Faculty Bibliography

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.

The present study tested the hypothesis that, during acute bleeding, the development of tissue hypoxia might be reflected by an abrupt widening in arteriovenous gradient for PCO2 (AV PCO2) and for pH (AV pH) as accurately as by an increase in blood lactate levels. Twenty-four anesthetized (isoflurane 1.4% end-tidal), paralyzed, and mechanically ventilated dogs submitted to progressive hemorrhage were studied. Oxygen uptake (VO2) was derived from expired gas analysis and oxygen delivery (DO2) was calculated by the product of the thermodilution cardiac index and the arterial O2 content. During the first part of the protocol, VO2 remained stable as the progressive reduction in DO2 was associated with a corresponding increase in O2 extraction (O2ER). Blood lactate increased slightly but not significantly. AV PCO2 and AV pH increased significantly, essentially related to venous respiratory acidosis. The critical value of DO2 below which VO2 decreased was 8.95 +/- 1.60 mL.min-1.kg-1. Below this value, there was a marked increase in blood lactate and an abrupt widening in AV PCO2 and AV pH gradients. The critical value of DO2 obtained from blood lactate, AV PCO2 and AV pH were similar to those obtained from VO2 (8.60 +/- 1.12; 8.73 +/- 1.40; 8.78 +/- 1.37, respectively; P = not significant). A significant correlation was found, during the hemorrhage protocol, between blood lactate and AV PCO2 (r = 0.84; P < 0.001) or AV pH (r = 0.78; P < 0.001). Therefore, AV PCO2 and AV pH represent simple but reliable indicators of tissue hypoxia during hemorrhagic shock.

Syndromes with impaired neuromuscular transmission are frequently treated with pyridine derivates. 3,4-diaminopyridine is thought to have fewer side effects than the commonly used, but less potent, 4-aminopyridine. We describe a patient with an initially unrecognized iatrogenic intoxication with 3,4-diaminopyridine. Except for a life threatening arrhythmia, symptoms were similar to a 4-aminopyridine intoxication. The patient made a full recovery with symptomatic treatment and withdrawal of the drug.