Difficult Airway in Obstetric Patients

Abstract

Although the use of general anesthesia in the obstetric population has decreased substantially, it remains the most appropriate choice in certain cases. While the use of general anesthesia is essential, maternal deaths associated with general anesthesia continue. Difficult airway remains the leading cause. Maternal mortality due to airway difficulty during general anesthesia is approximately four times higher than in general population. The incidence of failed tracheal intubation in obstetrics has remained unchanged over the past 40 years. The significant anatomic and physiologic changes of pregnancy, which are exacerbated during labor, explain the increased difficulty in airway management in obstetric patients. The presence of anesthesia staff with adequate knowledge of maternal airway management is vital to minimize the incidence of failed intubation in the parturient.

1. Introduction

Although the use of general anesthesia (GA) has been largely replaced by neuraxial anesthesia, there are certain clinical situations in which the administration of GA is most appropriate [1, 2]. GA is frequently preferred in emergent cases (e.g., fetal bradycardia, massive hemorrhage, maternal coagulopathy, uterine rupture, maternal trauma) as it has a rapid onset and allows for airway ventilation and hemodynamic control [2, 3]. Airway-related complications remain a leading cause of anesthesia-related maternal mortality [2, 3, 4, 5, 6, 7], with approximately 2.3 per 100,000 GAs versus 1 per 180,000 GAs in the general population. Although advanced airway devices (e.g., supraglottic airways, flexible bronchoscopes, and video laryngoscopy) have been increasingly available for difficult airway management, the incidence of failed tracheal intubation in obstetrics cases has remained unchanged over the past 40 years. A 2015 systematic review reported that the incidence of failed intubation for all obstetric procedures was 1 in 390 [8]. The rate of failed obstetric intubation is approximately eight times higher compared with non-obstetric procedures [9]. Significant anatomic and physiological changes of pregnancy have been considered to explain the increased difficulty in obstetric airway management [2, 3, 4]. Several suggestions have been proposed to reduce the difficulty of maternal airway management [10, 11].

2. Anatomic and physiologic risk factors for airway complications in obstetric patients

Pregnancy results in multiple anatomic and physiological changes, which impact airway management. While respiratory changes have the most significant effect, there are also gastroesophageal and other pregnancy-induced changes that increase the risk for difficult airway management.

2.1 Respiratory changes

Increases in the renin-aldosterone system result from augmented estrogen and progesterone production during normal pregnancy cause a physiological fluid retention [11, 12]. In the respiratory tract, this may lead to narrowing of the airway, increasing risk for airway obstruction during ventilation, poor laryngoscopic views, and difficulty with tracheal intubation [2, 3]. Although airway changes develop gradually from first to third trimester of pregnancy, even more drastic changes may be observed at delivery and during labor. Studies have shown an increase in the Mallampati score and a decrease in upper airway volume on acoustic reflectometry during labor, presumably due to increasing soft tissue edema [13, 14]. Rather than relying solely on prelabor assessment, it is necessary to reevaluate the airway immediately prior to induction of general anesthesia as the airway edema may be exacerbated during the second stage of labor following fluid resuscitation [13, 15, 16]. Capillary engorgement of airway mucosal lining in pregnant women can increase the risk for bleeding during manipulation of the upper airway, especially in the nasal cavity [2, 3]. Consequently, many practitioners are reluctant to perform a nasal intubation as it has higher risk for epistaxis during pregnancy [2]. However, a 2011 review from Arendt et al. suggests that nasal intubation is acceptable with proper preparation of the nasal mucosa using topical vasoconstrictors, and the intubation is performed by the fiberoptic nasotracheal intubation technique [17]. However, an individual assessment is required prior to this procedure, as topical vasoconstrictors may have an impact on maternal hemodynamic and uteroplacental perfusion [2].

Physical derangements of pregnancy increase the risk of maternal and fetal hypoxemia during induction of anesthesia and subsequent airway manipulation. As the gravid uterus expands toward diaphragm, functional residual capacity (FRC) decreases by approximately 20–30% at term. This reduction comprises a 25% reduction in expiratory reserve volume (ERV) and a 15% reduction in residual volume (RV) [2, 18, 19]. The reduction is more prominent during a supine position. Although FRC decreases significantly, the closing capacity (CC) remains unchanged in pregnancy, resulting in a reduced FRC/CC ratio. Consequently, more rapid closure of the small airways may occur, increasing the risk of atelectasis [2, 3, 20]. In addition to the upward movement of the diaphragm, there are also other diaphragm changes that occur as pregnancy advances: lengthening of muscle fibers, an increase in the zone of apposition, and an increase in the radius of curvature of the diaphragm [21, 22, 23]. These changes contribute to an increase in ribcage dimension and concurrent tidal volume increase of up to 45% at term [21, 22, 24]. Along with the increased respiratory rate that is observed during pregnancy, an approximately 48% increase is observed in minute ventilation during the first trimester. Due to increased minute ventilation, maternal PaCO2 decreases and arterial pH increases causing a mild respiratory alkalosis (typically 7.42–7.44) [3]. As the pregnancy progresses, oxygen consumption also increases significantly [2, 3, 25]. An approximately 60% increase in oxygen demand is observed during pregnancy as the fetus grows. Consequently, pregnant women are more susceptible to developing hypoxemia during the induction of GA [25].

2.2 Gastroesophageal changes

During pregnancy, the esophagus, stomach, and pylorus are displaced cephalad by the enlarging uterus, decreasing the competence of the lower esophageal sphincter (LES). Elevated levels of progesterone and estrogen during pregnancy further reduce LES tone [2, 3, 18]. In addition, gastrin secretion increases during pregnancy, leading to increased gastric hydrogen ion production, and thereby increasing gastric pressure. This increase in gastric pressure, plus the incompetence of the LES, increases risks of regurgitation, aspiration, and the development of esophagitis and acid pneumonitis [2, 3]. Although the increased risk of regurgitation and aspiration does not necessarily result in difficult laryngoscopy and intubation, it has been reported to cause death during general anesthesia [26].

Gastric emptying time is not prolonged during pregnancy compared with the nonpregnant women [27]. However, it begins to prolong with the onset of labor, due to pain, anxiety, and the administration of analgesics. It also further contributes to the increased risk of regurgitation and aspiration in pregnant women. Therefore, it is prudent to consider all pregnant women at increased risk for pulmonary aspiration during labor [2, 3].

2.3 Other changes

Most women gain between 10 and 15 kg during pregnancy due to increase in uterine size, fetal mass, fat deposition, blood, and interstitial fluid volume [18]. This may increase the risk of difficult airway management, as high BMI is associated with more difficult mask ventilation, laryngoscopy, and tracheal intubation, especially in short stature women. Moreover, a more rapid oxygen desaturation during the induction of GA is also associated with people with higher BMI. In addition to pregnancy-related weight gain, breast enlargement during pregnancy is also associated with more difficult laryngoscopy. Therefore, optimizing intubation position is necessary to facilitate correct placement of the laryngoscope blade [2, 3].

3. Airway assessment

Preanesthetic assessment of the airway should be performed, when possible, to detect the potential of difficulty airway [2, 3, 28, 29]. Preanesthetic assessment should consist of history taking and physical [3]. Any history of difficult airway management is vital in preanesthetic airway assessment [30]. Presence of pathological conditions associated with a difficult airway should also be noted, including snoring, which may make mask ventilation more difficult [31, 32]. A complete physical examination should always be performed to detect the physical characteristics associated with difficult airway. There are five specific components of the airway exam that should be evaluated: overall inspection of the face and neck, oropharyngeal and dental anatomy, neck anatomy and range of motion, mandibular protrusion ability, and submandibular space [3].

The overall inspection of face and neck is necessary to detect any pathological states involving the face or neck, such as massive face deformities, facial burns, retrognathia, tumor involving the face or neck, thick or short neck, or large goiter [3]. In the setting of pregnancy and trauma, the presence of a cervical collar has been shown to interfere with mask ventilation and direct laryngoscopy [33].

There are two important components in oropharyngeal and dental examination that should be evaluated: maximum voluntary mouth opening and Mallampati score [3]. Measurement of maximum mouth opening is achieved by measuring the inter-incisor distance when the patient voluntarily opens the mouth as wide as possible [3, 34, 35]. Inter-incisor distance of less than 3 cm, or 2 fingerbreadths, is associated with difficult intubation [34]. Some studies even suggest that a distance of less than 4–4.5 cm can increase the risk of a difficult airway [35]. In 1983, Mallampati et al. described a clinical sign to determine the difficulty of direct laryngoscopy and tracheal intubation, based on the size and position of the tongue relative to the pharyngeal size. To assess the Mallampati classification, the patient should be in an upright sitting position with the head in a neutral position, the mouth wide open, and the tongue protruding as far as possible without phonation. Higher scores on the Mallampati classification indicate more difficult laryngoscopy and tracheal intubation, because the tongue is large enough to obscure oropharyngeal view. The original version of Mallampati classification consisted of a three-point scale [36]. However, Samsoon and Young further modified the Mallampati classification into a four-point scale (see Table 1) [9].

Class	Definition
Class 1	When the soft palate, fauces, uvula, and faucial pillars are visible
Class 2	When the soft palate, fauces, and the uvula are visible
Grade 3	When the soft palate and the base of uvula are visible
Grade 4	When only the soft palate is visible

Table 1.

Modified Mallampati classification [9].

The dental condition of the patient has also been shown to affect airway management [34]. To prevent trauma and tooth aspiration, it is recommended to extract very loose teeth prior to laryngoscopy. Although the edentulous patient is almost always associated with easy tracheal intubation, face mask ventilation is often difficult [37].

A thick neck (neck circumference greater than 43 cm) has been shown to increase the risk of difficult tracheal intubation [33, 38]. In addition, neck mobility is also essential in airway examination as it is necessary to have an ideal neck position when doing laryngoscopy and intubation. The ideal intubating position is achieved by the extension of the atlantooccipital joint, in what is called the sniffing position, with the alignment of the oral, pharyngeal, and laryngeal axes. Normal atlantooccipital joint extension should be greater than 35° [39, 40]. Moreover, the sternomental distance can also be used to quantitatively assess neck mobility. The sternomental distance is the distance between the chin point and the sternal notch, measured when the head is in extension and the mouth is closed. Distance less than 12.5 cm has shown to increase the risk of difficult intubation [41]. Overall neck range of motion also can be used to predict the risk of difficult intubation. The assessment is performed by measuring the angle between forehead and neck when fully flexed and extended. An angle of less than 80° is associated with difficult intubation [42].

The mandibular protrusion test has been shown to have strong predictive value in determining a difficult laryngoscopy. It is performed by instructing the patient to extend the mandible as far as possible and then assessing the location of the mandibular teeth in comparison to the maxillary teeth. When the mandibular teeth can extend beyond the maxillary teeth, it is predictive of easy laryngoscopy [43]. Similar to mandibular protrusion test, the upper lip bite test (ULBT) is also shown to have predictive value in determining the likelihood of difficult airway, with higher specificity than the Mallampati classification. In the ULBT, the patient is instructed to bite their upper lip. The ability of biting the upper lip is then classified into three classes (see Table 2). The higher the class, the more difficult it is to laryngoscope and intubate [44, 45].

Class	Definition
Class 1	The lower incisor is able to bite the upper lip above the vermilion border
Class 2	The lower incisor is able to bite the upper lip below the vermilion border
Class 3	The lower incisor is not able to bite the upper lip

Table 2.

The upper lip bite test classification [44].

Evaluation of submandibular space is essential in determining the risk of difficult laryngoscopy and intubation. During direct laryngoscopy, the blade of the laryngoscope displaces the tongue into the submandibular space. A small submandibular space will cause inadequate visualization of the glottis. The submandibular space can be estimated by measuring the thyromental distance. It is measured from the lower border of the mentum to the thyroid cartilage notch. A distance of less than 6.5 cm or 3 fingerbreadths suggests an increased risk of difficult intubation [46, 47].

In pregnant women, a recent study found that the modified Mallampati test was shown to have better predictive value compared with ULBT, thyromental distance, and sternomental distance. In addition, this study also showed that the best cutoff point for the thyroid distance was 5 cm and for the sternomental distance was 15 cm. However, combining these various tests suggested to have a better diagnostic accuracy [48]. Moreover, several new modalities such as bedside endoscopy, point-of-care ultrasonography (POCUS), virtual laryngoscopy/bronchoscopy, or three-dimensional printing can be used to further evaluate the risk of airway difficulty, especially in patients with complex airway pathology [28].

4. Management

Management of the obstetric difficult airway requires adequate preoperative preparation, a throughout intraoperative plan, and multiple back-up plans. All practitioners should be familiar with the algorithms for anticipated and unanticipated difficult airway in OB.

4.1 Preoperative preparation

Preoperative preparation should consist of obtaining informed consent, assessing the airway, determining fasting policy, and administering premedication [49]. Prior to obtaining informed consent, the anesthesiologist must provide the patient with comprehensive information regarding the risks and benefits of the GA procedure in the obstetric population. It should also include possible airway management that may be undertaken to address possible airway difficulties during the procedure. Even if airway examination indicates no risk of difficult airway, it risk of unanticipated or unrecognized airway issues and complications is not eliminated. Therefore, the anesthesiologist should always have a management plan for unanticipated airway difficulties even before the general anesthesia is initiated [2, 50].

In addition to increased gastric pressure during pregnancy, prolonged gastric emptying during labor has also been shown to increase the risk of regurgitation and aspiration in laboring women. Therefore, it has been historically recommended to avoid ingesting solid food and clear fluid 6 and before 2 h, respectively, before the operative procedure [51, 52]. As the incidence of maternal death caused by aspiration decreases, more studies are suggesting liberal nil per oral (NPO) guidelines, allowing ingestion of isotonic fluids and light diet during labor [53]. Moreover, several premedication drugs are also used as aspiration prophylaxis. The purpose of these drug is to reduce pH and the amount of gastric volume. The aspiration prophylactic drugs include histamine-2 receptor antagonists (e.g., ranitidine), proton-pump inhibitors (e.g., omeprazole, lansoprazole), nonparticulate antacid (e.g., sodium citrate), or promotility drugs (e.g., metoclopramide) [49, 50, 54, 55]. The use of histamine-2 receptor antagonists with or without a promotility drug is the most common regimen for aspiration prophylaxis in the obstetric patient. Ranitidine and metoclopramide should be administered at least 30 min before induction [56, 57]. In emergent situation, a dose of sodium citrate 30 mL may also be used within 30 min of surgery [56, 58, 59].

In addition to patient preparation, the anesthesiologist should also have a discussion with the team whether to proceed with the procedure or wake the patient in the event of failed tracheal intubation [2, 49]. The Obstetric Anesthetists’ Association and Difficult Airway Society (OAA/DAS) provides guidelines for this decision (see Figure 1).

Figure 1.

Factors to consider in the decision to procced with surgery or wake the patient following failed tracheal intubation. Reproduced from Mushambi et al. [49], with permission from obstetric Anesthetists’ association/difficult airway society.

4.2 Rapid sequence induction and intubation

To minimize the risk of aspiration, rapid sequence induction and intubation (RSI) has become the standard induction technique in obstetric general anesthesia [2, 60, 61, 62]. The goal of RSI is to minimize the length of time between loss of consciousness and the establishment of optimal intubating condition. In the traditional RSI technique, after achieving ideal patient position, preoxygenation, and application of cricoid pressure, the administration of an intravenous induction agent is then rapidly followed by administration of an intravenous neuromuscular blocking agent; the trachea is intubated without attempts at positive-pressure ventilation (PPV) [3, 60]. The goal of avoiding PPV is to prevent gastric insufflation, as this may increase the risk of regurgitation [63]. However, OAA/DAS recommends considering the use of facemask ventilation, as the risk of regurgitation is low with correct application of cricoid pressure. Therefore, the steps in performing RSI in obstetric patient are: (1) proper patient positioning; (2) preoxygenation; (3) application of cricoid pressure; (4) administration of induction agent and neuromuscular blocking agent; (5) face mask ventilation; (6) tracheal intubation [49].

In obstetric procedures, propofol is the typical induction agent, barring hemodynamic or respiratory concerns. After the administration of induction agent, neuromuscular blocking drugs (NMDs) are then administered intravenously to facilitate optimal intubating condition. Succinylcholine or suxamethonium has historically been the most commonly used NMD for RSI in obstetric patients because of its rapid onset and short duration, allowing resumption of spontaneous ventilation in the event of failed intubation [2, 3, 64]. The optimal dose of succinylcholine is 1–1.5 mg/kg [3, 65, 66, 67]. Although the level of plasma pseudocholinesterase decreases during pregnancy, studies show that the duration of action of succinylcholine in pregnant women remains unchanged [68]. Since the advent of sugammadex, a fast-acting reversal agent specifically for rocuronium or vecuronium, nondepolarizing NMDs (e.g., rocuronium, vecuronium) can also be used in RSI technique as the alternative to succinylcholine [64, 69, 70]. The optimal dose of rocuronium is 1–1.2 mg/kg, and vecuronium is 0.3 mg/kg [71, 72, 73, 74, 75]. Sugammadex (16 mg/kg) can rapidly reverse the effects of rocuronium or vecuronium to prevent the prolong duration of action. Therefore, it can achieve the same clinical effects as succinylcholine without risk of hyperkalemia, bradycardia, myalgia, increased intragastric pressure, and increased intracranial pressure [71, 72, 73, 74, 75, 76].

In contrast to standard RSI, modified RSI with low-pressure ventilation (<12 cm H₂0) with correct application of cricoid pressure, is recommended in RSI for obstetric patients. Ventilation is carried out using a facemask with a maximum inflation pressure of 20 cm H₂O. The goal of PPV is to delay the onset of hypoxemia and increase the likelihood of successful facemask ventilation in the event of difficult or failed tracheal intubation [77, 78].

In pregnant women without risk of difficult airway, direct laryngoscopy using a Macintosh blade is preferred [2, 3, 79]. However, in patients at risk of difficult airway (e.g., obese) and those who fail tracheal intubation, practitioners should use a video laryngoscope to provide a better view of the glottis and thereby increase the chances of success [80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90]. Since all obstetric patients are at a higher risk for a difficult airway, video laryngoscope should always be available in all obstetric general anesthetics [49, 79]. If the view of the glottis is not optimal during the first laryngoscopy, the anesthesiologist may reduce or remove cricoid pressure and reposition the head and neck [91, 92]. Due to capillary engorgement and edema of the mucosal lining of the airway in pregnant women, the risk for airway obstruction and bleeding during upper airway manipulation is higher than in the general population [13, 14]. Therefore, a small endotracheal tube (e.g., size 6.5 or 7.0) is recommended to minimize the risk of trauma and increase the success rate in pregnant women. To minimize the risk of pulmonary aspiration, a cuffed endotracheal tube is used. In addition, endotracheal tube introducer (e.g., flexible stylet, bougie) can be used to improve the success rate of tracheal intubation [2, 49].

4.3 Management of the unanticipated difficult airway

Anesthesiologists must be prepared to manage difficult airway situations. Algorithms for the unanticipated difficult airway in the parturient have been developed by national and international organizations.

If intubation fails on the first attempt, a second attempt should be made by a more experienced anesthetist using alternative equipment as appropriate. Ventilation via facemask is recommended if there is a delay in the second attempt. During the second attempt at intubation, cricoid pressure should not be applied (see Figure 2) [49]. In addition, a second attempt at intubation should not be continued if there is a Cormack-Lehane grade 3b or 4 view at laryngoscopy to prevent airway trauma and loss of airway control [49, 93, 94, 95]. In case of two unsuccessful intubations, the anesthesiologist should declare a failed intubation and proceed to the failed intubation algorithm according to the OAA/DAS guideline (see Figure 2). However, in the presence of experienced anesthetist, this guideline also allows for a maximum of three attempts at intubation before declaring a failed intubation [49, 96].

Figure 2.

Safe obstetric general anesthesia. Reproduced from Mushambi et al. [49], with permission from obstetric Anesthetists’ association/difficult airway society.

If a failed intubation has been declared, airway management consists of three steps including (1) calling for help, (2) maintaining adequate oxygenation, (3) determining whether proceed or wake the patient (see Figure 3) [49]. A more experienced anesthesiologist should be called immediately to help in airway management [2, 3, 28, 29, 49]. To maintain adequate oxygenation, ventilation can be performed through a facemask or supraglottic airway device. When performing facemask ventilation, it is recommended to use the two-person (four-handed) technique and to reduce or release the cricoid pressure [28, 29, 49]. If facemask ventilation is found to be difficult or inadequate, a supraglottic airway device should be inserted immediately before the effects of the induction agent and NMD wear off [49]. The second-generation supraglottic airway device is recommended as it has an additional esophageal drainage port and oropharyngeal cuff to reduce the risk of pulmonary aspiration [28, 29, 49]. During the insertion of supraglottic airway device, cricoid pressure should be temporarily removed. Only two attempts at supraglottic device insertion should be performed in order to prevent bleeding or further airway trauma. Once the adequate oxygenation has been established, the anesthetist and team should determine whether to proceed with surgery or wake the patient. The final decision should be based on consideration of several factors that have been evaluated preoperatively (see Figure 1) [49] However, the presence of airway hazards and the degree of difficulty in airway management remain major factors in decision-making because maternal safety is a top priority for the anesthesiologist. If there is no evidence of a difficult airway or a life-threatening condition for the mother, the safest strategy is to awaken the mother. If the mother is in immediate jeopardy and no other anesthetic technique is feasible, anesthetist should consider proceeding with surgery. On the other hand, if the mother is stable with a life-threatening condition of the fetus, it is advisable to consider waking the mother. Despite the controversial decision, the risks of an unsecured airway and the increased risk of aspiration are considered to outweigh the benefits of proceeding with surgery [2, 49]. This is a difficult decision, and evidence does support both sides. Several studies have shown that continuing surgery with a well-functioning supraglottic airway device following failed tracheal intubation is considered as safe and is also recommended [29, 97].

Figure 3.

Management of failed tracheal intubation in obstetrics. Reproduced from Mushambi et al. [49], with permission from obstetric Anesthetists’ association/difficult airway society.

In the setting of a failed intubation, if the decision is made to wake the patient, the anesthesiologist must maintain adequate oxygenation and prevent pulmonary aspiration by applying cricoid pressure and changing the patient position to head-up or left-lateral position. In addition, the anesthesiologist should also assess for the possibility of persistent paralysis and laryngeal spasm. If there is persistent paralysis, sugammadex can be used to reverse the effects of rocuronium. To anticipate the occurrence of laryngeal spasm and “can’t intubate, can’t oxygenate” (CICO) situations, the anesthesiologist must also prepare the appropriate equipment, drugs, and personnel. Following waking, the obstetrician should review the urgency of delivery, and anesthetist should consider the safest alternative anesthetic option for the patient. Options for anesthetic technique include (1) regional anesthesia or (2) general anesthesia preceded by awake intubation or tracheostomy [2, 49]. If regional anesthesia is selected, anesthetist should prepare for a backup plan in case high or failed block happened. If general anesthesia is selected, awake intubation using video laryngoscope or flexible bronchoscope with topical anesthesia is recommended [49, 98, 99]. However, in the event of extreme difficulty or failure of tracheal intubation via upper airway, tracheostomy should be performed immediately [49].

If the decision to proceed with surgery has been made in the setting of failed intubation, anesthesiologist should consider the following issues: (1) maintenance of anesthesia, (2) selection of airway device, (3) maintenance of ventilation, (4) strategy to prevent pulmonary aspiration. To maintain adequate anesthesia, a non-irritant volatile agent such as sevoflurane is commonly used. In the event of uterine atony after delivery, total intravenous anesthesia with propofol may be considered as it has no effect on uterine muscle tone [49]. If a failed intubation has been declared, the anesthesiologist must choose whether to proceed with only a supraglottic airway device or to perform additional tracheal intubation attempts [29]. Although the use of supraglottic airway device is not advisable in elective surgery, its use in caesarian delivery has found to be effective and safe [29, 49, 97]. Again, a second-generation of supraglottic airway device is recommended. If the anesthetist decides to proceed with additional attempt at tracheal intubation, it should be noted that only one attempt by an experienced anesthesiologist with a planned intubation technique should be allowed [29]. The intubation technique must overcome the anatomical constraints that led to the earlier failure. Although the selection of intubation technique depends on anesthesiologist’s clinical judgment, it is recommended to use flexible bronchoscope-guided intubation to avoid airway trauma and esophageal intubation [29, 100]. If tracheal intubation fails to be performed safely, a definitive airway with tracheostomy is required [29, 49]. Although controlled ventilation is used in the vast majority of failed intubation cases in the United Kingdom, a case-by-case consideration should be exercised before deciding whether to use spontaneous or controlled ventilation [49, 79]. In addition, to prevent pulmonary aspiration during the procedure, cricoid pressure should be applied until after delivery (Figures 4and5) [49].

Figure 4.

Management after failed tracheal intubation in obstetrics. Reproduced from Mushambi et al. [49], with permission from obstetric Anesthetists’ association/difficult airway society.

Figure 5.

Management of “can’t intubate, can’t oxygenate” (CICO) in obstetrics. Reproduced from Mushambi et al. [49], with permission from obstetric Anesthetists’ association/difficult airway society.

Following failed tracheal intubation, persistent failure to ventilate using facemask and supraglottic airway device leads to a “can’t intubate, can’t oxygenate” (CICO) situation. The CICO situation may be caused by poor chest wall compliance and laryngeal spasm, which can be managed with NMDs [28, 29, 49]. Therefore, once a CICO situation has been identified, apart from calling an ear, nose, and throat surgeon and/or intensivist, it is imperative to rule out laryngeal spasm as the cause of CICO. The reason is to prevent invasive airway management when it can be managed with only NMD [29, 49]. If the succinylcholine has been administered during induction, then a combination of rocuronium and sugammadex is preferred [29, 49, 50]. When laryngospasm has been ruled out as the cause of CICO, front-of-neck procedure should proceed without delay. A front-of-neck procedure refers to procedure to securing airway access via front of the neck by either tracheotomy or cricothyrotomy [29]. Prior to front-of-neck procedure, patient should inhale 100% oxygen via a facemask or supraglottic airway device while waiting for the neuromuscular blockade to be confirmed or established [49]. Once the neuromuscular blockade has been established, front-of-neck procedure can be performed immediately. If an experienced surgeon is present, tracheotomy may be performed to provide definitive airway access [29, 101, 102]. However, cricothyrotomy may be more preferred in emergency setting [29, 50]. If adequate oxygenation is not achieved, a cardiac arrest protocol should be instituted, and undelivered fetus at >20 weeks’ gestation age should be delivered via cesarean section immediately [49, 103].

4.4 Management of the anticipated difficult airway

Anticipated difficult airway is defined as a clinical situation in which a trained anesthesiologist has anticipated difficulty in providing ventilation using facemask or a supraglottic airway, laryngoscopy, tracheal intubation, extubation, or invasive airway [104]. In pregnant women with an anticipated difficult airway, neuraxial anesthesia is more preferred compared with general anesthesia as it does not require any airway manipulation. However, anesthetist should always have backup plan for securing the airway in case high or failed block happened. If pregnant women with anticipated difficult airway must undergo general anesthesia, the safest option is to perform awake tracheal intubation [2].

4.5 Extubation of the trachea

Pulmonary aspiration is the one of the most common adverse events at the end of anesthesia, especially during the extubation [6, 105]. In obstetric patients, awake extubation is recommended. The position during extubation is also important to prevent regurgitation [49]. Recent study suggests a head-up position because it aids the patency of airway, respiratory function, and access to the airway [106].

5. Conclusion

Although the use of general anesthesia (GA) has been largely replaced by neuraxial anesthesia, in certain obstetric situations, GA is preferred. Advantages include rapid control of the airway and ventilation, improved hemodynamic control, and speed of onset. While maternal mortality associated with GA has decreased substantially, deaths from difficult airway in GA are still reported and are higher in obstetric patients compared with the general population. One of the leading causes of airway-related death during obstetric GA is difficult and failed intubation. The significant anatomic and physiologic changes of pregnancy have been considered to explain the increased difficulty in airway management in obstetric patients. Airway mucosal edema, capillary swelling, decreased functional residual capacity, and increased oxygen consumption during pregnancy have been shown to cause difficult airway in obstetric patients. In addition, gastroesophageal changes during pregnancy, such as decreased lower esophageal sphincter muscle competence, increased gastric pressure, and prolonged gastric emptying, are associated with an increased risk of pulmonary aspiration in pregnant women. These changes may be further exacerbated during labor; therefore, some modifications are needed in the obstetric airway management. These modifications include using certain specific equipment, administering additional premedication, performing additional procedures, and using different airway management algorithms. Therefore, it is necessary to have adequate knowledge regarding the management of difficult airways in obstetrics to prevent future airway-related mortality and morbidity of mothers and neonates.

Conflict of interest

The authors declare no conflict of interest.

Abbreviations

GA	general anesthesia
FRC	functional residual capacity
ERV	expiratory reserve volume
RV	residual volume
CC	closing capacity
ULBT	upper lip bite test
POCUS	point-of-care ultrasonography
CAFG	Canadian Airway Focus Group
CICO	cannot intubate, cannot oxygenate
CVCO	cannot ventilate, cannot oxygenate
OAA/DAS	Obstetric Anesthetists’ Association and Difficult Airway Society
RSI	rapid sequence induction and intubation
PPV	positive-pressure ventilation
FETO2	end-tidal oxygen fraction
NMDs	neuromuscular blocking drugs
eFONA	emergency front of neck access