Can an air-bubble in a syringe kill the patient?

Question

I have heard of stories where, while giving injection to patient, a doctor forgot to remove all the air from the syringe. The patient died when the air reached to brain.

Can injecting air into a vein with a syringe cause death?

Answer 1

Yes

What you have described is an air embolism. Incidences and cases of this happening has been recorded in several different procedures with some like seated posterior fossa surgery with a rate as high as 80%. 1

The variability in amount of air is because of the possible mechanisms by which it can cause death. 1

1. If a small amount of air is injected it forms micro emboli which can now either cause gradual obstruction to blood flow or spontaneous resorption, which again depends upon rate and volume of air entrained, comorbid conditions causing ventilation-perfusion defect.
2. A larger amount of air but remaining in venous circulation can cause obstruction of right ventricular outflow tract leading to cardiac arrest.
3. But when a large amount of air gets trapped on the right side it can increase the pressure in right atrium causing right to left shunting through foramen ovale giving access to arterial circulation.

For the last point its important to know that upto 35% of adults have been reported having undiagnosed patent foramen ovale. 2 As for arterial embolism, experimental procedure on dogs showed injecting 1 to 1 1/4 ml/kg of air in cerebral arterial circulation can cause mortality in 50%. 3 Rukstinant reported ventricular fibrillation on injecting 0.25 ml of air in coronary arteries. 4

Scientific literature on the amount of air for air embolism (venous). A case report in 2001 discussing the volume of air required stated that:

THE morbidity and mortality rates from venous air embolism is determined by the volume of air entrained, the rate of entrainment, and the position and the cardiac status of the patient. As early as 1809, Nysten estimated the lethal dose of air to be 40–50 ml in a small dog and 100–120 ml in a large dog. The exact amount, 7.5 ml/kg, however, was not determined in dogs until 1953 by Oppenheimer et al. In l963, Munson et al. demonstrated a lethal volume of only 0.55 ml/kg in rabbits. The lethal volume of air in an adult human is unknown but is estimated to range from 200 to 300 ml. These numbers are derived from the cases of fatalities reported by Martland, Yeakel, and Flanagan.

This case reported the volume as 200 ml and note Flanagal had reported around the same in 1969.5

Finally, coming to the case air-bubble in syringe. (Because your question also had injecting air in vein, so that was first).

In 2013 nobody (without a malicious intent) would deliberately inject air. Accidental injecting instead of contrast has been reported. Some syringes which come with prefilled air has been asked to expel them during manufacturing prior to packaging to avoid this rare adverse event, although this can be expelled manually prior to injecting by the healthcare personals. 6

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1. Palmon, S. C., Moore, L. E., Lundberg, J., & Toung, T. (1997). Venous air embolism: a review. Journal of clinical anesthesia, 9(3), 251-257.
2. Hagen, P. T., Scholz, D. G., & Edwards, W. D. (1984, January). Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts. In Mayo Clinic Proceedings (Vol. 59, No. 1, pp. 17-20). Elsevier.
3. Fries, C. C., Levowitz, B., Adler, S., Cook, A. W., Karlson, K. E., & Dennis, C. (1957). Experimental cerebral gas embolism. Annals of Surgery, 145(4), 461.
4. Rukstinat, G. (1931). Experimental air embolism of the coronary arteries. Journal of the American Medical Association, 96(1), 26-28.
5. Toung, T. J., Rossberg, M. I., & Hutchins, G. M. (2001). Volume of air in a lethal venous air embolism. Anesthesiology, 94(2), 360-361.
6. Marsh, M. (2007), Risk of air embolism from prefilled syringes. Anaesthesia, 62: 973. doi: 10.1111/j.1365-2044.2007.05245.x

Answer 2

There's a well referenced Straight Dope article on this - Can air injected into the bloodstream really kill you?

Brief summary - small bubbles can do serious harm but are unlikely to kill someone, large amounts of air are often fatal.

Small bubbles can block capillaries in vital organs, most urgently the brain, causing anything from pain and inflammation to neurological damage and paralysis. A small bubble impedes blood flow the same way a solid obstruction would — the bubble's surface tension relative to its size is too great for the force of blood to break it up or shove it along. Bad? Yes. Fatal? Probably not.