Flowmeters measure the rate at which a specific gas, that the flowmeter has been calibrated for, passes through. This calibration is done at room temperature and standard atmospheric pressure with an accuracy of +/- 2%.

Reading the flowmeter is done from the top of a bobbin (the midpoint of a ball). Oxygen is the last gas to be added downstream to the mixture delivered to the back bar as a safety feature. This prevents delivery of a hypoxic mixture.

Inaccurate flow measurements occur when the bobbin sticks to the inside wall of the flowmeter. Stannic oxide has been used as a successful antistatic substance thus, reducing the aforementioned risk.

Carbon dioxide being easily delivered is found on some older machines, but those attached flowmeters are limited by a maximum flow of 500 ml /min. Thus avoiding the delivery of a hypercarbic mixture.

Colligative properties are properties of solutions that depend on the number of dissolved particles in solution. They do not depend on the identities of the solutes.

All of the above have colligative properties with the exception of depression of melting point.

The osmolality from the concentration of a substance in a solution is measured by an osmometer. The freezing point of a solution can determines concentration of a solution and this can be measured by using a freezing point osmometer. This is applicable as depression of freezing point is directly correlated to concentration.

Vapour pressure osmometers, which measure vapour pressure, may miss certain volatiles such as CO2, ammonia and alcohol that are in the solution

The use of a freezing point osmometer provides the most accurate and reliable results for the majority of applications.

Colligative properties does not include melting point depression . Mixtures of substances in which the liquid phase components are insoluble, display a melting point depression and a melting range or interval instead of a fixed melting point.

The magnitude of the melting point depression depends on the mixture composition.

The melting point depression is used to determine the purity and identity of compounds. EMLA (eutectic mixture of local anaesthetics) cream is a mixture of lidocaine and prilocaine and is used as a topical local anaesthetic. The melting point of the combined drugs is lower than that individually and is below room temperature (18°C).

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.

Anticholinergic agents are a group of drugs that blocks the action of the neurotransmitter called acetylcholine at synapses in the central and peripheral nervous system.

Hyoscine, atropine, and glycopyrrolate are anticholinergic which acts at muscarinic receptors with little activity at the nicotinic receptors.

Hyoscine and atropine are naturally occurring esters. Since Glycopyrrolate is a synthetic quaternary amine, it does not cross the blood brain barrier. Noteworthy, hyoscine, butylbromide also does not cross the blood brain barrier significantly.

Erythromycin binds to the 50s subunit of bacterial rRNA complex and inhibits protein synthesis.

Gentamicin is a broad-spectrum antibiotic whose mechanism of action involves inhibition of protein synthesis by binding to 30s ribosomes. Its major adverse effect is nephrotoxicity and ototoxicity

Aminoglycoside bind to 30s subunit of ribosome causing misreading of mRNA

Tetracyclines inhibit protein synthesis through reversible binding to bacterial 30s ribosomal subunits, which prevent binding of new incoming amino acids (aminoacyl-tRNA) and thus interfere with peptide growth.

The ileocolic artery is the terminal branch of the superior mesenteric artery. It supplies:
1. terminal ileum
2. proximal right colon
3. cecum
4. appendix (via its branch of the appendicular artery)

As veins accompany arteries in the mesentery and are lined by lymphatics, high ligation is the norm in cancer resections—the ileocolic artery branches off the SMA near the duodenum.

The umbilical vein closes once the umbilical cord is clamped following birth. This causes a rise in systemic vascular resistance, closing the ductus venosus.

Upon birth, the pulmonary vascular resistance is decreased as the lungs are aerated.

At birth, there is a rise in oxygen tension which causes the corresponding constriction of the ductus arteriosus. This prevents a left to right shunt as it stops aortic blood and blood from the pulmonary artery from mixing. The ventricles do no have an opening connecting them.

The foramen ovale closes soon after birth. It is the septum opening between the left and right atrium.

An adult’s cardiac output is expected to be 5 L/min

Decreased stroke volume causes decreased ejection fraction which results in diastolic dysfunction.
Ejection fraction is not a useful measure in someone with diastolic dysfunction because stroke volume may be reduced whilst end-diastolic volume may be reduced.
Diastolic dysfunction may arise with reduced heart compliance.

Ejection fraction measures of the proportion of blood leaving the ventricles with each beat and is calculated as follows:
Stroke volume / end-diastolic volume.

A healthy ejection fraction is usually taken as 60% (based on a stroke volume of 70ml and end-diastolic volume of 120ml).

Respiratory inspiration causes a decreased pressure in the thoracic cavity, which in turn causes more blood to flow into the atrium.

Sitting up decreases venous because of the action of gravity on blood in the venous system.
Hypotension also decreases venous return.
A less compliant aorta, like in aortic stenosis increases end systolic left ventricular volume which decreases stroke volume.

Systemic vascular resistance = mean arterial pressure / cardiac output.
Increased vascular resistance impedes the flow of blood back to the heart.

Increased venous return increases end diastolic LV volume as there is more blood returning to the ventricles.

The tricuspid valve allows the tip of a pulmonary artery catheter to pass through the right atrium and into the right ventricle.

The balloon will be inflated before crossing the pulmonary valve and entering the pulmonary artery, where it will eventually wedge or occlude the artery, providing an indirect measure of left atrial pressure.

0-12 mmHg in the right atrium
2-25 mmHg in the right ventricle
12-25 mmHg in the pulmonary artery
8-12 mmHg is the occlusion pressure

The most likely of the differential diagnosis in this case is a duodenal ulcer located on the posterior abdominal wall.

These can cause an erosion of the abdominal wall, eventually affecting the gastroduodenal artery and resulting in major bleeding and haematemesis.

Gastroduodenal artery supplies the pylorus, proximal part of the duodenum, and indirectly to the pancreatic head (via the anterior and posterior superior pancreaticoduodenal arteries)