Dyggve-Melchior-Clausen (DMC) syndrome is a rare, autosomal recessive skeletal dysplasia characterised by spondyloepimetaphyseal dysplasia, microcephaly, mental retardation and coarse facies.1 In Smith-McCort dysplasia (SMC), a rare variant of DMC, the patients have normal intelligence.2,3 We present the airway problems in a patient with SMC undergoing surgery for atlanto-axial dislocation. The patient's mother has kindly given consent for publication.
An 18-year-old man, weighing 16 kg presented with complaints of neck pain and stiffness with associated weakness of lower limbs. The patient was 92 cm tall with a head circumference of 51 cm and normal intelligence. He had delayed developmental milestones and mouth breathing. Past medical history included uneventful surgery for repair of an inguinal hernia. He was scheduled for C1–C2 lateral mass fusion, foramen magnum decompression and C1 arch excision.
On examination, he had hyperteleorism, collapsed nasal bridge, short neck, bilateral cubitus valgus deformity, short limbs, rocker bottom feet and thoracic kyphoscoliosis. He had grade 4/5 muscle power with hypertonia in the lower limbs. The patient had a large tongue, short neck, maloccluded teeth, with a modified Mallampati grade 4 airway, a thyromental distance of 4 cm and mouth opening of 4 cm. Chest expansion at rest was only 1.5 cm. His full blood count, serum biochemistry and ECG were all normal. A transthoracic echocardiogram showed mitral valve prolapse (grade 1), mitral regurgitation with trivial aortic regurgitation and an ejection fraction of 60%. Radiographic examination showed wide and severely osteoporotic ribs, C1–C2 dislocation that was reducible on extension and D12-L1 kyphoangulation with thoracic kyphoscoliosis. An MRI scan revealed spinal cord compression at C1 level. Pulmonary function tests (PFTs) revealed a forced vital capacity of 0.36 l, forced expiratory volume in 1 second of 0.36 l and peak expiratory flow rate of 65 l min−.1 Autonomic function tests were normal, although DBP increase on isometric hand grip test was less than 15%. The patient's baseline oxygen saturation in room air was 91%.
An awake fibreoptic intubation was planned. The airway was anaesthetised by nebulised lignocaine 4% and 10% lignocaine spray. Awake intubation was attempted with a 4.2 mm fibreoptic bronchoscope (Hoya-Pentax, Shinjuku, Japan) loaded with a 7.0 mm internal diameter reinforced endotracheal tube (ETT). On multiple attempts, the bronchoscope entered the trachea, but the ETT could not be advanced further. The patient had episodes of oxygen desaturation requiring mask ventilation. As mouth opening seemed adequate and mask ventilation was possible, direct laryngoscopy was attempted under propofol sedation. The laryngoscopic view was Cormack and Lehane grade II. Attempted tracheal intubation with reinforced ETTs of sizes 6.5, 6.0 and 5.5 mm internal diameter was not successful. However, the trachea could be intubated with a 5.0 mm internal diameter ETT (Rusch, Teleflex Medical, Limerick, PA, USA). The patient was subsequently positioned prone for surgery. Anaesthesia was maintained with oxygen, nitrous oxide, isoflurane, morphine and intermittent doses of vecuronium. Intraoperatively, airway pressures were around 22 to 25 cm H2O and the end-tidal carbon dioxide pressure between 4.0 and 4.2 kPa.
After uneventful surgery and reversal of residual neuromuscular block, the patient was drowsy but obeying commands. Although muscle power was satisfactory, the trachea was not extubated in view of multiple attempts at intubation and associated desaturation. Mechanical ventilation was continued in the ICU. Over the next few days, the patient developed bronchospasm, chest infection and one episode of focal seizures, which were managed appropriately. As multiple attempts at weaning failed, a decision for tracheostomy was made to facilitate long-term ventilation. Due to the patient's short neck, locating the trachea was difficult, which culminated in a low lying tracheostomy. A 5 mm uncuffed tracheostomy tube, which was shortened distally (to prevent endobronchial placement), was inserted. A high risk of accidental decannulation and difficult reinsertion was anticipated; hence, maturation sutures were taken from the wall of tracheal stoma. Six hours later, the tracheostomy tube got misplaced. Despite pulling the tracheal sutures, the tracheal stoma could not be located. Orotracheal intubation was attempted but was unsuccessful, as the patient had undergone posterior fusion of cervical spine, which restricted the neck movements. Ventilation through a laryngeal mask airway (LMA) failed and the patient succumbed to hypoxia.
DMC is characterised by generalised bony dysplasia leading to short-trunked dwarfism, kyphoscolisis, protubrent abdomen, limited extension at various joints, rhizomelic shortening of limbs, macroglossia, flared ribs with widened costochondral junctions and pectus carinatum.1 DMC usually includes moderate to severe mental retardation and patients may also have a hypoplastic odontoid process.4 Atlanto-axial dislocation is a serious complication of this syndrome.5 DMC results from a mutation in DYM gene mapped in 18q12–12.1 chromosomal region.6
We made an error in estimating the ETT size based on the patient's age. Using the patient's height for calculating ETT size (formula: 2 + height in cm/30 = 5 mm internal diameter), we could have arrived at the correct size of the ETT. Measurement of minimal transverse diameter of the subglottic airway can guide correct choice of ETT. A large tongue added to the difficulty in intubation. Severe restrictive lung disease led to a poor respiratory reserve. Surprisingly, on direct laryngoscopy, vocal cords could be visualised, but intubation could be achieved with only a very narrow ETT. Eguchi et al.7 did not find any airway difficulty in their patient with DMC undergoing resection arthroplasty.
Maintaining the tracheostomy in place was another major challenge. The patient succumbed to hypoxia caused by our inability to reposition the displaced tracheostomy tube. Staff education decreased accidental decannulation from 4.2 ±0.9/1000 tracheostomy days to 2.7 ± 1.9/1000 in one study.8 Identification of patients at high risk of difficult airway management, having more than one caregiver during turning or moving of the patient, and the availability of a spare tracheostomy tube and minitracheostomy kit at bedside are some measures that may decrease the adverse impact of accidental decannulation. Implementation of these measures might have prevented the mishap.
In retrospect, errors in certain critical decisions caused an unfavourable outcome in our patient. The incorrect choice of fibreoptic bronchoscope and ETT, and early tracheostomy without due consideration of abnormal airway anatomy, were all contributing factors.
This report highlights two practical issues in the airway management of a patient with SMC. Firstly, laryngoscopy may not be difficult, but there may be a need for a small ETT. Secondly, airway abnormalities make it difficult to retain a tracheostomy tube in place.
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