Balloon pressure waveforms are also a source of information regarding the behaviour of the IABP and its interaction with the cardiovascular physiology of your patient.
Low IABP balloon plateau pressure
The balloon plateau is a function of the pressure inside the helium balloon and the pressure inside the aorta, which relates to the elastic recoil of the aortic walls (and to some extent to the systemic vascular resistance as a whole).
Balloon plateau pressure might be low in the following circumstances:
- Your balloon is too small for the patient
- Your patient is hypotensive, and has low peripheral vascular resistance (eg. septic shock or any other sort of vasoplegia)
- Your patient has a greatly reduced stroke volume (i.e. there is not enough ejected blood in the aorta to displace)
- Your balloon is positioned too high or too low in the aorta
The consequence of this is a decreased diastolic augmentation, as well as a high aortic end-diastolic pressure. The balloon's laughably low pressure cannot move much blood around the aorta, and the IABP is not being used to its full potential.
High IABP balloon plateau pressure
High balloon plateau pressure, with a square or rounded waveform, reflects either some sort of increase in pressure on the balloon itself, or some impedance to gas flow.
Balloon plateau pressure might be high in the following circumstances:
- Your balloon is too big for the patient
- Your patient is incredibly hypertensive
- Your balloon is positioned too high in the aorta
- The balloon catheter is kinked
The consequences of this could be severe - the balloon could actually rupture from too much pressure. Or, you could be injuring the aorta. If the catheter is kinked, the balloon cannot empty, and balloon deflation could be delayed, which results in either a failure to improve afterload, or an actual increase in afterload.
High IABP balloon filling pressure baseline
The baseline pressure in the helium circuit should be around 10-15mmHg. If this pressure rises, there is likely some mechanical fault with the circuit, which limits the normal emptying of the balloon.
Balloon filling pressure baseline might be high in the following circumstances:
- The balloon catheter is kinked and and balloon is not emptying properly
- The system is overpressurised because the IABP is malfunctioning.
The consequences of this are also dramatic. The balloon could rupture (eventually). Additionally, the increased baseline pressure is transmitted to the aorta, which results in increased afterload and increased myocardial oxygen demand. Decompensation ensues.
Most IABP consoles will begin to alarm with an irritating siren if the baseline pressure climbs over 20mmHg.
Low (or suddenly decreasing) IABP balloon filling pressure baseline
This could also be a major problem. The filling pressure is adjusted automatically; if this is not happening, there must be either a helium leak somewhere, or a failure of the automated filling mechanism. Alternatively, you have just run out of helium, and the tank needs to be replaced.
Alternatively, if the baseline filling pressure dives suddenly, the cause could be either a disconnection of the helium pipe, or (more disturbingly) a balloon rupture.
References
An excellent physiology-heavy article from the American Journal of Critical Care is available as free fulltext to describe the physiological effects of balloon inflation and deflation timing.
Additionally, Life In the Fast Lane has an excellent self-directed Q&A page about troubleshooting IABP timing, and recognizing problems with timing by looking at the waveforms.
Finally, Arrow have produced a quick-reference summary of timing guidelines, to assist with bedside identification and troubleshooting of IABP waveforms
Hanlon-Pena, Patricia M., and Susan J. Quaal. "Intra-aortic balloon pump timing: review of evidence supporting current practice." American Journal of Critical Care 20.4 (2011): 323-334.