Discussion
The salient findings of this study were 1) Unusually high prevalence of
RML amongst patients with AAD compared to other cardiac surgical patient
population 2) Strong association of RML with AKI 3) Patients with high
BMI were more involved in RML( even though the association didn’t reach
statistical significance ) 4) Delayed presentation for surgery was
associated with a lesser risk of rhabdomyolysis. To the best of our
knowledge no previous studies looked at these associations in Aortic
Dissection Surgery.
Our study substantiates the hypothesis that aortic dissection surgery is
associated with an unusually high incidence of RML (63%) when compared
to cardiac surgical cases in general reported by us before
(8.41%)1. The possible explanation for this
predisposition could be occult ischemia to the lower limb following
femoral cannulation, ischemia to paraspinal muscles due to malperfusion,
prolonged positioning due to comparatively longer duration of the
surgery1,15. It is postulated that the lumbar arteries
that supply the paraspinal muscles may become compromised because of
either hypoperfusion or occlusion from aortic cross-clamping, or
ligation of the vessels within the false lumen of the dissection, or
from athero-embolic phenomena. The resultant ischemia causes edema and
necrosis of the paraspinal muscles, subsequently increasing the pressure
within the paraspinal compartment15
Miller III et al. in an observational trial of 109 patients requiring
thoracic/thoraco-abdominal aortic repair reported a dialysis requirement
of 38% in the postoperative period. The dialysis rate was high in this
study because the liberal inclusion criteria used for the same.
Myoglobin levels were strongly predictive of postoperative renal
dysfunction which was in agreement with our observations as well. But
this study was done in patients undergoing thoraco-abdominal aortic
aneurysm surgery without the use of cardiopulmonary bypass. Still, risk
factors like femoral cannulation and prolonged positioning associated
muscle damage is apparently common to both the patient
cohorts16. The same group have also reported the
relationship between loss of Somato-Sensory Evoked Potential signals in
the cannulated leg and adverse renal outcome indicating leg ischemia as
a potential contributing factor for RML19
The proposed risk factors for RML like the presence of diabetes or
hypertension3 didn’t have a significant impact on the
incidence of RML in our study. Femoral cannulation could theoretically
be associated with a higher incidence of rhabdomyolysis because of the
potential for limb ischemia, but our study couldn’t demonstrate a
difference in outcome in terms of RML with femoral cannulation.
Patients who developed RML were more obese compared to the non-RML
group, but this difference failed to achieve statistical significance.
Zhao et al. (2015) reported a higher incidence of AKI (66.7%) among
obese patients with type A aortic dissection8. They
found elevated preoperative serum Creatinine level and 72-h drainage
volume as independent predictors of AKI, but they didn’t look into the
contribution of rhabdomyolysis to the development of kidney injury. The
association between BMI and risk of RML has been well documented in
bariatric and trauma surgeries as well20,21.