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

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

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

S͙U͙P͙E͙R͙I͙O͙R͙I͙T͙Y͙ A͙N͙D͙ E͙Q͙U͙I͙V͙A͙L͙E͙N͙C͙E͙ T͙R͙I͙A͙L͙S͙ ⬆️↔️

⬆️S͙U͙P͙E͙R͙I͙O͙R͙I͙T͙Y͙ T͙R͙I͙A͙L͙S͙

✔️Seek to establish that one treatment is better than another 

✔️The sample size is set so that there is high statistical power to detect a clinically meaningful difference between the two treatments 

↔️E͙Q͙U͙I͙V͙A͙L͙E͙N͙C͙E͙ T͙R͙I͙A͙L͙S͙

✔️Seek to test if a new treatment is similar  in effectiveness to an existing one

✔️Appropriate if the new treatment has certain benefits such as fewer side effects, being easier to use, or being cheaper 

✔️Designed to be able to demonstrate that, within given acceptable limits, the two treatments are equally effective 

✔️Equivalence is a pre-set maximum difference between treatments such that, if the observed difference is less than this, the two treatments are regarded as equivalent . The tighter the limits of equivalence are set, the larger the sample size that will be required 

✔️A serious condition requires tighter limits for equivalence than a less serious condition. 

✔️The calculated sample size tends to be bigger for equivalence trials than superiority trials 

🔴T͙H͙I͙N͙G͙S͙ T͙O͙ R͙E͙M͙E͙M͙B͙E͙R͙

👉🏿In general the design and implementation of equivalence trials is less straight forward than superiority trials 

👉🏿If patients are lost to follow-up or fail to comply with the trial protocol, then any differences between the treatments is likely to be reduced and so equivalence may be incorrectly inferred.

👉🏿So equivalence trials need very strict management and good patient follow-up to minimize these problems 

👉🏿It is often helpful to include a secondary analysis where subjects are analysed according to the treatment they actually received, ‘per protocol’ analysis 

#MedicalResearch ,#ClinicalResearch , #MedicalStatistics , #BioStatistics , #AnaesthesiaResearch , #Statistics ,#research

Reference: Oxford Handbook of Medical Statistics, Janet L. Peacock , Philip J. Peacock

ANESTHESIA INFO FROM THE LAY MEDICAL MAN- Facebook Page

XENON-THE STRANGER🌪

🍭colorless, odourless, tasteless gas

🍭four times denser than air. 

🍭density and viscosity are substantially higher than those of other inhalational anaesthetics. 

🍭occurs in extremely low concentrations (0.0875 ppm) in the atmosphere, hence its name from the Greek ‘xenos’ meaning ‘stranger’. 

🍭Xenon has been used experimentally as an anaesthetic for more than 50 years 

🍭Recently there has been a renewed interest in xenon as a safe, effective and more environmentally friendly substitute for nitrous oxide (Sanders et al. 2003). 

🍭manufactured by fractional distillation of liquefied air, currently at a cost of US $10 per litre (i.e. about 2,000 times the cost of producing N2O). This high cost is the major factor limiting its more widespread use, even when used in low-flow delivery systems. 

🍭Xenon has many of the properties of an ideal anaesthetic. 

🍭Its blood/gas partition coefficient (0.12) is lower than that of any other anaesthetic, giving rapid induction and emergence. 

🍭It is unlikely to be involved in any biochemical events in the body, and is not metabolised. 

🍭Xenon causes no significant changes in myocardial contractility, blood pressure or systemic vascular resistance, even in the presence of severe cardiac disease (Sanders et al. 2005). 

🍭The unique combination of analgesia, hypnosis, and lack of haemodynamic depression in one agent would make xenon a very attractive choice for patients with limited cardiovascular reserve 

🍭In contrast to other inhaled anaesthetic agents, xenon slows the respiratory rate and increases the tidal volume, thereby maintaining minute ventilation constant. 

🍭Airway pressure is increased during xenon anaesthesia, due to its higher density and viscosity rather than direct changes in airway resistance (Baumert et al 2002). 

🍭Because of its high cost xenon must be used in low-flow closed circuits. Crucial to this method of administration is accurate measurement of the concentration of xenon in the circuit. This measurement is generally difficult as xenon is  diamagnetic and does not absorb infrared radiation (commonly used to measure the  concentrations of other agents), and its low reactivity precludes the use of specific fuel cell or electrode-type devices. 

🍭Xenon conducts heat better than other gases, and a technique based on thermal conductivity has proved to be effective (Luginbuhl et al 2002). 

🍭Because xenon is heavier than air, the speed of sound is slower in xenon than that in air, and this difference has been also been used to measure xenon concentration. 

🍭Because xenon is a normal constituent of the atmosphere, it does not add to atmospheric pollution when emitted from the anaesthesia circuit. This is in contrast to the other inhalational anaesthetics, which have ozone-depleting potential and pollute the atmosphere when released from the anaesthesia system (Marx et al. 2001). 

🍭On a molecular basis, N2O is 230 times more potent as a greenhouse gas than carbon dioxide. N2O released as a waste anaesthetic contributes roughly 0.1% of total global warming. The lifetime of N2O in the atmosphere is long—approximately 120 years. 

🍭The anaesthetic actions of xenon are thought to result primarily from noncompetitive inhibition of  NMDA receptors (De Sousa et al. 2000), a property it shares with nitrous oxide. 

🍭In common with other NMDA receptor antagonists, xenon appears to have neuroprotective properties (Sanders et al. 2003). 

🍭Xenon is also an excellent analgesic, an action mediated by NMDA receptors (De Sousa et al. 2000). 

🍭Xenon also inhibits the plasma membrane Ca 2+   pump, altering neuronal excitability and inhibiting the nociceptive responsiveness of spinal dorsal horn neurones. 

(Reference : Jürgen Schüttler •  Helmut Schwilden Modern Anesthetics ,Handbook of Experimental Pharmacology, vol 182)

EXAMPLES OF RESEARCH QUESTIONS🔢

(From : Oxford Handbook of Medical Statistics, Janet L. Peacock, Philip J. Peacock, P:5)

❓What is the prevalence of diabetes mellitus in the population? 

🔴This is a simple descriptive study 

❓How effective is influenza vaccination in the community-based elderly? 

🔴This is a comparative study, comparing individuals who had vaccines with those who did not 

❓Does lowering blood pressure reduce the risk of coronary heart disease? 

🔴This is an evaluative study, investigating the effi cacy of lowering blood pressure 

❓Is prognosis following stroke dependent on age at the time of the event? 

🔴This is an observational study 

❓Why does smoking increase the risk of heart disease? 

🔴This is an explanatory study investigating the mechanism behind an observed relationship 

❓What evidence is there for the effectiveness of antidepressants in treating depression? 

🔴This study is a meta-analysis of existing interventional studies

STATES ASSOCIATED WITH AUTONOMIC DYSFUNCTION⚠️

💠Diabetes

💠Hypertension

💠Renal failure

💠Aging

💠Postcarotid endarterectomy 

💠Spinal cord injury

💠Shy-Drager Syndrome

💠Idiopathic orthostatic hypotension 

💠Chronic alcoholism

💠Posterior flossa tumors/surgery 

💠Guillain-Barré syndrome 

💠Malignancy

RISK FACTORS FOR POST OPERATIVE COGNITIVE DYSFUNCTION

📽---->>PROJECT THE RAYS CORRECTLY

(Basic facts about projection in X ray films)

📐Postero-anterior (PA) will not produce as much magnification of the heart and mediastinum as an antero-posterior (AP) projection. So PA films are the preferred ones.

📐A PA film is taken with the film cassette in front of the patient and the beam delivered from behind with the patient in an upright position. 

📐Portable films and those taken in ICUs are all AP projection. 

📐The supine position causes distension of the upper lobe blood vessels, which may be confused with elevated left atrial pressure 

📐A lateral X-ray is useful in localising lesions in the AP dimension, locate lesions behind the left side of the heart or in the posterior recesses of the lungs. 

📐A left lateral (with the left side of the chest against the film and the beam projected from the right) is the standard projection. 

📐The heart is magnified less with a left lateral as it is closer to the film. 

📐To visualize lesions in the left hemithorax, obtain a left lateral film and for right-sided lesions a right lateral. 

📐Expiratory films are used to assess air trapping in bronchial obstruction such as a foreign body. 

📐A pneumothorax always appears larger on an expiratory film and occasionally a small pneumothorax may only be visible on expiration. 

📐Films if accidentally taken in expiration, can result in spurious magnifcation of the heart and mediastinum.

#xray ,#radiology ,#imaging , #XrayBasics , #anaesthesia 

Reference: Radiology for Anaesthesia and Intensive Care (Richard Hopkins, Carol Peden and Sanjay Gandhi)