Volume-controlled ventilation. Variations on a theme

Mechanical ventilation modes for respiratory distress syndrome in infants: a systematic review and network meta-analysis

Introduction

The effects of different mechanical ventilation (MV) modes on mortality outcome in infants with respiratory distress syndrome (RDS) are not well known.

Methods

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, EMBASE, MEDLINE, CINAHL, and Web of Science for studies published through April 2014 that assessed mortality in infants with RDS given different MV modes. We assessed studies for eligibility, extracted data, and subsequently pooled the data. A Bayesian fixed-effects model was used to combine direct comparisons with indirect evidence. We also performed sensitivity analyses and rankings of the competing treatment modes.

Results

In total, 20 randomized controlled trials were included for the network meta-analysis, which consisted of 2,832 patients who received one of 16 ventilation modes. Compared with synchronized intermittent mandatory ventilation (SIMV) + pressure support ventilation (PSV), time-cycled pressure-limited ventilation (TCPL) (hazard ratio (HR) 0.290; 95% confidence interval (CI) 0.071 to 0.972), high-frequency oscillatory ventilation (HFOV) (HR 0.294; 95% CI 0.080 to 0.852), SIMV + volume-guarantee (VG) (HR 0.122; 95% CI 0.014 to 0.858), and volume-controlled (V-C) (HR 0.139; 95% CI 0.024 to 0.677) ventilation modes are associated with lower mortality. The combined results of available ventilation modes were not significantly different in regard to the incidences of patent ductus arteriosus and intraventricular hemorrhage.

Conclusion

Compared with the SIMV + PSV ventilation mode, the TCPL, HFOV, SIMV + VG, and V-C ventilation modes are associated with lower mortality.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0843-7) contains supplementary material, which is available to authorized users.

Volume-targeted ventilation is more suitable than pressure-limited ventilation for preterm infants: a systematic review and meta-analysis

OBJECTIVE

To assess the effect of volume-targeted ventilation (VTV) compared with pressure-limited ventilation (PLV) in preterm infants.

METHOD

We searched the Cochrane Library (Issue 3, 2013), PubMed (1966 to 5 March 2013), China National Knowledge Infrastructure (CNKI) and periodical databases (1979 to 5 March 2013). We selected randomised controlled trials (RCTs) and quasi-RCTs of VTV versus PLV as active interventions in preterm infants. We performed meta-analyses using the Cochrane statistical package RevMan 5.0.

RESULTS

Eighteen trials met our inclusion criteria. There was no evidence that VTV modes reduced the incidence of death (relative risk (RR) 0.73, 95% CI 0.51 to 1.05). The use of VTV modes resulted in a reduction in the incidence of bronchopulmonary dysplasia (BPD) (RR 0.61, 95% CI 0.46 to 0.82) and duration of mechanical ventilation (mean difference (MD) -2.0 days, 95% CI -3.14 to -0.86). VTV modes also resulted in reductions in intraventricular haemorrhage (IVH) (RR 0.65, 95% CI 0.42 to 0.99), grade 3/4 IVH (RR 0.55, 95% CI 0.39 to 0.79), periventricular leukomalacia (PVL) (RR 0.33, 95% CI 0.15 to 0.72), pneumothorax (RR 0.52, 95% CI 0.29 to 0.93), failure of primary mode of ventilation (RR 0.64, 95% CI 0.43 to 0.94), hypocarbia (RR 0.56, 95% CI 0.33 to 0.96), mean airway pressure (MD -0.54 cmH2O, 95% CI -1.05 to -0.02) and days of supplemental oxygen administration (MD -1.68 days, 95% CI -2.47 to -0.88).

CONCLUSIONS

Preterm infants ventilated using VTV modes had reduced duration of mechanical ventilation, incidence of BPD, failure of primary mode of ventilation, hypocarbia, grade 3/4 IVH, pneumothorax and PVL compared with preterm infants ventilated using PLV modes. There was no evidence that infants ventilated with VTV modes had reduced death compared to infants ventilated using PLV modes.

Early neonatal outcomes of volume guaranteed ventilation in preterm infants with respiratory distress syndrome

BACKGROUND

Volume guaranteed (VG) synchronized intermittent mandatory ventilation (SIMV) is a novel mode of SIMV that provides automatic adjustment of the peak inspiratory pressure for ensuring a minimum set tidal volume and there are limited data about the effects of VG ventilation on short term neonatal outcomes in preterm infants with respiratory distress syndrome (RDS).

OBJECTIVE

The main objective of this study was to evaluate the effect of VG ventilation on duration of ventilation and total supplemental oxygen. We also aimed to compare the early neonatal outcomes of VG ventilation versus conventional SIMV on short-term outcomes in preterm babies with RDS who were given surfactant.

METHODS

In this randomized controlled study, preterm infants who were admitted with RDS and given surfactant were divided into 2 groups: group 1 included infants ventilated on conventional SIMV (n = 30) and group 2 included infants ventilated on VG ventilation (n = 42). Neonatal morbidities such as air leak, bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH), retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC) and duration of mechanical ventilation and total oxygen supplementation were all recorded.

RESULTS

There were no significant differences between two groups in terms of demographic features. Infants ventilated with VG mode had significantly shorter duration of ventilation and need of total supplemental oxygen. The incidences of oxygen related short term complications including BPD, ROP, and IVH were also significantly lower in these infants compared with those ventilated with conventional SIMV. No significant differences were found between two groups with respect to NEC and air leak.

CONCLUSION

In conclusion, VG ventilation in combination with surfactant treatment significantly reduced both duration of mechanical ventilation and early neonatal oxygen related morbidities including BPD, ROP and IVH in preterm infants with RDS. This data favors the use of VG ventilation in respiratory support of premature infants.

Ventilatory management and bronchopulmonary dysplasia in preterm infants

Improvements in antenatal and neonatal care have resulted in increased survival of very preterm infants. However, the incidence of bronchopulmonary dysplasia (BPD) has not changed, probably as a consequence of a demographic shift. The underlying pathophysiology of BPD appears to differ for the current population of preterm infants compared to that described by Northway et al., and management strategies should be targeted to limit ventilator-induced lung injury. Non-invasive respiratory support techniques are currently under evaluation, but results of the trials have thus far failed to show a reduction in BPD. This review will focus upon various ventilation modalities for preventing and managing bronchopulmonary dysplasia.

Newer forms of conventional ventilation for preterm newborns

Although life saving, mechanical ventilation can cause complications such as ventilator-induced lung injury and bronchopulmonary dysplasia in very preterm babies. The ventilator-induced lung injury is multi-factorial. There has been an introduction of a number of newer forms of mechanical ventilation, which are aimed to reduce such complications. These are based on sound physiologic principles and clinicians should familiarize themselves with these advances.

Volume-targeted ventilation of newborns

Traditional management of neonatal respiratory failure has been accomplished with mechanical ventilation delivered by time-cycled, pressure-limited techniques. Although easy to use, this modality results in the delivery of tidal volumes that vary according to pulmonary compliance. In contrast, volume-targeted ventilation delivers a selected tidal volume at variable peak inspiratory pressure, resulting in consistent tidal volume delivery, even in the face of changing compliance. This article reviews salient features of volume-targeted ventilation and a review of the evidence base.

Mechanical ventilation of very low birth weight infants: is volume or pressure a better target variable?

OBJECTIVE

To compare the efficacy and safety of volume-controlled (VC) ventilation to time-cycled pressure-limited (TCPL) ventilation in very low birth weight infants with respiratory distress syndrome (RDS).

STUDY DESIGN

Newborns weighing between 600 and 1500 g and with a gestational age of 24 to 31 weeks who had RDS were randomized to receive either VC or TCPL ventilation and treated with a standardized protocol. The 2 modalities were compared by determining the time required to achieve a predetermined success criterion, on the basis of either the alveolar-arterial oxygen gradient <100 mm Hg or the mean airway pressure <8 cm H(2)O. Secondary outcomes included mortality, duration of mechanical ventilation, and complications commonly associated with ventilation.

RESULTS

The mean time to reach the success criterion was 23 hours in the VC group versus 33 hours in the TCPL group (P = .15). This difference was more striking in babies weighing <1000g (21 versus 58 hours; P = .03). Mean duration of ventilation with VC was 255 hours versus 327 hours with TCPL (P = .60). There were 5 deaths in the VC group and 10 deaths in the TCPL group (P = .10). The incidence of other complications was similar.

CONCLUSION

VC ventilation is safe and efficacious in very low birth weight infants and may have advantages when compared with TCPL, especially in smaller infants.

Volume-targeted ventilation and arterial carbon dioxide in neonates

OBJECTIVES

To review the arterial carbon dioxide tensions (PaCO(2)) in newborn infants ventilated using synchronized intermittent mandatory ventilation (SIMV) in volume guarantee mode (using the Dräger Babylog 8000+) with a unit policy targeting tidal volumes of approximately 4 mL/kg.

METHODS

Data on ventilator settings and arterial PaCO(2) levels were collected on all arterial blood gases (ABG; n = 288) from 50 neonates (<33 weeks gestational age) ventilated using the Dräger Babylog 8000+ ventilator (Dräger Medizintechnik GmbH, Lübeck, Germany) in SIMV plus volume guarantee mode. Data were analysed for all blood gases done on the entire cohort in the first 48 h of life and a subanalysis was done on the first gas for each infant (n = 38) ventilated using volume guarantee from admission to the nursery. The number of ABG showing severe hypocapnoea (PaCO(2) < 25 mmHg) and/or severe hypercapnoea (PaCO(2) > 65 mmHg) were determined.

RESULTS

The mean (SD) PaCO(2) during the first 48 h was 46.6 (9.0) mmHg. The mean (SD) PaCO(2) on the first blood gas of those infants commenced on volume guarantee from admission was 45.1 (12.5) mmHg. Severe hypo- or hypercapnoea occurred in 8% of infants at the time of their first blood gas measurement, and in <4% of blood gas measurements in the first 48 h.

CONCLUSIONS

Infants ventilated with volume guarantee ventilation targeting approximately 4 mL/kg (range: 2.9-5.1) have acceptable PaCO(2) levels at the first blood gas measurement and during the first 48 h of life; and avoid severe hypo- or hypercapnoea over 90% of the time.

Changing trends in the management of respiratory distress syndrome (RDS)

The management of respiratory distress syndrome (RDS) has advanced because of improvements in mechanical ventilators, promotion of antenatal steroids, availability of surfactant and overall advancements in neonatal intensive care. Intermittent mandatory ventilation still forms the mainstay of assisted ventilation. Newer modes of ventilation have not delivered the results as promised. Because of the continued high incidence of bronchopulmonary dysplasia, there is a renewed interest in non-invasive modes of ventilation like CPAP and nasal IPPV. The present trend is to follow gentle ventilatory strategies accepting higher arterial carbon dioxide and lower oxygen. The role of antenatal steroids has been established beyond doubt but still they fall short of universal acceptance. Surfactant replacement therapy is the standard of care for RDS but beyond the reach of majority in India. Postnatal steroids are out of vogue because of probable links with cerebral palsy and abnormal neurological outcomes.

Volume-guaranteed ventilation

Pressure-limited, time-cycled ventilation has been the primary mode of ventilation for neonates for several decades. But the realization that volume rather than pressure causes ventilator-induced lung injury has led to the development of new strategies for ventilation. Volume guarantee is a mode of ventilation that automatically adjusts the inspiratory pressure to achieve a set tidal volume according to changes in lung compliance or resistance or the patient's respiratory drive. Volume-guaranteed ventilation delivers a specific, preset volume of gas, and inspiration ends when it has been delivered. This mode of ventilation requires careful attention to the infant and to ventilator settings.

Newer techniques of mechanical ventilation: an overview

The introduction of newer, state-of-the-art, microprocessor controlled ventilator systems provides clinicians with opportunities to apply a number of advanced ventilatory modalities which were not previously available for treating newborns. Some of these techniques will need further scientific evaluation in controlled trials, but this should not preclude their use in clinical settings, as their safety has already been proved by "standard setters" for use in neonates. There is a firm physiological rationale for their use, and individual centres have already acquired substantial experience in the application of these modalities. The trend towards increasing sophistication and greater versatility is likely to continue, and clinicians involved in the care of sick newborn infants must keep abreast of these developments.

Weaning newborns from mechanical ventilation

While there is a relative consensus as to whether mechanical ventilation should be initiated, the management of babies during recovery from respiratory failure remains largely subjective and is predominantly determined by institutional or individual practices or preferences. This can lead to babies either being left on the ventilator too long, or extubated too hastily, thus requiring repeated re-intubation. The current scientific literature fails to provide a uniform view of the most appropriate way to wean babies from mechanical ventilation. This might stem from a lack of understanding of the relative merits of the different techniques of discontinuing mechanical ventilation, given the availability of a variety of primary ventilatory modes which were not available to a neonatal population before, and limited research into the pathophysiological mechanisms responsible for an unsuccessful extubation. The purpose of this paper is to review the physiological, mechanical, and clinical principles of weaning, and to highlight areas still in need of investigation.