Table 3 Role of TCD During Deep hypothermic Cardio Pulmonary Bypass (DHCPB), Deep Hypothermic Circulatory Arrest (DHCA) and Low Flow Cardio Pulmonary Bypass (LFCPB). MCA: middle cerebral artery. CPB: cardiopulmonary bypass. CBF: cerebral blood flow. CMRO2: cerebral metabolic rate of oxygen, CPP: cerebral perfusion pressure.
Author [reference] | Journal (Year of Publication) | Type of study and Number of patients | Main findings |
|---|---|---|---|
Norwood WI [9] | Journal of Thoracic Cardiovascular Surgery (1979) | Experimental study on neonatal rats | Hypothermia during CPB reduces metabolic activity, CBF and CMRO2, so that it is possible to maintain energy stores and provide organ protection during low flow state |
Greeley WJ [10] | Journal of Thoracic Cardiovascular Surgery (1991) | Prospective study on 46 pediatric patients | DHCA changes cerebral metabolism and blood flow after the arrest period |
Fox LS [11] | Journal of Thoracic Cardiovascular Surgery (1984) | Experimental study on 9 monkeys randomly assigned to 4 perfusion flow rates varying from 0.25 to 1.75 L/min/m2 | All areas of the brain remain perfused, even at low perfusion flow rates, during profoundly hypothermic cardiopulmonary bypass, and brain oxygen consumption is maintained in part by increased oxygen extraction and in part by redistribution of the perfusate from the remaining body to the brain |
Rebeyka IM [12] | Annals of Thoracic Surgery (1987) | Experimental study on 6 dogs and prospective study on 5 patients subjected to brief periods of low-flow CPB (Q = 1.0 L/min/m2.) at 21 degrees to 25 degrees C°. | In the absence of cerebral vascular disease, the flow rate threshold for incurring functional cerebral injury during hypothermic (25 degrees C) nonpulsatile CPB is less than 1.0 L/min/m2. |
Taylor R [13] | Anesthesia Analgesia (1992) | Observational study on 25 infants and neonates | 1) Autoregulation is preserved during normothermic CPB, it begins to be altered at temperature less than 25°C, and it is lost at temperature less than 20°C. 2) A significant decrease in CPP and CBF is shown during extreme low flow CPB. |
Jonassen A [14] | Journal of Thoracic Cardiovascular Surgery (1995) | Observational on 37 pediatric patients | Detectable cerebral blood flow at pump flow rate and mean arterial pressure values of 27 mmHg (lower than those reported by Taylor). |
Greeley WJ [15] | Circulation (1989) | Observational on 67 pediatric patients | During CPB rewarming, CBF returns to baseline values, except in patients exposed to periods of DHCA where CBF remains decreased. |
Astudillo R [16] | Annals of Thoraci Surgery (1993) | Observational on 22 small children | Low cerebral perfusion immediately following DHCA is characterized by a prolonged period of absent diastolic CBFV in MCA while patients subjected to continuous low-flow perfusion technique showed a CBFV close to baseline values at skin closure. |
Rodriguez R [17] | Journal of Thoracic Cardiovascular Surgery (1995) | Randomized trial on 16 infants treated with or without 10 minutes of cold reperfusion before rewarming after DHCA. | A delay in rewarming on reperfusion after DHCA may be beneficial as demonstrated by recovery of a diastolic doppler signal. |
Zimmerman A [18] | Journal of Thoracic Cardiovascular Surgery (1997) | Observational on 28 neonates | Cerebral perfusion can be detected by TCD in the MCA in some neonates at bypass flow as low as 10 ml/kg per minute. |