A modern theory of paraplegia in the treatment of aneurysms of the thoracoabdominal aorta: An analysis of technique specific observed/expected ratios for paralysis.

OBJECTIVE: To demonstrate that a modern theory of paraplegia prevention in thoracoabdominal aortic (TAAA) surgery is primarily non-anatomic and derives from experimentally validated interventions that prolong the ischemic tolerance, reduce reperfusion injury, and enhance the collateral perfusion of the spinal cord with or without assisted circulation.
METHODS: Using an accurate predictive model (r(2) > 0.95) for paraplegia risk we studied the effects of protective strategies in 82 clinical series reporting more than 15,000 patients treated from 1985 to 2008. The observed/expected (O/E) ratios were calculated for each series and the results were grouped by technique. The effect of interventions such as spinal fluid drainage (SFD), systemic hypothermia, epidural cooling, and naloxone on O/E ratios were studied. We analyzed changes in O/E ratios from Era 1 (1985 to 1997) to Era 2 (1997 to 2008) and within treatment techniques over time.
RESULTS: The mean O/E ratio for paraplegia for all patients declined from 1.13 in Era 1 to 0.26 in Era 2. Adding SFD to patients treated with assisted circulation (AC) decreased the O/E ratio from 1.03 to 0.24 (P < .0001). Adding SFD to patients treated with aortic clamping without AC (XCL) decreased O/E from 0.91 to 0.23 (P = .0013). O/E for hypothermic arrest (HA) declined from 0.42 to 0.14 with SFD. The addition of SFD to AC, XCL, and HA accounted for most of the decline in O/E between Eras. Other factors which played a less defined but important role in the decline in O/E ratios were attention to higher mean arterial pressures (MAPs), more hypothermia, and neurochemical protection.
CONCLUSION: Paraplegia causation is anatomic but paraplegia prevention is physiologic (non-anatomic). We demonstrate that by using hypothermia, SFD, and increasing MAP, clinicians had similar improvements in paraplegia, reducing O/E deficit ratios from 1.03 to as low as 0.16, with or without intercostal reimplantation, and whether or not assisted circulation was used. Understanding the fundamental principles of paraplegia prevention and how to apply protective strategies leads to a reduction in paralysis in clinical series with or without the use of assisted circulation. This modern theory of paraplegia has significant implications for the rapidly advancing field of TAAA repair with branched endografts where the same principles apply.