Anesthesia and Postoperative Management of Spinal Deformity Surgery in Growing Children

Fig. 51.1

Prone position with a Jackson table. The arms are extended less than 90° whenever possible. Pressure points are padded, and the chest and pelvis are supported to preserve pulmonary compliance and minimize intra-abdominal pressure

The patient’s arms should be placed in a well-padded position of no more than 90° of combined abduction and forward flexion, and care should be taken to avoid pressure in the axilla. The elbows should remain free of compression, with particular attention paid to the ulnar nerve. In the female patients, the breasts should be moved toward the midline, and generous padding should be placed over the anterior–superior iliac spine in all patients to decrease the risk of injury to the lateral femoral cutaneous nerve. The knees should be flexed and the feet be supported, but the toes should be allowed to hang freely.

The most important factor that influences the choice of anesthesia agents is the use of evoked potentials to assess spinal cord integrity. Only small concentrations of inhalation agents are used. Maintenance of general anesthesia usually consists of continuous infusions of propofol and remifentanil. In patients with intrathecal morphine, the addition of remifentanil is not necessary.

51.3.4 One-Lung Ventilation (OLV)

Pediatric scoliosis surgery may require single-lung ventilation for surgical access. Current methods of lung isolation are inadequate for some or all of these children. Spinal access in pediatric scoliosis correction surgery may require lung collapse for several hours and is traditionally achieved in larger children with a double lumen tube (DLT) or with specially designed selective endobronchial blockers that are placed with the assistance of a fiberoptic bronchoscope like the Univent endotracheal tube (Fuji Systems, Tokyo, Japan) and the Arndt endobronchial blocker (Cook Critical Care, Birmingham, IN). Other alternatives to providing bronchial blockade, such as a Fogarty embolectomy catheter or main bronchus intubation with a conventional endotracheal tube, are limited by nonspecific design [24]. They can result in inadequate isolation that requires direct lung compression, which is potentially traumatic for lung tissues. Although DLT is the standard technique for lung isolation in thoracic surgery, its use in scoliosis patients is limited for several reasons. The smallest size available is 26 Fr, which prevents its use in patients <8–10 years of age and in those who are difficult to intubate. In patients with abnormal airway anatomy, placement of a DLT may not be possible and may be contraindicated due to the potential traumatic injury to the airway.

For younger patients and those in whom the DLT or the Univent endotracheal tube is not indicated, the Arndt endobronchial blocker (Cook Critical Care, Birmingham, IN) is an alternative for providing lung isolation. There are three commercially available sizes of this device: 5, 7, and 9 Fr. Its application and successful use in small patients undergoing scoliosis surgery has been reported [25].

In small children, use of the smallest blocker is limited by its external diameter and can be placed only via an endotracheal tube with an internal diameter of 4.5 mm or larger, requiring a thin pediatric bronchoscope.

Dexterity in fiberoptic bronchoscopy and familiarity with these devices are essential for their successful use. Although single-lung isolation provides the optimal surgical access, it is not without risk of potential serious complications due to migration and tracheal occlusion by endobronchial balloons, resulting in inadequate ventilation. Constant vigilance is required, including uninterrupted auscultation of breath sounds on the nonisolated lung and monitoring of airway resistance, in order to identify this problem promptly and avoid serious complications.

51.3.5 Antibiotic Prophylaxis

The prophylactic administration of antibiotics is indicated during scoliosis surgery in order to decrease the risk of a surgical site infection, which is associated with increased morbidity, prolonged hospital stay, and added health care cost [26]. These infections are difficult to treat and often require multiple surgical debridements, long-term parenteral antibiotics, and hardware removal.

51.3.6 Hypothermia Prevention

Prevention of hypothermia secondary to a long procedure with an extensive exposed area is also very important. The goal is to prevent its vicious circle of coagulopathy and acidosis. There are several other consequences of hypothermia, those include impaired drug metabolism, impaired SSEP and MEP signals, prolonged recovery from anesthesia, cardiac irritability, wound infections, and postoperative shivering.

Routine use of environmental factors by changing the room temperature, forced warm air blankets, fluid warmers, and warmed gases will help maintain the temperature of the patient.

51.4 Neurological Risk

Paraplegia resulting from the operative treatment of scoliosis is the complication most feared by surgeons, anesthesiologists, and patients [27, 28]. Neurological injury is most often due to ischemic injury caused by spinal cord distraction or direct spinal cord compression by a hook or wire. The areas of the cord most vulnerable to ischemic injury are the motor pathways supplied by the anterior spinal artery. Rapid interventions, such as adjustment or removal of the hardware, can reverse neurological deficits and prevent permanent injury. Prevention of spinal cord injury (SCI) begins with maintaining spinal cord perfusion with reasonable MAP and agreed transfusion thresholds [29].

Recognition of the high-risk case is essential. Congenital kyphosis, neurofibromatosis, skeletal dysplasias, and postinfectious scoliosis carry higher neurological risk [30]. Congenital scoliosis also increases risk due to a higher incidence of occult spinal cord anomalies [31, 32]. Neurological deficit prior to the onset of treatment indicates an increased possibility of additional injury [28].

Intraoperative spinal cord monitoring is an integral part of almost all surgeries for scoliosis in pediatric patients. For a more comprehensive understanding, please refer to Chap. 53.

51.4.1 Intraoperative Management of Neurological Insult

If spinal cord injury (SCI) is suspected, immediate confirmation and appropriate action are necessary to reduce the likelihood of permanent damage. In general, the following events should occur in a timely and coordinated fashion:

The anesthesiologist should be informed and the patient’s blood pressure, hematocrit, and oxygenations should be optimized [33].

Wake-up test. The Stagnara wake-up test remains the gold standard to determine the presence or absence of injury to the anterior (motor) portion of the spinal cord. It requires two important elements: an anesthesiologist familiar with the procedure and a patient who can understand and follow directions. If the patient cannot follow directions due to mental retardation, significant preoperative weakness, or profound hearing loss, the surgeon will not be able to evaluate any abnormal result. Because the patient may struggle during this test, there is a risk of self-extubation [34]. Therefore, a gurney should be available in the room to turn the patient quickly into the supine position so that reintubation can be performed without delay.

Remove instrumentation if there is no change with previous maneuvers.

In the past, methylprednisolone had been administered for acute SCI; there is insufficient evidence to support the prophylactic administration of methylprednisolone as a standard treatment in acute SCI [35].

51.5 Anesthesia Techniques in Blood Conservation

Perioperative blood loss remains a significant concern for orthopedic surgeons performing spinal fusion and instrumentation. Mean blood loss per vertebral level correlates with the number of vertebral levels fused and has been reported to be as high as 503 mL per segment [36]. Many factors affect blood loss in patients undergoing spinal fusion and instrumentation; the surgical technique employed, duration of surgery, number of vertebrae fused, site of autologous bone graft harvest, MAP, the pressure in the inferior vena cava, and patient position affect the total blood loss. In addition, there may be other factors influencing blood loss during scoliosis surgery that are not affected by current techniques to decrease intraoperative bleeding. Yarom et al. [37] described abnormal platelet in vitro function and ultrastructure in patients with idiopathic scoliosis, and Udén et al. [38] noted both an increased bleeding time and decreased ability of collagen to aggregate platelets in patients with scoliosis when compared with nonscoliotic controls. These factors are exacerbated in scoliotic patients with an underlying neuromuscular disorder. In one study comparing neuromuscular scoliotic patients with idiopathic scoliotic patients, the former were found to have a nearly sevenfold risk of losing over 50 % of their estimated blood volume during scoliosis surgery, after adjusting for age, weight, number of levels fused, and coagulation profile [39]. Mean estimated blood loss associated with surgical procedures for neuromuscular scoliosis has been reported to range from 1000 mL for anterior procedures to 2000–3000 mL for posterior approaches [40]. Disseminated intravascular coagulation has also been described in patients undergoing surgery for scoliosis, suggesting that extensive decortication may stimulate the intrinsic system of the coagulation cascade, promoting the production of kallikrein, bradykinin, and plasmin, thereby increasing fibrinolytic activity, which may ultimately lead to a consumptive coagulopathy and increase perioperative blood loss.

There is considerable evidence that transfusion of allogeneic blood products is associated with serious complications, including transfusion reactions, transmission of infectious diseases, graft-vs. -host disease, acute lung injury, and immunosuppression.

Because major blood loss is to be expected, proper positioning, optimal ventilatory pressures, autologous blood donation, intraoperative hemodilution, the use of a cell saver, induced hypotension, and the use of antifibrinolytic agents should be considered. Transfusion decisions should be based on clinical judgment rather than reliance on a predetermined hemoglobin concentration as a “transfusion trigger.”

51.5.1 Positioning and Ventilation

Proper positioning plays an important role in blood conservation in patients in the prone position. Placing the patient with support below the pelvis and shoulder leaves the abdomen free. It has been shown that, by preventing pressure on the abdominal wall, the pressure on the vena cava is minimized, thus reducing blood flow through collateral vertebral venous plexuses, known as Batson’s plexus [41]. During mechanical ventilation, airway pressure increases, resulting in an increase in mean intrathoracic pressure. Because venous return to the thorax is dependent on the difference between peripheral venous pressure and intrathoracic pressure, venous return is, consequently, impeded during the inspiratory cycle of mechanical ventilation [42].

There is evidence that elevation in intrathoracic pressures during mechanical ventilation raises the peripheral vascular pressure to adequate level to affect blood loss. Spontaneous ventilation, on the other hand, assists venous return because of reduced mean intrathoracic pressure with inspiration. Therefore, the hemodynamic differences between spontaneous and mechanical ventilation can reduce intraoperative blood loss.

Another aspect of ventilation affecting venous return is expiratory and inspiratory resistance. Maintaining expiratory resistance as low as possible assists venous return by reducing intrathoracic pressure [43]. Appropriate management of reactive airway disease, appropriate setting of the inspiratory-to-expiratory ratio, allowance of adequate expiration time, and maintenance of unobstructed expiratory flows (e.g., avoidance of kinks or buildup of secretions in the endotracheal tube) may be beneficial in reducing blood loss.

51.5.2 Preoperative Autologous Blood Donation and Acute Normovolemic Hemodilution

Although preoperative donation of autologous blood was first suggested by Fantus in 1937, when he founded the first blood bank in the United States, the technique did not became popular until the 1980s. Advantages of this technique include reduced exposure to allogeneic blood, the availability of blood for patients with rare phenotypes, reduction of blood shortages, avoidance of transfusion-induced immunosuppression, and the availability of blood to some patients who refuse transfusions based on religious beliefs. There are no limitations in regard to a patient’s weight or age. Patients who weigh 50 kg or more can donate a standard unit of blood (450 mL), while those who weigh less than 50 kg can donate proportionately smaller volumes. The hematocrit (Hct) should be ≥33 % prior to each donation. Red blood cell production can be augmented by iron supplementation and the administration of erythropoietin. Donations may be made every 3 days, but the usual practice is to donate 1 unit per week. The last unit should be donated at least 5–7 days before surgery to allow plasma proteins to normalize and to restore intravascular volume. Autologous blood donation in pediatric patients undergoing spinal fusion is an efficient blood-saving technique, especially in idiopathic scoliosis. In some centers, almost 80 % of children and adolescents undergoing spinal fusion participate in the autologous blood predonation program; almost 90 % of the participants avoid receiving allogeneic blood. Patients with neurological causes of scoliosis less often participate in the predonation program and usually need transfusion of allogeneic blood.

Acute normovolemic hemodilution (ANH) involves removing and temporarily storing 2–4 units of a patient’s blood just before major elective surgery in which major blood loss is anticipated. The blood that has been withdrawn is then reinfused into the patient during or after surgery. Simultaneous infusions of crystalloids (3 mL of crystalloids per 1 mL of blood withdrawn) have been recommended. The rationale for the use of hemodilution is that, if intraoperative blood loss is relatively constant with or without preoperative normovolemic hemodilution, then it is better to lose blood at a lower rather than at a higher level of Hct. This procedure lowers the patient’s preoperative Hct to 28 %. If the perioperative Hct level falls to 24 %, the ANH blood units are reinfused in reverse order of their collection (i.e., last unit collected is the first unit transfused). The first unit of blood collected, and therefore the last unit reinfused, has the highest Hct, contains the most platelets, and has the highest concentration of clotting factors [44].

Clinical observations show that ANH reduces allogeneic blood use in 20–90 % of patients with no difference in postoperative outcomes [45, 46]. Furthermore, ANH is substantially more cost-effective than transfusion. ANH has been shown to decrease perioperative transfusion requirements of adolescents undergoing extensive spinal surgery. By allowing patients to arrive at surgery with a higher preoperative hemoglobin and Hct levels and by decreasing the quantity of predonated autologous blood collected and therefore used, the hemodilution method may indirectly decrease the quantity of postoperative autologous transfusion in this population.

51.5.3 Controlled Hypotension

Controlled hypotension involves the use of pharmacological agents to lower the MAP to 50–65 mmHg. This method significantly decreases both intraoperative blood loss and blood requirement. Blood loss during controlled hypotension is at least in part dependent on venous pressure [47, 48].

The potential contribution of venous pressure to blood loss can be further understood from studies using epidural anesthesia. Modig and Karlstrom [47] demonstrated that both intraoperative and postoperative blood loss are significantly lower during epidural anesthesia when compared with general anesthesia in patients undergoing total hip replacement.

In view of the ischemic nature of spinal cord injury, it is now suggested that MAP should be maintained in the low normal range, and hypotension should be quickly corrected if there is a loss of MAP [29]. It has been shown that the spinal cord is more sensitive to distraction and/or compression during controlled hypotension than at normotension as measured by reduction in somatosensory-evoked potentials [49, 50].

Several different agents and methods are used in spinal surgery to provide controlled hypotension, including direct-acting vasolidators (sodium nitroprusside, nitroglycerine), calcium channel blockers, and intrathecal opioids.

Only gold members can continue reading. Log In or Register to continue