Failure of the colloid oncotic-pulmonary artery wedge pressure gradient to predict changes in extravascular lung water

Prediction of pulmonary edema by plasma protein levels in patients with sepsis

PURPOSE

The difficulties of fluid therapy in patients with septic shock are to maintain sufficient vascular volume while preventing pulmonary edema formation. Thus, it is important to find a biomarker that can reliably predict pulmonary edema formation after fluid loading. We evaluated the association of plasma protein levels with the increase in extravascular lung water index (ΔEVLWI) after fluid loading.

METHODS

This was an observational study in which we retrospectively reviewed medical records of septic patients in whom hemodynamic variables were measured by transpulmonary thermodilution technique before and after fluid loading. Plasma protein levels were measured before fluid loading. Patients were divided into 2 groups according to the changes in EVLWI (ΔEVLWI ≥ 10%) after fluid loading. Diagnostic performance of plasma proteins in predicting pulmonary edema formation was assessed.

RESULTS

A total of 62 patients were included, and 27 of them showed a ΔEVLWI 10% or higher after fluid loading. Plasma albumin and transferrin were significantly lower in this group than in the group with ΔEVLWI less than 10% (21.7 ± 5.8 vs 25.3 ± 5.0 g/L for albumin, P < .05; 107.9 ± 50.1 vs 136.8 ± 44.2 mg/dL for transferrin, P < .05). Areas under the curve of albumin and transferrin were 0.68 (cardiac index, 0.54-0.83) and 0.72 (cardiac index, 0.59-0.86), respectively. At a cutoff value of 87.9 mg/dL, transferrin had a sensitivity of 0.91 in predicting ΔEVLWI 10% or higher.

CONCLUSIONS

Plasma transferrin and albumin levels were associated with ΔEVLWI 10% or higher after fluid loading. The high sensitivity of both biomarkers indicated that patients with normal values were less likely to develop pulmonary edema after fluid loading.

Hypoproteinemia predicts acute respiratory distress syndrome development, weight gain, and death in patients with sepsis. Ibuprofen in Sepsis Study Group

OBJECTIVE

Starling's equation indicates that reduced oncotic pressure gradients will favor edema formation, and the current consensus definition of acute respiratory distress syndrome (ARDS) excludes only the hydrostatic pressure contribution. We hypothesized that low serum total protein levels might correlate with the likelihood of ARDS in at-risk patients because serum total protein is the chief determinant of oncotic pressure in humans.

DESIGN

Regression analysis to compare outcomes in patients with low serum total protein levels with outcomes in patients with normal serum total protein levels with respect to weight change, development of ARDS, and mortality.

SETTING

Intensive care units (ICUs) of seven clinical centers in North America.

PATIENTS

A total of 455 ICU patients who met consensus criteria for severe sepsis (178 of whom developed ARDS) from a recently completed prospective clinical trial.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

We found that 92% of the patients developing ARDS had low or borderline serum total protein levels (<6 g/dL). Logistic and multiple regression analyses confirmed that of 18 clinical variables, initial serum total protein level and protein change over time were the most statistically significant predictors of weight gain, prolonged mechanical ventilation, ARDS development, and mortality in the study population. This correlation remained significant after adjustment for the other major predictors of outcome present at baseline (ie, Acute Physiology and Chronic Health Evaluation II score).

CONCLUSIONS

Hypoproteinemia is significantly correlated with fluid retention and weight gain, development of ARDS and poor respiratory outcome, and mortality in patients with sepsis. Prospective, randomized trials of serum protein manipulation are needed to establish whether there is a cause-effect relationship to this association.

Diuretic induced change in lung water assessed by electrical impedance tomography

Monitoring patients with left ventricular failure can be difficult. Electrical impedance tomography (EIT) produces cross-sectional images of changes in the impedance of the thorax. We measured changes in the electrical impedance of the lung in nine volunteers following a diuretic challenge. The hypothesis was that lung impedance would increase with diuretic induced fluid loss. Heart rate, blood pressure and urine output were also recorded. After diuretic the mean urine output was 1220 ml compared with 187 ml after placebo. Following diuretic administration, mean thoracic impedance increased by 13.6% (p < 0.01) and lung impedance increased by 7.8% (p < 0.05). Taken as a group there was a correlation between overall impedance change and total urine output. However, for each individual, the time course of change in impedance and urine output did not correlate significantly. Our findings show that EIT may offer a better guide to the response of the lung to diuretic treatment than simply measuring urine output. The urine output is neither specific nor sensitive in the assessment of lung water. Mean lung impedance, however, is largely determined by lung water. The study showed that lung impedance can be recorded at supra-normal values. EIT may help in the management of patients with excess lung water.

Monitoring patients with left ventricular failure by electrical impedance tomography

Acute left ventricular failure (LVF) is a common medical emergency but detection and monitoring of pulmonary oedema remains problematic. Fluid is an important determinant of tissue impedance. Electrical impedance tomography (EIT) is a non-invasive technique allowing localisation of impedance changes within tissue. We have investigated the relationship between LVF and the electrical impedance of lung tissue. Twenty patients with a clinical diagnosis of acute left ventricular failure were compared with 30 normal subjects. Patients were monitored using serial chest radiographs and electrical impedance tomography measurements of lung impedance during hospital admission. Radiographs were graded according to the severity of pulmonary oedema by two independent radiologists. Lung impedance was significantly (P<0.0001) lower than normal in patients with left ventricular failure. Values returned towards the normal range as LVF resolved. There was a similar improvement in the score of the chest radiographs. The electrical impedance of the lung is low in left ventricular failure and increases following treatment.

Intraoperative fluid management--what and how much?

An approach to intraoperative fluid management based on a monitored physiologic application of the Starling principles of cardiac function is recommended to individualize therapy to optimize hemodynamic function and tissue perfusion. The complexity of intraoperative fluid administration, beginning with preoperative cardiovascular function followed by innumerable intraoperative considerations, including anesthetic pharmacology, positive pressure ventilation, operative site, and surgical technique may lead to serious intraoperative and postoperative complications. Emphasis must be given to intraoperative fluid shifts resulting in hidden fluid loss and intravascular hypovolemia that must be replaced. Explanations for this fluid redistribution have included tissue trauma, endotoxemia, and proinflammatory cytokines with resultant increased capillary permeability.

Effect of large volume replacement with balanced electrolyte solutions on extravascular lung water in surgical patients with sepsis syndrome

We investigated the effect of large volume replacement with balanced electrolyte solutions on extravascular lung water (EVLW) in 16 adult surgical patients with sepsis syndrome. Patients entered the study within the 24 h period following surgical interventions for acute necrotizing pancreatitis, intra-abdominal abscesses, and/or peritonitis. Sequential measurements (n = 108) were made at intervals of 6-12 h over a 48 h period. There were no significant differences between initial and final values of thermal-dye EVLW (5.0 +/- 1.1 vs. 5.7 +/- 1.1 ml/kg), plasma colloid osmotic pressure (COP, 13.3 +/- 2.5 vs. 13.2 +/- 2.9 mmHg), pulmonary artery wedge pressure (PAWP, 9.2 +/- 3.0 vs. 10.8 +/- 3.0 mmHg), and COP-PAWP gradient (4.0 +/- 3.5 vs. 2.4 +/- 3.9 mmHg). All results expressed as (mean +/- SD). The EVLW did not correlate with plasma COP, PAWP, or COP-PAWP gradient. We conclude that large volume replacement with balanced electrolyte solutions with the secondary decrease in plasma COP and COP-PAWP gradient do not necessarily contribute to a substantial increase in EVLW. This study fails to show any causal relationship between decrease in plasma COP or COP-PAWP gradient and oedema formation in the lung.