**23. Counterpulsation – An anesthesiologists perspective**

As an anaesthetist, working in the perioperative care of cardiac surgery patients for the last 20 years, I have observed a significant change in the attitudes and uses of the intra aortic balloon pump. I have watched the use of the IABP change from a last resort salvage technique for the patient on maximal inotropes with low output syndrome and a dismal prognosis, to a first line tool aiming for preservation of myocardial tissue in unstable cardiac surgery patients. The presumed IABP's favorable myocardial oxygen supply/demand profile and the ease of percutaneous insertion have been instrumental in this change (*Trost JC 2006*).

In our institution IABPs are often inserted in preoperative cardiac surgery patients: who are experiencing unstable angina, especially post myocardial infarction, not responsive to standard non-invasive therapies; that have low output syndrome or congestive heart failure secondary to severe left ventricular dysfunction or mechanical complications such as a ventricular septal defect or mitral regurgitation induced by a myocardial infarction ; and rarely who have acute myocardial ischemia causing intractable arrhythmias. It appears that the earlier the balloon is placed in a hemodynamically struggling patient, the more stable the patient is in the post-operative period. This practice is consistent with the Task Force on Practice Guidelines of the American Heart Association and American College of Cardiology (*Ryan TJ 1999*). Frequently, IABPs are inserted for preoperative cardiac surgery patients with symptomatic left main disease. The intention of the IABP is the preservation of viable ïschemic myocardial tissue. The mechanism of the preservation may relate more to decreased myocardial demand and collateral flow as Kimura showed that in the presence of a coronary artery stenosis of greater than 90% the IABP diastolic augmentation did not result in an increased post-stenotic pressure (*Kimura A 1996*). The insertion of the IABP into the aforementioned patients facilitates the anaesthetist's ability to maintain cardiovascular stability and a favourable myocardial oxygen supply/delivery ratio at induction, maintenance and release from bypass. Replace with" The importance and validity of the IABP in maintaining a favorable myocardial oxygen supply/demand ratio is realized in the post-operative period (*Christenson 1997*).

Intra-Aortic Balloon Counterpulsation Therapy

**% Transfused**

and Its Role in Optimizing Outcomes in Cardiac Surgery 69

precluded or insertion has failed, transthoracic (in a peri-operative setting), transbrachial or subclavian insertion can also be performed with a positive impact on survival. Morbidity and mortality however are higher in these kinds of cases and may have to do with the preoperative risk factors these patients come into surgery for. The cardiac surgeon has to tread the fine line between deciding the optimal timing for IAB insertion by weighing the benefits of counterpulsation vs the low risk of complications. It is increasingly being understood that for a poor LV and /or a patient with a risk of peri-operative infarct, it is optimal to insert an IAB sooner rather than later. The catheter can easily be removed first or second postoperative day after the surgery has performed and the risk for infarct been mitigated. At Southlake, a 380 bed community hospital, we perform approximately 1000 heart surgeries and 3000 PTCA's annually. In support we insert 250 IAB catheters annually and are the largest IAB user in Ontario-Canada. We are a comparatively new heart centre, having started our cardiac surgery program in 2004. Aggressive use of counterpulsation reflects the new belief in early IAB insertion in cardiac patients at risk of pre, peri or post-operative infarct. Transfusion

**Red Blood Cell Transfusion Rates**

Apr 2004-Mar 2005 Feb- July 2007 Jan-June 2008 Feb-July 2009

**Knees Hips RP CABG Procedure**

Mortality at SRHC for late 2009 (July to Dec 2009) was based on Toronto Risk Score (TRS). The observed mortality ranged from 0.5% (TRS 2-4) to 8.5% (TRS >8) as shown in fig 27.

Fig. 26. Red Blood Cell Transfusion Rate for 2009 at SRHC.

Fig. 27. Observed and Expected Mortality at SRHC by Toronto Risk Score

rates at SRHC for CABG in the first half of 2009 approximate 26% (Fig 26).

Intraoperatively, IABPs are inserted into our patients when difficulty to wean from the bypass machine is anticipated due to instability in the pre-bypass or bypass period or for failure to wean from the bypass machine, once reversible causes for the failure are ruled out. There may be a survival advantage to placing the IABP prior to coming off bypass based on one review. Delaying insertion of the IABP in the unstable perioperative patient who is unresponsive to reasonable doses of inotropes or who has rapidly accelerating inotropic requirements may have deleterious effects. Theoretically this is supported by the following facts. High inotropic doses increase myocardial inotropy and tension resulting in increased myocardial oxygen demands. Impaired diastolic relaxation and increased ectopy and afterload, as seen with certain inotropes, may further tip the myocardial supply/demand balance in favour of demand (*Katz AM 1990*). Myocardial injury may be further exacerbated by the inotropes increased delivery of calcium to the cell, overcoming the ischemic myocardium's presumed protective attempt at limiting available calcium. Early insertion of the IABP in the unstable post-bypass patient appears to theoretically and anecdotally improve outcome (*Poole Wilson PA 1990*).

Postoperative insertion of the IABP in the majority of our cases is for myocardial failure or signs of ischemia. Many times there is a dramatic improvement post balloon insertion. The mechanism producing this improvement is often not clear .Possibilities include a heightened diastolic pressure overcoming decreased coronary flow secondary to low mean arterial pressure, left internal mammary spasm or air within a coronary artery, improved collateral flow (Kern MJ 1991), or decreased demands secondary to decreased afterload and preload resulting in decreased myocardial wall tension. The IABP often assists in stabilization of the patient, although more definitive therapy may be required. The location of the ischemia, as visualized by the electrocardiogram and often echocardiogram, the magnitude of the failure, the surgical knowledge of the coronary disease and surgery and the response to the IABP determine the need for further management.

We have come to use IABP's earlier, and the indications have broadened to include all stages of the perioperative care. The theoretical protective effect of the IABP with respect to the myocardial supply/demand ratio, the ease of insertion of the IABP by the percutaneous route clinical observations and limited studies support this practice.
