UBP Book 3

Question 1

Perioperative concerns for thoracoabdominal aortic aneurysm

Answer 1

Aneurysm rupture
Dissection propagation
Myocardial ischemia
Post-operative respiratory complications (one-lung ventilation, surgical manipulation diaphragm/lungs)
Paraplegia (disruption of radicular arteries supplying anterior spinal cord)
Post-op AKI
Visceral/mesenteric injury
Stroke
Difficult airway (aneurysm may compress airway)
Hemorrhage
CHF

Question 2

DeBakey classification of aortic dissection

Answer 2

Type I: originate in ascending aorta and extend distally to descending aorta
Type II: originate in ascending aorta and do not extend beyond brachiocephalic artery (first branch)
Type III: originate beyond L SCA and extend distally to diaphragm (IIIA) or aorto-iliac bifurcation (IIIB)

Type I and II = Type A (surgical emergency)
Type III = Type B (medical mgmt, surgical tx if e/o end organ ischemia, significant dilation, risk of rupture)

Question 3

Acute aortic regurgitation concerns

Answer 3

LV volume overload
Reduced effective forward stroke volume
Rapid increase in LVEDP = pulm edema
Increased myocardial O2 demand
Reduced myocardial blood supply (reduced DBP and increased LVEDP)

Question 4

Aortic dissection hemodynamic goals

Answer 4

Reduce intramural pressure
Reduce aortic shear force/force of ventricular contraction

This is accomplished by decreasing BP and force of ventricular contraction to reduce dP/dT (anti-impulse therapy)

Current guidelines recommend goal-directed therapy to achieve HR<60 and SBP 100-120.

Question 5

Crawford classification of TAA

Answer 5

Type I: originates below L SCA, extends to abdominal aorta
Type II: originates below l SCA, extends to infrarenal abdominal aorta
Type III: originates below 6th rib, involves remaining aorta
Type IV: originates at diaphragm, involves abd aorta only
Type V: originates below 6th rib, extends to renal arteries

Question 6

How does aortic cross clamping affect CSF pressure?

Answer 6

Cross clamp leads to hyperemia above clamp –> increased ICP –> redistribution of CSF to intrathecal space –> increase in CSF pressure by 10-15

Goal CSF pressure 8-10 to preserve spinal cord perfusion

Question 7

Complications of lumbar drain placement

Answer 7

Epidural/spinal hematoma
HA
Intracranial bleeding (tearing subdural veins w/ rapid CSF removal)
Meningitis
Chronic CSF leak

Question 8

How long to hold antiplatelet and anticoagulant agents prior to neuraxial instrumentation

Answer 8

Heparin gtt: 6 hours
Heparin SQ: 24 hrs (check aPTT for normalization)
Enoxaparin: 12 hrs (ppx dose) or 24 hrs (therapeutic dose)
Eptifibatide: 8 hours
Clopidogrel: 7 days (if high risk for thrombus, 5 days + platelet function test)
Apixaban: 3 days
Prasugrel: 7-10 days
Ticagrelor: 5 days
Warfarin: 5 days (check INR for normalization)

Question 9

Protamine reaction

Answer 9

Type I: Hypotension (histamine release)
Type II: True anaphylaxis (IgE) vs anaphylactoid
Type III: catastrophic pulmonary vasoconstriction

Question 10

Management of traumatic lumbar drain placement

Answer 10

Delay surgery for 24 hrs if heparinization will be used
If emergent case and unable to delay: delay systemic heparinzation for 60 mins, minimize heparin dosing, neurologic exam q1h, avoid local anesthetic through epidural if using to allow for motor exams

Question 11

Why use an epidural for thoracoabdominal aorta surgery?

Answer 11

• Excellent post-op pain control
• Improve resipratory function (decreased atelectasis, pulm infxn, respiratory failure)
• Improve graft patency (reduced coagulation response)
• Reduce postop myocardial ischemia (attenuate stress response)

Question 12

What is acute normovolemic hemodilution? What are the pros/cons?

Answer 12

ANH: autologous blood collected at beginning of case, then re-infused (need initial Hcg >33/Hgb >11). Collect 1-2 units blood and administer warmed crystalloid to maintain normovolemia.

Pros: reduce exposure to allogenic blood
Cons: only save up to 1-2 units pRBC, reduction in oxygen carrying capacity may not be tolerated by some patients

Contraindications:
- anemia (Hcg <33, Hgb <11)
- impaired renal function (since giving extra crystalloid)
- pt cannot tolerate increased cardiac output from decreased blood viscosity (e.g. AS)
- significant pulm disease (decreased oxygen content of blood)
- pre-existing coagulopathy

Question 13

Blood pressure goals during aortic cross-clamp for TAA repair

Answer 13

Above cross clamp: MAP ~100
Below cross clamp: MAP>50

Question 14

How to manage decrease in SSEP signal after aortic cross clamp placement

Answer 14

• optimize hemodynamics
• check ABG
• ask perfusionist to increase distal pump flows and correct hypo/hypercarbia and acisosis
• if needed, ask surgeon to reposition clamp (may be blocking critical intercostal artery)
• ensure adequate hypothermia (30-34 C)
• withdraw 10-20cc CSF from lumbar drain (target ICP 8-10)
• consider pharmacologic intervention (corticosteroids, Mg, CCB, mannitol, etc.)

Question 15

Causes of hypotension following aortic cross-clamp release

Answer 15

Central hypovolemia and decreased cardiac preload

There is tissue ischemia and vasoactive mediator release distal to cross-clamp, leading to decreased SVR, increased venous capacitance, and increased capillary permeability. Acid metabolites and vasoactive mediators released into bloodstream lead to decreased myocardial contractility and increased PVR.

Question 16

How does hypothermia result in a coagulopathy?

Answer 16

Mild hypothermia can cause coagulopathy secondary to cold-induced defects in platelet aggregation and adhesion. Additionally, coagulation enzyme activity is decreased below temperatures of 33 C.

Question 17

Anesthetic management of patient on lithium

Answer 17

Lithium toxicity: skeletal muscle weakness, sedation, ataxia, wide QRS, hypotension, seizures
Lithium can reduce MAC and prolong effects of depolarizing and non-depolarizing muscle relaxants
Monitor for AV block or dysrhythmias
Administration of sodium can prevent excess reabsorption of lithium

Question 18

Inadequately treated hyperthyroidism concerns

Answer 18

Signs of hyperthyroidism: tachycardia, diarrhea, warm moist skin, heat intolerance, arrhythmias, fatigue, fine tremor, hyperreactive reflexes, muscle weakness

Concerns:
- Hypovolemia (risk hypotension under anesthesia)
- HTN (worsens with sympathetic stimulation, eg laryngoscopy)
- Cardiac arrhythmias
- Thyroid storm

Note: it can take 7-14 days to achieve euthryoid state with propranolol and 6-8 weeks with PTU

Question 19

How do thyroid masses appear on flow-volume loops?

Answer 19

Note: flow-volume loops are poor predictors of perioperative respiratory complications

Large thyroid masses are often a fixed obstruction and may be intrathoracic or extrathoracic. Will see flattening of both limbs in the flow-volume loop.

Question 20

Thyroid function test interpretation

Answer 20

Total T4 and total T3: cannot be interpreted alone since thyroid binding globulin levels can vary depending on patient (TBG increases with pregnancy, oral contraceptive use, nephrotic syndrome, and liver disease)

Elevated FREE T4 and T3 can indicate patient is hyperthyroid.

Question 21

How to optimize thyroid status before surgery

Answer 21

• Consult endocrinologist
• continue PTU (inhibits organification of iodide, TSH synthesis and conversion of T4 to T3)
• Beta-blocker (propranolol also reduces peripheral confersion of T4 to T3)
• administer an iodide to reduce release of T4 and T3
• hydrate
• correct electrolyte abnormalities
• provide anxiolysis
• be prepared to treat hemodynamic instability

Question 22

How to differentiate between thyroid storm, malignant hyperthermia, and neuroleptic malignant syndrome?

Answer 22

Can be challenging: all present with hyperthermia, tachycardia, and AMS

• Thyroid storm does not usually have metabolic acidosis, profound hypercarbia, and muscle rigidity
• NMS usually progresses more slowly to critical temperature than MH
• NDMB will cause flaccid paralysis in NMS but not MH

If unsure whether NMS or MH, treat with dantrolene (may actually help NMS as well), consider bromocriptine (for treatment of NMS), cool patient

Question 23

Renal transplant urgency

Answer 23

Cadaveric kidneys can be maintained for 36-48 hours to allow for patient optimization (e.g. pre-op hemodialysis)

Question 24

Can a renal transplant be done under regional anesthesia?

Answer 24

I would not do the case under regional anesthesia since uricemia leads to decreased vWF levels and increases the risk of epidural hematoma and sympathectomy may complicate BP management, however regional does have benefits of reducing aspiration risk and avoiding intubating a difficult airway.

Question 25

Would you do a rapid sequence intubation in a patient with ESRD?

Answer 25

CKD can lead to gastroparesis, so yes. However, untitrated administration of induction medications increases the risk of hypotension or an exaggerated sympathetic response to laryngoscopy, so I would be prepared to manage these situations should they occur. It is safe to use succinylcholine if K <5.5.

Question 26

What medications are given prior to clamping the iliac vessel in renal transplant? What medications are given after reperfusion?

Answer 26

Before clamping: Heparin (to prevent clotting while clamped)
After reperfusion: manitol and/or furosemide (to reduce risk of ATN and help w/ urine formation)