Ergonomic problems associated with laparoscopic surgery

BACKGROUND

The Society of American Gastrointestinal Endoscopic Surgeons (SAGES) Task Force on Ergonomics conducted a subjective and objective assessment of ergonomic problems associated with laparoscopic instrument use. The goal was to assess the prevalence, causes, and consequences of operational difficulties associated with the use of laparoscopic instruments.

METHODS

A questionnaire was distributed asking respondents to rate the frequency with which they experienced pain, stiffness, or numbness in several body areas after laparoscopic operations. An ergonomics station was assembled to quantify forearm and thumb muscle workload. Processed electromyogram (EMG) signals were acquired from 27 volunteer surgeon subjects while they completed simulated surgical tasks using a hemostat and an Ethicon laparoscopic grasper, with the aid of an endoscopic trainer and video monitoring system.

RESULTS

Of 149 surgeons responding to the questionnaire, 8% to 12% reported frequent pain in the neck and upper extremities associated with laparoscopic surgery. The ergonomics station demonstrated that the peak and total muscle effort of forearm and thumb muscles were significantly greater (p < 0.01) when the grasping task was performed using the laparoscopic instrument rather than the hemostat.

CONCLUSION

These findings indicate that laparoscopic surgical technique is more taxing on the surgeon.

Further immunization and biochemical studies with a protective antigen complex from the microvillar membrane of the intestine of Haemonchus contortus

Immunization of sheep with a protective antigen complex from the intestinal cells of Haemonchus contortus in Freund's adjuvant stimulated individually variable antibody responses but still conferred significant protection against parasite infection. Correlation between antibody concentration and degree of protection was suggestive of antibody being the effector mechanism. The antigen is known as Haemonchus galactose-containing glycoprotein complex (H-gal-GP) because it binds to lectins with a specificity for N-acetyl-galactosamine. Polypeptide composition analysis by polyacrylamide gel electrophoresis indicated an apparent molecular weight of about 1000 kDa and SDS gels revealed four major polypeptides, containing between 2 and 5 disulphide linked subunits, nearly all being glycosylated. N-terminal amino acid sequence was obtained from 12 subunits, ten showing homologies with cDNAs from Haemonchus encoding either pepsin, metalloprotease or cysteine protease-like enzymes. pH optima, inhibitor and various substrate studies confirmed that the native complex possessed proteolytic activities in agreement with the sequence data. Although the cDNAs predicted water soluble enzymes, little of the complex was solubilized from worm membranes without the use of a detergent, such as Triton X-100. It is hypothesized that H-gal-GP is a gut membrane associated multiprotease complex which is involved in the digestion of the blood meal and which can be neutralized by specific antibodies with drastic consequences for the parasite.

Immunization with an affinity purified protein extract from the adult parasite protects lambs against infection with Haemonchus contortus

Young lambs were immunized with membrane protein extracts from adult Haemonchus contortus which had been enriched for cysteine protease activity using Thiol-Sepharose chromatography. The resulting extract comprised several peptides including cysteine as well as serine and metallo-protease activities although the former predominated. A limited number of the peptide components were glycosylated. Following a single challenge infection with the same parasite, vaccinated lambs had substantially reduced faecal egg outputs and final worm burdens (overall means of 77% and 47%, respectively, from three trials) compared with challenge controls. Antibody in sera from vaccinated lambs was almost exclusively bound to the surface of the parasite gut indicating that protection may be mediated by the inhibition of parasite digestion.

Cloning and characterization of glutamate dehydrogenase (GDH) from the gut of Haemonchus contortus

Vaccination of lambs with the membrane-bound (S3) thiol-Sepharose binding protein (TSBP) fraction derived from the gut of Haemonchus contortus confers significant protection against homologous challenge. The S3 TSBP peptide profile is dominated by a major protein of ca. 60 kDa which is strongly recognized by antisera from sheep demonstrably protected following immunization with S3 TSBP. In an attempt to identify this protein, sera from protected lambs were employed to screen a lambda gt11 cDNA library of the adult parasite and resulted in the isolation of numerous clones encoding a homologue of the mitochondrial enzyme, glutamate dehydrogenase (GDH). GDH enzyme activity was readily demonstrable in S3 TSBP material and immunolocalization studies showed that the enzyme was localized to the cytoplasm of the parasite's gut. Furthermore, the enzyme appeared to be developmentally regulated, with both GDH mRNA and protein expressed almost exclusively during the blood-feeding parasitic stages.

Propagating distributions up directed acyclic graphs

In a previous article, we considered game trees as graphical models. Adopting an evaluation function that returned a probability distribution over values likely to be taken at a given position, we described how to build a model of uncertainty and use it for utility-directed growth of the search tree and for deciding on a move after search was completed. In some games, such as chess and Othello, the same position can occur more than once, collapsing the game tree to a directed acyclic graph (DAG). This induces correlations among the distributions at sibling nodes. This article discusses some issues that arise in extending our algorithms to a DAG. We give a simply described algorithm for correctly propagating distributions up a game DAG, taking account of dependencies induced by the DAG structure. This algorithm is exponential time in the worst case. We prove that it is #P complete to propagate distributions up a game DAG correctly. We suggest how our exact propagation algorithm can yield a fast but inexact heuristic.

Prospects for vaccines of helminth parasites of grazing ruminants

Defined molecular vaccines for several ruminant heliminth parasites are being pursued at several different laboratories. The most fruitful sources of antigen have been oncosphere surface proteins, excretory/secretory products and integral gut membrane proteins. Nematode gut membrane proteins are unconventional in that they do not come into contact with the host immune response during infection, a feature which brings advantages as well as disadvantages. The genes encoding several of the protective antigens have been cloned, but only in the case of the oncosphere surface proteins has substantial protection been reported with recombinant versions. In addition to the problem of identifying suitable expression systems, issues such as choice of adjuvant and/or the possible use of a vaccine vector have to be solved before molecular vaccines for the economically important helminths can be launched. Of the latter, it seems that vaccines for Haemonchus and Fasciola are the brightest prospects.

Virtual ergonomic studies in endoscopic intervention

Virtual instrumentation provides a strong platform for the rapid design and prototyping of biomedical instruments. Virtual instrument software written using a block diagram approach familiar to instrument designers quickly turns a personal computer into a custom biomedical instrument. The portable VIs we have developed for ergonomic analysis of video-endoscopic surgery are quick to set up and convenient to use. We have collected a large amount of ergonomic data in a short time with these VIs because of their custom design and because we can take them to sites where there are many willing surgeon-subjects. We are preparing to use these VIs in studies of actual surgery.

IgE antibody during infection with the ovine abomasal nematode, Teladorsagia circumcincta: primary and secondary responses in serum and gastric lymph of sheep

A monoclonal antibody to ovine IgE was employed in an ELISA to investigate the IgE antibody responses in serum and gastric lymph to a primary infection of Teladorsagia circumcincta, and following challenge in previously infected sheep. During a primary response, IgE antibody to antigens derived from the infective third stage (L3) and adult (L5) worms were negligible, with low levels of IgE antibody detected in serum and lymph. In contrast, there was a pronounced IgE antibody response in 2/4 sheep to L3 antigens during 2-8 days after challenge of previously infected animals but low levels of IgE antibody to L5 antigens. This response was confirmed in a second but similar experiment, where relatively high levels of IgE antibody was detected to antigens from L3. Antibody levels were higher in lymph than in serum from the same animals, and Western blots of L3 antigen following SDS-PAGE under reducing conditions revealed several bands of MW26-96KD which reacted with the IgE antibody from gastric lymph. Immunohistochemical staining indicated that these IgE antibodies may be reacting with allergens associated with the surface cuticle of the worms.

IgE responses in the serum and gastric lymph of sheep infected with Teladorsagia circumcincta

The IgE response of naive or previously infected sheep to 50,000 infective larvae of Teladorsagia circumcincta was monitored in serum and gastric lymph using a monoclonal antibody generated to recombinant ovine IgE in a dot blot assay. In 4/5 naive sheep, lymph and serum IgE concentrations increased from days 8 and 14 after infection, respectively. In most previously infected sheep, the IgE response to challenge was more rapid, although not necessarily greater than that following a primary infection. IgE concentrations in lymph were some 4-fold higher than in serum indicating that its source was the mucosa or draining nodes.

Craniofacial electromyogram activation response: another indicator of anesthetic depth

OBJECTIVE

After finding that craniofacial EMG preceding a stimulus was a poor predictor of movement response to that stimulus, we evaluated an alternative relation between EMG and movement: the difference in anesthetic depth between the endpoint of EMG responsiveness to a stimulus and endpoint of movement responsiveness to that stimulus. We expressed this relation as the increment of isoflurane between the two endpoints.

METHODS

We measured EMG over the frontalis muscle, over the corrugator muscle, and between the Fp2 and the mastoid process as patients emerged from general anesthesia during suture closing of the surgical incision. Anesthesia was decreased by controlled washout of isoflurane while maintaining 70% N2O, and brain isoflurane concentrations ((C)isoBrain) were calculated. We studied a control group of 10 patients who received only surgical stimulation, and 30 experimental patients who intermittently received test stimuli in addition to the surgical stimulation. Patients were observed for movement responses and EMG records were evaluated for EMG activation responses. We defined an EMG activation response to be a rapid voltage increase of at least 1.0 microV RMS above baseline, with a duration of at least 30 s, in at least one of the three EMG channels. Patient responses to stimuli were classified as either an EMG activation response without a move response (EMG+), a move response without an EMG activation response (MV+), both an EMG activation response and a move response (EMG+MV+), or no response. We defined the EMG+ endpoint to be the threshold between EMG+ response and nonresponse to a stimulus, and estimated (C)isoBrain at this endpoint. We similarly defined the move endpoint and estimated the move endpoint (C)isoBrain. We then calculated the increment of (C)isoBrain at the EMG+ endpoint relative to the move endpoint.

MAIN RESULTS

For the 30 experimental patients, the initial response to a test stimulus was an EMG+ in 14 patients (47%), an EMG+MV+ in 12 patients (40%), and a MV+ in 1 patient (3%); no response occurred by the time surgery was completed in 3 patients (10%). No response occurred in 7 of the control patients (70%). Of the 14 patients with an initial EMG+ response to a test stimulus, 9 patients later had a move response. For these 9 patients, the increment of (C)isoBrain between the EMG+ endpoint and move endpoint was 0.11 +/- 0.04 vol%, (mean +/- SD).

CONCLUSIONS

Our results suggest that, given the circumstances of our study, an EMG activation response by a nonmoving patient indicates that the patient is at an anesthetic level close to that at which movement could occur. However, because the first EMG activation response may occur simultaneously with movement, the EMG activation response cannot be relied upon to always herald a move response before it occurs. Our results also suggest that EMG responsiveness to a test stimulus may be used to estimate the anesthetic depth of an individual patient.

The Virtual Instrumentation (VI) Laboratory facilitates customized on-site ergonomic analysis of minimally invasive surgery

Ergonomic studies are needed to understand and improve the visual and physical interface that minimally invasive surgery methods interpose between the surgeon and the operating field. We used the Virtual Instrumentation (VI) Laboratory of the Biomedical Engineering Program at California State University, Sacramento to develop a portable ergonomic analysis system to compare the physical workloads imposed on the surgeon by tradition open and laparoscopic surgery techniques. We used the system at a national surgery conference to measure electromyogram (EMG) activity from thumb and forearm muscles of volunteer subjects as they performed simulated surgical tasks using open and laparoscopic techniques. We found that EMG activity was significantly greater for the laparoscopic than for the open surgery technique, suggesting that the laparoscopic technique was more physically demanding. The portable ergonomic analysis VI system was quick to set up and convenient to use. We are using the rapid prototyping and modular design capabilities of the VI Lab to develop additional ergonomic analysis VI systems.

Molecular cloning and characterisation of a putative aspartate proteinase associated with a gut membrane protein complex from adult Haemonchus contortus

A cDNA was isolated from an adult Haemonchus contortus cDNA expression library the deduced amino acid sequence of which showed significant homology to mammalian pepsinogen sequences. The library was screened with antisera raised against Haemonchus galactose-containing glycoprotein complex, a gut membrane protein complex with aspartyl proteinase activity which has shown considerable potential as a protective antigen. The amino acid sequence obtained corresponded very closely in part to the N-terminal amino acid sequences of two polypetides within the complex. The enzyme was shown to be almost exclusively expressed by the blood-feeding parasite stages. The cDNA was expressed in E. coli, and antibody produced to the recombinant protein bound to the luminal surface of the gut in the adult parasite. The proteinase may play a central role in digesting the blood meal and is considered a potential sub-unit vaccine candidate.

Cloning and characterization of a microsomal aminopeptidase from the intestine of the nematode Haemonchus contortus

In order to characterise the integral membrane glycoprotein H11 from the intestinal microvilli of the nematode Haemonchus contortus, cDNA libraries prepared using mRNA from adult worms from the UK and Australia were immunoscreened with anti-H11 sera. Antibodies affinity purified on the protein expressed by insert DNA (295 bp) of a positive clone from a UK library bound specifically to H11. A longer clone (948 bp) was obtained from the Australian library by hybridisation. Using a primer based on sequence common to these, a polymerase chain reaction product of 3.3 kb was generated from cDNA from UK H. contortus. The sequences from the UK and Australian nematodes were essentially identical over the 929 bp region in which both were represented. All three cloned DNAs hybridised to mRNA of about 3.5 kb. Analysis of the deduced amino acid sequence, which showed 32% identity with those of mammalian microsomal aminopeptidases, indicated that H11 has a short N-terminal cytoplasmic tail, a single transmembrane region and a long extracellular region with putative N-linked glycosylation sites and the HEXXHXW motif characteristic of microsomal aminopeptidases. Microsomal aminopeptidase activity co-purifies with H11. It is inhibited by bestatin, phenanthroline and amastatin. The recombinant protein has been expressed in active form in insect cells.

Molecular cloning and characterisation of a developmentally regulated putative metallopeptidase present in a host protective extract of Haemonchus contortus

Antisera from lambs immunised with the Haemonchus contortus integral membrane protein complex, Haemonchus galactose-containing glycoprotein (H-gal-GP), the lambs being refractory to subsequent challenge, were used to identify several clones from an adult H. contortus lambda gt11 cDNA library. Using gene-specific oligonucleotide primers in conjunction with primers directed to a conserved nematode Spliced Leader (SL) sequence and to the polyA+ tail of mRNA, the remaining 5' and 3' sequences of one of these clones, metallopeptidase-1 (MEP1), were amplified. The 2.4 kb full-length coding sequences was subsequently amplified in a single reaction. Sequence analysis identified MEP1 as encoding a putative zinc metallopeptidase, which shared limited homology with the mammalian type II integral membrane protein neutral endopeptidase (NEP). Southern blotting indicated that MEP1 belonged to a multigene family. MEP1 was expressed in bacteria as a glutathione-S-transferase (GST) fusion protein, and a specific antiserum raised in sheep. This antiserum recognised several polypeptide components of H-gal-GP. Immunolocalisation studies showed that MEP1 encoded a protein located on the luminal surface of the nematode gut. Both MEP1 mRNA and protein are developmentally regulated with expression being limited to the blood-feeding stages of H. contortus.

Use of the virtual instrumentation laboratory for the assessment of human factors in surgery and anesthesia

There is a growing consensus that human factors issues for anesthesiologists, surgeons, and other operating room personnel require serious attention. We have established a program of collaboration between the University of California Davis Medical Center Departments of Anesthesiology and Surgery and the California State University Sacramento Biomedical Engineering Program to address ergonomic problems in anesthesiology and surgery using a Virtual Instrumentation Laboratory. A 17-workstation Virtual Instrument Laboratory using LabVIEW software on Power Macintosh platforms permits rapid prototyping of medical monitor displays as well as rapid development of data acquisition and processing circuits for physiologic data collection. The Virtual Instrument Lab has been used for three Master's thesis projects and a BME course titled Human Factors in the Design of Medical and Assistive Technology. Course projects have included: 1) The design of novel physiologic data displays for potential use in anesthesia workstations, and 2) The measurement of surface electromyographic signals and heart rate variability to investigate the physical and mental workload of performing laparoscopic surgery. The Virtual Instrument Lab allows BME students to investigate relatively complex human factors issues in anesthesiology and surgery in a short time span.

Cardiorespiratory kinetics during exercise of different muscle groups and mass in old and young

The purpose was to compare cardiorespiratory kinetics during exercise of different muscle groups (double-leg cycling vs treadmill walking and single-leg ankle plantar flexion) in old and young subjects. Oxygen uptake (VO2) during exercise transitions was measured breath by breath, and the phase 2 portion of the response was fit by a monoexponential for determination of the time constant (tau) of VO2. Two separate studies were performed: in study 1, 12 old (age 66.7 yr) and 16 young (aged 26.3 yr) subjects were compared during cycling and ankle plantar flexion exercise, and in the study 2, five old (aged 69.6 yr) and five young (24.4 yr) subjects were compared during cycling and treadmill walking. VO2 transients during square-wave cycling exercise were significantly slower in the old compared with the young groups. In contrast, VO2 kinetics did not differ between old and young groups during plantar flexion exercise. Heart rate (HR) kinetics followed the same pattern, with tau HR being significantly slower in the old vs young groups during transitions to cycling but not to plantar flexion. In study 2 tau VO2 and tau HR during on-transients to treadmill square-wave exercise were significantly slower in the old group compared with the young group, but tau VO2 was significantly faster during treadmill exercise than during cycling in the old group. The differences with aging between the modes of exercise may be related to the muscle mass involved and the circulatory demands. On the other hand, slowed VO2 kinetics with age appear to occur in a mode (cycling) in which the muscles are not accustomed to the activity, whereas in a mode of normal activity (walking) and with the muscle groups (plantar flexors) accustomed to the activity, VO2 kinetics are not slowed to the same degree with age.

A measure of association for assessing prediction accuracy that is a generalization of non-parametric ROC area

There is a need for a measure of prediction accuracy that generalizes non-parametric receiver operating characteristic (ROC) area to polytomous ordinal patient state. We describe such a measure, prediction probability PK derived from Kim's measure of association. We show that the value of PK equals the value of non-parametric ROC area for dichotomous patient state and is a meaningful generalization of non-parametric ROC area for polytomous state.

EEG Predicts movement response to surgical stimuli during general anesthesia with combinations of isoflurane, 70% N2O, and fentanyl

OBJECTIVE

Our objective was to evaluate the performance of the EEG as an indicator of anesthetic depth by measuring EEG prediction of movement response to surgical stimuli.

METHODS

While using 5 different combinations of isoflurane, 70% N2O, and fentanyl, we measured the EEG of 246 patients during pelvic laparoscopy and observed their movement responses to opening stimuli (defined as skin incision, CO2 needle insertion, or trocar insertion) and also to closing stimuli (defined as sutures during incision closure). The EEG was expressed as F95, the frequency in hertz below which resides 95% of the power in the EEG frequency spectrum. The relations between F95 and movement response were expressed as logistic regression curves. F95-response logistic regression curves, which are analogous to dose-response curves, were calculated for each of the 2 stimuli administered during each of the 5 anesthetic techniques. The prediction of patient responsiveness by F95 was tested using beta (beta), a measure of the slope of an F95-response logistic curve. The presence of shifts among the F95-response logistic curves was tested using the differences in F95 values between curves. Hypothesis tests used a level of significance of P = 0.05.

MAIN RESULTS

The slopes of the F95-response logistic regression curves showed a statistically significant ability to predict movement response to stimuli for 9 of the 10 combinations of stimuli and anesthetic techniques. We did not calculate an F95-response logistic curve for the tenth combination because it contained burst suppression, which our EEG analysis method was not designed to process. The F95-response logistic curves were shifted relative to each other, and the shifts were affected by the type of stimulus and the combination of anesthetic agents. Referenced to opening curves, the mean shift of the closing curves was +4.2 +/- 0.3 Hz (mean +/- SD). With increasing doses of fentanyl, the use of 70% N2O, or both, the curves shifted to higher values of F95; the range in shifts was 0.2 to 8.1 Hz. The slope beta values of the F95-response logistic curves and the shifts among the curves were similar to the beta values and shifts that might be expected from changes in anesthetic agent doses.

CONCLUSIONS

The EEG, expressed as F95, predicted movement response to surgical stimuli during combinations of isoflurane, 70% N2O, and fentanyl. The F95-response curves shifted upward on the frequency scale for the less intense stimuli and for anesthetic techniques using 70% N2O, fentanyl, or both. F95 prediction of movement response appeared to be related to anesthetic agent doses. Our F95-response curves may provide helpful guidelines for using F95 to titrate the administration of anesthetic agents and for assessing the depth of general anesthesia.

Prediction of movement during propofol/nitrous oxide anesthesia. Performance of concentration, electroencephalographic, pupillary, and hemodynamic indicators

BACKGROUND

Movement in response to painful stimulation is the end point classically used to assess the potency of anesthetic agents. In this study, the ability of modeled propofol effect-site concentration to predict movement in volunteers during propofol/nitrous oxide anesthesia was tested, then it was compared with the predictive abilities of the Bispectral Index and 95% spectral edge frequency of the electroencephalogram, pupillary reflex amplitude, and systolic arterial blood pressure. In addition, the relationships between simple end points of loss and recovery of consciousness, and pupillary, hemodynamic, and propofol concentration indicators were studied.

METHODS

Ten healthy volunteers were anesthetized with an infusion of propofol, which was increased in three equal steps to 21 mg.kg lean body mass-1.h-1. After loss of the ability to hold a syringe and of the eyelash reflex, 60% nitrous oxide was introduced and the trachea was intubated without the use of muscle relaxants. The propofol infusion rate then was decreased to 15.4 mg.kg lean body mass-1.h-1. Ten minutes later, tetanic electrical stimulation was administered to the thigh via needle electrodes: if movement was observed within 1 min, the propofol infusion rate was increased by 1.75 mg.kg lean body mass-1.h-1 5 min after the stimulus; if not, it was similarly decreased. This 15-min sequence was repeated until volunteers "crossed over" from movement to no movement (or vice versa) four times. The propofol infusion rate then was increased to 21 mg.kg lean body mass-1.h-1, nitrous oxide was discontinued, the trachea was extubated, and the infusion rate was decreased in five equal steps over 50 min. The times at which the eyelash reflex returned and the birth date was recalled were recorded. The electroencephalogram was monitored continuously (FP1, FP2, ref: nasion, ground: mastoid). Measurements of the pupillary response, arterial blood pressure, and heart rate were recorded during induction and awakening, just before and for 5 min after each stimulation. Arterial blood samples were obtained for propofol assay, and propofol effect-site concentrations were calculated at each time. The predictive value of indicators was compared using a new static, the prediction probability (PK).

RESULTS

Loss and return of the eyelash reflex occurred at greater propofol effect-site concentrations than either dropping the syringe or recall of the birthday. The propofol effect-site concentration (in the presence of 60% nitrous oxide) predicted to prevent movement after a supramaximal stimulus in 50% of volunteers was 1.80 micrograms/ml (95% confidence limits: 1.40-2.34 micrograms/ml). The Bispectral Index (PK = 0.86), 95% spectral edge frequency (PK = 0.81), pupillary reflex amplitude (PK = 0.74), and systolic arterial blood pressure (PK = 0.78) did not differ significantly from modeled propofol effect-site concentration (PK = 0.76) in their ability to predict movement.

CONCLUSIONS

Indicators of pharmacodynamic effect, such as the electroencephalogram, pupillary light reflex, and systolic arterial blood pressure, predict movement as well as effect-site concentration during propofol/nitrous oxide anesthesia. Loss and return of the eyelash reflex correspond to a deeper level of anesthesia than syringe-dropping or recall of the birth date.

Immunisation of sheep with an integral membrane glycoprotein complex of Haemonchus contortus and with its major polypeptide components

Sheep were immunised against Haemonchus contortus with an integral membrane glycoprotein complex isolated from the intestines of the parasite as antigen. This antigen has been termed Haemonchus galactose-containing glycoprotein complex. Sodium dodecyl sulphate (SDS) polyacrylamide gel analysis has shown that it is composed of several polypeptides but so far these have proved refractory to separation when in the native state. However when dissociated by SDS, it was found to be as efficacious as in its native state, although it was less consistently protective when tested after being dissociated and reduced. An attempt was therefore made to identify the protective ingredient(s) of the dissociated complex by testing its major polypeptides individually after they had been separated on SDS polyacrylamide gels under non-reducing conditions. Partial protection was induced by protein bands with molecular weights of about 200 kD and less than 50 kD, but none of the individual fractions tested was as efficacious as the unseparated complex, suggesting that either more than one component was essential for a consistent effect or that the separation technique had damaged crucial protective epitopes.

Measuring the performance of anesthetic depth indicators

BACKGROUND

An appropriate measure of performance is needed to identify anesthetic depth indicators that are promising for use in clinical monitoring. To avoid misleading results, the measure must take into account both desired indicator performance and the nature of available performance data. Ideally, anesthetic depth indicator value should correlate perfectly with anesthetic depth along a lighter-deeper anesthesia continuum. Experimentally, however, a candidate anesthetic depth indicator is judged against a "gold standard" indicator that provides only quantal observations of anesthetic depth. The standard anesthetic depth indicator is the patient's response to a specified stimulus. The resulting observed anesthetic depth scale may consist only of patient "response" versus "no response," or it may have multiple levels. The measurement scales for both the candidate anesthetic depth indicator and observed anesthetic depth are no more than ordinal; that is, only the relative rankings of values on these scales are meaningful.

METHODS

Criteria were established for a measure of anesthetic depth indicator performance and the performance measure that best met these criteria was found.

RESULTS

The performance measure recommended by the authors is prediction probability PK, a rescaled variant of Kim's dy.x measure of association. This performance measure shows the correlation between anesthetic depth indicator value and observed anesthetic depth, taking into account both desired performance and the limitations of the data. Prediction probability has a value of 1 when the indicator predicts observed anesthetic depth perfectly, and a value of 0.5 when the indicator predicts no better than a 50:50 chance. Prediction probability avoids the shortcomings of other measures. For example, as a nonparametric measure, PK is independent of scale units and does not require knowledge of underlying distributions or efforts to linearize or to otherwise transform scales. Furthermore, PK can be computed for any degree of coarseness or fineness of the scales for anesthetic depth indicator value and observed anesthetic depth; thus, PK fully uses the available data without imposing additional arbitrary constraints, such as the dichotomization of either scale. And finally, PK can be used to perform both grouped- and paired-data statistical comparisons of anesthetic depth indicator performance. Data for comparing depth indicators, however, must be gathered via the same response-to-stimulus test procedure and over the same distribution of anesthetic depths.

CONCLUSIONS

Prediction probability PK is an appropriate measure for evaluating and comparing the performance of anesthetic depth indicators.

Body mass indices and skeletal size in 394 Canadians aged 55-86 years

Demispan (finger web to midline) is the preferred index of stature in the study of the elderly where height is unreliable because of age-related loss or distortion. As a consequence, two alternative mass indices, Demiquet (male mass. demispan-2) and Mindex (female mass. demispan-1), have been proposed for use in the elderly, in place of body mass index calculated from height, which might be suspect. These gender-specific indices reflect the squared and linear relationship of height to mass in men and women respectively. To assess the independence of Demiquet and Mindex from stature and the reliability of demispan, height, demispan (second fingerweb to midline), and mass were recorded in a random sample of independent Canadian men (182) and women (212) aged 55-86 years. Both Demiquet and Mindex were highly correlated with mass, r = 0.81 (p = 0.001) and r = 0.96 (p = 0.001), respectively. In both gender groups these mass indices were independent of height and demispan. The demispan within- and between-observer errors were small -0.04(-0.16 to 0.08)cm and -0.09(-0.22 to 0.03) cm and the between-observer intraclass correlation estimate of reliability was 0.96 (lower-bound one-sided 95% CI 0.90). Demispan is a reliable and reproducible measure of stature in the elderly. Demiquet and Mindex are useful mass indices, independent of stature and suitable for use in the study of the elderly where the use of mass indices based on height may be questionable.

Effect of dietary protein supplementation on the development of immunity to Ostertagia circumcincta in growing lambs

Thirty four-and-a-half-month-old worm-free lambs were used to determine whether the rate of development of immunity to Ostertagia circumcincta infection in growing lambs could be influenced by the addition of a by-pass protein supplement. Sixteen lambs (groups 1 and 2) were fitted with an abomasal catheter and infected daily with 2000 O circumcincta L3 for eight weeks. Group 1 lambs received 45 g of crude protein day-1 (sodium caseinate) as a continuous infusion into the abomasum from week-1 to week 8. At week 9, groups 1 and 2, together with eight naive controls (group 3), were treated with anthelmintic and challenged one week later with 50,000 O circumcincta L3 and killed after a further 10 days. An additional six worm-free lambs provided feed intake and growth rate data. All the lambs were offered a complete ruminant ration (167 g crude protein kg-1) ad libitum. The cumulative liveweight gain of both the trickle-infected groups was less than that of the controls. The mean faecal egg counts were lower in group 1 from day 39 after infection and the mean worm burdens were significantly lower than in group 2. Total Ostertagia populations did not differ significantly between group 3 and either group 1 or 2 lambs. Early L4 stages constituted a greater percentage of the total worm population in group 1 (79.5) and group 2 (48.5) than in the challenge controls (group 3) (20.4). The trickle-infected lambs also had higher concentrations of gastric mast cell protease which correlated positively with the proportion of early L4 stages and negatively with the total worm burden. The provision of by-pass protein supplement accelerated the development of immunity to O circumcincta in these lambs.

Haemopoietic cell responses in the blood and bone marrow of sheep infected with the abomasal nematode Telodorsagia circumcincta

The generation of bone marrow and blood haemopoietic progenitor colony-forming cells (CFCs) in sheep given primary or challenge infections with the nematode parasite Telodorsagia circumcincta is described. Ten days after a primary infection, the frequency of early multipotential-CFCs, eosinophil-CFCs, macrophage-CFCs and mast cell or basophil-CFCs was greater than in controls. These frequencies then declined to pre-infection levels by day 21. Blood CFCs (mainly macrophage-CFCs and eosinophil-CFCs) also increased after infection, indicating a migration of CFCs, presumably to the site of infection. Ten days after challenge infection there was less marked myelopoiesis than in the primary infection on day 10, though both eosinophil-CFCs and mast cell or basophil-CFCs were significantly above control values. Blood CFC output (mainly macrophage-CFCs and eosinophil-CFCs) reached a peak 2-6 days after challenge, evidence of rapid recruitment to the site of infection. Telodorsagia circumcincta infection is therefore associated with an increase in myelopoiesis, particularly for the cell types characteristic of the local inflammatory response to abomasal nematodes. There was no correlation between any of the haemopoietic cell responses measured and worm burdens in individual animals after either primary or challenge infection.

Brief wakeful response to command indicates wakefulness with suppression of memory formation during surgical anesthesia

OBJECTIVE

In a previous study of patients emerging from anesthesia following surgery, we found that a brief wakeful response to command of an eye opening or single hand squeeze or count was not associated with memory formation, while the response of four hand squeezes or counts was associated with memory. We wanted to determine the anesthetic requirements for obtaining this brief wakeful response endpoint during surgery and to determine if memory occurred at this endpoint during surgical anesthesia.

METHODS

Six different combinations of isoflurane, 70% N2O, and fentanyl were administered to 326 patients undergoing pelvic laparoscopy. After insertion of the trocar, anesthesia was reduced while patients were given verbal commands, and they were observed for movement responses to surgery and to command. Patients were classified as either not arousing, arousing with a movement response to surgery, or arousing with a wakeful response to command. For the patients who aroused, we calculated the percentage of arousal responses that were wakeful responses to command. The effect of fentanyl dosage upon the percentage of arousal responses that were wakeful responses to command was determined by using a Mann-Whitney test to compare a group of patients receiving fentanyl 2 micrograms/kg or less, with a group receiving fentanyl 4 micrograms/kg. In a subset of 39 patients, the potential for memory formation was evaluated by presenting a target sound to 29 patients during a period of either no arousal, movement response to surgery, or wakeful response to command; for a control group of 10 patients, no target sound was presented. All 39 patients were tested for memory of the target sound; the results from each group receiving a target sound were compared with the results of the control group, using a Mann-Whitney test.

MAIN RESULTS

A total of 68 patients aroused with either a movement response or a wakeful response to command. Wakeful responses occurred with only 1 of 39 patients (3%) receiving fentanyl 2 micrograms/kg or less; but, wakeful responses occurred with 17 of 29 patients (59%) receiving fentanyl 4 micrograms/kg. The difference between the groups was significant at p = 0.01. None of the 68 patients had recall of intraoperative events or unpleasant dreams. None of these patients who were in the multiple-choice memory subset recalled the target sound. There were no statistically significant differences on the multiple-choice memory test between the groups presented with the target sound and the control group. Patient anecdotes suggested that some patients may have had memory of the target sound; but, memory was no more likely in patients with a brief wakeful response to command than in those who responded with a movement to surgical stimulation or those who did not have an arousal response.

CONCLUSIONS

A brief wakeful response to a command of opening the eyes or squeezing the hand was not associated with increased memory formation during surgery. A brief wakeful response to command was found during surgery when patients received fentanyl 4 micrograms/kg; but it was rarely found at fentanyl dosages of 2 micrograms/kg or less.