A Dark Side of the Cannula Injections: How Arterial Wall Perforations and Emboli Occur

Though most injectors prefer to use a cannula rather than a needle, there have been reported cases of blindness following cannula injections. This study investigated possible situations in which a cannula can injure an artery to gain more insight about the vascular complication and its prevention.

To understand how an arterial injury occurs, five situations favoring vascular injury were simulated and tested. Experiments were performed in 100 arterial segments of 10 soft embalmed cadavers with red latex injections to the arteries. The frontal branch of the superficial temporal artery with a diameter between 1.2 and 1.5 mm was chosen for the experiment with a 25G cannula. Five situations were created to simulate any possibility that the cannula can penetrate through the arterial wall. Two factors were varied for simulation of specific danger situations. Factors that vary were as follows: (1) the angles between the cannula and the artery when the cannula touched the artery, and (2) the segments of the artery with different features.

The cannula could penetrate the arterial wall in some specific situations with a different chance in each situation. The perpendicular angle between the artery and the cannula was one of the essential situations for vascular injury. Situations that had a similar effect of the perpendicular arterial surface related to the cannula axis also favored vascular injuries.

During a blinded insertion of cannula injections to reach the target area, the injector cannot discriminate the sensation at the cannula tip between the resistance of a fibrous septum in the way of the insertion and the resistance of encountering an artery. To prevent arterial emboli, the cannula trajectory should not be close to the main artery in the region. This allows a physician to safely perform an intermittent forceful insertion without an arterial injury during an attempt to perform a gentle cannula insertion.

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