Kirchhoff's law-based velocity-controlled motion models to predict real-time cutting forces in minimally invasive surgeries.

A theoretical framework, united by a "system effect" is formulated to model the cutting/haptic force evolution at the cutting edge of a surgical cutting instrument during its penetration into soft biological tissue in minimally invasive surgery. Other cutting process responses, including tissue fracture force, friction force, and damping, are predicted by the model as well. The model is based on a velocity-controlled formulation of the corresponding equations of motion, derived for a surgical cutting instrument and tissue based on Kirchhoff's fundamental energy conservation law. It provides nearly zero residues (absolute errors) in the equations of motion balances. In addition, concurrent closing relationships for the fracture force, friction coefficient, friction force, process damping, strain rate function (a constitutive tissue model), and their implementation within the proposed theoretical framework are established. The advantage of the method is its ability to make precise real-time predictions of the aperiodic fluctuating evolutions of the cutting forces and the other process responses. It allows for the robust modeling of the interactions between a medical instrument and a nonlinear viscoelastic tissue under any physically feasible working conditions. The cutting process model was partially qualitatively verified through numerical simulations and by comparing the computed cutting forces with experimentally measured values during robotic uniaxial biopsy needle constant velocity insertion into artificial gel tissue, obtained from previous experimental research. The comparison has shown a qualitatively similar adequate trend in the evolution of the experimentally measured and numerically predicted cutting forces during insertion of the needle.

Results of carotid endarterectomy in patients with contralateral internal carotid artery occlusion from the Mid-America Vascular Study Group and the Society for Vascular Surgery Vascular Quality Initiative.

OBJECTIVE: Carotid endarterectomy (CEA) is among the most commonly performed vascular procedures. Some have suggested worse outcomes with contralateral internal carotid artery (ICA) occlusion. We compared patients with and patients without contralateral ICA occlusion using the Society for Vascular Surgery Vascular Quality Initiative database. METHODS: Deidentified data were obtained from the Vascular Quality Initiative. Patients with prior ipsilateral or contralateral CEA, carotid stenting, combined CEA and coronary artery bypass graft, or <1-year follow-up were excluded, yielding 1737 patients with and 45,179 patients without contralateral ICA occlusion. Groups were compared with univariate tests, and differences identified in univariate testing were entered into multivariate models to identify independent predictors of outcomes and in particular whether contralateral ICA occlusion is an independent predictor of outcomes. RESULTS: Patients with contralateral ICA occlusion were younger and more likely to be smokers; they were more likely to have chronic obstructive pulmonary disease, preoperative neurologic symptoms (56% vs 47%), nonelective CEA (16% vs 13%), and shunt placement (75% vs 53%; all P < .001). The 30-day ipsilateral stroke risk was 1.3% with vs 0.7% without contralateral ICA occlusion (P = .004). The 30-day and 1-year survival estimates were 99.0% ± 0.5% and 94.1% ± 1.1% with vs 99.6% ± 0.1% and 96.0% ± 0.2% without contralateral ICA occlusion (log-rank, P < .001). Logistic regression analysis identified prior neurologic event (P = .046), nonelective surgery (P = .047), absence of coronary artery disease (P = .035), and preoperative angiotensin-converting enzyme inhibitor use (P = .029) to be associated with 30-day ipsilateral stroke risk, but contralateral ICA occlusion remained an independent predictor in that model (odds ratio, 2.29; P = .026). However, after adjustment for other factors (Cox proportional hazards), risk of ipsilateral stroke (including perioperative) during follow-up was not significantly greater with contralateral ICA occlusion (hazard ratio, 1.21; P = .32). Results comparing propensity score-matched cohorts mirrored those from the larger data set. CONCLUSIONS: This study demonstrates likely clinically insignificant differences in early stroke or death in comparing CEA patients with and those without contralateral ICA occlusion. After adjustment for other factors, contralateral ICA occlusion was not associated with a greater risk of ipsilateral stroke (including perioperative) in longer follow-up. Mortality was greater with contralateral ICA occlusion, and this difference was more pronounced at 1 year despite younger age of the contralateral ICA occlusion group. CEA risk remains low even in the presence of contralateral ICA occlusion and appears to be explained at least in part by other factors. CEA should still be considered appropriate in the face of contralateral ICA occlusion.

A comparison of results of carotid endarterectomy in octogenarians and nonagenarians to younger patients from the Mid-America Vascular Study Group and the Society for Vascular Surgery Vascular Quality Initiative.

OBJECTIVE: Carotid endarterectomy (CEA) reduces stroke risk in selected patients. However, CEA risk profile may be different in older patients. We compared characteristics and outcomes of octogenarians and nonagenarians with those of younger patients. METHODS: Deidentified data from CEA patients were obtained from the Society for Vascular Surgery Vascular Quality Initiative (VQI) database. Prior CEA, carotid artery stent, or combined CEA and coronary artery bypass were excluded, yielding 7390 CEAs in octogenarians and nonagenarians (≥80 years of age) and 35,303 CEAs in younger patients (<80 years of age). We compared post-CEA outcomes, including periprocedural cerebral ischemic events and death, and details such as operative time, bleeding, and return to surgery. RESULTS: Octogenarians and nonagenarians were more likely to have pre-CEA neurologic symptoms (51.4% vs 45.6%; P < .001) and to have never smoked (37.8% vs 22.0%; P < .001), and they were slightly more likely to have required urgent CEA (16.1% vs 13.4%; P < .001). Stenosis ≥70% was similar (octogenarians and nonagenarians, 94.2%; younger patients, 94.4%; P = .45). Perioperative ipsilateral neurologic events and ipsilateral stroke were slightly more common among octogenarians and nonagenarians (1.6% vs 1.1% [P < .001] and 1.2% vs 0.8% [P = .002]). Multivariate modeling (logistic regression) showed that pre-CEA neurologic symptoms (odds ratios, 1.35 [P = .005] and 1.42 [P = .007]), pre-CEA ipsilateral cortical ischemic event (odds ratios, 1.18 [P < .001] and 1.20 [P < .001]), and urgency (odds ratios, 1.75 [P < .001] and 1.67 [P < .001]) remained strong predictors of any ipsilateral neurologic event and any ipsilateral stroke, respectively. However, age ≥80 years remained a significant predictor of these outcomes (odds ratios, 1.37 [P = .003] and 1.44 [P = .004]). Kaplan-Meier estimated survival was lower for octogenarians and nonagenarians at 30 days and 1 year (98.6% vs 99.4% and 93.7% vs 97.0%; log-rank, P < .001). Age ≥80 years was also associated with a greater rate of discharge to other than home after CEA, a difference that was only partially explained by comorbidities in multivariate modeling. CONCLUSIONS: CEA was performed with low rates of perioperative neurologic events and mortality. Multivariate testing showed that the higher rate of neurologic complications in octogenarians and nonagenarians appeared partially related to symptomatic status and urgent surgery; but after adjusting for these factors, age ≥80 years still predicted a slightly higher rate. Periprocedural CEA outcomes appear similar in comparing older and younger patients, although longer term survival is lower for older patients, and older patients are at greater risk of discharge to other than home. CEA was associated with slightly higher risk of neurologic complications in older patients but may be considered appropriate for selected octogenarians and nonagenarians.

A comparison of results with eversion versus conventional carotid endarterectomy from the Vascular Quality Initiative and the Mid-America Vascular Study Group.

OBJECTIVE: Carotid endarterectomy (CEA) is usually performed with eversion (ECEA) or conventional (CCEA) technique. Previous studies report conflicting results with respect to outcomes for ECEA and CCEA. We compared patient characteristics and outcomes for ECEA and CCEA. METHODS: Deidentified data for CEA patients were obtained from the Society for Vascular Surgery Vascular Quality Initiative (SVS VQI) database for years 2003 to 2013. Second (contralateral) CEA, reoperative CEA, CEA after previous carotid stenting, or CEA concurrent with cardiac surgery were excluded, leaving 2365 ECEA and 17,155 CCEA for comparison. Univariate analysis compared patients, procedures, and outcomes. Survival analysis was also performed for mortality. Multivariate analysis was used selectively to examine the possible independent predictive value of variables on outcomes. RESULTS: Groups were similar with respect to sex, demographics, comorbidities, and preoperative neurologic symptoms, except that ECEA patients tended to be older (71.3 vs 69.8 years; P < .001). CCEA was more often performed with general anesthesia (92% vs 80%; P < .001) and with a shunt (59% vs 24%; P < .001). Immediate perioperative ipsilateral neurologic events (ECEA, 1.3% vs CCEA, 1.2%; P = .86) and any ipsilateral stroke (ECEA, 0.8% vs CCEA, 0.9%; P = .84) were uncommon in both groups. ECEA tended to take less time (median 99 vs 114 minutes; P < .001). However, ECEA more often required a return to the operating room for bleeding (1.4% vs 0.8%; P = .002), a difference that logistic regression analysis showed was only partly explained by differential use of protamine. Life-table estimated 1-year freedom from any cortical neurologic event was similar (96.7% vs 96.7%). Estimated survival was similar comparing ECEA with CCEA at 1 year (96.7% vs 95.9%); however, estimated survival tended to decline more rapidly in ECEA patients after ∼2 years. Cox proportional hazards modeling confirmed that independent predictors of mortality included age, coronary artery disease, chronic obstructive pulmonary disease, and smoking, but also demonstrated that CEA type was not an independent predictor of mortality. The 1-year freedom from recurrent stenosis >50% was lower for ECEA (88.8% vs 94.3%, P < .001). However, ECEA and CCEA both had a very high rate of freedom from reoperation at 1 year (99.5% vs 99.6%; P = .67). CONCLUSIONS: ECEA and CCEA appear to provide similar freedom from neurologic morbidity, death, and reintervention. ECEA was associated with significantly shorter procedure times. Furthermore, ECEA obviates the expenses, including increased operative time, associated with use of a patch in CCEA, and a shunt, more often used in CCEA in this database. These potential benefits may be reduced by a slightly greater requirement for early return to the operating room for bleeding.

Preemptive coil occlusion of major aberrant renal artery to allow endovascular repair of abdominal aortic aneurysm with crossed fused renal ectopia.

BACKGROUND: Crossed fused renal ectopia and other similar renal anomalies are nearly always associated with major renal arterial, venous, and collecting system anomalies. These complicate both open repair and endovascular repair (EVAR) of abdominal aortic aneurysms (AAA). We present a case of successful EVAR of an AAA with crossed fused renal ectopia. PATIENT DESCRIPTION: A 76-year-old man was followed with an AAA and was also noted to have crossed fused renal ectopia. The aneurysm increased in diameter to 5.5 cm, and repair was recommended. Anatomy appeared challenging for open repair but also for EVAR because of a highly angulated neck and the major renal artery to the ectopic segment originating from the upper part of the aneurysm. However, EVAR appeared feasible if this renal artery could be sacrificed. Coil embolization of this renal artery was performed before EVAR. The patient's renal function was stable, and he suffered only a few days of abdominal pain. EVAR was performed 25 days later and required adjunctive procedures to eliminate a type 1 endoleak as had been feared because of the highly angulated neck. The patient suffered no decline in renal function and remained well 6 months later with no evidence for endoleak or other complication. COMMENT: Renal anomalies present major challenges in aortic aneurysm repair. Preemptive sacrifice of a portion of the renal mass may allow successful repair without apparent deleterious effects.

Persistent sciatic artery presenting with limb ischemia.

The persistent sciatic artery (PSA) is a rare but clinically significant congenital vascular anomaly. Clinical presentation varies and PSA can cause a number of complications, including limb loss. We describe the presenting features and treatments in two patients. The former was found to have thrombosis of a PSA with distal thromboemboli and was treated with a bypass graft. The latter was treated for an ischemic foot following successful ruptured aortic aneurysm repair and was found incidentally to have patent PSA with concomitant stenosis of the common iliac artery, which was successfully treated with stent grafting.

Results with Viabahn-assisted subintimal recanalization for TASC C and TASC D superficial femoral artery occlusive disease.

OBJECTIVES: Many investigators including TransAtlantic Inter-Society Consensus (TASC) recommend against primary endovascular treatment for severe (TASC C and D) superficial femoral artery (SFA) disease. Vein bypass is preferable but may not be appropriate due to comorbidities or lack of suitable vein. This study reviews our results with Viabahn stent graft-assisted subintimal recanalization (VASIR) for TASC C and D SFA atherosclerosis. METHODS: In all, 13 males and 14 females, mean age 72 ± 11 years underwent 28 VASIR for severe (TASC C 8 of 28, TASC D 20 of 28, and 5 of 28 no continuous infrapopliteal runoff artery) SFA disease. Indications were claudication (14 of 28 limbs), ischemic rest pain (6 of 28), and tissue loss (8 of 28). Viabahn stent graft-assisted subintimal recanalization was chosen instead of bypass due to comorbidities or lack of vein. Patients received aspirin and, if not already taking warfarin, they also received clopidogrel. Patients were examined with Ankle-brachial Index (ABI) and duplex scan at 1 month, then every 3 months after VASIR. RESULTS: Viabahn stent graft-assisted subintimal recanalization was technically successful in all. Ankle-brachial Index averaged 0.47 ± 0.17 preprocedure, 0.89 ± 0.20 postprocedure, and increased by 0.15 or more in every case. Median follow-up is 20 months. There were 3 perioperative (<30 days) and 7 later failures including revision prior to any thrombosis. One patient required amputation. Four have died, 2 with patent grafts, none from causes related to VASIR, all more than 30 days post-VASIR. Estimated 1-year primary and secondary patency were 70% ± 11% and 73% ± 10%. Failure was not significantly associated with indications, comorbidities, or runoff status. There was a clear distinction between patients with early failure and the rest of the patients. None of the 8 patients with failure in the first 8 months after surgery has a patent graft. However, of 17 grafts primarily patent at 8 months, only 2 have failed (1 thrombosed and 1 required preemptive balloon angioplasty). There was a strong trend toward better patency with 6 and 7 mm diameter compared to 5 mm diameter stent grafts. Furthermore, although warfarin was not prescribed as part of the protocol, no patient taking warfarin before and who resumed warfarin after VASIR (n=4) suffered failure. CONCLUSIONS: Despite significant early failures, we found VASIR to be durable in those who did not have early failure. Viabahn stent graft-assisted subintimal recanalization is an acceptable alternative to vein bypass in selected patients with severe SFA disease. Smaller arterial or stent graft diameter may be associated with poorer results. Warfarin may be valuable to reduce the risk of failure after VASIR.

Superficial femoral vein graft interposition in situ repair for femoral mycotic aneurysm.

Femoral mycotic aneurysms require surgical treatment to prevent progressive sepsis and hemorrhage. Some surgeons recommend simple debridement and ligation of the femoral artery, whereas others recommend reconstruction in selected cases or all cases due to concerns about high risk of limb loss. In situ reconstruction has been discouraged due to concerns about anastomotic or graft disruption by persistent infection. However, the superficial femoral vein has been used successfully as an in situ replacement after removal of infected aortic prostheses. We present two patients with femoral mycotic aneurysms, both of whom were treated successfully with in situ reconstruction using autogenous superficial femoral vein.

Percutaneous Viabahn-assisted subintimal recanalization for severe superficial femoral artery occlusive disease.

PURPOSE: To evaluate Viabahn-assisted subintimal recanalization (VASIR) in long recanalizations of the superficial femoral artery (SFA). MATERIAL AND METHODS: Twenty-eight patients (15 men, 13 women; mean age, 70.6 years +/- 11.2) were studied. Comorbidities were hypertension (n = 24), coronary disease (n = 16), and diabetes (n = 11). Presenting symptoms were disabling claudication (n = 14), rest pain (n = 6), and tissue loss (n = 8). Lesions were angiographically severe (TransAtlantic Intersociety Consensus [TASC] class D, n = 18; TASC class C, n = 8; TASC class B, n = 2); four of the 28 patients had no continuous run-off vessels. The SFA was recanalized percutaneously with standard subintimal techniques and then repaved with Viabahn stent-grafts. The ankle-brachial index (ABI) was obtained and duplex imaging performed at 1 month and then every 3 months. RESULTS: Technical success was achieved in all 28 patients without complications. The mean ABI of 0.47 +/- 0.18 before the procedure increased to 0.88 +/- 0.20 after the procedure. Seventeen of the 28 patients developed palpable foot pulses. The mean follow-up was 8.2 months +/- 3.6 (range, 1-13 months). Twelve recanalizations failed 1 day to 8 months after the procedure. Four patients underwent successful salvage, five underwent bypass, two chose no further therapy, and one required amputation. Thus, life-table primary patency is only 44% +/- 16 but secondary patency is 57% +/- 17. There was no correlation between failure and symptoms, lesion severity, or run-off status, but in eight of 12 failures, in which stents went from the adductor canal to just short of the SFA origin, stenosis occurred at the ends of the stent-grafts, which suggests that deformational forces from knee flexion may play an important role. CONCLUSIONS: VASIR shows considerable promise as a primary treatment for SFA occlusions, with diligent follow-up and aggressive repeat intervention. When failure mechanisms are better understood, VASIR may be considered as a substitute for vein bypass in suitable patients.

Patient assessment and management examination: lack of correlation between faculty assessment and resident self-assessment.

BACKGROUND: The Patient Assessment and Management Examination (PAME) is a standardized patient examination designed to assess management skills of senior residents. This study explored the relationship between faculty and resident self-evaluation by using PAME. METHODS: Nine postgraduate year (PGY) 4 and PGY5 residents were examined with a 5 case PAME. Faculty rated interactions between residents and standardized patients and residents rated themselves based on review of audio-video recordings of their interactions. We examined correlations between faculty and resident self-assessments. RESULTS: Faculty and resident ratings of physical examination skills was the only competency that correlated significantly. Correlations were not significant for the other 15 competencies (Pearson r, -.197 to .262). Correlation was no better when examined within each case. CONCLUSIONS: Although PAME may be a useful tool, this study suggests that even senior residents do not assess their performance as clinicians similarly to faculty. Further research is needed to better understand the source of these disagreements.