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List 2 S/S of Diabetes Insipidus (DI)....
increased urine output, increased thirst, volume depeleting dehydration, increased H&H.
What is cerebral circulation?
Receives 20% of cardiac output or 750 ml/min. Must be maintained at a constant level despite any changes in posture or BP. Brain has a high metabolic demand (20% of O2 supply to oxidize glucose for energy) and does not store nutrients (irreversible damage in minutes). Blood pathway unique: flows against gravity
Arteries fill from below, Veins drain from above, Do not have valves to prevent blood from flowing backward. Lacks collateral circulation, Can lead to irreversible tissue damage.
What is autoregulation?
Maintenance of cerebral blood (CBF) flow despite changes in arterial pressure: CBF=amount of blood in ml passing thru 100g of brain tissue in 1 minute, Global CBF is approx 50 ml/min per 100g brain tissue. Accomplished by constriction and dilation of the
cerebral blood vessels. ***Effective with MAP between 50-150mmHg: Below 50, CBF is decreased and ischemia occurs, Above 150, vessels are maximally constricted and further vasoconstrictor response is lost.
What is the blood brain barrier?
Endothelial cells of the brain's capillaries form a
continuous tight junction (barrier) separating blood
from the brain. Barrier selectively permits substances to pass from the blood into the neurons. Permeable to water, oxygen, carbon dioxide, glucose, alcohol, general anesthetics and only slightly to electrolytes. Many medications cannot penetrate this barrier and thus are prevented from affecting the CNS. *Can be altered by trauma, cerebral edema or hypoxia.
What does cerebrospinal fluid do?
Acts as a shock absorber or cushion to brain and spinal cord. Helps to maintain constant intracranial pressure.
What is the circle of willis?
The basilar artery joins the blood supply of the internal carotid arteries in a ring at the base of the brain. This ring of arteries is called the circle of Willis. The circle of Willis provides a safety mechanism...if one of the
arteries gets blocked, the "circle" will still provide the brain with blood.
***What is ICP?
****The pressure exerted by the combined volume of
the 3 intracranial components: Brain tissue/fluids (80-85%), Intracranial blood volume (3-10%), Cerebrospinal fluid (CSF) (8-12%). Normal = 0-15 mmHg. All of these things have to be in balance. Any increase in any one of these components causes a change in the volume of the other (Munro-Kellie hypothesis). Increases in any component may result in: Displacement or shift of CSF, Increasing absorption of CSF, Decreasing cerebral blood volume. Without such changes, intracranial pressure will begin to rise. Normally, minor changes in blood volume and CSF occur with changes in posture, BP, ABG levels, and intrathoracic pressure (coughing, sneezing, straining): **Increased CO2-vasodilation, **Decreased CO2-vasoconstriction.
What pathologic conditions may alter the relationship between intracranial volume and pressure?
Head injury, Stroke, Infection, Brain tumor, Intracranial surgery. These cause swelling & edema.
What is the IICP?
**Serious and life threatening complication caused by an increase in any or all three components of the skull (blood, brain, CSF) that may result in herniation with
respiratory and cardiac arrest and death.
What are components of IICP?
Brain Tissue: any increase in the volume of the brain (tumor, trauma, edema, stroke) occupy space **compressing other structures. CSF: Adult volume=145cc and flows in a closed one-way system. Clear, colorless, odorless. Any obstruction to flow can cause an increase in ICP. Blood Volume: can be altered by cerebral blood flow, changes in BP, obstruction of venous outlet (neck flexion).
What is the pathophysiology of IICP?
As ICP increases. Cerebral blood flow decreases. Leading to hypoxia (decrease in O2) a decrease in pH (acid) and increased CO2 in blood (monitor ABGs). Causes cerebral vasodilation. This results in cerebral edema increasing pressure further. This cycle repeats itself and continues to worsen if not interrupted.
**What is cerebral perfusion pressure?
**Impaired autoregulatory mechanism may cause CPP to be >150 or <60mm Hg. With CPP < 50 mmHg: May result in irreversible neurologic, dysfunction due to decreased cerebral perfusion, Results in cellular changes and cerebral hypoxia. CPP = pressure needed to ensure blood flow to the brain. *Normal CPP is 60-100 mmHg. MAP is approximately 95 mmHg. Normal ICP should be <15 mmHg. To calculate MAP:
MAP= SBP + 2(DBP)/3, To calculate CPP: CPP=MAP-ICP.
**(BP 130/70, ICP 32). 130+2 X 70. 130+140=270.
270/3=a MAP of 90. MAP - ICP = CPP, 90 - 32 = 58. Usually there are orders for measures to initiate
if: ICP > 20-25 mmHg (for > few minutes) And to **notify Dr if > 40mmHg. Usually Dr is notified for CPP < 60mmHg: This is a relatively new guideline; you may
see some resources that still say CPP should be 70 mmHg or greater. This change reflects the QSEN requirement for Evidenced-based Practice.
What are S/S of IICP?
Decreasing LOC (earliest sign): Restless, lethargic, confused, disoriented. Headache: Intermittent or constant (more ominous). Vomiting. Papilledema (swelling of optic nerve) caused by interference with venous drainage of eyeball (observed by ophthalmoscope). Unequal pupils or abnormal response to light (from pressure on oculomotor nerve) CN III. Changes in V/S Pulse increases initially then decreases. Respiratory irregularities. Increased temperature. Cushing's Triad (late, ominous sign): Rising systolic BP with*widening pulse pressure, Bradycardia, Irregular respirations. Decrease in motor function, Abnormal posturing.
What neurologic testing of other cranial nerves can be done to assess for ICP?
In awake pt -- CN III, IV, VI can be assessed by eye movements. In unconscious pts, extraocular movements cannot be tested in the usual fashion: Testing corneal reflex provides information about
CN V, VII—if absent routine eye care should be
initiated, Eye movements can be elicited with the use of head movements (Oculocephalic and Oculovestibular).
What are responses to stimulation?
Central Stimulation: **sternal rub, sternocleidomastoid squeeze, supraorbital pressure. Peripheral Stimulation
nailbed pressure. Do central stimulation first to determine if pt. can localize (moves arms toward the central stimulation as if to remove it). Can only be done to central stimulation. After determining whether pt. can localize, check periph. stim. to see if pt withdraws (a lower level on the GCS).
What are complications of uncompensated IICP?
Herniation: Brain tissue compresses and is pushed out thru the foramen magnum (brain stem herniation), Condition is irreversible in the presence of herniation and death is imminent. DI or SIADH.
***What is Diabetes Insipidus?
**Result of decreased secretion of anti-diuretic hormone (AKA: vasopressin). Signs and Symptoms: Increased thirst (in awake patient), Increased urine output (usually > 5L/day), Volume depletion (high hematocrit, Na+). Treatment: Fluid and electrolyte replacement, Supplemental ADH (pitressin or desmopressin) AKA: DDAVP.
**What is syndrome of inappropriate Anti-diuretic hormone (SIADH)?
*Result of increased secretion of antidiuretic hormone (due to stimulation of pituitary). Signs and symptoms: Lethargy and confusion, coma, seizures, Decreased urine output, Volume overload: Hemodilution (low hematocrit and Na+). Treatment: Fluid restriction, Diuretics (Lasix), Dilantin (decrease ADH release), Declomycin (blocks effect of ADH on kidney).
What activities increase ICP?
Coughing or sneezing, Neck Flexion, Hip flexion 90 degrees or >, Vomiting, ROM, Suctioning, Straining (BM), Painful procedures, Use of footboard (heels pressing against board), Posturing or turning in bed without help.
What are ICP monitors?
Monitoring devices inserted to monitor ICP directly and in some cases to withdraw CSF. Connected to transducer and monitor that displays pressure and waveform. Maintain closed-system to prevent infection. Intraventricular catheter, Subarachnoid bolt or screw, Subdural (epidural) catheter/sensor, Fiberoptic probe or catheter (Camino).
Advantages & Disadvantages of Intraventricular catheter (IVC)?
Advantages: Accurate measurement of ICP. Allows drainage or sampling of CSF. allows instillation of contrast media. provides reliable evaluation of volume or pressure responses. Disadvantages: provides additional site for potential infection. most invasive method of monitoring ICP. must be balanced and re-calibrated frequently. catheter can become occluded by blood or tissue.
Advantages & Disadvantages of subarachnoid bolt or screw?
Advantages: allos sampling of CSF. lower infection rates than with IVC. quickly and easily placed. Disadvantages: tendency for dampened waveforms. less accurate at high ICP. may become occluded by tissue or blood. must be balanced and recalibrated frequently (i.e. q4hours and whenever the client is repositioned).
Advantages & Disadvantages of subdural, extradural catheter or sensor?
Advantages: least invasive, easily and quickly placed. Disadvantages: increasing baseline drift over time; therefore, accuracy and reliability are questionable. does not provide for CSF sampling.
Advantages & Disadvantages of fiberoptic probe or catheter?
Advantages: can be placed in subdural or subarachnoid space, in ventricle, or into brain tissue. easily transported. requires zeroing only once (during insertion). baseline drift to 1mmHg. no irrigation--less risk of infection. less waveform artefact. no need to adjust transducer to client's position. Disadvantages: does not provide for CSF sampling. cannot be re-calibrated after it is placed. breakage of the fiberoptic cable.
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