Post effect of repetitive exposures to pressure nitrogen-induced narcosis on the dopaminergic activity at atmospheric pressure.

Nitrogen at pressure produces a neurological syndrome called nitrogen narcosis. Neurochemical experiments indicated that a single exposure to 3 MPa of nitrogen reduced the concentration of dopamine by 20% in the striatum, a structure involved in the control of extrapyramidal motor activity. This effect of nitrogen was explained by enhanced GABAergic neurotransmission through GABAA receptors and, to a lesser extent, by a decreased glutamatergic input to DA cells through NMDA receptors. The aim of this study was to study, under normobaric conditions, possible alterations of NMDA receptor activity in the substantia nigra pars compacta (SNc) induced by repetitive exposures to nitrogen pressure. Under general anesthesia, male Sprague-Dawley rats were implanted in the striatum with multifiber carbon dopamine-sensitive electrodes and in the SNc with guide cannulae for drug injections. After recovery from surgery, the striatal dopamine level was recorded by voltammetry in freely-moving rats, in normobaric conditions, before and after 5 repetitive exposures to 1MPa of nitrogen (threshold of nitrogen narcosis occurrence in rat). The effect of NMDA receptor activity on DA concentration was investigated using agonist (NMDA) and specific antagonist (AP7) SNc administration. Following repetitive nitrogen exposures, the ability of NMDA to elevate DA concentrations was enhanced. In contrast, after nitrogen exposure AP7 produced a paradoxical increase in DA concentration compared to its inhibitory effect before any exposure. Similar responses were obtained after a single exposure to 3MPa nitrogen. Thus, repetitive exposures to nitrogen narcosis produced a sensitization of postsynaptic NMDA receptors on DA cells, related to a decreased glutamatergic input in SNc. Consequently, successive nitrogen narcosis exposures disrupted ion-channel receptor activity revealing a persistent nitrogen-induced neurochemical change underlying the pathologic process.

Iatrogenic cerebral air embolism: importance of an early hyperbaric oxygenation.

OBJECTIVES: To assess the relationship between the time period before hyperbaric oxygenation therapy (HBO) and clinical outcome in patients with iatrogenic cerebral air embolism. DESIGN AND SETTING: Retrospective study in a hyperbaric chamber and medical intensive care unit of a university hospital. PATIENTS: All patients with air embolism from 1980 to 1999. INTERVENTIONS: We retrieved the cases of 86 patients who benefited from an identical HBO and analyzed the relationship between the time period before HBO and clinical outcome. RESULTS: Patients treated with HBO less than 6 h had a better outcome than those treated later. In patients treated within this delay the cause was venous air embolism in 84% and arterial air embolism in only 16% of cases. After this delay the cause was venous air embolism (53%) and arterial air embolism (47%). Patients with venous air embolism and recovery had a shorter delay than patients with sequelae or death (2 h 15 min vs. 4 h). Patients with venous air embolism treated less than 6 h had a better outcome than those treated later. In patients with arterial air embolism the time period before HBO was longer than in venous air embolism (8 h vs. 3 h) and the outcome worse (recovery in 35% vs. 67%). In patients with arterial air embolism no difference in the time period was found between patients with recovery and sequelae or death. CONCLUSIONS: We stress the beneficial effect of an early HBO in air embolism, the importance of an increased awareness of physicians concerned with this severe complication, and the need to develop techniques to detect air emboli in the cerebral circulation.

Left atrial and ventricular filling in chronic obstructive pulmonary disease. An echocardiographic and Doppler study.

Abnormal left ventricular (LV) diastolic function has frequently been reported in patients with chronic obstructive pulmonary disease (COPD). In the present work, diastolic function was studied by a combined analysis of pulmonary venous and mitral blood flow velocities in 34 patients with COPD clinically stable and without history of heart disease, and 20 control subjects. We confirmed the increased contribution of the atrial contraction to the LV filling in COPD patients in comparison with control subjects; furthermore, a decreased left atrial (LA) filling during the ventricular systole was observed. Changes in LV filling were not the consequence of a systolic dysfunction, because LV systolic function was normal. Doppler indices indicated that LA pressure was below 15 cm H(2)O in all the patients with COPD and control subjects. Several factors can be put forward to explain these changes; the first one is tachycardia. In addition to hypoxemia and medications, echocardiography suggested that a decreased LV preload participated in increased heart rate. Analysis of Doppler transmitral and pulmonary venous flows demonstrated the role of the ventricular interdependence because a correlation existed between LA and LV filling pattern and right ventricle pressure and diameter.

Operation Everest III (Comex '97): modifications of cardiac function secondary to altitude-induced hypoxia. An echocardiographic and Doppler study.

During Operation Everest III (Comex '97), to assess the consequences of altitude-induced hypoxia, eight volunteers were decompressed in a hypobaric chamber, with a decompression profile simulating the climb of Mount Everest. Cardiac function was assessed using a combination of M-mode and two-dimensional echocardiography, with continuous and pulsed Doppler at 5,000, 7,000, and 8,000 m as well as 2 d after return to sea level (RSL). On simulated ascent to altitude, aortic and left atrial diameters, left ventricular (LV) diameters, and right ventricular (RV) end-systolic diameter fell regularly. Heart rate (HR) increased at all altitudes accompanied by a decrease in stroke volume; in total, cardiac output (Q) remained unchanged. LV filling was assessed on transmitral and pulmonary venous flow profiles. Mitral peak E velocity decreased, peak A velocity increased, and E/A ratio decreased. Pulmonary venous flow velocities showed a decreased peak D velocity, a decreased peak S velocity, and a reduction of the D/S ratio. Systolic pulmonary arterial pressure (Ppa) showed a progressive and constant increase, as seen on the elevation of the right ventricular/right atrial (RV/RA) gradient pressure from 19.0 +/- 2.4 mm Hg at sea level up to 40.1 +/- 3.3 mm Hg at 8,000 m (p < 0.05), and remained elevated 2 d after recompression to sea level (SL) (not significant). In conclusion, this study confirmed the elevation of pulmonary pressures and the preservation of LV contractility secondary to altitude-induced hypoxia. It demonstrated a modification of the LV filling pattern, with a decreased early filling and a greater contribution of the atrial contraction, without elevation of LV end-diastolic pressure.

Haemoptysis after breath-hold diving.

Pulmonary oedema has been described in swimmers and self-contained underwater breathing apparatus (Scuba) divers. This study reports three cases of haemoptysis secondary to alveolar haemorrhage in breath-hold divers. Contributory factors, such as haemodynamic modifications secondary to immersion, cold exposure, exercise and exposure to an increase in ambient pressure, could explain this type of accident. Furthermore, these divers had taken aspirin, which may have aggravated the bleeding.

Venous gas embolism: detection with pulsed Doppler guided by two-dimensional echocardiography.

BACKGROUND: Venous gas embolism is a rare but severe event in critically ill patients and the diagnosis should be obtained as soon as possible. Ultrasonography is a sensitive, non-invasive, and bedside means of detection. METHOD: We prospectively estimated the performance of two-dimensional (2D) echocardiography and pulsed Doppler guided by 2D echocardiography in the detection of venous embolism. We used, as a model of venous gas embolism, the decompression following a recreational dive. This activity is responsible for circulating bubbles related to nitrogen desaturation. RESULTS: Venous gas emboli were detected following 44 of 68 dives in 20 of 24 divers. Gas emboli in 36 cases (16 divers) was shown by 2D echocardiography. Parasternal short-axis and right-cavity longitudinal views were the best views for positive detection. Pulsed Doppler confirmed the existence of venous gas emboli in all of the 36 cases with positive detection by 2D echocardiography. In 8 other cases, pulsed Doppler detected circulating bubbles, which were not observed by using 2D echocardiography. Discrepancies were observed in 4 divers with an echographic image of medium or poor quality. CONCLUSION: Combined utilization of 2D echocardiography and pulsed Doppler provides a better method for the detection of venous gas embolism than 2D echocardiography alone. This protocol could be used for critically ill patients suspected of venous air embolism.

[Severe air embolism after surgical irrigation with hydrogen peroxide]. / Embolie gazeuse grave après une irrigation chirurgicale à l'eau oxygénée.

BACKGROUND: Hydrogen peroxide is widely used for its antiseptic properties. In certain circumstances, however the risk of air embolism can create a life-threatening situation. CASE REPORT: A 16-year-old adolescent required surgical treatment for femorotibial trauma. During the surgical procedure, cardiac arrest suddenly occurred when hydrogen peroxide was being used to irrigate the wound. A central catheter was inserted and aspiration of air bubbles in the line led to the diagnosis of air embolism. Outcome was unfavorable despite successful resuscitation. A chronic neurovegatative state ensued and the patient died 8 months later. DISCUSSION: Several cases of air embolism have been described due to hydrogen peroxide in surgical, medical and accidental circumstances. Our case emphasizes the potential danger of using hydrogen peroxide in certain situations, including orthopedic surgery. Clinicians should be aware that hydrogen peroxide is not a perfectly safe product.

[Significance of systematic endoscopic decannulation. Retrospective study on intensive care patients]. / Intérêt de la fibroscopie systématique de décanulation. Etude rétrospective portant sur des malades de réanimation.

We performed a retrospective study in 42 consecutive tracheotomy patients hospitalized in an intensive care unit. Endoscopy was used systematically to assess all patients at decanulation and whenever symptoms suggested possible tracheal granuloma. Nine tracheal granulomas were evidenced. There was no significant association between presence of a granuloma and patient status: age, underlying chronic respiratory failure, or tracheobronchial infection. In initial stages, tracheal granulomas usually have little clinical expression. Difficulty in weaning from ventilatory assistance is generally the main sign. The long-term course after decanulation can progress to major respiratory disorders due to tracheal stenosis. We emphasize the importance of systematic endoscopy at decanulation to recognize existing granulomas early when local treatment remains simple (usually laser vaporization).

[Fat embolism after intrapenile injection of sweet almond oil]. / Embolie graisseuse après injection intrapénienne d'huile d'amande douce.

We report a case of fat embolism following self injection of vegetable oil in the penis, to treat an impotence. The patient developed respiratory failure and neurological disorders as confusion. A chest roentgenogram revealed diffuse alveolar infiltrate. Initially, he presented an hemoconcentration, and fat globules in his urine. The outcome was favourable in 72 hours, with oxygen and hydration. The diagnosis of fat embolism was made after neurological improvement: the patient admitted to injection his penis with vegetable oil, in his corpus cavernosum.

Activation of coagulation in decompression illness.

In animal studies, many authors have observed coagulation activation in decompression illness (DCI). These hemostasis modifications have been attributed to circulating bubbles. We have studied molecular hemostasis markers in 25 consecutive divers, victims of DCI admitted to our hyperbaric center, and in 15 control divers. There was no significant difference in parameters studied in the patients and the control group (platelet, fibrinogen, antithrombin III, Thrombin Antithrombin III complexes, and D-Dimers). An activation of coagulation (D-Dimer > 500 ng.ml-1) was noted in three divers with neurologic troubles. However, such signs of coagulation activation were not correlated with the risk of sequeals. No control or study patient with an osteoarticular or vestibular accident presented signs of coagulation activation. Thus, there does not seem to be a correlation between the severity of the accident and the level of coagulation activation. Further studies will be necessary to evaluate the responsibility of hemostasis modifications in the physiopathology of decompression accidents in sports divers.

Decompression induced venous gas emboli in sport diving: detection with 2D echocardiography and pulsed Doppler.

The aim of this study was to determine the utility of pulsed Doppler and 2D echocardiography for the detection and the quantification of circulating bubbles after decompression. Twenty-three sport divers performed 60 SCUBA dives (mean 32 msw). An evaluation of circulating bubbles was performed using 2D images one hour after diving. Circulating bubbles were also detected with pulsed Doppler. The sample volume was placed in the outflow area of the right ventricle 1-2 cm below the pulmonary valve. 2D echocardiography showed circulating bubbles in right cavities of the heart in 32 cases. Short axis parasternal view and right cavities long axis view were the best incidences. Pulsed Doppler confirmed the results in these 32 cases and detected circulating bubbles in seven other cases. Isometric contraction of muscle limb must be performed to increase the sensitivity of detection. The count of the bubbles may be evaluated when using a combination of Spencer's and Powell's grading. We conclude that 2D echocardiography is less accurate than pulsed Doppler in the detection of circulating bubbles after decompression. Further studies are needed to compare pulsed Doppler guided by 2D echocardiography to continuous Doppler for the detection of circulating bubbles.

Diagnosis of nosocomial pneumonia in mechanically ventilated patients: repeatability of the bronchoalveolar lavage.

The repeatability of the bronchoalveolar lavage (BAL) was assessed prospectively in 44 mechanically ventilated patients with suspected nosocomial pneumonia. Two BAL were performed in the same lung area (contiguous segment) during two fibroscopic procedures performed with a thirty minute interval. All the bronchoscopies were performed by the same operator. The statistical analysis looked out for bias (MacNemar test), agreement, and repeatability (kappa test). In the 44 patients studied, the qualitative repeatability (i.e., presence or absence of bacteria) was excellent (95.4%). However, in the 16 patients having at least one positive culture, these results were more controversial. The quantitative repeatability for bacteria (same log10 for both BAL of the same patient) was the lowest of all the results (26.7%). The distinction between presence and absence of bacterial pneumonia (based on the 10[4] cfu/ml threshold) showed a repeatability of 75% with no bias, an agreement of 47% and a just-significant kappa test (test = 1.97; p = 1.96 for a 5% risk error). BAL seems to have excellent repeatability when sterile. Its repeatability when positive needs further studies to be assessed.

Left-sided superior vena cava: diagnosis by magnetic resonance imaging.

We describe a case of left-sided superior vena cava. The diagnosis was suggested by chest radiograph after central venous catheter placement. This was subsequently confirmed by magnetic resonance imaging.

Circulating bubbles and breath-hold underwater fishing divers: a two-dimensional echocardiography and continuous wave Doppler study.

Since the 1960s, decompression illness after breath-hold diving has been widely debated. The aim of this study was to detect circulating bubbles after breath-hold diving in underwater fishing divers. We used continuous Doppler (DUG, COMEX Pro) and transthoracic two-dimensional (2D) echocardiography (Kontron Sigma 1). This study was conducted during a training course organized by the French Federation of Subaquatic Sports at Minorca (Balearic Islands). Ten breath-hold divers performed repeated breath-hold dives for periods ranging from 2 to 6 h [mean maximum depth 35 meters of seawater (msw)]. A dive computer (Maestro Pro Beuchat, analyst PC interface) was used to record diving patterns. No circulating bubbles were detected in the right heart cavities (2D echocardiography) or in the pulmonary artery (continuous Doppler). However, this study had some limits: only 10 subjects were studied and the earliest detection was 3 min after immersion, further studies will thus be required.

Echocardiography on HIV patients admitted to the ICU.

A prospective echocardiographic study was conducted in 68 patients with the human immunodeficiency virus (HIV) admitted to the intensive care unit (ICU) (C3 stage 78%, i.v. drug abuse 71%) in order, firstly to, assess the prevalence of cardiac abnormalities, and, secondly, to make an early therapeutic decision. Only five patients presented clinical evidence of cardiac disease. Echocardiographic abnormalities were identified in 35 patients (51%): pericardial effusion: 20 cases (29%), with tamponade in 2 cases that led to an immediate pericardiocentesis. Left ventricular dysfunction: 15 cases (22%) requiring treatment of cardiac failure. Mitral bioprosthesis rupture in 1 patient that led to a surgical procedure. Vegetations of the tricuspid value in 3 drug addicts (4%) requiring early antibiotic treatment. Echocardiography proved to be very helpful in detecting hidden cardiac dysfunctions. It is immensely valuable in ICU management of HIV patients, since prompt initiation of appropriate treatment is essential.

Neurologic decompression illness: a gravity score.

Treatment of neurologic decompression accidents consists of various hyperbaric oxygen (HBO) protocols. To facilitate such comparisons between different protocols we developed a gravity score. A group of 96 divers was used to establish the score. On admission we first identified signs and symptoms that had possible predictive value (chi 2 test). The parameters included were repetitive dive, clinical course before HBO, objective sensory disorder, motor impairment, and urinary disturbances. Each parameter was assigned a coefficient. The sum of the coefficients for each accident, based on the most severe manifestations before decompression therapy, yielded a score for each diver. A multivariate analysis was used to evaluate the overall agreement between the model prediction and clinical observations, which was 78.7%. A second group (66 divers) was used to validate the score; this group showed a significant difference in the gravity score between the divers who had sequelae and those who did not (P = 0.0001), and between the divers who had incapacitating sequelae and those who had mild sequelae (P = 0.04). Eighty-six percent of the divers with a score above 7 developed sequelae. This index remains to be validated in a prospective multicenter study. If endorsed, valid comparisons can be made between the different therapeutic protocols.

Haemoconcentration in neurological decompression illness.

Decompression illness (DCI) is attributed to the formation of bubbles, resulting from the reduction of the ambient pressure. Circulating bubbles lead to capillary leak syndrome, extravasation of plasma and haemoconcentration. Experimental model on animals has shown that a haemoconcentration carried a poor prognosis. We measured the haematocrit level in fifty-eight consecutive sport divers, victims of neurological DCI, admitted to our hyperbaric center, and in sixteen control divers. No significant difference was found in the haematocrit values between the divers with neurological DCI (median 42.5%) and the controls (median 41.75%). The median haematocrit level was significantly higher for divers with neurological sequelae when compared with control (p = 0.01) or with divers without sequelae (p < 0.05). A haematocrit level > or = 48% was correlated with persistent neurological sequelae one month after the accident (p = 0.01). However, a haematocrit < 48% had no prognostic value.

Gallbladder abnormalities in medical ICU patients: an ultrasonographic study.

Patients in the intensive care unit (ICU) have many risks factors for gallbladder stasis or acute acalculous cholecystitis (ACC), including fasting, total parenteral nutrition, sedation, mechanical ventilation, infection and shock. We have performed a prospective study to estimate the prevalence of ultrasonographic gallbladder abnormalities in 30 consecutive medical ICU patients during the first 2 days of their stay in the ICU. Two patients had previously undergone cholecystectomy and were excluded from the study. Seventeen (61%) of the remaining 28 patients presented with gallbladder abnormalities. Considering three major criteria of ACC, 14 patients (50%) presented with either sludge (25%), wall thickening (22%) or hydrops (11%). However, none of the patients needed a surgical procedure during the study because of gallbladder disease. We conclude that an important proportion of ICU patients presented with gallbladder abnormalities shown by ultrasonography and that this may have implications for establishing a diagnosis of ACC using ultrasonographic criteria.

[Prognosis in iatrogenic gas embolism]. / La prognosi delle embolie gassose iatrogene.

Prognosis of iatrogenic air embolism is various according to previous studies. The purpose of this study was to determine the risks factors associated with the prognosis of iatrogenic air embolism. We conducted a retrospective analysis of 113 patients treated with HBO therapy in our hyperbaric center from 1979 to 1993. Initial symptomatology consisted in neurological disorders (71% of cases), respiratory disorders (43% of cases) and hemodynamic disorders (33% of cases). When neurological disorders were observed, HBO therapy included immediate compression to 6 atm abs for 10 to 15 mn with air followed by decompression to 2 atm abs where the patients received 100% oxygen during 1 hour. When no neurological disorders was observed, HBO therapy consisted in an oxygenation for 1 h, 2 atm abs, FiO2 = 1. Overall outcome was: recovery: 69 per cent of cases, sequelae: 26 per cent of cases, death: 5 per cent of cases. Prognosis was very different according to etiologies and existence of neurological disorders. Venous emboli had a better improvement than arterial emboli. In conclusion, patterns of air embolism can be divided clinically into two major categories, cerebral and pulmonary air embolism, which should be individualised in clinical studies. The studies must also individualised etiologies.