CCP Podcast 064: Papers of the Month May 2017

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Another look at some of the recent Papers of the Month to catch our eyes. This time Gavin (@DentonGavin) and I look at two papers, one focussing on the use of Ultrasound with central lines and the other a study in African children and the possibility of heart failure being caused by fluids.

Myocardial and haemodynamic responses to two fluid regimens in African children with severe malnutrition and hypovolaemic shock (AFRIM study)

The WHO guidelines recommend that fluids are reserved only for those presenting with advanced shock and the use of low volume hypotonic solutions- the malnourished heart is at risk of biventricular failure so unable to respond to isotonic fluid challenges.

In two previous trials, there had been no evidence of heart failure caused by fluids and Ringers Lactate had been shown to be superior in shock reversal and with a lower mortality compared to 5% dextrose.

Previously in the FEAST trial, there had been increased mortality in the fluid bolus arm. However, children with gastroenteritis were excluded from the study. It has also been shown in Kenyan children with severe malnutrition that 50% presented with severe diarrhoea and there was an overall 20% mortality rate amongst this group.

Aim of Study

To examine myocardial function and hemodynamic response to fluid resus in hypovolaemic shock due to gastroenteritis.

Inclusion

• Children 6-60 months
• Clinical signs of severe malnutrition (using standard scoring system)
• Acute Hypovolaemic diarrhoea
• Signs of severe dehydration
• Shock
  • 2 of 3
    • CRT equal to or greater than 3
    • Temperature gradient
    • rapid and weak pulse volume.

Study Procedure

2 groups- bolus group (1) and rehydration group (2).

Group one received a bolus of 15ml/kg of RL over one hour which was then repeated once if shock signs persist. They were then given half strength Darrows/5% Dextrose at 4ml/kg/hr.

Group 2 received 10ml/kg/hr of RL over five hours.

Both groups were switched to oral hydration once they could tolerate it. Blood was given if their Hb was less than 5 or the shock was unresponsive to crystalloid at 10ml/kg over 3 hours.

Blood was taken including TNI and BNP as were vitals, echo and ECG.

A total of 20 patients recruited- 11 in group 1 and 9 in group 2.

Interventions

Group 1- 9/11 (82%) received 2 boluses and 4 received blood.

Group 2- 3/9 received 10ml/kg/hr RL followed by blood transfusion. Four patients substantially improved after 3 hours of intravenous rehydration and two died whilst receiving rehydration.

Results and Discussion

Neither clinical signs nor echo indicated evidence of fluid overload leading to adverse outcome when using boluses.

WHO recommends hypotonic solutions given slowly to prevent heart failure and sodium overload.

Major risk is those with the Kwashiorkor phenotype:

• Deficiency in dietary protein.
• Characterised by oedema, enlarged fatty liver and distended abdomen.

There was no evidence of gross myocardial dysfunction. Trop I levels was low in both groups- therefore not supporting the hypothesis that perturbations of cardiac function are secondary to heart failure.

In the majority of patients, myocardial and haemodynamic functional response to fluid administration led to initial improvement in the stroke volume index.

High SVRI observed in both groups- this reduced briefly after fluid admin but then returned to supranormal levels and they had persistently high levels of BNP- pointing towards heart failure. This is not supported in this study as being the mechanism.

Neither baseline measurements, nor haemodynamic response to fluid resuscitation supports the contention of compromised function indicative of heart failure overloading secondary to isotonic IV fluid or rehydration in African children with severe malnutrition.

Ultrasound as a Screening Tool for Central Venous Catheter Positioning and Exclusion of Pneumothorax. Critical Care Medicine 2017. Amir R, Knio ZO, Mahmood F, et al.

Clinical Question

In patients requiring central venous catheter placement, does the use of ultrasound compared with chest X-ray, confirm catheter position and identify pneumothorax?

Design.

Single centre study in the United States of America.

Non-inferiority study.

Prospective observational, non-randomised.

It’s really a validation study.

132 patients were required for a 90% power to detect a 20% difference in success rates.

Setting

Central line insertions in the intensive care unit or the theatre environment.

Population

Adult patients requiring central venous catheter placement in the jugular or subclavian vein.

Inclusion criteria:

Patients received the insertion as part of operating room, surgical or trauma care.

Exclusion criteria:

Patients where adequate ultrasound views could not be obtained due to oedema, obesity, abdominal or thoracic wounds, intra-cardiac catheters or wires.
Intervention:

All lines were inserted under ultrasound guidance, including needle visualisation and confirmation of the guide wire in the target vein. Wire position was then confirmed in the superior venacava-right atrial junction using a sub-costal or four chamber view with transthoracic echo before insertions of the catheter. Catheter tip position was then confirmed using the same views and looking for a swirl sign after rapid injection of agitated saline. Ultrasound assessment for pneumothorax used M-mode and the absences/presence of the sea-shore sign to exclude pneumothorax.

Control:

All patients then received a chest X-ray following insertion and the ultrasound based position confirmation.

Outcome

Primary outcome:

Difference in success rates in confirmation of position. ??? difficult to decipher what this means.

137 patients studied, adequate cardiac views were attained in 124 cases, in 98% of these cases, cardiac ultrasound was able to confirm the catheter tip position. There was a 1.7% absolute difference between cardiac echo and chest X-ray in ability to confirm catheter tip position.

Both X-ray and ultrasound ruled out pneumothorax in 124 cases where both tests were applied.
Authors’ Conclusions

Ultrasound, in the majority of patients, except where inadequate echo views are obtained can replace the use of chest X-ray in the confirmation of catheter position. The presence of lung sliding on ultrasound can reliably replace the use of chest X-ray to rule out pneumothorax.

Strengths

Lung ultrasound and cardiac echo skills are not universal in critical care, limiting generalisability.

In this study wire and catheter confirmation were done with ultrasound during the insertion process. Is this practical with a single sterile operator?

Weaknesses

The lack of control group may have obscured the possible complication rate where ultrasound is not used to confirm catheter tip position.

The absence of any pneumothoracies in these insertions makes it impossible to assert the sensitivity of ultrasound for detecting pneumothoracies.

There were very few subclavian catheter insertions.

The Bottom Line.

The use of ultrasound can be used to replace the chest X-ray to confirm catheter tip position and rule out pneumothoraces for the insertion of central venous catheters.

URL link http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=28422778&retmode=ref&cmd=prlinks

DOI: 10.1097/CCM.0000000000002451

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