Nursing 54A - Acute Disorders of Brain Function. Complete Study Guide.

Chapter 44 Acute Disorders of Brain Function Question: The brain contributes ____% of body weight and uses ____% of the body’s O2 consumption? 2,20  It doesn’t weigh much  It does consume high amount of O2 and blood flow (relative metabolic rate is high) o Very significant in regards to ICP- amt of O2 consumption and therefore the amt of blood flow is high  Blood is a major component of ICP Question: Acute head injury produces high rates of both mortality and morbidity due to the damage produced by the primary brain injury. False Secondary injury  Primary injury- injury of the actual trauma (ex. necrosis from stroke)  Secondary injury- body’s response to that injury and the effects of that response  Really imp. in management. Can’t fix the primary injury (ex. dead tissue due to stroke), but can fix the Secondary injury issues (ex. inflammatory response to injury) typically. Mechanisms of Brain Injury  The ultimate outcome of the neurons is the ability to function as normalability to have ATP to function (goal: maintain O2 and perfusion of the cells) o We maintain ATP through O2 (maintain cell membrane (Na+ K+ pump and functioning of that cell)) o We maintain O2 through cell perfusion  Primary brain injury occurs as a direct result of the initial insult  Secondary injury refers to progressive damage resulting from the body’s physiologic response to the initial insult  A critical factor in determining the neuronal cell fate after injury is the degree of adenosine triphosphate (ATP) depletion Mechanisms of Brain Injury (Cont.) Ischemia and Hypoxia (la) Ischemia- lack of perfusion to the tissue (big factor in the secondary response)- causes lack of ATP / ATP depletion Hypoxia- lack of oxygenation to the tissue Hypoxemia- lack of O2 in the blood  Ischemia is a contributing factor either as the primary insult or as part of the secondary response to injury  Ischemia results in immediate neurologic dysfunction due to the inability of neurons to generate the ATP needed for energy-requiring processes Mechanisms of Brain Injury (Cont.) Factors of secondary injury- processes that are occurring with it  Excessive glutamate may be released because of impaired membrane integrity o Level of Glutamate and intracellular calcium- suspected to be a factor in secondary injury and cell injury  Nitric Oxide: vasodilation (generally a good thing but can have negative effects in ICP)  Reperfusion injury: When oxygen reenters cells, erratic transfer of electrons to oxygen can produce reactive oxygen products that behave as free radicals (hydroxyl radicals, superoxide, peroxide) (when cells are re-perfused (O2 delivery) they develop toxic O2 radicals which damage cells) o Reperfusion injury: Tissue damage caused when blood supply returns to the tissue after a period of ischemia or lack of O2 Question: An increase in PaCO2 or acidemia would be expected to decrease cerebral blood flow (False)  Elevated CO2- causes cerebro vasodilation Some body systems are too vital for the SNS/ PNS to fully regulate in terms of perfusion- ex. Heart and Brain- have complex method of auto regulation, includes levels of CO2 (through out the body and tissues (including the brain) SN: Heart & brain- regulated by 1. SNS/ PNS and 2. Autoregualted. One of the problems seen in secondary injury is the loss of auto regulation Mechanisms of Brain Injury (Cont.) Abnormal Autoregulation  Autoregulation - ability to regulate blood flow (in this case, to our brain)  Autoregulation is normally influenced by the partial pressures of carbon dioxide and oxygen in the arterial blood  Injury can cause local (specific areas of the brain) or global impairment (the entire brain) of autoregulation (with significant head injury)  Loss of matching between oxygen supply and demand occurs when autoregulatory mechanisms fail  When the body drops in BP the body’s natural response is to vasoconstrict but the brain vasodilates (it auto regulates).  Conversely, when tachycardia or too much fluid (BP) occurs, it auto regulates to try to keep the perfusion to the brain in the proper range.