Anesthesia Considerations for Craniofacial Surgery
Craniofacial surgery mainly consists of management of congenital craniofacial deformities like craniofacial clefts, craniosynostosis and craniofacial syndromes, but the same principles also apply to trauma as well as tumors of the ‘skull base’. Children with craniofacial abnormalities provide several challenges to an anesthesiologist. Most procedures are elective and the ideal age for surgical correction is usually between 3 to 10 months which is also the period when ‘physiological anemia of infancy’ might be present. Overall improvements in anesthesia techniques, availability of newer drugs and monitoring modalities have contributed in making more complex surgeries possible with relatively less mortality and morbidity.
Pre-operative Assessment: History taking should include an enquiry about allergies, snoring, sleep apnea, recent respiratory infection, convulsions, current medications and previous anesthesia and surgical procedures. During the pre-anesthetic visit, apart from a routine general health check-up, special attention should be paid to nutritional deficiency, detailed airway assessment, vascular access, neurodevelpomental status and other associated anomalies. Presence of choanal atresia, palatal deformities, a retroposed receding mandible with a relatively large tongue, presence of a large encephalocele, etc. can make the tracheal intubation difficult. Spinal deformities like atlanto-axial dislocation, Klippel–Feil syndrome etc. can also lead to difficulties in intubation (ICP). Children with uncorrected craniosynostosis may have increased intracranial pressure, decreased cerebral perfusion pressure and delayed neurological development. Besides, these children are prone to repeated respiratory tract infections and obstructive respiratory symptoms, particularly during sleep. Both these can produce pulmonary hypertension and cor-pumonale. Therefore a perioperative antibiotic cover is advisable. Anticonvulsant therapy is usually started 4-5 days prior to surgery. They are also prone to respiratory depression following opioids and sedatives.
Preoperative investigations include complete blood count and a hemoglobin level of more than 10 gms% is considered essential for major reconstructive surgery. A normal coagulation profile must be ensured. Other investigations include blood urea nitrogen and in case of preoperative diuretic therapy for raised intracranial pressure (ICP), serum electrolytes should be estimated. An X-ray chest should be done to assess the heart shadow and lung fields and X-ray spine may be needed to identify spine abnormalities. Arterial blood gases, electrocardiogram and echocardiography may be needed for patients with pulmonary a compromise or suspected cardiac anomalies. At least 3 units of cross matched packed cells (approximately 1000 cc) are kept available before surgery.
Premedication: The children are kept nil per oral for 4-6 hours preoperatively and premedication with sedatives in an unsupervised area is avoided for fear of airway obstruction or raised ICP. An antisialagogue agent like glycopyrrolate is given to dry out oral secretions. In absence of an airway abnormality, syrup midazolam may be given to alley anxiety with an anesthesiologist monitoring the child’s response.
Introperative monitoring commonly includes electrocardiography, pulse oximetry, end tidal carbon dioxide monitoring, arterial blood pressure, urine output and ‘core temperature’ monitoring. Use of invasive arterial blood pressure and central venous pressure are individualized as per the case.
Choice of Anaesthetic drugs: Usually intravenous induction is preferred in presence of increased intracranial pressure and a rapid and short acting inhalational agent like sevoflurane may be preferred in cases of difficult airway. Mostly individual drug choices are not important, but a ‘balanced general anesthesia’ using drugs which are short acting and easily titrable, and those not causing an increase in ICP are preferred.
Airway Management: A difficult tracheal intubation is commonly anticipated in most cases, particularly in craniofacial syndromic infants, special airway equipments like oropharyngeal airways, special laryngoscopes (including fiberoptic) for some cases, intubating stylets and supraglottic airway devices may be needed. A patient with a difficult airway is typically not paralysed till controlled effective ventilation with a mask is assured. Tracheostomy is avoided and if it is needed, it must be done by a person with experience in pediatric patients. An oral reinforced tube or a south preformed curved tube is used to preserve facial symmetry. A pharyngeal pack is needed as oral bleeding or a CSF trickle may occur. A silicone tube with a soft seal tracheal cuff may offer some advantage against pulmonary aspiration. Special attention should be paid to fixing the tube as the position of the head may be changed frequently leading to accidental extubation or endobronchial migration.
Positioning: The patient needs to be carefully positioned. His/her pressure points are protected with a padding to avoid ischemic injury. In prone or lateral positions appropriate size soft bolsters should be used to distribute weight evenly without compressing the abdomen or the neck. The limbs should be positioned without stretching any nerves as the procedures may be prolonged. Access to the patient and the lines under the drapes must be ensured before surgery commences. A perioperative tarsorrhaphy may be needed to protect proptotic eyes.
Fluid and Blood Loss: Meticulous attention must be provided to fluid homeostasis. There can be extensive blood loss and third space fluid loss from the scalp and the cranium and therefore venous access should be secured using at least 2 large bore lines. Invasive arterial pressure monitoring is needed for more complex procedures. About 6-8 ml/kg/hour or more isotonic fluid replacement is needed and blood loss should be replaced with packed red blood cells. Estimation of blood loss is difficult due to loss on the drapes and fluid irrigation. In addition to hemodynamic parameters, central venous pressure and monitoring of urine output help to estimate circulating blood volume. Intraoperative hemoglobin or hematocrit estimations are needed to judge the adequacy of blood replacement. In case of loss of a large blood volume fresh frozen plasma and platelet transfusion are required to prevent abnormalities of coagulation. Blood loss can be reduced by using judicious use of infiltration with vasopressors, meticulous surgical technique and avoiding dilutional coagulopathies.
Intracranial Pressure: During anesthesia, basic principles of neuroanesthesia are followed to prevent further increase in ICP. Mainly the cranial remodeling surgery is extradural but to minimize pressure by pressure on the brain, reducing brain bulk by appropriate drugs, 30 degree head high position, adjusting mild hyperventilation to control PaCO2 and administering diuretics like mannitol are useful. Lumbar CSF drainage may be employed in some cases.
Hypothermia: Prolonged surgery and extensive tissue exposure leads to loss of heat and water. Both core and skin temperature should be monitored. Hypothermia should be prevented by placing the patient on a heating mattress, covering the patient with heating blankets, wrapping limbs with cotton and plastic and using pre-warmed fluids. Humidification in the breathing system is advisable.
Bradycardia: Bradycardia occurs commonly due to pressure on the brain or a pull on the eye balls. The scalp flap should be placed carefully and pressure should be avoided especially during orbital reconstruction. Hemodynamically significant bradycadia, not responding to release of pressure on the eye balls, needs to be treated with intravenous atropine.
Venous Air embolism: Venous air embolism occurs frequently as throughout the procedure, many venous channels of the skull remain open in the head high position. This can cause hemodynamic instability and rarely hypoxia and cardiac arrest. In 50% of children younger than 5 years, paradoxical air embolism can take place due to functionally open foramen ovale. To reduce these associated adverse events, covering the sites of air entrapment with bone wax and saline soaked cotton patties, adequate hydration, maintaining higher central venous pressure and close observation for evidence of air embolism using a precordial Doppler or end tidal CO2 monitor should be done. If venous embolism develops, flooding the field with saline, jugular venous compression, making the patient horizontal and discontinuation of nitrous oxide should be used along with attempts to aspirate air from the central venous line placed in the right atrium.
Postoperative care: Postoperatively, before considering extubation, the patient needs to be reassessed for airway edema, level of consciousness, recovery of protective airway reflexes, ongoing blood loss, hemodynamic stability, adequacy of blood loss replacement and circulating hemoglobin. Use of short acting drugs allows early neurological assessment following surgery. Most patients with a normal airway can be extubated. In case of doubt, keeping the tube in situ and postoperative ventilatory support may be continued for some time. Tracheal tube patency must be checked regularly. This is the most important reason for mortality in the postoperative period. Patients should be kept in a postoperative intensive care unit which is geared to handle such pediatric patients for at least 24 to 48 hours following surgery. The causes for deterioration can be airway obstruction, hypoxia, hypercapnia, cerebral edema, intracranial bleeding, hypoglycemia or electrolyte imbalance. These should be detected early and treated appropriately.
Analgesia: Due to extensive surgical dissection, postoperative pain is severe and providing adequate analgesia is important. As opioids are associated with respiratory depression careful titration of doses with monitoring of respiration is needed. Use of multimodal analgesia using a combination of centrally acting drugs like opioids and peripherally acting drugs like NSAIDs or local anaesthetic agents is commonly used.
Careful planning and co-operation from multiple departments go a long way to achieve successful outcomes.
Dr. Hemangi Karnik (MD), Professor of Anaesthesiology, Neuro and Craniofacial services, LTMG Hospital, Mumbai.