 (4.1), and 36.7 (1.2) mg/L for 37-default, 33.5-theoretical, and 33.5-adjusted, respectively. The incidence of excessive high humidity was 10.3% (37-default, 31.0%; 33.5-theoretical, 0.0%; 33.5-adjusted, 0.0%), which was positively associated with the use of a counter-flow humidifier (p < 0.001), 37-default (compared with 33.5-theoretical and 33.5-adjusted, both p < 0.001) and higher fraction of inspired oxygen (p = 0.003). The incidence of excessively low humidity was 17.5% (37-default, 7.1%; 33.5-theoretical, 45.2%; 33.5-adjusted, 0.0%), which was positively associated with the use of a pass-over humidifier and 33.5-theoretical (both p < 0.001). All patients who used a counter-flow humidifier achieved the target gas humidity at the Y-piece (36.6 ± 0.5 mg/L) required for 33.5-adjusted with 33.5-theoretical. During cooling, 37-default is associated with excessively high humidity, whereas 33.5-theoretical leads to excessively low humidity. Future studies are needed to assess whether a new regimen with optimized Y-piece temperature and humidity control reduces serious respiratory adverse events during cooling.

The temperature change in an endotracheal tube during high frequency ventilation using an artificial neonatal lung model with Babylog® 8000 plus

OBJECTIVE

There is little available data on airway humidity during high-frequency ventilation (HFV). The purpose of this study is to evaluate the temperature drop in an endotracheal tube (ETT) during HFV.

METHODS

We examined the airway temperature in a neonatal HFV system using Babylog® 8000 plus. We measured the temperature change of inspired gases in the ETT under various oscillatory frequencies and oscillatory volumes with a fixed base flow. The temperatures in the ETT during HFV were compared with the temperatures during conventional intermittent positive pressure ventilation (IPPV).

RESULTS

As the oscillatory frequency was increased and the oscillatory volume (VThf) decreased, the difference in temperature between the Y piece and the inlet of an artificial lung in the ETT (ETT outside of body) increased. However, as the oscillatory frequency increased, there was no difference in the ETT temperature under constant oscillatory volume. In contrast, as the oscillatory volume was decreased, the difference in temperature in the ETT was greater under constant oscillatory frequency. Moreover, the temperature drop in the ETT with HFV was lower than that in the IPPV temperature with a similar respiratory volume.

CONCLUSIONS

The temperature change in the ETT was not dependent on the oscillatory frequency when the oscillatory volume was fixed; however, the temperature was dependent on the oscillatory volume when the oscillatory frequency was fixed.

Mechanical ventilation with heated humidifiers: measurements of condensed water mass within the breathing circuit according to ventilatory settings

Heated wire humidifiers (HWHs) are widely used to heat and humidify gases during mechanical ventilation. The control strategy implemented on commercial HWHs, based on maintaining constant gas temperature at the chamber outlet, shows weaknesses: humidifying performances depend on environmental temperature and ventilatory settings, and often condensation occurs. Herein, we analyzed in vitro HWH performances focusing on the condensation amount according to ventilatory settings. We used a physical model to define the parameters which mainly influence the HWH performances. In order to investigate the influence of minute volume (MV) and frequency rate (fr) on condensation, the other influencing parameters were kept constant during experiments, and we introduced a novel approach to estimate the condensation. The method, based on measuring the condensed vapor mass (Δm), provided more objective information than the visual-based scale used in previous studies. Thanks to both the control of other influencing factors and the accurate Δm measures, the investigation showed the Δm increase with MV and fr. Substantial condensation after 7 h of ventilation and the influence of MV and fr on Δm (i.e., Δm = 3 g at MV = 1.5 L min(-1) and fr = 8 bpm and Δm = 9.4 g at MV = 8 L min(-1) and fr = 20 bpm) confirm the weaknesses of `single-point temperature' control strategies.

An overview of recent applications of computational modelling in neonatology

This paper reviews some of our recent applications of computational fluid dynamics (CFD) to model heat and mass transfer problems in neonatology and investigates the major heat and mass-transfer mechanisms taking place in medical devices, such as incubators, radiant warmers and oxygen hoods. It is shown that CFD simulations are very flexible tools that can take into account all modes of heat transfer in assisting neonatal care and improving the design of medical devices.