Independence of a Marine Unicellular Diazotroph to the Presence of NO3.

Marine nitrogen (N2) fixation was historically considered to be absent or reduced in nitrate (NO3-) rich environments. This is commonly attributed to the lower energetic cost of NO3- uptake compared to diazotrophy in oxic environments. This paradigm often contributes to making inferences about diazotroph distribution and activity in the ocean, and is also often used in biogeochemical ocean models. To assess the general validity of this paradigm beyond the traditionally used model organism Trichodesmium spp., we grew cultures of the unicellular cyanobacterium Crocosphaera watsonii WH8501 long term in medium containing replete concentrations of NO3-. NO3- uptake was measured in comparison to N2 fixation to assess the cultures' nitrogen source preferences. We further measured culture growth rate, cell stoichiometry, and carbon fixation rate to determine if the presence of NO3- had any effect on cell metabolism. We found that uptake of NO3- by this strain of Crocosphaera was minimal in comparison to other N sources (~2-4% of total uptake). Furthermore, availability of NO3- did not statistically alter N2 fixation rate nor any aspect of cell physiology or metabolism measured (cellular growth rate, cell stoichiometry, cell size, nitrogen fixation rate, nitrogenase activity) in comparison to a NO3- free control culture. These results demonstrate the capability of a marine diazotroph to fix nitrogen and grow independently of NO3-. This lack of sensitivity of diazotrophy to NO3- suggests that assumptions often made about, and model formulations of, N2 fixation should be reconsidered.

Impact of high spinal anesthesia technique on fast-track strategy in cardiac surgery: retrospective study.

BACKGROUND AND OBJECTIVES: Although high spinal anesthesia (HSA) has been used in cardiac surgery, the technique has not yet been widely accepted. This retrospective study was designed to investigate the impact of HSA technique on fast-track strategy in cardiac surgery. METHODS: Elective cardiac surgery cases (n=1025) were divided into two groups: cases with HSA combined with general anesthesia (GA) (HSA group, n=188) and cases with GA only (GA group, n=837). In the HSA group, bupivacaine and morphine were intrathecally administered immediately before GA was induced. Outcomes included fast-track extubation (less than 6 hours), extubation in the operating room, fast-track discharge from the intensive care unit (ICU) (less than 48 hours) and hospital (less than 7 days). RESULTS: In the HSA group, 60.1% were extubated in less than 6 hours after ICU admission, as compared with 39.9% in the GA group (p<0.001). In the HSA group, 33.0% were extubated in the operating room, as compared with 4.4% in the GA group (p<0.001). LOS in the ICU was less than 48 hours in 67.6% in the HSA group, as compared with 57.2% of those in the GA group (p=0.033). LOS in the hospital was less than 7 days in 63.3% in the HSA group, as compared with 53.5% in the GA group (p=0.084). CONCLUSIONS: HSA technique combined with GA in cardiac surgery increased the rate of fast-track extubation (less than 6 hours) when compared with GA only.

A simulation study of common propofol and propofol-opioid dosing regimens for upper endoscopy: implications on the time course of recovery.

BACKGROUND: Using models of respiratory compromise, loss of response to esophageal instrumentation, and loss of responsiveness, the authors explored through simulation published dosing schemes for endoscopy using propofol alone and in combination with selected opioids. They hypothesized that models would predict adequate conditions for esophageal instrumentation and once drug administration is terminated, rapid return of responsiveness and minimal respiratory compromise. METHODS: Four published dosing regimens of propofol alone or in combination with opioids were used to predict the probability of loss of response to esophageal instrumentation for a 10-min procedure and the probability of respiratory compromise and return of responsiveness once the procedure had ended. RESULTS: Propofol alone provided a low probability (9-20%) and propofol-opioid techniques provided a moderate probability (15-58%) of loss of response to esophageal instrumentation. Once the procedure ended, all techniques provided a high likelihood of rapid return of responsiveness (less than 3 min). Propofol-opioid techniques required more time than propofol alone to achieve a high probability of no respiratory compromise (7 vs. 4 min). CONCLUSIONS: Propofol alone would likely lead to inadequate conditions for esophageal instrumentation but would provide a rapid return to responsiveness and low probability of respiratory compromise once the procedure ended. The addition of remifentanil or fentanyl improved conditions for esophageal instrumentation and had an equally rapid return to responsiveness. The time required to achieve a low probability of respiratory compromise was briefly prolonged; this is likely inconsequential given that patients are responsive and can be prompted to breathe.

An exploration of remifentanil-propofol combinations that lead to a loss of response to esophageal instrumentation, a loss of responsiveness, and/or onset of intolerable ventilatory depression.

BACKGROUND: Remifentanil and propofol are increasingly used for short-duration procedures in spontaneously breathing patients. In this setting, it is preferable to block the response to moderate stimuli while avoiding loss of responsiveness (LOR) and intolerable ventilatory depression (IVD). In this study, we explored selected effects of combinations of remifentanil-propofol effect-site concentrations (Ces) that lead to a loss of response to esophageal instrumentation (EI), LOR, and/or onset of IVD. A secondary aim was to use these observations to create response surface models for each effect measure. We hypothesized that (1) in a large percentage of volunteers, selected remifentanil and propofol Ces would allow EI but avoid LOR and IVD, and (2) the drug interaction for these effects would be synergistic. METHODS: Twenty-four volunteers received escalating target-controlled remifentanil and propofol infusions over ranges of 0 to 6.4 ng · mL(-1) and 0 to 4.3 µg · mL(-1), respectively. At each set of target concentrations, responses to insertion of a blunt end bougie into the midesophagus (40 cm), level of responsiveness, and respiratory rate were recorded. From these data, response surface models of loss of response to EI and IVD were built and characterized as synergistic, additive, or antagonistic. A previously published model of LOR was used. RESULTS: Of the possible 384 assessments, volunteers were unresponsive to EI at 105 predicted remifentanil-propofol Ces; in 30 of these, volunteers had no IVD; in 30, volunteers had no LOR; and in 9, volunteers had no IVD or LOR. Many other assessments over the same concentration ranges, however, did have LOR and/or IVD. The combinations that allowed EI and avoided IVD and/or LOR primarily clustered around remifentanil-propofol Ces ranging from 0.8 to 1.6 ng · mL(-1) and 1.5 to 2.7 µg · mL(-1), respectively, and to a lesser extent approximately 3.0 to 4.0 ng · mL(-1) and 0.0 to 1.1 µg · mL(-1), respectively. Models of loss of response to EI and IVD both demonstrated a synergistic interaction between remifentanil and propofol. CONCLUSION: Selected remifentanil-propofol concentration pairs, especially higher propofol-lower remifentanil concentration pairs, can block the response to EI while avoiding IVD in spontaneously breathing volunteers. It is, however, difficult to block the response to EI and avoid both LOR and IVD. It may be necessary to accept some discomfort and blunt rather than block the response to EI to consistently avoid LOR and IVD.

Apoplexy in pituitary microadenomas.

Pituitary apoplexy is a clinical syndrome of hemorrhage or infarction of a pituitary adenoma. It has classically been associated with pituitary macroadenomas. The authors report three cases of pituitary apoplexy that occurred in patients with pituitary microadenomas. The presentation, endocrine results, and radiological and clinical outcome of each patient are described. In each of these cases of pituitary apoplexy due to microadenoma, the presenting headache was mistakenly attributed to a different diagnosis. The authors propose that pituitary apoplexy associated with a microadenoma may be much more common than appreciated and could be misdiagnosed as headache of alternative cause. Clinicians and radiologists should be aware of this clinical presentation.