Venoarterial CO₂ difference during regional ischemic or hypoxic hypoxia

Abstract

To test the role of blood flow in tissue hypoxia-related increased veno-arterial PCO(2) difference (DeltaPCO(2)), we decreased O(2) delivery (&Ddot;O(2)) by either decreasing flow [ischemic hypoxia (IH)] or arterial PO(2) [hypoxic hypoxia (HH)] in an in situ, vascularly isolated, innervated dog hindlimb perfused with a pump-membrane oxygenator system. Twelve anesthetized and ventilated dogs were studied, with systemic hemodynamics maintained within normal range. In the IH group (n = 6), hindlimb DO(2) was progressively lowered every 15 min by decreasing pump-controlled flow from 60 to 10 ml. kg(-1). min(-1), with arterial PO(2) constant at 100 Torr. In the HH group (n = 6), hindlimb DO(2) was progressively lowered every 15 min by decreasing PO(2) from 100 to 15 Torr, when flow was constant at 60 ml. kg(-1). min(-1). Limb DO(2), O(2) uptake (VO(2)), and DeltaPCO(2) were obtained every 15 min. Below the critical DO(2), VO(2) decreased, indicating dysoxia, and O(2) extraction ratio (VO(2)/DO(2)) rose continuously and similarly in both groups, reaching a maximal value of approximately 90%. DeltaPCO(2) significantly increased in IH but never differed from baseline in HH. We conclude that absence of increased DeltaPCO(2) does not preclude the presence of tissue dysoxia and that decreased flow is a major determinant in increased DeltaPCO(2).

Gas tonometry for evaluation of gastrointestinal mucosal perfusion: experimental and clinical sepsis¹. part 2

“…Parte 2. Acta Cir Bras [serial online] 2002 Set-Out;17 (5). Disponível em URL: http://www.scielo.br/acb RESUMO -Evidências clínicas e experimentais substanciais indicam que o território circulatório mesentérico, principalmente na mucosa intestinal, é altamente vulnerável a redução na oferta de oxigênio e predisposto a lesão precoce na presença de alterações hemodinâmicas induzidas pela sepse e choque séptico.…”

“…Vallet et al 5 demonstrated, in a canine model of resuscitated endotoxic shock, a marked redistribution of blood flow within the gut wall, from the mucosa toward the muscularis, with a simultaneous decrease in intestinal mucosal PO 2 . These data contrast with Revelly et al, 6 who used microspheres to evaluate blood flow distribution within the intestinal wall during endotoxic shock in pigs.…”

“…A reasonable hypothesis to be tested is that the use of vasoactive agents, which optimize intestinal perfusion, can reduce the incidence of MODS in septic patients. 5,15 Total hepatosplanchnic blood flow, measured by indocianine green technique, and mucosal blood flow, measured directly by laser Doppler or indirectly by gas tonometry, have been used to assess regional oxygenation during the most commonly used hemodynamic interventions in sepsis, fluid replacement and vasoactive drug infusion.…”

Multimodal individualized concept of hemodynamic monitoring

“…In oxygen debt caused anaerobic metabolism, hydrogen ions are generated through the hydrolysis of ATP to ADP and increased production of lactic acid [43]. These hydrogen ions are buffered by bicarbonate presented in the cells, and this process will generate CO 2 production [44]. The Fick principle adapted to carbon dioxide demonstrates the inverse relationship between the CO and dCO 2 [45], in other words increased levels of dCO 2 reflect low flow states.…”

The venous–arterial partial pressure of carbon dioxide as a new monitoring of circulatory disorder: no so simple

“…Experimental studies on isolated limb [8] or small intestine mucosa [9], and further confirmed by theoretical mathematical models of CO 2 exchange during hypoxia [10] show that venous pCO 2 evolutions are different during ischemic and hypoxic hypoxia. The authors observed venous pCO 2 kinetics when reducing oxygen delivery beyond the critical threshold value while oxygen consumption becomes dependent on oxygen delivery.…”