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 Table of Contents  
Year : 2015  |  Volume : 28  |  Issue : 2  |  Page : 308-314

Challenge of morbid obesity in obstetric anesthesia

Department of Anesthesiology and Intensive Care, Faculty of Medicine, Menoufiya University, Menoufiya, Egypt

Date of Submission07-Jul-2014
Date of Acceptance21-Sep-2014
Date of Web Publication31-Aug-2015

Correspondence Address:
Noha Abd Allah Afify
Department of Anesthesiology and Intensive Care, Faculty of Medicine, Menoufiya University, Menoufiya 32713
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1110-2098.163874

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To discuss the pathophysiology of morbid obesity in pregnant ladies and the anesthetic management of morbidly obese parturients.
The association between obesity and pregnancy can result in further limitation of parturient physiological reserve. Indeed, maternal obesity is associated with an increased risk of delivery and postpartum complications.
Complete understanding of the physiology, pathophysiology, comorbidies and their implications for anesthesia and analgesia in morbidly obese parturients should lead to improvement of safety and anesthetic care.
2- Reviews and Meta-Analyses.

To determine the anesthetic and obstetric complications in morbidly obese parturient that had caesarean delivery.
Data analysis
was preformed through a search on the pub med, Google and ovid medline data base.
Recent Findings
early epidural analgesia during labor is valuable and that regional anesthesia is usually preferable, but a number of challenges arise.
Morbidly obese women experienced increased complications during pregnancy and childbirth. Due to the high rate of caesarean sections and the potential difficulties of emergency anesthesia among these women, epidural anesthesia during labor should be planned and administered as often as possible.

Keywords: complications, management, obesity, pregnancy

How to cite this article:
Eskandr AM, Mostafa AM, Metwally AA, Afify NA. Challenge of morbid obesity in obstetric anesthesia. Menoufia Med J 2015;28:308-14

How to cite this URL:
Eskandr AM, Mostafa AM, Metwally AA, Afify NA. Challenge of morbid obesity in obstetric anesthesia. Menoufia Med J [serial online] 2015 [cited 2021 Mar 8];28:308-14. Available from: http://www.mmj.eg.net/text.asp?2015/28/2/308/163874

  Introduction Top

Obesity rates are steadily increasing among women of reproductive age, making it a common condition during pregnancy. Anesthesiologists are thus increasingly being asked to care for morbidly obese parturients. The association between obesity and pregnancy can result in further limitation of parturient physiological reserve. Indeed, maternal obesity is associated with an increased risk of delivery and postpartum complications and poses a number of additional challenges in both general and neuroaxial anesthesia [1] .

  Obesity Top

A woman is defined as obese if her BMI is in the range of 30.0-34.9 kg/m 2 and morbidly obese if her BMI is 35.0 kg/m 2 or greater. The National Institute for Health and Clinical Excellence has further subcategorized obesity into classes I, II, and III on the basis of the BMI range (30.0-34.9, 35.0-39.9, and ³40.0 kg/m 2 , respectively). Being overweight is defined as a BMI higher than the normal range but below the threshold for frank obesity - that is, in the range of 25.0-29.9 kg/m 2 . This should be considered a rough guide because it may not correspond to the same degree of fatness in different individuals. Moreover, it does not take into account the body fat distribution; those with a central or abdominal (visceral) body fat pattern are generally at a higher cardiovascular risk [2] .

The clinical markers of visceral adiposity include waist and hip circumference and their ratio. The upper limit of normal waist circumference for adults is 80 cm or less for women and 94 cm or less for men. Increased waist circumference is a more important risk factor for future cardiovascular events compared with BMI. It is closely linked to hypertension, stroke, and type II diabetes [3] .

Physiological changes

Physiological changes occurring during pregnancy affect almost every organ system and influence the anesthetic and perioperative management of the morbid obese pregnant woman. The respiratory system is challenged during pregnancy but even more so when the parturient is obese. Pulmonary mechanics, lung volumes, functional residual capacity, oxygenation, and ventilation are altered in these individuals. Chest wall compliance decreases because of the increased weight of excess adipose tissue. Respiratory work and oxygen consumption are increased. Obstructive sleep apnea (OSA) is more likely in the morbidly obese parturient. In many cases, this disorder may be undiagnosed [4] . Diagnosis during pregnancy may be difficult because sleep disturbance and daytime fatigue are common during pregnancy, especially near term. Therefore, OSA should be suspected in women with BMI greater than 35 and/or neck circumference more than 16 inches. The use of continuous positive airway pressure may be beneficial for reducing postoperative respiratory complications as it has been shown to improve early anatomical and later functional aspects of the upper airway [5] .

Hypertension, ischemic heart disease, dilated cardiomyopathy, heart failure, and pulmonary hypertension can complicate the care of these patients. Gastroesophageal reflux disease, diabetes mellitus, and gestational diabetes are frequent disorders in morbidly obese parturients. Hypercoagulability results in venous thromboembolism and is a leading cause of maternal mortality [5] .

Obesity is associated with multiple endocrine alterations defined by changes in the level of circulating hormones and changes in the pattern of secretion or clearance of these circulating molecules. Of these alterations, some are most certainly secondary to the development of obesity, whereas others may be causative factors. Studies in human beings have shown that low concentrations of leptin are fully or partly responsible for starvation-induced changes in neuroendocrine axes, including low reproductive, thyroid, and insulin-like growth factor hormones. Disease states such as exercise-induced hypothalamic amenorrhea and anorexia nervosa are also associated with low concentrations of leptin and a similar spectrum of neuroendocrine abnormalities, which have great impact in anesthesia strategies [6] .

Renal blood flow increases during pregnancy, peaking in the third trimester at about 60-80% above prepregnancy levels. This coincides with a 50% increase in the glomerular filtration rate. Changes in renal blood flow are primarily caused by renal vasodilatation and are also altered by positional changes. Supine recumbency and sitting result in lower glomerular filtration rates. The kidneys increase excretion of bicarbonate ions, resulting in reduced plasma bicarbonate levels of ~20 mEq/l. The large size of the baby for morbidly obese pregnant women affects the renal function by pelvic compression, which leads to lower limb edema, back pressure on the renal pelvis, and urinary tract infection [7] .

Maternal and fetal complications

Morbidly obese pregnant women are at increased risk for hypertensive disorders (e.g. pre-eclampsia, chronic hypertension), coronary artery disease, respiratory disorders (e.g. asthma, sleep apnea), cerebrovascular disease, diabetes mellitus, nonalcoholic fatty liver disease, and thromboembolic disease. All of these conditions can complicate obstetric management and lead to greater maternal, neonatal, surgical, and anesthetic risks. Babies of obese women have increased risk of congenital anomalies, prematurity, stillbirth, neonatal ICU admissions, and neonatal death in complicated cases. Fetal macrosomia is also common and increases the risk of shoulder dystocia and birth trauma [8] .

Preoperative management

Preoperative evaluation

Ideally, anesthesiology consultation should be obtained early in the third trimester to ensure proper evaluation and development of an anesthetic plan. In reality, most cases are seen for the first time in the labor and delivery ward. Airway assessment is of great concern as the incidence of failed tracheal intubation is approximately one in 280 in the obstetric population compared with one in 2230 in the general surgical population. The incidence of difficult intubation in an obese population increases to 15.5% and to 33% as reported by D'Angelo and Dewan [9] . The standard clinical tests for predicting difficult intubation are less useful in the morbidly obese. It appears that there exists good evidence for measuring neck circumference as part of the preoperative airway evaluation in obese patients, in addition to Mallampati scoring and thyromental distance [10] . Further airway imaging (radiography and computed tomography) is questionable as the combined clinical and radiological measurements only improve predictability of a difficult airway by 0.04% compared with clinical assessments alone [11] .

Preadmission testing will help determine the patient's general state of health. This includes urinalysis, a complete blood count, fasting blood sugar, total cholesterol, high-density lipoprotein cholesterol, triglyceride, electrolyte, and liver enzyme levels. The patient may also need a chest radiograph, ECG, Doppler on lower limb veins, and sleep study [12] . In patients with pulmonary disease, preoperative posteroanterior and lateral chest radiography is mandatory because findings will often direct modification of the anesthetic technique used during surgery. Arterial blood gas testing on room air is also indicated. Preoperative pulmonary function tests such as spirometry and flow-volume loops are quite helpful. A quantitative measure of ventilatory function can also be used to assess the efficacy of both preoperative and surgical interventions [13] .

Preoperative preparation

Preparation of the operating room (OR) should include equipments for difficult airway management. Most OR tables can safely support a 500-pound patient. Many OR table manufacturers have produced heavy-duty OR tables capable of lifting and supporting patients weighing 800-1000 pounds. These newer tables have side extensions for added support for very wide patients. In facilities using older tables without these accessories, the addition of extra arm boards to the lower end of the table allows for additional support to lower extremities [14] .

Blood pressure (BP) monitoring, insertion of Foley catheter, establishing intravenous (IV) access, and estimation of drug dosing represent a challenge in preoperative preparation of the morbidly obese parturient as traditional BP cuffs do not fit the morbidly obese patient; therefore, the choice of an appropriate cuff and bladder size is essential for accurate BP assessment. Moreover, the appropriate cuff size in obese individuals depends not only on the arm circumference but also on its shape. A conical-shaped arm, common in obese individuals, makes it difficult to fit the cuff to the arm, increasing the likelihood of inaccurate BP measurements. The recommended dimensions for BP cuff bladders in obese adults by the British Hypertension Society are 12 × 40 cm and by the American Heart Association are 16-36 cm. Modern automated devices may also overcome the problem of miscuffing in obese individuals. These devices can yield accurate measurements over a wide range of arm circumferences, up to 40 cm and over, using a cuff of standard size. These oscillometric monitors are provided with a software that adjusts the device parameters on the basis of the characteristics of the individual arm in which BP is being measured [15] .

Foley catheter insertion may be difficult because of massive abdomen; therefore, in very large women, a catheter is sometimes placed more easily with the patient in a lateral position, with the upper leg flexed or lifted by a helper [16] . Moreover, establishing IV access is often difficult in the obese, and unsuccessful peripheral IV cannulation increases the chance of further complications such as bruising, bacterial infection, extravasation, phlebitis, thrombosis, embolism, or nerve damage. It can also lead to even more invasive procedures resulting in higher rates of infection and requiring more operator skill (e.g. central line placement, peripherally inserted central catheters, intraosseous, and venous cut-downs) [17] . A vein finder is a new device that can determine the direction of blood flow to distinguish arteries from veins to help in the insertion of an IV cannula. Drug dosing is markedly affected by the ratio of adipose tissue to lean body mass. Finally, if the drug is lipid soluble the volume of distribution is increased, and therefore its dose should be based on actual body weight (remifentanil is an exception). There is no change in the volume of distribution of H 2 O-soluble drugs, and therefore their dose is based on ideal or lean body weight [18] .


Small amounts of an anxiolytic (midazolam) may be administered to the very anxious patient. When premedication is necessary it should be administered orally, sublingually, or intravenously, as uptake by the intramuscular route is highly variable. However, for most obese patients sedative premedication should be avoided completely whenever possible [19] . Midazolam has become the drug of choice because its relatively short elimination half-life and lack of significant side effects contribute to a rapid recovery after ambulatory surgery [20] . Metoclopramide (20 mg IV or 0.2 mg/kg IV) seems to be effective in the prevention of post operative nausea and vomiting (PONV). Because of its short half-life, metoclopramide should be given near the end of surgery to ensure efficacy in the early postoperative period. The combination of metoclopramide, 10-20 mg IV, and low-dose droperidol, 0.5-1.0 mg IV, appears to be more effective compared with droperidol (1 mg) alone [21] . Prophylactic unfractionated heparin (UFH) doses of 5000 U twice/day typically used for venous thromboembolism prevention fail to elicit a measurable anticoagulant response in most pregnant patients. Monitoring UFH during pregnancy is challenging, as the activated partial thromboplastin time may be suppressed by excessive factor VIII and fibrinogen. As a result, the antifactor Xa assay concentration of 0.1-0.3 U/ml as the target range for intermediate-dose UFH may be preferred. This patient will need to wear antithrombotic hose, sequential compression stockings, or foot wraps throughout the hospital stay, from the preoperative period onward, to help prevent deep venous thrombosis [22] .

Analgesia for vaginal delivery

Neuroaxial analgesia is the preferred analgesic technique in morbidly obese parturients. Parenteral opioid and inhalation techniques can be used but often at the expense of maternal drowsiness, airway obstruction, and hypoxemia. Epidural techniques provide excellent pain relief with the benefits of reducing oxygen consumption and attenuating increases in cardiac output. If the patient is to have a cesarean section (CS), a labor epidural catheter can be used to avoid the risks of general anesthesia. Early catheter placement is imperative as successful placement of neuroaxial catheters can be time-consuming and technically more challenging [23] .

Anesthesia for cesarean section

Delivery by CS has been shown to occur more frequently in obese women. The association between excessive BMI and the need for a CS is independent of other factors such as maternal height and age, primiparity, macrosomia, and maternal diabetes. Anesthetic techniques such as spinal (single injection or continuous), epidural, combined spinal epidural (CSE), or general anesthesia are all acceptable techniques for CS. However, the choice of technique is dependent upon the clinical situation [24] .

Regional anesthesia

Major challenges in regional anesthesia for obese pregnant women include the identification of appropriate landmarks, adequate patient positioning before and after performing the block, choosing a needle of sufficient length, and the appropriate dose of local anesthetic. It has been recommended that doses of local anesthetics should be reduced by 25% for subarachnoid and epidural blocks in morbidly obese patients [24] .

The sitting position is recommended to assist with identification of the midline. If spinal processes cannot be appreciated with deep palpation, the line joining the occiput or the prominence of C7 and the gluteal cleft can be used to approximate the position of the midline sitting position, which allows the fat of the back to settle laterally and symmetrically and improves the identification of the midline [25] . Ultrasound imaging can also be helpful in identifying spinal processes. The horizontal lateral recumbent head-down position reduces the incidence of intravascular placement by reducing the venous congestion in the epidural veins [26] . It is also difficult to predict the depth to the epidural space, but the depth often positively correlates with BMI [27] . Hamza et al. [28] found that the distance from the skin to the epidural space was significantly shorter when the epidural was performed with the patient in a sitting position as compared with the lateral decubitus position. They also reported that weight and BMI were positively correlated with the distance to the epidural space. These findings are supported by a study in which computed tomography was used to measure the depth of the epidural space in nonpregnant patients and a significant correlation between BMI and distance from the skin to the epidural space was found [29] . In case difficult epidural placement is encountered, ultrasound imaging should be considered [30] .

In most cases, standard neuroaxial needles (9-10 cm) are usually of sufficient length. However, longer needles (16 cm) are sometimes needed in extremely obese parturients. These needles can cause serious injury and should be used only when a standard needle is inadequate [31] . Catheter dislodgment is another potential problem. Before the epidural catheter could be secured, Iwama and Katayama [32] noticed 3 cm skin movement in some patients. To avoid the tendency of epidural catheters to 'walk', they routinely place catheters of 7 cm in the epidural space.

CSE offers advantages when the surgical duration is unclear by providing rapid onset and dense blockade with the flexibility of prolonging the anesthetic. However, one potential disadvantage is an untested epidural catheter. Continuous spinal anesthesia must always be carried out with a consultant anesthetist. It is occasionally used in patients who have accidental dural puncture. It may be used when epidural is indicated and difficult to site. It provides reliable and predictable block and allows to titrate the block to desired level and duration [33] .

Many anesthesiologists use decreased amounts of neuroaxial local anesthetic in obese patients out of fear for an unpredictable and exaggerated spread with a possible high spinal block. Hogan et al. [34] found a lower average cerebrospinal fluid volume in individuals with a high BMI, which could explain the decreased local anesthetic dose requirements in obese patients due to decreased anesthetic dilution.

General anesthesia

General anesthesia should be avoided unless absolutely necessary. Hood and Dewan [35] found that one-third of morbidly obese parturients were difficult to intubate versus none in the nonobese control group. The anatomic changes produced by both pregnancy and obesity increase the risk for difficult intubation, rapid desaturation, and hypoxia during periods of apnea. The urgency of the obstetric situation must be weighed against the risk of general anesthesia. If general anesthesia is necessary, apart from the standard noninvasive monitoring, invasive monitoring may be required if there are comorbidities. An arterial line may also be required in the morbidly obese parturient for accurate BP monitoring as well as for frequent blood sampling, and additional experienced personnel and difficult airway equipment must be available. In all cases, proper positioning of the neck, shoulders, and chest is imperative and the key to successful intubation. In some cases, an awake fiberoptic intubation may be the safest option, but it poses its own problems. Nasal intubation should be avoided as it might result in mucosal engorgement and risk of hemorrhage. Hypertension and catecholamine release can adversely affect uterine blood flow [36] . Although fiberoptic intubation can be difficult and time-consuming, some recent reports suggest that a videolaryngoscope may be useful as the primary device or first alternative for securing the trachea [37] .

If the patient's airway appears normal, a rapid sequence intubation in a ramped position can be performed following denitrogenation. Denitrogenation can be accomplished with 3 min of tidal breathing or four maximal breaths with 100% oxygen. It has been shown that preoxygenation achieved by eight vital capacity breaths within 60 s at an oxygen flow of 10 l/min not only results in a higher partial pressure of arterial oxygen (PaO 2 ) but also in a slower hemoglobin desaturation [38] . Dosing of induction agents is based on lean body weight. Lean body weight is defined as 20-30% more than ideal body weight. Succinylcholine is the muscle relaxant of choice. The dose of succinylcholine (1.0-1.5 mg/kg up to a maximum of 200 mg) is based on total body weight [39] . Verification of proper endotracheal intubation can only be accomplished by capnography. If intubation is unsuccessful, a failed intubation drill should be instituted immediately [40] . The goal of a failed intubation management is to ensure maternal oxygenation despite concerns of fetal well-being or aspiration. Mask ventilation may require several people, one to continue cricoid pressure, a second to institute jaw-thrust, and the third to squeeze the bag and monitor the patient. Repeated attempts and additional succinylcholine are detrimental but a laryngeal mask airway can be lifesaving [41] . In morbidly obese parturients, there are further reductions in functional residual capacity due to supine positioning, use of volatile anesthetics, muscle relaxants, and retraction of the panniculus [42] . This leads to early closure of small airways and hypoxemia. Increased tidal volumes, high-inspired oxygen concentrations, reverse Trendelenburg positioning, and positive end-expiratory pressure have been used to maintain oxygenation and ventilation [43] . However, the use of positive end-expiratory pressure can worsen cardiac output and oxygen delivery to the fetus. Although isoflurane, sevoflurane, and desflurane can be used in standard concentrations, desflurane provides a faster recovery. Additional muscle relaxant may be needed, besides an intubating dose of succinylcholine. Titration of nondepolarizing muscle relaxants with the help of a twitch monitor is a reasonable approach [44] .

After the delivery of the baby, uterotonic drugs given to decrease blood loss that may affect the hemodynamics of the mother, such as methergine, similar to other ergot alkaloids, produce arterial vasoconstriction by the stimulation of a-adrenergic and serotonin receptors and inhibition of endothelial-derived relaxation factor release. Parenteral administration especially through the IV route is known to induce severe side effects due to widespread vasoconstriction of both a and β vessels. This leads to increased systemic vascular resistance, increased mean arterial BP, and increased central venous pressure. Because of this pharmacological effect of methergine, it is avoided in all cases of pregnancy-induced hypertension. In contrast, the other commonly used oxytocic agent, oxytocin, causes a dose-dependent decrease in arterial pressure due to peripheral vasodilatation, with a compensatory increase in heart rate and cardiac output. Obstetric patients have larger blood volume depending on their gestation, and any fluid overload along with a restricted cardiac output can theoretically cause acute pulmonary edema. Normally this effect is insignificant because in the usual obstetric age group severe hypertension/ischemic heart disease is uncommon [45] .

Although the induction of anesthesia was previously reported to be the most critical time during anesthetic administration in parturients, more recent reports suggest that emergence, extubation, and recovery are the most critical periods of anesthetic care in the obese parturient [46] . The morbidly obese parturient should only be extubated when she is awake with adequate reversal of muscle relaxant. Routine administration of a 'full' dose of neostigmine may not be appropriate. Current evidence suggests that the dose of anticholinesterase inhibitor should be titrated to the intensity of neuromuscular blockade at the time of reversal. Most important, train of four (TOF) monitoring of the ulnar nerve at the wrist, rather than at the eye muscles, should be used to determine the dose of neostigmine [47] . Sugammadex at 2 mg/kg can be used for reversing moderate neuromuscular blockade of rocuronium, whereas sugammadex at 4 mg/kg is used for reversing profound neuromuscular blockade. In situations when immediate reversal of rocuronium-induced blockade is required, the recommended dose is 16 mg/kg of sugammadex 3 min after rocuronium administration. A head-up position should also be used instead of supine positioning [48] .

Postoperative care

Morbid obesity increases the risk for postoperative complications, including hypoxemia, atelectasis, deep venous thrombosis, pulmonary embolism, pneumonia, pulmonary edema, postoperative endometritis, wound infection, and dehiscence. Goals of effective postoperative care should be aimed at enhancing pulmonary function and preventing venous thrombosis. Early ambulation, thromoboprophylaxis, chest physiotherapy, and effective postoperative pain control are essential in preventing complications in these patients [49] .

Effective postcesarean analgesia is important to hasten recovery. Opioids can be administered either neuroaxially or parenterally, but epidural morphine administration in the morbidly obese has been shown to result in earlier ambulation, fewer pulmonary complications, and shorter hospital stay compared with parenteral morphine administration [50] . Multimodal analgesic techniques (e.g. NSAIDs) should be used to decrease total opioid requirements. Because obesity and postoperative respiratory complications have been identified as significant risk factors for anesthesia-related mortality, respiratory monitoring must be vigilant. In addition, OSA is common and often undiagnosed in this patient population. The American Society of Anesthesiologists has published recommendations for postoperative monitoring [51] :

  1. Regional anesthetic techniques should be considered to reduce or eliminate the requirements for systemic opioids in patients with OSA.
  2. If neuroaxial anesthesia is planned, the benefits and risks of using an opioid or opioid-local anesthetic mixture as compared with local anesthetic alone must be considered.
  3. If patient-controlled systemic opioids are used, continuous background infusions should be avoided or used with extreme caution.
  4. NSAIDs and other modalities should be considered to reduce opioid requirements.
  5. Supplemental oxygen should be administered continuously to all patients who are at increased perioperative risk from OSA until they are able to maintain their baseline oxygen saturation while breathing room air.
  6. Hospitalized patients at increased risk of respiratory compromise from OSA should be monitored with continuous pulse oximetry after discharge from the recovery room.

  Acknowledgements Top

Conflicts of interest

There are no conflicts of interest.

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