BMI is the most common statistical tool used to assess obesity. The weight and height are required for BMI calculations and are typically determined using the weight and height measured in the clinical setting or the self-reported weight and height of individuals. BMI is the weight divided by height (kg/m²). Obesity is defined based on the World Health Organization's international classification of adult BMI; individuals with a BMI ≥ 30 are obese. This classification of BMI is used in individuals of the white, black, and Hispanic races. There is some debate about the World Health Organization classification because the cut-off values underestimate the risk of obesity in Asian and South Asian populations. In Asian and South Asian populations, some investigators insist that the cut-off value of BMI should be 25 or higher [5].

In Korean women, the frequency of obesity above BMI 25 is reported to be 28.1 percent for women aged 19 and older and 30.4 percent for women aged 30 and older [1]. Although lower than the percentage of obese women reported in Western countries, this increase in the number of obese women has been pointed out as a threat to the health of pregnant women and fetuses. The exact figure for the proportion of obese people among pregnant women in Korea is yet to be determined, however, it is estimated to be increasing.

Analgesia for labor is effective and important for a good outcome of the fetus and good satisfaction of the parturient. Neuraxial analgesia is effective and useful for reducing labor pain in parturients. For obese mothers, the epidural analgesic technique is the best and safest way to provide labor analgesia [28]. It is the best way to provide a good pain relief effect during the labor phase, and can be easily converted to surgical anesthetic conditions in the case of cesarean section, if required. Since the incidence of fetal macrosomia is high, epidural analgesia can help in the successful management of shoulder dystocia. Therefore, frequent evaluation for well-functioning epidural catheters is extremely important to verify that the epidural method can be reliably extended to provide appropriate surgical anesthesia, if required. However, the insertion of the epidural catheter in obese parturients is technically more difficult compared to that in non-obese parturients. Anesthesiologists have more difficulties in the identification of the midline in the lumbar spine, detection of epidural space, and placement of epidural catheters in obese parturients. Knee-chest positioning in the lateral decubitus is comparatively more difficult to sustain in the obese parturient than in the non-obese group. Gravity in the lateral decubitus position can also force the panniculus down, which obscures the midline of the lumbar spine. For this reason, the sitting position is preferred to easily locate the midline for epidural catheterization. More objectively, the midline can be identified under ultrasound, and the epidural space can be found using images to measure the depth from the skin to the epidural space. In pregnant women, ultrasound imaging before epidural catheterization can significantly reduce the number of attempts and help identify the correct intervertebral space and epidural depth. However, viewing ultrasound images is more difficult in obese parturients, and the fact that all anesthesiologists are not familiar with using ultrasound is still considered a limitation. The distance from the skin to the epidural space increases in proportion to BMI: 4.4 cm in mothers of normal weight and 7.5 cm in BMI 50 and above [29] (Table 2). Therefore, even in obese parturients, a typical Tuohy needle can be used to identify the epidural space; therefore, it is preferable to use a standard-length epidural Tuohy needle at first, which can be easier for anesthesiologists, but a longer Tuohy needle may be needed in some parturients. The medication and techniques for labor analgesia in obese parturients are not significantly different from those in mothers of normal weight. Patient-controlled epidural analgesia (PCEA) and programmed intermediate epidural boluses are widely used and dilute low concentrations of local anesthetics (< 0.1% bupivacine or equivalent potency of ropivacaine) mixed with opioids (fentanyl or sufentanil) are recommended as medications [30].

Anesthesiologists need thorough preparation, especially in obese parturients, prior to cesarean section. In particular, anesthesiologists should evaluate parturient airways completely prior to general anesthesia. Even if neuraxial anesthesia is performed, a thorough evaluation of the airway is needed because the anesthetic technique can be converted to general anesthesia due to inadequate sensory blockade or prolonged operation time. In obese pregnant women, intubation and manipulation of blade handling can be difficult because of the large breasts, increased anterior-posterior chest diameter, airway swelling, and shortening of the jaw and chest spacing. When laboring mothers present to the operating room for cesarean section, many staff members are required to move the parturient from the ward bed to the operating table. In the presence of a neuraxial blockade, it is difficult to safely bring an obese mother to the operating table. This shift poses a potential risk of injury to both the parturient and the staff supporting this transition. It can be very difficult to properly and safely position obese pregnant women in a surgical bed for a cesarean section, which must be supplied with right wedges for left-uterus displacement. In addition, medical staff must securely fasten the obese parturient to the bed to prevent falls before tilting to the left. However, it is more important to position the left uterus as soon as possible because SHS appears relatively faster and can be more serious than that in normal-weight pregnant women. Pulling the panniculus toward the head of a morbidly obese pregnant woman can cause pressure on the upper abdomen and chest, reducing venous return and cardiac output, resulting in hypotension.

Neuraxial blocks are the ideal anesthetic method and gold standard technique for cesarean section in obese pregnant women. There are three anesthetic techniques: spinal, epidural, and combined spinal-epidural (CSE). Single-shot spinal anesthesia is the most common type of anesthesia used for cesarean sections. The advantage of single-shot spinal anesthesia includes a dense, sufficient block of rapid onset. However, the associated problems include technical difficulties in obese women, potential risk for high spinal blockade, profound dense thoracic motor blockade leading to suppression of cardiorespiratory function, and inability to prolong the duration of anesthesia. Neuraxial anesthesia is very difficult in obese women because of the marked adipose tissue on the spine and the difficulty in palpating the spinous process [31]. A critical step for success in performing neuraxial anesthesia is the identification of the midline. The advantage of a midline approach in spinal or epidural anesthesia is that the success rate is high, and the provider can easily feel the needle tip through engagement in the supraspinous ligament. In cases where the midline approach is not used, a paramedian approach may be used. In a paramedian approach, there are no tactile advantages with respect to the location of the needle tip, as the needle is located in the para-spinous muscle and not the supraspinous ligament. It is widely accepted that local anesthetic requirements for neuraxial anesthesia are lower in pregnant women and in obese women. Obesity increases intra-abdominal pressure and causes compression of the inferior vena cava, which leads to the engorgement of the epidural venous plexus and increases the pressure of the epidural space. This mechanism reduces the cerebrospinal fluid volume in the subarachnoid space. Therefore, some anesthesiologists insist that the dose regimen should be adjusted in obese parturients, with the aim of achieving appropriate surgical anesthesia while minimizing hemodynamic complications. However, many researchers have reported that dose reduction in obese patients may not be recommended [32-34]. They reported that the ED50 of bupivacaine for successful spinal anesthesia in morbidly obese mothers was 9.8 mg, similar to the other reports in the non-obese group [32]. There were no significant differences in the incidence of nausea, vomiting, and phenylephrine dose requirement [32]. However, many anesthesiologists are concerned about high spinal anesthesia in a morbid obesity parturient, and single-shot spinal anesthesia with a pencil point needle may be technically difficult. Therefore, a CSE anesthetic technique is recommended as an attractive alternative method. Placing an epidural Tuohy needle may be easier than a spinal needle insertion and can be used as a guide for the spinal needle as a needle through the needle CSE method. In an obese parturient, the operation time can be longer than expected, and therefore, the CSE technique provides the advantage of rapid onset and intense block for prolonged operation with postoperative pain control. In addition, a lower dose of intrathecal bupivacaine can be administered, and the level of block can be adjusted with an epidural catheter to achieve adequate surgical anesthesia. In parturients with severe cardiovascular disease, a lower dose of intrathecal bupivacaine and slowly titrated local anesthetics lead to minimal hemodynamic changes, and therefore, a sudden onset of hypotension may be prevented effectively. CSE has a beneficial effect on obese parturients with cardiovascular diseases.

In Korea, approximately 28.8% of cesarean sections have been performed under general anesthesia over the past five years [35], but the rate of general anesthesia limited to the obese parturient group has not yet been reported. The rate of general anesthesia in Korea is significantly higher than that in Western countries [36]. Considering that the fatal complication rate is high under general anesthesia, if possible, it would be desirable to replace general anesthesia with regional anesthesia. Owing to the anatomic and physiologic changes in obese mothers, difficult intubation and urgent desaturation can occur in such patients. Therefore, proficient assistance may be needed to maintain airways. The jaw-thrust maneuver can also require the use of both hands of the anesthesiologists, and therefore, other staff may be needed for positive pressure ventilation and downward pressing on the cricoid cartilage. Various equipment (such as laryngoscope with short blades, supraglottic airway devices, video laryngoscope, fiberoptic intubation devices, Bullard laryngoscope, or cricothyrotomy devices) should be prepared for difficult intubation situations. If intubation fails, the intubation failure algorithm must be started, and help must be requested immediately [37]. If intubation is expected to be difficult, rapid sequence induction is recommended, and during apnea, pregnant women fall into hypoxia faster, with obese mothers reaching hypoxia even faster; therefore, sufficient preoxygenation should be performed before initiating general anesthesia. Proper parturient positioning for the best laryngoscopic view can assist in securing a difficult airway. The ramped position improves the laryngoscopic view compared to the traditional sniffing position and can be accomplished by elevating the head of an obese parturient above the shoulders by modifying the operating table or by applying blankets under the upper body [38,39] (Fig. 1). As soon as the parturient is transferred to the operating table, the facial mask is firmly fixed to the face, and oxygen administration begins subsequently. Preoxygenation is an essential process for delaying the desaturation of obese mothers and providing sufficient oxygen. The dosage of induction anesthetics in obese women should be calculated based on the ideal body weight rather than the actual weight [40]. Succinylcholine and rocuronium are widely used as neuromuscular blockers for rapid tracheal intubation during general anesthesia. One study attempted to determine the appropriate dose of succinylcholine for the ideal intubating condition in the non-pregnant morbidly obese group, concluding that 1.0 mg/kg based on the total body weight provides both complete paralysis and satisfactory intubating conditions [41]. Alternatively, rocuronium may be administered to provide an adequate laryngoscopic condition at a dose of 1-1.2 mg/kg based on ideal body weight [42]. Sugammadex can be administered to reverse the neuromuscular blocking induced by rocuronium or vecuronium in a short time [43]. In the supine position under general anesthesia, early closure of small airways due to decreased functional residual capacity, administration of volatile anesthetics, neuromuscular blockers, and cephalad retraction of the panniculus may lead to pulmonary hypoxemia. Many interventions (high tidal volumes, high inspired oxygen, and the use of positive end-expiratory pressure) have been used to maintain appropriate arterial oxygenation. Tracheal extubation should only be attempted in fully awake parturients with appropriate reversal of neuromuscular blockers, as failed extubation may occur easily in obese parturients [44]. A 30° head-up tilting is an excellent position for tracheal extubation in obese patients compared to a simple supine position [45].

The risk of postoperative complications (hypoxemia, pulmonary atelectasis, deep vein thrombosis, pulmonary edema, postpartum cardiomyopathy, and wound complications) is very high in the obese parturient group [46]. Moreover, a BMI-dependent decrease in respiratory function may occur even after regional anesthesia [47]. Postoperative pulmonary events may lead to severe complications. Therefore, postoperative early ambulation has also been reported to improve respiratory function during the postoperative period [47]. In morbidly obese parturients, postpartum complications occur after cesarean section and do not occur after vaginal delivery [44]. Postoperative pain should be properly controlled and reduced to facilitate postoperative mobilization and lung care because postoperative pulmonary complications are very important determinants of prognosis. PCEA with dilute local anesthetics mixed with opioids may improve the quality of postoperative pain relief. The risk factor of thrombosis is associated with pregnancy, cesarean section, and obesity, and postoperative pulmonary thromboembolism remains a major cause of maternal mortality. Both pharmacological and mechanical interventions can be used for prophylaxis; therefore, perioperative use of an adequate anticoagulant and intermittent pneumatic compression are recommended [48]. In obese parturients, postoperative wound complications occur more frequently than in the non-obese group, which often leads to prolonged recovery and long hospitalization, and the midline vertical abdominal incision is associated with a higher incidence of wound complications than a Pfannenstiel incision [49]. Morbidly obese parturients may be hospitalized for significantly longer duration because of the increased incidence of postoperative complications and antepartum medical disease. The length of hospital stay and costs in morbidly obese parturients have been shown to increase after both vaginal delivery and cesarean operations [50].