Something I found by a forensic pathologist that might be helpful:

Murder by air embolism is quite rare, despite the strong chances of a murderer escaping scot free in such cases. This is because such a technique requires great skill. Not everyone can handle a syringe, let alone puncture a vein successfully with it. I have a nagging fear that such type of murder might be very common among the drug addicts of our country. They are quite suited for committing such types of murder. They can handle syringes very deftly (almost as deftly as doctors, as they have to inject the drugs through the syringe all the time), and they need to do away with people fairly commonly.

In my whole life, I have encountered just one case of murder by air embolism and that too when I was in Edinburgh. The case was of a doctor husband who had got tired of his nagging wife. The husband was carrying on an affair with one of his female patients and his wife had got hint of that. She was having fits of faintness for quite sometime. So one day the doctor filled up a large syringe with air and injected air into her veins under the pretext that he was giving her some drug. About 200 c.c. of air is required to kill a person by air embolism. I do not know how he managed to inject that much amount through a syringe. Even a commonly used large syringe takes in about 20 c.c. of air only. He might have used a bigger syringe or may be he repeatedly pushed the air inside by removing the piston from the syringe again and again. Well, the important thing is that he did use the air for committing the murder. He would have gone scot free, but when I asked one of the witnesses as to what were the symptoms of the lady when she was dying, I was told that she was gasping for air. This immediately alerted me. This is a symptom of air embolism as we have already seen. Coupled with this was the fact that her husband was a doctor. He was ideally suited for committing such a type of act. So before opening the body, I decided to take a radiograph (X-ray) of the body. Sure enough the bubbles of air could be seen in the deceased woman's pulmonary arteries. Then I looked at the dead woman's forearms. They showed marks of injection. Immediately I alerted the Lothian and Borders Police (the police force that mans the city of Edinburgh). A detailed interrogation was done and sure enough the doctor admitted his guilt. This was yet another victory of Forensic Medicine.

I do z track myself usually but sometimes, like last night, it can be a pain if your fingers slip and the needle is still in ouch, today I have a bit of a limp