Dissolved inorganic carbon uptake in Thiomicrospira crunogena XCL-2 is Δp- and ATP-sensitive and enhances RubisCO-mediated carbon fixation.

The gammaproteobacterium Thiomicrospira crunogena XCL-2 is an aerobic sulfur-oxidizing hydrothermal vent chemolithoautotroph that has a CO2 concentrating mechanism (CCM), which generates intracellular dissolved inorganic carbon (DIC) concentrations much higher than extracellular, thereby providing substrate for carbon fixation at sufficient rate. This CCM presumably requires at least one active DIC transporter to generate the elevated intracellular concentrations of DIC measured in this organism. In this study, the half-saturation constant (K CO2) for purified carboxysomal RubisCO was measured (276 ± 18 µM) which was much greater than the K CO2 of whole cells (1.03 µM), highlighting the degree to which the CCM facilitates CO2 fixation under low CO2 conditions. To clarify the bioenergetics powering active DIC uptake, cells were incubated in the presence of inhibitors targeting ATP synthesis (DCCD) or proton potential (CCCP). Incubations with each of these inhibitors resulted in diminished intracellular ATP, DIC, and fixed carbon, despite an absence of an inhibitory effect on proton potential in the DCCD-incubated cells. Electron transport complexes NADH dehydrogenase and the bc 1 complex were found to be insensitive to DCCD, suggesting that ATP synthase was the primary target of DCCD. Given the correlation of DIC uptake to the intracellular ATP concentration, the ABC transporter genes were targeted by qRT-PCR, but were not upregulated under low-DIC conditions. As the T. crunogena genome does not include orthologs of any genes encoding known DIC uptake systems, these data suggest that a novel, yet to be identified, ATP- and proton potential-dependent DIC transporter is active in this bacterium. This transporter serves to facilitate growth by T. crunogena and other Thiomicrospiras in the many habitats where they are found.

Predictors of desaturation in the postoperative anesthesia care unit: an observational study.

STUDY OBJECTIVE: To evaluate predictors of desaturation and to identify practice for patient transport following general anesthesia. DESIGN: Observational quality assurance study. SETTING: Postanesthesia Care Unit (PACU) of a university-affiliated, tertiary-care hospital. PATIENTS: All adult postsurgical patients who received general anesthesia and who were admitted to the PACU. MEASUREMENTS: Patients were observed over a three-month study period during transfer to the PACU with or without oxygen supplementation. Sixteen variables related to patient, surgery, and anesthesia were recorded. RESULTS: The study recorded a total of 502 PACU admissions. The practice pattern showed that 57% of patients were transferred without oxygen and 19% of the entire sample had an initial oxygen desaturation of less than 90% on arrival to the PACU. Only 0.8% of patients experienced oxygen desaturation when they were transferred with oxygen supplementation. After logistic regression analysis, the most significant predictor of desaturation was transport without oxygen. CONCLUSIONS: The majority of anesthesiologists did not use supplemental oxygen for patient transfer. As a result, a higher incidence of postoperative desaturation was noted in their patients. Significant predictors of desaturation after general anesthesia included patients' sedation score, low respiratory rate, and transport without oxygen. The use of oxygen almost completely prevented desaturation during transport.

Monitored anesthesia care provided by registered respiratory care practitioners during cataract surgery: a report of 1957 cases.

OBJECTIVE: To evaluate the safety and feasibility of having monitored anesthesia care during cataract surgery provided by registered respiratory care practitioners (RRCPs). DESIGN: Retrospective case series. PARTICIPANTS: One thousand nine hundred fifty-seven consecutive patients undergoing cataract surgery at one surgical center between November 2001 and October 2003. METHODS: Phacoemulsification cataract surgery with intraocular lens insertion was performed using topical anesthesia, with or without IV sedatives. An RRCP, trained to function as an anesthesia assistant, provided monitored anesthesia care during all stages of surgery, with an anesthesiologist immediately available for consultation or assistance as required. MAIN OUTCOME MEASURES: The number of serious medical complications resulting from the anesthesia or surgery was measured. The rate of anesthesiologist intervention required at each stage of surgery--preoperative, intraoperative, and postoperative--was determined, along with the reasons for the interventions. Age, American Society of Anesthesiologists (ASA) risk class (a rating of preoperative physical status), and number of IV sedative agents given were analyzed as potential predictors of the need for anesthesiologist intervention. RESULTS: Among the 1957 cataract surgeries, there were no adverse medical events that resulted in death, hospitalization, or tracheal intubation. Two cases were aborted intraoperatively for medical reasons. A total of 78 cases (4.0%) required anesthesiologist intervention, with 34 (1.7%) requiring preoperative intervention, 43 (2.2%) requiring intraoperative intervention, and 3 (0.2%) requiring postoperative intervention; 4 cases required 2 separate interventions. The mean age of the intervention group (73.9 years) was statistically greater than that of the nonintervention group (71.0) (P = 0.02). A higher ASA rating (>2) correlated with an increased need for anesthesiologist intervention in terms of the total intervention rate (P<0.0001) and the intraoperative rate alone (P<0.0001). The use of more IV sedative agents (2 or 3 vs. 0 or 1) was marginally associated with a higher total intervention rate (P = 0.053) but not with a higher intraoperative intervention rate (P = 0.68). CONCLUSION: With the inherent safety of cataract surgery and the relatively low need for anesthesiologist intervention, we believe it is justified to allow RRCPs, trained as anesthesia assistants, to provide monitored anesthesia care during cataract surgery so long as anesthesiologist support is directly available when required. Potential benefits include cost savings in health care and decreased demand for anesthesiology services. To validate formally the preservation of patient safety from such a change in practice, however, a larger sample size would be required due to the inherently low rate of cataract surgery complications.