Monthly Archives: September 2018

EPIDURAL NEEDLE & CATHETER : KNOW THE MEASUREMENTS

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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

Tuohy 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

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

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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. This maintains a concentration gradient favouring the dissociation of the drug from protein binding sites, and thus the overall hepatic metabolism is mainly related to hepatic blood flow. E.g. Propranolol

In case of drugs with lower hepatic metabolic capacity, drug 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 the intake through these routes avoid first-pass metabolism.

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

Anesthesia concerns in Takotsubo / Stress Cardiomyopathy and it’s management in the ICU

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Various stress-related cardiomyopathy syndromes are

(1) classic Takotsubo cardiomyopathy, which presents as an acute coronary syndrome

(2) left ventricular dysfunction associated with acute intracranial disease, especially Aneurysmal SAH

(3) transient cardiomyopathy, which occurs during other critical illness, especially sepsis, and

(4) transient cardiomyopathy associated with pheochromocytoma and exogenous catecholamine administration

Takotsubo Cardiomyopathy is also known as takotsubo syndrome, broken heart syndrome, ampulla cardiomyopathy, transient left ventricular apical ballooing, apical ballooning syndrome, transient left ventricular dysfunction syndrome, and stress [induced] cardiomyopathy

It was first described in Japan in 1990

Patients don’t have significant epicardial coronary artery disease

It presents like an acute coronary syndrome ; but symptoms like chest pain, dyspnea, and ECG changes may not be there in all cases

Was most frequently described in postmenopausal elderly women

Was often triggered by stressful situations.

Classic pattern of wall motion abnormality observed is “apical ballooning” usually associated with hyperkinesia of the basal segments ( but its NOT pathognomonic of the disease)

Onset is often preceded / precipitated by emotional or physiologic stress (NOT invariably)

Researchers at the Mayo Clinic proposed diagnostic criteria in 2004, which have been modified recently :

(1) transient hypokinesis, akinesis or dyskinesis in the left ventricular mid segments with or without apical involvement; regional wall motion abnormalities that extend beyond a single epicardial vascular distribution; and frequently, but not always, a stressful trigger

(2) the absence of obstructive coronary disease or angiographic evidence of acute plaque rupture

(3) new ECG abnormalities (ST-segment elevation and / or T-wave inversion) or modest elevation in cardiac troponin; and

(4) the absence of pheochromocytoma and myocarditis.

The most commonly accepted cause is excessive adrenergic/ catecholamine stimulation, which damages cardiomyocytes

Reports of its acute precipitation by administration of catecholamines (like adrenaline or dobutamine) and its reproduction by infusion of adrenaline in primates support this hypothesis

Most patients recover without complications; but others may develop complications like congestive heart failure, pulmonary edema often requiring endotracheal intubation and mechanical ventilation, cardiogenic shock requiring vasopressor or inotropic therapy and even intraaortic balloon pumping

Regarding treatment in the acute phase, avoidance of adrenergic agonists and initiation of antiadrenergic therapy (e.g., adrenergic blocking drugs or centrally acting 2 agonists) have been advocated

In patients presenting with left ventricular outflow tract obstruction, catecholamines are particularly contraindicated

If inotropic therapy is needed (as in case of heart failure, pulmonary edema, and cardiogenic shock etc) there has been suggestions, that the calcium sensitizer levosimendan may be the better choice

One school of thought is that a substantial portion of the damage caused by catecholamine toxicity to the myocardium has likely occurred by the time of clinical presentation, and thus administration of antiadrenergic therapy at this time is unlikely to completely reverse injury. Infact, in a number of reported cases, catecholamines seem to have facilitated recovery in patients with acute left ventricular dysfunction

Reference: anesthesia-analgesia March 2010 • Volume 110 • Number 3 ,circ.ahajournals

DESFLURANE & ITS VAPORIZER

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#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

FLOWMETER : PRINCIPLES BEHIND

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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.

DRAW-OVER VAPORISERS IN A NUTSHELL FOR #Exams

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They are placed inside the breathing system and rely on a negative pressure downstream from the vaporiser to create the flow required to entrain the agent. This negative pressure is generated either by the patient’s own inspiration or by a self-inflating bag

So they must have a very low resistance to flow to avoid additional resistance to the patient’s breathing.

Goldman vaporiser, the Oxford miniature vaporiser (OMV) and the Epstein MacIntosh vaporiser (EMV) etc are draw-over vaporisers. The triservice apparatus, used by the military, incorporates two OMVs

They are simpler, lightweight, smaller and less expensive.

As it is not possible to calibrate for the large range of tidal volumes created by the patient/ self-inflating bag, they are inaccurate

So they are not generally used in hospitals, and are reserved for ‘in-the-field’ use, where portability is required.

Reference: Al-Shaikh B, Stacey S. Essentials of Anaesthetic Equipment, 2nd edn. Edinburgh: Churchill Livingstone, 2002 . Davis PD, Kenny GNC. Basic Physics and Measurement in Anaesthesia, 5th edn. Oxford: Butterworth–Heinemann, 2003 .

Physics For Anesthesiologist: IMPEDANCE

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Impedance is a term that is commonly used in the world of #electrophysiology and #BiomechanicalEngineering.

The chance of getting an electric shock is high when you have wet hands because the impedance of the skin is lower than when it is dry.

Thoracic impedance increases during inspiration.

When applying electric current to the chest during #defibrillation, less energy may reach the heart during the inspiratory phase than during the expiratory phase because of this phenomenon, thereby decreasing the possible success of defibrillation.

So better to attempt defibrillation during the expiratory phase of mechanical ventilation.

Where the #resistance of a circuit is dependent on the frequency of the current through it, the term impedance is used.

The unit of impedance is therefore the same as that of resistance (the ohm), but the symbol Z is used to differentiate it from the symbol used for resistance (Ω).

In case of a capacitor, as the frequency of the current increases, the current passes through the circuit more easily, i.e. the resistance of the capacitor falls with increasing current frequency.

In contrast, the resistance of an inductor rises as the frequency of the current increases.

#PhysicsForAnesthesiologist , #anesthesiologist , #anesthesia , #biomedical

Davis PD, Kenny GNC. Basic Physics and Measurement in Anaesthesia, 5th edn. Oxford: Butterworth–Heinemann, 2003; pp. 149–64 . Ewy GA, Hellman DA, McClung S, Taren D. Influence of ventilation phase on transthoracic impedance and defibrillation effectiveness. Crit Care Med 1980; 8: 164–6

HAVE YOU SEEN PERSISTENT UNEXPLAINED HYPOXAEMIA IN ADULT PATIENTS ? ONE IMPORTANT D.D. IS PFO

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Persistent unexplained hypoxaemia can result from the presence of a Patent Foramen Ovale (PFO)

A quarter of young adults have a #PFO

Actually there is no deficiency of atrial septal tissue per se, in such cases

In the absence of left atrial dilation, the defect functions as a flap valve, only allowing right-to-left flow.

Normally, left atrial pressure exceeds right atrial pressure and no shunting occurs.

However, if right-sided pressures increase, right-to-left shunting and therefore potential hypoxaemia can occur.

Acutely, this may become evident in such patients

during #ventilator asynchrony

with maintenance of high positive end-expiratory pressures (PEEP) during mechanical ventilation

in #ARDS patients with acute cor pulmonale or with right ventricular systolic dysfunction, particularly as part of the right ventricular infarction syndrome.

The diagnosis should be considered in any intensive care patient in whom the degree of hypoxaemia appears disproportionate, and should be detectable by colour Doppler.

Management might include a counterintuitive decrease in positive end-expiratory pressure ( #PEEP )and the re-establishment of spontaneous ventilation.

#Hypoxia , #MechanicalVentilation , #ICU , #CriticalCare , #Anaesthesia , #IntensiveCare

Reference: AAGBI Core Topics in Anaesthesia 2015 , Echocardiography and Anaesthesia, Jonathan H. Rosser and Nicholas J. Morgan-Hughes

Brainstem Testing for diagnosis of Brain Death

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The brain stem often fails from the rostral to caudal direction and therefore it is logical to undertake testing in the same manner.

PUPILLARY REFLEXES :

The pupillary light reflex involves cranial nerves II and III and localizes to midbrain. The pupils should be nonreactive to both direct and consensual light reflex.

POINTS:

Pinpoint pupils are indicative of damage to descending sympathetic fibers as a result of damage to pons.

The size of the pupils only provides an indication of the site of brainstem involvement and is not crucial for testing brain stem death.

Clues: 2,3 pupil in MID row, some inPONdS

OCULOCEPHALIC REFLEX :

It involves cranial nerves III, VI, and VIII and interneurons within the midbrain and pons. On head movement toward right or left, the eyes remain “fixed” on a point in an intact patient. In the brain-dead patient, the eyes move with the head, hence the name “dolls eye” reflex.

POINTS:

Before performing this test the physician must rule out cervical fracture or instability.

Clues: Oh…Cee…368 dolls in MID row and PONdS

CORNEAL REFLEX :

The reflex tests the V, VII, and III cranial nerves and localizes entirely to the pons. In the intact patient, touching the cornea with a cotton swab causes eyelid closure.

The eye rotates upward, demonstrating the cranial nerve III component, known as “bell’s phenomenon.”

Corneal= sensation ; hence 5&7; plus 3 bells

OCULOVESTIBULAR REFLEX :

The oculovestibular reflex tests cranial nerves III, VI, VIII, and IV. It involves the entire pons and midbrain.

PROCEDURE :

Elevate the head 30°C. Irrigate tympanic membrane with 50-cc iced water or saline. Wait 1 min for response. Repeat test on the other side after waiting 5 min. If the oculovestibular reflex is intact using cold water as stimulus, the eyes tonically deviate toward the side of the stimulus immediately followed by a fast recoil toward the contralateral side (apparent nystagmus). In the brain stem dead patient this response is absent.

Clues: ‘broad test’ Pons & Medulla; 3,4,6, 8 COWS

GAG AND COUGH REFLEXES :

They require a functioning medulla and test cranial nerves IX and X. Both reflexes should be absent in brain stem death.

The cough reflex is easily tested by stimulation of carina by suction through the endotracheal tube. The gag reflex can be elicited by stimulating the posterior pharynx with a tongue blade.

APNEA TESTING :

This final test aims to demonstrate the failure of medullary centers to drive ventilation. Apnea test should be the last brain stem reflex to be tested.

OBJECTIVE:

Is to stimulate the medulla while avoiding hypoxia and hemodynamic compromise associated with acidosis secondary to hypercarbia.

PROCEDURE:

After ensuring preoxygenation for 10 min a blood gas is performed to confirm baseline PaCO2 and SaO2 .

With oxygen saturation greater than 95% the ventilatior is disconnected inducing apnea for a period of time to achieve ETCO2 above 6 KPa (=45 mmHg). A repeat arterial blood gases is used to confirm that the PaCO2 is at least 6 KPa and the pH is less than 7.40.

An oxygen flow rate of 2–5 L/min via an endotracheal catheter or in difficult cases CPAP may be used to maintain oxygenation till this state is attained.

Apnea is continued for a further 5 min after a PaCO2 of 6 KPa (=45 mmHg) has been achieved.

If there is no spontaneous respiratory response, a presumption of absence of respiratory activity is made.

A further blood gas can be done to confirm that the PaCO2 has risen by 0.5 KPa (=4 mmHg) from the initial 45 mmHg baseline.

Reference: Brain Death in Neurosurgical Critical Care Amit Prakash, Basil Matta , Essentials of Neurosurgical Anesthesia & Critical Care 2012

UPPER GI BLEED IN ICU PATIENTS: THE POINTS WHICH YOU SHOULD KEEP IN MIND

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Incidence of overt Upper GI Bleed (UGIB) ranges from 1.5 to 8.5% of all ICU patients but may be as high as 15% if no prophylaxis is used.

RISK FACTORS

Mechanical ventilation >48 h

Coagulopathy – INR>1.5 or platelet count <50,000

Others: Shock, Sepsis, Hepatic failure,Acute Renal failure, Multiple trauma, Burns >35% of total body surface area, Organ transplantation, Head trauma, Spinal trauma, History of PUD or UGIB

SPECIFIC POINTS REGARDING TREATMENT

Thrombocytopenia can develop in neurosurgical patients on H2 Blockers

The use of H2Bs and PPIs may increase the frequency of nosocomial pneumonia.

PROPHYLAXIS IS RECOMMENDED FOR ICU PATIENTS WHO EXHIBIT:

Coagulopathy (platelet count < 50,000 per m 3 , INR > 1.5, partial thromboplastin time (PTT) >2 times the control value)

Mechanical ventilation >48 h

History of GI ulceration or bleeding within the past year

Two or more of the following risk factors: sepsis; ICU stay >1 week; occult GIB ≥6 days; glucocorticoid therapy (>250 mg hydrocortisone).

REASONS FOR UGIB IN ICU PATIENTS:

The glycoprotein mucous layer may be denuded by increased concentrations of refluxed bile salts or uremic toxins common in critically ill. Alternatively, or in addition, mucosal integrity may be compromised due to poor perfusion associated with shock, sepsis, and trauma.

Excessive gastrin stimulation of parietal cells has been detected in patients with head trauma as oppose to be normal or subnormal in most other ICU patients.

Systemic steroids double the risk of a new episode of UGIB or perforation. Concomitant use with high doses of NSAIDs has been associated with a 12-fold increased risk for upper GI complications.

Helicobacter pylori infection

EMPIRICAL THERAPY

Start with an IV bolus of 80 mg and continue IV infusion at 8 mg/h for a total of 72 h. If no signs of rebleeding after 24 h, switch to oral PPI.

Octreotide is used in variceal bleeding. Start with an IV bolus of 50 mcg and continue IV infusion at 50 mcg/h for 3–5 days.

UGIB IN HEAD INJURY & OTHER NEUROSURGICAL PATIENTS:

They are more prone for UGIB because of 1. Frequent use of systemic steroids 2. Increased gastrin secretion 3. Significant gastric intramucosal acidosis is common in severe head injury. 4. Primary insult to the central nervous system may result in derangement of splanchnic blood flow secondary to neurohumoral mechanisms.

In head injury, GI dysfunction also may manifest as gastroparesis, ileus, increased intestinal mucosal permeability

Plasma levels of cortisol and age are independent predictors of stress ulcers following acute head injury.

#GastroIntestinalBleed , #StressUlcer , #ICU , #Anesthesia , #CriticalCare, #IntensiveCare , #NeuroSurgery , #HeadInjury , #TBI,#NeuroCriticalCare

Reference: Gastrointestinal Hemorrhage in Neurosurgical Critical Care Meghan Bost, Kamila Vagnerova , Ch:84, Essentials of Neurosurgical Anesthesia & Critical Care 2012 Strategies for Prevention, Early Detection, and Successful Management of Perioperative Complications