Cardiopulmonary consequences of pyrogen-induced hyperpyrexia in man

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

Metabolism, temperature, and ventilation

In mammals and birds, all oxygen used (VO2) must pass through the lungs; hence, some degree of coupling between VO2 and pulmonary ventilation (VE) is highly predictable. Nevertheless, VE is also involved with CO2 elimination, a task that is often in conflict with the convection of O2. In hot or cold conditions, the relationship between VE and VO2 includes the participation of the respiratory apparatus to the control of body temperature and water balance. Some compromise among these tasks is achieved through changes in breathing pattern, uncoupling changes in alveolar ventilation from VE. This article examines primarily the relationship between VE and VO2 under thermal stimuli. In the process, it considers how the relationship is influenced by hypoxia, hypercapnia or changes in metabolic level. The shuffling of tasks in emergency situations illustrates that the constraints on VE-VO2 for the protection of blood gases have ample room for flexibility. However, when other priorities do not interfere with the primary goal of gas exchange, VE follows metabolic rate quite closely. The fact that arterial CO2 remains stable when metabolism is changed by the most diverse circumstances (moderate exercise, cold, cold and exercise combined, variations in body size, caloric intake, age, time of the day, hormones, drugs, etc.) makes it unlikely that VE and metabolism are controlled in parallel by the condition responsible for the metabolic change. Rather, some observations support the view that the gaseous component of metabolic rate, probably CO2, may provide the link between the metabolic level and VE.

LEFT VENTRICULAR DIASTOLIC FILLING CHARACTERISTICS ARE NOT IMPAIRED BUT SYSTOLIC PERFORMANCE WAS AUGMENTED IN THE EARLY HOURS OF EXPERIMENTAL ENDOTOXEMIA IN HUMANS

This study was performed to determine whether endotoxemia causes diastolic cardiac dysfunction. Eleven healthy volunteers, 30 +/- 6 years of age, underwent comprehensive transthoracic echocardiographic assessment including two-dimensional, M-mode transmitral and tissue Doppler of systolic and diastolic function at baseline and at 3 and 5 h after intravenous administration of purified Escherichia coli endotoxin (4 ng/kg). Data were analyzed by analysis of variance; P values of less than 0.05 were considered significant. Endotoxin administration resulted in a hyperdynamic state characterized by decreased mean arterial pressure and significant increase in cardiac index. This was accompanied by increases in several load-dependent systolic performance indices (3 and 5 h). Robust increases in peak systolic blood pressure/end-systolic volume index, one of the relatively load-independent contractility parameter, were also observed at 3 h after endotoxin administration. Transmitral peak early velocity (E), which represents early filling, significantly increased at 3 h after infusion. Late diastolic velocity (A), which represents atrial contraction, significantly increased at 3 and 5 h after infusion. The E/A ratio indicative of delayed relaxation significantly decreased due to increases in A (transmitral) and A (tissue Doppler) at 3 and 5 h after infusion. As expected, endotoxin infusion resulted in a hyperdynamic state associated with increases in systolic function indices including endocardial systolic velocities. The observed decreases in E/A (transmitral) and E/A (tissue Doppler) ratio were primarily due to increases in A and A. Moreover, isovolumic relaxation time and time constant for left ventricular relaxation, a load-independent parameter for ventricular relaxation, remained unchanged at 3 and 5 h after endotoxin infusion. Therefore, our findings are more likely due to enhanced atrial contractility resulting from increased sympathetic activity in response to reduction in left ventricular afterload and not due to altered diastolic filling characteristics.

Endotoxin removal by direct hemoperfusion with an adsorbent column using polymyxin B-immobilized fiber ameliorates systemic circulatory disturbance in patients with septic shock

Direct hemoperfusion (DHP) with an adsorbent column using polymyxin B-immobilized fiber (PMX-F) has been shown to improve the state of shock in patients with septic shock. However, no evidence has been presented for a direct link between endotoxin removal by DHP with PMX-F and improvement in septic shock. We retrospectively analyzed clinical profiles of 24 patients with septic shock (16 patients, gram-negative; 8 patients, non-gram-negative septic shock) who underwent DHP with PMX-F. Patients with gram-negative septic shock were characterized by hyperdynamic circulation. DHP with PMX-F reduced blood endotoxin concentrations and ameliorated shock, with an improvement in hyperdynamic circulation in patients with gram-negative septic shock. Mean arterial pressure also was elevated after therapy in patients with non-gram-negative septic shock, but systemic hemodynamics were unaffected. Regardless of the causative microorganism, patients with endotoxemia (blood endotoxin level > 10 pg/mL) showed hyperdynamic shock, and DHP with PMX-F reduced blood endotoxin levels and ameliorated hyperdynamic circulation, whereas patients without endotoxemia showed features of shock without hyperdynamic circulation, and DHP with PMX-F ameliorated shock without affecting cardiac performance. In patients with gram-negative septic shock, blood endotoxin concentration correlated positively with cardiac output and negatively with systemic vascular resistance before DHP therapy. Reduction in blood endotoxin concentration by DHP therapy positively correlated with the reduction in cardiac output. Our findings indicate that the improvement in hyperdynamic circulation was related directly to endotoxin removal by the PMX-F column, and endotoxin has an important role in the development of hyperdynamic circulation in patients with gram-negative septic shock.

Effect of endotoxin on ventilation and breath variability: role of cyclooxygenase pathway

To evaluate the effects of endotoxemia on respiratory controller function, 12 subjects were randomized to receive endotoxin or saline; six also received ibuprofen, a cyclooxygenase inhibitor, and six received placebo. Administration of endotoxin produced fever, increased respiratory frequency, decreased inspiratory time, and widened alveolar-arterial oxygen tension gradient (all p < or = 0.001); these responses were blocked by ibuprofen. Independent of ibuprofen, endotoxin produced dyspnea, and it increased fractional inspiratory time, minute ventilation, and mean inspiratory flow (all p < or = 0.025). Endotoxin altered the autocorrelative behavior of respiratory frequency by increasing its autocorrelation coefficient at a lag of one breath, the number of breath lags with significant serial correlations, and its correlated fraction (all p < 0.05); these responses were blocked by ibuprofen. Changes in correlated behavior of respiratory frequency were related to changes in arterial carbon dioxide tension (r = 0.86; p < 0.03). Endotoxin decreased the oscillatory fraction of inspiratory time in both the placebo (p < 0.05) and ibuprofen groups (p = 0.06). In conclusion, endotoxin produced increases in respiratory motor output and dyspnea independent of fever and symptoms, and it curtailed the freedom to vary respiratory timing-a response that appears to be mediated by the cyclooxygenase pathway.

Influence of Escherichia coli endotoxin on the pharmacokinetics and respiratory depressant effect of alfentanil in rabbits

Postoperative fever occurs in many surgical patients, due to release of pyrogens into the circulation. Pyrogens and fever may influence the pharmacokinetics and effects of drugs. The aim of this study was to investigate the interactions of a pyrogen with the opioid analgesic alfentanil in an animal model. Alfentanil was infused over 10 min into 17 conscious rabbits and over 120 min in another 12 animals. Some of them had been randomized to pretreatment with Escherichia coli endotoxin. Arterial plasma concentrations of alfentanil were determined repeatedly, and arterial blood gas values were recorded. Endotoxin antagonized the respiratory depressant effect of the 10-min infusion of alfentanil by increasing drug distribution clearance during the infusion. In addition, endotoxin raised the total volume of distribution of alfentanil from 0.70 to 1.4 L/kg. Plasma protein binding and elimination clearance were not affected. The increase in volume of distribution and the lack of effect of endotoxin on elimination clearance were confirmed in the 120-min infusion experiments. Apparent concentration-effect relationships for the actions of alfentanil on arterial CO2, O2, and pH were not influenced by the endotoxin. Circulating pyrogens can thus influence the pharmacokinetics and, indirectly, the effects of alfentanil.

Response of man to endotoxin

Endotoxin, a cell wall component of Gram-negative bacteria, plays a central role in the pathogenesis of septic shock. By administering small doses of intravenous endotoxin to humans, a variety of acute inflammatory responses are induced which are qualitatively similar to those that occur during the early stages of septic shock. Within hours of the administration of intravenous endotoxin to human volunteers, changes occur in systemic hemodynamics, ventricular function, pulmonary gas exchange and permeability. In conjunction with these changes in organ function, a wide variety of inflammatory mediators are released which appear to contribute to these responses. These include the release of proinflammatory cytokines (e.g. tumor necrosis factor-alpha, IL-1 beta, IL-6, IL-8), activation of the fibrinolytic system, kallikrein-kinin generation and phospholipase A2 release. Phagocytic leukocytes are primed for enhanced inflammatory responses following endotoxin administration. Counter-regulatory responses are initiated in parallel and may serve to limit some of the end-organ responses by the inflammatory mediators. This human model provides a unique opportunity to extend previous concepts of acute inflammation and to evaluate the earliest responses activated after exposure to an important bacterial component. Defining the pathways and responses initiated during acute human endotoxemia may allow a better understanding of host responses that are critical to the development of organ dysfunction and shock due to severe infections.

Pulmonary and oxygen transport effects of intravenously administered endotoxin in normal humans

Little data are available describing the initial changes in pulmonary function and oxygen transport during human endotoxemia. We studied 26 normal humans after intravenously administered endotoxin (4 ng/kg). To evaluate alterations in gas exchange, hemodynamic monitoring was performed in nine subjects given endotoxin and six subjects given saline only. Compared with the control subjects, no changes in gas exchange occurred at 3 h, but after volume loading (mean, 2.2 L saline infused from 3 to 5 h) the PaO2 fell (86.1 +/- 2.3 mm Hg, p = 0.042), and the AaPO2 widened (18.5 +/- 1.7 mm Hg, p = 0.005). Oxygen consumption and delivery both increased significantly at 3 h (219 +/- 17 and 1,030 +/- 43 ml/min.min2) and 5 h (203 +/- 7 and 949 +/- 48 ml/min.min2) (p less than or equal to 0.035), whereas oxygen extraction fell at 3 h (p = 0.041). Seventeen subjects underwent bronchoalveolar lavage 14 +/- 4 days before and at 1.5 to 3 h (n = 8) or 5 h after (n = 9) the administration of endotoxin. No increase in the total number of cells or percent or absolute number of neutrophils was found at either time point. The rate of clearance of inhaled 99mTc-diethylenetriamine pentacetate aerosol, a measure of alveolar epithelial permeability, increased in subjects scanned before 3 h (n = 8; p less than 0.05), whereas no significant changes occurred in subjects scanned 5 h after endotoxin (n = 5) or in control subjects (n = 6). Early inflammatory responses after intravenous administration of endotoxin to normal humans results in alterations in gas exchange and lung permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

The cardiovascular response of normal humans to the administration of endotoxin

Marked abnormalities in cardiovascular function accompany septic shock, and bacterial endotoxin is believed to be one of the principal mediators of these abnormalities. To evaluate the cardiovascular effects of endotoxemia in humans, we measured hemodynamic variables in nine normal subjects given an intravenous bolus dose of endotoxin (Escherichia coli, 4 ng per kilogram of body weight) and in six normal subjects given a bolus dose of saline, before and three hours after administration. All the subjects then underwent volume loading with normal saline (mean, 2217 ml) during the fourth and fifth hours after administration of the bolus, and the measurements were repeated. Three hours after the administration of endotoxin and before volume loading, the cardiac index had increased by 53 percent and the heart rate by 36 percent (both changes were significant; P less than or equal to 0.008), and the systemic vascular-resistance index had decreased by 46 percent (P = 0.004). After volume loading (five hours after the administration of endotoxin), the left ventricular ejection fraction decreased by 1 percent of the base-line value in the subjects given endotoxin, but increased by 14 percent in the controls (P = 0.008). The left ventricular end-diastolic and end-systolic volume indexes increased by 18 percent (P = 0.07) and 24 percent (P = 0.042), respectively. Left ventricular performance, as measured by the ratio of the peak systolic pressure to the end-systolic volume index, was depressed (a decrease of 0.90 in the subjects given endotoxin vs. an increase of 0.76 in the controls; P = 0.024). We conclude that the administration of endotoxin to normal subjects causes a depression of left ventricular function that is independent of changes in left ventricular volume or vascular resistance. The changes in function are similar to those observed in septic shock and suggest that endotoxin is a major mediator of the cardiovascular dysfunction in this condition.

The acid-base balance during the time course of endotoxin fever and sodium salicylate antipyresis in the rabbit

Blood acid-base balance in sodium salicylate antipyresis was investigated in adult rabbits at ambient temperature of 21.5 +/- 0.5 degrees C. The experimental fever elicited by iv injection of lipopolysaccharide Escherichia coli 1 microgram/kg/ was accompanied by a slight metabolic acidosis. A decrease in pH by 0.09 and HCO3- by 4.8 mEq/1 was noticed during the rising phase of pyrogen fever. There were no concomitant changes in blood PCO2 during that period of time. Although the concentrations of HCO3- were decreasing till the end of the experiment, the parallel falls in PCO2 led to a partial compensation of the noticed acidosis. Pretreatment with 200 mg/kg of sodium salicylate /an hour's iv infusion/reduced the febrile response by 42% and completely reversed the postpyrogen changes in pH and HCO3-. The falls in PCO2 during antipyresis, however, were similar to those observed in febrile rabbits. Possible mechanisms by which sodium salicylate could affect the pyrogen-induced disturbances of acid-base balance are being considered.

A correlation between PaCO2 and body temperature in febrile patients

Chapot, G., Muller, Michèle, Barrault, Nicole, Dargnat, Nicole, and Languillat, J-M. (1974).Thorax, 29, 104-105. A correlation between Paco₂and body temperature in febrile patients. Paco₂ has been measured in 49 patients with normal and raised body temperature. Within the temperature range 35·5°C-41·4°C, there was an inversely proportional relationship between Paco₂ and body temperature with a highly significant correlation coefficient.