[Knotted Seldinger wire]

Central venous catheters are usually positioned using the Seldinger technique with a guidewire. This article reports a case where the guidewire was inserted via the left subclavian vein with the landmark technique. The guidewire became kinked, pierced the vessel wall and became stuck forming several loops within the adjacent tissue of the vein. Several attempts were made to remove the guidewire by interventional radiology but were unsuccessful. Due to the critical condition of the patient an operation was considered too perilous and the guidewire was finally left in situ. No formation of local venous thrombosis could be detected.

Evaluation of aortic cannula jet lesions in a porcine cardiopulmonary bypass (CPB) model

In cardiosurgery patients atherosclerotic debris displaced from the cannulation site but also from the opposite aortic wall by the "sandblast-like" effect of the high-pressure jet emanating from the cannula is a potential source of intraoperative arterial embolization and consequently postoperative neurologic dysfunction. The present study examined the extent to which shear stress exerted on the intact aortic intima by an aortic cannula jet stream can cause endothelial lesions that promote thrombogenesis and consequently thrombembolism. A single-stream, straight-tip aortic cannula was used in a porcine cardiopulmonary bypass (CPB) model. Following a 120-minute CPB pump run, a 60-minute stabilization period was allowed before sacrificing the pigs (N.=40) for histological evaluation of the ascending aorta and the brain. Opposite the cannulation site endothelial lesions (diameter: 3.81±1.3 mm; depth: 0.017±0.003 mm) were present in 22.5% (9/40) of aortic specimens. Cerebral thrombembolic lesions were not found. The present study showed that single-stream, straight-tip aortic cannulas caused jet lesions of the formerly intact aortic endothelium opposite the cannulation site in 22.5% of cases in a porcine CPB model.

Lornoxicam characteristically modulates cerebral pain-processing in human volunteers: a functional magnetic resonance imaging study

BACKGROUND

Lornoxicam like other non-steroidal anti-inflammatory drugs (NSAIDs) is widely used for postoperative pain therapy. Evaluation of the effect of lornoxicam on cerebral processing of surgical pain was thus the aim of the present functional magnetic resonance imaging (fMRI) study.

METHODS

An fMRI-compatible pain model that mimics surgical pain was used to induce pain rated 4-5 on a visual analogue scale (VAS) at the anterior margin of the right tibia in volunteers (n=22) after i.v. administration of saline (n=11) or lornoxicam (0.1 mg kg(-1)) (n=11).

RESULTS

Lornoxicam, which significantly reduced pain sensation [VAS: mean (sd) 4.6 (0.7) vs 1.2 (1.5)], completely suppressed pain-induced activation in the SII/operculum, anterior cingulate cortex, insula, parietal (inferior), prefrontal (inferior, medial), temporal (inferior, medial/superior) lobe, cerebellum, and contralateral (e.g. left-sided) postcentral gyrus (SI). Only the hippocampus and the contralateral superior parietal lobe (BA 7) were activated.

CONCLUSIONS

As compared with saline, lornoxicam typically suppressed pain-induced brain activation in all regions except the hippocampus. Furthermore, de novo activation was found in the contralateral, superior parietal lobe (BA 7).

Does caffeine modulate verbal working memory processes? An fMRI study

To assess the effect of caffeine on the functional MRI signal during a 2-back verbal working memory task, we examined blood oxygenation level-dependent regional brain activity in 15 healthy right-handed males. The subjects, all moderate caffeine consumers, underwent two scanning sessions on a 1.5-T MR-Scanner separated by a 24- to 48-h interval. Each participant received either placebo or 100 mg caffeine 20 min prior to the performance of the working memory task in blinded crossover fashion. The study was implemented as a blocked-design. Analysis was performed using SPM2. In both conditions, the characteristic working memory network of frontoparietal cortical activation including the precuneus and the anterior cingulate could be shown. In comparison to placebo, caffeine caused an increased response in the bilateral medial frontopolar cortex (BA 10), extending to the right anterior cingulate cortex (BA 32). These results suggest that caffeine modulates neuronal activity as evidenced by fMRI signal changes in a network of brain areas associated with executive and attentional functions during working memory processes.

Bewertung eines Anatomieworkshops f�r die Regionalan�sthesieausbildung

BACKGROUND

The aim of the present investigation was to survey former participants (n=869) of a cadaver workshop using a mail questionnaire to assess the demographic data and the impact of these courses on daily practice.

METHODS

The deadline for acceptance of return mail was 60 days. Descriptive statistics were employed for analysis of results.

RESULTS

The response rate was 36.7% and the course was judged to be recommendable by 98.2%. The average course attendant was board certified and had spent a mean time of 9+/-6 years in anesthesiology. The highest quality and degree of subsequent practicability in daily routine was attributed to peripheral nerve block training on cadavers. Of the course participants two-thirds performed regional anesthesia procedures more often following attendance. The majority of course attendants had to defray at least a part of the course fee themselves, and one-third was required to invest leisure time to attend.

CONCLUSION

Attendance of a cadaver workshop increased knowledge of clinical anatomy and enhanced performance of regional anesthesia procedures. Courses of this format constitute a currently underestimated adjunct to contemporary regional anesthesia education.

Testing of a new pneumatic device to cause pain in humans

BACKGROUND

Surgical pain typically combines superficial and deep pain. We wished to generate pain that resembled surgical pain, reliably and reproducibly, in volunteers.

METHODS

We constructed a computer-controlled pneumatic device to apply pressure to the anterior tibia. The reproducibility of the pain was tested by rating the pressure that caused pain rated 4-5 on a visual analogue scale (VAS) on days 0, 7, and 24 in 10 volunteers. The effect of remifentanil (0.025, 0.05, 0.075, and 0.1 microg kg-1 min-1) on pain tolerance in another set of volunteers (n=11) was used as an indirect measure of the reliability of pain production.

RESULTS

The pressure needed (0.7 (0.3) to 0.9 (0.4) atm (mean (SD)) to induce pain rated 4-5 (VAS) did not vary, showing long-term reproducibility of the method. When pressure was applied to cause increasing pain in volunteers (n=11) 0.05 microg kg-1 min-1 remifentanil increased pain tolerance by 50%. An approximate doubling of the dose (0.1 microg kg-1 min-1) increased pain tolerance significantly more. The linear logarithmic dose-effect relationship shows that the device causes pain reliably, and this can be reduced with opioid treatment.

CONCLUSION

This pneumatic device can apply pain reliably and reproducibly.

[Evaluation of an established course of hospital management through structured telephone survey of former participants]

AIM OF THE STUDY

Participation in courses for health and hospital management is increasingly becoming a conditio sine qua non for candidates for executive positions in the health professions. The aim of this study was thus to evaluate the two-semester university course for health and hospital management offered by the University of Innsbruck since 1994.

METHODS

A structured telephone survey was conducted to poll the participants (n = 184) of previous courses concerning time invested, cost-benefit ratio, quality of the course as well as implementation of course content.

RESULTS

The university courses (n = 7) for health and hospital management of the University of Innsbruck evaluated in this study were rated in the upper half of the of the five-part scale (scores 2 to 3) for overall quality, cost-benefit ratio and implementation of course content. Only approx. 25 % of the course participants reported that the course had a positive influence on their career. The relatively high course fee was borne in part by the local hospital operator, a fact that had a certain influence on the selection of course participants. Participation in the course was largely made possible by exemptions from job duties (approx. 75 %) and to a lesser extent by vacation time (approx. 20 %) or time off for overtime (approx. 5 %). Of total absences from the course (3.18 +/- 3.41 d) 75 % was for job-related reasons, 6 % for illness and 19 % for other reasons. Overall, participants were absent more often, the larger the number of personnel in their department or clinic.

CONCLUSION

All in all, the courses were considered important and recommendable, particularly with regard to communication, organization, time management and cost awareness. Streamlining (i. e. more content in less time), stronger practical orientation and a switch from mainly local to more international speakers would be important steps toward improving course quality. Thanks to its demonstrated quality, it can be said that the university course for health and hospital management held by the University of Innsbruck and evaluated in this study is certainly a worthwhile course offered in a still emerging market, namely one that will come under increasing pressure from the candidates for executive positions in the health professions to provide what is best for their careers and the health services industry in general.

Remifentanil and nitrous oxide reduce changes in cerebral blood flow velocity in the middle cerebral artery caused by pain

BACKGROUND

Cerebral blood flow is affected by painful stimuli, and analgesic agents may alter the response of cerebral blood flow to pain. We set out to quantify the effects of remifentanil and nitrous oxide on blood flow changes caused by experimental pain.

METHODS

We simulated surgical pain in 10 conscious volunteers using increasing mechanical pressure to the tibia. We measured changes in cerebral blood flow velocity in the middle cerebral artery (CBFV(MCA)) caused by the pain, using transcranial Doppler sonography. We gave increasing doses of remifentanil (0.025, 0.05 and 0.1 micro g kg(-1) min(-1)) or nitrous oxide [20%, 35% and 50% end-tidal concentration (FE'(N(2)O))] and compared these effects on blood flow changes.

RESULTS

Nitrous oxide increased CBFV(MCA) only when given at 50% FE'(N(2)O). Remifentanil did not affect CBFV(MCA). Pain increased CBFV(MCA). Both agents attenuated this pain-induced change in CBFV(MCA) with the exception of nitrous oxide at 20% FE'(N(2)O).

CONCLUSIONS

Inhalation of nitrous oxide or adminstration of remifentanil attenuated pain-induced changes in CBFV(MCA).

Sevoflurane and nitrous oxide increase regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) in a drug-specific manner in human volunteers

Anesthesia for diagnostic procedures, e.g., MRI measurements, has increasingly used sevoflurane and nitrous oxide in recent years. Sevoflurane and nitrous oxide are known cerebrovasodilatators, however, which potentially interferes with MRI examination of cerebral hemodynamics. To compare the effects of relevant equianesthetic concentrations (0.4 MAC) of both drugs on regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) we used contrast-enhanced magnetic resonance imaging (MRI) perfusion measurement, which has the advantage of providing regional anatomic resolution. Sevoflurane increased rCBF more than did nitrous oxide in all regions except in parietal and frontal gray matter. Nitrous oxide, by contrast, increased rCBV in most of the gray matter regions more than did sevoflurane. In summary we show that, in contrast to nitrous oxide, sevoflurane supratentorially reversed the anterior-posterior gradient in rCBF and typically redistributed rCBF to infratentorial gray matter. In contrast, nitrous oxide increased rCBV more than did sevoflurane. Both inhalational anesthetics had a drug-specific influence on cerebral hemodynamics, which is of importance when interpreting MRI studies of cerebral hemodynamics in anesthetized patients.

Cardiological monitoring of sailors via offshore Internet connection

BACKGROUND

Sailing is becoming increasingly popular as a form of holiday recreation. The purpose of the present study was to profile the heart rate characteristics of non-professional crew members on a Mediterranean sailboat trip. Additionally, the practicability of transferring electronic data via the Internet while sailing offshore was also studied.

METHODS

Seven healthy male non-professional crew members responsible for steering and navigating the boat during the observation period were studied using continuous electrocardiographic recording (Holter). Manually measured blood pressure, side effects and sailing data were taped half-hourly.

RESULTS

While sailing we observed that the heart rate increased typically into the 120-170 beats/min range, mean arterial pressure remained stable between 80-90 mmHg. Heart rate changes and the incidence of supraventricular arrhythmias correlated with activity on board, boat speed and wind velocity. No subject showed ventricular arrhythmias during sailing. The minimal blood pressure changes correlated only with activity on board.

CONCLUSIONS

All these results indicate that sailboating on vacation, even in a non-professional status, does not promote disease-relevant changes in heart rhythm on trips in mild to moderate seas. Additionally, we were able to demonstrate that the online transfer of electronic data via the Internet from a sailboat offshore is possible, easy and inexpensive.

Influence of equianaesthetic concentrations of nitrous oxide and isoflurane on regional cerebral blood flow, regional cerebral blood volume, and regional mean transit time in human volunteers

Nitrous oxide and isoflurane have cerebral vasodilatory effects. The use of isoflurane in neuroanaesthesia is widely accepted, whereas the use of nitrous oxide in neuroanaesthesia is still the subject of debate. In the present study, contrast-enhanced magnetic resonance (MR) perfusion measurement was used to compare the effects of 0.4 MAC nitrous oxide (n=9) and 0.4 MAC isoflurane (n=9) on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV) and regional mean transit time (rMTT) in spontaneously breathing human volunteers. Nitrous oxide increased rCBF and rCBV in supratentorial regions more than did isoflurane. Isoflurane, by contrast, increased rCBF and rCBV in basal ganglia more than did nitrous oxide. An increased rMTT was caused by a relatively greater increase in rCBV than in rCBF supratentorially by isoflurane and infratentorially by nitrous oxide. In conclusion, nitrous oxide increases rCBF and rCBV predominantly in supratentorial grey matter, whereas isoflurane increases rCBF and rCBV predominantly in infratentorial grey matter.

Subanesthetic concentration of sevoflurane increases regional cerebral blood flow more, but regional cerebral blood volume less, than subanesthetic concentration of isoflurane in human volunteers

Both sevoflurane and isoflurane are used in moderate concentrations in neuroanesthesia practice. The limiting factors for using higher concentrations of inhalational anesthetics in patients undergoing neurosurgery are the agents' effects on cerebral blood flow (CBF) and cerebral blood volume (CBV). In particular, an increase in CBV, which is a key determinant of intracranial pressure, may add to the neurosurgical patient's perioperative risk. To compare the effects of a subanesthetic concentration (0.4 minimum alveolar concentration) of sevoflurane or isoflurane on regional CBF (rCBF), regional CBV (rCBV) and regional mean transit time (rMTT), contrast-enhanced magnetic resonance imaging perfusion measurements were made in spontaneously breathing human volunteers. Absolute changes in rCBF, regional CBV, and rMTT during administration of either drug in regions of interest outlined bilaterally in white and grey matter were nonparametrically (Mann-Whitney test) analyzed. Sevoflurane increased rCBF in practically all regions (absolute change, 4.44 +/- 2.87 to 61.54 +/- 2.39 mL/100g per minute) more than isoflurane did (absolute change, 12.91 +/- 2.52 to 52.67 +/- 3.32 mL/100g per minute), which decreased frontal, parietal, and white matter rCBF (absolute change, -1.12 +/- 0.59 to -14.69 +/- 3.03 mL/100g per minute). Regional CBV was higher in most regions during isoflurane administration (absolute change, 0.75 +/- 0.03 to 4.92 +/- 0.16 mL/100g) than during sevoflurane administration (absolute change, 0.05 +/- 0.14 to 3.57 +/- 0.14 mL/100g). Regional mean transit time was decreased by sevoflurane (absolute change, -0.18 +/- 0.05 to -0.60 +/- 0.04 s) but increased by isoflurane (absolute change, 0.19 +/- 0.03 to 0.69 +/- 0.04 s). In summary, regional CBV was significantly lower during sevoflurane than during isoflurane administration, although sevoflurane increased rCBF more than isoflurane, which even decreased rCBF in some regions. For sevoflurane and, even more pronouncedly, for isoflurane, the observed changes in cerebral hemodynamics cannot be explained by vasodilatation alone.

Increasing mean airway pressure reduces functional MRI (fMRI) signal in the primary visual cortex

Changes in both blood flow and blood oxygenation determine the functional MRI (fMRI) signal. In the present study factors responsible for blood oxygenation (e.g., FiO(2)) were held constant so that changes in pixel count would above all reflect changes in regional cerebral blood flow (rCBF). Continuous positive airway pressure (CPAP) breathing at 12 cm H(2)O, which was previously shown to influence rCBF, was applied in human volunteers (n = 19) to investigate the sensitivity of fMRI for changes in rCBF caused by increased mean airway pressure. Increasing the mean airway pressure decreased the pixel count in the primary visual cortex (median (range)): baseline: 219 (58-425) pixels vs. CPAP (12 cm H(2)O): 92 (0-262) pixels). These findings indicate that fMRI is sensitive to detect a reduced rCBF-response in the primary visual cortex. The underlying mechanism is likely to be a reduced basal rCBF due to constriction and/or compression of postcapillary venoles during CPAP breathing. These findings are important for interpreting fMRI results in awake and in artificially respirated patients, in whom positive airway pressure is used to improve pulmonary function during the diagnostic procedure.

The impact of increased mean airway pressure on contrast-enhanced MRI measurement of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional mean transit time (rMTT), and regional cerebrovascular resistance (rCVR) in human volunteers

Contrast-enhanced magnetic resonance imaging (MRI) measurement of cerebral perfusion is a diagnostic procedure increasingly gaining access to clinical practice not only in spontaneously breathing patients but also in mechanically ventilated patients. Effects of increased mean airway pressure on cerebral perfusion are entirely possible. Therefore, the present study used continuous positive airway pressure (CPAP) (12 cm H2O) to study the effects of increased mean airway pressure on cerebral perfusion in volunteers. CPAP significantly reduced regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) but increased regional mean transit time (rMTT) and regional cerebrovascular resistance (rCVR). Active vasoconstriction (e.g., arterial) and/or passive compression of capillary and/or venous vessel areas are the most likely underlying mechanisms. The number of interhemispheric differences in rCBF, rCBV, rMTT, and rCVR found at baseline rose when mean airway pressure was increased. These results, although obtained in volunteers, should be taken into consideration for the interpretation of contrast-enhanced MRI perfusion measurements in mechanically ventilated patients with an increased positive airway pressure.

Low-dose remifentanil increases regional cerebral blood flow and regional cerebral blood volume, but decreases regional mean transit time and regional cerebrovascular resistance in volunteers

We have used contrast media-enhanced perfusion magnetic resonance imaging MRI to measure regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional mean transit time (rMTT) and regional cerebrovascular resistance (rCVR) in volunteers at baseline and during infusion of remifentanil (0.1 microgram kg-1 min-1). Remifentanil increased rCBF and rCBV in white and grey matter (striatal, thalamic, occipital, parietal, frontal) regions, with a parallel decrease in rMTT in those regions with the exception of occipital grey matter. rCVR was decreased in all regions studied. The relative increase in rCBF was greater than that in rCBV. Cerebral haemodynamics were increased significantly in areas less rich in mu-opioid receptors with a tendency towards more pronounced increases in rCBF and rCBV in pain-processing areas. Furthermore, interhemispheric differences in rCBF, rCBV and rMTT found prior to drug administration were almost eliminated during infusion of remifentanil. We conclude that, apart from direct and indirect cerebrovascular effects of remifentanil, these findings are consistent with cerebral excitement and/or disinhibition.

A subanesthetic concentration of sevoflurane increases regional cerebral blood flow and regional cerebral blood volume and decreases regional mean transit time and regional cerebrovascular resistance in volunteers

Inhaled anesthetics exert metabolically mediated effects on cerebral blood vessels both directly and indirectly. We investigated the effects of a 0.4 minimum alveolar subanesthetic concentration of sevoflurane on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional cerebrovascular resistance (rCVR), and regional mean transit time (rMTT) in volunteers by means of contrast-enhanced magnetic resonance imaging perfusion measurement. Sevoflurane increased rCBF by 16% to 55% (control, 55. 03 +/- 0.33 to 148.83 +/- 1.9 mL. 100 g(-1). min(-1); sevoflurane, 71.75 +/- 0.36 to 193.26 +/- 2.14 mL. 100 g(-1). min(-1)) and rCBV by 7% to 39% (control, 4.66 +/- 0.03 to 10.04 +/- 0.12 mL/100 g; sevoflurane, 5.04 +/- 0.03 to 13.6 +/- 0.15 mL/100 g); however, sevoflurane decreased rMTT by 7% to 18% (control, 3.75 +/- 0.04 to 5. 39 +/- 0.04 s; sevoflurane, 3.4 +/- 0.03 to 4.44 +/- 0.03 s) and rCVR by 22% to 36% (control, 0.74 +/- 0.01 to 1.9 +/- 0.2 mm Hg/[mL. 100 g(-1). min(-1)]; sevoflurane, 0.54 +/- 0.01 to 1.41 +/- 0.01 mm Hg/[mL. 100 g(-1). min(-1)]). Interhemispheric differences in rCBF, rCBV, and rCVR were markedly reduced after the administration of sevoflurane. These findings are consistent with the known direct vasodilating effect of sevoflurane. The decrease in rMTT further shows that rCBF increases more than does rCBV. Furthermore, we can show that the observed increase in rCBF during inhalation of sevoflurane is not explained by vasodilation alone.

The effects of remifentanil on cerebral capacity in awake volunteers

Remifentanil, a short-acting potent mu-opioid agonist proposed for intraoperative analgesia but also for postoperative pain therapy, has not been investigated with regard to the effects of the drug on cerebral capacity in awake humans. We assessed cerebral capacity noninvasively by means of phase-contrast magnetic resonance imaging measurement of systolic cerebrospinal fluid peak velocity in the aqueduct of Sylvius before and during infusion of remifentanil (0.1 microg. kg(-1). min(-1) IV) in normocapnic humans. Remifentanil had no significant effect on systolic cerebrospinal fluid peak velocity as compared with baseline (mean +/- SD): baseline, -4.3 +/- 1.3 cm/s versus remifentanil (0.1 microg. kg(-1). min(-1)): -4.7 +/- 1.0 cm/s. Small-dose remifentanil (0.1 microg. kg(-1). min(-1)) did not influence cerebral capacity in healthy, awake volunteers free of intracranial pathology.

IMPLICATIONS

Knowledge about the influence of remifentanil on cerebral capacity is crucial before routine use of the drug in neuroanesthesia. Thus, we assessed the influence of remifentanil on cerebral capacity noninvasively by means of phase-contrast magnetic resonance imaging measurement of systolic cerebrospinal fluid peak velocity in the aqueduct of Sylvius in humans.

Effect of fluvoxamine on sufentanil antinociception and tolerance under chronic intravenous infusion in rats

Fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), significantly potentiates analgesia when administered in animals together with opioids. The aim of the present study was to investigate the effects of fluvoxamine on sufentanil antinociception and tolerance. Following animal care committee approval, the effects of continuous infusions of fluvoxamine and sufentanil were studied in behavioural tests (hot-plate test, tail-flick test, catalepsy test) in Sprague-Dawley rats with a jugular vein catheter. Saline was administered as a control. The time-effect curves for continuous intravenous sufentanil indicate dose-related antinociception and rapid development of tolerance in the hot-plate and tail-flick tests. Co-administration of fluvoxamine with continuous sufentanil enhances antinociception and attenuates development of tolerance, most clearly seen in the tail-flick test. Fluvoxamine alone and saline were not effective. No animal showed catalepsy. As a side effect we observed a marked loss of body weight. The IC50 values of sufentanil binding with and without fluvoxamine addition are 0.56+/-0.17 nM and 0.3+/-0.15 nM, respectively, indicating no direct effect on the occupancy of sufentanil on the mu-receptor by this serotonin reuptake inhibitor. In conclusion, we were able to show that the combination of an opioid with an SSRI at low doses improves analgesia and decreases development of tolerance in nociceptive tests in rats. The clinical implications of these promising results in an animal model, however, await further investigation.

Effects of hyperoxia and hypocapnia on regional venous oxygen saturation in the primary visual cortex in conscious humans

Hyperoxia can improve oxygen delivery in patients exposed to hypocapnia for neurosurgical procedures but this effect may be modified by regional differences in the degree of hypocapnic vasoconstriction. Using functional magnet resonance imaging (fMRI), we have investigated the influence of hyperoxia on blood flow and blood oxygenation in the primary visual cortex in hypocapnic volunteers. Consecutive fMRI measurements were performed in 10 awake, male volunteers during hypocapnia (mean PE'CO2 3.3 (SD 0.1) kPa) and normocapnia (PE'CO2 5.3 (0.1) kPa) at FIO2 values of 0.21 and 1.0, respectively. Hypocapnia significantly reduced the pixel count in the primary visual cortex (median 169 (quartiles 34-246) vs 21 (0-40) pixels at an FIO2 of 0.21). Additional hyperoxia had no influence on this reduction in pixel count (16 (0-28) pixels at FIO2 1.0 vs 21 (0-40) pixels at FIO2 0.21). Hyperoxia did not influence hypocapnic vasoconstriction in the primary visual cortex. These data suggest that in the primary visual cortex, administration of oxygen alone may not be sufficient to improve oxygen delivery under hypocapnic conditions.

Phase-contrast MRI measurement of systolic cerebrospinal fluid peak velocity (CSFV(peak)) in the aqueduct of Sylvius: a noninvasive tool for measurement of cerebral capacity

BACKGROUND

Cerebrospinal fluid (CSF) outflow to intra- and extracranial subarachnoid spaces caused by arterial inflow to the brain predominantly compensates systolic increases in cerebral blood volume. Phase-contrast magnetic resonance imaging is a new tool for noninvasive assessment of CSF displacement by measuring CSF peak velocity (CSFV(Peak)). The authors tested this new tool in an experimental human model of increased intracranial pressure and reduced cerebral capacity by means of continuous positive airway pressure (CPAP) breathing.

METHODS

The authors investigated systolic CSFV(Peak) in the aqueduct of Sylvius in 11 awake, normocapnic (end-tidal carbon dioxide [ET(CO2)] = 40 mmHg) volunteers without CPAP and at two different CPAP levels (6 and 12 cm H2O) by means of electroencephalography-gated phase-contrast magnetic resonance imaging.

RESULTS

Administration of 6 cm H2O CPAP did not change systolic CSFV(Peak) (-4.9+/-2.8 cm/s vs. control: -5.1+/-2.7 cm/s), whereas 12 cm H2O CPAP significantly reduced systolic CSFV(Peak) (-4.0+/-1.8 cm/s vs. control: -5.1+/-2.7 cm/s; P < 0.05).

CONCLUSIONS

These findings in awake volunteers show that monitoring CSFV(Peak) in the aqueduct of Sylvius is a sensitive method for detecting even minor impairment of cerebral capacity caused by experimentally induced increases in intracranial pressure.

Transcutaneous CO2/O2 and CO2/air suction in patients undergoing cataract surgery with retrobulbar anaesthesia

We investigated transcutaneous partial CO2 and O2 pressures and respiratory rate in unpremedicated elderly patients of ASA physical status 1 to 3 who underwent cataract surgery under retrobulbar anaesthesia. In group A no air suction was used. In group B suction was applied under the sterile drapes to avoid rebreathing of CO2. In group A transcutaneous partial CO2 pressure and respiratory rate significantly increased compared with baseline, whereas in group B they remained constant. In both groups transcutaneous partial O2 pressure and oxygen saturation as measured by pulse oximetry significantly rose after insufflating oxygen 31.min-1. Heart rate and mean arterial blood pressure remained constant. Our results demonstrate that the application of suction near the patient's head prevents CO2 rebreathing and subsequent hypercapnia associated with an elevated respiratory rate. The use of suction makes it unnecessary to raise oxygen administration. Suction combined with monitoring of partial CO2 pressure using transcutaneous sensors should be used in all ophthalmological operations under retrobulbar anaesthesia.

[Acceptance of an Ethics Committee (International Review Board)]

The work input of an institutional review board, the satisfaction or dissatisfaction of project applicants with its decisions, as well as the amount of time needed for preparatory and follow-up work for projects submitted to the board were surveyed in a questionnaire. An analysis of the status quo provided proposals for improvement, with the aim of increasing the satisfaction of all parties involved. Questionnaires were returned by 41.4% (101/244) of the specialist doctors surveyed. Of these, 42 were doctors who had submitted projects for review and whose evaluation was used for the study. The proportion of trained "clinical review doctors" was 14.3%. Analysis of work input showed that 13.5 +/- 15.2 hours were invested before submitting a project and 6.3 +/- 9.3 hours in the follow-up. Although the board's work was given a satisfactory grading with a score of 2.8 +/- 1.0, the surveyed satisfaction/importance profile showed marked deficits in many areas, primarily in organization and communication, as well as in the examination and evaluation of projects. The suggestions for improvement above all requested the introduction of a review system employing specialists from outside the institution or from other disciplines, standardization of project submission, optimization of organization and improvement in communication. In summary, the institutional review board plays an important role in clinical research. The acceptance of a review board's work, however, can only be improved when the suggestions for improvement are realized step by step. The results of this evaluation and the proposed solutions can also help other boards improve their work. At any rate, it would be desirable to take a new look in several years' time at how the proposals worked out in this study have been implemented.

Effect of the NMDA-antagonist, MK 801, on benzodiazepine-opioid interactions at the spinal and supraspinal level in rats

1. Benzodiazepines potentiate morphine antinociception at the spinal level via GABAergic mechanisms. At the supraspinal level, the inhibitory effect of midazolam on morphine antinociception cannot be easily explained by GABAA receptor activation. Since excitatory amino acids play a role in central transmission, we investigated the effect of dizocilpine (MK 801) on this interaction in spinal cord and brain. 2. In rats with an intrathecal or intracerebroventricular catheter, the mechanisms of the antinociceptive effect of benzodiazepine-morphine combinations were tested during thermal nociceptive tests. 3. The principal findings of this study were that at the spinal level, midazolam potentiation of morphine antinociception can be antagonized by the NMDA antagonist, MK 801 (10 micrograms), as assessed by hot-plate and tail-flick tests. When drugs were administered supraspinally, midazolam inhibited morphine antinociception only in the hot-plate test, an effect also inhibited by MK 801. In the tail-flick assay, midazolam failed to influence the morphine response. 4. The NMDA antagonist significantly affected midazolam antinociception at the spinal level, but was not effective following i.c.v. administration of the drugs. MK 801 had no effect on morphine antinociception after i.t. and i.c.v. administration of the drugs. 5. The paradoxical effect of midazolam on morphine antinociception and its reversal by MK 801 might be due to modulation at various levels of the neuraxis and/or modulation of different pathways mediated via both GABAA and NMDA receptor mechanisms.

Mechanisms of the influence of midazolam on morphine antinociception at spinal and supraspinal levels in rats

The mechanisms for the combined antinociceptive effect of midazolam and morphine administered at spinal (intrathecal, i.t.) and supraspinal (intracerebroventricular, i.c.v.) levels were investigated in rats. Nociceptive test results showed that co-administration of midazolam and morphine at the spinal level potentiated morphine-induced antinociception, and that this interaction was blocked by intraperitoneal (i.p.) naloxone and reversed by i.t. bicuculline and i.p. flumazenil. Also, bicuculline and flumazenil blocked midazolam-induced antinociception at the spinal level, and naloxone completely reversed morphine antinociception. In contrast, when drugs were injected intracerebroventricularly, midazolam inhibited the antinociceptive effect of morphine (as determined by the hot-plate test). The inhibitory effects of i.c.v. midazolam upon i.c.v. morphine antinociception were partly blocked by flumazenil and bicuculline. Midazolam-induced antinociception was increased by bicuculline and decreased by flumazenil; naloxone i.p. blocked both i.c.v. morphine antinociception and i.c.v. morphine-midazolam antinociception. Results after i.t. injection may be due to an interaction between morphine and midazolam/GABAA receptor-activated systems. At the supraspinal level, this interaction may also activate other systems that are distinct from those governing the individual action of each agonist.