Question 5.2
Figure 2:
b) What has caused the fall in blood pressure seen in the latter half of figure 2?
c) The recording depicted below was made from a patient on intermittent positive pressure ventilation. The upper trace represents the ECG, the middle trace the arterial pressure waveform and the lower trace respirations.
i. What important haemodynamic abnormality is demonstrated?
ii. List three causes of this abnormality.
College Answer
b) Causes
• Loss of atrial contraction
c)
i) Haemodynamic Abnormality
The important haemodynamic abnormality is pulse pressure variation (systolic pressure variation
also acceptable).
ii) Causes
Causes of this abnormality include:
• Hypovolaemia (fluid responsiveness acceptable)
• Acute severe asthma
• Cardiac tamponade
• Excessive tidal volume
Discussion
This is a pattern recognition question which relies on the candidate's familiarity with troubleshooting equipment.
Unfortunately, the college has removed the images, so nobody can recognise the patterns.
It is difficult to make much sense of it, but I can only assume the pattern in (b) was supposed to be an arterial line trace which suddenly dips in pressure and becomes irregular, demonstrating that the patient has gone into rapid AF. This, at least, is what I have attempted to re-create.
The pattern in (c) probably depicts a respiratory variation in arterial pressure, which can either be caused by inadequate right heart filling (eg. hypovolemia), excessive right heart afterload (eg. acute severe asthma) or decreased right ventricular compliance (cardiac tamponade). I went on and on about it in the stroke volume variation section of my PiCCO rant. The variation in stroke volume (or, more accurately, pulse pressure - because that is all you can measure directly with the arterial line).
But let us not get carried away.