• Information
  1. Introduction and Classification
  2. Venous Gas Embolism
  3. Arterial Gas Embolism

A. Introduction and Classification

1. Gas embolism is entry of gas into vascular structures
2. Usually iatrogenic
3. Usually air embolism, though other medical gases may be involved
4. Venous embolism occurs when gas enters systemic venous system
5. Arterial embolism occurs when gas enters arterial system

B. Venous Gas Embolism

1. Gas enters venous system and is transported to lungs
2. Gas embolus is strongly irritating to endothelium and neurons
3. Irritation cause by embolism leads to:
   1. Pulmonary arterial vasoconstriction
   2. Elevated right cardiac pressures (pulmonary hypertension)
   3. Right ventricular strain with potential for cor pulmonale
   4. Cardiac arrhythmias - tachyarrhythmias more common than bradyarrhythmias
   5. Eventual cardiac failure
   6. Large quantities of gas (>50mL) can cause cor pumonale, asystole or both
4. Risks
   1. Usually associated with incising of noncollapsing veins
   2. Presence of subatmospheric pressure in vessels also increases risk
   3. Neurosurgical operations are highest risk, especially with upright patients
   4. Entry of air through venous and hemodialysis catheters
   5. Entry of air through mymetrium during pregnancy and post-partum
5. Diagnosis
   1. "Mill-wheel" murmer - splasghin sound of gas in cardiac chambers
   2. Doppler ultrasonography is most sensitive and practical method
   3. Transesophageal echocardiagraphy is also sensitive but cumbersome
6. Treatment
   1. Prevent further entry of gas - identify source, increase venous pressure
   2. Increase venous pressure - intravenous fluids are mainstay
   3. Oxygen
   4. Catecholamines (vasopressors) may be needed
   5. May evacuate gas with multiluminal central venous catheter
   6. Patient in left lateral decubitus position for gas evacuation
   7. Adjunctive therapy if needed with hyperbaric oxygen
7. Paradoxical Embolism
   1. Passage of gas from venous circulation to arterial side through a shunt
   2. Causes symptoms of end-artery obstruction
   3. Most commonly due to patent foramen ovale, which is found in ~30% of normal adults
   4. Septal defects can also lead to embolism
   5. Treatment of paradoxical embolism is identical to that of arterial embolism

C. Arterial Gas Embolism

1. Gas enters pulmonary veins or directly into systemic arteries
2. May enter arteries from lung overexpansion or from paradoxical embolism
3. Only small amounts of air are required to obstruct small, end arteries
4. Embolization to cerebral or coronary circulation is most concerning
   1. Embolism to coronary arteries leads to ischemia and infarction
   2. Myocardial suppression is common
5. Cerebral embolism usually involves both ischemia and significant inflammation
6. Symptoms develop suddenly
   1. Specific symptoms depend on position, amount of gas, and areas of brain affected
   2. Minor motor weakness and headache may occur
   3. Moderate confusion can occur
   4. In severe conditions, hemiparesis, seizures, loss of conscioussness, coma can occur
   5. Asymmetry of pupils, hemianopia, Cheyne-Stokes respirations also occur
   6. Cardiac arrhythmias are common
   7. Delayed recovery from anesthesias
7. Risk Factors
   1. Craniotomy (patient sitting)
   2. Cesarean section
   3. Hip replacement
   4. Cardiac surgery with cardiopulmonary bypass
8. Diagnosis
   1. Patient's history with relationship of symptoms to invasive procedure most important
   2. Cerebral embolism is difficult to distinguish on CT or MRI
   3. Gas bubbles in vessels of retina may be helpful
   4. Note that the absence of retinal gas bublles does not rule out embolism
9. Treatment Overview
   1. Goal is protection and maintentance of vital functions
   2. Cardiopulmonary resuscitation may be required
   3. Endotracheal intubation for somnolent or comatose patients
   4. Oxygen - high levels or hyperbaric oxygen (see below)
   5. Patient in flat, supine position
   6. Maintain normovolemia
   7. Inotropic (vasopressor) support may be necessary
10. Hyperbaric Oxygen [2]
    1. Patient breaths 100% oxygen at >1 atmosphere of pressure
    2. Decreases size of gas bubble very effectively
    3. Arterial partial pressure of oxygen >2000 mm Hg often achieved
    4. This supersaturated oxygen drives nitrogen out of the gas bubble
    5. May also help prevent cerebral edema (anti-inflammatory, reduced vessel permeability)
11. Treatment of Generalized Seizures
    1. Benzodiazepines
    2. Barbiturates for patients not responding to benzodiazepines
12. Lidocaine
    1. Beneficial effects observed in animals
    2. Stabilizes cardiac and cerebral effects of gas embolism
    3. Bolus dose 1.5mg/kg then maintain therapeutic concentration
    4. Caution with dosing as overdose can be fatal
13. Glucocorticoid use is controversial

References

1. Muth CM and Shank ES. 2000. NEJM. 342(7):476
2. Tibbles PM and Edelsberg JS. 1996. NEJM. 334(25):1642