Shock States in Acute Care Surgery
Shock is a condition of insufficient oxygen delivery to the tissues to meet metabolic demands. Shock is not synonymous with hypotension albeit hypotension is almost always associated with shock. Arterial blood pressure, therefore, is not sufficient to diagnose shock. Rather the diagnosis relies on the presence of tissue hypoperfusion (increased arterial blood lactates). With shock, the cellular metabolism is shifted from aerobic to anaerobic. The metabolic consequence of prolonged shock is cellular energy depletion with calcium entry into the cytosol, increased production of reactive oxygen species (ROS), altered membrane permeability and swelling. This causes cellular membrane rupture and death. Subsequent reperfusion of damaged cells contributes to increased ROS production, endothelial barrier disruption with interstitial oedema formation. Ischaemia- reperfusion injury also causes a diffuse inflammatory response with activation of polimorphonuclear neutrophils (PMNs) and production of diffuse organ damage.
Haemorrhagic shock is by far the prevalent form of shock in the surgical care setting. Hypovolemia decreases intravascular volume, and anaemia reduces the haemoglobin content so that oxygen supply is severely diminished. The decrease of venous return by reduction of the stressed volume is the main mechanism of hypovolemia in haemorrhagic shock. However, up to 750 mL of blood can be lost without appreciable effects due to the physiological reserve.
- 2.World Health Organization. Injury chart book. A graphical overview of the global burden of injuries. Department of injuries and violence prevention. Noncommunicable diseases and Mental Health Cluster. Geneva: World Health Organization; 2002. http://www.who.int/violence _injury_prevention/pubblication/other_injury/chart/en/.Google Scholar
- 5.Guyton AC, Jones CE, Coleman TG. Circulatory physiology: cardiac output and its regulation. In: Guyton AC, editor. Philadelphia: WB Saunders; 1973.Google Scholar
- 13.Rixen D, Raum M, Bouillon B, Lefering R, Neugebauer E. Arbeits-gemeinschaft ‘Polytrauma’ of the Deutschen Gesellschaft Fur Unhallchirurgie: base deficit development and its prognostic significance in posttrauma critical illness: an analysis by trauma registry of the Deutsche Gesellschaft fur Unfallechirurgie. Shock. 2001;15:83–9.PubMedCrossRefGoogle Scholar
- 27.Cournard A, Motley HL, Werko L. Physiological studies of the effect of intermittent positive pressure breathing on cardiac output in man. Am J Physiol. 1948;152:169–74.Google Scholar
- 28.Scharf SM, Brown R, Tow DE, Parisi AF. Cardiac effects of increasing lung volume and decreasing pleural pressure. J Appl Physiol Respir Environ Exerc Physiol. 1979;47:253–62.Google Scholar