Obesity in Obstetrics

The parturient with a high BMI featured as an SAQ back in September 2018 (71% pass rate).

A repeat of the question as a CRQ in March 2022 (44% pass rate) saw examiners lament "superficial knowledge" of the impact of obesity on maternal/obstetric and neonatal complications.

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Obesity in pregnancy is common (affecting approximately a quarter of pregnancies) and increasing in prevalence
Said prevalence is highest amongst minority ethnic groups and those from low socio-economic backgrounds

The definitions of obesity in pregnancy are the same as for the non-pregnant individual i.e. a BMI >30kg/m²
There's no clear guidance on 'optimal' weight gain during pregnancy
Focus on a healthy diet during pregnancy is probably better than setting weight targets
Women should be managed as per the NICE guidelines (2010) on the topic
Anti-obesity or weight loss drugs are not recommended for use in pregnancy
Although booking weight and BMI are often used, one should consider re-weighing patients in the third trimester to more accurately plan equipment, staffing etc. for labour

Maternal complications	Neonatal complications
GDM	Miscarriage
Pregnancy-induced hypertension Pre-eclampsia	Foetal macrosomia Small for gestational age
Cardiovascular disease	Pre-term birth
OSA	Shoulder dystocia
Need for, and failed, instrumental delivery Need for LSCS	Neonatal death NICU admission
PPH	Stillbirth
VTE	Neural tube defects
Anaesthetic complications (see below)	Foetal distress
Longer length of stay
Increased mortality

Peripartum anaesthetic management of the obese parturient

Ante-natal review

Any woman with a BMI >40kg/m² should have a formal consultation with a senior anaesthetist in the third trimester of pregnancy
Ideally early 3^rd trimester to allow time for further investigation and optimisation in event of disease
A plan for delivery should be devised and documented in the patient's notes

History and examination

Focussed history and examination should screen for potential obesity-associated comorbidities
Examination of the spine should identify patients in whom neuraxial intervention could be challenging ± require US of back

System	Anaesthetic complication	Intervention
Airway	↑ risk difficult/failed intubation	Appropriate airway assessment, planning and equipment to manage airway
Respiratory	Reduced FRC, apnoea time and hypoxia OSA Pulmonary HTN Cor pulmonale	Detailed history and screening (STOP-BANG) HFNO at induction if GA
Cardiovascular	HTN IHD CCF Exacerbated effects of aortocaval compression	Focussed cardiac history & investigations Consider cardiology referral Consider prophylactic aspirin
Gastrointestinal	↑ risk of aspiration associated with HH/GORD Insulin resistance and GDM	Starvation timing Pre-medication with prokinetic and antacid Screen for DM & complications ± Endocrine referral + appropriate management in labour
Haematological	Higher rates of VTE	Actual body weight-based dosing of LMWH
Interventional	Difficult IV access Difficulty measuring NIBP Difficulty/failure of neuraxial techniques	Ultrasound available Consider arterial line Early labour epidural

Optimisation & education

MDT planning alongside Obstetric and Midwifery teams
Patient education and counselling, including:

Risk of dysfunctional labour
Higher rate of Caesarean delivery
Need for ultrasound-assisted IV access and epidural placement
Arterial line placement in some cases

Patients should be advised to have an epidural sited early in labour as:

It is likely to be more challenging, requiring multiple attempts, and may be more successful in early labour where pain and movement are less intense
There is a higher rate of failure of epidurals and early placement allows time to ensure it is working appropriately

Logistical planning

Delivery should take place in units with the appropriate staffing, equipment and accessibility to accommodate women with BMI >30kg/m²
BMI >35kg/m² should prompt delivery in consultant-led units with anaesthetic and neonatal services
Specialised anaesthetic equipment should be available:

Difficult airway equipment
Ultrasound
Long spinal and epidural needles
Appropriately sized NIBP cuffs and facility for intra-arterial BP monitoring
Ability to gain central venous access

Neuraxial techniques are ideal for labour analgesia in the obese parturient, benefitting from:

Effective analgesia
Fewest adverse maternal and neonatal effects
Ability to convert to surgical anaesthesia obviating the need for GA

Epidural catheters, CSE or dural puncture-epidural (DPE) remain common techniques

Intrathecal catheters are also an option

Epidural analgesia

Placement can be difficult as excessive subcutaneous tissue makes anatomical landmarks difficult to palpate
Sitting, flexed position and midline insertion is preferred
Ultrasound may be required to help localise the midline, aid estimation of depth to epidural space and reduce the number of attempts required
Long Tuohy needles may be required, but it is still recommended the initial attempt is with a standard needle

The technical difficulties of catheter placement in obesity are associated with:

Increased accidental dural puncture risk (4% vs. 1%)
Increased incidence of PDPH following dural puncture (40 - 45%)
Possible (paradoxical?) protection against PDPH in those with very high BMI (>50kg/m²)

Other neuraxial techniques

Labour CSE provides fast, reliable analgesia without sacral sparing
There is also a lower failure rate of epidural catheters due to correct identification of the epidural space as evidenced by CSF flow on needle-through-needle technique

A dural puncture-epidural technique can also be used
The dura is punctured without administering intrathecal medications, then a catheter is threaded into the epidural space as standard
Compared with standard epidural, there is:

Better sacral spread
Less unilateral/patchy block

Intrathecal catheters may be considered electively in patients with especially high BMI (>50kg/m2) and risk of potentially difficult airway management

Require specific training, impeccable communication antacid protocols for safe management
They carry a 40 - 50% risk of PDPH

Other analgesia

The standard array of pharmacological and non-pharmacological options are available
Opioids should be used judiciously due to high incidence of OSA and risk of respiratory depression - excessive BMI is a relative contraindication to a remifentanil PCA

Patients should be placed in the ramped position with left uterine displacement

This improves respiratory mechanics
It improves laryngeal view vs. traditional sniffing position

Meticulous pressure-point padding as higher incidence of nerve injuries

Cephalad retraction of the pannus to allow Pfannenstiel incision can:

Exacerbate aorto-caval compression
Contribute to respiratory difficult
Increased cephalad spread of spinal block

Neuraxial technique

Always preferred, unless contra-indicated
Single-shot spinal benefits from fast onset and reliable anaesthesia

Finite block duration may be of concern, especially if extra time is required for positioning, and between incision & closure
Dose reductions are not recommended until BMI >50kg/m²; giving a full dose to these patients may result in a high spinal
May be technically challenging, and a needle-through-needle CSE technique may be beneficial

Catheter-based techniques are more common to delivery extended neuraxial anaesthesia e.g. top-up, CSE
The latter may be particularly useful in those with concomitant cardiovascular disease or super-morbidly obese
Thoracic epidural catheters may be placed in addition to lumbar catheters for cases where supra-umbilical, vertical incisions are required for surgical access

GA technique

This carries significant risk, with multiple considerations
Difficult airway equipment should be available

Optimal positioning

Ramped position ± left displacement of uterus
Aims to optimise laryngoscopic view and improve respiratory mechanics by mitigating obesity-induced reductions in FRC

Can reduce challenges associated with inserting laryngoscope blade into women with large breasts
May reduce risk of reflux

Pre-oxygenation with HFNO or even CPAP to achieve ETO₂ >90%
Have two anaesthetists in case of failed/difficult intubation, and familiarity with the OAA/DAS guidelines

Drug dosing

Increased risk of AAGA in obese patients and obstetric surgery (NAP5)
Dose as per SOBA guidelines e.g. rocuronium (IBW), suxamethonium (actual BW)

Aspiration risk is higher at induction and emergence

Decompression with an OG tube prior to extubation should be considered
Extubation should occur in the head-up position, fully awake and able to protect airway

Commencing CPAP immediately post-emergence in patients with OSA who have had a GA may reduce incidence of airway obstruction and hypoxia peri-operatively

Active management of the third stage
There is an increased risk of post-partum complications:

Infection, both surgical site and other
VTE
Respiratory depression
Cardiovascular complications

The focus should be on minimising the risk of developing these e.g. prophylactic antibiotics at surgery, appropriate VTE prophylaxis or monitoring in an HDU environment

Analgesia

Optimum analgesia will improve respiratory mechanics, mobilisation and reduce VTE risk
Multi-modal analgesia should be employed:

Regular simple analgesia
Long-acting neuraxial opioid e.g. morphine/diamorphine
If no neuraxial opioids, consider parenteral opioids e.g. PCA
Regional anaesthetic techniques including TAP or QL blocks