Showing papers in "BJA: British Journal of Anaesthesia in 2003"

Anaesthetists’ Non‐Technical Skills (ANTS): evaluation of a behavioural marker system†

Abstract: Background. Non-technical skills are critical for good anaesthetic practice but are not addressed explicitly in normal training. Realization of the need to train and assess these skills is growing, but these activities must be based on properly developed skills frameworks and validated measurement tools. A prototype behavioural marker system was developed using human factors research techniques. The aim of this study was to conduct an experimental evaluation to establish its basic psychometric properties and usability. Method. The Anaesthetists’ Non-Technical Skills (ANTS) system prototype comprises four skill categories (task management, team working, situation awareness, and decision making) divided into 15 elements, each with example behaviours. To investigate its experimental validity, reliably and usability, 50 consultant anaesthetists were trained to use the ANTS system. They were asked to rate the behaviour of a target anaesthetist using the prototype system in eight videos of simulated anaesthetic scenarios. Data were collected from the ratings forms and an evaluation questionnaire. Results. The results showed that the system is complete, and that the skills are observable and can be rated with acceptable levels of agreement and accuracy. The internal consistency of the system appeared sound, and responses regarding usability were very positive. Conclusions. The findings of the evaluation indicated that the ANTS system has a satisfactory level of validity, reliability and usability in an experimental setting, provided users receive adequate training. It is now ready to be tested in real training environments, so that full guidelines can be developed for its integration into the anaesthetic curriculum.

Post‐dural puncture headache: pathogenesis, prevention and treatment

Abstract: Spinal anaesthesia developed in the late 1800s with the work of Wynter, Quincke and Corning. However, it was the German surgeon, Karl August Bier in 1898, who probably gave the first spinal anaesthetic. Bier also gained first-hand experience of the disabling headache related to dural puncture. He correctly surmised that the headache was related to excessive loss of cerebrospinal fluid (CSF). In the last 50 yr, the development of fine-gauge spinal needles and needle tip modification, has enabled a significant reduction in the incidence of post-dural puncture headache. Though it is clear that reducing the size of the dural perforation reduces the loss of CSF, there are many areas regarding the pathogenesis, treatment and prevention of post-dural puncture headache that remain contentious. How does the microscopic pattern of collagen alignment in the spinal dura affect the dimensions of the dural perforation? How do needle design, size and orientation influence leakage of CSF through the dural perforation? Can pharmacological methods reduce the symptoms of post-dural puncture headache? By which mechanism does the epidural blood patch cure headache? Is there a role for the prophylactic epidural blood patch? Do epidural saline, dextran, opioids and tissue glues reduce the rate of CSF loss? This review considers these contentious aspects of post-dural puncture headache.

Oxidative stress and gene expression in sepsis

Abstract: Dysregulation of the immuno-inflammatory response, as seen in sepsis, may culminate in host cell and organ damage. Lipopolysaccharide from Gram-negative bacterial cell walls induces gene activation and subsequent inflammatory mediator expression. Gene activation is regulated by a number of transcription factors at the nuclear level, of which nuclear factor κB appears to have a central role. The redox (reduction–oxidation) cellular balance is important for normal cellular function, including transcription factor regulation. In sepsis, a state of severe oxidative stress is encountered, with host endogenous antioxidant defences overcome. This has implications for cellular function and the regulation of gene expression. This review gives an overview of the mechanisms by which transcription factor activation and inflammatory mediator overexpression occur in sepsis, together with the events surrounding the state of oxidative stress encountered and the effects on the host's antioxidant defences. The effect of oxidative stress on transcription factor regulation is considered, together with the role of antioxidant repletion in transcription factor activation and in sepsis in general. Other interventions that may modulate transcription factor activation are also highlighted.

Tranexamic acid decreases external blood loss but not hidden blood loss in total knee replacement

Abstract: Background Total knee arthroplasty (TKA) is often carried out using a tourniquet and shed blood is collected in drains. Tranexamic acid decreases the external blood loss. Some blood loss may be concealed, and the overall effect of tranexamic acid on the haemoglobin (Hb) balance is not known. Methods Patients with osteoarthrosis had unilateral cemented TKA using spinal anaesthesia. In a double-blind fashion, they received either placebo (n=24) or tranexamic acid 10 mg kg−1 (n=27) i.v. just before tourniquet release and 3 h later. The decrease in circulating Hb on the fifth day after surgery, after correction for Hb transfused, was used to calculate the loss of Hb in grams. This value was then expressed as ml of blood loss. Results The groups had similar characteristics. The median volume of drainage fluid after placebo was 845 (interquartile range 523–990) ml and after tranexamic acid was 385 (331–586) ml (P Conclusions Tranexamic acid decreased total blood loss by nearly 30%, drainage volume by ∼50% and drastically reduced transfusion. However, concealed loss was only marginally influenced by tranexamic acid and was at least as large as the drainage volume. Br J Anaesth 2003; 90: 596–9

New concepts of atelectasis during general anaesthesia

Abstract: At the beginning of the last century, Pasteur described postoperative pulmonary atelectasis, 58 analysed postoperative pulmonary complications (PCC; see below) and noted: ‘when the true history of postoperative lung complications comes to be written, active collapse of the lung, from deficiency of inspiratory power, will be found to occupy an important position among determining causes’. 59 Indeed, atelectasis occurs regularly during general anaesthesia induction, 46 persists postoperatively 44 and may contribute to significant morbidity 78 and additional healthcare costs. 43 This review article will review the mechanism of perioperative atelectasis, discuss its clinical significance and describe preventive measures.

Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane in man†

Abstract: Background The motivation for this study was the current difficulty in estimating the total age-related MAC for a patient in a clinical setting. Methods Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane were developed for the clinically useful MAC range (0.6–1.6), age range 5–95 yr, and put in a convenient form for use by practising anaesthetists. The charts are based on Mapleson's meta-analysis (1996) of the available MAC data and can be used to allow for the contribution of nitrous oxide to the total MAC. Results The charts indicate the influence of age on anaesthetic requirements, showing, for example, that a total MAC of 1.2 using isoflurane and nitrous oxide 67% in oxygen requires an end-expired isoflurane concentration of only 0.25% in a patient of 95 yr vs 1% in a 5-yr-old patient. Colleagues found the charts to be helpful and simple to use clinically. Conclusions The iso-MAC charts show clearly how patient age can be used to guide the choice of end-expired agent concentration. They also allow a consistent total MAC to be maintained when changing the inspired nitrous oxide concentration, thereby reducing the chance of inadvertent awareness, particularly at the extremes of age.

Anaesthetics and cardiac preconditioning. Part I. Signalling and cytoprotective mechanisms

Abstract: Cardiac preconditioning represents the most potent and consistently reproducible method of rescuing heart tissue from undergoing irreversible ischaemic damage. Major milestones regarding the elucidation of this phenomenon have been passed in the last two decades. The signalling and amplification cascades from the preconditioning stimulus, be it ischaemic or pharmacological, to the putative end-effectors, including the mechanisms involved in cellular protection, are discussed in this review. Volatile anaesthetics and opioids effectively elicit pharmacological preconditioning. Anaesthetic-induced preconditioning and ischaemic preconditioning share many fundamental steps, including activation of G-protein-coupled receptors, multiple protein kinases and ATP-sensitive potassium channels (K(ATP) channels). Volatile anaesthetics prime the activation of the sarcolemmal and mitochondrial K(ATP) channels, the putative end-effectors of preconditioning, by stimulation of adenosine receptors and subsequent activation of protein kinase C (PKC) and by increased formation of nitric oxide and free oxygen radicals. In the case of desflurane, stimulation of alpha- and beta-adrenergic receptors may also be of importance. Similarly, opioids activate delta- and kappa-opioid receptors, and this also leads to PKC activation. Activated PKC acts as an amplifier of the preconditioning stimulus and stabilizes, by phosphorylation, the open state of the mitochondrial K(ATP) channel (the main end-effector in anaesthetic preconditioning) and the sarcolemmal K(ATP) channel. The opening of K(ATP) channels ultimately elicits cytoprotection by decreasing cytosolic and mitochondrial Ca(2+) overload.

Occupational stress and burnout in anaesthesia

Abstract: Background. Formal studies on stress in anaesthetists have usually measured stress through mental or physiological indicators. When using this approach, one must be careful not to confuse the effects of stress or outcome variables and the sources of stress or antecedent variables. To date, it seems from the literature that there is no clear evidence of a common pattern of physiological effects of stress for all the sources of stress. Furthermore, work characteristics such as job satisfaction, job control and job support may moderate the effects of stress. Methods. We measured the effects of stress together with the sources of stress and job characteristics, using self-reported questionnaires rather than physiological indicators in order to better diagnose stress in anaesthetists. Results. The mean stress level in anaesthetists was 50.6 which is no higher than we found in other working populations. The three main sources of stress reported were a lack of control over time management, work planning and risks. Anaesthetists reported high empowerment, high work commitment, high job challenge and high satisfaction. However, 40.4% of the group were suffering from high emotional exhaustion (burnout); the highest rate was in young trainees under 30 years of age. Conclusions. Remedial actions are discussed at the end of the paper.

Pharmacokinetics and efficacy of ropivacaine continuous wound instillation after joint replacement surgery

Abstract: Background. As continuous wound instillation with local anaesthetic has not been evaluated after hip/knee arthroplasties, our study was designed to determine whether this technique could enhance analgesia and improve patient outcome after joint replacement surgery. Methods. Thirty-seven patients undergoing elective hip/knee arthroplasties under spinal block were randomly assigned to two analgesia groups. Group M received continuous i.v. infusion of morphine plus ketorolac for 24 h. Then, a multi-hole 16 G catheter was placed subcutaneously and infusion of saline was maintained for 55 h. Group R received i.v. saline. Thereafter the wound was infiltrated with a solution of ropivacaine 0.5% 40 ml, then a multi-hole 16 G catheter was placed subcutaneously and an infusion of ropivacaine 0.2% 5 ml h −1 was maintained for 55 h. Visual analogue scale scores were assessed at rest and on passive mobilization by nurses blinded to analgesic treatment. Total plasma ropivacaine concentration was measured. Results. Group R showed a significant reduction in postoperative pain at rest and on mobilization, while rescue medication requirements were greater in Group M. Total ropivacaine plasma concentration remained below toxic concentrations and no adverse effects occurred. Length of hospital stay was shorter in Group R. Conclusion. Infiltration and wound instillation with ropivacaine 0.2% is more effective in controlling postoperative pain than systemic analgesia after major joint replacement surgery.

Anaesthesia for awake craniotomy—evolution of a technique that facilitates awake neurological testing

Abstract: Background There is an increasing trend towards performing craniotomy awake. The challenge for the anaesthetist is to provide adequate analgesia and sedation, haemodynamic stability, and a safe airway, with an awake, cooperative patient for neurological testing. Methods The records of all patients who had awake craniotomy at our institution were reviewed. Patients were divided into three groups according to anaesthetic technique. Patients in Group 1 were sedated throughout the procedure. Patients in Groups 2 and 3 had an asleep–awake–asleep technique. Those in Group 2 were anaesthetized with a propofol infusion and fentanyl, and breathed spontaneously through a laryngeal mask airway (LMA † †LMA ® is the property of Intavent Limited.). Patients in Group 3 had total i.v. anaesthesia with propofol and remifentanil, and ventilation was controlled using an LMA. We noted the incidence of complications in each group. Results There were 99 procedures carried out between 1989 and 2002. Group 3 had the fewest complications. No patients in Group 3 developed hypercapnia (e′ CO 2 >6 kPa), compared with all of the patients in Group 2. Patients in Group 1 had no e′ CO 2 monitoring, but 7% developed airway obstruction. No patients in Group 3 required additional analgesia for pain, compared with 70% of patients in Group 2. Conclusions We have developed a technique for craniotomy, which facilitates awake neurological testing, is safe, and has good patient satisfaction.

Constipation and its implications in the critically ill patient

Abstract: Background. Motility of the lower gut has been little studied in intensive care patients. Method. We prospectively studied constipation in an intensive care unit of a university hospital, and conducted a national survey to assess the generalizability of our findings. Results. Constipation occurred in 83% of the patients. More constipated patients (42.5%) failed to wean from mechanical ventilation than non-constipated patients (0%), P Conclusions. Constipation has implications for the critically ill.

The upper airway during anaesthesia

Abstract: Upper airway obstruction is common during both anaesthesia and sleep. Obstruction is caused by loss of muscle tone present in the awake state. The velopharynx, a particularly narrow segment, is especially predisposed to obstruction in both states. Patients with a tendency to upper airway obstruction during sleep are vulnerable during anaesthesia and sedation. Loss of wakefulness is compounded by depression of airway muscle activity by the agents, and depression of the ability to arouse, so they cannot respond adequately to asphyxia. Identifying the patient at risk is vital. Previous anaesthetic history and investigations of the upper airway are helpful, and a history of upper airway compromise during sleep (snoring, obstructive apnoeas) should be sought. Beyond these, risk identification is essentially a search for factors that narrow the airway. These include obesity, maxillary hypoplasia, mandibular retrusion, bulbar muscle weakness and specific obstructive lesions such as nasal obstruction or adenotonsillar hypertrophy. Such abnormalities not only increase vulnerability to upper airway obstruction during sleep or anaesthesia, but also make intubation difficult. While problems with airway maintenance may be obviated during anaesthesia by the use of aids such as the laryngeal mask airway (LMA†), identification of risk and caution are keys to management, and the airway should be secured before anaesthesia where doubt exists. If tracheal intubation is needed, spontaneous breathing until intubation is an important principle. Every anaesthetist should have in mind a plan for failed intubation or, worse, failed ventilation.

Long QT syndrome and anaesthesia

Abstract: Long QT syndrome (LQTS) is an arrhythmogenic cardiovascular disorder resulting from mutations in cardiac ion channels. LQTS is characterized by prolonged ventricular repolarization and frequently manifests itself as QT interval prolongation on the electrocardiogram (ECG). The age at presentation varies from in utero to adulthood. The majority of symptomatic events are related to physical activity and emotional stress. Although LQTS is characterized by recurrent syncope, cardiac arrest, and seizure-like episodes, only about 60% of patients are symptomatic at the time of diagnosis. 3 The clinical features of LQTS result from a peculiar episodic ventricular tachyarrhythmia called ‘torsade de pointes’. ‘Twisting of the points’ describes the typical sinusoidal twisting of the QRS axis around the isoelectric line of the ECG. Usually torsade de pointes start with a premature ventricular depolarization, followed by a compensatory pause. The next sinus beat often has a markedly prolonged QT interval and abnormal T wave. This is followed by a ventricular tachycardia that is characterized by variation in the QRS morphology, and a constantly changing R-R interval (Fig. 1). The ‘short-long-short’ cycle length sequence heralding torsade de pointes is a hallmark of LQTS. Commonly, the episode of torsade de pointes is self-terminating, producing a syncopal episode or pseudoseizure, secondary to the abrupt decrease in cerebral blood flow. The majority of episodes of sudden death in LQTS result from ventricular fibrillation triggered by torsade de pointes, although the mechanism of this deterioration is unknown. Traditionally, LQTS has been classified as either familial (inherited) or acquired. However, it is likely that many patients with previously labelled acquired LQTS carry a silent mutation in one of the genes responsible for congenital LQTS. 22 119 The evidence for this hypothesis has been gradually emerging over the past few years. It is important for anaesthetists to be aware of this concept, as it means that a much higher proportion of the general population may be affected by asymptomatic mutations in genes encoding cardiac ion channels than was thought previously. The prevalence of LQTS in developed countries may be as high as 1 per 1100‐3000 of the population. 32 119 About 30% of congenital LQTS carriers have an apparently normal phenotype, and thus a normal QT interval, and remain undiagnosed until an initiating event. 105 Fatal arrhythmias associated with primary electrical disease of the heart such as the Brugada and LQTS, probably account for 19% of sudden deaths in children between 1 and 13 yr of age, and 30% of sudden deaths that occur between 14 and 21 yr of age. 10 Furthermore, there is a strong association between prolonged corrected QT interval (QTc) in the first week of life and risk of sudden infant death syndrome. 86

Comparison of the effects of intrathecal ropivacaine, levobupivacaine, and bupivacaine for Caesarean section.

Abstract: Background. This study aimed to detect if intrathecal (i.t.) ropivacaine and levobupivacaine provided anaesthesia (satisfactory analgesia and muscular relaxation) and postoperative analgesia of similar quality to bupivacaine in patients undergoing Caesarean section. Methods. Ninety parturients were enrolled. A combined spinal-epidural technique was used. Patients were randomly assigned to receive one of the following isobaric i.t. solutions: bupivacaine 8 mg (n=30), levobupivacaine 8 mg (n=30), or ropivacaine 12 mg (n=30), all combined with sufentanil 2.5 mug. An i.t. solution was considered effective if an upper sensory level to pinprick of T4 or above was achieved and if intraoperative epidural supplementation was not required. Sensory changes and motor changes were recorded. Results. Anaesthesia was effective in 97, 80, and 87% of patients in the bupivacaine 8 mg, levobupivacaine 8 mg, and ropivacaine 12 mg groups, respectively. Bupivacaine 8 mg was associated with a significantly superior success rate to that observed in the levobupivacaine group (P<0.05). It also provided a longer duration of analgesia and motor block (P<0.05 vs levobupivacaine and ropivacaine). Conclusions. The racemic mixture of bupivacaine combined with sufentanil remains an appropriate choice when performing Caesarean sections under spinal anaesthesia.

Patient–ventilator interaction

Abstract: The respiratory control system consists of a motor arm, which executes the act of breathing, a control centre in the medulla oblongata and a number of pathways that convey information to the control centre. 69 On the basis of this information, the control centre activates spinal motor neurones serving respiratory muscles, with an intensity and rate that can vary substantially between breaths. The activity of spinal motor neurones is carried by peripheral nerves to the respiratory muscles, which contract and generate pressure (Pmus). According to the equation of motion for the respiratory system, Pmus is dissipated to overcome the resistance (Rrs) and elastance (Ers) of the respiratory system (inertia is assumed to be negligible), as follows:

Detection of awareness in surgical patients with EEG‐based indices—bispectral index and patient state index†‡

Abstract: Background Patient state index (PSI) and bispectral index (BIS) are values derived from the EEG, which can measure the hypnotic component of anaesthesia. We measured the ability of PSI and BIS to distinguish consciousness from unconsciousness during induction and emergence from anaesthesia and a period of awareness in surgical patients. Methods Forty unpremedicated patients were randomized to receive: (1) sevoflurane/remifentanil (≤0.1 μg kg−1 min−1), (2) sevoflurane/remifentanil (≥0.2 μg kg−1 min−1), (3) propofol/remifentanil (≤0.1 μg kg−1 min−1), (4) propofol/remifentanil (≥0.2 μg kg−1 min−1). Every 30 s after the start of the remifentanil, patients were asked to squeeze the investigator's hand. Sevoflurane or propofol were given until loss of consciousness (LOC1). Tunstall's isolated forearm technique was used during neuromuscular block with succinylcholine. After tracheal intubation, propofol or sevoflurane were stopped until return of consciousness (ROC1). Propofol or sevoflurane were re-started to induce LOC2. After surgery, drugs were discontinued and recovery (ROC2) was observed. PSI and BIS at LOC (LOC1 and LOC2) were compared with those at ROC (ROC1 and ROC2) (t-test). Prediction probability (Pk) was calculated from values at the last command before and at LOC and ROC. Values are mean ( sd ). Results At non-responsiveness, BIS (66 (17)) and PSI (55 (23)) were significantly less than at responsiveness (BIS, 79 (14); PSI, 77 (18); P Conclusions Despite significant differences between mean values at responsiveness and non-responsiveness for BIS and PSI, neither measure may be sufficient to detect awareness in an individual patient, reflected by a Pk less than below 70%.

Anaesthesia for spinal surgery in adults

Abstract: The spectrum of spinal surgery in adult life is considerable. Anaesthesia for major spinal surgery, such as spinal stabilization following trauma or neoplastic disease, or for correction of scoliosis, presents a number of challenges. The type of patients who would have been declined surgery 20 yr ago for medical reasons, are now being offered extensive procedures. They commonly have preoperative co-morbid conditions such as serious cardiovascular and respiratory impairment. Airway management may be difficult. Surgery imposes further stresses of significant blood loss, prolonged anaesthesia, and problematical postoperative pain management. The perioperative management of these patients is discussed. The advent of techniques to monitor spinal cord function has reduced postoperative neurological morbidity in these patients. The anaesthetist has an important role in facilitating these methods of monitoring.

Comparison of local anaesthetic effects of tramadol with prilocaine for minor surgical procedures

Abstract: Background Recent studies have shown that a local anaesthetic action of tramadol 5% was able to induce a sensory block to pinprick, touch, and cold similar to that of lidocaine 1%. The aim of this study was to compare the local anaesthetic effects of tramadol hydrochloride with prilocaine. Methods Sixty ASA I or II patients, undergoing excision of the cutaneous lesions under local anaesthesia, were included in the study. Patients were randomly assigned to receive either 1 ml of tramadol 5% (Group T, n =30) or 1 ml of prilocaine 2% (Group P, n =30) intradermally, in a double-blinded fashion. The degree of the burning sensation and pain at the injection site was documented. Sensory block was assessed 1 min after injection. The patient was asked to report the degree of sensation and to grade touch and pinprick sensation. Two minutes after drug administration, incision was performed and intensity of pain, felt by the patient was evaluated on a four-point scale (0–3). Any local adverse effects were recorded. Results There was no difference in the quality of block between the two groups. Side effects were noted in both groups with a significant increase in the incidence of local reaction (rash) in Group T (seven patients) when compared with Group P (one patient) ( P vs four patients in Group P complained of burning at the injection site ( P >0.05). Conclusions Intradermal tramadol 5% can provide a local anaesthesia similar to the prilocaine but the incidence of local adverse effects is higher.

Closed‐loop control of propofol anaesthesia using bispectral index™: performance assessment in patients receiving computer‐controlled propofol and manually controlled remifentanil infusions for minor surgery†

Abstract: Background. In a previous study we used the bispectral index (BIS)‘ for automatic control of propofol anaesthesia, using a proportional-integral-differential control algorithm. As control was less than optimal in some patients, we revised the constants of the control algorithm. The aim of the current study was to measure the performance of the revised system in patients undergoing minor surgery under propofol and remifentanil anaesthesia. Methods. Twenty adult patients scheduled for body surface surgery were enrolled. Anaesthesia was manually induced with target-controlled infusions (TCI) of propofol and remifentanil. After the start of surgery, when anaesthesia was clinically adequate, automatic control of the propofol TCI was commenced using the revised closed-loop system. For patients 11‐20, effect-site steering was also incorporated into the closed-loop control algorithm. Adequacy of anaesthesia during closed-loop control was assessed clinically, and by calculating the median performance error (MDPE), the median absolute performance error (MDAPE) and the mean offset of the control variable. Results. The system provided adequate operating conditions and stable cardiovascular values in all patients during closed-loop control. The mean MDPE and MDAPE were ‐0.42% and 5.63%, respectively. Mean offset of the BIS‘ from setpoint was ‐0.2. No patients reported awareness or recall of intraoperative events.

Evaluation of high fidelity patient simulator in assessment of performance of anaesthetists

Abstract: Background There is increasing emphasis on performance-based assessment of clinical competence. The High Fidelity Patient Simulator (HPS) may be useful for assessment of clinical practice in anaesthesia, but needs formal evaluation of validity, reliability, feasibility and effect on learning. We set out to assess the reliability of a global rating scale for scoring simulator performance in crisis management. Methods Using a global rating scale, three judges independently rated videotapes of anaesthetists in simulated crises in the operating theatre. Five anaesthetists then independently rated subsets of these videotapes. Results There was good agreement between raters for medical management, behavioural attributes and overall performance. Agreement was high for both the initial judges and the five additional raters. Conclusions Using a global scale to assess simulator performance, we found good inter-rater reliability for scoring performance in a crisis. We estimate that two judges should provide a reliable assessment. High fidelity simulation should be studied further for assessing clinical performance.

Cerebral oxygen vasoreactivity and cerebral tissue oxygen reactivity

Abstract: There has long been an appreciation that cerebral blood flow is modulated to ensure adequate cerebral oxygen delivery in the face of systemic hypoxaemia. There is increasing appreciation of the modulatory role of hyperoxia in the cerebral circulation and a consideration of the effects of such modulation on the maintenance of cerebral tissue oxygen concentration. These newer findings are particularly important in view of the fact that cerebrovascular and tissue oxygen responses to hyperoxia may change in disease. Such alterations provide important insights into pathophysiological mechanisms and may provide novel targets for therapy. However, before the modulatory effects of hyperoxia can be used for diagnosis, to predict prognosis or to direct therapy, a more detailed analysis and understanding of the physiological concepts behind this modulation are required, as are the limitations of the measurement tools used to define the modulation. This overview summarizes the available information in this area and suggests some avenues for further research.

Accuracy of the ‘Paedfusor’ in children undergoing cardiac surgery or catheterization

Abstract: Background A prototype paediatric propofol target-controlled infusion (TCI) system, the ‘Paedfusor’ has been developed. This system incorporates a paediatric pharmacokinetic data set and algorithm specific for children in a Graseby 3500 anaesthesia syringe driver. In this study we have evaluated the accuracy of the Paedfusor TCI system in children who underwent either cardiac surgery or cardiac catheterization procedures. Methods Twenty-nine children aged 1–15 yr were investigated. General anaesthesia was provided using propofol administered by the Paedfusor system. Accuracy of the system was evaluated by obtaining up to 9 arterial samples for measurement of propofol concentration both during anaesthesia and in the recovery period. Measured arterial propofol concentrations were then compared with values calculated by the Paedfusor. Results The predictive indices of median performance error (MDPE), and median absolute performance error (MDAPE) of the Paedfusor system were found to be 4.1% and 9.7%, respectively and the median value for wobble was 8.3%. These values are much better than those found with the adult ‘Diprifusor’ system. Conclusion The Paedfusor performance was found to be within the accepted limits for use as a TCI system.

Real‐time breath monitoring of propofol and its volatile metabolites during surgery using a novel mass spectrometric technique: a feasibility study

Abstract: Background. At present, there is no rapid method for determining the plasma concentration of i.v. anaesthetics. A solution might be the measurement of the anaesthetic concentration in expired breath and its relation to the plasma concentration. We used chemical ionization methods to determine whether an i.v. anaesthetic can be detected in the low concentrations (parts per billion by volume) in the expired breath of an anaesthetized patient. Method. Chemical ionization mass spectrometry can measure trace gases in air with high sensitivity without interference from major gases. We carried out a feasibility trial with a proton transfer reaction mass spectrometer (PTR-MS) to monitor the i.v. anaesthetic agent propofol and two of its metabolites in exhaled gas from an anaesthetic circuit. Exhaled gas was sampled via a 4 m long, unheated tube connected to the PTR-MS. Results. Propofol and its metabolites were monitored in real time in the expired breath of patients undergoing surgery. Conclusion. Routine measurement of i.v. agents, analogous to that for volatile anaesthetic agents, may be possible.

Xenon: no stranger to anaesthesia

Abstract: Xenon derives its name from the Greek for `stranger' because of its rarity, representing no more than 8.75 3 10% of the atmosphere or 0.0875 ppm. Discovered in 1898, it is manufactured by fractional distillation of air and is used commercially for lasers, high intensity lamps, ̄ash bulbs, jet propellant in the aerospace industry, X-ray tubes, and in medicine. The total amount of xenon in the atmosphere would occupy around 10 litres at atmospheric pressure, which is more than 10 million times the amount currently produced each year. Xenon has been used experimentally in clinical anaesthetic practice for more than 50 yrs. Over this period of time, reports of clinical studies reveal that several hundred surgical patients have successfully received this noble gas as part of their anaesthetic regimen. Xenon's safety and ef®cacy pro®le in this setting appears to be unequalled and only its relatively high cost has precluded its more widespread clinical use. Concerns over cost are now being mitigated by technological developments in the delivery and recycling of xenon that will permit much less total gas to be expended for each anaesthetic administration. Over the last decade there has been renewed interest in the use of xenon as an anaesthetic, as investigators have sought to ®nd a safe and effective substitute for nitrous oxide, which has caused environmental concerns because of its ozone-depleting properties. Since then, studies have demonstrated several advantages of using xenon when compared with not only nitrous oxide, but most other potent inhalation agents. These include: 1. A pharmacokinetic bene®t as a result of its extremely low blood/gas partition coef®cient, which results in a rapid onset and offset of its action. 46 2. Less cardiovascular depression. 10 33 35 3. Neuroprotection. 64 4. Profound analgesia. 48 This review will deal with some of the bene®ts of xenon anaesthesia, with a view to identifying those areas where it may be used to clinical advantage.

Spread of injectate with superficial cervical plexus block in humans: an anatomical study.

Abstract: Background This study was undertaken to investigate why the superficial cervical plexus block for carotid endarterectomy is so effective. Initial consideration would suggest that a superficial injection would be unlikely to block all terminal fibres of relevant nerves. One possibility is that the local anaesthetic crosses the deep cervical fascia and blocks the cervical nerves at their roots. Methods Superficial cervical plexus blocks (injections just below the investing fascia) were performed using methylene blue (30 ml) in four cadavers. In one additional control cadaver, a deep cervical plexus injection was performed. In a second control cadaver, a subcutaneous injection (superficial to investing fascia) was performed at the posterior border of the sternomastoid muscle. Results Anatomical dissection showed that with superficial block there was spread of the dye to structures beneath the deep cervical fascia. In the first control, dye remained in the deep cervical space. In the second control, dye remained subcutaneous. Conclusions The superficial cervical space communicates with the deep cervical space and this may explain the efficacy of the superficial block. The method of communication remains unknown. Our findings also indicate that the suitable site of injection for the superficial cervical plexus block is below the investing fascia of the neck, and not just subcutaneous.