2001 OPEN FORUM Abstracts
BALANCINGCARBON DIOXIDE LEVELS WITHIN THE EXTRACORPOREAL MEMBRANE OXYGENATOR PUMP PRIORTO INITIATING PATIENT USE.
Dwyer, Joseph G., Propper, KathrynE., The Johns Hopkins Hospital, Baltimore,Maryland.
INTRODUCTION: Thecontinued use of Extracorporeal Membrane Oxygenation (ECMO) has led toa search for ways to shorten the time required to completely prime an ECMO pumpfor patient use. Activation of the ECMO team is usually emergent in nature,thus making pump availability an important factor in patient outcome. Many aspectsof the priming process have been evaluated for reduction of time required. Thebalancing of Carbon Dioxide (CO2) in the fully primed pump is evaluatedin this technique review. By identifying the relationship between ECMO BloodFlow rate (pump flow), gas flow rates (sweep flow), and time of exposure betweenthe two, the amount of time required to fully balance the CO2 levels withinthe pump may be arrived at with relative certainty in a set time frame. Thetime prior to initiating ECMO is spent balancing blood gas values, sodium bicarbonatelevels and electrolytes. By creating repeatable trials of CO2 manipulation,a formula is derived that suggests the gas flow and time required at fixed pumpflow rates to achieve the desired CO2 level in the blood primed pump.
Methods: A standardMedtronic Cardiovascular 1/4? tubing circuit with a .8 meter squaredmembrane oxygenator set up according to departmental standards was used. Thecircuit was primed with human blood and hemoglobin levels were maintained above6.0gm% throughout trials. The ECMO blood flow rate was maintained at 200 cc/min(Due to the absence of a patient, the flow rate cannot be expressed in cc/kg/min.),and the sweep gas blender setting was held constant at 21% oxygen. CO2 levelswere manipulated by adjusting the Air/O2 flow rates or the CO2 flow rates dependingon desired outcome. For increasing CO2 levels a constant pump flow of 200 cc/minwith a CO2 flow rate of .2 lpm were used for various time increments. For decreasingCO2 levels a constant pump flow of 200 cc/min with an Air/O2 flow rate of 2lpm for various time increments.
Results: Thelinear nature of a graph depicting increasing CO2 by time increments suggestedthat a relative ratio exist that could be used to estimate CO2 manipulation.A graph depicting decreasing CO2 by time increments remained relatively linearup to three minutes then became more exponential. This suggests that a bloodgas or other evaluation method should be sampled at the three minute mark andadjustments made accordingly.
Conclusions:Averaging the values of the various time increment exposures led to the formulationof the following calculations.
Increasing CO2 by TimeIncrements sCO2 / TIME in Sec. = Average RatioFor All Values sCO2 / Sec. = .26
Decreasing CO2 by TimeIncrements sCO2 / TIME in Sec. = AverageRatio For Values Up To Three Minutes sCO2 / Sec. = .34