Fig. 18.1
Junker inhaler
Fig. 18.2
Nicaise. Chloroform anaesthesia
Fig. 18.3
Ombredanne inhaler and Ricard inhaler
Fig. 18.4
Robert Macintosh
18.2 Introduction
Obstetric anaesthesia is considered by many to be a high-risk subspecialty of anaesthesia practice that is laden with clinical challenges and medicolegal liability [1]. Evidence-based practice guidelines and reviews of mortality and morbidity, including closed malpractice claims, have been used to foster continual improvement in maternal safety and perioperative outcomes [2–5]. However, the effectiveness of these efforts in improving maternal outcomes has not been evaluated. First is because the incidences of serious complications related to obstetric anaesthesia remain largely unknown primary of the lack of large obstetric anaesthesia database, and second the incidences of complications reported in the literature are highly variable as they typically represent estimates from case reports, case series or limited institutional cohort [6].
Caesarean section is the most commonly performed surgical procedure in obstetrics, and although the operation has become very safe over the years, it is still associated with greater maternal mortality and morbidity [7, 8]. Compared with vaginal delivery, caesarean section is associated with a significantly increased risk of anaesthesia-related adverse events and with a four times risk of maternal death [7]. It is known that there is a greater risk of neonatal respiratory distress with caesarean section than vaginal delivery, regardless of gestational age [7]. Caesarean section is often described as elective (when it is planned) or emergency. The risk of anaesthesia-related adverse events during caesarean delivery is especially high when the procedure is unplanned, when it is performed under general anaesthesia and in women with pre-existing comorbidities [9–11]. The American Society of Anesthesiologists recommends neuraxial anaesthetic techniques for caesarean delivery, whenever possible [3]; however, general anaesthesia may be the most appropriate choice for urgent and emergent caesarean section, especially in such circumstances as foetal distress (Fig. 18.5), ruptured uterus (Fig. 18.6), severe haemorrhage and severe placental abruption (Fig. 18.7) [12–14]. One major reason is that the decision-to-delivery intervals with general anaesthesia can be significantly shorter than that with neuraxial anaesthesia [15].
Fig. 18.5
Foetal distress
Fig. 18.6
Ruptured uterus
Fig. 18.7
Severe placental abruption
This factor is especially important for urgent and emergent caesarean section due to foetal distress, as shorter decision-to-delivery intervals (e.g. less than 30 min) have been shown to be critical and correlate well with better foetal outcomes [16, 17] (Fig. 18.8).
Fig. 18.8
Woman does not want epidural analgesia
18.2.1 General Anaesthesia Indications
The Royal College of Anaesthetists audit book suggests that fewer than 15 % of emergency and fewer than 5 % of elective caesarean sections should be performed under general anaesthesia.
When general anaesthesia is used, the most common indications are urgency (≈35 % of cases in a non-teaching hospital), maternal refusal of regional techniques (20 %) (Fig. 18.8), inadequate or failed regional attempts (22 %) and regional contraindications including coagulation or spinal abnormalities (Fig. 18.9) (6 %) [18, 19]. Obstetric indications, such as placenta praevia, were in the past considered absolute indications for general anaesthesia (Fig. 18.10). However, published departmental audits have reported rates of 9–23 %, although other journals have quoted rates of 2–10 %. Of the caesarean sections performed due to immediate threat to the life of the mother or foetus, 41 % were performed with general anaesthesia [20]. A classification for the urgency of caesarean section is described in Table 18.1.
Fig. 18.9
Spinal abnormalities are important contraindication to regional anaesthesia
Fig. 18.10
Placenta praevia
Table 18.1
Indications to general anaesthesia for caesarean section
Non-reassuring foetal heart tracing | |
Massive haemorrhage | Placental abruption |
Uterine rupture – placenta accreta/percreta | |
Cord prolapse with non-reassuring FH tracing | |
Maternal disease | Severe pre-eclampsia |
Eclampsia | |
HELLP | |
C/I to regional anaesthesia | Coagulopathy/low platelet count |
Anticoagulants | |
Perceived lack of time for RA | |
Failed regional | |
Patient refusal | |
The 2007 American Society of Anesthesiologists Practice Guidelines for Obstetric Anaesthesia states that ‘neuraxial techniques are preferred to general anaesthesia for most caesareans deliveries’ [3]. This evidence-based, guideline-supported change in anaesthesia practice may explain the decrease in the proportion of general anaesthesia for unplanned (but not planned) caesarean deliveries. Although the proportion of general anaesthesia in obstetric practice decreased over the last two decades, the actual number given for caesarean sections is largely unchanged because of the increased section rate. The prevalence of advanced maternal age and pre-existing maternal chronic comorbidities, however, continue to increase, as indicated in the proportion of women older than 40 years [21–23].
Advantages of general anaesthesia include the ability to manipulate respiratory and cardiovascular parameters and the avoidance of sharp drops in systemic vascular resistance. General anaesthesia also negates the problem of having an insufficient block, particularly pertinent in cases where surgery is prolonged or complex. The major concerns in providing general anaesthesia for caesarean section are potential difficulty with airway management, the risk of awareness and the possible effects of anaesthetic agents on uterine tone and the newborn. Concern has also been raised about the sympathetic stimulation from direct laryngoscopy and intubation. The effect of positive pressure ventilation with a reduction in venous return, hypotension and raised pulmonary artery pressures must also be considered [24, 25].
Little evidence supports a particular general anaesthetic technique. Standard practice in obstetrics is to carry out a rapid sequence induction (RSI) with intravenous anaesthetics and a depolarising muscle relaxant such as suxamethonium. Suxamethonium or succinylcholine has a number of well-known disadvantages, but no other neuromuscular blocker has such favourable onset and offset characteristics. There is an increasing interest in the use of rocuronium, an aminosteroid non-depolarising neuromuscular blocking drug, in place of suxamethonium for RSI in the general and obstetric population. This is less common in obstetric anaesthesia as the duration of action of an effective dose of rocuronium exceeds most obstetric procedures. Sugammadex, a specifically designed γ-cyclodextrin, affects the possibility of rapidly reversing profound rocuronium neuromuscular blockade at the end of surgery [26].
Most anaesthetists ‘modify’ the standard RSI with the addition of an opioid [27]. The addition of an opioid obtunds the sympathetic response to laryngoscopy but risks respiratory depression in the neonate. The successful use of ultrashort-acting opioids such as remifentanil and alfentanil, with minimal neonatal respiratory depression, has been described [28]. Maintenance of anaesthesia is generally with inhalational agents, such as isoflurane and sevoflurane. Inhalational agents are negatively inotropic, reduce systemic vascular resistance and impair the pulmonary vascular response to hypotension, so must be used with care (Fig. 18.11).
Fig. 18.11
Rapid sequence induction
General anaesthesia for caesarean section appears to be associated with higher rates of serious and life-threatening complications than regional anaesthesia, and most anaesthetic-related maternal deaths still result from complications during general anaesthesia [29–31]. The major concerns in providing general anaesthesia for caesarean section are potentially difficulty with airway management, the risk of awareness and the possible effects of anaesthetic agents on uterine tone and the newborn.
Complications associated with general anaesthesia are listed in Table 18.2.
Table 18.2
Risks associated with general anaesthesia in obstetric patients
Risks of general anaesthesia |
|---|
Difficult and failed intubation |
Aspiration |
Awareness |
Nausea and vomiting |
Postoperative analgesia |
Uterine atony blood loss |
Development of chronic pain |
Postoperative thromboembolic disease |
Foetal asphyxiation |
Early neonatal depression |
Adverse effects on breast-feeding |
Parents’ experience of the delivery |
Oxygen toxicity |
18.2.2 Airway Problems for the Obstetric Patients
Airway disasters are the leading cause of anaesthesia-associated maternal morbidity [32–35]. The risk of failed intubation is higher in pregnant women than in the general surgical population [36, 37].
Anatomical and physiologic factors that place the pregnant patient at increased risk for airway management complications and difficult intubation include pregnancy-induced generalized weight gain and increase in breast size, respiratory tract mucosal oedema, decreased functional residual capacity (FRC) and increased oxygen consumption (Table 18.3).
Table 18.3
Physiologic changes of respiratory system during pregnancy
System | Changes |
|---|---|
Respiratory system | Increased alveolar ventilation (70 %) |
Relative hypocarbia (PaCO2 of 25–32 mmHg) | |
Reduced functional residual capacity (20 %) | |
Increase O2 consumption | |
Reduced venous oxygen saturation (SvO2) | |
Accumulation of adipose tissue around the airway | |
Vascular engorgement of the respiratory tract | |
Cardiovascular system | Increased cardiac output (40 %) – increased stroke volume 25 % and heart rate 25 % |
Reduced total peripheral resistance | |
Generalized body oedema | |
Normal CVP in superior vena cava distribution | |
Elevated CVP in inferior vena cava distribution (aorto-caval compression) | |
Increased circulating volume | |
Increased plasma volume (40–50 %) | |
Increased red cell mass (20 %) with a physiologic anaemia | |
Gastrointestinal | Reduced lower oesophageal sphincter tone |
Enlarging uterus with increasing intra-abdominal pressure | |
Higher gastric volumes | |
Lower gastric pH | |
Delayed gastric emptying |
Pregnancy results in significant increase in breast size. In the supine position, the enlarged breasts tend to fall back against the neck, which can interfere with insertion of the laryngoscope and intubation. Furthermore, it is not uncommon for the parturient to gain 20 kg or more during pregnancy. Obesity (Fig. 18.12) has been reported to further increase the risk of anaesthetic complications in parturients [38, 39]. A high body mass index (BMI) has been associated with an increased risk of airway management problems including difficult intubation [40]. Additionally, the obstetric literature indicates that parturients with a high BMI are at increased risk for caesarean section.
Fig. 18.12
Obesity
Healthy parturients typically have generalized body oedema due to the effect of increased progesterone levels and accumulation of adipose tissue around the airway, although this oedema is not clinically significant in the majority of these patients. Vascular engorgement of the respiratory tract during pregnancy leads to oedema of the nasal and oral pharynx, larynx and trachea [40–42].
Laryngeal oedema may inhibit the passage of standard size endotracheal tube (ETT), despite adequate vocal cord visualization at laryngoscopy, and requires a smaller internal diameter tube size. Furthermore, tongue enlargement may make it difficult to retract the tongue into the mandibular space during direct laryngoscopy (Fig. 18.13).
Fig. 18.13
Laryngeal oedema
Pregnant women, additionally, have reduced tolerance for apnoea and become hypoxaemic faster after failed intubation because of an increased metabolic rate and decreased functional residual capacity (FRC).
Thus, it is essential for the anaesthesiologist to perform a proper preanaesthetic evaluation and identify the factors predictive of difficult intubation. There is a subset of patients who have certain anatomical features that should indicate that endotracheal intubation via conventional means is very likely to be difficult if not impossible. Certain anatomical features (very large breasts and heavy chest wall, large tongue, no teeth and sunken cheeks, fixed head or neck flexion, massive jaw, upper airway mass) may also render mask ventilation difficult or impossible (Figs. 18.14, 18.15, 18.16, 18.17, 18.18, 18.19 and 18.20).
Fig. 18.14.
Large breast
Fig. 18.15
Heavy chest wall
Fig. 18.16
Large tongue
Fig. 18.17
No teeth and sunken cheeks
Fig. 18.18
Fixed head or neck flexion
Fig. 18.19
Massive jaw
Fig. 18.20
Upper airway mass
If there is any doubt regarding the ability to maintain airway patency during general anaesthesia, alternative methods of anaesthesia should be considered [40]. Options include the use of regional anaesthesia, local infiltration anaesthesia, or, if there is adequate time, an awake intubation followed by induction of general anaesthesia.
Regional anaesthesia is the best choice for caesarean section in most cases of anticipated difficulty with endotracheal intubation [43]. If a patient with a difficult airway requires urgent caesarean section, and if there is a contraindication to the use of spinal or epidural anaesthesia, local anaesthetic infiltration can be used as the primary anaesthetic technique [44, 45]. When the anaesthesiologist anticipates that management of the airway will be difficult, a very safe option is to secure the airway with an ETT, while the patient remains awake [39, 40, 43, 46, 47].
Successful awake endotracheal intubation requires proper preparation of the patients, ideal preparation results in a quiet and cooperative patient and a larynx that is nonreactive to physical stimuli. Topical anaesthesia is the primary anaesthetic for awake intubation [39, 40]. In some patients, topical anaesthesia provided sufficient time to anaesthetize all portions of the airway adequately. If the nasal route is chosen, the nasal mucosae should be sprayed. The pressure receptors that elicit the gag reflex at the root of the tongue are submucosal in location, and topical anaesthesia may not uniformly provide adequate blockade of these pressure receptors, and bilateral blockade of the lingual branch of the glossopharyngeal nerve may be required.
Judicious use of intravenous sedation helps relieve anxiety and increase the pain threshold in awake patients that should remain rational, alert and responsive to commands.
There is some controversy as to the appropriate use and extent of local anaesthesia for awake intubation in a patient with a presumed full stomach. The key to avoiding aspiration is to avoid oversedation; there is a low risk of aspiration of gastric contents in an awake, alert and rationale patient regardless of the extent of topical anaesthesia [40].
Once upper airway has been anaesthetized, adequately, there are numerous ways to intubate the trachea:
Fig. 18.21
Direct laryngoscopy
Fig. 18.22
Blind nasal intubation (tube Ø 6 mm)
Fig. 18.23
The retrograde intubation
Fig. 18.24
The fibre-optic bronchoscope
Direct laryngoscopy results in the most noxious stimulation for the patient; thus, it requires the best patient preparation.
Blind nasal intubation is much less stimulating than direct laryngoscopy, but a small endotracheal tube should be used (6.0 mm). Unfortunately, pregnant women have hyperaemic nasal mucosae, and instrumentation of the nose entails the risk of bleeding [40].
The retrograde intubation has been of value in the management of difficult airway in the past; today it has any value for the obstetric patient (Fig. 18.23).
The flexible fibre-optic intubation has become the ‘gold standard’ for airway management and the most useful aid to awake intubation in the parturient with known difficult airway [48, 49].
Fibre-optic laryngoscopy is much less stimulating than direct laryngoscopy and/or blind nasal intubation, and it can be performed either per os or nasally. It is also considered safer and less traumatic than nasal intubation. Insufflation of oxygen through the suction port also serves as a defogging mechanism, and it provides supplemental oxygen, which results in a higher FIO2 for the patient. An appropriately sized, well-lubricated ETT is placed on the bronchoscope before its insertion. Once the fibre-optic bronchoscope is passed into the trachea, the ETT is threaded off the fibre-optic bronchoscope, the bronchoscope is withdrawn, the ETT adaptor is reattached, and the ETT is connected to the breathing circuit [50].
In the event that intubation is not successful, the anaesthesiologist should have a well-formulated plan in mind, and appropriate equipment and supplies should be immediately available to implement that plan. Hence, it is important for institutions to provide obstetric anaesthesia to have appropriate unanticipated difficult airway and failed intubation protocols.
If the anaesthesiologist is confronted with an unexpected difficult intubation and if there is no foetal distress, the patient is hemodynamically stable, there is adequate gas exchange via mask, and only one anaesthesiologist has attempted intubation, time permits optimizing the chances of successful intubation:
Fig. 18.26
Applying external laryngeal pressure (over the thyroid cartilage)
Fig. 18.27
Using a different type of laryngoscope
When the anaesthesiologist is unable to intubate the trachea of an anaesthetized patient, it is essential to try to maintain gas exchange by mask ventilation between intubation attempts. During positive pressure mask ventilation, maintenance of cricoids’ pressure is mandatory. Failure to intubate the obstetric patient is often followed by difficulty with mask ventilation and by possible pulmonary aspiration. Either of these conditions rapidly leads to hypoxaemia for both the mother and the foetus. The adequacy of mask ventilation and the presence or absence of foetal distress are extremely important factors that must be taken into account in these situations.
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