Varughese M, Patole Sanjay, Shama A, Whitehall J
Department of Neonatology, Kirwan Hospital for Women, Townsville, Queensland 4814, Australia.
Pediatr Pulmonol. 2002 Jan;33(1):56-64. doi: 10.1002/ppul.10032.
Advances in neonatology have resulted in an increase in the absolute number of survivors with chronic lung disease (CLD), though its overall incidence has not changed. Though the single most important high-risk factor for CLD is prematurity, the focus of attention has recently changed over to minimizing the impact of other two risk factors: baro/volutrauma related to mechanical ventilation, and oxygen toxicity. Permissive hypercapnia (PHC) or controlled ventilation is a strategy that minimizes baro/volutrauma by allowing relatively high levels of arterial CO(2), provided the arterial pH does not fall below a preset minimal value. The benefits of PHC are primarily mediated by the reduction of lung stretch that occurs when tidal volumes are minimized. PHC can be a deliberate choice to restrict ventilation in order to avoid overdistention, while application of high airway pressures and large tidal volumes would permit normocapnia, or relative hypocapnia (PaCO(2), < or = 25-30 mmHg), but may result in CLD and be harmful to the developing lung. The current concept that PaCO(2) levels of 45-55 mmHg in high-risk neonates are "safe" and "well tolerated" is based on limited data. Further prospective trials are needed to study the definition, safety and efficacy of PHC in ventilated preterm and term neonates. However, designing disease/gestational-postnatal age-specific clinical trials of PHC will be difficult in neonates, given the diverse pathophysiology of their diseases and the various ventilatory modes/variables currently available. The potential benefits and adverse effects of PHC are reviewed, and its relationship to current ventilatory strategies like synchronized mechanical ventilation and high-frequency ventilation in high-risk neonates is briefly discussed.
新生儿学的进展使得慢性肺病（CLD）存活者的绝对数量有所增加，尽管其总体发病率并未改变。虽然CLD最重要的单一高危因素是早产，但最近关注的焦点已转向尽量减少其他两个危险因素的影响：与机械通气相关的气压/容量伤以及氧中毒。允许性高碳酸血症（PHC）或控制性通气是一种策略，通过允许相对较高水平的动脉血二氧化碳（CO₂）来尽量减少气压/容量伤，前提是动脉血pH值不低于预设的最小值。PHC的益处主要通过在潮气量减小时肺扩张的减少来介导。PHC可以是一种为避免过度扩张而限制通气的有意选择，而应用高气道压力和大潮气量会维持正常碳酸血症或相对低碳酸血症（动脉血二氧化碳分压[PaCO₂]≤25 - 30 mmHg），但可能导致CLD并对发育中的肺有害。目前认为高危新生儿的PaCO₂水平在45 - 55 mmHg是“安全的”且“耐受性良好”的观点基于有限的数据。需要进一步的前瞻性试验来研究PHC在机械通气的早产和足月新生儿中的定义、安全性和有效性。然而，鉴于新生儿疾病的病理生理学多样以及目前可用的各种通气模式/变量，针对PHC设计针对疾病/胎龄 - 出生后年龄的临床试验在新生儿中会很困难。本文综述了PHC的潜在益处和不良反应，并简要讨论了其与高危新生儿当前通气策略如同步机械通气和高频通气的关系。
