ANESTHETIC MANAGEMENT OF THE OBESE PARTURIENT

Abstract

During pregnancy, maternal physiology undergoes continual adaptation. These; often interlinked, changes affect all the body systems and are affected by the hormonal influences of the placenta and mechanical adaptations required to accommodate the growing fetus. These changes are exaggerated and become more prominent with obesity. Rates of obesity have increased sharply over last 20 years. Maternal obesity is associated with increased adverse outcomes for both mother and child. It is linked to complications during pregnancy which includes: gestational diabetes, pre-eclampsia and thromboembolism. Obesity is also linked to inflammation and insulin resistance. The common pathway through which inflammation leads to insulin resistance is likely to be through modulation of insulin signalling. In addition to alteration in glucose metabolism, maternal obesity is also accompanied by perturbations in inflammatory markers, adipokines and vascular dysfunction. Impact of maternal obesity on offspring is substantial, with increasing evidence of long-term morbidity in children born to obese mothers. Obese women are more likely than lean women to be delivered by Cesarean section. The extent of weight gain during pregnancy is also a positive predictor of the risk of Cesarean delivery. Pre-eclampsia and diabetes are two leading indications for Cesarean section, and both are more common among obese women. All obstetric units should develop protocols for the management of morbidly obese women. These should include pre-procedural assessment, special community, ward and theatre equipments such as large sphygmomanometer cuffs, beds and operating tables and long regional block needles. Morbidly obese patients should be referred for anesthetic assessment and advice as a part of their antenatal care by consultant anesthesiologists. Difficulties with airway management and intubation should be anticipated. Positioning the patient requires skill and sufficient manpower especially in the event of a requirement for induction of general anesthesia. Direct arterial pressure measurement may be useful in the morbidly obese patients where sphygmomanometer is often inaccurate. All morbidly obese parturients should be given prophylactic low-molecular weight heparin and the duration of therapy needs to be determined in view of the likely immobility. Thromboembolic stockings of appropriate sizes need to be available. Neuraxial anesthesia is the best possible choice in most cases of anticipated difficult airway in obese parturients. Either spinal or epidural anesthesia is acceptable, provided no contraindications exist in the absence of fetal compromise. When a Cesarean section is non-emergent, epidural anesthesia can be used. When time is limited, spinal anesthesia is the choice. The advantages of neuraxial over general anesthesia include the following: the mother is awake and can protect her airway, airway manipulation is not necessary, and the incidence of acid aspiration is decreased. If neuraxial anesthesia is administered to a patient with difficult airway, close monitoring by an experienced anesthesiologist is essential. General anesthesia is hazardous in the morbidly obese parturient. There are a number of features ofthemorbidly obese parturient that increase the risk of hypoxiaduring rapid sequence induction of anesthesia. However,general anesthesia may be required in emergency Cesareandelivery or when regional anesthesia is contraindicated or technically difficult. Obesity predisposes to fetal macrosomia that; in addition to increasing the risk for shoulder dystocia, contributes to perineal lacerations, fetal injury, and postpartum hemorrhage. An attempted operative vaginal delivery in the obese patient must be made judiciously with informed consent. Epidural and spinal analgesia are the most effective methods of intrapartum and postpartum pain relief during normal labor in contemporary clinical practice. Systemic opioids provide little to modest labor pain relief. Pain relief is incomplete, temporary, accompanied by sedation and is more effective in the early part of active labor. Opioids may lack effectiveness after 7 cm of cervical dilation. Despite their limitations, the temporary easing of labor pain following opioid administration may be a helpful and satisfactory pain management strategy for many parturients. For others seeking greater pain relief, the effect of systemically administered opioids may not be satisfactory. Although nitrous oxide is certainly not a potent analgesic, studies suggest a beneficial effect for many parturients. It is easy to be administered as a 50% concentration which appears to have been safely used by very large numbers of patients over many years. Although co-administration of nitrous oxide with opioids will undoubtedly provide more effective analgesia than either agent given alone, this would increase the risk of maternal unconsciousness and would require more vigilant monitoring.