Hawthorne effect explains the change in any behavioural aspect owing to the awareness that the person is being observed.
Simpson’s Paradox explains the association developed when the data from several groups is combined to form a single larger group.

The remaining terms are made up.

To denote large measured units, the following SI mathematical prefixes are used:

1 deca = 10 bytes (101)
1 hecto (h) = 100 bytes
1 kilo (k)= 1,000 bytes
1 mega (M) = 1,000,000 bytes
1 giga (G) = 1,000,000,000 bytes
1 Tera (T) = 1,000,000,000,000 bytes
1 Peta (P) = 1,000,000,000,000,000 bytes

The intrinsic pathway is best assessed by the aPTT time.

D-dimer is a fibrin degradation product which is raised in the presence of blood clots.

A 50:50 mixing study is used to assess if a prolonged PT or aPTT is due to factor deficiency or a factor inhibitor.

The thrombin time is a test used to assess fibrin formation from fibrinogen in plasma. Factors that prolong the thrombin time include heparin, fibrin degradation products, and fibrinogen deficiency.

Intrinsic pathway – Best assessed by APTT. Factors 8,9,11,12 are involved. Prolonged aPTT can be seen in haemophilia and use of heparin.

Extrinsic pathway – Best assessed by Increased PT. Factor 7 involved.

Common pathway – Best assessed by APTT & PT. Factors 2,5,10 involved.

Vitamin K dependent factors are factors 2,7,9,10

The commonest and most likely cause of a gradual rise in end-tidal CO2 (EtCO2) occurring during anaesthesia in a spontaneously breathing patient is hypoventilation. This occurs from the respiratory depressant effects of the opioid and sevoflurane.

Malignant hyperthermia should be sought if the EtCO2 shows further progressive rise.

Causes of rebreathing and a rise in the baseline of the capnograph can be caused by exhausted soda lime and inadequate fresh gas flow into the Bain circuit.

A sudden rise in EtCO2 can be caused deflation of the tourniquet.

Selection bias is when randomisation is not achieved and is often a result of in efficient recruiting method.

Recall bias is specifically appropriate to the case control studies that is when ever the memories retrieved by the participants differ in accuracy.

Measurement bias can be characterized by gathering of information in a manner that is distorted.

When the participants of a research study are recruited from the hospitals rather than the general population, its called Berkson Bias.

Confounding bias is the major player here because in this case the effects of smoking can be masked behind and can be read as outcomes of lower socio economic status. This extraneous factor (Smoking), distorts the founding.

Krebs’ cycle (tricarboxylic acid cycle or citric acid cycle) is a sequence of reactions in which acetyl coenzyme A (acetyl-CoA) is metabolised and this results in carbon dioxide and hydrogen atoms production.

This series of reactions occur in the mitochondria of eukaryotic cells, not the cytoplasm. The cycle requires oxygen and so, cannot function under anaerobic conditions.

It is the common pathway for carbohydrate, fat and some amino acids oxidation and is required for high energy phosphate bond formation in adenosine triphosphate (ATP).

When pyruvate enters the mitochondria, it is converted into acetyl-CoA. This represents the formation of a 2 carbon molecule from a 3 carbon molecule. There is loss of one CO2 but formation of one NADH molecule. Acetyl-CoA is condensed with oxaloacetate, the anion of a 4 carbon acid, to form citrate which is a 6 carbon molecule.

Citrate is then converted into isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, malate and finally oxaloacetate.

The only 5 carbon molecule in the cycle is alpha-ketoglutarate.

The left atrium is supplied by the left coronary artery and its major branch the left circumflex.

The heart receives blood supply from coronary arteries. The right and left coronary arteries branch off the aorta and supply oxygenated blood to all heart muscle parts.

The left main coronary artery branches into:
1. Circumflex artery – supplies the left atrium, side, and back of the left ventricle. The left marginal artery arises from the left circumflex artery. It travels along the obtuse margin of the heart.
The left marginal artery, a branch of the circumflex artery, supplies the left ventricle.
2. Left Anterior Descending (LAD) artery – supplies the front and bottom of the left ventricle and front of the interventricular septum

The right coronary artery branches into:
1. Right marginal artery
2. Posterior descending artery

The right coronary artery supplies the right atrium, right ventricle, interatrial septum, and the inferior posterior third of the interventricular septum. It also supplies the atrioventricular node + sinoatrial node in most patients. The posterior descending artery supplies the posterior third of the interventricular septum.

The patient is likely suffering from biliary colic since her pain is intermittent and comes and goes in waves. Biliary colic pain gets worse after eating, especially fatty food as bile helps digest fats. Gallstones are the most common cause of biliary colic and are usually located in the cystic duct or common bile duct. But since this patient has no signs of jaundice or steatorrhea, the duct most likely blocked is the cystic duct.

The cystic duct drains the gallbladder and combines with the common hepatic duct to form the common bile duct. The common bile duct then merges with the pancreatic duct and opens into the second part of the duodenum (major duodenal papilla).

The duodenojejunal flexure is attached to the diaphragm by the ligament of Treitz and is not associated with any common pathology.
The fourth part of the duodenum passes very close to the abdominal aorta and can be compressed by an abdominal aortic aneurysm.
The third part of the duodenum can be affected by superior mesenteric artery syndrome, where the duodenum is compressed between the SMA and the aorta, often in cases of reduced body fat.
The first part of the duodenum is the most common location for peptic ulcers affecting this organ.

Phosphate is the principal anion of the intracellular fluid, most of which is bound to either lipids or proteins. They dissociate or associate with different compounds, depending on the enzymatic reaction, thus forming a constantly shifting pool.

Calcium and magnesium are also present intracellularly, however in lesser amounts than phosphate.

Sodium is the most abundant extracellular cation, and Chloride and is the most abundant extracellular anion.

Doxazosin is selective alpha 1 blocker (it causes less tachycardia than a non-selective alpha-blocker) and is the drug of choice for a patient with hypertension and benign hyperplasia of the prostate (BHP).

The major adverse effect of an alpha-blocker is first-dose hypotension.

Atenolol and Labetalol are beta blockers. It works by relaxing blood vessels and slowing heart rate to improve blood flow and decrease blood pressure.

Clonidine is an α2A-adrenergic agonist used to treat high blood pressure, ADHD, drug withdrawal (alcohol, opioids, or nicotine), menopausal flushing, diarrhea, spasticity, and certain pain conditions.

Methyldopa is a centrally-acting alpha-2 adrenergic agonist used to manage hypertension alone or in combination with hydrochlorothiazide, and to treat hypertensive crises.

There are four parathyroid glands that lie on the medial half of the posterior surface of each lobe of the thyroid gland, inside its sheath. There are two superior and two inferior parathyroid glands.

The common carotid artery is a lateral relation of the inferior parathyroid.

The cricoid cartilage is a hyaline cartilage ring surrounding the trachea. It provides support for key phonation muscles.

The inferior border of the cricoid cartilage is attached to the thyroid cartilage and the inferior border is attached to the first tracheal ring through the cricotracheal ligament.

Application of pressure to the cricoid cartilage to reduce risk of aspiration of gastric contents (Sellick manoeuvre) does not stop tracheal aspiration and cannot stop regurgitation into the oesophagus.

A force of 44 newtons to the cricoid cartilage is needed to control regurgitation.

The tibial nerve lies on top of the vessels contained within the inferior aspect of the popliteal fossa.

In the superior aspect of the fossa, the tibial nerve runs lateral to the vessels, before then travelling superficial to the vessels, and then finally changing course to lie medial to the vessels.

The popliteal artery is the most deep structure present in the popliteal fossa

With regards to the autonomic nervous system (ANS)

1. It is not under voluntary control
2. It uses reflex pathways and different to the somatic nervous system.
3. The hypothalamus is the central point of integration of the ANS. However, the gut can coordinate some secretions and information from the baroreceptors which are processed in the medulla.

With regards to the central nervous system (CNS)
1. There are myelinated preganglionic fibres which lead to the
ganglion where the nerve cell bodies of the non-myelinated post ganglionic nerves are organised.
2. From the ganglion, the post ganglionic nerves then lead on to the innervated organ.

Most organs are under control of both systems although one system normally predominates.

The nerves of the sympathetic nervous system (SNS) originate from the lateral horns of the spinal cord, pass into the anterior primary rami and then pass via the white rami communicates into the ganglia from T1-L2.

There are short pre-ganglionic and long post ganglionic fibres.
Pre-ganglionic synapses use acetylcholine (ACh) as a neurotransmitter on nicotinic receptors.
Post ganglionic synapses uses adrenoceptors with norepinephrine / epinephrine as the neurotransmitter.
However, in sweat glands, piloerector muscles and few blood vessels, ACh is still used as a neurotransmitter with nicotinic receptors.

The ganglia form the sympathetic trunk – this is a collection of nerves that begin at the base of the skull and travel 2-3 cm lateral to the vertebrae, extending to the coccyx.

There are cervical, thoracic, lumbar and sacral ganglia and visceral sympathetic innervation is by cardiac, coeliac and hypogastric plexi.

Juxta glomerular apparatus, piloerector muscles and adipose tissue are all organs under sole sympathetic control.

The PNS has a craniosacral outflow. It causes reduced arousal and cardiovascular stimulation and increases visceral activity.

The cranial outflow consists of
1. The oculomotor nerve (CN III) to the eye via the ciliary ganglion,
2. Facial nerve (CN VII) to the submandibular, sublingual and lacrimal glands via the pterygopalatine and submandibular ganglions
3. Glossopharyngeal (CN IX) to lungs, larynx and tracheobronchial tree via otic ganglion
4. The vagus nerve (CN X), the largest contributor and carries ¾ of fibres covering innervation of the heart, lungs, larynx, tracheobronchial tree parotid gland and proximal gut to the splenic flexure, liver and pancreas

The sacral outflow (S2 to S4) innervates the bladder, distal gut and genitalia.

The PNS has long preganglionic and short post ganglionic fibres.
Preganglionic synapses, like in the SNS, use ACh as the neuro transmitter with nicotinic receptors.
Post ganglionic synapses also use ACh as the neurotransmitter but have muscarinic receptors.

Different types of these muscarinic receptors are present in different organs:
There are:
M1 = pupillary constriction, gastric acid secretion stimulation
M2 = inhibition of cardiac stimulation
M3 = visceral vasodilation, coronary artery constriction, increased secretions in salivary, lacrimal glands and pancreas
M4 = brain and adrenal medulla
M5 = brain

The lacrimal glands are solely under parasympathetic control.

Staphylococcus aureus infection is the most likely cause.

Surgical site infections (SSI) occur when there is a breach in tissue surfaces and allow normal commensals and other pathogens to initiate infection. They are a major cause of morbidity and mortality.

SSI comprise up to 20% of healthcare associated infections and approximately 5% of patients undergoing surgery will develop an SSI as a result.
The organisms are usually derived from the patient’s own body.

Measures that may increase the risk of SSI include:
-Shaving the wound using a single use electrical razor with a disposable head
-Using a non iodine impregnated surgical drape if one is needed
-Tissue hypoxia
-Delayed prophylactic antibiotics administration in tourniquet surgery, patients with a prosthesis or valve, in clean-contaminated surgery of in contaminated surgery.

Measures that may decrease the risk of SSI include:
1. Intraoperatively
– Prepare the skin with alcoholic chlorhexidine (Lowest incidence of SSI)
-Cover surgical site with dressing

In contrast to previous individual RCT’s, a recent meta analysis has confirmed that administration of supplementary oxygen does not reduce the risk of wound infection and wound edge protectors do not appear to confer benefit.

2. Post operatively
Tissue viability advice for management of surgical wounds healing by secondary intention

Use of diathermy for skin incisions
In the NICE guidelines the use of diathermy for skin incisions is not advocated. Several randomised controlled trials have been undertaken and demonstrated no increase in risk of SSI when diathermy is used.

ANOVA is based upon within group variance (i.e. the variance of the mean of a sample) and between group variance (i.e. the variance between means of different samples). The test works by finding out the ratio of the two variances mentioned above. (Commonly known as F statistic).

Work up bias involves comparing the novel diagnostic test with the current standard test. A portion of the patients undergo the standard test while others undergo the new test as the standard test is costly. The result can be alteration in specify and sensitivity.

Recall bias is specifically appropriate to the case control studies that is when ever the memories retrieved by the participants differ in accuracy.

Not publishing the results of a valid study just because they are negative or uninteresting can be termed as publication bias.

When information gathering is ill suited with respect to time i.e. collecting the data regarding a fatal disease many years after the death of its patients, it is termed as Late – look bias.

The case in point is an instance of lead time bias when upon comparing two tests, one is able to detect the condition earlier than the other but the overall outcome doesn’t change. There is a possibility that this will make the survival rates for the newer test look more promising.

According to the Safe Anaesthesia Liaison Group, the most important factor to consider the cannula access, and if the patient is properly receiving the total intravenous anaesthesia. The cannula access must be regularly checked for kinks, leaks and disconnections.

Below are the safety precautions and policies to be followed for total intravenous anaesthesia among children and adults:

When administering TIVA, a non-return valve must be used on any intravenous fluid line;
When using equipment, it is essential that clinical staff know its limitations and uses;
Sites of intravenous infusions should be visible so they may be monitored for disconnection, leaks or perivenous infusion into the subcutaneous tissues; and,
Organisations must give preference to clearly labelled intravenous connectors and valves.

Cardiopulmonary exercise testing (CPX, CPEX, CPET) is a non-invasive testing method used to determine the performance of the heart, lungs and skeletal muscle. It measures the exercise tolerance of the patient.

The parameters measured include:

ECG and ST-segment analysis and blood pressure
Oxygen consumption (VO2)
Carbon dioxide production (VCO2)
Gas flows and volumes
Respiratory exchange ratio (RER)
Respiratory rate
Anaerobic threshold (AT)

The anaerobic threshold (AT) is an estimate of exercise ability. Any measurement below 11 ml/kg/min is usually related with an increase in mortality, especially when there is a background of myocardial ischaemia occurring during the test.

Peak VO2 <20 mL/kg with a low AT have a correlation with postoperative complications and a 30 day mortality. The CPX test is used for risk-testing patients prior to surgery to determine the appropriate postoperative care facilities. The V slope measured in CPX testing represents VO2 versus VCO2 relationship. During AT, the ramp of V slope increases, but does not provide a picture of postoperative mortality.

Both incidence and prevalence are indicators of the disease frequency. While incidence tells us about the number of cases reported per population in a provided time period, prevalence is the factor you should be vigilant about as it tells us about the total number of cases that have been reported in a population at a particular point of time.

The cardiac action potential has several phases which have different mechanisms of action as seen below:
Phase 0: Rapid depolarisation – caused by a rapid sodium influx.
These channels automatically deactivate after a few ms

Phase 1: caused by early repolarisation and an efflux of potassium.

Phase 2: Plateau – caused by a slow influx of calcium.

Phase 3 – Final repolarisation – caused by an efflux of potassium.

Phase 4 – Restoration of ionic concentrations – The resting potential is restored by Na+/K+ATPase.
There is slow entry of Na+into the cell which decreases the potential difference until the threshold potential is reached. This then triggers a new action potential

Of note, cardiac muscle remains contracted 10-15 times longer than skeletal muscle.

Different sites have different conduction velocities:
1. Atrial conduction – Spreads along ordinary atrial myocardial fibres at 1 m/sec

2. AV node conduction – 0.05 m/sec

3. Ventricular conduction – Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles

The ?-2 adrenoceptor has three subtypes (2a, 2b and 2c). The receptors are generally presynaptic, meaning they prevent noradrenaline from being released at nerve endings. Both the central and peripheral nerve systems are affected by the ?-2 agonists. ?-2 agonists cause drowsiness, analgesia, and euphoria centrally in the locus coeruleus (in the brainstem), lower the MAC of volatile anaesthetic drugs, and are used to treat acute withdrawal symptoms in chronic opioid addicts.

The most common impact of ?-2 agonists on heart rate is bradycardia. The adrenoreceptors ?-1 and ?-2 are blocked by phenoxybenzamine.

Clonidine is a selective agonist for the ? -2 receptor, having a 200:1 affinity ratio for the ?-2: ?-1 receptors, respectively.

Tizanidine is similar to clonidine but has a few key variances. It has the same sedative, anxiolytic, and analgesic characteristics as clonidine, although for a shorter period of time and with less effect on heart rate and blood pressure.

Dexmedetomidine, like clonidine, is a highly selective ?-2 adrenoreceptor agonist having a higher affinity for the ?-2 receptor. In the case of ?-2: ?-1 receptors, the affinity ratio is 1620:1. It has a biphasic blood pressure impact and induces a brief rise in blood pressure and reflex bradycardia (activation of ?-2b subtypes of receptors in vascular smooth muscles), followed by a reduction in sympathetic outflow from the brainstem and hypotension/bradycardia.

A prodrug is methyldopa. It blocks the enzyme dopa-decarboxylase, which converts L-dopa to dopamine (a precursor of noradrenaline and adrenaline). It is also converted to alpha-methyl noradrenaline, a centrally active agonist of the ?-2 adrenoreceptor. These two processes contribute to its blood pressure-lowering effect. Without a rise in heart rate, cardiac output is generally maintained. The heart rate of certain patients is slowed.

Phentolamine is a short-acting antagonist of peripheral ?-1 and ?-2 receptors that causes peripheral vascular resistance to reduce and vasodilation to increase. It’s used to treat hypertensive situations that aren’t life threatening (e.g. hypertension from phaeochromocytoma).

A baroreceptor reflex commonly causes reflex tachycardia when systemic vascular resistance drops.

Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Using these values, you can determine the concentrations of solutions.

The reasons for adding adrenaline to a local anaesthetic solution are:

1. To Increase the duration of block
2. To reduce absorption of the local anaesthetic into the circulation
3. To Increase the upper safe limit of local anaesthetic (2.5 mg/kg instead of 2 mg/kg, in this case).

The addition of adrenaline to bupivacaine does not affect its potency, lipid solubility, protein binding, or pKa(8.1 with or without adrenaline).

The pH of bupivacaine is between 5-7. Premixed with adrenaline, it is 3.3-5.5.
The onset of a local anaesthetic and its ability to penetrate membranes depends upon degree of ionisation. Compared with the ionised fraction, unionised local anaesthetic readily penetrates tissue membranes to site of action. The onset of action of solution B is slower. this is because the relationship between pKa(8.1) and pH(3.3-5.5) of the solution results in a greater proportion of ionised local anaesthetic molecules compared with solution A.

Gas is composed of large numbers of molecules moving in random directions, separated by distances. They undergo perfectly elastic collisions with each other and the walls of a container and transfer kinetic energy in form of heat. These assumptions bring the characteristics of gases within the range and reasonable approximation to a real gas, particularly how any change in temperature and pressure affect the behaviour of gas. According to different theories and laws proposed, mathematical equations are derived to calculate the volume of gas, also different abbreviations are being used according to given conditions. The abbreviations used are ATP, BTPS, and STPD.
ATP stands for ambient temperature and barometric pressure, it is used to describe the conditions under which volume of gas is measured.
BTPS stands for body temperature and pressure saturated with water vapor. These are conditions under which volume of gas exist and all results of lung volume determination should be quoted at BTPS.
STPD stands for standard temperature and pressure, dry (0C and 760 mm Hg). These are the conditions that are used to describe quantities of individual gases exchanged in the lungs.

The laryngeal folds are comprised of two types of folds; the vestibular fold and the vocal fold. The vocal folds are mobile, and concerned with voice production. They are formed by the mucous membrane covering the vocal ligament. They are avascular, hence, are white in colour.

The internal branch of the superior laryngeal nerve provides sensation above the vocal cords. Lesions to this nerve may lead to loss of sensation above the vocal cords and loss of taste on the epiglottis.

The recurrent laryngeal nerve supplies the lateral and posterior cricoarytenoid, the thyroarytenoid. It also provides sensation below the vocal cords. Lesions to this nerve may cause respiratory obstruction, hoarseness, inability to speak and loss of sensation below the vocal cords.

The external branch of the superior laryngeal nerve supplies the cricothyroid muscle.

The glossopharyngeal nerve contains both sensory and motor components, and provides somatic innervation to the stylopharyngeus muscle, visceral motor innervation to the parotid gland, and carries afferent sensory fibres from the posterior third of the tongue, pharynx and tympanic cavity.

When using dry soda lime for VOCs, very high amounts of carbon monoxide may be produced, regardless of the inhalational anaesthetic agent used. The carbon monoxide produced is sufficient enough to cause cytotoxic and anaemic hypoxia. To prevent this, soda lime canisters are shaken well to even out the packing of granules. This can help to evenly distribute gas flow for proper CO2 absorption and ventilation.

Compound A is formed when dry soda lime, or soda lime in high temperature, reacts with the inhalational anaesthetic Sevoflurane. Animal studies have shown renal toxicity in rats, but renal adverse effects in humans are yet to be observed.

When monitors are not employed with VOCs, deleterious effects are not for certain. However, monitors not employed with vaporiser inside the circuit (VIC) can lead to significant adverse events.

Bilirubin is the tetrapyrrole and a catabolic product of heme. 70-90% of bilirubin is end product of haemoglobin degradation in the liver.

Bilirubin circulates in the blood in 2 forms; unconjugated and conjugated bilirubin.

Unconjugated bilirubin is insoluble in water. It travels through the bloodstream to the liver, where it changes from insoluble into a soluble form (i.e.; unconjugated into conjugated form).

This conjugated bilirubin travels from the liver into the small intestine and the gut bacteria convert bilirubin into urobilinogen and then into urobilin (not urobilin to urobilinogen). A very small amount passes into the kidneys and is excreted in urine.

Cardiac conduction

Phase 0 – Rapid depolarization. Opening of fast sodium channels with large influx of sodium

Phase 1 – Rapid partial depolarization. Opening of potassium channels and efflux of potassium ions. Sodium channels close and influx of sodium ions stop

Phase 2 – Plateau phase with large influx of calcium ions. Offsets action of potassium channels. The absolute refractory period

Phase 3 – Repolarization due to potassium efflux after calcium channels close. Relative refractory period

Phase 4 – Repolarization continues as sodium/potassium pump restores the ionic gradient by pumping out 3 sodium ions in exchange for 2 potassium ions coming into the cell. Relative refractory period

The internal jugular vein is found on both sides of the neck and collects blood from the brain, superficial regions of the face, and neck. It drains into the right atrium.

It is a continuation of the sigmoid sinus and begins in the posterior cranial fossa and exits the skull via the jugular foramen.
It runs within the carotid sheath as it descends in the neck and is accompanied by the vagus nerve posteriorly and the common carotid anteromedially.

The hypoglossal nerve emerges from the hypoglossal canal medial to the internal carotid artery and the internal jugular vein and ninth, tenth, and eleventh cranial nerves.

The internal jugular vein crosses anterior to the thoracic duct on the left side.