E. Gilbart

Detection of tissue hypoxia by arteriovenous gradient for PCO2 and pH in anesthetized dogs during progressive hemorrhage.

The present study tested the hypothesis that, during acute bleeding, the development of tissue hypoxia might be reflected by an abrupt widening in arteriovenous gradient for PCO2 (AV PCO2) and for pH (AV pH) as accurately as by an increase in blood lactate levels.Twenty-four anesthetized (isoflurane 1.4% end-tidal), paralyzed, and mechanically ventilated dogs submitted to progressive hemorrhage were studied. Oxygen uptake (VO2) was derived from expired gas analysis and oxygen delivery (DO2) was calculated by the product of the thermodilution cardiac index and the arterial O2 content. During the first part of the protocol, VO2 remained stable as the progressive reduction in DO2 was associated with a corresponding increase in O2 extraction (O2 ER). Blood lactate increased slightly but not significantly. AV PCO2 and AV pH increased significantly, essentially related to venous respiratory acidosis. The critical value of DO2 below which VO2 decreased was 8.95 +/- 1.60 mL centered dot min-1 centered dot kg-1. Below this value, there was a marked increase in blood lactate and an abrupt widening in AV PCO2 and AV pH gradients. The critical value of DO2 obtained from blood lactate, AV PCO2 and AV pH were similar to those obtained from VO2 (8.60 +/- 1.12; 8.73 +/- 1.40; 8.78 +/- 1.37, respectively; P = not significant). A significant correlation was found, during the hemorrhage protocol, between blood lactate and AV PCO2 (r = 0.84; P < 0.001) or AV pH (r = 0.78; P < 0.001). Therefore, AV PCO2 and AV pH represent simple but reliable indicators of tissue hypoxia during hemorrhagic shock. (Anesth Analg 1995;80:269-75)

Comparison of Halothane, Isoflurane, Alfentanil, and Ketamine in Experimental Septic Shock

The effects of four commonly used anesthetic agents, halothane, isoflurane, alfentanil, and ketamine, on cardiovascular function and oxygen balance were studied in a dog model of septic shock. After initial pentobarbital administration, the dogs were given Escherichia coli endotoxin (3 mg/kg) and, after 30 min, fluids to restore cardiac filling pressures to baseline levels. This resulted in a low resistance shock in all animals. Dogs were then given for 2 h either halothane (n = 9, 0.5 MAC), isoflurane (n = 9, 0.5 MAC), or alfentanil (n = 9, 150 μg/kg IV plus 2 mg·kg−1·min−1) or ketamine (n = 9, 2 mg/kg IV plus 0.2 mg·kg−1·min−1) or no anesthetic (control: n = 9). Mean arterial pressure increased in the control group (+11 ± 18 mm Hg) and with ketamine (+10 ± 20 mm Hg), remained unchanged with isoflurane (−2 ± 11 mm Hg), and decreased with halothane (−22 ± 23 rnm Hg) and alfentanil (−9 ± 23 mm Hg). Heart rate tended to increase in the control group but decreased with the four anesthetic agents, especially with alfentanil and halothane. Cardiac index and left ventricular stroke work index increased in the control group and in each anesthetic group except the halothane group. Systemic vascular resistance decreased in all groups except in the ketamine group. In the control group, the increase in cardiac index was associated with significant increases in oxygen delivery and consumption, and with a significant decrease in blood lactate levels. There was a dramatic decrease in oxygen consumption in all anesthetic groups, whereas oxygen delivery failed to increase only with halothane. Blood lactate increased significantly with halothane (5.0 ± 1.5 to 6.3 ± 1.4 mM/L) and isoflurane (4.8 ± 1.1 to 5.3 ± 1.2 mM/L), remained unchanged with alfentanil (4.5 ± 1.5 and 4.6 ± 0.8 mM/L), and tended to decrease with ketamine (4.9 ± 1.4 to 4.5 ± 1.4 mM/L). In conclusion, among the four anesthetic agents tested, halothane had the least desirable effects. Ketamine best preserved cardiovascular function and appeared to have the least deleterious effects on the hypoxic tissues. Thus, ketamine could be the anesthetic agent of choice in septic shock.

Cardiovascular effects of moderate normovolaemic haemodilution during enflurane–nitrous oxide anaesthesia in man

The cardiovascular effects of mild normovolaemic haemodilution during enflurane–nitrous oxide anaesthesia were studied in 20 patients with normal cardiac function before, during and after total hip replacement. After induction of anaesthesia, patients were randomly allocated to one control group (C), or one haemodiluted group (H) where Hct was decreased to 30% by replacement of blood volume by an identical volume of hydroxyethyl starch 200/0.5. Each patient was monitored with a pulmonary artery catheter allowing the measurement of right ventricular ejection fraction. During haemodilution, stroke index and right ventricular end–diastolic volume index increased from 33.1 7.9 to 39.3 7.1 ml M‐2 and from 73.8 20.3 to 94.9 18.5 mlM‐2 respectively (mean s.d., both P<0.05). However, heart rate decreased so that cardiac index did not change. O2 delivery decreased significantly (from 389 70 to 31163 ml–min‐1 –m‐2; P<0.05), but was not different to the control group. O2 consumption was maintained by an increase in O2 extraction. During the surgical procedure, cardiac index was higher in the haemodiluted group than in the control group, so that O2 delivery was similar in the two groups. O2 consumption tended to be greater in the haemodiluted group.

Effects of propofol, etomidate, and pentobarbital on critical oxygen delivery

Objective To test the hypothesis that propofol, etomidate, and pentobarbital increase critical oxygen delivery in a dose-dependent manner during progressive hemorrhage. Design Prospective, randomized laboratory investigation. Setting University laboratory. Subjects A total of 40 anesthetized, paralyzed, and mechanically ventilated dogs weighing 29.2 ± 4.6 kg. Interventions Dogs were randomly assigned to be anesthetized with propofol (n = 13), etomidate (n = 13), or pentobarbital (n = 14) at either low or high dosages. At 30 mins after splenectomy, the dogs underwent progressive hemorrhage by successive withdrawals of 3–5 mL/kg arterial blood. Measurements and Main Results At each step of hemorrhage, oxygen consumption and oxygen delivery were determined. Oxygen consumption was obtained from expired gas analysis, and oxygen delivery was determined from thermodilution cardiac output and calculated arterial oxygen content. In each animal, critical oxygen delivery and critical oxygen consumption were obtained from a plot of oxygen consumption vs. oxygen delivery as the point of intersection of the two best-fit regression lines determined by a least sum of squares method. Critical oxygen extraction was obtained by dividing critical oxygen consumption by critical oxygen delivery. In the three groups, animals receiving the higher anesthetic infusion had a significantly higher critical oxygen delivery (propofol: 10.5 ± 0.8 vs. 13.9 ± 2.5 mL/min/m2, p < .05; etomidate: 10.1 ± 0.7 vs. 13.4 ± 3.0 mL/min/m2, p < .05; pentobarbital: 7.8 ± 1.0 vs. 12.3 ± 2.5 mL/min/m2, p < .01) attributable to a lower critical oxygen extraction ratio (propofol: 41.1 ± 6.4% vs. 54.2 ± 2.5%, p < .01; etomidate: 42.7 ± 10.2% vs. 60.6 ± 7.1%, p < .01; pentobarbital: 42.2 ± 7.2% vs. 64.3 ± 8.8%, p < .01). Conclusions This study indicates that propofol, etomidate, and pentobarbital increased critical oxygen delivery in a dose-dependent manner. This effect was mainly related to a decrease in tissue oxygen extraction capabilities.

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.

Adrenergic support during anesthesia in experimental endotoxin shock: norepinephrine versus dobutamine

The effects of norepinephrine and dobutamine were compared during endotoxin shock in dogs anesthetized either with enflurane (E: 1.5%, N = 12) or with i.v. ketamine (K: 5 mg X kg‐1 + 0.2 mg X kg‐1 X min‐1, N = 12). An i.v. bolus of 1.5 mg X kg‐1 E. coli endotoxin was followed by saline infusion to restore left‐sided filling pressures at baseline. With E, heart rate, mean arterial pressure and stroke index decreased (P <0.01). The decrease in oxygen delivery (Do2) and in oxygen consumption (Vo2) was associated with an increase in blood lactate. In contrast, K anesthesia was associated with remarkable hemodynamic stability. Do2 was well maintained, Vo2 decreased (P <0.01) and blood lactate did not change. Under E anesthesia, mean arterial pressure increased more with norepinephrine and heart rate increased more with dobutamine. Under K anesthesia, cardiac index, stroke index and left ventricular stroke work index increased similarly with both agents. In both groups Do2 and Vo2 increased markedly. The amount of fluid infused was higher with dobutamine than with norepinephrine. Thus, enflurane but not ketamine had depressant cardiovascular effects at the doses used in this model. With both anesthetics, norepinephrine and dobutamine could effectively improve cardiac function. Dobutamine could therefore represent a valuable alternative to norepinephrine for cardiovascular support during anesthesia in septic shock.

Right ventricular function during pulmonary artery clamping: Effects of enflurane

Abstract Temporary or definitive suppression of blood flow and ventilation to one lung is frequent during thoracic surgery. Clamping of a pulmonary artery (PA) usually results in recruitment and passive distension of the vasculature of the other lung, allowing to overcome this acute right ventricular (RV) and pulmonary overload. We studied in dogs RV volumes and RV ejection fraction (RVEF) during these manoeuvres, using a modified thermodilution PA catheter (1). We also evaluated the effects of enflurane anaesthesia in these potentially deleterious circumstances.

Cardiovascular Effects of Moderate Normovolaemic Haemodilution During Enflurane-Nitrous Oxide Anaesthesia in Man

The cardiovascular effects of mild normovolaemic haemodilution during enflurane-nitrous oxide anaesthesia were studied in 20 patients with normal cardiac function before, during and after total hip replacement. After induction of anaesthesia, patients were randomly allocated to one control group (C), or one haemodiluted group (H) where Hct was decreased to 30% by replacement of blood volume by an identical volume of hydroxyethyl starch 200/05. Each patient was monitored with a pulmonary artery catheter allowing the measurement of right ventricular ejection fraction. During haemodilution, stroke index and right ventricular end-diastolic volume index increased from 33.1 +/- 7.9 to 39.3 +/- 7.1 ml.M-2 and from 73.8 +/- 20.3 to 94.9 +/- 18.5 ml.M-2 respectively (mean +/- s.d., both P < 0.05). However, heart rate decreased so that cardiac index did not change. O2 delivery decreased significantly (from 389 +/- 70 to 311 +/- 63 ml.min-1.m-2; P < 0.05), but was not different to the control group. O2 consumption was maintained by an increase in O2 extraction. During the surgical procedure, cardiac index was higher in the haemodiluted group than in the control group, so that O2 delivery was similar in the two groups. O2 consumption tended to be greater in the haemodiluted group. In patients with normal cardiac function, enflurane-nitrous oxide anesthesia could alter the normal physiologic response to mild normovolaemic haemodilution.

Effects of alfentanil on DO2/VO2 relationship

Abstract Oxygen consumption (V02) is normally independent of systemic oxygen delivery (DO2). When DO2 is reduced, the systemic oxygen extraction (ER) increases until a critical limit (DO2crit) is reached below which oxygen consumption (VO2) becomes limited by delivery. Alfentanil is a fentanyl derivative characterized by a rapid onset, and a short duration of action. As alfentanil better blunts the hormonal stress response than fentanyl (1), it has been especially recommended for open heart surgery. However, the precise effects of this agent on the DO2/VO2 relationship have not been defined. This study was performed to determine the effects of alfentanil on tissue 02 extraction capabilities on a model of progressive hemorrhage in 18 mongrel dogs (2).

Anesthetic Techniques in Circulatory Shock

This review will focus on the cardiovascular effects of the most common anesthetics, with special reference to the anesthesia of the shocked patient.