1997 OPEN FORUM Abstracts
SYRINGE TECHNIQUE FOR STATIC VOLUME-PRESSURE (VP) CURVES IN ARDS.
Carl Haas, MLS, RRT*; Lauren Stapp, RRT*; Linda Folk, RRT*; Daneile Mascheroni, MD+; Robert Bartlett, MD#. Critical Care Support Services* and the Department of Surgery# University of Michigan Health System, Ann Arbor MI; University of Milano, Milan Italy+
Introduction: Static VP curves may help adjust ventilators. Although recommended that PEEP be set above the lower inflection point (LIP) and that tidal volume or inflation pressure be limited to below the upper inflection point (UIP), the super-syringe technique (SST) of determining LIP and UIP has mainly been a research technique which many RCP's are not familiar with. Our study objectives were to: 1) determine SST safety; 2) determine the difference in LIP using 50 mL vs 100 mL incremental inflation steps; and 3) compare agreement of set PEEP with LIP and plateau pressure with UIP. Methods: Initially 2 ECMO patients were studied to ensure they would not decompensate during the procedure. In total 27 studies were performed on a convenience sample of 7 ARDS patients (3 ECMO, 4 non-ECMO). Either a 1.0 L or a 3.0 L super-syringe (calibrated in 20 mL or 100 mL increments, respectively) was connected in series to a filter, a pressure sensing port and patient connector. Pressure was transduced using the bedside hemodynamic monitoring equipment (Marquette Series 7000, Milwaukee WI) and continuously graphed. Prior to study, patients were determined to have no airleak, no respiratory effort (paralytic agent given if necessary), and to be hemodynamically stable. Baseline HR, BP, SpO2, SvO2 (if available), continuous cardiac output (if available), and ventilator settings were recorded while receiving an FIO2=1.0. HR, BP, SpO2, SvO2 and CCO were observed during and recorded at the end of the procedure. Duration off the ventilator was recorded. Test procedure was: fill syringe with pure oxygen; disconnect ventilator and start timer; allow 15 seconds for complete exhalation; attach super-syringe (disconnect and reattach if pressure sensed); inject either 50 or 100 mL volume; wait 2-3 sec and inject another volume; repeat until either 1.5 L, 50 cm H2O or maximum volume of syringe attained or patient decompensated (rise in HR>=20, drop in BP >=20 mmHg or drop in SpO2 to 80%.) Results: Objective 1: No study was stopped due to patient decompensation. The table shows that although SpO2 was statistically reduced, no clinically relevant changes occured in any measured parameter. Total duration off the ventilator was 77.4 ± 16.1 sec (range 56-115 sec).
HR Mean BP (mmHg) SpO2 (%) SvO2 (%) CCO (L/min)
Pre 110±18.1 84.5±10.1 95.1±3.5 80.3±5.8 9.6±2.5
Post 109±17.9 89.0±16.8 93.6±4.3 79.6±6.6 9.7±2.6
p/n 0.397/27 0.064/27 0.006/27 0.415/20 0.65/7
Objective 2: For LIP, although more accurate using 50 mL steps, there appears to be minimal clinical difference when directly comparing 50 vs 100 mL inflations (12.4 ± 3.4 vs 13.8 ± 4.7 cm H2O, p=0.206, n=7) or when extrapolating 100 mL inflation LIP from the 50 mL inflation curve (12.6 ± 3.8 vs 14.0 ± 4.0 cm H2O, p=0.0003, n=14). Objective 3: PEEP was generally set below LIP (10.1 ± 1.7 vs 12.6 ± 3.9 cm H2O, p=0.009). Only 9 of 27 studies (4 of 7 patients) showed an UIP. Although the mean UIP was 33.1 ± 5.4 cm H2O (range 26.5 to 42.0) and plateau was 34.6 ± 4.7, UIP was less than plateau by >=5 cm H2O in three cases. Conclusions: 1) The procedure can be safe, provided close monitoring is maintained; 2) LIP is most accurately determined with 50 mL steps; 3) PEEP may be under applied in many patients; 4) unrecognized overdistension may occur.