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[每周一问]NO.13-CPR之2
Cardiopulmonary resuscitation (CPR)
Cardiopulmonary resuscitation (CPR) is a skill that has significant impact on asystolic patient survival. This week, we'll discuss some recent changes in the performance of this skill. Today we'll discuss ventilation changes with CPR.
1.  What is an important change to the Guidelines 2000 for CPR in regards to ventilation?
2.  How do esophageal detector devices work?
3.  What are CO2 confirmation devices sometimes misleading?
4.  Any new recommendations in regards to ventilation tidal volume?
5.  Are there recommendations regarding endotracheal tube holders/securing devices?
CPR是对心搏停止患者的存活有显著影响的一种方法。本周，我们讨论关于该方法的一些近期变化。今天我们讨论CPR的机械通气变化。
1.  CPR2000年指南中关于机械通气的重要变化是什么？
2.  食道探测设备是如何工作的？
3.  CO2确认设备（注：如PETCO2）在什么情况下可出现误导？
4.  关于机械通气潮气量的新建议是什么？
5.  关于气管导管支架或安全设备有没有什么建议？

本期答案：
1.CPR2000年指南中关于机械通气的重要变化是什么？
虽然在上周的问题中我们讨论了CPR仅仅进行胸外心脏按压的作用，但是该技术需要进一步成功的确认。然而根据指南，众多学者[1]推荐的新建议中最重要的一条是，正确的气管导管位置必须由CPR实施者予以确定。包含在其中的是大多数麻醉学家非常熟悉的设备，如食道探测设备，呼吸末CO2定量检测设备，CO2图及capnometric设备（详细信息见1998年11月10 问题）

2.食道探测设备是如何工作的？
通过一大注射器或可压缩的弹性容器在气管导管末端产生一吸引力的设备，可帮助鉴别气管内插管术。在食道，靠近气管导管远端的粘膜溃烂，因此限制了注射器回抽的能力或弹性可压缩容器的膨胀性。相比之下，气管软骨环允许注射器或压缩容器的完全膨胀。

3.CO2确认设备（注：如PETCO2）在什么情况下可出现误导？
在低肺血流状态如完全心搏停止，呼吸末CO2不足将可能导致CO2确认设备错误地认为进行了食道插管。相比之下，对于摄入含CO2液体患者，食道插管可事实的产生CO2读数，因此延缓不正确气管内插管的纠正时机。因此，临床征象如胸廓移位、肺部和上腹部听诊，直接喉镜检查应该如同CO2确认设备一样重要的使用。
有趣的是，在非CPR情况下研究者发现CO2确认设备对于经鼻胃管位置的正确判断有帮助[2]。
4.关于机械通气潮气量的新建议是什么？
关于潮气量在新指南中有精细的差别。当对不安全气道使用囊-阀门设备（如呼吸囊辅助呼吸）时，指南建议使用低流量温和通气，潮气量为2S以上6-7 mL/kg。这个比气管内插管后建议的10-12 mL/kg低，期望胃膨胀降低，但是随后发现有反流误吸。
5.关于气管导管支架或安全设备有没有什么建议？
不同组织的复苏指南[1，4]认识到了大量发生在成功插管后的气管内导管移动现象。像这样，安全稳妥的固定导管位置应该被强调。并且，CO2检测设备和氧饱和度监测在长时间转运过程中被推荐使用。没有特别的气管内导管固定产品被推荐。

What is an important change to the Guidelines 2000 for CPR in regards to ventilation?
Although in yesterday's Question of the Day we discussed the use of chest compression only CPR, the promotion of these technique awaits further confirmation of its success. In terms of the guidelines, however, and considered one of the most important new recommendations by many experts (1) is that confirmation of proper tracheal tube position must be made by CPR responders. Included in these are devices which most anesthesiologists are very familiar, i.e. esophageal detector devices, qualitative end-tidal CO2 indicators, and capnographic and capnometric devices (for further details, see the Question of the Day for November 10, 1998).
How do esophageal detector devices work?
Devices that create a suction force at the tracheal end of an endotracheal tube, either through a large syringe or a compressible flexible bulb, may assist in identifying an endotracheal intubation. In the esophagus, the mucosa collapses against the distal end of the endotracheal tube, thereby limiting the ability to fully pull back on a syringe or for a flexible compressed bulb to reexpand. By contrast, the cartilaginous rings of the trachea allow for full expansion of a syringe or a compressed bulb.
What are CO2 confirmation devices sometimes misleading?
In low pulmonary blood flow states such as with a full cardiac arrest, an insufficient amount of expired CO2 would allow a CO2 confirmation device to falsely indicate an esophageal intubation. By contrast, in patients who have ingested carbonated liquids, an esophageal intubation may actually produce CO2 readings and delay the removal of an improperly sited endotracheal tube. Thus, clinical signs, such as chest excursion, auscultation of lungs and over the epigastrium, and direct laryngoscopy should be used as important confirmatory adjuncts.
Interestingly, in non-CPR situations, some investigators have found these CO2 confirmatory devices useful to confirm proper nasogastric tube placements (2).
Any new recommendations in regards to ventilation tidal volume?
There is a subtle distinction in the new guidelines in regards to tidal volume. When using bag-valve devices with an unsecured airway, the guidelines recommend a slow and gentle delivery of a tidal volume of 6-7 mL/kg over 2 seconds. This is lower than the 10-12 mL/kg recommended following the placement of an endotracheal tube, and conceivably a reduction in gastric inflation, subsequent regurgitation and aspiration may be seen.
Are there recommendations regarding endotracheal tube holders/securing devices?
A number of resuscitation guidelines by different organizations (1,4 ) recognize the significant number of endotracheal tube dislodgments that occur following a successful placement. As such, continued attention to securely tying or taping the tube in place has been emphasized. Moreover, the use of CO2 detectors and oxygen saturation monitors have been recommended for long transport efforts. No specific commercial endotracheal tube securing devices have been recommended.
References:
1.  Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 6: advanced cardiovascular life support: 7C: a guide to the International ACLS algorithms. The American Heart Association in collaboration with the International Liaison Committee on Resuscitation. Circulation. 2000;102(8 Suppl)142-57.
2.  Menegazzi JJ, Heller MB. Endotracheal tube confirmation with colorimetric CO2 detectors. Anesth Analg. 1990;71(4):441-2.
3.  Thomas BW, Falcone RE. Confirmation of nasogastric tube placement by colorimetric indicator detection of carbon dioxide: a preliminary report. J Am Coll Nutr. 1998;17(2):195-7.
4.  Cummins RO, Hazinski MF. Guidelines based on the principle 'First, do no harm'. New guidelines on tracheal tube confirmation and prevention of dislodgment. Resuscitation. 2000;46(1-3):443-7.
Site Editor: Stephen B. Corn, M.D. and B. Scott Segal, M.D.
Department of Anesthesia, Harvard Medical School
Founders and Editors-in-Chief: Stephen B. Corn, M.D. and B. Scott Segal, M.D.
Department of Anesthesiology, Perioperative and Pain Medicine, Harvard Medical School