Showing papers in "BJA: British Journal of Anaesthesia in 1995"

Descending control of pain.

Abstract: Thanks largely to the study of the brainstem nuclei that mediate stimulation analgesia, the involvement of the monoamines in the descending control of pain is now well established. The periaqueductal grey, the raphe nuclei (NRM and DRN) and the locus coeruleus are all key brainstem sites for the control of nociceptive transmission in the spinal cord. Although the initial emphasis was on 5-HT as the transmitter mediating this control at spinal levels, it is clear from more recent work that NA has an equally important part to play. How (or even if) the two amines differ in their roles and actions in analgesia is, however, still an open question. The small size and complexity of the brainstem areas from which analgesia may be elicited by electrical stimulation complicates the interpretation of the data. Stimulating currents may spread to surrounding regions mediating opposite effects to that of the main region stimulated. Opiates and GABA are clearly involved in descending control at both brainstem and spinal levels, although the relative roles of the different types of amino-acid and opiate receptors is still hotly debated. Despite the fact that the first report on stimulation analgesia appeared more than a quarter of a century ago in 1969, the precise connections and cord synaptology are still the basis of ongoing research. It is perhaps ironic, in an issue dedicated to new molecules and mechanisms, that those transmitters most involved in descending inhibition should be such old and familiar friends.

Inflammatory mediators of pain.

Abstract: While sensory fibres normally respond to a range of physical and chemical stimuli their activity and metabolism are profoundly altered by a variety of mediators generated by tissue injury and inflammation. These include substances produced by damaged tissue, substances of vascular origin as well as substances released by afferent fibres themselves, sympathetic fibres and various immune cells. The effects of inflammatory mediators, to activate or sensitize afferent fibres, are produced by changing membrane ion channels which are coupled directly via receptors or more commonly are regulated through receptor-coupled second messenger cascades. These latter processes also have the potential to alter gene transcription and thereby induce long-term alterations in the biochemistry of sensory neurones. This can have far-reaching consequences as the expression of novel proteins for ion channels (Na channels) and receptors (capsaicin, NPY) as well as the induction of novel enzymes (i-NOS) can profoundly affect the properties of nociceptors and their ability to transmit pain signals. However, such changes may be targeted successfully for the development of new analgesic and anti-inflammatory agents.

Increase in Mallampati score during pregnancy

Abstract: A photographic version of the Mallampati test was developed and applied to 242 pregnant patients at 12 weeks' gestation and again at 38 weeks' gestation. At 38 weeks the number of grade 4 cases had increased by 34% (P < 0.001). This is in agreement with other evidence which suggests that difficult laryngoscopy is slightly more frequent in obstetrics (1.7%) than in general surgery (1.3%). The increase in Mallampati score correlated with gain in body weight (r = 0.3, P < 0.001), which gives some support to the concept that fluid retention is the underlying cause. We conclude that pharyngeal oedema causes some hindrance to tracheal intubation in obstetrics, but not enough to explain the high failure rate reported. A case is made for rationalizing the management of difficult intubation. Our data also show that more research is needed on factors which affect Mallampati's test, particularly neck extension.

Spinal-cord pharmacology of pain

Abstract: The transmission of pain from peripheral tissues through the spinal cord to the higher centres of the brain is clearly not a passive simple process using exclusive pathways. Rather, circuitry within the spinal cord has the potential to alter, dramatically, the relation between the stimulus and the response to pain in an individual. Thus an interplay between spinal neuronal systems, both excitatory and in- hibitory, will determine the messages delivered to higher levels of the central nervous system. The incoming messages may be attenuated or enhanced, changes which may be determined by the particular circumstances. The latter state, termed central hypersensitivity [61], whereby low levels of afferent activity are amplified by spinal pharmacological mechanisms has attracted much attention [13, 15]. However, additionally, inhibitory controls are sub- ject to alteration so that opioid sensitivity in different pain states is not fixed [14]. This plasticity, the capacity for transmission in nociceptive systems to change, can be induced over very short time courses. Recent research on the pharmacology of nociception has started to shed some well-needed light on this rapid plasticity which could have profound conse- quences for the pharmacological treatment of pain [8, 13, 15, 23, 24, 35, 36, 41, 62]. The pharmacology of the sensory neurones in the dorsal horn of the spinal cord is complex, so much so that most of the candidate neurotransmitters and their receptors found in the CNS are also found here [4, 32]. The transmitters are derived from either the afferent fibres, intrinsic neurones or descending fibres. The majority of the transmitters and receptors are concentrated in the substantia gelatinosa, one of the densest neuronal areas in the CNS and crucial for the reception and modulation of nociceptive messages transmitted via the peripheral fibres [4]. Nociceptive C-fibres terminate in the outer lamina 1 and the underlying substantia gelatinosa, whereas the large tactile fibres terminate in deeper laminae. However, in addition to the lamina 1 cells which send long ascending axons to the brain, deep dorsal horn cesll aslo gvie rsie to ascendnig axons and respond to C-fibre stimulation. In the case of these deep cells the C-fibre input may be relayed via from the afferents will facilitate spinal excitation. By ; :

Prediction of difficult tracheal intubation

Abstract: Three hundred and fifty consecutive patients (322 non-obstetric, 28 obstetric; 185 female) were assessed before operation using the modified Mallampati test and by measuring thyromental and sternomental distances, forward protrusion of the mandible and interincisor gap with the mouth fully open. Tracheal intubation was difficult in 17(4.9%) patients, of whom four (1.14%) had a grade III or IV view on laryngoscopy. A sternomental distance of 12.5 cm or less with the head fully extended on the neck and the mouth closed predicted 14 of the 17 patients in whom tracheal intubation was difficult. As a screening test, sternomental distance appeared to be more sensitive (82.4%) and more specific (88.6%) than thyromental distance (64.7% and 81.4%, respectively), the modified Mallampati test (64.7% and 66.1%, respectively) and forward protrusion of the mandible (29.4% and 85.0%, respectively). The interincisor gap ranged from 2.0 to 5.0 cm in all patients except one. There was no correlation between the interincisor gap and the view on laryngoscopy ( P > 0.05, one-way ANOVA). There was also no difference in mean interincisor gap between those patients who presented no difficulty with tracheal intubation and those who did ( P = 0.7–0.8, two sample t test). Sternomental distance may be a useful bedside screening test for preoperative prediction of difficult tracheal intubation.

Volume preloading is not essential to prevent spinal-induced hypotension at caesarean section.

Abstract: We have compared the protective effect of 1000 ml preload with 200 ml preload of crystalloid solution, administered during the 10 min before spinal anaesthesia was induced, in 60 healthy women with no fetal compromise undergoing elective Caesarean section. The spinal anaesthetic was managed identically in both groups by an anaesthetist who was unaware of the volume of fluid administered. A prophylactic infusion of ephedrine 60 mg in Hartmann's solution 500 ml was given according to maternal arterial pressure. Hypotension was defined as > or = 30% reduction from baseline or or = 3 min compared with nine women in the 200-ml group, four lasting > or = 3 min. There was no difference between neonates in each group. We have now abandoned the routine of preloading before regional anaesthesia.

Assessment of preoperative anxiety: comparison of measures in patients awaiting surgery for breast cancer

Abstract: We have compared three measurements of anxiety to determine their equivalence in assessing anxiety before surgery. Forty-four patients awaiting breast cancer surgery completed the state scale of the state—trait anxiety inventory (STAI), the hospital anxiety and depression scale (HAD) and a 100-mm visual analogue scale (VAS). Analysis restricted to correlations between the scales gave the misleading impression that VAS scores were inconsistent with those of the HAD and STAI. However, when scores were considered in relation to normative cut-off values to categorize anxiety levels, the three scales showed good agreement. We conclude that the scales were equivalent in their assessment of anxiety before surgery, but that reference to normative data was important in establishing such equivalence and in determining the patient's state.

A statistical approach to measuring the competence of anaesthetic trainees at practical procedures.

Abstract: Cusum analysis is a statistical technique to distinguish deviations from an acceptable failure rate. The progress of anaesthetic trainees learning four practical procedures (obstetric extradural anaesthesia, spinal anaesthesia, central venous cannulation and arterial cannulation) was monitored from their first attempt using cusum analysis. Suitable acceptable and unacceptable failure rates for each procedure were chosen by consultant anaesthetists. For obstetric extradural anaesthesia, four trainees eventually achieved acceptable failure rates (5%) and the number of attempts required to demonstrate this statistically ranged from 29 to 185; three trainees had an unacceptable failure rate (10%) and five trainees had inconclusive records. For spinal anaesthesia, two trainees achieved an acceptable failure rate (10%) and the number of attempts required to demonstrate this statistically ranged from 39 to 67; two trainees had an unacceptable failure rate (20%) and four trainees had inconclusive records. One trainee demonstrated statistically an acceptable failure rate in arterial cannulation (20%) after 14 attempts and four trainees had inconclusive records. Two records of central venous cannulation were inconclusive. Some records showed variable failure rates which were sometimes associated with lack of practice or a change in technique. Cusum analysis can be used to monitor training in practical procedures and as a continuous audit of quality of clinical practice.

Capsaicin and pain mechanisms

Abstract: Capsaicin, the pungent ingredient in capsicum peppers, has been exploited extensively as a tool in sensory neuron biology and also employed clinically as a topical analgesic agent [1,2]. These uses of capsaicin result from its ability to excite and subsequently inhibit selectively the function of a sub-population of C- and Aδ-sensory nerve fibres, the polymodal nociceptors, which respond to noxious heat, mechanical and chemical stimuli [3,4]. Injection of capsaicin into human skin evokes a dose-related nerve fibre activation and the magnitude and duration of the discharge correlate with the subjective report of burning pain [5-8]. Local application of capsaicin to the skin by either injection or topical application also evokes a pronounced flare response [5,9,10] probably due to the action of calcitonin gene related peptide (CGRP) released from the peripheral nerve terminals [11]. Thus activation of capsaicin sensitive sensory neurons has effects on both the afferent and efferent functions of these nerves.

Tranexamic acid (Cyklokapron) reduces perioperative blood loss associated with total knee arthroplasty

Abstract: In this prospective, randomized, double-blind study, we have investigated the effect of an antifibrinolytic agent, tranexamic acid (Cyklokapron), on blood loss and transfusion requirements associated with total knee arthroplasty. Twenty-nine patients were allocated randomly to receive either tranexamic acid 15 mg kg-1 or an equal volume of placebo a few minutes before a tourniquet was deflated. Blood loss during surgery, in the recovery room and on the surgical ward was recorded, together with the number of units of blood transfused in hospital. Mean blood loss during surgery was 428 (SD 254) ml in the tranexamic acid group (n = 15) compared with 415 (244) ml in the placebo group (n = 13). In the recovery room the tranexamic acid group lost 127 (95) ml and the placebo group 576 (245) ml (P < 0.001). On the ward the respective volumes were 293 (200) ml and 558 (293) ml (P < 0.01). Total blood loss was 847 (356) ml in the tranexamic acid group and 1549 (574) ml in the placebo group (P < 0.001). During the hospital stay the treatment group received 1.5 (1.3) units of blood compared with 3.3 (1.8) in the control group (P < 0.005). Two patients in the placebo group experienced a thrombotic complication compared with none in the treatment group. We conclude that tranexamic acid reduced perioperative blood loss and transfusion requirements associated with total knee arthroplasty.

Cytokine balance and immunosuppressive changes at cardiac surgery: contrasting response between patients and isolated CPB circuits.

Abstract: In vitro work suggests that IL-10 plays a pivotal role in controlling the balance of pro- and anti-inflammatory cytokines and monocyte HLA-DR expression. In 20 patients undergoing cardiac surgery, we investigated elaboration of interleukin 10 (IL-10) and its relationship to pro- and anti-inflammatory cytokines and leucocyte expression of HLA-DR and adhesion molecules. There were small increases in pro-inflammatory cytokines (IL-1, IL-8 and tumour necrosis factor (TNF) after induction, returning to baseline on induction of cardiopulmonary bypass (CPB). After CPB another transient increase in IL-8 occurred (P 0.05). In contrast with the in vivo response where there was a phased anti-inflammatory response beginning with IL-10, in the isolated CPB model no anti-inflammatory cytokine response occurred.

Comparison of the effects of adrenaline, clonidine and ketamine on the duration of caudal analgesia produced by bupivacaine in children.

Abstract: Sixty boys, aged 1-10 yr, undergoing orchidopexy were allocated randomly to receive one of three solutions for caudal extradural injection. Group A received 0.25% bupivacaine 1 ml kg-1 with adrenaline 5 micrograms ml-1 (1/200,000), group C received 0.25% bupivacaine 1 ml kg-1 with clonidine 2 micrograms kg-1 and group K received 0.25% bupivacaine 1 ml kg-1 with ketamine 0.5 mg kg-1. Postoperative pain was assessed using a modified objective pain score and analgesia was administered if this score exceeded 4. The median duration of caudal analgesia was 12.5 h in group K compared with 5.8 h in group C (P

Manual compared with target-controlled infusion of propofol.

Abstract: We studied 160 ASA I-II patients, anaesthetized with propofol by infusion, using either a manually controlled or target-controlled infusion system. Patients were anaesthetized by eight consultant anaesthetists who had little or no previous experience of the use of propofol by infusion. In addition to propofol, patients received temazepam premedication, a single dose of fentanyl and 67% nitrous oxide in oxygen. Each consultant anaesthetized 10 patients in sequential fashion with each system. Use of the target-controlled infusion resulted in more rapid induction of anaesthesia and allowed earlier insertion of a laryngeal mask airway. There was a tendency towards less movement in response to the initial surgical stimulus and significantly less movement during the remainder of surgery. Significantly more propofol was administered during both induction and maintenance of anaesthesia with the target-controlled system. This was associated with significantly increased end-tidal carbon dioxide measurements during the middle period of maintenance only, but recovery from anaesthesia was not significantly prolonged in the target-controlled group. With the exception of a clinically insignificant difference in heart rate, haemodynamic variables were similar in the two groups. Six of the eight anaesthetists found the target-controlled system easier to use, and seven would use the target-controlled system in preference to a manually controlled infusion. Anaesthetists without prior experience of propofol infusion anaesthesia quickly became familiar with both manual and target-controlled techniques, and expressed a clear preference for the target-controlled system.

Complications of local anaesthesia for ophthalmic surgery.

Abstract: Topical local anaesthetic agents frequently sting, and are occasionally associated with temporary clouding of the cornea, making surgery more difficult [38]. This clouding was most often seen with cocaine and is much less common with amethocaine or oxybuprocaine. Corneal anaesthesia necessitates protection,of the eye by ensur ing that it is closed and protected by a pad.

Psychological characteristics and the effectiveness of patient-controlled analgesia

Abstract: We have evaluated the level of state and trait anxiety, neuroticism, extroversion and coping style as predictors of the effectiveness of patient-controlled analgesia (PCA) in 110 patients undergoing total abdominal hysterectomy. After operation patients were allocated to receive pain control with either PCA or im injections (IMI). Pain was assessed using the short form McGill pain questionnaire at 6, 18 and 24 h after operation, and by recording the amount of analgesic consumed in the first 24 h after surgery. Both state anxiety and coping style were significant predictors of postoperative pain, irrespective of the method of analgesia used. Patients using PCA experienced significantly better pain control than those receiving IMI. However, it was those with high levels of state anxiety who experienced the greatest reduction in pain with PCA. In addition to achieving better pain control, patients who received PCA used significantly less analgesia and were discharged earlier than patients who received IMI. (Br. J. Anaesth. 1995; 74:271–276)

Meningitis after combined spinal-extradural anaesthesia in obstetrics

Abstract: We report two cases of meningitis which developed after combined spinal-extradural procedures for obstetric analgesia. The first case was thought to be caused by aseptic or chemical meningitis and the second was a case of bacterial meningitis in a patient who also received an extradural blood patch. It is important that meningitis is considered as a differential diagnosis in patients who present with headache after spinal anaesthesia and that antibiotic therapy is selected to cover unusual organisms.

Gastric mucosal pH does not reflect changes in splanchnic blood flow after cardiac surgery

Abstract: Despite the widespread use of gastric tonometry to assess splanchnic oxygen transport, no human data are available on the relationship between splanchnic blood flow, splanchnic oxygen delivery and gastric mucosal pH. We have studied the effect of splanchnic blood flow and oxygen delivery on gastric mucosal pH after cardiac surgery. During the first postoperative hours of intensive care, dopexamine was infused to increase cardiac output in eight patients, while six patients served as controls. Gastric mucosal pH (gastric tonometry), splanchnic blood flow and splanchnic oxygen delivery and consumption (dye dilution) were measured. Dopexamine administration significantly increased splanchnic blood flow (0.72 vs 1.02 litre min−1 m−2 (P

Extradural, paravertebral and intercostal nerve blocks for post-thoracotomy pain.

Abstract: Forty-five patients were allocated randomly to receive either a single intrathoracic block of four intercostal nerves, a continuous thoracic extradural infusion or a continuous paravertebral infusion of bupivacaine. Patients were allowed additional i.v. boluses of morphine via a PCA device. Segmental spread of pinprick analgesia was comparable in the groups for up to 20 h. Up to 2 h after the block, plasma concentrations of bupivacaine were greater in the intercostal group and there was large interindividual variation. There were no significant differences between the groups in pain, morphine consumption, respiratory function or adverse events. Moderate to severe respiratory depression was detected in 14 patients more than 2 h after operation.

Gastric intramucosal pH, tissue oxygenation and acid-base balance

Abstract: It is widely accepted that global measurements of oxygen delivery, consumption and extraction do not provide reliable information on the adequacy of tissue oxygenation in patients who are, by all conventional clinical criteria, adequately resuscitated [13, 17, 29, 39, 51, 60, 103]. The indirect measurement of gastric intramucosal pH (pH,m) is being widely evaluated as a minimally invasive and sensitive means of assessing the adequacy of tissue oxygenation in these circumstances. Tissue acid-base balance is determined primarily by the balance between the protons released during the release of energy by ATP hydrolysis and consumed by the resynthesis of ATP by oxidative phosphorylation [64]. When the delivery of oxygen fails to resynthesize the ATP necessary to meet the energy demands of the tissue, the rate of ATP hydrolysis exceeds the rate of synthesis and pH decreases in proportion with the degree of unreversed ATP hydrolysis or dysoxia present [50, 91]. Measurement of gastric intramucosal pH provides a measure of tissue acid-base balance in a region of the body that is among the first to develop dysoxia in shock [25,28,59,71,79,85,88,92]. Use of the measurement suggests that approximately 50-60% of patients undergoing major surgery and 80 % of ICU patients [22, 35, 56, 75] may develop transient and sometimes sustained episodes of dysoxia despite the conventional appearances of being adequately resuscitated.

Somatic pain–pathogenesis and prevention

Abstract: because it is a key component of the body’s normal defence mech- anisms, protecting the body from a potentially hostile external environment by initiating behavioural and reflex avoidance strategies. This protective mech- anism operates as a result of the presence of a specific set of primary sensory neurones which encode the intensity, duration and quality of any noxious stimulus and, by virtue of their topographically organized projections to the spinal cord, its location [108]. Absence of these nociceptors, as in patients with congenital analgesia or peripheral neuropathies, is associated with tissue damage and poor healing as a consequence of the absence of the normal protective reflexes and behavioural responses elicited by the nociceptors. This “ouch” pain is, therefore, an important and adaptive element of the normal nervous system which, clinically, only needs to be temporarily suppressed or disabled during surgical procedures where damage is deliberately produced. The nociceptors terminate in a highly ordered way in the dorsal horn of the spinal cord with the thinly myelinated A ending in laminae I and V and the unmyelinated C-fibres in lamina II. These high threshold sensory fibres activate a large number of second order interneurones and projection neurones in the spinal cord, some of which are activated exclusively by noxious stimuli (

Hormonal effects of thoracic extradural analgesia for cardiac surgery.

Abstract: We have investigated the hormonal and metabolic effects of thoracic extradural analgesia with bupivacaine in addition to sufentanil 20 micrograms kg-1 in nine patients undergoing coronary artery bypass surgery. A control group received general anaesthesia alone. The catecholamine response was inhibited for 24 h after surgery in patients who had received extradural analgesia, and the cortisol response was suppressed during cardiopulmonary bypass. Blood glucose values were unchanged until 24 h after surgery in the extradural group. There were no significant differences in cardiac index between the two groups of patients, although heart rate and mean arterial pressure decreased before surgery in patients who received extradural analgesia. The benefits of this technique in terms of a reduction in postoperative morbidity remain to be determined.

Transient radicular irritation after spinal anaesthesia with hyperbaric 5% lignocaine

Abstract: We have studied prospectively 600 patients who had spinal anaesthesia for minor surgery, to evaluate the incidence of transient radicular irritation after the block. The anaesthetic agent (hyperbaric 5% lignocaine, hyperbaric 0.5% bupivacaine or plain 0.5% bupivacaine) was chosen according to the anticipated duration of surgery. We obtained information after operation from 537 patients (282 by telephone, 255 by letter). Ten percent of patients anaesthetized with hyperbaric 5% lignocaine (27 patients) had transient bilateral radiating pain in the lower extremities, buttocks, or both. Typically the pain started within 24 h after spinal anaesthesia, lasted less than 2 days and was described as mild. Lignocaine was the only variable that correlated with this pain. Two patients complained of symptoms after hyperbaric 0.5% bupivacaine but these were atypical compared with pain after lignocaine. None of the patients anaesthetized with plain bupivacaine had similar complaints. We conclude that the use of 5% hyperbaric lignocaine for spinal anaesthesia should be reconsidered. (Br. J. Anaesth. 1995; 74: 328–329)

Histamine-release haemodynamic changes produced by rocuronium, vecuronium, mivacurium, atracurium and tubocurarine.

Abstract: We have examined the effects of different benzyl-isoquinolinium and steroidal neuromuscular blocking compounds on plasma concentrations of histamine, heart rate and arterial pressure in surgical patients. A single, rapid (5-s) bolus of mivacurium 0.2 mg kg-1, atracurium 0.6 mg kg-1, tubocurarine 0.5 mg kg-1, vecuronium 0.1 mg kg-1 or rocuronium 0.6 mg kg-1 was administered to 75 patients (n = 15 in each group). Anaesthesia was induced with thiopentone 6 mg kg-1 i.v. and maintained with isoflurane and 70% nitrous oxide in oxygen. Venous blood samples were obtained before induction, 1 min after thiopentone and 1, 3 and 5 min after administration of the neuromuscular blocking drug. Mivacurium, atracurium and tubocurarine caused 370%, 234% and 252% increases in plasma histamine concentrations at 1 min, respectively. Corresponding values at 3 min were 223%, 148% and 157%, respectively. These changes were significant (P

Analgesic effect in humans of subanaesthetic isoflurane concentrations evaluated by experimentally induced pain.

Abstract: The analgesic effect of subanaesthetic concentrations of ether, trichloroethylene, methoxyflurane and halothane has been investigated previously using either clinical assessment or pain threshold measurements, but with conflicting results. The purpose of the present study was to evaluate the analgesic effect of isoflurane using experimental pain models. We studied 12 healthy volunteers at three randomly chosen subanaesthetic isoflurane concentrations: low (0.10-0.14 vol%), middle (0.16-0.20 vol%) and high (0.22-0.26 vol%). We used thermal pain detection and pain tolerance thresholds to argon laser stimulation, pressure pain detection and pain tolerance thresholds, immersion of the hand in ice water, and the nociceptive reflex to single and repeated (temporal summation) electrical stimulations, as experimental models to assess analgesia. There were no significant changes in the response to heat, cold or mechanical pressure at any of the subanaesthetic concentrations of isoflurane used. The nociceptive reflex thresholds to single stimulations, but not the thresholds for repeated stimulations, were significantly increased in all three isoflurane groups compared with baseline values. The difference between the different isoflurane concentrations was not statistically significant. In experimental pain models, subanaesthetic isoflurane concentrations have little or no analgesic potency.

Prevention of vomiting after paediatric strabismus surgery: a systematic review using the numbers-needed-to-treat method

Abstract: Randomized controlled studies were reviewed to assess the effectiveness and safety of antiemetics used for prophylaxis in paediatric strabismus surgery. Early and late vomiting (6 and 48 h after operation, respectively), and adverse effects were evaluated using the numbers-needed-to-treat method. In 27 reports with information on 2033 children, the mean incidence of early vomiting was 54% and of late vomiting 59%, without prophylaxis. Only three drugs were studied sufficiently for firm conclusions to be drawn. In the best documented regimen (droperidol 75 micrograms kg-1), four children have to be given the drug to prevent one vomiting; of the three others, one may vomit and two would not have vomited anyway; fewer than one child in 100 may have an extrapyramidal reaction and 16 may have minor adverse effects. Metoclopramide 0.15 and 0.25 mg kg-1 was significantly better than control only for early vomiting. Propofol had a high incidence of oculocardiac reflex without conferring any significant antiemetic effect: it should not be used. The benefits of prophylactic antiemetic therapy are not proven.

Cricoid pressure impedes placement of the laryngeal mask airway

Abstract: We have studied 22 patients to examine whether or not cricoid pressure affects ventilation of the lungs via the laryngeal mask and its correct positioning. In a randomized, crossover design, the laryngeal mask was inserted with or without cricoid pressure applied with a standardized force of 30 N using a cricoid yoke. A standardized pillow (6 cm in height) was placed under the patient occiput, but the neck was not supported. Ventilation of the lungs via the laryngeal mask was adequate in all patients when no cricoid pressurewas applied, but in only three of 22 patients when cricoid pressure was applied (P ≪0.001 ; 95% confidence interval (Cl) 0.72–1.0). The mask was positioned correctly in 18 patients when no pressure was applied, and in none after application of cricoid pressure (P ≪ 0.001; 95% Cl 0.66–0.98). We had planned to study, in an additional 20 patients, the effect of cricoid pressure without a pillow under the occiput; placement of the mask, however, was difficult even when cricoid pressure was not applied and there was a high incidence of bleeding from the oropharynx. We thus abandoned that part of the study after eight patients. In those eight patients, the success rate of ventilation via the laryngeal mask was lower when cricoid pressure was applied. We conclude that when sufficient force was applied, cricoid pressure, regardless of the method of application, did impede placement of the laryngeal mask. (Br. J. Anaesth. 1995; 74: 521–525)

Molecular biology of pain.

Abstract: We have attempted to define some of the patterns of expression of the IEG Fos in pain-related states. On one level, Fos may be used simply as marker of afferent stimulation and disease state, and in this respect Fos activation may be a useful tool after nociceptive stimulation to examine the effectiveness of different analgesic regimens. For example, certain analgesics such as opioids, alpha 2 agonists and local anaesthetics are more effective when given pre-emptively or early in the injury rather than later on. Furthermore, the persistent expression of Fos in the presence of high dose pre-emptive opioids is disturbing and yet it may explain variable success of studies attempting to show pre-emptive analgesia with opioid-based analgesic regimens. We suggest that Fos expression, as well as defining the magnitude and the duration of insult to the spinal cord seems also to signal the adaptive responses of the nervous system to nociceptive insult. Though we have focused on only one IEG, c-fos, and attempted to relate appearance to known functional changes within the spinal cord, there are in fact many more genes known to be upregulated with the same or slower kinetics (e.g. Fos B, FRA-1, FRA-2, Jun B, Jun D, NGFI-A). Increased understanding of the role of these genes is likely to lead to many novel targets in the search for normalization or restoration of spinal cord function in pain states and after nerve injury.

Analgesic and hypnotic effects of subanaesthetic concentrations of xenon in human volunteers: comparison with nitrous oxide

Abstract: The purpose of this study was to examine the effects of xenon and nitrous oxide in equipotent doses of 0.3 MAC on pain threshold and auditory response time in six healthy male volunteers. Compared with 100% oxygen inhalation, xenon and nitrous oxide significantly increased the pain threshold as measured by a radiant heat algometer. There was no significant difference in analgesic effects between xenon and nitrous oxide. Xenon significantly prolonged the response time to auditory stimuli compared with 100% oxygen, but nitrous oxide did not. The inhibitory effect of xenon on the auditory response time was significantly greater than that of nitrous oxide. The same six volunteers were studied to test if naloxone antagonized analgesia induced by xenon or nitrous oxide. The analgesic effects of xenon and nitrous oxide did not differ with or without naloxone.

Conventional pneumoperitoneum compared with abdominal wall lift for laparoscopic cholecystectomy.

Abstract: We have compared, in a randomized study, conventional carbon dioxide pneumoperitoneum with abdominal wall lift in 25 patients undergoing laparoscopic cholecystectomy. Intra-abdominal pressure (IAP) (11 (SD 2) mm Hg vs 2.7 (9) mm Hg) (P