Target temperature and flow rate
In our cohort, we opted for a rectal target temperature of 28°C. This
target temperature was perfectly aligned with the CPB temperatures
recorded during circulatory arrest of the lower part of the body,
attesting to a relatively stable hypothermia. Mean venous return and
arterial perfusion temperatures were 26.9°C and 26.4°C, with medians of
27°C and 26.5°C during CCMSP. According to our calculations, an ACP flow
rate of 25–35mL/Kg/min was adequate, whereas the mean flow rate
recorded was 32.6±10.0mL/kg/min, with a median of 30.5mL/Kg/min. A
temperature of 28°C and ACP flow rate of 25–35mL/Kg/min had been fixed
as objectives, based on our center’s experience in adult aortic surgery
and several studies involving hypothermic pump flow rates and blood gas
management published in the literature (12)(13)(14). Our target
parameters for cerebral and visceral protection are: right radial artery
blood pressure >50mmHg, bilateral near infrared
spectroscopy (NIRS) values >50%, transcranial Doppler flow
velocity >15-20cm/s, and mixed venous oxygen saturation
>60%. Body temperatures and cerebral perfusion rates
during circulatory arrest are a matter of endless debate. Several
authors have performed ACP during normothermia, aiming to achieve better
protection by staying as close as possible to the normal human
physiological state. To maintain normothermia, they are now
experimenting with splanchnic perfusion to prevent renal and gut
exposure to circulatory arrest. These authors have reported satisfactory
results in terms of visceral and neurological function (15). Notably,
Fraser and colleague recommended a higher ACP flow rate at
50–80mL/Kg/min (14). Nevertheless, our strategy of applying CCMSP at
28°C with flow rate of 25–35mL/Kg/min has so far yielded suitable
results, which will be discussed in more detail later.