The physiologic basis for goal directed hemodynamic and fluid therapy: the pivotal role of the venous circulation
PurposeUnderstanding cardiovascular physiology should help clinicians to understand the purpose of fluid and drug management during the perioperative period. The purpose of this narrative review is to describe the pivotal role of the venous circulation in goal directed hemodynamic and fluid therapy.SourceWe selected relevant literature that examines the appropriateness of fluid therapy and pharmacologic interventions during the perioperative period.Principal findingsThe interaction between the stressed and unstressed intravascular volume (Vs and Vu, respectively) regulates the venous return, which is the main determinant of cardiac output. The lack of hemodynamic response to an intravascular fluid challenge likely results from an unpredictable distribution of infused fluid between the Vs and Vu. Other factors affecting hemodynamic responses include the pharmacodynamics of common vasoactive drugs, which further highlight the complexity of the regulation of venous return during infusion of exogenous catecholamines. The response to even a highly selective agent can result in different hemodynamic effects. Low doses of a adrenergic agonists constrict veins and may often shift blood from the Vu to the Vs, subsequently increasing the venous return and cardiac output, whereas higher drug doses constrict arteries and usually decrease cardiac output.ConclusionsThe physiologic basis of goal directed hemodynamic therapy is complex and not necessarily reflected in the information received from hemodynamic monitors. Understanding the physiologic basis of such therapy is a logical step towards its optimal use.ResumeObjectifUne bonne comprehension de la physiologie cardiovasculaire aidera les cliniciens a comprendre les objectifs d'une prise en charge liquidienne et medicamenteuse en periode perioperatoire. L'objectif de ce compte rendu narratif est de decrire le role de la circulation veineuse dans la therapie hemodynamique et liquidienne ciblee.SourceNous avons selectionne des articles qui examinent la pertinence d'une therapie liquidienne et des interventions pharmacologiques en periode perioperatoire.Constatations principalesL'interaction entre le volume intravasculaire contraint et le volume non contraint regule le retour veineux, le principal determinant du debit cardiaque. L'absence de reponse hemodynamique a un bolus liquidien intravasculaire est probablement le resultat d'une distribution imprevisible du liquide perfuse entre le volume contraint et le volume non contraint. Parmi les autres facteurs affectant la reponse hemodynamique, citons la pharmacodynamie des medicaments vasoactifs courants, ce qui met encore plus en evidence la complexite de la regulation du retour veineux pendant une perfusion de catecholamines exogenes. La reponse a un agent meme tres selectif peut entrainer differents effets hemodynamiques. De faibles doses d'agonistes alpha adrenergiques compriment les veines et peuvent souvent faire migrer le sang du volume non contraint au volume contraint, ce qui augmente par la suite le retour veineux et le debit cardiaque, tandis que des doses plus importantes de medicaments compriment les arteres et reduisent en general le debit cardiaque.ConclusionLes fondements physiologiques de la therapie hemodynamique ciblee sont complexes et ne se refletent pas necessairement dans les informations transmises par les moniteurs hemodynamiques. La connaissance des fondements physiologiques d'une telle therapie constitue une etape logique vers son utilisation optimale.
Canadian Journal of Anesthesia/Journal canadien d'anesthesie