Regional Anaesthesia for Caesarean Section in the Morbidly Obese Patient.
Major regional blockade in the morbidly obese is complicated by a number of factors:
1. Psychological 'make-up' of the morbidly obese.
Contrary to the popular image of the plump, jovial matron these women often feel guilty about their physical condition and body configuration, depressed about anticipated problems with childbirth and infant rearing and, sometimes, hostile and defensive to an anaesthetist encountering genuine technical difficulty.
2. Effect of associated diseases.
Fatty accumulation in the liver can produce a pro-coagulant deficiency coagulopathy. These patients are also more prone to pregnancy-induced hypertension, gestational diabetes, failure to progress, shoulder dystocia, hiatus hernia, coronary artery disease and diabetes (Chapter 81) (2).
3. Difficulty may be encountered in gaining vascular access, in non-invasively measuring systemic arterial pressure, in assessing the airway and in adequately monitoring these parturients (2, 8, 11).
4. Inability to identify landmarks.
Often, it is impossible to identify any bony landmarks whatsoever in the lumbar area because of the presence of a lumbar fat pad.
If the left lateral position is to be used, the location of any vertebral spinous processes (even C7) should be marked prior to scrubbing as this will assist in identifying the midline. It may also be preferable to dispense with drapes (and to 'prep' a wider area than usual) to allow better recognition of the midline. An assistant may be required to pull the right lumbar fat pad upwards to reveal the midline.
5. Difficulty with appropriately positioning the parturient (2).
As it may be difficult to move these patients once motor block has been established, it may be appropriate to place the epidural catheter but not inject any local anaesthetic, until the patient has assumed an appropriate position.
Sometimes, the sitting position is preferable because this allows the back and buttock fat to fall away from the midline and to gain an idea of where the midline lies in the absence of bony landmarks.
6. Technical difficulty with placement of the regional blocks, (5, 10)
Obese women have a tendency to thoraco-lumbar Iordosis which can make an already technically difficult block even more difficult.
7. Erratic spread of the local anaesthetic solution. (1)
For any given dose of local anaesthetic, a higher level of epidural block (in proportion to the degree of obesity) can be anticipated (1).
8. Insufficiently long spinal, CSE and epidural needles.
Long (12cm) or extra-long (18 and 20cm) needles may be necessary to gain access to the epidural or subarachnoid spaces. In the massively obese, the effective length of a standard epidural needle is reduced by ~0.5-1.0cm if the Weiss flange wings are attached to the Tuohy-Borst epidural needle.
Even after a satisfactory regional block is achieved, Caesarean Section is not without hazard because of:
1. Difficulty breathing in the supine 'wedged' position, especially if head down tilt or Trendelenburg is employed (6). These patients already have increased oxygen requirement, increased work of breathing and abnormal chest wall compliance and reduced expiratory reserve volume and functional residual capacity. Pregnancy produces a worsening of respiratory function and the assumption of the supine position reduces the functional residual capacity even further (2, 3). Hypoxaemia is common (3) (Chapter 87). Administration of supplemental oxygen, 5-10 degrees reverse Trendelenburg and a large pillow under the head will go a long way towards reversing some of the respiratory abnormalities.
2. Inability to position the patient on a standard operating table (7, 9).
Two anchored standard width 50cm operating tables with arm boards may be necessary before caesarean section can commence.
3. Reluctance of staff to shift or lift these patients once they are unable to move themselves when the regional block takes effect (2).
4. Difficulty with surgical access produced by a large panniculus (4). There is still considerable debate as to whether a transverse incision or a vertical Caesarean incision is best, but most agree that a low suprapubic transverse incision (in the skin fold) is contraindicated (1).
5. Postoperative complications including bleeding, inadequate analgesia, deep vein thrombosis, hypoxaemia and myocardial ischaemia (6, 7, 8, 9).
The morbidly obese parturient should always be considered to be at high risk.
8. Vaughan R: Anesthetic Management of the Morbidly Obese Patient. Contemp Anes Practice 5:71-94, 1982.
9. Sicuranza B, Tisdall L: Cesarean Section in the Massively Obese. J Reprod Med 14:1:10-11,1975.
10. Ogden P: Failure of Intravenous Regional Analgesia using a Double Cuff Tourniquet. Anaes 39:5:456-459, 1984.
11. Burch GE: Sphygmomanometric Cuff Size and Blood Pressure Recordings. JAMA 225:1215, 1973.