What outcomes are important for patients after pelvic trauma? Subjective responses and psychometric analysis of three published pelvic-specific outcome instruments.

OBJECTIVE: The measurement of functional outcomes in pelvic fracture patients remains difficult for authors. The authors aimed to test the construct validity, respondent burden, floor and ceiling effects, and patient perception of 3 previously published pelvic outcome questionnaires. DESIGN: Prospective case series. SETTING: Level I Trauma Center. PATIENTS: Those with surgically treated Orthopaedic Trauma Association (OTA) B and C pelvic ring disruption at greater than 12 months after treatment. INTERVENTION: None. MAIN OUTCOME MEASUREMENT: Majeed Pelvic Score, Orlando Pelvic Score, Iowa Pelvis Score, Short Form-36, and Short Musculoskeletal Functional Assessment (SMFA). RESULTS: The authors recruited 38 patients, 15 OTA C and 23 OTA B fractures, who had a mean of 57 months from surgery (13-115 months). Patients cited recreational/mobility difficulty (30), emotional stress and family strain (24), employment and financial difficulty (17), sleep disturbance and anxiety (9), and sexual function (6) as the most important consequences of their injuries. Each of the 3 pelvic outcome questionnaires showed a high correlation with the Physical Component Score of the SF-36, and both indices of the SMFA. None had a high correlation with the Mental Component Score of the SF-36, indicating that these scores do not capture psychologic distress and well-being, social functioning, and overall vitality. All 3 questionnaires demonstrated ceiling effects, with 21%, 18%, and 15% of respondents reporting the highest possible scores on the Iowa, Majeed, and Orlando scores, respectively. The time for completion was 3.6 ± 0.4 minutes for the Iowa score, 7.4 ± 0.4 for the Orlando score (not including radiographic assessment), and 2.6 ± 0.2 for the Majeed score. Fifteen patients preferred the Iowa score, 12 the Orlando score, and 11 the Majeed instrument. CONCLUSIONS: Three previously published pelvic outcome instruments were found to have strong construct validity based on correlation with the Physical Component Score of the SF-36 and both indices of the SMFA. Subjects identified mental and emotional outcomes as important consequences of their injury; however, none of the pelvic questionnaires measure these domains, as they all correlate poorly with the Mental Component Score of the SF-36. Ceiling effects limit the utility of the all 3 current instruments, and their reliability and responsiveness over time remain unknown. No currently available outcome instrument seems to captures all of the important consequences of these injuries.

Temporal trends in the treatment of severe traumatic hemorrhage.

BACKGROUND: This study examined the evolution of damage control resuscitation (DCR) and outcomes in severe traumatic hemorrhage (STH) at a large Canadian trauma center. METHODS: This was a retrospective cohort study of trauma patients admitted to a level 1 trauma center between 2005 and 2010, who received 10 or more units of packed red blood cells within 24 hours of admission. Demographic and clinical findings were compared between survivors and nonsurvivors. RESULTS: Forty-five patients were included. Twenty-five percent of patients were coagulopathic at admission. Early crystalloid use declined over the study period. The mean 24-hour fresh-frozen plasma:platelets:packed red blood cells ratio was 1:1:2. Hemorrhage-related mortality was 69%. No pedestrians survived STH. A total of 1,032 blood product units were used in the first day for nonsurvivors. CONCLUSIONS: Principles of DCR crept into clinical practice even before the implementation of a formal STH protocol. DCR appeared to reduce the intensive care unit length of stay but not mortality. STH is associated with heavy use of blood bank resources and high mortality rates. Futility of resuscitative efforts may be predictable by mechanism and early physiological markers.

Nutrient co-limitation of primary producer communities.

Synergistic interactions between multiple limiting resources are common, highlighting the importance of co-limitation as a constraint on primary production. Our concept of resource limitation has shifted over the past two decades from an earlier paradigm of single-resource limitation towards concepts of co-limitation by multiple resources, which are predicted by various theories. Herein, we summarise multiple-resource limitation responses in plant communities using a dataset of 641 studies that applied factorial addition of nitrogen (N) and phosphorus (P) in freshwater, marine and terrestrial systems. We found that more than half of the studies displayed some type of synergistic response to N and P addition. We found support for strict definitions of co-limitation in 28% of the studies: i.e. community biomass responded to only combined N and P addition, or to both N and P when added separately. Our results highlight the importance of interactions between N and P in regulating primary producer community biomass and point to the need for future studies that address the multiple mechanisms that could lead to different types of co-limitation.

Herbivore metabolism and stoichiometry each constrain herbivory at different organizational scales across ecosystems.

Plant-herbivore interactions mediate the trophic structure of ecosystems. We use a comprehensive data set extracted from the literature to test the relative explanatory power of two contrasting bodies of ecological theory, the metabolic theory of ecology (MTE) and ecological stoichiometry (ES), for per-capita and population-level rates of herbivory across ecosystems. We found that ambient temperature and herbivore body size (MTE) as well as stoichiometric mismatch (ES) both constrained herbivory, but at different scales of biological organization. Herbivore body size, which varied over 11 orders of magnitude, was the primary factor explaining variation in per-capita rates of herbivory. Stoichiometric mismatch explained more variation in population-level herbivory rates and also in per-capita rates when we examined data from within functionally similar trophic groups (e.g. zooplankton). Thus, predictions from metabolic and stoichiometric theories offer complementary explanations for patterns of herbivory that operate at different scales of biological organization.

Producer nutritional quality controls ecosystem trophic structure.

Trophic structure, or the distribution of biomass among producers and consumers, determines key ecosystem values, such as the abundance of infectious, harvestable or conservation target species, and the storage and cycling of carbon and nutrients. There has been much debate on what controls ecosystem trophic structure, yet the answer is still elusive. Here we show that the nutritional quality of primary producers controls the trophic structure of ecosystems. By increasing the efficiency of trophic transfer, higher producer nutritional quality results in steeper ecosystem trophic structure, and those changes are more pronounced in terrestrial than in aquatic ecosystems probably due to the more stringent nutritional limitation of terrestrial herbivores. These results explain why ecosystems composed of highly nutritional primary producers feature high consumer productivity, fast energy recycling, and reduced carbon accumulation. Anthropogenic changes in producer nutritional quality, via changes in trophic structure, may alter the values and functions of ecosystems, and those alterations may be more important in terrestrial ecosystems.

A cross-system synthesis of consumer and nutrient resource control on producer biomass.

Nutrient availability and herbivory control the biomass of primary producer communities to varying degrees across ecosystems. Ecological theory, individual experiments in many different systems, and system-specific quantitative reviews have suggested that (i) bottom-up control is pervasive but top-down control is more influential in aquatic habitats relative to terrestrial systems and (ii) bottom-up and top-down forces are interdependent, with statistical interactions that synergize or dampen relative influences on producer biomass. We used simple dynamic models to review ecological mechanisms that generate independent vs. interactive responses of community-level biomass. We calibrated these mechanistic predictions with the metrics of factorial meta-analysis and tested their prevalence across freshwater, marine and terrestrial ecosystems with a comprehensive meta-analysis of 191 factorial manipulations of herbivores and nutrients. Our analysis showed that producer community biomass increased with fertilization across all systems, although increases were greatest in freshwater habitats. Herbivore removal generally increased producer biomass in both freshwater and marine systems, but effects were inconsistent on land. With the exception of marine temperate rocky reef systems that showed positive synergism of nutrient enrichment and herbivore removal, experimental studies showed limited support for statistical interactions between nutrient and herbivory treatments on producer biomass. Top-down control of herbivores, compensatory behaviour of multiple herbivore guilds, spatial and temporal heterogeneity of interactions, and herbivore-mediated nutrient recycling may lower the probability of consistent interactive effects on producer biomass. Continuing studies should expand the temporal and spatial scales of experiments, particularly in understudied terrestrial systems; broaden factorial designs to manipulate independently multiple producer resources (e.g. nitrogen, phosphorus, light), multiple herbivore taxa or guilds (e.g. vertebrates and invertebrates) and multiple trophic levels; and - in addition to measuring producer biomass - assess the responses of species diversity, community composition and nutrient status.

Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems.

The cycles of the key nutrient elements nitrogen (N) and phosphorus (P) have been massively altered by anthropogenic activities. Thus, it is essential to understand how photosynthetic production across diverse ecosystems is, or is not, limited by N and P. Via a large-scale meta-analysis of experimental enrichments, we show that P limitation is equally strong across these major habitats and that N and P limitation are equivalent within both terrestrial and freshwater systems. Furthermore, simultaneous N and P enrichment produces strongly positive synergistic responses in all three environments. Thus, contrary to some prevailing paradigms, freshwater, marine and terrestrial ecosystems are surprisingly similar in terms of N and P limitation.

Consumer versus resource control of producer diversity depends on ecosystem type and producer community structure.

Consumer and resource control of diversity in plant communities have long been treated as alternative hypotheses. However, experimental and theoretical evidence suggests that herbivores and nutrient resources interactively regulate the number and relative abundance of coexisting plant species. Experiments have yielded divergent and often contradictory responses within and among ecosystems, and no effort has to date reconciled this empirical variation within a general framework. Using data from 274 experiments from marine, freshwater, and terrestrial ecosystems, we present a cross-system analysis of producer diversity responses to local manipulations of resource supply and/or herbivory. Effects of herbivory and fertilization on producer richness differed substantially between systems: (i) herbivores reduced species richness in freshwater but tended to increase richness in terrestrial systems; (ii) fertilization increased richness in freshwater systems but reduced richness on land. Fertilization consistently reduced evenness, whereas herbivores increased evenness only in marine and terrestrial ecosystems. Producer community evenness and ecosystem productivity mediated fertilization and herbivore effects on diversity across ecosystems. Herbivores increased producer richness in more productive habitats and in producer assemblages with low evenness. These same assemblages also showed the strongest reduction in richness with fertilization, whereas fertilization increased (and herbivory decreased) richness in producer assemblages with high evenness. Our study indicates that system productivity and producer evenness determine the direction and magnitude of top-down and bottom-up control of diversity and may reconcile divergent empirical results within and among ecosystems.

Predators accelerate nutrient cycling in a bromeliad ecosystem.

Conventional ecological theory predicts that predators affect nutrient cycling by decreasing the abundance or activity of prey. By using a predator-detritivore-detritus food chain in bromeliads, we show that predators can increase nutrient cycling by a previously undescribed, but broadly applicable, mechanism: reducing nutrient export by prey emigration. Contrary to expectations, predation on detritivores increases detrital nitrogen uptake by bromeliads. Predation reduces detritivore emergence and hence export of nitrogen from the system. Detritivores therefore benefit their host plant, but only when predators are present. More generally, our results show that predator loss or extinction can dramatically and unexpectedly affect ecosystem functioning.