Increased left ventricular contractility during cross-clamping of the descending thoracic aorta

Regional distribution of blood flow during proximal aortic cross‐clamping: An experimental study using coloured microspheres

OBJECTIVE

To investigate the effect of thoracic aortic cross-clamping on blood perfusion of the brain, spinal cord, heart, muscular tissue and visceral organs.

MATERIAL AND METHODS

Nine pigs underwent 30 min cross-clamping of the descending thoracic aorta. Multiple coloured microspheres (15.0 microm +/- 0.1) were infused into the left ventricle before and during aortic cross-clamping (XC) and after declamping (DC). Tissue samples were analysed by spectrophotometry.

RESULTS

Blood perfusion of the middle and lower segments of the spinal cord was significantly reduced during aortic XC. Perfusion of the brain was not significantly altered by aortic XC, while perfusion of myocardium increased 3-fold. During XC, perfusion of the deltoid muscle and diaphragm increased 5-fold and 13-fold, respectively, while a decrease was found in the gluteus muscle. Renal blood flow was significantly reduced during XC. Finally, XC induced a significant decrease of perfusion in the bowel, spleen, liver and pancreas.

CONCLUSION

During XC of the thoracic aorta, the perfusion of the muscular tissue was significantly increased proximal to the level of XC. The circulation of the brain was unchanged, probably because of autoregulatory mechanisms. Blood perfusion of the myocardium increased 3-fold during XC.

Changes in hemodynamics and acid-base balance during cross-clamping of the descending thoracic aorta. A study in patients operated on for thoracic and thoracoabdominal aortic aneurysm

AIM OF THE STUDY

In the clinical situation there is discrepancy between various investigations regarding the cardiac response of thoracic aortic cross-clamping. The aim was therefore to investigate the hemodynamic response and blood gases during proximal aortic cross-clamping (XC) in patients operated for descending thoracic and thoracoabdominal aortic aneurysm without circulatory support.

PATIENTS AND METHODS

Altogether 51 patients operated on for thoracoabdominal (n=31) or descending thoracic aortic aneurysm (n=20) were included in the investigation. All patients were operated with aortic XC, but no circulatory support was applied. Hemodynamic variables and blood gases were recorded before and during XC.

RESULTS

A significant increase in cardiac output during XC from 4.7 to 6.0 liters/min was observed (p<0.01). There was a similar percentual increase in heart rate and also the proximal systolic blood pressure increased. A metabolic acidosis occurred during XC.

CONCLUSION

Cardiac output was significantly increased during XC in patients operated on for thoracoabdominal or descending thoracic aneurysm using direct aortic XC without circulatory support. Simultaneously, the heart rate was increased and there was a hyperdynamic circulatory state proximal to the aortic clamp. Redistribution of the blood volume in addition to catecholamine release may be responsible for the observed changes. These observations may influence the selection of operative strategy for some of these patients.

A prolonged spinal cord ischaemia model in pigs. Passive shunting offers stable central haemodynamics during aortic occlusion

OBJECTIVES

to evaluate the effect of a modified aortic shunt on central haemodynamic variables during experimental thoracic aortic occlusion in a prolonged spinal cord ischaemia model.

MATERIAL AND METHODS

central haemodynamic variables were evaluated during aortic cross-clamping. In the shunt group (n=11), after the placement of proximal and distal aortic clamps, distal aortic perfusion was restored through an aortoiliac shunt via the left subclavian artery. In the no-shunt group (n=11), spinal cord ischaemia was achieved with only proximal aortic cross-clamping. The clamping time was 60 minutes in the shunt group and 30 minutes in the no-shunt group.

RESULTS

in the no-shunt group, all animals needed inotropic support, vasodilators and buffers during the experiment. None of these drugs were needed in the shunt group. In the no-shunt group, cross-clamping caused a significant increase in mean arterial pressure and heart rate compared to baseline values. These variables were stable in the shunt group during aortic occlusion. In the reperfusion period cardiac output, heart rate and arterial pCO(2)were significantly higher in the no-shunt than in the shunt group.

CONCLUSION

the present experimental spinal cord ischaemia model, using double aortic cross-clamping with shunt, offers improved central haemodynamics. This enables the study of prolonged selective spinal cord ischaemia without interaction from vasoactive drugs or systemic reperfusion.

Cardiac output measurements during cross-clamping of the descending thoracic aorta in pigs. A comparison between transit-time ultrasound, thermodilution and pulsed Doppler ultrasound

BACKGROUND

Cross-clamping of the descending thoracic aorta (XC) induces an increase in cardiac output (CO). The intention of this study was to evaluate the high CO during XC by the use of clinically available methods (thermodilution and pulsed Doppler ultrasound) compared to transit-time ultrasound flowmetry of the ascending aorta as the gold standard.

METHOD

Ten pigs were anaesthetised with ketamine and fentanyl. The descending thoracic aorta was cross-clamped for 30 min, and cardiac output was measured with pulmonary artery thermodilution technique, pulsed Doppler ultrasound on the aortic annulus and transit-time ultrasound flowmetry of the ascending aorta.

RESULTS

At 15 min following XC, CO increased from 1.7 l/min to 4.6 l/min measured with transit-time ultrasound (P<0.05). With thermodilution technique, CO increased from 2.6ll/min to 5.7 l/min (P<0.05), and from 2.4 l/min to 6.0 l/min measured with Doppler ultrasound (P<0.05). There was an increase in mean arterial pressure of 81% and heart rate increased 76% (P<0.05).

CONCLUSION

XC of the descending thoracic aorta induces an increase in CO of 171%. Thermodilution and pulsed Doppler ultrasound are reliable methods for detecting high cardiac output during thoracic aortic surgery.

The importance of transesophageal echocardiography during surgery of the thoracic aorta

OBJECTIVES

To assess left ventricular dimensions and cardiac output during thoracic and thoracoabdominal aortic aneurysm repair.

MATERIAL AND METHODS

Nine patients undergoing thoracic and thoracoabdominal aneurysm repair using direct cross-clamping without shunt or by-pass were studied prospectively. Prior to, during cross-clamping (XC) and after declamping left ventricular cross-sectional areas were monitored with transesophageal echocardiography. A pulmonary artery catheter was used for measurements of cardiac output with the thermodilution technique.

RESULTS

Cardiac output increased 43% from baseline during XC (p < 0.01) and was still 55% above baseline at declamping (p < 0.05). Left ventricular end-systolic inner area was reduced 32% during XC (p < 0.01). Pulmonary artery pressures and central venous pressure increased during declamping (p < 0.05). Heart rate increased 38% from 66 beats/ min to 92 beats/min (p < 0.01) and was still 30% elevated at declamping (p < 0.01).

CONCLUSION

During thoracic aortic XC, cardiac output is increased and left ventricular end-systolic dimension is reduced. TEE is a valuable supplement to pressure measurements for the evaluation of cardiac function during surgery of the thoracic aorta.

Cerebral haemodynamics during thoracic- and thoracoabdominal aortic aneurysm repair

OBJECTIVE

To investigate cerebral haemodynamics during operations for thoracic and thoracoabdominal aortic aneurysms.

DESIGN

Prospective clinical study.

MATERIAL

10 patients operated on consecutively with resection for thoracic (5) or thoracoabdominal aortic (5) aneurysms.

METHODS

Blood flow velocity of the middle cerebral artery was measured through a temporal approach using a TC Doppler with a 2 MHz probe. Recordings were made during induction of anaesthesia and performed continuously before, during and after cross-clamping of the aorta.

RESULTS

Following 10 min. of aortic cross-clamping blood flow velocity of the middle cerebral artery increased from 44 to 55 cm/s (p < 0.01). A further increase to 69 cm/s (p < 0.01) was observed 5 min after declamping. The pulsatility index averaged 0.74 increasing to 1.21 (p < 0.05) at clamping and 0.87 (p < 0.05) after declamping.

CONCLUSION

There was an increased blood flow velocity of the middle cerebral artery during cross-clamping of the descending thoracic aorta in patients operated on for thoracic and thoracoabdominal aortic aneurysms. This increase in cerebral blood flow and blood volume could explain the acute increase in cerebrospinal fluid pressure observed during cross-clamping of the thoracic aorta.