Adjuvant hyperbaric oxygen therapy (HBO2)for treatment of necrotizing fasciitis reduces mortality and amputation rate.

OBJECTIVE: A retrospective analysis of 42 patients with necrotizing soft tissue infections treated with adjunctive HBO2 to ascertain efficacy and safety. Overall mortality was 11.9% and morbidity 5%. SUMMARY BACKGROUND DATA: Necrotizing soft tissue infections have historically high rates of mortality and morbidity, including amputation. Common misconceptions that prevent widespread use of adjunctive HBO2 for this diagnosis include delays to surgery, increased morbidity, and significant complications. METHODS: Forty-two consecutive patients (average age 56.1) with necrotizing fasciitis presenting to a major referral center were treated with adjunctive HBO2 as part of an aggressive program of surgery, antibiotics, and critical care. Involved areas included the lower abdomen (15 patients), thigh and perineum (9 patients), flank (4 patients), lower leg (3 patients), and arm, shoulder, and axilla (2 patients). Co-morbidities included diabetes mellitus, chronic renal failure, intravenous drug abuse, peripheral vascular disease, and malignancy. RESULTS: Mortality was 11.9% (5 patients). Both amputations (a finger and a penis), occurred prior to transport to our facility. The average number of surgical debridements was 2.8 per patient; 1.25 performed prior to the start of HBO. The infectious process was controlled after an average of 7 HBO2 treatments were administered to ensure successful wound closure. Complications consisted of only mild ear barotrauma in 3 patients (7%), and confinement anxiety in 17 (41%) but did not prevent treatment. CONCLUSION: Compared to national reports of outcomes with "standard" regimens for necrotizing fasciitis, our experience with HBO2, adjunctive to comprehensive and aggressive management, demonstrates reduced mortality (34% v. 11.9%), and morbidity (amputations 50% v. 0%). The treatments were safe and no delays to surgery or interference with standard therapy could be attributed to HBO2.

Noninvasive cardiac output by partial CO2 rebreathing after severe chest trauma.

BACKGROUND: In multiple trauma patients, early continuous cardiac output (CCO) monitoring is frequently desired but is difficult to routinely employ in most emergency departments because it requires invasive procedures. Recently, a noninvasive cardiac output (NICO) technique based on the Fick principle and partial CO2 rebreathing has shown promise under a variety of conditions. Since this method has not been tested after lung damage, we evaluated its utility in a clinically relevant model. METHODS: Anesthetized, ventilated swine (n = 11, 35-45 kg) received a unilateral blunt trauma via a captive bolt gun followed by a 25% hemorrhage. After 60 min of shock, crystalloid resuscitation was given as needed to maintain heart rate < 100 beats/min and mean arterial pressure > 70 mm Hg. Standard CCO by thermodilution (Baxter Vigilance, Irvine, CA) was compared with NICO (Novametrix Medical Systems Inc., Wallingford, CT) for 8 hr. RESULTS: The severity of the injury is reflected by seven deaths (average survival time = 4.25 hr). Trauma increased dead space ventilation (19%), airway resistance (30%), and lactate (3.2 mmol/L), and decreased dynamic compliance (48%) and Pao2/Fio2 (54%). In these extreme conditions, the time course and magnitude of change of CCO and NICO were superimposed. Bland-Altman analysis reveal a bias and precision of 0.01 +/- 0.69 liters/min. The linear relationship between individual CCO and NICO values was significant (p < 0.0001) and was described by the equation NICO = (0.74 +/- 0.1)CCO + (0.65 +/- 0.16 liters/min) but the correlation coefficient (r2 = 0.541) was relatively low. The cause for the low correlation could not be attributed to increased pulmonary shunt, venous desaturation, anemia, hypercapnia, increased dead space ventilation, or hyperlactacidemia. CONCLUSION: NICO correlated with thermodilution CCO, but underestimated this standard by 26% in extreme laboratory conditions of trauma-induced cardiopulmonary dysfunction; 95% of the NICO values fall within 1.38 liters/min of CCO; and with further improvements, NICO may be useful in multiple trauma patients requiring emergency intubation during initial assessment and workup.

Pulmonary edema associated with scuba diving : case reports and review.

Acute pulmonary edema has been associated with cold-water immersion in swimmers and divers. We report on eight divers using a self-contained underwater breathing apparatus (scuba) who developed acute pulmonary edema manifested by dyspnea, hypoxemia, and characteristic chest radiographic findings. All cases occurred in cold water. All scuba divers were treated with complete resolution, and three have returned to diving without further episodes. Mechanisms that would contribute to a raised capillary transmural pressure or to a reduced blood-gas barrier function or integrity are discussed. Pulmonary edema in scuba divers is multifactorial, and constitutional factors may play a role. Physicians should be aware of this potential, likely underreported, problem in scuba divers.

Insect herbivory accelerates nutrient cycling and increases plant production.

Ecologists hold two views about the role of herbivory in ecosystem dynamics. First, from a food web perspective in population/community ecology, consumption by herbivores reduces plant abundance. Second, from a nutrient cycling perspective in ecosystem ecology, herbivory sometimes slows down cycling, which decreases plant abundance, but at other times speeds up cycling, which possibly increases plant abundance. The nutrient cycling perspective on herbivory has been experimentally addressed more thoroughly in aquatic systems than in terrestrial systems. We experimentally examined how grasshoppers influence nutrient cycling and, thereby, plant abundance and plant species composition over a period of 5 years. We examined how grasshoppers influence nutrient (nitrogen) cycling (i) by their excrement, (ii) by changing the abundance of and the decomposition rate of plant litter, and (iii) by both. Grasshoppers may speed up nitrogen cycling by changing the abundance and decomposition rate of plant litter, which increases total plant abundance (up to 32.9 g/m(2) or 18%), especially, the abundance of plants that are better competitors when nitrogen is more available. However, whether grasshoppers enhance plant abundance depends on how much they consume. Consequently, ecosystems and food web perspectives are not mutually exclusive. Finally, under some conditions, grasshoppers may decrease nutrient cycling and plant abundance.

Chronic radiation proctitis treated with hyperbaric oxygen.

Chronic proctitis is a well-known complication of therapeutic irradiation. The results of hyperbaric oxygen therapy (HBO2) used in the treatment of chronic radiation proctitis are reported. From 1992 to 1995, 14 patients with chronic radiation-induced proctitis were treated with HBO2. Nine patients were treated in a monoplace chamber at 2.0 atm abs (203 kPa O2), and five patients were treated at 2.36 atm abs (239 kPa O2). Eight patients experienced complete resolution of symptoms and one patient had substantial improvement for a total response rate of 64%. Follow-up ranged from 5 to 35 mo. (mean 17 mo.). Five patients (36%) were classified as non-responders. Three experienced significant improvement during treatment but relapsed soon after therapy was discontinued, whereas two had no symptomatic improvement. Responders who had sigmoidoscopy after therapy showed documented improvement whereas no non-responders showed improvement. The authors conclude that HBO2 therapy should be considered in patients with chronic radiation proctitis.

The effect of hyperbaric oxygen therapy on a burn wound model in human volunteers.

A previous nonblinded study has suggested beneficial effects from hyperbaric oxygen treatment of superficial partial-thickness radiation burns in human volunteers. This protocol was designed to either confirm or challenge these previous findings in a randomized, blinded format. Twelve healthy, nonsmoking volunteers (7 males, 5 females) participated. All were screened for contraindications to hyperbaric oxygen therapy (acute sinusitis, otitis media, pneumonia, pregnancy, active cancer, pneumothorax) and given a single test hyperbaric exposure. A standardized wound model was employed for the painless creation of a volar forearm lesion on volunteers by applying a suction device to form a blister, excising its epidermal roof, and irradiating the exposed dermis with ultraviolet light. Subjects were randomized into either a hyperbaric oxygen group (100% oxygen at 2.4 ATA, n = 6) or the sea-level air-breathing equivalent control group (8.75% oxygen at 2.4 ATA, n = 6). Both groups then underwent standard hyperbaric therapy. The subjects, the hyperbaric oxygen chamber operators, and the monitoring clinicians were all blinded to the oxygen concentration administered. Each subject received two dives per day over a 3-day period. The wounds were studied noninvasively prior to treatment and once per day over 6 days for size, hyperemia, and exudation, with epithelialization as the endpoint. The averages for each measurement of the hyperbaric oxygen group versus the control group were computed by means of a one-tail t test; p was considered significant at less than 0.05. Daily wound size, hyperemia, and exudation measurements were significantly different on day 2. The hyperbaric oxygen group showed a 42 percent reduction in wound hyperemia, a 35 percent reduction in the size of the lesion, and a 22 percent reduction in wound exudation (p values of 0.05, 0.03, and 0.04, respectively). No significant difference was noted for epithelialization. Observed differences in wound size, hyperemia, and exudation were attributable to hyperbaric oxygen therapy. This study further supports earlier conclusions that hyperbaric oxygen therapy is beneficial in a superficial dermal wound.

Transcutaneous oxygen measurements predict healing of leg wounds with hyperbaric therapy.

Twenty-six patients with chronic leg wounds had transcutaneous oxygen measurements taken from the peri-wound area and a chest reference site before undergoing hyperbaric oxygen therapy in order to evaluate the utility of transcutaneous oxygen measurements in predicting the response of wounds to hyperbaric therapy. Wound scores and wound areas were determined before treatment and after 10 hyperbaric exposures. Patients whose wounds averaged a 5% or greater reduction in wound score per treatment were designated "responders." Nine patients' wounds exhibited at least a 5% reduction in wound score per treatment. There were no differences observed between responders and the 17 nonresponders in age, duration of the wound, initial wound area, initial wound score, or in wound or reference transcutaneous oxygen measurements. Responders required significantly fewer treatments to achieve wound closure than did nonresponders. Peri-wound transcutaneous oxygen pressure when the patient was exposed to 2.4 atmospheres absolute correlated directly with the improvement in wound score per treatment (r = 0.64, p = 0.03). An inverse correlation was noted between surface peri-wound transcutaneous oxygen pressure and improvement in wound score per treatment (r = -0.74, p = 0.006). Elevated peri-wound transcutaneous oxygen measurements at 2.4 atmospheres absolute and reduced peri-wound oxygen measurements at 1 atmosphere absolute were associated with a more rapid response to hyperbaric oxygen treatments in patients with chronic leg wounds. The use of these measurements should allow this expensive and time-consuming therapy to be limited to those patients most likely to benefit.

Influence of hyperbaric oxygen on the pharmacokinetics of single-dose gentamicin in healthy volunteers.

STUDY OBJECTIVE: To determine the single-dose pharmacokinetics of gentamicin in healthy humans undergoing hyperbaric oxygen (HBO) exposure. DESIGN: Randomized, crossover trial. SETTING: Specialized hyperbaric research facility within a United States Air Force medical center. SUBJECTS: Five healthy men between 28 and 43 years of age. INTERVENTIONS: Each subject received a total of two doses of intravenous gentamicin 1.5 mg/kg lean body weight spaced at least 2 weeks apart. One dose was infused under normobaric oxygen (NBO) conditions and the other under HBO conditions. MEASUREMENTS AND MAIN RESULTS: Gentamicin pharmacokinetic values were determined on 11 serum samples per subject collected sequentially out to 300 minutes after infusion. Using PCNONLIN, the following results demonstrated no difference between the pharmacokinetic values under HBO and NBO conditions, respectively: beta half-life (112, 115 min); volume of distribution (0.201, 0.184 L/kg); peak concentration (6.52, 7.23 mg/L); clearance (0.0754, 0.0676 L/kg/hr). CONCLUSIONS: Hyperbaric oxygen produced no changes in the measured pharmacokinetic values of gentamicin under the conditions specified in this study. It is possible that numerous HBO exposures could produce a cumulative effect on gentamicin pharmacokinetics that would not be discernible in a single-dose study. Because of the profound physiologic effects of HBO, drugs with narrow therapeutic indexes should be evaluated under HBO conditions if they are to be given to patients receiving HBO treatments.

Effects of spines and thorns on Australian arid zone herbivores of different body masses.

We investigated the effects of thorns and spines on the feeding of 5 herbivore species in arid Australia. The herbivores were the rabbit (Oryctolagus cuniculus), euro kangaroo (Macropus robustus), red kangaroo (Macropus rufus), sheep (Ovis aries), and cattle (Bos taurus). Five woody plants without spines or thorns and 6 woody plants with thorns were included in the study. The spines and thorns were not found to affect the herbivores' rates of feeding (items ingested/min), but they did reduce the herbivores' rates of biomass ingestion (g-dry/item). The reduction in biomass ingested occurred in two ways: at a given diameter, twigs with spines and thorns had less mass than undefended plants, and the herbivores consumed twigs with smaller diameters on plants with spines and thorns. The relative importance of the two ways that twigs with spines and thorns provided less biomass varied with herbivore body mass. Reduced twig mass was more important for small herbivores, while large herbivores selected smaller diameters. The effectiveness of spines and thorns as anti-herbivore defenses did not vary with the evolutionary history of the herbivores (i.e. native vs. introduced). Spines and thorns mainly affected the herbivores' selection of maximum twig sizes (reducing diameter and mass), but the minimum twig sizes selected were also reduced.

Time budgets of grassland herbivores: body size similarities.

The summer (May-September) time budgets of 14 generalist herbivore species living in the same grassland environment are presented in terms of various component activities (e.g., walking, feeding, resting, etc.). All the species exhibit a decrease in activity as average daily air temperature increases. Greater body size and variety of habitats used by a species lead to increased time spent active. Use of a greater variety of habitats may increase activity time because different habitats provide suitable thermal conditions for activity at different times of the day. Body size affects sn herbivore's thermal balance through metabolism, body surface area and thermal inertia. The time spent feeding, exclusive of time spent searching for foods, is less for large than small herbivores. This may arise because large species must spend more time walking in the search for food to satisfy their energy requirements. The observed feeding time differences for species composing a common trophic level in a single environment may help to explain their diet choice because feeding time constrains the variety of foods an herbivore can select. Diet differences, in turn, can explain the potential competition for food if food is in short supply.