UBP 6.7 (Long Form): Neuro – Cerebellar Tumor

Question 1

Intra-operative Management:

What monitors would you place for this case?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 1

I would start by placing the standard ASA monitors, recognizing that capnography is particularly important to ventilation management of this patient with elevated ICP.

Given her signs and symptoms of severely elevated ICP, I would ask the surgeon to consider performing a ventriculostomy to allow for continuous ICP monitoring and CSF drainage when necessary.

Given her cardiac condition (mitral valve prolapse with moderate mitral regurgitation increases the risk of hypotension), and considering the importance of maintaining adequate cerebral perfusion and accurately monitoring PaCO2, I would place an arterial line for continuous monitoring of systemic blood pressure and repetitive blood sampling for arterial blood gas analysis.

Since this case is going to be performed with the patient in the sitting position, I would place a precordial Doppler to aid in the detection of venous air embolism (place to the right of the sternum, between the 2^nd and 4^th ribs), and consider placing a central line to provide a means of aspirating embolized air from the heart (a multi-orifice catheter placed with the tip 2 cm below the superior vena caval-atrial junction allows for optimal aspiration of air).

Due to the length of the surgery and the potential need for drug-induced diuresis, I would place a Foley catheter.

In order to prevent hyperthermia and/or excessive hypothermia, I would place an esophageal temperature probe.

I would also discuss the use of neurophysiology monitoring, such as EEG, EMG, brainstem auditory evoked responses (BAERs), and somatosensory evoked potentials (SSEPs), with both the surgeon and the neurophysiologist.

Finally, if electromyography (EMG) monitoring were not planned, I would utilize a peripheral nerve stimulator to help ensure adequate neuromuscular blockade during this case where reliable patient relaxation is very important.

Question 2

Intra-operative Management:

Could you use transesophageal echocardiography to monitor for intracardiac air?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 2

Transesophageal echocardiography (TEE) would be useful for –

• monitoring the cardiac function of this patient with MVP and moderate mitral regurgitation; and for
• detecting and quantifying intracardiac air in this patient undergoing a craniotomy in the sitting position (increased risk of VAE).

However, in making a decision to use this modality, I would consider the possibility that the placement of a TEE probe may contribute, along with other oral instruments (ETT, esophageal stethoscope, and an oral airway) and excessive neck flexion, to impaired venous drainage from the tongue and subsequent macroglossia.

Question 3

Intra-operative Management:

The surgeon is planning to perform a ventriculostomy following induction. Given the severity of her intracranial hypertension, would you delay induction, intubation, and mechanical hyperventilation for placement of the arterial and central lines?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 3

Given this patient’s cardiac condition, severe intracranial hypertension, minimal intracranial compliance, and potentially rightward-shifted or compromised cerebral autoregulation,

I would prefer to place the arterial line prior to induction to allow for close hemodynamic monitoring to prevent excessive hypertension/hypotension and ensure adequate cerebral perfusion during induction and laryngoscopy.

However, considering her elevated PaCO2 and the importance of hyperventilation as a method of reducing her critically elevated ICP, I would immediately attempt to induce hyperventilation with cricoid pressure and gentle assisted ventilation until a definitive airway was established, recognizing that her nausea, vomiting, and mental status place her at increased risk of aspiration.

Placement of the central venous line, on the other hand, could be delayed until after induction and intubation if I believed that prior placement imposed an unacceptable delay to controlled ventilation via a secure ETT.

Moreover, if placement of the arterial line proved difficult, imposing an unacceptable delay, I would place a NIBP cuff in stat mode and proceed with induction, with the goals of avoiding significant hypotension during induction, avoiding excessive hypertension during laryngoscopy, quickly securing the airway with an ETT, and placing the arterial line immediately following the institution of mechanical hyperventilation.

Question 4

Intra-operative Management:

Where would you place the central line?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 4

Following placement of the ETT and the initiation of hyperventilation,

I would place a central venous line using either the brachial vein or the subclavian vein.

While the subclavian approach carries a higher risk of pneumothorax, I would avoid placement in the internal jugular vein due to the need to avoid the head-down position during placement and the potential for obstruction of cerebral venous drainage following placement, which could lead to increased ICP.

Given the increased risk of VAE when undergoing craniotomy in the sitting position, I would place with the tip of a multi-orificed catheter 2 cm below the superior vena caval-atrial junction to allow for optimal aspiration of intra-cardiac air.

I would then confirm the correct positioning using either x-ray or intravascular electrocardiography (TEE can also be used).

When using intravascular electrocardiography to place the multi-orificed catheter, I would –

• obtain a battery-operated ECG unit (reduces the risk of micro shock),
• flush the catheter with sodium bicarbonate,
• attach the leg lead to the hub of the CVP catheter,
• advance the catheter into the right ventricle using the pressure wave form as a guide, and
• pull the catheter back until the lead II P-wave is biphasic (this indicates mid-atrial positioning).

I would then pull the catheter further back until the P-wave and the QRS complexes are of equal amplitude.

Finally, I would pull the catheter back an additional centimeter and secure the line, placing the tip of the catheter near the sino-atrial node.

Question 5

Intra-operative Management:

How are you going to induce anesthesia in this patient?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 5

When inducing this patient with significant intracranial hypertension, I would have the following goals:

1. avoid hypotension, which could result in inadequate cerebral perfusion pressure;
2. maintain adequate muscle relaxation and depth of anesthesia to avoid sympathetic-induced hypertension with subsequent hyperemia, increased CBF, increased CBV, cerebral edema, and increased ICP;
3. maintain adequate ventilation to avoid hypoxia and/or increases in PaCO2, with the latter leading to cerebral vasodilation, and increases in CBF, CBV, and ICP;
4. avoid any factor, such as decreased systemic vascular resistance and/or increased myocardial contractility, that would result in more complete emptying of the left ventricle which, in the setting of MVP, often increases the severity of the mitral valve prolapse and regurgitation; and
5. avoid aspiration, in this patient with symptoms of nausea and vomiting.

Therefore, assuming the patient had a reassuring airway, I would – apply appropriate monitoring; pre-oxygenate with 100% oxygen and a tight mask seal; apply cricoid pressure (obtunded patient with symptoms of nausea and vomiting); administer lidocaine, esmolol, and fentanyl to blunt any sympathetic response to laryngoscopy; titrate on a small dose of etomidate to avoid hypotension; add a volatile agent, staying below 1 MAC to avoid cerebral vasodilation; administer a nondepolarizing muscle relaxant, assuming it does not interfere with neurophysiology monitoring; ensure adequate muscle relaxation using a peripheral nerve stimulator; perform careful direct laryngoscopy and secure the airway with an ETT; and be prepared to treat any hemodynamic instability.

Question 6

Intra-operative Management:

Wouldn’t you want to use succinylcholine?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 6

The use of succinylcholine would be desirable for this patient at increased risk of aspiration (obtunded patient with symptoms of nausea and vomiting) due to its ability to reliably provide optimum intubating conditions within a short period of time, facilitating the rapid replacement of an ETT, and thereby reducing the risk of aspiration.

However, even the transient increase in ICP associated with succinylcholine may not be tolerated in the setting of significantly decreased intracranial compliance.

Therefore, given her signs and symptoms suggesting significant intracranial hypertension (and decreased intracranial compliance), I would avoid this depolarizing muscle relaxant in this case.

Question 7

Intra-operative Management:

Following induction, the patient’s blood pressure drops to 88/40 mmHg.

Are you concerned?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 7

Considering this patient’s significant intracranial hypertension, and recognizing the risk of cerebral ischemia with a drop in mean arterial blood pressure (CPP = MAP - ICP),

I am very concerned about this substantial drop in blood pressure.

Moreover, I am concerned that this significant hypotension may represent a potentially serious complication other than hypovolemia and excessive anesthesia, such as:

1. tension pneumothorax, possibly secondary to central line placement;
2. brain herniation, with subsequent autonomic instability;
3. ventricular dysrhythmia, myocardial ischemia, and/or cardiac failure due to acutely worsening mitral regurgitation (presumably due to increased left ventricular emptying and worsening valve prolapse secondary to dedreased preload, decreased afterload, and/or increased inotropy); and
4. anaphylactic reaction, possibly secondary to antibiotic administration.

Question 8

Intra-operative Management:

After resection of the tumor the surgeon is unable to close the cranium because the brain tissue is too swollen.

What will you do?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 8

Recognizing that the quickest and most effective method of providing brain relaxation would be to drain CSF via the ventriculostomy, I would begin by draining CSF in 10-20 mL aliquots as tolerated.

If this were inadequate or not well tolerated, I would consider one or more of the following interventions:

1. hyperventilation to a PaCO2 of 30 mmHg to reduce cerebral blood volume (further reductions may cause more harm than good);
2. the administration of mannitol or hypertonic saline to increase plasma osmolarity and draw water from brain tissue (duration of affect is approximately 6 hours);
3. giving furosemide to promote diuresis and reduced intravascular volume (particularly useful when mannitol is inadequate or inappropriate → i.e. CHF or nephrotic syndrome);
4. administering dexamethasone to reduce tumor related edema;
5. eliminating any obstruction to venous drainage from the intracranial compartment (jugular venous outflow);
6. ensuring adequate anesthesia to prevent sympathetic-induced increases in blood pressure and CBV (use propofol, thiopental, or etomidate rather than a volatile agent);
7. treating excessive hypertension that could be leading to increased CBV;
8. reducing or discontinuing volatile agents to avoid their cerebral vasodilatory effects; and
9. ensuring an adequate serum sodium level, recognizing that hyponatremia could be contributing to cerebral edema.

Question 9

Post-operative Management:

The surgeon asks if you would extubate the patient in the operating room under a deep plane of anesthesia to avoid stimulation and increases in ICP.

Would you agree?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 9

Immediate post-operative extubation under a deep plane of anesthesia is desirable to allow for immediate neurological examination and to avoid excessive stimulation due to coughing and/or straining.

However, given this previously obtunded patient’s increased risk of aspiration (questionable airway reflexes and preoperative nausea and vomiting) and CO2 retention (compromised mental status pre-operatively, intra-operative opioid administration), I would delay her extubation until she was able to demonstrate intact airway reflexes and adequate spontaneous ventilation.

Moreover, following tumor resection in the posterior fossa (especially near the brainstem), post-operative edema and/or hematoma formation can lead to worsening neurologic status during the first couple of post-operative days, necessitating prolonged intubation.

If an immediate neurological exam were necessary, I would administer a short acting opioid, lidocaine, and esmolol (to avoid coughing, bucking, and hypertension); wake the patient; perform a quick neurological assessment; and then provide adequate sedation for transport to the ICU with the endotracheal tube still in place.

Question 10

Post-operative Management:

The patients seems slow to awake. What is your differential for the delayed emergence of this patient?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 10

Given her recent craniotomy and elevated ICP, my differential would include –

• hematoma formation,
• tension pneumocephalus,
• cerebral edema,
• cerebral ischemia/infarction,
• hypoxia,
• hypercarbia,
• seizure, and/or
• obstructive hydrocephalus.

However, my differential would also include those causes associated with routine anesthetic, such as – prolonged neuromuscular blockade, residual anesthetic, acid-base abnormality, electrolyte imbalance, and/or significant hypothermia.

Question 11

Post-operative Management:

How would you manage this patient?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 11

I would –

• examine the patient;
• review ICP pressures provided by the ventriculostomy;
• optimize hemodynamics;
• ensure adequate ETT placement and ventilation, order electrolytes and an ABG;
• use a peripheral nerve stimulator to check for residual neuromuscular blockade;
• review the chart for administered medications and their doses (especially opioids, nondepolarizers, and neuromuscular reversal agents);
• check the patient’s temperature;
• inform the surgeon;
• consider a CT or MRI, and provide supportive care.

If I believed her symptoms were the result of elevated ICP, I would consider draining CSF from the ventriculostomy; initiating more aggressive hyperventilation; administering mannitol, furosemide, or dexamethasone; and discuss surgical options with the surgeon.

Question 12

Post-operative Management:

Assuming you did not use nitrous oxide (N2O) during the case, could her delayed awakening be due to tension pneumocephalus?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 12

While the use of N2O following dural closure may signficantly augment the volume of any trapped intracranial air (35 times more soluble than nitrogen in blood);

a tension pneumocephalus may develop even when N2O is avoided.

This complication is most commonly associated with posterior fossa craniotomies performed in the sitting position, with air moving over the surface of the brain to become trapped in the upper cranium.

This is more likely to occur when aggressive brain relaxation measures are initiated (hyperventilation, osmotic diuresis, etc.), creating an available space for air to occupy.

The patient becomes symptomatic (delayed emergence, headache) when this volume is augmented by nitrous oxide, or with the reaccumulation of intracranial contents (CSF, venous blood, arterial blood, extracellular fluid, etc.)

Question 13

Post-operative Management:

On the second post-operative day, the nurse calls and reports the patient has impaired dorsiflexion of the right foot. What do you think is the cause?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 13

Her inability to dorsiflex her right foot is consistent with a foot drop injury,

which may be associated with a variety of conditions, such as –

• dorsiflexor injuries,
• peripheral nerve injuries (stretching of the sciatic or common peroneal nerves may occur in the sitting or lithotomy position),
• stroke,
• neuropathies,
• drug toxicities, or
• diabetes.

Given her recent surgery in the sitting position, I would consider specific causes of sciatic or common peroneal nerve injury related to this position, such as:

1. stretch injury with excessive flexion of the hips and/or insufficient bending of the knees; or
2. compression injury secondary to inadequate padding of the buttocks where the sciatic nerve emerges from the pelvis.

Considering her recent craniotomy and elevated ICP, I would also consider – parasagittal cortical or subcortical cerebral infarction.

Question 14

Post-operative Management:

What are the risk factors associated with peripheral nerve injury?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 14

The risk factors for peripheral nerve injury include –

• male gender,
• hospital stay greater than 14 days,
• intra-operative hypotension,
• history of vascular disease and/or hypertension,
• diabetes,
• smoking, and
• very thin or obese body habitus.

Fortunately, more than half of all patients who develop perioperative peripheral neuropathies regain full sensory and motor function within 1 year.

Question 15

Post-operative Management:

If this were a peripheral nerve injury, could it have been prevented?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 15

The mechanism of peripheral nerve injury is not fully understood and is most likely multifactorial.

While there is data to suggest that some peripheral nerve injury is not preventable, I would have attempted to reduce the risk as much as possible by:

1. performing a careful pre-operative assessment to evaluate the patient’s tolerance of the planned operative position (probably not possible in this obtunded patient);
2. ensuring appropriate patient positioning, particularly avoiding hip flexion beyond 90º (or beyond the patient’s comfort level as determined by the pre-operative assessment), insufficient bending at the knees, and excessive neck flexion (although this is not considered peripheral nerve injury, excessive neck flexion when undergoing posterior fossa surgery in the sitting position can lead to midcervical tetraplegia secondary to stretching of the spinal cord); and
3. ensuring adequate padding to common pressure points, including the buttocks and peroneal nerve at the fibular head.

Post-operatively, I would perform a careful assessment of extremity nerve function to facilitate early identification of any peripheral nerve injury.

Question 16

Post-operative Management:

How would you manage this patient?

What would you tell her family?

• (A 24-year-old female presents for emergent craniotomy and resection of a cerebellar tumor in the sitting position. She has a history of progressive headache, nausea, and imbalance over the previous two months; over the last 24 hours she has become obtunded and confused.*
• PMHx: Mitral valve prolapse, Depression, von Willebrand’s disease*
• Meds: Zoloft, Propranolol*
• Allergies: NKDA*
• PE: Vital Signs: HR = 58, BP = 188/94 mmHg, RR = 10, Temp = 36.4ºC*
• General: obtunded and confused*
• Head: Papilledema*
• CV: Systolic ejection click, 3/6 SEM*
• Labs: Hgb 12.4 g/dL; Urine HCG negative;*
• ABG pH 7.30; PaO2 110 mmHg; PaCO2 58 mmHg; SaO2 99% on 2 liters oxygen*
• CT: large posterior fossa mass with compression of the 4th ventricle.*
• Echo: moderate mitral regurgitation; dilated left atrium)*

Answer 16

I would review the chart, perform a focused history, and evaluate the patient to determine the type and severity of the injury.

Depending on my finding, I would consider a neurological consult with nerve conduction velocity studies and EMG to establish or confirm the diagnosis.

Ideally, given the preoperative mental status of the patient, I would have discussed the risk of peripheral nerve injury with her family.

At this time, I would inform the patient and her family of my concerns and my plans for further evaluation.

I would then reassure them that most cases of peripheral neuropathy resolve within 6-12 weeks without intervention and let them know I would arrange for consultation with a neurologist and the appropriate follow up care.