General Anesthesia for Vaginal Delivery of Twins in an Anticoagulated Obese Woman
This ongoing column is written by members of the International Society for the Perioperative Care of the Obese Patient (ISPCOP), an organization dedicated to the bariatric patient.
Column Editor: Stephanie B. Jones, MD
Dr. Jones is Associate Professor, Harvard Medical School and Vice Chair for Education, Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel, Deaconess Medical Center, Boston, Massachusetts.
This month:
General Anesthesia for Vaginal Delivery of Twins in an Anticoagulated Obese Woman
by Vilma E. Ortiz, MD
Dr. Vilma E. Ortiz is from the Department of Anesthesia, Critical Care & Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.
Abstract
The significant health-related consequences of maternal obesity, specifically the respiratory changes, may challenge the airway management during induction of a general anesthetic.
A 32-year-old obese woman at 35 weeks gestation with vertex/transverse twins was admitted in active labor. Her history was notable for a pulmonary embolus during this pregnancy, gastroesophageal reflux and recent treatment for suspected pneumonia. Full anticoagulation with enoxaparin contraindicated the use of neuraxial anesthesia. Anticipating the need for an intra-utero version of the second twin, she requested general anesthesia for a vaginal delivery.
The management of this case illustrates that a sound understanding of the pathophysiologic changes associated with excess weight, a cogent airway management strategy and communication among all team members are essential to the optimal care of the obese parturient undergoing a general anesthetic.
Introduction
The epidemic of overweight and obesity continues to rise and affect an increasing proportion of women of childbearing age. Elevated body mass index (BMI) with its attendant alterations in physiology places the laboring parturient at higher risk for obstetric and anesthetic complications.[1,2] Higher rates of preeclampsia, gestational diabetes mellitus, cesarean delivery, and need for general anesthesia have been associated with maternal obesity.[3] Current trends in obstetric anesthesia emphasize the use of neuraxial techniques. Consequently, provider experience with general anesthesia in the obstetric setting is declining. Unless requested by the patient, general anesthesia typically occurs in high-pressure settings (e.g., emergency, after hours) or when neuraxial blockade is either ineffective or contraindicated. Obesity and pregnancy increase the risk of difficulties during airway management underscoring the importance of a strategy for maintenance of oxygenation during induction of and emergence from general anesthesia in the parturient with obesity. Here, I present the case of a patient whose airway management was challenged by her BMI, gastroesophageal reflux (GERD), reactive airway from recent pulmonary infection, and initial request for induction of general anesthesia in the lithotomy position in preparation for a vaginal delivery.
Case Report
A 32-year-old, G2 P0 woman at 35 weeks gestation with dichorionic twins was transferred to our hospital in active labor. She was 5ft, 2in tall, and had a body mass index of 41kg/m[2]. Approximately 50 days previously, she suffered a pulmonary embolus (PE) and was anticoagulated with enoxaparin 90mg subcutaneously twice daily. The last dose was 9.5 hours prior to this admission. A hypercoagulable workup revealed neither factor V Leiden nor prothrombin gene mutations. Her anticardiolipin profile was unremarkable. Her history was complicated by GERD on pantoprazole, ranitidine, sucralfate, and metoclopramide, and recent completion of a 14-day oral regimen of amoxicillin/clavulanate potassium for suspected pneumonia. She had no history of hypertension, diabetes mellitus, or symptoms suggestive of obstructive sleep apnea (OSA) such as snoring, daytime sleepiness or witnessed episodes of apnea.
Her physical exam on admission was remarkable for a normal body temperature, a blood pressure of 114/88 mmHg, a heart rate of 97 beats per minute, a room air peripheral oxygen saturation (SpO2) of 98 percent and a reassuring airway exam (Mallampati class II, dentition in good condition, 4cm mouth opening, and unrestricted neck mobility). Her lung fields were clear to auscultation. Her vaginal exam revealed a cervical dilatation of 6cm and fetal ultrasound showed the presenting twin to be in vertex position; the second twin had a transverse lie (back up).
Because of her significant risk of bleeding, the obstetrician was reluctant to perform a cesarean. The obstetric plan was for vaginal delivery of both twins, with a strong likelihood of a painful intra–utero manipulation of the second twin to achieve a vertex presentation. Upon learning that recent administration of enoxaparin precluded her receiving a neuraxial anesthetic for labor analgesia, the patient insisted on receiving a general anesthetic. The anesthesiologist and obstetrician discussed the optimum timing for the induction of general anesthesia. The desire to minimize the exposure of the unborn babies to anesthetic agents was weighed against the desire to avoid a rushed induction in a laboring patient with obesity and GERD after delivery of the first of the twins.
The patient received intravenous nalbuphine for labor analgesia and was transferred to the operating room when the presenting baby’s head was visible at the introitus. She was placed in a 30-degree reverse Trendelenburg position with left-uterine displacement. While standard monitors were applied, she received 100 percent oxygen via tight fitting face mask until the end-tidal oxygen concentration reached 85 percent. A rapid sequence induction (RSI) of general anesthesia with propofol (200mg), succinylcholine (120mg), and cricoid pressure followed and direct laryngoscopy with a Miller 2 blade revealed a normal glottis. A 7.0mm (internal diameter) cuffed endotracheal tube was easily advanced into the trachea. The patient was subsequently placed in the lithotomy position for forceps-assisted vaginal delivery of a 4.3-pound baby girl, 16 minutes after induction of general anesthesia. Her Apgar scores were 1 and 7. One minute later, a second girl weighing five pounds followed by total breech extraction. Her Apgar scores were 2 and 7. Anesthesia was maintained with sevoflurane (minimum alveolar concentration= 1.0), 100mcg fentanyl and 1mg midazolam.
The vaginal deliveries and median episiotomy repair were completed in 34 minutes with an estimated blood loss of 300mL. Once awake and in a semi-recumbent position, the patient’s trachea was extubated. She was transported to her recovery room where she was maintained in a sitting position with supplemental oxygen via face mask. She was discharged home two days later with her enoxaparin resumed.
Discussion
As in the general population, the diagnosis of obesity during gestation is often based on BMI. BMIs above 30kg/m[2] have been associated with a higher risk of serious complications during airway management.[4] Potential contributors to airway difficulties include substandard airway assessment, improper selection of airway management devices, and lack of back-up plans in case of failure of the initial strategy.
Obesity significantly increases a patient’s pro-thrombotic potential.[5,6] The hypercoagulable state that accompanies pregnancy further exacerbates the risk of venous thromboembolism. Once its diagnosis has been established in the pregnant patient, current recommendation is for anticoagulation during pregnancy and the puerperium.[7] For the patient who presents with unexpected onset of labor, use of low molecular weight heparin (LMWH) presents the clinician with difficulties monitoring the anticoagulant response, incomplete reversibility with protamine, and a prolonged half-life. The American Society of Regional Anesthesia and Pain Medicine recommends that regional anesthesia be administered no sooner than 12 hours after the last dose of prophylactic and 24 hours after therapeutic LMWH administration.[8]
General anesthesia has been traditionally considered to be higher risk in the obstetric population, largely due to an increased incidence of difficulty in airway management and potential for aspiration of gastric contents. As the process of gestation evolves over a nine-month period, the pregnancy-related physiologic changes may impact the parturient’s airway in a dynamic fashion. Oropharyngeal tissue volume (Mallampati [MP] classification) has been noted to increase not only during gestation, but also during labor.[9] Furthermore, conditions such as preeclampsia and sleep-disordered breathing may impact the airway by their association with an increase in neck circumference.[10,11] Although gastric emptying is normal in healthy, non-laboring women (lean and obese), it is delayed by pain, opioids, and specific conditions, such as diabetic gastroparesis and GERD. Though no single abnormal finding on airway exam can accurately predict difficulties during airway management, the concurrence of several features, including limited mouth opening, protruding incisors, receding mandible, large neck, and limited atlanto-occipital joint mobility, portends difficulties, potentially precluding a RSI such as was described for this patient.
Obesity and pregnancy-related respiratory changes adversely impact pulmonary mechanics.[12] The higher rate of oxygen utilization characteristic of these states is coupled with a decrease in lung volume resulting from reduced chest wall compliance and cephalad displacement of the diaphragm, reducing functional residual capacity (FRC). This is worsened in the supine, Trendelenburg, and lithotomy positions where FRC may fall below closing capacity leading to collapse of small airways, worsening atelectasis and desaturation.
The importance of thorough preoxygenation has been illustrated by McClelland et al[13] using computer modeling to describe the effects of preoxygenation and apnea during RSI in several scenarios. The laboring subject with a BMI of 50kg/m2 demonstrated the fastest desaturation time, 98 seconds for the arterial saturation to fall below 90 percent. For the normal BMI parturient, the time was 292 seconds. Patient position must also be optimized before induction of general anesthesia. In lean parturients, higher capillary blood PO2 has been demonstrated in the sitting versus supine position.[14] In patients with severe obesity presenting for bariatric surgery, the head-up position, particularly reverse Trendelenburg (Figure 1), has been associated with higher pre-induction oxygen tensions and longer safe apnea period than the supine position.[15] Caudad displacement of the breasts, pannus, and viscera not only improves patient comfort and FRC, but may also facilitate access to the airway. As emergence from general anesthesia is also a time when airway problems may occur, tracheal extubation of the parturient with obesity should occur when the patient is fully awake and positioned with her head elevated or in the lateral decubitus position.
This case demonstrates the use of general anesthesia for the vaginal delivery of twins in an anticoagulated obese patient. Although the second twin was ultimately born by breech extraction, during the planning of this anesthetic we had to balance the likelihood of a painful intra-utero version with the risks of a general anesthetic. The timing of the induction of anesthesia also had to be considered as converting to general anesthesia after the first twin was born would have entailed a delay due to repositioning and preoxygenating the patient (made necessary by her size and history of reflux). The situation described illustrates the importance of communication among all team members, particularly when an unexpected condition such as full anticoagulation mandates a departure from routine practice.
References
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14. Ang CK, Tan TH, Walters WA, Wood C. Postural influence on maternal capillary oxygen and carbon dioxide tension. Br Med J. 1969;4:201–203.
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Funding: No funding was provided.
Disclosures: The author does not have any conflicts of interest relevant to the content of this article.
Category: Anesthetic Aspects of Bariatric Surgery, Past Articles
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