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Extracorporeal CO 2 removal by hemodialysis: in vitro model and feasibility

View Article: PubMed Central - PubMed

ABSTRACT

Background: Critically ill patients with acute respiratory distress syndrome and acute exacerbations of chronic obstructive pulmonary disease often develop hypercapnia and require mechanical ventilation. Extracorporeal carbon dioxide removal can manage hypercarbia by removing carbon dioxide directly from the bloodstream. Respiratory hemodialysis uses traditional hemodialysis to remove CO2 from the blood, mainly as bicarbonate. In this study, Stewart’s approach to acid-base chemistry was used to create a dialysate that would maintain blood pH while removing CO2 as well as determine the blood and dialysate flow rates necessary to remove clinically relevant CO2 volumes.

Methods: Bench studies were performed using a scaled down respiratory hemodialyzer in bovine or porcine blood. The scaling factor for the bench top experiments was 22.5. In vitro dialysate flow rates ranged from 2.2 to 24 mL/min (49.5–540 mL/min scaled up) and blood flow rates were set at 11 and 18.7 mL/min (248–421 mL/min scaled up). Blood inlet CO2 concentrations were set at 50 and 100 mmHg.

Results: Results are reported as scaled up values. The CO2 removal rate was highest at intermittent hemodialysis blood and dialysate flow rates. At an inlet pCO2 of 50 mmHg, the CO2 removal rate increased from 62.6 ± 4.8 to 77.7 ± 3 mL/min when the blood flow rate increased from 248 to 421 mL/min. At an inlet pCO2 of 100 mmHg, the device was able to remove up to 117.8 ± 3.8 mL/min of CO2. None of the test conditions caused the blood pH to decrease, and increases were ≤0.08.

Conclusions: When the bench top data is scaled up, the system removes a therapeutic amount of CO2 standard intermittent hemodialysis flow rates. The zero bicarbonate dialysate did not cause acidosis in the post-dialyzer blood. These results demonstrate that, with further development, respiratory hemodialysis can be a minimally invasive extracorporeal carbon dioxide removal treatment option.

No MeSH data available.


Related in: MedlinePlus

In vitro CO2 removal rates. The dual axes show experimental results, as well as the expected values when the system is scaled up by a factor of 22.5. The expected scaled up values are in gray, while the actual values are in black. Triangle symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 100 mmHg; diamond symbols: Qb = 18.7 mL/min (421 mL/min scaled up), pCO2, inlet = 50 mmHg; square symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 50 mmHg. Single asterisk indicates p < 0.05 between different blood flow rates (diamond and square symbols). Double asterisks indicate p < 0.05 between different inlet pCO2 values (triangle and square symbols)
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Fig2: In vitro CO2 removal rates. The dual axes show experimental results, as well as the expected values when the system is scaled up by a factor of 22.5. The expected scaled up values are in gray, while the actual values are in black. Triangle symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 100 mmHg; diamond symbols: Qb = 18.7 mL/min (421 mL/min scaled up), pCO2, inlet = 50 mmHg; square symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 50 mmHg. Single asterisk indicates p < 0.05 between different blood flow rates (diamond and square symbols). Double asterisks indicate p < 0.05 between different inlet pCO2 values (triangle and square symbols)

Mentions: CO2 removal rates measured from respiratory dialysis are shown in Fig. 2 are presented, by a dual axis, in terms of actual and scaled up (actual multiplied by the 22.5 scale factor) CO2 removal rates. At an inlet pCO2 of 50 mmHg and a blood flow rate of 18.7 mL/min (421 mL/min scaled up), the maximum CO2 removal rate was 3.5 ml/min (78 mL/min scaled up), a 24% increase compared to a blood flow rate of 11 mL/min (248 mL/min scaled up) at the same conditions (p = 0.048). The effect of doubling the inlet pCO2, 50 mmHg to 100 mmHg, was also evaluated at a blood flow rate of 11 mL/min (248 mL/min scaled up) (Fig. 2). There was an 85% increase in CO2 removal between the two inlet pCO2 conditions.Fig. 2


Extracorporeal CO 2 removal by hemodialysis: in vitro model and feasibility
In vitro CO2 removal rates. The dual axes show experimental results, as well as the expected values when the system is scaled up by a factor of 22.5. The expected scaled up values are in gray, while the actual values are in black. Triangle symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 100 mmHg; diamond symbols: Qb = 18.7 mL/min (421 mL/min scaled up), pCO2, inlet = 50 mmHg; square symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 50 mmHg. Single asterisk indicates p < 0.05 between different blood flow rates (diamond and square symbols). Double asterisks indicate p < 0.05 between different inlet pCO2 values (triangle and square symbols)
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Related In: Results  -  Collection

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Show All Figures
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Fig2: In vitro CO2 removal rates. The dual axes show experimental results, as well as the expected values when the system is scaled up by a factor of 22.5. The expected scaled up values are in gray, while the actual values are in black. Triangle symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 100 mmHg; diamond symbols: Qb = 18.7 mL/min (421 mL/min scaled up), pCO2, inlet = 50 mmHg; square symbols: Qb = 11 mL/min (248 mL/min scaled up), pCO2, inlet = 50 mmHg. Single asterisk indicates p < 0.05 between different blood flow rates (diamond and square symbols). Double asterisks indicate p < 0.05 between different inlet pCO2 values (triangle and square symbols)
Mentions: CO2 removal rates measured from respiratory dialysis are shown in Fig. 2 are presented, by a dual axis, in terms of actual and scaled up (actual multiplied by the 22.5 scale factor) CO2 removal rates. At an inlet pCO2 of 50 mmHg and a blood flow rate of 18.7 mL/min (421 mL/min scaled up), the maximum CO2 removal rate was 3.5 ml/min (78 mL/min scaled up), a 24% increase compared to a blood flow rate of 11 mL/min (248 mL/min scaled up) at the same conditions (p = 0.048). The effect of doubling the inlet pCO2, 50 mmHg to 100 mmHg, was also evaluated at a blood flow rate of 11 mL/min (248 mL/min scaled up) (Fig. 2). There was an 85% increase in CO2 removal between the two inlet pCO2 conditions.Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Background: Critically ill patients with acute respiratory distress syndrome and acute exacerbations of chronic obstructive pulmonary disease often develop hypercapnia and require mechanical ventilation. Extracorporeal carbon dioxide removal can manage hypercarbia by removing carbon dioxide directly from the bloodstream. Respiratory hemodialysis uses traditional hemodialysis to remove CO2 from the blood, mainly as bicarbonate. In this study, Stewart&rsquo;s approach to acid-base chemistry was used to create a dialysate that would maintain blood pH while removing CO2 as well as determine the blood and dialysate flow rates necessary to remove clinically relevant CO2 volumes.

Methods: Bench studies were performed using a scaled down respiratory hemodialyzer in bovine or porcine blood. The scaling factor for the bench top experiments was 22.5. In vitro dialysate flow rates ranged from 2.2 to 24&nbsp;mL/min (49.5&ndash;540&nbsp;mL/min scaled up) and blood flow rates were set at 11 and 18.7&nbsp;mL/min (248&ndash;421&nbsp;mL/min scaled up). Blood inlet CO2 concentrations were set at 50 and 100&nbsp;mmHg.

Results: Results are reported as scaled up values. The CO2 removal rate was highest at intermittent hemodialysis blood and dialysate flow rates. At an inlet pCO2 of 50&nbsp;mmHg, the CO2 removal rate increased from 62.6&thinsp;&plusmn;&thinsp;4.8 to 77.7&thinsp;&plusmn;&thinsp;3&nbsp;mL/min when the blood flow rate increased from 248 to 421&nbsp;mL/min. At an inlet pCO2 of 100&nbsp;mmHg, the device was able to remove up to 117.8&thinsp;&plusmn;&thinsp;3.8&nbsp;mL/min of CO2. None of the test conditions caused the blood pH to decrease, and increases were &le;0.08.

Conclusions: When the bench top data is scaled up, the system removes a therapeutic amount of CO2 standard intermittent hemodialysis flow rates. The zero bicarbonate dialysate did not cause acidosis in the post-dialyzer blood. These results demonstrate that, with further development, respiratory hemodialysis can be a minimally invasive extracorporeal carbon dioxide removal treatment option.

No MeSH data available.


Related in: MedlinePlus