“Special Patient Population: The Morbidly Obese”
This is a continuation of a series with our newest associate editor, Shayla Johnson, who is currently enrolled in a perfusion program. I asked her to join the editorial team because she reflects the passion and excitement that every perfusionist has- or otherwise they wouldn’t do it.
I am impressed that as a perfusion student she has the initiative to share her thoughts and impressions with us regarding the process of learning the art of perfusion technology from her own unique perspective:
“I am a first year perfusion student.I follow your facebook and website to stay updated on perfusion news from all around the world, and I love it. I saw the posting about needing bloggers and wanted to find out if you were interested in a student blogger. Either way, thank you for the work put into the website, it was valuable as I prepared to apply for my program as well as throughout it.
The name of the series is as above- LPM: A Student’s Perspective. There is a slight play on the acronym as the L stands for Learning as opposed to a metric for Q.
As we all know- regardless of experience level- we all learn minute by minute.
Shayla Johnson: Associate Editor
LPM: Special Patient Population: Morbidly Obese
Much like any student, on my drive to the hospital I go over my case in my head; the procedure itself, patient comorbidities, and any foreseeable complications. On most days, for a routine CABG or valve, my mental checklist is the same. Once I get to the hospital, I set up my pump, prime it, look over the patient history and proceed as usual. However, there will always be those cases that require just a little more effort, and it’s important to be prepared for anything while on pump.
I had one such case, with a patient who weighed over 200kgs and was presenting for an aortic valve replacement, secondary to infectious endocarditis. Of course the first adjustment was choosing an A-V loop that had a ½” venous line, as well as selecting larger cannulas to accommodate the higher flows that would be needed. Heparin dosing (at 400u/kg) was much larger than standard, and although it wasn’t all given as the loading dose, it required being cognizant of such a large dose and grabbing many more vials than usually kept at the pump as “back up”.
Of course those were the easier things, ensuring we had the proper materials on pump, in higher quantities than usual. The next line of thought was about how exactly such a large patient would affect our pump set-up. Would one oxygenator be enough? Perhaps for a linebacker we would have needed a second oxygenator, however we decided that it would most likely not be necessary for a patient that was not heavier due to muscle mass (as well as considering a normal BMI for a patient of that height). What we did anticipate, was large blood volume (at 65mL/kg)! Given the weight and approximated blood volume, a four liter reservoir would not be enough. The patient had a significant number of comorbidities, of which included renal failure. We also expected her to be fluid overloaded due to her kidney disease and so we made some circuit modifications. We cut into our recirculation line to add a cardiotomy where we could pump excess volume if necessary. We all had blood transfer bags ready, if necessary to pump extra volume into those as well.
After all our preparations were complete, and having discussed possible problems that could arise, the case proceeded. Surprisingly, on initiation of bypass, our first concern was alleviated. Blood volume was not nearly what we had anticipated, and so we never used our extra cardiotomy nor any blood bags. Oxygenation was also not a problem, maintaining venous saturations as well as cerebral O2 saturation, with a flow between 2.2-2.4 index. With no literature supporting adequate flow for patients of this size, flow was based on our monitoring devices (including CDI and intermittent blood gases) and adjusted accordingly. The patient was dialyzed with 0K+ dialysate throughout the case, with additional boluses of sodium bicarbonate. Electrolytes were all maintained within a normal range. Discussion was given to temperature management and accommodating for the time it may take to cool down as well as rewarm, given the patient’s size.
The case had the potential for problems but it went surprisingly smooth, with no real issues. The hematocrit was low preoperatively, and blood was given on pump and washed prior to administration in order to decrease the Potassium. A hemoconcentrator was already in-line prior to the start of the case and we had discussed using a larger one due to the possible large blood volume, which it ended up not being necessary. The surgical procedure was a valve replacement as well as possible root replacement. The abscess in the heart was supravalvular and so only a patch was necessary in addition to the valve replacement. Possible other considerations had been if the infection had spread below the valve and possibly towards the mitral valve, that it would be a double valve replacement. However, in a not very common occurrence, everything went much better than expected, and maybe a lot of that had to do with everyone being prepared and ready just in case anything went wrong.