Circulation：心脏骤停患者复苏后PaCO2紊乱影响神经系统预后

动脉二氧化碳分压（Paco2）可调节脑损伤后的脑血流量。最近的指南推荐心脏骤停患者成功复苏后Paco2维持在40 - 45 mmHg。但是目前缺乏心脏骤停后的Paco2异常的数据以及其与预后关系。美国新泽西州研究人员进行了一单学术医疗中心的前瞻性心脏骤停注册研究分析。研究结果发表在2013年5月28日的Circulation杂志上。

该研究纳入标准为：年龄大于18岁，非创伤性猝死，自主循环恢复后昏迷状态。研究人员在自主循环恢复后0-24h测定血气分析，确定患者是否存在低碳酸血症和高碳酸血症（定义为Paco2 ≤30 mm Hg and Paco2 ≥50 mm Hg，基于以往文献）。主要结局为出院时神经功能不佳，定义为脑功能分类（Cerebral Performance Category） ≥3。经已知因素校正后，通过多因素logistic回归分析和多因素敏感性分析对不佳神经功能预后进行预测分析，确定是否自主循环恢复后的低碳酸血症和高碳酸血症是神经功能不佳的独立预测因素。

在193例患者中，52例患者（27%）仅存在低碳酸血症，63例患者（33%）只有高碳酸血症，18例患者（9%）既出现低碳酸血症又出现高碳酸血症，60例患者（31%）无上述暴露因素；74%患者的神经功能预后不佳。结果显示，低碳酸血症和高碳酸血症均独立与较差的神经功能预后相关，比值比分别为2.43 （95%CI, 1.04–5.65）和 2.20 （95% CI, 1.03–4.71）。

研究指出，心脏骤停后的高碳酸血症和低碳酸血症较为常见，与神经功能预后不佳有关。这一数据说明Paco2紊乱对心脏骤停后复苏患者有潜在危害。

Association between postresuscitation partial pressure of arterial carbon dioxide and neurological outcome in patients with post-cardiac arrest syndrome.
BACKGROUND
Partial pressure of arterial CO2 (Paco2) is a regulator of cerebral blood flow after brain injury. Recent guidelines for the management of cardiac arrest recommend maintaining Paco2 at 40 to 45 mm Hg after successful resuscitation; however, there is a paucity of data on the prevalence of Paco2 derangements during the post-cardiac arrest period and its association with outcome.
METHODS AND RESULTS
We analyzed a prospectively compiled and maintained cardiac arrest registry at a single academic medical center. Inclusion criteria are as follows: age ≥18, nontrauma arrest, and comatose after return of spontaneous circulation. We analyzed arterial blood gas data during 0 to 24 hours after the return of spontaneous circulation and determined whether patients had exposure to hypocapnia and hypercapnia (defined as Paco2 ≤30 mm Hg and Paco2 ≥50 mm Hg, respectively, based on previous literature). The primary outcome was poor neurological function at hospital discharge, defined as Cerebral Performance Category ≥3. We used multivariable logistic regression, with multiple sensitivity analyses, adjusted for factors known to predict poor outcome, to determine whether post-return of spontaneous circulation hypocapnia and hypercapnia were independent predictors of poor neurological function. Of 193 patients, 52 (27%) had hypocapnia only, 63 (33%) had hypercapnia only, 18 (9%) had both hypocapnia and hypercapnia exposure, and 60 (31%) had no exposure; 74% of patients had poor neurological outcome. Hypocapnia and hypercapnia were independently associated with poor neurological function, odds ratio 2.43 (95% confidence interval, 1.04-5.65) and 2.20 (95% confidence interval, 1.03-4.71), respectively.
CONCLUSIONS
Hypocapnia and hypercapnia were common after cardiac arrest and were independently associated with poor neurological outcome. These data suggest that Paco2 derangements could be potentially harmful for patients after resuscitation from cardiac arrest.