Abstract
Airway management and difficult endotracheal intubation in the pregnant woman require unique considerations that differ from other patient populations. While most pregnant women deliver without the need for airway management, difficulty with endotracheal intubation remains a source of maternal morbidity, maternal mortality and concern for obstetric anaesthesiologists.
Introduction
Airway management and difficult endotracheal intubation in the pregnant woman require unique considerations that differ from other patient populations. While most pregnant women deliver without the need for airway management, difficulty with endotracheal intubation remains a source of maternal morbidity, maternal mortality and concern for obstetric anaesthesiologists. The most common indication for general anaesthesia and endotracheal intubation in a pregnant patient is emergency caesarean delivery.1 Any labouring parturient can develop sudden fetal bradycardia and require emergent induction of anaesthesia, requiring rapid decision-making and coordinated teamwork. When neuraxial anaesthesia is not possible, securing the airway for general anaesthesia in a safe and timely fashion remains a challenge. Emergent, unexpected caesarean delivery cases, in addition to specific anatomic and physiologic changes of pregnancy and labour, contribute to difficult airway management and increased maternal morbidity and mortality. This chapter will highlight the following topics:
Clinical situations in which airway management is indicated in obstetric patients
Anatomic and physiologic changes of pregnancy that impact airway management
Incidence and reasons for airway problems in pregnancy
Airway-related morbidity and mortality
Safety measures and clinical preparedness for intubation of a parturient, based on current guidelines for airway management in obstetric patients.
Indications for Endotracheal Intubation of a Pregnant Patient
The frequent use of neuraxial analgesia and anaesthesia during labour and delivery has minimized the need for general anaesthesia over the past 20 years.2, 3 However, the conditions shown in Table 24.11, 2, 3 can occur without notice, and warrant skill and readiness to provide rescue airway management to a parturient.
Table 24.1 Obstetric conditions that frequently require airway management
| Clinical scenario | Typical precipitating factors |
|---|---|
| Emergency caesarean delivery |
|
| Caesarean delivery with failed labour epidural |
|
| Local anaesthetic systemic toxicity | Epidural catheter migration into vein or artery
|
| Inadvertent intrathecal blockade (‘high spinal’) with obliteration of centrally mediated respiratory drive |
|
| Respiratory emergency | Severe asthma exacerbation
|
| Neurologic emergency |
|
| Maternal cardiac arrest |
|
General anaesthesia may also be required for caesarean delivery in patients who have absolute or relative contraindications to having a neuraxial technique, listed in Table 24.24, 5:
| Contraindication to neuraxial technique | Examples |
|---|---|
| Patient refusal | Social or cultural opinion against labour pain relief; anxiety, fear of needles |
| Uncorrected coagulopathy | Immune thrombocytopenic purpura; haemolysis, elevated liver enzymes, low platelet (HELLP) syndrome; pre-eclampsia with thrombocytopenia; disseminated intravascular coagulopathy (DIC) |
| Rash/infection at the site of injection | Pruritic urticarial papules and plaques of pregnancy (PUPPP); other |
| Untreated systemic infection/sepsis | Chorioamnionitis or other infection with evidence of systemic bacteraemia; primary outbreak of herpes simplex virus type-2 |
| Haemodynamic instability | Major post-partum haemorrhage with hypovolemia |
| Elevated intracranial pressure | Intracranial lesion with mass effect or midline shift |
| Indeterminate neurological disease | Chiari malformation with unknown cerebellar tonsil herniation and/or tethered cord; other |
All labouring parturients should undergo a physical examination to identify a potential difficult airway. Specific plans formulated for airway management, particularly for those with the combination of a difficult airway plus a contraindication to having a neuraxial technique, should be communicated to the entire care team (anaesthesiologists, obstetricians, nursing staff). Advanced risk stratification and anticipatory planning (Table 24.3)1, 2 is helpful.
Table 24.3 General principles for preventing airway morbidity in pregnant patients
| Principle | Intervention | Plan |
|---|---|---|
| Identify patients with a difficult airway | Evaluate every labouring patient, since emergency caesarean could occur any time |
|
| Favour the use of neuraxial anaesthesia | Identify labouring patients at high risk for caesarean delivery or difficult intubation: category 2 fetal heart tracing, modified Mallampati class 4 airway, prolonged induction of labour |
|
| Have awareness and a plan for patients who do not have a labour epidural | Verify airway equipment availability and functionality; discuss concerns with the entire care team |
|
NPO: Nil per os
Anatomic and Physiologic Changes in Pregnancy
The pregnancy-related changes that occur anatomically and physiologically can impact airway management plans, and are essential for the obstetric anaesthesiologist to recognize (Table 24.4).1
Table 24.4 Anatomic and physiologic changes in pregnancy that impact airway management
| Parameter | Change in pregnancy | Airway-related implications | Clinical manoeuvers |
|---|---|---|---|
| Functional residual capacity | Decreases due to upward displacement from the expanding uterus, exacerbated in the supine position and in the obese patient | Faster oxygen desaturation upon induction of general anaesthesia |
|
| Metabolic oxygen consumption | Increased6 | ||
| Body weight and breast tissue density | 15–20 kg weight gain during pregnancy,7 breast enlargement | Laryngoscope placement is difficult in the supine position |
|
| Lower esophageal sphincter tone | Decreased | Increased incidence of gastroesophageal reflux; higher risk of aspiration when unconscious |
|
| Circulating plasma volume | Increased | Increased airway tissue friability and swelling |
|
NPO: nil per os
Airway Changes in Pregnancy, Labour and Delivery
Airway changes in pregnancy occur in conjunction with weight gain, fluid retention and resulting tissue oedema. Fluid retention in the head and neck paired with reduced compliance make laryngoscopy more difficult.9 The diameter of the oropharynx narrows in pregnancy, leading to obstructive changes such as sleep-disordered breathing in the third trimester.10 The modified Mallampati classification (MMC; Figure 24.1) describes the extent that the tongue obscures the soft and hard palate and is used to predict degree of difficulty with intubation.11
Figure 24.2 Ramp positioning aligns the oral, pharyngeal and laryngeal axis to facilitate intubation. Reproduced with permission.
Airway evaluation of pregnant women between 12 and 38 weeks of gestation revealed a 34% increase in MMC IV airways.9 Furthermore, labour itself can worsen the airway exam: evaluation of the MMC and oropharyngeal volume at the onset and the end of labour demonstrated a significantly reduced oral volume, pharyngeal area and volume, and increase in the MMC by one grade in 33% of parturients and by two grades in 5% of parturients.12 Airway swelling may be exacerbated by intravenous fluids, pre-eclampsia, oxytocin infusion and valsalva manoeuvres during labour and delivery.12,13
Table 24.514,15 lists traditional components of an airway examination, findings that are non-reassuring for intubation and impact of pregnancy on those features.
Table 24.5 Components of an airway examination and impact of pregnancy
| Airway component | Non-reassuring finding | Effect of pregnancy |
|---|---|---|
| Length of upper incisors | Longer | None |
| Maxillary and mandibular incisor position with jaw closure | Maxillary anterior to mandibular (‘overbite’) | None |
| Interincisor distance | <3 cm | None |
| Shape of palate | Narrow, high arch | None |
| Compliance of mandibular space | Stiff, indurated, occupied by mass | May be reduced from generalized fluid retention |
| Visibility of uvula | Diminished (MMC class III or IV) | View can be diminished through gestation and also during labour |
| Neck length | Short | None |
| Neck circumference | > 43 cm | Increased with weight gain |
| Neck range of motion | Limited flexion or extension | Impaired by breast fullness |
MMC = modified Mallampti classification
In a study of 1500 patients undergoing emergency caesarean delivery under general anaesthesia, difficult intubation was associated with short neck, obesity, missing or protruding maxillary incisors and receding mandible, but not associated with generalized oedema or swollen tongue.16 Precautions and planning for airway management of a parturient with such features must be exercised, with the understanding that oxygen desaturation occurs more rapidly in a pregnant patient, rendering less time for rescue airway manoeuvres to be performed. Additional concern is warranted for those women who have risk factors for difficult mask ventilation, listed in Table 24.6.17
Incidence of Airway Problems During Pregnancy
Over the past two decades, the number of general anaesthetics provided for caesarean delivery has diminished,2,3 which has decreased the training and experience that anaesthesiologists receive for general anaesthesia and airway management in obstetric patients.18 More than 50% of general anaesthetics provided for caesarean delivery occur during night shifts when staff are potentially less experienced and fewer in number.3 In one report, 80% of failed intubations occurred with more junior trainees,19 and non-adherence to protocols in the setting of failed intubation has been described.20
The incidence of difficult intubation is 0.67–4.7% in pregnant patients,21–23 while that of failed intubation is reported to be from none in 343022 to one in 224 (0.4%) intubations.25 An analysis of failed intubations in obstetric patients reported an incidence of 0.23%, unchanged over the time period of 1970 through 2015, with one death per 90 failed intubations.24 Maternal deaths resulted from aspiration, hypoxaemia due to airway obstruction, or oesophageal intubation. The heterogeneity of reported incidence of difficult and failed intubation likely reflects differences in rate of elective vs emergent general anaesthetics provided for caesarean delivery. Centres that provide elective general anaesthesia more readily reported more general anaesthetics in cases that were non-emergent,22 while centres in which general anaesthesia is predominantly used during obstetric emergencies report intubation failure and greater morbidity and mortality.23,24 This is an important distinction to make; intubation failure may be more likely to occur in centres where general anaesthesia is reserved for emergency situations. Therefore, steps to minimize airway failure will be higher yield in these institutions. The use of simulation drills for education about general anaesthesia for caesarean delivery, rehearsal of airway device preparation and troubleshooting a difficult airway are warranted. See Figure 24.3 for a sample difficult-airway algorithm.
Figure 24.3 Obstetric Anaesthetists’ Association and Difficult Airway Society algorithm for difficult airway in obstetric patients. Can’t Intubate Can’t Oxygenate (CICO). Reproduced with permission.40
Consequences of Airway Problems During Pregnancy
Maternal Mortality and Morbidity
While anaesthesia-related maternal mortality is vanishingly rare, respiratory events remain a prominent cause. Adverse respiratory events in parturients are associated with both general and neuraxial anaesthesia.
General Anaesthesia-related Adverse Events
The incidence of maternal death during general anaesthesia for caesarean delivery in the United States has been reported in two sequential six-year analyses.26 A marked reduction in caesarean fatality rates under general anaesthesia occurred between 1991–1996 and 1997–2002 (16.8 to 6.5 per million). Reasons for improvement in general anaesthesia outcomes include:
Better monitoring via implementation of pulse oximetry and capnography
Use of the difficult airway algorithm
Introduction of the laryngeal mask airway
Introduction of video laryngoscopy.
Although outcomes have improved, preparedness for airway management in pregnancy remains a priority; general anaesthesia is most often needed when ASA status is >4 or when decision-to-incision interval is less than 15 minutes (sicker patients in emergency situations such as umbilical cord prolapse or severe maternal haemorrhage).27 Relevant morbidities that are increasingly prevalent are high body mass index with associated difficult airway and pre-eclampsia with pulmonary oedema.
Two deaths related to hypoventilation associated with general anaesthesia were reported in the United Kingdom from 2009–2012 (0.085 per 100 000 maternities).28 One death was attributed to undiagnosed bronchospasm, and one followed extubation. Recognition of extubation-related respiratory morbidity and mortality after caesarean delivery is critical. In Michigan from 1985–2003, five of eight anaesthesia-related maternal deaths resulted from hypoventilation or airway obstruction during emergence, extubation or recovery from general anaesthesia.29 Stringent risk assessment for patients at risk for sleep-obstructed breathing (such as obese parturients), allocation of resources for monitored recovery (pulse oximetry, capnography), and timely recognition and rescue of bronchospasm are key elements to lower morbidity at time of extubation and during recovery from general anaesthesia.
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