Hemodynamic and metabolic changes induced by temporary clamping of the thoracic aorta

Anesthetic Management for Open Thoracoabdominal and Abdominal Aortic Aneurysm Repair

Open thoracoabdominal and abdominal aortic aneurysm repairs are some of the most challenging cases for anesthesiologists because of the potential for rapid blood loss combined with clamping and reperfusion, potential use of left heart bypass, the potential need for lung isolation, and potential placement and management of a spinal drain. In addition, patients often present with other significant comorbidities and a detailed understanding of the disease process, the complex physiology throughout the case, and the intricacies of organ protection are critical.

Bilateral femoral artery compression as a technique to increase vital organ perfusion during intraoperative hypotension

Intraoperative hypotension is associated with adverse outcomes. The preferred treatment for intraoperative hypotension is to address its cause. In the interim the blood pressure can be supported by the anesthesia team with volume resuscitation and vasopressors. Additionally, preferential perfusion of vital organs, such as the myocardium and cerebrum, at the expense of non-vital vascular beds, such as the extremities, is desirable. In the state of shock, the flight or fight response will ensure perfusion of the extremities in order to prepare the organism for a physical confrontation. However, in the context of intraoperative hypotension this response is counter-productive. Therefore we propose bilateral femoral artery compression as a new technique to increase vital organ perfusion during intraoperative hypotension. This results in shunting of blood flow from the legs and towards the vital organs. Bilateral femoral artery compression can be employed by the surgical team to immediately improve blood pressure until other counter-measures against intraoperative hypotension take effect.

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.

Dopexamine hydrochloride does not modify hemodynamic response or tissue oxygenation or gut permeability during abdominal aortic surgery

PURPOSE

To assess the effects of intraoperative infusion of dopexamine (a DA-1 and B2 adrenoreceptor agonist) on hemodynamic function, tissue oxygen delivery and consumption, splanchnic perfusion and gut permeability following aortic cross- clamp and release.

METHODS

In a randomised double blind controlled trial 24 patients scheduled for elective infrarenal abdominal aortic aneurysm repair were studied in two centres and were assigned to one of two treatment groups. Group I received a dopexamine infusion starting at 0.5 microg x kg(-1) x min(-1) increased to 2 microg x kg(-1) x min(-1) maintaining a stable heart rate; Group II received a placebo infusion titrated in the same volumes following induction of anesthesia. Measured and derived hemodynamic data, tissue oxygen delivery and extraction and gut permeability were recorded at set time points throughout the procedure.

RESULTS

Dopexamine infusion (0.5 -2 microg x kg x min(-1)) was associated with enhanced hemodynamic function (MAP 65 +/- 5.5 vs 92 +/- 5.7 mm Hg, P = <0.05) only during the period of aortic cross clamping. However, during the most part of infrarenal abdominal aortic surgery, dopexamine did not reduce systemic vascular resistance index, mean arterial pressure nor oxygen extraction compared with the control group. The lactulose/ rhamnose permeation ratio was elevated above normal in both groups (0.22 and 0.29 in groups I and II respectively).

CONCLUSIONS

Dopexamine infusion (0.5 -2 microg x kg(-1) x min(-1)) did not enhance hemodynamic function and tissue oxygenation values during elective infrarenal abdominal aortic aneurysm repair.

Humoral factors and hemodynamics during cross-clamping of the thoracic aorta

The present study was designed to test the hypothesis that vasoactive compounds produced in the ischemic part of the body below an occluded aorta are responsible for the hemodynamic changes observed during cross-clamping of the thoracic aorta. The experiments were performed on 32 rabbits anesthetized with halothane that underwent experiments with cross-circulation; the blood from the inferior caval veins of rabbits A was pumped into the inferior caval veins of rabbits B. Simultaneously, exactly the same amount of blood was pumped from the jugular vein of rabbits B into the jugular vein of rabbits A. The aorta and inferior vena cava were exposed and then simultaneously cross-clamped directly below the diaphragm. The cross-clamping of the aorta and inferior vena cava in rabbits A was associated with a 29% to 44% increase in mean arterial pressure in rabbits B. The experiments support the hypothesis and suggest that endogenously produced humoral factors are responsible for at least one third to one half of the arterial hypertension that usually develops during aortic cross-clamping.

The influence of adenosine triphosphate on left ventricular function and blood flow distribution during aortic crossclamping in dogs

To evaluate the influence of adenosine triphosphate (ATP)-induced vasodilation on myocardial performance and blood flow during aortic crossclamping (XC), ten dogs were instrumented to measure left ventricular (LV) pressure and dimensions. Regional LV function was assessed from the percentage of systolic shortening, whereas the slope of the linear regression of the LV end-systolic pressure-diameter relationship was used as an index of overall contractility. The regional blood flow distribution was measured from sequential injections of radioactive microspheres. Following XC, systemic arterial pressure proximal to the clamp (SAPa), LV end-diastolic pressure (LVEDP), LV end-systolic meridional wall stress (WS), and central venous pressure (CVP) increased significantly, whereas the cardiac index (CI) and heart rate did not change. After 30 minutes of ATP infusion (1 mg/kg/min) SAPa, LVEDP, WS, and CVP returned to control levels, CI increased significantly compared with XC alone, and vascular resistance fell below the control level. ATP produced a threefold increase in myocardial blood flow and shifted the intramural distribution in favor of the endocardial layer. In conclusion, our investigation of the effect of ATP on aortic XC in a canine model showed the drug to produce a smooth, predictable, and rapid reduction in left ventricular preload and afterload. This was accomplished with minimal changes in distal organ perfusion, some improvement in measured cardiac performance, and a large increase in myocardial blood flow.

Spinal cord infarction in disease and surgery of the aorta

Diseases of the aorta and surgery of the aorta can produce spinal cord damage. There are major variations in blood supply to the spinal cord between individuals. The spinal cord may be tamponaded by increased spinal fluid pressure subsequent to clamping the aorta. Both of these factors may contribute to spinal cord infarction. The available methods and procedures to protect the spinal cord during surgery are discussed.

[Acid-base equilibrium and vascular exclusion of the liver: study of 30 extensive hepatectomies]

The acid-base disorders after hepatic vascular exclusion (HVE) were studied in 30 major liver resections. HVE included portal triad clamping and occlusion of the inferior vena cava below and above the liver, without venous shunt nor cooling. Clamping of the supra-coeliac abdominal aorta (AoC) was associated with HVE in 12 patients. HVE lasted 18 to 65 min (mean 37 min). Liver ischemia and splanchnic blood pooling resulted in metabolic acidosis and hyperlactatemia. In order to prevent his acidosis, prophylactic administration of NaHCO23 was used during the first 19 cases. This induced significant metabolic alkalosis during HVE and the early postoperative period; increasing experience made us reduce the amount of NaHCO3. After the release of the clamps, Paco2 increased 25% following HVE without AoC (p less than 0.001) and 53% following HVE with AoC (p less than 0.001). In an attempt to distinguish between the effects of the metabolic acidosis and the rise of Paco2 in the fall of pH which occurred after removal of the clamps, NAaHCO3 was deliberately not given in the last 11 patients. Acidosis appeared to be greater with AoC than without and mainly related to the rise of Paco2. A fall of Paco2 to its initial value was always followed by the return of pH to the normal range. This study demonstrated the human ability to correct spontaneously the acidosis which followed HVE. The need for NaHCO3 after HVE reflected a poor hemodynamic state after major liver resection rather than a metabolic consequence of hepatic ischaemia.