An Automated Electronic Screening Tool (DETECT) for the Detection of Potentially Irreversible Loss of Brain Function.

BACKGROUND: A major reason for the low number of organ donors in Germany is a deficit in the recognition of patients who may have impending irreversible loss of brain function (ILBF) in hospitals capable of organ retrieval. METHODS: We used anonymized data from the German Organ Procurement Organization (Deutsche Stiftung Organtransplantation, DSO) to compare two 12-month periods (a reference period and an evaluation period) before and after the implementation of an electronic screening tool (DETECT) at the University Hospital Dresden (UKD) with four other university hospitals without tool implementation (comparative cohort). DETECT is intended to aid in the recognition of potentially impending ILBF. The study endpoints encompassed patients with potentially unrecognized ILBF, patients with recognized ILBF, organ donations performed, and reports to the DSO. Changes in absolute risk were compared with Breslow-Day tests. RESULTS: 309 patients who died with primary or secondary brain lesions were identified in the UKD in the reference and evaluation periods (164 and 145 patients, respectively), and 1060 (529, 531) in the comparative cohort. In the UKD, the number of unrecognized cases of possibly impending ILBF was 14/164 (8.54%) in the reference period and 1/145 (0.69%) in the evaluation period, yielding an absolute reduction of 7.85% (95% confidence interval [--3.36; --12.33]); by contrast, in the comparative cohort, there was a 0.55% absolute increase between the two periods ([--2.21; 3.30]; p = 0.002 for the comparison between the two cohorts). Only minor differences in absolute risk change were seen with regard to the probability of recognized ILBF (7.09% [0.29; 13.88] vs. 2.42% [1.18; 6.01]; p = 0.234), organ donation (4.70% [--0.89; 10.28] vs. 0.55% [--2.17; 3.26]; p = 0.214), or reporting to the DSO (4.17% [--1.77; 10.11] vs. 2.22% [--1.44; 5.89; p = 0.447); these changes may have arisen by chance. CONCLUSION: These findings suggest that the use of DETECT can help to reduce the deficit in the recognition of patients with impending or manifest ILBF.

Performance of the partial CO2 rebreathing technique under different hemodynamic and ventilation/perfusion matching conditions.

OBJECTIVE: The partial CO2 rebreathing technique has been demonstrated to accurately measure the effective pulmonary capillary blood flow (PCBF) in different clinical situations. Usually, PCBF is calculated from changes in CO2 elimination (VCO2) and end-tidal partial pressure of CO2 (PetCO2 ), which can be obtained noninvasively. In this study, we investigated the performance of the partial CO2 rebreathing technique under different conditions of ventilation/perfusion matching and hemodynamic states. In addition, we investigated whether the determination of arterial blood gases combined with mathematical modeling of gas exchange can improve the performance of this method. DESIGN: Prospective, controlled animal laboratory study. SETTING: Experimental research facility of a university hospital. SUBJECTS: Sixteen female sheep weighing 45-55 kg. INTERVENTIONS: Cardiac output and ventilation/perfusion matching were manipulated during three phases: phase I, variation in cardiac output to achieve normal, hyperdynamic and hypodynamic states; phase II, increase of alveolar deadspace and variation in cardiac output; phase III, lung injury and increased alveolar deadspace. Partial CO2 rebreathing maneuvers were performed to obtain variations in VCO2 and PetCO2 between a nonrebreathing (NR) and a rebreathing (R) period. MEASUREMENTS AND MAIN RESULTS: PCBF was measured by the rebreathing method as PCBF = -DeltaVCO2/f(Pc'CO2 (R), Pc'CO2(NR), Hb), where f is the CO2 dissociation curve in blood, Pc'CO2 is the end-capillary partial pressure of CO2, Delta is the variation between NR and R periods, and Hb is hemoglobin concentration. Pc'CO2 was estimated from PetCO2 according to two algorithms. In the so-called "noninvasive algorithm," Pc'CO2 = PetCO2, with PetCO2(NR) and PetCO2(R) being determined as the mean PetCO2 value of the last 60 secs preceding rebreathing and within 15-30 secs of rebreathing, respectively. In the "semi-invasive algorithm," Pc'CO2(NR) was estimated as the PaCO2, and Pc'CO2(R) was estimated as follows: First, a monoexponential function was fitted to PetCO2 values during rebreathing and the asymptote represented PetCO2(R). Second, the Pc'CO2(R) to PetCO2(R) difference was calculated by means of a bicompartmental, tidal model of gas exchange, which showed that such differences decrease with the degree of rebreathing. PCBF values obtained with both algorithms were compared with thermodilution cardiac output minus intrapulmonary shunt flow. Bias and precision calculations with the noninvasive algorithm in phases I, II, and III were, respectively, -1.0 +/- 1.9, -2.1 +/- 2.6, and -2.4 +/- 1.2 L/min. The semi-invasive algorithm had an overall better performance in the phases investigated: -1.2 +/- 1.9, -0.6 +/- 2.0, and -0.2 +/- 3.0 L/min, respectively. The noninvasive algorithm showed a slight tendency to overestimate lower reference PCBF values and, importantly, to underestimate higher PCBF values in all three phases (r = -.66, p<.0001; r = -.75, p<.001; r = -.60, p<.0001, respectively). A similar figure was observed with the semi-invasive algorithm in phase I (r = -.47, p<.01) but not in phases II and III (r = -.1, p=.54; r =.62, p<.001, respectively). CONCLUSIONS: Although PCBF is systematically underestimated during hyperdynamic cardiac output states and high alveolar deadspaces, the performance of the partial CO2 rebreathing technique can be improved by means of arterial blood gas sampling and an algorithm that takes in account the effects of nonequilibration of PetCO2 during rebreathing and the variation of Pc'CO2 to PetCO2 differences from the nonrebreathing to the rebreathing period. Such an algorithm may prove useful under moderately increased alveolar deadspace and normal to hypodynamic cardiac output states.

One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure is injurious in the isolated rabbit lung model.

UNLABELLED: We tested the hypothesis that one-lung ventilation (OLV) with high tidal volumes (VT) and zero positive end-expiratory pressure (PEEP) may lead to ventilator-induced lung injury. In an isolated, perfused rabbit lung model, VT and PEEP were set to avoid lung collapse and overdistension in both lungs, resulting in a straight pressure-time (P-vs-t) curve during constant flow. Animals were randomized to (a) nonprotective OLV (left lung) (n = 6), with VT values as high as before randomization and zero PEEP; (b) protective OLV (left lung) (n = 6), with 50% reduction of VT and maintenance of PEEP as before randomization; and (c) control group (n = 6), with ventilation of two lungs as before randomization. The nonprotective OLV was associated with significantly smaller degrees of collapse and overdistension in the ventilated lung (P < 0.001). Peak inspiratory pressure values were higher in the nonprotective OLV group (P < 0.001) and increased progressively throughout the observation period (P < 0.01). The mean pulmonary artery pressure and lung weight gain values, as well as the concentration of thromboxane B(2), were comparatively higher in the nonprotective OLV group (P < 0.05). A ventilatory strategy with VT values as high as those used in the clinical setting and zero PEEP leads to ventilator-induced lung injury in this model of OLV, but this can be minimized with VT and PEEP values set to avoid lung overdistension and collapse. IMPLICATIONS: One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure (PEEP) is injurious in the isolated rabbit lung model. A ventilatory strategy with tidal volumes and PEEP set to avoid lung overdistension and collapse minimizes lung injury during one-lung ventilation in this model.

Evaluation of a new device for noninvasive measurement of nonshunted pulmonary capillary blood flow in patients with acute lung injury.

OBJECTIVES: To evaluate the performance of a new device for noninvasive measurement of nonshunted pulmonary capillary blood flow (PCBF) by partial CO2 rebreathing. DESIGN AND SETTING: Prospective clinical trial in an intensive care unit of a university hospital. PATIENTS AND PARTICIPANTS: Twenty mechanically ventilated patients with acute lung injury. INTERVENTIONS: Variations in PEEP of +/-3 cmH2O. MEASUREMENTS AND RESULTS: Initially PCBF was measured invasively as cardiac output minus venous admixture (Q(VA)/Q(t)) flow, and by partial CO2 rebreathing at baseline PEEP (PEEP(b)). The PEEP was then reduced by 3 cmH2O (to PEEP(b-3)) and measurements were repeated after 30 min. PEEP was then increased by 6 cmH2O (to PEEP(b+3)), and measurements were repeated after 10, 20, and 30 min. The overall correlation coefficient between noninvasive and invasive PCBF measurements at PEEP(b) was high ( r=0.97), with close agreement between methods being observed (0.1+/-0.6 l/min, bias and precision, respectively). Accordingly, both the correlation coefficient and agreement between methods for changes in PCBF from PEEP(b-3) to PEEP(b+3) levels were satisfactory ( r=0.71; 0.2+/-0.5 l/min, bias and precision). The new device was able to detect the correct PCBF trend in 17 of 20 patients investigated and in all patients who showed invasive PCBF changes equal to or greater than 0.3 l/min ( n=12). Noninvasive PCBF changes were stable as early as 10 min after variation in PEEP, as compared to 30 min values. CONCLUSIONS: The new device appears to be clinically useful for the monitoring of PCBF in patients suffering from acute lung injury. Our results suggest that titration of PEEP aimed at improving PCBF can be performed with the new device.