Criteria abstracted from The Users' Guide to Medical Literature, from the Health Information Research Unit and Clinical Epidemiology and Biostatistics, McMaster University

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Article Reviewed:

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Primary use of the venovenous approach for extracorporeal membrane oxygenation in pediatric acute respiratory failure.

Pettignano R, Fortenberry JD, Heard ML, et al.

Pediatr Crit Care Med 2003;4(3):291-8. [abstract]

Reviewed by Mahesh Sharma MD, Children's Hospital of Michigan, Detroit

Review posted December 31, 2003

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I. What is being studied?:

The study objective:

The study describes a single center's experience in primary use of venovenous cannulation for supporting pediatric acute respiratory failure with extracorporeal membrane oxygenation (ECMO). The authors also compare clinical features and complications of venovenous (VV) and venoarterial (VA) with ECMO.

The study design:

The study is a retrospective chart review.

The patients included:

All 82 patients from 2 weeks to 18 years who received ECMO support in the PICU for severe acute respiratory failure between January 1991 to April 2002.

The patients excluded:

Patients receiving ECMO for congenital heart disease or primary myocardial disease were excluded. The number of these patients is not specified.

The interventions compared:

Venovenous versus venoarterial cannulation.

The outcomes evaluated:

The duration of ECMO support, survival and selected complications (mechanical, hemorrhage, neurologic, cardiopulmonary, infections) were evaluated.

II. Are the results of the study valid?

Primary questions:

1. Was the assignment of patients to treatments randomized?

No randomization was done.

It has been noted elsewhere that prospective randomized trials of life support systems in patients near death are very difficult if not ethically impossible to conduct and mechanical life support cannot be studied in a blinded fashion (1).

2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?

Was followup complete?

Follow up data is provided for all patients until death or hospital discharge. ECMO survivors were patients who were discharged and did not die within one year of discharge from the primary disease necessitating ECMO.

Were patients analyzed in the groups to which they were randomized?

As mentioned above randomization was not done in this retrospective review. Patients were analyzed in two groups: VV and VA. One patient required conversion from VV to VA ECMO because of failure to oxygenate at 44 hours. Data from this patient's course was included in the VA group.

Secondary questions:

3. Were patients, health workers, and study personnel "blind" to treatment?

No, this was not a blinded study.

4. Were the groups similar at the start of the trial?

No. All patients selected for ECMO were considered candidates for VV cannulation unless in the attending physician's opinion significant hypotension, myocardial depression or cardiac arrest necessitated venoarterial cannulation, or if appropriate size venous cannulation could not be done. Out of 68 VV patients, 55 (~81%) required additional cannulation compared to 3 out of 14 VA patients (~21%). VA ECMO patients were younger and had worse oxygenation parameters (AaDO2 and PaO2/FiO2) at the time of cannulation than VV ECMO patients. Also there were 6 patients (all survived) with hypercarbic respiratory failure in the VV group and none in the VA group.

Of note, the use of VV cannulation increased compared to VA cannulation over the study period at this institution. After 1998, thirty consecutive patients had VV cannulation only. The details of diagnosis and oxygenation parameters of these 30 patients are not separately available in the article.

5. Aside from the experimental intervention, were the groups treated equally?

Yes. Aside from cannulation, the ECMO procedure and management was similar. Standard priming and 'hyper priming' was done for both VV and VA ECMO patients. Lung recovery was assessed by improving chest radiographs and improved gas exchange with decreased circuit flow rates. Decannulation was done when patients had acceptable mechanical ventilatory support and adequate oxygenation and ventilation on minimum bypass flow (< 50 ml.kg-1.min-1).

Other details of management are not provided (e.g., renal failure, ultrafiltration, nutrition).

III. What were the results?

1. How large was the treatment effect?

Since patients were not randomized and were not similar at the start of VV and VA ECMO, the usual measures of treatment effect (i.e., RR, ARR, RRR, and NNT) cannot be calculated. A summary of the findings are as follows.

Survival: 56 out of 68 (82%) in VV ECMO group, and 9 out of 14 (64%) in VA group.
Duration: for patients with hypoxemic respiratory failure, median of 227 hours (range106-291 hours) in VV ECMO group and a median of 247 hours (range 68-677 hours) in VA ECMO group, p = 0.6.
Complications: The VA group was reported to have a larger percentage of mechanical complications compared to VV group.

2. How precise was the estimate of the treatment effect?

Confidence intervals for usual measures of treatment effect (e.g., RR) cannot be calculated from the data provided.

IV. Will the results help me in caring for my patients?

1. Can the results be applied to my patient care?

This review demonstrates that VV ECMO is doable in children 2 weeks to 18 years of age with acute respiratory failure and a non cardiac diagnosis and may result in outcomes at least as good as venoarterial ECMO.

2. Were all clinically important outcomes considered?

Yes. The duration of ECMO support, survival rates and complications were considered. Other important outcomes like neuromotor development, cognitive performance will require long term follow up.

3. Are the likely treatment benefits worth the potential harms and costs?

Overall, the treatment benefit of ECMO ('survival') is worth the potential harm and cost, this is why ECMO is practiced in the absence of randomized trials.

Whether VV ECMO is more advantageous than VA ECMO is difficult to conclude from this study, since the VV and VA groups were dissimilar from the start. In literature VV and VA ECMO have compared favorably in both neonatal (2) and non neonatal population (3), however survival in patients treated with VV ECMO may be attributed to their favorable initial condition compared to patients treated with VA ECMO (4).

Still, the primary advantages of VV ECMO are reduced risk of arterial embolization and avoidance of carotid artery ligation (5).

References

1. Bartlett RH, et al. Extracorporeal life support. JAMA 2000, 287(7):904-908. [abstract]
2. Delius R, et al. Venovenous compares favorably with venoarterial access for extracorporeal membrane oxygenation in neonatal respiratory failure. J Thorac Cardiovasc Surg 1993,106(2):329-338. [abstract]
3. Zahraa JN, et al. Venovenous versus venoarterial extracorporeal life support for pediatric respiratory failure: are there differences in survival and acute complications. Crit Care Med 2000,28:521-525. [abstract]
4. Klien MD, et al. Venovenous perfusion in ECMO for newborn respiratory insufficiency. A clinical comparison with venoarterial perfusion. Ann Surg 1985, 201(4):520-526. [abstract]
5. Pettignano R, et al. Primary use of venovenous approach for extracorporeal membrane oxygenation in pediatric acute respiratory failure. Pediatr Crit Care Med 2003, 4(3):291-298. [abstract]

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