WHAT IS POYNTING EFFECT

This is an effect described with regards to the anesthetic gas ENTONOX

ENTONOX is a 50:50 mixture of gaseous oxygen and nitrous oxide

If the cylinder is stored below -6 degree (the pseudocritical temperature of ENTONOX) Celsius, the nitrous oxide component can separate as a liquid (lamination)

This can lead the delivery of uneven mixtures, too much oxygen at the beginning and too much N2O at the end of the cylinder life

Danger of lamination can be avoided by immersing the cylinder in water at 52 degree Celsius and inverting it 3 times, or by keeping it above a temperature of 10 degree Celsius for 2 hours before use.

Other methods are keeping the cylinder horizontal, at a temperature of 5 degrees or more for more than 24 hours OR by connecting a tube from the valve housing at the top to a point near the bottom which prevents the withdrawal of pure nitrous oxide

N.B. The critical temperature of a gas is the maximum temperature at which compression can cause liquefaction. Mixing gases may change their critical temperature. The Poynting effect produces a 50:50 mixture which reduces the crtical temperature of N20 (Critical temperature is 36.5 degree Celsius); so Entonox has a pseudocritical temperature of -6 degree Celsius

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.

PIN INDEX AND COLOUR CODING

EPIDURAL NEEDLE & CATHETER : KNOW THE MEASUREMENTS

📐 The adult needle is 10 cms long ( shaft measures 8 cms ). 15 cms long needles are also available for obese patients 

📐 The markings are 1 cm apart for the adult needle and 0.5 cm for the pediatric one

📐 For the adult 16 & 18 G are the commonly used ones, whereas for the pediatric 19 G needles are available 

📐 Touhy is the commonly used needle

📐 Regarding the tip: ✔️The bevel is angled at 20 degree with the shaft ✔️ It is known as Huber point ✔️ It's blunt ✔️ All these features aid in the effectiveness of Loss of Resistance Technique 

📐 Regarding the catheter: ✔️ It's made of nylon or teflon ✔️ The distal tip is rounded and closed ✔️So fluid can escape only through the side ports. All these features helps to reduce chances of dural puncture and vascular injury

📐 The adult catheter is 90 cms long

#anaesthesia , #anesthesia

VASOACTIVE AGENTS; DO YOU KNOW ?

Evidence suggests that dopamine can produce mild cerebral vasodilatation.

Phenylephrine can be the drug of choice when the cardiac index (CI) is sufficient but MAP is below the goal

Dobutamine does not have any dopaminergic agonist action.

In case of Labetalol, a reduction in MAP usually occurs when the dose is sufficient to decrease HR

propanolol shifts the hemoglobin-oxygen dissociation curve to the right.

Milrinone can induce thrombocytopenia as well as hypotension.

SNP is associated with the activation of the renin-angiotensin system ; reflex tachycardia can interfere with blood pressure reduction.

Occasionally, patients demonstrate relative resistance to SNP and they are at particular risk for developing cyanide toxicity.

SNP causes more arteriolar than venular vasodilatation, while NTG causes more venular than arteriolar vasodilatation.

Vasopressin increases arterial tone ; it is administered as a constant infusion, and not titrated up to avoid severe complications of distal ischemia.

Reference: Newfield, Philippa; Cottrell, James E., Handbook of Neuroanesthesia, 4th Edition

THE SECOND COMING OF METHOXYFLURANE

Ⓜ️Initially developed as an inhalational anesthetic, but withdrawn due to concerns about nephrotoxicity and hepatotoxicity. 

Ⓜ️In view of its analgesic properties it is now used, mainly in Australia and New Zealand, to provide short-term analgesia for painful procedures and in the prehospital setting (Grindlay and Babl, 2009). 

Ⓜ️Administration is via a dedicated single-use inhaler dispensing 0.2–0.4% methoxyflurane. 

Ⓜ️The limited data on efficacy suggest that methoxyflurane administered as a single dose as described above provides effective analgesia resulting in high patient satisfaction with no evidence of toxicity (Grindlay and Babl, 2009). 

Ⓜ️There is no good evidence regarding the safety of repeated doses, for example, for analgesia during daily dressing changes.

Ref: 

Acute Pain Management; A Practical Guide, Pamela E. Macintyre , Stephan A. Schug, 4/e

Systemic complications of aneurysmal subarachnoid hemorrhage

🔺Hypovolemia

🔺Hyponatremia

🔺Hypokalemia

🔺Hypocalcemia

🔺Electrocardiographic abnormalities

🔺Pulmonary edema

🔺Pneumonia

🔺Pulmonary embolus

🔺Hepatic dysfunction

🔺Renal dysfunction

🔺Thrombocytopenia

🔺Gastrointestinal bleeding

Predisposing factors for rebleeding after Aneurysmal SAH

🔹Large volume of blood in the subarachnoid space from the initial SAH

🔹Poor neurologic status owing to the devastation caused by the initial SAH

🔹Short interval from the initial hemorrhage

🔹Female gender: women rebleed twice as frequently as men

🔹Older age and poor general medical condition

🔹Systemic hypertension: the risk of rebleeding is directly related to the patient's systolic blood pressure

🔹Multiple previous episodes of rebleeding that increase the likelihood of subsequent rupture and death

🔹Presence of either an intracerebral or intraventricular hematoma

🔹Abnormal clotting parameters

🔹Posterior circulation aneurysms

Ref: Philippa Newfield, Audrée A. Bendo, Handbook of Neuroanesthesia, 4th Edition, 2007 Lippincott Williams & Wilkins

ANTERIOR AND POSTERIOR APPROACHES TO CERVICAL SPINE / SAFE Anesthesiologist Series [Surgical Aspects For Empowering Anesthesiologist]

ANTERIOR APPROACH TO CERVICAL SPINE

➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖

✔️ADVANTAGES

Easy access to disc

Little pain

Evacuate disc

Fusion by plate or graft

✖️DISADVANTAGES 

Multiple levels difficult 

May require fusion if unstable

Loss of mobility 

Risk of injury to adjacent structures

POSTERIOR APPROACH TO CERVICAL SPINE

➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖

✔️ADVANTAGES

Access to multiple levels

Direct visualisation of root

Fusion is usually not required

✖️DISADVANTAGES 

Risk of instability 

Poor access to disc space

Poor access to osteophytes

Higher risk of cord injury

Painful procedure

Ref: Bailey & Love’s Short Practice of Surgery, 24/e

ANESTHESIA INFO FROM THE LAY MEDICAL MAN- Facebook Page

〽️DIAPHRAGMATIC EVENTRATION

🔹 typically affects only a segment of the hemidiaphragm

🔹 is due to incomplete muscularisation of the diaphragm with a thin membranous sheet replacing the normal diaphragmatic muscle. 

🔹 Over time this region stretches and on inspiration does not contract normally. 

🗣Sudden rupture can occur with increase in intra-abdominal pressure (e.g. coughing, straining during light anesthesia or extubation etc)

🔹True rupture (if it happens)  - Effects: 

🔹mass effect of the abdominal viscera-->direct compression of the heart, mediastinal shift 

🔹Compression of vena cava and pulmonary veins--> impairs venous return, decreased cardiac output. 

👉🏿So we should maintain adequate depth of anaesthesia 

👉🏿Avoid Nitrous oxide (expansion of intra-abdominal viscera can impair the circulation and respiration)

#DiaphragmaticEventration , #eventration , #anaesthesia , #anesthesia , #DiaphragmaticHump ,#Radiology ,#cxr ,#ChestXray

Reference: Anaesthetic Management of an Adult Patient with Diaphragmatic Eventration

Azhar Rehman*, Zafar Ali Mirza, Saad Yousuf and Asma Abdus Salam, radiopaedia.org

RESPIRATORY STIMULANTS AND DEPRESSANTS

🏀Drugs that act as Respiratory stimulants 

⤴️Acetazolamide 

⤴️Aminophyllines 

⤴️Doxapram  

⤴️Progesterone 

⤴️Salicylates

🏀Drugs that act as Respiratory depressants 

⤵️Alcohol 

⤵️Anaesthetics 

⤵️Anticholinergics 

⤵️Antihistamines 

⤵️Barbiturates 

⤵️Benzodiazepines 

⤵️Opioids

#pharmacology , #pulmonology , #icu , #sedation , #anesthesia , #anaesthesia , #criticalcare