Venous Air Embolism

How will you diagnose and manage a case of VAE during Spine Surgery?

Detection of Venous Air Embolism

The monitors employed for the detection of VAE  are the combination of a precordial Doppler and expired CO2 monitoring and are the current standard of care. Doppler placement in a left or right parasternal location between the second and third or third and fourth ribs has a very high detection rate for gas embolization,and when good heart tones are obtained, maneuvers to confirm adequate placement seem to be unnecessary. TEE is more sensitive than precordial Doppler to VAE  and offers the advantage of identifying right-to-left shunting of air.  Its safety during prolonged use (especially with pronounced neck flexion) is not well established, however. Expired nitrogen analysis is theoretically attractive. The expired nitrogen concentrations involved in anything less than catastrophic VAE are very small, however, and push the available instrumentation to the limits of its sensitivity

Management of an Acute Air Embolic Event

Prevent further air entry    Notify surgeon (flood or pack surgical field)    Jugular compression    Lower the head Treat intravascular Air    Aspirate right heart catheter    Discontinue N2O    Fio2: 1.0    Pressors/inotropes    Chest compression

Right Heart Catheter

All patients who undergo sitting posterior fossa procedures are given  a right heart catheter. Although catastrophic, life-threatening VAE is relatively uncommon, a catheter that permits immediate evacuation of an air-filled heart is for resuscitation.

An example of a procedure for which the right heart catheter is usually omitted is microvascular decompression of the fifth cranial nerve for tic douloureux or the seventh cranial nerve for hemifacial spasm. The essentially horizontal semilateral position and the very limited retromastoid craniectomy these procedures require have resulted in a very low incidence of Doppler-detectable VAE. .

Positioning of the heart catheter-multi-orificed catheter is located with the tip 2 cm below the superior vena caval–atrial junction, and a single-orificed catheter should be located with the tip 3 cm above the superior vena caval–atrial junction. Although these small distinctions in location may be relevant for optimal recovery of small volumes of air when cardiac output is well maintained, for the recovery of massive volumes of air in the face of cardiovascular collapse, anywhere in the right atrium should suffice. Right heart placement can be confirmed by (1) x-ray, (2) pull back from the right ventricle while monitoring intravascular pressure, or (3) intravascular electrocardiogram (ECG)

Techniques for Reducing the Incidence of Venous Air Embolism

 PEEP has been advocated in the past as a means of reducing the incidence of VAE or of responding to an acute VAE event to prevent further air entry however  even 10 cm of PEEP would be unlikely to result in positive venous pressures in cerebral venous structures, which may be 25 cm above the heart. The ineffectiveness of PEEPand the relative superiority of jugular venous compression in increasing cerebral venous pressures have been confirmed by several investigations.

The release of a Valsalva maneuver promotes paradoxical embolism. In addition, the impairment of systemic venous return caused by the sudden application of substantial PEEP may be undesirable in the face of the cardiovascular dysfunction already caused by the VAE event.

It has been associated that a patient who has sustained a hemodynamically significant VAE should be placed in a lateral position with the right side up. The rationale is that air would remain in the right atrium, where it would notcontribute to an air lock in the right ventricle, and where it would remain amenable to recovery via a right atrial catheter. The first difficulty is that this repositioning is all but impossible with a patient in a pin head holder.and also it failed to identify any hemodynamic benefit

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