Awake tracheal intubation for blunt airway trauma

A 64-year-old man sustained blunt trauma to the anterior neck following a mechanical fall resulting in an isolated laryngeal fracture of the left cricoarytenoid complex. Although there was no acute airway compromise, he developed worsening airway oedema which necessitated tracheal intubation. He underwent oral awake tracheal intubation with a flexible bronchoscope to facilitate formation of a tracheostomy under general anaesthesia. The challenges encountered in the clinical management of this case relate to decision making for the patient with airway trauma in the absence of the need for emergency tracheal intubation. We describe the advantages and pitfalls of various airway management strategies in the context of blunt airway trauma.

Low doses of alpha 2-adrenoceptor antagonists augment spinal morphine analgesia and inhibit development of acute and chronic tolerance

BACKGROUND AND PURPOSE

Ultra-low doses of opioid receptor antagonists augment spinal morphine antinociception and block the induction of tolerance. Considering the evidence demonstrating functional and physical interactions between the opioid and alpha(2)-adrenoceptors, this study investigated whether ultra-low doses of alpha(2)-adrenoceptor antagonists also influence spinal morphine analgesia and tolerance.

EXPERIMENTAL APPROACH

Effects of low doses of the competitive alpha(2)-adrenoceptor antagonists-atipamezole (0.08, 0.8 ng), yohimbine (0.02, 2 ng), mirtazapine (0.02 ng) and idazoxan (0.08 ng) were investigated on intrathecal morphine analgesia, as well as acute and chronic morphine antinociceptive tolerance using the rat tail flick and paw pressure tests.

KEY RESULTS

At doses markedly lower than those producing alpha(2)-adrenoceptor blockade, atipamezole, yohimbine, mirtazapine and idazoxan, prolonged the antinociceptive effects of morphine. When co-administered with repeated acute spinal injections of morphine, all four agents blocked the induction of acute tolerance. Co-injection of atipamezole with morphine for 5 days inhibited the development of tolerance in a chronic treatment paradigm. Spinal administration of atipamezole also reversed established antinociceptive tolerance to morphine as indicated by the restoration of morphine antinociceptive potency. The effects of atipamezole on spinal morphine tolerance were not influenced by treatment with 6-hydroxydopamine.

CONCLUSIONS AND IMPLICATIONS

Low doses of competitive alpha(2)-adrenoceptor antagonists can augment acute morphine analgesia and block or reverse tolerance to spinal administration of morphine. These actions are interpreted in terms of their interaction with an opioid-alpha(2)-adrenoceptor complex, whose activity may have a function in the genesis of analgesic tolerance.

Augmentation of spinal morphine analgesia and inhibition of tolerance by low doses of mu- and delta-opioid receptor antagonists

BACKGROUND AND PURPOSE

Ultralow doses of naltrexone, a non-selective opioid antagonist, have previously been found to augment acute morphine analgesia and block the development of tolerance to this effect. Since morphine tolerance is dependent on the activity of micro and delta receptors, the present study investigated the effects of ultralow doses of antagonists selective for these receptor types on morphine analgesia and tolerance in tests of thermal and mechanical nociception.

EXPERIMENTAL APPROACH

Effects of intrathecal administration of mu-receptor antagonists, CTOP (0.01 ng) or CTAP (0.001 ng), or a delta-receptor antagonist, naltrindole (0.01 ng), on spinal morphine analgesia and tolerance were evaluated using the tail-flick and paw-pressure tests in rats.

KEY RESULTS

Both micro and delta antagonists augmented analgesia produced by a sub-maximal (5 microg) or maximal (15 microg) dose of morphine. Administration of the antagonists with morphine (15 microg) for 5 days inhibited the progressive decline of analgesia and prevented the loss of morphine potency. In animals exhibiting tolerance to morphine, administration of the antagonists with morphine produced a recovery of the analgesic response and restored morphine potency.

CONCLUSIONS AND IMPLICATIONS

Combining ultralow doses of micro- or delta-receptor antagonists with spinal morphine augmented the acute analgesic effects, inhibited the induction of chronic tolerance and reversed established tolerance. The remarkably similar effects of micro- and delta-opioid receptor antagonists on morphine analgesia and tolerance are interpreted in terms of blockade of the latent excitatory effects of the agonist that limit expression of its full activity.

Facilitation of spinal morphine analgesia in normal and morphine tolerant animals by neuropeptide SF and related peptides

Neuropeptide FF and related synthetic amidated peptides have been shown to elicit sustained anti-nociceptive responses and potently augment spinal anti-nociceptive actions of spinal morphine in tests of thermal and mechanical nociception. Recent studies have described the occurrence of another octapeptide, neuropeptide SF (NPSF) in the spinal cord and the cerebrospinal fluid and demonstrated its affinity for the NPFF receptors. This study examined the effects of NPSF and two putative precursor peptides, EFW-NPSF and NPAF, on the spinal actions of morphine in normal and opioid tolerant rats using the tailflick and pawpressure tests. In normal rats, NPSF demonstrated weak intrinsic activity but sub-effective doses of the peptide significantly increased the magnitude and duration of spinal morphine anti-nociception in both tests. A low-dose of NPSF also augmented the spinal actions of a delta receptor agonist, deltorphin. The morphine-potentiating effect of NPSF was shared by EFW-NPSF and the octadecapeptide NPAF. In animal rendered tolerant by continuous intrathecal infusion of morphine for 6 days, low dose NPSF itself elicited a significant anti-nociceptive response and potently increased morphine-induced response in both tests. In animals made tolerant by repeated injections of intrathecal morphine, administration of NPSF, EFW-NPSF, and NPAF with morphine reversed the loss of the anti-nociceptive effect and restored the agonist potency. The results demonstrate that in normal animals NPSF and related peptides exert strong potentiating effect on morphine anti-nociception at the spinal level and in tolerant animals these agents can reverse the loss of morphine potency.

Mannitol but not dantrolene prevents myocardial dysfunction following intra-cranial hypertension in rats

Cardiac complications stemming from intra-cranial hypertension may result from impaired intra-cellular Ca(2+) homeostasis. The aim of this study was to examine the effects of dantrolene, a blocker of sarcoplasmic reticulum (SR) Ca(2+) release, on myocardial dysfunction associated with intra-cranial hypertension in rats. Dantrolene (10 mg) with and without 15% mannitol was administered to halothane-anesthetized rats prior to induction of intra-cranial hypertension by subdural balloon inflation. Its effects were compared to 3% and 15% mannitol and 5% Pentaspan. Dantrolene with mannitol or 15% mannitol alone prevented the transient intra-cranial hypertension-induced hyperdynamic response and ensuing circulatory collapse that was found in animals pre-treated with 3% mannitol solution or pentaspan. Moreover, hemodynamic function was preserved irrespective of TnI cleavage. However, only animals treated with high dose 15% mannitol exhibited lower lipid peroxidation content in the heart. In contrast, pre-treatment with dantrolene alone did not prevent the cardiac complications associated with intra-cranial hypertension. In conclusion, 15% mannitol attenuated the cardiopulmonary complications associated with intra-cranial hypertension. Dantrolene without mannitol was without effect. Since mannitol exhibits free radical scavenging properties, protection could be the result of a decrease in oxidative stress after intra-cranial hypertension.

The release of spinal prostaglandin E2 and the effect of nitric oxide synthetase inhibition during strychnine-induced allodynia

The removal of spinal glycinergic inhibition by intrathecal strychnine produces an allodynia-like state in rodents. Our objective was to measure spinal prostaglandin E2 (PGE2) release during strychnine-allodynia and examine the effects of Nomega-nitro-L-arginine (L-NOARG), an inhibitor of nitric oxide synthetase. Under halothane, rats were fitted with intrathecal and spinal microdialysis catheters, and microelectrodes implanted into the locus coeruleus for measurement of catechol oxidation current (CAOC) using voltammetry. Animals were then administered urethane and treated as follows: 1) baseline control 10 min, intrathecal strychnine (40 microg) 10 min, 10 min of hair deflection, and 2) 10-min control followed by intrathecal strychnine (40 microg) with hair deflection for 60 min. Spinal dialysate samples were collected for PGE2 levels determined by using immunoassay. In separate experiments, the effect of intrathecal strychnine (40 microg) followed by hair deflection was studied in rats pretreated with intrathecal l-NOARG (50 nmol). After intrathecal strychnine, hair deflection significantly increased spinal PGE2 release (619% +/- 143%), locus coeruleus CAOC (181% +/- 6%), and mean arterial pressure (123% +/- 2%) P < 0.05. Pretreatment with intrathecal l-NOARG significantly inhibited strychnine-allodynia. In this model, hair deflection evokes spinal PGE2 release, locus coeruleus activation, and an increase in mean arterial pressure. L-NOARG pretreatment attenuated the locus coeruleus CAOC, a biochemical index of strychnine-allodynia, suggesting a mediator role of nitric oxide. A mediator role of nitric oxide is also implicated, helping to explain the pathophysiology of this allodynic pain.

Informed consent for labour epidurals: what labouring women want to know

PURPOSE

To determine A) what a labouring woman expects to hear about epidural analgesia before consenting, B) if she feels able to understand the risks and thereby assess if we are obtaining informed consent.

METHODS

Sixty actively labouring women were surveyed immediately after requesting an epidural. Demographic, labour, epidural and consent information were included in the questionnaire. Answers were categorical (yes/no, multiple choice) or scored on a scale from 0 to 10 (visual analogue scale).

RESULTS

The majority of parturients wanted all potential epidural complications but not their incidences disclosed in the consent process. However, a discussion of risks would not dissuade women from consenting to an epidural in the majority of cases. Labouring women have a moderate understanding of epidural risks. The ability to understand risks was not affected by labour pain, anxiety, opioid premedication, duration of labour pain, desire for an epidural, previous epidural experience, level of education or age.

CONCLUSION

This prospective survey characterizes what 60 reasonable labouring women wanted to know about labour epidural analgesia. Parturients wanted all risks of epidural analgesia disclosed in the informed consent process. The majority of women did not want the incidences quoted. This study suggests that labouring patients are as able to give informed consent as are other members of our patient population.

Management of prolonged QT interval during a massive transfusion: calcium, magnesium or both?

PURPOSE

This case report describes the intra-operative management of a prolonged QT interval in the setting of massive transfusion.

CLINICAL FEATURES

A previously healthy, 45-yr-old man presented for repair of a class IV thoraco-abdominal aneurysm. The initial stages of the operation were relatively uneventful, with the exception of an estimated blood loss of 5.0 L. At this point the patient's QT interval became markedly prolonged, and subsequently narrowed in response to supplemental calcium and magnesium. A blood sample taken just before QT prolongation revealed an ionized calcium of 0.98 mmol x L(-1) and an ionized magnesium of 0.37 mmol x L(-1), indicating, that low magnesium may have contributed to the QT interval prolongation.

CONCLUSION

This case illustrates the importance of following both ionized calcium and magnesium in the setting of a massive transfusion.

Autonomic circulatory and cerebrocortical responses during increasing depth of propofol sedation/hypnosis in humans

PURPOSE

To describe the relative effects of graded central nervous system (CNS) depression, using increasing propofol infusion rates, on neurovegetative brainstem-mediated circulatory control mechanisms and higher cortical activity in healthy humans.

METHODS

Propofol was administered using an infusion scheme designed to achieve three target blood concentrations in ten healthy volunteers. Blood propofol concentrations and sedation scores were determined at baseline, during the three propofol infusion levels, and 30 min into the recovery period. Electroencephalographic (EEG) power was measured in three frequency bands to quantify cortical activity, and autonomic heart rate control was quantified using spontaneous baroreflex assessment and power spectral analysis of pulse interval.

RESULTS

Sedation scores closely paralleled propofol blood concentrations (0, 0.53 +/- 0.34, 1.24 +/- 0.21, 3.11 +/- 0.80, and 0.96 +/- 0.42 microg x mL(-1) at baseline, three infusion levels and recovery respectively), and all subjects were unconscious at the deepest level. Indices of autonomic heart rate control were decreased only at the deepest levels of CNS depression, while EEG effects were apparent at all propofol infusion rates. These EEG effects were frequency specific, with power in the beta band being affected at light levels of sedation, and alpha and delta power altered at deeper levels.

CONCLUSIONS

The results of this study support a relative preservation of neurovegetative circulatory control mechanisms during the early stages of CNS depression using gradually increasing rates of infusion of propofol. Indices of circulatory control did not reliably reflect depth of sedation.

Who becomes depressed? The Islington community study of older people

BACKGROUND

Depression in older people is common and debilitating and associated with physical ill health. This is the first study of risk factors for depression in a representative sample of older people selected for high vulnerability because of physical ill health.

METHOD

Subjects identified in an epidemiological community survey of morbidity in people > or =65 years old, who had activity limitation (ADL) but no psychiatric morbidity were reinterviewed after 3 years.

RESULTS

79 (90%) of subjects were interviewed. Ten percent developed pervasive depression and 24% screened positive for depression. This latter group were more likely to consult doctors than others with similar levels of disability (P<0.005) mainly because of an acute physical illness. Frequent pain was associated with the development of depression (P<0.02).

CONCLUSION

Older people who are ADL limited are known to be at high risk for depression. For the majority who do not become depressed, chronicity of illness does not lead to depression. Those who become depressed are most likely to be those with an acute illness and those who are in pain. They will usually increase their consultation rate with doctors but will not complain of depression. They may be undertreated for both pain and depression. Further studies are needed to confirm other risk factors.

The integration of canine genetic maps with the canine karyotype using specific gene amplification of chromosome-specific DNA

We have used a rapid approach to place markers that are already represented in current genetic maps onto individual chromosomes in species for which chromosome paints exist. PCR-based techniques are used to look for the presence of individual marker genes within each chromosome-specific DNA pool. The presence of a given marker within a DNA pool allows assignment of the complete radiation hybrid group, or linkage group from which the marker is drawn, to an individual chromosome. We have used this method with a new set of canine chromosome paints (Yang et al., 1999). In this way, we have assigned 39 of 44 published RH or syntenic RH groups to canine chromosomes, together with 33 of 40 canine linkage groups in a recently published map (Neff et al., 1999).

Suppression of acute and chronic opioid withdrawal by a selective soluble guanylyl cyclase inhibitor

Previous studies have shown that activation of N-methyl-D-aspartate (NMDA) receptors and formation of nitric oxide (NO) contributes to the hyperactivity of locus coeruleus (LC) noradrenergic neurons and behavioural symptoms seen during opioid withdrawal. However, the role of soluble guanylyl cyclase (sGC), the 'physiological' target of NO, in this phenomenon is unclear. In this study, the effect of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a highly selective sGC inhibitor, on the naloxone-precipitated morphine withdrawal was examined using differential normal pulse voltammetry (DNPV) to measure LC activity, in vivo microdialysis to measure glutamate/aspartate release response, and behavioural assessment to evaluate withdrawal symptoms. In halothane-anaesthetized rats, acute intracerebroventricular (i.c.v.) morphine (10 microg) reduced the catecholamine oxidation current (CA.OC) (54.5+/-4.9% of baseline). Naloxone (2 mg/kg, i.v.) reversed this action of morphine and produced a rebound increase in CA.OC (136.1+/-6.0% of baseline), representing acute morphine withdrawal. Administration of ODQ (200 nmol, i.c.v.) blocked this response without affecting acute morphine action. In animals chronically treated with morphine (15 microg/microl/h, i.c.v., 5 days), naloxone significantly increased both the CA.OC signal (270.0+/-19.6% of baseline) and the release of L-glu (193+/-30.4%) and L-asp (221.5+/-28.4%) above baseline. These responses were attenuated in animals pretreated with ODQ. In unanaesthetized chronic morphine dependent rats, ODQ treatment suppressed the signs of withdrawal precipitated by naloxone (10 mg/kg). Taken together, the results of this study suggest that sGC plays an intermediary role in the genesis of LC neuronal hyperactivity and behavioural signs of morphine withdrawal.

Latex anaphylaxis causing heart block: role of ranitidine

PURPOSE

Treatment with H2 receptor antagonists may cause the heart to be more susceptible to atrioventricular conduction delay when exposed to an overwhelming insult by histamine released during an anaphylactic reaction. We present the case of a woman, pretreated with ranitidine, who developed 3:1 heart block secondary to latex anaphylaxis. We propose that H2 antagonist premedication alone in patients susceptible to anaphylaxis increases their risk of heart block.

CLINICAL FEATURES

A 38 yr old obese woman with cervical cancer presented for a radical hysterectomy. Systems review yielded a history of sleep apnea, orthopnea, gastroesophageal reflux, and sciatica. Medications included preoperative ranitidine, 150 mg. There was no history of atopy or allergy. Following general anesthesia induction, at the onset of the surgical procedure the patient developed a severe anaphylactic reaction which was heralded by the onset of 3:1 heart block, with decreases in SpO2, P(ET)CO2 and a decrease in systolic blood pressure to 45 mmHg. This was diagnosed as a possible latex reaction and treated using epinephrine boluses and infusion, fluids, 50 mg diphenhydramine, 50 mg ranitidine and 100 mg hydrocortisone. Following a 48 hr stay in the ICU the patient made an uneventful recovery. Allergy testing with intradermal latex injection and increased plasma tryptase levels confirmed a latex anaphylaxis.

CONCLUSION

The use of H2 antagonists alone as a prophylaxis for gastroesophageal reflux may increase the risk of heart block in patients who develop anaphylaxis.

Activation of the rostral ventrolateral medulla in an acute anesthetized rodent strychnine model of allodynia

After the administration of intrathecal strychnine, allodynia is manifested as activation of supraspinal sites involved in pain processing and enhancement of cardiovascular responses evoked by normally innocuous stimuli. The objective of this study was to investigate the effect of strychnine-induced allodynia on adrenergic neuronal activity in the C1 area of the rostral ventrolateral medulla (RVLM), a major site involved in cardiovascular regulation. The effect of intrathecal strychnine (40 microg) or saline followed by repeated hair deflection to caudal lumbar dermatomes in the urethane-anesthetized rat was assessed by measuring voltammetric changes in the RVLM catechol oxidation current (CA x OC), mean arterial pressure (MAP), and heart rate (HR). After the administration of intrathecal strychnine, hair deflection evoked a significant and sustained increase in the RVLM CA x OC and MAP (peak 146.4%+/-5.6% and 159%+/-18.4% of baseline, respectively; P < 0.05). There was a nonsignificant increase in HR (peak 128%+/-8.2%). In the absence of hair deflection, there was no demonstrable change. Intrathecal saline-treated rats failed to demonstrate changes in RVLM CA x OC, MAP, or HR. In the present study, we demonstrated that, after the administration of intrathecal strychnine, innocuous hair deflection evokes temporally related neuronal activation in the rat RVLM and an increase in MAP. This suggests that the RVLM mediates, at least in part, the cardiovascular responses during strychnine allodynia.

IMPLICATIONS

Neural injury-associated pain, as manifested by allodynia, is resistant to conventional treatment. In a rat model of allodynia, we demonstrated activation of the brain region involved in sympathetic control. Innovative therapies that target this region may be successful in managing this debilitating condition.

Spinal action of ketorolac, S(+)- and R(-)-ibuprofen on non-noxious activation of the catechol oxidation in the rat locus coeruleus: evidence for a central role of prostaglandins in the strychnine model of allodynia

BACKGROUND

Blockade of spinal glycine receptors with intrathecal strychnine produces an allodynia-like state in the anesthetized rat. Innocuous hair deflection in the presence of intrathecal strychnine induces a nociceptive-like activation of catechol oxidation in the locus coeruleus and enhances cardiovascular responses. Because prostaglandins play a central role in augmenting pain, this study evaluated the effect of intrathecal nonsteroidal antiinflammatory drugs in strychnine-induced allodynia.

METHODS

In urethane-anesthetized rats, changes in catechol oxidation in the locus coeruleus, measured using in vivo voltammetry, and cardiovascular parameters evoked by hair deflection of caudal dermatomes were determined after strychnine (40 microg) or saline were administered intrathecally. Subsequently, the effects of 30 microg ketorolac, 10 microg S(+)-ibuprofen, and 10 microg R(-)-ibuprofen administered intrathecally were evaluated.

RESULTS

After strychnine was administered intrathecally, hair deflection evoked an increase in the locus coeruleus catechol oxidation (peak, 149.7+/-7.2% of baseline) and mean arterial blood pressure (peak, 127.5+/-3.8% of baseline). These responses were not observed after saline was administered intrathecally. All hair deflection-evoked, strychnine-dependent peak responses were attenuated significantly with intrathecally administered ketorolac and S(+)-ibuprofen but not with R(-)-ibuprofen.

CONCLUSIONS

Locus coeruleus catechol oxidation is a sensitive biochemical index of strychnine-induced allodynia and is correlated temporally with the cardiovascular responses evoked by hair deflection during spinal glycinergic inhibition. The ability of intrathecally administered ketorolac and S(+)-ibuprofen, but not R(-)-ibuprofen, to suppress the locus coeruleus catechol oxidation and cardiovascular peak responses evoked during strychnine-induced allodynia provide evidence that central prostaglandins play an important role in the abnormal sensory processing of strychnine-induced allodynia.

Addition of opioids alters the density and spread of intrathecal local anesthetics? An in vitro study

PURPOSE

To determine whether the addition of opioids alters the density and spread of intrathecal local anesthetics in vitro.

METHODS

In Part I, the densities of hyperbaric bupivacaine 0.75% (HB), hyperbaric lidocaine 5% (HL) and isobaric bupivacaine 0.5% (IB) with and without morphine (M), and fentanyl (F) were measured at 22 degrees C. In Part II a model was constructed utilizing a column containing a solution similar in composition to cerebrospinal fluid (CSF) at 37 degrees C. The various local anesthetic-opioid solutions, coloured with crystalline methylene blue dye, were injected at 22 degrees C into the column at a controlled rate through a spinal needle. The direction and extent of spread of the injectates were compared.

RESULTS

The relative densities of the five solutions were: HB = HL > IB > M > F. The addition of fentanyl to IB reduced the density of the final solution (P < 0.05). In the model, IB alone and IB with morphine showed mainly downward spread, with the addition of fentanyl to IB resulting in upward movement (P = 0.004). The hyperbaric local anesthetics moved downward with or without opioids.

CONCLUSION

The addition of fentanyl reduces the density of IB in vitro and alters its movement in simulated CSF. This may prove to be important in predicting the level of spinal block in clinical practice.

Catechol activation in rat rostral ventrolateral medulla after systemic isocapnic metabolic acidosis

The catechol signal recorded using in vivo voltammetry within the rat rostral ventrolateral medulla (RVLM) can be interpreted as a catechol-specific index of the integrated activity of RVLM adrenergic barosensitive bulbospinal and nonbulbospinal neurons. To test the hypothesis that systemic acidosis leads to the activation of RVLM adrenergic neurons, the RVLM catechol signal was observed in rats after mild systemic acidosis (pH 7.20-7.25 for 30 min) induced by 1 M HCl under halothane anesthesia, controlled mechanical ventilation, and continuous infusion of Ringer lactate. Particular attention was paid to ensure that changes in mean arterial pressure (MAP) were <15 mmHg during HCl challenge. Saline administration was not associated with any significant change in all considered variables (n = 5). Mild isocapnic systemic acidosis was associated with an increase in catechol signal (n = 5), irrespective of carotid sinus nerve section (n = 5). In keeping with the aim of the study, there were minor (<15 mmHg) but significant changes in MAP among saline, intact, and deafferented groups. Changes in heart rate were not significant. In conclusion, a catechol activation is observed in the RVLM when arterial pressure is maintained during isocapnic systemic metabolic acidosis. This catechol activation appears primarily centrally mediated. Therefore, adrenergic RVLM neurons may relay inputs from the central respiratory generator to the sympathetic system and/or act as chemosensors for H+ next to the surface of the ventrolateral medulla.

Excitatory action of N-methyl-D-aspartate on the rat locus coeruleus is mediated by nitric oxide: an in vivo voltammetric study

Biochemical, electrophysiological and behavioural studies have provided evidence that activation of N-methyl-D-aspartate (NMDA) receptors contributes to the hyperactivity of noradrenergic neurons of the locus coeruleus (LC) in precipitated opioid withdrawal. Recently, it was demonstrated that central administration of nitric oxide (NO) synthase inhibitors suppresses this hyperactivity suggesting that NO mediates the NMDA receptor activation of LC in opioid withdrawal. Using a combination of microdialysis and in vivo voltammetry, this study examined whether local application of NMDA to the LC in opioid naive animals mimics the NO-dependent LC response seen in opioid withdrawal. In the urethane anaesthetized rat, perfusion of the LC (2 microliters min-1) with a solution of NMDA (5 mmol) via a microdialysis probe for 9 min resulted in a rapid and robust increase (290.1 +/- 32.2% above baseline) in the catechol oxidation current (CA.OC) recorded from the LC using differential normal pulse voltammetry (DNPV). The NMDA microdialysis also produced a large increase in the blood pressure (150.4 +/- 6.9% above baseline). An injection of the non-competitive NMDA receptor antagonist (+)MK-801 (0.5 mg kg-1 i.v.), given 45 min after the start of NMDA application, rapidly returned both the CA.OC signal and the blood pressure response to baseline levels. Pretreatment of animals with intraventricular nitric oxide synthase (NOS) inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME) (100 micrograms) significantly inhibited NOS activity in the LC, PAG-PVG and cerebellum. This dose of L-NAME, administered prior to application of NMDA by microdialysis abolished the NMDA-induced rise in the CA.OC recorded in the LC and the increase in systolic blood pressure. The results show that in voltammetry experiments, NMDA produces hyperactivity of LC and hypertension, responses that are dependent upon the synthesis of NO. Thus, in opioid naive rats, regional NMDA application via microdialysis mimics characteristics of the LC response that occur during the antagonist-precipitated opioid withdrawal.

The natural history of depression and the anxiety disorders in older people: the Islington community study

BACKGROUND

This study reports the outcome of depression and anxiety disorders in older people.

METHODS

Follow-up of 165 subjects age 65 or over, initially identified in a community study in inner London as depressed or having an anxiety disorder.

RESULTS

117 subjects still living in the area; 25 had died. Death was predicted only by activity limitation at first interview and not by other demographic or morbidity variables. Eighty-six subjects reinterviewed; 21 males, 65 females. Of the depressed, 34% had recovered, 39% were depressed and 27% were dead. Predictors from initial interview of continuing depression were female gender and more severe depression. Of those with phobic anxiety, 16% had recovered, 18% died and 66% were still phobic. Predictors of continuing phobic anxiety from initial interview were female gender and "stand-alone" phobic anxiety, i.e., not being depressed at initial interview. Sixty percent of those with early onset phobias had specific phobias; 82% of those with late-onset phobias had agoraphobia. Twenty-two subjects were prescribed psychotropics. The only significant predictor of psychotropic prescription was having sleep disturbance at initial interview. A low score on life satisfaction was significantly correlated with depression but not with phobic disorder. A high score was correlated with not having a current psychiatric disorder.

LIMITATIONS

Some subjects were lost to follow-up. Those on psychotropics were particularly likely to refuse an interview.

CONCLUSION AND CLINICAL RELEVANCE

In older people, neither depression nor the anxiety disorders generally remit spontaneously. Those with a particularly poor prognosis are women and those with a more severe depression. Agoraphobia may be precipitated in older people by stressful events and interferes with life satisfaction. There is potential for increased pharmacological treatment of older people with affective disorders.

Use of differential normal pulse voltammetry for the measurement of locus coeruleus catecholaminergic metabolism in an acute anaesthetized rodent model of allodynia: effect of mexiletine

Neuropathic pain can be triggered by non-painful stimuli (e.g., light touch), a sensory abnormality termed allodynia. The acute blockade of spinal glycine receptors with intrathecal strychnine induces a reversible allodynia-like state in the rat. We describe the application of in vivo differential normal pulse voltammetry with carbon fibre micro-electrodes for monitoring the catechol oxidation current (CAOC) of the locus coeruleus (LC) in the strychnine model of allodynia. In addition, we tested the effect of mexiletine, a drug useful in the management of clinical neuropathic pain in this model. Our results show that somatosensory processing in the spinal cord of urethane-anaesthetized rats is radically altered during glycine receptor blockade such that the normally innocuous stimulus of hair deflection causes the marked activation of the LC as determined using in vivo differential normal pulse voltammetry. Mexiletine suppressed the LC and cardiovascular responses of strychnine induced allodynia. Results of this study indicate that LC CAOC, an index of LC neuronal activity: (a) is a sensitive biochemical index of strychnine-allodynia; (b) is temporally correlated with the cardiovascular and motor responses evoked by hair deflection during glycine receptor blockade; and (c) can be used to quantitate allodynia in the strychnine model.

Epidural analgesia for labour and delivery: informed consent issues

OBJECTIVE

Many anaesthetists believe that informed consent for epidural analgesia during labour is inadequate. Patients are perceived to be poorly informed and unable to cope with the information given during labour for informed consent. We reviewed these two hypotheses: A) to define complications for which patients want clear information: B) to quantify the influence of pain, anxiety, opioid premedication, and the importance of level of education, on a patient's level of satisfaction with regard to the consent process: and C) to assess how satisfactory epidural pain relief correlates with satisfaction with the consent process.

METHODS

Sixty patients were surveyed during the first two months after vaginal delivery by two interviewers. Questions related to demographics, severity of labour pain, level of satisfaction with the epidural anaesthetic, risk of complications and satisfaction with information received were either categorical or scored on a scale from 0 to 10.

RESULTS

All epidural related complications were considered important to disclose (8.4/10). The level of satisfaction with the consent process was 8.1/10. Patient satisfaction was not affected by opioid premedication, anxiety, pain score, education group or level of pain relief.

CONCLUSION

Patients indicated they should be informed of all possible complications associated with epidural analgesia, regardless of severity or risk. In contrast to reports in the literature, non disclosure of serious risks during labour was not acceptable to parturients.

Extreme arterial blood pressure differentials in a patient with Takayasu's arteritis

PURPOSE

To describe the extreme arterial blood pressure differentials in a patient with Takayasu's arteritis and its implications for the preservation of cerebral perfusion during anaesthesia.

CLINICAL FEATURES

A 26-yr-old woman with Type III Takayasu's arteritis presented with a tentative diagnosis of mesenteric ischaemia. Determination of systolic arterial blood pressure assisted by oximetry revealed pressures of 114 mmHg in the left and 90 mmHg in the right arm while direct arterial line pressure monitoring of the left posterior tibial artery showed a pressure of 322/113 mmHg. Following induction of anaesthesia with thiopentone and succinylcholine and maintenance with N2O, isoflurane and fentanyl, posterior tibial arterial pressures were maintained (low of 213/96 mmHg) to maintain cerebral blood flow despite surgical requests to lower blood pressure. Epidural local anaesthesia was not considered for intra- or postoperative management due to the regional differences in blood pressure and the effect that sympatholysis may have had on cerebral perfusion.

CONCLUSION

In patients with Takayasu's arteritis, extreme arterial blood pressure differentials may exist which may affect regional blood flow, and monitoring of both upper and lower extremity arterial blood pressure should be considered.

Cardiac output estimation by visual inspection vs thermodilution during cardiac surgery

PURPOSE

The objectives of this study were: 1) to compare the estimated cardiac output (CO) by visual inspection with objective measurements by thermodilution: 2) to compare the estimated systemic vascular resistance (SVR) with objective measurements by thermodilution; and 3) to assess whether management of the patient, based on subjective values, would have differed from the management of the patient based on the objective values.

METHODS

A non-randomized, prospective, blinded study was conducted at a tertiary care university hospital. Following institutional ethics approval, 35 patients undergoing cardiac surgery, with pulmonary artery catheter (PAC) monitoring, were studied. Prior to the measurement of CO by thermodilution, but after separation from cardiac pulmonary bypass, the CO and SVR were estimated by the anaesthetist and the surgeon. Bland and Altman's method was used for statistical analysis.

RESULTS

Surgeons' estimates of CO were comparable with the objectively measured thermodilution measures: in each case (100%), the difference between the subjective estimate and the objective measurement was less than two standard deviations from the mean difference of the two methods. Anaesthetists' estimates, by visual inspection, were also comparable with the objectively measured thermodilution values; 94.6% of cases. The surgeons' and anaesthetists' estimates of SVR were also comparable with the thermodilution measures in all cases. Management based on subjective values would have differed from those based on objective values in only 8.6% of cases.

CONCLUSION

An advantage of cardiac surgery is the ability to observe the heart and assess its performance visually. This study demonstrated that estimates of CO and SVR by clinical observation are comparable with the pulmonary artery catheter's derived values.

Nitric oxide synthase inhibitors attenuate acute and chronic morphine withdrawal response in the rat locus coeruleus: an in vivo voltammetric study

Previous studies have demonstrated that activation of N-methyl-D-aspartate (NMDA) and non-NMDA receptors contributes to the hyperactivity of noradrenergic neurons of the locus coeruleus (LC) associated with opioid and non-opioid drug withdrawal syndromes. Using an in vivo voltammetric approach, we have examined the role of nitric oxide (NO), which mediates NMDA receptor function, in this withdrawal-induced LC hyperactivity. In the anaesthetized rat, acute morphine treatment (10 micrograms, i.c.v.) suppressed (55.7 +/- 4.4% of baseline) the catechol oxidation current (CA-OC) recorded from the LC using differential normal pulse voltammetry (DNPV). A subsequent intravenous injection of naloxone (2 mg/kg, i.v.) reversed the drug-induced inhibition of LC response and produced an increase (118.9 +/- 2.3% of baseline) in CA-OC above baseline, indicative of an acute withdrawal response. Systemic (100 mg/kg) and intracerebroventricular (i.c.v.) (100 micrograms) pretreatment of animals with the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) blocked the naloxone-induced LC withdrawal response without influencing the inhibitory effect of morphine on LC activity. In animals chronically infused with morphine (15 micrograms/h, i.c.v., 5 days) a naloxone challenge (2 mg/kg, i.v.) produced significant increase (253.7 +/- 19.3% of baseline) in CA-OC signal. This LC withdrawal response was significantly reduced by pretreatment with L-NAME (100 micrograms, i.c.v.) or N omega-nitro-L-arginine (L-NOARG 10 micrograms, i.c.v.). In unanaesthetized animals pretreated with chronic morphine, systemic (100 mg/kg) and central L-NAME (100 micrograms) pretreatment suppressed some of the behavioural signs of withdrawal precipitated by naloxone (10 mg/kg) injection. As doses of the NOS inhibitors used in this study have previously been reported to produce significant inhibition of brain NOS activity, their effect on opioid withdrawal response most likely is due to NOS inhibition. The results of this study indicate that NO plays an intermediary role in the LC neuronal hyperactivity associated with both acute and chronic morphine withdrawal.

Lower body nerve stretch: a role in essential hypertension or pre-eclampsia?

Despite the relatively high incidence of essential hypertension and pregnancy-induced hypertension, the etiologies of these disorders remain enigmatic. A link between stretching of neural structures in the lower body and the induction of hypertension in these disorders is hypothesized. Hypertension has been documented in patients undergoing femoral and tibial lengthening procedures; in experimental models the stretching of lower extremity nerves appeared to be responsible for the increase in blood pressure with bone lengthening. The upright posture of humans puts an added strain on nerves and an increased pressure on lumbar disks may put increasing tension on the nerve roots. The resultant nerve stretch in pregnant women may be exacerbated by the hormone relaxin. A possible link between the stretching of neural structures and the genesis of essential hypertension or pre-eclampsia/eclampsia is hypothesized.

Innocuous hair deflection evokes a nociceptive-like activation of catechol oxidation in the rat locus coeruleus following intrathecal strychnine: a biochemical index of allodynia using in vivo voltammetry

Blockade of spinal glycinergic inhibition with intrathecal (i.t.) strychnine induces a reversible allodynia-like state in both conscious and lightly-anaesthetized rats. Since the locus coeruleus (LC) is activated by noxious stimuli, we determined the effect of non-noxious hair deflection (HD) on noradrenergic neuronal activity in the LC of rats treated with i.t. strychnine. Differential normal pulse voltammetry was used to measure the catechol oxidation current (CA.OC), an index of LC activity. Rats were maintained in a light plane of anaesthesia with i.v. urethane and i.t. strychnine (40 micrograms) was injected near the L1-L2 segment. HD, applied to the caudal dermatomes affected by i.t. strychnine, evoked a significant increase (max. 141 +/- 7%, n = 5, P < 0.05) in CA.OC and mean arterial pressure as compared to baseline (no strychnine). In contrast, HD had no significant effect on CA.OC or mean arterial pressure in the saline-treated rats (n = 5). Pre-treatment with i.t. MK801 (30 micrograms) significantly blocked the increase in CA.OC and mean arterial pressure evoked by HD in strychnine-treated rats. The results of this study indicated that HD, in the presence of i.t. strychnine but not saline, can evoke noradrenergic activity in the LC of lightly anaesthetized rats. This effect on the LC is: (1) comparable to that observed with noxious stimulation without i.t. strychnine; (2) segmentally localized, corresponding to the spinal site of strychnine injection; and (3) mediated by spinal NMDA receptors, consistent with the role of excitatory amino acids in sensory transmission. These data provide the first neurochemical evidence that HD, in the presence of i.t. strychnine, is a nociceptive event, supporting the use of this preparation as an experimental model of allodynia.

Delayed bilateral spinal anaesthesia following interscalene brachial plexus block

PURPOSE

To present a case of delayed neuraxial blockade after interscalene brachial plexus block.

CLINICAL FEATURES

A 65-yr-old lady presenting for radial head excision underwent a right interscalene block using bupivacaine and lidocaine. She experienced excellent anaesthesia and had stable vital signs for the duration of surgery. However, after 65 min, she developed signs of bilateral neuraxial block, progressing over the following hour to involve the cervical to lumbar dermatomes, with sparing of the phrenic nerves. The patient remained alert and communicative throughout with haemodynamic stability. Two days following the block, the patient experienced severe frontal and occipital pain, typical of a post dural puncture headache, which responded to fluids and recumbency.

CONCLUSION

This example of delayed central neural blockade complicating interscalene block is presented in contrast to other reports, which have usually occurred promptly after injection, accompanied by complete sensory and motor block requiring cardio-respiratory support. The presumed mechanism of the delayed onset of bilateral neuraxial spread was a dural cuff puncture with slow CSF spread from a plexus sheath "depot" of local anaesthetic.

Involvement of excitatory amino acid pathways in the expression of precipitated opioid withdrawal in the rostral ventrolateral medulla: an in vivo voltammetric study

Previous studies have shown that catecholaminergic neurons in the rostral ventrolateral medulla (RVLM) become hyperactive during opioid withdrawal. In the present study, the role of excitatory amino acid pathways in the expression of opioid withdrawal in the RVLM was examined by using differential pulse voltammetry (DNPV) to measure changes in the catecholamine oxidation current (CA.OC) following naloxone challenge in rats treated with acute or chronic morphine. Acute morphine (10 micrograms i.c.v.) significantly reduced the CA.OC signal in the RVLM and the mean arterial pressure to 37.1 +/- 6.6% and 21.1 +/- 3.5% below baseline, respectively. Naloxone (1 mg kg-1 i.v.) reversed the morphine effect and produced a significant increase in the CA.OC signal to 25.6 +/- 15.2% above baseline. In animals treated with chronic morphine (10 micrograms h-1 i.c.v., 5 days), naloxone (1 mg kg-1 i.v.) produced a significant increase in the CA.OC signal to 54.2 +/- 16.5% above baseline. Both the nonselective excitatory amino acid antagonist, gamma-D-glutamylglycine (DGG, 200 micrograms i.c.v.) and the selective NMDA antagonist, D(-)-amino-7-phosphonoheptanoic acid (D-APH, 25 micrograms i.c.v.) attenuated the naloxone-induced increase in the CA.OC by 50.7% and 46.0% respectively. In morphine naive animals, DGG and D-APH depressed the CA.OC by 42.8 +/- 8.7% and 17.7 +/- 9.8%, respectively. To the extent that the CA.OC is an index of neuronal activity, these results suggest that RVLM hyperactivity during morphine withdrawal is dependent, in part, upon activation of NMDA receptors.

Prophylaxis against the systemic hypotension induced by propofol during rapid-sequence intubation

The objective of this study was to determine the effectiveness of two prophylactic approaches against the anticipated hypotension induced by propofol during rapid-sequence intubation. Thirty-six male or female nonpremedicated ASA class I-II patients aged 21-60 yr undergoing elective outpatient surgery were included in the study. Patients were randomly allocated to receive pre-induction ephedrine sulphate (70 micrograms x kg(-1)iv), pre-induction volume loading (12 ml x kg(-1) Ringer's lactate) or no treatment. Rapid-sequence intubation with cricoid pressure was then performed with propofol (2.5 mg. x kg(-1)) and succinylcholine (1.5 mg x kg(-1). The lungs were subsequently ventilated with 0.25-0.5% isoflurane in a 2:1 N2O/O2 mixture. Vecuronium was given once neuromuscular function had recovered from the succinylcholine. Heart rate and systemic arterial blood pressure were measured non-invasively before induction, after propofol administration and every minute for ten minutes after intubation. Pre-induction volume loading prevented the hypotension observed before surgical stimulation in control and ephedrine groups. Moreover, pre-induction volume loading was not associated with increases in heart rate after intubation as was ephedrine administration. The intubating conditions were excellent to satisfactory in most patients and the overall incidence of adverse events during intubation was mainly due to pain during injection of propofol. The present study showed that preoperative volume loading is more efficacious than pre-induction administration of ephedrine sulphate in maintaining haemodynamic stability during rapid-sequence induction with propofol and succinylcholine. In addition, propofol in combination with succinylcholine provides excellent conditions for rapid-sequence intubation.

Use of the laryngeal mask prior to definitive intubation in a difficult airway: a case report

The laryngeal mask, a relatively new airway adjunct, consists of a large tube with an inflatable shallow mask at its distal end which forms a seal around the glottic opening. We describe a case of a difficult intubation in the emergency department of an obese patient with microagnathia, a short bull neck, and a nasopharyngeal hemorrhage in which a laryngeal mask was used to temporarily manage the airway prior to definitive intubation. In difficult airway cases where it is impossible to ventilate the patient by face mask or intubate the trachea, ventilation with the laryngeal mask may be an alternative to transtracheal jet ventilation or cricothyrotomy. The laryngeal mask may be useful in managing the difficult airway provided that the risks of an inadequate seal, obstruction, coughing and laryngospasm, and lack of protection from aspiration are recognized.

The role of excitatory amino acids in the expression of precipitated acute and chronic clonidine withdrawal: an in vivo voltammetric study in the rat locus coeruleus

It has been previously shown that activation of excitatory amino acid (EAA) pathways contributes to hyperactivity of the locus coeruleus (LC) in antagonist precipitated opioid withdrawal. In this study, using differential normal pulse voltammetry to monitor catechol oxidation as an index of the activity of the LC, the role of EAA pathways in antagonist precipitated withdrawal after acute and chronic clonidine treatment was examined. Intracerebroventricular clonidine (10 micrograms i.c.v.) significantly reduced LC activity to 54.4 +/- 3.1% of baseline 45 minutes following the injection. Subsequent systemic injection of the selective alpha 2 receptor antagonist atipamezole (0.2 mg/kg i.v.) or yohimbine (0.5 mg/kg i.v.) resulted in a rapid reversal of the depressant effects and a significant increase in LC activity above baseline. Pretreatment with the non-selective EAA receptor antagonist gamma-D-glutamylglycine (DGG) (50 micrograms i.c.v.) attenuated the atipamezole-induced rebound response of the LC but not the reversal of clonidine action. However, both the yohimbine-induced rebound and reversal of clonidine effects were attenuated by DGG treated animals. In chronic clonidine treated animals (2, 5, 7, 10 micrograms/h i.c.v., 5 days), a challenge with atipamezole (0.2 mg/kg i.v.) produced an immediate increase in LC activity, blood pressure and heart rate. The magnitude of these responses was dependent on the dose of clonidine. The atipamezole-induced increase in LC activity and blood pressure was significantly attenuated by pretreatment with DGG (200 micrograms i.c.v.). These findings suggest that LC hyperactivity and blood pressure increases elicited during clonidine withdrawal are mediated in part by activation of EAA receptors. In this regard, the mechanisms underlying clonidine withdrawal closely resembles those underlying opioid withdrawal.

The effects of hypothermic and normothermic cardiopulmonary bypass on glyceryl trinitrate activity

Glyceryl trinitrate (GTN) is used to control arterial blood pressure during cardiopulmonary bypass (CPB) procedures, but its effects are often decreased during the period of extracorporeal support. The plasma and urine concentrations of GTN and glyceryl-1,2-dinitrate (1,2-GDN) and glyceryl-1,3-dinitrate (1,3-GDN) for male and female patients who received GTN during hypothermic CPB, and male and female patients who were given GTN during normothermic CPB, were measured by gas-liquid chromatography. During hypothermic CPB, the male and female subjects experienced significant decreases in GTN clearance (P < 0.05), 66% and 52%, respectively. Neither the males nor the females who underwent normothermic CPB experienced any significant change in GTN clearance. These results suggest that the lower core temperature during hypothermic CPB may decrease the biotransformation of GTN to GDNs and nitric oxide, thereby resulting in less dilation of blood vessels. Furthermore, the males in the hypothermic CPB group had significantly greater urinary concentrations of 1,3-GDN and 1,2-GDN than the females (P < 0.05), and the normothermic CPB males had a significantly greater urinary concentration of 1,2-GDN than the females in that group. The normothermic CPB males also had significantly higher plasma concentration of GTN at two time points, and 1,3-GDN at one time point, than the females. These data suggest that there may be a gender difference in GTN biotransformation.

Evidence for the involvement of excitatory amino acid pathways in the development of precipitated withdrawal from acute and chronic morphine: an in vivo voltammetric study in the rat locus coeruleus

Previous studies have demonstrated that activation of excitatory amino acid (EAA) pathways projecting to the locus coeruleus may be involved in the increased firing of locus coeruleus (LC) neurons during opioid withdrawal. Using differential normal pulse voltammetry to monitor catechol oxidation current (CA.OC), an index of neuronal activity in the LC, the role of EAA pathways in naloxone precipitated withdrawal after acute and chronic morphine treatment was examined. Acute morphine treatment (10 micrograms i.c.v.) significantly reduced the CA.OC signal in the LC to 54.3 +/- 3.1% of baseline. Naloxone challenge (1 mg/kg i.v.) completely reversed the morphine effect and produced a significant increase in the CA.OC signal above baseline, peak 145.4 +/- 10.1% of baseline. This naloxone-induced rebound response was attenuated by pretreatment with the EAA receptor antagonists gamma-D-glutamylglycine (DGG) (2, 20, 200 micrograms i.c.v.) and (-)-2-amino-7-phosphonoheptanoic acid (D-APH), but not L-APH (25 micrograms i.c.v.). In chronically morphine-treated rats (25 micrograms/h i.c.v., 5 days), naloxone challenge (1 mg/kg i.v.) produced a significant increase in CA.OC signal, peak 466.5 +/- 112.7% of baseline. This naloxone-induced response was attenuated by pretreatment with DGG (200 micrograms i.c.v.) or D-APH (25 micrograms i.c.v.). To the extent that CA.OC reflects locus coeruleus neuronal activity, the present findings further suggest that increases in locus coeruleus activity during naloxone precipitated withdrawal after both acute and chronic morphine treatment are mediated at least in part by activation of EAA pathways.

Diazepam's effect on systemic vascular resistance during cardiopulmonary bypass is not caused by its vehicle (alcohol-propylene glycol)

Control of hemodynamic parameters during cardiopulmonary bypass (CPB) is a desirable goal of the anesthesiologist. Diazepam is known to reduce systemic vascular resistance (SVR) during CPB. This study tested the hypothesis that diazepam reduces SVR during CPB through the action of its vehicle, alcohol-propylene glycol (APG). The study protocol was approved by the Institution's Human Experimentation Review Board and all patients gave informed consent. Premedication, induction, and maintenance of anesthesia were standardized. Thirty consecutive patients undergoing nonemergent cardiac surgical procedures were randomized to receive a standardized amount of diazepam, diazemuls, or alcohol-propylene glycol during stable CPB. SVR in the diazepam group decreased significantly (1,242 to 968 dyne.s.cm-5, P < 0.05) compared to baseline; whereas there was no significant change in SVR in the diazemul group, and a statistically significant increase in SVR (1,217 to 1,537 dyne.s.cm-5, P < 0.05) in the APG group. It is concluded that diazepam reduces SVR during CPB. Diazepam's vehicle does not reduce SVR during CPB, and is in fact associated with an increase in SVR.

Stereoselective effects of central α2-adrenergic agonist medetomidine on in vivo catechol activity in the rat rostral ventrolateral medulla (RVLM)

The stereoselective central effects of a novel, highly potent and selective alpha 2-agonist medetomidine on adrenergic neuronal activity, reflected by changes in catechol oxidation current, in the rostral ventrolateral medulla of the halothane-anesthetized rat were examined using in vivo differential normal pulse voltammetry. Dexmedetomidine, the active isomer, significantly decreased catechol oxidation current to 33.4 +/- 4.5% of baseline when given centrally (1 microgram, i.c.v.) and to 10.3 +/- 3.9% of baseline when given systemically (50 micrograms/kg, i.v.). Dexmedetomidine also significantly reduced mean arterial blood pressure by 19.9% following central administration but significantly increased mean arterial blood pressure by 59.9% following systemic administration. Levomedetomidine, the inactive isomer, had no effect on catechol oxidation current or blood pressure. The depressant effects of dexmedetomidine on catechol oxidation current were reversed by the selective alpha 2-adrenoceptor antagonist atipamezole (2 micrograms, i.c.v. or 200 micrograms/kg, i.v.). The results of the present study demonstrate, to our knowledge, for the first time the central stereoselective effects of medetomidine and antagonism by atipamezole on rostral ventrolateral medulla activity in the anesthetized rat.

In vivo catechol activity in the rat locus coeruleus following different nociceptive stimuli and naloxone

The nucleus locus coeruleus (LC) has been implicated in the processing of spinal reflexes following noxious stimuli. It has been demonstrated that noxious stimuli activate LC neuronal firing, but little is known about the neurochemical changes that might occur following such activation. To determine the effects of different noxious stimuli on LC neuronal activity, anaesthetized rats were exposed to mechanical (tail pinch), thermal (55 degrees C water), and chemical (5% Formalin injected in the hind paw) stimuli; the catechol oxidation current (CA.OC), an index of noradrenergic neuronal activity, in the locus coeruleus was monitored using differential normal pulse voltammetry. In addition, the effect of the opioid antagonist naloxone on the CA.OC in the LC was examined. Exposure to both mechanical and chemical stimuli significantly increased CA.OC indicating an increase in LC noradrenergic neuronal activity, while the thermal stimulus had no effect. Treatment with naloxone (1 mg/kg i.v.) had no effect on CA.OC in the LC. The results show a differential responsiveness of LC noradrenergic neurons to different modes of noxious stimuli and fail to demonstrate a tonic opioid regulation of these neurons in the anaesthetized rat.

Balloon flotation is more important than flow direction in determining the position of flow-directed pulmonary artery catheters

Pulmonary artery catheters (PAC) inserted using pressure monitoring usually advance into a branch of the right pulmonary artery (PA). However, in some clinical situations it may be desirable to locate the tip of the PAC in a branch of the left PA. A two-part study was undertaken to explore factors that determine the ultimate location of the tip of a PAC. In the clinical study, 33 patients were randomized to supine or right-side down patient positioning during insertion of the PAC. Five patients were excluded because of withdrawal of the PAC during surgery. Seven of 14 PACs inserted in right-side down position were located in a branch of the left PA, while all 14 inserted with the patients supine went to a branch of the right PA (P less than 0.005). This suggests that the effect of upward flotation of the air-filled balloon in the column of blood predominates over movement with the current of maximal blood flow. Using a cardiac bypass pump and a plexiglass model of the pulmonary arterial bifurcation, the effects of lateral positioning on the direction of travel of balloon-tipped catheters were studied. The tip floated upward preferentially, even when flow was obstructed to the upward limb (P less than 0.005). Varying the flow rate in the system between 0.5 and 3.0 L/min and changing the direction of the natural curve of the PAC tip had no impact on this tendency to float upward. The authors conclude that balloon flotation in the column of blood strongly influences PAC tip location, and that this fact can assist in preferentially directing its placement.

Sequestration of glyceryl trinitrate (nitroglycerin) by cardiopulmonary bypass oxygenators

The effectiveness of glyceryl trinitrate (nitroglycerin) in controlling myocardial ischemia and blood pressure during coronary artery bypass graft surgery is frequently lost during surgery, possibly as a result of drug sequestration by the cardiopulmonary bypass circuit. The objective of this study was to utilize a gas-liquid chromatographic assay to determine the extent of removal of glyceryl trinitrate from the priming fluid by the bubble and membrane oxygenators. The apparatus was maintained at either 25 or 37 degrees C, the two extreme temperatures experienced by the patient during bypass surgery. At apparent steady state, the circulating glyceryl trinitrate concentration was decreased by 20.6%, 46.6%, and 67.3% with the Maxima membrane oxygenator, Cobe membrane oxygenator, and Bentley bubble oxygenator, respectively. The three-layer defoaming filters that are used in the Bentley bubble oxygenator were studied by immersing each of the three filters in fluid containing 60 nM glyceryl trinitrate and monitoring the drug concentration in Plasmalyte. The filters sequestered approximately 90% of the glyceryl trinitrate from the bathing solution of which 31% was recovered with a single methanol wash of the polyurethane filter. These data demonstrate that the different oxygenators used in the cardiopulmonary bypass circuit remove glyceryl trinitrate to varying degrees from the circulating fluid.

Neurological phenomena during emergence from enflurane or isoflurane anaesthesia

During emergence from anaesthesia, transient neurological signs that would usually be considered pathological may appear. The objective of this randomized, patient (n = 30) and observer-blinded study was to compare prospectively the incidence and duration of post-anaesthetic neurological abnormalities in healthy patients undergoing minor elective procedures following thiopentone and succinylcholine induction, and enflurane-N2O or isoflurane-N2O anaesthesia. Patients were studied for 60 min after anaesthesia. Arousal state, muscle tone, deep tendon reflexes, plantar reflex, sustained clonus, shivering, intense muscular spasticity and temperature were assessed. Results of neurological examination were correlated with the patient's state of arousal. Transient emergent neurological abnormalities occurred more frequently following enflurane-N2O anaesthesia than isoflurane N2O anaesthesia. This was statistically significant (P less than 0.05) for quadriceps hyperreflexia, upgoing toes (positive Babinski reflex) and intense muscular spasticity. Neurological abnormalities occurred most commonly 5-20 min after anaesthesia and all abnormalities resolved within 60 min. Following enflurane anaesthesia, as patients became more alert the incidence of abnormalities declined, while the arousal state did not affect the incidence of abnormalities after isoflurane. There was no significant difference between axillary temperatures of those patients who shivered and those who did not. In conclusion, temporary emergent neurological abnormalities occurred more often following enflurane-N2O than after isoflurane-N2O anaesthesia.