Continuous retrograde hypothermic low flow cerebral perfusion during aortic arch surgery

Comparison of two sites of inflow pressure measurement during retrograde cerebral perfusion

OBJECTIVE

To determine whether internal jugular venous valves influence inflow pressure during retrograde cerebral perfusion.

DESIGN

Prospective study.

SETTING

Community hospital, university setting, single institution.

PARTICIPANTS

Ten patients undergoing reconstructive aortic arch surgery with profound hypothermic circulatory arrest.

INTERVENTIONS

During retrograde cerebral perfusion, inflow pressure was continuously measured at 2 separate sites relative to the left internal jugular venous valve (ie, superior vena cava inflow catheter [infravalvular pressure] and rostral left internal jugular vein [supravalvular pressure]).

MEASUREMENTS AND MAIN RESULTS

Infravalvular pressure of 29.8 +/- 3.5 mmHg and supravalvular pressure of 22.7 +/- 0.8 mmHg were significantly different (mean difference, 7.1 +/- 3.6 mmHg; p = 0.041). In 8 patients, the pressure difference was <6 mmHg; whereas in 2 patients, the pressure difference was >20 mmHg. Bland and Altman analysis revealed 95% limits of agreement on mean bias of -12.9 to 27.8 mmHg.

CONCLUSION

Internal jugular venous valves can obstruct retrograde cerebral perfusion inflow, manifest by an inflow pressure difference between the superior vena cava and internal jugular vein. In the presence of competent internal jugular venous valves, measurement of inflow pressure in the superior vena cava may be an inaccurate estimate of actual cerebral perfusion pressure. Internal jugular vein pressure should be monitored to avoid inadvertent cerebral hypoperfusion.

Arterial and venous blood gas analyses during retrograde cerebral perfusion

OBJECTIVE

To examine arterial and venous blood gas analyses during retrograde cerebral perfusion to quantify oxygen uptake and carbon dioxide production.

DESIGN

Prospective.

SETTING

Community hospital, university setting, single institution.

PARTICIPANTS

Twelve patients undergoing reconstructive aortic surgery with profound hypothermic circulatory arrest and retrograde cerebral perfusion.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

After 10 minutes of retrograde cerebral perfusion, blood gas analysis (measured at 37 degrees C, without temperature correction) was performed on blood samples drawn simultaneously from the arterial inflow and venous return (collected via aortic arch vessels) sites. Compared with arterial blood samples, PO2 (deltaPO2: 431.2+/-154.9 mm Hg; p<0.05), pH (deltapH: 0.16+/-0.09, p<0.05) and base excess (deltaBE: 1.0+/-0.85; p<0.05) decreased in venous blood samples, whereas PCO2 increased (deltaPCO2: 18.2+/-8.8 mm Hg; p<0.05). An arteriovenous content difference of 2.5+/-1.9 mL/dL reflected a total oxygen extraction of 20.5%+/-15.7%, although most extraction occurred from oxygen in solution.

CONCLUSION

These findings suggest that retrograde cerebral perfusion produces cerebral aerobic metabolism.

Assessment of arteriovenous blood flow during retrograde cerebral perfusion

OBJECTIVE

This study examined arterial and venous blood flow during retrograde cerebral perfusion (RCP) to quantify what proportion of arterial inflow is not recovered as venous outflow.

DESIGN

Prospective.

SETTING

Community hospital, university setting, single institution.

PARTICIPANTS

Twelve patients undergoing reconstructive aortic arch surgery with profound hypothermic circulatory arrest and RCP.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

RCP arterial inflow and venous outflow measurements were recorded at 2-minute intervals for 10 minutes, averaged, and then compared. Only 44.9%+/-16.3% of RCP inflow returned through the aortic arch. The remainder was not recovered.

CONCLUSION

Internal jugular venous valves, sequestration, and shunting may contribute to arterial inflow diversion during RCP.

Clinical decision making and operative approaches to thoracic aortic aneurysms

The care of the patient with thoracic aneurysms is quite complicated. The decision to treat an aneurysm must be based on the risk of rupture and the patient's life expectancy. The preoperative evaluation must include detailed imaging to allow proper preoperative planning. This is especially important to determine the need for hypothermic circulatory arrest or the potential to treat a descending aneurysm with an endovascular approach. Thorough preoperative preparation and intraoperative care are as important as surgical decision making and meticulous technique. Although significant advances have been made in operative approaches, cerebral and myocardial preservation, and postoperative care, the management of complicated aneurysms of the thoracic aorta is frequently a humbling experience.

Potential problems with simplified selective cerebral perfusion--experimental investigations and clinical improvements

Currently the most used perfusion techniques during aortic arch surgery to prevent cerebral damage include hypothermic circulatory arrest, retrograde cerebral perfusion and selective cerebral perfusion (SCP). The application of simplified SCP, which does not require deep hypothermia, has become an alternative procedure for brain protection. Including the physiological principle of autoregulated cerebral blood flow, cerebral perfusion flow is not predetermined, but differentiated from the different cannula sizes for the lower and upper body perfusion. In a mock circulation loop, we could show that resistance changes in the two compartments led to flow shifts between the systemic and brachiocephalic regions. In addition to mechanical factors cerebral perfusion is determined from physiological changes. In practice, these shifts can be initiated with disrupted autoregulation due to ph-stat management or dramatic pressure changes. To prevent mismatched cerebral perfusion extended perioperative monitoring was included in our clinical setting. With bilateral somatosensory evoked potentials, a computer aided topographical electroencephalometry system, transcranial doppler-sonography and jugular venous bulb saturation, we could provide a sufficient bihemispheric perfusion. Between 1990 and 1995 we operated on 21 patients using SCP. Intraoperatively no signs of cerebral ischaemia due to inadequate perfusion could be observed. Only temporary neurological changes were found postoperatively. In summary, the simplified SCP, despite its physiological basis, is intricately involved in control and influence. We think that the application of SCP is safe if extended neurophysiological monitoring is included in the clinical setting.