Question 30
An 82-year-old patient has been transferred to intensive care following aortic valve replacement for native aortic valve endocarditis. The patient is intubated and ventilated. Two hours post operatively, the vasoactive infusions are:
- Noradrenaline 12 mcg/min (0.15 mcg/kg/min)
- Dobutamine 5mcg/kg/min
The mean arterial pressure is 65 mmHg.
The patient is paced at 90 beats/min, DDD mode.
The following information is obtained from the pulmonary artery catheter:
- CVP 18 mmHg
- PAP 45/22 mmHg
- CI 4.6 L/min
- SVRI 745 dynes.sec.cm–5.m2
- SvO2 70%
a) Explain the information derived from the PA catheter. (20% marks)
b) List the most likely differential diagnosis for the clinical state. (30% marks)
Three hours postoperatively the patient becomes hypotensive. An ECG rhythm strip (ECG 30) taken at this time is shown on page 11. (Image removed from report)
a) List the abnormalities on the ECG. (20% marks)
b) Outline the management of the pacing issues. (30% marks)
College answer
Generally, well answered. Some candidates could not diagnose the issues in the first part of the question related to PA catheters adequately. The second part which was related to failure-to-capture was again well answered by most. Some candidates went into great depth about testing pacemakers, which didn't score marks and probably took a lot of time to write. Time management and answering the questions asked are two of the most important exam techniques which candidates can employ to score optimal marks for their level of knowledge.
Discussion
a)
Those PA catheter abnormalities:
- The CVP is raised
- The PA pressure is raised, and especially the PA diastolic pressure is raised, which suggests raised LA pressure (tenuously, insofar as PADP is a surrogate for PAOP, and PAOP is a surrogate for LA pressure).
- The cardiac index is rather high, if we accept 4.0 as the upper limit of normal. This suggests the circulation is hyperdynamic.
- The SVRI is extremely low, as the normal range of values is 1970 - 2390 dynes.sec.cm–5.m2. This suggests the patient is very vasodilated.
- The SvO2 of 70% is reasonably normal, which suggests that, whatever else is going on in the circulation, the tissue delivery of oxygen is not especially impaired.
In summary, the patient has well-corrected distributive shock and increased PA pressure.
b)
The most likely differential diagnosis for this is vasoplegia due to a combination of the effects of cardiopulmonary bypass and sepsis. The raised PA numbers could be attributed to a myriad possible causes (mechanical ventilation, protamine, pre-existing lung disease, what have you) but this question asked the trainees to "list the most likely differential diagnosis" and these would not necessarily make it onto that list. Incidentally, making some assumptions (eg. that PADP is virtually the same as PAOP, and that MPAP can be estimated by the same mathematical shortcuts as MAP) we can plug the other variables into the usual equation and get a PVRI of 133, which is not especially elevated.
c) The pacing spikes and the QRS complexes are completely unrelated to each other in this image (shamelessly stolen from emergencymedicinecases.com). The other abnormalities are:
- Right bundle branch block
- Junctional rhythm at rate 40
- Sensing, but failure to capture
- Diffuse deep T wave inversions
b)
Management of this would include:
- Try increasing the output to maximum
- Try reversing the leads
- Convert to unipolar pacing using a skin lead
- Remove the PA catheter from its sheath and instead float a balloon-tipped transvenous pacing wire
- Worst case scenario, pace externally or attempt to increase the junctional rate by increasing the dobutamine infusion dose
References
Reade, M. C. "Temporary epicardial pacing after cardiac surgery: a practical review." Anaesthesia 62.3 (2007): 264-271.
Wigfull, James, and Andrew T. Cohen. "Critical assessment of haemodynamic data." Continuing Education in Anaesthesia, Critical Care & Pain 5.3 (2005): 84-88.