a) Draw and label a diagram to show the key components of a continuous veno-venous haemofiltration circuit. (40% marks)
b) The following pressures are displayed on your Continuous Renal Replacement Therapy (CRRT) machine that is providing continuous veno-venous haemofiltration (normal values are provided in brackets).
Access pressure: -240 mmHg* (-50 to -150 mmHg)
Pre-Filter pressure 46 mmHg* (100 to 250 mmHg)
Return pressure: 38 mmHg* (50 to 150 mmHg)
Describe your approach to dealing with the problem (40% marks)
c) The problem resolves but the following day you are presented with a new issue
Access pressure: -110 mmHg (-50 to -150 mmHg)
Pre-Filter pressure. 450 mmHg* (100 to 250 mmHg)
Return pressure: 40 mmHg* (50 to 150 mmHg)
What is the likely cause?(20% marks)
a)
Either pre-or post-filter replacement fluid acceptable
Effluent pressure monitor not required
b)
Statement that this is a venous access problem
c)
Imminent clotting of the filter
Examiners Comments:
This was answered well by most candidates.
a)
It is pleasing to see the college offer some positive remarks to the candidates, a downtrodden species generally accused of having serious knowledge gaps. This time, they did well. It is equally pleasing to see the college offer a reasonable-looking diagram in their model answer. This one is not as easy to track down as some of the other Google images they used (it only appears in this presentation, although it very likely has some other source). As the official college diagram, it is superior to the locally available non-peer-reviewed options, and should be viewed as the Definitive CVVH Diagram for the purposes of exam revision.
b)
The pressure are:
Access pressure: -240 mmHg* (-50 to -150 mmHg)
Pre-Filter pressure 46 mmHg* (100 to 250 mmHg)
Return pressure: 38 mmHg* (50 to 150 mmHg)
This is just short of the values which in the Prismaflex machines give a "Access Pressure Extremely Negative" alarm (-250 mmHg). The following troubleshooting section is lazily cut-and-pasted from the chapter on the troubleshooting of the dialysis circuit:
Causes of low access pressure
Troubleshooting:
c)
The pressure we are presented with:
Access pressure: -110 mmHg (-50 to -150 mmHg)
Pre-Filter pressure. 450 mmHg* (100 to 250 mmHg)
Return pressure: 40 mmHg* (50 to 150 mmHg)
The extremely high pre-filter pressure and the unusually low return pressure suggests that the filter is clotting. This would generate a "Filter Pressure Extremely Positive" alarm.
Causes of high filter pressure
Troubleshooting:
The Gambro PRISMA Systems Operator's Manual is a wealth of information. However, it is very long.
This excellent nursing resource from Nepean ICU by Keren Mowbray is both succinct and complete.
So is this one (also from Nepean, by Alison Bradshaw - but it appears to be in Comic Sans)
Ricci, Zaccaria, Ian Baldwin, and Claudio Ronco. "Alarms and troubleshooting."Continuous Renal Replacement Therapy (2009): 15.
Carson, Rachel C., Mercedeh Kiaii, and Jennifer M. MacRae. "Urea clearance in dysfunctional catheters is improved by reversing the line position despite increased access recirculation." American journal of kidney diseases 45.5 (2005): 883-890.
Sutter, Mark, et al. "Hemodialysis complications of hydroxocobalamin: a case report." Journal of Medical Toxicology 6.2 (2010): 165-167.