Intravascular Fat Research Articles

The extracranial venous system in the heads of beaked whales, with implications on diving physiology and pathogenesis

Beaked whales are a poorly known but diverse group of whales that have received considerable attention due to strandings that have been temporally and spatially associated with naval sonar deployment. Postmortem studies on stranded carcasses have revealed lesions consistent with decompression sickness, including intravascular gas and fat emboli. These findings have been supported by analyses of intravascular gas emboli showing composition dominated by nitrogen gas. To increase our understanding of the pathophysiology of nitrogen bubble formation and intravascular embolization, we examined the gross and microscopic anatomy of the venous system in the head of beaked whales. Since the potential sources of intravascular fat and gas emboli were of greatest interest, focus was placed on the acoustic fat bodies and pneumatic accessory sinus system. Herein, we describe intimate arteriovenous associations with specialized adipose depots and air sinuses in beaked whales. These vascular structures comprise an extensive network of thin-walled vessels with a large surface area, which is likely to facilitate exchange of nitrogen gas and may, therefore, form anatomic regions that may be important in physiological management of diving gases. These structures may also be vulnerable to pathologic introduction of emboli into the vascular system. Expansive, thin-walled venous lakes are found within the pterygoid region, which suggest the potential for nitrogen exchange as well as for compensation of middle-ear pressures during descent on a dive. These findings warrant further research into the structure and function of this morphology as it relates to normal and pathologic physiology.

Fat Embolism and Severe Natural Disease: Challenges for Certification

Detectable intravascular fat has been reported in up to 90% of patients with long bone fractures. However, the more clinically significant fat embolism syndrome (FES) is less common. Despite its common occurrence, determining the significance of fat embolism as a cause of death remains controversial; however, helpful objective criteria through a tiered approach have recently been proposed. Patients with coexisting natural disease and fat embolism present an additional challenge for interpretation. We present an illustrative 59-year-old woman with severe comorbidities who died 11 days following a femoral neck fracture and discuss how the use of special techniques to demonstrate embolic fat and published guidelines for diagnosis were helpful in death certification. The case also provides a beautiful morphologic illustration of the accumulation of lipid laden alveolar macrophages as intravascular fat is absorbed into the tissues over time. Such macrophages can also be clinically detected by bronchoalveolar lavage, which can provide some objective support for a clinically suspected diagnosis of fat embolism.

Stroke Subtypes and their Possible Implication in Stroke Prevention Drug Strategies

Thrombotic strokes can affect large or small arteries in the brain. Drugs to prevent atherosclerosis complication such as thrombotic strokes, should be drugs able to prevent the accumulation of intravascular fat, reduce vascular proliferation, decrease blood pressure levels with the resulting shear stress, reduce platelet aggregation, and possibly partially or totally reverse carotid plaques. Any of the commonly used antihypertensive drugs lower the incidence of stroke, with larger reductions in BP resulting in larger reductions in risk. Experimental and clinical data suggest that reducing the activity of the renin-angiotensin aldosterone system (RAAS) may have beneficial effects beyond the lowering of blood pressure to reduce stroke incidence. In clinical trials, statins consistently reduced the risk of ischemic stroke in patients with or without CHD whereas the data on the effects of other lipid modifying drugs on stroke risk are limited. Approximately 25% of strokes are recurrent. Antiplatelet therapy is indicated for the prevention of recurrent stroke in patients with a history of noncardioembolic minor stroke or transient ischemic attack (TIA). Although clinicians may choose acetylsalicylic acid (ASA) as first-line therapy for secondary prevention, clinical guidelines and evidence from trials suggest that ASA may not be the most effective strategy. A recent review discussed results from clinical trials that have compared the efficacy of ASA monotherapy versus ASA + extended release dipyridamole in secondary stroke prevention. Therefore it is difficult to extrapolate the real benefit of pharmacological prevention strategies against atherothrombotic subtype for excellence in the TOAST classification subtype that is represented by the LAAS and also with regard to lacunar subtype as an expression of lipohyalinosis process which is a further aspect of atherosclerosis.

Employment of Needles

Sir:FigureAutologous fat grafting has become a well-established and frequently applied method for soft-tissue regeneration and augmentation with both cosmetic and reconstructive indications. Nowadays, capabilities of this surgical procedure to improve the tissue quality are well known.1–5 In the past 20 years, although many different techniques have been developed, a standard procedure has not been chosen. Variables include harvesting technique, centrifugation, and injection technique. In our opinion, injection technique is a possible factor that has biological effects on adipose tissue. In our experience, blunt cannulas are not the perfect instruments needed to reach our target, which is the ability to perform a quick, safe, and painless procedure. Our choice for the reinjection of transplanted fat is an 18-gauge angiographic sharp needle (Cordis Corp., Bridgewater, N.J.) and the Seldinger technique. This choice has matured as a result of our first experiences in the use of autologous fat grafting; indeed, we started to treat burn scars, whose damaged tissues were characterized by a high level of fibrosis that conditioned a significant resistance to the sliding of the devices used for fat injection. From 2005 until now, we have performed more than 1000 procedures to treat not only burn scars, but also surgical scars, hard-to-heal wounds, and radiodystrophic tissues, all cases with a common feature: the presence of overflowing fibrous tissue. During our experience, we noted that the sharp angiographic cannulas, compared with the blunt ones, allow us to achieve better results. We are able to perform a highly precise technique; angiographic cannulas allow us to easily overcome tissue resistance related to the presence of fibrous tissue, thus making it possible to lay a constant amount of fat at the dermal-hypodermal junction. The lysis of scar tissue is obtained by moving the needle through two different methods by which fat is released: the first one consists of pushing the plunger of the syringe and leveraging the strength of exiting fat to overcome the fibrous tissue resistance or, otherwise, we can use a retrograde technique that is performed entering the needle for its entire length at the dermal-epidermal junction and then, while extracting the needle, releasing fat. Moreover, we suppose that a sharp cannula stimulates new collagen deposition and remodeling of fibrous tissues, similar to a “needling” procedure used in aesthetic medicine. Using sharp cannulas, we do not need to perform skin incisions with a scalpel for cannula access, and this minimizes patient discomfort related to the surgical procedure and avoids causing new scars. Another worthy consideration is that 18-gauge angiographic sharp needles for the Seldinger technique are disposable, low-cost devices, adding an additional favorable point in comparison with classic blunt cannulas. The main risks are related to the risk of intravascular fat injection, which can be easily avoided by choosing the retrograde injection method (as described above). Furthermore, in our clinical experience using angiographic needles, we found that edema and bleeding of treated areas have been comparable to those of the standard technique, which are virtually nil. We think that sharp cannulas are the best option for autologous fat grafting, considering the versatility and the excellent results obtained. Fabio Caviggioli, M.D. Università degli Studi di Milano, MultiMedica Holding S.p.A., U.O.C. Chirurgia Plastica, Sesto San Giovanni, Milan, Italy Davide Forcellini, M.D. Università degli Studi di Milano, IRCCS Istituto Clinico Humanitas, U.O. Chirurgia Plastica 2, Rozzano, Milan, Italy Valeriano Vinci, M.D. Università degli Studi di Milano, MultiMedica Holding S.p.A., U.O.C. Chirurgia Plastica, Sesto San Giovanni, Milan, Italy Guido Cornegliani, M.D. Università degli Studi di Milano, IRCCS Istituto Clinico Humanitas, U.O. Chirurgia Plastica 2, Rozzano, Milan, Italy Francesco Klinger, M.D. Università degli Studi di Milano, MultiMedica Holding S.p.A., U.O.C. Chirurgia Plastica, Sesto San Giovanni, Milan, Italy Marco Klinger, M.D. Università degli Studi di Milano, IRCCS Istituto Clinico Humanitas, U.O. Chirurgia Plastica 2, Rozzano, Milan, Italy DISCLOSURE The authors have no financial interest to declare in relation to the content of this article. No outside funding was received.

Osmium impregnation detection of pulmonary intravascular fat in sudden death: A study of 65 cases

Pulmonary fat embolism is widely recognised in forensic pathology. Pulmonary fat embolism requires mobilisation of free fat, entry of free fat into the circulation and lodging of fat globules in fine venous capillaries. This paradigm of fat embolisation has been used to support the evidence of antemortem fat depot disruption when the presence of intravascular fat is confirmed at autopsy. However, sporadic reports of intravascular fat in various medical conditions, which contradict the above mechanism, have opened questions about the alternative pathogenesis. In this study, 65 cases of sudden deaths were examined for the presence of pulmonary intravascular fat (PIF) by osmium impregnation. Cases were selected based on the criteria that were designed to eliminate the possible confounding effect from medical intervention or postmortem changes. Slides were graded based on their ease of search and only the fat droplets confined by the blood vessel or capillary wall were considered as a positive finding. The results show surprisingly high PIF incidences of varying degrees in all the categories of sudden deaths. Further study is needed to devise criteria for diagnosis of fatal fat embolism since the histological appearance of the high-grade PIF in natural sudden death may not be easily distinguishable from the traumatic fat embolism.

Pathophysiology of Fat Embolism: A Rabbit Model

The objective of this study was to assess the effects of fat embolism on rabbit physiology. After anesthetic administration, both femoral condyles of the right knee only of 23 New Zealand white rabbits were exposed through a medial parapatellar approach to the knee. In the pulmonary fat embolism group (n = 15), the femoral canal was drilled in a retrograde fashion and then reamed and pressurized with a 1- to 1.5-mL cement injection. In the no-pressurization group (n = 4), after reaming, no cement was injected. In the control group (n = 4), the knee incision was immediately closed. Animals were then observed for 5 hours. Hemodynamics and blood gases were recorded at standard intervals. Postmortem, the lungs were removed en bloc and fixed for histologic assessment and quantitative histomorphometry. Four intraoperative deaths occurred in the pulmonary fat embolism group immediately after pressurization and may have been associated with hypotension and cardiac arrest. In the pulmonary fat embolism group, pulmonary artery pressure increased, and both mean arterial pressure and PaO2 decreased after pressurization. Approximately 2% of lung volume was occupied by intravascular fat and there were no signs of perivascular inflammation. Control and no-pressurization animals remained stable throughout the experiment. This model simulates pulmonary fat embolism after long-bone fractures. Despite cardiorespiratory dysfunction, there was no evidence of fat initiating pulmonary inflammation based on histologic data within the timeframe of the investigation.

Cardiovascular changes after PMMA vertebroplasty in sheep: the effect of bone marrow removal using pulsed jet-lavage

Clinically, the displacement of intravertebral fat into the circulation during vertebroplasty is reported to lead to problems in elderly patients and can represent a serious complication, especially when multiple levels have to be treated. An in vitro study has shown the feasibility of removing intravertebral fat by pulsed jet-lavage prior to vertebroplasty, potentially reducing the embolization of bone marrow fat from the vertebral bodies and alleviating the cardiovascular changes elicited by pulmonary fat embolism. In this in vivo study, percutaneous vertebroplasty using polymethylmethacrylate (PMMA) was performed in three lumbar vertebrae of 11 sheep. In six sheep (lavage group), pulsed jet-lavage was performed prior to injection of PMMA compared to the control group of five sheep receiving only PMMA vertebroplasty. Invasive recording of blood pressures was performed continuously until 60 min after the last injection. Cardiac output and arterial blood gas parameters were measured at selected time points. Post mortem, the injected cement volume was measured using CT and lung biopsies were processed for assessment of intravascular fat. Pulsed jet-lavage was feasible in the in vivo setting. In the control group, the injection of PMMA resulted in pulmonary fat embolism and a sudden and significant increase in mean pulmonary arterial pressure. Pulsed jet-lavage prevented any cardiovascular changes and significantly reduced the severity of bone marrow fat embolization. Even though significantly more cement had been injected into the lavaged vertebral bodies, significantly fewer intravascular fat emboli were identified in the lung tissue. Pulsed jet-lavage prevented the cardiovascular complications after PMMA vertebroplasty in sheep and alleviated the severity of pulmonary fat embolism.

Histopathological and biochemical changes following fat embolism with administration of corn oil micelles

Several experimental models have been used to produce intravascular fat embolism. We have developed a simple technique to induce fat embolism using corn oil emulsified with distilled water to form fatty micelles. Fat embolism was produced by intravenous administration of these fatty micelles in anaesthetised rats, causing alveolar oedema, haemorrhage and increased lung weight. Histopathological examination revealed fatty droplets and fibrin thrombi in the lung, kidney and brain. The arteriolar lumen was filled with fatty deposits. Following fat embolism, hypoxia and hypercapnia occurred. The plasma phospholipase A(2), nitrate/nitrite, methylguidanidine and proinflammatory cytokines were significantly increased. Mass spectrometry showed that the main ingredient of corn oil was oleic acid. This simple technique may be applied as a new animal model for the investigation of the mechanisms involved in the fat embolism syndrome.

Influence of Bone Marrow Fat Embolism on Coagulation Activation in an Ovine Model of Vertebroplasty

Intraoperative cardiovascular deterioration as a result of pulmonary embolization of bone marrow fat is a potentially serious complication during vertebroplasty. The release of fatty material and thromboplastin from the bone marrow cavity during vertebroplasty may activate the coagulation cascade resulting in thrombogenesis, and pharmacological prophylaxis may therefore prevent cardiovascular complications. Thus, the effects of bone marrow fat embolism on coagulation activation during vertebroplasty were investigated with use of an animal model. Polymethylmethacrylate was injected into three lumbar vertebrae of six sheep in order to force bone marrow fat into the circulation. Invasive blood pressures and heart rate were recorded continuously until sixty minutes after the last injection. Cardiac output, arterial and mixed venous blood gas parameters, and coagulation parameters were measured at selected time-points. Postmortem lung biopsy specimens were assessed for the presence of intravascular fat. Embolization of bone marrow fat resulted in a sudden and dramatic increase in mean pulmonary arterial pressure and a decrease in mean arterial blood pressure. There were no significant changes in any coagulation parameter from before the injection to after the injection. Intravascular fat and bone marrow cells were present in all lung lobes. Injection of polymethylmethacrylate into vertebral bodies caused embolization of bone marrow fat with subsequent transient cardiovascular deterioration, but no changes in coagulation parameters were observed. Thromboembolism did not contribute to the observed cardiovascular changes.

Plasma levels of endothelin‐1 after a pulmonary embolism of bone marrow fat

During orthopedic surgery, embolization of bone marrow fat can lead to potentially fatal, intra-operative cardiovascular deterioration. Vasoactive mediators may also be released from the bone marrow and contribute to these changes. Increased plasma levels of endothelin-1 (ET-1) have been observed after pulmonary air and thrombo-embolism. The role of ET-1 in the development of acute cardiovascular deterioration as a result of bone marrow fat embolization during vertebroplasty was therefore investigated. Bone cement was injected into three lumbar vertebrae of six sheep in order to force bone marrow fat into the circulation. Invasive blood pressures and heart rate were recorded continuously until 60 min after the last injection. Cardiac output, arterial and mixed venous blood gas parameters and plasma ET-1 concentrations were measured at selected time points. Post-mortem, lung biopsies were taken for analysis of intravascular fat. Cement injections resulted in a sudden (within 1 min) and severe increase in pulmonary arterial pressure (>100%). Plasma concentrations of ET-1 started to increase after the second injection, but no significant changes were observed. Intravascular fat and bone marrow cells were present in all lung lobes. Cement injections into vertebral bodies elicited fat embolism resulting in subsequent cardiovascular changes that were characterized by an increase in pulmonary arterial pressure. Cardiovascular complications as a result of bone marrow fat embolism should thus be considered in patients undergoing vertebroplasty. No significant changes in ET-1 plasma values were observed. Thus, ET-1 did not contribute to the acute cardiovascular changes after fat embolism.

Sildenafil Prevents Cardiovascular Changes after Bone Marrow Fat Embolization in Sheep

Sudden, intraoperative cardiovascular deterioration as a result of pulmonary embolization of bone marrow fat is a potentially fatal complication during total hip and knee arthroplasty, intramedullary nailing, and spine surgery. Anesthetic management is challenging in the presence of increased right ventricular afterload due to pulmonary hypertension. Selective pulmonary vasodilation may be an appropriate prophylactic or therapeutic measure. The effect of sildenafil (phosphodiesterase inhibitor) on cardiovascular deterioration after bone marrow fat embolization was therefore investigated. Bone cement (polymethylmethacrylate) was injected into three lumbar vertebrae in 12 sheep. Invasive blood pressures and heart rate were recorded continuously until 60 min after the last injection. Cardiac output and arterial and mixed venous blood gas variables were measured at selected time points. Before the first cement injection, 6 animals received a bolus injection (0.7 mg/kg) of sildenafil, with continuous infusion (0.2 mg . kg . h) thereafter. Postmortem lung and kidney biopsies were taken for semiquantitative analysis of intravascular fat. Fat embolism was associated with a transient increase (21 +/- 7mmHg) in pulmonary arterial pressure. A transient decrease in arterial blood pressure and temporary increases in central venous pressure and dead space were also observed. No significant changes in any cardiovascular variable were observed after fat embolism in the sildenafil group. There was significantly (P < 0.05) less intravascular fat in the lungs of the sildenafil (median count of 5 emboli per microscopic view) compared with the control group (median count of 1). Administration of sildenafil prevented the acute cardiovascular complications after bone marrow fat embolism in sheep.

Assessment of the Risk of Systemic Fat Mobilization and Fat Embolism as a Consequence of Liposuction: Ex Vivo Study

Adverse consequences of liposuction, including those associated with fat embolism, have been reported in the literature. Fat embolism syndrome after liposuction may be underestimated because of the unspecific nature of the symptoms. The aim of this study was to determine whether there is a generic risk of the generation of intravascular fat emboli as a consequence of liposuction. An animal study was conducted in which liposuction was performed on 10 Sprague-Dawley rats. The procedure was conducted with the animals under general anesthesia for 60 minutes, in a similar manner to that practiced clinically. Three blood samples were taken from each animal through a central line (one before liposuction and two at 30 and 60 minutes into liposuction) and examined for the presence of fat particles. The animals were then euthanized and the lungs and brain were removed for histological examination. In the control group, liposuction was not performed, but similar blood and histological samples were taken. In the study group, stained fat particles were seen in all blood samples taken during liposuction but not in those taken before liposuction. The difference between the 30- and 60-minute samples and the preliposuction control ones was statistically significant (p < 0.001 minimum). The differences between the 30-minute and 60-minute samples were also statistically significant (p = 0.017), demonstrating that fat mobilization during liposuction is a cumulative process. Nothing of significance was seen in the blood samples of the control group. Lipid deposits were seen in the lungs of all study group animals but not in the control group. With one possible exception, no lipid deposits were confirmed in brain specimens. The authors' experiments have demonstrated a significant risk of systemic fat mobilization and fat embolism after liposuction in the animal model. Further clinical investigation is required to evaluate the real clinical risk of this procedure from this perspective.

Parenteral lipids and the preterm infant: between Scylla and Charybdis

Intravenous lipid infusions are a valid option for a dense source of energy and essential fatty acids when the enteral route is unavailable. However, the use of these preparations in neonatal patients has been associated with metabolic concerns such as oxidative stress, and complications such as abnormal vascular tone, intravascular fat deposition and even fat embolism. Metabolic issues related to nutrient accretion and noxious biological reactions should be considered when prescribing parenteral lipids with high PUFA content to the critically ill newborn infant.

Cardiovascular Changes During Multiple Vertebroplasty With and Without Vent-Hole

An experimental study of cardiovascular complications arising during vertebroplasty (VP) of multiple levels. To investigate the cardiovascular changes during multiple VP and whether a vent-hole has a preventive effect. An experimental study and clinical reports showed that fat embolism (FE) and acute hypotension occur during VP. There is the concern that these complications may worsen during VP of multiple levels. Vent-holes may prevent FE during VP. In twenty-two sheep, four vertebral bodies were augmented with polymethylmethacrylate (PMMA). In ten sheep, a vent-hole was drilled into the pedicle contralateral to the injection site. Heart rate, arterial, central venous and pulmonary artery pressure, cardiac output and blood gas values were recorded. The lungs were subjected to histologic evaluation at postmortem. The consecutive augmentation of four vertebral bodies with PMMA induced a cumulative FE that gradually deteriorated baseline mean arterial blood pressure (MABP) and blood gas values. The deterioration of MABP and change in blood gas values were attenuated, when a vent-hole was drilled. The amount of intravascular fat in the lungs after multiple VP (19%) was reduced when a vent-hole was drilled (9%). Surgeons should be aware of the potential cardiovascular complications during VP of multiple levels. In the clinical setting, a needle in the contralateral pedicle could be used to decompress the vertebral body during the injection of bone cement.

Pressurization of Vertebral Bodies During Vertebroplasty Causes Cardiovascular Complications

An experimental study of cardiovascular complications arising during vertebroplasty (VP) of multiple levels in sheep. To investigate the effect of pressurizing vertebral bodies during VP using different materials in the development of fat embolism (FE) and any associated cardiovascular changes. Polymethylmethacrylate (PMMA) is the material of choice for VP. However, PMMA has several disadvantages, such as toxicity, exothermic curing, uncertain long-term biomechanical effects, and biocompatibility. Alternative materials are being developed for VP; however, there is the concern that an increase in intraosseous pressure and displacement of bone marrow contents could lead to FE and hypotension during VP regardless of what type of materials is used. In 20 sheep, four vertebral bodies were augmented either with PMMA or bone wax. Heart rate; arterial, central venous, and pulmonary artery pressure; cardiac output; and blood gas values were recorded. Postmortem the lungs were subjected to histologic evaluation. The consecutive augmentation of four vertebral bodies with PMMA induced a cumulative FE that gradually deteriorated baseline mean arterial blood pressure (MABP) and blood gas values. The augmentation with bone wax resulted in similar cardiovascular changes and amount of intravascular fat in the lungs. There are potential cardiovascular complications during VP of multiple levels regardless of the augmentation material used. The deteriorating baseline MABP during VP is associated with the pressurization of the vertebral bodies rather than with the use of polymethylmethacrylate.

Fat embolism and acute hypotension during vertebroplasty: an experimental study in sheep.

An experimental study of cardiovascular complications that arise during vertebroplasty was conducted. To investigate the sequential occurrence of fat embolism and hypotension during vertebroplasty. Vertebroplasty, the augmentation of vertebrae with polymethylmethacrylate, is a technique for treating osteoporotic compression fractures and achieving prophylactic stabilization of osteoporotic vertebral bodies at risk of fracture. However, there is concern that fat embolism and acute hypotension could occur as in a variety of other orthopedic procedures. In six sheep, 6 mL of polymethylmethacrylate was injected unilaterally into L1. Transesophageal echocardiography monitored the pulmonary artery for echodense particles. Heart rate, arterial and venous pressures, and blood gas values were recorded before and for 25 minutes after injection. The lungs were subjected to postmortem histologic evaluation and compared with lung specimens from two sheep that had not undergone vertebroplasty. Injection of cement elicited a very rapid decrease in heart rate (within 2 +/- 1 seconds) and a rapid increase in venous pressure (within 3 +/- 1 seconds), which was followed by a fall in arterial pressure (within 5 +/- 2 seconds) (phase 1). Thereafter, showers of echogenic material appeared (within 6 +/- 1 seconds) and lasted for 138 +/- 36 seconds. A second more severe fall in arterial pressure was observed beginning at 18 +/- 2 seconds (phase 2). The injection resulted in an increase in partial pressure of carbon dioxide and a decrease in pH. The histology showed intravascular fat globules and bone marrow cells in lung tissue. The results suggest that immediately after cement injection, there was a reflex fall in heart rate and arterial pressure. The second fall in arterial pressure was a consequence of fat emboli passing through the heart and getting trapped in the lungs.

Alcoholism, hypercortisonism, fat embolism and osseous avascular necrosis. 1971.

Alcoholism, hypercortisonism, fat embolism and osseous avascular necrosis. 1971.

Prolonged Coma after Unreamed, Locked Nailing of Femoral Shaft Fracture

USING transesophageal echocardiography, echogenic material can be shown in the right ventricle during many orthopedic procedures. 1 Recently, transcranial Doppler-recorded microembolic signals have been described during femoral fracture fixation, suggesting that medullary pressurization may be associated with systemic microembolism and pulmonary fat and marrow emboli. 2 Although reamed, locked intramedullary nailing is the procedure of choice for most femoral shaft fractures, some investigators advocate the use of small-diameter, locking, unreamed nails to decrease the risk of fat emboli. 3,4 We report a case of severe intraoperative fat embolism after an unreamed locked intramedullary nailing.

Pulmonary and systemic fat embolization after medullary canal pressurization: a hemodynamic and histologic investigation in the dog.

The potential to produce fat embolism may be important in determining the ideal method and timing of fracture treatment in patients with preexisting lung injury. Four dogs underwent femoral and tibial canal reaming and pressurization. Blood gas samples were analyzed, and pulmonary arterial pressure was monitored at 1 and 72 hours. Animals were killed 72 hours postoperatively, and the lungs, kidneys, and brain were examined histologically and compared with equivalent specimens from four control dogs that had not undergone femoral and tibial canal reaming and pressurization. Postmortem, intravascular fat persisted for 72 hours after induction of pulmonary fat embolism. Mean PaO2 was unchanged from baseline at 72 hours after canal pressurization. Canal pressurization caused a sustained increase in pulmonary arterial pressure (p=0.02) for 1 hour after canal pressurization. The mean pulmonary edema score at 72 hours was 29+/-3. Only a scant polymorph infiltrate (zero to two polymorphs per high-power field) was present at any time. No hyaline membranes were seen at any time. The percentage area occupied by intravascular fat in the lungs was 0.0214+/-0.0058 at 72 hours. No signs of ischemia or inflammation were seen in either the cerebral or the renal specimens. This study is the first to show that intravascular fat persists in the lungs, kidneys, and brain for 72 hours after canal pressurization and, by itself, does not cause pathologic evidence of acute inflammation.

Relationship of fat embolism to haemodynamic and echocardiographic changes during cemented arthroplasty.

Pressurisation of the medullary cavity during cemented arthroplasty causes "intravasation" of marrow fat. The purpose of this study was to examine the relationship between the amount of pulmonary intravascular fat and the haemodynamic and echocardiographic changes. Anaesthetised mongrel dogs (n = 16) underwent bilateral cemented arthroplasty (BCA) to create a large embolic load. Haemodynamic measurements included blood pressure (BP), pulmonary artery pressure (PAP), right atrial pressure and cardiac output as well as transoesophageal echocardiographic (TEE) assessment of right ventricular (RV) and left ventricular (LV) areas. Using quantitative morphometry on postmortem lung specimens, the proportion of lung tissue occluded by fat was measured. Mean BP decreased within one minute of BCA, coinciding with the appearance of echogenic material in the RV. The RV area increased by 56% (P < 0.05) and LV area decreased by 34% (P < 0.05) while PAP increased from 15 +/- 3 mmHg to 39 +/- 10 mmHg within one minute (P < 0.001). The PAP remained elevated throughout the study (30 min). Stroke volume decreased in 14/15 dogs, yet cardiac output was maintained by increased heart rate. There was a curvilinear relationship (r = 0.87) between the maximum increase in PAP and the proportion of lung occupied by fat. In this model, stroke volume decreased within one minute of BCA when fat embolism accompanied prosthesis insertion. The TEE detected an increased RV area and reduced LV area associated with decreased stroke volume. The maintenance of cardiac output after intraoperative fat embolism depends primarily on the ability to increase heart rate.