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Hypocapnia Causing Cerebral Desaturation
MECHANISM OF INJURY, ASSOCIATED OUTCOME AND INTERVENTION
Learn more about hypocania causing cerebral desaturation:
Mechanism of Injury
Cerebral vasculature vasoconstricts during a state of hypocapnia and vasodilates during hypercapnia. Consequently, the partial pressure of carbon dioxide is one of the most influential determinants of cerebral blood flow.1
The reactivity of the cerebral vasculature to alterations in carbon dioxide may be impaired by increasing time of cerebral desaturation.2
Carbon dioxide becomes more soluble during hypothermia, resulting in decreased partial pressure and alkalosis. Consequently, two strategies utilized for acid-base management during hypothermia have a significant influence on cerebral oxygen saturation during CPB :
pH-stat
Definition – Arterial PaCO2 is temperature adjusted to 40 mmHg as hypothermia in induced3
Effect on cerebral perfusion –
Higher CO2 levels cause vasodilation and hyperperfusion4
Autoregulation is inhibited4
Alpha-stat
Definition – Arterial PaCO2 is maintained at 40 mmHg at 37 degrees and not corrected for induction of hypothermia3
Effect on cerebral perfusion –
Reduced CO2 levels result in vasoconstriction and reduced cerebral blood flow4
Autoreguation is maintained4
Akca et al. demonstrated in constant flow rate cardiopulmonary bypass, hypercapnia positively influenced cerebral oxygen saturation as opposed to normocapnia.5
Associated Outcome
A systematic review evaluating the effect of the two acid-base management strategies on intraoperative and postoperative outcome in patients undergoing deep hypothermic circulatory arrest suggested that
Pediatric patients had improved outcome with pH-stat management3
Adult patients had improved outcome with alpha-stat management3
A randomized controlled trial evaluating the effect of the two acid-based management strategies determined that patients undergoing coronary artery bypass graft receiving alpha-stat management had less impairment of cerebral autoregulation and reduced postoperative cerebral dysfunction6
Intervention
% of all interventions7
Increasing EtCO2
18.2
MECHANISM OF INJURY, ASSOCIATED OUTCOME AND INTERVENTION
Learn more about hypocania causing cerebral desaturation:
Mechanism of Injury
Cerebral vasculature vasoconstricts during a state of hypocapnia and vasodilates during hypercapnia. Consequently, the partial pressure of carbon dioxide is one of the most influential determinants of cerebral blood flow.1
The reactivity of the cerebral vasculature to alterations in carbon dioxide may be impaired by increasing time of cerebral desaturation.2
Carbon dioxide becomes more soluble during hypothermia, resulting in decreased partial pressure and alkalosis. Consequently, two strategies utilized for acid-base management during hypothermia have a significant influence on cerebral oxygen saturation during CPB :
pH-stat
Definition – Arterial PaCO2 is temperature adjusted to 40 mmHg as hypothermia in induced3
Effect on cerebral perfusion –
Higher CO2 levels cause vasodilation and hyperperfusion4
Autoregulation is inhibited4
Alpha-stat
Definition – Arterial PaCO2 is maintained at 40 mmHg at 37 degrees and not corrected for induction of hypothermia3
Effect on cerebral perfusion –
Reduced CO2 levels result in vasoconstriction and reduced cerebral blood flow4
Autoreguation is maintained4
Akca et al. demonstrated in constant flow rate cardiopulmonary bypass, hypercapnia positively influenced cerebral oxygen saturation as opposed to normocapnia.5
Associated Outcome
A systematic review evaluating the effect of the two acid-base management strategies on intraoperative and postoperative outcome in patients undergoing deep hypothermic circulatory arrest suggested that
Pediatric patients had improved outcome with pH-stat management3
Adult patients had improved outcome with alpha-stat management3
A randomized controlled trial evaluating the effect of the two acid-based management strategies determined that patients undergoing coronary artery bypass graft receiving alpha-stat management had less impairment of cerebral autoregulation and reduced postoperative cerebral dysfunction6
1. Denault A, Deschamps A, Murkin JM. A proposed algorithm for the intraoperative use of cerebral near-infrared spectroscopy. Semin Cardiothorac Vasc Anesth. 2007;11(4):274-281. View Abstract
2. Kadoi Y, Kawauchi C, Kuroda M, et al. Association between cerebrovascular carbon dioxide reactivity and postoperative short-term and long-term cognitive dysfunction in patients with diabetes mellitus. Journal of anesthesia. 2011;25(5):641-647. View Abstract
3. Abdul Aziz KA, Meduoye A. Is pH-stat or alpha-stat the best technique to follow in patients undergoing deep hypothermic circulatory arrest? Interact Cardiovasc Thorac Surg. 2010;10(2):271-282. View Abstract
4. Halstead JC, Spielvogel D, Meier DM, et al. Optimal pH strategy for selective cerebral perfusion. European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery. 2005;28(2):266-273; discussion 273. View Abstract
5. Akca O, Sessler DI, Delong D, Keijner R, Ganzel B, Doufas AG. Tissue oxygenation response to mild hypercapnia during cardiopulmonary bypass with constant pump output. British journal of anaesthesia. 2006;96(6):708-714. View Abstract
6. Patel RL, Turtle MR, Chambers DJ, James DN, Newman S, Venn GE. Alpha-stat acid-base regulation during cardiopulmonary bypass improves neuropsychologic outcome in patients undergoing coronary artery bypass grafting. The Journal of thoracic and cardiovascular surgery. 1996;111(6):1267-1279. View Abstract
7. Deschamps A, Lambert J, Couture P, et al. Reversal of decreases in cerebral saturation in high-risk cardiac surgery. Journal of cardiothoracic and vascular anesthesia. 2013;27(6):1260-1266. View Abstract
