[Hypercapnic respiratory failure. Pathophysiology, indications for mechanical ventilation and management]

Low-flow CO2 removal in combination with renal replacement therapy effectively reduces ventilation requirements in hypercapnic patients: a pilot study

Background

Lung-protective strategies are the cornerstone of mechanical ventilation in critically ill patients with both ARDS and other disorders. Extracorporeal CO₂ removal (ECCO₂R) may enhance lung protection by allowing even further reductions in tidal volumes and is effective in low-flow settings commonly used for renal replacement therapy. In this study, we describe for the first time the effects of a labeled and certified system combining ECCO₂R and renal replacement therapy on pulmonary stress and strain in hypercapnic patients with renal failure.

Methods

Twenty patients were treated with the combined system which incorporates a membrane lung (0.32 m²) in a conventional renal replacement circuit. After changes in blood gases under ECCO₂R were recorded, baseline hypercapnia was reestablished and the impact on ventilation parameters such as tidal volume and driving pressure was recorded.

Results

The system delivered ECCO₂R at rate of 43.4 ± 14.1 ml/min, PaCO₂ decreased from 68.3 ± 11.8 to 61.8 ± 11.5 mmHg (p < 0.05) and pH increased from 7.18 ± 0.09 to 7.22 ± 0.08 (p < 0.05). There was a significant reduction in ventilation requirements with a decrease in tidal volume from 6.2 ± 0.9 to 5.4 ± 1.1 ml/kg PBW (p < 0.05) corresponding to a decrease in plateau pressure from 30.6 ± 4.6 to 27.7 ± 4.1 cmH₂O (p < 0.05) and a decrease in driving pressure from 18.3 ± 4.3 to 15.6 ± 3.9 cmH₂O (p < 0.05), indicating reduced pulmonary stress and strain. No complications related to the procedure were observed.

Conclusions

The investigated low-flow ECCO₂R and renal replacement system can ameliorate respiratory acidosis and decrease ventilation requirements in hypercapnic patients with concomitant renal failure.

Trial registration NCT02590575, registered 10/23/2015.

The features of AECOPD with carbon dioxide retention

Background

Chronic obstructive pulmonary disease (COPD) with carbon dioxide retention is associated with a worsening clinical condition and the beginning of pulmonary ventilation decompensation. This study aimed to identify the factors associated with carbon dioxide retention.

Methods

This was a retrospective study of consecutive patients with COPD (meeting the Global Initiative for Chronic Obstructive Lung Disease diagnostic criteria) hospitalized at The Ninth Hospital of Xi’an Affiliated Hospital of Xi’an Jiaotong University between October 2014 and September 2017. The baseline demographic, clinical, laboratory, pulmonary function, and imaging data were compared between the 86 cases with carbon dioxide retention and the 144 cases without carbon dioxide retention.

Results

Compared with the non-carbon dioxide retention group, the group with carbon dioxide retention had a higher number of hospitalizations in the previous 12 months (p = 0.013), higher modified Medical Research Council (mMRC) dyspnea scores (p = 0.034), lower arterial oxygen pressure (p = 0.018), worse pulmonary function (forced expiratory volume in one second/forced vital capacity [FEV₁/FVC; p < 0.001], FEV₁%pred [p < 0.001], Z5%pred [p = 0.004], R5%pred [p = 0.008], R5-R20 [p = 0.009], X5 [p = 0.022], and Ax [p = 0.011]), more severe lung damage (such as increased lung volume [p = 0.011], more emphysema range [p = 0.007], and lower mean lung density [p = 0.043]). FEV₁ < 1 L (odds ratio [OR] = 4.011, 95% confidence interval [CI]: 2.216–7.262) and emphysema index (EI) > 20% (OR = 1.926, 95% CI: 1.080–3.432) were independently associated with carbon dioxide retention in COPD.

Conclusion

Compared with the non-carbon dioxide retention group, the group with carbon dioxide retention had different clinical, pulmonary function, and imaging features. FEV₁ < 1 L and EI > 20% were independently associated with carbon dioxide retention in AECOPD.

Trial registration

ChiCTR-OCH-14004904. Registered 25 June 2014.

Electronic supplementary material

The online version of this article (10.1186/s12890-018-0691-8) contains supplementary material, which is available to authorized users.

[Update: acute hypercapnic respiratory failure]

BACKGROUND

Hypercapnic respiratory failure is a frequent problem in critical care and mainly affects patients with acute exacerbation of COPD (AECOPD) and acute respiratory distress syndrome (ARDS). In recent years, the usage of extracorporeal CO₂ removal (ECCO₂R) has been increasing.

OBJECTIVE

Summarizing the state of the art in the management of hypercapnic respiratory failure with special regard to the role of ECCO₂R.

METHODS

Review based on a selective literature search and the clinical and scientific experience of the authors.

RESULTS

Noninvasive ventilation (NIV) is the therapy of choice in hypercapnic respiratory failure due to AECOPD, enabling stabilization in the majority of cases and generally improving prognosis. Patients in whom NIV fails have an increased mortality. In these patients, ECCO₂R may be sufficient to avoid intubation or to shorten time on invasive ventilation; however, corresponding evidence is sparse or even missing when it comes to hard endpoints. Lung-protective ventilation according to the ARDS network is the standard therapy of ARDS. In severe ARDS, low tidal volume ventilation may result in critical hypercapnia. ECCO₂R facilitates compensation of respiratory acidosis even under "ultra-protective" ventilator settings. Yet, no positive prognostic effects could be demonstrated so far.

CONCLUSION

Optimized use of NIV and lung-protective ventilation remains standard of care in the management of hypercapnic respiratory failure. Currently, ECCO₂R has to be considered an experimental approach, which should only be provided by experienced centers or in the context of clinical trials.