Supraceliac aortic cross-clamping and declamping. Effects of dopexamine and dopamine on systemic and mesenteric hemodynamics, metabolism and intestinal tonometry in a rat model

The Potential Effect of Epidural Anesthesia on Mesenteric Injury after Supraceliac Aortic Clamping in a Rabbit Model

BACKGROUND

Epidural anesthesia is known to increase blood flow by producing vasodilatation on mesenteric circulation. In this experimental study, we aim to examine the effect of epidural anesthesia on mesenteric ischemic-reperfusion (IR) injury induced by supracoeliac aortic occlusion in a rabbit model.

METHODS

Twenty-eight male white New Zealand rabbits were assigned into 4 separate groups, with 7 rabbits in each group: group I, control group; group II, IR-only group; group III, IR plus epidural anesthesia group; group IV, epidural anesthesia-only group. IR model was produced by clamping supraceliac aorta with an atraumatic vascular clamp for 60 min, followed by reperfusion for 120 min. An epidural catheter was placed via Th12-L1 intervertebral space by using open technique before aortic clamping in those assigned to epidural anesthesia. IR injury was assessed using blood markers interleukin-6 and IMA and tissue markers superoxide dismutase and malondialdehyde. Also histopathological examination was performed to evaluate the degree of injury.

RESULTS

All biochemical markers in group II were significantly elevated in comparison with the other 3 groups (p < 0.05). This was paralleled by a more severe histopathological injury in IR- only group (group II). The group receiving IR plus epidural anesthesia (group III) had lower biochemical marker levels as compared with the IR-only group (group II).

CONCLUSIONS

Mesenteric IR injury that can occur during abdominal aorta surgery can be reduced by epidural anesthesia, which is commonly used during or after major operations for pain control. Controlled clinical studies are required to evaluate these findings.

Modelo experimental de isquemia: reperfusão intestinal por clampeamento de aorta abdominal em ratos Wistar

OBJETIVO: desenvolver um modelo experimental de isquemia global normotérmica transitória capaz de demonstrar os tempos de isquemia e reperfusão necessários para desenvolvimento de lesão de isquemia/reperfusão em intestinos delgados de ratos Wistar através clampeamento de aorta abdominal suprarrenal. MÉTODOS: Vinte ratos Wistar adultos machos, pesando entre 250 e 350g, foram distribuídos aleatoriamente em cinco grupos, com quatro ratos cada, e submetidos a tempos crescentes de isquemia (0 - 30 - 45 - 60 - 90 minutos). Dentro de cada grupo, à exceção do grupo controle, dois ratos foram submetidos à 60 minutos de reperfusão e dois à 90 minutos. Após os procedimentos, procedeu-se análise histológica através de medição de áreas de necrose. RESULTADOS: O grau de necrose intestinal variou de 15 a 54% (p=0,0004). Houve tendência de aumento progressivo no grau de lesão relacionado ao aumento no tempo de isquemia, contudo, os maiores graus de lesão foram observados nos menores tempos de reperfusão. A análise do coeficiente de variação de necrose entre os dez grupos de isquemia/reperfusão demonstrou diferença estatisticamente significante em 15 postos, sendo 13 relacionados ao grupo controle. CONCLUSÃO: O modelo foi capaz de demonstrar os tempos necessários para que ocorra lesão de isquemia/reperfusão intestinal através de clampeamento aórtico e poderá servir como base para facilitar o desenvolvimento de estudos voltados para a compreensão deste tipo de lesão.

Effects of dopexamine in a rat model of supracoeliac aortic cross-clamping and declamping

This experimental study in rats was designed to demonstrate effects of dopexamine (3 microg kg(-1) min(-1), n = 6) or physiologic saline solution (n = 6) on systemic as well as regional perfusion during 30 min of supracoeliac aortic cross-clamping and during 180 min of reperfusion following declamping. Rats were surgically instrumented with arterial, right atrial and portal venous catheters, ultrasonic flow probes around the abdominal aorta, superior mesenteric and carotid artery, and a paediatric tonometer for intestinal mucosal PCO(2) measurement. During 120 min of reperfusion, fluid resuscitation was titrated to keep abdominal aortic blood flow above 80% of baseline values. We found that during cross-clamping, values of arterial lactate (p = 0.002) and intestinal tonometric PCO(2) (p = 0.018) were higher in the dopexamine group than in the control group.

Terapêutica medicamentosa na isquemia e reperfusão mesentérica: revisão da literatura

Até pouco tempo atrás se acreditava que na isquemia mesentérica todas as alterações orgânicas desta afecção eram devidas à obstrução total ou parcial do fluxo arterial intestinal. Recentes descobertas quanto à fisiopatologia do processo de isquemia e reperfusão mesentérica demonstraram que os radicais livres, principalmente, atuam durante a reperfusão, levando à lesão tecidual muito mais importante do que as lesões que ocorrem na fase de isquemia isoladamente. Assim, surge uma nova possibilidade terapêutica além do tratamento cirúrgico, em que uma determinada substância poderia atuar de modo a inibir ou minimizar a cascata de alterações no nível celular que culminam na lesão e morte celular. Realizamos uma ampla revisão da literatura médica atual pelos bancos de dados LILACS e MEDLINE, visando verificar quais os fármacos estudados para este fim e os resultados obtidos nas pesquisas. Constatamos que inúmeras substâncias têm sido avaliadas em estudos experimentais, em sua maioria utilizando ratos e a maioria não apresentou resultados satisfatórios a ponto de permitirem seu emprego na prática clínica; algumas, entretanto, apresentaram resultados promissores, necessitando ainda de novos estudos a fim de se descobrir uma substância que possa ser empregada em seres humanos em situações de isquemia e reperfusão mesentérica, a fim de se evitar tratamentos intervencionistas com altos índices de morbi-mortalidade.

Effects of dopexamine on lipid peroxidation during aortic surgery in pigs: comparison with dopamine

OBJECTIVE

We investigated the dose-related effect of dopexamine and dopamine on free radical production and lipid peroxidation estimated by MDA measurements in an ischaemia-reperfusion model of supraceliac aortic repair.

DESIGN

Prospective, randomized, blinded experimental study.

MATERIALS

Twenty-five healthy pigs.

METHODS

All experiments were performed under general endotracheal anaesthesia. Supraceliac aortic cross clamping was performed in all pigs. The pigs were randomly assigned into five groups (n=5 in each group) and received a continuous intravenous infusion of normal saline (CTL), dopamine 2 microg kg(-1)min(-1) (dopa 2), dopamine 8 microg kg(-1)min(-1) (dopa 8), dopexamine 2 microg kg(-1)min(-1) (dopex 2), dopexamine 8 microg kg(-1)min(-1) (dopex 8). Cardiac output, mean arterial pressure, arterial blood gas analysis and blood sampling for plasma MDA measurements (to reveal lipid peroxidation) were recorded after induction of anaesthesia (baseline), 60 and 120 min after cross-clamping of aorta (ischaemia phase), and 60 and 120 min after restoration of flow (reperfusion phase).

RESULTS

Dopexamine and dopamine at 8 microgkg(-1)min(-1) reduced MDA at 60 and 120 min after reperfusion.

CONCLUSION

Dopexamine seems superior to dopamine in reducing oxygen free radicals and subsequent lipid peroxidation during reperfusion after supraceliac aortic cross clamping in pigs.

Influence of dobutamine on the variables of systemic haemodynamics, metabolism, and intestinal perfusion after cardiopulmonary resuscitation in the rat

BACKGROUND

Global left ventricular dysfunction after successful resuscitation from cardiac arrest may be treated successfully with dobutamine but the effects on intestinal perfusion are unknown.

METHODS

In 24 male Sprague-Dawley rats ventricular fibrillation was induced. After 4 min of untreated cardiac arrest, precordial chest compression was performed for 4 min; adrenaline (epinephrine) (90 microg kg(-1)) was injected, followed by defibrillation. Return of spontaneous circulation was achieved in 18 animals, which were allocated to receive saline 0.9% (control group, n = 6), dobutamine at 5 microg kg(-1) min(-1) (n = 6) or dobutamine at 10 microg kg(-1) min(-1) (n = 6). Measurements of haemodynamic variables and intestinal tonometer P(CO2) were made before induction of ventricular fibrillation and 15, 30, 60, and 120 min postresuscitation.

RESULTS

At 120 min postresuscitation, mean aortic pressure was 82 +/- 20, 104 +/- 19, and 113 +/- 15 mmHg for the control group, the dobutamine (5 microg kg(-1) min(-1)) group and the dobutamine (10 microg kg(-1) min(-1)) group (P < 0.05 for comparison of the dobutamine (10 microg kg(-1) min(-1)) group versus the control group). Respective abdominal aortic blood flow was 107 +/- 16, 133 +/- 49, and 145 +/- 18 ml min(-1) kg(-1) (P < 0.05 for comparison of the dobutamine (10 microg kg(-1) min(-1)) group versus the control group), and superior mesenteric artery blood flow was 25 +/- 9, 28 +/- 8, and 33 +/- 8 ml min(-1) kg(-1). Arterial lactate was significantly higher (P < 0.05) in the control group (2.3 +/- 0.6 mmol l(-1)) than in the dobutamine (5 microg kg(-1) min(-1)) group (1.6 +/- 0.3 mmol l(-1)) and dobutamine (10 microg kg(-1) min(-1)) group (1.5 +/- 0.3 mmol l(-1)). Tonometrically derived P(CO2) gap was highly elevated at 15 min of postresuscitation and returned to prearrest level at 120 min postresuscitation in all groups.

CONCLUSIONS

Dobutamine enhances the recovery of global haemodynamic and metabolic variables early after cardiac arrest.

Local Metabolic Effects of Dopexamine on the Intestine During Mesenteric Hypoperfusion

This self-controlled experimental study was designed to test the hypothesis that dopexamine, a synthetic catecholamine that activates dopaminergic (DA-1) and beta2-adrenergic receptors, improves oxygenation in the jejunal mucosa during intestinal hypotension. In six normoventilated barbiturate-anesthetized pigs, controlled reductions in superior mesenteric arterial pressure (PSMA) was obtained by an adjustable clamp around the artery. Dopexamine infusions (0.5 and 1.0 microg.kg(-1).min(-1)) were administered at a freely variable PSMA (i.e., with the perivascular clamp fully open) and at a PSMA of 50 mmHg and 30 mmHg. We continuously measured superior mesenteric venous blood flow (QMES; transit-time ultrasonic flowmetry), jejunal mucosal perfusion (laser Doppler flowmetry), and tissue oxygen tension (PO2TISSUE; microoximetry). Jejunal luminal microdialysate of lactate, pyruvate, and glucose were measured every 5 min. Measurements of mucosal PCO2 (air tonometry), together with blood sampling and end-tidal PCO2 measurements, enabled calculations of pHi and PCO2 gap. Dopexamine reduced mesenteric vascular resistance and increased QMES at a PSMA of 50 mmHg and 30 mmHg. At a PSMA of 30 mmHg, dopexamine increased mesenteric oxygen delivery but did not influence mesenteric oxygen uptake or extraction. In this situation, dopexamine had no beneficial effect on jejunal mucosal blood flow. On the contrary, dopexamine increased mesenteric net lactate production and PCO2 gap, whereas PO2TISSUE and pHi decreased. Jejunal luminal microdialysate data demonstrated an increased lactate concentration and a pattern of decreased glucose concentration and increased luminal lactate-pyruvate ratio. These negative metabolic effects of dopexamine should be taken into account in situations of low perfusion pressures.

Does dopexamine influence regional vascular tone and oxygenation during intestinal hypotension?

BACKGROUND

Local effects of dopexamine on intestinal vascular tone and oxygenation were investigated during intestinal hypotension. To this end, we employed an experimental model, in which the superior mesenteric arterial pressure (PSMA) was controlled by an adjustable perivascular clamp. This approach enabled us to keep the intestinal perfusion pressure (IPP) constant in the face of any systemic circulatory alterations.

METHODS

In 11 barbiturate-anesthetized pigs, we instrumented the superior mesenteric circulation for assessments of vascular resistance (RMES), IPP, jejunal mucosal perfusion (Laser Doppler) and intestinal tissue oxygenation (microoximetry). Measurements were carried out before and during dopexamine infusions (0.5 and 1.0 micro g.kg-1.min-1) at a freely variable PSMA (i.e. the perivascular clamp fully open) and at a PSMA of 50 mmHg and 30 mmHg.

RESULTS

At a constant PSMA of 50 mmHg, dopexamine had no significant intestinal vascular effects. However, at a constant PSMA of 30 mmHg, both doses of dopexamine were associated with decreases in RMES. Effects of dopexamine on intestinal oxygen delivery and extraction were minimal during these procedures, while a minor decrease in intestinal tissue oxygen tension was observed during dopexamine administration at the lowest IPP level.

CONCLUSION

At very low intestinal perfusion pressures (approximately 30 mmHg) dopexamine produces intestinal vasodilation in excess of what is produced by intrinsic autoregulation. This suggests that there is a vasodilatory reserve in the intestine under such conditions and that a pharmacological vasodilator like dopexamine may improve intestinal circulation during regional severe hypotension.

Resuscitation from cardiac arrest with adrenaline/epinephrine or vasopressin: effects on intestinal mucosal tonometer pCO(2) during the postresuscitation period in rats

BACKGROUND

The use of vasopressin instead of adrenaline/epinephrine during resuscitation improves vital organ perfusion, but the effects on mesenteric perfusion following successful resuscitation are not fully evaluated. The present study was designed to compare the effects of vasopressin and adrenaline/epinephrine, given to rats during resuscitation from ventricular fibrillation, on to mesenteric ischaemia, as determined by intestinal mucosal tonometer pCO(2) during the postresuscitation period.

METHODS AND RESULTS

Male Sprague-Dawley rats (n=28) were allocated randomly to receive vasopressin (0.8 U/kg) or adrenaline/epinephrine (90 microg/kg) after 5 min of ventricular fibrillation. Precordial chest compression was initiated 4 min after the start of ventricular fibrillation, continued for 4 min, and followed by defibrillation. Seven of 14 (vasopressin) and 12 of 14 (adrenaline/epinephrine) rats were successfully defibrillated (P=0.10, Fisher's exact test) and observed for 60 min. Intestinal mucosal tonometer pCO(2) measurements before cardiac arrest and 15, 30, and 60 min following return of spontaneous circulation were 47+/-3, 73+/-8, 63+/-7, and 56+/-6 mmHg in the vasopressin group and 48+/-5, 78+/-7, 67+/-6, and 62+/-6 mmHg in the adrenaline/epinephrine group (P<0.05 at 60 min between vasopressin and adrenaline/epinephrine). Right atrial hemoglobin oxygen saturations at these time points were 73+/-5, 51+/-12, 58+/-11, and 63+/-5% in the vasopressin group and 76+/-7, 44+/-10, 52+/-10 and 54+/-8% in the adrenaline/epinephrine group (P<0.05 at 60 min between vasopressin and adrenaline/epinephrine).

CONCLUSIONS

We conclude that in this rat model the administration of vasopressin instead of adrenaline/epinephrine for CPR tends to be associated with lower resuscitation success, but less mesenteric ischaemia during the postresuscitation period in successfully resuscitated rats.

Gastric tonometry: where do we stand?

Gastric tonometry has proved to be a sensitive but not specific predictor of outcome in the critically ill. The data accumulated to date indicate that those patients able to achieve or maintain a normal gastric mucosal pH do better than those who do not. In addition, therapy aimed at improving an abnormal gastric mucosal pH has proved to be less successful. These findings may simply indicate that tonometry identifies those "responders" and "nonresponders," as becomes increasingly apparent in populations of critical care patients receiving interventional therapy. Gastric tonometry has undergone a number of methodologic changes over the last decade, seeing a switch from saline to automated gas tonometry. Along with this switch of methodology has come a deeper scrutiny of the indices used to assess gut perfusion. Most studies (including all the interventional ones) have used gastric mucosal pH. The newer indices of gut luminal PCO2 (PgCO2) referenced to arterial CO2 (PgCO2-PaCO2) or end tidal CO2 (PgCO2-PeCO2), although relatively well validated, remain to be proven as predictors of outcome or guides to interventional therapy. If we take a fresh look at the interventional trials in intensive care patients, there is a very definite trend toward benefit in the protocol groups, although they are generally reported as negative studies. There is much to be accomplished, however, before we accept the gastric tonometer as a routine tool with which to guide therapy based on gastrointestinal perfusion, including a greater understanding of gastrointestinal physiology and, as ever, the call for an adequately powered prospective randomized controlled trial to evaluate the clinical utility of gas tonometry.

Differential effects of clonidine, dopamine, dobutamine, and dopexamine on basal and acid-stimulated mucosal blood flow in the rat stomach

OBJECTIVE

To analyze the effects of clonidine, dopamine, dobutamine, and dopexamine on gastric mucosal blood flow (GMBF) at baseline and after stimulation by acid back diffusion through a disrupted gastric mucosal barrier.

DESIGN

Prospective, randomized, unblinded study.

SETTING

University research laboratory.

SUBJECTS

Adult Sprague-Dawley rats.

INTERVENTIONS

Mean arterial blood pressure (MAP) and heart rate (HR) were recorded from a carotid artery of the phenobarbital-anesthetized animals. A jugular vein was cannulated for continuous infusion of saline and intravenous drug administration. The stomach was prepared for luminal perfusion and for recording GMBF with the hydrogen gas clearance technique. Gastric mucosal vascular conductance (GMVC) was calculated as GMBF divided by MAP.

MEASUREMENTS AND MAIN RESULTS

Clonidine (37.5 and 112.5 nmol x kg(-1)) lowered MAP and HR and caused gastric vasodilation as shown by a rise of GMVC. The 2.5-fold increase in GMVC elicited by gastric perfusion with HCl (0.15 M) plus ethanol (25%) was depressed by clonidine. All cardiovascular effects of clonidine were prevented by the alpha2-adrenoceptor antagonist idazoxan (2 micromol x kg(-1)). Infusion of dopamine (15 and 45 micromol x kg(-1) x hr(-1)), dobutamine, or dopexamine (each at 5 and 15 micromol x kg(-1) x hr(-1)) caused tachycardia. GMVC at baseline was attenuated by the higher dose of dopamine and dopexamine, but not dobutamine. In contrast, the acid-induced vasodilation in the gastric mucosa was depressed by dobutamine and dopexamine, but not dopamine.

CONCLUSIONS

Clonidine, dobutamine, and dopexamine at high dosage suppress the gastric mucosal vasodilator response to acid back diffusion, which is an important defense mechanism. Although the dose equivalence between rats and humans is not known, the antivasodilator effects highlight an adverse action whereby large doses of dobutamine, dopexamine, and clonidine may compromise gastric mucosal homeostasis and facilitate stress ulcer formation. Dopamine lacks this detrimental activity.