在成人，放置气管导管前端的正确位置应在气管隆突之上约5cm处。颈过伸位时，气管导管前端可向咽喉方向移动平均1.9cm；颈过屈位时气管导管前端可向隆突方向移动，颈向侧方旋转时导管前端可向咽喉方向移动0.7cm。
对于小儿是否也呈相应变化吗？
在现代麻醉学第三版中有写到：小儿颈过伸位时，气管导管前端可向隆突方向移动；颈过屈位时气管导管前端可向声门方向移动（见麻醉期呼吸管理章节中的特殊病人的呼吸管理一节中小儿麻醉的呼吸管理部分）。不知道是何原因？
A：颈部位置与气管插管的深度关系
根据在成人的放射学研究，患者头部的伸展和屈曲可造成气管导管在气管内的移动。当头部从过度伸展位转变成过度屈曲位时，气管导管向隆突方向平均移动3.8cm（左图）；而有一些患者，此种移动可多达6.4cm。
在患者体位改变、膈肌移动和气管或食管手术操作中，可发生气管导管的移位，在将患者置放成300的Trendelenburg体位后，具有相当高的主支气管插管发生率，此是由于气管隆突向头侧移位使已固定的气管导管进入主支气管的结果。当采用反向Trendelenburg体位时，可出现相反的结果。因为气管和食管均被同样的颈部筋膜所包绕，所以牵拉气管或食管均可使已正确固定的气管导管出现移位，如在实施食管闭锁修复的婴儿或实施食管镜检查的患者。
在小儿头部的伸展和屈曲造成的气管导管移动不同于成年人（可参考以下文献），在施行气管插管的婴幼儿应特别注意，头部呈屈曲位时易发生支气管内插管，而头部呈伸展位时又易发生意外性气管导管的脱出，尤其是在气管长度仅为4.7～5.7cm长的新生儿。故在婴幼儿实施气管插管时，应采取相应措施来保证气管导管尽可能插至气管远端但又未进入主支气管内。①采用距远端2.2cm处有环状标志的气管导管，在足月婴幼儿，可将此标志插至声带部位；在早产婴幼儿，此标志应稍高于声带部位；在体型稍大的婴幼儿，应将此标志插至声带以下部位。②采用分别在距远端2.2、2.4和2.6cm处有环形标志且直径为2.5mm、3.0mm和3.5mm的气管导管。
1.AJR Am J Roentgenol. 1976 Sep;127(3):433-4.
Radiographic evaluation of endotracheal tube position.
• Goodman LR, Conrardy PA, Laing F, Singer MM.
A malpositioned endotracheal tube is a potential hazard to the intubated patient. Ideally, the tube tip should be 5+/-2 cm from the carina when the head and neck are in neutral position. In 92 of 100 patients studied, the carina overlay T5, T6, or T7 on portable radiographs. Therefore, even when the carina is not visible, it can be assumed that a tube tip positioned at the level of T3 or T4 is safe. The degree of neck flexion or extension at the time of radiography may be determined by evaluating the position of the mandible relative to the vertebral bodies.
PMID: 183529 [PubMed - indexed for MEDLINE]
2.Br J Anaesth. 2006 Apr;96(4):486-91. Epub 2006 Feb 7.
Tracheal tube-tip displacement in children during head-neck movement--a radiological assessment.
• Weiss M, Knirsch W, Kretschmar O, Dullenkopf A, Tomaske M, Balmer C, Stutz K, Gerber AC, Berger F.
Department of Anaesthesia, University Children's Hospital Zurich, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland. markus.weiss@kispi.unizh.ch
BACKGROUND: Aims of this study were to assess the maximum displacement of tracheal tube tip during head-neck movement in children, and to evaluate the appropriateness of the intubation depth marks on the Microcuff Paediatric Endotracheal Tube regarding the risk of inadvertent extubation and endobronchial intubation. METHODS: We studied children, aged from birth to adolescence, undergoing cardiac catheterization. The patients' tracheas were orally intubated and the tracheal tubes positioned with the intubation depth mark at the level of the vocal cords. The tracheal tube tip-to-carina distances were fluoroscopically assessed with the patient supine and the head-neck in 30 degrees flexion, 0 degrees neutral position and 30 degrees extension. RESULTS: One hundred children aged between 0.02 and 16.4 yr (median 5.1 yr) were studied. Maximum tracheal tube-tip displacement after head-neck 30 degrees extension and 30 degrees flexion demonstrated a linear relationship to age [maximal upward tube movement (mm)=0 0.71 x age (yr)+9.9 (R(2)=0.893); maximal downward tube movement (mm)=0.83 x age (yr)+9.3 (R(2)=0.949)]. Maximal tracheal tube-tip downward displacement because of head-neck flexion was more pronounced than upward displacement because of head-neck extension. CONCLUSIONS: The intubation depth marks were appropriate to avoid inadvertent tracheal extubation and endobronchial intubation during head-neck movement in all patients. However, during head-neck extension the tracheal tube cuff may become positioned in the subglottic region and should be re-adjusted when the patient remains in this position for a longer time.
PMID: 16464981 [PubMed - indexed for MEDLINE]
3.Pediatr Pulmonol. 1999 Mar;27(3):199-202.
Comment in:
Pediatr Pulmonol. 2000 Mar;29(3):242-4.
Effect of neck position on endotracheal tube location in low birth weight infants.
• Rost JR,Frush DP, Auten RL.
Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710, USA.
Neck position can affect the position of the tip of the endotracheal tube (ETT) in normal neonates; this has not been systematically investigated in low birth weight (LBW) neonates. It was our intention to determine the effect of neck flexion and extension on ETT position in LBW infants. Eight LBW orotracheally-intubated infants underwent postmortem anteroposterior chest radiographs with the neck in a neutral position, in 55 degrees flexion, and in 55 degrees extension. Measurements from the thoracic inlet to the ETT were obtained in each position. The ETT always moved caudad with neck flexion (P = 0.001) and cephalad with neck extension (P = 0.001). The mean extent of ETT displacement was 3.1 mm (SD, 1.7 mm) with neck flexion, and 7.4 mm (SD, 5.2 mm) with extension (P < 0.05). We conclude that in LBW infants: 1) the direction of ETT movement with neck flexion and extension is predictable and identical to that seen in term infants and children, and 2) neck flexion should not be a principal consideration in management of ETT location.
PMID: 10213259 [PubMed - indexed for MEDLINE]
4.Anesth Analg. 1996 Feb;82(2):251-3.
Displacement of the endotracheal tube caused by change of head position in pediatric anesthesia: evaluation by fiberoptic bronchoscopy.
• Sugiyama K, Yokoyama K. Department of Anesthesia, Kagoshima University Dental Hospital, Japan.
Displacement of the endotracheal tube (ETT) caused by flexion and extension of the neck and the placement of a tongue depressor was investigated in 10 small children between the ages of 16 and 19 mo by means of a fiberoptic bronchoscope. The ETT tip moved a mean distance of 0.9 cm toward the carina with flexion and 1.7 cm toward the vocal cords with extension of the neck. After the placement of a tongue depressor, the ETT tip, which had once moved toward the vocal cords with neck extension, was displaced a mean distance of 1.2 cm toward the carina. Our results demonstrate that endobronchial intubation and accidental extubation could occur after significant changes of the head position and careless placement of a tongue depressor in small children.
PMID: 8561322 [PubMed - indexed for MEDLINE]
5.Anesth Pain Control Dent. 1992 Winter;1(1):29-33.
Displacement of the endotracheal tube caused by postural change: evaluation by fiberoptic observation.
• Sugiyama K, Mietani W, Hirota Y,Matsuura H.
Faculty of Dentistry, University of Kagoshima, Japan.
Unexpected displacement of the endotracheal tube during anesthesia caused by postural change of the neck or passive compression by the mouth gag was investigated under transluminal fiberoptic observation. Twenty-two patients were divided into orotracheal and nasotracheal intubation groups according to the technical requirements of the planned oral and maxillofacial surgery. Under nasotracheal intubation, the mean length of displacement from the carina was 21 mm by extension of the neck, and 8 and 7 mm by lateral rotation of the neck to the right and left sides, respectively. Under orotracheal intubation, the mean length of displacement from the carina was 12 mm by extension of the neck and almost 28 mm with application of the mouth gag. To avoid accidental extubation or one-sided bronchial intubation during anesthesia, the tip (distal end) of the endotracheal tube should be located less than 32 mm from the carina before extension of the neck and more than 41 mm from the carina before application of the mouth gag.
PMID: 1392680 [PubMed - indexed for MEDLINE]
6. Anaesth Intensive Care. 1994 Oct;22(5):586-8.
Alterations in endotracheal tube position during general anaesthesia.
• Yap SJ, Morris RW, Pybus DA.
Department of Anaesthesia, St George Hospital, Sydney, N.S.W.
The effect of head and neck movement and Trendelenburg tilt on endotracheal tube position, relative to the carina, was studied in fifty adult patients requiring intubation for elective surgery. On average, inward movement, that is shortening of the distance between the endotracheal tube tip and the carina, resulted from neck flexion (mean = -5.5 mm), whereas outward movement occurred with neck extension (mean = 6.3 mm). Neck rotation, to right and left, and Trendelenburg tilt did not show any trend towards inward nor outward movement (mean = 0.3 mm/1.7 mm/-0.6 mm, respectively). Whilst these mean positional changes for flexion and extension confirm the findings of earlier investigations, our range of maximum inward and outward displacement for flexion (23 mm in/19 mm out), extension (21 mm in/33 mm out), rotation to right (19 mm in/17 mm out), to left (22 mm in/19 mm out) and Trendelenburg tilt (22 mm in/16 mm out) indicate that for any given postural change in any one patient, the direction and magnitude of endotracheal tube displacement is not readily predictable.
PMID: 7818064 [PubMed - indexed for MEDLINE]
7.Crit Care Med. 1976 Jan-Feb;4(1):7-12.
Alteration of endotracheal tube position. Flexion and extension of the neck.
• Conrardy PA, Goodman LR, Lainge F, Singer MM.
PMID: 1253616 [PubMed - indexed for MEDLINE]
Q：尊敬的薛教授您好，我是丁香园会员dxyicu。请问诱导后发现未预见性的困难气管插管，应该如何紧急处理？困难气管插管时应该如何有效预防气道损伤？
A：一、原因
这种情况常见于手术前认为呼吸道正常的患者，在全身麻醉诱导后可由于肌张力的变化成为不易进行气管插管的困难气道，或者由于麻醉医师在手术前未能进行足够详细的评估而发现患者存在的问题，全麻诱导后才发现患者有呼吸道异常。
一旦麻醉诱导后出现未能预知的气管插管，由于操作者没有充分的心理准备，有时可出现一时的惊慌失措，从而延误解决问题的时机，甚至可造成严重的不良后果。因此，对于此类患者必须严格按照ASA制定的困难气道管理实用规则进行处理。
二、面罩通气无困难的患者
1、对于手术前未能预知的困难气管插管患者，只要面罩通气能够有效地进行，可采用前述用于清醒气管插管患者的各种技术多数进行处理。但应注意中断通气的时间不能过长，要保证患者有足够的气体交换。使用带自封式隔膜的内窥镜操作专用面罩和气管插管专用口咽通气道，可以在全身麻醉肌肉松弛状态下采用FOB进行气管插管操作，同时又不间断而罩通气和吸入麻醉药。
2、除了急诊手术，或者是手术能够在极短时间内完成以外，即使是用面罩等方式能够维持患者满意的呼吸，手术亦应暂时停止。
3、最理想的情况是辅助患者呼吸，直到麻醉诱导药或肌肉松弛药的作用消失，停止使用肌肉松弛药，必要时可进行拮抗，尽快使患者恢复呼吸。已有胃胀气者，插入鼻胃管进行减压，待患者清醒，再考虑进行清醒气管插管操作。
4、如果试图在患者清醒前继续试行气管插管，理应由手术室中最有经验的麻醉医师主持，首先保证患者的生命安全。
5、对于气管插管试操作屡屡失败的患者，情况相对较急，咽喉部多数有血性分泌物，喉显露多不清楚，除非有熟手和FOB在场，否则应尽快采取逆行引导气管插管技术。
6、在处理困难气管插管时，操作应轻柔、准确，不应使用暴力。因为呼吸道内的所有组织均十分脆弱，任何外力的碰撞都会造成不同程度的损害，其中包括牙齿碎裂、脱落，以及呼吸道组织的水肿、出血等。一旦这些问题出现，气管插管会变得更加困难，原来通畅的呼吸道会变为阻塞性呼吸道。在因气管插管困难而致严重后果的患者，大多是因麻醉医师反复进行气管插管操作，使呼吸道组织肿胀程度不断增加，更进一步缩小了呼吸道的内径，最后导致呼吸道完全堵塞，并造成危及患者生命的后果。
三、气管插管失败且面罩通气不能的患者
在麻醉诱导后出现未能预知的气管插管困难的患者，如果同时存在面罩通气困难，这种情况则被称为面罩不能通气且气管插管失败（CVCI）情况，如果这种情况持续3～5分钟就会导致患者脑缺O2，甚至脑死亡。研究表明，在普通患者中有1%～4%的困难气管插管发生率0.05%～0.2%的患者气管插管失败；但CVCI的发生率极低，大约为0.0001%～0.02%。值得注意的是，这一研究是对条件设备很好、人员和训练均完善的大医院进行调查完成的，地方性、基层性小医院的困难气管插管、气管插管失败和CVCI发生率可能会更高。近年来，由于对这一问题的重视，再加上呼吸道管理器械的改进，使得CVCI这种危急状况的发生率已明显降低。尽管这种情况异常危急，但处理时应保持镇静，在合理的范围内，根据具体情况，循序渐进。这些处理措施包括非手术方式和紧急手术方式。
（一）非手术处理方式
1、联合导气管 联合导气管是一新型的紧急气道。在CVCI处理中，应用联合导气管的主要优点有：①插入不需要喉镜、良好的照明和其他器械，所以建立通畅呼吸道不受不利环境因素或缺乏熟练操作人员的阻碍。②因其使用毋需显露声门，所以对于声门显露困难的气管插管不再是障碍。③如联合导气管进入食管，则可经气管腔进行胃液抽吸，口咽部套囊能有效地防止口内容物的误吸。④如果需将其替换成气管导管，口咽部套囊放气后可用直接喉镜或FOB寻找声门。⑤联合导气管毋需要进行外固定，因为口咽部套囊充气后正好挡在硬腭的后面。
2、喉罩通气道（LMA） LMA是比面罩通气功能确实，并有气管导管作用的新型通气道。在困难气管插管患者，不仅可协助完成气管插管操作，而且可作为CVCI患者的应急气道。在一些困难气道患者的CVCI处理中，及时正确地使用LMA可避免经气管通气。
(二) 紧急手术处理方式
1、经气管喷射通气（transtracheal jet ventilation，TTJV） TTJV不是一种间接气管插管技术，但在危急情况下和困难气管插管时可成功的运用，能快速短暂供氧，提供宝贵的抢救时间。
2、气管切开术或环甲膜切开术 如果经上述的处理方式无法解决问题，就应该立即采用紧急气管切开术或环甲膜切开术。即使外科医师不在场，麻醉医师亦可作简单的类似手术。与气管切开术相比，环甲膜穿刺切开术更为简单、安全，经过适当的训练可在30秒内完成整个手术过程，尤其是经皮扩张环甲膜切开术。这些训练均已被列入医学院校麻醉科的教学课程之中。
有关此类患者的处理可详见我编写的书籍〔《现代呼吸道管理学—麻醉与危重症治疗关键技术》，郑州大学出版社，2002年12月出版，第28章和第21章）〕以及《困难气管插管技术》，科学技术文献出版社（2002年4月出版）中的相关内容。
