Microbial metabolomic responses to changes in temperature and salinity along the western Antarctic Peninsula

Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.

Temperature sensitivity of carbon concentrating mechanisms in the diatom Phaeodactylum tricornutum

Marine diatoms are key primary producers across diverse habitats in the global ocean. Diatoms rely on a biophysical carbon concentrating mechanism (CCM) to supply high concentrations of CO₂ around their carboxylating enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to be highly sensitive to temperature, as temperature impacts CO₂ concentration, diffusivity, and the kinetics of CCM components. Here, we used membrane inlet mass spectrometry (MIMS) and modeling to capture temperature regulation of the CCM in the diatom Phaeodactylum tricornutum (Pt). We found that enhanced carbon fixation rates by Pt at elevated temperatures were accompanied by increased CCM activity capable of maintaining RuBisCO close to CO₂ saturation but that the mechanism varied. At 10 and 18 °C, diffusion of CO₂ into the cell, driven by Pt's 'chloroplast pump' was the major inorganic carbon source. However, at 18 °C, upregulation of the chloroplast pump enhanced (while retaining the proportion of) both diffusive CO₂ and active HCO₃^- uptake into the cytosol, and significantly increased chloroplast HCO₃^- concentrations. In contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a slight increase in activity. While diffusive uptake of CO₂ into the cell remained constant, active HCO₃^- uptake across the cell membrane increased resulting in Pt depending equally on both CO₂ and HCO₃^- as inorganic carbon sources. Despite changes in the CCM, the overall rate of active carbon transport remained double that of carbon fixation across all temperatures tested. The implication of the energetic cost of the Pt CCM in response to increasing temperatures was discussed.

Effects of RuBisCO and CO2 concentration on cyanobacterial growth and carbon isotope fractionation

Carbon isotope biosignatures preserved in the Precambrian geologic record are primarily interpreted to reflect ancient cyanobacterial carbon fixation catalyzed by Form I RuBisCO enzymes. The average range of isotopic biosignatures generally follows that produced by extant cyanobacteria. However, this observation is difficult to reconcile with several environmental (e.g., temperature, pH, and CO₂ concentrations), molecular, and physiological factors that likely would have differed during the Precambrian and can produce fractionation variability in contemporary organisms that meets or exceeds that observed in the geologic record. To test a specific range of genetic and environmental factors that may impact ancient carbon isotope biosignatures, we engineered a mutant strain of the model cyanobacterium Synechococcus elongatus PCC 7942 that overexpresses RuBisCO across varying atmospheric CO₂ concentrations. We hypothesized that changes in RuBisCO expression would impact the net rates of intracellular CO₂ fixation versus CO₂ supply, and thus whole-cell carbon isotope discrimination. In particular, we investigated the impacts of RuBisCO overexpression under changing CO₂ concentrations on both carbon isotope biosignatures and cyanobacterial physiology, including cell growth and oxygen evolution rates. We found that an increased pool of active RuBisCO does not significantly affect the ¹³ C/¹² C isotopic discrimination (ε_p ) at all tested CO₂ concentrations, yielding ε_p of ≈ 23‰ for both wild-type and mutant strains at elevated CO₂ . We therefore suggest that expected variation in cyanobacterial RuBisCO expression patterns should not confound carbon isotope biosignature interpretation. A deeper understanding of environmental, evolutionary, and intracellular factors that impact cyanobacterial physiology and isotope discrimination is crucial for reconciling microbially driven carbon biosignatures with those preserved in the geologic record.

Resurrected Rubisco suggests uniform carbon isotope signatures over geologic time

The earliest geochemical indicators of microbes-and the enzymes that powered them-extend back ∼3.8 Ga on Earth. Paleobiologists often attempt to understand these indicators by assuming that the behaviors of extant microbes and enzymes are uniform with those of their predecessors. This consistency in behavior seems at odds with our understanding of the inherent variability of living systems. Here, we examine whether a uniformitarian assumption for an enzyme thought to generate carbon isotope indicators of biological activity, RuBisCO, can be corroborated by independently studying the history of changes recorded within RuBisCO's genetic sequences. We resurrected a Precambrian-age RuBisCO by engineering its ancient DNA inside a cyanobacterium genome and measured the engineered organism's fitness and carbon-isotope-discrimination profile. Results indicate that Precambrian uniformitarian assumptions may be warranted but with important caveats. Experimental studies illuminating early innovations are crucial to explore the molecular foundations of life's earliest traces.

Large Diversity in Nitrogen- and Sulfur-Containing Compatible Solute Profiles in Polar and Temperate Diatoms

Intense bottom-ice algal blooms, often dominated by diatoms, are an important source of food for grazers, organic matter for export during sea ice melt, and dissolved organic carbon. Sea-ice diatoms have a number of adaptations, including accumulation of compatible solutes, that allows them to inhabit this highly variable environment characterized by extremes in temperature, salinity, and light. In addition to protecting them from extreme conditions, these compounds present a labile, nutrient-rich source of organic matter, and include precursors to climate active compounds (e.g., dimethyl sulfide [DMS]), which are likely regulated with environmental change. Here, intracellular concentrations of 45 metabolites were quantified in three sea-ice diatom species and were compared to two temperate diatom species, with a focus on compatible solutes and free amino acid pools. There was a large diversity of metabolite concentrations between diatoms with no clear pattern identifiable for sea-ice species. Concentrations of some compatible solutes (isethionic acid, homarine) approached 1 M in the sea-ice diatoms, Fragilariopsis cylindrus and Navicula cf. perminuta, but not in the larger sea-ice diatom, Nitzschia lecointei or in the temperate diatom species. The differential use of compatible solutes in sea-ice diatoms suggests different adaptive strategies and highlights which small organic compounds may be important in polar biogeochemical cycles.

It's what's inside that matters: physiological adaptations of high-latitude marine microalgae to environmental change

Marine microalgae within seawater and sea ice fuel high-latitude ecosystems and drive biogeochemical cycles through the fixation and export of carbon, uptake of nutrients, and production and release of oxygen and organic compounds. High-latitude marine environments are characterized by cold temperatures, dark winters and a strong seasonal cycle. Within this environment a number of diverse and dynamic habitats exist, particularly in association with the formation and melt of sea ice, with distinct microalgal communities that transition with the season. Algal physiology is a crucial component, both responding to the dynamic environment and in turn influencing its immediate physicochemical environment. As high-latitude oceans shift into new climate regimes the analysis of seasonal responses may provide insights into how microalgae will respond to long-term environmental change. This review discusses recent developments in our understanding of how the physiology of high-latitude marine microalgae is regulated over a polar seasonal cycle, with a focus on ice-associated (sympagic) algae. In particular, physiologies that impact larger scale processes will be explored, with an aim to improve our understanding of current and future ecosystems and biogeochemical cycles.

Use of exogenous glycine betaine and its precursor choline as osmoprotectants in Antarctic sea-ice diatoms1

Wide salinity ranges experienced during the seasonal freeze and melt of sea ice likely constrain many biological processes. Microorganisms generally protect against fluctuating salinities through the uptake, production, and release of compatible solutes. Little is known, however, about the use or fate of glycine betaine (GBT hereafter), one of the most common compatible solutes, in sea-ice diatoms confronted with shifts in salinity. We quantified intracellular concentrations and used [¹⁴ C]-labeled compounds to track the uptake and fate of the nitrogen-containing osmolyte GBT and its precursor choline in three Antarctic sea-ice diatoms Nitzschia lecointei, Navicula cf. perminuta, and Fragilariopsis cylindrus at -1°C. Experiments show that these diatoms have effective transporters for GBT, but take up lesser amounts of choline. Neither compound was respired. Uptake of GBT protected cells against hyperosmotic shock and corresponded with reduced production of extracellular polysaccharides in N. lecointei cells, which released 85% of the retained GBT following hypoosmotic shock. The ability of sea-ice diatoms to rapidly scavenge and release compatible solutes is likely an important strategy for survival during steep fluctuations in salinity. The release and recycling of compatible solutes may play an important role in algal-bacterial interactions and nitrogen cycling within the semi-enclosed brines of sea ice.

The role of Rubisco kinetics and pyrenoid morphology in shaping the CCM of haptophyte microalgae

The haptophyte algae are a cosmopolitan group of primary producers that contribute significantly to the marine carbon cycle and play a major role in paleo-climate studies. Despite their global importance, little is known about carbon assimilation in haptophytes, in particular the kinetics of their Form 1D CO2-fixing enzyme, Rubisco. Here we examine Rubisco properties of three haptophytes with a range of pyrenoid morphologies (Pleurochrysis carterae, Tisochrysis lutea, and Pavlova lutheri) and the diatom Phaeodactylum tricornutum that exhibit contrasting sensitivities to the trade-offs between substrate affinity (Km) and turnover rate (kcat) for both CO2 and O2. The pyrenoid-containing T. lutea and P. carterae showed lower Rubisco content and carboxylation properties (KC and kCcat) comparable with those of Form 1D-containing non-green algae. In contrast, the pyrenoid-lacking P. lutheri produced Rubisco in 3-fold higher amounts, and displayed a Form 1B Rubisco kCcat-KC relationship and increased CO2/O2 specificity that, when modeled in the context of a C3 leaf, supported equivalent rates of photosynthesis to higher plant Rubisco. Correlation between the differing Rubisco properties and the occurrence and localization of pyrenoids with differing intracellular CO2:O2 microenvironments has probably influenced the divergent evolution of Form 1B and 1D Rubisco kinetics.

The potential for co-evolution of CO2-concentrating mechanisms and Rubisco in diatoms

Diatoms are a diverse group of unicellular algae that contribute significantly to global photosynthetic carbon fixation and export in the modern ocean, and are an important source of microfossils for paleoclimate reconstructions. Because of their importance in the environment, diatoms have been a focus of study on the physiology and ecophysiology of carbon fixation, in particular their CO2-concentrating mechanisms (CCMs) and Rubisco characteristics. While carbon fixation in diatoms is not as well understood as in certain model aquatic photoautotrophs, a greater number of species have been examined in diatoms. Recent work has highlighted a large diversity in the function, physiology, and kinetics of both the CCM and Rubisco between different diatom species. This diversity was unexpected since it has generally been assumed that CCMs and Rubiscos were similar within major algal lineages as the result of selective events deep in evolutionary history, and suggests a more recent co-evolution between the CCM and Rubisco within diatoms. This review explores our current understanding of the diatom CCM and highlights the diversity of both the CCM and Rubisco kinetics. We will suggest possible environmental, physiological, and evolutionary drivers for the co-evolution of the CCM and Rubisco in diatoms.

Rubisco Extraction and Purification from Diatoms

This protocol describes a method to extract ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) from diatoms (Bacillariophyta) to determine catalytic performance. This protocol has been adapted from use in cyanobacteria and higher plants (Andrews, 1988; Whitney and Sharwood, 2007). First part (steps A1-A3) of the extraction provides a crude extract of Rubisco that is sufficient for carboxylation assays to measure the Michaelis constant for CO₂ (K_C) and the catalytic turnover rate ( k_cat ^c ). However, the further purification steps outlined (steps B1-B4) are needed for measurements of Rubisco CO₂/O₂ Specificity (S_C/O, [ Kane et al., 1994 ]).

Large variation in the Rubisco kinetics of diatoms reveals diversity among their carbon-concentrating mechanisms

While marine phytoplankton rival plants in their contribution to global primary productivity, our understanding of their photosynthesis remains rudimentary. In particular, the kinetic diversity of the CO2-fixing enzyme, Rubisco, in phytoplankton remains unknown. Here we quantify the maximum rates of carboxylation (k cat (c)), oxygenation (k cat (o)), Michaelis constants (K m) for CO2 (K C) and O2 (K O), and specificity for CO2 over O2 (SC/O) for Form I Rubisco from 11 diatom species. Diatom Rubisco shows greater variation in K C (23-68 µM), SC/O (57-116mol mol(-1)), and K O (413-2032 µM) relative to plant and algal Rubisco. The broad range of K C values mostly exceed those of C4 plant Rubisco, suggesting that the strength of the carbon-concentrating mechanism (CCM) in diatoms is more diverse, and more effective than previously predicted. The measured k cat (c) for each diatom Rubisco showed less variation (2.1-3.7s(-1)), thus averting the canonical trade-off typically observed between K C and k cat (c) for plant Form I Rubisco. Uniquely, a negative relationship between K C and cellular Rubisco content was found, suggesting variation among diatom species in how they allocate their limited cellular resources between Rubisco synthesis and their CCM. The activation status of Rubisco in each diatom was low, indicating a requirement for Rubisco activase. This work highlights the need to better understand the correlative natural diversity between the Rubisco kinetics and CCM of diatoms and the underpinning mechanistic differences in catalytic chemistry among the Form I Rubisco superfamily.

Slow carboxylation of Rubisco constrains the rate of carbon fixation during Antarctic phytoplankton blooms

High-latitude oceans are areas of high primary production despite temperatures that are often well below the thermal optima of enzymes, including the key Calvin Cycle enzyme, Ribulose 1,5 bisphosphate carboxylase oxygenase (Rubisco). We measured carbon fixation rates, protein content and Rubisco abundance and catalytic rates during an intense diatom bloom in the Western Antarctic Peninsula (WAP) and in laboratory cultures of a psychrophilic diatom (Fragilariopsis cylindrus). At -1°C, the Rubisco turnover rate, kcat (c) , was 0.4 C s(-1) per site and the half saturation constant for CO2 was 15 μM (vs c. 3 C s(-1) per site and 50 μM at 20°C). To achieve high carboxylation rates, psychrophilic diatoms increased Rubisco abundance to c. 8% of biomass (vs c. 0.6% at 20°C), along with their total protein content, resulting in a low carbon : nitrogen ratio of c. 5. In psychrophilic diatoms, Rubisco must be almost fully active and near CO2 saturation to achieve carbon fixation rates observed in the WAP. Correspondingly, total protein concentrations were close to the highest ever measured in phytoplankton and likely near the maximum possible. We hypothesize that this high protein concentration, like that of Rubisco, is necessitated by slow enzyme rates, and that carbon fixation rates in the WAP are near a theoretical maximum.

Gross and net production during the spring bloom along the Western Antarctic Peninsula

This study explores some of the physiological mechanisms responsible for high productivity near the shelf in the Western Antarctic Peninsula despite a short growing season and cold temperature. We measured gross and net primary production at Palmer Station during the summer of 2012/2013 via three different techniques: incubation with H2 (18) O; incubation with (14) CO2 ; and in situ measurements of O2 /Ar and triple oxygen isotope. Additional laboratory experiments were performed with the psychrophilic diatom Fragilariopsis cylindrus. During the spring bloom, which accounted for more than half of the seasonal gross production at Palmer Station, the ratio of net-to-gross production reached a maximum greater than c. 60%, among the highest ever reported. The use of multiple techniques showed that these high ratios resulted from low heterotrophic respiration and very low daylight autotrophic respiration. Laboratory experiments revealed a similar ratio of net-to-gross O2 production in F. cylindrus and provided the first experimental evidence for an important level of cyclic electron flow (CEF) in this organism. The low ratio of community respiration to gross primary production observed during the bloom at Palmer Station may be characteristic of high latitude coastal ecosystems and partially supported by a very active CEF in psychrophilic phytoplankton.

Low temperature reduces the energetic requirement for the CO2 concentrating mechanism in diatoms

The goal of this study is to investigate the CO2 concentrating mechanism (CCM) of the dominant phytoplankton species during the growing season at Palmer station in the Western Antarctic Peninsula. Key CCM parameters (cellular half-saturation constants for CO2 fixation, carbonic anhydrase activity, CO2 /HCO3 (-) uptake, δ(13) Corg ) in natural phytoplankton assemblages were determined. Those results, together with additional measurements on CO2 membrane permeability from Fragilariopsis cylindrus laboratory cultures, were used to develop a numerical model of the CCM of cold water diatoms. The field data demonstrate that the dominant species throughout the season possess an effective CCM, which achieves near saturation of CO2 for fixation. The model provides a means to examine the role of eCA activity and HCO3 (-) /CO2 uptake in the functioning of the CCM. According to the model, the increase in δ(13) Corg during the bloom results chiefly from decreasing ambient CO2 concentration (which reduces the gross diffusive flux across the membrane) rather than a shift in inorganic carbon uptake from CO2 to HCO3 (-) . The CCM of diatoms in the Western Antarctic Peninsula functions with a relatively small expenditure of energy, resulting chiefly from the low half-saturation constant for Rubisco at cold temperatures.

The minimal CO2-concentrating mechanism of Prochlorococcus spp. MED4 is effective and efficient

As an oligotrophic specialist, Prochlorococcus spp. has streamlined its genome and metabolism including the CO2-concentrating mechanism (CCM), which serves to elevate the CO2 concentration around Rubisco. The genomes of Prochlorococcus spp. indicate that they have a simple CCM composed of one or two HCO3(-) pumps and a carboxysome, but its functionality has not been examined. Here, we show that the CCM of Prochlorococcus spp. is effective and efficient, transporting only two molecules of HCO3(-) per molecule of CO2 fixed. A mechanistic, numerical model with a structure based on the CCM components present in the genome is able to match data on photosynthesis, CO2 efflux, and the intracellular inorganic carbon pool. The model requires the carboxysome shell to be a major barrier to CO2 efflux and shows that excess Rubisco capacity is critical to attaining a high-affinity CCM without CO2 recovery mechanisms or high-affinity HCO3(-) transporters. No differences in CCM physiology or gene expression were observed when Prochlorococcus spp. was fully acclimated to high-CO2 (1,000 µL L(-1)) or low-CO2 (150 µL L(-1)) conditions. Prochlorococcus spp. CCM components in the Global Ocean Survey metagenomes were very similar to those in the genomes of cultivated strains, indicating that the CCM in environmental populations is similar to that of cultured representatives.

Rubisco is a small fraction of total protein in marine phytoplankton

Ribulose 1,5 bisphosphate carboxylase oxygenase (Rubisco) concentrations were quantified as a proportion of total protein in eight species of microalgae. This enzyme has been assumed to be a major fraction of total protein in phytoplankton, as has been demonstrated in plants, potentially constituting a large sink for cellular nitrogen. Representative microalgae were grown in batch and continuous cultures under nutrient-replete, nitrogen (N)-limited, or phosphorus (P)-limited conditions with varying CO(2). Quantitative Western blots were performed using commercially available global antibodies and protein standards. Field incubations with natural populations of organisms from the coast of California were conducted under both nutrient-replete and N-limited conditions with varying CO(2). In all experiments, Rubisco represented < 6% of total protein. In nutrient-replete exponentially growing batch cultures, concentrations ranged from 2% to 6%, while in nutrient-limited laboratory and field cultures, concentrations were < 2.5%. Rubisco generally decreased with increasing CO(2) and with decreasing growth rates. Based on a calculation of maximum Rubisco activity, these results suggest that phytoplankton contain the minimum concentration of enzyme necessary to support observed growth rates. Unlike in plants, Rubisco does not account for a major fraction of cellular N in phytoplankton.

The influence of secondary gain on surgical outcome: a comparison between cervical and lumbar discectomy

Although the expectation of monetary compensation has been associated with failures in lumbar discectomy, the issue has not been investigated in patients undergoing cervical disc surgery. The authors analyzed the relationship between economic forms of secondary gain and surgical outcome in a group of patients with a common pay scale, retirement plan, and disability program. All procedures were performed at the Portsmouth Naval Medical Center between 1993 and 1995; active-duty military servicepersons treated for cervical radiculopathy were prospectively included. Clinical, demographic, and financial factors were analyzed to determine which were predictive of outcome. Financial data were used to create a compensation incentive, which is proportional to the patient's rank, years of service, potential disability, retirement eligibility, and base pay and reflects the monetary incentive of disability. The results of cervical surgery were compared to a previously reported companion population of patients treated for lumbar disc disease. A good outcome was defined as a return to active duty, whereas a referral for disability was considered a poor surgical result. A 100% follow-up rate was obtained for 269 patients who underwent 307 cervical operations. Only 16% (43 of 269) of patients who underwent cervical operation received disability, whereas 24.7% (86 of 348) of patients who underwent lumbar discectomy obtained a poor result (p = 0.0082). Although economic forms of secondary gain were not associated with a poor outcome in cervical disease, both the rank (p = 0.002) and duration (p = 0.03) of an individual's military career were significant factors (p = 0.02). Of the medical variables tested, multilevel surgery (p = 0.03) and revision operations at the same level (p = 0.03) were associated with referral for medical discharge. Secondary gain in the form of economic compensation influences outcome in lumbar but not cervical disc surgery patients; the increased rate of disability referral in patients who underwent lumbar discectomy may reflect an expectation of economic compensation. Social factors that are independent of the anticipation of economic compensation seem to influence the outcome in cervical disc surgery patients.

Multi-dose crystalloid cardioplegia preserves intracellular sodium homeostasis in myocardium

The goal of this study was to assess the effect of multi-dose St Thomas' cardioplegia on intracellular sodium homeostasis in a rat heart model. A new magnetic resonance method was applied which enable us to detect intracellular Na changes without chemical shift reagents. Three groups of isolated rat hearts were subjected to 51 min of ischemia and 51 min of reperfusion at 37 degrees C: Group 1-three infusions of St Thomas' cardioplegia every 17 min for 2 min (n=7); Group 2-single-dose infusion of cardioplegia at the beginning of stop-flow ischemia (n=8); and Group 3-clamp ischemia (n=3) without cardioplegia administration. Performance of the heart was assessed by rate-pressure product relative to the pre-ischemic level (RPP). An NMR method was applied which continuously detects the Na(i) concentration in the heart, using the ability of bound sodium to exhibit triple-quantum transitions and the growth of the corresponding signal when sodium ions pass from extracellular to intracellular space. Clamp ischemia without cardioplegia and 50 min of reperfusion left the heart dysfunctional, with Na(i) growth from the pre-ischemic level of 13.9+/-1.2 mM to 34.9+/-1.3 mM and 73. 9+/-1.9 mM at the end of ischemia and reperfusion, respectively. During single-dose cardioplegia the corresponding values for Na(i) were 30.2+/-1 mM and 48.5+/-1.7 mM (RPP=29%). Multiple infusions of cardioplegic solution resulted in a remarkable preservation of the heart's intracellular Na concentration with a non-significant increase in Na(i) during ischemia and only 16.7+/-1 mM, (P=0.01), after subsequent reperfusion (RPP=85%). The time course of Na(i) changes in the rat heart model demonstrates a prominent potential of multi-dose St Thomas' cardioplegia in preserving intracellular sodium homeostasis at 37 degrees C. The growth of Na(i) concentration during ischemia, as an indicator of the viability of the myocytes, can have a prognostic value for the heart's performance during reperfusion.

Secondary gain influences the outcome of lumbar but not cervical disc surgery

BACKGROUND

The expectation of monetary compensation has been associated with poor outcomes in lumbar discectomy, fueling a reluctance among surgeons to treat worker's compensation cases. This issue, however, has not been investigated in patients undergoing cervical disc surgery. This study analyzes the relationship between economic forms of secondary gain and surgical outcome in a group of patients with common pay scales, retirement plans, and disability programs.

METHODS

All procedures were performed at the Portsmouth Naval Medical Center between 1993 and 1995; active duty military servicepersons who were treated for cervical radiculopathy were prospectively included. Clinical, demographic, and financial factors were analyzed to determine which were predictive for outcome. Financial data were used to create a compensation incentive (CI) which is proportional to the rank, years of service, potential disability, retirement eligibility, and base pay and reflects the monetary incentive of disability. The results of cervical surgery were compared to a previously reported companion population of patients treated for lumbar disc disease. A good outcome is defined as a return to active duty, whereas a referral for disability is considered a poor surgical result.

RESULTS

One hundred percent follow-up was obtained for 269 patients who were treated with 307 cervical operations. Only 16% (43/269) of cervical patients received disability, whereas 24.7% (86/348) of lumbar patients obtained a poor result (p = 0.0082). Although economic forms of secondary gain were not associated with outcome in cervical disease, both the position (p = 0.002) and duration of an individual's military career were significant factors (p = 0.02). Of the medical variables tested, multilevel surgery (p = 0.03) and revision operations at the same level (p = 0.03) were associated with referral for medical discharge.

CONCLUSIONS

Secondary gain in the form of economic compensation influences outcome in lumbar but not cervical disc surgery; this observation may in part account for the success of cervical surgery relative to lumbar discectomy. Social factors that are independent of the anticipation of economic compensation seem to influence the outcome of cervical disc surgery.

Modified open-door laminoplasty for treatment of neurological deficits in younger patients with congenital spinal stenosis: analysis of clinical and radiographic data

OBJECT

Multilevel anterior cervical decompressive surgery and fusion effectively treats cervical myeloradiculopathy that is caused by severe cervical spinal stenosis, but degenerative changes at adjacent vertebral levels frequently result in long-term morbidity. The authors performed a modified open-door laminoplasty procedure in which allograft bone and titanium miniplates were used to treat cervical myeloradiculopathy in younger patients with congenital canal stenosis while maintaining functional cervical motion segments. Pre- and postoperative magnetic resonance imaging and/or computerized tomography myelography were performed to assess changes in cervical spinal canal dimensions. Pre- and postoperative flexion-extension radiographs were compared to determine the residual motion of the targeted operative segments.

METHODS

Twenty younger patients (average age 37.7 years) underwent modified open-door laminoplasty for treatment of myelopathy or myeloradiculopathy related to significant cervical spinal stenosis with or without associated central or lateral disc herniation or foraminal stenosis. These surgeries were performed during a 2-year period and follow-up review remains ongoing (average follow-up period 21.6 months). Reconstructive procedures were performed on an average of 4.1 levels (range three-six). Operative time averaged 186 minutes (range 93-229 minutes). Average blood loss was 305 ml (range 100-650 ml). No cases were complicated by neurological deterioration, infection, wound breakdown, graft displacement, or hardware failure. The patients' Nurick Scale grade improved from a preoperative average of 1.8 to a postoperative average of 0.5. Pre- and postoperative sagittal spinal diameter averaged 11.2 mm (8-14 mm) and 16.6 mm (13-19 mm), respectively. The sagittal compression ratio (sagittal/lateral x 100%) increased from 48% pre- to 72% postoperatively. The spinal canal area increased an average of 55% (range 19-127%). In patients in whom pre- and postoperative flexion-extension radiographs were obtained, 72.7% residual neck motion was maintained. No patient developed increased neck or shoulder pain. Neurological symptoms improved in all patients, with total relief of myelopathy in 50% and partial improvement in 50%.

CONCLUSIONS

Modified open-door laminoplasty with allograft bone and titanium miniplates effectively treats neurological deficits in younger patients with congenital and spinal stenosis. Although long-term results are unknown, short-term results are good and there is a low incidence of complications.

Sodium TQF NMR and intracellular sodium in isolated crystalloid perfused rat heart

The feasibility of monitoring intracellular sodium changes using Na triple quantum filtered NMR without a chemical shift reagent (SR) was investigated in an isolated rat heart during a variety of interventions for Na(i) loading. Perfusion with 1 mM ouabain or without K+ present in the perfusate for 30 min produced a rise of the Na TQF signal with a plateau of approximately 190% and approximately 228% relative to the preintervention level, respectively. Stop-flow ischemia for 30 min resulted in a TQF signal growth of approximately 147%. The maximal Na TQF signal increase of 460% was achieved by perfusion without K+/Ca2+, corresponding to an elimination of the Na transmembrane gradient. The observed values of Na NMR TQF growth in the physiological and pathological ranges are in agreement with reported data by other methods and have a linear correlation with intracellular sodium content as determined in this study by Co-EDTA method and by sucrose-histidine washout of the extracellular space. Our data indicate that the increase in Na TQF NMR signal is determined by the growth of Na(i), and the extracellular Na contribution to the total TQF signal is unchanged at approximately 64%. In conclusion, Na TQF NMR without using SR offers a unique and noninvasive opportunity to monitor alterations of intracellular sodium. It may provide valuable insights for developing cardioprotective strategies and for observing the effects of pharmaceutical treatments on sodium homeostasis.

Antegrade cold blood cardioplegia is not demonstrably advantageous over cold crystalloid cardioplegia in surgery for congenital heart disease

OBJECTIVE

The superiority of blood cardioplegia in pediatric cardiac surgery has not previously been challenged in a controlled clinical trial. The purpose of this study was to compare antegrade cold blood versus cold crystalloid cardioplegia in pediatric cardiac surgery.

METHODS

One hundred thirty-eight pediatric patients (mean age 32 months; 95% CL 24.2 to 39.8 months; range 1 day to 15 years) were prospectively randomized to receive either cold blood (4:1 dilution, blood/Plegisol, potassium chloride 15 mEq/L; n = 62) or cold crystalloid (Plegisol; n = 76) cardioplegic solution during a variety of operations for congenital heart disease. Multiple doses of cold (4 degrees C) cardioplegic solution was administered antegradely in addition to topical cooling during ischemic arrest. Myocardial recovery and outcome measures were assessed by five clinical end points: (1) inotropic support, (2) echocardiographic assessment of ventricular function, (3) overall complication rate, (4) length of stay in the intensive care unit, and (5) 30-day survival. Multiple logistic regression and multivariate analysis of variance were used to investigate which of the following clinical determinants were contributory: (1) cardioplegia, (2) urgency of operation, (3) aortic crossclamp time, (4) age, and (5) cyanosis. Population data did not differ between the two cardioplegia groups (p > 0.05).

RESULTS

The most important clinical determinant of studied end points was the aortic crossclamp time (p < 0.05). The type of cardioplegic solution (blood vs crystalloid) was less important (p > 0.05). The only statistically significant difference between blood and crystalloid cardioplegia for the measured clinical end points was the level of intraoperative inotropic support (p < 0.05), although this did not correlate with any significant differences in measured ventricular function.

CONCLUSION

Our results suggest no clear clinical advantage of antegrade cold blood cardioplegia over crystalloid cardioplegia during hypothermic cardioplegic arrest in pediatric cardiac surgery. The aortic crossclamp time was the strongest predictor of measured outcomes.

Lumbar disc surgery in a fixed compensation population: a model for influence of secondary gain on surgical outcome

BACKGROUND

Reported outcomes in patients undergoing surgical procedures for lumbar disc herniation are poorer in patients eligible for workers' compensation or with pending litigation. In the civilian community, the amount of compensation for one's disability is variable and thus its influence on surgical outcome is difficult to quantify. In the military, all members are covered by a standardized workers' compensation system, and have generally standardized work requirements, a standard pay scale, and third party evaluation of disability based on the Veterans Affairs rating system. This made the military a good system in which to study the effect of potential compensation on surgical outcome.

METHODS

The study population consisted of active duty military members who underwent sequential lumbar microdiscectomies over a 31-month period. Omitted were lumbar fusions, decompressive laminectomies, and far lateral discectomies. Clinical and demographic variables, along with financial data for each patient were derived from these data. A good result was defined as return to active military duty.

RESULTS

Three hundred forty-nine lumbar discectomies were performed in 348 active duty military members. Overall, 75.3% (262) of the 348 patients were able to return to full military duty after surgery, and 24.7% (86) received disability compensation. Chi-square univariate analysis showed higher compensation incentive was a significant determinant of poor surgical outcome (p = 0.0021). The influence of compensation incentive was proportional to the amount of anticipated payout, and relative to a military service member's usual income. In mutivariate analysis, lower base pay (0.0005) and female gender (p = 0.038) were predictive of poor outcome.

CONCLUSIONS

Secondary gain in the form of disability pay has a proportionally adverse effect on outcome following lumbar disc surgery. Although studying this issue in the military system allowed standardization of secondary gain values, the influence of other factors could not be eliminated entirely. Potential disability pay is proportionally greater in lower ranked service members. Thus, other variables such as income level, education, and job satisfaction may contribute to the poorer results in this subgroup of military members.

Effects of specific sodium/hydrogen exchange inhibitor during cardioplegic arrest

BACKGROUND

The accumulation of intracellular sodium during myocardial ischemia couples an inappropriate calcium influx and depressed cardiac recovery during subsequent reperfusion. The effects of the selective sodium/ hydrogen exchange inhibitor HOE 694 are evaluated during myocardial ischemia and reperfusion.

METHODS

Ten isolated rat hearts were subjected to a 2-minute infusion of St. Thomas' cardioplegia +/- 1 mumol/L HOE 694 followed by 50 minutes' normothermic (37 degrees C) global ischemia. Intracellular sodium accumulation was continuously measured using triple quantum filtered 23Na nuclear magnetic resonance spectroscopy without chemical shift reagents. Hemodynamic variables were assessed before and after ischemia.

RESULTS

The addition of 1 mumol/L HOE 694 to St. Thomas cardioplegic solution (n = 5) attenuated the accumulation of intracellular sodium after 50 minutes' ischemia (160.5% +/- 9.1% versus 203.4% +/- 10.9% [mean +/- standard error], HOE 694 versus control, respectively; p = 0.014) and after the initial reperfusion period (first 30 minutes) (288.7% +/- 10.2% versus 335.9% +/- 10.3%; p = 0.008). HOE 694-treated hearts showed significantly improved postischemic recovery of left ventricular developed pressure (53.5% +/- 8.4% versus 26.4% +/- 6.6%; p = 0.036) and rate-pressure product (40.2% +/- 6.9% versus 13.2% +/- 5%; p = 0.014). Postischemic recovery of coronary flow was not significantly different between the two groups (68.6% +/- 5.9% versus 55.5% +/- 4.6%, HOE 694 versus control, respectively; p = 0.11).

CONCLUSIONS

The addition of 1 mumol/L HOE 694 to cardioplegic solution attenuates the increase of intracellular sodium during myocardial ischemia and early reperfusion. This is coupled with an improved recovery of contractile function, possibly as a result of decreased sodium and calcium overload of ischemic myocardium.

Two-portal endoscopic carpal tunnel release surgery: report of early experience

Endoscopic carpal tunnel release is increasingly performed to treat median nerve entrapment neuropathy at the transverse carpal ligament. Proponents of these procedures claim that there are early postoperative advantages to be gained by the patient in the form of decreased pain and weakness, thus facilitating an earlier return to function. However, serious complications associated with the use of these techniques have been reported, especially during the surgeon's purported initial steep learning curve. A prospective analysis of the authors' first 51 cases using a two-portal endoscopic technique was conducted to determine whether these learning curve complications occurred. The authors did experience a learning curve; however, it was not significant. They encountered no serious complications and patient satisfaction was very high. It is concluded that the procedure is relatively easy to learn and safe to perform.

Preperitoneal suprahepatic pacemaker generator placement in the pediatric population

We have used a preperitoneal suprahepatic location for pacemaker generator placement in pediatric patients requiring permanent pacemakers with epicardial leads. The technique is rapid, simple, and safe, and cosmesis is excellent, making this approach particularly advantageous in the younger infant and neonate.

Pericardial substitute and emergency resternotomy: life-saving combination

Retrosternal adhesions prolong operating time during reoperative pediatric cardiac surgery and promote myocardial injury. A case is presented in which a polytetrafluoroethylene pericardial substitute facilitated a rapid, life-saving emergency resternotomy in a moribund patient.

Simultaneous manipulation of the nitric oxide and prostanoid pathways reduces myocardial reperfusion injury

The effects of aspirin and L-arginine (biological precursor of nitric oxide) on the production of hydroxyl radicals, cyclic guanosine monophosphate levels, vascular tone, and the recovery of the ischemic myocardium were investigated in isolated rat hearts subjected to ischemia and reperfusion. After 30 minutes of perfusion, hearts were arrested with St. Thomas' Hospital cardioplegic solution, global ischemia was induced at 37 degrees C for 45 minutes, and the hearts were then reperfused at 37 degrees C for 30 minutes. The percent change in recovery of pulse pressure and maximal change of this pressure with time were better in the group perfused with Krebs-Henseleit solution containing aspirin plus L-arginine (17% +/- 23%, p = 0.001, and 10% +/- 25%, p = 0.002, respectively) compared with these values in the control group perfused with Krebs-Henseleit solution alone (-7% +/- 14% and -11% +/- 16%, respectively). Coronary vascular resistance before and after ischemia were lower in the aspirin plus L-arginine group (0.19 +/- 0.03 dynes.sec/cm5, p = 0.001, and 0.23 +/- 0.04 dynes.sec/cm5, p = 0.01, respectively) compared with those of the control group (0.24 +/- 0.02 and 0.28 +/- 0.07 dynes.sec/cm5, respectively). Cyclic guanosine monophosphate levels increased from 22.5 +/- 6 pmol/100 mg of tissue in the control group to 37.1 +/- 8.9 pmol/100 mg (p = 0.002) in the aspirin plus L-arginine group. Adding N omega-nitro-L-arginine methyl ester to the perfusion medium caused a deterioration in pulse pressure and maximal change of this pressure with time, a decrease in cyclic guanosine monophosphate, and a rise in coronary vascular resistance. The addition of L-arginine to the solution in the Krebs-Henseleit solution plus aspirin group increased the production of hydroxyl radicals from 0.32 +/- 0.18 nmol/gm per 3 minutes to 0.75 +/- 0.33 nmol/gm per 3 minutes (p = 0.03). Despite the association of nitric oxide with increased hydroxyl radical production, it appears that nitric oxide has an overall beneficial effect on the recovery of the ischemic myocardium. The synergism between aspirin and arginine may be caused in part by the scavenging of hydroxyl radicals. Alternatively, by inhibiting the prostaglandin pathway, aspirin may reduce the generation of superoxide anion, a free radical that inactivates nitric oxide. The prolonged half-life of nitric oxide may explain the increased levels of cyclic guanosine monophosphate seen in the group perfused with Krebs-Henseleit solution plus aspirin plus L-arginine. Aspirin and L-arginine, both readily available, may be useful adjuncts to clinical cardioplegia strategy.

Modified surgical palliation for a rare type of L-transposition with aortic atresia

L-Transposition of the great arteries with aortic atresia without an outlet chamber is a rare congenital heart defect. We used a modified Norwood procedure incorporating a type of direct coronary transfer for successful palliation of this lesion in a neonate.

Left thoracotomy for emergent repair of ventricular rupture during mitral valve replacement

Ventricular rupture is a dreaded complication of mitral valve replacement. We present a case of ventricular rupture that occurred during mitral valve replacement and was successfully repaired through a left thoracotomy approach.

Balloon occlusion scintigraphy of aortopulmonary collaterals

We evaluated two children with pulmonary atresia for coil embolization of aortopulmonary collateral vessels after placement of palliative aortopulmonary shunts. To determine vessel distribution and lung perfusion prior to collateral embolization, perfusion scintigraphy with technetium 99m-labeled macroaggregated albumin assessed pulmonary blood flow before and after balloon wedge catheter occlusion of the collaterals. In the first patient we found no perfusion defect during collateral occlusion, and we proceeded with embolization. In the second child, perfusion scintigraphy during occlusion of the collateral vessels demonstrated a filling defect, and embolization was not performed, thus avoiding the creation of a potential perfusion defect in this patient. Assessing the physiologic significance of aortopulmonary collateral vessels by utilizing temporary balloon occlusion of the collateral vessels and concurrent perfusion scintigraphy as an adjunct to selective angiography can provide a significant contribution to the safety and accuracy of coil embolization.

Partial sensory trigeminal rhizotomy at the pons for trigeminal neuralgia

Microvascular decompression is preferred among open procedures for the treatment of trigeminal neuralgia. However, in some cases the decompression cannot be performed, either because no significant vascular compression of the trigeminal nerve is found at surgery or because a patient's vascular anatomy makes it unsafe. Partial sensory rhizotomy is a commonly used alternative in these instances. The outcome after partial sensory rhizotomy was reviewed retrospectively in 83 patients with an average follow-up period of 72 months. Sixty-four (77%) of these patients had no evidence of vascular contact at operation. The remaining 19 patients (23%) had vascular structures in proximity to the trigeminal nerve but still underwent partial sensory rhizotomy in place of or in addition to microvascular decompression either because the offending vessel could not be moved adequately (11 cases) or because the vascular contact was considered insignificant (eight cases). Outcome was classified as: excellent if there was no trigeminal neuralgia postoperatively; good if pain persisted or recurred but was less severe than preoperatively; and poor if persistent or recurrent pain was equal to or greater than the preoperative pain in severity and was refractory to medication, or was severe enough to require additional surgery. The outcome was excellent in 40 patients (48%), good in 18 (22%), and poor in 25 (30%); follow-up durations were similar for the three outcome categories. The failure rate was 17% for the 1st year and averaged 2.6% each year thereafter. Two variables were predictive of a poor outcome: prior surgery and lack of preoperative involvement of the third trigeminal division. Major complications occurred in 4% of cases and minor complications in 11%. The authors conclude that partial sensory rhizotomy is a safe and effective alternative to microvascular decompression when neurovascular compression is not identified at operation or when microvascular decompression cannot be performed for technical reasons.

Solitary eosinophilic granuloma invading the clivus of an adult: case report

A 41-year-old white man with facial pain and diplopia was found to have an invasive lesion of the clivus. The final pathological diagnosis was eosinophilic granuloma. The patient's symptoms resolved completely after transsphenoidal resection of the lesion. The pathological and radiological diagnosis and the treatment of solitary eosinophilic granulomas are discussed.

Dorsal third ventricular cyst: an entity distinct from holoprosencephaly

The treatment and subsequent developmental progress of six children with dorsal third ventricular cysts are described. This cystic malformation has a radiological appearance which is superficially similar to that of the dorsal cyst of alobar holoprosencephaly, especially when the third ventricular cyst is large. Indeed, previous reports have identified this abnormality as a form of holoprosencephaly. However, careful study reveals that the dorsal third ventricular cyst is a distinct entity both developmentally and clinically. The six patients in this series were effectively treated with shunts, and their subsequent developmental progress was assessed by means of the Prescreening Developmental Questionnaire-Revised as well as the Bayley Scales of Infant Development. The nomenclature and differences between this entity and the holoprosencephalies are reviewed. The authors conclude that dorsal third ventricular cysts have a developmental and clinical course more similar to that of arachnoid cysts than to that of the holoprosencephalies.

Mechanism of spreading depression: a review of recent findings and a hypothesis

Spreading depression of Leão (SD) can be provoked by numerous nonspecific mechanical, electrical, and chemical stimuli. A similar, if not identical, phenomenon can be provoked by hypoxia. SD is characterized by drastic depolarization of neurons, severe reduction of membrane resistance, and redistribution of ions across cell membranes. Glial cells also depolarize but retain membrane resistance. Tetraethylammonium hastens the onset of hypoxic SD but reduces the sustained potential shift and K+ outflow from cells; 4-aminopyridine also accelerates SD but has no effect on the voltage shift. N-Methyl-D-aspartate receptor antagonists delay the onset of SD, while nickel and cobalt reduce the amplitude of SD-related redistribution of Ca2+. Yet, no specific blocker of SD has been found. Microdialysis of high-K+ solution in hippocampal CA1 region induces recurrent waves of SD propagating semi-independently in adjacent tissue layers, and a prolonged unstable depressed state that has not previously been described. Neither the release of K+ ions nor of glutamate is the unique agent of SD propagation. On the basis of recent findings we propose a hypothetical sequence of events that reconcile many of the previously seemingly paradoxical observations.

Suppression of presynaptic calcium currents by hypoxia in hippocampal tissue slices

We tested the hypothesis that suppression of inward calcium current in presynaptic terminals is the cause of failure of synaptic transmission early during cerebral hypoxia. Postsynaptic responses in CA1 zone of hippocampal tissue slices were blocked either by the combined administration of 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 3-((+-)-2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP) or by lowering extracellular calcium concentration ([Ca2+]o). Repetitive orthodromic activation of central neurons caused transient decrease of [Ca2+]o (measured by ion selective microelectrodes) in neuropil, attributable to influx of Ca2+ in presynaptic terminals. Presynaptic [Ca2+]o responses were rapidly and reversibly suppressed when oxygen was withdrawn from hippocampal tissue slices. The 'resting' baseline level of [Ca2+]o declined at first gradually, then precipitously as in spreading depression (SD). Presynaptic volleys during high frequency train stimulation were also depressed somewhat before SD began. We conclude that (1) presynaptic Ca2+ currents fail during hypoxia, perhaps because 'resting' intracellular free Ca2+ activity is increased and, in part, also because of partial failure of presynaptic impulse conduction; (2) the influx of Ca2+ into brain cells in hypoxic spreading depression is not mediated by glutamate/aspartate dependent channels.

Deafferentation syndrome in the rat: effects of sex, age, and lesion type

A deafferentation syndrome can be produced in Sprague-Dawley rats following dorsal root sections. The behavior may be objective evidence of dysesthesias, thus serving as an experimental model to study chronic dysesthesias caused by deafferentation in humans. This article examines the effects of sex, age, and lesion type on the expression of the deafferentation syndrome in Sprague-Dawley rats. No significant differences were found in the expression of the deafferentation syndrome with respect to age and weight in male rats within the ranges studied. Sex and lesion type did alter the expression of the syndrome.

Nuclear magnetic resonance imaging of the palliative operation for hypoplastic left heart syndrome

Electrocardiographic-gated nuclear magnetic resonance (NMR) imaging has been shown to be effective for the evaluation of congenital heart disease, particularly in supracardiac regions. This study evaluated the postoperative status after a stage I palliative operation (Norwood procedure) for hypoplastic left heart syndrome. The NMR images from three patients were compared with those of angiography and depicted all components of the reconstructed supracardiac and intracardiac anatomy after this operation. Nonobstructive anastomosis of the main pulmonary artery to the proximal aorta was clearly demonstrated in each patient. The caliber of the central or branch pulmonary artery, patency and caliber of the systemic to pulmonary artery shunt and the size of the atrial communication were also depicted in each patient and these findings corresponded with angiographic results. The results suggest that NMR imaging is effective for assessing the results of initial palliative surgery for hypoplastic left heart syndrome, which seems to be important for managing patients before subsequent definitive surgery.

Calcium, magnesium, and long-term recovery from hypoxia in hippocampal tissue slices

Ortho- and antidromic responses recovered and remained robust for 5 h in slices exposed to transient hypoxia in low calcium, while responses remained depressed in slices made hypoxic in normal calcium. Elevating magnesium in addition to reducing calcium did not improve recovery compared to reducing calcium alone. Spreading depression-like hypoxic depolarization occurred earlier in low calcium than in control fluid. We conclude that loss of function was triggered by calcium uptake by neurons and not by cell swelling, and that activation of NMDA receptors probably played no part.

Hemangiopericytoma of the sciatic nerve. Case report

The authors report the case of a hemangiopericytoma arising in a sciatic nerve. It was found to be invasive within the epineurium but sparing surrounding tissues. Adequate resection required sacrifice of the nerve. Hemangiopericytomas can be added to the short list of mesodermal peripheral-nerve tumors.

Porcine heparin increases postoperative bleeding in cardiopulmonary bypass patients

One hundred thirteen patients undergoing cardiopulmonary bypass were randomly assigned to receive either bovine or porcine heparin. Heparin was infused at 4.5 mg/kg during bypass and administered at the lesser of 70 units/kg or 5000 units/dose at 12-hour intervals postoperatively. Platelet counts decreased to 45% of preoperative levels during the first 3 days postoperatively (porcine, 44 +/- 13%, n = 50; bovine, 46 +/- 15%), but returned to preoperative levels by the seventh postoperative day. The average blood loss in the porcine heparin group significantly exceeded that of the bovine heparin group (porcine, 1350.7 +/- 727.8 ml; bovine, 1059.6 +/- 381.0 ml; p less than .01). Consequently, the platelet transfusion requirement was greater in the porcine heparin group (porcine, 1.7 +/- 3.9 units; bovine, 0.5 +/- 1.7 units; p less than .05); however, blood and blood component (with the exception of platelets) administration was not significantly different between the two groups. The four patients taking anticoagulants or antiinflammatory agents in the porcine group required a mean of 8.5 units of red blood cells (RBC) plus supplemental platelets. The seven such patients in the bovine group received a mean of 3.0 units of RBC and no platelets. Thus, the use of porcine heparin resulted in a generalized increase in postoperative bleeding with increased management problems in patients undergoing cardiopulmonary bypass.

Omental pedicle grafting in the treatment of postcardiotomy sternotomy infection

Postcardiotomy sternal infection occurred in 20 (2%) of 1007 patients undergoing cardiac surgery between September 1985 and December 1987, a 10-fold increase over the preceding 33 months (4 [0.24%] of 1627 patients). Cultures were sterile in 5 patients and yielded staphylococci in 12 and a variety of bowel organisms in 3. The cause for the increased occurrence of sternal wound infection is unclear after multivariate analysis, although infections have precipitously dropped subsequent to changing to cefuroxime sodium antibiotic prophylaxis. Treatment has evolved to appropriate antibiotics and early débridement of involved sternum and cartilage. Rewiring the sternum is not attempted. If gross purulence is not present, primary closure is accomplished using muscle flaps (2 patients) or omental pedicle grafts (17 patients). In the presence of gross purulence, the wound is packed open for 5 days and then closed in the above fashion. Two patients required skin grafts for primary closure. The omental pedicle flap is preferred due to simplicity and improved coverage of the sternal defect inferiorly. Nineteen patients healed primarily. A superficial wound infection was drained in 1 patient. Midline incisional hernias developed in 3 muscular patients. Omentum is now harvested through a left subcostal incision. Hospital stay was under 2 weeks in 13 patients. One death occurred due to multisystem failure prior to completion of wound closure. In our experience, early sternal débridement and omental pedicle grafting with primary closure is appropriate therapy for postcardiotomy sternotomy infections. The presence of gross purulence may require 5 days of open packing prior to omental grafting. No significant complications occurred, and mortality was low. A left subcostal incision for omental harvesting is utilized to avoid the occurrence of delayed incisional hernias.

Surgical management of traumatic disruption of the descending aorta

During an 11 1/2-year period, 20 consecutive patients presenting with a traumatic disruption of the proximal descending aorta underwent an emergency operative repair. The mean age was 26 years (range 15 to 62), and 13 (65%) were male. Associated injuries were frequent and required additional major operative procedures in half of the cases. Two patients died as a result of associated intracranial injuries, for a hospital survival of 90%. The operative repair was accomplished by graft replacement of the involved segment of the aorta in all but one patient who underwent a primary repair. Simple aortic crossclamping was used in 8 patients (40%) and heparinless femoral-femoral venoarterial bypass in 12 patients (60%). Neither renal failure nor paraplegia in any of the patients. Four patients required thoracic reoperations. These results indicate that an aggressive multidisciplinary surgical approach can produce favorable results in patients with traumatic descending aortic injuries.

Internal banding for palliation of truncus arteriosus in the neonate

A method for surgically limiting pulmonary blood flow in the critically ill neonate with truncus arteriosus is described. Two recent cases utilizing this technique are presented. Comparisons are made between this and other palliative surgical procedures used in truncus arteriosus.

A new insulated caudalis nucleus DREZ electrode. Technical note

A new insulated radiofrequency electrode for making nucleus caudalis dorsal root entry zone lesions reduces the incidence of ataxia.