Respiratory gas conditioning in infants with an artificial airway

Effect of inspired gas temperature on lung mechanics and gas exchange in neonates in normothermia or therapeutic hypothermia

BACKGROUND

Respiratory critical care guidelines suggest heating the air/oxygen mixture but do not recommend a specific temperature target. We aimed to clarify if the inspired gas temperature influences lung mechanics and gas exchange in intubated patients treated with whole body hypothermia (WBH) or normothermia (NT).

METHODS

Prospective cohort study enrolling neonates ventilated for perinatal asphyxia resuscitation (no lung disease) or acute hypoxemic respiratory failure. Patients were divided between those ventilated in NT or WBH. Compliance (Cdyn), airway resistances (Raw), oxygenation index (OI), PaO2/FiO2, A-a gradient, a/A ratio, estimated alveolar dead space (VDalv), ventilatory index (VI) and CO2 production (VCO2) were registered at the study beginning (inspired gas at 37°C). Then, gas temperature was decreased (32 °C) and variables were recorded again after 1 and 3 h. Data were analysed with univariate and multivariate repeated measures-ANOVA.

RESULTS

Cdyn, Raw, OI, PaO2/FiO2, A-a gradient, a/A ratio, VDalv, VI and VCO2 are similar between WBH and NT at any timepoint (between-subjects effect); these results do not change adjusting for the presence of respiratory failure. When this is considered in multivariate ANOVA (within-subjects effect), Cdyn (p = 0.016), Raw (p = 0.034) and VDalv (p < 0.001) were worse in patients with respiratory failure than in those without lung disease.

CONCLUSIONS

Decreasing the gas temperature from 37 °C to 32 °C for 3 h does not change lung mechanics and gas exchange, neither in neonates with, nor in those without respiratory failure and in those treated in NT or WBH. These findings fill a knowledge gap regarding the effect of inspired gas temperature during WBH: they may inform future respiratory critical care guidelines.

An evaluation of temperature stability and resistance in neonatal ventilator circuits

Background

Gas conditioning minimizes complications associated with invasive ventilation of neonates. Poorly conditioned gas contributes to humidity deficit, facilitates condensate pools, and contributes to safety events. The specific aim was to objectively quantify the temperature drop across the unheated portion of a neonatal circuit and the impact condensation has to resistance to flow in the ventilator circuit.

Methods

Ventilator circuits and filters were obtained, assembled according to manufacturer recommendations, and operational verification procedures were performed prior to data collection. A neonatal test lung was connected to each Servo-I ventilator with the following settings: pressure control IMV mode; inspiratory pressure: 14 cm H₂O to achieve an exhaled tidal volume of 6.0 mL; PEEP: 5 cm H₂O; pressure support: 5 cm H₂O, F_IO_2: 0.21; set frequency 40/min; and inspiratory time: 0.4 s. The Fisher and Paykel MR850 and ChonchaTherm Neptune heaters were set at a temperature of 40°C. To evaluate both systems under similar conditions, the ChonchaTherm Neptune heater humidity control was set to midline. Heaters were turned on simultaneously and given 1 h to equilibrate. Readings for room temperature, airway temperature at the patient connection, airway resistance, exhaled tidal volume, and direct observation of circuit condensation and (or) pooling were recorded hourly for a 48-h period. Summary statistics were calculated for the variables of interest.

Results

Mean (±SD) air temperature was 26.3°C (±1.4) for the Fisher & Paykel MR850 system and 26.2°C (±1.5), for the ChonchaTherm Neptune system. Mean (±SD) airway resistance was 229.3 cm H₂O/L/s (±81.0) for the Fisher & Paykel system and 196.2 cm H₂O/L/s (±39.4) for the ChonchaTherm Neptune system. Mean (±SD) tidal volume for the Fisher & Paykel MR850 system was 6.5 mL (±0.4), and for the ChonchaTherm Neptune system was 7.2 mL (±0.6).

Conclusion

Circuit condensate increased tidal volume delivery and airway resistance. Temperature at the patient connection was lower than the temperature monitored by the system 12 inches distally, which can negatively impact gas conditioning.

Tracheostomy in Infants in the Neonatal Intensive Care Unit

Approximately half of all pediatric tracheostomies are performed in infants younger than 1 year. Most tracheostomies in patients in the NICU are performed in cases of chronic respiratory failure requiring prolonged mechanical ventilation or upper airway obstruction. With improvements in ventilation and management of long-term intubation, indications for tracheostomy and perioperative management in this population continue to evolve. Evidence-based protocols to guide routine postoperative care, prevent and manage tracheostomy emergencies including accidental decannulation and tube obstruction, and attempt elective decannulation are sparse. Clinician awareness of safe tracheostomy practices and larger, prospective studies in infants are needed to improve clinical care of this vulnerable population.

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.

Predictors of unfavorable thermal outcome during newborn emergency retrievals

OBJECTIVE

Maintenance of normal body temperature is a challenge during transports. We aimed to identify predisposing factors for unfavorable thermal outcome during emergency retrievals of neonates.

METHODS

Demographic data and clinical variables for transports performed over a 2-year period were extracted from the Newborn Emergency Transport Service (Victoria, Australia) database. Arrival temperatures outside normothermia (36.5°-37.5°C) were defined as an unfavorable outcome.

RESULTS

Normothermia on arrival at the receiving hospital was achieved in 78% of 1,261 transports. The strongest predictor of unfavorable thermal outcome was an abnormal temperature at the start of the retrieval (odds ratio [OR] = 8.04; 95% confidence interval [CI], 5.91-10.95; P < .001) followed by very low weight on transport (< 1,500 g; OR = 2.49; 95% CI, 1.63-3.80; P < .001) and respiratory support (OR = 1.81; 95% CI, 1.29-2.54; P = .001). Medications (eg, inotropes and sedation/muscle relaxation) or central/peripheral venous/arterial lines were not significant predictors of outcome when temperature at retrieval start, weight at transport, and respiratory support were adjusted as cofactors. Mode of transport (road, fixed wing, or rotary wing aircraft) and outside temperature were not associated with thermal outcome.

CONCLUSION

Abnormal temperature at the start of the retrieval, very low transport weight, and respiratory support were strong predictors of unfavorable thermal outcome during neonatal emergency transports.

Aerosol delivery to ventilated newborn infants: historical challenges and new directions

There are several aerosolized drugs which have been used in the treatment of neonatal respiratory illnesses, such as bronchodilators, diuretics, and surfactants. Preclinical in vitro and in vivo studies identified a number of variables that affect aerosol efficiency, including particle size, aerosol flows, nebulizer choice, and placement. Nevertheless, an optimized aerosol drug delivery system for mechanically ventilated infants still does not exist. Increasing interest in this form of drug delivery requires more controlled and focused research of drug/device combinations appropriate for the neonatal population. In the present article, we review the research that has been conducted thus far and discuss the next steps in developing the optimal aerosol delivery system for use in mechanically ventilated neonates.

Humidified and heated air during stabilization at birth improves temperature in preterm infants

OBJECTIVE

Neonatal resuscitation guidelines recommend techniques to minimize heat loss in the delivery room. The use of humidified and heated gas is standard of care for preterm infants who need respiratory support in the NICU, but international resuscitation guidelines do not stipulate use of this therapy during stabilization at birth. We aimed to investigate the effect of humidified and heated gas on admission temperature in preterm infants who require respiratory support at birth.

METHODS

Two cohorts of very preterm infants born at < or = 32 weeks' gestational age in the Leiden University Medical Center were compared prospectively before (the "cold" cohort) and after (the "heated" cohort) introduction of the use of heated and humidified gas during respiratory support at birth (continuous positive airway pressure or intubation). The primary outcome was the infant's rectal temperature at admission in the NICU.

RESULTS

There was a difference in the mean (SD) rectal temperature between the cold and heated cohorts (35.9 [0.6] vs 36.4 [0.6], respectively; P < .0001). Normothermia (36.5 degrees C-37.5 degrees C) occurred less often in the cold cohort than in the heated cohort (12% vs 43%; P < .0001). There was no difference in occurrence of mild hypothermia (36.0 degrees C-36.4 degrees C) between groups (33% vs 35%; not significant). Moderate hypothermia (<36.0 degrees C) occurred more often in the cold cohort (53% vs 19%; P < .001).

CONCLUSIONS

The use of heated and humidified air during respiratory support in very preterm infants just after birth reduced the postnatal decrease in temperature. Heating and humidifying the gas during stabilization merits additional investigation.

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

During neonatal respiratory support, maintaining optimal humidity minimizes the risk of airway occlusion and chronic lung disease. With neonatal respiratory support using a heated humidifier,condensation following decreases in temperature within the unheated part of the inspiratory circuit represents a serious problem, due to the resulting drop in absolute humidity. Several reports describing the temperature/humidity gradient in the unheated inspiratory limb have excluded the endotracheal tube (ETT). The present study investigated the extent to which the temperature gradient in the ETT affects breathing gas conditioning in premature infants, who display tiny minute volumes. By measuring temperature/dew point at various sites along the inspiratory circuit, including inside the ETT, we evaluated the effects of temperature change in the ETT using an in vitro model of a micropremie on mechanical respirator care in an incubator. We confirmed significant moisture loss (absolute humidity loss; 7.5-10.1 mg/L) with decreasing gas temperature in the ETT external to the body, with subsequent drying of the gas (relative humidity drop, 10.7-22.3%) as temperature increased in the ETT inside the body. The present results suggest that temperature decreases in the ETT represent an important issue in the respiratory care of very premature infants.

Heated, humidified high-flow nasal cannula therapy: yet another way to deliver continuous positive airway pressure?

OBJECTIVE

The goal was to estimate the level of delivered continuous positive airway pressure by measuring oral cavity pressure with the mouth closed in infants of various weights and ages treated with heated, humidified high-flow nasal cannula at flow rates of 1-5 L/minute. We hypothesized that clinically relevant levels of continuous positive airway pressure would not be achieved if a nasal leak is maintained.

METHODS

After performing bench measurements and demonstrating that oral cavity pressure closely approximated levels of traditionally applied nasal continuous positive airway pressure, we successfully measured oral cavity pressure during heated, humidified, high-flow nasal cannula treatment in 27 infants. Small (outer diameter: 0.2 cm) cannulae were used for all infants, and flow rates were left as ordered by providers.

RESULTS

Bench measurements showed that, for any given leak size, there was a nearly linear relationship between flow rate and pressure. The highest pressure achieved was 4.5 cmH2O (flow rate: 8 L/minute; leak: 3 mm). In our study infants (postmenstrual age: 29.1-44.7 weeks; weight: 835-3735 g; flow rate: 1-5 L/minute), no pressure was generated with the mouth open at any flow rate. With the mouth closed, the oral cavity pressure was related to both flow rate and weight. For infants of < or = 1500 g, there was a linear relationship between flow rate and oral cavity pressure.

CONCLUSIONS

Oral cavity pressure can estimate the level of continuous positive airway pressure. Continuous positive airway pressure generated with heated, humidified, high-flow nasal cannula treatment depends on the flow rate and weight. Only in the smallest infants with the highest flow rates, with the mouth fully closed, can clinically significant but unpredictable levels of continuous positive airway pressure be achieved. We conclude that heated, humidified high-flow nasal cannula should not be used as a replacement for delivering continuous positive airway pressure.

An experimental model for the measurement of inspired gas temperatures in ventilated neonates

OBJECTIVE

To determine the inspired gas temperature at points from the endo-tracheal tube (ETT) circuit manifold to the tip of the ETT in a model neonatal lung.

DESIGN

A model lung attached to standard ventilator circuit, autofeed chamber and humidifier was ventilated using typical pressure-limited, time cycled settings. Temperatures were measured at various distances along the ETT using a K-type thermocouple temperature probe.

RESULTS

The inspired gas temperature dropped from the circuit temperature probe site (40 degrees C) to the proximal end of the ETT (37 degrees C). The temperature dropped further as it passed through the exposed part of the ETT (34 degrees C) but then warmed again on entering the lung model so that the inspired gas at the distal end of the ETT was 37 degrees C. Statistically significant differences were found with a one-way ANOVA P-value of <0.0001. The differences between each pair of mean temperatures were statistically significant (all P<0.001) except when comparing the proximal end of the ETT with midway down the ETT (Bonferroni's Multiple Comparison Test, P>0.05).

CONCLUSIONS

Inspired gas temperature drops as it passes through the circuit temperature probe site, the proximal end of the ETT and the exposed part of the ETT. The inspired gas rewarms on entering the model lung and exits the ETT at the desired temperature. The effect of measuring temperature closer to the patient, setting the circuit temperature higher and/or increasing the ambient temperature through which the circuit passes, need to be evaluated.

ETCare: a randomized, controlled, masked trial comparing two solutions for upper airway care in the NICU

BACKGROUND

Small quantities of normal saline are sometimes instilled into the endotracheal tube of intubated neonates, to assist with the removal of thick secretions and maintain patency of the endotracheal tube. However, saline is detrimental to the innate immune system of the upper airway mucosa, rapidly unfolding and inactivating antimicrobial peptides such as LL-37. We previously reported the preparation and feasibility testing of 'ETCare', a low-sodium, physiologically based solution for airway care, and we now report results of a randomized, masked, controlled, two-centered study testing ETCare vs sterile saline among 60 intubated NICU patients.

STUDY DESIGN

Sixty intubated NICU patients were randomized to having their airway care with ETCare vs saline. Three hypotheses were tested: (1) tolerance - patients will tolerate ETCare for airway care as well as they tolerate saline, (2) nosocomial infections - ETCare will result in fewer tracheal aspirates where organisms grow and fewer cases of nosocomial sepsis, and (3) chronic lung disuse - ETCare will result in fewer patients discharged home on supplemental O2.

RESULTS

Thirty NICU patients with an endotracheal tube in place were randomized to receive their airway care with ETCare, and 30 to receive their care with saline. Only the pharmacist was aware of the randomization; the two solutions were visually indistinguishable and were dispensed in identical syringes. Tolerance of the solutions was similar. The ETCare recipients had trends toward fewer positive blood cultures (odds ratios (OR), 0.48; 95% confidence interval (CI), 0.13 to 1.68), and fewer discharges home on supplemental O2 (OR, 0.43; 95% CI, 0.14 to 1.32; P=0.075).

CONCLUSIONS

On the basis of this study and our previous 10-patient feasibility trial, we maintain that, for airway care, intubated NICU patients tolerate ETCare as well as saline. Data from this study can be used in estimating the sample sizes needed for a phase III trial. We speculate that such a trial will demonstrate that, compared with saline, ETCare will result in fewer nosocomial infections and less chronic lung disease.

Airway humidification with a heat and moisture exchanger in mechanically ventilated neonates

OBJECTIVE

We set out to evaluate the efficacy of passive inspiratory gas conditioning in mechanically ventilated neonates and compared it with that of a heated humidifier (HH).

DESIGN

Prospective, randomized, controlled study.

SETTING

Neonatal and pediatric intensive care unit.

PATIENTS

Fourteen mechanically ventilated neonates nursed in incubators.

INTERVENTIONS

The HH was set to deliver a temperature of 37 degrees C and an absolute humidity of 40 mgH(2)O/l at the incubator entrance. Inspired temperature (T degrees ) and absolute humidity (AH) were measured by the psychometric method, transpulmonary pressure (Tpres) by means of a differential pressure transducer. Measurements were performed at 5, 10, and 15 min.

MEASUREMENTS AND RESULTS

The values of T degrees were significantly higher using the HH (34.6+/-1.6 degrees C) than the heat and moisture exchanger (HME) (33.8+/2.3, p<0.001). The values of AH were significantly higher using the HH (36.6+/-2.5 mgH(2)O/l) than the HME (32.4+/-2.8 mgH(2)O/l, p<0.001). No significant changes were observed in transpulmonary pressure. A significant positive correlation was observed between incubator temperature and the temperature delivered by the HH (R(2)=0.61, p<0.001).

CONCLUSIONS

The use of HMEs in neonates made it possible to achieve an absolute humidity of 28 mgH(2)O/l or more and a temperature of 30 degrees C or more. Higher values are obtained using a HH.

Inspired gas temperature in ventilated neonates

The warming and humidification of inspired gases for ventilated neonates are routine. There are no data on the temperature of the gas at the airway opening in ventilated neonates. Is the inspired gas temperature at the airway opening, as expected and set on the humidifier, around 37 degrees C? We aimed to measure temperature at the airway opening and compare this with the circuit temperature. This was an observational study in a neonatal intensive care unit. Twenty-five mechanically ventilated infants were studied. All had humidifiers with chamber temperature set at 36 degrees C and the circuit temperature set at 37 degrees C. Two temperature probes were inserted and rested at the circuit-exit and at the airway opening, and temperatures were measured for 2 min in each infant. At this time, the circuit temperature was also noted. The mean (SD) temperature at the airway opening in infants nursed in incubators was 34.9 (1.2) degrees C, compared with radiant warmers where the mean (SD) was 33.1 (0.5) degrees C. The mean (SD) difference in temperature from the circuit temperature probe to the airway opening was greater under radiant warmers, with a mean (SD) drop of 3.9 (0.6) degrees C compared with a mean (SD) drop of 2.0 (1.3) degrees C in the incubators. In conclusion, the temperature at the circuit temperature probe does not reflect the temperature at the airway opening. Inspired gas temperatures are lower than the expected 37 degrees C with the normal circuits and usual humidifier settings.

Effective strategies to prepare infants and families for home tracheostomy care

In neonates tracheostomies are most often indicated to provide a stable airway for infants with congenital or acquired airway obstructions and to provide long-term mechanical ventilation. Learning to care for an infant with a tracheostomy can be challenging for both professionals and families. This article provides an overview of tracheostomy care and the essential elements of family teaching. The surgical procedure and basic anatomical changes are reviewed. Complications such as accidental decannulation, mucus plugging, infection, bleeding, and granulation tissue formation are discussed. Humidification is critical for the infant with a tracheostomy and humidification delivery methods are discussed. Further, an overview of the impact of the tracheostomy on normal development, such as swallowing and language development, is provided. Teaching parents to safely care for the infant with a tracheostomy at home requires careful planning and systematic education. The parents must acquire a unique set of technical skills demonstrating competence and comfort in providing stoma care, suctioning, and tube changes. Parents must be prepared to initiate cardiopulmonary resuscitation (CPR) and need to understand alterations in CPR techniques in infants with a tracheostomy. They also need to develop critical thinking skills to handle emergency situations. A safe transition to the home can be accomplished by using a multidisciplinary approach to coordinate all facets of care.