British Journal of Anaesthesia, Vol 81, Issue 6 965-967, Copyright © 1998 by The Board of Management and Trustees of the British Journal of Anaesthesia
S. Jankowski, J. Knighton, R. Dunnill and D. Dickson
Abdominal aortic surgery may produce significant haemodynamic instability
(from a combination of factors: hypovolaemia, acid-base disturbances,
vasoactive metabolite release from ischaemic tissues and hypocalcaemia).
Calcium is often given after aortic unclamping to attenuate this
instability. We studied 20 patients undergoing elective abdominal aortic
surgery and observed a triphasic change in ionized calcium concentrations
and acid-base status. Initially, during the cross-clamp period (when
patients were cardiovascularly stable), ionized calcium concentrations
decreased significantly (mean 1.06 (SD 0.08) to 0.91 (0.13) mmol litre-1; P
< 0.01), while a significant metabolic acidosis developed (pH 7.38
(0.05) to 7.30 (0.05); P < 0.05). Second, release of the aortic
cross-clamp resulted in further acidosis (pH 7.27 (0.05) (P < 0.05)
mixed respiratory and metabolic) with a decrease in mean arterial pressure,
with no change in ionized calcium concentrations. The third phase was
associated with spontaneous restoration of acid-base status and ionized
calcium concentrations to normal over 2 h. There was no correlation between
units of blood given, volume of blood lost, fluid volume given or duration
of aortic cross- clamping and degree of ionized hypocalcaemia. We conclude
that ionized hypocalcaemia occurred during the cross-clamp period of aortic
surgery, was unrelated to the volume of blood given and did not appear to
be responsible for the changes in arterial pressure during surgery.
SHORT COMMUNICATIONS
Changes in ionized calcium concentrations and acid-base status during abdominal aortic vascular surgery
Royal Bournemouth Hospital, Bournemouth BH7 7DW
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