Oxygen diffusion: an enzyme-controlled variable parameter.

Previous oxygen microelectrode studies have shown that the oxygen diffusion coefficient (DO2) increases during extracellular PO2 decreases, while intracellular PO2 remained unchanged and thus cell function (spike activity of neurons). Oxygen dependency of complex multicellular organisms requires a stable and adequate oxygen supply to the cells, while toxic concentrations have to be avoided. Oxygen brought to the tissue by convection diffuses through the intercellular and cell membranes, which are potential barriers to diffusion. In gerbil brain cortex, PO2 and DO2 were measured by membrane-covered and by bare gold microelectrodes, as were also spike potentials. Moderate respiratory hypoxia was followed by a primary sharp drop of tissue PO2 that recovered to higher values concomitant with an increase of DO2. A drop in intracellular PO2 recovered immediately. Studies on the abdominal ganglion of aplysia californica showed similar results.Heterogeneity is a feature of both normal oxygen supply to tissue and supply due to a wide range of disturbances in oxygen supply. Oxygen diffusion through membranes is variable thereby ensuring adequate intracellular PO2. Cell-derived glucosamine oxidase seems to regulate the polymerization/depolymerisation ratio of membrane mucopolysaccharides and thus oxygen diffusion.Variability of oxygen diffusion is a decisive parameter for regulating the supply/demand ratio of oxygen supply to the cell; this occurs in highly developed animals as well as in species of a less sophisticated nature. Autoregulation of oxygen diffusion is as important as the distribution/perfusion ratio of the capillary meshwork and as the oxygen extraction ratio in relation to oxygen consumption of the cell. Oxygen diffusion resistance is the cellular protection against luxury oxygen supply (which can result in toxic oxidative species leading to mutagenesis).

Effects of simultaneous aortocaval occlusion on oxygen consumption in patients.

The effects of simultaneous occlusion of the thoracic aorta and inferior vena cava on oxygen consumption (V O 2) have not yet been reported in humans. Ten patients (all ASA II) needed such simultaneous occlusion to allow hypoxic abdominal perfusion in the treatment of pancreatic cancer. With the development of the PhysioFlex anaesthesia machine for closed-circuit anaesthesia, intra-operative real-time curves of V O 2 became available. Thus, we can continuously measure F I O 2, V E, V O 2, and air consumption. By placing a pulmonary artery catheter, we could also intermittently calculate D O 2 during the several phases of the perfusion procedure. Immediately after the simultaneous aortocaval occlusion started, V O 2 decreased by 35% (68 ml min-1 m-2) and D O 2 decreased below the critical value of 330 ml min-1 m-2. At reperfusion, repayment of the oxygen debt was by a two-stage pattern: a fast repayment stage with an increase of about 65% was followed by a slow repayment stage of 14% increase (values compared to steady state). Oxygen consumption in women was found to be significantly lower than in men (P = 0.02), with significant variation between the sexes during different stages of the procedure. The oxygen debt was not completely repaid by the end of the procedure. We conclude that the significant variation found in oxygen consumption will have consequences while performing low-flow anaesthesia, that additional oxygen supply during the recovery period because of the initially incomplete repayment of oxygen debt may be useful and that studies on oxygen consumption must present gender-specific data because of the gender-dependent variation found in oxygen consumption.

Multicenter randomized comparison of the efficacy and safety of xenon and isoflurane in patients undergoing elective surgery.

BACKGROUND: All general anesthetics used are known to have a negative inotropic side effect. Since xenon does not have a negative inotropic effect, it could be an interesting future general anesthetic. The aim of this clinical multicenter trial was to test the hypothesis of whether recovery after xenon anesthesia is faster compared with an accepted, standardized anesthetic regimen and that it is as effective and safe. METHOD: A total of 224 patients in six centers were included in the protocol. They were randomly assigned to receive either xenon (60 +/- 5%) in oxygen or isoflurane (end-tidal concentration, 0.5%) combined with nitrous oxide (60 +/- 5%). Sufentanil (10 mcirog) was intravenously injected if indicated by defined criteria. Hemodynamic, respiratory, and recovery parameters, the amount of sufentanil, and side effects were assessed. RESULTS: The recovery parameters demonstrated a statistically significant faster recovery from xenon anesthesia when compared with isoflurane-nitrous oxide. The additional amount of sufentanil did not differ between both anesthesia regimens. Hemodynamics and respiratory parameters remained stable throughout administration of both anesthesia regimens, with advantages for the xenon group. Side effects occurred to the same extent with xenon in oxygen and isoflurane-nitrous oxide. CONCLUSION: This first randomized controlled multicenter trial on the use of xenon as an inhalational anesthetic confirms, in a large group of patients, that xenon in oxygen provides effective and safe anesthesia, with the advantage of a more rapid recovery when compared with anesthesia using isoflurane-nitrous oxide.

Questionnaire as diagnostic tool in chronic pelvic pain (CPP): a pilot study.

OBJECTIVES: No standard screening instrument is available enabling physicians to assign the diagnosis chronic pelvic pain (CPP) to women with lower abdominal pain. Therefore, our aim was to evaluate an easy-to-use questionnaire, which can be applied as a validated primary screening test for diagnosing CPP. STUDY DESIGN: From the general female population, 577 women completed a questionnaire addressing chronic symptoms in the pelvic region. Included were (amongst others) questions on lower abdominal pain, low back pain, voiding symptoms, dyspareunia, pelveo-perineal dysesthetic feelings and evacuation problems. Serious chronic lower abdominal pain of unknown origin was considered as CPP. Three criteria were applied to validate the questionnaire: construct validity, comparison with results of a previous study and content validity. In addition, the internal consistency was checked to ascertain the reliability of the questionnaire. RESULTS: All items, with the exception of those concerning voiding symptoms and dyspareunia, withstood the validity tests applied, were interrelated and occurred significantly more often in women with CPP than those without. There were no significant differences in the frequency of the occurrence of low back pain, dyspareunia and evacuation problems between CPP women in the current community study and outpatients diagnosed with CPP in an earlier study performed at the University Hospital Rotterdam. Compared to our current study group, pelveo-perineal dysesthesia (PPD) and voiding symptoms were significantly more often reported by the CPP outpatients. CONCLUSION: The CPP questionnaire can be considered as a validated tool for primary screening of CPP.

Eficácia e segurança do tramadol versus morfina na dor pós-operatória moderada e severa com especial atençäo à depressäo respiratória / Efficacy and safety of tramadol versus morphine for moderate and severe postoperative pain with special regard to respiratory depression

A eficácia analgésica e a segurança do tramadol e da morfina foram comparadas em um estudo randomizado e duplo-cego realizado em 150 mulheres após cirurgia ginecológica. Se necessário, as pacientes poderiam receber até três doses intravenosas ou de 50 mg de tramadol ou de 5 mg de morfina dentro de um período de 6 horas. A intensidade da dor (escore de resposta verbal) foi registrada antes da administraçäo e 0,5 1, 2, 3, 5 e 6 horas depois da dose inicial; nestes períodos o alívio da dor também foi monitorada continuamente através de pulso-oximetria por ao mínimo 30 minutos depois de cada administraçäo. Em 13,3 por cento do grupo morfina (mas em nenhuma do grupo tramadol) a saturaçäo transcutânea de oxigênio na artéria radial diminuiu para menos de 86 por cento, em 50 por cento destas pacientes a reduçäo já ocorreu depois da primeira dose de 5mg de morfina. Ambas as drogas produziram uma analgesia aceitável e näo foram observados efeitos adversos clinicamente significativos. Pela demonstraçäo da ausência de depressäo respiratória clinicamente relevante com o tramadol nós enfatizamos a sua segurança no alívio da dor pós-operatória