2003 waveform pocket guide BENNETT

a P-V loop during a mandatory breath that displays the characteristic “figure eight” often seen if inspiratory flow is set too low to meet the patient’s demands, or a descending ramp flow waveform results in inadequate end-inspiratory flow As the patient’s demand begins to outstrip the flow delivery of the ventilator, the pressure starts to decrease (A) while volume continues to increase Exhalation becomes slightly positive at the beginning (B) and then assumes a normal configuration as the lungs empty Detecting Air Leaks or Air Trapping VT 1000 mL 900 Insp Area 0.000 800 700 600 500 3.0 cm H2O 400 300 200 100 -100 PCIRC -30 -20 -10 10 20 30 40 50 60 cmH2O Figure 69 Air Leaks or Air Trapping 53 54 Application FLOW-VOLUME LOOP 3.0 2.5 EXH A 2.0 1.5 V L sec The flow-volume loop may be helpful in gauging the effects of bronchodilators on patients Evaluating the Effect of Bronchodilators 1.0 0.5 VT mL 0.5 PRE-BRONCHODILATOR 3.0 EXH 2.5 INSP V 200 400 600 800 1000 1200 1400 1600 L sec 1.5 1.0 B 0.5 VT mL 0.5 Figure 70 Typical Flow-Volume Loop 55 D 1.0 0.5 VT mL 1.0 1.5 1.5 2.0 Figure 70 shows a typical flow-volume loop The peak expiratory flow rate is noted at (A); peak inspiratory flow rate is noted at (B) Flow is plotted on the vertical axis and volume on the horizontal The lower half of the loop represents inspiration; the upper half represents exhalation The loop arrangement resembles that of a pulmonary function test, in which exhalation is plotted first followed by the next inspiration V L sec 0.5 1.0 2.5 EXH 2.0 1.5 200 C 2.5 A 2.0 1.5 2.0 2.5 POST-BRONCHODILATOR 3.0 B 1.0 INSP 200 200 400 600 Figure 71 Pre-Bronchodilator Flow-Volume Loop 800 1000 2.0 2.5 INSP 200 200 400 600 800 1000 Figure 72 Post-Bronchodilator Flow-Volume Loop Figures 71 and 72 show pre- and post-bronchodilator flow-volume loops that indicate a positive response to the bronchodilator administration The flowvolume loop before bronchodilator administration shows a low peak expiratory flow rate (A) and a scalloped shape near the end of exhalation (B) that is characteristic of poor airway conductivity The post-bronchodilator loop shows an improved peak expiratory flow (C) as well as improved flow toward the end of exhalation (D) 56