Neurophysiologically-informed markers of individual variability and pharmacological manipulation of human cortical gamma

The ability to quantify synaptic function at the level of cortical microcircuits from non-invasive data would be enormously useful in the study of neuronal processing in humans and the pathophysiology that attends many neuropsychiatric disorders. Here, we provide proof of principle that one can estimate inter-and intra-laminar interactions among specific neuronal populations using induced gamma responses in the visual cortex of human subjects - using dynamic causal modelling based upon the canonical microcircuit (CMC; a simplistic model of a cortical column). Using variability in induced (spectral) responses over a large cohort of normal subjects, we find that the predominant determinants of gamma responses rest on recurrent and intrinsic connections between superficial pyramidal cells and inhibitory interneurons. Furthermore, variations in beta responses were mediated by inter-subject differences in the intrinsic connections between deep pyramidal cells and inhibitory interneurons. Interestingly, we also show that increasing the self-inhibition of superficial pyramidal cells suppresses the amplitude of gamma activity, while increasing its peak frequency. This systematic and nonlinear relationship was only disclosed by modelling the causes of induced responses. Crucially, we were able to validate this form of neurophysiological phenotyping by showing a selective effect of the GABA re-uptake inhibitor tiagabine on the rate constants of inhibitory interneurons. Remarkably, we were able to recover the pharmacodynamics of this effect over the course of several hours on a per subject basis. These findings speak to the possibility of measuring population specific synaptic function - and its response to pharmacological intervention - to provide subject-specific biomarkers of mesoscopic neuronal processes using non-invasive data. Finally, our results demonstrate that, using the CMC as a proxy, the synaptic mechanisms that underlie the gain control of neuronal message passing within and between different levels of cortical hierarchies may now be amenable to quantitative study using non-invasive (MEG) procedures.

Asynchronous partial contact motion due to internal resonance in multiple degree-of-freedom rotordynamics

Sudden onset of violent chattering or whirling rotor-stator contact motion in rotational machines can cause significant damage in many industrial applications. It is shown that internal resonance can lead to the onset of bouncing-type partial contact motion away from primary resonances. These partial contact limit cycles can involve any two modes of an arbitrarily high degree-of-freedom system, and can be seen as an extension of a synchronization condition previously reported for a single disc system. The synchronization formula predicts multiple drivespeeds, corresponding to different forms of mode-locked bouncing orbits. These results are backed up by a brute-force bifurcation analysis which reveals numerical existence of the corresponding family of bouncing orbits at supercritical drivespeeds, provided the damping is sufficiently low. The numerics reveal many overlapping families of solutions, which leads to significant multi-stability of the response at given drive speeds. Further, secondary bifurcations can also occur within each family, altering the nature of the response and ultimately leading to chaos. It is illustrated how stiffness and damping of the stator have a large effect on the number and nature of the partial contact solutions, illustrating the extreme sensitivity that would be observed in practice.

Meta-analysis of high- versus low-chloride content in perioperative and critical care fluid resuscitation

Background

The objective of this systematic review and meta-analysis was to assess the relationship between the chloride content of intravenous resuscitation fluids and patient outcomes in the perioperative or intensive care setting.

Methods

Systematic searches were performed of PubMed/MEDLINE, Embase and Cochrane Library (CENTRAL) databases in accordance with PRISMA guidelines. Randomized clinical trials, controlled clinical trials and observational studies were included if they compared outcomes in acutely ill or surgical patients receiving either high-chloride (ion concentration greater than 111 mmol/l up to and including 154 mmol/l) or lower-chloride (concentration 111 mmol/l or less) crystalloids for resuscitation. Endpoints examined were mortality, measures of kidney function, serum chloride, hyperchloraemia/metabolic acidosis, blood transfusion volume, mechanical ventilation time, and length of hospital and intensive care unit stay. Risk ratios (RRs), mean differences (MDs) or standardized mean differences (SMDs) and confidence intervals were calculated using fixed-effect modelling.

Results

The search identified 21 studies involving 6253 patients. High-chloride fluids did not affect mortality but were associated with a significantly higher risk of acute kidney injury (RR 1·64, 95 per cent c.i. 1·27 to 2·13; P < 0·001) and hyperchloraemia/metabolic acidosis (RR 2·87, 1·95 to 4·21; P < 0·001). High-chloride fluids were also associated with greater serum chloride (MD 3·70 (95 per cent c.i. 3·36 to 4·04) mmol/l; P < 0·001), blood transfusion volume (SMD 0·35, 0·07 to 0·63; P = 0·014) and mechanical ventilation time (SMD 0·15, 0·08 to 0·23; P < 0·001). Sensitivity analyses excluding heavily weighted studies resulted in non-statistically significant effects for acute kidney injury and mechanical ventilation time.

Conclusion

A weak but significant association between higher chloride content fluids and unfavourable outcomes was found, but mortality was unaffected by chloride content.

Four phases of intravenous fluid therapy: a conceptual model

I.V. fluid therapy plays a fundamental role in the management of hospitalized patients. While the correct use of i.v. fluids can be lifesaving, recent literature demonstrates that fluid therapy is not without risks. Indeed, the use of certain types and volumes of fluid can increase the risk of harm, and even death, in some patient groups. Data from a recent audit show us that the inappropriate use of fluids may occur in up to 20% of patients receiving fluid therapy. The delegates of the 12th Acute Dialysis Quality Initiative (ADQI) Conference sought to obtain consensus on the use of i.v. fluids with the aim of producing guidance for their use. In this article, we review a recently proposed model for fluid therapy in severe sepsis and propose a framework by which it could be adopted for use in most situations where fluid management is required. Considering the dose-effect relationship and side-effects of fluids, fluid therapy should be regarded similar to other drug therapy with specific indications and tailored recommendations for the type and dose of fluid. By emphasizing the necessity to individualize fluid therapy, we hope to reduce the risk to our patients and improve their outcome.

Indications and management of mechanical fluid removal in critical illness

BACKGROUND

The Acute Dialysis Quality Initiative (ADQI) dedicated its Twelfth Consensus Conference (2013) to all aspects of fluid therapy, including the management of fluid overload (FO). The aim of the working subgroup 'Mechanical fluid removal' was to review the indications, prescription, and management of mechanical fluid removal within the broad context of fluid management of critically ill patients.

METHODS

The working group developed a list of preliminary questions and objectives and performed a modified Delphi analysis of the existing literature. Relevant studies were identified through a literature search using the MEDLINE database and bibliographies of relevant research and review articles.

RESULTS

After review of the existing literature, the group agreed the following consensus statements: (i) in critically ill patients with FO and with failure of or inadequate response to pharmacological therapy, mechanical fluid removal should be considered as a therapy to optimize fluid balance. (ii) When using mechanical fluid removal or management, targets for rate of fluid removal and net fluid removal should be based upon the overall fluid balance of the patient and also physiological variables, individualized, and reassessed frequently. (iii) More research on the role and practice of mechanical fluid removal in critically ill patients not meeting fluid balance goals (including in children) is necessary.

CONCLUSION

Mechanical fluid removal should be considered as a therapy for FO, but more research is necessary to determine its exact role and clinical application.

Dietary triggers in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a frequently occurring, benign functional gastrointestinal disorder with a complex poorly understood pathology which appears to be multifactorial in nature. There is no association with structural or biochemical abnormalities in the gastrointestinal tract. Functional variations in myoelectrical activity, visceral hypersensitivity and illness behaviours have all been observed in patients experimentally. In conjunction with environmental, psychological and alimentary factors, these mechanisms have been proposed as the major determinants of symptom genesis. Certainly, dietary factors are frequently perceived by sufferers as powerful symptom triggers, with many reporting multiple food intolerance. Physicians, however, remain divided upon the relevance of food to the disorder, with many eschewing a nutritional connection. This is unsurprising as, despite much experimental work to determine the clinical relevance of food intolerance and allergy to the aetiology of the disorder, the vast range of foodstuffs available for testing, inherent procedural problems with test foods, methodological insufficiencies and the continually evolving knowledge of the disorder, particularly the subgrouping of sufferers, have restricted the scientific validity of current findings. At the present time, it is difficult to make informed judgement upon the importance of food in IBS, and rigorously designed, large scale trials devised in the light of recent knowledge are required before conclusions can be drawn.

Regional brain blood flow in man during acute changes in arterial blood gases

Despite the importance of blood flow on brainstem control of respiratory and autonomic function, little is known about regional cerebral blood flow (CBF) during changes in arterial blood gases.We quantified: (1) anterior and posterior CBF and reactivity through a wide range of steady-state changes in the partial pressures of CO2 (PaCO2) and O2 (PaO2) in arterial blood, and (2) determined if the internal carotid artery (ICA) and vertebral artery (VA) change diameter through the same range.We used near-concurrent vascular ultrasound measures of flow through the ICA and VA, and blood velocity in their downstream arteries (the middle (MCA) and posterior (PCA) cerebral arteries). Part A (n =16) examined iso-oxic changes in PaCO2, consisting of three hypocapnic stages (PaCO2 =∼15, ∼20 and ∼30 mmHg) and four hypercapnic stages (PaCO2 =∼50, ∼55, ∼60 and ∼65 mmHg). In Part B (n =10), during isocapnia, PaO2 was decreased to ∼60, ∼44, and ∼35 mmHg and increased to ∼320 mmHg and ∼430 mmHg. Stages lasted ∼15 min. Intra-arterial pressure was measured continuously; arterial blood gases were sampled at the end of each stage. There were three principal findings. (1) Regional reactivity: the VA reactivity to hypocapnia was larger than the ICA, MCA and PCA; hypercapnic reactivity was similar.With profound hypoxia (35 mmHg) the relative increase in VA flow was 50% greater than the other vessels. (2) Neck vessel diameters: changes in diameter (∼25%) of the ICA was positively related to changes in PaCO2 (R2, 0.63±0.26; P<0.05); VA diameter was unaltered in response to changed PaCO2 but yielded a diameter increase of +9% with severe hypoxia. (3) Intra- vs. extra-cerebral measures: MCA and PCA blood velocities yielded smaller reactivities and estimates of flow than VA and ICA flow. The findings respectively indicate: (1) disparate blood flow regulation to the brainstem and cortex; (2) cerebrovascular resistance is not solely modulated at the level of the arteriolar pial vessels; and (3) transcranial Doppler ultrasound may underestimate measurements of CBF during extreme hypoxia and/or hypercapnia.

Coronary revascularization in transition from on-pump to off-pump: the effect of the off-pump coronary artery bypass on medium-term outcome

AIM

We previously reported that early patient outcome, chiefly ischaemic injury, was reduced in patients allocated to off pump coronary artery bypass (OPCAB) surgery. This report concerns the medium-term outcome for this cohort of patients.

METHODS

A prospective observational study was carried out in a single cardiothoracic specialty hospital. Forty-four patients scheduled for elective multivessel coronary artery bypass grafting (CABG) surgery using either off pump (OPCAB) (n=21) or on pump (cardiopulmonary bypass, CPB) (n=23) were included in the study. Data on the symptoms, quality of life, need for cardiovascular therapy, and occurrence of cardiovascular events or death among patients at 6- and 12-months after surgery were collected by a patient questionnaire and reviewing the medical charts.

RESULTS

Compared with patients who underwent CPB surgery, OPCAB patients required a smaller increase in cardiovascular medication (5.6% versus 47.1%; P=0.007) at the 6-month follow-up and demonstrated a trend toward improved symptoms (dyspnea at 6 months, 0, range 0-4 versus 1, range 0-4; P=0.03) and quality of life (Duke Activity Status Index at 6 months, 20.8+5.6 versus 19+6.8; P=0.13). No differences in the incidence of cardiologic intervention or mortality were observed between groups.

CONCLUSIONS

The trend toward improved medium-term outcome variables among patients treated with OPCAB may have owed to the reduced cardiac ischemic injury associated with OPCAB compared with CPB.

Effects of isoflurane, pentobarbital, and urethane on apoptosis and apoptotic signal transduction in rat kidney

BACKGROUND

Renal cell apoptosis contributes significantly to the pathogenesis of acute renal failure. Anesthetic agents have been shown to modulate apoptotic signal transduction in various tissues. We examined the effects of 6 h of different general anesthetic techniques on renal cell apoptosis in rat kidneys.

METHODS

Twenty-one male Sprague-Dawley rats were randomly allocated into four groups: (i) control, non-anesthetized rats (n= 3) and rats anesthetized with (ii) inhaled isoflurane (n= 6), (iii) intraperitoneal pentobarbital (n= 6), and (iv) intraperitoneal urethane (n= 6). Animals were sacrificed 6 h after the induction of anesthesia.

RESULTS

Apoptosis was assessed by terminal deoxynucleotidyl transferase-fluorescein end-labeling analysis. RNA was extracted from the left kidney to probe cDNA microarrays. Gene expression was measured as a percentage of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and subsequently confirmed using reverse transcriptase-polymerase chain reaction (RT-PCR). Compared with the control (no anesthesia), urethane significantly (P < 0.001) induced apoptosis in both the renal cortex and medulla. Isoflurane significantly (P < 0.001) inhibited apoptosis in the medulla. Microarray analysis revealed that urethane up-regulated more (74) genes than pentobarbital (16) and isoflurane (10). Isoflurane down-regulated more genes (85) than pentobarbital (74) and urethane (12). These anesthetic-induced modulations were significant (P < 0.05) for 60 isoflurane-, 30 pentobarbital- and 4 urethane-modulated genes.

CONCLUSION

Our results suggest that general anesthetic drugs have an effect on renal cell apoptosis and apoptotic signal transduction, and thus may potentially affect the risk of subsequent acute renal failure.

Daystay hamstring ACL reconstruction performed under regional anaesthesia

Daycase ACL reconstruction is commonly performed under general anaesthesia with a patella tendon graft. We report our experience with hamstring reconstruction under regional anaesthesia. Over a 14-month period, 104 daycase arthroscopic ACL reconstructions were performed by one surgeon and one anaesthetist. All operations were performed under spinal anaesthesia with a femoral nerve block. Patients were discharged with oral analgesia, brace and a cryocuff. One hundred and two patients were prospectively evaluated with a visual analogue pain score (0-10) and a patient satisfaction questionnaire. Of these 102 patients, 101 (99%) were happy to be discharged on the same day. One patient was admitted from the daycase unit, and one patient was re-admitted. Patients were very satisfied with the pain relief provided. The mean visual analogue pain score was 1.0 at discharge, 1.8 in the middle of the first night, and 2.1 on the first post-op day. Patients experienced significantly more pain the day after surgery than the evening of surgery (p=0.04). We conclude that hamstring ACL reconstruction under regional anaesthesia is well tolerated by patients as a daycase procedure.

Transcriptional responses of rat skeletal muscle following hypoxia-reoxygenation and near ischaemia-reperfusion

AIM

The effect of ischaemia/reperfusion or hypoxia/reoxygenation on gene expression has not been extensively studied. We hypothesized that in skeletal muscle, tissue hypoxia of similar magnitude but induced by different mechanisms would lead to different transcriptional responses.

METHODS

Muscle gene transcription was assessed using microarray analysis and reverse transcriptase polymerase chain reaction in 18 rats exposed to regional hind limb near ischaemia/reperfusion (n = 6), hypoxia/reoxygenation (n = 6) or sham operation (n = 6). Hypoxic burden was measured by the area under the PtO(2)-time curve.

RESULTS

PtO(2) was reduced in both the near ischaemia/reperfusion and hypoxia/reoxygenation groups. Although the hypoxic burden was similar, the genomic response was different for each condition. Near ischaemia/reperfusion had a greater effect on gene expression than hypoxia/reoxygenation. Using stringent criteria for changes in gene expression (i.e. more than or equal to twofold change vs. control) unique patterns of gene expression could be identified suggesting individualized transcriptional responses to each of these injuries. Several genes, including insulin-like growth factor 1 (IGF-1) and cyclin-dependent kinase inhibitor (p27(Kip1)) were induced by both injury types and these may have potential clinical application as markers of tissue damage. In contrast, no single gene was downregulated by both injury conditions.

CONCLUSIONS

The mechanism of skeletal muscle hypoxia has a profound effect on its subsequent transcriptional response. We identified several potential candidates as markers of skeletal muscle ischaemic damage.

Monitoring ventilator weaning--predictors of success

Improving the prediction of successful ventilator weaning and extubation is a goal that all Intensivists and perioperative physicians strive for. The successful wean and extubation of ventilated patients decreases hospital length of stay and associated costs, but more importantly it also reduces patient morbidity and mortality. This review evaluates traditional and novel indices used in the assessment for ventilatory wean readiness. Novel equipment such as the Bicore pulmonary monitor and the CO2 SMO Plus are now available on the market to assess and monitor ventilator weaning and may offer some value in this process. We also review the non-respiratory factors affecting weaning and the role of the bedside nurse and respiratory therapist. Resolution of the pulmonary compromise and an understanding of respiratory physiology, used in conjunction with monitored indices of weaning parameters in a consistent fashion will continue to improve our success rates of ventilator weaning and extubation.

Primary and secondary metabolism, and post-translational protein modifications, as portrayed by proteomic analysis of Streptomyces coelicolor

The newly sequenced genome of Streptomyces coelicolor is estimated to encode 7825 theoretical proteins. We have mapped approximately 10% of the theoretical proteome experimentally using two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Products from 770 different genes were identified, and the types of proteins represented are discussed in terms of their annotated functional classes. An average of 1.2 proteins per gene was observed, indicating extensive post-translational regulation. Examples of modification by N-acetylation, adenylylation and proteolytic processing were characterized using mass spectrometry. Proteins from both primary and certain secondary metabolic pathways are strongly represented on the map, and a number of these enzymes were identified at more than one two-dimensional gel location. Post-translational modification mechanisms may therefore play a significant role in the regulation of these pathways. Unexpectedly, one of the enzymes for synthesis of the actinorhodin polyketide antibiotic appears to be located outside the cytoplasmic compartment, within the cell wall matrix. Of 20 gene clusters encoding enzymes characteristic of secondary metabolism, eight are represented on the proteome map, including three that specify the production of novel metabolites. This information will be valuable in the characterization of the new metabolites.

Influence of an advance directive on the initiation of life support technology in critically ill cancer patients

OBJECTIVE

To determine whether the presence of an advance directive at admission to an intensive care unit (ICU) influenced the decision to initiate life support therapy in critically ill cancer patients.

DESIGN

Matched-pairs case-control design.

SETTING

The University of Texas M. D. Anderson Cancer Center ICU.

PATIENTS

Of 872 patients treated in the ICU from 1994 to 1996, 236 (27%) were identified as having advance directives. One hundred thirty five patients who had advance directives were successfully matched to 135 patients who did not on the basis of type of malignancy, reason for admission to ICU, severity of illness, and age. These pairs comprised the study group.

INTERVENTIONS

Life-supporting interventions were compared between the matched groups using the McNemar and Wilcoxon matched-pairs signed ranks tests.

MEASUREMENTS AND MAIN RESULTS

No significant difference was found in the frequency with which the following interventions were applied in patients with and without advance directives (respectively): mechanical ventilation, 44% vs. 42%; inotropic support, 31% vs. 31%; pulmonary artery catheterization, 11% vs. 12%; cardiopulmonary resuscitation, 7% vs. 12%; and renal dialysis, 3% vs. 7%. There were also no differences in ICU (75% vs. 73%, respectively) or hospital (56% vs. 59%, respectively) survival. More patients with advance directives than those without had do-not-resuscitate orders within the first 72 hrs (19% vs. 11%, p =.046) and patients with advance directives had shorter ICU durations and lower ICU charges than patients without advance directives.

CONCLUSIONS

After controlling for type of malignancy, reason for admission to the ICU, severity of illness, and age, the decision to initiate life-supporting interventions did not differ significantly among patients with and without advance directives. The presence of an advance directive, however, may have helped guide decisions earlier regarding duration of therapy and resuscitation status.

Effect of ispaghula husk on the faecal output of bile acids in healthy volunteers

Faecal bile acids are associated with both colorectal cancer and serum cholesterol levels. We investigate whether dosing with ispaghula husk affects the faecal bile acid weights and concentrations in healthy adults. Sixteen healthy volunteers consumed 7.0 g/day ispaghula husk, containing 5.88 g/day Englyst-determinable dietary fibre, for the middle 8 weeks of a 12-week period. Stool samples were collected, analysed for faecal bile acids and their form and dry weight determined. Correlations between the faecal bile acids, the stool parameters and the dietary intake were tested. Ispaghula husk treatment significantly lowers faecal lithocholic and isolithocholic acids and the weighted ratio of lithocholic acids to deoxycholic acid. These effects revert towards their initial states at the end of the treatment period. These changes in the faecal bile acid profiles indicate a reduction in the hydrophobicity of the bile acids in the enterohepatic circulation.

Rapid analysis of high-dimensional bioprocesses using multivariate spectroscopies and advanced chemometrics

There are an increasing number of instrumental methods for obtaining data from biochemical processes, many of which now provide information on many (indeed many hundreds) of variables simultaneously. The wealth of data that these methods provide, however, is useless without the means to extract the required information. As instruments advance, and the quantity of data produced increases, the fields of bioinformatics and chemometrics have consequently grown greatly in importance. The chemometric methods nowadays available are both powerful and dangerous, and there are many issues to be considered when using statistical analyses on data for which there are numerous measurements (which often exceed the number of samples). It is not difficult to carry out statistical analysis on multivariate data in such a way that the results appear much more impressive than they really are. The authors present some of the methods that we have developed and exploited in Aberystwyth for gathering highly multivariate data from bioprocesses, and some techniques of sound multivariate statistical analyses (and of related methods based on neural and evolutionary computing) which can ensure that the results will stand up to the most rigorous scrutiny.

Lactose intolerance: problems in diagnosis and treatment

Lactose malabsorption and lactase deficiency are chronic organic pathologic conditions characterized by abdominal pain and distention, flatulence, and the passage of loose, watery stools. Though malabsorption of the sugar lactose is determinable by breath hydrogen test or jejunal biopsy, intolerance can only be confirmed by challenge with lactose-containing food, the response to which may not be immediate. The difficulty of making a positive diagnosis of these conditions has led to a proportion of lactose-intolerant patients being misdiagnosed with irritable bowel syndrome (IBS), which has a remarkably similar symptom complex and for which there is no current pathophysiologic marker. The incidence of the two disorders is approximately equal, but the actual proportion of patients with IBS incorrectly diagnosed in this way varies as a function of the methodology used. Once correct diagnosis is established, introduction of a lactose-free dietary regime relieves symptoms in most patients. Symptom similarity and the resultant incorrect diagnosis of IBS may explain the refractory nature of some patients labeled as IBS who remain largely unaware of the relationship between food intake and symptoms.

Variable selection and multivariate methods for the identification of microorganisms by flow cytometry

BACKGROUND

When exploited fully, flow cytometry can be used to provide multiparametric data for each cell in the sample of interest. While this makes flow cytometry a powerful technique for discriminating between different cell types, the data can be difficult to interpret. Traditionally, dual-parameter plots are used to visualize flow cytometric data, and for a data set consisting of seven parameters, one should examine 21 of these plots. A more efficient method is to reduce the dimensionality of the data (e.g., using unsupervised methods such as principal components analysis) so that fewer graphs need to be examined, or to use supervised multivariate data analysis methods to give a prediction of the identity of the analyzed particles.

MATERIALS AND METHODS

We collected multiparametric data sets for microbiological samples stained with six cocktails of fluorescent stains. Multivariate data analysis methods were explored as a means of microbial detection and identification.

RESULTS

We show that while all cocktails and all methods gave good accuracy of predictions (>94%), careful selection of both the stains and the analysis method could improve this figure (to > 99% accuracy), even in a data set that was not used in the formation of the supervised multivariate calibration model.

CONCLUSIONS

Flow cytometry provides a rapid method of obtaining multiparametric data for distinguishing between microorganisms. Multivariate data analysis methods have an important role to play in extracting the information from the data obtained. Artificial neural networks proved to be the most suitable method of data analysis.

Nitrous oxide and carbon dioxide have no effect on the blood-gas solubilities of sevoflurane and isoflurane

Nitrous oxide (N2O) has been shown to decrease the solubility (lambdaB:G) of volatile anesthetics in human blood and, consequently, affect their rate of uptake. If this is true, then carbon dioxide (CO2) may also have an effect, which is important because methods that measure the tension of volatile anesthetics in blood washout CO2 in the process. Blood samples were obtained from fasted, healthy volunteers and patients undergoing major surgery. Each sample was divided into two aliquots: one was equilibrated at 37 degrees C in a closed glass tonometer with a mixture of isoflurane 1% and sevoflurane 2% in a test gas mixture of either 50:50 N2O/O2 or 5:95 CO2/O2; the other aliquot was equilibrated with isoflurane and sevoflurane in O2 alone as a control. Using a two-stage headspace technique using gas chromatography, we measured the lambdaB:G of isoflurane and sevoflurane in the presence and absence of the test gas in each subject. There was no significant difference between the lambdaB:G of sevoflurane and isoflurane obtained from the N2O group and their controls or between the CO2 group and their controls. We conclude that neither N2O nor CO2 has an effect on the lambdaB:G of sevoflurane or isoflurane in the concentrations tested.

IMPLICATIONS

The blood solubilities of sevoflurane and isoflurane were measured with and without nitrous oxide and carbon dioxide. No differences were found. Nitrous oxide does not affect the kinetics of other anesthetics by altering their solubility. Carbon dioxide tensions need not be controlled when measuring anesthetic tensions in blood.

Anaesthesia for video-assisted thoracoscopic patent ductus arteriosus ligation

The case notes of children undergoing video-assisted thoracoscopic ligation of a patent ductus arteriosus were reviewed with particular emphasis on the anaesthetic management. All children were managed using one-lung ventilation with no serious adverse sequelae. The lungs could be isolated easily in all cases and no special equipment was required. We describe our initial series of 13 cases and discuss the anaesthetic implications arising from this surgical technique. We also discuss the different ways of monitoring duct closure.

The island posterior calf fasciocutaneous flap: an alternative to the gastrocnemius muscle for cover of knee and tibial defects

The gastrocnemius muscle remains the workhorse for providing soft tissue over the knee and upper tibia. Nevertheless, we have found the island posterior calf fasciocutaneous flap to be a valuable alternative. We describe 10 cases in which an island posterior calf fasciocutaneous flap was used to cover defects over the knee and tibia. Three cases were after knee arthroplasty wound dehiscence, three cases were of traumatic soft-tissue loss, three cases involved replacement of unstable skin, and one case required closing a synovial fistula. This series is compared with 10 contemporaneous consecutive cases of soft-tissue loss around the knee that were reconstructed with a gastrocnemius muscle flap. Nine posterior calf fasciocutaneous flaps survived completely, and one flap had to be replaced because of poor flow. Although this flap is technically more demanding, we have found that it offers some advantages over the gastrocnemius. These include a greater flexibility of size and shape, a longer arc of rotation to reach suprapatellar defects, the provision of sensate skin with protective though crude sensation, less bulk, and the avoidance of a twitch. The flap is also easy to re-elevate from the recipient site for subsequent orthopedic work.

Epidemiology and outcome of tibial diaphyseal fractures in footballers

A retrospective analysis of tibial diaphyseal fractures caused by football was undertaken to establish the epidemiology and severity of these common injuries. Analysis showed that the commonest fracture types were Tscherne C0 and C1 fractures and that only 73.9 per cent of the patients had unimpaired sporting function after the injury. The time to return to football was significantly related to the severity of the fracture but there was no correlation with the skill of the player. The time to return to football for the C0 fractures averaged 7-8 months and it is therefore suggested that it is unlikely that any player will return to football in the same season.

Knee pain after intramedullary tibial nailing: its incidence, etiology, and outcome

OBJECTIVES

To establish the incidence and clinical effects of anterior knee pain after intramedullary nailing of the tibia.

DESIGN

A retrospective study.

SETTING

The Royal Infirmary of Edinburgh, Scotland.

PATIENTS

169 patients who presented with a tibial diaphyseal fracture and were treated by intramedullary nailing.

INTERVENTION

All patients were treated with a reamed Grosse Kempf tibial nail.

MAIN OUTCOME MEASUREMENTS

Anterior knee pain was assessed with an analogue scale and functional outcome was examined using a series of routine daily activities.

RESULTS

Anterior knee pain was found in 56.2% of patients. The only distinguishing feature between patients with and without pain was that the patients who had pain were significantly younger. Most patients had mild pain but there was considerable functional impairment with 91.8% of patients experiencing pain on kneeling and 33.7% having pain even at rest. Nail removal resolved or improved the symptoms in almost all cases.

CONCLUSIONS

Anterior knee pain is a significant complication of intramedullary nailing of the tibia.

Burn injuries caused by chip-pan fires: the Edinburgh experience

Thirty-two patients were admitted to the South-East Scotland Burn Unit over a 4-year period (1990-94), with burns sustained as a consequence of chip-pan fires. This represented 7 per cent of all admissions to the unit. Fourteen patients came from the Edinburgh city area, and 18 from surrounding countries. There were 14 males and 18 females, and an average age of 51.6 years. The average burn surface area was 4.7 per cent. Eighteen patients had burns to their hands, this being the most common area involved. Fourteen patients were managed conservatively, and 18 needed operative intervention. The patients spent an average of 19.4 days in hospital, and they required 46.3 days for complete healing to take place. Prevention by increased community awareness and widespread education is necessary to minimize the incidence, morbidity and cost of this relatively common and preventable type of burn.

A simple assessment of surgical sutures and knots

The Surgeons' knot is both technically complex and difficult for junior surgeons to tie, especially when using heavy monofilament material. Knot slippage or breakage can pass unrecognized as a cause of wound dehisence, and it has been suggested that the Aberdeen knot and the Half-blood knot are easier and safer than the Surgeons' knot for tying these materials. The effect of different knots upon the breaking strain of common monofilament sutures was assessed using an Instron Tensiometer. The Surgeons' knot significantly reduced the breaking strength of all materials (P < 0.001). Using the Half-blood knot to commence closure had no significant effect upon strength. The Surgeons' knot, tied using the penultimate loop as at termination of closure, was associated with a significant risk of slippage, most noticeably with looped nylon. The Aberdeen knot, used for closure, showed no such slippage, and did not significantly weaken the suture (P < 0.05), except for polydiaxanone. In view of the ease of tying, security of knot and non-weakening properties, we recommend starting midline closure with a Half-blood knot and terminating with an Aberdeen knot.

Vascular trauma of the upper limb and associated nerve injuries

In an analysis of vascular audit data on upper limb vascular trauma over a 10 year period in a major UK injury centre it was found that 15 patients required operation for subclavian or axillary artery injuries. Eleven cases were the result of blunt injury. Twelve patients had an ischaemic arm on presentation, all of whom had an associated brachial plexus lesion. Subclavian or axillary artery transections, irrespective of limb viability, also were found to have associated plexus trauma. Twenty-eight patients had brachial artery injuries repaired, 46 per cent of whom had an associated nerve injury. A good functional result was achieved in only half of the patients who underwent repair of a peripheral nerve injured in association with the brachial artery. Vascular reconstruction was successful in all cases. The long-term outcome of brachial plexus lesions was very poor and the role of exploratory surgery is discussed. The long-term outcome of upper limb injury is not dependent on the vascular injury which can be successfully managed, but upon the recognition, treatment, and outcome of the associated nerve injuries.

The importance of the non-palpable lesion in women under 50, detected by mammography on self-referral for screening, symptoms or follow up

Between 1.1.88 and 31.12.91, 349 consecutive patients had an x-ray localization excision of a non-palpable breast lesion less than 10 mm in diameter detected by 2-view mammography performed as a result of self-referral for screening (133), breast symptoms (164), or follow-up for breast disease (52). All lesions greater than 11 mm were excluded. 250 had benign and 99 (28%) had malignant lesions. 37 of 99 (37%) patients with malignancy were aged 49 or under. 133 patients requested screening, 33 (25%) had carcinoma of whom 11 (33%) were aged 49 or less. 164 patients presented with breast symptoms; 47 (29%) had cancer and 15 (32%) of these were aged 49 or less. 52 patients requested follow up for breast diseases including previous cancers, 19 (37%) had carcinoma of which 11 were 49 years or less (58%). 223 had microcalcifications, of which 68 (31%) were positive for cancer, and 126 had no microcalcification, of which 31 (25%) patients had cancer. The specific spiculate radiological lesions yielded 16 carcinomas in 31 cases (52%). Microcalcification was seen in 110 patients under 49 with 27 (25%) carcinomas detected. Microcalcification was a significant diagnostic criterion in the patients aged 49 or less, accounting for 27/37 (73%) patients. Dutal carcinoma in situ accounted for 18/37 (49%) in patients aged 49 or less, and 19/62 (31%) in patients over 50 years. Mammography should not be withheld from patients who are seeking screening, have symptoms, or who wish to be followed up, irrespective of age.

Crush syndrome following unconsciousness: need for urgent orthopaedic referral

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Effect of cardiopulmonary bypass on gastrointestinal perfusion and function

Gastric mucosal tonometry was used to determine the adequacy of gastrointestinal perfusion in 10 patients undergoing elective myocardial revascularization. Patients were prospectively randomized to receive either pulsatile or nonpulsatile flow during cardiopulmonary bypass. All patients showed a reduction in gastric mucosal perfusion during bypass, manifested by a reduction in the gastric mucosal pH, which occurred independently of variations in the arterial pH. In the group of patients receiving nonpulsatile flow, this reduction was significantly greater (p < 0.05). Cardiopulmonary bypass using nonpulsatile flow is associated with the development of a gastric mucosal acidosis, which may have implications for the development of postoperative complications.