Over the last 30 years the number of maternal deaths associated with failed intubation has declined, though it remains one of the main reasons for advising regional, rather than general, anaesthesia for obstetric procedures. It is important to remember that patients do not die from failed intubation; they die from hypoxia or acid aspiration if the failed intubation is unrecognised or the corrective measures are inadequate. Pressure to achieve tracheal intubation may lead to prolonged attempts during which hypoxia occurs.
Problems and special considerations
Tracheal intubation is more difficult in obstetric anaesthesia, and the incidence of failed or difficult intubation is usually quoted as approximately 1 in 300-500 obstetric general anaesthetics, 10 times higher than for non-obstetric general anaesthetics. There are many reasons for difficulties with intubation and the increased risk of developing hypoxia (Table 38.1). Laryngoscopy and placement of a tracheal tube may thus be more difficult, while hypoxaemia develops more rapidly than in general surgical patients. This is compounded by the anaesthetist being under considerable stress during induction of anaesthesia.
The consequences of failed intubation in obstetrics are serious for both maternal and fetal health. Obstetric anaesthetists have been encouraging the use of regional anaesthesia, to reduce the number of general anaesthetics administered. As a result, the percentage of general anaesthetics has decreased, although the absolute number may not have fallen dramatically. However, there are now many obstetric units where very few general anaesthetics are given - and this, although a commendable trend, has led to a reduction in training opportunities, not only for trainees but also for trainers. It has been suggested that simulation courses may help address the issue of reduced training in general anaesthesia for obstetrics, but although simulation has been shown to improve practical skills, it is yet to be validated as a training tool.
Table 38.1 Causes of increased incidence of problems relating to trachealintubation in obstetric anaesthesia
|
Anatomical |
Difficulty inserting laryngoscope Poor laryngoscopic view |
Large breasts Weight gain/increased fatty tissue Oedema (especially pre-eclampsia) Complete dentition Cricoid pressure Weight gain/increased fatty tissue Laryngeal oedema Cricoid pressure causing distortion Swollen mucosa |
|
Physiological |
Increased risk of aspiration Increased oxygen demand Reduced lung capacity |
|
|
Iatrogenic |
Incorrectly applied cricoid pressure Urgency leading to haste Inexperience of staff |
Management options
If general anaesthesia is to be administered then it is important to do the following:
• Attempt to predict difficult intubation
• Use an anaesthetic technique that will minimise the risk of failing
• Have a failed intubation drill
Prediction of difficult intubation
Prediction of difficult intubation is attempted using the same clinical examination as in the non-pregnant patient:
• Mallampati score
• Coexisting neck pathology
• State of dentition
• Mouth opening
• Thyromental distance
Unfortunately, even in combination these tests have low predictive value (i.e. relatively few of the cases predicted as being difficult will actually be difficult), partly because of the poor function of the tests and partly because difficult intubation is uncommon, even in obstetric cases. Mallampati scores have been shown to change during pregnancy and even during labour.
Anaesthetic technique
The delivery suite theatre should be well equipped for a difficult intubation, and the equipment should include a variety of aids to intubation as well as equipment to aid oxygenation if a problem arises. A video laryngoscope may be a useful piece of equipment in the obstetric setting, and the majority of obstetric units now have some form of device in their difficult airway trolley. Skilled assistance for the anaesthetist is essential.
The anaesthetist should ensure that the patient is well positioned and that adequate doses of induction agent and neuromuscular blocking drug are given after a full 3 minutes’ preoxygenation or 3-5 vital capacity breaths. Proper fitting of the facemask is important to ensure efficient preoxygenation. The correct application of cricoid pressure by a trained assistant is important, since badly applied cricoid pressure can make laryngoscopy difficult (see Chapter 37, Cricoid pressure).
Although suxamethonium has long been considered the standard neuromuscular blocking drug, it has been suggested that with the availability of sugammadex, rocuronium may be more suitable for obstetrics, since it avoids some of the side effects of suxamethonium while providing a longer period of optimal conditions, with the possibility of rapid and reliable reversal by sugammadex should this be required. However, this remains controversial; many anaesthetists may not be familiar with the appropriate dose of sugammadex (16 mg/kg actual bodyweight), which may take several minutes to draw up, and not all units have sugammadex readily available because of its high cost. Sugammadex can, however, reverse 1 mg/kg rocuronium in 3 minutes, compared with the ~9 minutes that suxamethonium may take to wear off.
In order to avoid a catastrophe there should be a plan that comes into effect as soon as failure to view the larynx or to intubate the trachea becomes evident. It is at this point that a previously rehearsed ‘failed intubation drill’ should commence.
Failed intubation guideline
A national obstetric-specific difficult airway guideline was developed in the UK by the Obstetric Anaesthetists’ Association (OAA) and the Difficult Airway Society (DAS) in 2015. This should replace the multiplicity of failed intubation drills that previously existed, allowing a consistent approach to a fraught situation (Figures 38.1, 38.2, 38.3, 38.4). The prime focus is to maintain oxygenation.
Figure 38.1 OAA/DAS master algorithm: obstetric general anaesthesia and failed intubation. Reproduced with permission from Mushambi MC, Kinsella SM, Popat M, et al. Obstetric Anaesthetists’ Association and Difficult Airway Society guidelines for the management of difficult and failed trachealintubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
Figure 38.2 OAA/DAS algorithm 1: safe obstetric general anaesthesia. Reproduced with permission from Mushambi MC, Kinsella SM, Popat M, etal. Obstetric Anaesthetists’ Association and Difficult Airway Society guidelines for the management of difficult and failed trachealintubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
The key factors in the OAA/DAS failed intubation guidelines are:
• Assessment of the airway and preparation for difficulties.
• Up to three attempts at intubation, optimising conditions, equipment and experience.
If necessary, cricoid pressure should be altered or released, since oxygenation takes precedence over protection from aspiration.
• Communicating with the team and declaring an emergency early.
• Maintaining oxygenation through a facemask or second-generation supraglottic airway if necessary. Nasal oxygen may also be applied.
• Performing a front-of-neck procedure, and if oxygenation is still not established moving to maternal life support with a perimortem caesarean section.
• Deciding whether to wake or proceed once oxygenation and anaesthesia have been established and maintained.
These guidelines recognise that it may be particularly difficult in obstetrics to decide whether to proceed with surgery, given the presence of two patients with conflicting interests. It is important to remember that the primary duty of the anaesthetist is to the mother; thus, the initial course of action is to allow the mother to wake up, irrespective of the risk to the fetus, and to proceed with a regional anaesthetic. Exceptions to this would be if the mother herself requires the surgery as a life-saving procedure (e.g. major haemorrhage) or if the person making the decision to continue is of sufficient experience and seniority. Factors that may influence this choice have been listed in the guidelines to help inform decision making (Figure 38.5).
Figure 38.3 OAA/DAS algorithm 2: obstetric failed tracheal intubation. Reproduced with permission from Mushambi MC, Kinsella SM, Popat M, et al. Obstetric Anaesthetists’ Association and Difficult Airway Society guidelines for the management of difficult and failed trachealintubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
Figure 38.4 OAA/DAS algorithm 3: can’t intubate, can't oxygenate. Reproduced with permission from Mushambi MC, Kinsella SM, Popat M, et al. Obstetric Anaesthetists' Association and Difficult Airway Society guidelines for the management of difficult and failed trachealintubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
Figure 38.5 OAA/DAS table 1: proceed with surgery? Reproduced with permission from Mushambi MC, Kinsella SM, Popat M, et al. Obstetric Anaesthetists’ Association and Difficult Airway Society guidelines for the management of difficult and failed trachealintubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
Proceeding with a caesarean section under general anaesthesia using a laryngeal mask airway or facemask risks aspiration and airway obstruction during the procedure; this has been reported to occur in nearly 10% of failed obstetric airways. While a literature review has shown that the tendency has been towards proceeding with surgery since the late 1990s, trainees should be reassured that they will always be supported if they wake a mother up after a failed intubation. If surgery proceeds, a senior anaesthetist and obstetrician should facilitate a quick procedure, and extubation/waking should be planned. Consideration should be given to whether immediate waking is appropriate or transfer to an intensive care unit for delayed extubation more appropriate; before waking, the stomach should be emptied with a large-bore gastric tube, neuromuscular blockade must be fully reversed, and intravenous antacids should be administered if not already given (Figure 38.6).
Figure 38.6 OAA/DAS table 2: management after failed trachealintubation. Reproduced with permission from Mushambi MC, Kinsella SM, Popat M, etal. Obstetric Anaesthetists’ Association and Difficult Airway Society guidelines for the management of difficult and failed trachealintubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
Key points
• The patient does not die from failure to intubate the trachea but from failure to stop trying to intubate.
• Oxygenation must be maintained at all times.
• The failed intubation drill should be regularly rehearsed.
Further reading
Kinsella SM, Winton AL, Mushambi MC, et al. Failed tracheal intubation during obstetric general anaesthesia: a literature review. Int J Obstet Anesth 2015; 24: 356-74.
Mhyre JM, Healy D. The unanticipated difficult intubation in obstetrics. Anesth Analg 2011; 112: 648-52.
Mushambi MC, Kinsella SM, Popat M, et al. Obstetric Anaesthetists’ Association and Difficult Airway Society guidelines for the management of difficult and failed tracheal intubation in obstetrics. Anaesthesia 2015; 70: 1286-306.
Quinn AC, Milne D, Columb M, Gorton H, Knight M. Failed tracheal intubation in obstetric anaesthesia: 2 yr national case-control study in the UK. Br J Anaesth 2013; 110: 74-80.