Evaluating the Impact of Cardiopulmonary Bypass Priming Fluids on Bleeding After Pediatric Cardiac Surgery: A Systematic Review and Meta-Analysis

OBJECTIVES

Cardiopulmonary bypass (CPB) predisposes young children to coagulopathy. The authors evaluated possible effects of CPB priming fluids on perioperative bleeding in pediatric cardiac surgery.

DESIGN

Meta-analysis and systematic review of previously published studies.

SETTING

Each study was conducted in a surgical center or intensive care unit.

PARTICIPANTS

Studies investigating patients <18 years without underlying hematologic disorders were included.

INTERVENTIONS

The authors evaluated randomized controlled trials (RCTs) published between 1980 and 2020 on MEDLINE, EMBASE, PubMed, and CENTRAL databases. The primary outcome was postoperative bleeding; secondary endpoints included blood product transfusion, mortality, and safety.

MEASUREMENTS AND MAIN RESULTS

Twenty eligible RCTs were analyzed, with a total of 1,550 patients and a median of 66 patients per study (range 20-200). The most frequently assessed intervention was adding fresh frozen plasma (FFP) to the prime (8/20), followed by albumin (5/20), artificial colloids (5/20), and blood-based priming solutions (3/20). Ten studies with 771 patients evaluated blood loss at 24 hours in mL/kg and were included in a meta-analysis. Most of them investigated the addition of FFP to the priming fluid (7/10). No significant difference was found between intervention and control groups, with a mean difference of -0.13 (-2.61 to 2.34), p = 0.92, I² = 69%. Further study endpoints were described but their reporting was too heterogeneous to be quantitatively analyzed.

CONCLUSIONS

This systematic review of current evidence did not show an effect of different CPB priming solutions on 24-hour blood loss. The analysis was limited by heterogeneity within the dataset regarding population, type of intervention, dosing, and the chosen comparator, compromising any conclusions.

Pressure recording analytical method for measuring cardiac output in critically ill children: a validation study

BACKGROUND

Pressure recording analytical method (PRAM) is a novel, arterial pulse contour-based method for measuring cardiac output (CO). Validation studies of PRAM in children are few, and have not assessed both absolute accuracy and ability to track changes in CO across a broad case mix. We aimed to compare CO as measured by PRAM with that using a transpulmonary dilution method in a cohort of critically ill children.

METHODS

Forty-eight, mechanically ventilated children with a median (inter-quartile) weight of 10.7 (5.5-15) kg with arterial and central venous catheters in situ were studied. CO was measured simultaneously using PRAM and the comparator method, transpulmonary ultrasound dilution (UD). Measurements were repeated before and after therapeutic interventions that were intended to augment CO (e.g. fluid bolus).

RESULTS

In total, 210 paired measurements were compared. The mean (sd) CO was 1.9 (1.2) litre min(-1) with UD when compared with 1.92 (0.5) litre min(-1) using PRAM. The mean bias was 0.02 litre min(-1) with wide limits of agreement: ± 2.21 litre min(-1), giving a percentage error of 116%. The concordance between PRAM and UD for measuring changes in CO was also poor, with only 37% of measurements falling within the pre-defined polar plot limits of ±30°.

CONCLUSIONS

There is an unacceptably poor agreement between UD and PRAM. We do not recommend the use of PRAM for measuring CO in critically ill children with the current algorithm.

An economic comparison of hospital-based and community-based glaucoma clinics

INTRODUCTION

We have established one model for community care of glaucoma clinic patients. Community optometrists received training and accreditation in glaucoma care. Once qualified they alternated between running half day glaucoma clinics in their own High Street practices and assisting in a hospital-based glaucoma clinic session. This paper reports the cost of this model.

METHODS

Micro-costing was undertaken for the hospital clinic. A consensus meeting was held to agree costs for community clinics involving all optometrists in the project along with representatives of the multiple chain optometry practices who had participated. Costs to patients both indirect and direct were calculated following structured interviews of 197 patients attending hospital clinics and 194 attending community clinics.

RESULTS

The estimated cost per patient attendance to the hospital clinic was £63.91 and the estimated cost per attendance to the community clinic was £145.62. For patients the combined direct and indirect cost to attend the hospital clinic was £6.15 and the cost to attend the community clinic £5.91.

DISCUSSION

The principal reason for the higher cost in the community clinic was higher overhead costs in the community. Re-referral to the hospital system only occurred for 9% of patients and was not a large contribution to the increased cost. Time requested to next appointment was similar for the two clinics. Sensitivity analysis shows a strong effect of increasing patients seen per clinic. It would, however, require 25 patients to be seen per clinician per day in the community in order to make the costs comparable.

The future of glaucoma clinics

The number of patients seen with glaucoma related pathologies is predicted to increase significantly over the next few years as a result of an ageing population, increased optometric screening, and raised public awareness. In addition, the recent glaucoma literature proposes more aggressive management of ocular hypertension, open angle glaucoma, and narrow angle pathologies. This will overburden many glaucoma services and demands a reappraisal of current management strategies. Using a database of patients compiled from their tertiary referral glaucoma service as an example, the authors discuss the current controversies relating to each glaucoma subtype, encompassing issues relating to disease prognosis, efficacy of treatment, and resource management. They also suggest a range of strategies aimed at streamlining glaucoma clinics. Examples include shared care schemes, multidisciplinary teams, clinic guidelines/protocols, and alteration of clinic review times. The predicted effect of such schemes on clinic workloads is discussed, together with any existing validation.

Should parents accompany critically ill children during inter-hospital transport?

BACKGROUND

Parental accompaniment during inter-hospital transportation (retrieval) of critically ill children is not commonplace in the United Kingdom.

METHODS

A three month pilot of parental accompaniment was undertaken in 2002 (143 retrievals), after which time the policy was adopted as standard practice. A follow up audit was performed in 2004 (136 retrievals).

RESULTS

Findings were remarkably consistent between the two periods. Staff perceived little or no added stress during the majority of transfers (96% in 2002, 98% in 2004), and felt able to perform medical interventions without hindrance (98% in 2002, 100% in 2004). There was good agreement between medical and nursing staff regarding perception of stress and ability to perform interventions (phi statistic 0.57 to 1.00). Adverse events occurred during 11 (3.9%) retrievals; six of these involved a parent exclusively. Stress tended to be associated with adverse events or parental behaviour rather than disease acuity. Staff vetoed the offer of accompaniment on 11 occasions, for a variety of reasons. The majority of parents found the experience safe, beneficial, and perceived a reduction in stress as a result. These data may inform other retrieval services who are considering adopting a similar policy.

A pilot study of a system for grading of drainage blebs after glaucoma surgery

PURPOSE

To develop and evaluate a novel bleb grading scheme for clinical and photographic evaluation.

METHOD

A system for grading bleb photographs using widely applicable parameters was designed, and reference color photographs printed. A prospective masked agreement study was undertaken comparing slit lamp examination with mono and stereo photographs; 36 eyes of 28 patients with previous glaucoma surgery were graded according to defined parameters on a 1 to 10 scale clinically at the slit lamp by four ophthalmologists and two optometrists. Standardized stereo and mono photographs of the blebs were taken on the same day. The photographs were graded at least one week later in a masked fashion by the same observers, with grading of mono and stereo photographs also separated by one week. Analysis was performed to determine the variability and agreement between slit lamp results and photographic results, and to identify the presence of systematic bias.

RESULTS

High levels of agreement were found between slit lamp and both stereo and mono photographs for vascularity indices, bleb wall thickness, and bleb elevation. Lower levels of agreement were found for the relative components of demarcated versus diffuse areas of the bleb, and for the total width of the bleb. The interquartile range for the median difference between slit lamp and photograph grading was -1.0 to 1.0 for all criteria except diffuse component (-2.0 to 2.0), and the median difference for all scores was 0.0. The median interobserver difference for all criteria was 0.0; the quartile range for all scores was between -0.5 and 1.0 except for diffuse component and width assessments whose quartiles fell in the -1.75 to 1.0 range. Examiners agreed with photographic grading within +/- 1 in more than 80% of gradings for vascularity and bleb height, within +/- 1 in more than 75% of gradings for bleb wall thickness, within +/- 2 in 61% of bleb width assessments, and +/- 2 in 59% of diffuse component.

CONCLUSION

This bleb grading system is reproducible clinically and photographically. High levels of agreement between scores for photographs versus slit lamp examination were found for most categories, with good interobserver agreement for both photograph and slit lamp grading. Further refinement of scoring and reference photographs is required for optimization, especially for grading of bleb morphology.

The cost-effectiveness of technology transfer using telemedicine

The high burden of disease in developing countries often makes it difficult for health systems in these countries to attain the same level of specialist skills as industrialized countries. Technology transfer is one way to improve specialist skills whilst at the same time reducing the burden of disease. This paper describes the use of teleophthalmology, a form of telemedicine, as a mode of technology transfer between the United Kingdom and South Africa. As the burden of eye disease in South Africa is high, the country cannot afford the level of ophthalmic specialization achieved in the UK. The paper estimates the cost-effectiveness of the technology transfer project in terms of a cost per Disability Adjusted Life Year (DALY) averted. We found the technology transfer project to be cost-effective in reducing the burden of eye disease, and that practitioners in South Africa also learned novel procedures that could help future patients and improve cost-effectiveness. Technology transfer using telemedicine is a cost-effective method that richer countries can employ to aid capacity building in the health care systems of poorer countries.

Glaucoma case finding: a cluster-randomised intervention trial

PURPOSE

To assess the effect of an intervention comprising training in optic disc assessment, explicit referral criteria and ophthalmologist feedback on referred patients, on the number of optometrist referrals for suspected glaucoma seen at a referral site and the positive predictive value of those referrals.

METHODS

Optometric practices routinely referring to the Ealing Hospital Eye Clinic were randomly divided into two groups taking into consideration those practices, which shared an optometrist (a cluster) and the number of optometrist days worked per week. One group of practices acted as controls, while the other practices were invited to receive the intervention. Data on 397 new patients referred and presenting to Ealing Hospital with suspected glaucoma were collected over a 20-month period. The data on patients who had failed to attend their appointment were collected over 7 months of this period. The number of referrals seen, the positive predictive value of those referrals, and the attendance rate were calculated. Optometrist's opinions of the intervention were assessed qualitatively. Data relating to optometrist compliance with the intervention were also collected.

RESULTS

The number of glaucoma referrals presenting to Ealing Hospital from the intervention practices was almost double that from the control practices (210 vs 119). When cluster randomisation, the number of optometrist days per cluster and the number of assessed referrals in the preintervention period are taken into consideration, it is estimated that the intervention is associated with a 52% increase in the number of referrals reaching Ealing Hospital. However, the design effect resulting from the cluster randomisation was unexpectedly high (of the order of 13-14)and so the confidence intervals around the estimate of 52% are very wide (95% c.i. 35% decrease to 253% increase, P = 0.34). There was no evidence of an association between optometrist compliance with the intervention and the number of referrals seen at Ealing Hospital. The positive predictive value (PPV)of referrals was similar for the intervention(0.49 (95% c.i. 0.42, 0.55)) and control groups(0.46 (95% c.i. 0.33, 0.60)). Optometrist opinions of the intervention were largely favourable. All expressed a willingness to participate in future programmes.

CONCLUSION

A large difference in the number of referrals between the practice groups was observed. Since the PPV of referral was unchanged, the potential impact of the intervention in terms of numbers of new cases of glaucoma detected in the community is substantial. However, because of its large design effect, this trial does not provide conclusive evidence of an impact of the intervention on referral numbers. A considerably larger trial will be required to produce conclusive evidence of an effect.

Severe and unrecognised: pertussis in UK infants

AIMS

To diagnose pertussis using culture, polymerase chain reaction, and serology, in children admitted to intensive care units (PICUs) and some paediatric wards in London, and in their household contacts to determine the source of infection.

METHODS

Infants <5 months old admitted to London PICUs between 1998 and 2000 with respiratory failure, apnoea and/or bradycardia, or acute life threatening episodes (ALTE), and children <15 years admitted to paediatric wards at St Mary's and St George's Hospitals between 1999 and 2000 with lower respiratory tract infection, apnoea, or ALTE were studied.

RESULTS

Sixty seven per cent of eligible children (142/212) were recruited; 23% (33/142) had pertussis, 19.8% (25/126) on the PICU and 50% (8/16) on wards. Two died. Only 4% (6/142) were culture positive. Pertussis was clinically suspected on admission in 28% of infants (7/25) on the PICU and 75% (6/8) on the wards. Infants on PICU with pertussis coughed for longer, had apnoeas and whooped more often, and a higher lymphocyte count than infants without pertussis. Pertussis and respiratory syncytial virus (RSV) co-infection was frequent (11/33, 33%). Pertussis was confirmed in 22/33 (67%) of those who were first to become ill in the family. For 14/33 children the source of infection was a parent; for 9/33 the source of pertussis was an older fully vaccinated child in the household.

CONCLUSIONS

Severe pertussis is under diagnosed. An RSV diagnosis does not exclude pertussis. Future changes to the UK vaccination programme should aim to reduce pertussis transmission to young infants by their parents and older siblings.

Sensitivity and specificity of two glaucoma case-finding strategies for optometrists

Current best practice for primary open-angle glaucoma case-finding comprises history-taking, disc examination, intraocular pressure measurement and suprathreshold visual field analysis (SVFA). An alternative case-finding technique was formulated replacing SVFA with computerised quantitative disc assessment, using the Heidelberg retinal tomograph II (HRT II). Each approach was adopted by four optometrists who screened 29 POAG and 37 normal patients. Average sensitivities and specificities were similar in the two groups [sensitivity 71% (SVFA) vs 69% (HRT II); specificity 94% both groups]. Our inclusion of pre-perimetric glaucoma cases limited the sensitivity of the optometrists in this study. There was evidence to suggest that the optometrists tended to miss early changes at the optic disc such as disc haemorrhage, nerve fibre layer defects and subtle neuroretinal thinning.

Hypoalbuminaemia in critically ill children: incidence, prognosis, and influence on the anion gap

AIMS

Hypoalbuminaemia has significance in adult critical illness as an independent predictor of mortality. In addition, the anion gap is predominantly due to the negative charge of albumin, thus hypoalbuminaemia may lead to its underestimation. We examine this phenomenon in critically ill children, documenting the incidence, early evolution, and prognosis of hypoalbuminaemia (<33 g/l), and quantify its influence on the anion gap.

METHODS

Prospective descriptive study of 134 critically ill children in the paediatric intensive care unit (ICU). Paired arterial blood samples were taken at ICU admission and 24 hours later, from which blood gases, electrolytes, and albumin were measured. The anion gap (including potassium) was calculated and then corrected for albumin using Figge's formula.

RESULTS

The incidence of admission hypoalbuminaemia was 57%, increasing to 76% at 24 hours. Neither admission hypoalbuminaemia, nor extreme hypoalbuminaemia (<20 g/l) predicted mortality; however, there was an association with increased median ICU stay (4.9 v 3.6 days). After correction for albumin the incidence of a raised anion gap (>18 mEq/l) increased from 28% to 44% in all samples (n = 263); this discrepancy was more pronounced in the 103 samples with metabolic acidosis (38% v 73%). Correction produced an average increase in the anion gap of 2.7 mEq/l (mean bias), with limits of agreement of +/-3.7 mEq/l.

CONCLUSION

Admission hypoalbuminaemia is common in critical illness, but is not an independent predictor of mortality. However, failure to correct the anion gap for albumin may underestimate the true anion gap, producing error in the interpretation of acid-base abnormalities. This may have treatment implications.

Incidence of hyponatraemia and hyponatraemic seizures in severe respiratory syncytial virus bronchiolitis

AIM

To document the incidence and early evolution of hyponatraemia (serum sodium < 136 mmol l(-1)) associated with respiratory syncytial virus (RSV) bronchiolitis in infants requiring intensive care.

METHODS

In a retrospective review over two winter seasons, 130 infants were admitted with confirmed RSV infection, of whom 39 were excluded because of either pre-existing risk factors for hyponatraemia: diuretic therapy (n = 14), cardiac disease (n = 10), renal disease (n = 2) or lack of admission sodium data (n = 13).

RESULTS

The incidence of admission hyponatraemia in the remaining infants (median age 6 wk) was 33% (30/91), with 11% (10/91) exhibiting a serum sodium less than 130 mmol l(-1) . Hyponatraemic and normonatraemic infants were of a similar age (median 6 vs 7 wk, p = 0.82). With fluid restriction and diuretic therapy, the incidence of hyponatraemia at 48 h had decreased to 3.3%, odds ratio 0.07 (95% confidence interval 0.02-0.24, p < 0.001). Four infants (4%) suffered hyponatraemic seizures at admission (sodium 114-123 mmol l(-1)); three had received hypotonic intravenous fluids at 100-150 ml kg(-1) d(-1) before referral to intensive care. All four were managed successfully with hypertonic (3%) saline, followed by fluid restriction, resulting in immediate termination of seizure activity and normalization of serum sodium values over 48 h.

CONCLUSION

Hyponatraemia is common among infants with RSV bronchiolitis presenting to intensive care. Neurological complications may occur and fluid therapy in vulnerable infants should be tailored to reduce this risk.

Monitoring cardiac function in intensive care

Systolic cardiac function results from the interaction of four interdependent factors: heart rate, preload, contractility, and afterload. Heart rate can be quantified easily at the bedside, while preload estimation has traditionally relied on invasive pressure measurements, both central venous and pulmonary artery wedge. These have significant clinical limitations; however, adult literature has highlighted the superiority of several novel preload measures. Measurement of contractility and afterload is difficult; thus in clinical practice the bedside assessment of cardiac function is represented by cardiac output. A variety of techniques are now available for cardiac output measurement in the paediatric patient. This review summarises cardiac function and cardiac output measurement in terms of methodology, interpretation, and their contribution to the concepts of oxygen delivery and consumption in the critically ill child.

A comparison of three scoring systems for mortality risk among retrieved intensive care patients

AIMS

To assess the impact of two paediatric intensive care unit retrieval teams on the performance of three mortality risk scoring systems: pre-ICU PRISM, PIM, and PRISM II.

METHODS

A total of 928 critically ill children retrieved for intensive care from district general hospitals in the south east of England (crude mortality 7.8%) were studied.

RESULTS

Risk stratification was similar between the two retrieval teams for scores utilising data primarily prior to ICU admission (pre-ICU PRISM, PIM), despite differences in case mix. The fewer variables required for calculation of PIM resulted in complete data collection in 88% of patients, compared to pre-ICU PRISM (24%) and PRISM II (60%). Overall, all scoring systems discriminated well between survival and non-survival (area under receiver operating characteristic curve 0.83-0.87), with no differences between the two hospitals. There was a tendency towards better discrimination in all scores for children compared to infants and neonates, and a poor discrimination for respiratory disease using pre-ICU PRISM and PRISM II but not PIM. All showed suboptimal calibration, primarily as a consequence of mortality over prediction among the medium (10-30%) mortality risk bands.

CONCLUSIONS

PIM appears to offer advantages over the other two scores in terms of being less affected by the retrieval process and easier to collect. Recalibration of all scoring systems is needed.

Changes in intraocular pressure following diagnostic mydriasis with cyclopentolate 1%

PURPOSE

To assess the effect of diagnostic mydriasis with 1% cyclopentolate on the intraocular pressure (IOP) of patients attending glaucoma, medical retina and cataract clinics.

METHODS

Levels of agreement for IOP assessment were determined and 95% of repeated readings found to be within +/-2 mmHg. The IOP of 83 cataract, 87 medical retinal and 100 glaucoma patients was measured with Goldmann applanation tonometry before and 45 min after dilatation with 1% cyclopentolate. Those showing a substantial (>10 mmHg) increase in IOP underwent gonioscopy to determine if their angles remained open and were medically treated to lower their IOP.

RESULTS

An approximately normal distribution of change in IOP following dilatation was seen in all three groups (mean change 0.4 mmHg (95% CI 0.1-0.8)). The proportion of patients with a rise of 5 mmHg or more in the right eye was 7% (95% CI 4-10%). Logistic regression using all right eyes, looking at age, sex, diagnosis, ethnicity, ocular medication, iris colour and lens status (phakic/pseudophakic/aphakic) as risk factors for a rise of IOP of 5 mmHg or more did not reveal any significant contribution. Correlation between results obtained for right and left eyes in the glaucoma group was lower (0.43) than for the other groups (0.66 and 0.72), but the extent to which the direction of change in one eye predicted that in the other was shown to be high. Two glaucoma patients with open angles developed a clinically important (>10 mmHg) sustained rise in IOP requiring treatment.

CONCLUSIONS

Individual variability in the effects of cyclopentolate on aqueous dynamics may account for the approximately normal distribution of IOP seen following dilatation in all three groups. This variation was in excess of that due to observation error alone. It is recommended that the IOP be rechecked after dilation in glaucoma patients with significantly damaged optic nerve heads. In medical retina and cataract patients, sustained clinically important rises in intraocular pressure following dilation seem rarer.

High-frequency oscillation in adolescents

BACKGROUND

High-frequency oscillation (HFO) is a widely used lung-protective ventilatory strategy in paediatric and neonatal acute lung injury. Its safe and effective use has been hindered by inadequate recruitment of the lung during oscillation and, until recently, the lack of an adequately powered oscillator for use in adult practice.

METHODS

We present data from three adolescents with severe acute respiratory distress syndrome (ARDS) who received HFO with the Sensormedics 3100B oscillator after failure of conventional mechanical ventilation. A manual recruitment manoeuvre was used in all patients prior to mechanical ventilation (conventional or HFO) and following tracheal suctioning or disconnection from the ventilator. Changes in oxygenation index were used to assess therapy.

RESULTS

All patients showed at least a 25% reduction in oxygenation index within 2 h of HFO, with return to conventional ventilation after 27-65 h.

CONCLUSIONS

We found HFO, in conjunction with manual recruitment and prone positioning, to be a well-tolerated mode of ventilation in adolescents with ARDS and who were unresponsive to conventional ventilation. Given this success we hope to renew interest in this method for adults with ARDS, together with concurrent use of manual recruitment.

Utilization and practical aspects of tele-ophthalmology between South Africa and the UK

A tele-ophthalmology service was established between a regional hospital in South Africa and a specialist eye hospital in the UK. The aim of the service was to provide secondary specialist advice in the diagnosis and treatment of difficult ophthalmology cases in South Africa. Over 12 months, the South African medical officers saw 16,458 ophthalmology patients and would have liked a second opinion in 5.7% of these cases. Case discussions conducted by videoconferencing at 384 kbit/s were carried out in 0.5% of cases. No significant connection problems were experienced during the 12-month study period. On 4% of occasions, the case discussions were conducted at a bandwidth of 256 kbit/s, but this did not affect the quality of the still images. The South African medical officers valued the educational benefits gained from the case discussions with the UK specialists.

Subspecialty adnexal ophthalmological examination using telemedicine

We studied the clinical outcome of examination of a group of patients with adnexal (eyelid and orbit) conditions. Seventeen patients with adnexal problems were assessed by an ophthalmologist at a distance using telemedicine, and then subsequently by an ophthalmologist in a face-to-face consultation. Measurements such as palpebral aperture, levator muscle function and eyelid skin crease position were recorded. The clinical outcomes from both consultations were recorded independently by the consultants and then compared. The study showed that certain adnexal conditions, such as congenital and involutional ptosis, could be accurately assessed using telemedicine, but that other conditions, such as socket problems in patients who had a previous enucleation or those with non-specific ocular pain with less clear-cut features, were better assessed in a face-to-face consultation. Overall, teleconsultations appeared to be suitable for the assessment of uncomplicated ptosis but not for less well defined conditions. Other factors, such as family dynamics and language problems, also limited the usefulness of the technique.

Soluble Fas may be a proinflammatory marker after cardiopulmonary bypass in children

OBJECTIVES

Ischemia-reperfusion injury after cardiopulmonary bypass is known to provoke an inflammatory response, which can be attenuated with steroid pretreatment. Cardiopulmonary bypass is also known to stimulate apoptosis. Induction of the cellular apoptotic cascade occurs via interaction between two membrane receptors: Fas and Fas ligand. Both molecules also exist in soluble forms, whose significance remains undetermined; however, both may have a proinflammatory role. We aimed to document the temporal profile of soluble Fas and soluble Fas ligand after cardiopulmonary bypass and to investigate whether steroid pretreatment alters this response.

METHODS

The study was of a non-randomized, non-blinded, prospective nature. Twenty-seven infants were monitored prospectively, of whom 13 received dexamethasone at induction of anesthesia. Soluble Fas, soluble Fas ligand, and interleukin 6 were measured from induction of anesthesia until 24 hours after admission to the intensive care unit. Data on clinical and laboratory variables were also collected at the same time intervals.

RESULTS

As expected, dexamethasone pretreatment attenuated interleukin 6 release and the clinical systemic inflammatory response after bypass. Soluble Fas showed a remarkably similar profile to interleukin 6, in terms of temporal release and attenuation with steroids. There was also a correlation between maximum soluble Fas and markers of capillary leak (colloid requirement and drain loss). Conversely, soluble Fas ligand release was unchanged by cardiopulmonary bypass and steroid administration. However, patients with higher soluble Fas ligand levels exhibited a more dramatic drop and delayed recovery in monocyte count, consistent with the role of this molecule in apoptosis.

CONCLUSIONS

Release of soluble Fas and soluble Fas ligand follows a markedly different temporal profile after cardiopulmonary bypass. The similarity between soluble Fas and interleukin 6, together with the attenuation of both with steroids, may suggest a role for soluble Fas as a proinflammatory marker.

What optic disc parameters are most accurately assessed using the direct ophthalmoscope?

PURPOSE

It has been suggested that over-reliance on the cup-to-disc ratio is a major factor in the misinterpretation of the optic disc. In spite of this optometrist assessment of the optic disc tends to be restricted to measurement of the cup-to-disc ratio and cup depth only. Would interpretation of the disc improve if optometrists were to evaluate other parameters? The aim of this study was to evaluate the accuracy of optometrist assessment of nine parameters of the optic nerve head using direct ophthalmoscopy.

METHODS

Eight optometrists evaluated nine parameters of the optic nerve head (vertical disc diameter, vertical cup-to-disc ratio, neuroretinal rim configuration, cup shape, neuroretinal rim colour, vessel path, presence/ absence of haemorrhage, extent and location of peripapillary atrophy and classification of health status of the disc) in 50 eyes of 50 patients using direct ophthalmoscopy. Intensive training in optic nerve head assessment was given prior to assessing the patients. Criteria for evaluation were discussed. The 'gold standard' reference was the classification of the parameters by a consultant ophthalmologist with a special interest in glaucoma.

RESULTS

Interobserver agreement for vertical cup-to-disc ratio was almost perfect (mean weighted kappa 0.84). Agreement for neuroretinal rim configuration, cup shape, haemorrhage and final classification of the disc was good (mean kappa 0.62-0.67). There was moderate agreement for vessel configuration (mean kappa 0.53). For assessment of peripapillary atrophy, disc size and neuroretinal rim colour, agreement was fair (mean kappa 0.22-0.34).

CONCLUSIONS

Accuracy of assessment was greatest for vertical cup-to-disc ratio, neuroretinal rim configuration and cup shape. Improved agreement has been demonstrated for the final classification of the disc compared with previous reports. The combination of training and assessment of additional disc parameters appears to improve interpretation of the optic nerve head by optometrists.

The value of the chloride: sodium ratio in differentiating the aetiology of metabolic acidosis

OBJECTIVE

Stewart's physicochemical approach to acid-base balance defines the aetiology of a metabolic acidosis by quantifying anions of tissue acids (TA), which consist of unmeasured anions (UMA) and/or lactate. We hypothesised that an increase in TA during metabolic acidosis would lead to a compensatory fall in the plasma chloride (Cl) relative to sodium (Cl:Na ratio) in order to preserve electro-neutrality. Thus, the Cl:Na ratio could be used as a simple alternative to the anion gap in identifying raised TA.

PATIENTS

Two hundred and eighty two consecutive patients who were admitted to our Paediatric Intensive Care were enrolled in the study.

INTERVENTIONS

We obtained 540 samples (admission n = 282, 24 h n = 258) for analysis of blood chemistry, lactate and quantification of TA and UMA. Samples were subgrouped into those with metabolic acidosis (standard bicarbonate < 22 mmol/l) either with or without increased UMA (> 3 mEq/l).

MEASUREMENTS AND RESULTS

Metabolic acidosis occurred in 46% of samples, of which 52.3% (120/230) had increased UMA. The dominant component of TA was UMA rather than lactate, and these two components did not always rise in tandem. Our hypothesis of relative hypochloraemia was supported by a lower Cl:Na ratio (P < 0.0001) but not a lower absolute Cl (P = 0.5) in the acidotic subgroup with raised UMA, and by the inverse relationship between TA and the Cl:Na ratio. (coefficient of determination (r2) = 0.37, P < 0.0001). The best discriminator for the presence of raised TA was the albumin-corrected anion gap (AGcorr), however, this could not track changes in TA with clinical accuracy. The Cl:Na ratio discriminated reasonably well, a ratio of < 0.75 identified TA (positive predictive value (PPV) 88%) with a likelihood ratio (LR) similar to the AG (7.8 vs7.4). Conversely, a high ratio (> 0.79) excluded TA (PPV 81%, LR 4.5). Base deficit (BD) and lactate performed poorly.

CONCLUSION

In metabolic acidosis due to TA, plasma Cl concentration decreases relative to sodium. The Cl:Na ratio is a simple alternative to the AG for detecting TA in this setting.