Quantitative futility in emergency laparotomy: an exploration of early-postoperative death in the National Emergency Laparotomy Audit.

BACKGROUND: Quantitative futility is an appraisal of the risk of failure of a treatment. For those who do not survive, a laparotomy has provided negligible therapeutic benefit and may represent a missed opportunity for palliation. The aim of this study was to define a timeframe for quantitative futility in emergency laparotomy and investigate predictors of futility using the National Emergency Laparotomy Audit (NELA) database. METHODS: A two-stage methodology was used; stage one defined a timeframe for futility using an online survey and steering group discussion; stage two applied this definition to patients enrolled in NELA December 2013-December 2020 for analysis. Futility was defined as all-cause mortality within 3 days of emergency laparotomy. Baseline characteristics of this group were compared to all others. Multilevel logistic regression was carried out with potentially clinically important predictors defined a priori. RESULTS: Quantitative futility occurred in 4% of patients (7442/180,987). Median age was 74 years (range 65-81 years). Median NELA risk score was 32.4% vs. 3.8% in the surviving cohort (p < 0.001). Early mortality patients more frequently presented with sepsis (p < 0.001). Significant predictors of futility included age, arterial lactate and cardiorespiratory co-morbidity. Frailty was associated with a 38% increased risk of early mortality (95% CI 1.22-1.55). Surgery for intestinal ischaemia was associated with a two times greater chance of futile surgery (OR 2.67; 95% CI 2.50-2.85). CONCLUSIONS: Quantitative futility after emergency laparotomy is associated with quantifiable risk factors available to decision-makers preoperatively. These findings should be incorporated qualitatively by the multidisciplinary team into shared decision-making discussions with extremely high-risk patients.

Randomised, placebo controlled trial of nebulised furosemide for breathlessness in patients with cancer.

BACKGROUND: Breathlessness is a common and difficult symptom to treat in patients with cancer. Case reports suggest that nebulised furosemide can relieve breathlessness in such patients but few data are available. METHOD: Patients with primary or secondary lung cancer and a Dyspnoea Exertion Scale score of >or=3 were recruited. Following familiarisation, patients received either nebulised furosemide 40 mg or nebulised 0.9% saline under double blind conditions or no treatment, in random order on 3 consecutive days. Patients undertook number reading and arm exercise tests to assess breathlessness and its impact, and were asked to report subjective benefit and any preference between nebulised treatments. RESULTS: 15 patients took part. There were no differences between furosemide, saline and no treatment in the outcomes of the number reading test (eg, mean number read per breath was 6.7, 6.4 and 6.7, respectively) or arm exercise test (eg, mean Borg score at maximum equivalent workload was 2.3, 2.5 and 2.7, respectively). No adverse effects were reported, although there was a small fall in forced expiratory volume in 1 s and forced vital capacity following saline. Six patients considered that their breathlessness improved with nebulised treatment, three preferring saline, one furosemide and two reporting they were of equal benefit. CONCLUSIONS: Our findings do not support a beneficial effect from nebulised furosemide in patients with cancer related breathlessness. Listed on the National Research Register (N0170118249) and the UK Clinical Research Network Portfolio Database (1428).

Frisby Davis distance stereoacuity values in visually normal children.

AIMS: To establish the range of normal distance stereoacuity in young children using the Frisby Davis distance stereo test (FD2). METHODS: Children passing preschool vision screening assessments underwent measurement of distance stereoacuity with the FD2 using a standard testing protocol. RESULTS: 59 visually normal children aged between 36 months and 68 months were recruited to this study. All 59 were able to understand the test requirements and were examined with the FD2 stereo test. Four (6.8%) had no measurable stereoacuity; 13 (24%) had stereoacuity measurable only at a 3 metre testing distance (mean 92.3 seconds of arc; SD 52.6). These children were significantly younger than the remaining 42 (76%) who demonstrated a stereoacuity response at a 6 metre testing distance (mean 29.6 seconds of arc; SD 13.1, p=0.008). CONCLUSION: The FD2 stereo test enables the measurement of distance stereoacuity in young children. There appears to be a maturational effect with distance stereoacuity improving between 36 months and 68 months. The data on age related normal values will provide a baseline from which to compare outcomes in clinical populations.

Potential for drug interactions involving cytochrome P450 in patients attending palliative day care centres: a multicentre audit.

AIM: To determine the potential for drug interactions involving cytochrome P450 (CYP) in patients receiving palliative day care. METHODS: Drugs used by patients attending four specialist palliative day care centres were reviewed to identify combinations that could result in a pharmacokinetic interaction via any of the five main human forms of CYP. RESULTS: Of 160 patients, 145 (91%) were prescribed at least one drug that was a substrate, inhibitor or inducer of one of the five main CYP isoforms. Twenty-four drug combinations, involving 34 patients, could have given rise to a clinically important interaction. CONCLUSIONS: Prescribers should be aware that in this group of patients, one in five are at risk of a clinically important CYP-mediated drug interaction.

Depth cue reliance in surgeons and medical students.

BACKGROUND: Depth perception is reduced in endoscopic surgery, although little is known about the effect this has on surgical performance. METHODS: To assess the role of depth cues, 45 subjects completed tests of depth cue reliance. Surgical skill was assessed using the Minimally Invasive Surgical Trainer-Virtual Reality, a previously validated laparoscopic simulator. RESULTS: We could demonstrate no difference in cue reliance for three depth cues--namely stereo, texture, and outline--between surgeons and medical students. Greater dominance on stereo for medical students was a positive finding and a negative finding for the surgeons when correlated with surgical performance. CONCLUSIONS: We suggest that surgeons learn to adapt to the nonstereo environment in MIS, and this is the first study to show evidence of this phenomenon. This difference in stereo reliance is a reflection of the experience that surgeons have with laparoscopy compared with medical students, who have none.

Can tonic accommodation predict surgical performance?

BACKGROUND: Pilots undergo many visual tests for both selection and assessment, and we know that there are many similarities between pilots and surgeons. Hence, it would not be unreasonable to bring similar visual tests into surgery. Tonic accommodation (TA) is a stable parameter that is adopted by the eye in the absence of any stimulation. Over recent years, surgery has undergone change from traditional open surgery to minimally invasive procedures, bringing many advantages. However, not every surgeon has the ability to perform under conditions where the operative field is represented on a flat monitor. METHOD: We determined the TA values in medical students and then correlated this with their performance on a virtual reality surgical simulator. RESULTS: We found that TA values predicted the number of errors made with the dominant hand, accounting for 27% of the variance. CONCLUSION: The data suggest that TA may play a role in the individual differences that are noted when surgeons perform laparoscopic surgery. Further studies are needed to evaluate the exact role of TA in surgical performance.

Differential modes of alaryngeal communication and long-term voice outcomes following pharyngolaryngectomy and laryngectomy.

Patterns of vocal rehabilitation for 37 pharyngolaryngectomy patients and 55 total laryngectomy patients over a 5-year period were compared. An electrolarynx (EL) was introduced as the initial communication mode immediately after surgery for 98% of patients, with 30% of pharyngolaryngectomy and 74% of laryngectomy patients subsequently developing tracheoesophageal speech (TES) as their primary mode of communication. Follow-up with 14 of 37 pharyngolaryngectomy patients and 36 of 55 laryngectomy patients was conducted 1-6 years following surgery and revealed that 90% of the pharyngolaryngectomy patients maintained the use of TES in the long term compared to 69% of the laryngectomy group. Long-term outcomes relating to communication disability and handicap did not differ significantly between the two surgical groups, however the laryngectomy patients had significantly higher levels of wellbeing. Across the whole group of patients, statistical comparison revealed that patients using TES had significantly lower levels of disability, handicap and distress than EL users. Considering that lower levels of disability, handicap and distress are associated with TES, and the data supports that suitably selected patients can maintain functional TES in the long term, increased application of this form of communication rehabilitation should be encouraged where viable for the pharyngolaryngectomy population.

Effect of signal length on the performance of independent component analysis when extracting the lambda wave.

The aim of the study was to investigate the effect of signal length on the performance of a signal source separation method, independent component analysis (ICA), when extracting the visual evoked potential (EP) lambda wave from saccade-related electro-encephalogram (EEG) waveforms. A method was devised that enabled the effective length of the recorded EEG traces to be increased prior to processing by ICA. This involved abutting EEG traces from an appropriate number of successive trials (a trial was a set of waveforms recorded from 64 electrode locations in a study investigating saccade performance). ICA was applied to the saccade-related EEG and electro-oculogram (EOG) waveforms recorded from the electrode locations. One spatial and five temporal features of the lambda wave were monitored to assess the performance of ICA applied to both abutted and non-abutted waveforms. ICA applied to abutted trials managed to extract all six features across all seven subjects included in the study. This was not the case when ICA was applied to the non-abutted trials. It was quantitatively demonstrated that the process of abutting EEG waveforms was useful for ICA preprocessing when extracting lambda waves.

Swallowing outcomes following laryngectomy and pharyngolaryngectomy.

OBJECTIVES: To determine the incidence of dysphagia (defined as the inability to manage a diet of normal consistencies) at hospital discharge and beyond 1 year postsurgery and examine the impact of persistent dysphagia on levels of disability, handicap, and well-being in patients. DESIGN: Retrospective review and patient contact. SETTING: Adult acute care tertiary hospital. PATIENTS: The study group, consecutively sampled from January 1993 to December 1997, comprised 55 patients who underwent total laryngectomy and 37 patients who underwent pharyngolaryngectomy with free jejunal reconstruction. Follow-up with 36 of 55 laryngectomy and 14 of 37 pharyngolaryngectomy patients was conducted 1 to 6 years postsurgery. MAIN OUTCOME MEASURES: Number of days until the resumption of oral intake; swallowing complications prior to and following discharge; types of diets managed at discharge and follow-up; and ratings of disability, handicap, and distress levels related to swallowing. RESULTS: Fifty four (98%) of the laryngectomy and 37 (100%) of the pharyngolaryngectomy patients experienced dysphagia at discharge. By approximately 3 years postsurgery, 21 (58%) of the laryngectomy and 7 (50%) of the pharyngolaryngectomy patients managed a normal diet. Pharyngolaryngectomy patients experienced increased duration of nasogastric feeding, time to resume oral intake, and incidence of early complications affecting swallowing. Patients experiencing long-term dysphagia identified significantly increased levels of disability, handicap, and distress. Patients without dysphagia also experienced slight levels of handicap and distress resulting from taste changes and increased durations required to complete meals of normal consistency. CONCLUSIONS: The true incidence of patients experiencing a compromise in swallowing following surgery has been underestimated. The significant impact of impaired swallowing on a patient's level of perceived disability, handicap, and distress highlights the importance of providing optimal management of this negative consequence of surgery to maximize the patient's quality of life.

Brain stem compression by a giant vertebrobasilar aneurysm mimicking seronegative myasthenia.

A patient is described with a vertebrobasilar aneurysm who was erroneously thought to have myasthenia gravis on the basis of the clinical presentation and investigations, which were interpreted as supportive of a disorder of the neuromuscular junction. Despite the correct diagnosis being made at a late stage the patient made a full recovery after radiological intervention.

Exploring sequential stereopsis for co-planarity tasks.

We used the sequential stereopsis paradigm and apparatus described by Enright (Vision Research, 36, (1996) 307-312). The observer's task was to set targets to equidistance in Experiments 1-3, and to make them co-planar in Experiment 4. However, it is argued that in all experiments observers exploited a co-planarity setting strategy. Sequential stereopsis produced good performance throughout in terms of low disparity thresholds when head position was varied by rotations around three axes: vertical (azimuth condition); horizontal (elevation); and midline (tilt). It also produced good performance when the targets were shifted in position so that they both lay on one side of the median plane of the head. These results cannot be accounted for by Enright's isovergence hypothesis unless it is extended to incorporate other information about eye positions. Performance was better but not greatly so in control simultaneous stereopsis conditions, nor did it deteriorate much when the observer's view was restricted solely to the targets by removing visibility of the room in which the apparatus was located. Target settings were typically located on a concave arc centred on the median plane. This effect was quantitatively modelled using disparity correction for a relief task of co-planarity (Gârding, Porrill, Mayhew, & Frisby. Vision Research, 35 (1995) 703-722). This modelling indicated over-estimations of c.10-20 cm in fixation distance for target distances in the range 71.5-112.5 cm.

Instability of torsion during smooth asymmetric vergence.

Several categories of torsional eye movements obey Listing's law; however, systematic deviations from this law occur during vergence. Two kinematic models attempt to incorporate these deviations, both of which are supported by experimental evidence; however, they lead to different torsion predictions. These discrepancies have been explained in terms of experimental procedures, but it now seems likely from several recent studies that individual differences in torsion patterns may also be important. This study therefore examines the variation of torsion during a smooth asymmetric vergence task in which a fixation target was moved along the line-of-sight of the right eye at 15 degrees elevation; each of five subjects observed five trials of both inward and outward target motion, repeated in two sessions several weeks apart. There were no significant group differences in left or right eye torsion between trials or sessions, suggesting that monocular torsion patterns were relatively stable over time. When examined more closely, however, the torsion patterns shown by some individuals did vary for inward versus outward target motion. Hence, monocular torsion was idiosyncratic and depended on the direction in which fixation was changing (convergence or divergence). In a binocular analysis, cycloversion varied dramatically between subjects and depended on the direction of target motion; however, this was not the case for cyclovergence. In summary, cyclovergence is relatively stable and depends on where the eyes are looking, whereas cycloversion (and hence monocular torsion) is relatively unstable and depends on how they came to be in that particular horizontal and vertical orientation. These findings help to explain the controversy surrounding the torsional behaviour of the human eye during vergence.

An orientation anisotropy in the effects of scaling vertical disparities.

Gårding et al. (Vis Res 1995;35:703-722) proposed a two-stage theory of stereopsis. The first uses horizontal disparities for relief computations after they have been subjected to a process called disparity correction that utilises vertical disparities. The second stage, termed disparity normalisation, is concerned with computing metric representations from the output of stage one. It uses vertical disparities to a much lesser extent, if at all, for small field stimuli. We report two psychophysical experiments that tested whether human vision implements this two-stage theory. They tested the prediction that scaling vertical disparities to simulate different viewing distances to the fixation point should affect the perceived amplitudes of vertically but not horizontally oriented ridges. The first used elliptical half-cylinders and the 'apparently circular cylinder' judgement task of Johnston (Vis Res 1991;31:1351-1360). The second experiment used parabolic ridges and the amplitude judgement task of Buckley and Frisby (Vis Res 1993;33:919-934). Both studies broadly confirmed the anisotropy prediction by finding that large scalings of vertical disparities simulating near distances had a strong effect on the perceived amplitudes of the vertically oriented stimuli but little effect on the horizontal ones. When distances > 25 cm were simulated there were no significant differential effects and various methodological reasons are offered for this departure from expectations.

Robust and optimal use of information in stereo vision.

Differences between the left and right eye's views of the world carry information about three-dimensional scene structure and about the position of the eyes in the head. The contemporary Bayesian approach to perception implies that human performance in using this source of eye-position information can be analysed most usefully by comparison with the performance of a statistically optimal observer. Here we argue that the comparison observer should also be statistically robust, and we find that this requirement leads to qualitatively new behaviours. For example, when presented with a class of stereoscopic stimuli containing inconsistent information about eccentricity of gaze, estimates of this gaze parameter recorded from one robust ideal observer bifurcate at a critical value of stimulus inconsistency. We report an experiment in which human observers also show this phenomenon and we use the experimentally determined critical value to estimate the vertical acuity of the visual system. The Bayesian analysis also provides a highly reliable and biologically plausible algorithm that can recover eye positions even before the classic stereo-correspondence problem is solved, that is, before deciding which features in the left and right images are to be matched.

The 'ecological' probability density function for linear optic flow: implications for neurophysiology.

A theoretical analysis of the recovery of shape from optic flow highlights the importance of the deformation components; however, pure deforming stimuli elicit few responses from flow-sensitive neurons in the medial superior temporal (MST) area of the cerebral cortex. This finding has prompted the conclusion that MST cells are not involved in shape recovery. However, this conclusion may be unjustified in view of the emerging consensus that MST cells perform nonlinear pattern matching, rather than linear projection as implicitly assumed in many neurophysiological studies. Artificial neural models suggest that the input probability density function (PDF) is crucial in determining the distribution of responses shown by pattern-matching cells. This paper therefore describes a Monte-Carlo study of the joint PDF for linear optic-flow components produced by ego-motion in a simulated planar environment. The recent search for deformation-selective cells in MST is then used to illustrate the importance of the input PDF in determining cell characteristics. The results are consistent with the finding that MST cells exhibit a continuum of responses to translation, rotation, and divergence. In addition, there are negative correlations between the deformation and conformal components of optic flow. Consequently, if cells responsible for shape analysis are present in the MST area, they should respond best to combinations of deformation with other first-order flow components, rather than to the pure stimuli used in previous neurophysiological studies.

The variation of torsion with vergence and elevation.

Two recently developed kinematic models of human eye movements predict systematic departures from Listing's law which are associated with changes in vergence. This vergence-dependent torsion t is proportional to elevation e and vergence v, that is t = kev/2. The proposed value for k is either 1 (Van Rijn, L. J., & Van den Berg, A. V. (1993). Vision Research, 33, 691-708) or 1/2 (Minken, A. W. H., Gielen, C. C. A. M., & Van Gisbergen, J. A. M. (1995). Vision Research, 35, 93-102). One implication of both models is that an eye with a constant fixation direction should exhibit systematic torsional variation during movements of the other eye. This paper therefore examines the torsion produced by moving a fixation target inwards and outwards along the line-of-sight of the right eye at five different viewing elevations (0, +/- 15 and +/- 30 degrees). In a monocular analysis, each eye generally showed intorsion during convergence at positive elevation angles, whereas extorsion occurred at negative elevations; the opposite was true during divergence. However, the torsion response was visibly different between the five subjects, and depended on the direction of target motion. In a binocular analysis, cycloversion (mean of left and right eye torsion) varied dramatically both between subjects and between convergence and divergence; however, cyclovergence (torsional difference) was much less variable. Least-squares methods were used to estimate the constant k from monocular torsion, yielding values between 0.2 and 1.0; however, corresponding estimates based on cyclovergence were all close to 1/2. These findings support suggestions that a binocular control system couples the three-dimensional movements of the eyes, and that an existing model of monocular torsion should be generalised to the binocular case.

Vergence control across saccades in dyslexic adults.

Many aspects of vision have been investigated in developmental dyslexia. Some research suggests deficits in vergence control (e.g. Buzzelli, 1991, Optom. Vision Sci. 68, 842-846), although ability to control vergence across saccades has not yet been investigated. We have explored this question indirectly using Enright's (1996 Vision Res. 36, 307-312.) sequential stereopsis task. The task requires observers to set two adjacent targets (whose textures cannot be resolved simultaneously if either is fixated) to appear equi-distant. Enright has argued that sequential stereopsis stereoacuity thresholds offer an indication of vergence control across saccades. We report two experiments using a total of 17 dyslexic and 18 control adults. Performance was measured on a sequential stereopsis task and an ordinary 'simultaneous' stereopsis task. No significant differences between groups were found. However, whereas practice of the sequential task lowered control group thresholds on the simultaneous task, for the dyslexic group it significantly raised thresholds, suggesting that visual fatigue is especially important in investigations of visual functions in dyslexia. Although the small samples used limit conclusions at this stage, the main sequential stereopsis results suggest that, if Enright is correct, dyslexic adults can show normal vergence control across saccades.

The role of 3-D surface slope in a lightness/brightness effect.

Adelson has shown how two patches in a 5 by 5 array of grey patches can be perceived to consist of different shades, depending on whether they are represented at a 3-D horizontal or vertical ridge. Adelson interprets the illusion in terms of the orientation of the patches with respect to the inferred illuminant. We investigated: (1) the illusion in the vertical and horizontal stimuli and added a flat (ridgeless) control stimulus; (2) stimuli of varying ridge amplitudes to examine the effect more fully. 3-D renderings of real surfaces were modelled with computer graphics and displayed to observers who used a mouse to alter the brightness of a square to match patches indicated in the stimuli. Five observers were used for the vertical, flat and horizontal stimuli, while a larger group (n = 20) was used for an independent design when varying ridge amplitudes. A significant effect in the flat surface demonstrates that patches lying in the same plane can have their brightness altered without changes in their orientation. When the surface was seen as a 3-D ridge the size of the effect was a function of 3-D slope of the surface. By measuring each patch independently we have shown that the effect changes the brightness of the two patches to differing degrees. We offer an explanation of this based on a proposed qualitative shading rule for identifying reflectance and illumination edges.