Thorpe tube and oxygen flow restrictor: what's flow accuracy?

Oxygen gas flowmeters (OGF) are used to regulate the oxygen flow in acute and chronic care. In hospitals, Thorpe tubes (TT) are the classical systems most used for delivering oxygen. In recent years, the oxygen flow restrictor (OFR) has appeared. These devices use a series of calibrated openings in a disk that can be adjusted to deliver different flow rates. These devices have a reputation for delivering more accurate oxygen flow rates compared to classical OGFs. However, to our knowledge, few study has examined this supposition. This study aimed to compare and evaluate the accuracy and precision of the ready-to-use TTs and OFRs. OGFs were selected from hospitals in Belgium and France. Before performing the flow measurements, the inlet pressure was checked. The accuracy of the OGF was analyzed with a calibrated thermal mass flowmeter (RED Y COMPACT™ GCM-0 to 20 L/min-VÖGTLIN Instruments). Different flows (2, 4, 6, 9 or 12 L/min) were evaluated. Linear regression analysis, bias (with confidence interval) and lower and upper limit of the agreement were calculated for TTs and OFRs. All measurements are expressed in absolute values. Four-hundred-seventy-six TTs and 96 OFRs were analyzed. The intra-class correlation coefficient calculated for the calibrated thermal mass flowmeter was > 0.99 and reflected the excellent reliability of our measurements. For TTs, the bias value was - 0.24 L/min (± 0.88), and the limits of agreement were - 1.97 to 1.48 L/min. For OFRs, the bias value was - 0.30 L/min (± 0.54), and the limits of agreement were - 1.36 to 0.77 L/min. As the flow increased, the accuracy of all analyzed OGFs decreased. With the increasing flow, some data fell outside the limits of agreement, and the trend increased with the elevated oxygen flow. TTs were less accurate compared to OFRs due to the increased flow variability. However, for TTs and OFRs, as the required flow is elevated, the dispersion of values increases on both sides of the actual flow.

Plasma fibrinolysis is related to the degree of organ dysfunction but not to the concentration of von Willebrand Factor in critically ill patients.

BACKGROUND: Endothelial cell dysfunction, by promoting fibrin deposition, has been implicated in the development of multiple organ failure. Altered fibrinolysis during inflammation may participate in microvascular alterations. We sought to determine whether plasma fibrinolysis was related to the severity of organ dysfunction and/or to the levels of von Willebrand factor (vWF antigen), as a marker of endothelium dysfunction, in critically ill patients. METHODS: Forty-nine consecutive patients admitted to an adult medico-surgical intensive care unit (ICU) with (18) or without sepsis (31) were included. C-reactive protein and vWF levels were measured on ICU admission and plasma fibrinolysis was assessed by the Euglobulin Clot Lysis Time (ECLT). The sequential organ failure assessment (SOFA) score and the simplified acute physiology score (SAPS) II were calculated on admission. RESULTS: ECLT was significantly longer in septic than in non-septic patients [1033 min (871-1372) versus 665 min (551-862), p = 0.001]. There were significant correlations between ECLT and C-reactive protein (CRP) concentrations (r = 0.78, p < 0.001) and the Sequential Organ Failure Assessment (SOFA) score (r = 0.39, p = 0.006). The level of vWF was not correlated with the ECLT (r = -0.06, p = 0.65) or the SOFA score (r = -0.02, p = 0.88). CONCLUSION: ECLT measurement at admission could be a marker of organ dysfunction and a prognostic indicator in critically ill patients.