If a PA is assigned to a patient who suffers harm due to misdiagnosos and/or improper treatment under the PA's care, who is legally responsible for the harm done?

Is a malpractice suit already pending? Please give more information.

Can depend on state law if in the US, or national law in other countries.
PA and the practice can be sued, they would have malpractice insurance anyway. Also to get to the point of a suit, all of the notes and all of the records would have been reviewed, to see if there was anyone else who aided in this. Did someone read x-rays, did someone do lab work and so on.

Next of course you have to prove actual fault, was their error done by not following some normal practice.

Many times all doctors are not right at first and do follow up, so actual fault has to be established, not merely a wrong treatment, if that treatment is supported by the symptions

The patient was being observed in the hospital following abdominal surgery (polyp removal via bisection) and developed a rapid heartbeat, shallow breating, disorientation, etc. The surgeon requested a consult from the hospitalists to determine cause. The hospitalists assigned a PA to perform the consult since it was after hours and all hospitalists had left the hospital. The PA was to consult with them via phone if he thought he needed help. During the evaluation, the patient went into septic shock. The patient was referred by the PA to Intensive Care approximately 5 hours after the consult was begun and the ICU physician determined that additional surgery was necessary. The PA said that he recognized that the patient was in critical condition while he was treating them, but he did delay referring them to Intensive Care until the testing was complete. It turned out that the cause of sepsis was a leakeage in the small intestine induced during the original surgery. At some point during this process (diagnosis and surgery) the patient suffered an anoxic brain injury. The PA did not consult with the hospitalist or the surgeon until his normal briefing the next morning, which was about 10 hours after the consult was originally requested.

It sounds totally by what you've said that the PA was careless and negligent. However, medical malpratice is very difficult to prove because you need expert witnesses (who charge a small fortune) who are willing to testify AGAINST a fellow medical professional. In this case the treating Physician, surgeon, PA, anyone else involved would need to be mentioned in a lawsuit.

Then the next problem is what caused the additional medical issues - the time delay, a bad result from the initial surgery, something else?

IF the patient would have been taken to ICU IMMEDIATELY would it have changed the course of things?

Was the failure to discuss the patient's condition until the following morning somehow detrimental to the patient's health OR was this normal practice?

I would consult with an Attorney who specializes in medical malpractice - it's a fairly narrow field but you need an expert in the field to review the records.

As I said - this is an expensive lawsuit because of the cost of obtaining medical records outside a Subpoena AND the cost of expert medical testimony.

I am personally aware that the hospital/Physicians are going to argue that the brain damage was caused by the infection, not by the lack of oxygen. Been there, heard that.