- It’s the maximal rate of airflow during forced expiration
- Dependent on patient-effort
- Repeated 3 times and the best of the 3 is taken
- Trends in Peak Expiratory Flow helps to assess the severity status of an acute episode, response to treatment etc
- Normal values: Females: 250-500 L/min Males:450-700 L/min
- METHODS TO MEASURE:
- Wright’s Peak flow meter : Commonly used clinically and is a constant pressure variable orifice device
- Pneumotachograph : Used for research purposes and is a variable pressure constant orifice device
- From flow volume loops : They are plots of airflow at various lung volumes. Help to distinguish between obstructive & restrictive devices
WHAT WILL HAPPEN IF WE GIVE A LARGE CARBOHYDRATE DIET TO AN ALREADY MALNOURISHED PATIENT IN THE ICU?
If we introduce nutritional support ( enteral or parenteral) based on the requirements of a regular healthy adult, to a malnourished patient, there will be a significant rise in basal insulin secretion, which will draw Potassium and Phosphate into the cell leading to hypokalemia, hypophosphatemia and fatal fluid shifts. ( Both rapid initiation and large amounts are dangerous). Phosphate depletion is also associated with increased urinary Magnesium excretion.
It can also be associated with Renal failure, Respiratory failure, Neuromuscular failure, Cardiac failure and Arrhythmias
This is known as “Refeeding Syndrome“
So to avoid this, in patients at risk ( e.g. chronic alcoholics, those who have not eaten anything in last 5 days etc) , we should introduce nutritional support at not more than 50% of the daily requirement , for the first two days.
Feeding rates can be increased to normal levels, if there is no evidence of refeeding syndrome clinically and biochemically, thereafter.
NICE guidelines for the high risk patients : start support with a maximum 10 kCal per kg per day, with thiamine & B complex supplementation. Biochemical parameters to be monitored closely.
There is no need for Prefeeding correction of electrolytes
#ICU , #nutrition , #NutritionInICU , #CriticalCare , #Anesthesia , #Anaesthesiology
Reference: Mehanna HM, Moledina J. Refeeding syndrome: What it is, and how to prevent and treat it. BMJ. 2008; 336(7659): 1495–1498
A FEW FACTS ABOUT THE ADJUSTABLE PRESSURE LIMITING (APL) VALVE
- When fully opened the APL valve maintains a pressure of around 1.5 cm of H2O
- As we close the APL valve, the pressure builds up inside
- There is a safety overpressure release valve incorporated in modern APL valves, to avoid this rising to dangerous levels. This system starts opening at a pressure of 30 cm of H2O and fully opens at 60 cm of H2O and at this point, allows the gases to escape at a rate of 50L/ min
- When the patient inspires, the APL valve , if intact, should not allow entrainment of air from the environment
- As the modern reservoir bags are less compliant, compared to the older latex ones, the importance of overpressure relief valves has increased
- As the APL valve will always produce a small resistance to expiration, even when maximally loosened, it helps to maintain PEEP
AMNIOTIC FLUID EMBOLISM (AFE) : WHICH ARE THE CONSISTENT CLINICAL FEATURES @ PRESENTATION?
Hypotension , Hypoxemia and DIC are hallmarks (MNEMO> “AFE is Highly Dangerous”)
Hypotension & Fetal Distress occur in 100% of cases
DIC occur in 83% and indicate a bad prognosis
Cardiac arrest occur in around 87% of patients
Mortality is >60% ; it has been observed that only 15% survive with intact neurological function
Pulmonary Hypertension, CHF and DIC are key events in the pathogenesis
Pulmonary edema (occur in >90% of cases), Dyspnoea (occur in 49%) & Bronchospasm (occur in 15%) are the respiratory signs
Reference: Dedhia JD, Mushambi M. Amniotic fluid embolism. Contin Educ Anaesth Crit Care Pain. 2007; 7(5): 152–156. Gist RS, Stafford IP, Leibowitz AB et al. Amniotic fluid embolism. Anaesth Analg. 108(5): 1599–1602.
The Risk Factors as per EuroSCORE II System used for risk stratification of patients undergoing Cardiac Surgery
Patient factors
• Sex: Female
• Age: >60 years
• Co-morbidities including renal, neurological and extra-cardiac arterial disease
Disease factors
• Recent MI
• Left ventricular dysfunction
• Unstable angina
Operative factors
• Redo or emergency surgery
• Non-isolated coronary artery bypass grafting
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
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?
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
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
#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
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.
The Lay Medical Man 