Title: Mayday! Acute Loss of Signals with Sky Rocketing Elevation of Liver Enzymes Celiac Artery in Danger During Spine Distraction

Transcription

1 Title: Mayday! Acute Loss of Signals with Sky Rocketing Elevation of Liver Enzymes Celiac Artery in Danger During Spine Distraction Moderators: Aysha Hasan MD; Sophie R. Pestieau MD After attending the PBLD, the attendee will be able to: 1. Understand the relevance of spinal neuromonitoring and its impact on intraoperative and post operative outcomes 2. Recognize and discuss the positive and negative outcomes of awakening a patient intra operatively 3. Prepare a plan of action in the event of loss of evoked potential signals 4. Design an anesthetic tailored to provide optimal conditions for neuromonitoring with emphasis on the selection of anesthetic agents that least affect SSEPs and MEPs 5. Formulate decisions as to when it is appropriate to wake up patients to evaluate motor function and weigh the risk of recall 6. Predict accurately intra operative events that can lead to critical perfusion to the spinal cord 7. Acutely recognize the symptoms of post operative complications that are rare but need early detection and treatment 8. Incorporate INVOS (in vivo optical spectroscopy) into intraoperative management 9. Facilitate intraoperative care using INVOS as a tool for guidance of preventing ischemic organ damage

2 Question Stem and Key Questions: A 10 year old, 40 kg male scheduled for posterior spinal fusion with instrumentation walked back to the operating room for his procedure. He was healthy with the exception of a diagnosis of idiopathic thoraco lumbar scoliosis (T4 L2) with an 84 degrees curvature per his last clinic. This was confirmed with x rays a month prior to surgery. In the OR, a single intravenous line was placed along with standard ASA monitors. The patient underwent a smooth intravenous (IV) induction with 150 mg of propofol, 25 mcg of fentanyl and 20 mg of rocuronium. After securing the airway another peripheral intravenous line was placed, as well as an arterial blood pressure line, neuromonitoring leads, and a foley catheter. Prior to being placed in the prone position the patient underwent a neuraxial injection of 0.2mg of morphine (preservative free). After positioning the patient, an infusion of 0.2mcg/kg/min of remifentamil and 150 mcg/kg/min of propofol was started along with 0.5 MAC of desflurane for maintenance of anesthesia. 1. How does idiopathic scoliosis differ from other types of scoliosis? 2. What is the Cobb angle? How does it affect perioperative management? 3. What are the benefits of neuraxial opioids in this surgical setting? Prior to surgical incision, the neuromonitoring technician performed sensory and motor tests. He stated all of twitches from neuromusclar blockade had returned; yet motor evoked potential signals were absent. 1. What would you do in the absence of MEP signals? 2. What are some differentials for loss of evoked potentials? The patient s hemodynamics were stable: BP: 98/54, HR: 105, SpO2: 100% RR: 16 (controlled ventilation). The patient has received 100 cc of fluid so far. Arterial blood pressure waveform was normal and correlated with the non invasive blood pressure cuff. The neuromonitoring technician was still unable to attain motor evoked potentials. The surgeon insists that he has not yet instrumented the spine. 1. What will you do now? 2. Should you consider changing your anesthetic? 3. Should the patient be awakened and the surgery cancelled?

3 The patient remains stable, SSEPs are present, but MEPs are still unavailable. Due to the persistent absence of MEP signals, desflurane was turned off and the total intravenous anesthetic was supplemented with ketamine at an infusion rate of 0.3 mg/kg/min, in addition to the remifentanil and propofol infusion. A single dose of 0.5 mg/kg of etomidate was also given and the patient's mean arterial pressure was optimized to >80mmHg. Despite these measures, and the neuromonitoring technician confirming lead placement, the motor evoked potential signals still remained absent. 1. If the surgeon decides to proceed, would you want to perform a wake up test? If so, when? 2. How do you facilitate a wake up test? 3. What are the pros and cons of a wake up test? 4. Should this be discussed with the family? A wake up test was performed prior to incision. The patient was awakened and was able to move his lower extremities. Immediately thereafter, the level of anesthesia was promptly restored to adequate depth and the surgical team proceeded with the planned surgical procedure. 1. Should the spine be instrumented? 2. Should a wake up test be repeated? If so, when? 3. Does the spine need to be imaged? An additional wake up test was performed after rod placement. Final surgical hardware was secured and the spine was fused from T4 L2. The patient was awakened and he was able to move all of his extremities. He was able to follow commands and was extubated in the OR. He was sent to the PICU for close postop monitoring. Post operative labs showed elevated pancreatic enzymes as well as elevated liver enzymes, and elevated BUN and creatinine. 1. What is the etiology of this? How should this be managed? 2. What other intraoperative monitors could have been used to detect organ damage or ischemia? 3. How do you explain this to the parents?

4 Discussion: Different types of Scoliosis: Types of idiopathic scoliosis are categorized by both age at which the curve is detected and by the location of the curve. Three commonly described scoliosis by age are the following: Infantile (ages birth to 3 years old), Juvenile Scoliosis (ages 3 years old to 9 years old) and Adolescent scoliosis (ages 10 years to 18 years old). Adolescent scoliosis is the most common type of idiopathic scoliosis. 10 years to 18 years is the time frame of when the greatest amount of curvature growth occurs. The types of scoliosis based on location are also descriptive. These types are known as the following: Thoracic scoliosis is the curvature of the thoracic or middle part of the spine. This is the most common location of spinal curvature. Lumbar scoliosis, as the name suggests, is curvature of the lumbar portion of the spine. Finally, thoracolumbar scoliosis is the curvature of both the lower thoracic portion and upper lumbar portion of the spine. Other types of scoliosis can be further classified into the following: Idiopathic (most common), congenital (develops in utero, which is a rare occurrence), neuromuscular (also known as myopathic scoliosis, seen in cerebral palsy and muscular dystrophy children) and degenerative scoliosis (commonly seen later in life). Scoliosis can also be described by the direction of the curve. Kyphosis is the posterior curvature of the spine whereas lordosis is the anterior curvature of the spine. Dextroscoliosis is a spinal curve to the right. This type of curvature is more common especially in the thoracic spine. Whereas levoscoliosis is spinal curve to the left, more commonly occurring in the lumbar spine. If levoscoliosis curvature is noted in the thoracic spine there is a high suspicion of a spinal cord tumor. Scoliosis can affect pulmonary and cardiac function. The Cobb s angle, first described by Dr. John R Cobb, is used to quantify the magnitude of spinal deformities. The Cobb angle is measured by using the upper and lower limits of the vertebrae of the deformed portion of the spine. A Cobb angle greater than 40 to 50 degrees will predispose the patient to pulmonary function abnormalities (restrictive lung function). A Cobb angle

5 greater than 90 degrees predisposes to an increased risk of post operative cardiorespiratory failure. Anesthetic management of scoliosis repair is challenging because of the many comorbidities that may be associated with the condition, the extensive nature of the surgery, constraints secondary to neuromonitoring, and post operative problems. Common post operative problems are continued blood loss, syndrome of inappropriate antidiuretic hormone release and superior mesenteric artery syndrome. Post operative pain management can also be severe and requires a multimodal approach. With severe scoliosis (Cobb angles greater than 65 degrees) it is important to recognize the possibility of poor pulmonary and cardiac functions. V/Q mismatch, respiratory failure and pulmonary hypertension are important to assess. Curves >100 degrees are a risk factor for severe respiratory compromise.. Surgery will not reverse the restrictive pulmonary disease but it will stop its progression. Preoperative management begins with assessment of daily activities and pulmonary and cardiac functions. Additional information in the preoperative assessment should include co morbidities and the type of scoliosis as well as the Cobb angle. Supplemental exams such as pulmonary function tests, cardiac echo and blood work are important to investigate. Intra operatively, the anesthetic plan should focus on hemodynamics and pain management, compression neuropathies secondary to positioning, neurologic injury, blood loss, coagulopathy, venous air embolism, and post operative visual loss. Pain management and intraoperative blood loss remain areas of concern. However, studies show that the use of 2 5microgram/kg of intrathecal morphine has helped in not only helping with post operative pain management, but also helps with a decrease in intraoperative blood loss. These benefits with the use of intrathecal morphine has made its use an integral part of the anesthetic management. Causes of neurologic injury can arise from stretching of the spinal cord, epidural hematoma, distraction injury of the spinal cord, reduction in blood flow to the spinal cord, and direct contusion from instrumentation to the spinal cord. Continuous intraoperative monitoring of sensory and motor evoked potentials provides vital information of cord function. However, when the evoked potentials do not provide signals, it is important to quickly and adequately assess motor function of the spinal cord.

6 Sensory evoked potentials (SEPs) evaluate the integrity of ascending sensory tracts while motor evoked potentials (MEPs) deal with the functionality of descending motor pathways. Sensory motor evoked potentials are less sensitive to anesthetic depth changes than are motor evoked potentials. It is imperative to maintain constant anesthetic drug levels during recording of EPs (evoked potentials). Large boluses in IV infusions or abrupt changes in MAC values of inhaled agents can be detrimental, particularly during critical portions of a procedure. When recording cortical EPs (SSEPs) one should generally incorporate intravenous techniques, as high concentrations of volatiles can completely eliminate cortical EPs. Nevertheless, all volatile anesthetics increase cortical latency and decrease cortical amplitude. However, desflurane and sevoflurane appear to be more forgiving with SSEPs than agents such as enflurane and isoflurane. For instance, desflurane at up to 1 MAC without nitrous oxide is compatible with cortical median nerve SSEP monitoring during scoliosis surgery. Regarding intravenous agents, studies on thiopental have shown that even with doses far in excess of what is required to produce an isoelectric EEG, SSEP and BAEP waveforms are preserved even if there is a predictable increase in latency and decrease in amplitude. Propofol increases latency and decreases amplitude of cortical EPs, but is considered an integral component of balanced intravenous neurosurgical anesthesia. Opioids produce minimal changes in SEP waveforms, even in high doses. Because of this, they are recommended for use as infusions during EP monitoring. Both clonidine and dexmedetomidine decrease anesthetic requirements and have minimal effects on cortical EPs and are considered safe to use during monitoring. For practical purposes, ALL intravenous agents have negligible effect on cortical SSEP s, except for etomidate and ketamine, which can actually increase amplitude. MEPs are exquisitely sensitive to anesthetics, especially inhalational agents. Volatile agents, therefore, should be avoided during recording of myogenic MEPs. Benzodiazepines, barbiturates, and propofol all depress MEPs, however, adequate recordings can be obtained during propofol anesthesia by controlling serum levels and increasing stimuli rates. Muscle relaxants can affect the recorded EMG response by depressing myoneural transmission. However, adequate MEP recordings can be achieved as long as one or two twitches on train of four can be maintained. In order to assess the motor function (but not sensory function) a wake up test may be performed. The wake up test allows for intraoperative emergence to test for motor function of the lower extremity but does not provide information about the sensory pathway. Although confirmation of function is reassuring, loss of function may be irreversible. Any loss of function mandates the surgeon to remove all implants. The wake up test requires patient cooperation. Furthermore, patient movement can result in accidental extubation, loss of IV access and increase risk of venous air embolism.

7 Although acute postoperative pancreatitis is a relatively frequent complication after open biliary tract surgery and gastric surgery, acute pancreatitis after spine surgery is a rare complication. A recent case of acute pancreatitis was reported by Tauchi et. al (2014) after posterior lumbar interbody fusion in a 53 year old patient. The patient recovered gradually, and clinical symptoms disappeared. At 6 months after the operation, she had experienced no recurrence of abdominal symptoms, and solid spinal fusion was achieved. Laplaza et al also reported acute pancreatitis as a complication after spine surgery for various spine diseases such as scoliosis and lumbar disorders. In this series of 8 patients, older age and lower body index mass were the only factors relating to postoperative pancreatitis. Pancreatitis is major cause of morbidity after spinal fusion surgery in patients with cerebral palsy. Patients with preoperative GERD with feeding difficulties and reactive airway disease had a higher risk of developing postoperative pancreatitis. While the etiology of pancreatitis in the postoperative orthopedic population is not clear, acute pancreatitis must be considered as possibility when unusual abdominal symptoms with elevated serum amylase levels occur after spine surgery. Postoperative pancreatitis causes delays in feeding and increases the duration of hospitalization. Prompt diagnosis and supportive therapy are essential to minimize morbidity and mortality. In vivo optical spectroscopy, also known as, INVOS, detects venous weighted regional hemoglobin saturation (rso2) in tissue directly under its sensor keys. rso2 reflects the hemoglobin bound oxygen remaining after the tissue has extracted the oxygen requirements needed. Decreases in venous reserve, as detected by this monitor, will indicate increased ischemic risk and compromised tissue perfusion. The unique quality of this device is that it does not require pulsatile flow to measure rso2. It measures the capillary s perfusion under its sensor. Furthermore, it measures both end organ oxygenation and perfusion. While studies are limited, the current literature is supportive of using INVOS in helping to assess blood transfusion guidelines. Vretzakis et. al demonstrated that during cardiac surgery, using INVOS helped guide their blood transfusion thresholds based on the values of rso2. Blood transfusions are not without its own risk, but INVOS helped minimize the incidence of unnecessary blood transfusion (and risk) with evidence of adequate brain tissue perfusion and oxygenation. While most of the studies are related to INVOS use in the brain, many are using INVOS in other parts of the body, including the renal, pancreatic and liver organ systems. While studies are currently limited, its use seems promising. Furthermore, the use of INVOS in the pediatric population is gaining popularity and is encouraged for optimal intraoperative management.

8 References: 1. Gibson, P. Anaesthesia for Correction of Scoliosis in Children. Anaesthesia Intesnive care (4), Tauchi, R., Imagama, S., Ito, Z., Ando, K., Hirano, K., Ukai, J Ishiguro, N. Acute pancreatitis after spine surgery. A case report and review of literature. Eur J Orthop Surg Traumatol European Journal of Orthopaedic Surgery & Traumatology Laplaza, F., Widmann, R., Fealy, S., Moustafellos, E., Illueca, M., Burke, S., & Boachi Adjei, O. (n.d.). Pancreatitis After Surgery in Adolescent Idiopathic Scoliosis: Incidence and Risk Factors. Journal of Pediatric Orthopaedics Borkhuu B, Nagaraju D, Miller F, Moamed Ali MH, Pressel D, Adelizzi Delany J, Miccolis M, Dabney K, Holmes L Jr. Prevalence and risk factors in postoperative pancreatitis after spine fusion in patients with cerebral palsy. J Pediatr Orthop Apr May;29(3): Thomas N. Pajewski, Vincent Arlet, Lawrence H. Phillips. Current approach on spinal cord monitoring: the point of view of the neurologist, the anesthesiologist and the spine surgeon. Eur Spine J Nov; 16(Suppl 2): Gall, Olivier, Jean Vincent Aubineau, Josée Bernière, Luc Desjeux, and Isabelle Murat. "Analgesic Effect of Low dose Intrathecal Morphine after Spinal Fusion in Children." Anesthesiology 3, Vol Urban, Michael K., Kethy Jules Elysee, Barbara Urquhart, Frank P. Cammisa, and Oheneba Boachie Adjei. "Reduction in Postoperative Pain After Spinal Fusion With Instrumentation Using Intrathecal Morphine." Spine Mar1;27(5): Eschertzhuber, S., M. Hohlrieder, C. Keller, E. Oswald, G. Kuehbacher, and P. Innerhofer. "Comparison of High and Low dose Intrathecal Morphine for Spinal Fusion in Children." British Journal of Anaesthesia (2008): Monitoring of Brain Oxygen Saturation (INVOS) in a Protocol to Direct Blood Transfusions during Cardiac Surgery: A Prospective Randomized Clinical Trial. BioMed Central, Print. 10. Tweddell, James S., Nancy S. Ghanayem, and George M. Hoffman. "Pro: NIRS Is Standard of Care for Postoperative Management." Seminars in Thoracic and Cardiovascular Surgery: Pediatric Cardiac Surgery Annual:

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