INTRODUCTION

Carbon dioxide (CO₂) removal systems (ECCO₂R - extracorporeal carbon dioxide removal) have been utilized since the 1970s. In 1986, Gattinoni⁽¹⁾ published a series of 43 patients with severe acute respiratory distress syndrome (ARDS) treated with an ECCO₂R device together with mechanical ventilation (MV) with a low respiratory frequency (LFPPV - low frequency positive-pressure ventilation) and pressure limitation (“lung at rest”), with improvement in lung function in 78.8% of patients. In 1990, Terragni⁽²⁾ showed that a system including a 0.33m2 neonatal membrane lung and a hemofiltration cartridge could reduce the tidal volume (Vt) below 6 mL/kg predicted body weight, normalizing the hypercapnia generated and reducing the cytokine concentration in bronchoalveolar lavage fluid at 72 hours in 32 patients with ARDS.

Currently, these systems have become popular due to technological advances and greater knowledge of lung damage induced by mechanical ventilation (VILI - ventilator-induced lung injury). They are capable of efficiently removing CO₂; therefore, they are promising for facilitating protective or ultraprotective MV in ARDS, with the hypothesis that a greater reduction in Vt and plateau pressure (Pplat) could be accompanied by a decrease in mortality, avoiding alveolar overdistention that occurs with the use of protective MV.^(3,4) In the recently published SUPERNOVA study, these systems were able to facilitate ultraprotective MV in patients with moderate ARDS.⁽³⁾

These systems, which operate with lower blood flow and membrane surface than does an ECMO (extracorporeal membrane oxygenation) system and whose function is to remove CO_2, have potential indications in hypercapnic patients.^(5,6) In patients with chronic obstructive pulmonary disease (COPD), ECCO₂R systems avoid the need for MV and are used as alternatives to MV when noninvasive MV (NIMV) fails or for facilitating extubation. As a bridge to lung transplantation (LT), these systems are viable alternatives that improve the physical condition of patients while they wait for a compatible organ, avoiding complications arising from MV and enhancing rehabilitation, respiratory physiotherapy, nutritional status and, even mobility, which are important in these patients.^(7,8)

Currently, we have a broad spectrum of ECCO₂R systems, most of which are veno-venous. Some only remove CO₂ while others escalate therapy to ECMO, and some have a membrane attached to the pump while others have an independent membrane. The addition of a CO₂ removal membrane together with a hemofilter would maintain vascular access, increase system safety, adapt anticoagulation, combine it with continuous renal replacement techniques (CRRTs) and possibly increase the efficiency of CO₂ lavage.⁽²⁾ In addition, with this “lung-kidney” support, a reduction in vasopressor requirements has been demonstrated.⁽⁹⁾

We present a case in which a combined ECCO₂R-CRRT system was used, describing its effects and discussing the most important technical aspects.

CASE REPORT

A 49-year-old male patient was admitted to the intensive care unit (ICU) for acute respiratory failure. The patient underwent two-lung transplantation due to idiopathic pulmonary fibrosis 2 months earlier, with grade 2 primary graft dysfunction and A2B1 acute cellular rejection. Cultures were taken, empiric antibiotic therapy was initiated, and immunosuppressive therapy was adjusted, requiring MV for global respiratory failure, with a marked reduction in respiratory compliance (11.4mL/mbar) with a plateau pressure (Pplat) of 35cmH₂O and peak pressure (Pp) of 40cmH₂O, with a Vt of 330mL and 20 breaths/minute. With a fraction of inspired oxygen (FiO₂) of 0.4 and positive end-expiratory pressure (PEEP) of 5cmH₂O, arterial gas analysis showed the following: pH, 7.11; partial pressure of carbon dioxide (PaCO₂), 55.7mmHg; partial pressure of oxygen (PaO₂), 113mmHg; bicarbonate, 24mmol/L; and excess of bases, -0.4mmol/L. The Vt gradually decreased to 220mL, and the respiratory rate (RR) decreased to 15 breaths/minute. PEEP was withdrawn in the presence of bilateral tension pneumothorax and Pplat flow limitations. Next, PaCO₂ was increased to 87 mmHg with pH 7.11.

The patient also presented with acute kidney injury (AKI), with creatinine and urea levels of 0.7mg/dL and 26mg/dL, respectively, and with oliguria, bleeding from thoracic drainages, previous barotrauma and severe thrombocytopenia (46000/mm³). A Prismalung system was implanted using a 13.5 Fr femoral cannula. Hemodynamic monitoring was performed by intermittent invasive blood pressure measures of central venous oxygen saturation (SatvO₂), and a negative fluid balance was monitored during therapy.

Figure 1 shows the details of the parameters and pressures generated through the system with a blood flow of 350mL/minute. At the time of initiating therapy, PaCO₂ decreased to 62mmHg with a pH of 7.21. The pH improved, and PaCO₂ decreased without modifying PaO₂ (Figure 2). After 24 hours, the flow was increased to 390mL/minute with an increase in pre-filter pressure (Figure 1) without modifying PaCO₂.

Figure 1 - Detail of the parameters and pressures for the extracorporeal carbon dioxide removal-continuous extrarenal replacement system with a flow of 350mL/minute and with a flow of 390mL/minute (side panel).

Download

Figure 1 - Detail of the parameters and pressures for the extracorporeal carbon dioxide removal-continuous extrarenal replacement system with a flow of 350mL/minute and with a flow of 390mL/minute (side panel).

Figure 2 - pH, PaCO₂ and PaO₂ curves before and after device implantation. pH - hydrogen potential; PaCO₂ - partial pressure of carbon dioxide; PaO2 - partial pressure of oxygen.

Download

Figure 2 - pH, PaCO₂ and PaO₂ curves before and after device implantation. pH - hydrogen potential; PaCO₂ - partial pressure of carbon dioxide; PaO2 - partial pressure of oxygen.

On the first day of support, a maximum activated partial thromboplastin time (aPTT) of 1.5 was maintained for thrombocytopenia. On the second day, the minimum aPTT was 1.09, and the maximum was 1.23. After 48 hours, thrombosis within the hemofilter was present, with an aPTT ratio of 1.1, and the CO₂ removal membrane was removed. Renal support therapy was continued, percutaneous tracheostomy was performed, and after an initial improvement, pneumonia associated with P. aeruginosa and MV developed. The patient died of multiorgan failure without device-related complications.

DISCUSSION

The elimination of CO₂ with extracorporeal systems, both through ECMO and with ECCO₂R devices, is effective, but the latter contributes minimally to oxygenation, as they are low-flow systems. The potential indications for ECCO₂R are included in the introduction.

The possible adjustment of MV (increasing PEEP) and increase in alveolar O₂ pressure by reducing the alveolar CO₂ pressure (PACO₂) may explain the slight improvement in oxygenation. In addition, according to the hemoglobin dissociation curve, in an arteriovenous ECCO₂R system, the oxygenating capacity is lower because only a few milliliters of O₂ can be added to oxygenated blood; however, in the case of veno-venous systems_, approximately 35mL of O₂ can be supplied (assuming venous O₂ saturation of 75% and a hemoglobin level of 10g/dL).⁽¹⁰⁾

Definition of ECCO₂ R and the basis of its operation

ECCO₂R systems are low-flow (250 - 1500mL/minute) partial respiratory support devices, with a smaller membrane surface (0.33 - 0.67m2, with larger surfaces used with versatile systems that allow transition to ECMO). The diffusion capacity of CO₂ across the membrane is approximately 20 times higher than that of O₂, and 200 - 250mL/minute of CO₂ production in an adult can be removed with a flow of 500mL/min.^(5,10,11) In our case, the increase in flow from 350 to 390mL/minute increased the pre-filter pressure (Figure 1).

The main determinant of CO₂ lavage is air flow, with a maximum of 10L/minute recommended for most devices.^(10,11) In our case, the increase to 12 - 15L/minute did not further reduce PaCO₂. Regarding blood flow, in a bovine animal model, a flow between 750 - 1000mL/minute was more effective than a flow between 250 - 500mL/minute, regardless of the membrane size used, although a membrane surface of 0.8m2 was more effective than a membrane surface of 0.4m2.⁽¹²⁾ However, in a porcine venous model with veno-venous ECMO, an increase in both blood flow and air flow reduced PaCO₂ in apneic ventilation.⁽¹³⁾

A very recent publication concluded that low-flow ECCO₂R systems should be limited to mild respiratory acidosis or to facilitate MV in ARDS.⁽¹⁴⁾Table 1 shows the different membrane surfaces used in the studies published with ECCO₂ R-CRRT combined systems.

Table 1 - Summary of the studies with combined extracorporeal carbon dioxide removal and continuous extrarenal replacement systems

Author	Population	No. of cases	Configuration	Membrane(m2)	Hemofilter (m2)	Blood flow (mL/min)	Air flow (L/min)	Cannula (Fr)	Anticoagulation
Terragni et al.(2)	Humans	32	VV	0.33 Polystan	Medica D200	500	8	14 DL	aPTT ratio 1.5
Forster et al.(9)	Humans	10	VV	0.67	1.4 polysulfone	250 - 500	6 - 7	13 DL	aPTT at 60 sec. ACT: 120 - 200 sec
Young et al.(16)	Animal	9	AV	5	-	470 - 600	10	-	ACT 200 - 300 sec
Quintard et al.(17)	Humans	16	VV	0.65 polypropylene	1.4 polysulfone	400 - 500	10	DL: 13.5 jugular (15cm) or 13.5 femoral (24cm) or 16 femoral (27cm) DUL 13.5	aPTT 45 - 50 sec
Allardet-Servent et al.(18)	Humans	11	VV	0.65 polymethylpentene	1.5 polysulfone	410 ± 30	8	15.5 DL (15 and 20cm)	aPTT ratio 1.5

VV - veno-venous; DL - double-lumen cannula; aPTT - activated partial thromboplastin time; AV - arteriovenous; ACT - activated clotting time; DUL - two single-lumen cannula.

Table 1 - Summary of the studies with combined extracorporeal carbon dioxide removal and continuous extrarenal replacement systems

CONCLUSION

Combined extracorporeal carbon dioxide removal-continuous extrarenal replacement with a flow rate that did not reach 400mL/minute was effective for the removal of carbon dioxide but was limited by rapid thrombosis of the hemofilter.