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Meta-Analysis
. 2004 Oct 18;2003(4):CD004503.
doi: 10.1002/14651858.CD004503.pub2.

Long versus short inspiratory times in neonates receiving mechanical ventilation

C O F Kamlin  1 , P G Davis
Affiliations
Meta-Analysis

Long versus short inspiratory times in neonates receiving mechanical ventilation

C O F Kamlin et al. Cochrane Database Syst Rev. .

Abstract

Background: When intermittent positive pressure ventilation (IPPV) was introduced in newborn infants with hypoxic respiratory failure from hyaline membrane disease (HMD), mortality was high and air leaks problematic. This barotrauma was caused by the high peak inspiratory pressures (PIP) required to oxygenate stiff lungs. The primary determinants of mean airway pressure (and thus oxygenation) on a conventional ventilator are the inspiratory time (IT), PIP, positive end expiratory pressure and gas flow rates. In the 1970s uncontrolled studies on a small number of infants demonstrated a benefit in reducing barotrauma using a long IT and slow rates. This strategy was subsequently widely adopted. Current neonatal ventilators have been designed to minimise lung injury but rates of bronchopulmonary dysplasia (BPD) remain high. It is therefore important that the inspiratory time causing least harm is used.

Objectives: To determine in mechanically ventilated newborn infants whether the use of a long rather than a short IT reduces the rates of death, air leak and BPD.

Search strategy: The standard search strategy of the Cochrane Neonatal Review Group (CNRG) was used. Searches of electronic and other databases were performed. These included MEDLINE (1966 - April 2004) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2003). In order to detect trials that may not have been published, the abstracts of the Society for Pediatric Research, and the European Society for Pediatric Research were searched from 1998 - 2003.

Selection criteria: All randomised and quasi-randomised controlled trials enrolling mechanically ventilated infants with or without respiratory pathology evaluating the use of long versus short IT (including randomised crossover studies with outcomes restricted to differences in oxygenation).

Data collection and analysis: The standard method of the Cochrane Collaboration and its Neonatal Review Group were used. Two authors independently assessed eligibility, and the methodological quality of each trial, and extracted the data. The data were analysed using relative risk (RR) and risk difference (RD) and their 95% confidence intervals. A fixed effect model was used for meta-analyses.

Main results: In five studies, recruiting a total of 694 infants, a long IT was associated with a significant increase in air leak [typical RR 1.56 (1.25, 1.94), RD 0.13 (0.07, 0.20), NNT 8 (5, 14)]. There was no significant difference in the incidence of BPD. Long IT was associated with an increase in mortality before hospital discharge that reached borderline statistical significance [typical RR 1.26 (1.00, 1.59), RD 0.07 (0.00, 0.13)].

Reviewers' conclusions: Caution should be exercised in applying these results to modern neonatal intensive care, because the studies included in this review were conducted prior to the introduction of antenatal steroids, post natal surfactant and the use of synchronised modes of ventilatory support. Most of the participants had single pathology (HMD) and no studies examined the effects of IT on newborns ventilated for other reasons such as meconium aspiration and congenital heart disease (lungs with normal compliance). However, the increased rates of air leaks and deaths using long ITs are clinically important; thus, infants with poorly compliant lungs should be ventilated with a short IT.

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Conflict of interest statement

None

Figures

1.1
1.1. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 1 Mortality before discharge.
1.2
1.2. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 2 Air leak.
1.3
1.3. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 3 BPD (supplemental oxygen at 28 days).
1.4
1.4. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 4 AaDO2 (mmHg) values after 6 hours of intervention.
1.5
1.5. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 5 IVH (all grades).
1.6
1.6. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 6 Patent ductus arteriosus (PDA).
1.7
1.7. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 7 Cerebral palsy in survivors less than 33 weeks gestation at birth.
1.8
1.8. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 8 Visual impairment in survivors less than 33 weeks gestation at birth.
1.9
1.9. Analysis
Comparison 1 Long vs Short IT as defined by investigators (all trials), Outcome 9 Sensorineural hearing loss in survivors less than 33 weeks gestation at birth.
2.1
2.1. Analysis
Comparison 2 Long (greater than 0.5 seconds) vs Short IT (less than or equal to 0.5 seconds), Outcome 1 Mortality before discharge.
2.2
2.2. Analysis
Comparison 2 Long (greater than 0.5 seconds) vs Short IT (less than or equal to 0.5 seconds), Outcome 2 Air leak.
2.3
2.3. Analysis
Comparison 2 Long (greater than 0.5 seconds) vs Short IT (less than or equal to 0.5 seconds), Outcome 3 BPD (supplemental oxygenation at 28 days).
2.4
2.4. Analysis
Comparison 2 Long (greater than 0.5 seconds) vs Short IT (less than or equal to 0.5 seconds), Outcome 4 IVH (all grades).
3.1
3.1. Analysis
Comparison 3 Long vs Short IT in HMD (subgroup analysis by diagnosis), Outcome 1 Mortality before hospital discharge.
3.2
3.2. Analysis
Comparison 3 Long vs Short IT in HMD (subgroup analysis by diagnosis), Outcome 2 Air leak.
3.3
3.3. Analysis
Comparison 3 Long vs Short IT in HMD (subgroup analysis by diagnosis), Outcome 3 BPD (supplemental oxygen at 28 days).
4.1
4.1. Analysis
Comparison 4 Long vs Short IT (subgroup analysis by trials allowing use of muscle relaxation), Outcome 1 Mortality before discharge.
4.2
4.2. Analysis
Comparison 4 Long vs Short IT (subgroup analysis by trials allowing use of muscle relaxation), Outcome 2 Air leak.
4.3
4.3. Analysis
Comparison 4 Long vs Short IT (subgroup analysis by trials allowing use of muscle relaxation), Outcome 3 BPD (supplemental oxygen at 28 days).
4.4
4.4. Analysis
Comparison 4 Long vs Short IT (subgroup analysis by trials allowing use of muscle relaxation), Outcome 4 IVH (all grades).
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References

References to studies included in this review

Greenough 1989 {published data only}
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