UBP 2.2 (Long Form): Pediatrics – Scoliosis Flashcards
Secondary Subject -- Cobb Angle/Wake-up Test/Prone Positioning/Monitoring/ Transfusion/Spinal Cord Monitoring (MEPs and SSEPs)/ Deliberate Hypotension/ Extubation Criteria/Hypoxia Differential/Post-operative Vision Loss/Duchenne's Muscular Dystrophy/ Venous Air Embolism
Intra-operative Management:
What precautions would you take in positioning the patient for this case?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE:* Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
There are several precautions that I would take to avoid injury from lying in the prone position for a lengthy surgical case.
The head should be in the neutral position with frequent checks performed to ensure that the ears and eyes were free of pressure to prevent necrosis of ear cartilage and reduce the risk of vision loss respectively.
Given this child’s neuromuscular disease, I would take into account any contractures and limitations in range of motion during positioning.
Injury to the brachial plexus would be avoided by abducting the arms in relation to the trunk by no more than 90 degrees and by ensuring that the frame of the bed is not compressing the axillary sheath.
Additionally, I would provide padding at the ulnar nerve, avoid any direct pressure on the knees, and attempt to minimize pressure on the abdomen which can lead to increased shunting of blood through vertebral venous plexus and subsequently increased venous bleeding during the procedure.
Intra-operative Management:
What monitors would you utilize for this case?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
First I would require the standard monitors, such as a pulse oximeter, a capnograph, an ECG, a blood pressure cuff, and a temperature monitor (i.e. an esophageal stethoscope).
Given the length of the case, the need for frequent blood draws, and the risk of spinal cord injury, venous air embolism (especially since he exhibits kyphosis), significant blood loss, and cardiopulmonary depression, I would utilize the following specialized monitors:
- an arterial line, for frequent blood draws and continuous blood pressure monitoring… especially if planning deliberate hypotension;
- a precordial Doppler, placed to the right of the sternum, between the 2nd and 4th ribs, to detect venous air embolism;
- a central venous catheter, for fluid management and potential treatment of venous air embolism; and
- neurologic monitoring, such as somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), electromyography (monitoring of peripheral nerves is often employed to prevent nerve root injury during pedicle screw placement), an ankle clonus test (bilateral ankle clonus, which occurs during emergence due to the return of spinal reflexes while higher centers are still inhibited by anesthesia, is consistent with an intact spinal cord), and a wake-up test.
Intra-operative Management:
The surgeon wants you to place a pulmonary artery catheter. Would you agree to this?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Given the severity of his disease, the potential for massive blood loss, and his signs and symptoms suggestive of pulmonary hypertension and right heart failure (ECG: right ventricular hypertrophy; his diminished breath sounds; a widely split and fixed 2nd heart sound heart on auscultation; increasing dyspnea; echocardiogram: Posterobasilar hypokinesis, slow relaxation phase, right ventricular hypertrophy, and pulmonary hypertension),
I think it would be reasonable to place a pulmonary artery catheter.
While I recognize that there are risks with pulmonary artery catheter placement, especially in the presene of pulmonary hypertension, this monitor could facilitate intraoperative fluid management during this case where adequate spinal cord perfusion is crucial, and where fluid overload risks exacerbating right heart failure and pulmonary edema.
Moreover, it may provide valuable information during postoperative management.
Intra-operative Management:
Is it necessary to monitor MEPs and perform a wake-up test if you are monitoring SSEPs?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
SSEPs directly monitor the functional integrity of the posterior columns of the spinal cord and serve as an indirect monitor of anterior cord function since most injuries to the spinal cord affect both posterior and anterior function.
However, given the multiple case series reporting false negatives with SSEP monitoring alone, and considering the increased sensitivity of MEPs for detecting motor injury, many practitioners consider MEP monitoring a useful adjunct to SSEP monitoring during procedures that place the spinal cord at risk.
While the use of SSEP and MEP monitoring makes the routine use of a wake-up test unnecessary, it would still be an appropriate test in the setting of significant changes in the evoked potentials that failed to resolve with corrective action.
Intra-operative Management:
Is monitoring of EMG’s necessary?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
While the use of EMG monitoring is not universally utilized during scoliosis surgery, it can help to avoid nerve root injury during pedicle screw placement.
Repetitive stimulation of the shank of an implanted pedicle screw while monitoring the corresponding innervated muscle group for a compound muscle action potential (CMAP) is employed to identify a malpositioned screw that may lead to nerve injury.
With a properly implanted screw, surrounding bone shields adjacent nerve tissue from low current electrical stimulation (< 7 mA).
However, when an improperly placed screw breaches the pedicle wall, a low resistance pathway between the implant and nerve tissue may be created, leading to a CMAP in the corresponding myotome even with low current stimulation.
Intra-operative Management:
Are there any risks associated with the Wake-up test?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Yes.
Complications of the wake-up test include inadvertent extubation, intra-operative recall, pain, air embolism (with vigorous spontaneous inhalation), dislodgment of surgical instruments, and removal of intravenous and arterial lines.
Therefore, if a wake-up test were required, I would make sure the endotracheal tube and all lines were secure, provide adequate analgesia to prevent pain, and ask the surgeon to fill the wound with saline to reduce the risk of air entrainment with subsequent embolism.
In addition to the potential complications, the wake-up test is unlikely to detect isolated nerve root injury and is limited to neurologically normal children who are able to follow instructions.
Intra-operative Management:
How would you induce this patient?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Given this patient’s increased risk for aspiration (delayed gastric emptying and diminished laryngeal reflexes associated with DMD) and potential difficult airway management (macroglossia secondary to DMD), I would:
- ensure that the patient had received aspiration prophylaxis;
- have difficult airway equipment in the room;
- place the patient in slight reverse-trendelenburg position;
- apply cricoid pressure;
- carefully titrate intravenous ketamine for induction; and
- quickly secure the airway with an endotracheal tube.
I would utilize ketamine for induction because –
- it preserves airway reflexes (patient is at risk for aspiration),
- maintains respiratory drive (potential difficult airway),
- induces bronchodilation (potentially helpful if there is an obstructive component to his respiratory disease), and
- increases endogenous catecholamine release.
Despite his increased risk for aspiration, I would avoid succinylcholine due to the risk of hyperkalemia, muscle rigidity, rhabdomyolysis, myoglobinuria, arrhythmias, and cardiac arrest.
It would not be necessary to avoid succinylcholine due to an association between DMD and malignant hyperthermia, since there is no clear evidence to substantiate this link.
Intra-operative Management:
If you were concerned about a difficult airway, could you just perform an inhalational induction?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
An inhalational induction might be desirable for the maintenance of spontaneous ventilation, and therefore, avoid the risk of apnea in the setting of a difficult airway.
However, I would not expose a child with DMD to a volatile agent due to the risk of rhabdomyolysis and hyperkalemia, which has occurred with exposure to volatile agents alone or in combination with succinylcholine.
Moreover, an inhalational induction may result in unacceptable cardiac depression and would not facilitate the rapid endotracheal tube placement desired when a patient is at increased risk for aspiration (an intravenous induction would be quicker).
Finally, volatile agents (and nitrous oxide) cause a dose-dependent depression of evoked potentials (especially MEPs).
Intra-operative Management:
The surgeon requests muscle relaxation.
Would you agree to this?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Muscle relaxation would be beneficial in facilitating tissue retraction during surgery and inhibiting movement during stimulus generation.
However, since we are planning to utilize EMG and MEP monitoring, I would prefer to avoid neuromuscular blockade in this patient with DMD who is likely to experience an increased maximal effect and duration of action (neuromuscular blockade depresses the sensitivity of EMG monitoring in a dose-dependent manner).
If muscle relaxation became necessary, I would attempt to maintain a constant and consistent 2 out of 4 twitches of the train-of-four response, which should allow for acceptable CMAP monitoring.
Intra-operative Management:
You are expecting significant blood loss due to the number of vertebral levels that will be decorticated.
What options do you have to minimize transfusion requirements?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Strategies to minimize transfusion requirements include –
- preoperative donation of autologous blood
- (may not be advisable in this case because a body weight of < 50 kg and significant myocardial dysfunction are relative contraindications),
- acute normovolemic hemodilution,
- intraoperative blood salvage,
- deliberate hypotension,
- antifibrinolytic therapy,
- avoiding hypothermia
- (hypothermia causes platelet dysfunction, impaired vasoconstriction, and decreased coagulation factor activity), and
- proper positioning to minimize intra-abdominal pressure.
- The latter is important because increased intra-abdominal pressure can lead to excessive shunting of blood through the vertebral venous plexus with subsequent increased venous bleeding during the procedure
- (blood loss can double secondary to increased intra-abdominal pressure from poor positioning).
All of these options have their own limitations and risks; the decision to implement one or more of these techniques requires weighing potential risks against potential benefits.
These strategies may be of particular importance during scoliosis surgery on a patient with DMD, where the estimated blood loss is about 200-280 mL per vertebral level fused
- (the estimated blood loss in a patient with idiopathic scoliosis is about 60-150 mL per vertebral level).
It is theorized that the lack of dystrophin in vascular smooth muscle may impair the vasoconstrictor response, resulting in increased bleeding.
Intra-operative Management:
Given the risk of perioperative vision loss associated with spine surgery, would you agree to deliberate hypotension during this case?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Since this patient has no history of chronic hypertension, and recognizing that there is no reliable evidence suggesting an association between deliberate hypotension and the development of perioperative vision loss, I would consider employing deliberate hypotension as a blood conservation strategy if I believed the benefits outweighed the theoretical risk of inadequate perfusion of the optic nerve.
However, I would not completely dismiss the theoretical concern that hypotension could lead to optic nerve ischemia secondary to – anatomic variation in the circulation supplying the optic nerve, abnormal autoregulation, and/or inadequate compensation for decreased perfusion pressure.
In fact, many of the consultants and specialty members surveyed for the ASA practice advisory for perioperative visual loss associated with spine surgery believed that deliberate hypotension should be avoided in high-risk patients (patients anticipated preoperatively to undergo prolonged procedures, have substantial blood loss, or both) even in the absence of preoperative chronic hypertension.
In addition to concerns of inadequate perfusion of the optic nerve, deliberate hypotension may place the patient at risk for cerebral and spinal cord ischemia (especially when hemodilution is used concomitantly to minimize transfusion requirements).
Therefore, I would attempt to optimize end-organ perfusion by ensuring adequate oxygen carrying capacity and monitoring the ECG, CVP, motor evoked potentials, urine output (output should be at least 0.5-1.0 mL/kg/hr), and periodic arterial blood gases (to check for metabolic acidosis).
Intra-operative Management:
The surgeon asks you to employ deliberate hypotension to reduce bleeding and improve visualization in the surgical field.
What technique will you use to produce hypotension?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
While there are many options for inducing hypotension, I would reduce his mean arterial pressure to no lower than 60 mmHg using Clonidine and remifentanil, with the addition of short acting agents, such as sodium nitroprusside and esmolol, as required.
These short acting agents would facilitate the performance of a wake-up test and are less likely to interfere with evoked potential monitoring than are volatile agents.
As I mentioned before, given the risk of ischemic injury to the optic nerve, heart, brain, and spinal cord, I would ensure adequate intravascular volume, maintain a hemoglobin of at least 7-8 g/dL, and carefully monitor his ECG, motor evoked potentials, urine output, and blood gases for signs of inadequate end-organ perfusion.
Intra-operative Management:
Two hours into the case, decreased amplitude and increased latency are noted while monitoring SSEPs. What will you do?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
A 50% decrease in amplitude and/or a 10% increase in latency of the SSEP signal and/or a 50% decrease in amplitude of the MEP signal would be considered clinically significant (some sources suggest that a “significant” decrease in MEP amplitude requires a 75-80% change).
Therefore, assuming the changes were significant, I would:
- correct any hypoxemia, hypotension, hypovolemia, anemia, and hypo/hypercarbia in order to optimize oxygen delivery to the spinal cord and reverse any conditions that may result in false-positives;
- make sure that the depth of anesthesia had remained stable and was not interfering with the evoked potential readings; and
- ask the surgeon to rule out surgical causes of spinal cord injury such as excessive distraction.
If the SSEP and/or MEP signals remained abnormal despite these actions, I would – perform a wake-up test to determine if further steps, such as removing surgical instruments, were necessary.
Intra-operative Management:
Due to persistent evoked potential signal changes, you perform a wake-up test and the patient is able to appropriately move his feet and toes while squeezing your hand.
Soon after reestablishing general anesthesia, his blood pressure drops to 68/30 mmHg and you notice a decrease in his end-tidal CO2.
What do you think is going on?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
A concomitant drop in both blood pressure and end-tidal CO2 following a wake-up test (where the patient may have vigorously inhaled) is consistent with venous air embolism (VAE).
However, any event that resulted in a significant reduction in cardiac output could present with a similar decline in blood pressure and end-tidal CO2.
Therefore, other etiologies I would be considering would include – aspiration (hypoxic pulmonary vasoconstriction can lead to acute pulmonary hypertension with subsequent cardiac failure), massive hemorrhage, myocardial ischemia, congestive heart failure, cardiac dysrhythmia, tension pneumothorax, anesthetic overdose, and delayed anaphylactic reaction.
In order to determine if this clinical picture were secondary to VAE, I would listen for sporadic roaring sounds from the precordial Doppler, auscultate the heart for the characteristic “millwheel” murmur (best heard through an esophageal stethoscope), attempt to aspirate air through the central venous catheter, and/or consider transesophageal echocardiography.
Intra-operative Management:
You hear sporadic roaring sounds from the precordial Doppler. What would you do?
- (A 28 kg, 11-year-old male presents for posterior repair of kyphoscoliosis.*
- HPI: His mother states that her son has Duchenne’s muscular dystrophy (DMD), has been wheelchair bound since he was 9 years old, and has experienced increasing shortness of breath over the past 6 months.*
- PSH: Tympanostomy at 2 years of age, no surgical or anesthetic complications*
- Medications: Prednisolone, Enalapril*
- Allergies: None*
- PE: Vital Signs: P = 108 b/min; BP = 100/64 mmHg; R = 12*
- Airway: Macroglossia; Mallampati II; good neck and TMJ range of motion.*
- CV: Sinus tachycardia; widely split and fixed 2nd heart sound; mid-systolic click*
- Lungs: Clear to auscultation with diminished breath sounds bilaterally*
- CXR: Thoracolumbar kyphoscoliosis; Cobb angle of 70º,*
- ECG: RVH; right atrial enlargement; sinus tachycardia; inverted T-waves*
- Lab: Hgb = 15.6*
- ABG: pH = 7.42, pCO2 = 43, pO2 = 78*
- PFTs: FEV1 and FVC are both < 30% of predicted*
- Stress Echo: Posterobasilar hypokinesis; slow relaxation phase; right ventricular hypertrophy; pulmonary hypertension)*
Since this finding is consistent with a venous air embolism, I would –
- immediately ask the surgeon to flood the field with saline;
- discontinue nitrous oxide (probably should be avoided in the first place) and deliver 100% oxygen;
- attempt to aspirate entrained air through the central venous catheter (to remove air that may be interfering with right-sided cardiac output);
- administer fluids to increase central venous pressure and provide cardiovascular support;
- provide vasoconstrictors, inotropes, and chest compressions as necessary; and
- treat bronchospasm with B2-adrenergic agonists (reflex bronchospasm may occur with the entry of air into the pulmonary artery).
If necessary, I would consider placing the patient in the left lateral decubitus position to facilitate the displacement of air into the right atrium and away from the pulmonary outflow tract, where the formation of an air lock can obstruct forward flow.
