Table 5. While the addition of spinal fluid drainage (SFD) significantly improved results (Table 4) which explains most of the improvement in paralysis risk between era 1 and era 2 (Figure 5B), Assisted circulation with SFD showed improved O/E ratios between eras, while assisted circulation with cross clamp and risk remained stable. The most likely factors for improvement for Assisted circulation + SFD across eras was the transition from normothermic to hypothermic assisted circulation and an emphasis on higher mean arterial pressures and more aggressive control of spinal fluid pressures.

Group	Number of patients	O/E Ratio	% Paralysis	P-value
Assisted circulation 1 + SFD	532	0.42	6.6	0.182
Assisted circulation 2 + SFD	5,321	0.23	4.2
Hypothermic arrest 1	297	0.44	7.1	0.0257
Hypothermic arrest 2 + SFD	505	0.16	3.3
Cross clamp 1	1,241	0.91	13.5	0.8073
Cross clamp 2	230	0.92	14.3
Assisted circulation 1	4,273	1.03	15.3	0.5593
Assisted circulation 2	152	0.94	13.9