Hypoxia during VV ECMO

Pranay Oza

doi:10.1055/s-0038-1626681

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Editorial

1 (

2

); 57-59

doi:

10.1055/s-0038-1626681

Hypoxia during VV ECMO

Pranay Oza^1,

1 Riddhivinayak Critical Care and Cardiac Centre, Mumbai, Maharashtra, India

Pranay Oza, BHMS Riddhivinayak Critical Care and Cardiac Centre S.V. Road, Malad (W), Mumbai 4000064, Maharashtra India drpranay.oza@gmail.com

Journal of Cardiac Critical Care TSS

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Disclaimer:
This article was originally published by Thieme Medical and Scientific Publishers Private Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Venovenous extracorporeal membrane oxygenation (VV ECMO) is the preferred mode for any kind of acute respiratory failure. The desired PO₂ is > 50 and SPO₂ > 88% but the acceptable values can be PO₂ > 45 and S_PO₂ > 80%. In case if we are accepting lower PO₂, we have to keep a higher hematocrit and meticulously monitor neurological status, lactates, and urine output to maintain oxygen delivery. Saturation during ECMO run depends on ECMO circulation, native circulation, and ratio of ECMO flow to cardiac output (Table 1). Whenever the effective ECMO circulation decreases, saturation decreases. So, decrease in ECMO flow, ECMO FiO₂, failing membrane oxygenator, and increase in recirculation will lead to hypoxia. Similarly, anything that decreases the contribution from native circulation will also lead to hypoxia. So, decrease in ventilator settings and worsening lung status lead to hypoxia. Anything that increases metabolism, such as fever and restlessness, will also cause hypoxia due to increased consumption.

Table 1

Causes of hypoxia during ECMO

Abbreviation: ECMO, extracorporeal membrane oxygenation.

Technical problem

Ventilator related

Ventilator malfunctioning

ET tube blockage

ECMO related

Decreased ECMO flow or

FiO₂

Oxygenator failure

Increase recirculation

Lung condition worsening

Parenchymal worsening

Pneumothorax

Increased ratio of ECMO flow/cardiac output

Increased cardiac output

Recirculation is defined as the flow of oxygenated blood from the returning cannula to the draining cannula without entering systemic circulation. It decreases the efficacy of VV support. Around 30% of recirculation is average.¹ The factors on which the recirculation depends are pump flow (Fig. 1), catheter position, cardiac output, and RA size or intravascular volume. The recirculation can be calculated with the help of following equation:²

Management of hypoxia will depend on treating the underlying cause (Fig. 2). The usual strategy is to increase oxygen transfer by increasing ECMO flow, ECMO FiO₂, or by increasing hematocrit and thereby improving oxygen delivery. Many a times hypoxia is secondary to increased metabolic rate and just controlling that (controlling fever, giving sedation) will improve saturation. Recirculation can be managed by adjusting the flow; sometimes a higher flow is the cause of recirculation and just by decreasing flow we can get better saturation.³ Too close placement of tip of drainage and return cannula may lead to recirculation and just repositioning of cannula can improve saturation.⁴ If the recirculation persists, the last solution is to put additional cannula for drainage and switch to VVV ECMO.

Approach to hypoxia during VV ECMO. VV ECMO, venovenous extracorporeal membrane oxygenation.

In spite of all the above measures if the patient remains hypoxic and lactates are rising, then the last resource is to induce hypothermia and ultimately switch to VA or VAV ECMO (Table 2).

Table 2

Management of hypoxia during VV ECMO

Abbreviations: ECMO, extracorporeal membrane oxygenation; IVC, inferior vena cava; SVC, superior vena cava; VAV, veno-arterial-venous, VV, venovenous.

Maximizing gas transfer

Increase blood flow through the ECMO

Increasing FiO₂ of ECMO

Increasing hematocrit

Minimizing oxygen utilization

Decreasing metabolic rate: control fever, sedation, etc

Hypothermia

Decreasing recirculation in VV ECMO

Define the curve

Cannula reposition

Add cannula: for drainage, cannula can be added in IVC, SVC, and preferred cephalad cannula

Conversion to VA or VAV ECMO

Conclusion

Management of hypoxia during VV ECMO requires attentive monitoring and expedited, algorithmic monitoring.⁵ It is a balancing act that requires intense vigilance and expertise.

Acknowledgments

We sincerely thank the entire mobile ECMO team of the Riddhivinayak Critical Care and Cardiac center for their dedication and hard work.

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