AICD

Question 1

64 year old with AICD/PM is schedule for ESWL with 1st generation lithotripter. how does ESWL disintegrate renal calculi?

Answer 1

the sudden vaporization of water by an energy source generates a pressure wave that is focused on the urinary stone. when the shock wave encounters a sudden change in impedance (as occurs at the tissue-stone interface) compressive energy is released causing shear forces on the stone. the acoustic impedance of water and body tissue is similar and as such, the wave travels through the body without much dissipation of energy, causing minimal surrounding tissue damage.

however, bruising, flank ecchymosis and hematuria will occur. moreover, if the waves were directed at an air-tissue interface (such as lungs or intestine), the difference in acoustic impedance can lead to dissipation of energy and significant tissue damage.

Question 2

how would you provide anesthesia for this case?

Answer 2

IV analgesia/sedation may be sufficient for 2nd and 3rd generation lithotripters, but the increased discomfort associated with more powerful 1st generation often requires general anesthesia. neuraxial anesthesia or flank infiltration with/without intercostal blocks is also an option. however, the rapid onset, reduced diaphragmatic excursion and quicker recovery make general more desirable in my opinion. general is however, a/w peripheral nerve injury (positioning while unconscious) and can complicate transport if patient needs adjunctive procedure.

Question 3

would anesthetic plan change if patient had a MPIII airway?

Answer 3

if i was concerned about difficult airway management, i would consider epidural/spinal to avoid airway manipulation. the slow onset/recover of epidural and the hypotension associated with spinal are the primary disadvantages of these modalities.

Question 4

could you proceed with flank infiltration and intercostal nerve block?

Answer 4

this is a viable option, however i believe neuraxial anesthesia would provide a more reliable plane of anesthesia, thus reducing the need for additional sedation. since one of my goals in managing this patient with potentially difficult airway is to maintain spent vent and avoid airway manipulation, i would prefer to proceed with neuraxial.

Question 5

what are the risks of ESWL in patient with AICD?

Answer 5

overall risk is low, but there is some risk that the patient will experience shock-wave induced intraoperative arrhythmia. moreover, lithotripter-induced shock waves can lead to cardiac rhythm management device malfunction - magnet mode, pacing suppression, oversensing of asynchronous shocks, damage to the rate-sensing piezoelectric crystals. ESWL is only contraindicated if the generator is located in the abdomen.

Question 6

how would you minimize the risks?

Answer 6

1. ascertain the indication for placement, underlying rhythm/rate, degree of PM dependency
2. determine type, manufacturer, programmability, functionality
3. verify behavior when exposed to a magnet (usually disables tachydysrhythmia detection and therapy)
4. ensure availability of programming device, trained programmer, and alternative pacing modality
5. make sure the device is not in the ESWL path
6. continuous telemetry
7. begin with low energy shock waves and gradually increase
8. terminate lithotripsy if arrhythmia develops
9. use a magnet only if there was inhibition of the PM function

Question 7

would you require preop interrogation?

Answer 7

not if the device had been check in the past 6 months (AICDs should be checked within 6 months, PM within 12).

Question 8

postop, his hemoglobin drops from 14 to 10.4. are you concerned? what is the cause?

Answer 8

this is significant and would raise my concern for intraabdominal or retroperitoneal hemorrhage. i would examine the abdomen, stabilize his hemodynamics, look for other sources of bleeding and consider x-ray/CT to investigate.

other possible causes: hemodilution