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author:("aka, oman")
1.  Correlation between Bispectral Index, Observational Sedation Scale, and Lower Esophageal Sphincter Pressure in volunteers using dexmedetomidine or propofol 
Many anesthetics reduce lower esophageal sphincter pressure (LESP) and consequently the gastro-esophageal pressure gradient (GEPG); thus they may promote gastro-esophageal reflux and contribute to aspiration pneumonia. Our goals were to evaluate the association between LESP and 2 measures of sedation: bispectral index (BIS) and the responsiveness component of the Observer’s Assessment of Alertness score (OAA/S).
Eleven healthy volunteers were each sedated on 2 separate days. Subjects were given sedative infusions of increasing target plasma concentrations of dexmedetomidine or propofol. LESP and GEPG were recorded after starting each infusion phase. Generalized estimating equation modeling was used to assess the relationship between LESP and, respectively, BIS and OAA/S. The existence of a drug-dependent association was evaluated within these models by testing an interaction term. Wald tests were used to evaluate the relationships within the models.
We found a significant relationship between LESP and BIS (P=0.0043) after adjusting for the main effect of sedative type – a deepening of sedation as measured by a decrease in BIS of 10% was associated with a decrease [Bonferroni-adjusted 95% CI] in LESP of −1.34 [−2.39, −0.29] mmHg. After adjusting for the main effect of sedative drug, LESP significantly declined with declining OAA/S (P=0.001); a unit decrease of OAA/S was associated with a decrease [Bonferroni-adjusted 95% CI] in LESP of −2.01 [−3.20, −0.81] mmHg.
Deeper sedation, as measured by either BIS or OAA/S, significantly reduces LESP.
PMCID: PMC3560568  PMID: 23018351
BIS; lower esophageal sphincter; dexmedetomidine; propofol
2.  Tissue Oxygenation Response to Mild Hypercapnia during Cardiopulmonary Bypass with Constant Pump Output 
British journal of anaesthesia  2006;96(6):708-714.
Tissue oxygenation is the primary determinant of wound infection risk. Mild hypercapnia markedly improves cutaneous, subcutaneous, and muscular tissue oxygenation in volunteers and patients. However, relative contributions of increased cardiac output and peripheral vasodilation to this response remains unknown. We thus tested the hypothesis that increased cardiac output is the dominant mechanism.
We recruited 10 ASA III patients, aged 40–65 years, undergoing cardiopulmonary bypass for this crossover trial. After induction of anaesthesia, a Silastic tonometer was inserted subcutaneously in the upper arm. Subcutaneous tissue oxygen tension was measured with both polarographic electrode and fluorescence-based systems. Oximeter probes were placed bilaterally on the forehead to monitor cerebral oxygenation. After initiation of cardiopulmonary bypass, in random order patients were exposed to two arterial CO2 partial pressures for 30 minutes each: 35 (normocapnia) or 50 mmHg (hypercapnia). Bypass pump flow was kept constant throughout the measurement periods.
Hypercapnia during bypass had essentially no effect on PaO2, mean arterial pressure, or tissue temperature. PaCO2 and pH differed significantly. Subcutaneous tissue oxygenation was virtually identical during the two PaCO2 periods (139 [50,163] vs. 145 [38,158], P=0.335) (median [range]). In contrast, cerebral oxygen saturation (our positive control measurement) was significantly less during normocapnia (57 [28,67]%) than hypercapnia (64 [37,89]%, P=0.025).
Mild hypercapnia, which normally markedly increases tissue oxygenation, did not do so during cardiopulmonary bypass with fixed pump output. This suggests that hypercapnia normally increases tissue oxygenation by increasing cardiac output rather than direct dilation of peripheral vessels.
PMCID: PMC1464052  PMID: 16675511
Carbon Dioxide; Hypercapnia; Hypercarbia; Acidosis; Respiratory; Oxygenation; Oxygen; Tissue; Cutaneous; Subcutaneous; Cerebral; Perfusion; Cerebrovascular; Cardiac Output
3.  Supplemental Intravenous Crystalloid Administration Does Not Reduce the Risk of Surgical Wound Infection 
Anesthesia and analgesia  2005;101(5):1546-1553.
Wound perfusion and oxygenation are important determinants of the development of postoperative wound infections. Supplemental fluid administration significantly increases tissue oxygenation in surrogate wounds in the subcutaneous tissue of the upper arm in perioperative surgical patients. We tested the hypothesis that supplemental fluid administration during and after elective colon resections decreases the incidence of postoperative wound infections. Patients undergoing open colon resection were randomly assigned to small (n=124, 8 mL·kg-1·h-1) or large volume (n=129, 16-18 mL·kg-1·h-1) fluid management. Our major outcomes were two distinct criteria for diagnosis of surgical wound infections: 1) purulent exudate combined with a culture positive for pathogenic bacteria and 2) Center for Disease Control criteria for diagnosis of surgical wound infections. All wound infections diagnosed using either criterion by a blinded observer in the 15 days following surgery were considered in the analysis. Wound healing was evaluated with the ASEPSIS scoring system. Of the patients given small fluid administration, 14 had surgical wound infections; 11 given large fluid therapy had infections, P=0.46. ASEPSIS wound healing scores were similar in both groups: 7±16 (small volume) vs. 8±14 (large volume), P=0.70. Our results suggest that supplemental hydration in the range tested does not impact wound infection rate.
PMCID: PMC1388094  PMID: 16244030
Fluid: Intravenous administration, Balance; Infection: Surgical wound
4.  The New Perilaryngeal Airway (CobraPLA™)1 Is as Efficient as the Laryngeal Mask Airway (LMA™)2, But Provides Better Airway Sealing Pressures 
Anesthesia and analgesia  2004;99(1):272-278.
The Laryngeal Mask Airway (LMA) is a frequently-used efficient airway device, yet it sometimes seals poorly, thus reducing the efficacy of positive-pressure ventilation. The Perilaryngeal Airway (CobraPLA) is a novel airway device with a larger pharyngeal cuff (when inflated). We tested the hypothesis that the CobraPLA was superior to LMA with regard to insertion time and airway sealing pressure and comparable to LMA in airway adequacy and recovery characteristics. After midazolam and fentanyl, 81 ASA I-II outpatients having elective surgery were randomized to receive an LMA or CobraPLA. Anesthesia was induced with propofol (2.5 mg/kg, IV), and the airway inserted. We measured 1) insertion time; 2) adequacy of the airway (no leak at 15-cm-H2O peak pressure or tidal volume of 5 ml/kg); 3) airway sealing pressure; 4) number of repositioning attempts; and 5) sealing quality (no leak at tidal volume of 8 ml/kg). At the end of surgery, gastric insufflation, postoperative sore throat, dysphonia, and dysphagia were evaluated. Data were compared with unpaired t-tests, chi-square tests, or Fisher’s Exact tests; P<0.05 was significant. Patient characteristics, insertion times, airway adequacy, number of repositioning attempts, and recovery were similar in each group. Airway sealing pressure was significantly greater with CobraPLA (23±6 cm H2O) than LMA (18±5 cm H2O, P<0.001). The CobraPLA has insertion characteristics similar to LMA, but better airway sealing capabilities.
PMCID: PMC1364541  PMID: 15281543
Airway: Sealing. Cuff Pressure. Insertion. Leak. Pharynx; Equipment: Laryngeal mask airway. Perilaryngeal airway; Ventilation: Controlled. Spontaneous; Anesthesia
5.  Magnesium Sulfate Only Slightly Reduces the Shivering Threshold in Humans 
British journal of anaesthesia  2005;94(6):756-762.
Background: Hypothermia may be an effective treatment for stroke or acute myocardial infarction; however, it provokes vigorous shivering, which causes potentially dangerous hemodynamic responses and prevents further hypothermia. Magnesium is an attractive antishivering agent because it is used for treatment of postoperative shivering and provides protection against ischemic injury in animal models. We tested the hypothesis that magnesium reduces the threshold (triggering core temperature) and gain of shivering without substantial sedation or muscle weakness.
Methods: We studied nine healthy male volunteers (18-40 yr) on two randomly assigned treatment days: 1) Control and 2) Magnesium (80 mg·kg-1 followed by infusion at 2 g·h-1). Lactated Ringer's solution (4°C) was infused via a central venous catheter over a period of approximately 2 hours to decrease tympanic membrane temperature ≈1.5°C·h-1. A significant and persistent increase in oxygen consumption identified the threshold. The gain of shivering was determined by the slope of oxygen consumption vs. core temperature regression. Sedation was evaluated using verbal rating score (VRS, 0-10) and bispectral index of the EEG (BIS). Peripheral muscle strength was evaluated using dynamometry and spirometry. Data were analyzed using repeated-measures ANOVA; P<0.05 was statistically significant.
Results: Magnesium reduced the shivering threshold (36.3±0.4 [mean±SD] vs. 36.6±0.3°C, P=0.040). It did not affect the gain of shivering (Control: 437±289, Magnesium: 573±370 ml·min-1·°C-1, P=0.344). The magnesium bolus did not produce significant sedation or appreciably reduce muscle strength.
Conclusions: Magnesium significantly reduced the shivering threshold; however, due to the modest absolute reduction, this finding is considered to be clinically unimportant for induction of therapeutic hypothermia.
PMCID: PMC1361806  PMID: 15749735
Magnesium; Temperature; Thermoregulation; Therapeutic hypothermia; Brain protection; Cardiac protection; Shivering
6.  The Timing of Acupuncture Stimulation Does Not Influence Anesthetic Requirement 
Anesthesia and analgesia  2005;100(2):387-392.
Studies suggest that acupuncture is more effective when induced before induction of general anesthesia than afterwards. We tested the hypothesis that electro-acupuncture initiated 30 minutes before induction reduces anesthetic requirement more than acupuncture initiated after induction. Seven volunteers were each anesthetized with desflurane on 3 study days. Needles were inserted percutaneously at 4 acupuncture points thought to produce analgesia in the upper abdominal area and provide generalized sedative and analgesic effects: Zusanli (St36), Sanyinjiao (Sp6), Liangqiu (St34), and Hegu (LI4). Needles were stimulated at 2-Hz and 10-Hz, with frequencies alternating at two-second intervals. On Preinduction day, electro-acupuncture was started 30 minutes before induction of anesthesia and maintained throughout the study. On At-induction day, needles were positioned before induction of anesthesia, but electro-acupuncture stimulation was not initiated until after induction. On Control day, electrodes were positioned near the acupoints, but needles were not inserted. Noxious electrical stimulation was administered via 25-G needles on the upper abdomen (70 mA, 100 Hz, 10 seconds). Desflurane concentration was increased 0.5% when movement occurred and decreased 0.5% when it did not. These up-and-down sequences continued until volunteers crossed from movement to no-movement 4 times. The P50 of logistic regression identified desflurane requirement. Desflurane requirement was similar on the Control (5.2±0.6%, mean±SD), Preinduction (5.0±0.8%), and At-induction (4.7±0.3%, P=0.125) days. This type of acupuncture is thus unlikely to facilitate general anesthesia or decrease the need for anesthetic drugs.
PMCID: PMC1360236  PMID: 15673863
Anesthetic technique: Acupuncture, Electro-acupuncture; Potency: anesthesia requirement; Anesthetics, volatile: desflurane

Results 1-6 (6)