UBP 6.3 (Long Form): Pediatrics – Strabismus Surgery

Question 1

Intra-operative Management:

You are unable to properly seat the LMA and decide to place an endotracheal tube.

Would you use succinylcholine for this case?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 1

I would prefer NOT to use succinylcholine for this case because –

it may interfere with the forced duction test often used during strabismus surgery (it may interfere with the test for up to 20 minutes), and due to the risk of undiagnosed muscular dystrophy in this patient < 8 years of age.

Children with dystrophinopathies often do not exhibit signs of the disease in the early stages.

Despite a lack of outward symptoms, the disease can lead to a proliferation of extrajunctional normal, nicotinic (neuronal), and fetal (containing y (gamma) subunits) acetylcholine receptors.

The activation of these extrajunctional acetylcholine receptors by succinylcholine may result in rhabdomyolysis and life threatening hyperkalemia.

Therefore, in the absence of a compelling indication, it is recommended that succinylcholine be avoided in all children under the age of 8 (especially males).

Clinical Notes:

• Strabismus surgery is no longer considered a predisposing factor for MH.
• The only disorders considered linked to MH are the rare muscle disorders, Central Core Disease and King Denborough Syndrome.
• The use of triggering agents (succinylcholine and volatile agents) for a patient with certain muscular dystrophies (i.e. Duchenne’s Muscular Dystrophy) may lead to an “MH-like” event, with rhabdomyolysis and hyperkalemia. This response is not, however, considered a true MH reaction.

Question 2

Intra-operative Management:

After performing an inhalational induction, and without consulting you, the resident administers succinylcholine. A couple of minutes later, you are unable to open the patient’s mouth. What do you think might be causing this problem?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 2

Assuming that an adequate dose of succinylcholine was delivered through a working intravenous line, this could represent –

• succinylcholine-induced masseter muscle rigidity (MMR),
• undiagnosed myotonic syndrome,
• temporomandibular dysfunction,
• undiagnosed muscular dystrophy, or
• a malignant hyperthermia reaction.

Although it is unusual for this to significantly inhibit ventilation, the development of MMR is concerning because it may suggest a susceptibility to malignant hyperthermia (MH).

Due to the risk of a developing MH reaction (around 30-50% following significant MMR) or rhabdomyolysis (often occurs following MMR independent of a MH reaction), this elective case should be cancelled and the patient admitted to the hospital for 12-24 hours of monitoring for myoglobinuria (rhabdomyolysis can lead to hyperkalemic dysrhythmias, myalgias, peripheral compartment syndrome, acute tubular necrosis, and obstructive neuropathy), generalized rigidity (rigidity of the chest and/or extremities increases the risk of progression to MH), and/or signs of hypermetabolism.

Patient care should also include –

• a neurology evaluation for the presence of occult myopathy, and
• close monitoring of –
  
  • serum electrolytes (rhabdomyolysis can lead to hyperkalemia),
  • temperature, and
  • creatine kinase levels (in the absence of a myopathy, a CK level > 20,000 IU increases the likelihood that the patient is MH susceptible).

Clinical Note:

• MHAUS (Malignant Hyperthermia Association of the United States) recommends immediately initiating MH treatment and cancelling any elective procedure following significant MMR.
  
  • “If a patient has received succinylcholine and his/her jaw cannot be opened or the patient has peripheral muscle rigidity, the clinician should assume this is an MH event and immediately begin MH treatment.” MHAUS website
  • “… whenever MMR occurs following succinylcholine, elective surgery should be postponed. If the procedure is emergent, the anesthetic may continue with nontrigger agents.” MHAUS website.

Question 3

Intra-operative Management:

Could this be malignant hyperthermia, if he had a previously uncomplicated anesthetic?

• (Resident gave succinylcholine* after inhalational induction. A couple minutes later, you are unable to open the patient’s mouth.)
• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 3

The variable expressivity of MH makes it possible for a patient to experience one or more exposures to a triggering agent without copmlication, prior to developing MH with a subsequent exposure.

Unfortunately, it seems that once a patient experiences an MH reaction to a triggering agent, subsequent exposures will always result in MH.

Question 4

Intra-operative Management:

Assuming there were no additional signs of malignant hyperthermia, would you recommend a Caffeine Halothane Contracture Test (CHCT) based on this event?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 4

If the MMR was severe, or mild to moderate with evidence of rhabdomyolysis,

I would recommend the patient undergo a Caffeine Halothane Contracture Test (CHCT) to further evaluate his susceptibility to MH.

Assuming the child met the minimal criteria for the test (at least 7 years of age and 20 kg in weight), testing would potentially provide a more definitive diagnosis (97% sensitivity and 78% specificity), allow for greater anesthetic choices in the future (assuming a negative result), and/or aid in the identification of affected family members (assuming a positive result).

However, in making this decision, family members will have to consider expense (travel and the procedure itself) and the risks of allowing their child to undergo another invasive procedure.

Question 5

Intra-operative Management:

You explain the problem to the mother, who is extremely upset that you want to cancel the case. She reminds you that you cancelled the case last time because of an upper respiratory tract infection, forcing her to ask her boss for another day off from work. She is crying and tells you that she will lose her job if she asks for another day off.

Would you proceed with the case?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 5

Assuming the facility was properly equipped to treat MH, I would consider proceeding with this elective case after a frank discussion of the risks with the mother and the surgeon.

I would explain to them that the decision to proceed under these conditions is somewhat controversial due to the risk of a malignant hyperthermia reaction developing despite proceeding with a non-triggering anesthetic.

If, after this discussion, the surgeon and mother still wished to proceed with the case, I would ensure the immediate availability of Dantrolene; prepare a “clean” anesthesia machine; plan to carefully monitor temperature, end-tidal CO2, and arterial blood gases; and provide a non-triggering anesthetic.

Clinical Notes:

• This issue is controversial, and many practitioners and authors argue that it is reasonable to continue with an elective procedure using a nontriggering anesthetic, as long as preparations for MH treatment are made, and the patient is appropriately monitored.
• However, keep in mind that, as noted earlier, MHAUS (Malignant Hyperthermia Association of the United States) recommends immediately initiating MH treatment and cancelling any elective procedure following significant MMR.
  
  • “If a patient has received succinylcholine and his/her jaw cannot be opened or the patient has peripheral muscle rigidity, the clinician should assume this is an MH event and immediately begin MH treatment.” MHAUS website
  • “… whenever MMR occurs following succinylcholine, elective surgery should be postponed. If the procedure is emergent, the anesthetic may continue with nontrigger agents.” MHAUS website

Question 6

Intra-operative Management:

After explaining the risks to the mother, you decide to proceed with the case (examiner note: Make sure the case proceeds, even if you need to have one of the candidate’s partners agree to continue the case and then have to leave for emergency).

Would you administer prophylactic dantrolene?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 6

Assuming there were no signs of generalized rigidity or hypermetabolism, I would NOT administer prophylactic dantrolene.

Given the extremely low likelihood of a MH reaction during a non-triggering anesthetic and, recognizing that dantrolene is associatd with several side effects including – nausea, vomiting, and pain at the injection site, I would avoid dantrolene until the patient exhibited signs consistent with a MH reaction.

However, my threshold for the initiation of treatment would be low.

• Clinical Note:*
• While the prophylactic use of dantrolene is not recommended, some practitioners would initiate treatment based on the occurrence of significant MMR (trismus), given it’s relatively high association with malignant hyperthermia. MHAUS would concur with this course of action.

Question 7

Intra-operative Management:

How would you prepare the anesthesia machine for the case?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 7

In order to prepare the machine to deliver a non-triggering anesthetic, I would –

remove any succinylcholine from the area,

physically disengage all vaporizers (or at least place tape across the dials),

replace the anesthetic circuit and CO2 absorbent, and

flush the anesthesia machine with 10 L/mm of oxygen for at least 10 minutes (newer machines may require longer periods of flush time or may be autoclavable – refer to manufacturer guidelines).

Additionally, I would ensure the presence of iced solutions, appropriate monitors, and adequate supplies of dantrolene.

Question 8

Intra-operative Management:

The surgery is proceeding and the child’s heart rate falls to 62 beats/minute.

What would you do?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 8

I would first –

• ask the surgeon to cease any manipulation of the eye,
  
  • since this bradycardia is possibly a result of the oculocardiac reflex.

I would then ensure proper endotracheal tube placement, auscultate the lungs, ensure adequate ventilation and oxygenation, evaluate the cardiac rhythm and blood pressure, and assess the patient’s volume status and anesthetic depth

(insufficient anesthetic depth could leave the patient more susceptible to the oculocardiac reflex, while excessive anesthetic depth could lead to cardiac depression with subsequent bradycardia).

If I believed this to be the result of the oculocardiac reflex, in addition to stopping surgical manipulation, I would –

• correct any hypercarbia or hypoxemia
  
  • (believed to augment this reflex),
• deepen the anesthetic
  
  • (since light anesthesia may be contributory), and
• consider the administration of intravenous atropine
  
  • (Dose: 0.02 mg/kg.
  • Some authors discuss atropine as a treatment option to interrupt the reflex;
  • others suggest that atropine administration while the reflex is active could trigger more serious cardiac dysrhythmias.)

If the bradycardia persists despite these measures, I would –

• have the surgeon infiltrate the rectus muscle with local anesthetic.

Question 9

Intra-operative Management:

What is the oculocardiac reflex?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 9

The reflex may be triggered by surgical manipulation of the eye and orbital structures and most commonly occurs in pediatric patients undergoing strabismus surgery

(the reflex most often occurs with manipulation of the medial rectus muscle, but may result following stimulation of any of the orbital structures).

The afferent limb of the reflex involves the ciliary nerves and ophthalmic division of the trigeminal nerve, (V)

while the efferent limb is the vagal nerve. (X)

Stimulation of this reflex, which may occur under local or general anesthesia, most commonly results in bradycardia, but can lead to a wide variety of cardiac dysrhythmias.

Fortunately, this reflex seems subject to fatigue and, if the episode is successfully treated, the reflex is less likely to reoccur with repeated stimulation.

Question 10

Post-operative Management:

The PACU nurse calls you 10 minutes after you leave your patient in the unit to report that his pulse rate has increased to 118 beats/minute.

What would you do?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 10

First I would evaluate the patient’s volume status and ensure adequate pain control, oxygenation, and ventilation.

Next, given the fact that there is an increased incidence of MH in patients who experience an episode of significant MMR, I would evaluate the patient for other signs of MH such as – generalized rigidity, tachypnea, changes in blood pressure, arrhythmias, increased temperature, peripheral mottling, rhabdomyolysis (tea colored urine), sweating, and cyanosis.

If optimization of the patient’s ventilation, volume status, and pain control did not resolve the tachycardia, I would – obtain an arterial blood gas (decreased PO2, metabolic and respiratory acidosis) and check for hyperkalemia, hypercalcemia, myoglobinemia, and elevated serum creatine kinase.

If after a brief investigation I were still concerned that this may be MH, I would administer 2.5 mg/kg of dantrolene and continue to monitor him closely.

Question 11

Post-operative Management:

You get an ABG: pH = 7.15; PaCO2 = 64; HCO3 = 24; PaO2 = 88; SpO2 = 96% on 10 L O2 by simple mask.

How would you interpret this?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 11

This ABG shows an uncompensated respiratory acidosis with low oxygen tension.

Recognizing that during the initial stages of a MH reaction an arterial blood gas may show a nearly pure respiratory acidosis, I would remain concerned about malignant hyperthermia.

Inappropriate release of calcium from the sarcoplasmic reticulum leads to intense muscle contractions and uncontrolled aerobic and anaerobic metabolism.

The hypermetabolic state of MH results in – increased oxygen consumption, increased CO2 production, and severe lactic acidosis.

Therefore, if the patient’s ventilation appeared adequate, I would order a mixed or peripheral venous blood gas and, if the results indicated a hypermetabolic state (PvO2 < 40 mmHg despite supplemental oxygen due to increased oxygen consumption), initiate aggressive treatment.

Clinical Note:

• A mixed or peripheral venous blood gas analysis is a more sensitive measurement of the decreased oxygen saturation, increased lactate production, and increased CO2 levels associated with the hypermetabolic state.
  
  • Normal Mixed Venous Oxygen Saturation (SvO2) = 60-80%
  • Normal Partial Pressure of Oxygen in Venous Blood (PvO2) = 40 mmHg
  • Normal PvO2 with supplemental oxygen = > 60 mmHg

Question 12

Post-operative Management:

How would you manage this patient with suspected malignant hyperthermia?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 12

I would:

1. call for assistance;
2. hyperventilate the patient with 100% oxygen by face mask;
3. administer dantrolene (2.5 mg/kg of Dantrolene every 5-10 minutes as necessary to control symptomatology);
4. maintain urine output with intravenous fluids, mannitol, and lasix;
5. monitor urine output, potassium, calcium, and arterial blood gases;
6. order serum creatine kinase, liver function tests, and a coagulation profile; and
7. treat hyperkalemia (dextrose and regular insulin), acidosis (bicarbonate), hyperthermia (cold intravenous fluids; ice packs over major arteries of the groin and axilla; gastric, bladder, rectal, and wound lavage; cold peritoneal dialysis; and even cardiopulmonary bypass), rhabdomyolysis (mannitol), and dysrhythmias as necessary.
8. Finally, after resolution of the crisis, I would – continue intravenous dantrolene, 1 mg/kg every 6 hours, for 24-48 hours to prevent relapse; and
9. monitor the patient for up to 72 hours in the ICU for signs of disseminated intravascular coagulation, myoglobinuric renal failure, and recrudescence (relapse).

Question 13

Post-operative Management:

The patient’s temperature is rapidly rising.

What are your options for active cooling of the patient?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 13

My options for actively cooling the patient include the infusion of cold intravenous fluids;

the placement of ice packs over major arteries (groin and axilla);

iced saline gastric, bladder, rectal, and wound lavage;

cold peritoneal dialysis; and even

cardiopulmonary bypass.

Active cooling should be discontinued when the temperature drops to 38-38.5ºC to prevent hypothermia.

Question 14

Post-operative Management:

How long would you continue dantrolene after the patient’s ABGs returned to normal?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 14

As I mentioned before, I would –

continue dantrolene, 1 mg/kg every 6 hours, for 24-48 hours, because up to 25% of patients may experience relapse within the first 24 hours.

Dantrolene should be administered every 6 hours because, although the half-life is about 12 hours, serum levels remain therapeutic for only 4-6 hours after a dose.

Question 15

Post-operative Management:

During the first couple of hours following the acute episode, the patient’s urine output is only 0.5 mL/kg/hr.

Does this concern you?

• (A 7-year-old male presents for strabismus surgery.*
• PMH: His mother says that he experiences asthmatic attacks requiring a breathing treatment 1-2 times every month. She reports that 4 weeks ago, he had a cold with a mild fever and productive cough.*
• Anesthetic Hx: He experienced no anesthetic problems when he had his tonsils removed three years ago.*
• Physical Exam: VS: BP = 105/65 mmHg; P = 102; R = 14; T = 37ºC*
• General: Child appears to be active and healthy*
• Airway: Mallampati I, no loose teeth*
• CV: RRR*
• Lungs: CTA bilaterally)*

Answer 15

This relatively low urine output is concerning due to the risk of myoglobinuric renal failure.

Malignant hyperthermia often leads to rhabdomyolysis and myoglobinuria, which can then cause acute tubular necrosis and obstructive nephropathy.

Therefore, if the patient developed myoglobinuria, I would attempt to improve urine output by – administering intravenous fluids and mannitol or lasix.

In addition, if the patient’s urine was acidic, I would give – bicarbonate to help prevent renal tubule injury (helps prevent cast formation).