Noradrenaline acts as a sympathomimetic effect via alpha as well as a beta receptor. However, they have weak β2 action.

Natural catecholamines are Adrenaline, Noradrenaline, and Dopamine

The cephalic vein is one of the primary superficial veins of the upper limb. The superficial group of upper limb veins begin as an irregular dorsal arch on the back of the hand.

The cephalic vein originates in the anatomical snuffbox from the radial side of the arch and travels laterally up, within the superficial fascia to join the basilic vein via the median cubital vein at the elbow.

Near the shoulder, it passes between the deltoid and pectoralis major muscles. It pierces the coracoid membrane (continuation of the clavipectoral fascia) to terminate in the axillary vein’s first part.

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

Carbonic anhydrase is an enzyme which contains zinc and can be found in:
1. Erythrocytes
2. Pulmonary endothelium
3. The intestine
4. Pancreas
5. Cardiac muscle and skeletal muscle.

To date, there have been seven isoenzymes identified. Of note, isoenzyme IV is found in the brush border of the proximal convoluted tubule and isoenzyme II is found within the luminal cells.

Acetazolamides a carbonic anhydrase inhibitor and is used as prophylaxis against mountain sickness and in glaucoma management.

Spironolactone is a potassium diuretic and is an aldosterone antagonist.

The inguinal triangle of Hesselbach’s is an important clinical landmark on the posterior wall of the inguinal canal. It has the following relations:
Inferiorly – medial third of the inguinal ligament
Medially – lower lateral border of the rectus abdominis
Laterally – inferior epigastric vessels

Direct inguinal hernia is when the bowel bulges directly through the abdominal wall. These hernias usually protrude through Hesselbach’s triangle.

The pH of CSF is 7.31 which is lower than plasma.

Compared to plasma, it has a lower concentration of potassium, calcium, and protein and a higher concentration of sodium, chloride, bicarbonate and magnesium.

CSF usually has no cells present but if white cells are present, there should be no more than 4/ml.

The pressure of CSF should be less than 20 cm of water.

The concentration of glucose is approximately two-thirds of that of plasma, and it has a concentration of approximately 3.3-4 mmol/L.

Mapleson classified breathing systems into A, B, C, D and E. Jackson-Rees subsequently modified the Mapleson E by adding a double-ended bag to the end of the reservoir tubing, creating the Mapleson F. A Mapleson E or T-piece does not have a reservoir bag.

A Mapleson A system is a very efficient system for use during spontaneous ventilation. However, it is not suitable for use with patients less than 25 kg, due to the increased dead space at the distal / patient end. This system can be modified into a Lack system or coaxial Mapleson A, where the fresh gas flows through an outer tube (30 mm) and exhaled gases flow through the inner tube (14 mm).

The adjustable pressure limiting valve (APL) or expiratory valve allows exhaled gas and excess fresh gas to leave the breathing system. It is a one-way, adjustable spring-loaded valve, and gases escape when the pressure in the system exceeds the valve opening pressure. During spontaneous ventilation a pressure of less than 1 cm of water (0.1 kPa) is needed when the valve is in the open position (not 2 cm of H2O).

The reservoir bag is highly compliant and when over inflated, the rubber bag can limit the pressure in the system to about 40 cm of H2O.

This is due to the law of Laplace, which states that the pressure will fall as the radius of the bag increases:

Pressure = 2 x tension/radius.

Primary FRCA is concerned with two issues. The first is a working knowledge of the Henderson-Hasselbalch equation, and the second is a working knowledge of logarithms and antilogarithms.

The pH at which the drug exists in 50 percent ionised and 50 percent unionised forms is known as the pKa.

To calculate the proportion of ionised to unionised form of a drug, use the Henderson-Hasselbalch equation.

pH = pKa + log ([A-]/[HA])

or

pH = pKa + log [(salt)/(acid)]
pH = pKa + log ([ionised]/[unionised])

Hence, if the pKa ˆ’ pH = 0, then 50% of drug is ionised and 50% is unionised.

In this example:
7.4 = 8.4 + log ([ionised]/[unionised])
7.4 ˆ’ 8.4 = log ([ionised]/[unionised])
log ˆ’1 = log ([ionised]/[unionised])

Simply put, the antilog is the inverse log calculation. In other words, if you know the logarithm of a number, you can use the antilog to find the value of the number. The antilogarithm’s definition is as follows:

y = antilog x = 10x

Antilog to the base 10 of 0 = 1, ˆ’1 = 0.1, ˆ’2 = 0.01, ˆ’3 = 0.001 and, ˆ’4 = 0.0001.

[A-]/[HA] = 0.1

Assuming that we can apply the approximation [A-] << [HA} then this means the acid is 0.1 x 100% = 10% ionised

so the percentage of (non-ionized) acid will be 100% – 10% = 90%

The external iliac artery is the larger of the two branches of the common iliac artery. It forms the main blood supply to the lower limbs. The common iliac bifurcates into the internal and external iliac artery anterior to the sacroiliac joint.

The external iliac artery courses on the medial border of the psoas major muscles and exits the pelvic girdle posterior to the inguinal ligament. Here, midway between the anterior superior iliac spine and the pubic symphysis, the external iliac artery becomes the femoral artery and descends along the anteromedial part of the thigh in the femoral triangle.

The pectineus forms the posterior border of the femoral canal.
The femoral vein forms the lateral border of the femoral canal.
The medial border of the adductor longus muscle forms the medial wall of the femoral triangle.
The medial border of the sartorius muscle forms the lateral wall of the femoral triangle.

Pulse oximeters combine the principles of oximetry and plethysmography to noninvasively measure oxygen saturation in arterial blood. A sensor containing two or three light emitting diodes and a photodiode is placed across a perfused body part, commonly a finger, to be transilluminated. Oximetry depends on oxyhaemoglobin and deoxyhaemoglobin, and their ability to absorb the beams of light produced by the light emitting diodes: red light at 660 nm and infrared light at 960 nm.

The isosbestic point is the point wherein two different substances absorb light to the same extent. For oxyhaemoglobin and deoxyhaemoglobin, the points are at 590 nm and 805 nm. These are considered reference points where light absorption is independent of the degree of saturation.

Non-constant absorption of light is often due to the presence of an arterial pulsation, whilst constant absorption of light is seen in non-pulsatile tissues.

Most pulse oximeters are inaccurate at low SpO2, but is accurate at +/- 2% within the range of 70% to 100% SpO2. All pulse oximeters demonstrate a delay in between changes in SaO2 and SpO2, and display average readings every 10 to 20 seconds, hence they are unable to detect acute desaturation episodes.