© Borgis - Postępy Nauk Medycznych 8/2012, s. 651-659
*Paweł Dąbek, Włodzimierz Hendiger, Grzegorz Madycki, Walerian Staszkiewicz
Zmiany przepływu krwi w obrębie naczyń trzewnych i miednicy u chorych po implantacji stentgraftu z powodu tętniaka aorty brzusznej
Changes in blood flow within visceral vessels and vessels of the pelvis in patients after stent graft implantation due to an abdominal aortic aneurysm
Department of Vascular Surgery and Angiology of the Medical Centre for Postgraduate Education, The Jerzy Popiełuszko Memorial Bielański Hospital
Head of Department: prof. Walerian Staszkiewicz MD, PhD
Wstęp. Operacje tętniaków aorty i tętnic biodrowych wiążą się z występowaniem pooperacyjnego niedokrwienia okrężnicy i umieralnością ogólną z tego powodu 1-8%. Wewnątrznaczyniowe techniki leczenia tętniaków przy użyciu stentgraftu nie uwolniły chirurgii od tego powikłania. Posługując się badaniem USG-cdd tętnic trzewnych uzyskujemy informacje o stanie łożyska trzewnego, co pozwala określić ryzyko wystąpienia tego powikłania.
Materiał i metody. Rozpoczęto badania prospektywne USG-cdd tętnic trzewnych na 60-osobowej grupie chorych leczonych z powodu TAB stentgraftem w porównaniu do 78-osobowej grupy kontrolnej chorych leczonych odlegle z powodu TAB i zespołu Leriche operacją otwartą wszczepienia protezy aortalnodwuudowej. W obu grupach posługiwano się techniką USG-cdd i oceniano morfologicznie i czynnościowo tętnice trzewne: PT, TKG, TKD, tętnice biodrowe wewnętrzne. Wstępnie przebadano 10 chorych. Określano standardowe parametry przepływu krwi metodą dopplerowską. Pomiary wykonywano przed i po operacji wszczepienia stentgraftu. Dla określenia ryzyka niedokrwienia posługiwano się opracowanymi wcześniej tzw. wskaźnikami niedokrwienia: prędkościowym i oporowym.
Wyniki. W przebadanym materiale prognozowano przy pomocy USG-cdd przed operacją i potwierdzono klinicznie po operacji 3 łagodne przypadki niedokrwienia miednicy pod postacią chromania i 1 przypadek niedokrwienia okrężnicy pod postacią przemijającej biegunki. Opisano ultrasonograficzne czynniki ryzyka niedokrwienia i ustalono sposób określenia rodzaju niedokrwienia (okluzyjne/nieokluzyjne).
Wnioski. 1) USG-cdd tętnic trzewnych pozwala prognozować niedokrwienie okrężnicy po operacji TAB. 2) Parametrem prognostycznym niedokrwienia okluzyjnego jest wskaźnik prędkościowy niedokrwienia (WPN) znacznie niższy do jedności (<< 1,0), a pomocniczym wskaźnik oporowy niedokrwienia (WON) wyższy od jedności (≥ 1,0). 3) Parametrem prognostycznym niedokrwienia nieokluzyjnego jest wskaźnik oporowy niedokrwienia (WON) niższy od jedności (≤ 1,0), a pomocniczym wskaźnik prędkościowy niedokrwienia (WPN) wyższy od jedności (≥ 1,0). 4) Po operacji wszczepienia stentgraftu dominuje czynnik okluzyjny niedokrwienia. 5) Po operacji klasycznej TAB działają oba czynniki niedokrwienia okluzyjny i nieokluzyjny.
Introduction. Surgery of aortic aneurysms and iliac artery aneurysms are associated with postoperative ischemic colitis and corresponding general mortality of 1-8%. Endovascular aneurysm treatment technique using stent graft did not prevent the occurrence of this complication. Using CDD ultrasound for the visceral arteries evaluation, we obtain information on condition of the celiac vascular bed, which allows determining the risk of this complication occurrence.
Material and methods. A prospective study started in reference to Colour Duplex-Doppler (CDD) ultrasound evaluation of the visceral arteries in a group of 60 patients treated for AAA by a stent graft compared to a control group of 78 patients undergoing long-term treatment due to AAA and Leriche syndrome treated with open surgery of aortobifemoral Y-graft implantation. In both groups, CDD ultrasound technique was used in order to evaluate morphological and functional aspect of the visceral arteries: CT, SMA, IMA, and the internal iliac arteries. Initially, 10 patients were examined. Standard parameters of blood flow were determined by Doppler method. Measurements were performed before and after a stent graft implantation. In order to determine the risk of ischemia previously developed so-called indicators of ischemia were used: velocity and resistance.
Results. In the studied material, predictions with CDD ultrasound were made before surgery and these predictions were verified after a surgery, which resulted in clinical confirmation of three cases of mild pelvic ischemia in the form of intermittent claudication, and 1 case of ischemic colitis in the form of transient diarrhoea. The ultrasound risk factors for ischemia were described and the manner of establishing type of ischemia (occlusive/non-occlusive) was developed.
Conclusions. 1) CDD ultrasound evaluation of the visceral arteries is able to predict colonic ischemia after AAA surgery. 2) A prognostic parameter for an occlusive ischemia is the velocity ratio of ischemia (VRI), which is significantly lower than one (<< 1.0), and the secondary resistance ratio of ischemia (RRI), which is higher than one (≥ 1.0). 3) A prognostic parameter for a non-occlusive ischemia is RRI lower than one (≤ 1.0), and secondary VRI higher than one (≥ 1.0). 4) After a stent graft implantation, an occlusive factor of ischemia is dominating. 5) After the AAA surgery, both factors of ischemia are acting, an occlusive and non-occlusive.
In recent years, classical open surgeries for implantation of an artificial bypass graft in treatment of abdominal aortic aneurysms (AAA) have been replaced with a stent graft implantation through an inguinal approach (1).
Inserting prosthesis into the aneurysmal sac-implantation of a stent graft through a small cut at the femoral artery, and then with use of new excellent equipment, through percutaneous puncture of the artery, is commonly used method of protecting the patient against severe complications or death due to the aneurysm rupture (2).
Abdominal aortic aneurysms are quite frequently accompanied by aneurysmal dilation of the iliac arteries, which also require endovascular repair (3).
Endovascular repair surgery of the abdominal aorta with a stent graft (EVAR) related to lower surgical risk, is not free from secondary interventions, also after a few years following implantation (4, 5).
EVAR allows performing the procedure in a patient, who is at high risk of classical surgery (6, 7). During the procedure, the vessels, which are the branches of the abdominal aorta (the inferior mesenteric artery – IMA, the lumbar arteries), or sometimes the branches of the common iliac arteries (internal iliac arteries – IIA), are covered with an implant (8).
Complete morphological evaluation of the trunks of the visceral arteries and iliac arteries is sufficient in CT-scan with administration of the contrast medium (CT angiogram) (9).
Morphological and functional evaluation is possible in ultrasound evaluation using colour duplex Doppler technique (CDD ultrasound) (10). Collaterals and final intestinal arteries remain beyond the range of a direct evaluation (11). Through measurement of some flow ratios (pulsation index – PI, resistance index – RI) we may establish approximate condition of the intestinal resistance bed, which includes arterioles, precapillary sphincters and capillaries (fig. 1) (12).
Fig. 1. Vascular components of the peripheral resistance.
Evaluation of the visceral arteries under constant technical conditions, and under fasting condition, is conducted before and after surgery (11). A question arises regarding ability to evaluate the visceral bed of the inferior segment of the alimentary tract in patients undergoing endovascular surgeries (13).
aim of the study
Detection of changes in blood flow parameters within the area of the abdominal cavity and the pelvis after stent graft implantation in treatment of the aortic aneurysm comparing to classical surgeries.
Material and methods
A control group comprised 78 patients treated with classical surgery method at the Clinic of Vascular Surgery and Angiology in 1995-2002 due to the abdominal aortic aneurysms and aortoiliac occlusive disease. The patients were qualified for surgery based on clinical and ultrasound evaluation. The group included 50 patients with simple aneurysms located below the renal arteries, 5 patients with ruptured aneurysms and 23 with impaired patency of the aorta and the iliac arteries, who belonged to the same risk group in terms of evaluation of the visceral flow hemodynamics.
Qualification started in reference to 60 patients treated with aortoiliac stent graft implantation due to abdominal aortic and iliac artery aneurysm. Initially, 10 patients were evaluated (fig. 2).
Fig. 2. Material.
Previous experience gained in evaluation of the control group was transferred to a current studied group in order to conduct comparative analysis.
All fasted patients underwent standard CDD ultrasound study, which was focused on results of morphological and functional evaluation of the visceral arteries and the iliac arteries. Ultrasound machine Siemens Antares Premium and a broad-band probe convex 5 MHz were used.
Basic study includes evaluation of the coeliac trunk (CT), the superior mesenteric artery (SMA), the inferior mesenteric artery (IMA), and the internal iliac arteries (IIA).
Morphological evaluation includes detecting and establishing percent of stenosis of the visceral artery.
Functional evaluation includes quantitative and qualitative assessment of flow with support of analysis of the blood flow velocity using Fourier analysis curve, automatically performed by the ultrasound machine.
Quantitative assessment relates to the level of the systolic velocity (SV), average velocity (AV), end diastolic velocity (EDV), resistance index (RI), and pulsation index (PI).
Qualitative assessment (nature of the flow) includes detecting flow direction, grouping velocity components above or below the baseline, recognizing high resistance flow or low resistance flow, and establishing type of a flow phase (single-phase, two-phase, three-phase).
Using so-called ultrasound ischemia ratios established in a control group (velocity ratio of ischemia (VRI) and resistance ratio of ischemia (RRI)), it was planned that after evaluation of the whole material, the risk of a potential ischemia would be determined and form of ischemia would be predicted (occlusive or non-occlusive ischemia).
10 patients, who underwent endovascular aneurysm repair (EVAR) procedure, have been examined so far. In 70% of patients stent graft was implanted into the aorta and the common iliac arteries, and in 30% of patients it was implanted into the aorta and the external iliac arteries (EIA) (fig. 3).
Fig. 3. Classification of the studied group by type of the stent graft.
IMA was initially patent in 80% of patients. Similar results were obtained in the control group. In classical surgery, the straight prosthesis was implanted in 75%, and branched prosthesis in 25% of the patients (fig. 4), and IMA was patent in 93% of cases.
Fig. 4. Classification of the control group by type of the prosthesis.
Based on results of ultrasound evaluation, it was predicted that symptoms of ischemia in the pelvis and the colon would occur in all patients with the prosthesis, which branches were placed in EIA (30%) – IIA coverage. The risk of ischemia was established by visualizing common iliac artery aneurysms reaching the orifices of IIA.
The risk group included the patients with SMA stenosis exceeding 60%. High degree stenoses in SMA were not detected. Small and medium stenoses located in the initial segments, were caused by laminae coming out of the aortic wall.
Superiority in flow parameters of IMA over SMA was established before surgery in 3 patients. No significant morphological and functional changes were detected in CT; therefore, the role of this artery was omitted in perfusion of the pelvis and the colon.
Based on clinical evaluation, signs of ischemia in pelvis were established in 2 patients in form of pelvic claudication. Claudication and postoperative diarrhoea without signs of rectal bleeding occurred in 1 patient. The diarrhoea receded after 5 days. In all 3 patients with mild symptoms of ischemia (30%), the claudication was present on the day of discharge from the hospital. The symptoms occurred in 2 patients with the prosthesis in EIA and in 1 patient due to primary occlusion and stenosis in IIA.
Stenoses in IIA were located in places of branching off. Single aneurysm of the right IIA was located, and then it was covered with a branch. In the control group, half of the patients revealed abnormalities within IIA: stenoses, one- or two-sided occlusions, aneurysms.
In the studies group, we established that there was no difference in flow parameters in the arteries without stenoses and in the ones with stenoses comparing to the control group, and similarly, statistically significant increase in systolic velocity in SMA and its statistically significant increase or decrease in IMA and decrease in IIA, comparing to reference value for healthy subjects.
Similarly, RI values in CT, SMA, and IIA in both groups oscillated at higher levels comparing to reference value for healthy subjects. In cases, where parametric superiority of IMA occurs, the flow reveals low-resistance, and in SMA it reveals high-resistance. No other differences in reference to IMA were observed comparing to reference value for healthy subjects.
Before a surgery, it was observed in patients at risk of ischemia, who belonged to the control group, that flow in IMA revealed signs of low-resistance, and in SMA, it revealed signs of high-resistance. These patients demonstrated the highest number of indications for repeated implantation into IMA.
In 3 patients from the studied group, symptoms of ischemia were confirmed by results of ultrasound measurements of ratios of ischemia (VRI and RRI).
Detected values of PI in both groups oscillated at the similarly higher levels than it did in healthy subjects.
In studied group, ultrasound evaluation is a method of choice in detection and control of AAA (14). Specificity and sensitivity of ultrasound evaluation in detection of AAA reaches 100%. Disadvantage of ultrasound method is the fact that the aorta and its collaterals are not visible due to obesity or flatulence. There is a phenomenon of variable evaluation of the diameter and morphology of the wall depending on experience of an evaluating person. Morphological evaluation of suprarenal and subrenal part, para-aortic area and detection of iliac artery aneurysms are applicable (9, 15-17). If there is imminent need to perform surgical intervention, we perform basic preoperative evaluation – CT angiogram. CT angiogram allows selecting surgical method (classical, endovascular) and correct measurement in order to select an appropriate prosthesis for EVAR procedure (18).
In 30-day observation following classical surgery, general mortality rate is approximately 1-8%. Rate of other complications reaches 13-40%. Disturbance of intestinal function, ischemia and occlusion occur in 2-11% of cases (19). Special complication with general mortality rate of 2% is a colonic ischemia. Incidence of postoperative colonic ischemia reaches 11-36% after classical elective surgeries and 40-60% after surgeries performed in ruptured aneurysms (20). Mortality rate is 50% after elective surgeries and 90% after surgeries performed in ruptured aneurysms (11, 21, 22).
Previous comparison of results obtained in ultrasound evaluation of the visceral arteries in the control group with postoperative results of fibersigmoidoscopy (FSS), allowed determining the risk of ischemia. Indications were established for protecting perfusion of the colon by reimplantation of IMA to the vascular prosthesis. Necessity to use the aortobifemoral Y-graft, if IMA is ligated and reversed inflow is impaired to both IIA, was considered as an indication for implantation of IMA to the prosthesis. Ultrasound indications included: hemodynamically significant, average or large SMA stenosis, large CT stenosis coexisting with SMA stenosis, parametric superiority of flow in normal IMA over the flow in SMA, impaired inflow to IIA, anatomical anomalies of the visceral arteries (documented lack of connections in collateral circulation).
In case of less invasive EVAR method, in postoperative 30-day observation, general mortality rate is 1.2-4.6%. Percentage of cardiological complications is lower – 3.3%, renal complications up to 5.5% and local complications up to 9-16% (23). It is difficult to define incidence of specific complications, which include internal leaks outside of the prosthesis lumen (endoleaks). They lead to filling the aneurismal sac, endograft migration and they contribute to the aneurysm rupture in later period (24, 25).
Covering IMA and IIA with a stent graft results in ischemia in the intestines and the pelvis. Symptoms of ischemia with low and medium progression are associated with occurrence of the rest pain and exercise pain of the hips (pelvic claudication) and disturbed defecation. In advanced ischemia, typical symptoms occur and they include severe pain, abdominal bloating, diarrhoea and bleeding from the final segment of the gastrointestinal tract, worsening in general condition, gradual development of multiorgan failure (MOF) with respiratory failure and renal failure (26, 27).
Approximately 20% of EVAR in ruptured aneurysms are followed by an abdominal compartment syndrome (ACS), which is an effect as well as a cause of prolonged non-occlusive ischemia of the intestines, which leads to necrosis (28-30).
Furthermore, about 11% of patients suffer from ischemia of the spinal cord, which in mild forms lead to the urine retention, and in acute forms it leads to a lower limb paralysis (31).
Contrast medium used before surgery in CT angiography and during surgery intensifies renal failure caused by lowered flow, hypotension and embolism resulted from thrombi of the aortic aneurysm (32, 33).
In the studied group after EVAR, except for 3 cases of mild ischemia, one patient suffered from transient renal failure, which was controlled with intravenous infusions of fluids. All patients were safely discharged from the hospital.
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