Optimal values for oxygen transport during hypothermia in sepsis and ARDS

The Effects of Abnormal Body Temperature on the Prognosis of Patients with Septic Shock

We aimed to use temperature and the area under temperature curve to represent the severity of abnormal body temperature of patients with septic shock and to observe their impact on the prognosis. Five hundred twenty-eight adult patients with septic shock admitted to intensive care unit (ICU) were analyzed. Within the first 24 hours and throughout the period in ICU, the maximum temperature (24hT_max, T_max), lowest temperature (24hT_min, T_min), and the temperature range (24hT_max-min, T_max-min) were aggregated. Patients were divided into the survival group and the death group. Binary logistic regression was used to assess the relationship between body temperature aberrations and survival. The following risk factors of death in 21 days were identified: T_max (odds ratio [OR] 2.967, 95% confidence interval [CI] 1.626-5.414, p < 0.001), T_min (OR 0.337, 95% CI 0.143-0.794, p = 0.013), and T_max-min (OR 3.259, 95% CI 1.847-5.749, p < 0.001). This is an observational study, so one can infer association but not causation. Therefore, we infer that abnormal body temperature is associated with an adverse prognosis in patients with septic shock.

Effects of Constant Flow vs. Constant Pressure Perfusion on Fluid Filtration in Severe Hypothermic Isolated Blood-Perfused Rat Lungs

Background

Victims of severe accidental hypothermia are prone to fluid extravasation but rarely develop lung edema. We hypothesize that combined hypothermia-induced increase in pulmonary vascular resistance (PVR) and a concomitant fall in cardiac output protect the lungs against edema development. Our aim was to explore in hypothermic-isolated blood-perfused rat lungs whether perfusion at constant pressure influences fluid filtration differently from perfusion at constant flow.

Methods

Isolated blood-perfused rat lungs were hanging freely in a weight transducer for measuring weight changes (ΔW). Fluid filtration coefficient (Kfc), was determined by transiently elevating left atrial pressure (Pla) by 5.8 mmHg two times each during normothermia (37°C) and during hypothermia (15°C). The lung preparations were randomized to two groups. One group was perfused with constant flow (Constant flow group) and the other group with constant pulmonary artery pressure (Constant PPA group). Microvascular pressure (Pmv) was determined before and during elevation of Pla (ΔPmv) by means of the double occlusion technique. Kfc was calculated with the formula Kfc = ΔW/ΔPmv/min. All Kfc values were normalized to predicted lung weight (P_LW), which was based on body weight (BW) according to the formula: P_LW = 0.0053 BW − 0.48 and presented as Kfc_PLW in mg/min/mmHg/g. At cessation, bronchoalveolar lavage (BAL) fluid/perfusate protein concentration (B/P) ratio was determined photometrically. Data were analyzed with parametric or non-parametric tests as appropriate. p < 0.05 considered as significant.

Results

Perfusate flow remained constant in the Constant flow group, but was more than halved during hypothermia in the Constant PPA group concomitant with a more fold increase in PVR. In the Constant flow group, Kfc_PLW and B/P ratio increased significantly by more than 10-fold during hypothermia concerted by visible signs of edema in the trachea. Hemoglobin and hematocrit increased within the Constant flow group and between the groups at cessation of the experiments.

Conclusion

In hypothermic rat lungs perfused at constant flow, fluid filtration coefficient per gram P_LW and B/P ratio increased more than 10-fold concerted by increased hemoconcentration, but the changes were less in hypothermic lungs perfused at constant PPA.

Perfusion with lipopolysaccharide negative blood eliminates lipopolysaccharide induced lung injury

We investigated whether perfusion with control blood improves pulmonary functions compromised by lipopolysaccharide (LPS) infusion. This was an animal study in a research laboratory at a university hospital by using Sprague-Dawley rats (n = 19), each weighing 325 to 350 g. All animals were pretreated with a 24 hour infusion of either LPS (5 mg/kg) or vehicle, after which, excised lungs were reperfused for 2 hours with either LPS+ or control blood. Three groups were studied: (1) group S (n = 6); LPS pretreated lungs reperfused with LPS containing blood to mimic persistent sepsis, (2) group N (n = 6); LPS pretreated lungs reperfused with control blood to mimic the removal of the septic blood components, and (3) group C (n = 7); vehicle pretreated lungs reperfused with normal blood as a control. Blood gas exchange, shunt fraction (Qs/Qt), alveolar-arterial oxygen gradient (A-aDO2), and variables for lung mechanics were measured. Leukosequestration was quantified with a myeloperoxidase (MPO) assay. The PO2 (mm Hg) values at 90 min after reperfusion in groups S, N, and C were 67.8 +/- 7.0*, 85.2 +/- 9.2, and 90.1 +/- 7.5, respectively (*p < 0.05; vs. group N and C). In addition to PO2, A-aDO2 and Qs/Qt significantly deteriorated in group S. MPO activity in the lungs after LPS infusion was significantly higher than that after vehicle infusion (1.7 +/- 0.3 vs. 0.12 +/- 0.04 units/g tissue; p < 0.001). Subsequent reperfusion with LPS+ blood (group S) increased MPO activity to 3.1 +/- 0.6 (p < 0.05), but reperfusion with normal blood (group N) caused a significant decrease to 1.1 +/- 0.2 (p < 0.05). MPO activity in group C did not significantly change compared with those after vehicle infusion. Reperfusion with control blood normalized lung function compromised by pretreatment with LPS and significantly reduced leukosequestration. These results favor the possibility that the removal of LPS+ blood components may eliminate septic lung injury.