Obesity increases the demands on the cardiopulmonary system. The effects of obesity and pregnancy on the respiratory and cardiovascular systems are summarized in Table 48.1 and Table 48.2 . As energy expenditure increases in proportion to the increase in body mass, oxygen consumption and carbon dioxide (CO ₂ ) production also increase in proportion to the increase in work performed. Minute ventilation is increased owing to the elevated respiratory demand, except in the 5% to 10% of obese patients with Pickwickian syndrome , who display a reduced sensitivity to CO ₂ . Obesity affects the body’s ability to meet these demands by changing pulmonary mechanics, altering lung volumes, and impairing oxygen consumption.

Obesity increases the weight of the chest wall; thus, greater energy expenditure is required during ventilation to move this mass. Morbidly obese patients expend a disproportionately high percentage of total oxygen consumption on respiratory work compared with lean controls, even during quiet breathing. The weight gain during pregnancy further increases the work of breathing. In obese individuals, frequent shallow respirations may represent a more efficient breathing pattern than large tidal volumes. This pattern of frequent shallow respirations contrasts with the increased tidal volumes that typically accompany pregnancy.

Greater abdominal weight restricts diaphragm movement, especially in the supine or Trendelenburg positions, requiring smaller tidal volumes. Functional residual capacity (FRC) decreases at the expense of expiratory reserve volume and may be less than closing capacity. Both chest wall and lung compliance decrease, but airway resistance increases as a result of reduction in lung volumes.

Pulmonary diffusion typically remains normal in most women with morbid obesity. Decreased chest wall compliance and greater abdominal weight promote airway closure in the dependent portions of the lung. Ventilation preferentially occurs in the more compliant, nondependent portions of the lung. In contrast, pulmonary blood flow preferentially occurs in the dependent portions of the lungs, resulting in ventilation-perfusion mismatch and hypoxemia. Consistent with the positional deterioration of lung volumes, oxygenation worsens in obese individuals in the supine and Trendelenburg positions.

Blood volume and cardiac output are increased, the latter from increases in both stroke volume and heart rate. Both preload and left ventricular afterload are increased. These changes can result in both eccentric and concentric left ventricular hypertrophy. Among morbidly obese pregnant women, left atrial size, left ventricular thickness, interventricular septal thickness, and left ventricular mass are increased compared with nonobese pregnant women. The increase in heart rate limits the time for diastolic filling; thus, diastolic relaxation is impaired. Pulmonary blood volume increases in proportion to increases in cardiac output and total blood volume. Pulmonary hypertension can occur in up to 5% of obese, otherwise healthy, individuals. Aortocaval compression in the supine position may be greater in obese parturients, particularly those with a large fat panniculus.

The risks of chronic hypertension , gestational hypertension , and preeclampsia are also increased in women with obesity. It is estimated that the risk of preeclampsia doubles for every 5 to 7 kg/m ² increase in BMI, and is three to four times higher in those with class II or III obesity, compared with those with class I obesity.

It is unclear whether obesity in pregnancy is associated with an increase in gastric volume and a decrease in gastric pH. Roberts and Shirley reported that gastric volumes aspirated from obese laboring women undergoing cesarean delivery were significantly higher than those obtained from lean controls. Studies in the general surgical population, however, reported conflicting results; some confirmed these findings and others reported no difference in gastric volume and pH in obese patients compared with lean patients.

Similarly, data for gastric emptying in the obese population are conflicting; studies have reported delayed, unchanged, or more rapid rates of gastric emptying in obese subjects compared with lean subjects. In nonobstetric obese patients, Maltby et al. reported that drinking 300 mL of clear fluid 2 hours before surgery had no effect on gastric fluid volume and pH compared with fasting after midnight. Similarly, Wong et al. found that gastric emptying in obese, nonlaboring term pregnant volunteers was not delayed after ingestion of 300 mL compared with 50 mL of water; gastric volume returned to baseline 60 minutes after ingestion. A study using ultrasonography to assess the gastric antrum in women undergoing elective cesarean delivery reported a positive correlation between the antral cross-sectional area and BMI, and a higher gastric volume in obese parturients with BMI ≥ 30 kg/m ² compared with those with lower BMI.

Both gastroesophageal reflux and hiatal hernia are more common in obese than in nonobese patients. Obesity is also associated with a higher risk for difficult airway management, which is a known risk factor for pulmonary aspiration. Therefore, morbidly obese patients are likely at increased risk for pulmonary aspiration of gastric contents.

Obesity is associated with an increased risk for thromboembolic complications. Venous thromboembolism is a leading cause of direct maternal mortality. In the United Kingdom, 72% of women who died from thromboembolic complications in 2017 to 2019 were overweight or obese.

Obesity is associated with changes in coagulation, venous stasis, and endothelial injury that contribute to the pathogenesis of venous thromboembolism. For instance, adipose tissue secretes the following: (1) adipokines such as plasminogen activator inhibitor-1, which results in impaired fibrinolysis; (2) leptin, which promotes platelet aggregation; and (3) interleukin-6, which stimulates the liver to produce coagulation factors. C-reactive protein levels are also elevated in obese women, leading to platelet activation. Venous stasis is worsened in obese women by increased intraabdominal pressure, which leads to increased iliofemoral venous pressure. Obesity was shown to be associated with endothelial dysfunction in the nonpregnant population. Therefore, all risk factors that contribute to the pathogenesis of thromboembolic complications are likely to be exacerbated by obesity. The risk is further increased by reduced mobility, comorbidities such as preeclampsia, and an increased frequency of operative delivery.

Gestational and nongestational diabetes mellitus occur more frequently in obese patients. The pathologic process is attributed to the following: (1) peripheral insulin resistance as a result of augmentation of free fatty acids by visceral obesity, (2) increased proinflammatory cytokine levels, (3) relative gonadotropin resistance, and (4) low sex hormone–binding globulin concentration, which leads to hyperandrogenism and decreased insulin sensitivity. The concentration of adiponectin, an adipokine with insulin-sensitizing properties, is also decreased in obesity, which leads to decreased insulin sensitivity.

Obesity is a significant risk factor for obstructive sleep apnea (OSA) , which is characterized by repeated episodes of complete or partial upper airway collapse that lead to hypoxemia and hypercarbia. Repeated periods of hypoxemia and reoxygenation lead to endocrine and metabolic disturbances, which result in increased risks for hypertension, myocardial infarction, stroke, diabetes, and metabolic syndrome. It is estimated that 15% to 20% of obese pregnant women have OSA. The prevalence and severity of OSA are higher among gravidas with chronic hypertension compared with BMI- and gestational age-matched normotensive pregnant women.

The changes of pregnancy may both worsen and protect against OSA. For example, weight gain and estrogen-induced hyperemia and edema of nasal mucosa might promote OSA, whereas sleeping in the lateral position, reduced rapid eye movement sleep, and the progesterone-induced increase in minute ventilation might protect against it.

OSA may adversely affect maternal and neonatal outcomes. A large in patient database study showed that pregnant women with OSA are at increased risk for preeclampsia , eclampsia , cardiomyopathy , and pulmonary embolism , and are five times more likely to die in the hospital during a pregnancy or delivery admission than women without OSA. These differences were unchanged after controlling for obesity, but the associations with preeclampsia and severe cardiovascular complications were stronger in obese women. Using nationwide data, Frappaolo et al. investigated outcomes associated with OSA in a sample of 76,753,013 delivery hospitalizations from 2000 to 2019. After adjusting for obesity and other clinical, demographic, and hospital characteristics, OSA was associated with increased odds for mechanical ventilation or tracheostomy , acute respiratory distress syndrome, hypertensive disorders of pregnancy, stillbirth, pulmonary edema/heart failure, peripartum hysterectomy, and preterm birth .

Obesity is associated with an increased risk for a number of disease states compared with lean controls, as shown in Table 48.3 . These comorbidities complicate the care of obese parturients.

Obesity results in greater use of healthcare resources. Chu et al. reported that obese pregnant women receive significantly more prenatal tests, ultrasonographic examinations, medications, and prenatal visits with a physician, and they are at greater risk for having a high-risk pregnancy, cesarean delivery, and prolonged hospitalization compared with pregnant women of normal weight.

Obesity is associated with an increased incidence of maternal, fetal, and neonatal complications. These include a higher risk for spontaneous abortion (miscarriage), thromboembolic complications, gestational diabetes mellitus, hypertensive disorders of pregnancy, dysfunctional labor, shoulder dystocia, operative vaginal delivery, cesarean delivery, postpartum hemorrhage (PPH), wound infection, fetal macrosomia, fetal congenital anomalies, stillbirth, and neonatal death ( Table 48.4 ).

Most importantly, obesity increases the risk for death during pregnancy . In a French population–based case-control study that included 364 maternal deaths from the 2007 to 2012 French National Confidential Inquiry into Maternal Deaths (ENCMM, Enquête Confidentielle sur les Morts Maternelles), the adjusted odds ratio (OR) of death was 1.65 (95% confidence interval [CI], 1.24 to 2.19) in overweight women, 2.22 (95% CI, 1.55 to 3.19) in women with class I obesity, and 3.40 (95% CI, 2.17 to 5.33) in women with class II to III obesity, compared with women with normal BMI. The report of the Confidential Enquiries into Maternal Deaths in the United Kingdom (MBRRACE-UK Saving Lives, Improving Mothers’ Care) for 2018 to 2020 showed that 51% of women who died were overweight or obese, a trend that has been consistent for the last several reports. The increased risk for death associated with obesity has been attributed to the associated comorbidities such as hypertensive disorders of pregnancy. The impact of obesity on maternal mortality is particularly evident in women who die of thromboembolism or cardiac disease.

Obesity has also been identified as a risk factor for anesthesia-related complications and anesthesia-related maternal mortality. A study of all maternal cardiac arrests in the United Kingdom over a 2-year period found that 24% of cases were solely as a consequence of anesthesia, three-fourths of whom were obese. In the United States, Mhyre et al. reported that six of eight pregnant women who died of anesthesia-related deaths in Michigan between 1985 and 2003 were obese. Because of the increased risk for complications, guidelines published both in the United Kingdom and by the American College of Obstetricians and Gynecologists (ACOG) recommend a multidisciplinary approach to the care and treatment of obese pregnant women, including referral consultation with an anesthesia provider. The ACOG recommends anesthetic consultation before labor or in early labor in women with obesity to allow for adequate time to plan for care. In the United Kingdom, the recommendation is to refer pregnant women with a booking BMI ≥ 40 kg/m ² for antenatal anesthetic assessment and to involve a senior anesthesiologist in the care of those patients intrapartum.

The progress of labor appears to be affected by obesity. A large multicenter study involving 118,978 patients whose labor management reflected current practice in the United States found that labor progressed more slowly with increasing BMI for both nulliparous and parous women. The median time to progress from 4 to 10 cm cervical dilation was greater in morbidly obese women compared with lean women for both nulliparous women (7.7 versus 5.4 hours, respectively) and parous women (5.4 versus 4.6 hours, respectively). These findings were independent of gestational age and induction of labor. Entry into the active phase of labor was also delayed in parous women as a function of BMI. Possible explanations include increased fetal size, higher labor induction rates, and/or decreased responsiveness to oxytocin.

Poor uterine contractility has also been demonstrated in obese parturients. Myometrium obtained from obese women at cesarean delivery contracted with less force and frequency and had less calcium flux compared with myometrium from normal-weight women. This observation may be attributable to the inhibitory effect of cholesterol and/or adipokines (e.g., leptin, ghrelin, apelin), which inhibit human uterine contractility in vitro . Inadequate myometrial contractility has also been implicated in a higher rate of uterine atony and PPH, after both vaginal and operative deliveries, in obese women. However, the literature has been mixed with regard to the effect of BMI on the risk of PPH. In a large retrospective study of 30,298 pregnancies over an 8-year period, the risk for PPH was significantly higher with increasing BMI (OR, 2.7; 95% CI, 2.2 to 3.4 for obesity class III versus nonobesity). Similarly, in a large cohort study involving 1,114,071 women from Sweden over a 12-year period, the risk of atonic PPH was 14% higher in women with obesity class I, 47% higher in those with obesity class II, and 114% higher in those with obesity class III, compared with normal-weight women, irrespective of the mode of delivery. Conversely, a retrospective cohort study of 2,176,673 women in California reported only a modest increase in the risk of hemorrhage or atonic hemorrhage after vaginal delivery among overweight and obese women. After cesarean delivery, however, women in any obesity class had up to 14% decreased odds of severe hemorrhage. Furthermore, a metaanalysis found no association between obesity and the risk of atonic PPH. However, an increased dose requirement for oxytocin to achieve adequate uterine tone during scheduled cesarean delivery was reported among obese patients.

Obesity is also associated with a higher risk for failed medical induction of labor . In a secondary analysis of data from a large labor induction trial involving 1273 patients, the duration of labor, oxytocin requirement, and cesarean delivery rate were significantly higher in women with a greater BMI. In a large series from Sweden involving 233,887 deliveries, Cedergren found a fourfold increase in the risk for cesarean delivery in parturients with a BMI > 40 kg/m ² compared with parturients of normal weight, primarily because of failed or obstructed labor. Operative vaginal delivery, with its associated maternal and fetal morbidity, is also more likely in the obese parturient.

Risk for fetal macrosomia is higher with obesity, which increases the risk for shoulder dystocia and its associated birth trauma, and predisposes to perineal lacerations, newborn infant injury, and PPH. One study examining maternal anthropometric parameters associated with shoulder dystocia reported a 2.7-fold increase in the risk for shoulder dystocia in obese compared with lean parturients, even after adjustment for potential confounders such as macrosomia and diabetes.

Higher BMI, increased prepregnancy weight, and excessive maternal weight gain increase the risk for both elective and emergency cesarean delivery. This risk is further increased by obesity-related pregnancy complications such as macrosomia, fetal growth restriction, diabetes mellitus, and hypertensive disorders of pregnancy . In a metaanalysis of 33 trials, the unadjusted ORs of cesarean delivery were 1.46 (95% CI, 1.34 to 1.60), 2.05 (1.86 to 2.27), and 2.89 (2.28 to 3.79) among overweight, obese, and morbidly obese women, respectively, compared with normal-weight pregnant women.

Many of the options for labor analgesia have limitations in the obese parturient. For example, obese parturients with OSA may be more susceptible to the respiratory depressant effect of systemic opioids , leading to episodes of apnea and oxyhemoglobin desaturation. Pudendal nerve block may be technically difficult in obese patients. Inhalation analgesia is useful in some patients; however, nitrous oxide has limited effectiveness and is not available in many birthing rooms. Further, inhalation analgesia may lead to a reduced level of consciousness, which can be dangerous in an obese woman with a difficult airway.

Neuraxial analgesia is the best option for pain relief in the obese parturient. Given the greater risks for fetal macrosomia and shoulder dystocia in obese patients, adequate analgesia is often needed to facilitate an atraumatic vaginal delivery. The use of epidural analgesia during labor allows the anesthesia provider to extend epidural analgesia to surgical anesthesia for cesarean delivery and thus avoid the need for general anesthesia with its associated risks. Given the increased likelihood for cesarean delivery and the greater risk for general anesthesia in the obese parturient, the early administration of neuraxial labor analgesia is recommended in the obese parturient.

When performing neuraxial anesthesia in the obese parturient, technical difficulties may include (1) inability to palpate the spinous processes or identify the midline ; (2) greater depth of the epidural space, which may exaggerate minor needle directional errors and increase the likelihood of identifying a lateral portion of the epidural space ; and (3) the presence of fat pockets as well as hormonal softening of the ligaments, which may result in a false loss of resistance and/or higher risk for unintentional dural puncture. In most obese parturients, however, the epidural space can be identified with a standard-length epidural needle. Therefore, it seems prudent to use a standard-length needle first, which allows the provider better control, before considering switching to a longer needle.

Observing the prominence of the seventh cervical vertebra and the gluteal cleft can facilitate identification of the midline. Asking the parturient about the perceived location of the needle during block placement (relative to the midline) can also facilitate identification of the midline. Marroquin et al. reported that 77% of morbidly obese parturients who were questioned about the position of the needle during a difficult labor epidural needle placement provided useful feedback to the anesthesia provider. More objectively, ultrasonographic guidance can be used to identify the midline, image the epidural space, and measure the distance from the skin to the epidural space (see Chapter 12 ). Sahin et al. reported that fewer attempts were needed to establish spinal anesthesia in obese parturients undergoing cesarean delivery when preprocedure ultrasonography was performed. Ultrasound image quality, which is often compromised by excessive lumbar adiposity in obese patients, may be improved with the paramedian sagittal oblique plane compared with the transverse plane. Balki et al. found a strong correlation between the skin-to-epidural space distance measured by ultrasonography and that measured by the epidural needle in obese parturients. However, soft tissue compression with the ultrasound probe resulted in underestimation of the depth of the epidural space in obese women.

Placing the patient in the sitting position facilitates identification of the midline and is preferred by many anesthesia providers when performing neuraxial anesthesia in obese parturients. In the lateral position, gravity may cause lateral adipose tissue to sag downward and obscure the midline. Further, the distance from the skin to the epidural space is minimized when the patient is in the sitting-flexed position.

Care is needed to avoid dislodgement of the epidural catheter after insertion. Movement of the epidural catheter relative to the skin is most striking in obese patients. Hamilton et al. demonstrated that patient movement from the sitting-flexed to the lateral decubitus position caused redistribution of the soft tissue of the back. The distance from the skin to the epidural space increases, and an unsecured catheter will appear to be drawn inward by as much as 1.0 to 2.5 cm. An epidural catheter secured with tape to the back of a patient in the sitting flexed position can be unintentionally dislodged from the epidural space when the patient moves from the sitting to the lateral decubitus position. Therefore, these investigators recommended that patients be positioned in the lateral position before the epidural catheter is secured to the skin. Alternatively, when placing the block in the sitting-flexed position, the patient should be asked to sit upright before taping the catheter to the skin.

Many authors have documented technical difficulties with neuraxial techniques in obese parturients. Several studies have reported the need for more attempts to identify the epidural space and a higher failure rate of epidural catheters in obese compared with nonobese patients. A metaanalysis reported greater likelihoods of epidural failure (OR, 1.82; 95% CI, 1.23 to 2.68) and need for multiple attempts (OR, 2.21 [95% CI, 1.39 to 3.52]) in obese compared with nonobese pregnant patients. Although some investigators have reported a higher incidence of unintentional dural puncture in morbidly obese parturients than in lean parturients, others have not confirmed this finding.

It is not clear if epidural local anesthetic dose requirements are altered in morbidly obese parturients. Hodgkinson and Husain administered 20 mL of epidural bupivacaine 0.75% in the L3 to L4 interspace to women undergoing elective or emergency cesarean delivery. The patients remained supine for 40 minutes after drug injection. Twenty-seven percent of patients with BMI < 28 kg/m ² or weight < 73 kg needed supplementation of the block at 30 minutes, whereas none of the patients with BMI > 28 kg/m ² or weight > 73 kg required additional local anesthetic to achieve surgical anesthesia. The cephalad extent of block was associated with patient BMI and weight but not with height. Similarly, using an up-down sequential allocation study design to estimate the ED ₅₀ (median effective dose) of epidural bupivacaine (administered in a volume of 20 mL), Panni and Columb found that obese women required significantly less epidural bupivacaine for initiation of labor analgesia than lean parturients. In contrast, Milligan et al. observed that neither patient position nor obesity affected the extent of sensory blockade when 12 mL of bupivacaine 0.25% was administered for epidural labor analgesia. Duggan et al. found that obesity had only a weak effect in enhancing the spread of epidural local anesthetics; this effect was only observed with the largest volume and concentration used in the study (15 mL of bupivacaine 0.75%), but not with a lower volume (10 mL) and concentration (0.5%) of bupivacaine.

The goals of epidural labor analgesia should be the provision of excellent pain relief with minimal motor block (see Chapter 24 ). Epidural administration of a dilute solution of local anesthetic with a lipophilic opioid provides analgesia for labor while minimizing adverse effects such as hypotension and motor block. The neuraxial blockade provided to obese parturients in labor should be bilateral and provide excellent analgesia. Otherwise, the epidural catheter should be removed and replaced because an inadequate block with a frequent need for top-up doses may lead to failure should extending the block for cesarean delivery be required. Regular evaluation of the parturient’s neuraxial block is therefore essential to allow for early replacement of an inadequate catheter.

The combined spinal-epidural (CSE) technique provides a rapid onset of pain relief. In the past, some providers were concerned that an epidural catheter sited as part of a CSE technique remains untested until the spinal block has regressed. Thus, recognition of a malpositioned catheter might be delayed and result in failed epidural anesthesia should the need for emergency cesarean delivery arise. Several studies have refuted these concerns and reported a higher success rate for epidural catheters sited using a CSE technique compared with those sited using a standard epidural technique. Presumably, the higher success rate can be attributed to observing backflow of cerebrospinal fluid (CSF) through the spinal needle, thus indirectly confirming correct epidural needle position. Further, Booth et al. found that catheter failure was more often recognized within the first 30 minutes of placement in catheters sited as part of a CSE technique compared with those sited with an epidural technique.

The dural puncture epidural (DPE) technique is a modification of the CSE technique in which a spinal needle is used to puncture the dura, but no intrathecal drug is injected (see Chapter 12 ). Some investigators have noted that the DPE technique provides improved quality of analgesia compared with the standard epidural technique, and fewer adverse effects compared with the CSE technique. DPE analgesia may be a useful technique to consider in obese parturients with anticipated difficulty in identifying the epidural space. The backflow of CSF through the spinal needle confirms midline placement and that the tip of the epidural needle is located in the posterior epidural space, decreasing the risk for block failure. Furthermore, the translocation of local anesthetics administered epidurally through the dural puncture may enhance the quality and symmetry of the block. However, these potential advantages were not confirmed in a prospective study that compared the quality of labor analgesia between the DPE and standard epidural techniques in obese women with BMI ≥ 35 kg/m ² . The primary outcome of the quality of labor analgesia was a composite of five components: (1) asymmetrical block, (2) epidural top-ups, (3) catheter adjustment, (4) catheter replacement, and (5) failed conversion to epidural anesthesia, requiring general anesthesia or replacement neuraxial anesthesia for cesarean delivery. The study found no differences between the groups in the composite primary outcome or any of its individual components. It is important to note that the blocks were placed by experienced providers in this study. Conversely, a retrospective study reported that epidural catheter failure in parturients with superobesity (BMI ≥ 50 kg/m ² ) was higher with the standard epidural technique (18/63, 29%) compared with a group that included catheters placed with a CSE or DPE technique (14/153, 9%). Most blocks in this study were performed by residents in training, and catheter migration accounted for 29% of failures. The benefits of those techniques involving dural puncture in this patient population might therefore be more evident in the hands of inexperienced providers.

In cases of unintentional dural puncture, continuous spinal analgesia can be used to provide labor analgesia. In addition to providing reliable labor analgesia, continuous spinal analgesia may be converted to spinal anesthesia for emergency cesarean delivery. It is crucial, however, that the catheter be clearly labeled, and all personnel are made aware of its intrathecal location. Unintentional administration of an epidural dose of local anesthetic through the spinal catheter markedly increases the risk for high spinal block and subsequent respiratory arrest.

Some have suggested that the risk for post–dural puncture headache (PDPH) may be lower in the obese parturient, perhaps secondary to reduced CSF leak through the dural puncture site caused by the higher intraabdominal pressure that results from a large abdominal panniculus. However, data are conflicting. In a retrospective study of 516 women with unintentional dural puncture with a 17-gauge Tuohy needle, Peralta et al. reported a significantly lower incidence of PDPH in women with BMI ≥ 31.5 kg/m ² compared with those with BMI < 31.5 kg/m (39% versus 56%, respectively), even after controlling for pushing during the second stage of labor. Conversely, two other retrospective studies found no difference in the risk for PDPH between obese and nonobese parturients. A third study found no reduction in the risk for PDPH in obese parturients compared with lean parturients, except in those with a BMI ≥ 50 kg/m ² where the risk of PDPH was 46% compared with 72% in those with BMI < 30 kg/m ² . So, while the evidence is conflicting on whether the risk of PDPH is reduced in obese compared with nonobese patients, the risk is still at least 40% following dural puncture with a Tuohy needle.

A thorough preanesthetic evaluation is critical to the safe care of the obese parturient undergoing cesarean delivery. Of particular importance is a thorough airway assessment. Large breasts, the greater anteroposterior diameter of the chest, airway edema, and reduced chin-to-chest distance increase the likelihood of difficult laryngoscopy and failed tracheal intubation in obstetric patients. Obesity exaggerates many of the anatomic changes of pregnancy. Increased fat in the neck and shoulders increases the difficulty of positioning the patient for laryngoscopy and tracheal intubation. Excess fat deposition may also cause distorted anatomy, such as an enlarged tongue and redundant pharyngeal and palatal soft tissue. Further, the fat pads on the back of the shoulders often restrict the range of motion of the neck, exacerbating the difficulty of mask ventilation, laryngoscopy, and tracheal intubation.

All morbidly obese parturients undergoing cesarean delivery should be placed in a ramped position with left uterine displacement, regardless of the planned anesthetic technique. This position was shown to improve laryngoscopic view compared with the traditional sniffing position in morbidly obese patients undergoing elective bariatric surgery. Folded blankets, a positioning pillow, or a padded ramp designed for this purpose are placed under the chest and head to achieve horizontal alignment between the external auditory meatus and the sternal notch ( Fig. 48.1 ). This position aligns the oral, pharyngeal, and tracheal axes to facilitate tracheal intubation and has been shown to improve hemodynamic and respiratory parameters during laparoscopic gastric bypass surgery. Modern surgical tables can also be flexed at a number of angles and this feature can be used to optimize the patient position for laryngoscopy and tracheal intubation.

Positioning the obese patient to facilitate intubation of the trachea. (A) Patient in the supine position using standard head support. Note that the dashed line (compare with B ) is not parallel to the floor. (B) Elevating the patient’s head with neck and shoulder supports so that an imaginary line drawn through the external auditory meatus and the sternal notch (upper dashed line) is parallel to the floor may facilitate tracheal intubation. (C) Similar positioning achieved by repositioning the operating table. Note the similarity of the upper and lower dashed lines with use of the second and third positioning techniques.

It may be difficult to position the obese patient appropriately and safely. The protuberant abdomen may shift markedly with left uterine displacement. The patient must be secured to the operating table before the table is tilted leftward; however, it is important to initiate left uterine displacement as soon as possible.

The anesthesia provider should confirm that the patient’s weight does not exceed the weight limits of the operating table, consider the use of lateral table extenders, and use appropriate pads to ensure that the shoulders and arms are positioned in a horizontal plane. Correct arm position will maximize patient comfort, improve stability, and avoid neurologic injury to the upper extremity.

The anesthesia care team may be asked to participate in cephalad retraction of the large panniculus by tethering retractors to an object such as the ether screen or the head of the table. Both the obstetric and the anesthesia providers must remain cognizant of the risks for hypotension, difficulty with ventilation, and fetal compromise during cephalad retraction of the panniculus in morbidly obese patients. Hodgkinson and Husain reported an intraoperative fetal death in a morbidly obese patient who had received epidural anesthesia for cesarean delivery. The death was attributed to prolonged hypotension associated with cephalad retraction of a large panniculus. A vertical and cephalad suspension of the panniculus has been suggested to avoid maternal hypotension and hypoxemia. Commercially available retraction devices can also be used to retract the panniculus, but there are no data to indicate whether these devices are associated with reduced risk for hypotension or ventilation compromise compared with cephalad retraction.

Pharmacologic aspiration prophylaxis is crucial in this patient population. Oral administration of 30 mL of a 0.3 M solution of sodium citrate effectively increases gastric pH within 5 minutes. The anesthesia provider must be aware that the patient remains at risk for aspiration at the end of surgery; the efficacy of sodium citrate wanes 45 to 60 minutes after administration. Administration of a histamine-2 (H ₂ )-receptor antagonist and metoclopramide provide additional protection (see Chapter 28 ).

General Anesthesia

Difficult mask ventilation and tracheal intubation are associated with more rapid oxyhemoglobin desaturation during apnea in obese patients than in lean individuals. The association between obesity and a short neck can make tracheal intubation difficult in this population. In a series of patients who received general anesthesia for cesarean delivery, the incidence of difficult tracheal intubation was 33% among women who weighed more than 300 lb (136.4 kg). This study was performed at a time when videolaryngoscopes were not available in routine practice. Quinn et al. conducted a 2-year survey of failed tracheal intubation in obstetric patients in the United Kingdom and reported that BMI was an independent predictor of failed intubation; the odds increased by 7% for each 1-kg/m ² increase in BMI. Reale et al. used data from the Multicenter Perioperative Outcomes Group from 2004 to 2019 and reported that BMI ≥ 40 kg/m ² was associated with an increased risk of difficult intubation compared with BMI < 25 kg/m ² (OR, 2.02; 95% CI, 1.12 to 3.64), with an estimated incidence of 1 in 28.

Airway management

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