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Saturday, December 26, 2015

CHASING THE ICP..SORRY CHASING THE WELLNESS OF THE BRAIN❗️



📛In the absence of disease, ICP may rise by 50 mmHg during coughing or sneezing without noticeable neur ologic impairment. 

▶️Therefore, it is the interaction of raised  ICP with other intracranial pathology which produces the pathologic consequences, as  opposed to the rise in ICP per se.  

Monitoring of intracranial pressure (ICP)
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📛"Some patients with suspected intracranial hypertension and a decreasing level of consciousness might require invasive ICP monitoring, although its added value beyond clinical or radiological monitoring has not yet been proven"

📛Monitoring methods currently available include ventriculostomy, subarachnoid bolt, epidural sensor, and fiberoptic intraparenchymal monitor; the latter is the most commonly used.

▶️DO YOU KNOW?

📛The major drawback of intraventricular catheters is the rate of infection which is much higher than that observed using intraparenchymal probes. 

📛Additionally, interpretation of ICP data after craniectomy is difficult.

Monitoring of CBF
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▶️Normal average CBF in the human is approximately 55 ml/100g (of brain)/min, though values may vary widely across grey and white matter. The ischemic threshold for CBF is approximately 18 ml/100g/min, with 10 ml/100g/ min often considered the threshold for irreversible injury. 

📛Laser Doppler flowmetry (LDF) is a parenchymal or surface Doppler probe that measures tissue local CBF in a quantitative manner. 

📛Brain tissue oxygen tension (P bt O 2 ) monitoring allows direct measurement of focal tissue oxygen tension in a specific region of the brain. A P bt O 2  level below 10-15 mmHg has generally been the threshold identified at which outcome is worsened 

📛 Transcranial Doppler ultrasonography is a useful non-invasive monitor of cerebral hemodynamics, but has been severely disadvantaged by the inability to fix the  probe in position. 

 📛 Jugular venous bulb oximetry is a global hemispheric measure with low sensitivity for detecting regional ischaemia. 

🔹The normal SjvO 2  level is approximately 60%
🔹an SjvO 2  of < 50% for greater than 10 min has generally been considered to represent an ischemic desaturation. 
🔹High SjvO 2 levels may reflect hyperemia (typically >90%) or an inability of the brain to extract oxygen due to metabolic depression from sedative agents, poor oxygen unloading (e.g. sickle cell disease), or severe brain injury. 

📛Near-infrared spectroscopy (NIRS) 

🔹measures cerebral regional oxygen saturation by measuring near-infrared light reflected off the chromophobes in the brain, the most important of which are oxyhemoglobin, deoxyhemoglobin, and cytochrome A3. 
🔹Its major limitations include the intersubject variability, the variable length of the optical path, the potential contamination from extracranial blood, and most important, the lack of a definable threshold. 🔹Because of the thin scalp and skull in the neonate and infant, NIRS holds promise in this patient population but remains an investigative tool in its present form.

📛Microdialysis catheters, typically inserted in conjunction with an ICP or tissue Po2 monitor, allows sampling of small molecules in the interstitial fluid. 

🔹An increasing lactate/pyruvate ratio is sensitive to the onset of ischemia. 
🔹High levels of glycerol suggest inadequate energy to maintain cellular integrity and the resultant membrane breakdown. 
🔹Excitatory amino acids, such as glutamate, are both a marker for neuronal injury and a factor in its exacerbation.
🔹Currently, the microdialysis catheter is primarily used in two situations: (a) extensive subarachnoid hemorrhage where subsequent vasospasm is likely and (b) traumatic brain injury (TBI) 

▶️️At present, none of the methods available is sufficiently reliable or well tested to en able us to influence the clinical management of neurologically i njured patient with absolute certainty


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Reference:

Advanced cerebral monitoring in neurocritical care Nobl Barazangi, J. Claude Hemphill III, eurology India | October-December 2008 | Vol 56 | Issue 4

Intraoperative Neurophysiological Monitoring Second Edition Aage R. Møller

Postoperative management of adult central neurosurgical patients: Systemic and neuro-monitoring David Pfister, Stephan P. Strebel , Basel, Switzerland Luzius A. SteinerBest Practice & Research Clinical Anaesthesiology Vol. 21, No. 4, pp. 449–463, 2007 

Textbook of Neuroanaesthesia and Critical Care by Basil F Matta

Handbook of Neuroanesthesia, 4th Edition, James E. Cottrell

Monday, December 21, 2015

BASICS: POTENCY, DURATION AND ONSET OF ACTION OF LOCAL ANESTHETICS⚙



🗡POTENCY: 

👉🏿is affected by several factors including:

🔹Hydrogen ion balance
🔹Fiber size, type, and myelination
🔹Vasodilator/vasoconstrictor properties (affects rate of vascular uptake)
🔹Frequency of nerve stimulation
🔹pH (acidic environment will antagonize the block)
🔹Electrolyte concentrations (hypokalemia and hypercalcemia antagonizes blockade)

↔️Duration of action 

🔹is associated with lipid solubility. 
🔹Highly lipid soluble local anesthetics have a longer duration of action due to decreased clearance by localized blood flow and increased protein binding.

⏱ONSET OF ACTION

🔹Local anesthetics are weak bases and contain a higher ratio of ionized medication compared to non- ionized. 
🔹Increasing the concentration of non-ionized local anesthetic will speed onset. 
🔹In general, local anesthetics with a pKa that approximates physiologic pH have a higher concentration of non- ionized base resulting in a faster onset. 
🔹On the other hand, a local anesthetic with a pKa that is different from physiologic pH will have more ionized medication which slows onset. 
🔹For example, the pKa for lidocaine is 7.8 and 8.1 for bupivacaine. Lidocaine is closer to physiologic pH than bupivacaine. Lidocaine has a greater concentration on non-ionized local anesthetic than bupivacaine which results in a faster onset. 
🔹 Non-ionized and ionized portions of local anesthetic solution exert distinct actions. 
🔹 Lipid soluble, non-ionized form of the local anesthetic penetrates the neural sheath and membrane. 
🔹 In the cell, the non-ionized and ionized forms equilibrate. 
🔹 The ionized form of the local anesthetic binds with the sodium channel. Once “bound” to the sodium channel, impulses are not propagated along the nerve.

🔹 Clinically, onset of action is not the same for all local anesthetics with the same pKa. This is due to the intrinsic ability of the local anesthetic to diffuse through connective tissue. 

🔹 Local anesthetics with a pKa closest to the physiological pH generally have a higher concentration of non-ionized molecules and a more rapid onset. 

🔹 Two notable exceptions are chloroprocaine and benzocaine. Chloroprocaine has a high pKa and rapid onset. Benzocaine does not exist in an ionized form and exerts its effects by alternate mechanisms.
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#LocalAnesthetics, #RegionalAnesthesia , #Pharmacology , #anaesthesia

References
Heavner, J.E. (2008). Pharmacology of local anesthetics. In D.E. Longnecker et al (eds) Anesthesiology. 
Joyce, J.A. (2002). A pathway toward safer anesthesia: stereochemical advances. AANA Journal, 70, 63-67.
Katzung, B.G. (1992). Section 1: basic principles. In B.G. Katzung Basic & clinical pharmacology, 5th edition. Norwalk, Connecticut: Appleton and Lange.
Morgan, G.E., Mikhail, M.S., Murray, M.J. (2006). Local Anesthetics. In G.E. Morgan et al Clinical Anesthesiology, 4th edition. 
Stoelting, R.K. & Hillier, S.C. (2006). Pharmacology and pharmacodynamics of injected and inhaled drugs. In R.K. Stoelting & S.C. Hillier (eds) Pharmacology & Physiology in Anesthetic Practice, 4th edition. 
Strichartz, G.R. & Berde, C.B. (2005). Local Anesthetics. In R.D. Miller Miller’s Anesthesia, 6th edition

Sunday, December 20, 2015

AN ADULT STORY: HOW ADULTS LEARN❓


👉🏿Malcolm Knowles introduced the term “andragogy” to North America, defining it as “the art and science of helping adults learn.” Andragogy is based on five assumptions—about how adults learn and their attitude towards and motivation for learning.

👉🏿Andragogy—five assumptions about adult learning
🔹Adults are independent and self directing
🔹They have accumulated a great deal of experience, which is a rich resource for learning
🔹They value learning that integrates with the demands of their everyday life
🔹They are more interested in immediate, problem centred approaches than in subject centred ones
🔹They are more motivated to learn by internal drives than by external ones

👉🏿Most theorists agree that andragogy is not really a theory of adult learning, but they regard Knowles’ principles as guidelines on how to teach learners who tend to be at least somewhat independent and self directed.  

👉🏿His principles can be summarised as follows:
🔹Establish an effective learning climate, where learners feel safe and comfortable expressing themselves
🔹Involve learners in mutual planning of relevant methods and curricular content
🔹Involve learners in diagnosing their own needs—this will help to trigger internal motivation.
🔹Encourage learners to formulate their own learning objectives—this gives them more control of their learning
🔹Encourage learners to identify resources and devise strategies for using the resources to achieve their objectives
🔹Support learners in carrying out their learning plans
🔹Involve learners in evaluating their own learning—this can develop their skills of critical reflection.

#teaching , #learning ,#psychology ,#MedicalTeaching ,#andragogy