Alterations in pulmonary microanatomy after fat embolism. In vivo observations via thoracic window of the oleic acid-embolized canine lung

Warm retrograde perfusion can remove more fat from lung grafts with fat embolism in a porcine model

OBJECTIVE

In lung transplantation, unexpected pulmonary emboli, including thrombi and fat, have been observed with high probability and are associated with potential primary graft dysfunction. We evaluated a new perfusion method using warm retrograde flushing that removes more fat than conventional cold retrograde flushing.

METHODS

We developed a novel porcine donor model for pulmonary fat embolism by administering autologous fat in the left pulmonary artery. The left pulmonary artery and the left superior and inferior pulmonary veins were cannulated for flushing and collecting these solutions. After flushing, the left lung was reperfused under observation for 3 h. Two groups underwent warm and cold additional retrograde flush (WS; warm solution group, CS; cold solution group).

RESULTS

The fat removal rate in the antegrade flush was equal in both groups (3.0 ± 0.6% vs 3.0 ± 0.4%, p = 0.46); however, the rate was significantly greater in the WS group in retrograde flush (25.2 ± 3.2% vs 8.0 ± 1.4%, p = 0.01). Histology with Oil Red O staining and its software analysis showed more residual fat in the CS group (0.12 ± 0.01% vs 0.38 ± 0.07%, p = 0.01). There was no significant difference in the pulmonary function and hemodynamics during the 3-h period after reperfusion.

CONCLUSION

Warm retrograde perfusion can remove more fat from lung grafts with fat embolism in a porcine donor model.

Spinal cord infarction as a rare complication of fat embolism syndrome following bilateral intramedullary nailing of femur fractures

Fat embolism syndrome (FES) is a rare and potentially fatal complication occurring most often after long bone or pelvic fractures and orthopaedic procedures. It can consist of pulmonary, central nervous system and cutaneous manifestations. The exact pathophysiology of emboli reaching the arterial circulation is poorly understood.1 It is suggested that this may occur by either 'paradoxical' embolism or microembolism.2 3 Its true incidence is unknown but increases in the presence of multiple closed fractures. It can be a diagnostic dilemma for clinicians and if suspected diffusion-weighted MRI is the modality of choice for the investigation of the central nervous system.4 We present the case of a 22-year-old man who developed multifocal cerebral infarcts, a right-sided cerebellar infarct and an infarct in the anterior cord bilaterally at the level of C5-C6 as a result of FES.

Effects of oleic acid-induced lung injury on oxygen transport and aerobic capacity

We tested the hypothesis that oleic-acid (OA) infusion impairs gas exchange, decreases total cardiopulmonary O2 delivery and lowers maximal aerobic capacity ( [Formula: see text] ). We infused 0.05ml OAkg(-1) (∼3ml) and ∼563ml saline into the right atria of four goats [59.1±14.0 (SD) kg] prior to running them on a treadmill at [Formula: see text] 2-h and 1-d following OA-induced acute lung injury, and with no lung injury. Acute lung injury decreased [Formula: see text] , O2 delivery, arterial O2 concentration and arterial O2 partial pressure compared to no lung injury. The [Formula: see text] positively correlated with O2 delivery and inversely correlated with alveolar-arterial O2 partial pressure difference, suggesting that impaired pulmonary gas exchange decreased O2 delivery and uptake. Results indicate OA infusion may be a useful model for acutely impairing pulmonary gas exchange for exercise studies. Seven OA infusions induced smaller chronic gas exchange and arterial O2 partial pressure changes than acute infusion.

Increased isoprostane levels in oleic acid-induced lung injury

The present study was performed to examine a role of oxidative stress in oleic acid-induced lung injury model. Fifteen anesthetized sheep were ventilated and instrumented with a lung lymph fistula and vascular catheters for blood gas analysis and measurement of isoprostanes (8-epi prostaglandin F2alpha). Following stable baseline measurements, oleic acid (0.08 ml/kg) was administered and observed 4 h. Isoprostane was measured by gas chromatography mass spectrometry with the isotope dilution method. Isoprostane levels in plasma and lung lymph were significantly increased 2 h after oleic acid administration and then decreased at 4 h. The percent increases in isoprostane levels in plasma and lung lymph at 2 h were significantly correlated with deteriorated oxygenation at the same time point, respectively. These findings suggest that oxidative stress is involved in the pathogenesis of the pulmonary fat embolism-induced acute lung injury model in sheep and that the increase relates with the deteriorated oxygenation.

Estabilidade do modelo animal de lesão pulmonar aguda induzida por ácido oleico

OBJETIVO: Avaliar a estabilidade das variáveis hemodinâmicas, da mecânica respiratória e de troca gasosa do modelo animal de lesão pulmonar aguda induzida por ácido oleico. MÉTODOS: Trata-se de um estudo experimental no qual foram utilizados 10 cães de raça indeterminada. As variáveis foram aferidas inicialmente e em 30, 60, 90 e 120 min após a administração do ácido oleico. Para analisar as medidas repetidas, foram testados efeitos lineares e quadráticos e foram utilizados ajustes de modelos lineares mistos com estruturas de variâncias e covariâncias diversificadas, dependendo da variável analisada. RESULTADOS: Observamos estabilidade da pressão arterial média aos 30 min, assim como da frequência cardíaca, da pressão arterial pulmonar e da pressão de capilar pulmonar aos 60 min. Frequência respiratória, volume corrente, volume minuto e trabalho respiratório estabilizaram aos 30 min. Quanto às variáveis de troca gasosa, PaO2, relação PaO2/FiO2 e fração de shunt pulmonar estabilizaram-se aos 30 min. As demais variáveis mantiveram-se em ascensão ou queda contínuas. CONCLUSÕES: O modelo de lesão pulmonar aguda induzida por ácido oleico é estável para algumas das variáveis testadas; porém, a estabilização se dá em momentos diferentes. As variáveis da mecânica respiratória e de troca gasosa estabilizaram em 30 min, e as hemodinâmicas, em 60 min.

Fat embolism syndromes following liposuction

Fat embolism syndrome (FES) after liposuction is likely a life-threatening disorder, though its incidence is low. The three chief clinical manifestations include respiratory insufficiency, cerebral involvement, and petechial rash. Although FES is a multisystem disorder, the most seriously affected organs are the lungs, brain, cardiavascular system, and skin. Many laboratory findings are characteristic but nonspecific. The pathogenesis of FES after liposuction has been looked at both mechanically and biochemically. Diagnosis is difficult; Gurd and Wilson's diagnostic criteria based on clinical examination is still extensively used in clinics at present. There is no specific therapy for FES after liposuction for the moment, so prevention, early diagnosis, and supportive therapies are important. In this article we discuss the clinical presentation, pathogensis, and current methods to prevent FES and, if possible, ways to treat this complication.

Experimental pulmonary fat embolism: computed tomography and pathologic findings of the sequential changes

This study was done to demonstrate the computed tomography (CT) and pathologic findings of the sequential changes for experimental pulmonary fat embolism (PFE), and to correlate the CT and pathologic findings of rabbit lung. PFE was induced by an intravenous injection of 0.2 mL linoleic acid in 24 rabbits. The rabbits were divided into 4 groups of 6 rabbits each. CT scans were obtained sequentially at 2 hr (n= 24), day 1 (n=18), day 3 (n=12) and day 7 (n=6) after fat embolization. The pathologic findings were analyzed and CT-pathologic correlation was done. CT scans showed bilateral ground-glass opacity (GGO), consolidation and nodule in all cases. The findings of PFE at 2 hr after fat embolization were areas of decreased attenuation, GGO, consolidation and nodule. These findings were aggravated on the follow- up CT after 1 day and 3 days. The follow-up CT revealed linear density in the subpleural lungs after 7 days. On CT-pathology correlation, wedge-shaped ischemic necrosis in the subpleural lungs correlated with nodule at 2 hr. GGO and consolidation at day 1 on CT correlated with congestion and edema, and these findings at day 3 were correlated with inflammation and hemorrhagic edema. The linear density in the subpleural lungs correlated with interstitial fibrosis and pleural contraction at day 7. In conclusion, PFE was caused by using linoleic acid which is kind of free fatty acid and this study served as one model of the occurrence of nontraumatic PFE. CT accurately depicted the natural evolution of PFE in the serial followup, and this correlated well with the pathologic findings.

Hypertonic saline reduces inflammation and enhances the resolution of oleic acid induced acute lung injury

Background

Hypertonic saline (HTS) reduces the severity of lung injury in ischemia-reperfusion, endotoxin-induced and ventilation-induced lung injury. However, the potential for HTS to modulate the resolution of lung injury is not known. We investigated the potential for hypertonic saline to modulate the evolution and resolution of oleic acid induced lung injury.

Methods

Adult male Sprague Dawley rats were used in all experiments. Series 1 examined the potential for HTS to reduce the severity of evolving oleic acid (OA) induced acute lung injury. Following intravenous OA administration, animals were randomized to receive isotonic (Control, n = 12) or hypertonic saline (HTS, n = 12), and the extent of lung injury assessed after 6 hours. Series 2 examined the potential for HTS to enhance the resolution of oleic acid (OA) induced acute lung injury. Following intravenous OA administration, animals were randomized to receive isotonic (Control, n = 6) or hypertonic saline (HTS, n = 6), and the extent of lung injury assessed after 6 hours.

Results

In Series I, HTS significantly reduced bronchoalveolar lavage (BAL) neutrophil count compared to Control [61.5 ± 9.08 versus 102.6 ± 11.89 × 10³ cells.ml^-1]. However, there were no between group differences with regard to: A-a O2 gradient [11.9 ± 0.5 vs. 12.0 ± 0.5 KPa]; arterial PO2; static lung compliance, or histologic injury. In contrast, in Series 2, hypertonic saline significantly reduced histologic injury and reduced BAL neutrophil count [24.5 ± 5.9 versus 46.8 ± 4.4 × 10³ cells.ml^-1], and interleukin-6 levels [681.9 ± 190.4 versus 1365.7 ± 246.8 pg.ml^-1].

Conclusion

These findings demonstrate, for the first time, the potential for HTS to reduce pulmonary inflammation and enhance the resolution of oleic acid induced lung injury.

Perfusion characteristics of oleic acid--injured canine lung on Gd-DTPA--enhanced dynamic magnetic resonance imaging

RATIONALE AND OBJECTIVES

We conducted an animal study to describe and interpret the perfusion characteristics of oleic acid (OA)-injured lungs on gadopentetate dimeglumine (Gd-DTPA)-enhanced dynamic perfusion magnetic resonance (MR) imaging.

METHODS

Fourteen dogs received an intravenous OA infusion in the supine (n = 4), prone (n = 4), and right lateral decubitus (n = 6) positions, and 10 minutes later these animals in the same postures underwent the dynamic MR study. Regional Gd-DTPA kinetics was analyzed by the time-signal intensity (SI) curves and by qualitative functional map images of the mean transit time that was representative of the mean circulation time in the vascular bed and the average cumulative sum of the relative increases in SI representative of Gd-DTPA distribution volume during Gd-DTPA first pass. The results were compared with those in six control animals and in another six animals that underwent the MR study 3 minutes (n = 3) and 60 minutes (n = 3) after OA infusion. The MR findings were correlated with the distribution of lung damage and the infused OA particles as assessed by histology.

RESULTS

The dynamic MR study showed postural shifts on the gravity-dependent perfusion map of normal lungs. Contrast enhancement during Gd-DTPA first pass in the lung was lower and more heterogeneous in the OA-injured lung models than in controls but was followed by conversely greater and persistent enhancement during the Gd-DTPA redistribution phase. Regardless of the postures for OA infusion, these abnormalities were predominant in the dependent lungs and became more pronounced with time after OA infusion, where more prominent capillary obstruction with OA droplets and alveolar/interstitial edema were histologically observed. On the functional map images, greater mean transit time and the average cumulative sum of the relative increases in SI values were also predominantly distributed in the dependent lungs.

CONCLUSIONS

Low and heterogeneous enhancement was observed during Gd-DTPA first pass but was followed by persistent enhancement during the Gd-DTPA redistribution phase, and predominant abnormalities in the dependent lungs may be characteristic features of the perfusion of OA-injured lungs. The histological correlations indicate that these abnormalities may reflect OA-induced pathophysiologies associated with capillary OA obstruction, increased vascular resistance, and capillary permeability/extravascular spaces and that lung damage may be gravity dependent.

Fat embolism

Fat embolism syndrome is a collection of respiratory, haematological, neurological and cutaneous symptoms and signs associated with trauma and other disparate surgical and medical conditions. The incidence of the clinical syndrome is low (< 1% in retrospective reviews) whilst the embolisation of marrow fat appears to be an almost inevitable consequence of long bone fractures. There is debate over the pathogenesis of fat embolism syndrome and it seems a variety of factors interact to produce a spectrum of end organ damage. Many therapeutic interventions and prophylactic strategies have been tried with varying success. Current treatments are supportive and the condition is usually associated with a good outcome. The literature on fat embolism syndrome is extensive and this review aims to discuss the incidence, aetiology, pathophysiology, diagnosis and treatment of fat embolism.

Fat embolism syndrome

Since it was initially described, fat embolism syndrome (FES) has remained one of the least clearly understood complications of trauma. This article is a review of the classic and current literature on FES with regard to its causes, pathophysiology, clinical presentation, diagnosis, and treatment. FES is associated with many traumatic and nontraumatic conditions, but is most commonly associated with fractures of long bones of the lower extremity. The pathophysiology is thought to be a cascade of events which can lead to adult respiratory distress syndrome (ARDS). Signs and symptoms of clinical FES usually begin within 24 to 48 hours after trauma. The classic triad involves pulmonary changes, cerebral dysfunction, and petechial rash. Clinical diagnosis is key because laboratory and roentgenographic diagnosis is not specific. Treatment consists of careful initial handling, early stabilization of fractures, careful volume replacement, analgesia, respiratory support, and perhaps steroids. The vast majority of patients today survive FES without sequelae.

Effect of regional alveolar hypoxia on gas exchange in pulmonary edema

We studied the effects of left lower lobe (LLL) alveolar hypoxia on ventilation-perfusion (VA/Q) heterogeneity in anesthetized dogs with acute (1-h-old) and mature (24-h-old) permeability pulmonary edema, induced by intravenous administration of 0.05 ml/kg of oleic acid. The left upper lobe was removed and a bronchial divider was placed to allow separate ventilation of the right lung (fraction of inspired oxygen [FIO2] = 1.0) and the LLL (FIO2 = 1.0 or 0.05). Gas exchange was assessed using the multiple inert gas elimination technique. In acute pulmonary edema, LLL hypoxia reduced LLL blood flow and increased true shunt of the LLL compared with a hyperoxic control group. VA/Q heterogeneity of the LLL was markedly increased, indicated by increases in the logarithmic standard deviation of the perfusion distribution (log SDQ) and the retention index of dispersion corrected for shunt (DISPR*). Increases in true shunt and log SDQ were significantly greater than those observed with lobar hypoxia in normal lungs before oleic acid injury. In mature oleic acid injury, LLL alveolar hypoxia resulted in a similar reduction in LLL blood flow and increase in inert gas shunt and DISPR*. We conclude that lobar alveolar hypoxia increased VA/Q heterogeneity of the hypoxic lobe to a greater degree in oleic acid-induced pulmonary edema compared with normal lungs. Phase of oleic acid injury (acute versus mature) did not affect gas exchange during alveolar hypoxia.

Effect of free fatty acid on pulmonary transvascular fluid and protein exchange

We demonstrated the effect of infusion of oleic acid, a common free fatty acid, on pulmonary vascular permeability in anesthetized dogs prepared with a lung lymph fistula. Infusion of oleic acid caused significant increases in lung lymph flow with no change in L/P protein ratio, resulting in significant increases in transvascular protein clearance. Pulmonary arterial and pulmonary arterial wedge pressures increased significantly from baseline but their elevation was slight. Cardiac output decreased significantly after oleic acid infusion. In contrast to the effects of oleic acid, left arterial hypertension caused increases in lung lymph flow that were associated with decreases in the L/P protein ratio. Lung water content was increased after oleic acid infusion, despite little effect on pulmonary vascular pressures. These findings indicate that oleic acid produced endothelial lung injury and increased pulmonary vascular permeability.

Cardiopulmonary dynamics during arteriovenous perfusion: cardiac output, pulmonary arterial resistance, and right venticular stroke work

The effects of arteriovenous perfusion on myocardial performance, pulmonary circulatory dynamics, and organ preservation were studied in dogs in order to evaluate the applicability of arteriovenous extracorporeal membrane oxygenation for partial respiratory support. Studies were made on normally oxygenated dogs, on dogs made hypoxic by oxygen deprivation and ventilatory depression, and on dogs with pulmonary injury and moderate pulmonary hypertension induced by injection of oleic acid into the right ventricle. The latter two groups were included to assess the changes that occur in cardiopulmonary dynamics in the presence of hypoxia and pulmonary hypertension. A microchannel membrane oxygenator was employed to provide partial respiratory support to the group of animals with pulmonary injury. The results indicate that no deleterious hemodynamic changes occurred in any of the groups of animals with arteriovenous flow for periods of up to 5 hours at rates corresponding to 20 to 35% of the total cardiac output. Adequate systemic oxygenation was provided by the microchannel oxygenator at these rates of arteriovenous perfusion.

Effects of methylprednisolone on experimental pulmonary injury

We studied the effects of methylprednisolone on pulmonary function of unanesthetized dogs with oleic acid induced pulmonary edema observed over a four day period. Methylprednisolone (30 mg/kg) was administered to 11 dogs three and 24 hours after pulmonary injury. Eleven animals were untreated after pulmonary injury and served as controls. There was no difference between the two groups until 72 hours after injury, when the venous admixture of the steroid treated animals was 11 +/- 3% (SD) compared to 22 +/- 8% (p less than 0.001) in the untreated with respective PaO2 values of 76 +/- 6 torr and 64 +/- 8 torr (p less than 0.001). Light microscopic examination of the lungs 96 hours after injury revealed a marked proliferation of Type II pneumocytes in the methylprednisolone treated animals. We conclude that, in the oleic acid or fat embolism model of pulmonary injury, methylprednisolone significantly increases resolution of the pulmonary injury presumably by stimulation of active proliferation and maturation of Type II pneumocytes.

Fat embolism syndrome: a puzzling phenomenon

Fat emboli are a life-threatening source of respiratory insufficiency. Whether they are of mechanical or chemical origin remains a subject of controversy. Fat embolism syndrome is most often seen after fracture of long bones, and immobilization of the fracture site may decrease risk of its development. Adequate oxygenation is the most important aspect of therapy; most patients given vigorous supportive treatment recover with no residual lung injury.

Cardiac and pulmonary fat embolectomy for suspected fat embolus

Nelson, C. S. (1974).Thorax, 29, 134-137. Cardiac and pulmonary fat embolectomy for suspected fat embolus. There is no specific treatment of fat embolism, whether the embolism is predominantly cerebral, pulmonary, renal or mesenteric.

A 46-year-old man had fractured his right femur for the third time in December 1971. Seventy hours later he suddenly developed the cardiovascular, respiratory, and cerebral manifestations of post-traumatic fat embolism. His chest radiograph at the onset of symptoms was consistent with fat embolism. He underwent cardiac and pulmonary embolectomy on 7 December 1971 and made a most dramatic recovery. His haemobronchorrhoea, dyspnoea, tachypnoea, hyperpyrexia, and profound shock disappeared at the end of the operation. His only postoperative cerebral disturbance was mild disorientation.

The pathophysiological changes accompanying fat embolism are due to toxic vasculitis and fat macroglobule aggregations blockading the pulmonary arterioles and capillaries. The blockading concept is the basis for cardiac and pulmonary fat embolectomy. Only a larger series embodying a multicentre trial will show whether or not cardiopulmonary fat embolectomy is a specific treatment of massive fat embolism.

The purpose of this paper is to report on the technique and result of embolectomy for a suspected fat embolus following fracture of the femur.