Posterior Fossa Craniotomy/VAE

Question 1

What does the posterior fossa contain?

Answer 1

medulla
pons
cerebellum 
motor and sensory pathways 
respiratory and CV centers and cranial nerve nuclei

Question 2

What are the options for positioning a PFC?

Answer 2

Sitting
Horizontal 
Lateral 
Park bench 
3/4 lateral
Prone

Question 3

What are major risks of sitting position in PFC? Explain risks of each one

Answer 3

-VAE
-Hypotension (GA can impair RAAS system-exaggerated in elderly), decreased venous return
Hyperflexion of neck can result in brain and facial swelling, quadriplegia or paraplegia from compromised blood flow to the cervical cord or direct compression of the cord-more likely in elderly and those with pre-existing cervical spine disease-exacerbated by hypotension, ETT can migrate deeper-verify equal breath sounds after positioning!
-Peripheral nerve injuries-espiecailly ulnar, peroneal, sciatic

Question 4

What do you want to verify after sitting positioning in PFC?

Answer 4

B/l breath sounds to make sure ETT didn’t migrate deeper

Question 5

Benefits of PFC sitting position

Answer 5

-Fewer cranial nerve deficits due to less retraction
-Edema and hemorrhage: less potentia for swelling of brain and hemorrhage due to venous ad csf drainage via gravity
Increased FRC and better v/q matching
Better surgical exposure

Question 6

As for the horizontal position, what are some cons? Pros?

Answer 6

Cons: Poor access to airway, chest, and extremities,
cerebellar edema and hemorrhage, more cranial nerve damgage due to deficits
Prone: facia and tongue swelling and ischemic neuropathy
Benefits: Lower risk of VAE
Improved CV stability
decreased chance of cervical cord injury

Question 7

If pt has delayed awakening following PFC that was in sitting position, what are you thinking and why?

Answer 7

I’m thinking that the brain, blood, and CSF volume could’ve increased when we made the patient supine again-that combined with trapped air can cause tension pneumocephalus

Question 8

Nitrous oxide and VAE

Answer 8

d/c it before dural closure and continue to avoid it for two weeks

Question 9

Monitoring for PFC:

Answer 9

EKG and A line is mandatory
I’d place a central line especially if in sitting position-we may need to aspirate air
SSEPs and BAEPs

Question 10

Post PFC: how long should patients be monitored?

Answer 10

For at least 24 hours to look at frequent neurological assessments, arterial BP moniotroing and EKG

Question 11

Any alterations in neuro, htn or bradycardia post PFC: what are you thinking?

Answer 11

Immediate exploration as it could be an indication of bleeding, edema, or brainstem compression

Question 12

What is ischemic neuropathy?

Answer 12

Vision loss due to lack of blood flow to optic nerve

Question 13

A VAE can occur when?

With a VAE, the surgical site is ___ such that the pressure at that height is _____

Answer 13

when operative field is greater than or equal to 5 cm above right atrium.
Surgical site is elevated such that the pressure at that height is greater than the central venous back pressure, therefore setting the environment to entrain air

Question 14

Explain the pathophys of VAE:

Answer 14

air bubbles mechanically obstruct the pulmonary vasculature. This leads to hypoxemia and v/q mismatch. Increase in dead space will lower ETCO2 and increase arterial carbon dioxide. Large bubbles can cause an air lock-increasing RV afterolad, decreasing LV filling, resulting in CV collapse

Question 15

What is a PAE?

when is PAE more likely?

Answer 15

Air from VAE can cross into arterial system via probe patent foramen ovale, right to left intracardiac shunt, or transpulmonary passage
PAE is more likely when right heart pressures exceed the left. This can happen in the sitting position.

Question 16

Avoid sitting position in PFC in which patients?

Answer 16

Those with known intracardiac shunts

Question 17

What can help decrease the rap to LAP gradient?

Answer 17

Generous fluid admin, but be careful in CHF patients or ESRD patients

Question 18

What should you avoid to prevent VAE while in sitting position? What can help prevent VAE?

Answer 18

avooid PEEp and valsalva, they can increase RAP to LAP gradient.
Prevention: Early detection, minimize elevation of head, use of bone wax, maintain euvolemia, avoid PEEP/valsalva

Question 19

As far as detection of VAE, list fro most sensitive to least sensitive

Answer 19

(TEE, Precordial doppler, PAC, Capnography, CO (decrease) and CVP (increase)

Question 20

How does the precordial doppler work? where do you place it?

Answer 20

High pitched doppler sounds indicate turbulent flow
Transducer is placed at right sternal border between 3rd-6th intercostal spaces where audible signals from right atrium are maximized. You can’t use this alone-you also have to have ETCO2.

Question 21

How can the PAC help with VAE?

Answer 21

It can detect increases in PAP secondary to pulmonary vasoconstriction, it can also detect when RAP is greater than PCWP so that you can give a fluid bolus

Question 22

Central venous catheter and PFC/VAE: when are you placing one, where should it be?

Answer 22

You can use it to aspirate embolized air from the RA-for optimal recovery of air-multi orifice catheter should be positioned 2 cm below the SVC/RA junction. Confirm by radiograph.
Place one in all sitting postion PFC-I’m going to place one in all PFC

Question 23

Can VAE happen if not sitting/

Answer 23

Yes

Question 24

If VAE is supsected, what are you going to do?

Answer 24

Alert surgeon and call for elp
Flood surgical field with saline, bone wax, and back surgical field
D/c any nitrous (confirm none on-cuz i know i won’t be using it)
Compress neck veins (increases venous pressure and may prevent further air entry)
Place pt in Trendelenburg and LLD position to help release air from RV outflow tract if airlock is suspected.
Aspirate air from properly positioned CVC
Chest compression to release air
Avoid PEEP and valsalva (will increase right atrial pressure)
Supportive therapy: maintain euvolemia, may need pressors

Question 25

Pre-op work up in pt getting PFC

Answer 25

CBC 
BMP 
T&S 
EKG 
TEE to r/o PFO 
if poor exercise tolerance-stress echo 
Full H&P r/o CHF signs

Question 26

How will you maintain anesthesia in PFC patients? This answer is also a way to answer other things like this

Answer 26

Balanced maintenance technique using a volatile anesthetic, opioid, and a muscle relaxant can be used to maintain hemodynamic stability