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.
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.
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.
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.
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)].
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.
當新生兒因為呼吸窘迫症候群 (hyaline membrane disease) 導致缺氧呼吸衰竭，而開始使用間歇性的正壓呼吸 (IPPV) 時，致死率和氣漏的比率偏高；壓力損傷起因於為了使未成熟肺部換氣，而使用較高的吸氣期最大壓力 (PIP) 。在傳統呼吸器中，決定平均氣道壓力 (如此影響氧合狀態) 的因子有吸氣時間 (IT) 、PIP、吐氣末正壓 (positive end expiratory pressure) 和氣體氣流速 (gas flow rates) 。在1970年代有一些小型的研究顯示使用長吸氣時間以及慢速率可以減少壓力損傷，之後這結果被廣泛的採用。目前新生兒呼吸器是設計為減少肺部的傷害，可是肺支氣管發育不良 (BPD) 的發生率仍然偏高，所以使用適當的吸氣時間來減少傷害是很重要的。
使用Cochrane Neonatal Review Group的標準搜尋方式，搜尋電子資料和其他資料，包含MEDLINE (1966 April 2004) 和Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2003) ；為了找出未出版的研究，也含括1998 – 2003間，Society for Pediatric Research和European Society for Pediatric Research的摘要。
所有內容為比較呼吸器吸氣時間長短不論是否有呼吸道病理的隨機和準隨機 (randomised and quasirandomised controlled) 試驗(包含結果侷限於氧合狀況的隨機橫斷試驗)。
使用Cochrane Collaboration和其Neonatal Review Group的標準方法。兩位專家獨立評估每個研究的可納入與否方法品質和選取資料，這些資料使用relative risk (RR) 和risk difference (RD) 以及其95% 信賴區間來分析，使用fixed effect model來做統合分析 (metaanalyses) 。
在五個研究的694個嬰兒中，長的吸氣時間有較高的機會發生氣漏[typical RR 1.56 (1.25, 1.94), RD 0.13 (0.07, 0.20), NNT 8 (5, 14)]，BPD的發生機率則沒有差別，長吸氣時間增加出院前死亡率達到統計學有意義的邊緣[typical RR 1.26 (1.00, 1.59), RD 0.07 (0.00, 0.13)]。
因為這些研究都是在發展出使用產前類固醇、產後表面張力素以及使用同步呼吸模式之前所做，因此要應用這些結果需特別小心。多數列入研究的嬰兒的病因皆為呼吸窘迫症候群 (HMD) ，沒有研究檢視吸氣時間和其他使新生兒需使用呼吸器的原因之相關性，像是胎便吸入症候群或是先天性心臟病(肺部的彈性為正常者)。但是長吸氣時間會造成較高的機率的氣漏和死亡在臨床上非常重要，所以肺部彈性不好的嬰兒在使用呼吸器時應該採用短吸氣時間方式。
此翻譯計畫由臺灣國家衛生研究院 (National Health Research Institutes, Taiwan) 統籌。