Scoliosis Surgery

Question 1

A 13-year-old male patient is undergoing spinal surgery for correction of
his scoliosis.

What is scoliosis?

Answer 1

• Scoliosis is a condition defined by lateral curvature of the spine with varying degrees of rotation. There may be associated deformity of the rib cage.
• Scoliosis involves other body systems, principally the respiratory and cardiovascular systems.

Question 2

What are the potential causes of scoliosis in this patient?

Answer 2

• Idiopathic (about 70% of patients).
• Congenital.
• Secondary to neuromuscular disorders e.g. cerebral palsy, muscular
  dystrophy.

Question 3

What are the complications and implications for anaesthesia in patients with an uncorrected scoliosis?

A, B…?

Answer 3

Airway:
* Airway difficulties may occur where the scoliosis involves the upper thoracic or cervical spine.

• Devices such as halo traction may make intubation more challenging.

Respiratory:
* Restrictive lung disease and poor pulmonary function due to limited lung and diaphragmatic movement. This may result in alveolar hypoventilation, ventilation-perfusion mismatch, increased dead-space and a reduced total lung capacity.

• In patients with neuromuscular disorders, patients may also have
  further respiratory muscle dysfunction.
• The respiratory complications outlined above necessitate a thorough history, examination and appropriate investigations preoperatively (including pulmonary function tests) to assess the disease severity and the ability of the patient to tolerate a general anaesthetic. Patients may require preoperative chest physiotherapy.
• Patients with increased curvature and more significant pulmonary sequelae are likely to need a longer period of ventilation postoperatively.
• Long-term restrictive lung dysfunction may lead to a chronic type II respiratory failure and right-sided cardiac disease.

Question 4

What are the complications and implications for anaesthesia in patients with an uncorrected scoliosis?

C, D….?

Answer 4

Cardiac:
* The primary cause of cardiac dysfunction in scoliosis patients occurs secondary to severe lung disease, but patients with congenital or neuromuscular disorders may also present with structural cardiac defects or cardiomyopathies.

• Severe curvature may distort the mediastinum causing a restrictive pericarditis, impaired ventricular filling and a fixed cardiac output state.
• The preoperative anaesthetic assessment should include a detailed cardiac history and examination, and further investigations as directed by the initial findings.

Other
* Patients with scoliosis secondary to congenital or neuromuscular disorders may also have significant comorbidities including cognitive dysfunction, learning difficulties, generalised muscular spasticity or atrophy, and bowel dysfunction. These need to be considered when formulating the anaesthetic plan.

Question 5

The patient in question has idiopathic scoliosis, mild restrictive lung disease and no signs of right-sided cardiac failure. What are your key concerns when anaesthetising this patient?

Answer 5

• Positioning: This depends on whether a posterior or anterior approach is used. In the posterior approach, the prone position will be employed, requiring satisfactory patient padding and support to prevent pressure sores. A reinforced endotracheal tube will need to be correctly checked and secured, and the eyes should also be well protected with padding and goggles. With an anterior approach, the patient will be supine with the spinae accessed via a thoracotomy.
• Blood loss: Anaemia should be corrected prior to surgery. There is a known risk of major haemorrhage in spinal surgery, so tranexamic acid and cell salvage are routinely used. Large bore intravenous access should be easily accessible. Increases in intra-abdominal pressure should be minimised due to the risk of epidural vein engorgement contributing to additional blood loss.

Question 6

Key concerns continued….?

Answer 6

• Intraoperative monitoring: AAGBI monitoring should be in place together with invasive blood pressure, central venous pressure and cardiac output monitoring. EEG monitoring should be used where a TIVA anaesthetic technique is employed. Specialist nerve monitoring is also essential to identify and prevent damage to the spinal cord – both somatosensory and motor-evoked potentials are commonly performed.
• Duration of surgery: Prolonged procedural time means that temperature monitoring and warming are essential, particularly given the risk of blood loss and patient exposure.

Question 7

How do anaesthetic agents affect neuromuscular monitoring?

Answer 7

• Volatile agents (at >0.5 MAC) affect both somatosensory and motor- evoked potentials.
• Neuromuscular blocking agents affect motor-evoked potentials.
• Propofol had a dose-dependent increase in effect on motor-evoked
  potentials.
• Opioid agents have no effect on either somatosensory or motor-
  evoked potentials.

Question 8

What is the wake-up test?

Answer 8

• The wake-up test involves lightening anaesthesia to the point at which the patient is able to respond to commands, and this procedure is done after spinal rod placement to ensure that nerve function has been preserved.
• It is not routine, particularly with the use of neuromuscular monitoring.