Gavriely N, April 2012
INTRODUCTION & AIMS: Mild to moderate CD after TKA is a common side-effect of an otherwise successful procedure. Despite improvement in the majority of the cases within weeks to a few months, this is a source of concern and disappointment. This analysis presents a possible mechanism for post-TKA cognitive changes.
METHOD: We reviewed the literature on the hemodynamic events around limb exsanguination, tourniquet placement and release during TKA. The majority of this literature is in anesthesia journals, with only a few in orthopedic journals (e.g., Berman, JBJS, 1998, 389-96). Once the data were collected, we scrutinized it for validity and in order to identify a plausible etiology that links between the TKA operating procedure and CD.
RESULTS: Limb elevation, Esmarch bandage, or Rhys-Davis exsanguinators are used prior to tourniquet inflation. Blond et al, (Acta Orthop Scand. 2002; 73:89–92) showed that at best, 70% of the limb’s blood was exsanguinated. Miller et al. (Ann. Surg. 1979; 190: 227-230) demonstrated that blood remaining inside the vessels of an occluded limb coagulates. Parmet et al (Lancet. 1993; 341:1057-8) observed a shower of echogenic material in the right atrium approximately 30 seconds after tourniquet release in ALL patients. Berman et al., (JBJS, 1998, 389-96) documented that this echogenic material consisted of fresh thrombi and not fat, bone marrow or cement. These thrombi partially occlude the pulmonary circulation, elevating the pressure in the right heart. As such, the blood pressure balance across the septum of the right atrium reverses. For patients with patent foramen ovale, blood flows from right to left. This brings echogenic material to the cerebral circulation in over 50% of TKA patients as detected by transcranial Doppler ~50 seconds after tourniquet release (Sulek, Anesthesiology 1999; 91:672–6). These cerebral emboli were associated with new brain infarcts detected by pre- and post-TKA MRI imaging (Koch, J Neuroimaging. 2007 17:332-5). The last step in this chain-of-evidence analysis is the statistics of CD post-TKA (Rodriguez, J Arthroplasty. 2005 20:763-71.)
CONCLUSIONS: The disproportionate prevalence of CD post-TKA as compared to other surgical procedures performed under similar types of anesthesia and in similar patients is worrisome. This hemodynamic analysis invokes a hypothesis that links incomplete limb exsanguination with cognitive dysfunction. Prospective studies where near-perfect exsanguination is applied in comparison with the current methods should be performed.