Intraaortic Balloon Pump Counterpulsation and Cerebral Autoregulation: an observational study

Abstract

Background: The use of Intra-aortic counterpulsation is a well established supportive therapy for patients in cardiac failure or after cardiac surgery. Blood pressure variations induced by counterpulsation are transmitted to the cerebral arteries, challenging cerebral autoregulatory mechanisms in order to maintain a stable cerebral blood flow. This study aims to assess the effects on cerebral autoregulation and variability of cerebral blood flow due to intra-aortic balloon pump and inflation ratio weaning.

Methods: Cerebral blood flow was measured using transcranial Doppler, in a convenience sample of twenty patients requiring balloon counterpulsation for refractory cardiogenic shock (N = 7) or a single inotrope to maintain mean arterial pressure following an elective placement of an intra-aortic balloon pump for cardiac surgery (N = 13). Simultaneous blood pressure at the aortic root was recorded via the intra-aortic balloon pump. Cerebral blood flow velocities were recorded for six minute intervals at a 1:1 balloon inflation-ratio (augmentation of all cardiac beats) and during progressive reductions of the inflation-ratio to 1:3 (augmentation of one every third cardiac beat). Real time comparisons of peak cerebral blood flow velocities with systolic blood pressure were performed using cross-correlation analysis. The primary endpoint was assessment of cerebral autoregulation using the time delay between the peak signals for cerebral blood flow velocity and systolic blood pressure, according to established criteria. The variability of cerebral blood flow was also assessed using non-linear statistics.

Results: During the 1:1 inflation-ratio, the mean time delay between aortic blood pressure and cerebral blood flow was -0.016 seconds (95% CI: -0.023,-0.011); during 1:3 inflation-ratio mean time delay was significantly longer at -0.010 seconds (95% CI: -0.016, -0.004, P < 0.0001). Finally, upon return to a 1:1 inflation-ratio, time delays recovered to those measured at baseline. During inflation-ratio reduction, cerebral blood flow irregularities reduced over time, whilst cerebral blood flow variability at end-diastole decreased in patients with cardiogenic shock.

Conclusions: Weaning counterpulsation from 1:1 to 1:3 inflation ratio leads to a progressive reduction in time delays between systolic blood pressure and peak cerebral blood flow velocities suggesting that although preserved, there is a significant delay in the establishment of cerebral autoregulatory mechanisms. In addition, cerebral blood flow irregularities (i.e. surrogate of flow adaptability) decrease and a loss of cerebral blood flow chaotic pattern occurs during the end-diastolic phase of each beat in patients with cardiogenic shock.

Figure 1

Aortic pressures and Transcranial Doppler tracings. Upper figure: IABP pressures (y axis) during 1:3 inflation-ratio over time (x axis). IABP augments every third cardiac beat, showing characteristic traces such as an augmented peak diastole, reduced end-diastolic pressure and decreased non-augmented peak systole; these pulse pressure variations imply a left ventricular afterload reduction whilst increasing diastolic pressures (to improve coronary perfusion). Lower figure: Cerebral blood flow velocities using TCD (y axis) at the Mean Cerebral artery, over time (x axis). Notice that the end-diastolic velocities become negative; known as "reversal flow" and are considered to be the result of a steeling phenomena from the deflation of the IABP in the Aortic root. Both traces are represented in a real time, beat-to-beat correlation, using the integrated software of a Power lab computer.

Figure 2

Time delays and inflation ratios. Time delays in couples of group 1 - left and group 2 - right, showing the relative delay for 1:1(continuous line), 1:2 (dotted line), 1:3 (dashed line) and 1:1-end (intermittent dashed-dotted line) IABP inflation ratio.

Figure 3

Cerebral blood flow variability represented in a scale of colors. Non-linearities represented in dark orange colors, shifting to the right on the (x) axis, for group 1(patients electively supported with IABP): Top-left: 1:1 ratio; top-right: 1:2 ratio; bottom left: 1:3 ratio; bottom right: 1:1-end ratio. Notice the progressive increase of time-lag of the cerebral blood flow variability as the IABP inflation-ratio is weaned; suggesting that cerebral blood flow variability takes longer to be established as the IABP is weaned off.

Figure 4

Cerebral blood flow variability represented in a scale of colours. Non-linearities represented in dark orange colours, shifting to the right on the (x) axis, for group 2 (patients in refractory shock): Top-left: 1:1 ratio; top-right: 1:2 ratio; bottom left: 1:3 ratio; bottom right: 1:1-end ratio. Notice the progressive increase of time-lag of the cerebral blood flow variability as the IABP inflation-ratio is weaned; suggesting that cerebral blood flow variability takes longer to be established as the IABP is weaned off. Overall reduction in cerebral blood flow variabilities are shown, when compared with subjects in group 1-fig 3.

Figure 5

Representation of cerebral blood flow chaotic pattern. Real tracing from a representative subject in group 1 (patients with elective support of IABP) showing: Upper row: left figure corresponds to 1:1 IABP inflation-ratio trace (in red) superimposed to CBFV (in blue) during the same beat. Middle figure corresponds to 1:2 IABP inflation-ratio trace (in red) superimposed to CBFV (in blue) during another beat. Right figure corresponds to IABP inflation-ratio trace (in red) superimposed to CBFV (in blue) during a cardiac beat. Lower row: simultaneous representation of CBFV non-linearities (variability) expressed as a time function of log ratio (y - axis) and time (x - axis). Notice that the moment of maximum variability corresponds to the end-diastole in each beat

Figure 6

Representation of cerebral blood flow chaotic pattern. Real tracing from a representative subject in group 2 (patients in refractory shock) showing: Upper row: left figure corresponds to 1:1 IABP inflation-ratio trace (in red) superimposed to CBFV (in blue) during the same beat. Middle figure corresponds to 1:2 IABP inflation-ratio trace (in red) superimposed to CBFV (in blue) during another beat. Right figure corresponds to IABP inflation-ratio trace (in red) superimposed to CBFV (in blue) during a cardiac beat. Lower row: simultaneous representation of CBFV non-linearities (variability) expressed as a time function of log ratio (y - axis) and time (x - axis). Notice that the moment of maximum variability corresponds to the end-diastole in each beat, however in this case variability is minimum when compared with group 1.