Faculty Bibliography

STUDY OBJECTIVES/OBJECTIVE:To establish the value of electrical impedance tomography (EIT) in assessing pulmonary edema in noncardiogenic acute respiratory failure (ARF), as compared to the thermal dye double indicator dilution technique (TDD). DESIGN/METHODS:Prospective clinical study. SETTING/METHODS:ICU of a general hospital. PATIENTS/METHODS:Fourteen ARF patients. INTERVENTIONS/METHODS:In order to use the TDD to determine the amount of extravascular lung water (EVLW), a fiberoptic catheter was placed in the femoral artery. MEASUREMENTS AND MAIN RESULTS/RESULTS:Fourteen consecutive ARF patients receiving mechanical ventilation were measured by EIT and TDD. EIT visualizes the impedance changes caused by the ventilation in two-dimensional image planes. An impedance ratio (IR) of the ventilation-induced impedance changes of a posterior and an anterior part of the lungs was used to indicate the amount of EVLW. For the 29 measurements in 14 patients, a significant correlation between EIT and TDD (r = 0. 85; p < 0.001) was found. The EIT reproducibility was good. The diagnostic value of the method was tested by receiver operator characteristic analysis, with 10 mL/kg of EVLW considered as the upper limit of normal. At a cutoff level of the IR of 0.64, the IR had a sensitivity of 93%, a specificity of 87%, and a positive predictive value of 87% for a supranormal amount of EVLW. Follow-up measurements were performed in 11 patients. A significant correlation was found between the changes in EVLW measured with EIT and TDD (r = 0.85; p < 0.005). CONCLUSION/CONCLUSIONS:We conclude that EIT is a noninvasive technique for reasonably estimating the amount of EVLW in noncardiogenic ARF.

OBJECTIVE:To compare a recently introduced hand-held lactate analyser to a reference point of care analyser (POCI) and the hospital laboratory in a critical care setting. SETTING/METHODS:10-bed surgical/medical intensive care unit in a teaching hospital. PATIENTS AND METHODS/METHODS:In 39 critically ill patients, 50 convenience measurement cycles consisting of three paired measurements at 30-min intervals were carried out with a hand-held analyser, reference POCI and hospital laboratory using arterial blood samples. Duplicate measurements with the hand-held analyser were done in 129 blood samples. RESULTS:Lactate levels ranged from 1.1 to 21.0 mmol/l. Regression analysis of the hand-held analyser and laboratory showed a slope of 1.01, bias of -0.38 mmol/l, R(2) = 0.97 and mean error of 14.9 %. Reference POCI versus laboratory: slope = 1.07, bias = -0.29 mmol/l, R(2) = 0.98 and mean error of 6.4 %. Hand-held analyser versus reference POCI: slope = 0.90, bias = 0.09 mmol/l and R(2) = 0. 92. The hand-held analyser showed acceptable precision. CONCLUSION/CONCLUSIONS:The hand-held lactate analyser can reliably measure arterial blood lactate levels in critically ill patients.

STUDY OBJECTIVES/OBJECTIVE:A new noninvasive practical technique called electrical impedance tomography (EIT) was examined for the measurement of alveolar recruitment. DESIGN/METHODS:Prospective clinical study. SETTING/METHODS:ICU of a general hospital. PATIENTS/METHODS:Acute respiratory failure (ARF) patients. MEASUREMENTS/METHODS:The ventilation-induced impedance changes (VICs) of the nondependent and the dependent part of the lung were determined by EIT as a measure of tidal volume distribution. By the use of an impedance ratio (IR), defined as the VIC of the nondependent part of the lung divided by the VIC of the dependent part of the lung, the ventilation performances in both parts of the lung were compared to each other. RESULTS:Between patients, the VIC of the nondependent part of the lung was significantly lower in the patients with a level of positive end-expiratory pressure (PEEP) of > 10 cm H2O than in patients with a PEEP of < 5 cm H2O (p < 0.05). A significantly lower IR (-/+ SD) was found in the group with PEEP of > 10 cm H2O than in the group with PEEP between 0 and 5 cm H2O (1.28+/-0.58 vs 2.99+/-1.24, respectively; p < 0.01). In individual patients, the VIC of the whole lung increased when the PEEP level was increased. The VICs of the nondependent part of the lung and of the dependent part of the lung showed significant increases at a PEEP of 10 cm H2O compared to a PEEP of 0 cm H2O (p < 0.05). Also the IR decreased in individual patients when the PEEP was increased; a significant decrease was found at 10 cm H2O compared to 0 cm H2O (1.67+/-1.24 vs 2.23+/-1.47, respectively; p < 0.05). CONCLUSIONS:The decrease in IR indicates an increase in VIC in the dependent part of the lung above the nondependent part of the lung. The increase in VIC can be regarded as an increase in lung volume, implying alveolar recruitment in the dependent part of the lung. The same results also have been shown in earlier reports by CT scan. Since EIT is far more practical than CT scanning and also is a bedside method, EIT might help in the adjustment of ventilator settings in ARF patients.

The purpose of this study was to investigate the influence of pulmonary oedema as measured with the double indicator dilution technique on the accuracy of cardiac output (CO) measurement using thoracic impedance cardiography (TIC) compared with thermodilution in thirteen sepsis patients. Differences in the Kubicek and Sramek-Bernstein equation with respect to pulmonary oedema were explored theoretically and experimentally. From a parallel two cylinder model a hypothesis can be derived that CO determined with the Kubicek equation is oedema independent, whereas CO determined using the Sramek-Bernstein equation is oedema dependent. Experimentally, CO determined using Kubicek's equation correlated better with thermodilution CO (r = 0.75) than CO determined with the Sramek-Bernstein equation (r = 0.25). The effect of oedema on the accuracy of TIC was investigated by comparing the differences in the CO of impedance and thermodilution to the extravascular lung water index. For the Kubicek equation the difference was not influenced by oedema (r = 0.04, p = 0.84), whereas for the Sramek-Bernstein equation the difference was affected by oedema (r = 0.39, p = 0.05). Thus, the effects of pulmonary oedema on the accuracy of TIC measurements can better be understood with the parallel cylinder model. Moreover, the Kubicek equation still holds when pulmonary oedema is present, in contrast to the Sramek-Bernstein equation.

The study investigates the effects of non-cardiogenic oedema, especially the accumulation of protein in extracellular fluid, on thoracic impedance and proposes a new method of oedema measurement based on an impedance ratio from a dual-frequency measurement. In vitro measurements in a cell containing an albumin-in-saline solution yield a resistance increase when the albumin concentration increases. Subsequently, 13 patients having acute respiratory failure are measured. The single-frequency Z0 measurements and the proposed impedance ratio are compared with extravascular lung water (EVLW) determined by the double indicator dilution method. The single-frequency measurement correlates poorly with EVLW (r = -0.24, p = 0.56). In some patients, a total thoracic impedance increase is found with increasing EVLW. The correlation between the impedance ratio and EVLW is r = -0.79 (p < 0.0005). The ratio decreases as EVLW increases. Thus, when oedema is measured using bio-impedance, cardiogenic and non-cardiogenic oedema yield different results. It is well recognised that cardiogenic oedema decreases total thoracic impedance. In non-cardiogenic oedema, however, protein accumulation causes an impedance increase. The decrease in the impedance ratio as EVLW increases can be explained by the accumulation of albumin in the extracellular compartment.

A 19-year-old male patient developed thrombocytopenia and leukopenia due to acute folate deficiency while recovering from a multiple organ failure syndrome, Risk factors for acute folate deficiency are extensive tissue damage due to sepsis, trauma or surgery and acute renal failure requiring renal replacement therapy. The diagnosis is based on bone marrow examination showing marked megaloblastic changes whereas serum folate levels and red cell folate levels are normal, Recognition of this serious complication of critical illness is important because it should be readily prevented by folic acid therapy.

BACKGROUND:Despite successful initial resuscitation, septic shock frequently evolves into multiple system organ failure (MSOF) and death. Since blood lactate levels can reflect the degree of cellular derangements, we examined the relation between serial blood lactate levels and the development of MSOF, or mortality, in patients with septic shock. PATIENTS AND METHODS/METHODS:In 87 patients with a first episode of septic shock, we measured initial lactate (at onset of septic shock), final lactate (before recovery or death), "lactime" (time during which blood lactate was > 2.0 mmol/L, and the area under the curve (AUC) for abnormal values (above 2.0 mmol/L). These measurements were correlated with survival and organ failure and scored for four systems (ie, respiratory, renal, hepatic, and coagulation), adding to a maximal score of 8. RESULTS:Thirty-three (38%) patients survived. Of the 54 (62%) nonsurvivors, the 13 patients who died during the first 24 hours of septic shock had higher initial blood lactate levels than those who died later (mean +/- standard deviation 9.6 +/- 5.3 mmol/L versus 5.6 +/- 3.7 mmol/L, P< 0.05). The 74 patients who survived the first 24 hours of shock, were studied in more detail. On presentation, survivors had a significantly higher mean arterial pressure (76 +/- 12 mm Hg versus 63 +/- 20 mm Hg, P < 0.001) and arterial pH (7.40 +/- 0.07 versus 7.37 +/- 0.09, P< 0.05) than nonsurvivors. Although the differences in initial blood lactate levels between survivors and nonsurvivors did not reach statistical significance (4.7 +/- 2.5 mmol/L versus 5.6 +/- 3.7 mmol/L), only the survivors had a significant decrease during the first 24 hours of septic shock. The survivors had a significantly lower lactime and AUC than the nonsurvivors. The duration of lactic acidosis was the best predictor of survival (multiple regression analysis, R2 = 0.266, P <0.001), followed by age, heart rate, and mean arterial pressure. Patients with lower organ failure scores had lower initial blood lactate, lactime, and AUC. The duration of lactic acidosis was the only significant predictor of organ failure. CONCLUSIONS:In patients with septic shock, serial determinations of blood lactate levels are good predictors of the development of MSOF an death. In this respect, the duration of lactic acidosis is more important than the initial lactate value. Although a number of factors may contribute to hyperlactatemia, these observations are compatible with a direct role of prolonged tissue hypoxia in the development of complications following septic shock.