Derived cardiorespiratory variables, systemic vascular resistance, pulmonary vascular resistance, arterial and mixed venous oxygen content, oxygen delivery, oxygen consumption, and oxygen extraction ratio were calculated using standard and previously described formulae. Where appropriate, cardiorespiratory and hemodynamic variables were normalized, using the calculated body surface area for each patient. Mean ± standard error of the mean was calculated for each of the cardiorespiratory variables, both before and after institution of PC-IRV. Comparison between values before and after initiation of PC-IRV was performed by a paired Students f-test. Differences were considered to be significant for p<0.05. read
Table 1 summarizes the characteristics of the patient population studied. Four men and five women were included. The average age was 46 ±4 years. Arterial blood gas values, arterial oxygen saturation and peak inspiratory pressures before and after initiation of PC-IRV are presented in Table 2. All patients showed an increase in Pa02 after the institution of PC-IRV, with the range of improvement in Pa02 being 1 to 18 mm Hg. The P&C02 decreased in seven patients and pH rose in six patients with initiation of PC-IRV The PIP fell in eight of the nine patients after inverse ratio ventilation was begun. For the entire patient group, the changes in PaC02 and PIP after beginning PC-IRV were not statistically significant. Minute ventilation did not significantly change after initiation of inverse ratio ventilation, 16.5 ±4.1 L/min before PC-IRV and 18.2 ± 4.1 L/min after starting PC-IRV.
Cardiorespiratory parameters in the pre- and post-PC-IRV periods are shown in Table 3. In the control period, when the patients were ventilated with conventional I:E ratios, they demonstrated a relative hyperdynamic state, with increased HR, Cl, Do2, 02Ext, and Vo2. Pulmonary artery pressures and PVRI were elevated. Following the initiation of PC-IRV there were no significant changes in the mean values for any of the cardiorespiratory parameters. In three patients, changes of more than 10 percent in MAP, Cl, Do2, or Vo2 accompanied the institution of PC-IRV In patient 4, the MAP decreased from 76 to 63 mm Hg. This fall in blood pressure was accompanied by greater than 30 percent decreases in cardiac output (from 4.0 to 2.7 L/min/m2), CVP (from 16 to 10 mm Hg), WP (from 18 to 10 mm Hg), Do2 (from 396 to 273 ml/min/m2), 02Ext (from 28.3 to 21.3 percent), and Vo2 (from 84 to 59 ml/min/m2). In this patient, SVRI was found to increase by 31 percent (from 1200 to 1570 dynes*s*cm_5/m2).
The other two patients showing greater than 10 percent changes in cardiorespiratory values after initiation of PC-IRV had increases in Cl and Do2, accompanied by a decrease in SVRI, but only minimal alteration in MAP. In patient 7, Cl increased by 20 percent (from 2.5 to 3.0 L/min/m2), and Do2 by 25 percent (from 353 to 440 ml/min/m2), while SVRI fell by 14 percent (from 789 to 676 dynes*s*cm_5/m2). In patient 8, greater than 20 percent increases were found for Cl (3.6 to 4.6 L/min/m2), Do2 (486 to 621 ml/min/m2), CVP (14 to 20 mm Hg), WP (12 to 15 mm Hg), and Vo2 (216 to 276 ml/min/m2). In this patient, both SVRI (from 1111 to 852 dynes#s*cm~ /m2) and PVRI (from 356 to 273 dynes*s*cm ~ /m2) fell with the institution of PC-IRV.
Table 2—Ventilatory Barometers
|Pa02, mm Hg||RlCOa, mm Hg||pH||SaOs, %||PIP, cm HaO|
|Before PC-IRV||63±4||46±5||7.37 ±.05||93±2||44±4|
|After PC-IRV||76 ±8*||39 ±6||7.42± .04||94±2||39 ±2|
Table 3—Cardiorespiratory Barometers
|Before PC-IRV||After PC-IRV|
|MAP (mm Hg)||78 ±6||75 ±4|
|HR (beats/min)||119±7||111 ±5|
|Cl (L/min/Ms)||4.8± .7||4.9± .7|
|SVRI (dynes*s*cm/m2)||1154 ±181||1114 ± 175|
|CVP (mm Hg)||12 ±2||14 ±2|
|WP (mm Hg)||13 ± 1||14 ± 1|
|PAS (mm Hg)||44±4||45±4|
|PAD (mm Hg)||23±3||24±3|
|PVRI (dynes*s«cm – /m2)||376 ±66||326 ±59|
|CaO, (ml)||12.7 ± .5||12.6± .6|
|CvO, (ml)||8.7 ± .4||9.1 ±.5|
|Do, (ml/min/m2)||577 ±102||544 ± 129|
|Vo, (ml/min/m2)||159 ±22||157 ±27|
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