Anesthetic management of descending thoracic aortobifemoral bypass for aortoiliac occlusive disease: Our experience.

BACKGROUND: Complete obstruction of the abdominal aorta at the renal artery level is a difficult surgical problem. Aortic clamping and declamping can lead to profound haemodynamic changes, myocardial infarction, ventricular failure or even death may result. These complications are important challenges in anesthetic management of these patients.
METHODS: Between August, 2010 and April, 2012, descending thoracic aorta to femoral artery bypass grafting was used to revascularize lower limbs in 11 patients in our institute. The anesthetic management of these patients is described here. Epidural catheter placement was done in T 5-6 or T 6-7 space for post operative pain relief. Induction was done by, Inj. Glycopyrolate 0.2 mg, Inj. Fentanyl 5 μg/kg., Inj. Pentothal sodium 5 mg/kg, Inj. Rocuronium 0.9 mg/kg, IPPV done. Left sided double lumen tube was inserted, Maintenance of Anesthesia was done by O2 + N2 O (30:70). Increments of Vecuronium and Fentanyl were given Monitoring of Heart rate, arterial pressure, central venous pressure were continuously displayed. The available pharmacological agents were used when there is deviation of more than 15% from base line.
RESULTS: In our study, inspite of measures taken to control rise in blood pressure during aortic cross clamping, a rise of 90 mm of Hg in one patient and 60-80 mm of Hg in four patients was observed, which was managed by sodium nitropruside infusion. At the end of surgery seven patients were extubated on the operation table. In remaining four patients DLT was replaced by single lumen endotracheal tube and were shifted to ICU on IPPV. They weaned off gradually in 3-5 hours. In our series blood loss was 400 ml to 1000 ml. There was no mortality in the first 24 hours. Postoperative bleeding was reported in one case which was re-explored and stood well.
CONCLUSION: The anesthetic technique during aortic surgery is directed at minimizing the hemodynamic effects of cross clamping in order to maintain the myocardial oxygen supply demand ratio.

INTRODUCTION

Atherosclerotic disease is generally diffuse involving single or multiple regions of blood vessel. Atherosclerosis of peripheral arterial system contributes to significant morbidity and mortality. The standard method of aortoiliac revascularization for occlusive disease is through a transabdominal approach. When this option is considered hazardous or not feasible, the usual alternative is axillobifemoral bypass. Axillobifemoral bypass is suitable for certain patients with high medical risk. However, a more durable, long-term alternative is desirable for those with a longer life expectancy.[1]

Descending thoracic aorta to femoral artery bypass has major advantages over axillofemoral bypass because it provides better inflow, requires a shorter graft length, offers better protection of the graft from infection and mechanical trauma, and carries a superior patency rate.[2]

The purpose of the study was to discuss anesthetic management and problems of aortic cross clamping which is the major anesthetic challenge. The anesthetist should be aware of the problems of proximal aortic clamping, renal preservation during clamping and declamping of the aorta posed by this surgical approach, and the potential need for massive blood transfusion with its associate problems.

The anesthetic management and the problem faced by anesthetist during these surgeries are discussed with particular emphasis on the consequences and management of aortic cross clamping.

Method

Eleven patients were treated with descending thoracic aortobifemoral bypass for aortoiliac occlusive disease between August, 2010 and April, 2012. Demographic data, comorbid factors, and preoperative finding were noted [Table 1].

Table 1

Demographic data and preoperative findings

Age of the patients ranged from 48 to 77 years (mean, 59 years). All patients were male. Weight of the patients ranged from 40 to 70 kg (mean, 55 kg).

All patients had disabling intermittent claudication or rest pain. Five patients had ischemic ulcers; four had gangrenous toes or distal foot.

Angiography revealed stenosis of infrarenal aorta, juxtarenal aortic occlusion, and stenosis of common and external iliac artery in all cases [Figure 1]. Abdominal aortobifemoral was considered to be hazardous as there was no suitable site for aortic cross clamping.

Figure 1

Preoperative angiography

Pulmonary function tests showed mild chronic obstructive pulmonary disease in four, moderate obstructive changes in two, normal in four, and severe restrictive changes in one patient. Other comorbidities were coronary artery disease in two patients, hypertension in seven, renal impairment in two patients, and diabetes in one patient.

COPD: chronic obstructive pulmonary disease

CAD: coronary artery disease

Anesthetic Management

All the patients were evaluated thoroughly in the preoperative visit.

One day before operation, all patients were taken in the operation theater for thoracic epidural catheter placement in T 5-6 or T 6-7 space for postoperative pain relief.

All patients received oral premedication with Tab. Alprazolam 0.5 mg. at 6 a.m and patients who were on anti-hypertensive drugs were also given with a sip of water. On arrival in the O.T., IV access was taken on dorsum of left hand by 18G. cannula. ECG (electrocardiography) electrodes were applied and after sedation with IV midazolam 2 mg, radial artery cannulation was done. Right internal jugular vein was cannulated for CVP (cental venous pressure) measurement under local anesthesia.

Induction was done by Inj. Glycopyrrolate 0.2 mg, Inj. Fentanyl 5 μg/kg., Inj. Pentothal sodium 5 mg/kg, Inj. Rocuronium 0.9 mg/kg, IPPV(Intermittent positive pressure ventilation) done.

Left-sided double lumen tube (DLT) was inserted; appropriate maneuver were carried out to ensure correct positioning of DLT before and after positioning of the patients.

Maintenance of anesthesia was done by O2 + N2 O (30:70). Increments of Vecuronium and Fentanyl were given during the procedure.

After induction, patients were catheterized by Foley's catheter, nasogastric tube was introduced and checked, and temperature probe was introduced in the nasopharynx.

Monitoring of heart rate, ECG, arterial pressure, and central venous pressure were continuously displayed [Table 2]. The available pharmacological agents were used when there is deviation of more than 15% from the baseline.

Table 2

Hemodynamic and ventilatory variables before cross clamping of aorta

EtCo2 (End-tidal carbon dioxide tension), Spo2, temperature, and urine output were monitored.

In order to facilitate an instantaneous response to change in hemodynamic parameters, during surgery Inj. Sodium nitroprusside (50 mg in 500 ml 5% dextrose.conc.100 mic/ml), Inj. Dopamine (400 mg in 500 ml 5% dextrose conc. 800 μg/ml), and Inj. Nitroglycerine (50 mg in 500 ml 5% dextrose conc. 100 μg /ml) were prepared and connected with infusion pump.

The patients were positioned with the left hemithorax elevated 30 to 45° and pelvis as flat as possible to allow access to both groins [Figure 2].

Figure 2

Patient position

Surgical Technique

The chest, abdomen, and both groins were prepared and draped. Antero-lateral thoracotomy was done, via the 7th intercostals space. Proximal anastomosis of a 14 × 7 mm Dacron bifurcated graft was performed end-to-side at the lower descending thoracic aorta [Figure 3]. The graft limbs were drawn through a tunnel between rectus abdominal muscle and peritoneum to a short midline incision at level of umblicus, from which each limb of the graft was drawn through a subcutaneous tunnel to each side of the groin and anastomosed to each common femoral artery.

Figure 3

Aortobifemoral bypass graft in-situ

Aortic cross clamping

In order to decrease the likelihood of an initial massive rise in systolic blood pressure, the aortic clamp was not applied until the effect of the vasodilator infusion was apparent.

EtCO2 was maintained between 18-35 mmHg. Fractional inspired oxygen concentration (Fio2) was increased from 0.3 to 0.5 during one lung ventilation.

Patients were heparinized with inj. Heparin 1 mg/kg 5 minutes prior to aortic cross clamping.

Arterial blood gas was measured, and if metabolic acidosis was found, it was corrected by inj. sodium bicarbonate.

In our series, clamp time varied from 15 to 35 minutes

Aortic declamping

Vasodilator therapy was discontinued and fluid volume was transfused to keep CVP above 10 cm of H2O.

All patients received 25 g mannitol to improve urine flow following the period of renal ischemia.

Blood transfusion and fluid management were done according to losses. In our series, no patients required massive blood transfusion. Transfusion of blood varied from 400 to 1000 ml of whole blood.

At the end of surgery, of 11 patients, seven of them were extubated on the operation table after proper reversal. In the remaining four patients, DLT was replaced by single lumen endotracheal tube and were shifted to ICU on IPPV. They weaned off gradually in 3 to 5 hours. Postoperative pain relief was done by continuous infusion of inj. Ropivacaine 0.2% 8 ml/hour for 48 hours. Thoracic epidural catheter was removed after all aseptic precaution and watched for bleeding from the site.

Postoperatively (3 weeks after surgery) CT angiography was done showing good flow in the Aortobifemoral grafts [Figure 4].

Figure 4

Postoperative CT angiography

DISCUSSION

Descending thoracic aorta to femoral artery bypass grafting is considered a good alternative procedure for revascularization in cases of aortic graft failure, graft infection, and other intra-abdominal pathologies not amenable to standard aortofemoral revascularization. Thoracofemoral bypass was first described by Blaisdell et al.[3] as an alternative to the standard aortofemoral bypass. Subsequently, several groups have recommended this technique as an alternative or first choice procedure for aortoiliac occlusion.[45]

Thoracic aortic cross clamping with pharmacological control of cardiovascular hemodynamics, described by Crawford, is associated with increased survival and fewer complications.[6] The hemodynamic response to aortic cross clamping depends on the site of clamping, the presence or absence of collateral vessels, and left ventricular function. Infrarenal cross clamping is associated with a 36 to 40% increase in vascular resistance.[78] The viscera and liver receive 30% of cardiac output and the kidneys just under 25%[9] so that clamping above the coeliac axis is likely to cause greater hemodynamic changes. Thoracic aortic clamping can cause a rise of 68% in total peripheral resistance compared with baseline values.[10] In our study, despite of measures taken to control rise in blood pressure during aortic cross clamping, a rise of 90 mm of Hg in one patient and 60 to 80 mm of Hg in four patients was observed [Table 3], which was managed by sodium nitroprusside infusion at the rate of 3 to 60 ml/hour. Aortic clamping above the coeliac artery decreases ejection fraction and produces ventricular wall motion abnormalities, stroke volume and cardiac output therefore fall which can be determined by transesophageal echocardiography.[11]

Table 3

Hemodynamic and ventilatory variables during cross clamping of aorta

Patients with coronary artery disease are at greater risk of reduction in cardiac output than those with normal myocardial function.[1213] In one of our patient who was a known case of CAD, we preferred to infuse NTG during aortic cross clamping as it may be useful in these patients to reduce PCWP and improve myocardial contractility by moving them to more favorable position on the frank–Starling curve.[14]

Heart rate is a determinant of coronary artery blood flow and is of particular importance in patients with coronary artery disease in whom tachycardia may lead to myocardial ischemia. In such patients, we used esmolol 0.5 mg/kg. The cardiac output measurement was not possible in our series as we did not put pulmonary artery catheter, so ventricular functions were assessed indirectly by arterial pressure and CVP.

Cross clamping of the thoracic aorta decreases renal blood flow by 85 to 94%.[15] In anticipation of renal ischemia, we infused mannitol 25 g during aortic clamp. Patients were observed for urine output continuously and none of our patients had decrease in urine output.

Hypotension following aortic declamping occurs because of sudden fall in peripheral vascular resistance and blood loss from the graft. Reduced distal organ perfusion also causes a metabolic acidosis on clamp release, leading to dysrhythmias and myocardial depression. To prevent hypotension, vasodilator therapy was discontinued and fluid volume was transfused to keep CVP above 10 cm of H2 O; despite of this, systolic pressure fell to 50-80 mm of Hg in six patients, with little or no change in the remaining five patients [Table 4]. In the three patients, restoration of blood pressure was achieved by rapid infusion of blood and in the other three patients, Dopamine @5 ml/hour was also infused. Massive blood loss can occur during graft replacement and needs careful management. Blood transfusion and fluid management was done according to losses. In our series, transfusion of blood varied from 400 to 1000 ml of whole blood [Table 5]. The hemodynamic events of declamping can be avoided by the administration of intravenous fluids, correction of acidosis, and electrolyte imbalance with increments of inj. sodabicarb 7.5% before release of aortic clamp and if needed use of inotropes. Saleh et al. preferred continuous infusion of bicarbonate instead of bolus administration in the prevention of systemic acidosis.[16] Temporary or permanent ischemia of organs distal to the site of aortic clamping may result if clamp time is prolonged or collateral circulation is cut off. In our series, clamp time varied from 15 to 35 minutes and also there might be presence of collateral vessels in patients of chronic obstruction of aorta;[17] hence, we did not face such problem.

Table 4

Hemodynamic and ventilatory variables after de clamping of aorta

Table 5

Operative data and outcome

The major limitation to this surgical technique is the morbidity rate associated with thoracotomy in a relatively high-risk vascular surgery population. The minimally invasive video endoscopic procedure has been shown to improve the post-operative course and comfort of patients in general and thoracic surgery. The same benefits could be expected from a video endoscopic surgery involving the thoracic aorta.[18]

Summary

The problems of anesthesia during aortic surgery have been outlined. The hemodynamic consequences of thoracic aortic cross clamping and the method employed to overcome them have been discussed. The results of surgery in 11 patients have been presented.

The anesthetic technique during aortic surgery is directed at minimizing the hemodynamic effects of cross clamping in order to maintain the myocardial oxygen supply demand ratio. Dysrhythmias, myocardial infarction, and ventricular failure may otherwise occur. For success in such major surgery, a thorough preoperative assessment of the patients should be done to optimize the condition. Close monitoring of hemodynamic parameters and their rapid control during clamping and declamping is essential. Need for close cooperation between surgeon and anesthetist at all stages should be emphasized.