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PBLD – 3

Patient with Cervical Spine injury for Occiput to C-4 Posterior Cervical Fusion

Author: Letha Mathews M.D

CASE: 78 year old male who sustained a cervical spine injury following a fall is scheduled for a posterior cervical fusion from occiput to C-4 with possible decompression. His magnetic resonance imaging (MRI) revealed a fracture of the C2 vertebral body with posterior displacement of the dens with moderate spinal cord compression along with posterior displacement of the anterior arch of C1. His neurologic exam is grossly intact except minimal left sided weakness.

PMH is significant for hypertension (HTN), atrial fibrillation (A Fib), osteoarthritis (OA), and mild dementia. He has also had a history of alcohol abuse and several falls in the last few months.

Medications: Aspirin (ASA) 81 mg QD, Amlodipine-Benazepril (5/10) QD, Metoprolol 50 mg QD, furosemide 20 mg QD, and Hydrocodone/Acetaminophen (7.5/500) PRN.

Physical Examination: He is alert and oriented and is in a C-collar with cervical traction. BP 160/78 mmHg, RR-12, height- 170 cm, weight 73 Kg. EKG shows HR 112 bpm, A fib, and minimal ST depression in all leads.

Neurologic Examination: Grossly normal, Mild Left sided weakness with 4/5 motor strength in both upper and lower extremities.

Labs: Normal, except for mild hyponatremia with Na+ 133 mEq.

Key Questions

  1. What other information would you like to have before proceeding to surgery? How would you prepare this patient for surgery?
  2. What is your anesthetic plan? The surgeon has requested intraoperative neuromonitoring

(IONM) with Somatosensory Evoked Potentials (SSEPs) and Transcranial Motor Evoked Potentials (TcMEPs). Would that alter your anesthetic plan?

What intraoperative monitoring will you use for this case?

  1. How will you intubate this patient? Discuss the various options.

After considering various options and discussion with the surgeon, you decide to do an awake flexible scope (FSI) intubation. How will you prepare the patient for awake intubation?

  1. The surgeon would like to obtain baseline SSEP and TcMEP signals before positioning the patient prone. Anesthesia was induced and the patient remained stable.

After demonstration of satisfactory SSEP and MEP signals, patient’s head was placed in Mayfield pins and positioned prone very carefully. Vital signs : BP 105/62, HR 100, SpO2 96%. Breath sounds are equal and bilateral.

The next run of IONM showed diminished amplitude and increased latency in all leads.  How would you respond? What changes would you make to the anesthetic management, if any? If the signals didn’t improve with changes in anesthetic management, how would you proceed?

IONM signals improve with raising the mean arterial pressure (MAP) to baseline (pre induction) and it was decided to proceed with surgery.

  1. What are the physiologic factors that influence electrophysiological (EP) signals?
  2. Surgery is completed uneventfully in 5 hours and the surgeon would like to do a neurologic exam before transferring the patient. What is your emergence plan? What is your post-operative plan, ICU vs Post Anesthesia Care Unit (PACU)?

The emergence was smooth and the patient followed commands and moved all four extremities. He had mild weakness on the left side. His Vital Signs were stable and he was extubated. But given his PMH and high C-spine surgery, it was decided to transfer the patient to Neuro ICU. While you were giving report to the ICU nurse, Spo2 was noted to be 91% and the patient appeared obtunded. You attempted mask ventilation which was not very effective. BP 180/110, HR 121. Spo2-84%.

How would you establish effective ventilation? Discuss the probable causes of hypoxia?

  1. SpO2 improved with intubation, but you noticed that the EKG showed a HR of 160 and an irregular narrow complex rhythm. BP 70/30.

How would you manage this? Would you manage it medically or cardiovert? The patient was treated appropriately and remained stable in sinus rhythm with BP 140/78.

  1. Patient emerged smoothly and followed commands. Would you extubate? Why or why not? You transferred the patient to ICU and a full report was given to ICU staff.

During your post op rounds several hours later, the patient seemed stable, but complained of swollen, painful tongue.  Discuss the causes and management of painful tongue.

Patient recovered fully and was discharged to the ward and eventually to a rehabilitation facility.

 DISCUSSION

  1. Preoperative Considerations: Patients with a cervical spine injury should be evaluated for the stability of the spinal column and the degree of spinal cord compromise, in addition to the usual preoperative assessment. Therefore a thorough physical examination with special attention to neurologic status and documentation of motor and sensory deficits is critical. Imaging studies should be reviewed to confirm the pathology and the degree of spinal cord compromise. In the presence of a history of A-fib and frequent falls, cardiac evaluation is important. If functional status is difficult to assess, transthoracic echocardiogram (TTE) may be indicated to estimate ejection fraction (EF) and to rule out valvular dysfunction. Ideally, in this patient with chronic A-fib not on any anticoagulants, transesophageal echocardiogram (TEE) should be considered to rule out intracardiac thrombus. But this can be challenging in the presence of an unstable C-spine and the benefits should be weighed against the potential risks of obtaining a TEE.

Since patient has been on aspirin, a discussion with the surgeon is important about the potential for platelet dysfunction and bleeding diathesis. Consider withholding Amlodipine-Benazepril for 24 hours because of the potential for intraoperative hypotension in the presence of angiotensin converting enzyme (ACE) inhibitors [1, 2] . Metoprolol should be continued [1].

Airway Assessment – A comprehensive airway exam and assessment of the patient’s mental status and ability to follow instructions is extremely important to make appropriate plans for endotracheal intubation.

If the decision is to do an awake flexible scope intubation (FSI), details and expectations should be explained to the patient. Consider premedication with an anticholinergic agent such as glycopyrrolate to minimize secretions.

  1. Anesthetic Management: Since the patient’s C-spine is unstable with spinal cord compression and myelopathy, the anesthetic management should be tailored to minimize secondary insults to the spine. General Endotracheal Anesthesia (GETA) with close monitoring of hemodynamics and careful positioning is indicated. As the surgeon has requested IONM, the anesthetic should be tailored to facilitate monitoring. SSEP and MEP tests the functional integrity of the posterior column and corticospinal tracts respectively. Total Intravenous Anesthesia (TIVA) with propofol along with a narcotic such as remifentanil or sufentanil along with lidocaine and/or ketamine infusion is commonly used during spine surgery when IONM is used to monitor the integrity of the spinal cord.  All inhaled anesthetic agents have been shown to cause a dose dependent decrease in the amplitude and increased latency of SSEPs [3, 4]. Nitrous Oxide has been shown to cause significant decrease in amplitude and increased latency especially when combined with halogenated agents; therefore should be avoided. Volatile anesthetic agents even in very low concentrations (0.2 MAC) have been shown to abolish transcranial MEP [[5, 6]. However recent studies [7, 8]have shown that desflurane use at ½ MAC had minimal effects on SSEP and MEP compared to the TIVA. Intravenous agents such as narcotics and propofol have less of an impact particularly on MEP [[3, 9]. Ketamine can cause an increase in amplitude of SSEP and MEP [10]and therefore may be a good agent to add considering its excellent analgesic and hypnotic properties. Dexmedetomidine, an alpha-2 agonist with excellent analgesic and anxiolytic effects can be used as an adjunct along with propofol for TIVA with minimal effect on SSEP and MEP [11].Lidocaine infusion at 2 mg/min has been shown to help reduce the total dose of propofol thereby facilitating a quicker emergence from anesthesia and time to neurologic evaluation [12]. Therefore, a combination of intravenous agents such as propofol, ketamine, lidocaine and narcotic of choice is routinely used during these procedures. There isn’t one ideal agent, but the agent used will depend on the practice at your institution. So, a discussion with the surgeon, neurologist and neurophysiologist prior to a bringing the patient to the OR is encouraged. Most centers would use TIVA with a combination of drugs with minimal or no halogenated volatile agents.

Monitoring:  Standard ASA monitors, Arterial Line (preferably pre induction) to monitor MAP closely. BIS (Bispectral Index) may be helpful in determining the depth of anesthesia when TIVA is used for maintenance. It is critical to avoid hypotension following induction which is not uncommon, therefore a pre-induction A-line may be helpful. Large bore peripheral IVs should suffice. Central Venous Access may be indicated if the patient has poor peripheral IV access and administration of vasoactive agents is expected.

  1. Airway: The assessment of a patient’s airway during the preoperative visit and his ability to follow instructions and cooperate will help determine the intubation technique. Consider various options: Asleep vs awake, Flexible Scope Intubation (FSI) vs Indirect Laryngoscopy using video laryngoscope (McGrath, C- MAC, Glideslope, Airtraq etc.) with manual inline stabilization (MILS). All airway maneuvers are associated with some degree of cervical spine movement.[13]Since this patient has C2 vertebral body fracture and is in a c-collar with traction, consider various options carefully. FSI is routinely used in these situations in our institution. FSI causes minimal movement of the cervical spine if the patient is adequately topicalized [14]. If the patient is not adequately topicalized, coughing and gagging can cause displacement of unstable upper C-spine resulting in spinal cord injury. Therefore thorough topicalization, control of secretions and mild sedation will help make the awake intubation smooth. However the expertise of the anesthesia provider should be taken into consideration. FSI has a high failure rate in emergency situations if the provider is inexperienced[15].The other disadvantages of FSI are the availability of advanced equipment and the need for significant patient cooperation. If a patient is obtunded or not cooperative enough to tolerate awake intubation, low dose ketamine, propofol, or dexmedetomidine may be used for sedation. FSI can prolong time to intubation especially in inexperienced hands.

If mask ventilation is required at any point, use oral or nasal airway, but avoid neck extension. Jaw thrust and chin lift to aid mask ventilation should also be avoided as it can cause cervical motion, particularly at the C1-2 junction. Given the nature of patient’s C-spine injury, Direct Laryngoscopy (DL) after induction of anesthesia is probably the least favored option. Many studies have demonstrated motion of cervical spine during intubation in patients without cervical spine injury and in cadavers with unstable spines [16, 17]. The clinical significance of the c spine motion is small[18]. Therefore it is best to use a technique that the provider is most comfortable with while taking care to minimize motion of the c-spine. If using DL or Video laryngoscopes, manual Inline stabilization (MILS) should be applied. MILS, when correctly applied, decreases the degree of motion, but does not eliminate it [13, 19]. Video laryngoscopes have become very popular for intubation in recent years and studies have shown that they improve glottic visualization. However the safety of these devices is still debatable especially in high cervical spine injury such as this patient [20, 21].

To summarize, the airway management technique chosen should be based on the individual patient risk factors, expertise of the anesthesiologist and the ability of the patient to cooperate. Review of literature does not show better neurologic outcome with the use a specific device; therefore the best strategy is the one that has the highest likelihood of success on the first attempt with lowest biomechanical influence on the unstable cervical spine.[22]

Supraglottic airways (LMA, AirQ) should only be used as rescue devices since the patient would be positioned prone in Mayfield pins. There are reports of spinal cord injury from the use of LMA in previously unrecognized neck injury.[23]

Since this patient is awake and able to follow commands and participate in the process, it’d be feasible to do an Awake Flexible Scope (FSI) intubation Awake Intubation would help facilitate neurologic examination after intubation and offers the advantage of maintaining normal muscle tone which may help splint the spinal column. If FSI is the chosen intubation technique, the patient should be counselled, reassured and prepared for awake intubation. Other back up options such as Video laryngoscopes should be available in the event of an unanticipated difficulty with awake intubation.
The patient’s nares should be sprayed with a vasoconstrictive agent such as oxymetazoline and nasopharynx and oropharynx should be topicalized with nebulized 4 % lidocaine or similar agent of choice. An antisialogogue such as glycopyrrolate to reduce secretions could be helpful, but consider the side effects.

Once the patient is adequately topicalized, mild sedation can be achieved with ketamine or dexmedetomidine or low dose propofol with or without narcotics, based on your preference and local practice. It is important to avoid deep sedation to prevent episodes of apnea. Ketamine infusion with narcotics should help alleviate the discomfort associated with needle placement.

4&5.Neuromonitoring Considerations: It is not an uncommon practice to obtain baseline SSEP and MEP after intubation of the trachea. This can be done after intubation in an awake patient under sedation or after induction of general anesthesia. GA can be induced with intravenous anesthetic of choice, making sure to avoid hypotension with induction. Avoid long acting neuromuscular blocking (NMB) agents to facilitate monitoring of MEPs. Another set of signals should be obtained after induction of anesthesia and prior to positioning to demonstrate the extent of depression by the anesthetic agents.  Extreme caution should be used during positioning to avoid C-spine motion and to avoid other positioning related injuries.

There are multiple physiologic parameters that influence EP signals. When signal changes are reported, the surgeon, anesthesiologist and neuromonitoring team should collaborate and investigate the potential causes. Since the signal deterioration in this case occurred soon after positioning, consider the potential for improper position. But before a change in patient’s position is made, consider the influence of anesthesia and the physiologic impacts.  The influence of various anesthetic agents has been discussed already (See Q.2 above). Other significant physiologic parameters that affect neuromonitoring are blood pressure, PaO2, PaCo2, temperature and hematocrit. Spinal Cord Blood flow regulation is similar to cerebral blood flow and the importance of maintaining mean arterial pressure (MAP) at or above baseline cannot be emphasized enough. Reduction in MAP can affect cortical signals such as EEG and cortical evoked potential monitoring[24]. There are case reports of intraoperative loss of evoked potential signals due to hypotension, which improved with raising BP[25, 26]. Therefore, close monitoring of BP during the entire procedure is recommended and the addition of vasoactive agents such as a phenylephrine infusion is routinely used during these procedures. Since our institutional practice is to use TIVA during SSEP and MEP monitoring, hypotension is anticipated and phenylephrine or other agents such as nor- epinephrine infusion is started at induction. In this case the decline in EP signals improved by raising MAP to baselines.

Hypoxia and hypocarbia also should be avoided since these can affect spinal cord perfusion and affect IONM [27-29].

Body temperature has been shown to influence EEG, SSEPs, MEPS and BAEPs. Hypothermia prolongs latency and decreases amplitude of EP signals and it is suggested that core body temperature be maintained within 2-2.5 degree C of normal[30].  In addition, hypothermia can also inhibit metabolism of drugs and affect emergence from anesthesia.

If the electrophysiological signals do not improve with raising MAP (as in this case) consider repositioning the neck and check Arterial Blood Gas (ABG) to rule out anemia or other electrolyte abnormalities. Wake up test can be performed as a last resort if no improvement is observed in EP signals with the above measures.

  1. Postoperative Considerations: A detailed plan for post- operative care should be discussed at the outset and followed through. Consider the context sensitive half-life of propofol when given as infusion and titrate the dose down appropriately. A neurological examination is expected at conclusion of case; therefore plan emergence accordingly. Should the patient be extubated? Since this patient has had a high cervical lesion, the possibility of spinal cord edema and potential for post-operative complications such as respiratory arrest and airway compromise should be taken into account before the patient is extubated. If the patient is alert and oriented with stable vital signs and no airway edema, the patient could be extubated. It is ideal to send patients with high cervical lesion to ICU or at the very least to a monitored bed.

Hypoventilation and Hypoxia following extubation: The most common cause of hypoventilation and hypoxia in the immediate post op period is the presence of residual anesthesia drugs such as narcotics, neuromuscular blockers or hypnotics. Also, this patient could have spinal cord injury and edema leading to hypoventilation. Consider injury to recurrent laryngeal nerves during anterior cervical spine procedures. This is unlikely to be the case here. Mask ventilation was attempted, but failed. It is imperative that the airway is secured. Attempt intubation with the aid of a video laryngoscope while holding MILS.  Supraglottic airway can be used as rescue if a videoscope is not immediately available. Once intubated give 100 % O2 and restore adequate ventilation.

  1. The patient developed unstable supraventricular tachycardia. EKG shows irregular narrow complex tachycardia associated with hypotension. Most likely causes are A-fib, Aflutter or multifocal atrial tachycardia. Since the patient is unstable, synchronized cardioversion at 120-200 J is the recommended treatment in the ACLS algorithm by AHA[31].Consider the risks of cardioversion such as embolization in the presence of chronic A-fib. If the EKG showed wide complex tachycardia consider vagal maneuvers or treatment with adenosine, beta blockers or diltiazem. The patient was successfully cardioverted and remained stable.
  2. The patient was reintubated and had cardio respiratory complications; it would be best to leave the patient intubated overnight and reassess his condition the following morning.

During the post op visit patient was stable, extubated, but c/o painful swollen tongue. The differential diagnoses are: injury during intubation improperly placed oral airway, injury during TcMEP stimulation or patient biting down on the tongue during emergence. It is hypothesized that obstruction of either the venous outflow or the arterial inflow can lead to lingual compartment syndrome.[32] There are multiple case reports of bite injuries resulting from jaw clenching during transcranial MEP (TcMEP) stimulation.[33] Therefore it is standard practice to use bite guard of some kind when TcMEP is used during IONM. The bite blocks most commonly used are soft rolls or squares from gauze or commercially available bite guards. The most likely cause of tongue injury this patient suffered could be from stimulation causing jaw clenching. It’s possible that the bite block fell out during surgery and went unnoticed. Assess the extent of injury making sure to rule out extensive lacerations. If the laceration is deep and bleeding surgical suturing may be required.

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