What the Anesthesiologist Should Know before the Operative Procedure
The morbidly obese parturient is a high-risk patient with significantly greater morbidity and mortality compared to non-obese pregnant women. Since there are no pregnancy-specific definitions of morbid obesity, the most common classification is the definition advocated by the World Health Organization (WHO) using the body mass index (BMI). The WHO divides obesity into three classes: Class I obesity (BMI=30-34.9), Class II obesity (BMI=35-39.9), and Class III obesity (BMI=40+).
Morbidly obese patients have a 2-3 times higher risk of cesarean section, instrumentation and shoulder dystocia secondary to macrosomia, resulting fetal compromise, and longer surgical times with increased time from skin incision, and increased blood loss. Morbidly obese patients are at higher risk for post-operative wound infections, opioid-related respiratory depression, repeat cesarean section, gestational diabetes, preeclampsia, abnormal placental implantation, and hysterectomies.
Neuraxial anesthesia failure rates are higher in the obese parturient when compared to their non-obese counterpart, including difficulty in placement, insufficient anesthetic duration, and failure of a previously functioning epidural. Increased congenital anomalies, stillbirths, and NICU admissions are seen with neonatal deliveries of obese parturients. Obesity increases the risk of an infant being born with a low umbilical cord pH and/or a low Apgar score.
1. What is the urgency of the surgery?
What is the risk of delay in order to obtain additional preoperative information?
Since the morbidly obese pregnant patients potentially have multiple co-morbidities, they are often followed closely by the obstetricians. Ideally, these patients have had an anesthetic consultation during the early to mid-third trimester and have an anesthetic plan developed with the obstetricians.
In reality, most of these patients are presented to the anesthesiologist at the time of admission for labor. Close communication with the obstetrician is essential in order to obtain necessary testing and formulate an anesthetic plan. The risks of delay include limitation of anesthetic choices and increased risk to the patient, as well as the unborn child. The mother’s well-being is imperative and should never be endangered to save a compromised fetus.
Emergent: Indications for emergent cesarean deliveries include category three fetal heart rate tracing, umbilical cord prolapse, placental abruption, uterine rupture, high spinal or epidural blockade, and uncontrolled eclampsia.
Urgent: Indications for urgent cesarean deliveries include category two fetal heart rate tracing, severe preeclampsia, chorioamnionitis, poor uteroplacental perfusion, or prolonged labor with failure to progress.
Elective: When a non-urgent patient presents for cesarean section, a limited time, usually in the span of days, exists for optimizing the patient’s condition for surgery.
2. Preoperative evaluation
The obese parturient is at risk for many comorbid conditions during her pregnancy, including preeclampsia, hypertensive disorders, sleep apnea, asthma, cerebrovascular disease, diabetes, fatty liver disease, cholelithiasis, and thrombophilias. All of her comorbid conditions should be evaluated.
In addition to a thorough physical and airway exam, potential for difficult IV access should be evaluated. Since obese parturients have an increased risk of difficult or failed intubation, careful airway examination is critical. The Mallampati score and thyromental distance have the highest positive predictive value and sensitivity in predicting a difficult intubation. Obtaining knowledge regarding placental location, fetal size, and gestational age can provide information regarding mode and difficulty of delivery.
Delivery of the fetus will alleviate many of the acute symptoms caused by the gravid uterus.
Medically unstable conditions warranting further evaluation include: uncontrolled hypertension and diabetes, abnormal EKG findings (cardiac strain, hypertrophy, ischemia), or acute respiratory distress.
Delaying surgery may be indicated if: severe hypertension, therapeutic or iatrogenic anti-coagulation, respiratory distress, or cardiac decompensation.
3. What are the implications of co-existing disease on perioperative care?
Obese parturients may have many comorbid conditions that will alter perioperative monitoring and management.
Perioperative evaluation: This should include an assessment of all comorbid conditions, airway and physical examination, available laboratory data, fetal size, gestational age, and placental location.
Perioperative risk reduction strategies: It is paramount that all chronic medications are continued through the perioperative period, including CPAP/BiPap, and frequent glucose monitoring and treatment are provided if applicable. Appropriate bariatric operating room tables, large blood pressure cuffs, invasive monitors, and difficult airway tools must be immediately available. Premedications should include aspiration prophylaxis.
b. Cardiovascular system
Morbidly obese pregnant women can have a host of cardiovascular diseases, including hypertension, ischemic heart disease, cardiomyopathy, and pulmonary hypertension. A thorough history and physical and electrocardiogram, if indicated, may be prudent to screen for cardiovascular disease.
Hypertension is common in the obese population (up to 60% of obese parturients) and is positively correlated with BMI. In parturients, obesity is an independent risk factor for developing preeclampsia. The incidence of preeclampsia risk doubles with each 5 to 7 kg/m2 increase in pre-pregnancy BMI.
Both hypertension and preeclampsia in obese parturients independently increase the risk of cesarean delivery. Hypertension can also cause left ventricular hypertrophy secondary to increased afterload and diastolic dysfunction. Hypertensive disease continues to be one of the leading causes of maternal mortality.
The pre-anesthetic treatment strategy is dependent on the type of planned anesthetic. If planning for a neuraxial block, the sympathectomy is likely to significantly decrease maternal blood pressure. If planning for a general anesthesia, the laryngoscopy can exacerbate the hypertension to a dangerous level. Also, obese parturients have an increased level of leptin, which increases sympathetic drive via the hypothalamus, leading to hypertension and sodium and water retention.
i. Perioperative evaluation: Signs and symptoms of acute as well as chronic hypertension need to be determined. With severe preeclampsia, blood pressure and end organ ischemia must be assessed.
ii. Perioperative risk reduction: The major goal is to maintain hemodynamic stability. Prior treatment with short acting anti-hypertensive medications and analgesics to blunt the pain from the anesthetic intervention may be required. Since a neuraxial anesthetic will likely cause a decrease in blood pressure, the goal is to prevent additional increases in blood pressure secondary to anxiety as well as pain from the insertion of spinal and/or epidural blockade.
Blood pressure should be maintained within 20% of baseline to ensure end organ perfusion, including placental flow, as this is not autoregulated. All chronic antihypertensives should be continued. Remember that calcium channel blockers, nitroglycerin and magnesium are also tocolytics and can cause uterine atony.
Ischemic Heart Disease
Ischemic heart disease should always be considered in an individual with metabolic syndrome with hypertension. Even without metabolic syndrome, the obese term parturients without hypertension can have left ventricular hypertrophy, as every 100g of fat can increase cardiac output up to 50mL/min. The increase in ventricular wall thickness may lead to sub-endocardial ischemia and/or diastolic dysfunction. Long-standing diastolic dysfunction may result in pulmonary hypertension.
i. Perioperative evaluation: Evaluate anginal symptoms and EKG findings for evidence of ischemia or strain.
ii. Perioperative risk reduction: Maintain blood pressure and heart rate within 20% of baseline for coronary and end organ perfusion. Continue all anti-hypertensive, diuretic, and antiarrhythmic medications. Prevent acute hemodynamic changes with anxiolytics and pain control.
Poor Cardiac Function
Poor cardiac function is associated with obesity during pregnancy. Obesity cardiomyopathy is a clinical syndrome generally found in patients with BMI≥40 for more than ten years. Since the blood volume, stroke volume, and cardiac output must increase to meet the metabolic demands of the increase in body mass, the increase in blood volume leads to left ventricular dilation, increased left ventricular wall stress, compensatory left ventricular hypertrophy, and diastolic dysfunction.
The right ventricle is similarly affected by the aforementioned mechanisms as well as the pulmonary hypertension secondary to obesity hypoventilation syndrome. Over time, these patients can develop progressive congestive heart failure and sudden cardiac death. Obesity is an independent risk factor for the development of heart failure, and the risk increases with increasing BMI. Although obesity is associated with hypertension, coronary artery disease, left ventricular hypertrophy, and diabetes mellitus, all of which are important causes of heart failure, multivariate analysis conclude that BMI is a significant independent predictor of heart failure.
i. Perioperative evaluation: Evaluate fluid, respiratory, and cardiac status. If applicable, obtain transthoracic echocardiography. If there is concern for heart failure, evaluation of BNP levels may be indicated.
ii. Perioperative risk reduction: Maintain stable hemodynamics and avoid fluid overload. Continue all perioperative cardiac medications. Early neuraxial intervention for labor and delivery analgesia is important. If there is significant dependence on preload for cardiac output, consider epidural anesthesia with controlled titration versus abrupt sympathectomy with spinal anesthesia for cesarean delivery.
Supine Hypotension Syndrome
Supine hypotension syndrome (SHS) is a well-known phenomenon in parturients after mid-second trimester. Cardiovascular deaths have been reported in obese patients in the supine position. The weight of the obese abdominal wall further enhances the gravid uterine compression on the aorta and inferior vena cava, resulting in decreased cardiac preload, reflex tachycardia, and decreased cardiac output. Studies have shown that the usual pelvic tilt maneuver used to offload this aortocaval compression is often not effective in the obese pregnant patient; therefore, at least 30-degree tilt in is required.
i. Perioperative evaluation: Continuous hemodynamic monitoring to assess stability.
ii. Perioperative risk reduction: Left uterine and pannicular displacement is therefore essential to prevent SHS. However, as noted above, this may not be as effective in the morbidly obese patient and a more exaggerated tilt maybe needed.
Morbid obesity and pregnancy can both cause restrictive lung disease by virtue of reducing chest wall compliance. The posture of the obese parturient has an accentuated thoracolumbar lordosis (kyphosis) and a modified thoracic curvature. Rib cage and sternal mechanics are diminished, resulting in increased work in breathing and a deterioration of ventilatory parameters. To maximize efficiency of breathing, the morbidly obese parturient will alter her breathing pattern by decreasing tidal volume and increasing respiratory rate. The progesterone effects of pregnancy may alleviate some of the restrictive symptoms.
The parturient’s pulmonary system is augmented to meet the increased oxygenation and ventilation demands of the fetus. Since oxygen consumption and carbon dioxide production is increased in direct proportion to the additional adipose tissue, its functions are furthered taxed in the morbidly obese parturient.
When supine, the pulmonary mechanics are further restricted due to the adipose tissue exerting additional forces on the chest wall and the abdominal viscera. This restrictive state results in greater atelectasis formation, a further decrease in functional reserve capacity (FRC) and expiratory reserve volume (ERV), and an increase in closing volume that often exceeds FRC. This greater closing volume promotes pulmonary shunt, a ventilation-perfusion mismatch, resulting in impaired arterial oxygenation. Lithotomy and Trendelenburg position exacerbates the respiratory impairment.
Some have found that the relaxation effect of progesterone on smooth muscles in pregnancy may decrease airway resistance and actually improve the respiratory function in obese women.
i. Perioperative evaluation: To elucidate the effects of airway closure, room air oxygen saturation can be measured in the sitting and supine position to identify those individuals who may require additional respiratory assistance (e.g. supplemental oxygen, chest physiotherapy).
ii. Perioperative risk reduction: Supplemental oxygen as needed and reverse Trendelenberg with left uterine displacement if supine. Encourage incentive spirometry in the perioperative setting.
Obstructive Sleep Apnea
Obstructive sleep apnea (OSA) is more prevalent in the morbidly obese parturient and may be undiagnosed. OSA should be suspected in parturients with BMI > 35, neck circumference > 16 inches, history of snoring, apnea, and profound daytime somnolence. The hormone-induced increase in respiratory center sensitivity during early pregnancy may decrease OSA symptoms. Later in pregnancy women tend to sleep in the lateral position, which decreases the likelihood of airway obstruction. Sleep disturbance is common.
Obesity hypoventilation syndrome, also known as Pickwickian syndrome, is a combination of severe obesity and obstructive sleep apnea. Chronic hypoxemia and hypercapnia may lead to polycythemia, pulmonary hypertension, and right heart failure (cor pulmonale). The existence of Pickwickian syndrome in pregnancy may be mitigated by the increase in progesterone.
i. Perioperative evaluation: Consider CXR if supplemental oxygen is required. Look for EKG signs of right heart strain, or TTE findings of pulmonary hypertension and elevated right-sided pressures. Consider referral to a pulmonologist and/or cardiologist if symptoms are severe, such as in Pickwickian syndrome.
ii. Perioperative risk reduction: Supplemental oxygen as needed and maintain the use of CPAP/BiPap in the perioperative period, especially in PACU. Be prepared with nasal and oral airways during mask ventilation and while in the PACU, as airway obstruction is common. Consider continuous pulse oximetry. Neuraxial anesthesia is preferred.
Asthma is more prevalent in the morbidly obese population, possibly due to the high incidence of gastroesophageal reflux disease.
i. Perioperative evaluation: Lung auscultation and evaluation of respiratory effort. Consider CXR if indicated.
ii. Perioperative risk reduction: Continue all scheduled respiratory medications. Remember systemic beta agonists medications are also tocolytics.
Gastric Content Regurgitation
The frequency of GERD is strongly correlated with increasing BMI. Physiologic changes in normal pregnancy include a decrease in lower esophageal sphincter tone. In laboring women, gastric motility decreases and emptying may cease completely, but in non-laboring obese parturients there is no delayed emptying.
Morbidly obese patients have larger volumes of gastric fluid as well as lower gastric pH compared to non-obese parturients. Morbidly obese parturients are less mobile, which also increases the chance of aspiration. Use of opioids further contributes to decreases in gastric motility.
i. Perioperative evaluation: Evaluate NPO status and reflux symptoms.
ii. Perioperative risk reduction: The increased risk of pulmonary aspiration necessitates strict NPO guidelines and the use of non-particulate antacids, motility agents, and H2 blockers prior to induction of anesthesia. Rapid sequence induction is required when utilizing general anesthesia.
Fatty liver is commonly observed in morbidly obese patients. It is the most common cause for elevated transaminases in the United States. The risk of steatosis increases with type 2 diabetes mellitus, hyperlipidemia, and/or hypertension. Unlike the clinically significant microvesicular steatosis found in fatty liver of pregnancy, the macrovesicular fatty liver associated with obesity is usually a benign process. In rare cases, the fatty liver associated with obesity may progress to fibrosis, cirrhosis, and liver failure.
i. Perioperative evaluation: Consider obtaining liver function tests and a coagulopathy panel.
ii. Perioperative risk reduction: If liver function is compromised, altered drug metabolism and clearance must be considered. If a coagulopathy is present, neuraxial procedures may be contraindicated.
Type 2 Diabetes Mellitus and Gestational Diabetes Mellitus
Type 2 diabetes mellitus (DM) and gestational diabetes mellitus (GDM) are common in the morbidly obese parturient. Morbidly obese parturients have two risk factors for developing DM: pregnancy and obesity. Development of type 2 DM is strongly correlated with increasing BMI. Since the placenta secretes contra-insulin hormones, insulin resistance becomes increasingly common as pregnancy progresses. The treatment corresponds to the degree of insulin resistance, beginning with diet control and exercise and then oral medications (e.g., metformin, sulfonylureas and meglitinides) when needed.
When insulin resistance becomes severe, use of exogenous insulin will be required to control blood glucose. The combination of pre-existing insulin resistance of obesity and the insulin resistance of pregnancy likely leads to the large amounts of insulin required to achieve glycemic control. The large insulin requirement, in turn, may lead to further gestational weight gain. Thus, a vicious cycle of increasing insulin and weight gain ensues.
DM has significant adverse effects on the fetus. Perinatal mortality is increased by almost four-fold. The incidence of congenital anomalies is doubled. There is a three-fold increase in both neural tube defects and congenital heart disease. Maternal obesity is a risk factor for fetal macrosomia, independent of diabetes mellitus. Good glycemic control reduces the risk of adverse perinatal outcomes. HgbA1C levels should be less than 7%.
i. Perioperative evaluation: Obtain glucose values as frequently as indicated. HbA1C is a great indicator of recent control of blood glucose levels.
ii. Perioperative risk reduction: Maintain good glycemic control and consider insulin infusion if indicated.
g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (e.g., musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
Hypercoagulability increases the risk of venous thromboembolism (VTE), a leading cause of maternal mortality. The incidence of VTE in obese parturients is greater than twice that of non-obese controls.
Multiple reasons may account for the increased incidence of venous thrombus formation:
2. Increased lower extremity venous stasis secondary to increased inferior vena cava stasis, as a result of increased intra-abdominal pressure
3. Vascular damage, as a result of both vaginal deliveries and cesarean sections
4. Decreased fibrinolytic activity (decreased in individuals with a combination of hyperlipidemia and insulin resistance)
5. Fibrinogen levels increases in proportion to BMI
6. Increased thromboxane production secondary to hyperlipidemia
7. Polycythemia secondary to increased blood viscosity
8. Increased plasma concentration of factors I, VII, VIII, and X
Anticoagulation with low molecular weight heparin (LMWH) and unfractionated heparin prophylaxis protects against venous thrombi formation. Sequential compression devices are essential for all obese parturients who are not ambulatory. An anticoagulated patient is at increased risk of epidural hematoma following placement of a neuraxial block. Obtain a PTT and platelet count for all patients on unfractionated heparin prior to neuraxial placement. The timing of neuraxial procedures should be delayed in anticoagulated patients as recommended in the American Society of Regional Anesthesia (ASRA) guidelines.
4. What are the patient’s medications and how should they be managed in the perioperative period?
All chronic medications are to be continued throughout the perioperative period and altered as the patient’s condition changes. If the patient is NPO, her medications can be converted to IV or taken PO with sips of water.
h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?
Some antihypertensives, such as calcium channel blockers, can be tocolytics, and alternatives may be selected if labor is planned. Anticoagulation with low molecular weight heparin is usually transitioned to unfractioned heparin at 36 weeks gestation and held 4 hours prior to induction or cesarean delivery. Coumadin is considered teratogenic in the first trimester and is not usually used early in pregnancy. In addition, coumadin does cross the placenta (heparins do not cross) and hemorrhage can occur in the fetus, without an effective way to reverse the coagulopathy in the fetus until after birth.
i. What should be recommended with regard to continuation of medications taken chronically?
j. How To modify care for patients with known allergies –
The most effective way to reduce the likelihood of an allergic reaction in the operating room is to remove the inciting allergen.
k. Latex allergy- If the patient has sensitivity to latex (e.g., rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.
Caution should be taken to avoid the use of latex-containing products.
l. Does the patient have any antibiotic allergies- – Common antibiotic allergies and alternative antibiotics]
Common antibiotic allergies include penicillin and sulfa. Alternative antibiotics should be discussed with the obstetric team. Cephalosporins can be used in penicillin-allergic patients, if the reaction is mild.
m. Does the patient have a history of allergy to anesthesia?
Neuraxial anesthesia can be maintained with either amide or ester local anesthetics. If malignant hyperthermia is a concern, general anesthesia can be induced and maintained with total intravenous anesthesia using an appropriately prepared anesthesia machine.
Avoid all trigger agents such as succinylcholine and inhalational agents:
Proposed general anesthetic plan: General anesthesia can be induced and maintained with total IV anesthesia using an appropriately prepared anesthesia machine.
Insure MH cart available: Follow MH protocol.
Family history or risk factors for MH
Avoid inhalational agents and succinylcholine. All local anesthetics can be used for neuraxial techniques.
5. What laboratory tests should be obtained and has everything been reviewed?
A complete blood count should be ordered. A type and screen should be performed before all cesarean deliveries and for laboring patients with risk of postpartum hemorrhage.
There is a normal physiologic anemia, and gestational thrombocytopenia occurs in 6-8% of pregnancies. Hemoglobin is usually greater than 9 and platelets usually remain above 70,000.
Hemoglobin levels: Usually greater than 9.
Electrolytes: Typically normal, unless the patient is diabetic.
Coagulation panel: Typically normal, unless the patient has liver dysfunction, preeclampsia, abruption, or fetal demise.
Imaging: Indicated based on history and physical exam (CXR for hypoxia or decompensated heart failure).
Other tests: Indicated based on history and physical exam.
Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
There are several options for management of labor analgesia, including local (paracervical and pudendal blocks), parenteral opioids, nitrous oxide and neuraxial techniques. Anesthesia for cesarean delivery may be provided using general anesthesia or neuraxial techniques, including single-shot spinal, epidural, combined-spinal epidural, or continuous spinal anesthesia.
The recommended technique for this population is neuraxial analgesia/anesthesia, unless contraindications exist, such as hypovolemia, coagulopathy, increased intracranial pressure, infection at insertion site, or patient refusal.
However, in all surgical situations the provider should:
i. Administer aspiration prophylaxis (promotility agents, H2 blocker, and nonparticulate antacid).
ii. Verify weight limitations of the OR table (most will accommodate up to 160kg).
iii. Check the availability of additional arm supports and assure the ventilator can provide higher peak pressures.
iv. Assure adequate IV access, as these patients are often difficult IV placements and increased blood loss is more likely in the obese parturient.
v. Be sure to have the appropriate BP cuff size and fit. An arterial line may be indicated for accurate blood pressure readings.
vi. Perform an airway exam. Mallampati and thyromental distance have the highest positive predictive value and sensitivity when predicting difficult intubations.
vii. Position the patient so that the external auditory meatus and sternal notch line up in the horizontal axis to increase intubation success. We recommend using blankets under the shoulders. This will also allow the breast tissue to fall away from the chin and neck.
viii. Always place the parturient in left lateral tilt to minimize aortocaval compression. The pannus can be positioned caudad or cephalad for abdominal surgery. If positioned cephalad, watch for hypotension and respiratory distress secondary to venocaval compression and a decrease in chest wall compliance.
ix. Use a short handled laryngoscope, as excessive breast tissue can hinder blade positioning. Have an LMA available (if possible) and consider fiberoptic intubation/video laryngoscope. Avoid nasal intubation due to mucosal engorgement.
Benefits: Minimal medication exposure to the fetus and decreased overall pulmonary, cardiac, and airway complications. Excellent postoperative pain control with a decreased risk for respiratory depression when compared to parenteral opioids.
Drawbacks: Potential for high spinal/epidural blockade, resulting in respiratory and cardiac depression; therefore medication should be titrated slowly. Pulmonary function testing showed that neuraxial blocks as high as T5 result in a significant decrease in spirometry values. This decrease correlated well with BMI. The parturient will likely need a urinary catheter for potential urinary retention. There is a higher risk of an inadvertent dural puncture, as obese parturients can be difficult placements.
Issues: Aggressive management of hypotension is paramount. Utilize phenylephrine or ephedrine (depending on maternal heart rate). The placenta is not autoregulated, so maintaining baseline blood pressure is paramount. If anticoagulation has been in use, then coagulation and platelet levels should be obtained. Longer spinal/epidural needles may be needed (11cm will usually suffice). The patient can be helpful in directing you to midline as well, based on her sensation during placement (detection to the left or right). Using a “finder” needle (22G pencil point spinal needle) can assist in locating the dura and determining depth. Ultrasound guidance may help decrease the number of attempts prior to successful placement. Secure the catheter about 5cm in the epidural space and allow the patient to position herself laterally before securing the catheter (allowing the catheter to pull into the subcutaneous fat and not out of the epidural space). No reduction in spinal dose is needed. A spinal dose of 12 mg of bupivacaine should provide an adequate block level. We recommend a combined spinal epidural technique, as the surgical duration will likely be increased. If an inadvertent dural puncture occurs, consider conversion to continuous spinal technique, as the risk of a postdural puncture headache may be less in the obese parturient (10% versus >50%).
Peripheral Nerve Block Transversus Abdominal Plane (TAP) blocks may provide supplemental pain relief postoperatively in patients who could not receive neuraxial anesthesia or neuraxial morphine. We recommend placement of these blocks with ultrasound, as anatomical landmarks may not be discernible.
Benefits: Minimal fetal exposure, no motor blockade or urinary retention. No respiratory or hemodynamic compromise.
Drawbacks: Requires a trained provider and associated with a rare risk of bowel injury.
Issues: Does not provide complete pain relief, and most patients will need supplemental opioids.
Benefits: Complete surgical relaxation and a secured airway.
Drawbacks: Difficult intubation and ventilation creating high peak pressures, which could lead to lung inflammation. Fetal exposure to all anesthetic agents except paralytics. Potential uterine atony if >0.5 MAC used (can supplement with nitrous oxide). The mother is unable to participate in the birth.
Other issues: Inhalational agents cause vasodilation, so maintenance of blood pressure is paramount. MAC is decreased by up to 40% in pregnancy and should be adjusted in the operating room. Careful titration of opioids is critical to prevent post-extubation hypoventilation and airway obstruction. Narcotics should not be given until after the fetus is delivered.
Airway concerns: It is estimated that one third of morbidly obese parturients were difficult intubations. Fat deposition in the orophayrnx, soft tissue changes during pregnancy, airway mucosal edema associated with labor, and preeclampsia all contribute to difficulty in visualizing pertinent airway structures. The overall incidence of failed tracheal intubation is estimated to be 1:280 in the obstetric population. In the obese parturient (average BMI=33), a UK review covering six years found the incidence of failed intubation to be 1:249. Video laryngoscopy may decrease the risk of failed intubation. Since Mallampati classification can worsen during the course of labor, a thorough airway assessment should be conducted just prior to induction of anesthetic care. The airway evaluation should include Mallampati score, neck circumference, mouth opening, dentition, thyromental distance, neck mobility, and the ability to sublux the lower incisors beyond the upper incisors. Difficult laryngoscopy and failed intubation in the obstetric population have been associated with large breasts, increased antero-posterior chest distance, airway mucosal edema, and reduced chin-to-chest distance. Most airway complications occur in the PACU, so consider recovery in the main OR PACU. Always use pulse oximetry and have experienced personnel recovering these patients. We recommend having nasal and oral airways in the PACU, as well as CPAP if the patient has a history of OSA.
6. What is the author’s preferred method of anesthesia technique and why?
Our preferred technique for cesarean delivery and labor analgesia in this population is combined spinal epidural (CSE). This provides adequate pain relief for as long as necessary, while still maintaining a patent airway. Having an epidural in place allows for careful titration of anesthetic without compromising the patient hemodynamically or causing respiratory depression.
After cesarean delivery, adequate post-operative pain relief can be achieved. Since the parturient will not be ambulating until sufficient motor strength has returned, be sure that SCDs are in place. We recommend placement of the CSE early in labor and replacing any catheters that are not functioning optimally as soon as possible.
For labor CSE, we recommend 2-2.5 mg of bupivacaine with 10-15 mcg of fentanyl (or 5 mcg of sufentanil) in the spinal dose if the parturient has reached greater than 4 cm of cervical dilation. If less than 4 cm, we recommend a narcotic only (20-25 mcg of fentanyl) intrathecal dose. Adequate labor epidural analgesia can be obtained with 0.08% bupivacaine and 2 mcg/mL of fentanyl, with rate adjusted to desired block height.
For cesarean delivery, we recommend 12 mg of bupivacaine in the spinal dose with 10-25 mcg of fentanyl. If additional anesthesia is required, titrate 2% lidocaine in 5cc increments until adequate block height is achieved. The use of epidural morphine is controversial in the obese parturient. A dose of 3-4 mg epidural morphine may be considered for postoperative pain management.
What prophylactic antibiotics should be administered
Cefazolin 2 grams or 3 gram (>120 kg) IV within one hour of incision targeted to skin flora. Discuss with the obstetric team prior to incision. Consider re-dosing if there is excessive blood loss (EBL >1500 mL) or surgery is prolonged.
What do I need to know about the surgical technique to optimize my anesthetic care?
The typical incision is a Pfannenstiel skin incision across the lower abdomen, and a sensory blockade of at least T4 is necessary because the surgeon exteriorizes the uterus for closure. In emergency situations, the surgeons may use a classical longitudinal midline abdominal incision and the patient will likely be under general anesthesia. If neuraxial anesthesia is utilized, a sensory level of T4 will be necessary.
What can I do intraoperatively to assist the surgeon and optimize patient care?
Prior to delivery, it is paramount to maintain baseline blood pressure for fetal stability. Supplement oxygen as determined by pulse oximetry, ideally via a non-rebreather mask to maximize FiO2. Oxytocin will be required immediately after fetal delivery. Communicate with the surgeons regarding uterine tone.
What are the most common intraoperative complications and how can they be avoided/treated?
1. Postpartum hemorrhage: Be prepared with postpartum hemorrhage medications (especially in situations where the mother has been maintained on magnesium sulfate, oxytocin, or in the presence of uterine infection). Avoid methergine in uncontrolled hypertension and carboprost in reactive airway disease or pulmonary hypertension.
2. Hemodynamic instability: Vasopressors may be required to maintain maternal blood pressure within 20% of baseline. Phenylephrine is the preferred vasopressor in obstetrics, but ephedrine may be indicated in the setting of maternal bradycardia.
Cardiac complications: Obese parturients are at high risk for thromboembolic complications, and SCDs should be used at all times when the patient is not ambulating. Pharmacological prophylaxis should be considered as well. Obese patients may also have pre-existing cardiac conditions, and cardiac evaluation may help prevent complications. Hypotension can be detrimental to both mother and fetus, so maintain baseline blood pressure.
Pulmonary: Obese parturients are at higher risk for airway obstruction and respiratory depression, so supplemental oxygen may be needed, as well as reverse Trendelenberg to improve ventilation. Always be prepared to assume control of the airway. There is higher risk for pulmonary edema secondary to lower oncotic pressures in pregnancy, so use fluids appropriately and consider diuretics if indicated.
Unique to procedure: Amniotic fluid embolism is an uncommon but potentially lethal complication that can result in cardiac collapse. While there are no preventative measures, the provider should be aware of this complication and provide supportive measures, including invasive monitoring, pharmacological support, and transfusion for coagulopathic states.
b. If the patient is intubated, are there any special criteria for extubation?
Parturients are full stomachs and should be extubated when completely awake with full reversal of muscle relaxant. If the parturient has OSA, make CPAP available in the PACU. Consider recovery in the main OR.
c. Postoperative management
What analgesic modalities can I implement?
There are multiple modalities for post operative pain control, and many methods are appropriate in this setting: continuous epidural/spinal catheters, patient controlled epidural analgesia (PCEA), patient controlled analgesia (PCA), NSAIDS (unless contraindicated), IV opioids, and TAP blocks. Avoid basal PCA rates.
What level bed acuity is appropriate?
Usually PACU on the OB floor if the patient is stable and there is no concern for airway obstruction. SICU is appropriate if the patient is not stable or intubated.
What are common postoperative complications, and ways to prevent and treat them?
Common postoperative complications include DVT/PE, respiratory depression, and postpartum hemorrhage. All patients should be provided with SCDs and ambulate early. If ambulation is unlikely immediately after surgery, then pharmacologic prophylaxis should be implemented. Continuous pulse oximetry should be considered in OSA parturients. All patients should be monitored for postoperative blood loss (> 500 for vaginal delivery or >1000 for cesarean delivery is considered hemorrhage). In case of hemorrhage, appropriate protocols should be followed, including adequate IV access, transfusion, fluid resuscitation, and notification of surgical staff in cases of surgical bleeding or retained placenta.
What’s the Evidence?
WHAT ANESTHESIOLOGISTS SHOULD KNOW BEFORE THE OPERATIVE
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- What the Anesthesiologist Should Know before the Operative Procedure
- 1. What is the urgency of the surgery?
- What is the risk of delay in order to obtain additional preoperative information?
- 2. Preoperative evaluation
- 3. What are the implications of co-existing disease on perioperative care?
- b. Cardiovascular system
- c. Pulmonary
- d. Renal-GI:
- e. Neurologic:
- f. Endocrine:
- 4. What are the patient’s medications and how should they be managed in the perioperative period?
- i. What should be recommended with regard to continuation of medications taken chronically?
- j. How To modify care for patients with known allergies -
- k. Latex allergy- If the patient has sensitivity to latex (e.g., rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.
- l. Does the patient have any antibiotic allergies- - Common antibiotic allergies and alternative antibiotics]
- m. Does the patient have a history of allergy to anesthesia?
- 5. What laboratory tests should be obtained and has everything been reviewed?
- 6. What is the author’s preferred method of anesthesia technique and why?
- a. Neurologic:
- b. If the patient is intubated, are there any special criteria for extubation?
- c. Postoperative management