Hi, I don't know why some of our children in the ICU react this way over others, but here is why you can actually get sicker after being initially treated with antibiotics.
Pseudomonas is a gram negative bacteria. The gram negative bacteria have very well "padded" coating - the outside is made up of several layers of membranes compared to gram positive bacteria. There is a complex lipopolysaccharide that has a lipid component that acts as an endotoxin (natural to the bacteria, bad for us). If released from the bacteria into our blood stream, it causes our body to mount a response and release a whole slew of agents into the blood stream. So you will actually feel cruddier initially as this happens. The bacteria don't produce and release endotoxin -- as it is part of the bacteria's cell membrane, the only way is when the bacteria are killed (hence, antibiotic therapy). Thus, bacteria killed = lots of endotoxin around.
We've used clindamycin on occasion in the past to help with this (there are studies showing this can help, but not for all cases by any means) -- some kids do worse after we start gram negative coverage... it's par for the course... most people don't progress to septic shock from this although it has been shown to happen. Usually you do supportive care (maintaining a good cardiac output by giving more fluids or starting bp meds, minimizing body's oxygen consumption, supporting respiratory if needed).
I hope this helped... it's a heck of a lot more complex especially when one gets into what agents are released when the endotoxins are in the bloodstream... I can't even remember all of the agents -- some good and some are bad.
I hope you feel better!! You are not alone with that process... it's just never really mentioned as it doesn't happen with every person with a gram negative infection who gets treated with antibiotics.
PM if you have any other questions.
Jenn
30 yo cf, cfrd, osteoporosis, critical care pediatric nurse practitioner