Fred Colbert |  |
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A few colleagues very timely remember us that using a low operating volumes at adult flow rates can significantly increase the number of bubbles exiting the venous
reservoir. This resulted in the advice of adding an extra 200cc in the venous reservoir, which represents a small increase in total volume (patient + prime). The resulted low increase in hemodilution would then be well worth.
We should be aware that the level of venous reservoir is usually a function of arterial flow and the perfusionist´s experience, according to the old time rule of 15 seconds. This means that the venous reservoir should have enough volume to assure a high level of safety to the patient. For a 1 liter/min arterial flow, the "level" (better saying volume) in the oxygenator should usually be 250 ml (1/4) considering the 15 seconds rule of thumb. This means that in case of any mechanical problem that interferes with arterial flow, the perfusionist will have 15 seconds to take an appropriate measure. This has been known as the "response time", meaning the time that a perfusionist needs to detect a problem and reduce arterial flow to buy more time to definitely correct the existing problem. Coincidently this level also works as a protector against air bubbles entering the venous blood being pumped out to the arterial line.
A well trained perfusionist using modern well designed oxygenators can reduce "response time" to 10 seconds without increasing the risks of massive air emboli to the patient in front of an emergency situation. This is to say that it is reasonable to keep a venous reservoir with a volume of 533 ml (500 ml) for a 80kg patient with an arterial flow of 3,200 ml/min (40 ml/kg/min). Levels in the venous reservoir lower than this are unnecessary and certainly increases risks involved (reduces safety) and certainly produce more air microbubbles.
In conclusion, the 10 seconds "response time" is just a volume corresponding to 1/6 of the arterial flow. June 5, 2008 11:00 am - England |
Cloves Serra | |
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Air in the arterial line as microemboli or macroemboli has been a concern of all involved with CPB. Some people worry about detecting 70-100 bubbles/min exiting the venous reservoir to the oxygenator and the arterial line while others usually see much greater amounts or venous air entering the arterial side of circuit without caring as much.
Carotid artery emboli, detected ultrasonically, have been observed after venous air entrainment into the CPB circuit, and vacuum assisted venous drainage allows the use of smaller circuits but introduce much air into them. Also, in order to reduce prime volume and hemodilution, several teams start CPB with an empty venous line. It is not surprising that these last two techniques introduce much more air into the arterial side of our perfusion circuits.
We need to know the real significance of this air and take measures to get rid of the bubbles that will eventually be harmful to our patients.
June 6, 2008 12:16 pm - Santiago, Chile. |
Carlos Martinez | |
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Dear colleagues:
We should not forget that a simple measure to correct a low hematocrit or a higher than desired ratio of hemodilution is an extra dose of furosemide. In our days, with normothermic (isothermic) cardiopulmonary bypass, a single dose of furosemide can remove 400-500 mL of water just by enhancing diuresis. June 12, 2008 10:22 am - Guatemala |
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