The clinical assessment of lung water

Lung water density is increased in patients at risk of heart failure and is largely independent of conventional cardiovascular magnetic resonance measures

Aims

Non-invasive methods to quantify pulmonary congestion are lacking in clinical practice. Cardiovascular magnetic resonance (CMR) lung water density (LWD) mapping is accurate and reproducible and has prognostic value. However, it is not known whether LWD is associated with routinely acquired CMR parameters.

Methods and results

This was an observational cohort including healthy controls and patients at risk of heart failure. LWD was measured using CMR with a free-breathing short echo time 3D Cartesian gradient-echo sequence with a respiratory navigator at 1.5 T. Associations were assessed between LWD, lung water volume and cardiac volumes, left ventricular (LV) mass and function, myocardial native T1, and extracellular volume fraction. In patients at risk for heart failure (n = 155), LWD was greater than in healthy controls (n = 15) (30.4 ± 5.0 vs. 27.2 ± 4.3%, P = 0.02). Using receiver operating characteristic analysis, the optimal cut-off for LWD was 27.6% to detect at-risk patients (sensitivity 72%, specificity 73%, positive likelihood ratio 2.7, and inverse negative likelihood ratio 2.6). LWD was univariably associated with body mass index (BMI), hypertension, right atrial area, and LV mass. In multivariable linear regression, only BMI remained associated with LWD (R 2 = 0.32, P < 0.001).

Conclusion

LWD is increased in patients at risk for heart failure compared with controls and is only weakly explained by conventional CMR measures. LWD provides diagnostic information that is largely independent of conventional CMR measures.

Correlation between Extravascular Lung Water and Oxygenation in ALI/ARDS Patients in Septic Shock: Possible Role in the Development of Atelectasis?

This study aimed to evaluate the relationship between PaO2/FiO2 ratio and extravascular lung water in septic shock-induced acute respiratory distress syndrome in a prospective observational clinical trial.

Twenty-three patients suffering from sepsis induced acute respiratory distress syndrome were recruited. All patients were ventilated in pressure control/support mode. Haemodynamic parameters were determined by arterial thermodilution (PiCCO) eight hourly for 72 hours. At the same time blood gas analyses were done and respiratory parameters were also recorded. Data are presented as mean±SD. For statistical analysis Pearson's correlation test, and analysis of variance (ANOVA) was used respectively.

Significant negative correlation was found between extravascular lung water and PaO2/FiO2 (r= −0.355, P<0.001), and significant positive correlation was shown between extravascular lung water and PEEP (r=0.557, P<0.001). A post-hoc analysis was performed when “low” PEEP: <10 cmH2O and “high” PEEP: (10 cmH2O PEEP was applied, and neither the oxygenation, nor the driving pressure or the PaCO2 differed significantly, but the extravascular lung water showed significant difference when “high” or “low” PEEP was applied (13±5 vs 9±2 ml/kg respectively, P=0.001).

This study found significant negative correlation between extravascular lung water and PaO2/FiO2. The mechanism by which extravascular lung water affects oxygenation is unknown but the significant positive correlation between PEEP and extravascular lung water shown in this trial suggests that the latter may have a role in the development of alveolar atelectasis.

Reading chest radiographs in the critically ill (Part II): Radiography of lung pathologies common in the ICU patient

This is part II of two series review of reading chest radiographs in the critically ill. Conventional chest radiography remains the cornerstone of day to day management of the critically ill occasionally supplemented by computed tomography or ultrasound for specific indications. In this second review we discuss radiographic findings of cardiopulmonary disorders common in the intensive care patient and suggest guidelines for interpretation based not only on imaging but also on the pathophysiology and clinical grounds.

Small increases in extravascular lung water are accurately detected by transpulmonary thermodilution

BACKGROUND

Detection of small (10-20%) increases in lung water may be relevant to detect incipient pulmonary edema but no clinically usable method has demonstrated this capability to date.

METHODS

In six pigs weighing 28 to 35 kg, we performed 18 determinations of extravascular lung water (EVLW; transpulmonary thermodilution method) before and immediately after the intratracheal introduction of 50 mL of saline solution. Six determinations were performed in normal lung and 12 in edematous lung.

RESULTS

In normal lung, the mean of EVLW increased from 245 +/- 18 mL to 288 +/- 19 mL (p < 0.001) after the intratracheal introduction of 50 mL of saline solution; therefore, 43 of the 50 mL (84%) were detected (range, 37-48 mL). In edematous lung, the EVLW increased from 491 +/- 106 mL to 530 +/- 108 mL after the introduction of 50 mL of saline solution; therefore, 39 of the 50 mL (77%) were detected (range, 15-67 mL).

CONCLUSION

The transpulmonary thermodilution technique accurately detects small increases in extravascular lung water and may permit accurate diagnosis of incipient pulmonary edema.

Accuracy of transpulmonary thermodilution versus gravimetric measurement of extravascular lung water

OBJECTIVE

Pulmonary edema is a severe and often life-threatening condition. The diagnosis of pulmonary edema and its quantification have great clinical significance and yet can be difficult. A new technique based on thermodilution measurement using a single indicator has recently been developed (PiCCO, Pulsion Medical Systems, AG Germany). This method allows the measurement of extravascular lung water and thus can quantify degree of pulmonary edema. The technique has not been compared with a gold standard, gravimetric measurement of extravascular lung water. Therefore, the objective of this study was to determine the ability of extravascular lung water measurement with the PiCCO to reflect the extravascular lung water as measured with a gravimetric technique in a dog model of pulmonary edema.

DESIGN

Prospective, randomized animal study.

SETTING

A university animal research laboratory.

SUBJECTS

Fifteen mongrel dogs (n = 5/group) weighing 20-30 kg.

INTERVENTIONS

The dogs were anesthetized and mechanically ventilated. Five dogs served as controls; in five dogs hydrostatic pulmonary edema was induced using inflation of a left atrial balloon combined with fluid administration to maintain a high pulmonary artery occlusion pressure; and in five dogs pulmonary edema was induced by intravenous injection of oleic acid. After a period of stabilization in a state of pulmonary edema, extravascular lung water was measured with the PiCCO monitor. The animals were then killed, and extravascular lung water was measured using a gravimetric technique.

MEASUREMENTS AND MAIN RESULTS

There was a very close (r =.967, p <.001) relationship between transpulmonary thermodilution and gravimetric measurements. The measurement with the PiCCO was consistently higher, by 3.01 +/- 1.34 mL/kg, than the gravimetric measurement.

CONCLUSIONS

Measurement of extravascular lung water using transpulmonary thermodilution with a single indicator is very closely correlated with gravimetric measurement of lung water in both increased permeability and hydrostatic pulmonary edema.

Quantification of lung water by transpulmonary thermodilution in normal and edematous lung

PURPOSE

To analyze the accuracy of the transpulmonary thermodilution method in the determination of extravascular lung water (EVLW).

MATERIAL AND METHODS

Acute lung injury was produced in eight adolescent pigs weighing 28 to 35 kg by bronchoalveolar lung lavage. EVLW was measured by transpulmonary thermodilution method before and after the intratracheal introduction of 250 or 500 mL of saline solution in different lung injury conditions. No corrections for anatomic dead space were made.

RESULTS

When 250 mL was introduced, 195 +/- 17 mL was detected in normal (uninjured) lungs versus 74 +/- 57 mL in edematous (injured) lungs (P <.05). When 500 mL was introduced, 343 +/- 67 mL was detected in normal lungs versus 160 +/- 51 mL in edematous lungs (P <.001). Considering all determinations together, there was a very high negative correlation between the baseline EVLW and the percentage of EVLW detected (r = -0.92, P <.001).

CONCLUSION

The transpulmonary thermodilution method is very accurate to detect changes in EVLW in normal lungs. In edematous lung, this method may underestimate the EVLW.

Diuretics in the treatment of patients who present congestive heart failure and hypertension

The main operational objective of diuretic therapy in patients who present congestive heart failure and hypertension is to reduce or to suppress excess bodily fluid. Effective diuretic therapy decreases cardiac size when the heart is dilated, and it reduces lung congestion and excess water. Consequently, external respiratory work diminishes and cardiac output would be redistributed in favour of systemic vascular beds other than that of the respiratory muscles; dyspnoea decreases markedly and there is a slight reduction in fatigue. This clinical improvement and the fall in body weight caused by diuretics entail an increase in effort capacity. Subsequent exercise training ameliorates the abnormal ventilatory response to physical effort and the skeletal muscle myopathy that occur in heart failure, and thereby it attenuates dyspnoea and decreases fatigue further. Loop and/or thiazide-type diuretics may be used to augment natriuresis in patients with congestive heart failure and hypertension. The state of renal function, the existence of certain co-morbid conditions, potential untoward drug actions, and possible interactions of diuretics with nutrients and with other drugs are some of the factors that must be considered at the time of deciding on the diuretic drug(s) and dose(s) to be prescribed. Spironolactone has been found to increase life expectancy and to reduce hospitalisation frequency when added to the conventional therapeutic regimen of patients with advanced congestive heart failure and systolic dysfunction. Therefore, spironolactone should be the drug of choice to oppose the kaliuretic effect of a loop or of a thiazide-type diuretic.

Chest radiographic appearances in severely burned adults. A comparison of early radiographic and extravascular lung thermal volume changes

Chest radiographs (CXRs) have previously been used as a diagnostic tool to detect changes in lung water. In this study CXR changes in severely burned adults, in the absence of an inhalation injury, preceded detectable increases in extravascular lung thermal volume (ELTV) by 3 to 5 days. The hypothesis that early CXR density changes in burned patients have an infectious cause, not related to changes in ELTV, was tested. Blood cultures, CXRs, and ELTV were evaluated during the first 15 days after injury in severely burned adults who had no identified inhalation injury. Chest radiographs were scored daily on a 1 to 5 scale, with 1 = normal, 2 = peribronchial cuffing, 3 = mild interstitial infiltrates, 4 = severe interstitial infiltrates, and 5 = alveolar infiltrates. In all patients, except those who were septic, increases in their CXR density scores correlated well with increases in ELTV. The ELTV/CXR score ratios for septic burn patients on days 1 to 6 postburn was 1.7 +/- 0.2 compared with 4.2 +/- 0.4, (means +/- SEM) for nonseptic (P < .001), whereas the ELTV/CXR score ratios for septic and nonseptic patients, 7 to 15 days postburn, were 3.8 +/- 0.4 and 3.4 +/- 0.5, respectively. We suggest that before any measurable change in ELTV early increases in CXR density scores in burned patients without a concomitant inhalation injury are caused by intraalveolar pneumonitis or hyaline membrane atelectasis and not increased ELTV.

Pulmonary edema induced by allergen challenge in the rat: noninvasive assessment by magnetic resonance imaging

The course of pulmonary edema formation after an intratracheal (i.t.) instillation of ovalbumin was followed noninvasively by magnetic resonance imaging (MRI) in actively sensitized Brown Norway (BN) rats. Changes in edema volume assessed by MRI mimicked the results from the analysis of the number and activation of inflammatory cells recovered from the broncho-alveolar lavage (BAL) fluid. Rats treated with budesonide did not develop edema following challenge with ovalbumin, and these animals showed a significant decrease in BAL fluid inflammatory cell numbers and eosinophil peroxidase and myeloperoxidase activities. Thus, following lung edema formation by MRI provides a reliable means of assessing pulmonary inflammation after allergen challenge. Unlike BAL fluid analysis, which requires killing animals at each time point, this method is noninvasive. MRI could be of importance for the noninvasive profiling of anti-inflammatory drugs in animal models of asthma and in the clinic. Magn Reson Med 45:88-95, 2001.

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.

Novel assessment of acute lung injury by in vivo near-infrared spectroscopy

We investigated the feasibility and validity of near-infrared (NIR) spectroscopy for evaluation of acute lung injury (ALI). In an in vitro model simulating the spectrophotometric characteristics of the lung, NIR spectroscopy could precisely detect changes in water volume, suggesting its ability to assess the extent of pulmonary edema caused by ALI. The different grades of ALI were induced in rats by administering oleic acid and varying the pulmonary ventilation conditions, and NIR spectroscopy was employed to determine lung water content and hemoglobin (Hb) oxygenation of the lungs. NIR spectroscopy detected increased water content even in histologically mild ALI. The changes in lung water content measured by NIR spectroscopy were significantly correlated with gravimetric lung water content (r = 0.877, p < 0.0001). Deoxy-Hb measured by NIR spectroscopy consistently reflected the histological changes in the lungs, and the deoxy-Hb levels correlated with changes in SaO2 (r = -0.798, p < 0.0001). These findings demonstrate that NIR spectroscopy can evaluate lung water content and Hb oxygenation quantitatively, and may be a useful tool for assessing pathological status in ALI.

Role of platelet-activating factor on extravascular lung water after coronary reperfusion in dogs

Platelet-activating factor (PAF), one of the harmful substances released after coronary reperfusion, has been reported to increase pulmonary vascular permeability and induce pulmonary edema. In this study, we sought to examine the possible role of PAF in the genesis of pulmonary edema after coronary reperfusion. Extravascular lung water (EVLW) was measured by the thermal-dye double indicator dilution method during coronary ligation and after reperfusion in situ in dogs. The proximal left anterior descending coronary artery was occluded for 15 min and reperfused in 5 dogs (group 1), while five other dogs (group 2) were treated with PAF-antagonist (TCV-309, 1 mg/kg) before coronary artery occlusion. EVLW and hemodynamic indices were measured at baseline, 15 min of coronary occlusion, and 15 and 30 min after coronary reperfusion. EVLW increased at 15 min of coronary occlusion in both groups, but there was no significant difference between the two groups (6.4 to 10.3 ml/kg and 5.4 to 7.1 ml/kg in groups 1 and 2, respectively). After coronary reperfusion, EVLW increased further in group 1 (6.4 to 16.5 ml/kg, p < 0.01), but no further increase was observed in group 2 at 30 min after coronary reperfusion. There were no significant differences in hemodynamic indices between the two groups throughout the test. Thus, PAF-antagonist attenuated the increase in EVLW after coronary reperfusion independent of hemodynamic indices, and hence, PAF may play an important role in the genesis of pulmonary edema caused by coronary reperfusion.

EITS changes following oleic acid induced lung water

We present the results of using electrical impedance tomographic spectroscopy (EITS) to follow the changes in lung water induced by oleic acid. Measurements were made on three goats before and after the injection of oleic acid. In addition to the EITs measurements, lung water was also measured using a double-indicator technique. Large falls in lung electrical impedance were seen as a result of the increase in lung water but the size of the fall was a function of the frequency at which the measurements were made. These changes have been modelled using the Cole equation. Four-electrode measurements were also made on two extracted porcine lungs and Cole equation modelling carried out following the introduction of saline into the lungs. Results were similar in the two sets of animal experiments.

Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a serious and complex clinical problem that often threatens the lives of patients. Emerging clinical data suggest that the survival of patients with this disorder may have improved during the last two decades, presumably because of advances in supportive medical care. Among the supportive therapies used to treat patients with ARDS, none is more complex than mechanical ventilation. New strategies for administering mechanical ventilation to patients with ARDS may reduce the occurrence of iatrogenic volotrauma and oxygen toxicity, accounting in part for the recently observed improvements in patient survival. Prevention and cure of ARDS have remained elusive goals because of the lack of specific therapies directed against the known pathogenic factors. Ongoing investigations are aimed at identifying specific therapies to interrupt the mechanisms of inflammation and lung injury responsible for this syndrome. Until such therapies become available, clinicians caring for patients with ARDS should attempt to minimize additional morbidity and mortality resulting from nosocomial infections and iatrogenic injuries.

Loop diuretics versus others in the treatment of congestive heart failure after myocardial infarction

Most frequently, diuretic therapy in congestive heart failure has as its main objective ridding the lungs of water. The work of the muscles of external respiration is thus decreased, the fraction of cardiac output that is distributed to vascular beds other than that of the respiratory muscles is consequently increased, and the functional and clinical condition of the patient improves. Diuretic therapy does not change cardiac output significantly in most cases; in some circumstances diuretic therapy may increase cardiac output in a clinically relevant fashion, and in some other cases diuretic therapy may lower cardiac output to the extent of impairing the overall functional situation. The dose of diuretics should be the minimal compatible with the prosecution of the main clinical objective (class betterment), to minimize possible increases in the afterload to the left ventricle (intravenous administration), to minimize hemodynamically detrimental decreases in the preload, and to minimize the likelihood of development or the severity of undesired changes in plasma biochemistry (hyponatremia, hypokalemia, hypomagnesemia, hyperuricemia, etc.). Loop diuretics are preferred shortly after myocardial infarction, given the ample dose-effect range of these substances and their relatively benign effect on renal blood flow. During chronic therapy, loop diuretics at low doses may be tried first, and the dose may be increased if necessary, provided higher doses do not cause symptomatic falls in cardiac output through the striking renal excretory response that these drugs elicit shortly after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic basis for management of the septic surgical patient

The physiologic events accompanying postoperative septic complications in surgical patients represent a coordinated response to bacterial invasion, which is aimed at maintaining the function of key organ systems. When sepsis is prolonged or overwhelming, physiologic dysfunction and multiorgan failure develop. This review outlines the pathophysiologic response to sepsis and correlates it with recent therapeutic advances in the metabolic management of the postoperative septic patient.

Role of platelet-activating factor in pulmonary edema after coronary ligation in dogs

To evaluate whether PAF is related to the precipitation of pulmonary edema after myocardial ischemia, we studied the effect of a specific PAF antagonist, CV-6209, on the extravascular lung water level measured by the thermal-dye double indicator dilution method, ETV, after coronary ligation in dogs. Eight dogs served as sham control animals (group 1). The proximal left anterior descending coronary artery was ligated for 45 min in eight dogs (group 2), and the coronary artery was ligated after pretreatment with CV-6209 (1 mg/kg) in eight dogs (group 3). The ETV increased significantly after coronary ligation in groups 2 and 3. The amount of increase in ETV in group 2 was significantly larger than in group 3. Thus, CV-6209 can prevent the accumulation of extravascular lung water after coronary ligation without producing changes in pulmonary vascular dynamics, indicating that PAF may play an important role in pulmonary edema after myocardial ischemia.

Effects of platelet-activating factor antagonist CV-3988 in preservation of heart and lung for transplantation

The preservation of heart and lung for transplantation remains a major concern in extended ischemic intervals. This experiment evaluated the effect of high molecular weight deferoxamine and a platelet-activating factor antagonist (CV-3988) in ischemic reperfused tissue. Heart-lung transplantation was performed in a swine model after 4 hours 45 minutes of ischemia. Animals were divided into three groups. Group A was a control without pharmacological intervention. In group B, high molecular weight deferoxamine, 50 mg/kg, was used, and in group C, platelet-activating factor antagonist CV-3988, 10 mg/kg, was used. The results of functional variables (cardiac index, stroke index, lung water, oxygen and carbon dioxide tensions, alveolar-arterial gradient, and alveolar-arterial ratio) demonstrated superior heart and lung function for groups B and C compared with the control group. These alterations of heart and lung function were significantly less (p less than 0.001) in group C, in which the platelet-activating factor antagonist (CV-3988) was used. The study revealed that formation of hydroxyl radicals and platelet-activating factor play an important role in the pathogenesis of ischemia reperfusion injury. Prevention of hydroxyl radical formation with high molecular weight deferoxamine and inactivation of platelet-activating factor with CV-3988 reduce the ischemia-reperfusion injury significantly.

Sodium MRI with coated magnetite: measurement of extravascular lung water in rats

This study was done to see if signal intensity in sodium images of edematous rat lungs made after iv administration of a negative intravascular contrast agent could serve as a measure of the edema fluid present. First, a method to produce a stable condition of hydrostatic pulmonary edema was developed and verified by CT. Second, dose-response curves for coated magnetite preparations were constructed by giving edematous rats varied doses of these preparations and measuring signal intensity changes of various organs by sodium MRI in a 31-cm-bore 1.9-T magnet. Third, rats were given varied levels of pulmonary edema followed by a constant dose of coated magnetite to eliminate the plasma sodium signal. Finally, coated magnetite particles of two sizes were administered to rats, and the differences in effects on signal from various organs were measured. Signal intensity of the lungs after magnetite correlated (r = 0.86) with extravascular lung water measured gravimetrically, suggesting that sodium MRI may be useful for measuring pulmonary edema fluid. Smaller particles appear to remain in the blood longer than larger particles.

Pulmonary function testing in the intensive care unit

A number of tests of pulmonary function have been successfully developed for use in the intensive care unit. When performed in the ICU on critically ill patients, many of the traditional laboratory-based tests will have different clinical implications than when performed in ambulatory patients, for example vital capacity measurement. Also, the clinical questions posed in the ICU are often different, such that estimates of lung water may be clinically more useful than more traditional measures, such as the flow-volume loop. There is a need for further research to identify the clinical utility of these measurements. As the understanding of ARDS and MOF improves, new therapies may be developed which will require sensitive methods in order that they can be evaluated accurately. Similarly, the potential for new methods of respiratory support such as jet ventilation, extracorporeal techniques and lung transplantation reinforce the need for the pulmonary physician to be able to make an accurate assessment of respiratory function on the intensive care unit.