Week 1 - Prerecorded Lecture - Altered Cerebral Perfusion (2024) - Flinders University PDF

22/07/2024 1 PARA2005 Week 1 Pre-Recorded Lecture Altered Cerebral Perfusion 2 1 ...

22/07/2024 1 PARA2005 Week 1 Pre-Recorded Lecture Altered Cerebral Perfusion 2 1  22/07/2024 Learning Objectives At the end of this tutorial students will be given the information to: Outline what is considered normal blood supply to the brain Explain the role of baroreceptors & chemoreceptors to monitor cerebral perfusion Describe the other ANS compensation to support cerebral perfusion Explain the concept of cerebral “autoregulation” This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 3 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 4 2  22/07/2024 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 5 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 6 3  22/07/2024 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 7 What do you know about: BP = CO X PVR Peripheral vascular resistance = vasodilation or vasoconstriction Cardiac output = SV x HR Stroke volume = EDV – ESV End diastolic volume = blood volume in LV at end of diastole End systolic volume = blood volume in LV at end of systole Heart rate = tachycardic or bradycardic Chronotropic = increased heart rate Inotropic = increased force of contraction This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 8 4  22/07/2024 Cardiac output (CO): CO = HR × SV If CO ↓, then heart rate (HR) and/or stroke volume (SV) need to ↑ in order to be able to maintain CO (hence we see the tachycardia). This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 9 Blood pressure (BP): BP = CO x PVR In order to maintain BP, the person’s CO will ↑ (as above) and pulmonary vascular resistance (PVR) will also ↑ (tachycardia may be seen with poor distal perfusion as ↑ PVR causes vasoconstriction of peripheral vessels). This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 10 5  22/07/2024 Mean arterial pressure (MAP): MAP = 1/3 pulse pressure + diastolic BP BP = 110/80………..MAP = 90mmHg GCS + MAP or Systolic BP = “stable perfusion” This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 11 Cerebral Perfusion Pressure This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 12 6  22/07/2024 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 13 CPP = MAP - ICP This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 14 7  22/07/2024 CPP = MAP – ICP The brain accounts for only 2% of total body weight but consumes over 20% of the body’s total oxygen requirements and 15% of the total cardiac output. The maintenance of cerebral perfusion is critical. Cerebral perfusion pressure (CPP) is the difference between out flow and in flow and is the driving pressure for cerebral blood flow (CBF). The formula for CPP is: CPP = MAP – ICP Therefore, CPP is used as a measure of CBF. This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 15 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 16 8  22/07/2024 Cerebral perfusion pressure (CPP): CPP = MAP – ICP If MAP is reduced: Baroreceptors and chemoreceptors notice change in the normal levels, and will…. HR can increase SV can increase Leading to an overall increase in CO This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 17 Cerebral perfusion pressure (CPP): If MAP is reduced: The brain will cause vasodilation of the arteries Increase blood flow by increasing width of arteries Increase blood flow will increase blood pressure within the brain This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 18 9  22/07/2024 Cerebral Perfusion Pressure (CPP) This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 19 Intracranial Pressure This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 20 10  22/07/2024 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 21 Munroe-Kelly doctrine The Monro–Kellie hypothesis states that the cranial compartment is inelastic and that the volume inside the cranium is fixed This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 22 11  22/07/2024 This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 23 Brain tissue + CSF + Blood = ICP Once the fontanelles have fused, usually by 2 years of age, the brain is enclosed in a rigid vault = Inelastic! Cerebral circulation is vulnerable to conditions that increase intracranial volume. Normal intracranial pressure (ICP) is usually less than 15 mmHg and is determined by the volume of the brain parenchyma (1300 mL in an adult), CSF (100–150 mL) and intravascular blood (100–150 mL). CPP = 90 mmHg (MAP) – 15 mmHg (ICP) This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 24 12  22/07/2024 Cerebral Autoregulation This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 25 Autoregulation Under normal circumstances, CBF is maintained by local (brain) microcirculation that results from changes in arterial pressure. This is termed “autoregulation” and ensures that brain tissue is adequately perfused with oxygen and that wastes are removed. Autoregulation of CBF has a functional CPP range between 50 and 150 mmHg. When CPP falls below 50 mmHg, autoregulation is diminished. The major regulatory mechanisms for maintaining adequate CBF are the partial pressure of carbon dioxide (PaCO2), blood pressure and blood pH. This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 26 13  22/07/2024 Autoregulation Alteration in PaCO2, blood pressure or blood pH will result in cerebral vasoconstriction or vasodilation. Hypotension and/or hypoventilation results in an increase in PaCO2 and a decrease in pH (acidosis); as a consequence, cerebral vasodilation occurs in an attempt to increase CBF and deliver more oxygen. Conversely, hypertension, hyperventilation and an increase in pH (alkalosis) can cause cerebral vasoconstriction and a reduction in CBF. Hypocapnia is capable of reducing CBF by 4% for each mmHg change in PaCO2. Baroreceptors constantly monitor systemic blood pressure and provide a positive feedback loop. Regulation of systemic blood pressure is achieved by arterial vasodilation OR vasoconstriction, thus altering peripheral vascular resistance (PVR) in an effort to maintain adequate CPP and blood flow. This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 27 Blood supply to the brain This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 28 14  22/07/2024 Clinical Perspective Any space-occupying mass, such as a haematoma or oedema, within the cranial vault can result in compression and displacement of the cerebral contents. Initially, circulating CSF and blood volume (principally venous) are reduced but as the mass size is increased, the space- occupying lesion compresses brain tissue and reduces CBF due to increased ICP. As ICP rises outside the normal range, autoregulation is lost, and perfusion to the brain becomes totally dependent upon CPP – so MAP must increase to overcome a higher ICP Rapid rises in ICP can lead to compression of the brain tissue and herniation where the brain tissue itself is displaced and moves towards the foramen magnum. The common phenomenon known as the Cushing reflex/triad —hypertension, bradycardia and irregular respiration—is a direct result of a rapid rise in ICP. This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 29 Cushing's Triad This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 30 15  22/07/2024 Answer these questions Cushing’s Triad: Why hypertensive? Why bradycardia? Why irregular respirations? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 31 Foramen Magnum This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 32 16  22/07/2024 Cushing’s Triad Why Hypertensive? When there is an elevated ICP due to for example intracranial bleeding or oedema, cerebral vasculature will be increasingly compressed with rising ICP, leading to cerebral ischemia. To combat this the sympathetic nervous system is activated. The increased sympathetic tone will primary constrict the arterioles of the body, mediated by alpha 1 adrenergic receptors. Since our mean arterial blood pressure (MAP) is the product of cardiac output (CO) and systemic vascular resistance (SVR), the MAP will rise, in other words, the patient will develop hypertension. An increased pulse pressure (difference between systolic and diastolic blood pressure) is also seen, because primary the systolic blood pressure rises, whereas the diastolic pressure remains the same. The cerebral vessels are not affected by this vasoconstriction, protecting the brain form ischemia. The hypertension seen in patients with increased ICP is part of the cerebral autoregulation, trying to keep cerebral perfusion pressure (CPP) relatively constant, even though the ICP increases. CPP is the difference between MAP and ICP (CPP=MAP-ICP), so increasing MAP by contracting arterioles makes sense when the ICP is elevated. The brain also shunts away cerebrospinal fluid in order the combat the rising ICP. If these and other compensatory mechanisms are inadequate, ICP will continue to rise, reducing CPP to levels leading to global ischemia of brain tissue. When ICP equals MAP, the CPP will be 0, and there will be no circulation to the brain, a state known as brain tamponade. CPP = MAP - ICP http://emergencymedicine1.blogspot.com/2013/06/understanding-cushingstriad-thecushings.html This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 33 Cushing’s Triad Why Bradycardia? The initial sympathetic tone will initially cause tachycardia, and increased contractility of the heart mediated primarily by beta 2 adrenoreceptors. This will increase cardiac output, and thus increasing MAP together with the increased systemic vascular resistance. The increased MAP will stretch and activate the high pressure Baroreceptors baroreceptors in the aortic arch and carotid sinus, which via the vagus and glossopharyngeal nerve respectably, will signal that there is and increased MAP to the cardiovascular control center in & medulla oblongata. When there is an elevated MAP sympathetic tone will be reduced Brain herniation and parasympathetic tone will be increased, leading to bradycardia. The signal to the arterioles to constrict, due to the high ICP, remains leaving the patient with both hypertension and bradycardia. This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 34 17  22/07/2024 Cushing’s Triad Why irregular respiratory rate? The irregular breathing pattern seen inpatients with elevated ICP is due to inadequate function of the respiratory control centre located in the medulla oblongata Reduced cerebral perfusion pressure and or direct damage to this structure, leads to neuronal dysfunction Cheyne-Stokes respirations are the common pattern seen in Cushing’s triad This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 35 Clinical Perspective Patient is hypotensive due to opiate overdose, how is cerebral blood flow maintained? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 36 18  22/07/2024 Clinical Perspective Patient is hypotensive due to external blood loss, how is cerebral blood flow maintained? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 37 Clinical Perspective Patient is hypotensive due……..loss, how is cerebral blood flow maintained? Get the idea? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 38 19  22/07/2024 Clinical Perspective Patient has suffered a traumatic head injury and is bleeding into his brain. How is the patient’s cerebral blood flow maintained? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 39 Clinical Perspective The same patient is now unconscious due to extensive intracranial bleed. How is the patient’s cerebral blood flow maintained? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 40 20  22/07/2024 Questions? This material has been reproduced and communicated to you by or on behalf of Flinders University in Accordance with section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. 41 21