Failed tracheal intubation is more frequent in obstetrics than in the nonobstetric population, and it has remained unchanged for many years at 1 in 390 for obstetric general anesthesia and 1 in 443 general anesthetics for cesarean deliveries.1 Maternal physiologic and anatomic changes, comorbidities such as obesity, increasing maternal age, the remote location of most labor wards, the urgency of cesarean delivery, and finally the need for rapid-sequence induction for most obstetric general anesthetics2 all add to the complexity of managing the obstetric airway. Most failed intubations occur during emergencies,1, 2 and the time pressure to deliver the baby often leads to poor preparation, planning, and performance of the rapid-sequence induction. The number of obstetric general anesthetics (GAs) is declining, leading to reduced experience for trainees.3, 4 It is therefore essential that teaching and training should focus on delivering a safe obstetric GA and aim to reduce adverse airway events and optimize the management of failed intubation should it occur. Careful planning and preparation prior to the administration of a GA are crucial in preventing serious untoward airway incidents. The aim of this chapter is to address first the management of the predicted difficult airway with emphasis on careful team planning and preparation and choice of a safe anesthetic strategy for the individual patient and secondly safe management of the unanticipated difficult airway.
Case Study
Anticipated Difficult Airway
This Case Study describes the management a 25-year-old pregnant woman (height 146 cm; weight 45 kg) with Klippel-Feil syndrome (KFS) who had a posterior placenta previa and a previous cesarean delivery. The patient had severe kyphoscoliosis (Figure 32.1) with significant back pain and was unable to lie flat owing to shortness of breath. A spinal anesthetic for her cesarean delivery 2 years previously had been extremely difficult, and she had found it difficult to breathe during surgery. She had a history of recurrent chest infections and shortness of breath walking 20 meters. On examination, her chest was clear, but she had obvious difficulty in breathing and very restricted rib movements. Airway assessment showed severely restricted neck movement from previous neck surgery (Figure 32.2) and a Mallampati grade 4. Pulmonary function tests showed restrictive lung disease with a FEV1 of 1.2L, FVC of 1.3L, and FEV1/FVC ratio of 92 percent. Her echocardiogram was normal.
Figure 32.2 View of the back of patient’s neck showing a scar from previous surgery and a webbed neck
The patient was discussed at a multidisciplinary team (MDT) meeting, and an agreement was reached for the obstetric and anesthetic management plans. An elective cesarean delivery under general anesthetic with awake fiberoptic intubation (AFI) was planned. The documented plan in the notes included a plan should the patient have an admission out of hours.
When the patient arrived in the OR, two 14-gauge cannulae were sited, and full monitoring was instituted, including a radial arterial line. Cell salvage and a Level 1 rapid infuser were set up. Glycopyrrolate 200 mcg was administered intravenously. The patient was asked to gargle with 3 ml 2% lidocaine gel (Instillagel) to help reduce the gag reflex. Further topical anesthesia to the mouth and oropharynx was achieved using 3 ml 4% lidocaine with a Mucosa Atomising Device (MAD). The supraglottic area, glottis, and infraglottic area were anesthetized using a spray-as-you-go (SAYGO) technique (total 3 ml 4% lidocaine). Supplementary oxygen was administered via nasal cannulae. Sedation was achieved using midazolam (1 mg) and a remifentanil infusion starting at 0.05 µg/kg/min. A cut Berman airway was used to prevent the patient biting on the fiberoptic scope and to act as a conduit for the fiberscope. The gag reflex was difficult to suppress and was successfully obtunded with the injection of 1 ml 4% lidocaine through the cricothyroid membrane using a 20-gauge cannula. Once the fiberoptic scope was in the trachea, a size 6.0-mm reinforced cuffed endotracheal tube (ETT) was railroaded over the scope. After confirmation of correct placement of the ETT in the trachea with a capnograph, general anesthesia was induced using propofol and muscle paralysis with atracurium, and the endotracheal cuff was then inflated. Postintubation laryngoscopy revealed a Cormack and Lehane grade 4 view.
The baby’s Apgar scores were 2 and 5 at 1 and 10 minutes with an umbilical venous and an arterial pH of 7.30 and 7.23. After an uneventful operation with a blood loss of 500 ml, the patient was transferred to the ICU and extubated after a few hours when she was awake, had good arterial blood gases, and was able to generate adequate tidal volumes.
Key Points
Management of this patent involved an anticipated difficult airway and a potential risk of hemorrhage from a placenta previa.
Regional anesthesia was not an option in this patient.
General anesthesia following an awake fiberoptic intubation was therefore the technique of choice.
Discussion
Klippel-Feil syndrome (KFS) is an autosomal-dominant condition that leads to an abnormal fusion of cervical vertebrae. This may be associated with craniocervical junction anomalies (Figure 32.3), unstable cervical spine, kyphoscoliosis, and cardiac and genitourinary abnormalities.5, 6 My patient was of short stature and had severe symptomatic restrictive lung disease. Placenta previa, especially in a patient with a previous cesarean delivery, is associated with a possible risk of major hemorrhage at surgery.7, 8 This combination presents a dilemma of how to manage the anesthesia safely. Such patients should be discussed at MDT meetings in order to formulate a plan. The plan should be communicated to all labor ward staff and to the patient. A decision on the mode of delivery should be made based on what is the safest option for mother and baby. The only option for this patient was delivery by elective cesarean delivery. Regional anesthesia (RA) is considered by many anesthetists to be the anesthetic of choice in patients with a known difficult airway,9 and it has been used in patients with KFS.10, 11 However, RA techniques can have significant drawbacks in such patients. It is difficult to estimate the local anesthetic volume in a single-shot spinal (SSS), particularly in a patient of such short stature, and there is a real risk of a high or total spinal anesthetic developing. Epidural anesthesia has a high intraoperative GA conversion rate (4.3 percent),12 which is less desirable in a patient with a difficult airway. Combined spinal-epidural (CSE) anesthesia has been associated with inadequate intraoperative anesthesia in a patient with KFS.11 Continuous spinal anesthesia (CSA) with a spinal catheter offers several advantages over SSS and CSE. It enables titration by injecting small volumes of local anesthetic through the catheter until the desired level of anesthesia is achieved. However, CSA is unfamiliar to many anesthetists and has a high failure rate and a high post–dural puncture headache rate.13 For these reasons, and in addition to the patient’s previous experience, RA was considered unsafe in this patient.
Figure 32.3 An X-ray of a patient with Klippel-Feil syndrome showing the abnormal cervical spine
Awake Fiberoptic Intubation (AFI) in a Pregnant Patient
AFI in a pregnant woman differs in many ways from that in a nonpregnant patient. The presence of a fetus means that any drugs administered to the mother can affect the baby. Neonatologists therefore should be made aware in advance. The nasal mucosa is congested and more vascular during pregnancy, and this makes oral intubation the preferred route of intubation. Occasionally, the oral route is not possible due to oral pathology. Cocaine is a very effective vasoconstrictor, but it is associated with reduced placental blood flow and therefore should be avoided during pregnancy.14, 15 Phenylephrine 0.5%/lidocaine 5% combination (Co-phenylcaine) and xylometazoline hydrochloride 0.1% spray are safer alternatives. However, vasoconstrictors should be used with care in preeclamptic patients because they may exacerbate the hypertension. Oral intubation is also more difficult than nasal intubation, and it requires more dense topical anesthesia in order to suppress the gag reflex.
It is important that aortocaval compression is avoided. Premedication should include an H2 antagonist and 30 ml of 0.3 M sodium citrate immediately prior to starting sedation. An antisialogogue – glycopyrrolate 200 µg IV – will help to reduce secretions. Two experienced anesthetists are required, one to perform the endoscopy and the other to administer and monitor sedation. The help of an experienced anesthetic assistant is essential.
Some form of sedation such as midazolam, fentanyl, alfentanil, remifentanil, or propofol is recommended. Midazolam 0.5–1 mg is useful to ensure a degree of amnesia. Remifentanil is gaining popularity because it provides the best analgesia for the mother with conscious and cooperative sedation and suppression of the gag reflex, which gives good intubating conditions. Infusion rates of 0.05–0.5 µg/kg/min and a target controlled infusion (TCI) of 3–5 ng/ml have been used in nonobstetric patients with or without propofol (TCI 0.5–0.8 µg/ml).16–18 TCI with propofol has been used for AFI in obstetrics with a target concentration of 0.6–1.0 µg/ml combined with midazolam 1 mg and topical anesthesia.19
Excessive sedation should be avoided because it reduces the protective laryngeal reflexes and increases the likelihood of aspiration. Antagonists such as flumazenil and naloxone should be readily available. Oxygen should be administered.
There have been concerns about the use of topical airway anesthesia in patients at risk of regurgitation and aspiration. However, studies have showed that the sedation provided is not excessive, and there is no evidence of an increased risk of regurgitation and aspiration.20
The nose, mouth and pharynx may be anesthetized by direct spray using a device such as the commercially produced Mucosal Atomising Device (MAD) (Figure 32.4a) or the Mackenzie technique, which uses an 18- or 20-gauge cannula attached by a three-way tap to oxygen tubing that is connected to 2 L/min oxygen (Figure 32.4b).21 The patient may also be asked to gargle using 2% lidocaine gel (Instillagel). The remainder of the airway can be anesthetized using one of three techniques: the SAYGO technique, glossopharyngeal and superior laryngeal nerve blocks, and nebulized lidocaine. Nerve blocks are seldom carried out, and nebulized lidocaine, when used alone, does not provided sufficient topical anesthesia.
