- Settings of Venous Air Emboli (VAE)
- Signs of VAE (Diagnosis)
- Consequences of VAE:
- Immediate Management of Suspected or Known Gas Embolism
VAE may occur in any case where open veins or venous access can entrain air. This happens more commonly in cases where the open veins or open venous access are 5 cm or more above the heart or the open veins are exposed to air under pressure, including
- endoscopy/laparoscopy utilizing air insufflation,
- lung biopsy, mediastinoscopy
- caesarian section, esp. with exteriorized uterus
- prone, spine, or sitting intracranial cases.
This is made less likely, but not eliminated by, the use of CO2 for insufflation.
Air emboli can also occur when air is introduced under pressure into the vascular tree such as during cardiac bypass or intravascular pressurized infusions.
Awake Patients experiencing an air embolus will often report
- dyspnea or
- chest pain, and
- there may be symptoms and signs of acute bronchospasm and pulmonary edema.
The Anesthetized Patient will not have symptoms, making intraoperative monitoring the principle method of diagnosis.
- The most sensitive, but nonspecific, diagnostic test is measurement of end-tidal CO2, which may signify air embolism with a reduction of as little as 2 mm Hg.
- A substantial number of patients will have also reduced oxygen saturation, and, if found together with reduced end-tidal CO2, is more suggestive of air embolism.
- There are several nonspecific electrocardiographic changes, including premature ventricular contractions, heart block, and ST-segment depression.
- Precordial auscultation may reveal a “millwheel murmur”, though this is not sensitive and when present suggests Cardiac Arrest is imminent.
- Precordial Doppler ultrasound can also detect a characteristic sound pattern indicative of air emboli entering the right heart. It may be difficult to place on some patients, especially those with a chest wall deformity or who are obese and is very sensitive, nonspecific and interrupted during electrocautery. It is also probably most effective as a monitoring tool as the change in sound is more reliable than interpreting the sound de novo.
- Transesophageal echocardiography is more sensitive and specific, but due to cost and availability constraints is used primarily to confirm the diagnosis.
If the embolized gas is of sufficient volume, it may interfere with gaseous exchange and cause:
- cardiac arrhythmias,
- pulmonary hypertension, and, ultimately,
- decreased pulmonary venous return,
- reduced cardiac output, and
- arterial embolization.
- Administer 100% oxygen
(Oxygen may reduce bubble size by increasing the gradient for nitrogen to diffuse out)
- Intubate for significant respiratory distress, refractory hypoxemia, hemodynamic instability or neurologic symptoms.
- Promptly place patient in head down and right side up (left side down) position.
(This maneuver helps trap air in the apex of the ventricle, prevents its ejection into the pulmonary arterial system, and maintains right ventricular output)
- Maintain systemic arterial pressure with fluid resuscitation and vasopressors/beta-adrenergic agents if necessary.
- Treat for RV failure.
- Consider TTE or TEE and examine heart for air and to confirm intra-cardiac air and presence of ASD
- Consider utilizing in situ or placing central venous catheter into right heart to aspirate till air return clears
- Consider head CT for persistent CNS symptoms
- Consider transfer to a hyperbaric chamber for persistent CNS symptoms or hemodynamic instability and suspicion of air emboli
- Contact MGH ED Access Nurse for Hyperbaric Rx: 617 724 3890
- Contact REMIS to Arrange Transport by Ground
- Circulatory collapse should be addressed with CPR, and consideration should be given to more invasive procedures as described above
- Treat for RV shock
from MAINE MEDICAL CENTER DEPARTMENT OF CARDIAC SURGERY
CLINICAL POLICY & PROCEDURE MANUAL
Author: Robert Groom
PURPOSE: Eliminate and minimize detrimental effects of a massive air embolus delivered during cardiopulmonary bypass.
1. Instruct perfusionist to “Stop the Pump”.
2. Verify the source of air with the perfusionist.
3. If left sided air is confirmed or suspected:
a. Remove arterial cannula and keep purse string open as a vent.
b. Pump suckers in field once proper rotation and tubing direction confirmed by perfusionist.
c. Forward fill arterial line and deair.
d. Attach bypass arterial line to SVC or innominate vein (via arterial cannula, venous cannula, or endotracheal tube) and ensure RCP flow with SVC snare (or balloon with endotracheal tube).
4. Call for TEE or epiaortic echo to aid in ongoing evaluation of air evacuation from aorta and heart.
5. Initiate retrograde cerebral perfusion (RCP):
a. 0.4 L/min/m2 for 2 minutes or until no further air seen returning from carotids by TEE or epiaortic echo.
b. Adjust flow for a CVP of 25-35 mmHg.
c. Allow aortic cannulation site to vent or use second stab incision.
6. Instruct perfusionist to end RCP and prepare for traditional CPB.
7. Place aortic and venous cannula(e) and instruct perfusionist to resume CPB.
8. LV vent for ongoing air removal as needed.
9. Administer retrograde cardioplegia if significant air found in coronaries. Apply ice to heart for topical cooling.
10. Cool to 18 degrees Celsius and maintain for 30-60 minutes to maximize reabsorption of residual air in the microvasculature and removal at the oxygenator.
11. Initiate second run of RCP once patient cooled and stable on CPB.
12. Maintain a high pump flow and pressure to facilitate air removal from the microvasculature and at the oxygenator.
13. Intraoperative Neurology consult; consider postoperative CT scan for non contrast head CT. If air is confirmed via head CT or if symptoms of MAE persist, arrange transport to Contact Hyperbaric Facility – Mass General Hospital ED Access Nurse ph 617 724 3890
14. Arrange Transport to MGH Boston with REMIS
1. Stop the pump and clamp the arterial and venous lines. Turn off all pump heads until reservoir venting and proper head rotation/raceway tubing direction is confirmed.
2. Set heat exchanger to 15 degrees Celsius.
3. Set cooling blanket to 15 degrees Celsius.
4. Verify circuit integrity. Deair circuit and add volume as necessary to provide RCP via sucker bypass.
5. Ensure 100% oxygen is the sweep gas source. Set at a 2:1 V/Q ratio for the anticipated RCP flow to maximize nitrogen removal in the oxygenator.
6. Initiate RCP flow at 0.4 L/min/m2 (adult 1- 1.5 l/min.) and titrate to a CVP pressure of 25-30 mmHg (consideration should be given to the effect of Trendelenburg on the transducer height). RCP is performed 2 minutes or until air ceases to exit the aorta as determined by inspection and echo.
7. Reinstitute traditional bypass with pH stat blood gas management as instructed by the surgeon once cannulae are in their proper locations. Cool to 18 degrees Celsius and maintain for 30-60 minutes to maximize reabsorption of residual air in the microvasculature. Give 0.5 g/Kg mannitol and 30 mg/Kg methylprednisolone regardless of whether it was already administered at the onset of CPB.
8. Maintain a higher than normal pump flow and pressure to facilitate air removal from the microvasculature and at the oxygenator.
9. Rewarm to 34 degrees Celsius when directed by surgeon.
1. Place patient in steep Trendelenburg.
2. Place ice on head.
3. Perform intermittent bilateral carotid compression during retrograde cerebral perfusion to aid in air removal from vertebral arteries.
4. Consult with surgeon regarding physically shaking head to dislodge trapped cerebral air.
5. Verify mannitol and steroid delivery by perfusionist.
6. Consult with surgical and ICU team for postoperative care.
1. Coordinate medication plan and head CT with Neurology consult service.
2. Postoperative ICU treatment plan to consider:
a. Patient paralyzed and sedated.
b. Topical cooling for 36 hours (34-35 C).
c. 100% FiO2 6-12 hours
d. Fluid restriction (3% saline if likely cytotoxic CNS injury to target Na ˜ 150 mmol/L and Osmolarity of >300 mmol/L.
e. Head of bed up 30 degrees.
f. Continuous NIRS
3. Repeat head CT 48-72 hours postoperatively.
4. Consult with hyperbaric treatment facility. Mass General Hospital ED Access Nurse ph 617 724 3890
Revised:06/93 05/96 06/99 10/99, 08/29/2012
Reviewed: Robert Groom