Where can I find this paper?

 

Where can I find this paper?

http://www.ncbi.nlm.nih.gov/pubmed/23426248

What is this paper about (what is the research question)?

Can we use bedside ultrasound measurement of IVC diameter as a proxy for fluid status (as determined by CVP measurement) in children?

Summary of the Paper

Design: prospective observational study

Objective: to compare bedside US assessment of volume status with CVP measurement in critically ill paediatric patients

Outcomes: correlation of US assessment of volume depletion with CVP assessment

Test of interest: beside US measurement of IVC diameter and calculation of IVC/aorta ratio, defining dehydration as “collapsability index of 50% or greater and an IVC/Ao ratio of 0.8 or less.” Diameter measured in subxiphoid sagittal and subxiphoid transverse views.

Reference Standard: invasive CVP measurement by digital transduction at distal port of previously sited CVC

Participants: convenience sample of patients aged <21y admitted to the Paediatric Critical Care Unit (Intensive Care) at a single centre between July 2010 and June 2011

• Inclusions: patients requiring invasive haemodynamic monitoring
• Exclusions: patients in whom US measurement of IVC could not be performed due to technical limitations

Results: 

72 eligible patients of whom 51 enrolled to the study. Sagittal view was obtained in 100%, transverse view in 84% of subjects.

Correlation of collapsibility index and CVP: -0.23 (P=0.11)

Correlation of IVC/Ao ratio and CVP: -0.19 (P=0.22)

Authors’  conclusions

We did not find a correlation between the 1-point measurement of either the collapsibility index or the IVC/Ao ratio and CVP measurements in critically ill paediatric patients.

On the study design

This paper is an interesting one; the use of ultrasound to determine the need for and response to fluid resuscitation is controversial in adult patients, so it is not surprising to see that the uncertainty about clinical usefulness translates to paediatric practice. In addition, assessment of hydration/dehydration in children is notoriously difficult and the search for objective measures which reflect clinical endpoints is clearly relevant.

This paper is an observational study which means that there was no change made to the patient’s care in response to the measured data. The population may or may not reflect our ED patients; by definition, patients already admitted to PICU (at least in the UK) have usually a) been unwell for some time and b) had some level of resuscitation – so it is difficult to know how their volume status might be affected by preceding use of fluid boluses (particularly if hypertonic solutions were used). That said, the vast majority of critically ill paediatric patients in the ED do not have central access amenable to CVP monitoring and there are obvious issues with designing a study which necessitates insertion of CVCs which might not be necessary (unethical) or are going to be inserted in the ED (impractical – numbers likely to be very small). The fact that the recruitment was a convenience sample also reflects the otherwise small numbers and unpredictable nature of critical illness in children and while a more robust sampling method would be preferable, convenience sampling is often seen in studies where a single investigator has a particular skill set necessary for the collection of study data.

A bigger problem is the use of CVP as a marker of haemodynamic status; although it is frequently measured in the ICU and PICU, it is notoriously poor at reflecting volume status as a single measure and demonstrating clinically relevant response to fluid bolus when measured continuously, as raised in this review paper from 2008. So the study is comparing a questionable method of determining fluid status with one which is equally questionable – not exactly a great starting point. Perhaps a longer term outcome – such as fluid balance over the subsequent 24-48h, urine output, need for fluid boluses – might have given a clearer and more reliable picture.

There was also little consistency between the patients; CVC measurement occurred at a variety of anatomical sites and there was no correction or account taken for other variables which might affect CVC readings (such as abdominal surgery or positive pressure ventilation).

What were the results and what does this mean?

This is a great opportunity to revise correlation!

There’s a great wikipedia article on Spearman’s rank correlation coefficient here, but essentially correlation measures the level of interdependence between two non-parametric variables. It tells us whether as one variable increases, the other increases, and the strength of this relationship.

In the paper, both correlation co-efficients quoted in the results section were negative, suggesting that as CVP increases the IVC variable (IVC/Ao ratio or collapsibility index) decreases, and vice versa. The small numbers (-0.11 and -0.23) imply a near random relationship (remember, the nearer the correlation coefficient is to zero the less related the two variables appear to be; the nearer to 1 or -1, the stronger the relationship and the more predictive one variable is of the other). The performance characteristics (sensitivity, specificity, NPV and PPV) for both US-calculated variables were poor.

However, there are very small numbers here; of the 52 children included, only 21 actually had a CVP <8mmHg (the cutoff used by the authors to determine intravascular volume depletion). In any study where such a small number of patient have the target condition we have to wonder whether different patterns might be seen in a larger sample – the probability of a type II error is high.

What can we take from this paper into clinical practice?

So, assessment of paediatric intravascular volume status remains a mystery for now. Previously published studies have suggested that IVC/Ao ratio is lower in children who are otherwise clinically assessed as being dehydrated and that the value rises following fluid boluses, but we cannot be sure from this current paper that US measurement reflects CVP. Should we use ultrasound to assess intravascular status? This paper finds it a poor proxy for CVP – which again is a poor proxy for volume status. So on the basis of this study – no, but there is clearly more work to be done here.

More questions to ask

• Do serial IVC measurements reflect response to fluid bolus in a clinically meaningful way?
• Would we see better correlation using a single CVC line site, or excluding “less central” central lines such as femoral CVC?
• Should we be aggressively fluid-resuscitating children anyway?! – see this interesting FOAM paper on new insights from the FEAST trial

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Where can I find this paper?

http://www.ncbi.nlm.nih.gov/pubmed/23375510

What is this paper about (what is the research question)?

In children with blunt torso trauma, which clinical features predict low risk of associated intra-abdominal trauma requiring intervention (IAI) and potentially obviate need for abdominal computerised tomography (CT)?

Summary of the Paper

Design: Multi-centre prospective observational chart study

Objective:  To derive a clinical prediction rule to identify children with blunt torso who are at a very low risk for intra-abdominal injury requiring acute intervention.

Outcome: Radiographically or surgically apparent intra-abdominal injury necessitating acute intervention.

Population:  Children with blunt torso (thorax and abdomen) trauma evaluated in the emergency department of one of the 20 participating centres from May 2007 – January 2011

Inclusion:

• Decreased level of consciousness in association with blunt torso trauma (but not isolated head injury)
• Blunt traumatic event with paralysis and/or multiple non-adjacent long bone fractures
• Blunt torso trauma due to: Motor vehicle crash: high speed (>40mph), ejection or rollover, Automobile versus pedestrian/ bicycle: automobile moderate to high speed (>5mph), Falls >20ft, Crush injury to torso, Physical assault involving the abdomen
• Physician concern for abdominal trauma resulting in any of the following diagnostic or screening tests: Abdominal CT or ultrasound (FAST), Laboratory testing to screen for intra-abdominal injury, Chest or pelvic radiography

Exclusion:

• Injury occurring >24hrs before presentation
• Penetrating trauma
• Pre-existing neurologic disorders impeding reliable examination
• Known pregnancy
• Transfer from another hospital with prior abdominal CT or diagnostic peritoneal lavage

Results:

12044 children were enrolled (81% of those eligible) with a median age of 11.1 years. 5514 patients underwent abdominal CT scan. 761 patients were identified with intra-abdominal injuries of which 203 underwent acute intervention.  The derived prediction rule identified 7 variables with good interrater reliability.

Combining the variables in a prediction rule gave the following test characteristics for the primary outcome

Prediction rule sensitivity:            97.0%    (95% CI 93.7-98.9)

Prediction rule specificity:            42.5%    (95% CI 41.6-43.4)

Negative predictive value:           99.9%    (95% CI 99.7-1.0)

Positive predictive value:             2.8%      (95% CI 2.4-3.2)

Negative Likelihood ratio:            0.07        (95% CI 0.03-0.15)

23% of all the CTs performed represented patients in the very low risk category and with use of the clinical decision tree would therefore have been potentially avoidable.

Authors’ Conclusions:

A prediction rule consisting of 7 patient history and physical examination findings, and without laboratory or ultrasonographic information, identifies children with blunt torso trauma who are at very low risk for intra-abdominal injury undergoing acute intervention. These findings require external validation before implementation.

On the study design

The study techniques all adhered to accepted best practice for the derivation of a prediction rule.  The authors selected variables for potential inclusion into the decision making rule based on previous literature and biological/physiological plausibility.

The group used variables based on history and examination which would be immediately accessible to all ensuring generalisability across departments and excluding FAST scan and laboratory investigations which may not be universally available.

Standardised data collection of patient history and examination findings were collected prior to CT scanning and then CTs performed at the discretion of the treating physicians according to local protocols.

15 initial variables were proposed, all with at least moderate interrater agreement and then binary recursive partitioning was used to develop a clinical decision rule consisting of seven of these.

The agreed outcome of intra-abdominal injury requiring intervention was then identified by immediate follow-up and then later telephone contact/ mail contact and review of hospital and morgue data to account for cases which may have been initially missed and they achieved impressive follow-up rates.

They were also rigorous in comparing those eligible but not enrolled with those enrolled and no enrollment bias was identified.

What were the results and what does this mean?

Whilst the recruitment into the study was good with large initial numbers (12044 patients) the final outcome of those with intra-abdominal injury requiring acute intervention (203 patients) resulted in inevitability small numbers and it is from this group that the decision rule has been derived essentially.

The final decision rule shows high sensitivity but low specificity in keeping with the intended use as a “rule-out” tool.

23% of all the CTs performed represented patients in the very low risk category and with use of the clinical decision tree would therefore have been potentially avoidable. 

There were 6 children however, who were not identified by the clinical prediction rule but required acute intervention for their intra-abdominal injuries. The authors suggest that these children all had clinical features such as haematuria or alcohol intoxication which are likely to have been recognised as an additional risk factor by the treating physician and therefore more caution was used in applying the decision making tool. This fits with the decision rule identifying patients with “low risk”

What can we take from this paper into clinical practice?

Reconfiguration of trauma services within the UK gives opportunities for improved pathways of care; optimizing management whilst minimizing unnecessary investigations and interventions particularly in light of the longstanding concerns about radiation risk from CT scanning in the paediatric population.

Research such as this is therefore highly relevant and yet often difficult to achieve due to relatively the low numbers of paediatric trauma cases so this large study has the potential to make a significant contribution to our future practice.

Caution must be taken though in assuming the impact would be comparable within our population groups and healthcare systems in the UK, where it is possible that there is a different baseline threshold for investigation.

This study also included young people up to the age of 18 which is not true of most paediatric units in the UK and may represent a subgroup with different mechanisms of injury and trauma patterns.

At present this is a derivation study and prior to implementation requires validation in an external setting, allowing for assessment of performance accuracy and refinement.

As the authors correctly identify there is potential risk that the tool may be over-utilised as a “rule-in” decision maker and therefore mean more CTs are undertaken rather than less. In the study population this could have meant a 33% increase in scans

There is likely to be added value from using this tool in assessing risk but not in isolation –  rather in combination with investigations as appropriate and most importantly clinical acumen.

More questions to ask

• How can the use of FAST scans and laboratory results be incorporated into the use of this tool?
• Will the surgical teams involved in these cases be happy to reduce the imaging or will it defer imaging to the inpatient rather than ED setting?
• What is the most important outcome?  Is it identifying those injuries which require intervention, or knowing about all injuries?

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