Randomised controlled trial of respiratory system compliance measurements in mechanically ventilated neonates

What CPAP to use in the delivery room? Bench comparison of two methods to provide continuous positive airways pressure in neonates

BACKGROUND

Continuous positive airway pressure (CPAP) is a recommended first-line therapy for infants with respiratory distress at birth. Resuscitation devices incorporating CPAP delivery can have significantly different imposed resistances affecting airway pressure stability and work of breathing.

AIM

To compare CPAP performance of two resuscitation devices (Neopuff T-piece resuscitator and rPAP) in a neonatal lung model simulating spontaneous breathing effort at birth.

METHODS

The parameters assessed were variation in delivered pressures (∆P), tidal volume (VT), inspiratory effort (model pressure respiratory muscle (PRM)) and work of breathing (WOB). Two data sequences were required with Neopuff and one with rPAP: (1) set PRM with changes in VT and (2) constant VT (preterm 6 mL, term 22 mL) with increased effort. Data were collected at CPAP settings of 5, 7 and 9 cmH2O using a 1 kg preterm (Compliance: 0.5 mL/cmH2O) and 3.5 kg term (1.0 mL/cmH2O) model.

RESULTS

2298 breaths were analysed (760 rPAP, 795 Neopuff constant VT, 743 Neopuff constant PRM). With CPAP at 9 cmH2O and set VT the mean ∆P (cmH2O) rPAP vs Neopuff 1.1 vs 5.6 (preterm) and 1.9 vs 13.4 (term), WOB (mJ) 4.6 vs 6.1 (preterm) and 35.3 vs 44.5 (term), and with set PRM mean VT (ml) decreased to 6.2 vs 5.2 (preterm) and 22.3 vs 17.5 (term) p<0.001. Similar results were found at pressures of 5 and 7 cmH2O.

CONCLUSION

rPAP had smaller pressure swings than Neopuff at all CPAP levels and was thus more pressure stable. WOB was higher with Neopuff when VT was held constant. VT reduced with Neopuff when respiratory effort was constant.

An Official American Thoracic Society/European Respiratory Society Workshop Report: Evaluation of Respiratory Mechanics and Function in the Pediatric and Neonatal Intensive Care Units

Ready access to physiologic measures, including respiratory mechanics, lung volumes, and ventilation/perfusion inhomogeneity, could optimize the clinical management of the critically ill pediatric or neonatal patient and minimize lung injury. There are many techniques for measuring respiratory function in infants and children but very limited information on the technical ease and applicability of these tests in the pediatric and neonatal intensive care unit (PICU, NICU) environments. This report summarizes the proceedings of a 2011 American Thoracic Society Workshop critically reviewing techniques available for ventilated and spontaneously breathing infants and children in the ICU. It outlines for each test how readily it is performed at the bedside and how it may impact patient management as well as indicating future areas of potential research collaboration. From expert panel discussions and literature reviews, we conclude that many of the techniques can aid in optimizing respiratory support in the PICU and NICU, quantifying the effect of therapeutic interventions, and guiding ventilator weaning and extubation. Most techniques now have commercially available equipment for the PICU and NICU, and many can generate continuous data points to help with ventilator weaning and other interventions. Technical and validation studies in the PICU and NICU are published for the majority of techniques; some have been used as outcome measures in clinical trials, but few have been assessed specifically for their ability to improve clinical outcomes. Although they show considerable promise, these techniques still require further study in the PICU and NICU together with increased availability of commercial equipment before wider incorporation into daily clinical practice.

Advances in respiratory support for high risk newborn infants

BACKGROUND

A significant proportion of premature infants present with respiratory failure early in life and require supplemental oxygen and some form of mechanical respiratory support.

FINDINGS

Many technical advances in the devices for neonatal respiratory support have occurred in recent years and new management strategies have been developed and evaluated in this population. This article describes some of these novel methods and discusses their application and possible advantages and limitations.

CONCLUSION

Newer methods of respiratory support have led to marked improvement in outcome of premature infants with respiratory failure. Some of these strategies are very promising but further investigation to evaluate their short term efficacy and impact on long term respiratory and other relevant outcomes is needed before wider use.

Automated respiratory cycles selection is highly specific and improves respiratory mechanics analysis

OBJECTIVE

Selected optimal respiratory cycles should allow calculation of respiratory mechanic parameters focusing on patient-ventilator interaction. New computer software automatically selecting optimal breaths and respiratory mechanics derived from those cycles are evaluated.

DESIGN

Retrospective study.

SETTING

University level III neonatal intensive care unit.

SUBJECTS

Ten mins synchronized intermittent mandatory ventilation and assist/control ventilation recordings from ten newborns.

INTERVENTION

The ventilator provided respiratory mechanic data (ventilator respiratory cycles) every 10 secs. Pressure, flow, and volume waves and pressure-volume, pressure-flow, and volume-flow loops were reconstructed from continuous pressure-volume recordings. Visual assessment determined assisted leak-free optimal respiratory cycles (selected respiratory cycles). New software graded the quality of cycles (automated respiratory cycles). Respiratory mechanic values were derived from both sets of optimal cycles. We evaluated quality selection and compared mean values and their variability according to ventilatory mode and respiratory mechanic provenance. To assess discriminating power, all 45 "t" values obtained from interpatient comparisons were compared for each respiratory mechanic parameter.

MEASUREMENTS AND MAIN RESULTS

A total of 11,724 breaths are evaluated. Automated respiratory cycle/selected respiratory cycle selections agreement is high: 88% of maximal κ with linear weighting. Specificity and positive predictive values are 0.98 and 0.96, respectively. Averaged values are similar between automated respiratory cycle and ventilator respiratory cycle. C20/C alone is markedly decreased in automated respiratory cycle (1.27 ± 0.37 vs. 1.81 ± 0.67). Tidal volume apparent similarity disappears in assist/control: automated respiratory cycle tidal volume (4.8 ± 1.0 mL/kg) is significantly lower than for ventilator respiratory cycle (5.6 ± 1.8 mL/kg). Coefficients of variation decrease for all automated respiratory cycle parameters in all infants. "t" values from ventilator respiratory cycle data are two to three times higher than ventilator respiratory cycles.

CONCLUSIONS

Automated selection is highly specific. Automated respiratory cycle reflects most the interaction of both ventilator and patient. Improving discriminating power of ventilator monitoring will likely help in assessing disease status and following trends. Averaged parameters derived from automated respiratory cycles are more precise and could be displayed by ventilators to improve real-time fine tuning of ventilator settings.

Accuracy of tidal volume, compliance, and resistance measurements on neonatal ventilator displays: an in vitro assessment

OBJECTIVE

To determine the accuracy of measures of respiratory mechanics derived from neonatal ventilators using an in vitro passive physical lung model to simulate newborn pulmonary conditions.

DESIGN

Test lung models.

SETTING

Laboratory-based measurements.

INTERVENTIONS

Three test lungs were constructed to simulate three severities of neonatal lung disease, with ranges of compliance from 0.5 to 2.0 mL/cm H2O and resistance from 25 to 150 cm H2O/(L/sec). Each ventilator was tested using 27 combinations of peak inspiratory pressure (15-25 cm H2O), positive end-expiratory pressure (5-7 cm H2O), and rate settings (20-60 B/min). Data were compared for five different ventilators across simulated lung severity as the ratio of ventilator readout to test lung reference value. A ratio of 1.0 indicated a completely unbiased result.

MAIN RESULTS

Overall, four of the five ventilators under-read expired tidal volume by about 1%-12% across all lung conditions, whereas the VIP Bird readout ranged from -4% to +4% bias. Changes in ventilator settings had only a modest effect on mechanics readout. As peak inspiratory pressure progressed from 15 to 25 cm H2O, bias in tidal volume readout changed from +5.0% to -2.5% (p < .001) in the VIP Bird, and from -11% to -9% (p < .001) in the Draeger Babylog VN500. Between positive end-expiratory pressure levels of 5 and 7 cm H2O, tidal volume bias in the Babylog varied between -13% and -7% (p < .001). In progressing from simulated normal to severely ill lung condition, bias in compliance measurements by the Avea and SLE5000 increased from -18% to -40% whereas in the VIP Bird it remained between -17% to -13%, and in the Draeger Evita XL-neo it changed from +17% to -13% and from -8% to -16% in the Babylog. Ratio of ventilator resistance readout to reference value with progressing simulated lung condition changed from 2.0 to 1.0 for the Draeger Evita, 1.6 to 1.1 for the Babylog, 4.2 to 2.0 for the SLE, and from 11.7 to 5.6 for the VIP Bird. The Avea, by design, did not display resistances >100 cm H2O/(L/sec), but overestimated the simulated normal lung resistance of 25 cm H2O/(L/sec) by a factor of 2.5.

CONCLUSIONS

Neonatal ventilator respiratory mechanics measurements and computation methods need further standardization to be useful in clinical settings.

Telemedicine for the support of parents of high-risk newborn infants

BACKGROUND

Telemedicine is the use of electronic communications technology to provide care for patients when distance separates the practitioner and the patient. As the parents and families of infants admitted to the NICU require major support from health professionals in terms of information and time, telemedicine has the potential to increase this support.

OBJECTIVES

To evaluate if the use of telemedicine technology to support families of newborn infants receiving intensive care affects the length of hospital stay and parental/family satisfaction.

SEARCH METHODS

We searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, 2011, Issue 8), MEDLINE (from 1966 to September 2011), EMBASE (1980 to September 2011). We also searched ClinicalTrials.gov (http://www.clinicaltrials.gov) and the EudraCT (http://eudract.emea.eu.int) web sites. We searched the proceedings of conferences of the Canadian Society of Telehealth, American Telemedicine Association, the International Society for Telemedicine, the Annual Conference of The International e-Health Association, American Medical Informatics Association and MedInfo.

SELECTION CRITERIA

We attempted to identify randomised controlled trials that assessed the use of telemedicine designed to support parents of infants cared for in a Neonatal Intensive Care Unit (NICU) compared with standard support measures. Our primary outcome was the length of hospital stay, and secondary outcomes included parental and staff satisfaction, emergency hospital visits post-discharge and family utilisation of infant health-related resources.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the studies, extracted the data and assessed the risk of bias of the one included study using the standard methods of the Cochrane Neonatal Review Group. We planned to express treatment effects as risk ratio (RR), risk difference (RD), number needed to treat (NNT) and mean difference (MD) where appropriate, using a fixed-effect model.

MAIN RESULTS

A single study was included for analysis in this review. This study compared the use of telemedicine (Baby Carelink) for parents and families of infants in the NICU with a control group without access to this programme and assessed the length of hospital stay for the infants and family satisfaction in multiple components of infant care. The study shows no difference in the length of hospital stay (average length of stay: telemedicine group: 68.5 days (standard deviation (SD) 28.3 days), control group: 70.6 days (SD 35.6 days), MD -2.10 days (95% confidence interval: -18.85 to 14.65 days). There was insufficient information for further analysis of measures of family satisfaction.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or refute the use of telemedicine technology to support the parents of high-risk newborn infants receiving intensive care. Clinical trials are needed to assess the application of telemedicine to support parents and families of infants in NICU with length of hospital stay and their perception of NICU care as the major outcomes.

Evidence-based guideline for suctioning the intubated neonate and infant

The endotracheal tube (ETT) is the most common artificial airway used in NICUs. Suctioning of the ETT is imperative to maintain patency and prevent complications. An extensive review of the literature revealed a lack of standardized criteria or guidelines for suctioning the ETT of neonates and infants in the NICU. The purpose of this article is to report the implementation of an evidence-based guideline that can be utilized in NICU care.

Lung function tests in neonates and infants with chronic lung disease: lung and chest-wall mechanics

This is the fifth paper in a review series that summarizes available data and critically discusses the potential role of lung function testing in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy (CLDI). This review focuses on respiratory mechanics, including chest-wall and tissue mechanics, obtained in the intensive care setting and in infants during unassisted breathing. Following orientation of the reader to the subject area, we focused comments on areas of enquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically with respect to relevant methods, equipment and study design, limitations and strengths of different techniques, and availability and appropriateness of reference data. Recommendations to guide future investigations in this field are provided. Numerous different methods have been used to assess respiratory mechanics with the aims of describing pulmonary status in preterm infants and assessing the effect of therapeutic interventions such as surfactant treatment, antenatal or postnatal steroids, or bronchodilator treatment. Interpretation of many of these studies is limited because lung volume was not measured simultaneously. In addition, populations are not comparable, and the number of infants studied has generally been small. Nevertheless, results appear to support the pathophysiological concept that immaturity of the lung leads to impaired lung function, which may improve with growth and development, irrespective of the diagnosis of chronic lung disease. To fully understand the impact of immaturity on the developing lung, it is unlikely that a single parameter such as respiratory compliance or resistance will accurately describe underlying changes. Assessment of respiratory mechanics will have to be supplemented by assessment of lung volume and airway function. New methods such as the low-frequency forced oscillation technique, which differentiate the tissue and airway components of respiratory mechanics, are likely to require further development before they can be of clinical significance.

Neonatal research: the parental perspective

OBJECTIVES

To investigate the recollections of parents consenting for their infants to be research subjects and determine their views about the need for consent.

SUBJECTS

Parents of 154 sick newborn infants enrolled in a randomised trial in the early neonatal period. All parents had given written consent and received printed information.

METHODS

A questionnaire and accompanying letter was sent to the parental home 18 months later. Non-responders were sent a further questionnaire and letter.

RESULTS

Response rate was 64% (99/154). Some respondents (12%) did not remember being asked to consent to their baby joining a study, and a further 6% were unsure. Most of the respondents (79%) were happy, 13% neutral, and 8% unhappy with their decision to give consent. None felt heavy pressure to agree. Entering the trial caused 24% of respondents to feel more anxious, 56% neutral, and 20% less anxious about their baby. Most of the respondents (83%) would be unhappy to forgo the consent process for trials passed by the institutional ethics committee.

CONCLUSIONS

A significant proportion of parents who give written consent for a trial in the early neonatal period do not later remember having done so. Parents who have had experience of neonatal research would be unhappy for their baby to be enrolled in a study that had ethics committee approval without their consent being obtained.

Accuracy of displayed values of tidal volume in the pediatric intensive care unit

OBJECTIVES

To assess the accuracy of the expired tidal volumes (VT(E)) displayed by one of the most frequently used ventilators that measures exhaled volume at the expiratory valve.

DESIGN

Prospective study.

SETTING

The intensive care units of a pediatric tertiary referral center in London, UK.

PATIENTS

A total of 56 intubated children aged between 3 wks and 16.6 yrs who were clinically stable and ventilated with a Servo 300 ventilator.

INTERVENTIONS

The CO2SMO Plus respiratory monitor, which measures flow at the airway opening, was validated using calibrated syringes and appropriate tracheal tubes and connections. Simultaneous in vivo recordings of VT(E) from the Servo 300 and CO2SMO Plus were compared before (displayed Servo VT(E)) and after (effective Servo VT(E)) compensating for ventilator circuit compliance.

MEASUREMENTS AND MAIN RESULTS

The in vitro accuracy of the CO2SMO Plus was within +/-5% over a wide range of volumes and measurement conditions. The displayed Servo 300 VT(E) overestimated the true VT(E) by between 2% and 91%. The magnitude of error varied within and between children, according to pressure change (peak inspiratory pressure minus positive end-expiratory pressure), VT(E), and circuit size. Mean (sd) error was 32% (20%) in 40 children with displayed Servo VT(E) of <160 mL and 18% (6%) in 16 subjects with displayed Servo VT(E) of >/=160 mL. After correcting for gas compression, effective VT(E) from the Servo 300 underestimated the true VT(E) by up to 64% in the smallest infants but continued to overestimate by as much as 29% in older children.

CONCLUSIONS

The accuracy of tidal volume values is crucially dependent on the site of measurement. Unless measured at the airway opening, displayed values are an inconsistent and misleading indicator of the true volumes delivered.

Effect of delayed sternal closure after cardiac surgery on respiratory function in ventilated infants

OBJECTIVE

Studies examining the effect of sternal closure on respiratory function have not been published, and currently there is little evidence to guide ventilation management immediately after closure. The aim of this study was to establish the impact of delayed sternal closure on expired tidal volume, respiratory system compliance, and CO2 elimination immediately after the procedure in infants who had undergone open heart surgery.

DESIGN

Prospective study of respiratory function before and after delayed sternal closure.

SETTING

Cardiac intensive care unit, Great Ormond Street Hospital, London.

PATIENTS

Seventeen infants (median age, 2 wks) with open median sternotomy incisions after cardiac surgery. Data were collected between August 1998 and March 2000.

INTERVENTIONS

Respiratory function was measured continuously for 30 mins before and after delayed sternal closure in paralyzed ventilated infants.

MEASUREMENTS AND RESULTS

Four babies were excluded from the study because they required either immediate increase in ventilation after delayed sternal closure (n = 3) or removal of pericardial blood collection (n = 1). In the remaining 13 infants, expired tidal volume and CO2 elimination decreased significantly (p < .005) by a mean of 17% and 29%, respectively, after sternal closure. In five of the remaining 13 patients, the magnitude of tracheal tube leak increased by > or = 10% after delayed sternal closure, thereby invalidating recorded changes in respiratory system compliance. Of the eight infants in whom there was a minimal change in leak, respiratory system compliance decreased significantly (p < .05) by a mean of 19%.

CONCLUSIONS

This study supports the hypothesis that respiratory function may be compromised after delayed sternal closure and that ventilatory support should be increased to counteract the anticipated decrease in tidal volume. Extra vigilance should be applied in monitoring blood gases after delayed sternal closure to assess clinical responses to sternal closure or changes in ventilatory support. Accurate assessment of change in respiratory system compliance after any therapeutic intervention may be precluded by changes in tracheal tube leak during the procedure.

Enhancement of mechanical ventilation of neonates by computer technology

Mechanical ventilation is often required in the extremely small preterm infant because of transient failure of the immature control of breathing system, chest wall instability, weakness of the respiratory pump, and chronic lung disease. To better address some of these issues, computer algorithms have been developed for continuous automated control of the arterial hemoglobin oxygen saturation (by changing the fraction of inspired oxygen), of the tidal volume (by varying peak inspiratory pressure), and of minute ventilation (by changing respirator rate). Feasibility studies have shown that closed-loop computer control of physiologic target variables may stabilize oxygenation, decrease the transpulmonary pressure cost of ventilation, and expedite weaning from mechanical ventilation. In addition to synchronizing the upstroke in ventilator pressure with the onset of the spontaneous respiratory effort, computer technology may render the changeover from inspiration to expiration patient-cycled in a mode called pressure support ventilation. Proportional assist ventilation enhances ventilation in near perfect synchrony with the patient's spontaneous respiratory efforts. With this mode, the clinician selects gains for elastic and/or resistive unloading to tailor the ventilator pressure contour to the specific derangement in pulmonary mechanics (restrictive and/or obstructive). Most of these newer ventilatory strategies are as yet unproven and require randomized, controlled clinical study. Similarly, although on-line pulmonary mechanics monitoring during mechanical ventilation has become available with the adent of computer technology, its clinical utility is still not well established.

Ventilator-induced overdistension in children: dynamic versus low-flow inflation volume-pressure curves

We applied to 20 paralyzed ventilated children (0.15 to 14.3 yr, six with acute respiratory distress syndrome [ARDS]) the low-flow inflation (LFI) technique providing quasi-static volume-pressure (V-P) curves and compared the assessment of overdistension (OD) on dynamic and LFI (reference) inspiratory V-P curves. Dynamic curves were obtained at the airway opening during regular constant flow ventilation (Servo 300). Then LFI curves were obtained. Two analyses were performed: First, the nonlinear coefficient c of a second order polynomial equation (SOPE) fitted to dynamic data obtained during constant flow was compared with the c of SOPE fitted to LFI curve (within tidal volume [VT]). Second, the dynamic C20/C (ratio of compliance of the last 20% of the curve (C20) to total compliance [C]) was compared with the determination of the upper inflection point (UIP) on the LFI curve. OD was defined as a negative value of c, a C20/C < 0.80, an UIP included within the VT range for that child during regular ventilation. Using LFI V-P curves as reference, SOPE offered a better detection of OD than dynamic C20/C or the determination of the UIP by graphical means. Indeed the first analysis showed a substantial agreement (kappa 0.75) between dynamic c and LFI c detection of OD whereas the second analysis showed a poor agreement (kappa 0.22) between C20/ C and LFI detection of the UIP. In conclusion, quasi-static V-P curves can easily be obtained in children with the LFI technique. SOPE offers a good detection of OD on dynamic and LFI V-P curves but the C20/C index seems to be an inadequate measure of OD.