Ann Thorac Surg 2010;89:672-673. doi:10.1016/j.athoracsur.2009.08.047
© 2010 The Society of Thoracic Surgeons
Correspondence
A Target for Perioperative Blood Pressure During Cardiac Operations
John C. Chen, MDa,
Stanton K. Shernan, MDb,
Cornelius Dyke, MDc,
Solomon Aronson, MDd
a Department of Cardiothoracic Surgery, Hawaii Kaiser Permanente Medical Center, 3288 Moanalua Rd, Honolulu, HI 96819-1469
b Department of Anesthesiology, Brigham and Women's Hospital, Boston, MA
c Southeast Texas Cardiovascular Group, Houston, TX
d Department of Anesthesiology, Duke University Medical Center, Durham, NC
(Email: john.c.chen{at}kp.org).
To the Editor:
Hypertension is a frequent occurrence in cardiovascular interventions. Patients with preexisting hypertension are especially susceptible to blood pressure (BP) elevations in the perioperative period and are at increased risk for morbidity and death associated with the procedure. During the induction of anesthesia, BP elevations and tachycardia may develop in patients with and without preoperative hypertension [1].
Perioperative changes in BP are characterized by acute mechanical and physiologic perturbation related to orotracheal intubation, institution of cardiopulmonary bypass, systemic inflammatory response, application of aortic occlusive clamps, excessive release of catecholamine, reperfusion injury, rapid intravascular volume shifts, peripheral vasoconstriction, altered cardiac reflexes, and inadequate anesthesia, which in combination or separately can compromise microvascular blood flow [2, 3]. Moreover, perioperative hypertension increases myocardial oxygen consumption, left ventricular end-diastolic pressure, and contributes to subendocardial coronary hypoperfusion [4].
Cardiac surgical patients who experience volatility in BP outside a target range may be susceptible to a plethora of instigating variables, including the surgical stress response, manipulation of the operative field, institution and weaning from mechanical ventilation, or a lack of vigilance by clinicians for maintaining tight BP control. In the past, nonextreme fluctuations in BP had to be tolerated in the absence of pharmacotherapy that allowed precise control. With newer, more precise, antihypertensive agents, clinicians now have the ability to maintain BP within a narrow target range. The intriguing question is simple: Can tighter regulation of BP during cardiovascular operations improve outcomes?
Recently, Aronson and colleagues [5] characterized BP variability as an area under the curve (AUC) that was measured to reflect the range of BP beyond prespecified criteria [5]. The AUC is a linear variable that reflects an integral of degree and duration of pressure incursions described in mm Hg x min units (Fig 1).
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Fig 1. Analysis of systolic blood pressure (SBP) lability during a 24-hour period is shown as the area under the curve of SBP excursions outside of the defined range (mm Hg x min).
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Three AUC variables were calculated for various systolic BP (SBP) threshold criteria: area above a value (eg, 135 mm Hg), area below a value (eg, 95 mm Hg), or the combined areas beyond a range (eg, > 135 or < 95 mm Hg). After 3.1 million individual BP evaluations were analyzed in 5038 cardiac surgical patients, a cumulative perioperative BP incursion beyond a systolic BP range exceeding 135 mm Hg or less than 95 mm Hg predicted higher mortality after coronary artery bypass grafting (CABG). SBP variability was subsequently validated in a cohort of 2466 patients [6].
On the basis of presented observational data, we speculate that an optimal target range may exist for perioperative control of BP in cardiac surgical patients that includes both a level and duration of hemodynamic instability. The AUC is a new metric to assess the precisions of blood pressure management. A lack of consideration for this comprehensive measure may account for the conflicting outcomes of prior randomized trials that only compared high vs low mean arterial pressures during CABG [7, 8]. Newer generations of heart and lung machines are equipped with automated continuous recording computer software, and some institutions have automated record keeping for the entire intraoperative period that makes future data analysis quite feasible. Now we may have objective tools to confirm that, indeed, tighter control of hemodynamics is safer for our patients.
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