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[Conception of a decompression table].

After a given time at bottom, different tissues become saturated to different extents with nitrogen. In diving back to the surface a hydrostatic decompression occurs first, followed by the desaturation process some time later. It is during this time interval that all important events are taking place, namely: either a monophasic desaturation, whereby inert nitrogen gas is given off at the alveolar capillary interface. or a biphasic desaturation takes place, giving rise to gas bubbles in the blood-stream as well as in the tissues. We may then encounter pathologies which are benign incidents or, worse, lead to decompression sickness grade II. Since Paul Bert dedicated his thoughts in 1878 to this problem, numerous authors tried to explain this time delay, for trying to suppress it would be entirely unrealistic. Unfortunately, mathematical reasoning has too often overshadowed physiological thinking in these matters. We also stuck to Haldane's concept of 1908, in incorporating Workman's improvements of 1965. This method is based on two main principles: 1. all calculations were done with several "tissues" in mind. Their anatomical boundaries are of no importance as, only their desaturation half-times are relevant. 2. a natural limit is given by the critical saturation-coefficient (CS). It expresses the ratio between the partial pressure of the dissolved gas and the reduction of hydrostatic pressure during ascent (given as pressure gradient). Through experience we were able to put up tables which were more and more safe, in examining foremost the CS ratio and the desaturation times of certain tissues. Several examples are given, the values of which are statistically highly significant, as they incorporate the results of more than 60,000 air dives.

Decompression↗

Doppler bubble detection and decompression sickness: a prospective clinical trial.

Decompression sickness in human beings exposed to high ambient pressure is thought to follow from gas bubble formation and growth in the body during return to low pressure. Detection of Doppler-shifted ultrasonic reflections in major blood vessels has been promoted as a noninvasive and sensitive indicator of the imminence of decompression sickness. We have conducted a double-blind, prospective clinical trial of Doppler ultrasonic bubble detection in simulated diving using 83 men, of whom 8 were stricken and treated for the clinical disease. Diagnosis based only on the Doppler signals had no correlation with clinical diagnosis. Bubble scores were only slightly higher in the stricken group. The Doppler technique does not appear to be of diagnostic value in the absence of other clinical information.

Clinical Trials as Topic↗

Statistical aspects of the design and testing of decompression tables.

Before a decompression procedure is recommended for general use it is subjected to a limited number of human trial dives. Based on the trial, one attempts to reject unsafe procedures but accept those with a low incidence of decompression sickness (DCS). Binomial confidence regions are often so broad that even after 40 dives it may be impossible to distinguish between the possibility that the table being tested has a 0.6% risk of DCS and the possibility that it has a 17% risk. Our proposed alternative is to select some rule (e.g., one or more cases of DCS in 10 dives) for rejecting tables and to calculate the probabilities of accepting tables as a function of the probability of DCS. With such calculations we conclude that (a) generally one cannot reduce the risk of adopting unsafe tables without increasing the risk of rejecting safe ones unless one chooses to increase the number of test dives; (b) truncated sequential designs could reduce the number of dives required for testing by 15 to 20%; and (c) rules similar to the ones tested will always have a zone of indifference. Tables with a probability of DCS in this zone will be accepted or rejected with nearly equal frequency even if tested with hundreds of dives. The use of models describing the probability of DCS as a function of dive parameters should allow us to combine information from dives previously analyzed separately and perhaps to improve our selection of new tables to be tested.

Atmospheric Pressure↗

Reversal of pressure-induced tremors in rats by step decompression and by inert gases.

A method for continuously recording the motor activity of pressurized rats was used to monitor their condition after 1) holding pressure constant after compression, 2) decompression, and 3) adding nitrogen prior to holding pressure constant. After procedures 1 and 2 the logarithm of activity plotted linearly against time in two distinct phases. A short initial decline was followed by a slower, longer decline that was incomplete after 5 h. The rate of the second, slower decline was inversely related to the holding pressure and unaffected by prior convulsions. The addition of 4.8 atm N2 was very effective at decreasing the activity at constant pressure compared to a large (43%) decompression step. The slopes obtained from plots of activity against pressure, which provide a measure of the sensitivity of the animal to compression, were unaltered by the early inclusion of 4.8 atm N2 or 0.19 atm N2O but were displaced to higher pressures. Activity appears to be the net result of activity-generating and accommodation processes, and there was no evidence that it was in equilibrium with pressure.

Animals↗

Case report on a diver with type II decompression sickness and viral meningitis.

A 33-yr-old man came to the emergency department with the chief complaint of a severe headache and decreased sensation in his right hand following a deep dive on scuba. Physical examination before recompression treatment was remarkable only for hypesthesia on the right hand. We diagnosed type II decompression sickness and the patient underwent standard recompression therapy. The patient experienced near-complete resolution of his symptoms, his only residual complaint being that of neck pain with head movement. To investigate other causes of headache, a computed tomography of the head was performed which was normal, and a lumbar puncture was performed which was consistent with viral meningitis. This is the first reported case of recompression treatment on a patient with viral meningitis and decompression sickness.

Adult↗

Diving decompression fails to activate complement.

The present study evaluated complement activation during decompression after air dives in a hyperbaric chamber. Intravascular bubbles were quantified by Doppler ultrasound scoring. Eighteen subjects completed 92 dives, of which 74 produced bubbles. Complement activation was assessed by plasma C3a des Arg and red-cell-bound C3d before and after each dive. These parameters of in vivo complement activation failed to show significant activation. In vitro complement activation susceptibility tests on pre-dive sera were performed to explore their association with in vivo complement activation and intravascular bubbles. Such tests failed to identify a distinct complement-sensitive group and did not correlate with in vivo complement activation during the dives and/or intravascular bubble appearance. Two subjects developed decompression sickness but were not different from the rest of the group regarding in vitro complement sensitivity or complement activation during dives.

Adult↗

[Decompressive hemicraniectomy for malignant middle cerebral artery infarction. Report of two cases].

Malignant middle cerebral territory infarction represents 5 to 10% of all brain infarctions. Its mortality is 80%, due to brain herniation and it is not reduced by medical treatment. Decompressive hemicraniectomy reduces mortality to 12%, and the subsequent quality of life of patients is acceptable. We report two male patients aged 61 and 54 years, with a malignant middle cerebral territory infarction who were treated with decompressive hemicraniectomy. After two years of follow up, both patients are self-sufficient and live at home with their families.

Craniotomy↗

The role of computed tomography in the assessment of neurologic sequelae of decompression sickness.

Computed tomographic (CT) scans were performed on 47 patients who had received recompression treatment for decompression sickness. A retrospective review of the case notes disclosed that 24 of the 47 patients had symptoms that suggested cerebral involvement. None of the reported CT abnormalities could be correlated with the clinical manifestations at presentation. It was concluded that the CT scan is not a cost-effective investigative tool for the posttreatment evaluation of decompression sickness.

Brain↗

Helium and oxygen treatment of severe air-diving-induced neurologic decompression sickness.

BACKGROUND: The use of helium and oxygen recompression treatment of neurologic decompression sickness (DCS) has several theoretical advantages over the traditionally used air and oxygen recompression tables that have been confirmed by findings from recent animal experiments. OBJECTIVES: To evaluate the outcome of patients with neurologic DCS who had been treated with a helium-oxygen protocol and to compare it with that of a retrospective control group that was treated with air-oxygen tables. DESIGN: The study and control groups included 16 and 17 diving casualties, respectively. The severity of neurologic DCS was estimated according to a 9-point scale weighting motor, sensory, and sphincter control functions. The study group was treated with a helium-oxygen decompression protocol, and the control group was treated with the US Navy air-oxygen Table 6 or 6A. Persistent residual dysfunction was treated in both groups with daily hyperbaric oxygen sessions, at 2.5 absolute atmospheres for 90 minutes, until no further clinical improvement was noted. SETTING: The Israel Naval Medical Institute (Israel's national hyperbaric referral center), Haifa. RESULTS: Significant clinical score increments were found for both the helium-oxygen- and air-oxygen-treated groups: 2.8 +/- 2.4 (mean +/- SD) and 7.4 +/- 1.1 at presentation vs 7.6 +/- 2.1 and 8.1 +/- 1.5 at discharge, respectively (P < .001 and P = .005, respectively). Although the score at presentation was significantly lower for the helium-oxygen-treated group (P < .001), no difference was found between the groups' average outcome scores. While most of the improvement in the patients in the study group could be attributed to the helium-oxygen treatment and not to the supplemental hyperbaric oxygen, in the control group, no significant difference could be demonstrated between the scores at presentation and at completion of the air-oxygen recompression table. In 5 patients who were treated with the use of the air-oxygen tables, deterioration was observed after recompression. No deterioration or neurologic DCS relapse occurred in the helium-oxygen-treated group. CONCLUSION: The results suggest an advantage of helium-oxygen recompression therapy over air-oxygen tables in the treatment of neurologic DCS.

Decompression Sickness↗

Thoracic outlet decompression for subclavian vein thrombosis: experience in 71 patients.

HYPOTHESIS: There is a difference in outcomes when patients have neurogenic thoracic outlet syndrome in addition to subclavian vein thrombosis. METHODS: Analysis of a prospectively developed database, medical record review, and a patient questionnaire were used to summarize clinical experience from December 1990 to December 2001 on the basis of the patient's original evaluation. Patients were stratified on the presence (group 1) or absence (group 2) of additional neurogenic pathologic features. RESULTS: Of 928 patients evaluated for thoracic outlet syndrome, 71 underwent 73 operative procedures for subclavian vein obstruction. Men predominated (55%), and the mean age was 32 years. Group 1 (41%) had more preoperative disability, a higher incidence of persistent pain (24%), and less likelihood of returning to full activity compared with group 2 (67% vs 93%; P = .01). Catheter-directed thrombolysis was used in 65% of veins. Preoperative balloon angioplasty was used selectively (34%), and only 4% required stents. Supraclavicular decompression and venolysis were usually delayed 3 weeks to allow for healing of the venous endothelium. Complications included wound infection (3%) and postoperative hematoma (8%). CONCLUSIONS: Patients with isolated subclavian vein obstruction have a more favorable outcome relative to those with combined neurogenic and venous pathologic features. Decompression following thrombolysis should be delayed to reduce the incidence of postoperative complications.

Adult↗

Decompressive craniectomy for the treatment of refractory high intracranial pressure in traumatic brain injury.

BACKGROUND: High intracranial pressure (ICP) is the most frequent cause of death and disability after severe traumatic brain injury (TBI). High ICP is treated by general maneuvers (normothermia, sedation etc) and a set of first line therapeutic measures (moderate hypocapnia, mannitol etc). When these measures fail to control high ICP, second line therapies are started. Among these, second line therapies such as barbiturates, hyperventilation, moderate hypothermia or removal of a variable amount of skull bone (known as decompressive craniectomy) are used. OBJECTIVES: To assess the effects of secondary decompressive craniectomy (DC) on outcome and quality of life in patients with severe TBI in whom conventional medical therapeutic measures have failed to control raised ICP. SEARCH STRATEGY: We searched the Cochrane Injuries Group's Trial Register, CENTRAL, MEDLINE, EMBASE, Best Evidence, Clinical Practice Guidelines, PubMed, CINAHL, the National Research Register and Google Scholar. We also handsearched relevant conference proceedings and contacted experts in the field and the authors of included studies. SELECTION CRITERIA: Randomized or quasi-randomized studies assessing patients over the age of 12 months with a severe TBI who underwent DC to control ICP refractory to conventional medical treatments. DATA COLLECTION AND ANALYSIS: Two authors independently examined the electronic search results for reports of possibly relevant trials and for retrieval in full. One author applied the selection criteria, performed the data extraction and assessed methodological quality. Study authors were contacted for additional information. MAIN RESULTS: We found one trial with 27 participants conducted in the pediatric population (>18 years). DC was associated with a risk ratio (RR) for death of 0.54 (95% CI 0.17 to 1.72), and RR of 0.54 for death, vegetative status or severe disability 6 to 12 months after injury (95% CI 0.29 to 1.07). AUTHORS' CONCLUSIONS: There is no evidence to support the routine use of secondary DC to reduce unfavourable outcome in adults with severe TBI and refractory high ICP. In the pediatric population DC reduces the risk of death and unfavourable outcome. Despite the wide confidence intervals for death and the small sample size of the only study identified, this treatment maybe justified in patients below the age of 18 when maximal medical treatment has failed to control ICP. To date, there are no results from randomised trials to confirm or refute the effectiveness of DC in adults. However, the results of non-randomized trials and controlled trials with historical controls involving adults, suggest that DC may be a useful option when maximal medical treatment has failed to control ICP. There are two ongoing randomized controlled trials of DC (Rescue ICP and DECRAN) that may allow further conclusions on the efficacy of this procedure in adults.

Brain Injuries↗

Open versus arthroscopic subacromial decompression: analysis of one-year results.

The results of open subacromial decompression (OSD) were compared with arthroscopic subacromial decompression (ASD) after 1 year in 32 subjects (4 bilateral), and the correlation between the two shoulder rating scales for impingement was documented. Patients were evaluated clinically on the modified University of California at Los Angeles (UCLA) shoulder rating scale, and Constant scale. Scapular position and rotation were evaluated as well as a rotation and abduction shoulder strength test using the Cybex II dynamometer. No parameters revealed significant differences between the groups, except for the UCLA score which indicated an advantage for the ASD group (p = 0.046). The OSD group scored 24.5 (5.45) on the UCLA scale and 73.8 (18.9) on the Constant scale, whereas the ASD group scored 28.3 (5.6) and 80.8 (16.4). To study the correlation between both scales, the Pearson correlation product-moment coefficient was calculated and a high correlation (r = 0.81) obtained. Less mobility was found in the operated arm for all parameters, with the exception of glenohumeral abduction in both groups and passive elevation in the OSD group. Only in the OSD group did the scapula in the operated extremity show more abduction of the inferior angle of the scapula. Weaker abduction strength in the operated side was found in the ASD group, whereas in the OSD group there was significantly less adduction and external rotation strength at 180 degrees/s en 240 degrees/s. We conclude that after one year the open group tends to catch up with the arthroscopic patients and that the main benefits after arthroscopic surgery as described in literature are more evident in the shorter period.

Adult↗

Lumbar spinal decompression with a pneumatic orthesis (Orthotrac): preliminary study.

AIM: We present a preliminary study on the conservative treatment of chronic low back pain (LBP) using an easy to manage and extremely practical orthesis. It consists of a pneumatic custom made lumbar vest (Orthotrac), which permits both support-stabilisation and decompression. This system is versatile since the patient is not impeded and can perform any activity while wearing it. MATERIAL: The study included 41 patients (23 males and 18 females, aged between 19 and 25 years) with radicular pain due to degenerative discopathy including: dark disc, discal protrusion with neural foramina involvement, stenosis of the foramina, syndrome of the facets, Grade 1 listhesis. Patients had to wear the Orthotrac vest according to a precise protocol, 60 minutes 3 times a day for 5 weeks. RESULTS: 32 patients (78%) have showed a significant subjective and clinical improvement with subsequent better quality of life. All patients referred a decrease or disappearance of radicular pain. Outcome measures were evaluated according to SF-36 system which is used in clinical practice and research. As in any innovative therapy, selection of patients is extremely important. The pneumatic vest is not indicated in all patients, but it can play an important role in non-surgical therapy for LBP. CONCLUSION: The system seems to give an effective spinal decompression and deserves a careful consideration when lumbar discal disease is treated conservatively. Further multicenter and interdisciplinary studies on a greater number of patients are obviously needed to confirm these preliminary results.

Back Pain↗

Decompressive craniectomy in traumatic brain injury: the randomized multicenter RESCUEicp study (www.RESCUEicp.com).

The RESCUEicp (Randomized Evaluation of Surgery with Craniectomy for Uncontrollable Elevation of intracranial pressure) study has been established to determine whether decompressive craniectomy has a role in the management of patients with traumatic brain injury and raised intracranial pressure that does not respond to initial treatment measures. We describe the concept of decompressive craniectomy in traumatic brain injury and the rationale and protocol of the RESCUEicp study.

Biomedical Research↗

Which paediatric head injured patients might benefit from decompression? Thresholds of ICP and CPP in the first six hours.

Severe head injury in childhood continues to be associated with considerable mortality and morbidity. Early surgical decompression may be beneficial and the objective of this study was to examine the relationship between age-related thresholds of mean intracranial pressure (ICP) and cerebral perfusion pressure (CPP) over the first 6 hours and age outcome in paediatric head injury patients. A total of 209 head injured children admitted to five UK hospitals were studied. Patients aged 2 to 16 years were included if they had a minimum of six hours of invasive pressure monitoring. Mean values of ICP and CPP over this period were calculated and compared to those with independent (good recovery and moderate disability) and poor outcome (severe disability, and death) for different age groups. There were 148 children with independent outcome (92 good recovery, 56 moderately disabled), and 61 with poor outcome (30 severely disabled, 31 deaths). There was a significant difference between those with independent compared to poor outcome in relation to ICP (p < 0.001) and CPP (p < 0.001). Patients were divided into three groups according to age. The sensitivity of ICP and CPP in predicting outcome was similar for all groups but the specificity differed between groups. At a CPP of 50 mmHg the specificity varied between the age groups (2 to 6 years: 0.47, 7 to 10 years: 0.28 and 11 to 16 years: 0.10) and similarly for an ICP of 25 mmHg (2 to 6 years: 0.53, 7 to 10 years: 0.44 and 11 to 16 years: 0.38). Younger children may be able to tolerate lower perfusion pressures and still have an independent outcome. Our threshold values for young children are likely to be important in the identification of patients who might benefit from new treatments such as surgical decompression.

Adolescent↗

[Fatal decompression sickness following therapeutic hyperbaric environment (author's transl)].

In Hannover/Germany in 1976 a so called "Society for Regenerative Hyperbaric Therapy" (Gesellschaft für Regenerative Uberdruck-Therapie) subjected 20 patients within two coupled multi-place chambers to a simulated hyperbaric environment, equivalent to a maximum of 4 ata, followed usually by gradual reductions of the pressure. The patients were of an average age of 67.2 years and were afflicted by various disorders. During one of the "dives" a patient developed air embolism of the central nervous system. During ensuing confusion of the chamber was opened suddenly, with resultant explosive reduction of the high pressure. This resulted in five letal accidents of decompression sickness. Post mortem examination revealed diffuse distribution of gas bubbles throughout the entire body. By elecronmicroscopy each bubble was covered by an osmiophilic coat. Post mortem findings are discussed and correlated with well-known and new clinical symptomes. These observations present for the first time fatal accidents of decompression sickness in humans, associated with hyperbaric air-therapy.

Aged↗

Blood biochemical and cellular changes during decompression and simulated extravehicular activity.

Blood biochemical and cellular parameters were measured in human subjects before and after exposure to a decompression schedule involving 6 h of oxygen prebreathing. The exposure was designed to simulate extravehicular activity for 6 h (subjects performed exercise while exposed to 29.6 kPa). There were no significant differences between blood samples from subjects who were susceptible (n = 11) versus those who were resistant (n = 27) to formation of venous gas emboli. Although several statistically significant (P less than 0.05) changes in blood parameters were observed following the exposure (increases in white blood cell count, prothrombin time, and total bilirubin, and decreases in triglycerides, very-low-density lipoprotein cholesterol, and blood urea nitrogen), the changes were small in magnitude and blood factor levels remained within normal clinical ranges. Thus, the decompression schedule used in this study is not likely to result in blood changes that would pose a threat to astronauts during extravehicular activity.

Adult↗

Effects of exercise on the incidence of decompression sickness: a review of pertinent literature and current concepts.

The effects of exercise on the incidence of decompression sickness (DCS) are not completely understood. This paper reviews studies that have addressed this question. Studies have involved exposures of animals and human subjects to high pressures, which would occur in SCUBA diving operations, and to low pressures, which exist during high-altitude aircraft flights and extravehicular activities during space flight. The temporal course of the exercise in relation to the decompression procedure and the nature of the exercise may influence effects on DCS incidence. Effects of exercise on the uptake and elimination of nitrogen, the production of bubbles due to limb movements, the potential role of carbon dioxide, and current plans for further research are discussed.

Aerospace Medicine↗