Long-term evaluation of gas exchange and hydrodynamic performance of a heparinized artificial lung: comparison of two different hollow fiber pore sizes.

We compared the performance of a heparinized hollow fiber artificial lung (Medtronic, Minimax) featuring standard hollow fibers (Group A) and experimental hollow fibers with a smaller pore size (Group B). Four sheep in each group underwent a veno-venous bypass for 72 hours. Every 6 hours, at 3 different blood flow rates (BFr) (400, 800, 1200 ml/min), at a constant gas flow rate (Gfr = 4 L/min), and at a constant blood inlet PCO2 (45-55 mmHg), we measured the oxygenation performance (O2 transfer = VO2 and blood outlet PO2 = PO2out), CO2 removal (CO2 transfer = VCO2 and PCO2 outlet = PCO2out) and pressure drop across the device (delta P). A total of about 50 measurement sets were obtained for each group at different time points and blood flow rates. Both groups showed a good oxygenation performance (PO2out always higher than 200 mmHg) and no differences were observed between the two groups (at 1200 ml/min BFr, the average VO2 of all time points was 47 +/- 15 ml/min in group A and 44 +/- 11 ml/min in group B, mean +/- SD, NS). During the first 24 hours, the VCO2 was higher in Group B than in Group A at each BFr (at 1200 ml/min BFr, 81 +/- 18 vs 67 +/- 20 ml/min, p < 0.01), while no differences were observed during the subsequent 48 hours. Throughout the entire experiment, VCO2 increased with increasing BFr in both groups, (in group B, from 43 +/- 14 ml/min at 400 ml/min BFr, to 73 +/- 17 ml/min at 1200 ml/min BFr, average of all time points, p < 0.01). In both groups the delta P increased with the increasing BFr, but it was lower in Group B than in Group A at BFr 800 and 1200 ml/min (at 1200 ml/min BFr, 51 +/- 15 mmHg vs 65 +/- 17 mmHg, p < 0.01), and remained stable for the entire experimental period.

Total hepatectomy, recombinant activated factor VII and rescue liver transplantation.

The aim of this paper was to describe a case of acute liver failure treated with total hepatectomy, recombinant activated factor VII and rescue liver transplantation. We reported our experience with a 51-year-old-woman who developed a massive portal thrombosis after cadaveric liver transplantation for hepatic epithelioid hemangioendothelioma and who then required a total hepatectomy and porto-caval shunt as a bridge procedure while waiting for an urgent new liver transplantation. Subsequently, the patient developed severe hemodynamic instability, massive abdominal and mucosal bleeding and acute renal failure that were managed with infusion of high doses of inotropes, red blood cells and fresh frozen plasma as well as continuous veno-venous hemofiltration. Due to persistent, uncontrolled bleeding, we considered the off-label use of rFVIIa. This caused a correction of the prothrombin times and allowed for sufficient hemostasis. The patient received a new cadaveric liver that was reperfused 38 hours after the first graft was removed. The transplanted liver showed immediate recovery, the hemodynamics ameliorated and the patient was fully awake at day five. In the case of an anhepatic phase complicated by severe bleeding that is unresponsiveness to several transfusions, a single administration of rFVIIa should be considered as a rescue therapy to control massive bleeding.

Effects of heat and moisture exchangers on minute ventilation, ventilatory drive, and work of breathing during pressure-support ventilation in acute respiratory failure.

OBJECTIVES: To evaluate the effect of two commonly used heat and moisture exchangers on respiratory function and gas exchange in patients with acute respiratory failure during pressure-support ventilation. DESIGN: Prospective, randomized trial. SETTING: Intensive care unit of a university hospital. PATIENTS: Fourteen patients with moderate acute respiratory failure, receiving pressure-support ventilation. INTERVENTIONS: Patients were assigned randomly to two treatment groups, in which two different heat and moisture exchangers were used: Hygroster (DAR S.p.A., Mirandola, Italy) with higher deadspace and lower resistance (group 1, n = 7), and Hygrobac-S (DAR S.p.A.) with lower deadspace and higher resistance (group 2, n = 7). Patients were assessed at three pressure-support levels: a) baseline (10.3 +/- 2.4 cm H2O for group 1, 9.3 +/- 1.3 cm H2O for group 2); b) 5 cm H2O above baseline; and c) 5 cm H2O below baseline. Measurements obtained with the heat and moisture exchangers were compared with those values obtained using the standard heated hot water humidifier. MEASUREMENTS AND MAIN RESULTS: At baseline pressure-support ventilation, the insertion of both heat and moisture exchangers induced in all patients a significant increase in the following parameters: minute ventilation (12.4 +/- 3.2 to 15.0 +/- 2.6 L/min for group 1, and 11.8 +/- 3.6 to 14.2 +/- 3.5 L/min for group 2); static intrinsic positive end-expiratory pressure (2.9 +/- 2.0 to 5.1 +/- 3.2 cm H2O for group 1, and 2.9 +/- 1.7 to 5.5 +/- 3.0 cm H2O for group 2); ventilatory drive, expressed as P41 (2.7 +/- 2.0 to 5.2 +/- 4.0 cm H2O for group 1, and 3.3 +/- 2.0 to 5.3 +/- 3.0 cm H2O for group 2); and work of breathing, expressed as either power (8.8 +/- 9.4 to 14.5 +/- 10.3 joule/ min for group 1, and 10.5 +/- 7.4 to 16.6 +/- 11.0 joule/min for group 2) or work per liter of ventilation (0.6 +/- 0.6 to 1.0 +/- 0.7 joule/L for group 1, and 0.8 +/- 0.4 to 1.1 +/- 0.5 joule/L. for group 2). These increases also occurred when pressure-support ventilation was both above and below the baseline level, although at high pressure support the increase in work of breathing with heat and moisture exchangers was less evident. Gas exchange was unaffected by heat and moisture exchangers, as minute ventilation increased to compensate for the higher deadspace produced in the circuit by the insertion of heat and moisture exchangers. CONCLUSIONS: The tested heat and moisture exchangers should be used carefully in patients with acute respiratory failure during pressure-support ventilation, since these devices substantially increase minute ventilation, ventilatory drive, and work of breathing. However, an increase in pressure-support ventilation (5 to 10 cm H2O) may compensate for the increased work of breathing.

Effects of the prone position on respiratory mechanics and gas exchange during acute lung injury.

We studied 16 patients with acute lung injury receiving volume-controlled ventilation to assess the relationships between gas exchange and respiratory mechanics before, during, and after 2 h in the prone position. We measured the end-expiratory lung volume (EELV, helium dilution), the total respiratory system (Cst,rs), the lung (Cst,L) and the thoracoabdominal cage (Cst,w) compliances (end-inspiratory occlusion technique and esophageal balloon), the hemodynamics, and gas exchange. In the prone position, PaO2 increased from 103.2 +/- 23.8 to 129.3 +/- 32.9 mm Hg (p < 0.05) without significant changes of Cst,rs and EELV. However, Cst,w decreased from 204.8 +/- 97.4 to 135.9 +/- 52.5 ml/cm H2O (p < 0.01) and the decrease was correlated with the oxygenation increase (r = 0.62, p < 0.05). Furthermore, the greater the baseline supine Cst,w, the greater its decrease in the prone position (r = 0.82, p < 0.01). Consequently, the oxygenation changes in the prone position were predictable from baseline supine Cst,w (r = 0.80, p < 0.01). Returning to the supine position, Cst,rs increased compared with baseline (42.3 +/- 14.4 versus 38.4 +/- 13.7 ml/cm H2O; p < 0.01), mainly because of the lung component (57.5 +/- 25.1 versus 52.4 +/- 23.3 ml/cm H2O; p < 0.01). Thus, (1) baseline Cst,w and its changes may play a role in determining the oxygenation response in the prone position; (2) the prone position improves Cst,rs and Cst,L when the supine position is resumed.