Circle of Willis : #ShortNote ❗️

⭕️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

Paravertebral blocks

• A paravertebral block is essentially a unilateral block of the spinal nerve, including the dorsal and ventral rami, as well as the sympathetic chain ganglion. These blocks can be performed at any vertebral level. However, they are most commonly performed at the thoracic level because of anatomic considerations.
• They provide analgesia for ✔️Unilateral thoracic pain ✔️Rib fracture ✔️Refractory angina✔️Hyperhydrosis etc
• Usually a single level injection may cover less than four dermatomes
• Can be given under USG guidance or using a landmark technique 
• Point to be marked at a point 25 mm lateral to the spinous process of the level to be blocked
• After local anesthetic infiltration an 18 G epidural catheter is inserted to a depth, not greater than 35 mm till transverse process are hit (they are fairly superficial) and then the needle should be walked off the transverse process caudally, until it is 10mm deeper than the depth at which bone was initially contacted. (cranial walking of the needle increases the chance of pneumothorax)
• A loss of resistance to injection when the costotransverse ligament is passed is a clue to achieving of correct needle position,; but this is not as marked as the loss of resistance achieved during epidural insertion.
• If using a peripheral nerve stimulator, contraction of intercostal muscle or transverse abdominis may be elicited
• 3-5 mL of ropivacaine or levobupivacaine can be used per level. Addition of clonidine may prolong the blockade

reference: Deegan CA, Murray D, Doran P et al. Effect of anaesthetic technique on oestrogen receptor-negative breast cell cancer function in vitro. Br J Anaesth. 2009; 103(5): 685–690. Tighe SQM, Greene MD, Rajadurai N. Paravertebral block. Contin Educ Anaesth Crit Care Pain. 2010; 10(5): 133–137.

WHEN VENTILATOR GIVEs ALARM & SHOWS 'PATIENT-DEMAND IS HIGH' : #TroubleshootingVentilator

⁉️Check for causes: 

✔️Increased airway resistance- if so give bronchodilators

✔️Anxiety--> increased RR + muscle tension--> increased airway resistance  --> increased demand: Optimise sedation 

✔️Check for leaks in circuit and correct

✔️If flow rate seems too low: Set higher inspiratory flow rate or reduce inspiratory time especially if patient is showing tachypnea

✔️If Tidal volume or RR set too low: Increase it

🌵Double triggering or breath stacking can happen if inspiratory time set is lower compared to that of the patient and ventilatory demand is high: Try increasing the inspiratory time or change to pressure control modes