Delirium in Intensive Care Unit

Delirium in Intensive Care Unit from Unnikrishnan P

HOW METABOLISM AFFECTS THE JOURNEY OF DRUGS TO THE TARGET SITE❓

🚀Oral administration --> cross the gut mucosa --> enter portal circulation -->  pass through the liver -->  enter the systemic circulation. 

🚀Only un-ionised molecules can cross the mucosal barrier

🚀Weakly acidic drugs (e.g. aspirin) begin to be absorbed in the acidic environment of the stomach

🚀Weakly basic drugs only begin to be absorbed in the small intestine.

🚀Drugs that are permanently ionised (e.g. the NDMR) are not absorbed from the gut at all.

 🚀Metabolism occurring in the liver is called ‘first-pass’ metabolism. The metabolism which happens in gut wall as in case of NTG is also first-pass metabolism. First-pass metabolism reduces the amount of drug that reaches its target site.

🚀If liver is having a high metabolic capacity, in case of a particular drug, any drug entering the hepatocyte is quickly broken down. Now the drug fraction which is protein bound dissociates freely and enters hepatocyte. In this case the overall hepatic metabolism is mainly related to hepatic blood flow. E.g. Propranolol 

🚀In case of drugs with lower hepatic metabolic capacity remains bound to protein and so,  the degree of protein binding influences entry to the hepatocyte than the hepatic blood flow 

🚀Sublingual and nasal routes have the advantage of rapid onset and bypassing of the portal circulation and hence avoidance of first-pass metabolism.

🚀Rectal  route also avoids first-pass metabolism, but absorption is slow and can be incomplete.

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DESFLURANE & ITS VAPORIZER

🎈#Desflurane has a saturated vapour pressure of 664 mm of Hg @ 20 degree C and a boiling point of 22.6 degree C

🎈This is less than other agents; thus it requires a specific vaporizer

🎈The Tec Mk 6 vaporizer is a plenum vaporizer and is designed for desflurane.

🎈It operates at 39 °C and 2 atmospheres (All other vaporizers operate at atmospheric pressure and temperature). 

🎈It takes 5–10 minutes to warm up to the correct temperature.

🎈It will not operate until the vaporisation chamber has reached 39 °C.

🎈It needs an external power supply, and it has a 9 V battery as a backup in case of mains failure.

🎈Unlike other plenum vaporisers, the Tec Mk 6 vaporizer is designed so that the fresh gas flow does not enter the chamber. The desflurane vapour is added to the fresh gas flow as it leaves the vaporiser.

#anesthesia , #anaesthesia , #anesthetist

Reference: Al-Shaikh B, Stacey S. Essentials of Anaesthetic Equipment, 2nd edn. Edinburgh: Churchill Livingstone, 2002

#Hyponatremia CORRECTION ; a template for #Anesthesiologists and #CriticalCare #Physicians

FLOWMETER : PRINCIPLES BEHIND

🔸The flowmeter / rotameter is a variable-orifice device used to measure the flow of oxygen, air and nitrous oxide in the anesthesia machine

🔸It usually contains a bobbin

🔸The pressure of gas beneath the bobbin pushes it up the flowmeter until the force beneath it is balanced by the force of gravity pulling it back to its resting position. 

🔸The variable orifice of the flowmeter means that the flow of gas past the bobbin at low flows is laminar, but at high flows it is turbulent. 

🔸The flutes on the bobbin are to ensure continuous movement of the bobbin as gas passes it, showing that it is not stuck. 

🔸The variable orifice of the flowmeter is responsible for the turbulent flow.

HOW EVOKED POTENTIALS BEHAVE , WHEN BRAIN SUFFERS FROM ISCHEMIA ❓

🕶Cerebral ischemia slows neurotransmission and neuronal energy metabolism, resulting in decreased amplitude and increased latency of specific peaks. 

🕶For SSEPs, a 50% reduction in amplitude and/or a 10% increase in latency [changes in the central conduction times, namely, the interpeak latencies between the N14 and N20 peaks] of SSEP signals from the baseline are generally accepted to be a significant change 

🕶A 50% reduction on SEP amplitude has been shown to occur when cerebral blood flow decreases below 14 mL/100 g/min 

🕶MEP have less well-defined warning criteria as compared to SSEPs; however, increased stimulus thresholds and/or decreased MEP amplitudes in relation to dramatic events (i.e., clip application) are indicative of pending neurologic insult. 

🕶For BAEP, an increase in latency of more than 1 msec, particularly in wave V, is considered to be clinically significant. 

🕶Unlike EEG monitoring the evoked potential tests can detect subcortical functional status by way of perforating branches such as the anterior choroidal and medial striate arteries 

Reference: Anesthesiology Research and Practice Volume 2014, Article ID 595837, Controversies in the Anesthetic Management of Intraoperative Rupture of Intracranial Aneurysm, Tumul Chowdhury, Andrea Petropolis,Marshall Wilkinson, Bernhard Schaller  Nora Sandu and Ronald B. Cappellani