The inferior vena cava is formed by the union of the right and left common iliac veins. This occurs at the L5 vertebral level. The IVC courses along the right anterolateral side of the vertebral column and ascends through the central tendon of the diaphragm at the T8 vertebral level.

Compliance of the respiratory system describes the expandability of the lungs and chest wall. There are two types of compliance: dynamic and static.

Dynamic compliance describes the compliance measured during breathing, which involves a combination of lung compliance and airway resistance. Defined as the change in lung volume per unit change in pressure in the presence of flow.

Static compliance describes pulmonary compliance when there is no airflow, like an inspiratory pause. Defined as the change in lung volume per unit change in pressure in the absence of flow.

For example, if a person was to fill the lung with pressure and then not move it, the pressure would eventually decrease; this is the static compliance measurement. Dynamic compliance is measured by dividing the tidal volume, the average volume of air in one breath cycle, by the difference between the pressure of the lungs at full inspiration and full expiration. Static compliance is always a higher value than dynamic

Static compliance can be computed using the formula:

Cstat = Tidal volume/Plateau pressure – PEEP

Substituting the values given,

Cstat = 800/50-10
Cstat = 20 ml/cmH2O

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.

A nominal volume of 2 litres is contained in a CD cylinder. It has a pressure of 230 bar when full and contains litres 460 L of useable oxygen at STP.

For every 1000 mL 100% oxygen there will be an entrainment of 1000 mL or air (20% oxygen) in an air/oxygen mix.

The average concentration is, therefore, 120/2=60% or 0.6.

Detsky’s Modified cardiac risk classification system in patients undergoing non-cardiac surgery:

Age more than 70: 05 points

History of myocardial infarction:

Less than 6 months: 10 points
More than 6 months: 5 points

Angina Pectoris:

Angina with minimal exertion: 10 points

Angina at any level of exertion: 20 points

Pulmonary Oedema:

Within 7 days: 10 points
At any time: 5 points

Suspected aortic valve stenosis with valve area <0.6cm2: 20 points Arrhythmia: Any rhythm other than sinus or sinus with premature atrial complexes (PACs): 5 points More than 5 premature ventricular contractions: 5 points
Emergency Surgery: 10 points
Deficient general medical condition: 5 points

Risk classification:

Grade I: 0-15 points = low risk
Grade II: 15-30 points = moderate risk
Grade III: >30 points = high risk

Adenosine receptors are expressed on the surface of most cells.
Four subtypes are known to exist which are A1, A2A, A2B and A3.

Of these, the A1 and A2 receptors are present peripherally and centrally. There are agonists at the A1 receptors which are antinociceptive, which reduce the sensitivity to a painful stimuli for the individual. There are also agonists at the A2 receptors which are algogenic and activation of these results in pain.

The role of adenosine and other A1 receptor agonists is currently under investigation for use in acute and chronic pain states.

Muscle fibre myosin ATPase histochemistry is used to divide the biochemical classification into two groups: type 1 and type II.

Type I (slow twitch) muscle fibres rely on aerobic glycolytic and aerobic oxidative metabolism to function. They have a lot of mitochondria, a good blood supply, a lot of myoglobin, and they don’t get tired easily.

Because they contain more motor units, Type II (fast twitch) muscle fibres are thicker. They are more easily fatigued, but produce powerful bursts. The capillary networks and mitochondria are less dense in these white muscle fibres than in type I fibres. They have a low myoglobin content as well.

Muscle fibres of type II (fast twitch) are divided into three types:

Type IIa – aerobic/oxidative metabolism is used.
Type IIb – anaerobic/glycolytic metabolism is used by these fibres.

When compared to skeletal muscle, cardiac and smooth muscle twitch at a slower rate.

Second messengers relay signals to target molecules in the cytoplasm or nucleus when an agonist interacts with a receptor on the cell surface. They also amplify the strength of the signal. The most ubiquitous and abundant second messenger is calcium and it regulates multiple cellular functions in the body.

These include:
Muscle contraction (skeletal, smooth and cardiac)
Exocytosis (neurotransmitter release at synapses and insulin secretion)
Apoptosis
Cell adhesion to the extracellular matrix
Lymphocyte activation
Biochemical changes mediated by protein kinase C.

cAMP is either inhibited or stimulated by G proteins.

The receptors in the body that stimulate G proteins and increase cAMP include:

Beta (?1, ?2, and ?3)
Dopamine (D1 and D5)
Histamine (H2)
Glucagon
Vasopressin (V2).

The second messenger for the action of nitric oxide (NO) and atrial natriuretic peptide (ANP) is cGMP.

The second messengers for angiotensin and thyroid stimulating hormone are inositol triphosphate (IP3) and diacylglycerol (DAG).

Sugammadex is a modified cyclodextrin that works as an aminosteroid neuromuscular blocking (nmb) reversal agent. By encapsulating each molecule in the plasma, it rapidly reverses rocuronium and, to a lesser extent, vecuronium-induced neuromuscular blockade. Consequently, a  concentration gradient favours the movement of these nmb agents away from the neuromuscular junction.  Pancuronium-induced neuromuscular blockade at low levels has also been reversed.

By inhibiting voltage-dependent calcium channels at the neuromuscular junction, antibiotics in the aminoglycoside group potentiate neuromuscular blocking agents. This can be reversed by giving calcium but not neostigmine or sugammadex.

Sugammadex will not reverse the effects of mivacurium, which belongs to the benzylisoquinolinium class of drugs.

A phase II or desensitisation block occurs when the motor end-plate becomes less sensitive to acetylcholine as a result of an overdose or repeated administration of suxamethonium. The use of neostigmine has been shown to be effective in reversing this weakness.

An ankle block is commonly used for anaesthesia and postoperative analgesia when operating on bunions. It results in the selective block of the superficial peroneal, deep peroneal, and posterior tibial nerves.

The deep peroneal nerve supplies sensory input to the web space between the first and second toes (L4-5).

The L2-S1 nerve, often known as the superficial peroneal nerve, is a mixed motor and sensory neuron. It gives sensory supply to the anterolateral region of the leg, the anterior aspect of the 1st, 2nd, 3rd, and 4th toes, and innervates the peroneus longus and brevis muscles (with the exception of the web space between 1st and 2nd toes).

The sensory area of the saphenous nerve (L3-4) in the foot stretches from the proximal portion of the midfoot on the medial side to the proximal part of the midfoot on the lateral side.

The lateral side of the little (fifth) toe is innervated by the sural nerve’s sensory supply (S1-2). The heel, medial (medial plantar nerve), and lateral (lateral plantar nerve) soles of the foot are all served by the posterior tibial nerve.

Control of Substances Hazardous to Health (COSHH) was established by government under the Health and Safety at Work act in 1989. Their employers work on identification and management of those substances that are dangerous to health. The implications for anaesthetists include gas scavenging, equipment contamination and environmental safety. Adequate ventilation is required in areas where anaesthetic gases are present. The minimum air supply that is legally required in each specific area is: Operating theatres: 0.65 m3/second. Anaesthetic rooms: 0.15 m3/s. Preparation rooms: 0.1 m3/s. Recovery rooms need 15 air changes per hour

To begin, one must determine the child’s approximate weight. There are a variety of formulas to choose from. It is acceptable to use the advanced paediatric life support formula:

(Age + 4) 2 = Weight

A 5-year-old child will weigh around 18 kilogrammes.

10 mcg/kg (0.1 ml/kg of 1 in 10 000 adrenaline) = 180 mcg is the appropriate dose of intravenous or intraosseous adrenaline.

The correct energy level to deliver is 4 J/kg, which equals 72 joules.

The pad size that is appropriate for this patient is 8-12 cm. For an infant, a 4.5 cm pad is appropriate.

To allow adequate separation in infants and small children, the pads should be placed anteriorly and posteriorly on the chest.

When using a bag and mask to ventilate, take two breaths for every 15 chest compressions. If chest compressions are being applied intubated and without interruption, a ventilation rate of 10-20 breaths per minute should be given.

Chest compressions should be done at a rate of 100-120 per minute, the same as an adult.

Heme a exists in cytochrome a and heme c in cytochrome c; they are both involved in the process of oxidative phosphorylation. 5′-Aminolevulinic acid synthase (ALA-S) is the regulated enzyme for heme synthesis in the liver and erythroid cells.

There are two forms of ALA Synthase, ALAS1, and ALAS2.

Funnel plot is essentially a scatterplot of the effect of treatment against a particular measure of study precision. Its primal purpose is to serve as a visual aid and help in detection of bias or systematic heterogenity.

The incidence of vertebral canal haematoma following neuraxial blockade was reported (third National Audit Project (NAP3)) as 0.85 per 100 000 (95% CI 0-1.8 per 100 000). The incidence following neuraxial blockade in coagulopathic patients is likely to be higher hence coagulopathy remains a relative contraindication for conducting a spinal or epidural. When indicate, risk and benefits are weighed, and it is only performed by experienced personnel in this case.

Acceptable time to perform a block after the last dose of rivaroxaban in a patient with a creatinine clearance of greater than 30mL/minute is 18 hours.

Acceptable time to perform a block after the last dose of subcutaneous LMWH as prophylaxis is 12 hours.

Acceptable time to perform a block after the last dose of subcutaneous UFH as prophylaxis is 4 hours.

Acceptable time to perform a block after the last dose of thrombolytic therapy (streptokinase or alteplase) is 10 days.

Clopidogrel should be stopped 7 days prior to surgery, particularly if a central neuraxial procedure is considered.

The static-response defines how a measuring system behaves while it is in equilibrium (i.e. when the measured values are not changing). If the value being measured changes over time, the reaction of a measuring system will change as well which would be a dynamic response.
The dynamic response of a measuring system can be subdivided into zero-order, first-order and second-order responses:

Zero-order:
Consider a thermometer that has been left in a room for a week. The thermometer will display the current ambient temperature when you enter the room.

First-order:
Consider the use of a mercury thermometer to check a patient’s temperature. It is comprised of a mercury column that expands as it warms up. The scale’s initial temperature is room temperature, but when it’s placed under the patient’s tongue, the temperature readings rise until they reach body temperature.

Second-order
Consider putting weights on a mechanical weighing scale. The weight as reported on the measuring dial, will wobble around the correct value at first until reaching equilibrium. An example of this is in clinical practice is the direct measurement of arterial pressure with a transducer. The value of the input fluctuates around a central point.

Drift is the progressive deterioration of a measurement system’s precision. With time, the measurement deviates from the genuine, calibrated value. The graph between this measurement and the real value should, ideally, be linear (e.g. on the y-axis the measured end-tidal CO2 against true value of the end-tidal CO2). Drift is split into three types: zero-offset, gradient, and zonal drift.

Randomisation allows for performance of experimental trials in a random order. Using this method gives us control over the confounding variables that are not supposed to be held constant.

For an instance, by employing randomisation we get to control biological differences among individual human beings during experimental trials.

Ventricular fibrillation (VT) is an arrhythmia caused by a distortion in the organized contraction of the ventricles leading to an inability to pump blood out into the body.

Amiodarone is an anti arrhythmic drug used for the treatment of ventricular and atrial fibrillations. It is the gold standard of treatment for refractory pulseless ventricular tachycardia (VT) and ventricular fibrillation (VF).

Guidelines for emergency treatment state that only the rescuer carrying out chest compressions on the patient may stand near the defibrillator as it charges.

Cardio-pulmonary resuscitation (CPR) during cardiac arrest is required for 2 minute cycles.

Hypovolaemia is as a cause of pulseless electrical activity (PEA) can be reversed using fluid resuscitation, whereas hypotension during cardiac arrest is either persistent or undetectable and is therefore irreversible.

Hyperkalaemia and hypocalcaemia are treated using calcium salts, but calcium chloride is often preferred over calcium gluconate.

During a pulseless VT or VF, a single precordial thump will be effective if administered within the first seconds of the occurrence of a shockable rhythm.

The Nernst equation is used to calculate the membrane potential at which the ions are in equilibrium across the cell membrane.

The normal resting membrane potential is -70 mV (not + 70 mV).

The equation is:
E = RT/FZ ln {[X]o
/[X]i}

Where:
E is the equilibrium potential
R is the universal gas constant
T is the absolute temperature
F is the Faraday constant
Z is the valency of the ion
[X]o is the extracellular concentration of ion X
[X]i is the intracellular concentration of ion X.

When the loading dose of Digoxin is given, the primary thing to consider is the volume of distribution. The volume of distribution is the proportionality factor that relates the total amount of drug in the body to the concentration. LD is computed as:

LD = Volume of distribution X (desired plasma concentration/bioavailability)

Digoxin is an anti-arrhythmic drug with a large volume of distribution and high bioavailability, and only a small percentage of Digoxin is bound to plasma proteins (,20%).

In the case, since the arrhythmia is not life-threatening, there is no need for the medication to work rapidly.

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.

The functional residual capacity (FRC) is the volume in the lungs at the end of passive expiration. It is determined by opposing forces of the expanding chest wall and the elastic recoil of the lung. A normal FRC = 1.7 to 3.5 L. It a marker for lung function, and, during this time, the alveolar pressure is equal to the atmospheric pressure.

FRC cannot be measured by spirometry because it contains the residual volume.

Tidal volume, inspiratory reserve volume, forced expiratory volume in 1 second, and vital capacity can be measured directly.

Tramadol is weak agonist at the mu receptor. It inhibits the neuronal reuptake of serotonin and norepinephrine, and inhibits pain neurotransmission. It is given for moderate pain, chronic pain syndromes, and neuropathic pain.

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI). It inhibits the neuronal reuptake of serotonin by inhibiting the serotonin transporter (SERT). It is the drug of choice for major depressive disorder, and is given for other psychiatric disorders such as anxiety, obsessive-compulsive, post-traumatic stress, and phobias.

When tramadol is given with SSRIs, serotonin syndrome may occur. Serotonin syndrome is characterized by fever, agitation, tremors, clonus, hyperreflexia and diaphoresis. The onset of symptoms may occur within a few hours, and the first-line treatment is sedation, paralysis, intubation and ventilation.

The anterior cerebral artery supplies the midline portion of the frontal lobe and the superior medial parietal lobe of the brain. It also supplies the front four-fifths of the corpus callosum and provides blood to deep structures such as the anterior limb of the internal capsule, part of the caudate nucleus, and the anterior part of the globus pallidus.

The cerebral hemispheres are supplied by arteries that make up the Circle of Willis. The Circle of Willis is formed by the anastomosis of the two internal carotid arteries and two vertebral arteries.

Clinically, the internal carotid arteries and their branches are often referred to as the anterior circulation of the brain. The anterior cerebral arteries are connected by the anterior communicating artery. Near their termination, the internal carotid arteries are joined to the posterior cerebral arteries by the posterior communicating arteries, completing the cerebral arterial circle around the interpeduncular fossa, the deep depression on the inferior surface of the midbrain between the cerebral peduncles.

The middle cerebral artery supplies part of the frontal, temporal and parietal lobes.

The posterior cerebral artery supplies the occipital lobe.

With regards to compensatory response to blood loss, the following sequence of events take place:

1. Decrease in venous return, right atrial pressure and cardiac output
2. Baroreceptor reflexes (carotid sinus and aortic arch) are immediately activated
3. There is decreased afferent input to the cardiovascular centre in medulla. This inhibits parasympathetic reflexes and increases sympathetic response
4. This results in an increased cardiac output and increased SVR by direct sympathetic stimulation. There is increased circulating catecholamines and local tissue mediators (adenosine, potassium, NO2)
5. Fluid moves into the intravascular space as a result of decreased capillary hydrostatic pressure absorbing interstitial fluid.

A slower response is mounted by the hypothalamus-pituitary-adrenal axis.
6. Reduced renal blood flow is sensed by the intra renal baroreceptors and this stimulates release of renin by the juxta-glomerular apparatus.
7. There is cleavage of circulating Angiotensinogen to Angiotensin I, which is converted to Angiotensin II in the lungs (by Angiotensin Converting Enzyme ACE)

Angiotensin II is a powerful vasoconstrictor that sets off other endocrine pathways.
8. The adrenal cortex releases Aldosterone
9. There is antidiuretic hormone release from posterior pituitary (also in response to hypovolaemia being sensed by atrial stretch receptors)
10. This leads to sodium and water retention in the distal convoluted renal tubule to conserve fluid
Fluid conservation is also aided by an increased amount of cortisol which is secreted in response to the increase in circulating catecholamines and sympathetic stimulation.

A ‘double blind crossover study’ happens when every patient receive both treatments.

It is incorrect to say that only half of the patients do not know which treatment they receive because in a double blind placebo control clinical trial ALL of the patients are blind to their treatment choice .

If some of the patients are not treated, they would be aware that they were not being treated and it could not be considered a blind trial.

In a double blind placebo control clinical trial both the clinician and the patient are blind to the treatment choice. The clinician assessing the effects of the treatment, therefore, does not know which treatment the patient has been given.

There are different types of temperature measurement. These include:

Thermistor – this is a type of semiconductor, meaning they have greater resistance than conducting materials, but lower resistance than insulating materials. There are small beads of semiconductor material (e.g. metal oxide) which are incorporated into a Wheatstone bridge circuit. As the temperature increases, the resistance of the bead decreases exponentially

Thermocouple – Two different metals make up a thermocouple. Generally, in the form of two wires twisted, welded, or crimped together. Temperature is sensed by measuring the voltage. A potential difference is created that is proportional to the temperature at the junction (Seebeck effect)

Platinum resistance thermometers (PTR) – uses platinum for determining the temperature. The principle used is that the resistance of platinum changes with the change of temperature. The thermometer measures the temperature over the range of 200°C to1200°C. Resistance in metals show a linear increase with temperature

Tympanic thermometers – uses infrared radiation which is emitted by all living beings. It analyses the intensity and wavelength and then transduces the heat energy into a measurable electrical output

Gauge/dial thermometers – Uses coils of different metals with different co-efficient of expansion. These either tighten or relax with changes in temperature, moving a lever on a calibrated dial.

Caudal analgesia using bupivacaine is a widely employed technique for achieving both intraoperative and early postoperative pain relief. 0.5 ml/kg of 0.25% plain bupivacaine is favoured by many practitioners who employ this fixed scheme for procedures involving sacral dermatomes (circumcision, hypospadias repair) as well as lower thoracic dermatomes (orchidopexy). However, there are other dosing regimens for caudal blocks with variable analgesic success rates: These include 0.75 ml/kg, 1.0 ml/kg and 1.25 ml/kg.

A study indicated that plain bupivacaine 0.25% at a dose of 0.75 ml/kg compared to a dose of 0.5 ml/kg when administered for herniotomies provided improved quality of caudal analgesia with a low side effects profile. There were consistently more patients with favourable objective pain scale (OPS) scores at all timelines, increased the time to the analgesic request with similar postoperative consumption of paracetamol in the group of patients who received 0.75 ml/kg of 0.25% bupivacaine.

Metronidazole is a nitroimidazole antiprotozoal drug that is selectively absorbed by anaerobic bacteria and sensitive protozoa. Once taken up be anaerobes, it is nonenzymatically reduced by reacting with reduced ferredoxin. This reduction results in products that accumulate in and are toxic to anaerobic cells. The metabolites of metronidazole are taken up into bacterial DNA, forming unstable molecules. This action occurs only when metronidazole is partially reduced, and, because this reduction usually happens only in anaerobic cells, it has relatively little effect on human cells or aerobic bacteria.