Hemodynamic and cardiometabolic effects of infrarenal aortic and common iliac artery declamping in man--an approach to optimal volume loading

The Effects of Fluid Loading on Hemodynamic Changes and Right Ventricular Function with Aortic Unclamping During Abdominal Aortic Surgery

The authors investigated the effects of fluid loading on hemodynamic changes and right ventricular function (RVF) with aortic unclamping during abdominal aortic aneurysmal surgery in 12 patients. An ejection fraction volu metric pulmonary artery catheter was inserted through the right internal jugu lar vein to assess cardiac output and RVF with the use of an REF-1 computer. Anesthesia was maintained with a continuous infusion of sufentanil (0.5-1 μg/kg/hr), isoflurane (0.5-1%), and air/O2 (FIO2= 0.5). Fluid loading with Ring er's lactate and 5% albumin was initiated ten to twenty minutes before aortic unclamping. Hemodynamic measurements and assessment of RVF were per formed ten to twenty minutes before and after aortic unclamping. Aortic un clamping after fluid loading decreased right ventricular end-diastolic and end-systolic volumes (RVEDV, RVESV) but increased right ventricular ejection fraction (RVEF) (p < 0.01). There were no significant changes in cardiac index (CI), stroke volume (SV), systemic vascular resistance (SVR), and cardic filling pressures: central venous pressure (CVP), and pulmonary capillary wedge pres sure (PCWP). There was a poor correlation between RVEDV and PCWP. The authors conclude that adequate fluid loading before aortic unclamping, esti mated by RVEDV, provided stable hemodynamic states (CI, SV, RVEF) follow ing aortic unclamping. Volume expansion following fluid loading can be better assessed by RVEDV than by cardiac filling pressures.

The pathophysiology of aortic cross-clamping

During open aortic surgery, interrupting the blood flow through the aorta by applying a cross-clamp is often a key step to allow for surgical repair. As a consequence, ischemia is induced in parts of the body distal to the clamp site. This significant alteration in the blood flow is almost always associated with hemodynamic changes. Upon release of the cross-clamp, the blood flow is restored, triggering an ischemia-reperfusion response, leading to many pathophysiological processes such as inflammation, humoral changes, and metabolite circulation that could lead to injury in many organ systems and may significantly influence the postoperative outcome. It is therefore important to understand these processes and how they can be treated in order to allow for safe surgical aortic repairs while ensuring the best possible outcomes.

Intravenous fluids for abdominal aortic surgery

BACKGROUND

Surgery on the abdominal aorta to treat aneurysms or occlusive disease is a major undertaking which requires intensive physiological support and fluid management. Blood products are often used but the main fluid replacement is with crystalloids or colloids. For years there has been controversy over which fluid is optimal and a number of studies have examined the subject. This is an update of a Cochrane review first published in 2000 and previously updated in 2002.

OBJECTIVES

To determine the effectiveness of different non-blood replacement fluids used in abdominal aorta procedures with a view to identifying the optimal fluid for use.

SEARCH STRATEGY

The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (August 2009) and the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, Issue 3) for publications describing randomised controlled trials of non-blood replacement fluids in abdominal aortic surgery. In addition, the reference lists from retrieved trials were screened for further information about trials.

SELECTION CRITERIA

Randomised controlled trials assessing the effects of at least one specific non-blood fluid used for replacement therapy in operations on, and confined to, the abdominal aorta.

DATA COLLECTION AND ANALYSIS

Data were extracted and then entered into the Review Manager software where statistical analyses were performed.

MAIN RESULTS

Thirty-eight trials involving 1589 patients were included. Patients undergoing aortic surgery had various physiological parameters measured before and after their operation (these were cardiac, respiratory, haematological, and biochemical). Patients were randomised to a fluid type. This review demonstrated that no single fluid affects any outcome measure significantly more than another fluid across a range of outcomes. The death rate in these studies was 2.45% (39 patients).

AUTHORS' CONCLUSIONS

Despite the confirmed beneficial effects of colloids in this review, further studies are still required. There are no studies examining the effects of combination fluid therapy. The primary research outcome was death, for which results were limited; therefore, future studies should pay more attention to short-term outcomes such as minimising the need for allogenic blood transfusion, complications (organ failure), and length of stay in both the intensive care unit and hospital.

Anesthésie et réanimation pour chirurgie réglée de l'anévrisme de l'aorte abdominale

OBJECTIVES

Patient scheduled for infrarenal abdominal aortic aneurysm surgery carries a high risk of cardiac or respiratory comorbidity. To outline the perioperative management for these patients.

METHODS

Review of the literature using MesH Terms "abdominal aortic aneurysm", "anesthesia", "analgesia" "critical care" and/or "surgery" in Medline database.

RESULTS

Cardiac preoperative evaluation and management have recently been reviewed. Intermediate and high-risk patients should undergo non-invasive cardiac testing to decide between a preoperative medical strategy (using betablocker+/-statin and aspirin) and an interventional strategy (coronary angioplasty or cardiac surgery). Perioperative myocardial ischaemia should also be investigated by clinical, electrocardiographic and biologic monitoring such as plasmatic troponin Ic dosage. Specific score could also assess the respiratory failure risk preoperatively. Epidural analgesia decreases this risk. There is no evidence that a pharmacological treatment decreases the incidence of acute renal failure after aortic surgery. Endovascular repair is actually recommended for older, higher-risk patients or patients with a hostile abdomen or other technical factors that may complicate standard open repair.

Anaesthetic management of baboons undergoing heterotopic porcine cardiac xenotransplantation

A detailed anaesthetic technique for baboons (Papio anubis) undergoing heterotopic abdominal cardiac xenotransplantation is described. Twenty-two baboons served as transplant recipients. Donors were either crossbred farm pigs (Sus scrofa) (n = 4) or transgenic pigs (Sus scroefa) (n = 18) expressing human complement regulatory proteins on the endothelium. Intra-operative management was complicated by the physiological consequences of infrarenal. abdominal aortic cross-clamping, in addition to the immunological sequelae related to cross-species transplantation. In choosing anaesthetics for this procedure, we considered the need for maximal cardiac stability throughout a long surgical procedure that required abdominal aortic cross-clamping to facilitate the implantation of an oversized porcine cardiac graft. Baboons received a balanced anaesthetic consisting of inhaled isoflurane in oxygen, intravenous fentanyl and intravenous pancuronium. The pharmacological techniques employed were found to be safe and reliable and were well tolerated by our recipients without any significant side-effects.

Monitoring of end-tidal carbon dioxide partial pressure changes during infrarenal aortic cross-clamping: a non-invasive method to predict unclamping hypotension

BACKGROUND

To assess the variations in end-tidal CO2 in response to aortic cross-clamping and the relationship with systolic arterial pressure (SAP) changes induced by unclamping.

METHODS

Thirty-three patients undergoing infrarenal aortic abdominal aneurysm repair by aorto-aortic prothetic bypass were prospectively studied. All patients were anesthetized with i.v. midazolam (0.05 mg x kg(-1)), thiopentone (3-5 mg x kg(-1)), fentanyl (5 microg x kg(-1)), pancuronium (0.1 mg x kg(-1)) and the maintainance of anesthesia used was 1-1.5% end-tidal isoflurane and i.v. fentanyl. The perioperative management was standardized. End-tidal CO2 and SAP were measured 5 min before (Pre-XAA), 15 min after infrarenal aortic cross-clamping (XAA), 5 min before (Pre-UXAA) and immediately after unclamping (UXAA).

RESULTS

A total of 16 (48.5%) from 33 patients presented decrease in SAP following aortic unclamping, and 13 out of these patients had arterial hypotension defined as SAP<90 mmHg. End-tidal CO2 variation (PreXAA-PreUXAA) induced by aortic clamping was correlated with SAP variation (PreUXAA-UXAA) induced by unclamping (r=0.763; P=0.0001). An end-tidal CO2 reduction above 15% after aortic cross-clamping was found to have a 100% sensitivity to detect a SAP decrease greater than 20% after unclamping, with a 100% specificity and a negative predictive value of 1.0. Complete aortic occlusion duration was not correlated to SAP unclamping variation (deltaSAP). Intraoperative characteristics (fluid loading, hematocrits, urinary output) were comparable, although blood loss was higher in patients experiencing deltaSAP>20%.

CONCLUSIONS

End-tidal CO2 variation monitoring during aortic cross-clamping may provide a reliable and non-invasive method to predict unclamping hypotension. When the aortic clamp was released, systolic hypotension (>20%) occurred in those subjects who had a decrease in end-tidal CO2 greater than 15% during aortic cross-clamping.

Pulmonary arterial and right ventricular responses to prophylactic albumin administration before aortic unclamping during abdominal aortic aneurysmectomy

During abdominal aortic aneurysmectomy (AAAectomy) and before aortic unclamping (XU), we studied the effects of albumin administration on pulmonary arterial and right ventricular responses in 39 anesthetized patients using a modified thermodilution technique. Group 1 patients (n = 18) were given no extra IV fluids. Group 2 patients (n = 21) were given additional albumin administration (5% albumin at 10 mL/kg) before XU. After XU, mean arterial blood pressure (MAP) decreased significantly in each group, and MAP and stroke volume index (SVI) were not significantly higher in Group 2 than in Group 1. At 5 min after XU, the patients in Group 2 had a higher mean pulmonary arterial pressure and pulmonary vascular resistance index and a lower right ventricular ejection fraction than those in Group 1 (P < 0.05), but their SVIs were well maintained. These results indicate that albumin administration before XU may not always prevent post-XU hypotension. It caused a significant increase in right ventricular afterload and a significant dilation of the right ventricular cavity; however, right ventricular function was almost equally maintained in both groups. However, because SVI did not increase in some patients (Group 2) with the increase in right ventricular end-diastolic volume index after XU, albumin administration should be performed carefully before XU during AAAectomy.

IMPLICATIONS

We studied the effects of albumin administration before aortic unclamping on pulmonary arterial and right ventricular responses during abdominal aortic aneurysmectomy using a modified thermodilution technique. Albumin administration before aortic unclamping may not always prevent hypotension, and it may cause a higher pulmonary arterial pressure than in patients without albumin administration.

Xanthine oxidase inactivation attenuates postocclusion shock after descending thoracic aorta occlusion and reperfusion in rabbits

"Declamping shock" is observed after aortic crossclamping, with hypovolemia, hypotension, and metabolic acidemia invariably present. We hypothesized that oxidants derived from xanthine oxidase influence the resuscitative interventions required to maintain baseline hemodynamic and acid-base status after aortic occlusion and reperfusion in rabbits. We also hypothesized that inactivation of xanthine oxidase with sodium tungstate could reduce systemic injury as assessed by the release of lactate dehydrogenase and alkaline phosphatase. To test these hypotheses, we established aortic occlusion in rabbits (n = 10, standard diet; n = 8, tungstate diet) for 40 minutes by inflation of a 4F Fogarty catheter in the descending thoracic aorta followed by 2 hours of reperfusion. Sham-operated rabbits (n = 10, standard diet; n = 9, tungstate diet) served as controls. Tungstate-pretreated rabbits required significantly less Ringer's solution (28%), phenylephrine (68%), and sodium bicarbonate (30%) during reperfusion (p < 0.005). Lactate dehydrogenase and alkaline phosphatase release during reperfusion was significantly attenuated by tungstate pretreatment (p < 0.05). Tungstate pretreatment resulted in plasma xanthine oxidase activities significantly lower than those in the sham group administered a standard diet (p = 0.007). Resuscitation requirements and systemic injury were reduced by inactivation of xanthine oxidase in a rabbit model that simulates the situation of human thoracic aorta operations.

Stimulation of endogenous nitric oxide pathway by L-arginine reduces declamp mortality and attenuates hypertension associated with aortic cross-clamp-induced hindlimb ischemia in rats

We tested the hypotheses that maintaining the activity of nitric oxide by L-arginine infusion would counteract the release of an endogenous nitric oxide synthase inhibitor, improve survival, and decrease intraoperative hypertension after infrarenal aortic cross-clamp surgery. Hindlimb ischemia was generated by infrarenal aortic cross-clamping and tying of the left femoral artery for 5 hours in rats with bilateral femoral and sciatic nerves cut. Mean blood pressure significantly increased during the 5-hour ischemic period in ischemic rats (no drug treatment). Baroreceptor function was inhibited in ischemic rats assessed by intravenous dose response to phenylephrine and nitroprusside after 5 hours of ischemia, suggesting baroreceptor resetting. In ischemic rats infused with L-arginine the intraoperative hypertension was prevented during the 5-hour period, suggesting that this hypertension may be mediated by nitric oxide inhibition. The rates of survival and arrhythmias 2 hours after declamping were 50% in ischemic rats and 100% in ischemic rats treated with N omega-nitro-L-arginine (a nitric oxide synthase inhibitor) 10 minutes before declamping. In ischemic rats infused with L-arginine the survival rate was significantly increased to 100% and the arrhythmic rate was inhibited. We conclude that L-arginine prevents hypertension during cross-clamping and decreases the mortality rate and arrhythmias after declamping by maintaining nitric oxide synthesis. These results suggest that humoral factors released from the ischemic hindlimb may inhibit endogenous nitric oxide production, thus contributing to intraoperative hypertension, arrhythmias, and high mortality rate after aortic cross-clamp surgery.

Neuroendocrine and haemodynamic responses to abdominal aortic cross clamp and release during high-dose opiate-oxygen-isoflurane anaesthesia

The haemodynamic and neuroendocrine responses and beta adrenoceptor distribution associated with aortic cross clamping and release were quantified in 14 patients undergoing elective abdominal aortic aneurysm surgery using a high-dose opiate-oxygen-isoflurane anaesthetic technique. These changes were correlated with neutrophil beta adrenoceptor distribution. Aortic cross clamp application was associated with increased systemic vascular resistance (SVR), and decreased cardiac index (CI). Left ventricular stroke work index remained constant during the period of cross clamp application and following release. Cross clamp release was associated with increased CI and decreased SVR. Plasma cortisol concentrations did not change during the study period. Plasma catecholamine concentrations, although elevated prior to surgery, remained unchanged during aortic cross clamping and following release. The percentage of internalised beta adrenoceptors was elevated before surgery and was unaffected by surgical intervention. This study suggests that a high-dose fentanyl-oxygen-isoflurane anaesthetic technique in a patient population with high circulating catecholamine levels and downregulation of beta adrenoceptors is associated with cardiovascular stability and attenuated neuroendocrine responses.

A review of anaesthesia for ruptured abdominal aortic aneurysm with special emphasis on preclamping fluid resuscitation

Ruptured abdominal aortic aneurysm (RAAA) remains a critical emergency with an average hospital mortality of 50%. There has been no significant improvement in survival despite advances in anaesthesia, surgery and intensive care over the last 30 years. It is believed that early diagnosis, aggressive surgical management and meticulous attention to haemodynamic status and coagulation may improve survival, but this is unsubstantiated. Mortality is closely linked to the degree of preoperative hypotension and other related factors such as massive blood transfusion and cardiac arrest. Survival depends not only on the severity of rupture, but also the ability to compensate physiologically, and is linked to the premorbid state of the patient. Management priorities are dictated chiefly by the clinical signs and symptoms at presentation. There is controversy regarding the appropriate preoperative fluid regimen for RAAA.

A haemodynamic comparison of intrathecal morphine and sufentanil supplemented with general anaesthesia for abdominal aortic surgery

The haemodynamic changes associated with intrathecal morphine (IM) compared to intrathecal sufentanil (IS) as a supplement to general anaesthesia for elective bypass grafting in patients with aortoiliac occlusive disease were studied. Thirty-six, ASA Grade 2, patients randomly received morphine hydrochloride (0.1%) 50 micrograms kg-1 (n = 18) or undiluted sufentanil, 150 micrograms (n = 18) intrathecally at T12-L1, combined with light general anaesthesia. Haemodynamics were measured before and after endotracheal intubation, abdominal incision, aortic cross-clamping and the first revascularisation. The major differences were recorded after abdominal incision. Heart rate, systemic blood pressure and coronary perfusion pressure were significantly lower in the IS group. The probable cause was greater systemic absorption of sufentanil and its faster binding to the specific opiate receptors, resulting in a more efficacious supraspinal and spinal blockade during the first surgical period. However, both opioids provided adequate analgesia during the whole surgical procedure.

Intraoperative management of abdominal aortic aneurysms. The anesthesiologist's viewpoint

Factors that influence the choice of anesthetic, monitoring methods, and fluid management for aneurysm repair are reviewed, with particular attention to epidural anesthesia and analgesia and the pulmonary artery catheter. Management of bleeding, renal preservation, temperature control, and myocardial ischemia are discussed, and special anesthetic issues associated with ruptured aneurysms and juxtarenal and suprarenal surgery are summarized.

Neuroleptanesthesia versus thoracic epidural anesthesia for abdominal aortic surgery

The hemodynamic consequences of abdominal aortic surgery with infrarenal cross-clamping were studied in 21 patients randomized in two groups. In Group I (11 patients), neuroleptanesthesia was utilized, while Group II (10 patients) received thoracic epidural anesthesia at the T8-9 level. Hemodynamic measurements were performed using Swan-Ganz catheters during the surgical procedures in all patients, with special attention to the periods of clamping and unclamping of the abdominal aorta. The thoracic epidural anesthesia group was characterized by greater hemodynamic stability during surgery, while patients in the neuroleptanesthesia group had significant lability of blood pressure, heart rate, and cardiac index. Nevertheless, in the two groups of patients, it is suggested that cardiac function was unfitted to the tissue oxygen demand after unclamping of the aortic prosthesis because the saturation in oxygen of the mixed venous blood and an increase in arteriovenous difference in oxygen were documented. These results point out that, whatever the anesthesia technique, the critical period in abdominal surgery could be aortic unclamping.

Determination of right ventricular volumes during aortic surgery

The aim of the present study was to evaluate right ventricular (RV) preload by measurements of right ventricular volumes during aortic clamping and unclamping. Nine patients (aged 67 +/- 9 years) undergoing infrarenal aortic aneurysmectomy were monitored with a pulmonary artery catheter equipped with a fast-response thermistor, allowing determination of RV volumes by the thermodilution technique. Anesthesia consisted of a continuous infusion of alfentanil and 50% N2O. Aortic clamping resulted in a significant decrease in cardiac index (CI) and a significant increase in systemic vascular resistance (SVR). There was no significant change in right ventricular ejection fraction (RVEF) (from 35% +/- 6% to 33% +/- 8%) in the presence of a significant decrease in stroke index (from 37.2 +/- 9.8 to 31.1 +/- 10.0 mL/beat/m2, P less than 0.05), indicating a significant decrease in RV end-diastolic volume (from 106 +/- 17 to 92 +/- 19 mL, P less than 0.01). There were no significant changes in cardiac filling pressures. Aortic unclamping was associated with a significant increase in CI and a significant decrease in SVR. There were no significant changes in cardiac filling pressures, RVEF, or RV volumes. Measurements of RV volumes indicated that aortic clamping resulted in a decrease in RV preload, which is usually not demonstrated by measurements of right atrial pressure alone.

Effect of calcium entry and beta blockade during infrarenal aortic clamping

Clamping and declamping during aortic surgery produce a hemodynamically significant myocardial stress. The cardiovascular (CV) response to this stress may be adversely altered by calcium antagonists and beta-adrenoreceptor blockade employed to control symptomatic coronary artery disease. This study evaluated the effect of verapamil (V), propranolol (P), and their combination (P + V) on the CV response to infrarenal abdominal aortic cross-clamping and declamping in anesthetized dogs. Six dogs received P as a bolus of 0.5 mg/kg 20 min before clamping. Six additional dogs received V as a 300 micrograms/kg bolus followed by a V infusion of 6 micrograms/kg/min for 20 min before clamping. A third group of six dogs received the P bolus followed 20 min later by the V regimen (P + V). In both the V and P + V groups, 6 micrograms/kg/min V was infused throughout the clamping and declamping sequence. A fourth group of six control dogs received no cardioactive drugs during the experiment. Heart rate, mean aortic blood pressure, left ventricular end-diastolic pressures, peak rate of rise of left ventricular pressure, cardiac output, and systemic vascular resistance were measured in all animals before aortic cross-clamping, at 5 and 40 min after clamping, and 5 min after declamping. The results demonstrated additive negative chronotropic and inotropic properties of P + V therapy with a more significantly adverse effect than that of either drug alone. The implications of this study warrant added caution when patients treated with these drugs undergo abdominal aortic surgery.

The influence of collateral vascularisation on haemodynamic performance during abdominal aortic surgery

The extent of periaortic collateral vascularisation has been proposed as a possible mechanism of an altered haemodynamic response to infra-renal aortic cross-clamp in patients undergoing by-pass grafting for aorto-iliac occlusive disease (AOD) compared with patients undergoing abdominal aortic aneurysm (AAA) resection. The haemodynamic responses following clamping, during the clamp time and following clamp release were studied in 18 patients undergoing AAA resection and 12 patients undergoing bypass grafting for AOD. The role of preoperative aortography in predicting cardiovascular performance during aortic vascular surgery was assessed. During the cross-clamp period LVSWI and CI decreased while SVR increased in the AAA group while the AOD group showed an improved CI, stable LVSWI and reduced SVR, which correlated with the extent of periaortic vascularisation on preoperative aortography. Chronic collateral circulation associated with AOD may permit continuous lower extremity perfusion during aortic cross-clamp. The extent of periaortic collateralisation may influence the choice of monitoring techniques and anaesthetic management.

Experimental methods in the pathogenesis of limb ischemia

Ischemia of extremities is responsible for considerable morbidity and mortality and the pathophysiology of this condition warrants further study. The purpose of this review is to discuss techniques used in the evaluation of limb ischemia and reperfusion. It is of critical importance to study limb blood flow distribution to the microcirculation where nutritive exchange occurs. Skeletal muscle ischemia progresses to infarction when critical deficits of cellular metabolites develop, which mandates that studies be focused at the cellular level. It is clear that the adverse effects of ischemia can be exacerbated by a reperfusion injury to the endothelium of the microvasculature. Investigators wishing to study limb ischemia have a wide spectrum of methodology and established models available to use in improving the understanding of the complex events of ischemic injury.

Spinal cord infarction in disease and surgery of the aorta

Diseases of the aorta and surgery of the aorta can produce spinal cord damage. There are major variations in blood supply to the spinal cord between individuals. The spinal cord may be tamponaded by increased spinal fluid pressure subsequent to clamping the aorta. Both of these factors may contribute to spinal cord infarction. The available methods and procedures to protect the spinal cord during surgery are discussed.

The effect of infrarenal aortic clamping and declamping on central haemodynamics and tissue blood flow in pigs--a comparison of fluid replacement between a colloid and a cristalloid

A study has been undertaken to compare the effect of fluid administration of a cristalloid (Ringer glucose) with that of a colloid (dextran 40) on central haemodynamics and organ blood flow distribution during clamping and after declamping of infrarenal aorta in pigs. The declamping hypotension was significantly greater in the cristalloid group where a decrease in cardiac output was also seen. Tissue blood flow to the kidneys decreased in the cristalloid group during clamping but was maintained in the dextran group. At declamping there was a reactive kidney hyperaemia in the dextran group, while the medullar flow was still significantly decreased in the cristalloid group. The reactive hyperaemia seen in pancreas and small intestines was also greater in the dextran group.

The value of nuclear angiography in the preoperative assessment of patients undergoing elective aortic surgery

Eighteen patients undergoing elective aortic surgery, either for peripheral vascular insufficiency or abdominal aneurysm, were studied preoperatively by nuclear angiography. By this technique the resting ventricular function of each patient was measured. Nuclear angiography is a safe non-invasive technique which has been shown to have excellent correlation with conventional contrast angiography in the assessment of ejection fraction. Throughout the intraoperative period, measurements of the central venous pressure and pulmonary capillary wedge pressure were taken simultaneously at approximately five-minute intervals. An average of 18 data points was established in each case. The correlation between central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) was examined. Ten of our patients had preoperative resting ejection fractions less than 55 per cent. In only four of these patients (40 per cent) was correlation between CVP and PCWP judged to be good intraoperatively. Eight of our patients had preoperative ejection fractions greater than 55 per cent. Six of these (75 per cent) showed good correlation between CVP and PCWP intraoperatively. We also assessed our ability to predict by purely clinical means which patients would show poor correlation between CVP and PCWP. Evaluation on purely clinical grounds was as good as the scans at predicting in which patients CVP would not correlate with PCWP and we feel that the routine use of this test would not modify our use of Swan Ganz catheters for intraoperative monitoring in patients undergoing aortic surgery, in the future.

Anaesthesia for the patient with impaired renal function

Patients with renal disease are at risk of further deterioration of renal function and acute tubular necrosis when subjected to anaesthesia and surgery. Optimal fluid loading and careful selection of anaesthetic techniques and agents, appropriate monitoring and the use of mannitol and dopamine assist in the maintenance of renal blood flow and help preserve renal function in these patients. In association with renal failure, physiological changes in other systems result in reduced oxygen supply to the tissues, metabolic disturbances, impairment of the coagulation and immune defence mechanisms and an increased risk of cardiac and cerebrovascular catastrophe. Although many anaesthetic techniques including regional analgesia may be used successfully in these patients caution with most drugs, especially pethidine, phenoperidine, suxamethonium and all non-depolarising neuromuscular relaxants is recommended. Of the volatile anaesthetics currently available, halothane is the agent of choice. Oxygen therapy and close monitoring of cardiorespiratory function are necessary postoperatively.

[Combination of nitroglycerin and vascular loading in abdominal aorta surgery]

Haemodynamic investigations were performed in nine patients during aortic surgery for Leriche's syndrome. Most of these patients had ischaemic heart disease without cardiac failure. Fluid loading was carried out before and during aortic clamping. It was controlled according to the optimal wedge pulmonary pressure determined the day before surgery. Only six of the nine patients receive nitroglycerin (NTG : 0.2 micrograms X kg-1 X min-1) throughout the operation. Before clamping, cardiac index was improved in patients treated with NTG. During clamping, the patients not treated with NTG showed a drop in cardiac index, an increase in peripheral resistance and in left cardiac work. After declamping, there were no haemodynamic differences between the two groups. Two patients not treated with NTG developed azotaemia postoperatively; one patient developed cardiac failure requiring a dopamine perfusion during surgery. In this series, the association of optimal volume loading with a peroperative perfusion of 0.2 micrograms X kg-1 X min-1 NTG gave a good haemodynamic stability.

Invasive analysis of non-invasive indicators of myocardial work and ischaemia during anaesthesia soon after myocardial infarction

Atrial pacing was used for preoperative evaluation of six patients with recent anterior myocardial infarction (MI) (e.g. within 6 weeks) scheduled for abdominal emergency surgery. Central and coronary haemodynamics were used to compare changes in myocardial work and oxygenation with alternations of the non-invasive variables rate pressure product (RPP) (systolic blood pressure X heart rate), triple product (TP) (systolic blood pressure X heart rate X mean pulmonary arteriolar occlusion pressure) and ST-T segments (lead V5). There was good correlation between myocardial oxygen consumption and rate pressure product and triple product during pacing to stable angina pectoris. ST-T-segment depressions were recorded already at moderate chest discomfort and correlated well with a decrease in coronary vascular resistance. Changes in myocardial oxygen consumption induced by combined thoracic epidural analgesia (T3-4 to L1-2) and light general anaesthesia with nitrous oxide and fentanyl were poorly correlated with changes in rate pressure product or triple product. ST-T-segment depressions were recorded on five occasions in four of the patients, all in association with intubation and/or extubation. Only on one of these occasions could RPP or TP have indicated that myocardial oxygen demand exceeded supply. On the other four occasions, it was probable that myocardial ischaemia was induced by transient arterial hypoxaemia. The V5 ST-T-segment was the most sensitive non-invasive variable to monitor. The anaesthetic method was safe in all patients, as judged by good intraoperative cardiovascular stability, low morbidity and absence of intra- or postoperative reinfarction.

Effects of thiopentone on cardiac performance, coronary hemodynamics and myocardial oxygen consumption in chronic ischemic heart disease

Thiopentone was administered as induction agent for general anesthesia to eight patients with stable ischemic heart disease; 6 mg/kg of the drug induced decrease in arterial blood pressure (-27%), systematic vascular resistance (-20%), stroke volume index (-14%), mean pulmonary arteriolar occlusion pressure (-15%) and left ventricular stroke work index (-38%), while heart rate increased by 10% and cardiac output remained unchanged. Total body oxygen consumption decreased by 30%. Myocardial oxygen consumption decreased by 39% with unchanged or decreased myocardial oxygen extraction and myocardial lactate uptake decreased by 40%. Arterial and coronary sinus hypoxanthine levels were unchanged and no ST-T-segment changes or dysrhythmias were recorded. In the present experimental setting, the results indicate that thiopentone substantially decreased myocardial oxygen requirements. In spite of the marked reduction in coronary perfusion, myocardial oxygen demand was matched by supply, myocardial dysoxia was not induced and cardiodepression was clinically negligible. Rate pressure product was a poor indicator of changes in myocardial oxygen consumption after thiopentone administration.

Temporary incomplete ischemia of the legs induced by aortic clamping in man: effects on central hemodynamics and skeletal muscle metabolism by adrenergic block

The hemodynamic changes which occur when clamping and unclamping the aorta during reconstructive surgery might be a threat to the elderly patient with concomitant cardiac disease. In addition, the cross-clamping induces a temporary ischemia of the legs, with severe metabolic derangement after the release of the aortic clamp. We have studied the effect of a intraoperative adrenergic block (phenoxybenzamine plus metoprolol) on the central circulation and the skeletal metabolism in 14 patients undergoing aortic reconstruction to treat occlusive arteriosclerotic disease. Cardiac output, heart rate, arterial and pulmonary artery pressures, and cardiac filling pressures, as well as femoral venous blood flow were studied. Biopsy specimens of the lateral vastus muscle and blood samples from the radial artery and iliac vein were taken before aortic clamping, and before, 30 minutes, four and 16 hours after the aorta was unclamped, as well as five days postoperatively. In addition, intramuscular temperature and pH were measured. Glycogen, glucose, lactate, pyruvate, ATP, ADP, AMP, phosphocreatine (PCr) and creatine (Cr) contents of the muscle and lactate and pyruvate concentrations in iliac venous and radial arterial blood were determined using enzymatic fluorometric techniques. Mean arterial blood pressure (MAP) averaged 80 mmHg before clamping, chiefly because of the low systemic vascular resistance (SVR), and left ventricular stroke work (LVSW) was normal. At clamping MAP, SVR, LVSW, remained unchanged. MAP and LVSW were unaffected even though SVR decreased slightly after the aorta was unclamped and resulted in an increased cardiac output, mainly due to a higher stroke volume. No major change in the pulmonary circulation was observed. During clamping the muscle lactate/pyruvate ratio increased, intramuscular pH and femoral venous blood flow decreased indicating insufficient tissue perfusion. Energy charge (EC), the adenylate (ATP + ADP + AMP) and creatine (PCr + Cr) pools were, however, unchanged. In spite of a restored blood flow to the legs, a severe metabolic derangement of the muscle was observed after declamping, with lowered EC, ATP + ADP + AMP and PCr + Cr indicating cellular damage. No improvement in the condition of the cells was observed 16 hours after operation. In conclusion, we found that by using neurolept anesthesia and an intraoperative adrenergic block in combination with a differentiated fluid therapy the central circulation stabilized and was largely unaffected by the clamping and unclamping procedures. In spite of the improved central hemodynamics no favorable effect on the skeletal muscle metabolism was observed.

Temporary incomplete ischemia of the legs caused by aortic clamping in man: improvement of skeletal muscle metabolism by low molecular dextran

Temporary infrarenal clamping of the aorta during reconstructive surgery induces incomplete ischemia of the leg muscle. After release of the clamp, severe muscle metabolic derangement with loss of high-energy phosphate compounds has been observed, indicating a dysfunction or damage of the muscle cells. In six patients operated on for occlusive aortoiliac disease, low-molecular-weight dextran (LMWD) was peroperatively administered for optimal volume loading and prevention of clotting. No heparin was used. Before, during and after the clamping period the central hemodynamics were monitored, and glycogen, glucose, lactate, pyruvate, phosphocreatine (PCr), creatine (Cr), ATP, ADP and AMP content in the thigh muscle were analyzed using enzymatic fluorometric techniques. Even though ischemia developed during the occlusion, no decline in the adenylate (ATP + ADP + AMP) or creatine (PCr + Cr) pools occurred after the clamp was released, and the energy charge of the adenine nucleotides remained unchanged. It is suggested that LMDX prevents rheologic changes impairing the microcirculation during and after the ischemic period, and thereby improves oxygenation of the muscle tissue upon reperfusion.