General Anaesthesia

General Anaesthesia

There are intravenous and inhalational agents used in general anaesthesia to achieve loss of conciousness. The most widely used intravenous agents are,

·        Thiopentone sodium

·        Propofol

·        Ketamin

The widely used inhalational agents are,

·        Halothane

·        Isoflorane

·        Sevoflorane

Thiopentone Sodium

·        Thiopentone sodium is a barbiturate.

·        Dose – 4mg/kg

·        Produce anaesthesia in less than 30 seconds.

·        Consciousness is regained in 5-10 minutes.

·        Other effects- precipitate laryngeal and bronchospasms

                     Depress respiration, apnoea may occur

                     Depress the myocardium

                     Produce peripheral vasodilatation

·        Metabolized in the liver and excreted via the kidneys.

·        Contraindications – porphyria

                             Airway obstruction

                             Bronchial spasms

Propofol

·        A non barbiturate

·        Dose – 2-2.5 mg/kg

·        For induction and maintenance (TIVA)

·        Rapid recovery

·        Little hang over effect

·        Less incidences of post operative nausea and vomiting

·        Laryngeal and pharyngeal reflexes are depressed to a greater degree, and tracheal intubation can be achieved with Propofol alone.

·        Other effects – Apnoea

Arterial vasodilatation

Pain on injection

·        CI – children

       Pregnancy

       Electroconvulsive therapy

Ketamin

·        An non barbiturate

·        Produce dissociative anaesthesia

·        Dose – 1-2 mg/kg

·        Unconscious for 10-15 min

·        Potent analgesic

·        Muscle tone is maintained; therefore airway obstruction does not occur. Therefore, useful in difficult airway.

·        Pharyngeal and laryngeal reflexes are preserved.

·        Produce bronchodilatation – useful in asthmatics.

·        Other effects – increase heart rate

Increase arterial pressure (sympathomemetics activity)

Increased salivation – may require atropine

·        CI – Ischaemic heart disease

Hypertension

         Head injury

        Open eye injury

Other Intravenous general anaesthetic agents –

·        Etomidate – most cardiovascular stable induction agent

                      Less respiratory depression

                      CI – epilepsy

                             Adrenocortical insufficiency

·        Benzodiazepines – induction, sedation, anxiolytic, anticonvulsant, muscle relaxation

o   Diazepam

o   Midazolam

o   Flumazenil

Inhalational Agents

Halothane 

·        For induction and maintenance

·        0.5-2%

·        A bronchodilator

·        Lowers cardiac output and blood pressure

·        Sensitizes the myocardium to catecholamines.

·        Uterine relaxation at concentrations >2%

·        SE – hepatotoxicity

Isoflurane

·        Less myocardial depression

·        Arterial dilatation causes hypotension

Sevoflurane

·        Used in children

·        It is metabolized to flurane, which is hepatotoxic. Therefore, not used in patients with renal diseases.

·        Soda lime also degrades it into another hepatotoxic agent: Compound A.

Renal Failure: An Overview

How do they present

1.     Acumilation of fluid

2.     Reduction in Normal Renal Functions

Accumulation of fluid

 

• Generalized edema

o   Periorbital edema

o   Ascites

o   Ankle edema

• Pulmonary edema

 

Reduction in Normal Renal Functions

·        Uremic Symptoms

o   Nausea

o   Vomiting

o   Loss of apetite

·        In chronic renal failure

o   Anemia

o   Tiredness

o   Tachycardia

·        Hypertensive features

 

Differential Diagnosis

·        Renal Failure

·        Hypovoluemia

 

Immediate Management

·        Maintain an input output chart.

·        Take blood for,

o   Blood urea

o   Serum creatinine

o   Electrolytes

o   Full Blood Count

·        Do a fluid challenge.

·        Give 10 units of insulin along with 50 cc dextrose.

·        Take an ECG – Tall tempted T wawes

 

 How to find out the etiology of Renal Failure?

·        Investigations

   USS Abdomen

   X- Ray KUB

   Renal Biopsy

 

 Renal Failure is of two Types

·        Acute renal failure

·        Chronic renal failure

 

 Causes of Acute Renal Failure

o       Poisoning

• Snake Bites

§     Cobra

§     Viper

§     Hump nosed viper

o         Wasp Bites

o         Leptospirosis

o         Pyelonephritis

o         Bilateral Ureteric Obstruction

o         Heavy Metal Poisoning

o         Organic  compounds – Break Oil

o         Crush Injuries

 

Causes of Chronic Renal Failure

·        Diabetic Nephropathy

·        Persistent Long standing Hypertension

·        Recurrent Pyelonephritis

·        Renal Calculi

 

 

Treatment

·        Dialysis

·        Renal Transplant

·        Dugs

   Erythropoietin

   1 alpha Cholecalciferole

   Phosphate Binders

   Iron Supplements

   Folic acid

·        Management of the underlying Disease/s

 

 

No Improvement of Dandruff, after using every single anti-dandruff product available? It could be due to Psoriasis

Some people experience alopecia and dandruff. Most of the time this is due to dandruff, but some times it could be due to Psoriasis. If you have psoriatic lesions all over the body, it is not very hard to diagnose it. But if there are not any other significant lesions in other places of the body, the diagnosis becomes a little harder.

These people may go on trying various commercially available anti-dandruff agents, but still get no improvement. A dermatologist can easily differentiate such situations as psoriasis, only by looking at the lesion. How do they do that?

They do it by careful examination of the lesion. The psoriatic lesions are described as erythematous patches topped with large silvery scales. The key feature in differentiating these two is “large scales and patchy distribution”. Dandruff is usually distributed throughout the skull and psoriatic lesions presents as patched.  The psoriatic scales are large and dandruff scales are very small.

The dermatologist will do a thorough examination in other places too, and may find several such lesions in other parts of the body too. 

Why Patients in the ICU are made unconscious?

People are admitted to the ICU (Intensive care unit) due to various reasons. They are all critically ill people who need continuous care, support and monitoring. Out of these people, some are brought to the hospital when they are still conscious. They may be having difficulty in walking, talking and doing things, but they are still conscious. For example, people with head injury. But, after surgery, they are brought to the ICU and they remain unconscious for days. 

Some times this is not because they are actually unconscious. Sometimes they are unconscious because they are made unconscious. Now, you might think why? To understand this you should know what happens in head injury and after surgery.

If we take a brain hemorrhage, that is bleeding in side the brain, there is accumulation of blood and edema fluid within the skull. As the brain is in a confined cavity, the brain tissue gets compressed and herniated. If the pressure goes very high, the herniation can even cause death. Therefore the anaestherists take measures to reduce further brain edema. Meanwhile they should also prevent further brain damage by maintaining good blood flow to the brain.

The measures they take to achieve these targets involves 2 kinds of actions.

• Brain protection by maintaining -  

•  normal oxygen level
•  normal carbon dioxide level 
• normal pressure
• normal glucose level
• normal temperature
• normal blood volume

• Brain relaxation by – 

• Sedation                                  
• Paralyzing and ventilation
• Giving antiepileptics
• Positioning the patient in 20⁰ angle
• Neutral position of the neck and head
• Flexing the hip

As you can see the some of the above measures includes sedation and paralysis. The artificial ventilation also needs the patient to be in an inhibited state, so he/she won’t feel the uncomfortable instruments that are put in to their throats.  

As their conditions gradually starts to improve, the anaesthetists will slowly reduce the sedating drugs and make the patient able to talk. Then he/she is fit enough to go to a ward and get treatments.

                                   

 Emergency & Critical Care Pocket Guide 

Icu Intern Pocket Survival Guide (INTERN POCKET SURVIVAL GUIDE SERIES) 

Why we can’t give 100% Oxygen for People with Chronic Lung Diseases?

Some people suffer from chronic lung diseases like bronchiactasis, chronic obstructive pulmonary disease (COPD) etc. As the lung functions are compromised in these patients, there oxygen saturation of blood is decreased. Most of these people face acute exacerbations of the disease where the respiration becomes hard. 

IF you have chronic lung disease and face such situation, you may crave for oxygen. Some people ask for oxygen, sometimes the physician may not let you have any oxygen. Many patients become irritated when they face such problem. But, they should understand that it is the best way to manage. 

Why?

Now you must be wondering why. To understand it you should have a clear understanding about the physiology of respiration and how it is controlled. 

How the respiratory rate is maintained. 

The respiration is controlled by the respiratory centre situated in the brain stem. There are several inputs to this respiratory centre. They are,

• Inputs from the higher centers enabling voluntary control over respiration.
• Information from the peripheral circulation indicating the amounts of oxygen and Carbon Dioxide.
• Inputs from the chemoreceptor area situated near the respiratory centre which detects the amount of CO₂ present in the brain.

Out of above the inputs from the chemoreceptor area plays a major role. As the CO₂ in the brain increased the respiratory centre increases the respiratory rate to get rid of the excess CO₂. 

In chronic lung diseases they are persistently high amount of CO₂ in the brain making the respiratory centre insensitive to its presence. At this time the respiratory rate is maintained by the peripheral oxygen concentrations. If the peripheral oxygen content reduces the massage is sent to the respiratory centre to increase the respiratory rate.

So, if we give 100% oxygen for such person once the peripheral oxygen content raises the stimulation of the respiratory centre reduces. As a result the respiratory rate reduces. This ultimately leads to reduction of oxygen. Therefore, 100% oxygen is not given for patients with chronic lung diseases. 

Oxygen Therapies [VHS] 

Why Thiopentone sodium is not used as a maintenance agent?

Maintenance of unconsciousness requires the maintenance of an appropriate blood level of the anaesthetic agents. Thiopentone sodium is a drug which is highly soluble in lipid. Therefore, once it is injected in to a vein it reaches brain one arm brain circulation time. At the brain it passes through the blood brain barrier as it is lipid soluble. Due to these reasons thiopentone sodium has a rapid onset o faction. The drug comes out of the brain as quickly as it entered into the brain. This is the reason for rapid recovery of the person. On the other hand, as the drug is lipid soluble, it go and stored in the fat tissues. If a continuous infusions given, the drug may accumulate in the fat tissues.  Later they can be released back in to the blood, creating many     problems. Therefore, it is not used as a maintenance agent.