Saddlesore, there is no invasive procedure that doesn’t carry some risks or side effects. But, very generally, here’s what likely what happened to you.
The nerves come out of the Cervical spinal column in various bundles break down from larger to smaller as they get peripheral (closer to the shoulder). They are enclosed in sheaths or fascia.
During the block after the needle punctures the sheath (following finding it in the first place) some of the local anesthetic invariably flows medially (toward the spinal column) as well as peripherally. This is where you need a skilled practitioner and why this block should be place while the patient is awake — to observe minute-by-minute effects.
As it flows medially it often knocks out the phrenic nerve on that side which causes a hemi paralysis of the diaghram. This is not totally uncommon and normally not a problem in a relatively healthy, young, non-smoking patient. The resp rate may be noted to increase a bit to compensate. This scenario is also one reason to do this while the patient is awake so this effect of the block if it occurs can be monitored, correlating it with the dose given. Obviously too great a dose given moving medially and affecting the nerves as they exit the spinal cord can even cause a “total spinal” in which case a patient needs to be resuscitated, perhaps even intubated, and place on a ventilator until the drug wears off. If done asleep under controlled ventilation, this scenario goes unnoticed until the patient comes out of the general anesthetic at which time you have serious problems.
Which brings up the issue of doing this block on the elderly, the obese, or any patient with respiratory compromise regardless of cause. I wouldn’t. I don’t know if any of these fit you but for example I generally wouldn’t perform this block on an over-sixty patient with a history of heavy smoking and at least some degree of COPD.
Nevertheless, on appropriate patients, and done with precision, it is a great pain-saver.
