The pathophysiology of shock

Lipopolysaccharide attenuates mRNA levels of several adenylyl cyclase isoforms in vivo

Signals that elevate intracellular levels of cyclic adenosine monophosphate (cAMP) are among the factors that control lipopolysaccharide (LPS)-mediated inflammatory mediator production by macrophages. cAMP signaling is also involved in maintaining body functions that are commonly impaired in sepsis, including the endothelial cell barrier function and heart function. Several agents successfully used for sepsis intervention target cAMP signaling, and it was recently shown that liver and lung may be protected from inflammation injury by cAMP-elevating phosphodiesterase inhibitors. Here, we show that LPS attenuates adenylyl cyclase (AC) mRNA levels in liver, lung, heart, spleen and kidney in an animal model of endotoxemia, and in macrophages from liver and lung. In particular, AC5, AC6, AC7 and AC9 mRNA were reduced in most tissues examined and in tissue macrophages. In Kupffer cells, prostaglandin E2-mediated cAMP production was inhibited by LPS treatment. The reduction in AC mRNA by LPS would be expected to lead to a lowered potential for cAMP production in most organs, and in particular, changes in AC6 mRNA may affect endothelial cell barrier function and heart function. In contrast, AC4 mRNA was elevated in heart and lung. The present work indicates a possible mechanism for LPS-mediated alteration of cAMP signaling in vivo.

Endothelin 1 impairs oxygen delivery in livers from LPS-primed animals

Endothelin 1 (ET-1) is a potent vasoactive peptide that acts at sinusoidal and extrasinusoidal sites in the liver. Sensitivity to ET-1 increases in LPS-primed animals and is associated with impaired liver microcirculation in these animals. We hypothesized that LPS priming leads to an exacerbation in the impaired oxygen delivery in response to intraportal infusion of ET-1. Rats were studied 24 h after LPS injection (1 mg/kg, i.p.). Surface PO2 was determined using a recently developed technology of O2 mapping. The baseline portal pressure was higher in LPS-primed animals (P < 0.05), and increased to'similar magnitude as sham animals after a 10-min infusion of ET-1. The resultant portal pressure remained elevated in LPS compared to sham animals. There was no significant difference in baseline mean arterial pressure, and no significant systemic response to ET-1 in either group. In contrast to the macrohemodynamic, the decrease in tissue surface PO2 in response to ET-1 infusion was potentiated by LPS treatment (increased from baseline levels 33.8+/-9 to 46.8+/-8.3 in sham; 42.3+/-9.1 to 69+/-6.5 gray scale units in LPS; P < 0.01, sham vs. LPS) at end of infusion of ET-1 for 10 min. This indicates tissue hypoxia in response to ET-1, which is exacerbated in livers from LPS-primed animals compared to sham. Frequency distribution analysis showed a shift in mode from lower intensity (higher PO2) to areas with higher fluorescent intensity ranges (lower PO2), indicating areas with shut down in perfusion in LPS-treated animals. In the whole liver, ET-1 suppressed oxygen consumption, and this response was potentiated by LPS pretreatment. We propose that ET-1 impairs oxygen delivery in the liver during endotoxemia, resulting in areas of focal hypoxia. This response is possibly due to potentiated action of ET-1 at both sinusoidal and extrasinusoidal sites in the liver during endotoxemia.

Avoiding coagulopathy in vascular surgery

The possibility of coagulopathy can be minimized by attending to certain general perioperative details to avoid hypothermia, hypotension-shock, and multiple transfusions. In this paper, we present our protocol for avoiding coagulopathy in vascular surgery. In the past 1 1/2 years, we have used perioperative plasmapheresis in 204 patients undergoing cardiac or aortic peripheral vascular surgery. Autologous platelet-rich plasma is transfused at the completion of the operation after heparin reversal. Our data show an approximate 50% reduction in homologous blood product requirement. Seventy-five percent of patients having aortic surgery received no homologous blood products during their hospital stay. For those undergoing cardiac surgery, there has been about a 45% reduction in the use of homologous blood products. In our experience, autologous platelet-rich plasma not only decreases the risk of transmittable disease, but promotes hemostasis.

Pathophysiology of haemorrhagic shock

The immediate effect of sudden blood loss is the activation of a variety of homeostatic responses. These include increased sympathetic activity and increased release or production of renin, angiotensin, anti-diuretic hormone, aldosterone, adrenocorticotrophic hormone, beta-endorphins, glucocorticoids, glucagon, erythropoeitin, 2-3 diphosphoglycerate, prostaglandins and complement. This may be followed by the release of many substances, some initially appropriate locally, and some the products of damaged cells, which may go on to cause both local and systemic damage. These include lysosomal enzymes, kinins, histamines, serotonin, lactic acid, free oxygen radicals, neutrophil proteases, fibrinogen degradation products, endotoxins, myocardial depressant polypeptides, and passive transferable lethal factor. The early and late effects on the cardiovascular and respiratory systems, and on the blood, brain, kidneys, gut, liver, pancreas, and on overall metabolism and cellular function, are considered in turn. Although an enormous research effort has increased our understanding of the pathophysiology of haemorrhagic shock, no special measures have yet been shown to influence morbidity or mortality in man. Management still hinges on the early recognition and treatment of bleeding, on general supportive measures, and on safeguarding each link in the oxygen delivery chain.

Problems in the treatment of septic shock

A small review is presented on the problems encountered in the treatment of septic shock. The discussion is focussed on haemodynamic problems. At least three and possibly four haemodynamic mechanisms seem to be involved: peripheral pooling, increased vascular permeability, myocardial failure (right and/or left heart failure) and probably peripheral vascular failure. A method is indicated to study some of these mechanisms.

The early detection of the effects of surgical shock on the viscera

One hundred and one patients, in shock after operations were reviewed to examine the visceral effects on their prognoses. The shock was caused in 65 cases by hypovolaemia and in 36 cases by sepsis. The effects were studied on the heart and cardiovascular system, liver, kidneys, gastrointestinal system, central nervous system, lungs and blood clotting system. Surgical shock affected more frequently the lung and liver (P less than 0.05 and P less than 0.01). The lungs were most frequently involved in hypovolaemia (25 patients) and sepsis (25 cases). Pathology of the lung was associated with the highest mortality rate (P less than 0.005), followed by kidney (P less than 0.01) then heart and central nervous system (P less than 0.025). Involvement of the gastrointestinal tract or clotting system alone was not associated with higher mortality rates, except in the presence of other visceral derangements. Lung affection also had a greater mortality followed by kidney and the central nervous system. Involvement of one or several organs in failure to survive septic shock is dealt with in the discussion. It is concluded that visceral involvement secondary to shock could be of importance for prognosis.