What mechanical criteria should be used to establish the actual PEEP setting for a mechanically ventilated patient? I. During a recruitment maneuver, the upper inflection point determines the ideal PEEP level. II. During a recruitment maneuver, the lower inflection point determines the optimal PEEP. III. The pressure-volume loop helps determine the best PEEP/ Vt combination. IV. The optimal PEEP

corresponds with the best lung compliance along the deflation limb following a recruitment maneuver.

A. I, II only
B. III, IV only
C. I, II, III only
D. II, III, IV only

ANS: B
A. Incorrect response: The upper and lower inflection points are obtained from a pressure-volume curve. Refer to the following diagram.
The upper inflection point is the point of intersection of a straight line drawn over the upper flat portion of the curve, and a straight line drawn through the steep part of the curve. The lower inflection point is the point of intersection of a straight line drawn through lower flat portion of the curve, and a straight line drawn through the steep part of the curve.
B. Correct response: The mechanical criteria involve one of the two approaches: (1) pressure-volume curves and (2) best compliance determinations. The pressure-volume curve sets the PEEP/ Vt combination to place the lung between the upper and lower inflection points of a pressure-volume loop in an attempt to minimize overdistention and recruitment-derecruitment injury. The best compliance approach uses step changes in PEEP to determine the PEEP level that gives the best compliance. As with the pressure-volume approach, the best PEEP is probably optimally determined after a recruitment maneuver has placed the lung on the deflation limb of the loop. Refer to the following diagram. ? ??
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B