Category Archives: Neuroanesthesia

VIVA AID: BISPECTRAL INDEX

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💆The EEG bispectrum is a high-order statistical computation derived from the analog EEG.

💆The BIS is a combination of three weighted parameters: (i) the burst suppression ratio (the proportion of isoelectric EEG signal in an epoch); (ii) the beta ratio (a measure of the proportion of signal power in the high vs medium frequency range); and (iii) the SynchFastSlow (relative synchrony of fast and slow waves)

💆Changes in frequency and power alone ( as done with conventional power spectral analysis) have been shown to be inconsistent when attempting to measure anesthetic depth.

💆Bispectral analysis incorporates information on power and frequency with the phase coupling information that is more indicative of anesthetic depth but not present in other clinical applications of EEG.

💆The BIS uses a combination of EEG subparameters that were selected after analysis of a large database of EEGs to demonstrate specific ranges for varying phases of anesthetic effect

💆These parameters were then combined to form the optimum configuration for monitoring of the hypnotic state.

💆The BIS is then displayed as a dimensionless number between 0 and 100 with the lower numbers corresponding to deeper levels of hypnosis.

💆There are normal, genetically determined low-voltage EEG variants among the population that can result in abnormally low BIS values in awake patients; therefore, it is important to obtain baseline values before the induction of anesthesia

💆BIS is not able to predict movement in response to surgical stimulation because the generation of reflexes is likely to be at spinal cord rather than cortical level

💆BIS does not fully reflect the synergistic effect of opioids with hypnotic agents

💆The presence of electromyographic artefacts, poor signal quality, and electrical artefacts such as those from electro-cautery and forced air warming units can cause spurious values to be displayed by the BIS monitor.

💆With the administration of ketamine, the BIS may remain high, possibly due to the excitatory actions of ketamine, and, therefore, the BIS monitor is not reliable when used to monitor hypnosis with ketamine.

💆There have been studies in which the BIS monitor has not been shown to reflect the hypnotic contribution to the anesthetic by nitrous oxide.

💆Potential benefits from the routine use of the BIS monitor include

➖decreased risk of awareness

➖improved titration of anesthetic agents and

➖decreased recovery room time

💆The BIS also gives the anesthetist additional information to consider when selecting drugs for interventions, for example, when making the decision whether to deepen anesthesia with a volatile agent, add more analgesia with an opioid, or use a vasoactive drug.

💆Also note:

➖The BIS may drop after giving a neuromuscular blocking agent if excessive EMG was present prior to giving it.

➖Ischemia attenuates the amplitude and frequency of the EEG signal, which may result in a decrease in BIS

➖Hypothermia decreases brain activity, and may decrease BIS

➖Muscle shivering, tightening, twitching etc may increase EMG and increase BIS

➖Artifacts in the higher frequency ranges [e.g. use of any mechanical device that could generate high frequency activity like patient warmer]can artificially increase the BIS value

➖Is the BIS decreasing when you think it should be increasing? Think of Paradoxical Delta pattern (characterized by a pronounced slowing of the EEG) which occurs over a short period of time (2-3 minutes).

➖If the sensor is placed over the temporal artery, pulse artifacts can cause the BIS value to be inappropriately low. Check EEG waveform for presence of pulse artifacts and move sensor if necessary.

➖Blinking or rolling his/her head by the patient, may cause artifacts that mimic slow frequency EEG patterns.

Reference: The BIS monitor: A review and technology assessment, James W. Bard, AANA Journal/December 2001/Vol. 69, No. 6

A FEW PROSPECTIVE TECHNIQUES TO MEASURE ANALGESIA INTRA-OPERATIVELY 

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🤖Current electroencephalogram (EEG)-derived measures like BIS, provide information on cortical activity and hypnosis but are less accurate regarding subcortical activity, which is expected to vary with the degree of antinociception. 
🤖Efforts to develop methods for monitoring these subcortical activities produced a few indices, which may provide some use intra-operatively 
🤖Recently, the neurophysiologically based EEG measures of cortical input (CI) and cortical state (CS) have been shown to be prospective indicators of analgesia/anti-nociception and hypnosis, respectively. Composite Cortical State (CCS) is an alternate measure of CS.
🤖Composite Variability Index (CVI) is another recently developed EEG-derived measure of antinociception based on a weighted combination of BIS and estimated electromyographic activity.
🤖CCS and BIS show strong correlations, suggesting that they behave similarly as indicators of hypnosis.
Reference: Comparisons of Electroencephalographically Derived Measures of Hypnosis and Antinociception in Response to Standardized Stimuli During Target-Controlled 

Propofol-Remifentanil Anesthesia, Mehrnaz Shoushtarian, Marko M. Sahinovic, Anthony R. Absalom, Alain F. Kalmar, Hugo E. M. Vereecke, David T. J. Liley and Michel M. R. F. Struys, anesthesia-analgesia, February 2016 • Volume 122 • Number 2

WHAT IS SURGICAL STRESS INDEX (SSI)❓

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🔵 SSI is an index which measures the surgical stress response in patients under anesthesia

🔵 It assess the balance between the intensity of surgical stimulation and the level of antinociception (e.g. Opioid analgesia , neuraxial or nerve blockade)
🔵 SSI uses two continuous cardiovascular variables, both obtained from Photo Plethysmography (PPG) waveforms of SpO2
(1) The interval between successive hearts beats (HBI)
(2) PPG amplitude (PPGA)
🔵Photoplethysmography (PPG), i.e. pulse oximetry, is primarily used to produce an estimation of the relative concentration of oxyhemoglobin in blood.
🔵 PPG is related to volume changes and contains information about the peripheral blood circulation, including skin vasomotion. Skin vasomotion is controlled by the sympathetic nervous system, which is activated during surgical stress.
🔵 Changes in PPG amplitude (PPGA) reflect changes in the peripheral vascular bed, controlled by the sympathetic nervous system . Increased PPGA response has been associated with nociception during general anesthesia.
🔵SSI values near 100 correspond to a high stress level, and values near zero to a low stress level.
🔵 In trials, SSI correlated positively with the intensity of painful stimuli and negatively with the analgesic concentration
🔵 SSI has been shown to be capable of differentiating decreases in HR achieved with opioid from those accomplished with a beta blocker (Ahonen et al. 2007).
🔵 An optimal range for SSI during anesthesia has not yet been recommended.
Reference: Measurements of adequacy of anesthesia and level of consciousness during surgery and intensive care, Johanna Wennervirta, Department of Anesthesiology and Intensive Care Medicine, Helsinki University Hospital
#anaesthesia , #anaesthesiology , #anaesthesiologist

👁➖BE AWARE OF AWARENESS ➖👁

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💣Premedication with amnestic reduces the chance of awareness. Also, if awareness occurs, psychological trauma is less likely without recall.
💣Light induction doses and liberal use of muscle relaxants ,without giving adequate concern to the depth of anaesthesia can increase the chance of awareness.
💣Better to give re-bolus with i.v. hypnotic during multiple intubation attempts. Consider using inhalation induction technique.
💣Beta-blockers, can reduce MAC-Awake and may also decrease the likelihood of PTSD.
💣We can consider ear plugs or headphones to reduce awareness of noises in the OR.
💣Nitrous oxide, Ketamine and Opioids suppress cortical arousal during painful stimulation, which may reduce the probability of awareness. But BIS (Bi Spectral Index) and other EEG monitors do not accurately predict the depth of anesthesia with these drugs. (Because, even though they produce hypnosis, they do not modulate GABA-A receptors and are associated with unchanged or increased high frequency EEG signals.)
💣Propofol, barbiturates, etomidate, and halogenated volatile anesthetic agents all modulate GABA-A receptor activity and shift the cortical EEG to lower frequencies. So, BIS and other EEG-based monitors provide strong correlation with hypnosis for this group of general anesthetics.
💣MAC for N2O & volatile anesthetics is additive (i.e. a mixture of 0.5 MAC N2O plus 0.5 MAC volatile suppresses movement in response to pain like 1 MAC volatile. The HYPNOTIC activities of nitrous oxide and volatile anesthetics are sub-additive. (i.e. a mixture of 0.5 MAC-awake N2O + 0.5 MAC-awake volatile anesthetic is not as hypnotic as 1 MAC-awake volatile. This suggests that N2O has an action which antagonizes the hypnosis induced by volatile anesthetics, perhaps via direct cortical arousal.
💣Many studies say, BIS is not useful in case of dexmedetomidine also; while some others say it will help.
#awareness , #anesthesia , #sedation , #AwarenessAnesthesia , #bis , #AwarenessSurgery

➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖
Reference:

CampagnaJA,MillerKW,FormanSA:Mechanismsofactionsof inhaled anesthetics. N Engl J Med 348:2110-2124, 2003
SleighJW,BarnardJP:Entropyisblindtonitrousoxide.Canwesee why? Br J Anaesth 92:159-161, 2004 39.
ChortkoffBS,BennettHL,EgerEI2nd:Doesnitrousoxideantagonize isoflurane-induced suppression of learning? Anesthesiology 79: 724-732, 1993 40.
KatohT,IkedaK,BitoH:Doesnitrousoxideantagonizesevofluraneinduced hypnosis? Br J Anaesth 79:465-468, 1997
Update on Bispectral Index monitoring Jay W. Johansen,Best Practice & Research Clinical Anaesthesiology Volume 20, Issue 1, March 2006, Pages 81–99

NEURO #ANATOMY OF THE OLFACTORY SYSTEM : How some smells induce tears and sniffing in you❓

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😤 Olfactory receptors 1️⃣ are the most important cells of the olfactory epithelium and they are the first order neurons of the cranial nerve I
😤There are approximately 100 million such receptors in the olfactory epithelium found along the roof of the nasal cavity including the superior and upper middle conchae
😤Olfactory receptors project through the cribriform plate in the ethmoid bone
😤They have multiple cilia immersed in a surrounding matrix of mucus and a long dendrite
😤Odiferous chemicals get dissolved in this mucus and then trigger the olfactory receptors
😤The impulses pass through the neuron to the olfactory bulb (lies in base of frontal cortex in anterior fossa), which has projections to cortical areas
😤The primary olfactory area in the temporal lobe process such informations through it’s connections with the hypothalamus, thalamus and frontal cortex
😤The other major cell type is basal cells 2️⃣ found deep to the olfactory neurons (olfactory neurons have a half-life of one month) and replace them, as they mature
😤3️⃣Sustentacular or supporting cells constitute the columnar mucus epithelium found between the receptors
😤There are 4️⃣Olfactory (Bowman’s) glands found in the connective tissue beneath the olfactory epithelium which produce the mucus in which the odiferous chemicals dissolve
❓➡️ 🅰️ Finally answer to the question
😤The innervation of the olfactory epithelial cells from cranial nerve VII (facial nerve) explains the tears and sniffing evoked by some smells.
Reference: Tortora GJ, Grabowski SR. Principles of Anatomy and Physiology, 8th edn. New York, NY: HarperCollins, 1996; pp. 454–5
#smell , #Olfaction , #PhysiologyForExams , #NeuroAnatomy , #anesthesiology

CEREBRAL PHYSIOLOGY

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Circle of Willis : #ShortNote ❗️

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 ⭕️The #CircleofWillis is a vital arterial structure on the ventral surface of the brain that joins the two internal carotid arteries (ICAs) (two-thirds of the supply) with the two vertebral arteries to supply the contents of the cranium 
⭕️The vertebral arteries enter the cranial cavity through the foramen magnum and join to become the basilar artery, which supplies blood to the posterior portion of the circle of Willis. 
⭕️The internal carotid arteries enter the skull through the carotid canals and supply the anterior circulation of the brain.
⭕️After entering the skull, the ICA branches into two main vessels: the Anterior Cerebral Artery (ACA) and Middle Cerebral Artery (MCA).
⭕️The MCA supplies the lateral surface of the brain, traveling in the Sylvian fissure
⭕️The ACAs also originate from the ICA and run anterior and medially towards the midline, coursing over the corpus callosum, between the hemispheres in the longitudinal fissure, and supplying the medial aspect of the hemispheres as far back as the splenium. The anterior cerebral arteries are joined together by a single anterior communicating artery(ACom)
⭕️An ACA #stroke can result in paralysis or sensory loss of the legs, whereas a MCA stroke can result in loss of paralysis or sensory loss of the face and/or arms. A MCA stroke of the dominant hemisphere may injure the language centers and produce aphasia.
⭕️The two vertebral arteries lie on either side of the medulla and join anteriorly at the caudal border of the pons to form the basilar artery. 
⭕️The vertebral arteries give off the posterior inferior cerebellar artery(PICA), before joining to form the basilar artery
⭕️Another important single artery that is created by the merger of the two vertebral arteries is the anterior spinal artery.
⭕️The basilar artery gives rise to a number of important paired branches. Posterior to anterior, these are: anterior inferior cerebellar artery(AICA), superior cerebellar artery(SCA).
⭕️The vertebral arteries supply the medulla via small, penetrating branches. 
⭕️The basilar artery supplies the pons through small penetrating vessels.
⭕️PICA supply the inferior surface of the cerebellum, as well as the lateral medulla
⭕️AICA supplies the anterior portions of the cerebellum and the lateral pons.
⭕️SCAs supply the cerebellum and lateral midbrain
⭕️The basilar artery gives rise to the posterior cerebral arteries (PCAs), which join the anterior part of the circle of Willis via the posterior communicating arteries(PCom). PCAs supply the occipital lobe and lateral midbrain 
⭕️The thalamus is supplied by perforators that originate from the tip of the basilar artery and the proximal PCA
⭕️Basilar artery strokes usually are fatal because they cause the loss of cardiac, respiratory, and reticular activating function. Patients who survive may have a clinical syndrome known as locked-in syndrome in which the patient cannot move as the ventral brainstem tracts (motor) are destroyed, but the sensory tracts (more dorsal) may be left intact. These patients are unable to move, speak, or communicate with the world, except by blinking and possibly through upgaze.

N.B.: VENOUS DRAINAGE

🔻The superior sagittal sinus lies along the attached edge of the falx cerebri, dividing the hemispheres, and usually drains into the right transverse sinus. 
🔻The inferior sagittal sinus lies along the free edge of the falx and drains via the straight sinus into the left transverse sinus (The straight sinus lies in the tentorium cerebelli.) 
🔻The transverse sinuses merge into the sigmoid sinuses before emerging from the cranium as the internal jugular veins.  
🔻Deeper cranial structures drain via the two internal cerebral veins, which join to form the great cerebral vein (of Galen). This also drains into the inferior sagittal sinus.  
🔻The cavernous sinuses lie on either side of the pituitary fossa and drain eventually into the transverse sinuses.
#Anatomy , #NeuroAnatomy , #BloodSupplyOfBrain , #Neurology , #NeuroAnesthesia , #NeuroSurgery , #NeurologyICU , #ICU