Scoliosis is a condition where spine has an irregular curve in the coronal plane. While the degree of curvature is measured on the coronal plane, scoliosis is actually a more complex, three-dimensional problem which involves the following planes: Coronal plane, Sagittal plane and Axial plane.
The use of intraoperative neuromonitoring (IONM) during pediatric scoliosis repair has become commonplace to reduce the risk of potentially devastating postoperative neurologic deficits. It monitors the functional integrity of certain neural structures.
TIVA (Total Intravenous Anesthesia) is preferred for intraoperative neuromonitoring because it provides greater stability for neural functions without altering evoked potential amplitudes and latencies. Total intravenous anaesthesia (TIVA) describes the maintenance of general anaesthesia without inhaled hypnotics. Drugs with fast onset and offset times are most useful for balancing adequate hypnosis/analgesia with rapid recovery. Remifentanil and propofol are commonly used for TIVA due to their characteristics of ease of titration, as well as rapid onset and offset of action.
Adequacy of TIVA depends on the maintenance of brain propofol and remifentanil concentrations which are clinically appropriate and in equilibrium with levels in the plasma. The best way to achieve this state is by TCI (Target Controlled Infusion) pumps. A TCI pump contains a microprocessor programmed with pharmacokinetic models for relevant drugs. The user selects the drug and pharmacokinetic model to be used by that TCI pump and inputs the patient characteristics such as body weight and age, and the target plasma or ‘brain’ (effect-site) concentration, with the pump determining the initial bolus and subsequent infusion rates. These devices solve the complex equations which describe the distribution of agents between compartments and allow for rapid adjustments in targets to achieve the desired clinical effect.
Patient was a 15 years aged male who was diagnosed with severe right scoliosis which was progressive in nature. Patient was a known case of type 1 Neurofibromatosis. Patient has had wheeze since 5 years for which he was on inhaler every 2 hours and improved with traction twice a day. On examination, patient had a large plexiform neurofibroma on his back as well as cafe au lait spots and freckles. Patient was planned for Scoliosis correction and debulking of neurofibromatous lesion by Spine and plastic team. Traction was applied one month prior to the surgery.
The preanesthetic evaluation requires a multidisciplinary approach. An integral part of this assessment is the identification of decompensated functions or organ reserves that could bring possible perioperative complications and its maximal preoperative optimization. On examination, patient had bilateral interscapular area rhonchi. All his blood reports were within normal limits. CT whole spine showed Cobb’s angle of 93 degrees. Pulmonary Function Test revealed severe restriction with early small airway obstruction. Pulmonologist opinion was sought and advised for nebulizers and opined as moderate risk of post-operative pulmonary complications. Preoperative incentive spirometry was advised. Adequate blood and blood products were reserved.
First stage of the surgery involved Neurofibroma excision with pedicle screw fixation. Patient was induced with intravenous propofol (2 mg/kg), fentanyl (2 mcg/kg), and cisatracurium (0.2 mg/kg). The patient was intubated and mechanically ventilated. Central venous catheter and invasive arterial blood pressure line were placed for hemodynamic monitoring. Neuromonitoring leads were connected. Patient was then shifted to prone position and was initiated with TIVA infusion using TCI pump which included Propofol and Remifentanyl. No further muscle relaxants were used throughout the procedure. Total duration of the surgery was about 14 hours during which he was infused with about 7 litres of IV fluids. Urine output was about 1100 ml and the blood loss was around 2500 ml. 2 units of PRBC, 600 ml of self-salvageable (autologous) PRBC, 4 units of FFP and 4 units of RDP were transfused. Patient required Noradrenaline infusion during the surgery. Patient was electively ventilated postoperatively and shifted to ICU for close monitoring. He was extubated on the following day.
Second stage of the surgery involved Corpectomy with rod fixation after 72 hours. Similar steps were followed for anaesthesia as done during the first stage of surgery. Total duration of the surgery was about 11 hours during which he was infused with about 2 litres of IV fluids. Urine output was about 2000 ml and the blood loss was around 1000 ml. 1 unit of PRBC, 700ml of self-salvageable (autologous) PRBC, 3 units of FFP and 3 units of RDP were transfused. Patient was electively ventilated postoperatively and shifted to ICU for close monitoring. He was extubated on the following day.
Concerns associated with Scoliosis correction include intraoperative neurophysiological monitoring (IONM), high blood loss, patient positioning – typically pronation, fluid management, long surgical hours and body temperature loss.
Neurological complications are an uncommon but significant complication of scoliosis correction. A neurophysiologist should monitor somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) intraoperatively to enable early identification of and intervention for possible neurological injuries. Anaesthetic management, including oxygenation, ventilation, massive blood loss, or hypotension, can influence the IONM reproducibility. Anaesthesiologic aspects include maintaining normoxia with normocapnia, preventing severe hypothermia and ensuring adequate blood flow to the spinal cord. This means maintaining normotension during surgery.
The prone position is the most frequent position for scoliosis surgery to facilitate access to the spine. This position is associated with several complications caused by raised intra-abdominal or thoracic pressure. In addition, prone positioning is associated with a higher risk of postoperative visual loss. Aside from careful positioning on the operating room table, the anaesthesia team should elevate the upper part of the body to decrease the intraocular pressure.
Fluid balance can be a point of contention in the operating theatre as anaesthetists and surgeons try to balance the consequences of hypovolaemia and fluid overload.
Patients with neuromuscular disease are at a high risk of extensive blood loss because of prolonged and extensive procedures. Adequate blood and blood products should be reserved pre-operatively. Antifibrinolytics’ effect in reducing blood loss and transfusion administration has been described in scoliosis surgery. Tranexamic acid is one of the most widely used antifibrinolytics. Another means to reduce allogeneic blood transfusion is intraoperative cell salvage (Cell Saver). The blood is collected from the wound into a reservoir. Red blood cells can be re-infused to the patient after purification of the collected blood.
Severe hypothermia, with a decrease in temperature of more than 2.5 °C from the baseline, interferes with IONM. Patients with neuromuscular disease, a lower body mass index, or a larger Cobb angle are at a higher risk of hypothermia. Other adverse effects include prolonged metabolism of anaesthetic agents, coagulopathy with higher blood loss, and wound or respiratory infections. Preoperative and intraoperative active warming is recommended to prevent hypothermia.
Management of pediatric patients for scoliosis surgery represent a significant challenge for all healthcare providers. This heterogeneous team involves surgeons, anaesthesiologists, neurophysiologists, pediatricians, nurses, nutritionists, and physiotherapists. Healthcare providers have to consider all risks arising from the surgery, anaesthesia, and the nature of the disease as a multidisciplinary and individual approach to each patient can improve the postoperative outcome. Firstly, mentioned data focus on the maximal optimization of altered functions before surgery and patients´ complex multidisciplinary prehabilitation. Secondly, adequate preparation of the anaesthetic management is essential for safety in the perioperative period. Thirdly, postoperative care in the ICU with adequate prevention, early identification, and treatment of possible complications can improve the postoperative outcome.
Dr. Haripriya 1st year PG Anaesthesia Department Kauvery Hospital, Alwarpet Chennai
