Case Study
A high-risk nulliparous woman with a body mass index (BMI) of 45 kg/m2 at booking, and now estimated to be 55 kg/m2, presented to the labor ward at 39 weeks’ gestation. On arrival, she was in spontaneous labor and contracting three times in 10 minutes. Vaginal examination revealed that her cervix was 3 cm dilated.
The woman had been reviewed in the antenatal clinic by an obstetric anesthesiologist, who had advised her to consider an early epidural and had warned her that epidural insertion may be technically challenging. Airway assessment demonstrated a Mallampati grade 3 jaw slide B with good mouth opening.
Based on the advice she had received, she requested an epidural for labor analgesia. A 16-gauge IV cannula was inserted on the dorsum of her left hand under ultrasound guidance. The ultrasound was then used to locate the midline, and an estimation of the depth of epidural space of 8 cm was made.
The epidural was inserted after three attempts. The epidural space was found at a depth of 8.5 cm, and 4 cm of catheter was left in the space. Patient-controlled epidural analgesia was started.
Labor pain was initially well controlled. However, as labor progressed, the patient needed further clinician boluses of the low-dose epidural mixture (0.1% bupivacaine and 2 µg/ml fentanyl) because of a unilateral block.
Before the labor epidural could be resited, a pathologic cardiotocographic (CTG) trace necessitated an emergency Category 2 cesarean delivery, and the patient was transferred to the operating room (OR).
In the OR, the patient’s epidural was topped up using 20 ml 2% lidocaine and 1:200,000 epinephrine with alkalization using 2 ml 8.4% sodium bicarbonate (equivalent to 2 mmol). On testing with ethyl chloride following the epidural top-up, the patient was found to have an established block to T8 unilaterally. This was deemed unsatisfactory, requiring conversion to general anesthesia (GA).
Because the patient had an anticipated difficult airway, an airway strategy had already been devised. Plan A consisted of using a videolaryngoscope. She was placed on an Oxford Head Elevating Laryngoscopy Pillow (HELP) pillow, given antacid prophylaxis, and underwent a rapid-sequence induction with preoxygenation and cricoid pressure. On induction of anesthesia, IV propofol 3 mg/kg and rocuronium 1.2 mg/kg were administered. After a Cormack-Lehane grade 1 intubation, anesthesia was maintained with 50% nitrous oxide in oxygen and sevoflurane.
Key Points
This high-risk patient with morbid obesity class 3 experienced inadequate pain relief in labor and subsequently required emergency cesarean delivery.
Epidural top-up failed to establish adequate anesthesia for surgery, requiring conversation to general anesthesia.
Discussion
In recent years, the prevalence of obesity among women in the United Kingdom has increased substantially, with approximately 40 percent being overweight and 25 percent obese in 2010.1 In women of childbearing age, the excess body weight is of concern because obese parturients experience an increased incidence of complications compared with normal-weight mothers. In addition to the maternal risks associated with excess body weight, fetal morbidity and mortality are also increased compared with pregnancies of normal-weight mothers. Furthermore, the increased use of maternity services associated with obesity in pregnancy adds significantly to healthcare costs compared with normal-weight mothers. With an ever-increasing number of obese parturients, the labor ward anesthesiologist will be required to anticipate and safely assist in the prevention of peripartum complications associated with excess body weight.
Obesity can be quantified by using the body mass index (BMI). The BMI classification is currently the preferred standard by which to stratify maternal body weight (Table 15.1).
Table 15.1 The WHO Classification of Obesity.
| BMI | Risk of comorbidities | |
|---|---|---|
| Underweight | <18.5 | Low |
| Normal | 18.5–24.9 | Average |
| Overweight | 25–29.9 | Increased |
| Mild obesity: class 1 | 30–34.5 | Moderate |
| Moderate obesity: class 2 | 35–9.9 | Severe |
| Morbid obesity: class 3 | >40 | Very severe |
BMI does not consider frame size or the distribution of body fat.
Obese parturients have severely limited physiologic reserve and a higher risk of emergency surgical intervention. Hence the anesthetic risks increase greatly. Obesity and pregnancy each have multisystem effects, many of which are additive (Table 15.2).
| Anatomic changes in pregnancy | Physiologic changes in pregnancy | Physiologic changes in obese parturient | |
|---|---|---|---|
| Airway |
| Mucous membranes in the airway are edematous and prone to bleeding |
|
| Respiratory |
|
| |
| Cardiovascular |
|
| |
| Gastrointestinal |
|
| |
| Metabolic |
|
| |
| Renal |
| ||
| Endocrine |
|
| |
| Hematology |
|
Neuraxial Procedures in Obese Parturients
The anesthetic management of obese parturients should begin in the antenatal clinic, with obese women being offered a consultation with an obstetric anesthesiologist. Many maternity units will refer all pregnant women with a BMI greater than 40 kg/m2 to the anesthetic high-risk clinic for assessment. As obesity in pregnancy becomes more prevalent, some units are raising the threshold for referral and are referring only women with a BMI greater than 50 kg/m2 for assessment. During the consultation, maternal expectations should be explored, and an anesthetic management plan for labor and delivery should be discussed and agreed to. Specific risks associated with obesity in pregnancy should be identified and explained. The anesthesiologist should pay close attention to the possibility of associated cardiopulmonary pathology. Practical issues with difficult venous access, regional anesthesia, and pain relief for labor and operative procedures should be discussed.
Risk factors for fetal macrosomia and shoulder dystocia, which are increased in obese parturients, result in more painful contractions and complicated labors.2 Although there are various modalities of pain relief, analgesia using neuraxial blockade has been shown to be the most effective.3 The anticipated technical difficulties should not preclude the use of epidural analgesia in obese parturients. It has been shown that effective pain relief during labor can improve maternal respiratory function and attenuate sympathetically mediated cardiovascular responses.4, 5 Available evidence shows that the rate of cesarean delivery does not increase with epidural analgesia during labor,3 although obesity increases the need for cesarean delivery. Therefore, electively placing a functional epidural catheter early in labor is advantageous to avoid any time delay because of difficult insertion, should any emergency operative intervention be required. In addition, epidural analgesia can be extended into the postoperative period, where adequate pain relief can optimize care.
Technical problems for neuraxial block include achieving appropriate positioning of the patient, identification of the midline, and a high failure rate for epidural catheter placement (up to 42 percent),6 and multiple attempts at catheter placement are common. The sitting position often allows for easier identification of the midline and should be used routinely in obese parturients.7
Early placement and confirmation of optimal epidural analgesia during early labor are prudent. This allows sufficient time to manage a failed epidural block. Not only is the incidence of failed initial epidural catheter placement high in obese parturients, but the incidence of failed epidural during labor due to migration of the epidural catheter in fatty subcutaneous tissues is also high.8–10 An appropriate length of epidural catheter should be left in the epidural space in anticipation of such migration, and an appropriate fixation device should be used.11
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