The effects of low flow, low pressure pulsatile bypass.

The effects of low flow low pressure pulsatile bypass were studied in 90 consecutive patients undergoing coronary artery surgery. Overall pump flow rate (OFR) was 19-49 (mean 31 +/- 7) ml/kg/min at all temperatures. Moderate (28 degrees C) hypothermia was used. When cross-clamped flow was 17-49 (mean 27 +/- 7) ml/kg/min and mean perfusion pressure 50-60 mmHg. Priming volume (PV) was reduced to 1.45 +/- 0.02 L (range 1.2-2.0 L) PV, cardioplegia and volume additions were considered as total bypass crystalloid (TBC) and this correlated positively with increased post-operative positive water balance (r = 0.58, P less than 0.001). Bypass urine output averaged 135 +/- 24 ml (range 0-1,000 ml) was unrelated to OFR and correlated only with TBC (r=0.47, P less than 0.001). In 86 a single cardioplegia dose of 0.7 L (range 0.4-0.8 L) sufficed for this ischaemic period (mean 46 +/- 16 min). Four required a further 0.2-0.3 L. Their ischemic times were 44-74 min (mean 59 +/- 13 PNS). Inotropes were used in only 3 patients. Post-operatively 7 required diuretics for low hourly urine flow. Of the 76 with normal pre-operative renal function urea rose transiently in 15. Three had raised urea for over 9 days. Creatinine rose transiently in 7 but persisted in only one. Plasma cortisol (n=78) rose in 67 and fell in 11, indicating, overall, an adequate metabolic response. Plasma free haemoglobin before and after bypass varied widely and did not correlate with flow rate or perfusion time.(ABSTRACT TRUNCATED AT 250 WORDS)