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Biomedical subjects

N Herman

Publications and source records attributed to N Herman.

11 recordsLinked to original sources
PubMed2006

Preservation of micro-organisms by drying; a review.

The preservation of micro-organisms by different drying methodologies has been used for decades. Freeze drying in particular is the preferred method for transporting and storing vast culture collections of micro-organism strain types. The literature on drying and preserving micro-organisms is extensive, but is often specific to one particular strain. This review attempts to draw some similar concepts and findings together in one paper, to compare different drying techniques, with specific reference to microorganisms. The main topics covered are cell growth phases and concentration, inducing drying tolerance in microbial cells, drying methods, rehydration of dried cells and packaging and storage conditions. Also, particular attention has been paid to the use of freeze drying and the protective matrices used to improve microbial cell viability after drying.

Bacteria↗
PubMed2004

Production of precise microbiology standards using flow cytometry and freeze drying.

BACKGROUND: Quality control standards provide a quantity of microorganisms for routine use in microbiology to demonstrate the efficacy of testing methods and culture media. Standards are normally prepared by diluting a culture of microorganisms to obtain a suspension that contains an estimated number of colony-forming units per milliliter. The variability and inaccuracy of these standards increase the potential for false results. Flow cytometry has been used extensively to prepare precise standards of Cryptosporidium and Giardia that contain exact numbers of organisms in a volume of liquid (1). However, the same levels of accuracy have yet to be obtained for bacterial quality control standards. METHODS: A modification of a Becton Dickinson FACScalibur flow cytometer enabled 30 bacterial cells to be sorted into a single droplet, mixed with a cryoprotective solution within the droplet, and frozen in liquid nitrogen. The frozen droplets were then freeze dried for stable preservation of the viable bacterial cells. RESULTS: A freeze-dried sphere 3 mm in diameter was produced, which contained 30 microorganisms. The within-batch variation for these freeze-dried spheres was no greater than two standard deviations, and the between-batch variation was less than one standard deviation. CONCLUSIONS: Bacterial reference controls can now be produced with consistent accuracy and unparalleled precision, thus enabling harmonization across the microbiological testing industry.

Animals↗
PubMed1999

Transfer of lidocaine across the dual perfused human placental cotyledon.

Factors affecting lidocaine transfer across the normal term human placenta were studied using the dual perfused isolated single cotyledon. Experiments were performed using perfusates which provided equal protein binding in both the maternal and fetal circuits as well as perfusates that approached the actual in vivo maternal/fetal protein binding gradient. Additional experiments were performed to investigate the effects of increasing maternal lidocaine concentration (5, 10, 40, 80 microg/mL) on maternal to fetal (M-->F) lidocaine transfer across the human placenta. Lidocaine crossed the placenta rapidly in both the M-->F and fetal to maternal (F-->M) directions. When protein binding was similar in the two circuits, M-->F transfer ratios (lidocaine transfer/antipyrine transfer) were significantly lower than the transfer ratios seen in the F-->M direction (0.59+/-0.04 versus 0.84+/-0.06, P<0.05). Transfer ratios (M-->F: 0.83+/-0.06, F-->M: 0.96+/-0.06) were not reduced when the physiological maternal/fetal protein binding gradient was present. Lidocaine transfer was not diminished by increasing maternal concentrations and, in contrast to bupivacaine, was not significantly affected by its binding.

Journal Article↗
PubMed1999

A comparison of the placental transfer of ropivacaine versus bupivacaine.

UNLABELLED: This study compares the placental transfer of ropivacaine and bupivacaine using the dual perfused, single cotyledon human placental model. We studied the effects of maternal/fetal protein binding, maternal ropivacaine concentration, and fetal pH on ropivacaine transfer. At a clinically relevant maternal concentration (1 microg/mL), the calculated transfer ratios (local anesthetic percent transfer/antipyrine percent transfer) of ropivacaine (0.82 +/- 0.03) and bupivacaine (0.74 +/- 0.01) were comparable at the completion of the perfusion experiment (120 min). When the perfusates were modified to simulate actual in vivo plasma protein binding values, the maternal-to-fetal transfer of ropivacaine and bupivacaine decreased significantly (P < 0.05) as indicated by transfer ratios of 0.42% +/- 0.07% and 0.40% +/- 0.03%, respectively. No saturation of the transfer process was observed for either drug at the maternal concentrations investigated. The placental transfer of both local anesthetic agents increased significantly as the fetal pH decreased. This investigation shows that ropivacaine and bupivacaine cross the human placenta at a similar rate, despite their differences in lipophilicity and stereochemistry. Placental transfer of both compounds is highly influenced by maternal and fetal protein concentration and the fetal pH. IMPLICATIONS: The placental transfer of ropivacaine was shown to be similar to that of bupivacaine, and is thus highly influenced by the degree of maternal and fetal protein binding and fetal pH.

Adult↗
PubMed1998

The chemical stability and sterility of sodium thiopental after preparation.

UNLABELLED: Manufacturer's instructions recommend discarding unused portions of sodium thiopental 24 h after reconstitution. Heeding this recommendation may result in the disposal of a large proportion of prepared thiopental. Although thiopental is relatively inexpensive, the volume prepared by many anesthesia departments could make this waste significant. To address this possibility, we investigated the chemical stability and sterility of thiopental in pharmacy-prepared, prefilled syringes. Stock solutions of thiopental were mixed and drawn into syringes under sterile conditions by pharmacists or pharmacy assistants. Fifty-six samples were stored under refrigeration (3 degrees C); the remaining 56 samples were stored at room temperature (22 degrees C). Each day for 7 days, eight samples from each group were analyzed by using high-performance liquid chromatography for chemical stability and cultured for microbiological colonization. Differences in thiopental concentration between the room temperature and the refrigerated samples were measured over time by using repeated-measures analysis of variance (P < or = 0.05). Three positive culture samples (S. epidermidis and S. hemolyticus) most likely represent laboratory contamination and not colonization. At 22 degrees C, thiopental remains stable and sterile for 6 days and well beyond 7 days at 3 degrees C. IMPLICATIONS: This study examines the shelf life of the anesthetic drug thiopental in pharmacy-filled syringes stored at either room temperature or under refrigeration. The results justify the use of prepared solutions beyond the package insert recommendation of 24 h.

Anesthetics, Intravenous↗
PubMed1997

The placental transfer of sufentanil: effects of fetal pH, protein binding, and sufentanil concentration.

This study investigated factors that influence the placental transfer of sufentanil using the dual-perfused, single-cotyledon human placental model. Placentas were collected from healthy women. Experiments were designed to elucidate the effects of maternal protein binding, changing maternal sufentanil concentration (1, 10, 20, and 100 ng/mL) and decreasing fetal pH (fetal acidemia 7.2, 7.0, 6.8) on the placental transfer of sufentanil. Sufentanil crossed the placenta rapidly at a rate two-thirds that of the transfer marker, antipyrine. Sufentanil transfer increased linearly with the maternal concentration (r = 0.999). Sufentanil/antipyrine maternal to fetal (M-->F) transfer ratios were significantly reduced (0.66 +/- 0.05 vs 0.40 +/- 0.04, P < 0.05) when fresh frozen plasma was added to the maternal circuit to enhance protein binding. Fetal pH and sufentanil transfer were related because sufentanil M-->F clearance increased significantly as the fetal pH decreased (r = 0.973, P < 0.05). Sufentanil appears to cross the placenta by passive diffusion but is modulated by the degree of maternal protein binding. Sufentanil M-->F transfer is enhanced by fetal acidemia.

Adult↗
PubMed1996

No additional metal particle formation using the needle-through-needle combined epidural/spinal technique.

BACKGROUND: Combined epidural/spinal analgesia utilizing a needle-through-needle technique has become very popular in anesthesia. However, findings of concave deformities at the orifice of Tuohy needles after spinal needle passage have raised concerns that metal fragments might be deposited within the epidural space. This study was proposed to investigate whether the needle-through-needle technique does produce metallic flecks. METHODS: Ten unused Tuohy and Hustead epidural needles were inspected microscopically and photomicrographed prior to flushing saline through each into a single tissue culture well. After drying, a single pass was made with a 120 mm 24-gauge Sprotte needle through each epidural needle to maximal extension while the orifice was within another tissue culture well. Each needle was again flushed into a third well before reexamination and photomicroscopy. Each of the wells was inspected for metallic particles by microscopy. Additional freshly unpackaged Tuohy needles were microscopically examined after exposure to a magnetic field. RESULTS: Comparison of micrographs before and after needle experiments revealed concave deformities at the orifice of all the Tuohy and Hustead needles. No particles were observed in either of the two saline-flushed wells or within the well in which the needle-through-needle passes were made. Inspection of unused Tuohy needles exposed to a magnetic field revealed metal filings "standing up" along the bevel of every needle examined. CONCLUSIONS: Metallic particles are not produced by the needle-through-needle technique. However, metal particles are an apparent contaminant of all epidural needles and are probably routinely introduced into patients when the needle is placed.

Analgesia, Epidural↗
PubMed1995

Bupivacaine transfer across the human term placenta. A study using the dual perfused human placental model.

BACKGROUND: Bupivacaine is widely used for obstetric analgesia, yet published information on the mechanism of human placental bupivacaine transfer is sparse. The dual perfused human placental model was used to elucidate the factors governing the placental transfer of bupivacaine. METHODS: Bupivacaine transfer was studied using the recirculating (closed) model and the single pass (open) model. Single placental cotyledons were perfused with either heparinized Krebs-Ringer's buffer (KRB) supplemented with human albumin (fetal and maternal circuits) or 100% fresh frozen plasma (maternal circuit) to control the bupivacaine protein binding in those circuits. In the open model, bupivacaine clearance was compared before and after being subjected to either increasing concentrations of bupivacaine or its structural analog, mepivacaine. RESULTS: For those studies in which the maternal and fetal protein binding was equal, the maternal to fetal (M-->F) transfer was significantly greater (P < 0.05) than that in the fetal to maternal (F-->M) direction. When the perfusates were modified to simulate actual in vivo plasma protein concentrations, bupivacaine transfer was shown to be related to the degree of protein binding found in the two circuits. In the open studies, bupivacaine transfer was similar at all concentrations investigated, unaffected by mepivacaine, and related to the pH of the fetal perfusate. A concentration effect was seen within the placental tissue at the end of the experiment. CONCLUSIONS: Bupivacaine placental transfer characteristics suggest passive diffusion rather than active drug transport and appear to be influenced by the maternal and fetal plasma protein binding, fetal pH, and placental uptake.

Antipyrine↗
PubMed1992

Total intravenous anesthesia with a continuous propofol-alfentanil infusion.

A total intravenous anesthetic using propofol and alfentanil was evaluated to determine if it would provide a shorter recovery-room stay than a more traditional balanced anesthetic using isoflurane and alfentanil. Forty-three ASA I or II patients between 17 and 50 years of age undergoing major abdominal or orthopedic procedures were studied. The propofol group received alfentanil 50 mg/kg followed by propofol 1 mg/kg for anesthesia induction. Continuous propofol infusion was initiated at induction using 170 mg/kg/min for 10 minutes, followed by 130 mg/kg/min for 10 minutes, then maintained at 100 mg/kg/min until 10 minutes before the end of surgery. Ventilation was supported with an air-oxygen mixture. The group receiving balanced anesthesia received alfentanil 1 mg/kg, and anesthesia was induced with sodium thiopental 4 mg/kg. A 1% isoflurane inhalation with air-oxygen was initiated immediately upon induction. Both groups received a continuous infusion of alfentanil titrated to maintain heart rate within 10% of preinduction levels. Recovery from anesthesia was measured using a subjective pain assessment, a verbal fluency test, and a short-term memory test. No differences were detected in the rate of recovery at 30 minutes or 60 minutes postextubation. Hemodynamic stability during induction and intubation was slightly better in the propofol group than in the isoflurane group. One episode each of intraoperative awareness and delayed eye opening occurred in the propofol group. Total intravenous anesthesia using propofol and alfentanil is just as effective as a balanced inhalation anesthetic and provides equally rapid recovery. However, practitioners are cautioned to include an amnestic adjuvant when using propofol as the sole anesthetic agent.

Adolescent↗