Model of pleural fluid turnover

A simple size-tailored algorithm for the removal of chest drain following minimally invasive lobectomy: a prospective randomized study

Background

The pleural space can resorb 0.11–0.36 ml/kg of body weight/hour (h) per hemithorax. There are only a limited number of studies on thresholds for chest drain removal (CDR) and all are based on arbitrary amounts, for example, 300 ml/day. We studied an individualized size-based threshold for CDR–specifically 5 ml/kg, a simple, easily applicable measure.

Methods

This is a single-center prospective randomized trial enrolling 80 patients undergoing VATS lobectomy. There were two groups: an experimental (E) group, in which once the daily output went down to 5 ml/kg the chest drain was removed and a control (C) group, with chest drain removal as per our current practice of less than 250 ml/day.

Results

The groups did not differ in pre- and peri- and postoperative characteristics, except for chest drain duration (mean, SD 2.02 ± 0.97 vs. 3.25 ± 1.39 days, p < 0.001) and length of hospital stay (median, IQR 4.5; 3 vs. 6; 2.75 days, p = 0.008) in favor of E group. The re-intervention rate was the same in both groups (once in each group).

Conclusion

The new threshold for chest drain removal following thoracoscopic lobectomy of 5 ml/kg/d leads to both shorter chest drainage and hospital stay without apparent increase in morbidity. (Clinical registration number: DRKS00014252).

Mediastinal micro-vessels clipping during lymph node dissection may contribute to reduce postoperative pleural drainage

BACKGROUND

Postoperative pleural drainage markedly influences the length of postoperative stay and financial costs of medical care. The aim of this study is to retrospectively investigate potentially predisposing factors related to pleural drainage after curative thoracic surgery and to explore the impact of mediastinal micro-vessels clipping on pleural drainage control after lymph node dissection.

METHODS

From February 2012 to November 2013, 322 consecutive cases of operable non-small cell lung cancers (NSCLC) undergoing lobectomy and mediastinal lymph node dissection with or without application of clipping were collected. Total and daily postoperative pleural drainage were recorded. Propensity score matching (1:2) was applied to balance variables potentially impacting pleural drainage between group clip and group control. Analyses were performed to compare drainage volume, duration of chest tube and postoperative hospital stay between the two groups. Variables linked with pleural drainage in whole cohort were assessed using multivariable logistic regression analysis.

RESULTS

Propensity score matching resulted in 197 patients (matched cohort). Baseline patient characteristics were matched between two groups. Group clip showed less cumulative drainage volume (P=0.020), shorter duration of chest tube (P=0.031) and postoperative hospital stay (P=0.022) compared with group control. Risk factors significantly associated with high-output drainage in multivariable logistic regression analysis were being male, age >60 years, bilobectomy/sleeve lobectomy, pleural adhesion, the application of clip applier, duration of operation ≥220 minutes and chylothorax (P<0.05).

CONCLUSIONS

This study suggests that mediastinal micro-vessels clipping during lymph node dissection may reduce postoperative pleural drainage and thus shorten hospital stay.

Air leak after lung resection: pathophysiology and patients' implications

Protocols for the management of air leaks are critical aspects in the postoperative course of patients following lung resections. Many investigations in the last decade are focusing on the chest tube modalities or preventative measures, however, little is known about the pathophysiology of air leak and the patient perception of this common complication. This review concentrates on understanding the reasons why a pulmonary parenchyma may start to leak or an air leak may be longer than others. Experimental works support the notion that lung overdistension may favor air leak. These studies may represent the basis of future investigations. Furthermore, the standardization of nomenclature in the field of pleural space management and the creation of novel air leak scoring systems have contributed to improve the knowledge among thoracic surgeons and facilitate the organization of trials on this matter. We tried to summarize available evidences about the patient perception of a prolonged air leak and about what would be useful for them in order to prevent worsening of their quality of life. Future investigations are warranted to better understand the pathophysiologic mechanisms responsible of prolonged air leak in order to define tailored treatments and protocols. Improving the care at home with web-based telemonitoring or real time connected chest drainage may in a future improve the quality of life of the patients experience this complication and also enhance hospital finances.

Determining optimal fluid and air leak cut off values for chest drain management in general thoracic surgery

BACKGROUND

Chest drain duration is one of the most important influencing aspects of hospital stay but the management is perhaps one of the most variable aspects of thoracic surgical care. The aim of our study is to report outcomes associated with increasing fluid and air leak criteria of protocol based management.

METHODS

A 6-year retrospective analysis of protocolised chest drain management starting in 2007 with a fluid criteria of 3 mL/kg increasing to 7 mL/kg in 2011 to no fluid criteria in 2012, and an air leak criteria of 24 hours without leak till 2012 when digital air leak monitoring was introduced with a criteria of <20 mL/min of air leak for more than 6 hours. Patient data were obtained from electronic hospital records and digital chest films were reviewed to determine the duration of chest tube drainage and post-drain removal complications.

RESULTS

From 2009 to 2012, 626 consecutive patients underwent thoracic surgery procedures under a single consultant. A total of 160 did not require a chest drain and data was missing in 22, leaving 444 for analysis. The mean age [standard deviation (SD)] was 57±19 years and 272 (61%) were men. There were no differences in the incidence of pneumothoraces (P=0.191), effusion (P=0.344) or re-interventions (P=0.431) for drain re-insertions as progressively permissive criteria were applied. The median drain duration dropped from 1-3 days (P<0.001) and accordingly hospital stay reduced from 4-6 days (P<0.001).

CONCLUSIONS

Our results show that chest drains can be safely removed without fluid criteria and air leak of less than 20 mL/min with median drain duration of 1 day, associated with a reduced length of hospital stay.

Lymphatic drainage between thorax and abdomen: please take good care of this well-performing machinery…

INTRODUCTION

Patients with sepsis often receive large amounts of fluids and the presence of capillary leak, trauma or bleeding results in ongoing fluid resuscitation. This increases interstitial and intestinal edema and finally leads to intra-abdominal hypertension (IAH), which in turn impedes lymphatic drainage. Patients with IAH often develop secondary respiratory failure needing mechanical ventilation with high intrathoracic pressure or PEEP that might further alter lymphatic drainage. This review will try to convince the reader of the importance of the lymphatics in septic patients with IAH.

METHODS

A Medline and PubMed literature search was performed using the terms "abdominal pressure", "lymphatic drainage" and "ascites formation". The references from these studies were searched for relevant articles that may have been missed in the primary search. These articles served as the basis for the recommendations below.

RESULTS

Induction of sepsis with lesion of the capillary alveolar barrier results in an increased water gradient between the capillaries and the interstitium in the lungs. The drainage flow to the thoracic duct is initially increased in order to protect the lung and maintain the pulmonary interstitium as dry as possible, however this results in increased intrathoracic pressure. Sepsis also increases the permeability of the capillaries in the splanchnic beds. In analogy to the lungs the lymphatic flow in the splanchnic areas increases together with the pressure inside as a physiological response in order to limit the increase in IAP. At a critical IAP level (around 20 cmH2O) the lymph flow starts to decrease and the splanchnic water content progressively increases. The lymph flow from the abdomen to the thorax is progressively decreased resulting in increased splanchnic water content and ascites formation. The presence of mechanical ventilation with high PEEP reduces the lymph drainage further which together with the increase in IAP decreases the lymphatic pressure gradient in the splanchnic regions, with a further increase in water content and IAP triggering a vicious cycle.

CONCLUSION

Although often overlooked the role of lymphatic flow is complex but very important to determine not only the fluid balance in the lung but also in the peripheral organs. Different pathologies and treatments can markedly influence the pathophysiology of the lymphatics with dramatic effects on endorgan function.

The rate of pleural fluid drainage as a criterion for the timing of chest tube removal: theoretical and practical considerations

Clinicians place chest tubes approximately 1 million times each year in the United States, but little information is available to guide their management. Specifically, use of the rate of pleural fluid drainage as a criterion for tube removal is not standardized. Absent such tubes, pleural fluid drains primarily through parietal pleural lymphatics at rates approaching 500 mL of fluid per day or more for each hemithorax. Early removal of tubes does not appear to be harmful. A noninferiority randomized trial currently in progress comparing removal without considering the drainage rate to a conservative threshold (2 mL/kg body weight in 24 hours) may better inform tube management.

Translocation pathways for inhaled asbestos fibers

We discuss the translocation of inhaled asbestos fibers based on pulmonary and pleuro-pulmonary interstitial fluid dynamics. Fibers can pass the alveolar barrier and reach the lung interstitium via the paracellular route down a mass water flow due to combined osmotic (active Na+ absorption) and hydraulic (interstitial pressure is subatmospheric) pressure gradient. Fibers can be dragged from the lung interstitium by pulmonary lymph flow (primary translocation) wherefrom they can reach the blood stream and subsequently distribute to the whole body (secondary translocation). Primary translocation across the visceral pleura and towards pulmonary capillaries may also occur if the asbestos-induced lung inflammation increases pulmonary interstitial pressure so as to reverse the trans-mesothelial and trans-endothelial pressure gradients. Secondary translocation to the pleural space may occur via the physiological route of pleural fluid formation across the parietal pleura; fibers accumulation in parietal pleura stomata (black spots) reflects the role of parietal lymphatics in draining pleural fluid. Asbestos fibers are found in all organs of subjects either occupationally exposed or not exposed to asbestos. Fibers concentration correlates with specific conditions of interstitial fluid dynamics, in line with the notion that in all organs microvascular filtration occurs from capillaries to the extravascular spaces. Concentration is high in the kidney (reflecting high perfusion pressure and flow) and in the liver (reflecting high microvascular permeability) while it is relatively low in the brain (due to low permeability of blood-brain barrier). Ultrafine fibers (length < 5 mum, diameter < 0.25 mum) can travel larger distances due to low steric hindrance (in mesothelioma about 90% of fibers are ultrafine). Fibers translocation is a slow process developing over decades of life: it is aided by high biopersistence, by inflammation-induced increase in permeability, by low steric hindrance and by fibers motion pattern at low Reynolds numbers; it is hindered by fibrosis that increases interstitial flow resistances.

Transmural pressure in rat initial subpleural lymphatics during spontaneous or mechanical ventilation

The role played by the mechanical tissue stress in supporting lymph formation and propulsion in thoracic tissues was studied in deeply anesthetized rats (n = 13) during spontaneous breathing or mechanical ventilation. After arterial and venous catheterization and insertion of an intratracheal cannula, fluorescent dextrans were injected intrapleurally to serve as lymphatic markers. After 2 h, the fluorescent intercostal lymphatics were identified, and the hydraulic pressure in lymphatic vessels (P lymph) and adjacent interstitial space (P int) was measured using micropuncture. During spontaneous breathing, end-expiratory P lymph and corresponding P int were -2.5 +/- 1.1 (SE) and 3.1 +/- 0.7 mmHg (P < 0.01), which dropped to -21.1 +/- 1.3 and -12.2 +/- 1.3 mmHg, respectively, at end inspiration. During mechanical ventilation with air at zero end-expiratory alveolar pressure, P lymph and P int were essentially unchanged at end expiration, but, at variance with spontaneous breathing, they increased at end inspiration to 28.1 +/- 7.9 and 28.2 +/- 6.3 mmHg, respectively. The hydraulic transmural pressure gradient (DeltaP tm = P lymph - P int) was in favor of lymph formation throughout the whole respiratory cycle (DeltaP tm = -6.8 +/- 1.2 mmHg) during spontaneous breathing but not during mechanical ventilation (DeltaP tm = -1.1 +/- 1.8 mmHg). Therefore, data suggest that local tissue stress associated with the active contraction of respiratory muscles is required to support an efficient lymphatic drainage from the thoracic tissues.

Normal volume and cellular contents of pleural fluid

Because of the technical difficulties in obtaining a-traumatical access to the normal pleural space, the exact volume and cellular content of normal pleural fluid in humans were still unknown until very recently, and animal-derived extrapolation data had to be used. After having developed a minimally invasive thoracoscopic technique for performing sympathectomy in patients suffering from essential hyperhidrosis, but with otherwise absence of thoracic disease, we have been able to achieve minimally traumatic access to normal pleural spaces. Using pleural lavage, a technique consisting of injection and immediate aspiration of 150 mL of prewarmed saline into the pleural space, we were able to determine the total and differential cell content of the few milliliters of original pleural fluid. The exact volume of this original pleural fluid could be measured using urea as an endogenous marker of dilution. Expressed per kilogram of body mass, total pleural fluid volume in healthy, non-smoking humans was 0.26+/-0.1 mL kg(-1). Total white blood cell count (after correction for dilution) was 1.716 x 10(3) cells mL(-1). Differential cell counts yielded median 75% (IR 16%) macrophages, 23% (IR 18%) lymphocytes, and marginally present mesothelial cells (1%, IR 2%), neutrophils (0%, IR 1%) and eosinophils (0%, IR 0%). There was no significant correlation between age and pleural lavage results in a study population aged 17 to 54 years old, which suggests that these results may be extrapolated to the situation in children and adolescents.

Pleural mechanics and fluid exchange

The pleural space separating the lung and chest wall of mammals contains a small amount of liquid that lubricates the pleural surfaces during breathing. Recent studies have pointed to a conceptual understanding of the pleural space that is different from the one advocated some 30 years ago in this journal. The fundamental concept is that pleural surface pressure, the result of the opposing recoils of the lung and chest wall, is the major determinant of the pressure in the pleural liquid. Pleural liquid is not in hydrostatic equilibrium because the vertical gradient in pleural liquid pressure, determined by the vertical gradient in pleural surface pressure, does not equal the hydrostatic gradient. As a result, a viscous flow of pleural liquid occurs in the pleural space. Ventilatory and cardiogenic motions serve to redistribute pleural liquid and minimize contact between the pleural surfaces. Pleural liquid is a microvascular filtrate from parietal pleural capillaries in the chest wall. Homeostasis in pleural liquid volume is achieved by an adjustment of the pleural liquid thickness to the filtration rate that is matched by an outflow via lymphatic stomata.

Respiratory fluid mechanics and transport processes

The field of respiratory flow and transport has experienced significant research activity over the past several years. Important contributions to the knowledge base come from pulmonary and critical care medicine, surgery, physiology, environmental health sciences, biophysics, and engineering. Several disciplines within engineering have strong and historical ties to respiration including mechanical, chemical, civil/environmental, aerospace and, of course, biomedical engineering. This review draws from a wide variety of scientific literature that reflects the diverse constituency and audience that respiratory science has developed. The subject areas covered include nasal flow and transport, airway gas flow, alternative modes of ventilation, nonrespiratory gas transport, aerosol transport, airway stability, mucus transport, pulmonary acoustics, surfactant dynamics and delivery, and pleural liquid flow. Within each area are a number of subtopics whose exploration can provide the opportunity of both depth and breadth for the interested reader.

Steady-state pleural fluid flow and pressure and the effects of lung buoyancy

Both theoretical and experimental studies of pleural fluid dynamics and lung buoyancy during steady-state, apneic conditions are presented. The theory shows that steady-state, top-to-bottom pleural-liquid flow creates a pressure distribution that opposes lung buoyancy. These two forces may balance, permitting dynamic lung floating, but when they do not, pleural-pleural contact is required. The animal experiments examine pleural-liquid pressure distributions in response to simulated reduced gravity, achieved by lung inflation with perfluorocarbon liquid as compared to air. The resulting decrease in lung buoyancy modifies the force balance in the pleural fluid, which is reflected in its vertical pressure gradient. The data and model show that the decrease in buoyancy with perfluorocarbon inflation causes the vertical pressure gradient to approach hydrostatic. In the microgravity analogue, the pleural pressures would be toward a more uniform distribution, consistent with ventilation studies during space flight. The pleural liquid turnover predicted by the model is computed and found to be comparable to experimental values from the literature. The model provides the flow field, which can be used to develop a full transport theory for molecular and cellular constituents that are found in pleural fluid.

Normal volume and cellular contents of pleural fluid

The pleural space in healthy humans was thought to contain a few milliliters of fluid, based on extrapolation from animal studies. However, because of the obvious technical difficulties in atraumatically retrieving such a small volume of fluid, the exact volume and cellular content of human pleural fluid has not been known. Development of a minimally invasive pleural lavage technique has allowed, for the first time, the measurement of volume and cellular content of the pleural fluid in healthy humans.

Yellow nail syndrome: does protein leakage play a role?

Yellow nail syndrome is characterized by primary lymphoedema, recurrent pleural effusion and yellow discoloration of the nails. Although mechanical lymphatic obstruction is assumed to be the underlying pathology, it cannot explain the common finding of high albumin concentration in the pleural space. This paper describes a case of yellow nail syndrome presenting with the classical triad of lymphoedema, recurrent pleural effusion and yellow discoloration of the nails, associated with persistent hypoalbuminaemia and increased enteric loss of albumin. Based on the findings in this case and those in the literature, it is speculated that increased microvascular permeability may contribute to the pathogenesis of this syndrome.

Subatmospheric pressure in the rabbit pleural lymphatic network

1. Hydraulic pressure in intercostal and diaphragmatic lymphatic vessels was measured through the micropuncture technique in 23 anaesthetised paralysed rabbits. Pleural lymphatic vessels with diameters ranging from 55 to 950 microm were observed under stereomicroscope view about 3-4 h after intrapleural injection of 20 % fluorescent dextrans. 2. Lymphatic pressure oscillated from a minimum (Pmin) to a maximum (Pmax) value, reflecting oscillations in phase with cardiac activity (cardiogenic oscillations) and lymphatic myogenic activity. With intact pleural space, Pmin in submesothelial diaphragmatic lymphatic vessels of the lateral apposition zone was -9.1 +/- 4.2 mmHg, more subatmospheric than the simultaneously recorded pleural liquid pressure amounting to -3.9 +/- 1.2 mmHg. In extrapleural intercostal lymphatic vessels Pmin averaged -1.3 +/- 2. 7 mmHg. 3. Cardiogenic pressure oscillations (Pmax - Pmin), were observed in all recordings; their mean amplitude was about 5 mmHg and was not dependent upon frequency of cardiac contraction, nor lymphatic vessel diameter, nor the Pmin value. 4. Intrinsic contractions of lymphatic vessel walls caused spontaneous pressure waves of about 7 mmHg in amplitude at a rate of 8 cycles min-1. 5. These results demonstrated the ability of pleural lymphatic vessels to generate pressure oscillations driving fluid from the subatmospheric pleural space into the lymphatic network.

Anatomy of the pleura

The lung and heart, the vital organs, have to be protected and also have to move and change volume continuously to function. For the best protection and function of the lung, the thorax is shaped almost like a bellows with the diaphragm as the moving part. Furthermore, the outer surface of the lung and the inner surface of the protective thoracic cage are covered by an elastic, serous, and lubricating membrane to form the pleural cavity. This is almost like inserting a sealed-wet and stretchable-plastic bag between the lung and the thoracic wall and diaphragm to decrease friction. The lubrication is accomplished by the facing mesothelial cells that have bushy-surface microvilli enmeshing hyaluronic acid-rich glycoproteins. The amount of fluid in the pleural cavity is regulated by the hydrostatic-osmotic pressure relationship and pleuro-lymphatic drainage. Excess fluid, large particles, and cells in the pleural cavity are removed through preformed stomas assisted by respiratory movements. The stoma is found only in the anterior lower thoracic wall and diaphragm and is like the drain of a sink. Finally, clinical and subclinical injuries of the pleura appear to occur often. Reactive mesothelial cells constantly repair the damages and keep the pleural cavity open. Without mesothelial cells, the lung cannot function properly and the pleural cavity will be quickly obliterated by fibrosis.

Roles of the visceral pleura in the production of pleural effusion in permeability pulmonary edema

We investigated the roles of the mesothelium of the visceral pleura on hydraulic conductivity in dogs under normal conditions and condition of permeability pulmonary edema. Nineteen mongrel dogs were divided into following 4 groups: thoracotomy alone (control group, n = 7); thoracotomy and striping of the mesothelium using Gelfilm (C + G group, n = 4); injection of oleic acid to increase the permeability of the pulmonary vessels (OA group, n = 4); injection of oleic acid and striping of the mesothelium (OA + G group, n = 4). A hemispherical capsule filled with physiological saline was attached to the visceral pleura. The transpleural fluid flow (delta V) was measured at given incremental or decremental hydrostatic pressures (delta Pcap) in the capsule. Hydraulic conductivity was calculated from the slope of linear regression line obtained from relationship between delta Pcap and the fluid flow rate (v) according to the Starling's equation. The conductivity obtained were 1.49 +/- 0.69 (nl.min-1.cmH2O-1.cm-2) in the control group, 1.37 +/- 0.88 in the C + G group, 3.75 +/- 0.74 in the OA + G group, and 7.07 +/- 2.49 in the OA + G group. The hydraulic conductivity was not increased by striping of the mesothelium (1.49 +/- 0.69 [nl.min-1.cmH2O-1.cm-2] vs. 1.37 +/- 0.88, in the control group vs. C + G group, respectively). Visceral pleural hydraulic conductivity following OA injection was increased by striping of the mesothelium (3.75 +/- 0.74 vs. 7.07 +/- 2.49 in OA group vs. OA + G group, respectively). These findings suggest that the wall of pulmonary vessels acts as a barrier to movement of pleural effusion under normal conditions, whereas the mesothelium of the visceral pleura acts as that under condition of permeability pulmonary edema.

Idiopathic dilated cardiomyopathy in dogs: survival and prognostic indicators

To further define the prognosis and identify clinical findings predictive for survival in dogs with dilated cardiomyopathy (DCM), we performed Kaplan Meier survival analysis of 37 dogs with idiopathic DCM. Survival analysis showed that the 50% probability of survival occurred at 2.3 months. Probability of survival at 1 year was 37.5% and at 2 years was 28%. Bivariate Cox proportional hazard ratios identified pleural effusion and pulmonary edema, both signs of congestive heart failure, as independent prognostic indicators for dogs with DCM (P < .01). Hazard ratios for these prognostic indicators were 2.354 and 3.291, respectively. Multivariate Cox stepwise regression identified pleural effusion, left ventricular free-wall thickening fraction, ventricular ectopy, and weight loss as significant prognostic indicators for dogs with DCM. Because of the retrospective nature of this study, the effects of different drug treatments were not evaluated. The type of cardiac-related death, progressive failure versus sudden death, was not addressed in this study and requires further evaluation.