Hensley's Practical Approach to Cardiothoracic Anesthesia

16. Anesthetic Considerations for Surgical Myectomy in Patients With Hypertrophic Cardiomyopathy 351

surgical success. While some patients have elevated pulmonary pressures typically related to postcapillary pulmonary hypertension, we rarely initiate milrinone intraoperatively be cause it can decrease systemic vascular resistance and exacerbate SAM. Post-cardiopulmo nary bypass coagulopathy is uncommon, and blood product transfusion is rarely required. CLINICAL PEARL Goals of intraoperative management include maintenance of LV preload and afterload, avoidance of tachycardia, and suppression of myocardial hypercontractility as needed. Hemodynamic swings in re sponse to anesthesia and surgery are not uncommon. Emergency drugs, such as phenylephrine, vaso pressin, esmolol, and calcium chloride should be ready to use. Careful de-airing is recommended before separation from bypass. C. Intraoperative Monitoring In addition to standard monitors recommended by the American Society of Anesthesiology, invasive blood pressure monitoring and central venous access are required. A pulmonary ar tery catheter allows an assessment of pulmonary artery pressure, which is frequently elevated. Many patients have decreased cardiac output at baseline; both parameters are expected to improve after a successful myectomy. TTE and TEE are essential in identifying the distribution of LV hypertrophy, MR and LVOT gradient severity, mitral valve anatomy, and the presence of SAM (Figures 16.2, 16.3). TEE imaging should be performed preceding cardiopulmonary bypass in all cases. At some centers, direct needle measurements of the gradient between the LV and the aorta are checked before and after cardiopulmonary bypass to assess the adequacy of relief of LVOT obstruction. Of note, it is not uncommon to observe some discrepancy in hemodynamic values character izing LVOT obstruction preoperatively and in the operating room under general anesthesia. 21 Before the institution of cardiopulmonary bypass, a 2.5-inch, 22-G spinal needle is inserted into the aorta near the inflow cannula, and a 3.5-inch, 22-G spinal needle is inserted through the right ventricle and septum into the LV (Figure 16.5A). Simultaneous pressures at both locations are measured to calculate the gradient. The surgeon then induces a premature ven tricular contraction by gently tapping the heart to accentuate any transaortic gradient, the Brockenbrough-Braunwald-Morrow response (Figure 16.5B). 22,23 In some patients, we use a bolus of isoproterenol 4-12 μg IV to unmask a latent gradient. It is useful to have IV esmolol

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FIGURE 16.5 Intracavitary gradients determined by direct needle measurements of peak-to-peak pressures between the aorta and the left ventricle. (A) Positioning of the needles in left ventricle and aorta. (B) Arterial and left ventricu lar pressure tracing. Note two important changes after induced premature ventricular contraction: a decline in a pulse pressure on arterial pressure tracing and increase in a gradient between the left ventricle and the aorta. (Used with per mission of Mayo Foundation for Medical Education and Research. All rights reserved.)