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304 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

FIGURE 12.6 IABP during 1 : 1 assist (counterpulsation on every beat). Balloon inflation at the start of Diastole and deflation just before next systole. IABP
during 1 : 2 assist (counterpulsation on every second beat). Inflation of the balloon rapidly at the inflation point (IP) raises diastolic pressure, producing a
peak diastolic pressure (PDP) that exceeds the systolic pressure (PSP). The balloon remains inflated during diastole. With balloon deflation just prior to the
next systole there is a rapid decline in pressure to the balloon-assisted end-diastolic pressure (BAEDP), which is lower than normal, reducing afterload. The
ensuing systole is achieved with a reduced systolic pressure (the assisted peak systolic pressure, APSP).

peak now appearing on the waveform, described as the Real timing
‘augmented diastolic’ or ‘balloon-assisted peak diastolic’ In contrast to conventional timing, during real timing
pressure. This peak is usually at least 10 mmHg higher (also referred to as R wave deflate) the balloon remains
than the systolic pressure (Figure 12.6). inflated for slightly longer, and is deflated not before but
at the same time as systole. The reduction in aortic end-
Balloon Deflation diastolic pressure is therefore not seen, but deflating
As the inflated balloon largely obstructs the aorta, it must simultaneously with left ventricular contraction still
48
be deflated to permit systolic emptying of the left ven- favourably effects left ventricular emptying. Thus there
tricle. Two separate approaches to the timing of balloon is improved stroke volume, systolic pressure reduction,
deflation have emerged: ‘conventional timing’, and ‘real and decreased ventricular work and oxygen demands as
47,49
timing’. seen during conventional timing. Box 12.1 sum-
marises the impact of balloon inflation and deflation on
haemodynamic status and the oxygen supply:demand
Conventional timing balance.
In conventional timing, the balloon is deflated immedi- The arterial pressure wave reveals the impact of IABP
ately prior to systole. Rapid deflation induces a precipi- therapy on haemodynamic status. Placing the pump into
tous drop in aortic pressure at the end of diastole (a 1 : 2 assist (balloon pumping on only every second beat)
reduced aortic end-diastolic pressure). This reduces the is useful to highlight balloon pump impact and how
duration of the left ventricle isovolumetric contraction assisted beats vary from the normal pressure cycle during
phase of cardiac cycle (most oxygen consuming phase of systole and diastole. Figure 12.6 depicts the impact of
cardiac cycle), left ventricular afterload and improves left IABP on haemodynamic status and the arterial pressure
ventricular emptying, improving stroke volume and waveform.
cardiac output. 46,47 In addition, less pressure is required
for left ventricular emptying, so systolic work and oxygen
demands on the myocardium are reduced. Thus defla- COMPLICATIONS OF INTRA-AORTIC
47
tion during conventional timing should see the aortic BALLOON PUMPING
pressure drop to below normal at end-diastole, just in Serious complications are uncommon during IABP treat-
advance of the subsequent systole. Systolic pressure ment and continue to decrease in frequency in the last
should be lower than during non-assisted beat. decade with advances in pump technology and smaller