The effects of non-invasive respiratory support on oropharyngeal temperature and humidity: a neonatal manikin study

Non-invasive respiratory support in preterm infants

Survival of preterm infants has increased steadily over recent decades, primarily due to improved outcomes for those born before 28 weeks of gestation. However, this has not been matched by similar improvements in longer-term morbidity. One of the key long-term sequelae of preterm birth remains bronchopulmonary dysplasia (also called chronic lung disease of prematurity), contributed primarily by the effect of early pulmonary inflammation superimposed on immature lungs. Non-invasive modes of respiratory support have been rapidly introduced providing modest success in reducing the incidence of bronchopulmonary dysplasia when compared with invasive mechanical ventilation, and improved clinical practice has been reported from population-based studies. We present a comprehensive review of the key modes of non-invasive respiratory support currently used in preterm infants, including their mechanisms of action and evidence of benefit from clinical trials.

Optiflow vs Vapotherm as extended weaning mode from nasal continuous positive airway pressure in preterm infants ≤ 28 weeks gestational age

INTRODUCTION

Current evidence supports nasal continuous positive airway pressure (NCPAP) weaning. Heated humidified high-flow nasal cannula (HHFNC) reduces NCPAP time in infants less than 28 weeks gestational age (GA) without increasing morbidity. The aim of the study was to compare the two most frequently used HHFNC devices in weaning from NCPAP.

METHODOLOGY

We performed a retrospective matched-pair case-control study of infants less than or equal to 28 GA born in a single tertiary neonatal center managed with Optiflow or Vapotherm after being weaned from NCPAP. Patients were matched for antenatal steroid doses, delivery mode, birth plurality, GA, birthweight, gender, surfactant doses, length of mechanical ventilation, and length of NCPAP. Outcome measures were duration of HHFNC, low-flow nasal cannula, nasal bridge lesions, pneumothorax, bronchopulmonary dysplasia, postnatal steroids, necrotizing enterocolitis, sepsis, intraventricular hemorrhage, retinopathy of prematurity, length of stay, discharge weight, and mortality. Results were displayed as median (interquartile range) or ratio (percentage). Statistical analysis was performed using Mann-Whitney U and χ² tests.

RESULTS

70 patients were recruited retrospectively. Thirty-five infants were weaned from NCPAP to Optiflow and 35 infants to Vapotherm with gestational ages and birthweights of 27 GA (26-27) and 1010 g (835-1165) and 27 GA (26-28) and 960 g (788-1191), respectively. There was no statistically significant difference in any outcome measure. Infants managed with Vapotherm required a not statistically significant shorter length of time on HHFNC and low-flow nasal cannula.

CONCLUSIONS

Optiflow and Vapotherm seem to be equally effective and safe for weaning from NCPAP. However, infants weaned to Vapotherm appear to spend less time on non-invasive respiratory support.

A Review on Non-invasive Respiratory Support for Management of Respiratory Distress in Extremely Preterm Infants

Majority of extremely preterm infants require positive pressure ventilatory support at the time of delivery or during the transitional period. Most of these infants present with respiratory distress (RD) and continue to require significant respiratory support in the neonatal intensive care unit (NICU). Bronchopulmonary dysplasia (BPD) remains as one of the major morbidities among survivors of the extremely preterm infants. BPD is associated with long-term adverse pulmonary and neurological outcomes. Invasive mechanical ventilation (IMV) and supplemental oxygen are two major risk factors for the development of BPD. Non-invasive ventilation (NIV) has been shown to decrease the need for IMV and reduce the risk of BPD when compared to IMV. This article reviews respiratory management with current NIV support strategies in extremely preterm infants both in delivery room as well as in the NICU and discusses the evidence to support commonly used NIV modes including nasal continuous positive airway pressure (NCPAP), nasal intermittent positive pressure ventilation (NIPPV), bi-level positive pressure (BI-PAP), high flow nasal cannula (HFNC), and newer NIV strategies currently being studied including, nasal high frequency ventilation (NHFV) and non-invasive neutrally adjusted ventilatory assist (NIV-NAVA). Randomized, clinical trials have shown that early NIPPV is superior to NCPAP to decrease the need for intubation and IMV in preterm infants with RD. It is also important to understand that selection of the device used to deliver NIPPV has a significant impact on its success. Ventilator generated NIPPV results in significantly lower rates of extubation failures when compared to Bi-PAP. Future studies should address synchronized NIPPV including NIV-NAVA and early rescue use of NHFV in the respiratory management of extremely preterm infants.

Nasal high flow therapy for neonates: Current evidence and future directions

Nasal high flow (nHF) therapy is a commonly used method of providing non-invasive respiratory support for neonates. It has several potential mechanisms of action: continuous distending pressure, nasopharyngeal dead space washout, provision of heated and humidified gases and reduction of work of breathing. nHF is used in a number of clinical scenarios for preterm and term infants, including primary respiratory and post-extubation support. In recent years, large trials have generated evidence pertinent to these indications. Novel applications for nHF in neonates warrant further research: during endotracheal intubation, for initial delivery room stabilisation of preterm infants and in conjunction with minimally invasive surfactant therapy.

A humidifier in the invasive mode during noninvasive respiratory support could increase condensation and thereby impair airway patency

AIM

Humidifying noninvasively ventilated preterm infants is critical to prevent dehydration of respiratory mucosa, but over-humidification can result in impaired airway patency and lung mechanics. This neonatal bench study investigated the humidity delivered using invasive and noninvasive humidification modes during nasal continuous positive airway pressure.

METHODS

The study was conducted at the neonatal intensive care unit of Emma Children's Hospital, the Netherlands, in March 2014. A mannequin was connected to a CareFusion Infant Flow SiPAP system, combined with a Fisher & Paykel MR850 humidifier and a Carefusion Infant Flow LP Generator. We measured the temperature, relative humidity and absolute humidity at the humidification chamber's expiratory port and at the patient's mask.

RESULTS

The absolute humidity at the mask was 35-40 mg H₂ O/L at 38-39°C (relative humidity 74-80%) for the invasive mode of the humidifier and 23-27 mg H₂ O/L at 34-35°C (relative humidity 63-70%) for the noninvasive mode. The absolute humidities exceeded the recommended values for the invasive mode of the humidifier, but not the noninvasive mode, and could be associated with increased condensation.

CONCLUSION

The absolute humidity delivered by the humidifier in invasive mode could be associated with increased condensation, which has been associated with airway impairment.

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.

Differential impact of flow and mouth leak on oropharyngeal humidification during high-flow nasal cannula: a neonatal bench study

BACKGROUND

Heated humidification is paramount during neonatal high-flow nasal cannula (HFNC) therapy. However, there is little knowledge about the influence of flow rate and mouth leak on oropharyngeal humidification and temperature.

METHODS

The effect of the Optiflow HFNC on oropharyngeal gas conditioning was investigated at flow rates of 4, 6 and 8 L min^-1 with and without mouth leak in a bench model simulating physiological oropharyngeal air conditions during spontaneous breathing. Temperature and absolute humidity (AH) were measured using a digital thermo-hygrosensor.

RESULTS

Without mouth leak, oropharyngeal temperature and AH increased significantly with increasing flow (P < 0.001). Mouth leak did not affect this increase up to 6 L min^-1, but at 8 L min^-1, temperature and AH plateaued, and the effect of mouth leak became statistically significant (P < 0.001).

CONCLUSIONS

Mouth leak during HFNC had a negative impact on oropharyngeal gas conditioning when high flows were applied. However, temperature and AH always remained clinically acceptable.

Nasal high-frequency oscillatory ventilation impairs heated humidification: A neonatal bench study

OBJECTIVE

Nasal high-frequency oscillatory ventilation (nHFOV) is a novel mode of non-invasive ventilation used in neonates. However, upper airway obstructions due to viscous secretions have been described as specific adverse effects. We hypothesized that high-frequency oscillations reduce air humidity in the oropharynx, resulting in upper airway desiccation. Therefore, we aimed to investigate the effects of nHFOV ventilatory settings on oropharyngeal gas conditions.

METHODS

NHFOV or nasal continuous positive airway pressure (nCPAP) was applied, along with heated humidification, to a previously established neonatal bench model that simulates oropharyngeal gas conditions during spontaneous breathing through an open mouth. A digital thermo-hygro sensor measured oropharyngeal temperature (T) and humidity at various nHFOV frequencies (7, 10, 13 Hz), amplitudes (10, 20, 30 cmH₂ O), and inspiratory-to-expiratory (I:E) ratios (25:75, 33:66, 50:50), and also during nCPAP.

RESULTS

Relative humidity was always >99%, but nHFOV resulted in lower mean T and absolute humidity (AH) in comparison to nCPAP (P < 0.001). Specifically, decreasing the nHFOV frequency and increasing nHFOV amplitude caused a decline in T and AH (P < 0.001). Mean T and AH were highest during nCPAP (T 34.8 ± 0.6°C, AH 39.3 ± 1.3 g · m^-3 ) and lowest during nHFOV at a frequency of 7 Hz and an amplitude of 30 cmH₂ O (T 32.4 ± 0.3°C, AH 34.7 ± 0.5 g · m^-3 ). Increasing the I:E ratio also reduced T and AH (P = 0.03).

CONCLUSION

Intensified nHFOV settings with low frequencies, high amplitudes, and high I:E ratios may place infants at an increased risk of upper airway desiccation. Future studies should investigate strategies to optimize heated humidification during nHFOV.

Nasal high flow treatment in preterm infants

Nasal High Flow (HF) is a mode of ‘non-invasive’ respiratory support for preterm infants, with several potential modes of action, including generation of distending airway pressure, washout of the nasopharyngeal dead space, reduction of work of breathing, and heating and humidification of inspired gas. HF has several potential advantages over continuous positive airway pressure (CPAP), the most commonly applied form of non-invasive support, such as reduced nasal trauma, ease of use, and infant comfort, which has led to its rapid adoption into neonatal care. In recent years, HF has become a well-established and commonly applied treatment in neonatal care.

Recent trials comparing HF and CPAP as primary support have had differing results. Meta-analyses suggest that primary HF results in an increased risk of treatment failure, but that ‘rescue’ CPAP use in those infants with HF failure results in no greater risk of mechanical ventilation. Even in studies with higher rates of HF failure, the majority of infants were successfully treated with HF, and rates of important neonatal morbidities did not differ between treatment groups. Importantly, these studies have included only infants born at ≥28 weeks’ gestational age (GA). The decision whether to apply primary HF will depend on the value placed on its advantages over CPAP by clinicians, the approach to surfactant treatment, and the severity of respiratory disease in the relevant population of preterm infants.

Post-extubation HF use results in similar rates of treatment failure, mechanical ventilation, and adverse events compared to CPAP. Post-extubation HF appears most suited to infants ≥28 weeks; there are few published data for infants below this gestation, and available evidence suggests that these infants are at high risk of HF failure, although rates of intubation and other morbidities are similar to those seen with CPAP. There is no evidence that using HF to ‘wean’ off CPAP allows for respiratory support to be ceased more quickly, but given its advantages it would appear to be a suitable alternative in infants who require ongoing non-invasive support. Safety data from randomised trials are reassuring, although more evidence in extremely preterm infants (<28 weeks’ GA) is required.

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.

Continuous Positive Airway Pressure: To Bubble or Not to Bubble?

Continuous positive airway pressure (CPAP) systems can be broadly grouped into continuous flow or variable flow devices. Bubble CPAP (bCPAP) is a continuous flow device and has physiologic properties that could facilitate gas exchange. Its efficacy has been reported to be similar to variable flow CPAP systems when used as a primary mode of respiratory support. Post-extubation bCPAP is reported to significantly reduce extubation failure rates among preterm infants ventilated for less than 2 week when compared to Infant flow driver CPAP (variable flow). bCPAP has been successfully used in resource-poor settings. The success on CPAP is however dependant on good nursing care and clear management protocols for weaning and escalation of care.

Respiratory support with heated humidified high flow nasal cannula in preterm infants

The incidence of bronchopulmonary dysplasia (BPD) has not decreased over the last decade. The most important way to decrease BPD is by weaning the patient from the ventilator as soon as possible in order to reduce ventilator-induced lung injury that underlies BPD, and by using a noninvasive ventilator (NIV). Use of a heated, humidified, high flow nasal cannula (HHHFNC), which is the most recently introduced NIV mode for respiratory support in preterm infants, is rapidly increasing in many neonatal intensive care units due to the technical ease of use without sealing, and the attending physician's preference compared to other NIV modes. A number of studies have shown that nasal breakdown and neonatal complications were lower when using a HHHFNC than when using nasal continuous positive airway pressure (nCPAP), or nasal intermittent positive pressure ventilation. The rates of extubation failure during respiratory support were not different between patients who used HHHFNC and nCPAP. However, data from the use of HHHFNC as the initial respiratory support "after birth", particularly in extremely preterm infants, are lacking. Although the HHHFNC is efficacious and safe, large randomized controlled trials are needed before the HHHFNC can be considered an NIV standard, particularly for extremely preterm infants.