The impact of instrumental dead-space in volume-targeted ventilation of the extremely low birth weight (ELBW) infant

Ventilation practices in the neonatal intensive care units in Saudi Arabia, survey of the utilization of volume-targeted ventilation among practicing neonatologists

OBJECTIVE

To assess the current practice in using volume-targeted ventilation among neonatologists working at the Neonatal Intensive Care Units (NICU) of Saudi Arabia.

METHODS

The questionnaire was provided electronically to 153 practicing Neonatologists working in 39 NICUs. The survey's results were received and statistically analyzed.

RESULTS

One hundred nineteen (119) responses were received with, a 78% response rate. Volume Targeted Ventilation (VTV) was used routinely by 67.2%, whereas 21.8% still use only pressure control (PC)/pressure limited (PL) mode. During the acute phase of ventilation support, Assist Control was the most popular synchronized mode, whereas Synchronized Intermittent Mandatory Ventilation (SIMV) with pressure support (PS) or PSV were the two most common modes during the weaning phase, 31.8%, and 31% respectively. The majority of the neonatologists used a tidal volume of 4 ml/kg as the lowest and 6 ml/kg as the highest. The major reasons for not implementing VTV were the limited availability of ventilator devices that have an option of VTV, followed by lack of experience.

CONCLUSION

VTV is the predominant ventilation practice approach among neonatologists working in the KSA. Limited availability and lack of experience in using are the main challenges. Efforts to equip NICUs with the most advanced ventilation technology, enhance practitioners' experience and sufficient training in its use are warranted.

Volume-targeted ventilation

Despite strong evidence of important benefits of volume-targeted ventilation, many high-risk extremely preterm infants continue to receive traditional pressure-controlled ventilation in the United States and elesewhere. Reluctance to abandon one's comfort zone, lack of suitable equipment and a lack of understanding of the subtleties of volume-targeted ventilation appear to contribute to the relatively slow uptake of volume-targeted ventilation. This review will underscore the benefits of using tidal volume as the primary control variable, to improve clinicians' understanding of the way volume-targeted ventilation interacts with the awake, breathing infant and to provide information about evidence-based tidal volume targets in various circmstances. Focus on underlying lung pathophysiology, individualized ventilator settings and tidal volume targets are essential to successful use of this approach thereby improving important clinical outcomes.

A Flipped Classroom Pilot in Neonatal Mechanical Ventilation

Background

Pediatric residents frequently manage critically ill neonates but have limited systematic training in mechanical ventilation (MV). Competing demands, varying learner levels, and topic complexity contribute to inconsistent education. A blended learning approach may be ideally suited to achieve meaningful learning but has not been described for this topic and learner.

Objective

To design, implement, and evaluate a flipped classroom for pediatric residents in neonatal MV.

Methods

We used Kern's six-step framework for curricular development to create a flipped classroom curriculum in neonatal MV. Individual prework included interaction with six prerecorded animated whiteboard videos, while in-person learning occurred in small groups at the bedside of a ventilated infant. A mixed-methods evaluation included surveys, quantitative knowledge test scores (before, immediately after, and six months after course completion), and qualitative analysis of participant focus groups.

Results

Twenty-six learners participated in the curriculum. Mean knowledge test scores rose and were sustained after course completion (51% baseline, 82% immediate posttest, 90% retention; P < 0.001). Learners identified various design elements, technology affordances, and instructor factors as meaningful, and they identified unexpected impacts of the curriculum beyond knowledge acquisition, including effects on professional identities, interdisciplinary communication skills, and contribution to the culture of safety.

Conclusion

This curriculum aligned with resident roles, was meaningful to learners, and led to long-term increases in knowledge scores and access to quality education; flipped classroom design using meaningful learning theory and leveraging animated whiteboard technology may be a useful strategy for other highly complex topics in graduate medical education.

Effect of additional dead space using end-tidal CO2 measurement on ventilating preterm infants: An experimental study

BACKGROUND

Dead space is the part of the airway where no gas exchange takes place. Any increase in dead space volume has a proportional effect on the required tidal volume and thus on the risk of ventilation-induced lung injury. Inserts that increase dead space are therefore not used in small preterm infants. This includes end-tidal CO2 measurement.

OBJECTIVE

The aim of this study was to investigate the effect of the end-tidal CO2 measurement adapter on ventilation.

METHODS

In an experimental setup, an end-tidal CO2 measurement adapter, three different pneumotachographs (PNT-A, PNT-B, PNT-Neo), and a closed suction adapter were combined in varying set-ups. The time required for CO2 elimination by a CO2-flooded preterm infant test lung was measured.

RESULTS

PNT-A prolonged CO2 elimination time by 0.9 s (+3.3%), Neo-PNT by 3.2 s (+11.6%) and PNT-B by 9.0 s (+32.7%). The end-tidal CO2 measurement adapter prolonged the elimination time by an additional second without the pneumotachograph (+3.6%) and in combination with PNT-A (+3.1%) and PNT-Neo (+3.1%). In conjunction with PNT-B, the end-tidal CO2 measurement adapter reduced the elimination time by 0.3 seconds (-1%). The use of a closed suction adaptor increased the CO2 elimination time by a further second with PNT-Neo (+3.1%) and by an additional two seconds with no flow sensor (+6.9%), with PNT-A (+6.4%) and with PNT-B (+5.5%).

CONCLUSION

The flow sensor had the greatest influence on ventilatory effort, while end-tidal CO2 measurement had only a moderate effect. The increased ventilatory effort levied by the CO2 measurement was dependent on the flow sensor selected. The use of closed suctioning more negatively impacted ventilatory effort than did end-tidal CO2 measurement.

Invasive and non-invasive ventilatory strategies for early and evolving bronchopulmonary dysplasia

In the age of surfactant and antenatal steroids, neonatal care has improved outcomes of preterm infants dramatically. Since the early 2000's neonatologists have strived to decrease bronchopulmonary dysplasia (BPD) by decreasing ventilator-associated lung injury and utilizing many novel modes of non-invasive respiratory support. After the initial success with nasal continuous positive airway pressure, it was established that discontinuing invasive ventilation early in favor of non-invasive respiratory support is the most effective way to reduce the incidence of BPD. In this review, we discuss the management of the preterm lung from the time of delivery, through the phases of respiratory distress syndrome (early BPD) and then evolving BPD. The goal remains to optimize respiratory support of the preterm lung while minimizing ventilator-associated lung injury and oxygen toxicity. A multidisciplinary approach involving the medical team and family is quintessential in reaching this goal and involves adequate respiratory support, optimizing nutrition and fluid balance as well as preventing infections.

Instrumental dead space: A glass ceiling for extremely low birth weight preterm infants? A dead space washout bench study

BACKGROUND

When ventilating extremely low birth weight infants, clinicians face the problem of instrumental dead space, which is often larger than tidal volume. Hence, aggressive ventilation is necessary to achieve CO₂ removal. Continuous tracheal gas insufflation can wash out CO₂ from dead space and might also have an impact on O₂ and water vapor transport. The objective of this bench study is to test the impact of instrumental dead space on the transport of CO₂ , O₂ , and water vapor and the ability of continuous tracheal gas insufflation to remedy this problem during small tidal volume ventilation.

METHODS

A test-lung located in an incubator at 37°C was ventilated with pressure levels needed to reach different tidal volumes from 1.5 to 5 mL. End-tidal CO₂ at the test-lung exit, O₂ concentration, and relative humidity in the test-lung were measured for each tidal volume with and without a 0.2 L/min continuous tracheal gas insufflation flow.

RESULTS

CO₂ clearance was improved by continuous tracheal gas insufflation allowing a 28%-44% of tidal volume reduction. With continuous tracheal gas insufflation, time to reach desired O₂ concentration was reduced from 20% to 80% and relative humidity was restored. These results are inversely related to tidal volume and are particularly critical below 3 mL.

CONCLUSION

For the smallest tidal volumes, reduction of instrumental dead space seems mandatory for CO₂ , O₂ , and water vapor transfer. Continuous tracheal gas insufflation improved CO₂ clearance, time to reach desired O₂ concentration and humidification of airways and, thus, may be an option to protect lung development.

Respiratory support strategies in the prevention and treatment of bronchopulmonary dysplasia

Neonates who are born preterm frequently have inadequate lung development to support independent breathing and will need respiratory support. The underdeveloped lung is also particularly susceptible to lung injury, especially during the first weeks of life. Consequently, respiratory support strategies in the early stages of premature lung disease focus on minimizing alveolar damage. As infants grow and lung disease progresses, it becomes necessary to shift respiratory support to a strategy targeting the often severe pulmonary heterogeneity and obstructive respiratory physiology. With appropriate management, time, and growth, even those children with the most extreme prematurity and severe lung disease can be expected to wean from respiratory support.

Pathophysiology of gas exchange impairment in extreme prematurity: Insights from combining volumetric capnography and measurements of ventilation/perfusion ratio

Background

Infants born extremely preterm often suffer from respiratory disease and are invasively ventilated. We aimed to test the hypothesis that gas exchange in ventilated extremely preterm infants occurs both at the level of the alveoli and via mixing of fresh deadspace gas in the airways.

Methods

We measured the normalised slopes of phase II and phase III of volumetric capnography and related them with non-invasive measurements of ventilation to perfusion ratio (V_A/Q) and right-to-left shunt in ventilated extremely preterm infants studied at one week of life. Cardiac right-to-left shunt was excluded by concurrent echocardiography.

Results

We studied 25 infants (15 male) with a median (range) gestational age of 26.0 (22.9-27.9) weeks and birth weight of 795 (515-1,165) grams. The median (IQR) V_A/Q was 0.52 (0.46-0.56) and shunt was 8 (2-13) %. The median (IQR) normalised slope of phase II was 99.6 (82.7-116.1) mmHg and of phase III was 24.6 (16.9-35.0) mmHg. The V_A/Q was significantly related to the normalised slope of phase III (ρ = -0.573, p = 0.016) but not to the slope of phase II (ρ = 0.045, p = 0.770). The right-to-left shunt was not independently associated with either the slope of phase II or the slope of phase III after adjusting for confounding parameters.

Conclusions

Abnormal gas exchange in ventilated extremely preterm infants was associated with lung disease at the alveolar level. Abnormal gas exchange at the level of the airways was not associated with quantified indices of gas exchange impairment.

Ventilator Management in Extremely Preterm Infants

Advances in ventilation strategies for infants in the NICU have led to increased survival of extremely preterm infants. More than 75% of infants born at less than or equal to 27 weeks' gestation require initial mechanical ventilation for survival due to developmental immaturity of their lungs and respiratory drive. Various ventilators using different technologies and involving multiple management strategies are available for use in this population. Centers across the world have successfully used conventional, high-frequency oscillatory and high-frequency jet ventilation to manage respiratory failure in extremely preterm infants. This review explores the existing evidence for each mode of ventilation and the importance of individualizing ventilator management strategies when caring for extremely preterm infants.

Dead space washout by intentional leakage flow during conventional ventilation of premature infants-an experimental study

OBJECTIVE

Invasive mechanical ventilation poses a strong risk factor for the development of chronic lung disease in preterm infants. A reduction of the dead space as part of the total breathing volume would reduce the ventilation effort and thereby lower the risk of ventilator-induced lung injuries. In this experimental study, we compared the efficacy of mechanical dead space washout via uncontrolled and controlled leakage flow in their ability to eliminate CO₂ during conventional ventilation in preterm infants.

METHODS

Three frequently used neonatal ventilators, operating under standard conventional ventilating parameters, were individually connected to a test lung. To maintain a constant physiological end-expiratory pCO₂ level during ventilation, the test lung was continuously flooded with CO₂ . A side port in the area of the connector between the endotracheal tube and the flow sensor allowed breathing gas to escape passively or in a second experimental setup, regulated by a pump. Measurements of end-expiratory pCO₂ were taken in both experiments and compared to end-expiratory pCO₂ levels of ventilation without active dead space leakage.

RESULTS

Following dead space washout, a significant reduction of end-expiratory pCO₂ was attained. Under conditions of uncontrolled leakage, the mean decrease was 14.1% while controlled leakage saw a mean reduction of 16.1%.

CONCLUSION

Washout of dead space by way of leakage flow is an effective method to reduce end-expiratory pCO₂ . Both controlled and uncontrolled leakage provide comparable results, but precise regulation of leakage allows for a more stable ventilation by preventing uncontrolled loss of tidal volume during inspiration.

Novel Ventilation Strategies to Reduce Adverse Pulmonary Outcomes

Extremely preterm infants who must suddenly support their own gas exchange with lungs that are incompletely developed and lacking adequate amount of surfactant and antioxidant defenses are susceptible to lung injury. The decades-long quest to prevent bronchopulmonary dysplasia has had limited success, in part because of increasing survival of more immature infants. The process must begin in the delivery room with gentle assistance in establishing and maintaining adequate lung aeration, followed by noninvasive support and less invasive surfactant administration. Various modalities of invasive and noninvasive support have been used with varying degree of effect and are reviewed in this article.

Factors associated with initial tidal volume selection during neonatal volume-targeted ventilation in two NICUs: a retrospective cohort study

OBJECTIVE

To quantify initial tidal volume (VT) during neonatal volume-targeted ventilation (VTV) and to characterize the agreement of initial VT with the limited-evidence available.

STUDY DESIGN

We performed a multi-center retrospective observational cohort study in two Neonatal Intensive Care Units evaluating 313 infants who received VTV as the initial ventilation modality prior to postnatal day 14. We generated descriptive statistics and performed multivariable logistic regression analysis to determine factors associated with initial VT use that agreed with available literature.

RESULTS

154 (49%) infants received an initial VT of 5.0 mL/kg (median 5.0 mL/kg, IQR 5.0-5.1). 45 (14%) infants received an initial VT that was congruent with available literature. A birth weight of 700 -<1250 g was significantly associated with an initial VT in agreement with VT literature (aOR 9.4, 95% CI 1.7-50.4).

CONCLUSIONS

Most infants receive an initial VT of 5.0 mL/kg.

Volume-Targeted Ventilation

Volume-targeted ventilation (VTV) has been increasingly used in neonatology. In systematic reviews, VTV has been shown to reduce the risk of neonatal morbidities and improve long-term outcomes. It is adaptive ventilation using complex computer algorithms to deliver ventilator inflations with expired tidal volumes close to a target set by clinicians. Significant endotracheal tube leak and patient-ventilator interactions may complicate VTV and make ventilator parameters and waveforms difficult to interpret. In this article, we review the rationale for using VTV and the evidence supporting its use and provide practical advice for clinicians ventilating newborn infants.

Implementing Volume-targeted Ventilation to Decrease Hypocarbia in Extremely Low Birth Weight Infants during the First Week of Life: A Quality Improvement Project

Hypocarbia in neonates increases the risk of poor neurodevelopmental outcomes. Volume-targeted ventilation (VTV) is associated with decreased hypocarbia and other respiratory morbidities. We noticed a high incidence of hypocarbia in extremely low birth weight (ELBW; <1,000 g) neonates in our Neonatal Intensive Care Unit. Thus, we undertook a quality improvement project to decrease the incidence of hypocarbia (the occurrence of PCO₂ < 35 mm Hg) in ELBW neonates during the first week of life by 50% over 1 year.

Methods

Our major interventions were employing VTV as the primary mode of mechanical ventilation in neonates less than 28 weeks of gestation or ELBW at birth and increasing staff knowledge regarding hypocarbia. The baseline period spanned May-August 2016. We implemented the interventions in October 2016 and tracked the use of VTV and the incidence of hypocarbia during the first week of life for 12 months.

Results

We analyzed data on 28 and 77 patients in the baseline and postintervention periods, respectively. The use of VTV increased from 39% to 65%. However, the incidence of hypocarbia was not reduced (57% preintervention vs. 64% postintervention). In the postintervention cohort, the incidence of hypocarbia was comparable between VTV and other modes (60% vs. 70%; 95% confidence interval: -32%, 12%; P = 0.367), but we noted decreased blood gas sampling and earlier extubation in the VTV group (P = 0.002 and P = 0.046, respectively).

Conclusions

Successfully increasing VTV in our Neonatal Intensive Care Unit did not decrease hypocarbia during the first week of life. However, we observed the safety of VTV and obtained other desirable results.

Early volume targeted ventilation in preterm infants born at 22-25 weeks of gestational age

BACKGROUND

Early hypocapnia in preterm infants is associated with intraventricular hemorrhage (IVH) and bronchopulmonary dysplasia (BPD). Volume targeted ventilation (VTV) has been shown to reduce hypocapnia in preterm infants. Less is known of VTV in infants born at <26 weeks gestational age (GA).

OBJECTIVES

Our aim was to investigate the short- and long-term effects of early VTV as compared to pressure limited ventilation (PLV) in extremely preterm infants on the incidence of hypocapnia, days on ventilatory support, IVH, and BPD.

STUDY DESIGN

A retrospective observational study of 104 infants born at 22-25 weeks GA (mean ± SD; 24⁺⁰  ± 1⁺¹ GA; birth weight 619 ± 146 g), ventilated with either VTV (n = 44) or PLV (n = 60) on their first day of life. Ventilatory data and blood gases were collected at admission and every fourth hour during the first day of life, together with perinatal characteristics and outcomes.

RESULTS

Peak inflation pressure (PIP) was lower in the VTV-group than in the PLV-group during the first 20 h of life (p < .05), without any difference in respiratory rate or FiO₂ . Incidence of hypocapnia (PaCO₂ < 4.5 kPa) was lower with VTV than PLV during the first day of life (32% vs. 62%; p < .01). Infants in the VTV-group were more frequently extubated at 24 h (30% vs. 13%; p < .05). IVH Grade ≥3, BPD, and time on mechanical ventilation did not differ between the groups.

CONCLUSIONS

VTV is safe to apply in infants born at <26 GA and was observed to result in a lower incidence of hypocapnia compared to infants ventilated by PLV, without any differences in outcomes.

Diaphragmatic activity and neural breathing variability during a 5-min endotracheal continuous positive airway pressure trial in extremely preterm infants

BACKGROUND

Extremely preterm infants are often exposed to endotracheal tube continuous positive airway pressure (ETT-CPAP) trials to assess extubation readiness. The effects of ETT-CPAP trial on their diaphragmatic activity (Edi) and breathing variability is unknown.

METHODS

Prospective observational study enrolling infants with birth weight ≤1250 g undergoing their first extubation attempt. Diaphragmatic activity, expressed as the absolute minimum (Edi min) and maximum values (Edi max), area under the Edi signal, and breath-by-breath analyses for breath areas, amplitudes, widths, and neural inspiratory and expiratory times, were analyzed during mechanical ventilation (MV) and ETT-CPAP. Neural breathing variability of each of these parameters was also calculated and compared between MV and ETT-CPAP.

RESULTS

Thirteen infants with median (interquartile range) birth weight of 800 g [610-920] and gestational age of 25.4 weeks [24.4-26.3] were included. Diaphragmatic activity significantly increased during ETT-CPAP when compared to MV:Edi max (44.2 vs. 38.1 μV), breath area (449 vs. 312 μV·s), and amplitude (10.12 vs. 7.46 μV). Neural breathing variability during ETT-CPAP was characterized by increased variability for amplitude and area under the breath, and decreased for breath time and width.

CONCLUSIONS

A 5-min ETT-CPAP in extremely preterm infants undergoing extubation imposed significant respiratory load with changes in respiratory variability.

IMPACT

ETT-CPAP trials are often used to assess extubation readiness in extremely preterm infants, but its effects upon their respiratory system are not well known. Diaphragmatic activity analysis demonstrated that these infants are able to mount an important response to a short trial. A 5-min trial imposed a significant respiratory load evidenced by increased diaphragmatic activity and changes in breathing variability. Differences in breathing variability were observed between successful and failed extubations, which should be explored further in extubation readiness investigations. This type of trial cannot be recommended for preterm infants in clinical practice until clear standards and accuracy are established.

Volume-targeted ventilation with a Fabian ventilator: maintenance of tidal volumes and blood CO2

OBJECTIVE

To analyse the performance of the Fabian +NCPAP evolution ventilator during volume guarantee (VG) ventilation in neonates at maintaining the target tidal volume and what tidal and minute volumes are required to maintain normocapnia.

METHODS

Clinical and ventilator data were collected and analysed from 83 infants receiving VG ventilation during interhospital transfer. Sedation was used in 26 cases. Ventilator data were downloaded with a sampling rate of 0.5 Hz. Data were analysed using the Python computer language and its data analysis packages.

RESULTS

~107 hours of ventilator data were analysed, consisting of ~194 000 data points. The median absolute difference between the actual expiratory tidal volume (VTe) of the ventilator inflations and the target tidal volume (VTset) was 0.29 mL/kg (IQR: 0.11-0.79 mL/kg). Overall, VTe was within 1 mL/kg of VTset in 80% of inflations. VTe decreased progressively below the target when the endotracheal tube leak exceeded 50%. When leak was below 50%, VTe was below VTset by >1 mL/kg in less than 12% of inflations even in babies weighing less than 1000 g. Both VTe (r=-0.34, p=0.0022) and minute volume (r=-0.22, p=0.0567) showed a weak inverse correlation with capillary partial pressure of carbon dioxide (Pco₂) values. Only 50% of normocapnic blood gases were associated with tidal volumes between 4 and 6 mL/kg.

CONCLUSIONS

The Fabian ventilator delivers volume-targeted ventilation with high accuracy if endotracheal tube leakage is not excessive and the maximum allowed inflating pressure does not limit inflations. There is only weak inverse correlation between tidal or minute volumes and Pco₂.

"Current concepts of mechanical ventilation in neonates" - Part 1: Basics

Mechanical ventilation is potentially live saving in neonatal patients with respiratory failure. The main purpose of mechanical ventilation is to ensure adequate gas exchange, including delivery of adequate oxygenation and enough ventilation for excretion of CO₂. The possibility to measure and deliver small flows and tidal volumes have allowed to develop very sophisticated modes of assisted mechanical ventilation for the most immature neonates, such as volume targeted ventilation, which is used more and more by many clinicians. Use of mechanical ventilation requires a basic understanding of respiratory physiology and pathophysiology of the disease leading to respiratory failure. Understanding pulmonary mechanics, elastic and resistive forces (compliance and resistance), and its influence on the inspiratory and expiratory time constant, and the mechanisms of gas exchange are necessary to choose the best mode of ventilation and adequate ventilator settings to minimize lung injury. Considering the pathophysiology of the disease allows a physiology-based approach and application of these concepts in daily practice for decision making regarding the use of modes and settings of mechanical ventilation, with the ultimate aim of providing adequate gas exchange and minimising lung injury.

Volume Targeted Ventilation and High Frequency Ventilation as the Primary Modes of Respiratory Support for ELBW Babies: What Does the Evidence Say?

Respiratory management of the extremely low birth weight (ELBW) newborn has evolved over time. Although non-invasive ventilation is being increasingly used for respiratory support in these ELBW infants, invasive ventilation still remains the primary mode in this population. Current ventilators are microprocessor driven and have revolutionized the respiratory support for these neonates synchronizing the baby's breath to ventilator breaths. High frequency ventilators with the delivery of tidal volumes less than the dead space have been introduced to minimize barotrauma and chronic lung disease. Despite these advances, the incidence of chronic lung disease has not decreased. There is still controversy regarding which mode is ideal as the primary mode of ventilation in ELBW infants. The most common modes seem to be pressure targeted conventional ventilation, volume targeted conventional ventilation and high frequency ventilation which includes high frequency oscillatory ventilation, high frequency jet ventilation and high frequency flow interrupter. In recent years, several randomized controlled trials and meta-analyses have compared volume vs. pressure targeted ventilation and high frequency ventilation. While volume targeted ventilation and high frequency ventilation does show promise, substantial practice variability among different centers persists. In this review, we weighed the evidence for each mode and evaluated which modes show promise as the primary support of ventilation in ELBW babies.

Ventilation strategies in transition from neonatal respiratory distress to chronic lung disease

Despite the advance in neonatal care over the past few decades, preventing preterm infants with respiratory distress syndrome progress to bronchopulmonary dysplasia remained challenging. In this review, we will discuss the respiratory support strategies in preterm infants with RDS evolving into BPD based on the changes in pulmonary mechanics and pathophysiology as well as currently available evidence.

Clinical use of volumetric capnography in mechanically ventilated patients

Capnography is a first line monitoring system in mechanically ventilated patients. Volumetric capnography supports noninvasive and breath-by-breath information at the bedside using mainstream CO₂ and flow sensors placed at the airways opening. This volume-based capnography provides information of important body functions related to the kinetics of carbon dioxide. Volumetric capnography goes one step forward standard respiratory mechanics and provides a new dimension for monitoring of mechanical ventilation. The article discusses the role of volumetric capnography for the clinical monitoring of mechanical ventilation.

Volume-targeted ventilation: one size does not fit all. Evidence-based recommendations for successful use

Despite level 1 evidence for important benefits of volume-targeted ventilation (VTV), many vulnerable extremely preterm infants continue to be exposed to traditional pressure-controlled ventilation. Lack of suitable equipment and a lack of appreciation of the fact that 'one size does NOT fit all' appear to contribute to the slow uptake of VTV. This review attempts to improve clinicians' understanding of the way VTV works and to provide essential information about evidence-based tidal volume (V_T) targets. Focus on underlying lung pathophysiology, individualised ventilator settings and V_Ttargets are keys to successful use of VTV thereby improving important clinical outcomes.

Optimal management of apparatus dead space in the anesthetized infant

Mechanical ventilation of the anesthetized infant requires careful attention to equipment and ventilator settings to assure optimal gas exchange and minimize the potential for lung injury. Apparatus dead space, defined as dead space resulting from devices placed between the endotracheal tube and the Y-piece of the breathing circuit, is the primary source of dead space controlled by the clinician. Due to the small tidal volumes required by infants and neonates, it is easy to create excessive apparatus dead space resulting in unintended hypercarbia or increased minute ventilation in an effort to achieve a desirable PCO₂ . The goal of this review was to evaluate the apparatus that are commonly added to the breathing circuit during anesthesia care, and develop recommendations to guide the clinician in selecting apparatus that are best matched to the clinical goals and the patient's size. We include specific recommendations for apparatus that are best suited for different size pediatric patients, with a particular focus on patients <5 kg.

Effect of inspiratory flow rate on the efficiency of carbon dioxide removal at tidal volumes below instrumental dead space

OBJECTIVE

The ability to ventilate babies with tidal volumes (V_Ts) below dead space has been demonstrated both in vivo and in vitro, though it appears to violate classical respiratory physiology. We hypothesised that this phenomenon is made possible by rapid flow of gas that penetrates the dead space allowing fresh gas to reach the lungs and that the magnitude of this phenomenon is affected by flow rate or how rapidly air flows through the endotracheal tube.

METHODS

We conducted two bench experiments. First, we measured the time needed for complete CO₂ washout from a test lung to assess how fixed V_T but different inflation flow rates affect ventilation. For the second experiment, we infused carbon dioxide at a low rate into the test lung, varied the inflation flow rate and adjusted the V_T to maintain stable end tidal carbon dioxide (ETCO₂).

RESULTS

At all tested V_Ts, lower flow rate increased the time it took for CO₂ to washout from the test lung. The effect was most pronounced for V_Ts below dead space. The CO₂ steady-state experiment showed that ETCO₂ increased when the flow rate decreased. Ventilating with a slower flow rate required a nearly 20% increase in V_T for the same effective alveolar ventilation.

CONCLUSIONS

Inflation flow rate affects the efficiency of CO₂ removal with low V_T. Our results are relevant for providers using volume-controlled ventilation or other modes that use low inflation flow rates because the V_T required for normocapnia will be higher than published values that were generated using pressure-limited ventilation modes with high inflation flows.

Basic principles of respiratory function monitoring in ventilated newborns: A review

Respiratory monitoring during mechanical ventilation provides a real-time picture of patient-ventilator interaction and is a prerequisite for lung-protective ventilation. Nowadays, measurements of airflow, tidal volume and applied pressures are standard in neonatal ventilators. The measurement of lung volume during mechanical ventilation by tracer gas washout techniques is still under development. The clinical use of capnography, although well established in adults, has not been embraced by neonatologists because of technical and methodological problems in very small infants. While the ventilatory parameters are well defined, the calculation of other physiological parameters are based upon specific assumptions which are difficult to verify. Incomplete knowledge of the theoretical background of these calculations and their limitations can lead to incorrect interpretations with clinical consequences. Therefore, the aim of this review was to describe the basic principles and the underlying assumptions of currently used methods for respiratory function monitoring in ventilated newborns and to highlight methodological limitations.

Influence of gestational age on dead space and alveolar ventilation in preterm infants ventilated with volume guarantee

BACKGROUND

Ventilated preterm infant lungs are vulnerable to overdistension and underinflation. The optimal ventilator-delivered tidal volume (VT) in these infants is unknown and may depend on the extent of alveolarisation at birth.

OBJECTIVES

We aimed to calculate respiratory dead space (VD) from the molar mass (MM) signal of an ultrasonic flowmeter (VD,MM) in very preterm infants on volume-targeted ventilation (VT target, 4-5 ml/kg) and to study the association between gestational age (GA) and VD,MM-to-VT ratio (VD,MM/VT), alveolar tidal volume (VA) and alveolar minute volume (AMV).

METHODS

This was a single-centre, prospective, observational, cohort study in a neonatal intensive care unit. Tidal breathing analysis was performed in ventilated very preterm infants (GA range 23-32 weeks) on day 1 of life.

RESULTS

Valid measurements were obtained in 43/51 (87%) infants. Tidal breathing variables were analysed using multivariable linear regression. VD,MM/VT was negatively associated with GA after adjusting for birth weight Z score (p < 0.001, R(2) = 0.26). This association was primarily influenced by the appliance dead space. Despite similar VT/kg and VA/kg across all studied infants, respiratory rate and AMV/kg increased with GA.

CONCLUSIONS

VD,app rather than anatomical VD is the major factor influencing increased VD,MM/VT at a younger GA. A volume guarantee setting of 4-5 ml/kg in the Dräger Babylog® 8000 plus ventilator may be inappropriate as a universal target across the GA range of 23-32 weeks. Differences between measured and set VT and the dependence of this difference on GA require further investigation.

Setting the Ventilator in the NICU

Success in providing respiratory support to the neonate requires a clear understanding of the context in which it is being applied. Perhaps more than for any other age group, the array of different situations in which ventilation is applied to the newborn infant is extremely broad, with in each case different pathophysiological disturbances and often the need to use a specific approach to apply ventilation optimally. Table 42.1 provides a list of the more common situations in which conventional ventilation is used in the neonate and includes some considerations regarding ventilator settings for each situation. For each situation, a suggested mode of ventilation is indicated, along with target ranges for positive end-expiratory pressure (PEEP) and tidal volume (V_T). Further discussion of the physiological rationale and available evidence for ventilator settings is set out below.

Dead space reduction by Kolobow's endotracheal tube does not justify the waiving of volume monitoring in small, ventilated lungs

In ventilated preterm infants the flow sensor contributes significantly to the total apparatus dead space, which may impair gas exchange. The aim of the study was to quantify to which extent a dead space reduced Kolobow tube (KB) without flow sensor improves the gas exchange compared with a conventional ventilator circuit with flow sensor [Babylog 8000 (BL)]. In a cross-over trial in 14 tracheotomized, surfactant-depleted (saline lavage) and mechanically ventilated newborn piglets (age <12 h; body weight 705-1200 g) BL and KB was applied alternately for 15 min and blood gases were recorded. The inner diameter of the endotracheal tube was 3.6 mm and the apparatus dead space of BL and KB including the endotracheal tube were 3.0 and 1.34 mL. Despite a 50 % apparatus dead space reduction with KB compared to BL statistically significant improvements were only observed for body weights <900 g. In this weight group median paCO2 was decreased by 5 mmHg (p < 0.01), whereas the improvement decreased with decreasing baseline paCO2. Furthermore, median paO2 was increased by 4 mmHg (p < 0.05) and O2 saturation was increased by 2.5 % (p < 0.05). No significant changes were seen in the circulatory parameters. In very small, ventilated lungs the use of KB improved the gas exchange; however, the improvement was moderate and does not justify the waiving of volume monitoring.

A practical guide to neonatal volume guarantee ventilation

A recent systematic review and meta-analysis shows that volume-targeted ventilation (VTV) compared with pressure-limited ventilation (PLV) reduce death and bronchopulmonary dysplasia, pneumothorax, hypocarbia and severe cranial ultrasound abnormalities. In this paper, we present published research and our experience with volume guarantee (VG) ventilation, a VTV mode available on the Dräger Babylog 8000plus and VN500 ventilators. The VG algorithm measures the expired tidal volume (V(T)) for each inflation and adjusts the peak inflating pressure for the next inflation to deliver a V(T) set by the clinician. The advantage of controlling expired V(T) is that this is less influenced by endotracheal tube leak than inspired V(T). VG ventilation can be used with an endotracheal tube leak up to ∼50%. Initial set V(T) for infants with respiratory distress syndrome should be 4.0 to 5.0 ml kg(-1). The set V(T) should be adjusted to maintain normocapnoea. Setting the peak inflating pressure limit well above the working pressure is important to enable the ventilator to deliver the set V(T), and to avoid frequent alarms. This paper provides a practical guide on how to use VG ventilation.

Effects of instrumental dead space reduction during weaning from synchronized ventilation in preterm infants

OBJECTIVE

A majority of the modalities of synchronized ventilation in preterm infants require the use of flow sensors that can increase dead space and may adversely affect ventilator weaning. The objective of this study was to assess the effects of flow sensor dead space during synchronized intermittent mandatory ventilation (SIMV) weaning in preterm infants.

STUDY DESIGN

Twelve preterm infants (gestational age 25+/-2 weeks, birth weight 705+/-158 g, age: 31+/-186 days, SIMV rate: 25+/-8 breaths min(-1), peak inspiratory pressure 18+/-2 cm H(2)O, positive end-expiratory pressure: 5+/-0.5 cm H(2)O, pressure support: 9+/-3 cm H(2)O, fraction of inspired oxygen: 34+/-6%) underwent two 2.5-h weaning periods during which SIMV rate was reduced twice by 5 breaths min(-1) at 30-min intervals as tolerated, with and without reduction of flow sensor dead space, in random sequence. A 30-min baseline was obtained before each weaning period. Dead space was reduced by flushing the flow sensor with a continuous gas leak flow in the endotracheal tube connector.

RESULT

Transcutaneous CO(2) tension during SIMV weaning periods without and with reduced dead space did not differ from baseline, whereas total minute ventilation and tidal volume were lower during the SIMV weaning period with reduced dead space. Three infants did not tolerate SIMV weaning without while one infant did not tolerate weaning with reduced dead space.

CONCLUSION

SIMV weaning elicited a compensatory rise in spontaneous ventilation. When flow sensor dead space was reduced during SIMV weaning, gas exchange was maintained with lower minute ventilation. Instrumental dead space imposes a ventilatory burden during SIMV weaning in small preterm infants.

The proper tidal volume target using volume guarantee ventilation in the course of neonatal respiratory distress syndrome: a crucial endpoint

Volume guarantee ventilation (VGV) is an optional ventilation mode which has become the most widely and extensively studied in the last 10 years in premature infants. Nonetheless, theoretical expected endpoints are intriguing and even though VGV has not yet become 'the' standard ventilation mode, a great deal of information has been acquired and stored. In our experience, VGV during the course of respiratory distress syndrome is useful and can be considered a standard ventilation mode. Weaning occurs in real time as described earlier, and synchronized intermittent positive pressure ventilation and pressure support ventilation (PSV) seem to be the preferred combined modes. Management during the acute phase requires more care since several sudden changes take place in both the lung mechanics and clinical behavior. The software is designed to protect the lung, and subsequently, sudden changes in lung compliance following iatrogenic procedures such as surfactant administration are powerfully counteracted. VGV has been extensively studied and the proposed algorithm has been found to function as planned. Although the 'superiority' of one method over another cannot be demonstrated, the use of new technologies require 'a staff learning curve' and homogeneity of treatment, while at the same time other factors, such as patient heterogeneity or illness phase, should be taken into due account.

INSURE, Infant Flow, Positive Pressure and Volume Guarantee--tell us what is best: selection of respiratory support modalities in the NICU

Selecting the optimal mode of respiratory support remains a daily challenge for the practicing neonatologist. We are faced with a bewildering array of modalities and a paucity of definitive studies to guide our decisions. In this context the choice of therapies must be guided by evidence-based guidelines, supplemented by a solid understanding of the pathophysiology of lung injury, an appreciation of the individual patient's specific disease process/physiologic derangement. The sequential application of the least invasive treatment to achieve the relevant therapeutic goal with frequent re-evaluation of the patient's need and possible escalation of support as needed, coupled with the application of lung-protective strategies of respiratory support appears to offer the best chance of minimizing adverse pulmonary and neurodevelopmental outcomes.

State of the art in conventional mechanical ventilation

Despite a shift to noninvasive respiratory support, mechanical ventilation remains an essential tool in the care of critically ill neonates. The availability of a variety of technologically advanced devices with a host of available modes and confusing terminology presents a daunting challenge to the practicing neonatologist. Many of the available modes have not been adequately evaluated in newborn infants and there is paucity of information on the relative merits of those modes that have been studied. This review examines the special challenges of ventilating the extremely low birth weight infants that now constitute an increasing proportion of ventilated infants, attempts to provide a simple functional classification of ventilator modes and addresses the key aspects of synchronized ventilation modes. The rationale for volume-targeted ventilation is presented, the available modes are described and the importance of the open-lung strategy is emphasized. The available literature on volume-targeted modalities is reviewed in detail and general recommendations for their clinical application are provided. Volume guarantee has been studied most extensively and shown to reduce excessively large tidal volumes, decrease incidence of inadvertent hyperventilation, reduce duration of mechanical ventilation and reduce pro-inflammatory cytokines. It remains to be seen whether the demonstrated short-term benefits translate into significant reduction in chronic lung disease. Avoidance of mechanical ventilation by means of early continuous positive airway pressure with or without surfactant administration may still be the most effective way to reduce the risk of lung injury. For babies who do require mechanical ventilation, the combination of volume-targeted ventilation, combined with the open-lung strategy appears to offer the best chance of reducing the risk of bronchopulmonary dysplasia.