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Lesson 2 Physiology of Life and Death Maintenance of Life • Body systems – Interrelated – Interdependent • Every cell and every organ work together to: – Sustain cellular energy production – Maintain vital metabolic processes Energy • Energy powers all body functions – Energy sustains cellular and organ functions • Cells make energy from oxygen and glucose • Energy is stored in the form of adenosine triphosphate (ATP) molecules • Without energy, cellular functions cease • The goal is to help ensure that the patient’s body maintains energy production Systems and Components (1 of 2) • Airway – Must be patent • Breathing (lungs) – Adequate oxygen must: • Reach alveoli • Cross alveolar/capillary wall • Enter the circulation – Carbon dioxide (CO2) must be removed Systems and Components (2 of 2) • Circulation – Distributes red blood cells (RBCs) – Ensures adequate number of RBCs – Transports oxygen to every cell in every organ Airway (1 of 3) • An open airway is essential to deliver air (oxygen) to the alveoli Airway (2 of 3) • Normal air movement – Inhalation results from negative intrathoracic pressure as the chest expands • Air fills the alveoli Airway (3 of 3) • Normal air movement (cont’d) – Exhalation results from increased intrathoracic pressure as the chest relaxes • Forces air out of the alveoli Breathing (Lungs) (1 of 2) • When air reaches the alveoli: – Oxygen crosses the alveolar–capillary membrane • Oxygen – Enters the RBCs – Attaches to hemoglobin for transport Breathing (Lungs) (2 of 2) • CO2 in the plasma and cells – A by-product of aerobic metabolism and energy production – Crosses the alveolar–capillary membrane into the alveoli – Is removed during exhalation Circulation (1 of 2) • Oxygen-enriched RBCs are pumped through the blood vessels of the body to deliver oxygen to target organs Circulation (2 of 2) • Oxygen is then off-loaded from the RBCs to fuel the metabolic processes of the cell • CO2 is transferred from the cells to the plasma for elimination via the lungs Cellular Metabolism — Aerobic (1 of 3) • Aerobic metabolism – Most efficient method of energy production – Uses oxygen and glucose to produce energy via chemical reactions known as glycolysis and the Krebs cycle – Produces large amounts of energy – Waste products • Carbon dioxide • Water Cellular Metabolism — Aerobic (2 of 3) • Aerobic metabolism is dependent upon: – Adequate and continuous supply of oxygen – Patent airway – Functioning lungs (pulmonary system) – Functional heart • Pump blood to the cells Cellular Metabolism — Aerobic (3 of 3) • Aerobic metabolism is dependent upon (cont’d): – Intact vascular system – Adequate supply of RBCs • Carry and transport oxygen • Remove waste Aerobic Metabolism Cellular Metabolism — Anaerobic (1 of 2) • An injury that affects any of these three components of the oxygen delivery system will affect energy production • Anaerobic metabolism is a metabolic process that functions in the absence of oxygen Cellular Metabolism — Anaerobic (2 of 2) • Metabolism without adequate oxygen • Uses stored glucose in the form of glycogen for energy production • Capable of sustaining energy requirements only for a short time • Produces only small amounts of energy – 19-fold decrease in energy – Increased lactic acid as a by-product Anaerobic Metabolism Shock • Inadequate energy production required to sustain life • Change from aerobic to anaerobic metabolism – Secondary to hypoperfusion – Delivery of oxygen is inadequate to meet metabolic demands – Decreased energy production • Cellular and organ death Consequences of Hypoperfusion (1 of 4) • Cellular hypoxia • Decreased ATP (energy) production • Cell dysfunction – Lactic acid buildup – Low pH Consequences of Hypoperfusion (2 of 4) • Cell dysfunction (cont’d) – Autodigestion of cells • Leads to cellular death and organ failure – Entry of sodium and water into the cell • Cellular edema (swelling) worsens with overhydration – Continuation of cycle • Unless oxygenated red blood cells reach the capillaries – If further loss of intravascular (blood) volume • The cycle continues Consequences of Hypoperfusion (3 of 4) • Inadequate ATP • Cells and organs do not function properly – Hypothermia • Decreased heat production Consequences of Hypoperfusion (4 of 4) • Cells and organs do not function properly – Acidosis • What little ATP is being produced is used to shiver • Lactic acid production increases – Coagulopathy • As body temperature drops, blood clotting becomes impaired Triangle of Death Cascade of Death Types of Shock • Shock is any condition that causes decreased cellular energy production • Hypovolemic – Dehydration – Hemorrhage • Distributive – Neurogenic – Septic – Anaphylactic – Psychogenic • Cardiogenic – Pump failure (intrinsic versus extrinsic) Trauma-Related Types of Shock • Hypovolemic – Dehydration – Hemorrhage • Distributive – Neurogenic – Septic – Anaphylactic – Psychogenic • Cardiogenic – Pump failure (intrinsic versus extrinsic) Hemorrhagic Shock • Most common cause of hypoperfusion after trauma • Internal or external blood loss • Classes of shock Neurogenic “Shock” • Associated with spinal cord injury • Interruption of the sympathetic nervous system resulting in vasodilation • Patient has normal blood volume but vascular container has enlarged, thus decreasing blood pressure Cardiogenic Shock — Extrinsic • Results from external compression of the heart • Ventricles cannot fully expand – Less blood is ejected with each contraction • Blood return to the heart is decreased • Causes from trauma include: – Pericardial tamponade – Tension pneumothorax Pathophysiology of Shock (1 of 6) • Shock is progressive • Changes in shock include: – Hemodynamic – Cellular (metabolic) – Microvascular • Compensatory mechanisms – Short-term – Will fail without interventions Pathophysiology of Shock (2 of 6) • The heart must be an effective pump – Primed by return of blood through the vena cavae • Starling’s Law • Stroke volume (SV) – Amount of blood ejected with each contraction – Depends on adequate return of blood – If blood volume decreases • SV will decrease • Cardiac output (CO) will decrease unless the heart rate (HR) increases CO = SV × HR Pathophysiology of Shock (3 of 6) • Adequate blood pressure – Required to maintain cellular perfusion • CO is one factor in maintaining blood pressure (BP) • If CO falls – Vasoconstriction occurs – Systemic vascular resistance (SVR) increases in an attempt to maintain BP BP = CO × SVR Pathophysiology of Shock (4 of 6) • Vasoconstriction leads to the ischemic phase of shock • Microvascular changes – Early • Precapillary and postcapillary sphincters constrict • Resulting in ischemia in the tissues • Must then produce energy anaerobically Pathophysiology of Shock (5 of 6) – As acidosis increases: • The precapillary sphincters relax • The postcapillary sphincters remain constricted • This results in stagnation of blood in the capillary bed Pathophysiology of Shock (6 of 6) – Finally: • The postcapillary sphincters relax • Results in washout • Releases microemboli • Aggravates acidosis • Causes infarction of organs by microemboli Signs Associated with Types of Shock Organ System Failure Due to Shock • If not recognized and promptly corrected, shock will lead to organ dysfunction: – First in oxygen-sensitive organs – Then in other less oxygen-sensitive organs • This cascading effect will lead to multi-organ dysfunction syndrome and patient death – Failure of one major organ system • Mortality rate of approximately 40% – As additional organ systems fail, mortality approaches 100% Organ Sensitivity to Hypoxia • Extremely sensitive – Brain, heart, lungs • Moderately sensitive – Kidneys, liver, gastrointestinal tract • Least sensitive – Muscle, bone, skin Organ System Failure Due to Shock (1 of 4) • Acute renal failure – May result if oxygen delivery is impaired for more than 45–60 minutes – Will result in: • Decreased renal output • Reduced clearing of toxic products Organ System Failure Due to Shock (2 of 4) • Acute respiratory distress syndrome (ARDS) – Results from: • Damage to the alveolar cells • Hyper-resuscitation (fluid overload) – Results in: • Leakage of fluid into the interstitial spaces and alveoli Organ System Failure Due to Shock (3 of 4) • Hematologic failure – Impaired clotting cascade • May result from: – Hypothermia – Dilution of clotting factors from fluid administration – Depletion of clotting factors Organ System Failure Due to Shock (4 of 4) • Hepatic failure – Results from prolonged shock • Overwhelming infection – Results from decreased function of the immune system due to ischemia and loss of energy production Summary (1 of 3) • Cellular function depends on adequate energy production • Adequate energy production depends on a continuous and adequate supply of oxygen • A continuous and adequate supply of oxygen depends on: – Patent airway – Functioning lungs – Functioning heart – Intact circulation Summary (2 of 3) • Interruption of the oxygen supply for any reason will lead to anaerobic metabolism • Anaerobic metabolism provides insufficient energy to sustain cellular function for any length of time • This leads to cellular dysfunction and cell death, organ dysfunction and organ death, and ultimately patient death Summary (3 of 3) • Knowledge, understanding, and early recognition of impaired energy production resulting from airway compromise, pulmonary injury, and impaired circulation are key to early recognition of shock. • Prompt intervention by prehospital care providers to correct these conditions can prevent the cascade of cellular dysfunction that leads to organ death. • This will improve the survival rate for victims of traumatic injury. 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