Surfactant Attenuates Air Embolism-Induced Lung Injury by Suppressing NKCC1 Expression and NF-κB Activation

Excessive amounts of air can enter the lungs and cause air embolism (AE)-induced acute lung injury (ALI). Pulmonary AE can occur during diving, aviation, and iatrogenic invasive procedures. AE-induced lung injury presents with severe hypoxia, pulmonary hypertension, microvascular hyper-permeability, and severe inflammatory responses. Pulmonary AE-induced ALI is a serious complication resulting in significant morbidity and mortality. Surfactant is abundant in the lungs and its function is to lower surface tension. Earlier studies have explored the beneficial effects of surfactant in ALI; however, none have investigated the role of surfactant in pulmonary AE-induced ALI. Therefore, we conducted this study to determine the effects of surfactant in pulmonary AE-induced ALI. Isolated-perfused rat lungs were used as a model of pulmonary AE. The animals were divided into four groups (n = 6 per group): sham, air embolism (AE), AE + surfactant (0.5 mg/kg), and AE+ surfactant (1 mg/kg). Surfactant pretreatment was administered before the induction of pulmonary AE. Pulmonary AE was induced by the infusion of 0.7 cc air through a pulmonary artery catheter. After induction of air, pulmonary AE was presented with pulmonary edema, pulmonary microvascular hyper-permeability, and lung inflammation with neutrophilic sequestration. Activation of NF-κB was observed, along with increased expression of pro-inflammatory cytokines, and Na-K-Cl cotransporter isoform 1 (NKCC1). Surfactant suppressed the activation of NF-κB and decreased the expression of pro-inflammatory cytokines and NKCC1, thereby attenuating AE-induced lung injury. Therefore, AE-induced ALI presented with pulmonary edema, microvascular hyper-permeability, and lung inflammation. Surfactant suppressed the expressions of NF-κB, pro-inflammatory cytokines, and NKCC1, thereby attenuating AE-induced lung injury.

Protective effects of fluoxetine on decompression sickness in mice

Massive bubble formation after diving can lead to decompression sickness (DCS) that can result in central nervous system disorders or even death. Bubbles alter the vascular endothelium and activate blood cells and inflammatory pathways, leading to a systemic pathophysiological process that promotes ischemic damage. Fluoxetine, a well-known antidepressant, is recognized as having anti-inflammatory properties at the systemic level, as well as in the setting of cerebral ischemia. We report a beneficial clinical effect associated with fluoxetine in experimental DCS. 91 mice were subjected to a simulated dive at 90 msw for 45 min before rapid decompression. The experimental group received 50 mg/kg of fluoxetine 18 hours before hyperbaric exposure (n = 46) while controls were not treated (n = 45). Clinical assessment took place over a period of 30 min after surfacing. At the end, blood samples were collected for blood cells counts and cytokine IL-6 detection. There were significantly fewer manifestations of DCS in the fluoxetine group than in the controls (43.5% versus 75.5%, respectively; p = 0.004). Survivors showed a better and significant neurological recovery with fluoxetine. Platelets and red cells were significantly decreased after decompression in controls but not in the treated mice. Fluoxetine reduced circulating IL-6, a relevant marker of systemic inflammation in DCS. We concluded that fluoxetine decreased the incidence of DCS and improved motor recovery, by limiting inflammation processes.

Pneumomediastinum, stomach wall and hepatic portal vein gas secondary to partial necrosis of the stomach wall

The combination of pneumomediastinum, gastric wall gas and hepatic portal vein gas is a challenging clinical problem. Although different causes of the individual gas sign have been reported in the literature, the cause of a triad of these signs in a single patient is less clear, and represents an extremely rare condition. A 65-year-old man presented with severe lower chest and epigastric pain of a few hours' duration. Initial assessment confirmed epigastric tenderness. Computed tomography showed pneumomediastinum, air in the stomach wall, hepatic portal vein gas and bowel dilatation. Small bowel and right colon dilatation was confirmed at laparotomy. The patient was treated subsequently with antibiotics to cover Gram-positive and Gram-negative bacteria, and anaerobes. The patient was discharged in good general condition on the 12th postoperative day. In conclusion, the triad of pneumomediastinum, gastric wall gas and hepatic portal vein gas is an extremely rare condition and associated with gastric necrosis.

Hepatic portal venous gas complicating septic thrombophlebitis of the superior mesenteric vein

Hepatic portal venous gas is a rare radiological finding with a wide spectrum of underlying pathologies. We describe a case of hepatic portal venous gas due to septic thrombophlebitis of the superior mesenteric vein. The clinical management of portomesenteric venous gas and the importance of computed tomography in delineating its underlying causes are discussed.

Reduction in Air Bubble Size Using Perfluorocarbons During Cardiopulmonary Bypass in the Rat

BACKGROUND

Perfluorocarbon (PFC) emulsions are artificial oxygen-carrying compounds with a high solubility for gases that have experimentally been shown to ameliorate cerebral air embolism. Cerebral air embolism has been associated with adverse cerebral outcomes after cardiac surgery using cardiopulmonary bypass (CPB). We designed this study to test whether PFC emulsions could reduce the volume of bubbles within the CPB circuit.

METHODS

Male Sprague-Dawley rats undergoing 60 min of normothermic nonpulsatile CPB were randomized to one of the three groups. The PFC group (n = 10) received 60% O(2)/36% N(2)/4% CO(2) via the membrane oxygenator and 2.7 g/kg (4.5 mL/kg) of PFC into the venous reservoir; the control group (n = 10) received the same gas mixture and 4.5 mL/kg of saline; the N(2)O group (n = 6) was exposed to 36% N(2)O/60% O(2)/4% CO(2) and received 4.5 mL/kg of saline. After 10 min and 35 min of CPB, 400 microL of air was injected into a bubble chamber in the CPB circuit. After 20 min, the bubble was removed for volumetric analysis.

RESULTS

Compared with baseline, the bubble decreased 13% +/- 5% in size in the PFC group and increased 46% +/- 9% in the nitrous oxide group, both of these changes significantly different from the control group (P < 0.0001).

CONCLUSION

The results suggest that PFC administration may be useful in reducing the volume of gaseous bubbles present during CPB.

A case of non-lethal pulmonary air embolism after leukapheresis catheter removal

Mononuclear cell leukapheresis requires good-quality venous access. Catheter placement and removal of the catheter may be associated with life-threatening local or systemic complications. Thus, prompt recognition of these complications and appropriate therapy can be life-saving. We report the case of a young man who presented with an air embolism following removal of a jugular venous catheter after peripheral blood stem cell collection. We have reviewed the signs and symptoms presented by the patient and the methodology used to remove the catheter. Catheter removal requires careful attention in order to avoid potentially serious complications.

Role of the Endothelin System in Secondary Pulmonary Hypertension Related to Air Embolism: Lessons Learned from Testing Four Classes of Endothelin Blockers in a Rat Model

A rat model of acute pulmonary air embolism (APAE) was developed. These animals had a higher right ventricular systolic pressure (RVSP) (+ 69% at 15-minute peak, and 21-34% at 30-180 minutes), as well as a reduced mean arterial blood pressure (10-20% at 60-180 minutes), heart rate (20-26% at 60-180 minutes) and PaO2 (9-11% at 30-180 minutes) compared with control rats. The role of the endothelin (ET) system, known to be involved in pulmonary hypertension of various etiologies, was investigated by evaluating the effect of the four classes of ET blockers: ET-converting enzyme inhibitor (ECEi) (CGS 35066), selective endothelin-A receptor antagonist (ETA-Ra) (Atrasentan, ABT-627), endothelin-B receptor antagonist (ETB-Ra) (A-192621) or mixed endothelin-A/endothelin-B receptor antagonist (ETA/B-Ra) (A-182086) in this animal model. All four were effective, to various degrees, at reducing the APAE-induced rise in RVSP. The relative efficacy of those compounds in reducing the acute elevation (15 minutes) of RVSP was ECEi >or= ETA/B-Ra >> ETA-Ra = ETB-Ra. The sustained elevation (30-180 minutes) of RVSP was totally abolished by ECEi and attenuated by other ET blockers with a relative efficacy of ETA-Ra > ETA/B-Ra >or= ETB-Ra. ET receptor antagonists did not affect right ventricular basal tone (control rats) whereas ECEi reduced it by up to 12% after 2 hours. The APAE reduction in mean arterial blood pressure was unaffected by ETARa, was completely normalized by ETB-Ra, but was further reduced by either ETA/B-Ra or ECEi. The basal mean arterial blood pressure in control rats was unaffected by ETA-Ra, was elevated by ETB-Ra, but was depressed by ETA/B-Ra and ECEi. All ET blockers maintained normal oxygen saturation in APAE. These results support a role for ETs in rat APAE, since ET blockers can attenuate the cardiopulmonary deterioration and blood gas exchange. However, modulation of the central hemodynamic profile is more complex and may limit the usefulness of some ET blockers.

Surfactant Reduction in Embolism Bubble Adhesion and Endothelial Damage

Background

Surfactants may reduce the adhesion force holding bubbles to the vessel wall in gas embolism. The authors measured bubble adhesion force using excised microvessels. They assessed endothelial damage by measuring vessel reactivity and with microscopy.

Methods

Microbubbles injected into arterioles resided for 5, 10, or 30 min, with intact or damaged endothelium. Perfusion was with rat serum alone (control) or with 1% Perftoran (OJSC SPC Perftoran, Moscow, Russia) or 1% Pluronic F-127 (Molecular Probes, Eugene, OR) added. Pressure across the bubble, bubble length, and bubble diameter were measured, and adhesion force per unit surface area, K = deltaPD/4 l, was calculated. Vessel reactivity was assessed using topical application of phenylephrine and acetylcholine.

Results

With the endothelium intact, K was higher in controls than with Perftoran at 10 and 30 min or Pluronic F-127 at 10 min (P &lt; 0.05). With surfactant added after air perfusion to damage the endothelium, K was lower (P &lt; 0.05) at all times for both Perftoran and Pluronic F-127. With surfactant in the perfusate before air perfusion, K was lower at 10 and 30 min for Perftoran and at 10 min for Pluronic F-127 than for controls (P &lt; 0.05). Phenylephrine-induced vasoconstriction was identical among groups. Acetylcholine-induced vasodilatation was the same among groups with an intact endothelium but was found to be lower in controls after air perfusion that followed surfactant exposure than in either surfactant group (P &lt; 0.05).

Conclusions

Surfactants reduced bubble adhesion force and preserved basic endothelial structure and vasodilatory function despite attempts to damage the endothelium. Surfactants seem to protect the endothelium from mechanically induced injury in addition to decreasing bubble adhesion forces.

Effects of a selective endothelin A receptor antagonist, ABT-627, in healthy normotensive anaesthetized rats developing acute pulmonary air embolism

Acute pulmonary air embolism (APAE) injures the vascular endothelium in the lung and results in pulmonary hypertension (PH). Endothelins (ETs), a family of potent vasoactive peptides, are known to be associated with PH of various aetiologies. We evaluated the effects of ABT-627, a selective ET(A) receptor (ET(A)-R) antagonist in a rat model of APAE over 3 h. APAE rats developed a higher right ventricular systolic pressure (RVSP), lower mean arterial blood pressure (MABP), and had lower PaO(2). At 3 h, arterial plasma levels of ET-1 were increased. ABT-627-treated controls showed no effects. However, ABT-627 significantly lowered RVSP during APAE, abolished the short recovery phase (within 10-25 min) of MABP without affecting the subsequent lowering of MABP, and improved oxygen saturation in APAE rats. These results show that ET(A)-R subtype is involved in the pathogenesis of APAE since a blockade of this receptor subtype attenuated the cardiopulmonary deterioration and improved blood gas exchanges in rats with this disease.

Accelerated arteriolar gas embolism reabsorption by an exogenous surfactant

BACKGROUND

Cerebrovascular gas embolism can cause profound neurologic dysfunction, and there are few treatments. The authors tested the hypothesis that an exogenous surfactant can be delivered into the bloodstream to alter the air-blood interfacial mechanics of an intravascular gas embolism and produce bubble conformations, which favor more rapid bubble absorption.

METHODS

Microbubbles of air were injected into the rat cremaster microcirculation after intravascular administration of either saline (control, n = 5) or Dow Corning Antifoam 1510US (surfactant, n = 5). Embolism dimensions and dynamics were directly observed after entrapment using intravital microscopy.

RESULTS

To achieve embolization, the surfactant group required twice as many injections as did controls (3.2 +/- 1.3 vs. 1.6 +/- 0.9; P < 0.05). There was no difference in the initial lodging configuration between groups. After bubble entrapment, there was significantly more local vasoconstriction in the surfactant group (24.2% average decrease in diameter) than in controls (3.4%; P < 0.05). This was accompanied by a 92.7% bubble elongation in the surfactant group versus 8.2% in controls (P < 0.05). Embolism shape change was coupled with surfactant-enhanced breakup into multiple smaller bubbles, which reabsorbed nearly 30% more rapidly than did parent bubbles in the control group (P < 0.05).

CONCLUSIONS

Intravascular exogenous surfactant did not affect initial bubble conformation but dramatically increased bubble breakup and rate of reabsorption. This was evidenced by both the large shape change after entrapment and enhancement of bubble breakup in the surfactant group. These dynamic surfactant-induced changes increase the total embolism surface area and markedly accelerate bubble reabsorption.

Successful management of venous air embolism with inotropic support

PURPOSE

Since venous air embolism may occur during many different types of surgery, management of this clinical emergency can be required in patients who do not have a previously established central venous access for aspiration of air. Recent reviews suggest that management of right heart syndromes in patients with embolism is critical in improving outcome.

CLINICAL FEATURES

Abrupt decreases in oxygen saturation (from 98% to 40%) and end-tidal carbon dioxide tension (from 24 to 6 mm Hg), compatible with venous air embolism were observed in a 73-yr-old woman during craniotomy for meningioma in the supine position. Since no access for aspiration of air was readily available, therapy was directed at inotropic support of the right heart using a bolus of ephedrine. Cardiorespiratory variables rapidly returned to normal, and the patient recovered from anesthesia and surgery without sequelae.

CONCLUSIONS

Venous air embolism places an acute load on the right ventricle and may provoke right heart failure, even in the absence of total cardiovascular collapse. Treatment that supports right heart function may allow sufficient time for redistribution of embolized air and produce a good outcome when access for central aspiration of air is not available.

Propofol for sedation and control of intracranial pressure in children

Following central nervous system insults, control of intracranial pressure may lessen the incidence of morbidity and mortality. Therapies to control intracranial pressure include osmolar agents, prevention of and control of seizures, drainage of cerebrospinal fluid, hypothermia, and barbiturates. Control of agitation and excessive patient movement are additional components in the management of ICP. Although opioids and benzodiazepines are generally effective, in a small subset of patients, alternative agents may be necessary. The authors present 2 children with increased ICP in whom propofol was used to provide sedation and control ICP. The use of propofol in this setting and its possible applications in the children with increased ICP are discussed.

Inhaled nitric oxide improves hemodynamics during a venous air infusion (VAI) in dogs

OBJECTIVE

To evaluate the hemodynamic effects of inhaled nitric oxide (NO) during a venous air infusion (VAI) in dogs. We also addressed the question of whether NO therapy changes thromboxane (Tx) A(2) release and nitrate/nitrite production during a VAI.

DESIGN

Prospective trial.

SETTING

University laboratory.

INTERVENTIONS

Anesthetized mongrel dogs received a VAI (0.2 ml x kg(-1)x min(-1)) after the measurement of baseline hemodynamics. Control dogs (n = 8) received no further treatment. After 30 min of VAI, NO 3 ppm inhalation was initiated (n = 7) for 30 min, followed by 30 min without NO inhalation, and then a final 30 min of NO 40 ppm treatment. Hemodynamic variables were registered and arterial and mixed venous blood samples were drawn for gas analysis and for the determinations of serum TxB(2) (by enzyme-linked immunosorbent assay) and nitrate/nitrite (by high-performance liquid chromatography) levels.

RESULTS

The cardiac index increased 24 % and the pulmonary vascular resistance index decreased 30 % during both periods of NO inhalation. Arterial oxygen tension and arterial oxygen saturation were slightly lower after NO therapy. Nitrate/nitrite concentrations were unaltered in the control group and there were no differences between the arterial and mixed venous serum nitrate/nitrite levels. Nitrite concentrations remained below 1 microM in both groups of animals, but the nitrate concentration increased after inhalation of 40 ppm NO. Serum TxB(2) increased after 60 min of VAI in the control group, but there was no increase in NO-treated animals (all p < 0.05)

CONCLUSIONS

Nitrate/nitrite concentrations were unaltered after VAI in dogs. NO therapy attenuated TxA(2) release and improved hemodynamics, but not blood oxygenation, in dogs with a VAI. There were no differences between the responses to 3 ppm and 40 ppm NO.

Successful management of right coronary air embolus after intracoronary administration of verapamil

A case of a 50 year-old male with a coronary air embolism is described. The case was successfully treated with intracoronary administration of verapamil.

Doxycycline reduces early neurologic impairment after cerebral arterial air embolism in the rabbit

BACKGROUND

Previous studies indicate leukocytes play a role in the pathogenesis of cerebral arterial air embolism. Because doxycycline inhibits numerous leukocyte activities, the authors hypothesized doxycycline would decrease neurologic impairment after cerebral arterial air embolism.

METHODS

New Zealand White rabbits anesthetized with methohexital received either intravenous saline (n = 7) or 10 mg/kg doxycycline (n = 7) 1 h before administration of 100 microl/kg of air into the internal carotid artery. Somatosensory-evoked potentials (SSEPs) were recorded at 30-min intervals for the next 2 h. After the final recording, the anesthetic was discontinued, and animals recovered. Animals were neurologically evaluated 4 h after air embolism on a scale of 0 (normal) to 99 (coma) points.

RESULTS

At 4 h, doxycycline animals had lesser neurologic impairment (46 +/- 23; median, 41) than animals that received saline (77 +/- 20; median, 81); P = 0.007. SSEP amplitude was greater in the doxycycline group at 60, 90, and 120 min after air embolism; P = 0.001, 0.006, 0.026, respectively. SSEP amplitudes at 30, 60, 90, and 120 min inversely correlated with 4 h neurologic impairment; tau = -0.43, -0.75, -0.85, -0.79, respectively.

CONCLUSIONS

Doxycycline decreased electrophysiologic and neurologic abnormalities after cerebral air embolism. Because groups could be distinguished electrophysiologically as soon as 1 h after air embolism and because SSEP amplitude inversely correlated with neurologic impairment, doxycycline appears to inhibit a key early (approximately 1 h) process in the pathophysiology of cerebral air embolism.

Dibutyryl cAMP prevents increased vascular permeability caused by air embolism in isolated rat lungs

BACKGROUND AND HYPOTHESIS

Venous gas bubbles are routinely detected in astronauts undergoing extravehicular activities at lower suit pressure. Venous air embolism increases the pulmonary arterial pressure and the vascular permeability leading to acute lung injury. In the present study we evaluated the protective effect of dibutyryl cAMP, aminophylline, and pentoxifylline on the pulmonary vasculatures after air embolism.

METHOD

In isolated and perfused rat lungs, we induced air embolism by introducing air bubbles into the pulmonary artery. We measured the pulmonary arterial pressures and capillary pressure. Vascular permeability was determined by measuring the filtration coefficient (Kf) and the protein concentration in the lung lavage fluid.

RESULTS

Air infusion caused pulmonary hypertension and increased vascular permeability, resulting in pulmonary edema. The Kf (in g.min-1.cm H2O-1.100 g-1) increased from 0.44 +/- 0.05 at baseline to 2.98 +/- 0.47 after air infusion. Pretreatment with DBcAMP prevented the increase in Kf (0.63 +/- 0.09) caused by air embolism without altering the hemodynamics. Aminophylline and pentoxifylline did not prevent lung injury induced by air embolism. Although aminophylline did not alter the response of pulmonary arterial pressure to air infusion, it elevated the capillary pressure to 5.1 +/- 0.4 mmHg, which was significantly greater than that in the lung receiving air infusion alone.

CONCLUSION

Our results suggest that DBcAMP prevents the increase in vascular permeability caused air embolism. The ineffectiveness of aminophylline and pentoxifylline on the prevention of air embolism-induced lung injury remains for further investigation.

Heparin reduces neurological impairment after cerebral arterial air embolism in the rabbit

BACKGROUND AND PURPOSE

Neurological injury after cerebral air embolism may be due to thromboinflammatory responses at sites of air-injured endothelium. Because heparin inhibits multiple thromboinflammatory processes, we hypothesized that heparin would decrease neurological impairment after cerebral air embolism.

METHODS

To first establish a dose of air that would cause unequivocal neurological injury, anesthetized New Zealand White rabbits received either 0, 50, 100, or 150 microL/kg of air into the internal carotid artery (n = 5 in each group). One hour later, anesthesia was discontinued. Animals were neurologically evaluated at 24 hours with the use of a scale ranging from 0 (normal) to 97 (coma) points. In a subsequent experiment, anesthetized rabbits received either heparin (n = 17) or saline (n = 15) 5 minutes before air injection (150 microL/kg). Heparin was given as a 200-IU/kg bolus and followed by a constant infusion of 75 IU.kg-1.h-1 for 2 hours. Equal volumes of saline were given to control rabbits. Two hours later, anesthesia was discontinued. Animals were neurologically evaluated 24 hours after air embolism.

RESULTS

There was a monotonic relationship between dose of air and severity of neurological impairment at 24 hours (P = 1.1 x 10(-7)). Animals receiving 150 microL/kg of air were unequivocally injured (score, 60 +/- 16). In the second experiment, heparin animals had significantly less neurological impairment at 24 hours (34 +/- 14) than saline controls (52 +/- 8) (P = .0013).

CONCLUSIONS

When given prophylactically, heparin decreases neurological impairment caused by severe cerebral arterial air embolism.

Effect of phenytoin on acute lung injuries in unanesthetized sheep

OBJECTIVE

To determine if the intravenous administration of phenytoin attenuates or prevents acute experimental lung injury.

DESIGN

Placebo-controlled, longitudinal animal investigative study.

SETTING

University research laboratory.

SUBJECTS

Sixteen yearling female lambs weighing 30 +/- 3 kg.

INTERVENTION

After administration of anesthesia, the animals were endotracheally intubated and mechanically ventilated. Using sterile techniques, four thoracotomies were performed. Through the left fourth intercostal space, cannulas for pressure measurements were inserted directly into the main pulmonary artery and left atrium. An ultrasound flow cuff for determination of cardiac output was placed around the main pulmonary artery. Through the left tenth intercostal space, the diaphragmatic and mediastinal parietal pleura were widely cauterized. Through the right tenth intercostal space, the caudal mediastinal lymph node was identified and divided at the caudal margin of the right pulmonary ligament, and a 1- to 2-cm portion of the node distal to the ligament was resected. The diaphragmatic and mediastinal parietal pleura were widely cauterized. Through the right sixth intercostal space, the efferent duct (or ducts) was identified, ligated at the site of entry into the thoracic duct, and cannulated. The lymph cannula was brought to the outside of the thorax through a separate stab wound.

MEASUREMENTS AND MAIN RESULTS

Unanesthetized sheep were studied 7 to 10 days after surgery. Hemodynamic, lung fluid balance, and arterial blood variables were measured in uninjured sheep and in sheep injured by intravenous infusions of Escherichia coli endotoxin (1 microgram/kg iv over 30 mins), air bubbles (0.056 to 0.074 mL/kg/min over 4 hrs), or oleic acid (0.06 mL/kg over 1 hr). The sheep were studied when untreated and after pretreatment with phenytoin. We found that the expected increase in protein-rich lung lymph flow with injuries, resulting from increased microvascular permeability in the lungs, was attenuated by phenytoin when the lungs were injured by endotoxin or air bubbles. In contrast, phenytoin had no effect on oleic acid-induced lung injury or on uninjured lungs.

CONCLUSIONS

Phenytoin attenuates acute lung injuries in sheep that are thought to be caused by stimulation of host inflammatory responses (e.g., endotoxin and air bubbles), but has no effect on direct injuries to the lungs (e.g., oleic acid). A plausible mechanism for this finding is phenytoin inhibition of polymorphonuclear leukocyte function.

Effects of treatment with Pluronic F-68 during continuous venous air embolism in swine

Treatment with the surface-active agent Pluronic F-68, shown to modulate the hemodynamic effects of venous air emboli (VAE) in dogs, may be useful for treatment of VAE in divers. We report on the effects of injections of Pluronic F-68 on responses to continuous air infusion in swine. Pretreatment made no significant difference in any hemodynamic or ventilatory variables, but the rise of pulmonary vascular resistance caused by air infusion was greater in surfactant-treated animals; this was also evident after a second treatment during the air infusion. The small effect of surfactant treatment in our study on swine contrasts the effects reported previously in dogs, and could be due to species-specific differences in lung physiology-anatomy, or due to difference in experimental design. We speculate that the minor changes we observed were caused by deeper penetration of the bubbles into the pulmonary arterial tree after surfactant treatment.

Effect of lidocaine on somatosensory evoked response and cerebral blood flow after canine cerebral air embolism

BACKGROUND AND PURPOSE

Victims of air embolism often recover rapidly on hyperbaric treatment then deteriorate again, even if hyperbaric treatment is continued. In previous animal experiments, lidocaine has been shown to improve recovery of somatosensory evoked response amplitude after air embolism. However, animals in these experiments rarely deteriorated. We have shown that the induction of air embolism and transient hypertension in canines produces deterioration despite hyperbaric treatment, and we decided to test the effect of lidocaine on somatosensory evoked potential recovery and cerebral blood flow in this model.

METHODS

Dogs were treated with repeated doses of lidocaine or equivalent volumes of saline during hyperbaric therapy after internal carotid air embolism and transient hypertension. The investigators were unaware of treatment group assignment during the experiments. The amplitude of the median nerve somatosensory evoked potential and cerebral blood flow measured with carbon-14-labeled iodoantipyrine autoradiography were used to assess effect of therapy.

RESULTS

Lidocaine-treated dogs recovered 60 +/- 10% (mean +/- 95% confidence limits) of the baseline somatosensory evoked potential amplitude 220 minutes after air embolism; saline-treated dogs recovered 32 +/- 10% (a significant difference at p less than 0.01). Lidocaine-treated dogs also had higher cerebral blood flow values than saline-treated dogs 220 minutes after air embolism.

CONCLUSIONS

Lidocaine ameliorated the delayed deterioration of evoked potential associated with air embolism and hypertension in this canine model. The improved cerebral blood flow may be a mechanism of action of lidocaine or an associated effect of improved neuronal survival.

Timing of corticosteroid treatment. Effect of lung lymph dynamics in air injury in awake sheep

In paired experiments, we studied the effects of high-dose methylprednisolone on the acute pulmonary injury caused by 4 h of venous air embolization in 19 chronically instrumented, unanesthetized sheep with lung lymph fistulas. We compared the effect of methylprednisolone (30 mg/kg intravenous bolus) given before embolization, early (1 H) in the course of embolization, late (3 h) in the course of embolization, or after embolization (at the beginning of the recovery period). We measured pulmonary hemodynamics and lymph dynamics. In six sheep we also fixed lung tissue for semiquantitative histology, and in some we measured leukocyte concentrations in blood and in pulmonary lymph. Methylprednisolone did not significantly affect pulmonary hemodynamics but it largely prevented lung injury when it was given before embolization. It also lessened the degree of lung injury when it was given during embolization, although this effect became less marked as treatment was delayed. Methylprednisolone had no effect on lung injury when given after embolization was completed (4 h). We found fewer leukocytes attached to air emboli and fewer endothelial cell gaps in the lungs of sheep given methylprednisolone as prophylaxis. Leukocyte counts were lower in lung lymph and higher in the circulating blood of methylprednisolone-treated sheep. We conclude that methylprednisolone has a preventive effect on air embolism lung injury, such that its effect is greater when given earlier during the development of injury.

Treatment of venous air embolism with papaverine

Two cases of venous air embolism are described. One case occurred in a 12-year-old girl operated for ureteroileo-cutaneostomy; the other case occurred in a 44-year-old patient who underwent a hemihepatectomy. The haemodynamic and pulmonary consequences were successfully treated with intravenous papaverine.

Effect of lidocaine after experimental cerebral ischemia induced by air embolism

To investigate possible approaches to the treatment of neural damage induced by air embolism and other forms of acute cerebral ischemia, somatosensory evoked potentials (SEP's) were measured after cerebral air embolism in the anesthetized cat. Air was introduced into the carotid artery in increments of 0.08 ml until the SEP amplitude was reduced to approximately 10% or less of baseline values. Either a saline or lidocaine infusion was begun 5 minutes after inducing cerebral ischemia. In the saline-treated group, SEP amplitude was reduced to 6.7% +/- 1.6% (mean +/- standard error of the mean) of baseline, with a return to 32.6% +/- 4.7% of baseline over a 2-hour period. In the lidocaine-treated group, SEP amplitude was reduced to 5.9% +/- 1.5%, with a return to 77.3% +/- 6.2% over a 2-hour period. The results suggest that lidocaine administration facilitates the return of neural function after acute cerebral ischemia induced by air embolism.

Effects of serotonin inhibition in air embolism in dogs

Serotonin can induce pulmonary hypertension, hypoxia and bronchoconstriction, and ketanserin has been shown to reverse these effects on various experimental models of acute respiratory failure. In the present study, the hemodynamic and gasometric effects of ketanserin were studied during acute respiratory failure induced by an air infusion at a rate of 10 ml/min in dogs. During a 60-min air infusion, 10 dogs received 4 mg of ketanserin i.v. and 10 dogs served as control. Ketanserin-treated dogs had similar pulmonary hypertension even though more significant decreases in arterial pressure and systemic vascular resistance characterized the systemic effects of ketanserin. Similarly, a marked increase in hematocrit observed in control dogs (from 36.9 to 43.8%, p less than 0.01) was totally prevented by ketanserin (from 40.3 to 40.4%, NS). Hypoxia was similar, although the increase in pulmonary shunt was attenuated (259 instead of 468%). Therefore, the influence of serotonin is very limited in acute respiratory failure secondary to air embolization. Serotonin might have a more important influence on the systemic than on the pulmonary vasculature in these conditions.

Pulmonary barotrauma in submarine escape trainees and the treatment of cerebral arterial air embolism

The reports of all dysbaric incidents occurring during submarine escape training at the Royal Navy's training facility in HMS Dolphin during 1954-84 were reviewed. All cases treated for unequivocal arterial gas embolism were used to assess the effectiveness of various treatments. Presentation and accident rates were analysed. As training techniques and treatments have varied over the years, the data were not uniform thus making comparison of treatments difficult. Both long air tables and RN Table 63 (USN6A) appear to offer effective treatment. There was insufficient data to assess the efficacy of prophylactic steroids in preventing relapse. It was concluded that the current recommendations for treating AGE by commencing on RN Table 63 with a change to RN Table 54 in the event of no response or of relapse should remain unchanged.

Cardiorespiratory effects of venous air embolism in dogs receiving a perfluorocarbon emulsion

The cardiorespiratory effects of a nonlethal venous air embolism were studied in dogs in the presence of a perfluorocarbon emulsion (PFE). Prior to embolization, five dogs received 20 cc/kg of hydroxyethyl starch (6% HES) and five received PFE oxypherol (20% FC-43). Determinations of mean systemic arterial pressure (MAP), pulmonary artery pressure (PAP), left ventricular pressure (LVP), first and second derivatives of LVP with respect to time (dP/dt and Vmax), cardiac index (CI), stroke index, left and right ventricular stroke work index (LVSWI and RVSWI), PaCO2, PaO2, and venous admixture (Qs/Qt) were made before and then 1, 5, 10, and 30 minutes after placement of the venous air emboli (0.75 cc/kg/min for 5 minutes). After emboli were introduced, PaO2, MAP, LVSWI, dP/dt, Vmax, and CI decreased; the average decrease during the first 5 minutes was significantly less in the PFE group. Following introduction of venous air emboli, PAP, PaCO2, RVSWI, and Qs/Qt increased less in the PFE group than in the HES group, with statistical significance achieved at various times during the first 10 minutes after embolism. All parameters returned toward baseline values by 30 minutes in both groups. This study indicates that FC-43, when administered before venous air embolism, helps to attenuate some of the detrimental cardiorespiratory effects of the embolism.

A review of the pathophysiology and potential application of experimental therapies for cerebral ischemia to the treatment of cerebral arterial gas embolism

This review considers the pathophysiology of air embolism that occurs as a result of diving and iatrogenic accidents. Various experimental therapies are classified according to their potential mechanism of action. The effectiveness and prospects for application to the clinical situation are assessed for each therapy. Hyperbaric oxygen remains the most effective therapy, and it is one that is simple to apply. The physiologic changes that occur after gas embolism are complex, however, and future improvements in therapy will demand close clinical supervision and multiple individually tailored therapeutic decisions rather than a simple protocol.

Fluorocarbons: a potential treatment of cerebral air embolism in open-heart surgery

This study was designed to assess whether an oxygenated fluorocarbon solution could reduce ischemic brain damage related to arterial air embolism. Air embolism was produced by injecting air bubbles into the carotid artery of barbiturate-anesthetized rats breathing 100% oxygen. Results were assessed on electrocorticogram. In an additional set of experiments, mass spectrometry was used to provide continuous monitoring of intracerebral tissue oxygen (PO2) and carbon dioxide (PCO2) tensions and intermittent measurement of cerebral blood flow (CBF). Fluorocarbon or saline solution (containing the emulsifying agent of fluorocarbons) was given intravenously after the initial air embolism (0.2 ml), and injections of air (0.1 ml) were repeated thereafter every five minutes. The maximal amount of air required to achieve complete and irreversible flattening of the electrocorticogram was 1.60 +/- 0.06 ml (mean +/- standard error of the mean) in the saline-treated rats and 5.20 +/- 0.44 ml in the fluorocarbon-treated group (p less than 10(-7)). In the second experiment, air embolism caused CBF to rise in both groups, the average percent of increase being higher in treated (41.6%) than in control animals (38.3%) (p less than 0.02). However, in the control group, the increase in CBF did not prevent intracerebral tissue PO2 from decreasing by 7.4 +/- 7.0% over the same period; conversely, in the fluorocarbon group, PO2 levels fell by only 2.5 +/- 3.7% (p less than 0.001 versus controls), but this time-averaged percentage was calculated over a longer period of cumulative ischemia because of the greater number of air emboli tolerated by treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide dismutase with heparin prevents increased lung vascular permeability during air emboli in sheep

We studied the effects of bovine superoxide dismutase on the increased lung microvascular permeability to fluid and protein during air emboli in unanesthetized sheep. We measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, and lymph and plasma protein concentrations. In air emboli experiments we continuously infused the same dose of air bubbles 1 mm in diameter into the right atrium of each sheep to increase pulmonary vascular resistance to 2-4 times base-line values. We did experiments in pairs so that each sheep served as its own control. We found an increase in protein-rich lymph flow from the lung during embolization in untreated sheep, indicating an increase in microvascular permeability to both fluid and protein. When we pretreated the sheep with heparin (300 U/kg) and infused them with intravenous bovine superoxide dismutase (1 mg X kg-1 X h-1 beginning before the air infusion), we found that vascular pressures and pulmonary vascular resistance were not different from untreated sheep but that the expected increases in transvascular fluid and protein flow during emboli were significantly decreased (P less than 0.0005). Heparin alone did not significantly attenuate the increased microvascular permeability but we found that it greatly enhanced the effectiveness of superoxide dismutase in preserving microvascular functional integrity during air emboli. We conclude that superoxide anion, probably produced and released by leukocytes, is a central factor in the microvascular injury that results in increased permeability in the lungs of sheep during air microembolization.

Delayed cerebral edema complicating cerebral arterial gas embolism: case histories

A disquieting and rarely described feature of the treatment of arterial gas embolism (AGE) is the high incidence of relapse following good to excellent initial responses to recompression therapy. This paper includes a discussion of the issues involved in the etiology and clinical approach to the specific problem of relapse and relates experience from selected clinical cases to a modified therapeutic approach that has been introduced into Royal Navy diving and submarine medicine practice. It illustrates how and why current treatment procedures have been expressly designed to minimize the incidence of relapse and to modify favorably the pathophysiological responses (particularly vasogenic cerebral edema) associated with cerebral AGE.

Restoration of pulmonary perfusion by a serotonin antagonist

R 41 468, a selective serotonin receptor blocking agent, was found to improve pulmonary perfusion in patients with venous air embolism, in patients with adult respiratory distress syndrome (ARDS), and in certain cases of impairment of the pulmonary circulation during prolonged major surgery accompanied by blood transfusion. Continuous monitoring of end-tidal (CO2 (FETCO2) by means of infra-red capnography combined with blood gas estimations were the principle methods of assessment used.

[Hyperbaric oxygenation in a large hyperbaric chamber (author's transl)]

Hyperbaric Oxygenation has been used routinely with 503 persons (1100 compressions) in a large walk-in hyperbaric chamber. An optimal interdisciplinary teamwork and mastering of the transportation problems by helicopter is mandatory to make this treatment accessible for patients in distant hospitals as an additional conservative management. In 51 operations under pressure (28 congenital heart disease cases) the luxury oxygenation was a protective measure. The procedure can be done safely with plenty of working time.

Recovery from experimental paraplegia after levodopa administration

In decompression sickness and during some surgical procedures, air emboli that form sometimes cause serious damage if the gas bubbles find their way to the vital organs. Paralysis of the spinal cord is one of the most serious manifestations induced by air emboli. Exposure to compression chambers is effective in air emboli treatment, but availability of chambers is inadequate and the treatment is lengthy. Until now there has been no fully effective injectable agent that can remedy the damage caused by air embolization. In this work levodopa was chosen as an injectable drug that might help to improve recovery from experimental paraplegia because of the reported effects of levodopa on muscle tone, spasticity and locomotion. To induce air emboli, the descending aorta of rats was chronically cannulated. Two weeks later, after full recovery from surgery, air was injected through the chronically implanted cannula into unanesthetized rats (0.35 ml of air per 100 g, during 4 sec). The paraplegia (paralysis of both hind legs) was manifested 2-10 minutes later. Only animals that had total paraplegia, without any sensation, were used in the experiments. Levodopa was administered 2 minutes after paraplegia was established. The levodopa treatment was repeated each day during one week. After six days, ten levodopa treated (intra-arterially) animals in a group of twelve and six levodopa treated (intraperitoneally) animals in a group of eight recovered completely from paraplegia. In control groups only three from thirteen (untreated), or two from twelve (solvent administration) animals recovered from paraplegia.