The Life of P.I. (PERFUSION INDEX)🐾

🚤 Reduction of plethysmographic pulse wave amplitude (PPWA) has been proven to be a reliable method for detecting the IV injection of an exogenous vasopressor ( for e.g. The adrenaline in epidural test dose)

🚤 Currently, a numerical value has been added to new pulse

oximeters indicating the PPWA, termed the perfusion index (PI), to augment its clinical applicability.

🚤i.e. PI is the numerical value of the amplitude of the

plethysmographic pulse wave that is displayed on

many pulse oximeters.

🚤 Using pulse oximetry, a variable amount of light is absorbed by pulsating arterial flow (AC) and a constant amount of light is absorbed by nonpulsating blood and tissue

(DC). The pulsating signal indexed against nonpulsating signal and expressed as ratio is commonly referred to as the perfusion index

🚤 It depends on the distensibility of the vascular wall and the intravascular pulse pressure. Usually the effect of autonomic impulses upon distensibility is so strong that it predominates the opposite effect of pulse pressure.

🚤 Decreases in PI resulting from pain and other stressful stimuli are due to vasoconstriction of the finger arterial bed rather than changes in the pulse pressure

Reference: The Efficacy of Perfusion Index as an Indicator for Intravascular Injection of Epinephrine-Containing Epidural Test Dose in Propofol-Anesthetized Adults, Anesth Analg 2009;108:549 –53) 

ROBOTIC🤖 PROSTATECTOMY: #Anesthesia CONCERNS

🏈FACTS ABOUT THE SURGERY

▪️There is a master console; surgeon sits here & controls the robotic surgical manipulator, once it has been docked

▪️Robot is bulky and is positioned over the chest and abdomen

▪️Patient is positioned in lithotomy with a steep Trendelenberg tilt

▪️Needs immobility of the patient till the robot is undocked

▪️Table position should not be altered until the surgical instruments are disengaged

▪️Discharge may occur as early as within 24 hours after surgery

🏈ADVANTAGES

▪️Better continence & erectile function 

▪️Less pain and hence less analgesic requirements 

▪️Less blood loss

▪️Shorter hospital stay

🏈ANESTHESIA CONCERNS

▪️Since immobility is very important, it can be established by continuous infusion of a non depolarizing muscle relaxant

▪️As the procedure may take long time, it's better to use agents with rapid offset

▪️Because patient is positioned in steep head-down position 

➖Ensure pressure points are protected adequately 

➖Fluids are infused cautiously to reduce chances of cerebral and laryngeal oedema ( N.B.: Rule out cerebral oedema in case of delayed emergence )

➖As the position of the robot interferes with resuscitation, prior practice-drills and good communication are necessary to manage such a situation effectively 

➖Epidural analgesia, if at all required, are used only postoperatively, as the steep head-down position will increase the risk of high block

Reference: Irvine M, Patil V. Anaesthesia for robot-assisted laparoscopic surgery. Contin Educ Anaesth Crit Care Pain. 2009; 9(4): 125–129.

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

Mechanical Ventilation Facts

LOW FLOW #Anesthesia

🌧Low flow anesthesia allows for economy of volatile anesthetics, makes possible heating and humidification of gases and reduces environmental pollution 

🌧Sodalime contains 94% Calcium hydroxide, 5% Sodium hydroxide snd also Potassium hydroxide, Silica and dying agent

🌧 CO2 + 2NaOH --> Na2CO3 + water + heat

      Na2CO3 + Ca(OH)2 --> 2NaOH + CaCO3

..this sequence gets back Sodium hydroxide, back in the game💁♂️

🌧 1 Kg of Sodalime can absorb >120 L of CO2

🌧 Carbon monoxide which is a byproduct of protein metabolism can accumulate in the system, but levels are <4%

🌧 If there is intoxication by alcohol or poisoning by Carbon monoxide or severe diabetic ketosis, alcohol or CO or acetone from the expired gases, will recirculate and accumulate inside the system; so low flow anesthesia is contraindicated in such states

🌧 Prolonged anesthesia with sevoflurane may generate Compound A inside the system, which can cause acute tubular necrosis in rats at concentrations around 250 ppm, a dose that is nearly 200 times seen in clinical practice. So any proteinuria, glycosuria or enzymuria which does develop in such a context has not been shown to have any clinical significance, even in patients with proteinuria

Reference: Al-Shaikh B, Stacey S. Essentials of Anaesthetic Equipment, 2nd edn. Edinburgh: Churchill Livingstone, 2002; pp. 74–9 . Nunn G. Low-flow anaesthesia. Contin Educ Anaesth Crit Care Pain 2008; 8: 1–4. 

SJOGRENS SYNDROME-anesthesia implications ➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖

🏳️🌈Preoperative abnormalities

1. Symptoms of the sicca syndrome include dryness of the eyes and skin.

2. Check for associated RA, SLE, scleroderma, the polymyositis, polyarteritis nodosa, chronic active hepatitis, and Grave's disease.

3.Lung / airway : desiccation of the nose and bronchial tree, obstructive airways disease, interstitial lung disease

4.sensory / motor neuropathy may occur and CNS lesions have been described.

5.The patient may be taking corticosteroids or occasionally immunosuppressive agents.

🏳️🌈Anaesthetist's concerns

1. Sometimes gross swelling of the salivary glands may make mask anaesthesia difficult.

2.The problems of pulmonary disease, if present.

3.The dry eyes are susceptible to damage during anaesthesia.

4.Allergy to antimicrobial agents, particularly penicillin, cephalosporins and trimethoprim

Management

1. careful assessment of the primary disease, and of any pulmonary involvement.

2. Drying agents should be avoided if possible.

3. The eyes should be protected with pads.

4. Anaesthetic gases should be humidified.

5. Steroid supplements may be required.

6. Care should be taken when prescribing antimicrobial agents

#anesthesia , #anaesthesia , #anesthesiology , #anaesthesiology , #PerioperativeCare , #comorbidities , #PreAnestheticCheckup , #PAC

BIOSTATISTICS FOR MEDICAL STUDENTS : TYPES OF DATA

POSTOPERATIVE VISUAL LOSS

👀 Corneal abrasion is the most common ocular complication after general anesthesia

👀 Ischemic Optic neuropathy (ION) and Central Retinal Artery Occlusion (CRAO) are the commonest causes for postoperative visual loss

👀 ISCHEMIC OPTIC NEUROPATHY (ION)

🌵More common among the two

🌵Most often seen after prolonged surgery in prone position 

🌵Venous congestion--> Raised Intra Ocular Pressure (IOP) due to Raised Intra Orbital Pressure --> Intra Orbital ‘Compartment Syndrome’

🌵Hypotension, Diabetes, Vascular disease, Smoking etc also may be important in the etiopathogenesis

🌵Treatment:

➖ Reduce optic nerve edema as it passes through posterior scleral foramen with steroids and mannitol 

➖ Optimal oxygen delivery by ensuring normal blood pressure and hematocrit  

➖ Clear all obstruction to venous drainage 

🌵Chance of visual recovery is less

👀 CENTRAL RETINAL ARTERY OCCLUSION (CRAO)

🌵 External pressure on eye and embolism are risk factors 

🌵 An echocardiogram and carotid ultrasound may help us to find an embolic source

Reference: White E, David DB. Care of the eye during anaesthesia and intensive care. Anaesth Intens Care Med. 2007; 8(9): 383–386.