NEUROANESTHESIA ADJUNCT THERAPY (MANNITOL AND HYPERVENTILATION) IS ASEFFECTIVE AS CEREBROSPINAL-FLUID DRAINAGE FOR PREVENTION OF PARAPLEGIA AFTER DESCENDING THORACIC AORTIC CROSS-CLAMPING IN THE DOG

We compared cerebrospinal fluid (CSF) drainage (Group D; n = 8) to neu roanesthesia adjunct therapy (hyperventilation and mannitol administra tion; Group N; n = 8) for the prevention of paraplegia using a canine model of descending thoracic aortic cross-clamping (AXC; 2.5 mm distal to the left subclavian artery for 30 min). We expected no difference in neurologic outcome between groups. After surgical preparation and a 30-min stabilization period, dogs in Group D had CSF drained prior to application of the AXC During the period of AXC, CSF was allowed to d rain freely in an attempt to have cerebrospinal fluid pressure (CSFP) no greater than central venous pressure (CVP). Dogs in Group N were hy perventilated (PaCO2 28-32 nun Hg) and received 2 g/kg of mannitol pri or to AXC and then 1 g . kg(-1). hr(-1) during clamping. Systemic hemo dynamics, CSFP, and arterial blood gases were measured at 1) baseline, 2) 2 min after AXC, 3) 20 min after AXC, 4) 5 min after AXC release, and 5) 30 min after resuscitation. With release of the AXC, PaCO2 was not controlled in Group D; in Group N the minute ventilation was furth er increased to maintain PaCO2 constant. At precisely 24 h after AXC, the animals were assessed for incidence and severity of paraplegia, us ing the Tarlov score, by an observer unaware of the experimental proto col. The animals were then killed, and the entire spinal cord was remo ved for histologic assessment. Multiple sections of the lumbar spinal cord were processed and stained with hematoxylin and eosin, then exami ned by light microscopy for nonviable neurons in the anterior spinal c ord. At baseline, CSFP was significantly higher in Group D before CSF drainage. The CSFP was significantly less in Group D for all subsequen t time periods (treatment X time interaction; P = 0.0001). However, in Group N, CSFP was always less than baseline values in Group D. There was no difference in spinal cord perfusion pressure (SCPP; distal mean arterial pressure CSFP) between groups during cross-clamping. Acidosi s was significantly worse in Group D with AXC release. The neurologic outcome was the same in both groups; Tarlov score was 3 in seven anima ls and 4 in one animal in each group (P = 1.0; Mann-Whitney rank-sum t est). There was no difference in the ratio of dead: total lumbar anter ior spinal cord neurons between groups (0.010 +/- 0.016 and 0.015 +/- 0.033 for Groups D and N, respectively; P = 0.720). We conclude that n euroanesthesia adjunct therapy is as effective as CSF drainage for the prevention of paraplegia in this canine model. Such therapy is less i nvasive than drainage of CSF and may be of use clinically to decrease the incidence and severity of paraplegia after surgery on the descendi ng thoracic aorta.