Morbid obesity in obstetrics
Obesity is one of the most commonly occurring risk factors in obstetric practice. The prevalence has increased markedly from 9–10% of the obstetric population in the early 1990s to 16–19% in the 2000s. The significance of obesity as a risk factor was highlighted in the 2003–2005 Confidential Enquiry into Maternal and Child Health (CEMACH) report, and this has resulted in the consensus guidelines from CMACE and the RCOG. Obese women should receive pre-conception counselling to explain the risks of pregnancy, the requirement for increased monitoring antenatally, and the problems of intrapartum management. They should receive dietary and exercise advice. Obesity is a significant risk factor for anaesthesia-related maternal mortality, and, as a result, it is recommended that women with a BMI ≥40 kg/m2 are assessed by a consultant obstetric anaesthetist antenatally. It is especially important that this assessment identifies women with both difficult backs and difficult airways, as discussions with obstetric staff are essential to plan for a safe delivery.
1 Define different degrees of obesity in pregnancy and their respective anaesthetic and obstetric implications
2 Discuss the difficulties of regional anaesthesia in the obese parturient
3 Outline the manual handling and positioning issues during operative delivery.
2B01; 2B03; 2B04
A 23-year-old primigravida attends her appointment with the midwife to book at estimated gestation of 10 weeks. She has a history of depression and is a smoker. She has no allergies and is not taking any medication at present. She has had a general anaesthetic at age 15 for dental extractions which was uneventful. The midwife notes that her height is 1.56 m, and she weighs 115 kg. Her BMI is calculated at 47.2 kg/m2.
This lady is obese class 3 (formerly called morbid obesity), using the following accepted definitions*:
◆ Class 1 is BMI 30–34.9
◆ Class 2 is BMI 35–39.9 (5% of the UK population)
◆ Class 3 is BMI ≥40 kg/m2 (2% of the UK population).
Any patient with a BMI ≥40 kg/m2 should be referred for antenatal consultation with a consultant obstetric anaesthetist. Women with a BMI ≥35 kg/m2 should be referred to a consultant obstetrician to have an informed discussion regarding the intrapartum complications associated with an increased BMI.
◆ Miscarriage
◆ Fetal congenital anomaly: neural tube defects, omphalocele, and heart defects. Maternal size means that antenatal ultrasound diagnosis is technically difficult
◆ Macrosomia
◆ Stillbirth
◆ Neonatal death
◆ Breastfeeding difficulties.
◆ Thromboembolism
◆ Gestational diabetes
◆ Pre-eclampsia: this patient has two moderate risk factors for pre-eclampsia, with a BMI ≥35 kg/m2 being a primigravida. Optimal management should include the administration of aspirin 75 mg from 12 weeks’ gestation
◆ Caesarean section rates are 2–3 times higher in obese women
◆ Post-partum haemorrhage
◆ Wound infections.
The 2003–2005 CEMACH report suggested that obesity is a risk factor for maternal death, as 28% of mothers who died were obese, compared to a prevalence of 16–19% in the population.
◆ Diabetes
◆ Hypertension
◆ Ischaemic heart disease
◆ Secondary pulmonary hypertension and chronic right ventricular failure.
Patients with a BMI ≥30 kg/m2 should have screening for gestational diabetes with a 2-hour 75 g oral glucose tolerance test between 24 and 28 weeks’ gestation.
◆ Obstetric history and plans for the mode of delivery
◆ Past medical history, with systemic enquiry regarding cardiorespiratory disease, diabetes, and snoring/sleep apnoea
◆ Anaesthetic history
◆ Medications and allergies
◆ Airway assessment
◆ Difficulty of venous access
◆ Assess the back for difficulty of regional anaesthesia ± lumbar spine ultrasound to assess the depth of the epidural space
◆ Further investigations might include ECG, echocardiogram, oxygen saturations, CXR, pulmonary function tests.
Women with a BMI ≥35 kg/m2 should be delivered in a consultant-led obstetric unit. Many would suggest that women with a BMI ≥50 kg/m2 should be delivered in tertiary referral centres. She should have 6-hourly ranitidine orally during labour, as symptomatic reflux occurs in nearly all obese, pregnant women.
The lady should have early venous access (ideally two cannulae), due to the potential difficulty of insertion and the increased risk of post-partum haemorrhage. An intraosseous needle should be available for emergency access. An arterial line may be required if there are difficulties with NIBP monitoring, as very large cuffs are required and these may not be available.
An early epidural or combined spinal/epidural (CSE) technique for labour should be advised, due to the difficulty that there may be in siting this, the increased chance of requiring an operative delivery, and the initial higher failure rates (up to 42% in one hospital study). There is also an increased rate of accidental dural puncture and the need for re-siting an epidural with increasing BMI.
The consultant anaesthetist documents that her airway does not predict difficulty but that her venous access is difficult, and she has no palpable landmarks on assessing her back. Ultrasound of her back identifies the midline and estimates her epidural space at 7.5 cm.
This lady’s pregnancy continues, and she is induced at 41 + 5 weeks for being post-dates. She is admitted to the labour ward following an artificial rupture of membranes at 2 cm dilatation.
The duty anaesthetist for the labour ward should be advised of the admission of any woman with a BMI ≥40 kg/m2. This allows them to review the anaesthetic and obstetric plan for the lady.
The obstetric staff should be made aware of this lady. It is recommended that senior obstetric and anaesthetic staff are available for women with a BMI ≥40 kg/m2.
The lady makes slow progress in labour, and it is decided that she should be commenced on a Syntocinon® infusion to augment her labour. She decides that she would like an epidural.
There is likely to be significant difficulty in palpating the landmarks for regional anaesthesia. Ask the patient if you are palpating her hips and the middle of her back, whether it feels like you are pressing on a bone or a space. A second assistant may be beneficial to retract fat pads. It may be advisable to insert the epidural in theatre where conditions are better, in terms of lighting and bed, than the labour ward, and the anaesthetic assistant can help in positioning the patient. There is the potential for requiring longer needles, e.g. 10–12 cm long, although standard 8 cm long Tuohy needles can be used in the majority of cases.
There may be fat indentation when inserting the epidural, such that the markings on the Tuohy needle underestimate the actual depth of the epidural space. It is therefore advisable to leave more catheter in the space, e.g. 5–6 cm in the space. Asking the patient to sit upright, prior to securing the catheter in place, allows for it to be pulled inwards. There is the potential for a higher block than in non-obese women, so top-up doses should be administered incrementally and with caution. CTG monitoring during epidural insertion may be impossible, so a fetal scalp electrode may be required.
Aortocaval compression occurs in all, but full upright and lateral, positions, so patient positioning during labour is important.
An epidural is inserted by a senior anaesthetic trainee and functions well, with regular epidural review taking place. Despite augmentation with Syntocinon®, this lady fails to progress beyond 4 cm dilatation, and the decision is made to take the lady for emergency Caesarean section. Her epidural has been working well, and the decision is made to top it up for the section.
Less local anaesthetic is required to achieve a block to T4 bilaterally in the obese patient. It is therefore advisable to give a smaller volume and assess the block.
Ensure that the operating table is capable of taking the patient’s weight; a specialized bariatric table may be required. There are several considerations relating to the manual handling and positioning of this patient:
◆ Use a head-up tilt, with a pillow ramp or a propriety device such as the Oxford Help pillows, even with regional anaesthesia. This will prevent the block from spreading too cephalad and also places the patient in an ideal ramped position, should she require a general anaesthesia
◆ The patient’s arms need to be out on arm boards for venous and potential arterial access
◆ Lateral tilt of the operating table to 15° or wedging the patient to reduce aortocaval compression
◆ She may require lateral support if the pannus swings to the left
◆ Carefully protect pressure areas with appropriate gel pads
◆ All obese patients should have a 40 IU Syntocinon® infusion commenced at delivery
◆ If there is difficulty in measuring BP, consideration should be given to the insertion of an arterial line.
In the event that a general anaesthetic is required, the difficult airway trolley should be brought into theatre, and several laryngoscopes, particularly the polio blade, may be required. PEEP is usually necessary to maintain oxygenation.
◆ Post-partum haemorrhage: 40 IU Syntocinon® infusion
◆ VTE: aim for early mobilization; large TED stockings. Higher doses of LMWH are required when the weight exceeds 90 kg at booking. It is also advisable for patients with a BMI ≥40 kg/m2 to have thromboprophylaxis for a minimum of 1 week post-partum, irrespective of the mode of delivery
◆ Wound infection: antibiotics given prior to commencing surgery. The obstetricians may alter where they make their incision, e.g. supraumbilical. Often staples and extra compression sutures are used on the skin
◆ Hypoxia: nurse the patient sitting up. Avoid hypothermia wherever possible, as shivering increases oxygen consumption. Oxygen saturations and RR should be monitored. If a general anaesthetic had been required, then supplemental oxygen should be administered for 24 hours, and chest physiotherapy may be beneficial. Very obese patients should be taken to HDU for 24 hours.
Summary
In this case, the patient had an uneventful Caesarean under epidural top-up. It is important to ensure that the epidural is functioning well, and, if there is any doubt about this, then it should be re-sited. However, if she had had no epidural and a de novo spinal was required for operative delivery, a CSE technique has advantages. The epidural needle acts as a long introducer, and a smaller dose of spinal can be used to avoid a high block, and epidural top-ups then used if the spinal block is too low. Finally, as surgery is likely to be prolonged, due to the technical difficulties caused by her obesity, the anaesthetic can be prolonged with epidural top-ups. In some cases, the epidural can be maintained for post-operative analgesia if the patient is deemed at high risk of chest complications. Post-partum education on weight loss is essential, as it is well known that the weight gained during pregnancy is often not lost in obese women whose problems are therefore compounded in the next pregnancy.
National Institute for Health and Clinical Excellence (2008). Diabetes in pregnancy: management of diabetes and its complications from pre-conception to the postnatal period. Clinical guidelines, CG63. Available at: <http://www.nice.org.uk/CG063>.
* Data from World Health Organization, ‘Obesity: Preventing and managing the global epidemic’, 2000, p.9.