The upper limb venous drainage is divided into superficial and deep. The superficial veins are accessible to draw blood for investigations. The cephalic, basilic, and median cubital veins are superficial veins.

The median cubital vein connects the cephalic vein and basilic vein. It is located anteriorly in the antecubital fossa and is preferred for venepuncture due to its palpability and ease of access.

The basilic vein and cephalic vein are the primary veins that drain the upper limb. They begin as the dorsal venous arch. The basilic vein originates from the ulnar side, while the cephalic vein originates from the radial side of the dorsal arch of the upper limb.

Iron is a necessary micronutrient for proper erythropoietic function, oxidative metabolism, and cellular immune responses. Although dietary iron absorption (1-2 mg/d) is tightly controlled, it is only just balanced by losses.

The adult body contains 35-45 mg/kg iron (about 4-5 g)

Iron can be found in a variety of forms, including haemoglobin, ferritin, haemosiderin, myoglobin, haem enzymes, and transferrin bound proteins.

With respect to oxygen transport in cells, almost all oxygen is transported within erythrocytes. There is limited solubility and only 1% is carried as solution. Thus, the amount of oxygen transported depends upon haemoglobin concentration and its degree of saturation.

Haemoglobin is a globular protein composed of 4 subunits. Haem is made up of a protoporphyrin ring surrounding an iron atom in its ferrous state. The iron can form two additional bonds – one is with oxygen and the other with a polypeptide chain.
There are two alpha and two beta subunits to this polypeptide chain in an adult and together these form globin. Globin cannot bind oxygen but can bind to CO2 and hydrogen ions.
The beta chains are able to bind to 2,3 diphosphoglycerate. The oxygenation of haemoglobin is a reversible reaction. The molecular shape of haemoglobin is such that binding of one oxygen molecule facilitates the binding of subsequent molecules.

The oxygen dissociation curve (ODC) describes the relationship between the percentage of saturated haemoglobin and partial pressure of oxygen in the blood.
Of note, it is not affected by haemoglobin concentration.

Chronic anaemia causes 2, 3 DPG levels to increase, hence shifting the curve to the right

Haldane effect – Causes the ODC to shift to the left. For a given oxygen tension there is increased saturation of Hb with oxygen i.e. Decreased oxygen delivery to tissues.
This can be caused by:
-HbF, methaemoglobin, carboxyhaemoglobin
-low [H+] (alkali)
-low pCO2
-ow 2,3-DPG
-ow temperature

Bohr effect – causes the ODC to shifts to the right = for given oxygen tension there is reduced saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues. This can be caused by:
– raised [H+] (acidic)
– raised pCO2
-raised 2,3-DPG
-raised temperature

Dopamine (DA) is a dopaminergic (D1 and D2) as well as adrenergic ? and?1 (but not ?2 ) agonist.

The D1 receptors in renal and mesenteric blood vessels are the most sensitive: i.v. infusion of a low dose of DA dilates these vessels (by raising intracellular cAMP). This increases g.f.r. In addition, DA exerts a natriuretic effect by D1 receptors on proximal tubular cells.

Moderately high doses produce a positive inotropic (direct?1 and D1 action + that due to NA release), but the little chronotropic effect on the heart.

Vasoconstriction (?1 action) occurs only when large doses are infused.

At doses normally employed, it raises cardiac output and systolic BP with little effect on diastolic BP. It has practically no effect on nonvascular ? and ? receptors; does not penetrate the blood-brain barrier—no CNS effects.

Dopamine is used in patients with cardiogenic or septic shock and severe CHF wherein it increases BP and urine outflow.

It is administered by i.v. infusion (0.2–1 mg/min) which is regulated by monitoring BP and rate of urine formation

The blood brain barrier (BBB) consists of the ultrafiltration barrier in the choroid plexus and the barrier around cerebral capillaries. The barrier is made by endothelial cells which line the interior of all blood vessels. In the capillaries that form the blood–brain barrier, endothelial cells are wedged extremely close to each other, forming so-called tight junctions.

Outside of the BBB lies the hypothalamus, third and fourth ventricles and the chemoreceptor trigger zone (CTZ).

Water, oxygen and carbon dioxide cross the BBB freely but glucose is controlled. The ability of chemicals to cross the barrier is proportional to their lipid solubility, not their water solubility. It’s ability to cross is inversely proportional to their molecular size and charge.

In neonates, the BBB is less effective than in adults. This is why there is increased passage of opioids and bile salts (kernicterus) into the neonatal brain.

In meningitis, the effectiveness and permeability of the BBB is affected, and as a result, this effect helps the passage of antibiotics which would otherwise not normally be able to cross.

After a paediatric case, you’ll frequently have to calculate and prescribe maintenance fluids. The ‘4-2-1 rule’ should be used as a guideline:

1st 10 kg – 4 ml/kg/hr
2nd 10 kg – 2 ml/kg/hr
Subsequent kg – 1 ml/kg/hr

Hence

1st 10 kg = 4 × 10 = 40 ml
2nd 10 kg = 2 × 10 = 20 ml
Subsequent kg = 1 × 1 = 1 ml
Total = 61 ml/hr

61 × 12 = 732 ml over 12 hrs.

Therapeutic index is a measure which relates the dose of a drug required to produce a desired effect to that which produces an undesired effect.

In humans, it is usually defined as the ratio of the toxic dose for 50% of the population (TD50) to the minimum effective dose for 50% of the population (ED50) for some therapeutically relevant effect. In animal studies, the therapeutic index can be defined as the ratio of the median lethal dose (LD50) to the ED50.

The heart has two venous drainage systems:
1. Greater venous system – it parallels the coronary arterial circulation and provides 70% venous drainage to the heart
2. Lesser venous system – includes the thebasian veins and provides up to 30% of the venous drainage to the heart

Thebasian veins (also called venae cordis minimae) are the smallest coronary veins and run in the myocardial layer of the heart. They serve to drain the myocardium and are present in all four heart chambers. They are more abundant on the right side of the heart and, more specifically, are most abundant in the right atrium. Thebesian veins drain the subendocardial myocardium either directly, via connecting intramural arteries and veins, or indirectly, via subendocardial sinusoidal spaces.

Once the decision to deliver a baby by caesarean section has been made, it should be carried out with a level of urgency commensurate with the baby’s risk and the mother’s safety.

There are four types of caesarean section urgency:

Category 1: A threat to the life of the mother or the foetus. 30 minutes to make a delivery decision
Category 2 : Maternal or foetal compromise that is not immediately life threatening. In most cases, the decision to deliver is made within 75 minutes.
Category 3 – Early delivery is required, but there is no risk to the mother or the foetus.
Category 4: Elective delivery at a time that is convenient for both the mother and the maternity staff.

There may be evidence of foetal compromise in the example above (late foetal pulse decelerations and a borderline pH).

Blood samples from the foetus:
normal: 7.25 or above
borderline: 7.21 to 7.24
abnormal: 7.20 or below

When a foetal deceleration occurs, the mother should be given oxygen, kept in a left lateral position, and given a tocolytic if the foetal deceleration is hyper stimulating. Maintaining adequate hydration will reduce the likelihood of a caesarean section.

The autonomic nervous system is divided into the sympathetic and parasympathetic nervous system. They are anatomically and physiologically different.

The sympathetic nervous system arises from the thoracolumbar outflow (T1-L5 ) at the lateral horns of grey matter of the spinal cord. Their preganglionic neurones are usually short myelinated and synapse in ganglia lateral to the vertebral column and have acetyl choline (Ach) as the neurotransmitter. Their postganglionic neurones are longer and unmyelinated and synapse with effector organ where the neurotransmitter is either adrenaline or noradrenaline.

The outflow of the parasympathetic nervous system is craniosacral. The cranial part originates from the midbrain and medulla (cranial nerves III, VII, IX and X) and the sacral outflow is from S2, S3 and S4. Their preganglionic neurones are usually long myelinated and synapse in ganglia close to the target organ and has Ach as its neurotransmitter. The unmyelinated postganglionic neurones is shorter and they synapse with effector organ. The neurotransmitter here is also Ach.

Both sympathetic and parasympathetic preganglionic neurons are cholinergic. Only the postganglionic parasympathetic neurons are cholinergic.

Laminar flow can be defined as the motion of a fluid where every particle in the fluid follows the same path of its previous particles. The following are properties of laminar flow of gas or fluids:

1. Smooth unobstructed flow of gas through a tube of relatively uniform diameter
2. Few directional changes
3. Slow, steady flow through straight smooth, rigid, large calibre, cylindrical tube
4. Outer layer flow slower than the centre due to friction, results in discrete cylindrical layers, or streamlines
5. Double flow by doubling pressure as long as the flow pattern remains laminar

Poiseuille’s Law relates the factors that determine laminar flow. It indicates the degree of resistance to fluid flow through a tube. The resistance to fluid flow through a tube is directly related to the length, flow and viscosity; and inversely related to the radius of the tube to the fourth power. This means that, when the radius is doubled, there is increase in flow by a factor of 16.

The positive predictive value is the ratio of patients truly diagnosed as positive to all those who had positive test results. In this case, this is 60/(60+20)=75%.

The negative predictive value is the ratio of patients truly diagnosed as negative to all those who had negative test results. In this case, this is 80/(80+40)=67%.

The sensitivity is the ratio of patients with the disease who test positive i.e. true positive patients to the total number of people with the disease. In this case, this is 60/(60+40)=60%.

The specificity is the ratio of people who don’t have the disease who test negative i.e. true negatives to the total number of people without the disease. In this case, this is 80/(20+80)=80%.

70% is not the result of any screening measurements

The popliteal fossa is the shallow, diamond-shaped depression located in the back of the knee joint.

The structures that lie within in from superficial to deep are:

The tibial and common fibular nerve: Most superficial. They arise from the sciatic nerve.
The popliteal vein
The popliteal artery: Lies deepest. It arises from the femoral artery

Boundaries of the popliteal fossa:

Laterally
Biceps femoris above, lateral head of gastrocnemius and plantaris below

Medially
Semimembranosus and semitendinosus above, medial head of gastrocnemius below

Floor
Popliteal surface of the femur, posterior ligament of knee joint and popliteus muscle

Roof
Superficial and deep fascia

Closing capacity refers to volume of gas within the lungs at which the conducting small airways begin to close, that is, the point during expiration when small airways close.

It is calculated mathematically as:

Closing capacity = Closing volume (CV) + Residual volume (RV)

Functional residual capacity (FRC) is the volume of gas still present within the lungs post expiration.

Closing capacity is lower than the functional residual capacity in younger adults, but begins to rise to eventually equal, and then exceed it with increasing age (at about middle age), increasing intrabdominal pressure, decreasing blood flow in the pulmonary system and parenchymal disease within the pulmonary system.

As there is no brachiocephalic artery on the left side, the artery is entered by the catheter on the right side.

The brachiocephalic artery branches into the common carotid and the right subclavian artery, so the catheter is most likely to enter the right subclavian artery, or also possibly the right carotid.

ACTH production is stimulated through the secretion of corticotropin-releasing hormone (CRH) from the hypothalamic nuclei.

ACTH secretion has a circadian rhythm. A high level of cortisol in the body stops its production. ACTH is secreted maximally in the morning and concentrations are lowest at midnight.

ACTH can be expressed in the placenta, the pituitary and other tissues.

Conditions where ACTH concentrations rise include: stress, disease and pregnancy.

Glucocorticoids (not mineralocorticoids – aldosterone) switch off ACTH production through a negative feedback loop .

Immunoglobulin E (IgE) are an antibody subtype produced by the immune system. They are the least abundant type and function in parasitic infections and allergy responses.

The most predominant type of immunoglobulin is IgG. It is able to be transmitted across the placenta to provide immunity to the foetus.

IgE is involved in the type I hypersensitivity reaction as it stimulates mast cells to release histamine. It has no role in type 2 hypersensitivity.

Its concentration in the serum is normally the least abundant, however certain reactions cause a rise in its concentration, such as atopy, but not in acute asthma.

The adrenal medulla comprises chromaffin cells (pheochromocytes), which are functionally equivalent to postganglionic sympathetic neurons. They synthesize, store and release the catecholamines noradrenaline (norepinephrine) and adrenaline (epinephrine) into the venous sinusoids.
The majority of the chromaffin cells synthesize adrenaline.

Systemic vascular resistance (SVR) is a derived value based on:

SVR = (MAP-CVP)/CO x 80

= (60 -10)/5 x 80 = 800 dynes.s.cm-5

A correction factor of 80 is needed in converting mmHg to dynes.s.cm-5
Normal values is between 700 -1600 dynes.s.cm-5

Pulmonary resistance (PVR) = (MPAP-PCWP)/CO x 80

= (10 – 5)/5 x 80 = 80 dynes.s.cm-5

To account for body size, cardiac index (CI) can be used instead of CO. CI = CO/body surface area (m2) or mL/minute/m2.
N/B: either MAP and CVP, or MPAP and PCWP are used in calculation to get dynes.s.cm-5

The right atrium receives blood supply from the SVC, IVC, and coronary sinus. It forms the right border of the heart.

The interior of the right atrium has 5 distinct features:
1. Sinus venarum – smooth, thin-walled posterior part of the right atrium where the SVC, IVC, and coronary sinus open
2. Musculi pectinati – an anterior rough, wall of pectinate muscles
3. Tricuspid valve orifice – the opening through which the right atrium empties blood into the right ventricle
4. Crista terminalis – separates the rough (musculi pectinati) from the smooth (sinus venarum) internally
5. Fossa ovalis – a thumbprint size depression in the interatrial septum which is a remnant of the oval foramen and its valve in the foetus

The trabeculae carneae are irregular muscular elevations that form the interior of the right ventricle.

A decrease in the functional residual capacity (FRC) is the most important physiologic change to consider for such patients.

FRC is the sum of the expiratory reserve volume and the residual volume. It is the resting volume of the lung, and is an important marker for lung function. During this time, the alveolar pressure is equal to the atmospheric pressure. When morbidly obese individuals lie supine, the FRC decreases by as much as 40% because the abdominal contents push the diaphragm into the thoracic cavity.

Chest wall compliance is expected to reduce because of fat deposition surrounding adjacent structures.

Inspiratory reserve volume (IRV) is expected to increase, and peak expiratory flow is expected to decrease, however the decrease in FRC is more important to consider because of the risk of hypoxia secondary to premature airway closure and ventilation-perfusion mismatch.

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

The most likely diagnosis is a spinal epidural haematoma, a neurological emergency. A full examination must be carried out to determine the nature of the neurological problem before conducting any investigations or imaging.

The effects of spinal anaesthesia should have worn off by this time point, and the severe back pain is a red flag.

The patient will also require an urgent neurological team referral as a spinal epidural haematoma requires immediate evacuation for spinal decompression. Analgesics may be prescribed for pain management.

Heparin would have been fully metabolised and so a reversal is unnecessary.

A spinal epidural haematoma is a pooling of blood in the epidural space, which can cause compression of the spinal cord. Its presenting symptoms are:

Usually begins with severe backpain and percussion tenderness
Cauda equina syndrome
Paralysis of the lower extremities.
If infected, a fever occurs in 66% of cases
Lower limb weakness developing after stopping an epidural infusion or weakness of the lower limbs which does not resolve within four hours of cessation of infusion of epidural local anaesthetic
Meningism.

Every surgical procedure is associated with a stress response which comprises a number of endocrine, metabolic, and immunological changes triggered by neuronal activation of the hypothalamic-pituitary-adrenal axis. The overall metabolic effect of the stress response to surgery includes an increase in secretion of catabolic hormones, such as cortisol and catecholamine, and a decrease in secretion of anabolic hormones, such as insulin and testosterone. The increase in levels of catabolic hormones in plasma stimulates glucose production, and there is a relative lack of insulin together with impaired tissue insulin sensitivity and glucose utilization, which is called insulin resistance. Consequently, blood glucose concentrations will increase, even in the absence of pre-existing diabetes.

A study compared the effects of spinal and general anaesthesia on changes in blood glucose concentrations during surgery in nondiabetic patients. Although mean blood glucose concentrations showed a significant proportional increase during surgery in both groups, this effect was much more significant with general anaesthesia than with spinal anaesthesia. These results indicate that spinal anaesthesia is more effective than general anaesthesia in attenuating the hyperglycaemic response to surgery.

The body of the Entonox cylinder is usually blue (occasionally white), with blue and white shoulders. Entonox contains a 50:50 mixture of oxygen and nitrous oxide, with a full cylinder pressure of 13700 KPa (137 bar). The cylinder is equipped with a two-stage pressure regulator for safe operation.

The cylinder body and shoulder of nitrous oxide are (French) blue.

In today’s anaesthetic workstations, carbon dioxide cylinders are no longer used.

The body of an oxygen cylinder is black, with a white shoulder.

The white Heliox (21 percent oxygen and 79 percent helium) cylinder has a brown and white shoulder. The administration of this gas mixture, which is less dense than air, is used to reduce turbulence (stridor) of inspiratory flow in patients with upper airway obstruction.

99.7% of the values within 3 standard deviations of the mean.

For 99.7% confidence interval, you can find the range as follows:

1. Multiply the standard error by 3.

2. Subtract the answer from mean value to get the lower limit.

3. Add the answer obtained in step 1 from the mean value to get the upper limit.

For a confidence interval of 68%, multiply the standard error with 1 and repeat the process. For a 95% confidence interval, Standard Error is multiplied by 1.96 to get the interval.

The correlation coefficient gives us the idea about relation between two parameters. i.e. to what extent change in parameter A could prompt a change in parameter B. The numerical value of correlation coefficient could not be greater than 1.

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

Key Point: While finding out confidence intervals, standard errors are used. Standard error and Standard deviation are two distinct entities and should not be confused.

For 99.7% confidence interval, you can find the range as follows:

Multiply the standard error by 3.

Subtract the answer from mean value to get the lower limit.

Add the answer obtained in step 1 from the mean value to get the upper limit.

The range turns out to be 1-13 mmol/L.

For a confidence interval of 68%, multiply the standard error with 1 and repeat the process. The range found for this interval is 3-11 mmol/L.

For a 95% confidence interval. Standard Error is multiplied by 1.96 which gives us the limit ranging from 3.08 to 10.92 mmol/L which could be approximated to 3-11 mmol/L.