Joan E. Spiegel, MD
Assistant Professor
Beth Israel Deaconess Medical Center
Harvard Medical School
Boston, Massachusetts
Editorial Advisory Board Member, Anesthesiology News
Matthew Hellman, MD
Clinical Fellow in Anesthesiology
Beth Israel Deaconess Medical Center
Boston, Massachusetts
Achondroplasia is the most common cause of dwarfism. As a genetic disorder of skeletal dysplasia, it literally translates to “without cartilage formation.” Affected patients fail to achieve a height of 148 cm by adulthood, and have a typical appearance of shortened limbs and a large head in comparison with body size. Midgets, by contrast, are proportionately small.
Achondroplasia is observed in approximately 1 to 1.5 of every 10,000 births as a result of a spontaneous fibroblast growth factor receptor gene mutation. Therefore, most achondroplastic patients will have parents of normal height. Achondroplasia is also transmitted in an autosomal dominant fashion. As a result of inhibition of cartilage formation, there is premature ossification in the epiphyseal growth plates with concurrent restriction of growth. Clinically, patients will have deformations of the spine and airway, and hypoplasia of structures of the head. The functioning of many organ systems can be affected by achondroplasia, but intelligence and life expectancy are usually normal. The safe delivery of an anesthetic requires an understanding of this disorder and the particular pathophysiology of the patient undergoing surgery.
Anatomy in Dwarfism
Major anatomic differences can create difficulties in the anesthetic management of achondroplastic dwarfs (Table). Airway abnormalities include narrowed nasal passages from mucopolysaccharide deposition, tracheal narrowing, sternal prominence, pharyngeal and maxillary hypoplasia, and thickening of pharyngeal and laryngeal structures. Laryngomalacia can spontaneously cause stridor, whereas subglottic stenosis has been reported to necessitate tracheostomy. Patients may have a large tongue, tonsils, and adenoids along with a stiff temporomandibular joint. An estimated 40% of patients with achondroplasia have obstructive sleep apnea, even in childhood.
Spinal deformations in achondroplasia include a short neck, odontoid hypoplasia, thoracolumbar kyphosis, pelvic narrowing, lordosis, and moderate to severe spinal stenosis. The narrowing of the spinal column can result in cauda equina syndrome, nerve root compression, thoracolumbar spinal cord compression, or, rarely, high cervical cord compression secondary to stenosis of the foramen magnum.
Quadriplegia resulted in a patient with dwarfism and severe kyphosis after surgery, and in an infant with achondroplasia with foramen magnum stenosis secondary to normal range of motion of the neck resulting in atlantoaxial subluxation. The concave shape of the occipital bone may prevent optimal positioning for intubation due to entrapment of the atlas. Additionally, high cervical stenosis or foramen magnum stenosis can cause central sleep apnea. Respiratory function may be impaired from having a small rib cage, obesity, and spinal deformations.
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Surgical Optimization
Achondroplastic dwarfs must be carefully assessed before undergoing anesthesia, ideally in a preoperative testing center with sufficient time for any workup, if needed. As previously mentioned, contributions to airway difficulties include anatomic differences in both airway structure and stability.
Thoracolumbar anatomic differences such as severe scoliosis and rib cage deformities resulting in restrictive lung diseases, pulmonary hypertension, cor pulmonale, and heart disease may warrant echocardiography, pulmonary function tests, chest radiography, and a baseline blood gas analysis. Patients with severe sleep apnea and/or chronic respiratory illnesses may require consultation with an otolaryngologist to identify airway anomalies.
Flexion–extension lateral cervical spine radiographs as well as a view of the odontoid process should be standard due to the risk for atlantoaxial subluxation secondary to odontoid hypoplasia. MRI or CT scanning should be considered if radiographs fail to provide adequate imaging before surgery, or if there is concern for high cervical stenosis or foramen magnum stenosis. All neurologic symptoms necessitate further consultation and workup before elective surgery.
Airway Management
Previous airway management records should be obtained when possible. Pharyngeal and maxillary hypoplasia along with narrow nasal passages and an enlarged tongue can cause problems with routine laryngoscopy. Thus, awake FOI is probably the safest method of securing the airway, but direct laryngoscopy has been reportedly successful. There are reports of minimal problems with masking, ventilating, and intubating these patients when appropriately sized—usually smaller—airway adjuncts are used.
The concern for atlantoaxial instability and alterations in the base of the skull may suggest the use of in-line stabilization with video laryngoscopy. Awake intubation with a GlideScope (Verathon) is not recommended, as these patients suffer from high levels of anxiety, making sedation and compliance difficult. Administering an anticholinergic drug before intubation may aid in the identification of airway structures because hypersalivation is frequently encountered. Laryngeal mask airways are still very much a part of the difficult airway algorithm; however, pediatric-sized LMAs should be readily available.
Ventilatory difficulty with LMAs may be encountered if underlying pulmonary disease is present, or if a distorted airway prevents an optimal fit. Careful attention should be paid to respiratory rate and tidal volume, as lung anatomy and function may be significantly reduced.
Regional Anesthesia
Neuraxial regional anesthesia in achondroplastic dwarfs may prove difficult, impossible, or perhaps dangerous—even for the experienced provider. Patients with achondroplasia are known to have narrowed and stenosed spinal canals, decreased distances between lumbar pedicles, kyphoscoliosis, osteophyte formation, engorged epidural veins, and a reduced epidural space. There may be difficulty in advancing catheters, unpredictable and patchy or high spread of anesthesia, and increased risk for venous and dural puncture.
Epidural anesthesia is preferred over spinal anesthesia, as careful titration is desirable. Unintentional dural puncture may be difficult to detect in the setting of severe spinal stenosis because of low or absent cerebrospinal fluid.
Clear dosage recommendations are lacking for neuraxial procedures in patients with achondroplasia. Peripheral nerve blocks can be performed following careful documentation of preexisting abnormalities. Chronic pain syndromes are encountered more commonly in achondroplasia as a result of bony malformations.
Obstetric Considerations
Pregnancy is an especially high-risk condition for achondroplastic dwarfs. Thoracic structural abnormalities with potential restrictive lung function cause a further reduction in the functional residual capacity normally seen in parturients, resulting in exaggerated shunts and ventilation/perfusion mismatch. This limited pulmonary reserve, coupled with the even greater airway management difficulty in a parturient with achondroplasia, warrants early scheduled cesarean delivery to avoid emergent airway intervention.
Obstetric patients with achondroplasia have a very high rate of elective cesarean deliveries due to the likelihood of a cephalopelvic disproportion in those with a contracted pelvis, a common coexisting condition. A carefully titrated epidural is the preferred anesthetic for these patients. However, any neuraxial choice can be complicated by high-level, patchy, or incomplete neuraxial spread of the anesthetic.
There are a handful of cases in the literature documenting the safe administration of spinal anesthesia for cesarean delivery. In one case, a standard amount of medication (12 mg of hyperbaric bupivacaine, 25 mcg of fentanyl, and 0.3 mg of morphine) was used without creating too high a level.
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Conclusion
Achondroplastic dwarfism presents many anesthetic challenges, and deaths have been reported despite careful preparation. The anatomic variations and their effects on organ systems and airway management can make these patients unexpectedly difficult to manage. The prevalence of achondroplasia makes it likely that most anesthesia providers will encounter one of these patients at least once. An understanding of the pathophysiology of these patients, careful preparation, and communication of the anesthetic plan with the surgical team are essential components of perioperative management.
Additional Reading
- Berkowitz ID, Raja SN, Bender KS, et al. Dwarfs: pathophysiology and anesthetic implications. Anesthesiology. 1990;73(4):739-759.
- Cevik B, Colakoglu S. Anesthetic management of achondroplastic dwarf undergoing cesarean section—a case report.Middle East J Anaesthesiol. 2010:20(6):907-910.
- Jain A, Jain K, Makkar JK, et al. Anaesthetic management of an achondroplastic dwarf undergoing radical nephrectomy—a case report.South Afr J Anaesth Analg. 2010;16(2):77-79.
- Krishnan BS, Eipe N, Korula G. Anaesthetic management of a patient with achondroplasia.Paediatr Anaesth. 2003;13(6):547-549.
- Mayhew JF, Katz J, Miner M, et al. Anaesthesia for the achondroplastic dwarf.Can Anaesth Soc J. 1986;33(2):216-221.
- Oppitz F, Speulda E. Anesthesia recommendations for patients suffering from achondroplasia.orpha.net/data/patho/Pro/en/Achondroplasia_EN.pdf. Accessed June 30, 2015.
- Mitra S, Dey N, Gomber KK. Emergency cesarean section in a patient with achondroplasia: an anesthetic dilemma.J Anesth Clin Pharmacol. 2007;23(3):315-318.
- Tetzlaff J, Benedetto P. Skin and bone disorders. In: Fleisher L, ed.Anesthesia and Uncommon Diseases, 6th Edition. Philadelphia, PA: Saunders; 2012.