A reduced rate of endochondreal ossification in association with normal periosteal bone formation4 results in the characteristic
appearance of achondroplastic dwarfs: short stature with proximal limb shortening; large head with frontal bossing, flattened nasal bridge and maxillary hypoplasia as well as spinal deformities in the form of lumbar hyperlordosis and thoracolumbar kyphosis.1
The brachycephalic large head, facial features, large tongue and narrow upper airway predispose these patients to upper airway obstruction and obstructive sleep apnoea.1,4,5 There are
also several case reports of difficult laryngoscopy and tracheal intubation6-8 but Mayhew, Katz, Miner et al. encountered no
difficulty in the airway management of 26 achondroplastic patients presenting for 37 general anaesthetics.4 It is however
important to note that none of the 26 patients were pregnant. Proximal spinal cord compression caused by foramen magnum stenosis may result in central apnoea in patients with achondroplasia1 and hyperextension of the neck should always
be avoided.3 This limitation of neck extension may contribute to
the difficulties encountered in tracheal intubation.6,7 It has also
been postulated that the increased incidence of hydrocephalus in achondroplastic patients may be due to reduced cerebrospinal fluid flow at the level of the foramen magnum stenosis.1
Numerous other spinal abnormalities in patients with achondroplasia may result in neuraxial anaesthesia being very difficult to perform. Bony landmarks are often difficult to identify due to the lumbar hyperlordosis and thoracic kyphoscoliosis.9
Abnormally shaped vertebrae and hyperplastic discs result in smaller than usual epidural and subarachnoid spaces.1 This
may result in difficulties in identifying the epidural space as well as difficulties in feeding epidural catheters. Accidental dural puncture is also more common and more difficult to identify.9Engorged epidural veins increase the risk of venous
puncture and contribute to the unpredictable spread of local anaesthetic.10
The kyphoscoliosis and lumbar hyperlordosis commonly seen in patients with achondroplasia may lead to restrictive pulmonary dysfunction characterized by reduced vital capacity and reduced functional residual capacity.1 The restrictive lung disease as
well as the upper airway obstruction and sleep apnoea may contribute to the development of pulmonary hypertension and cor pulmonale.1 In pregnant achondroplastic patients the
foetal head often cannot engage in the narrow pelvis. As a result the uterus remains entirely intra-abdominal and splints the diaphragm, further reducing the functional residual capacity.9
The haemodynamic effects of aorto-caval compression by the intra-abdominal uterus are also likely to be more pronounced especially with neuraxial anaesthesia.3,10
Anaesthetic technique
The anaesthetic management of a patient with achondroplasia presents unique challenges to the anaesthetist. The addition of the anaesthetic risks associated with the third trimester of pregnancy mandates meticulous planning by a multidisciplinary team consisting of anaesthetists, obstetricians, neonatologists and midwives. A thorough preoperative workup of the patient is essential.
Historically, despite the potential difficulties associated with the airway management of achondroplastic patients, general anaesthesia has been favoured over regional anaesthesia.7
Southern African Journal of Anaesthesia and Analgesia 2017; 23(2)(Supplement 1) 148
being performed under regional anaesthesia in patients with achondroplasia.3,9,11,12
Due to the proximal limb shortening, non-invasive blood pressure monitoring may be difficult.3 Peripheral intra-arterial
blood pressure monitoring should be considered in anticipation of the more pronounced haemodynamic effects of aorto-caval compression. The placement of peripheral lines may be more difficult due to the presence of excess skin and soft tissue, and the landmarks for the placement of central venous catheters may be more difficult to identify.4The main concern with providing
general anaesthesia to pregnant patients with achondroplasia is the potential difficulty of the airway management. Aspiration prophylaxis should always be administered but sedative premedication is contraindicated in patients with central or obstructive sleep apnoea. A meticulous airway management plan should be in place and excessive extension of the neck should always be avoided.3 The endotracheal tube size should
be reduced and should be based on the patient’s weight.4 If
significant thoracolumbar kyphosis is present, cardio-respiratory
function may be compromised2 and ventilation may be
problematic.
All anaesthetic drugs should be dosed according to the patient’s weight as the use of average adult dosages will possibly result in overdosing.13The anatomical abnormalities present in the
thoracolumbar spine may make regional anaesthesia technically more difficult in patients with achondroplasia and the risk of complications is increased due to the smaller than usual epidural and subarachnoid spaces.8,11 Due to the unpredictable spread of
local anaesthesia, there are no epidural dosage guidelines. The volume of the test dose should be reduced and local anaesthesia should be titrated against the block height in small incremental doses.9 Wardall and Frame reported that a dose of only 5 ml of
0.5% plain bupivacaine produced a block to T4 in a pregnant patient with achondroplasia.10 The slow onset of bupivacaine
makes it difficult to titrate precisely and it has been suggested that the use of a local anaesthetic with shorter onset time may be more appropriate.3 Carstoniu, Yee and Halpern gave a test dose
of 1 ml lidocaine 2% with epinephrine 1:200 000 as a test dose. 5 minutes later they administered 3 2 ml doses of the same solution at 3 minute intervals followed by a 1 ml bolus together with 50 µg fentanyl prior to skin incision. A T5 level was established.11
As epidural anaesthesia allows for titration of the local anaesthetic, it is preferred to spinal anaesthesia. However, the titration of dose to block height is time consuming and epidural anaesthesia may not be ideal in patients presenting for emergency Caesarean section. There are only a few case reports of the successful use of spinal anaesthesia for Caesarean section in patients with achondroplasia. Ravenscroft, Govender and Rout reduced their standard subarachnoid dosage regime
for emergency Caesarean section by 30% and produced a block to T3.12 Osorio Rudas, Socha García, Upegui et al. administered
5 mg of hyperbaric bupivacaine together with 64 µg of morphine and 16 µg of fentanyl into the subarachnoid space as part of a combined spinal epidural technique and produced a sensory block up to T4.14 Crawford and Dutton recommend
the use of microspinal catheters and the administration of incremental doses of local anaesthetic, if spinal anaesthesia is to be considered.15
Irrespective of which neuraxial technique is used, the haemodynamic effects of aorto-caval compression may be more severe than in patients who do not have achondroplasia and should be aggressively managed.
Summary
The management of a pregnant patient with achondroplasia requires a multidisciplinary team approach. After a thorough preoperative assessment of the patient a meticulous anaesthesia plan needs to be devised. Both general and regional anaesthesia pose significant risk to patients with achondroplasia, especially during the third trimester of pregnancy, and management plans need to be individualized.
References
1. Berkowitz ID, Raja SN, Bender KS, Kopits SE. Dwarfs: Pathophysiology and Anesthetic Implications. Anesthesiology. 1990;73(4):739-59.
2. Dubiel L, Scott G, Agaram R, McGrady E, Duncan A, Litchfield K. Achondroplasia: anaesthetic challenges for caesarean section. Int J Obstet Anesth. 2014;23(3):274-8.
3. Brimacombe J, Caunt J. Anaesthesia in a gravid achondroplastic dwarf. Anaesthesia. 1990;45(2):132-4.
4. Mayhew JF, Katz J, Miner M, Leiman B, Hall ID. Anaesthesia for the achondroplastic dwarf. Can J Anesth. 1986;33(2):216-21.
5. Krishnan B, Eipe N, Korula G. Anaesthetic management of a patient with achondroplasia. Pediatr Anesth. 2003;13(6):547-9.
6. Mather J. Impossible direct laryngoscopy in achondroplasia. Anaesthesia. 1966;21(2):244-8.
7. Walts LF, Finerman G, Wyatt GM. Anaesthesia for dwarfs and other patients of pathological small stature. Can J Anesth. 1975;22(6):703-9.
8. Huang J, Babins N. Anesthesia for cesarean delivery in an achondroplastic dwarf: a case report. AANA J. 2008;76(6):435.
9. Morrow M, Black I. Epidural anaesthesia for caesarean section in an achondroplastic dwarf. Br J Anaesth. 1998;81(4):619-21.
10. Wardall G, Frame W. Extradural anaesthesia for caesarean section in achondroplasia. Br J Anaesth. 1990;64(3):367-70.
11. Carstoniu J, Yee I, Halpern S. Epidural anaesthesia for caesarean section in an achondroplastic dwarf. Can J Anaesth. 1992;39(7):708.
12. Ravenscroft A, Govender T, Rout C. Spinal anaesthesia for emergency caesarean section in an achondroplastic dwarf. Anaesthesia. 1998;53(12):1236-7.
13. Kalla G, Fening E, Obiaya M. Anaesthetic management of achondroplasia. Br J Anaesth. 1986;58(1):117-9.
14. Osorio Rudas W, Socha García NI, Upegui A, Ríos Medina Á, Moran A, Aguirre Ospina O, et al. Anesthesia for cesarean section in a patient with achondroplasia. Revista Colombiana de Anestesiología. 2012;40(4):309-12.
15. Crawford M, Dutton D. Spinal anaesthesia for caesarean section in an achondroplastic dwarf. Anaesthesia. 1992;47(11):1007-.
© 2017 The Author(s) FCA 2 REFRESHER COURSE Open Access article distributed under the terms of the
Creative Commons License [CC BY-NC-ND 4.0] http://creativecommons.org/licenses/by-nc-nd/4.0