by similar significant decreases in cardiac index, stroke volume index, and MAP after change from the supine to the sitting position.6 If one considers the potential for peripheral vasodilatation and myocardial depression that can occur in patients who are anesthetized with potent inhalational agents, the detrimental effects of the upright position and anesthesia can be significant.2
FIGURE 58.2 Allen Lift Assist beach chair attachment configures to any standard operating room table and allows the patient to be positioned optimally for shoulder arthroscopic procedures between horizontal and 90 degrees (A–D). (Allen Medical Systems, One Post Office Square, Acton, MA 01720. www.allenmedical.com.)
autoregulation curve as traditionally shown in Figure 58.4. Rather than sharp and incorrect inflection points at the LLA and ULA, the “shoulders” should be rounded, thereby reflecting the range of normal LLA rather than a specific value of 50 mmHg20,21 (see Fig. 58.5).
FIGURE 58.3 Frontal view of the beach chair attachment showing the head and arm holders. The two lateral support pads can be removed, allowing free surgical access to the upper arms and shoulders.
TABLE 58.1 Lower Limit of Cerebral Autoregulation in Human Studies
replacement with 0.75% bupivacaine epidural anesthesia and adjunctive midazolam, fentanyl, and thiopental sodium as needed. The patients were randomly assigned to one of two levels of intraoperative MAP management: A markedly hypotensive MAP range of 45 to 55 mmHg and a less hypotensive range of 55 to 70 mm Hg.
FIGURE 58.4 A classic representation of the CBF-pressure (autoregulation) curve is made up of three straight lines: one horizontal line between the LLA and the ULA and two sloped lines below the LLA and above the ULA, respectively. Between the LLA and ULA, CBF is autoregulated by changing vessel diameter, and CBF remains constant. Vessels dilate as pressure decreases and reach their maximal size when pressure falls below the LLA. Similarly, vessels constrict as pressure increases and maintain their minimal size when pressure rises above ULA. The two sloped lines are parallel, and the LLA and LUA are represented as specific points (knees) at 50 mmHg and 150 mm Hg, respectively. CBF, cerebral blood flow; LLA, lower limit of cerebral autoregulation; ULA, upper limit of cerebral autoregulation; MAP, mean arterial pressure.
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