SI UNITS & NON SI UNITS OF PRESSURE

▪️Pressure is force applied over a unit area. Pressure  = Force/Area. It's SI unit is Pascal.

▪️️There are 7 base SI units , from which others are derived (which are known as derived SI units)

▪️Pascal is a derived SI unit. It is N.m-2. It is represented by the symbol Pa.

▪️One pascal is equal to a force of one newton applied over an area of one square metre. (N.m−2) 

▪️The pascal is a small amount (1 N is equal to just 102 g weight) 

▪️For this reason kilopascals (kPa) are used as standard.

▪️The standard atmospheric pressure is: 101.325 kPa = 1.013 bar = 14.696 psi =1 atm

VISCOUS FACTS❗️

⌛️Dynamic or absolute viscosity is a measure of the resistance of a fluid or gas to flow. It is measured using a viscometer or rheometer.

⌛️The SI unit of dynamic (or absolute) viscosity is the pascal-second (Pa·s), equivalent to N·s/ m2.

⌛️Viscosity is independent of flow rate

⌛️Viscosity is independent of pressure

⌛️️For a gas, viscosity decreases as its temperature increases 

⌛The relationship between viscosity and temperature and pressure only holds true for those fluids and gases that exhibit ‘Newtonian’ properties, i.e. substances that will always flow irrespective of forces acting upon them (e.g. crystalloid solutions and water). 

⌛️ Blood is a non-Newtonian fluid and its viscosity depends largely on haematocrit (and varies with flow rate).

⌛️Blood viscosity is increased by volatile anaesthetic agents, smoking and aging❗️

⌛️A thixotropic substance is one that becomes less viscous over time when agitated. If it becomes more viscous with agitation, this is known as a rheopectic material.

⌛️Kinematic velocity is defined as the dynamic velocity of a substance divided by its density.

ERRORS THAT CAN HAPPEN WITH THE SAMPLING FOR ARTERIAL BLOOD GAS ANALYSIS AND POSSIBLE CONSEQUENCES

❎AIR BUBBLES IN SYRINGE: may wrongly increase the Pao2 , Sao2 and pH

❎DILUTION OF THE SAMPLE WITH SALINE FLUSH OR HEPARIN: may wrongly increase Pao2 , while it decrease Paco2 , glucose, lactate , potassium and hemoglobin 

❎VENEPUNCURE DURING SAMLE COLLECTION: may wrongly decrease Po2 and So2 while it increases Pco2

❎ CLOTTING OF THE SAMPLE: may wrongly increase the potassium concentration 

#ABGerrors , #abg , #AbgSampling

ERRORS IN ABG SAMPLING: CAUSES & CONSEQUENCES

🔹Reduced pH (anaerobic metabolism)

🔹Reduced PaO2 (utilization of dissolved oxygen)

🔹Raised PaCO2 ( production of CO2 from continued metabolism)

🔹Reduced glucose ( utilization if glucose stores)

🔹Increased lactate( anaerobic metabolism)

#abg , #AbgErrors

CALCULATION OF THE VOLUME OF OXYGEN CYLINDER REQUIRED FOR A TRANSFER

▫️For this, we should know:

     1. Oxygen delivered = FiO2 x Minute Volume 

     2. Duration of the transfer

▫️For e.g. If we are expecting a duration of 2 hours (120 minutes) and we are having Size E cylinders and also need to deliver an FiO2 of 1 @ 6L / min

1. O2 delivered = 1 x 6 = 6L/ min

2. Size E has 660 L of O2, which will suffice for 660/6= 110 minutes ; so for 120 minutes, we need 2 cylinders 

#AnesthesiaGas , #OxygenCylinder

DIPPING IN DOPPLER

🎯The Doppler effect can be explained by considering a series of water-waves travelling out from the centre of a pond, in a circular form

🎯The frequency of the waves is related to the medium and the speed at which they are travelling. 

🎯The frequency of the waves reaching the periphery is less than the frequency nearer the centre. 

🎯If a detector was in the periphery it would detect the frequency of the waves whose frequency will be less

🎯But if the detector then started moving towards the source, the frequency would increase as the detector would be picking the waves nearer to the centre, whose frequency will be more.

🎯The Doppler effect describes the change in frequency of sound waves if the source of sound is moving in relation to the detector. The frequency is increased if the source is moving towards the detector and reduced if it is moving away.

🎯APPLICATIONS OF DOPPLER EFFECT

✔️It allows the confirmation of flow within peripheral arteries as well as in the brain, where the circle of Willis can be scanned.

✔️In echocardiography

✔️in obstetric practice when a fetal heart rate monitor is used

#doppler ,#anesthesia , #usg

MOBILE PHONES & MEDICAL EQUIPMENTS

🔹Researchers at University of Amsterdam have recorded nearly 50 incidents of electromagnetic interference in hospitals and classified 75% of them as hazardous.

🔹Researchers are of the opinion that mobile phones should not come within 1 meter to hospital beds and equipment 

🔹They are likely to induce errors in the functioning of equipments such as Ventilators , Pacemakers , Syringe pumps etc

🔹They observed that the General Packet Radio Service ( GPRS ) signal generation technology that allows wireless internet access has been particularly associated with the problem 

🔹 More studies are needed to get more clear information about this issue.

#MobilePhoneHazards , #ICUequipments , #MobilephonesHospital

LOCAL ANESTHETICS : AMIDES & ESTERS

FUROSEMIDE , THIAZIDES & NSAIDs : A FEW FACTS❗️

⚜Furosemide is a loop diuretic

⚜It interferes with the concentrating capacity of the loop of Henle.

⚜It is effective in patients with renal dysfunction, whereas the thiazides are NOT.

⚜It potentiates the nephrotoxic effects of cephalosporins and the ototoxic effects of aminoglycosides.

⚜NSAIDs inhibit renal prostaglandin, causing sodium to be retained, which reduces the diuresis caused by furosemide.

⚜ Furosemide is a venous and arteriolar dilator and thus reduces both preload and afterload in a time frame just before the period of onset of a significant diuresis.

PERIOPERATIVE CONCERNS IN THE SURGICAL MANAGEMENT OF PATIENTS WITH MOYAMOYA SYNDROME

PERIOPERATIVE ANESTHESIA CONCERNS IN THE SURGICAL MANAGEMENT OF PATIENTS WITH MOYAMOYA DISEASE

⌛️Moyamoya disease is characterized by progressive occlusion of the distal portion of the Internal Carotid Artery and the proximal Anterior and Middle Cerebral Arteries. 

⌛There is production of lots of factors promoting angiogenesis. This will cause 

(1) intimal proliferation of smooth muscle and eventual occlusion of vessels.

(2)Profuse lenticulostriate collateral formation at the base of the brain (These collaterals are known as Moyamoya vessels) 

(3)Vasodilatation of collaterals

⌛️Patients are at risk for both hemorrhagic ( due to rupture of the abnormal vessels) and ischemic stroke ( due to ischemia because of vasoocclusion) .

⌛️Presentation:

🔹Ischemic (80%): stroke , TIA etc

🔹Others: epilepsy (5%), ICH (2.5%)

⌛️On cerebral angiography, in more advanced stages of the disease, the hemispheric perfusion appears as a ‘puff of smoke’, from which the disease derives its name (Moyamoya= Puff of smoke in Japanese).

⌛️Associations: Optic/ hypothalamic glioma , Craniopharyngoma , NF-1 , Renal Artery Stenosis , Hypertension

⌛️Usual neurosurgical treatment involves Superficial Temporal Artery to Middle Cerebral Artery (MCA) Anastamosis through a small craniotomy, if there is a suitable MCA target. If not, an encephalo-duro-arterio-synangiosis (EDAS) can be performed by opposing a Superficial Temporal Artery pedicle to the cortical surface. This helps collateral formation from extra to intra cranial circulation over time (months to years).

⌛Intraoperative Concerns: ️Excessive hypertension may cause hemorrhage from friable vessels and hypotension may cause ischemic stroke from hypoperfusion

⌛️Blood pressure, blood volume, and PaCO2 require careful monitoring because moyamoya patients have a diminished cerebral perfusion reserve and deviation from normal levels can result in stroke.

⌛️So we have to take special care to avoid hypotension , hypovolemia ( give optimal preoperative, intraoperative and postoperative hydration) hyperthermia, and hypocarbia ( to avoid hypocarbia induced cerebral vasoconstriction)

#neurology , #anesthesia , #moyamoya , #stroke , #neurosurgery , 

Reference 

Surgical Management of Moyamoya Syndrome Edward R. Smith, R. Michael Scott , Skull Base. 2005;15(1):15-26.

Parray T, Martin TW, Siddiqui S. Moyamoya disease: a review of the disease and anesthetic management. J Neurosurg Anesthesiol. 2011 Apr;23(2):100-9.