The accuracy of optical scanning: influence of convergence and die preparation.

The purpose of this study was to determine the reliability of the data acquisition and modeling process of laser and white light scanners by evaluating the reproducibility of digitized simulated crowns with different convergences. A secondary purpose was to analyze the influence of die preparation by testing this hypothesis with a set of dies without ditching compared with a set with well-defined margins. Ditching or trimming the die defines the position of the margin and acts as a guide to gingival contour when the restoration is being waxed. Two light scanners (a white light optical scanner [Steinbichler Gmbh, Neubeuern, Germany] and red laser light scanner [TurboDent System, Taichung, Taiwan]) were evaluated. Two sets of simulated crowns were fabricated as cone frustrum models with a total occlusal convergence (TOC) of 0°, 5°, 10°, 15°, 20°, and 25° and a 9-mm base and 3-mm height using a precision milling machine and computer-aided design/computer-aided manufacturing (CAD/CAM) technique. One set of the dies was ditched immediately below the finish line to enhance marginal definition. Each die was optically digitized five times directly with the two different measuring systems. The area of each triangle in the scan that is occlusal to the margin line was calculated and summed to produce the final surface area measurement provided. The digitizing error was compared with the computed surface area of the original master die sets and compared with a paired t-test (df=4; 95% CI). There was no difference in accuracy of the untrimmed dies between the two systems evaluated. We also did not find any difference in the 0° (p=0.12) and 5° degree (p=0.21) groups among the ditched dies. However, when the TOC exceeded 5°, there was a significant difference between the two groups, with the laser groups having a smaller error percentage. Three-dimensional light scanning was not affected by the convergence angle except in the 0°-5° range. Trimming the dies greatly affected the accuracy of scanning.

Oxygen transport patterns in patients with sepsis syndrome or septic shock: influence of treatment and relationship to outcome.

OBJECTIVE: To investigate the relationship between oxygen transport patterns and outcome in patients with sepsis syndrome or septic shock managed according to two different treatment regimens. DESIGN: Retrospective study of a subgroup of patients with sepsis syndrome or septic shock taken from a randomized, prospective, controlled trial. SETTING: General intensive care units in a teaching and a district general hospital. PATIENTS: Seventy-eight patients classified according to predetermined criteria as having sepsis syndrome or septic shock were drawn retrospectively from a larger study group of 109 consecutive patients considered to be at risk for developing multiple organ failure. INTERVENTIONS: All patients received volume expansion to an optimal pulmonary artery occlusion pressure. If the therapeutic goals (cardiac index of > 4.5 L/min/m2, oxygen delivery [DO2] of > 600 mL/min/m2, and oxygen consumption [VO2] of > 170 mL/min/m2) were not achieved with fluids alone, patients were randomized to either a control group or a treatment group. In the treatment group, dobutamine (5 to 200 micrograms/kg/min) was administered to increase cardiac index and DO2 until all three goals were simultaneously achieved. In the control group, dobutamine was administered only if the cardiac index was < 2.8 L/min/m2. In both groups, norepinephrine was infused to maintain mean arterial pressure at 80 mm Hg. MEASUREMENTS AND MAIN RESULTS: Hemodynamic, oxygen transport, and lactate measurements were made at the time of admission to the study, at the time of optimal volume administration, at 1, 2, 4, 8, 12, 16, 20, and 24 hrs, then every 6 hrs for the next 24 hrs, and at least every 8 hrs thereafter. The time at which all therapeutic goals were first achieved simultaneously or the time of maximal DO2 was identified and termed "tmax." Survivors from both the control and treatment groups significantly (p < .001) increased cardiac index and DO2 in response to maximal resuscitation, and despite an associated decrease in oxygen extraction (p < .01), there was a significant (p < .01) increase in VO2. In nonsurvivors from both groups, despite significant increases in cardiac index (p < .05) and DO2 (p < .01) at tmax, oxygen extraction decreased (p < .01) and VO2 remained unchanged. DO2 and VO2 were significantly lower (p < .05) at tmax in nonsurvivors than in survivors from both groups. Persistently high lactate concentrations were characteristic of nonsurvivors. CONCLUSIONS: Survivors of sepsis syndrome or septic shock are characterized by an ability to increase both DO2 and VO2. In contrast, nonsurvivors typically have reduced cardiac reserve, they fail to increase VO2 following resuscitation, and when delivery is enhanced with aggressive inotropic support, oxygen extraction falls. These patterns of response were similar in both treatment and control groups, although the magnitude of the changes was exaggerated in the treatment group. These observations may help to explain the findings by some investigators that treatment aimed at achieving survivor values of cardiac index, DO2, and VO2 fails to improve outcome when instituted following admission to intensive care.

Elevation of systemic oxygen delivery in the treatment of critically ill patients.

BACKGROUND: Elevation of systemic oxygen delivery and consumption has been associated with an improved outcome in critically ill patients. We conducted a randomized trial to determine whether boosting oxygen delivery by infusing the inotropic agent dobutamine would improve the outcome in a diverse group of such patients. METHODS: On the basis of previously published recommendations, we established the following goals: a cardiac index above 4.5 liters per minute per square meter of body-surface area, oxygen delivery above 600 ml per minute per square meter, and oxygen consumption above 170 ml per minute per square meter. If these goals were not achieved with volume expansion alone, patients were randomly assigned to a treatment or control group. The treatment group received intravenous dobutamine (5 to 200 micrograms per kilogram of body weight per minute) until all three goals had been achieved. Dobutamine was administered to the control group only if the cardiac index was below 2.8 liters per minute per square meter. RESULTS: A total of 109 patients were studied. In nine patients the therapeutic goals were achieved with volume expansion alone; all nine patients survived to leave the hospital. Fifty patients were randomly assigned to the treatment group, and 50 to the control group. During treatment, there were no differences between the two groups in mean arterial pressure or oxygen consumption, despite a significantly higher cardiac index and level of oxygen delivery in the treatment group (P < 0.05). Although the predicted risk of death during hospitalization was 34 percent for both groups, the in-hospital mortality was lower in the control group (34 percent) than in the treatment group (54 percent) (P = 0.04; 95 percent confidence interval, 0.9 to 39.1 percent). CONCLUSIONS: The use of dobutamine to boost the cardiac index and systemic oxygen delivery failed to improve the outcome in this heterogeneous group of critically ill patients. Contrary to what might have been expected, our results suggest that in some cases aggressive efforts to increase oxygen consumption may have been detrimental.

Response of critically ill patients to treatment aimed at achieving supranormal oxygen delivery and consumption. Relationship to outcome.

STUDY OBJECTIVE: To evaluate the response to therapy aimed at achieving supranormal cardiac and oxygen transport variables (cardiac index [CI] > 4.5 L/min/m2, oxygen delivery [DO2] > 600 ml/min/m2, and oxygen consumption [VO2] > 170 ml/min/m2) in a heterogenous group of critically ill patients and to assess its relationship to outcome. DESIGN: Patients were divided retrospectively into two groups. Group 1 (n = 15) achieved supranormal values for CI, DO2 and VO2 simultaneously during the first 24 h. Group 2 (n = 17) failed to achieve these goals simultaneously at any time point. SETTING: General intensive care units in a teaching and a district general hospital. PATIENTS: Thirty-two patients at risk of developing multiple organ failure were studied prospectively. INTERVENTIONS: Patients received volume expansion and then, if necessary, dobutamine (5 to 200 micrograms/kg/min) to increase CI and DO2 until all three goals were achieved simultaneously. RESULTS: In group 2, target VO2 could never be reached despite the fact that 11 (65 percent) patients achieved target CI and DO2 simultaneously. In this group, lactate levels did not fall and 16 patients died. In contrast, in group 1, attainment of all goals was associated with a significant reduction (p < 0.05) in blood lactate levels, and all but one of these patients survived. The persistently raised lactate levels in group 2 were associated with significantly higher venous oxygen saturation (SvO2) and lower oxygen extraction ratio (OER); in these patients, SvO2 rose and OER fell in response to increases in DO2. CONCLUSION: These results suggest that failure to increase VO2 was related predominantly to an inability of the tissues to extract or utilize oxygen rather than a failure to increase DO2. These findings support the hypothesis that in order to survive a critical illness, patients must achieve a high level of VO2. An inability to do so is reflected in persistently elevated blood lactate levels and an extremely poor prognosis.

Symmetrical peripheral gangrene: association with noradrenaline administration.

The syndrome of symmetrical peripheral gangrene is characterised by distal ischaemic damage in two or more extremities, without large vessel obstruction. Four patients with bilateral pedal ischaemia are described and their haemodynamic profiles presented. In all four cases the syndrome developed in association with noradrenaline administration, sepsis and DIC, despite a high cardiac output and a low calculated systemic vascular resistance index. Early treatment with epoprostenol was instituted in the final case and was successful.