The blood vessel well is divided into 3 parts, namely:

The tunica intima, which is the deepest layer. It contains endothelial cells separated by gap junctions

The tunica media, primarily consisting of the involuntary smooth muscle fibres, laid out in spiral layers with elastic fibres and connective tissue.

The tunica adventitia, which is the most superficial layer. It consists of the vasa vasorum, fibroblast and collagen.

Mapleson breathing system (or circuit) analysed five different arrangements of components of the breathing system:
Mapleson A – It is the most efficient for spontaneous respiration. The flow of fresh gas required is 70-85 ml/kg/min, i.e., approximately 5-6 lit./min fresh gas flow for an average adult.
Mapleson B and C – inefficient for both SV and PPV; requires gas flow of two to three times minute volume (100 ml/kg/min). Not commonly used but category C may be used for emergency resuscitation.
Mapleson D – efficient for PPV at gas flow equivalent to patient’s minute volume; the Bain’s circuit is a coaxial version of the Mapleson D
Mapleson E and F – for paediatric use; requires gas flow at two to three times the patient’s minute volume. The Mapleson F consists of an open-ended reservoir bag (Jackson-Rees modification).

Because of the low pH in the stomach, paracetamol absorption is minimal (pKa value is 9.5). Paracetamol is absorbed quickly and completely in the alkaline environment of the small intestine. Oral bioavailability is approaching 100%. As a result, measuring paracetamol levels in plasma after an oral paracetamol dose has been used as a surrogate marker of gastric emptying. This method has been used to investigate the effects of drugs on gastric emptying. At clinically used doses, paracetamol is ideal because it has very few side effects.

Scintigraphic imaging is the gold standard for determining gastric emptying.

Although aspirin (acetyl salicylic acid) is absorbed primarily in the small intestine, some may also be absorbed in the stomach. The oral bioavailability ranges from 70 to 100 percent, making it less reliable than paracetamol.

Propranolol is a lipophilic drug that is rapidly absorbed after administration. However, it is highly metabolised by the liver in the first pass, and only about 25% of propranolol reaches the systemic circulation. It’s not the best indicator of gastric emptying.

Oral bioavailability of gentamicin and vancomycin is low. Only antibiotic-induced pseudomembranous colitis is treated with oral vancomycin.

Erythromycin is a pro-kinetic agent that acts as a motilin receptor agonist.

Nausea and vomiting occur commonly due to Chemoreceptor Trigger Zone (CTZ) stimulation by dopamine (Domperidone but not metoclopramide can be used for the treatment of this vomiting)

Dopamine itself cannot cross the blood-brain barrier (BBB) but its precursor levodopa can cross BBB.

Dopamine can modulate extrapyramidal symptoms like acute dyskinesia, tardive dyskinesia, Parkinsonism, and Neuroleptic malignant syndrome.

Dopamine inhibits the secretion of prolactin from the pituitary gland.

When the convulsion lasts for five or more than five minutes, or if there are recurrent episodes of convulsions in a 5 minute period without returning to the baseline, it is termed as Status Epilepticus.
The first priority in the patient with seizures is maintaining the airway, breathing, and circulation.

Guideline for the management of Status Epilepticus in children by Advanced Life Support Group is as follow:

Step 1 (Five minutes after the start of seizures):

If intravascular access is available start treatment with lorazepam 0.1 mg/kg IV
If no intravascular access then give buccal midazolam 0.5 mg/kg or rectal diazepam 0.5 mg/kg.

Step 2 (Ten minutes after the start of seizure):

If the convulsions continue then a second dose of benzodiazepine should be given. Senior should be called on-site and phenytoin should be prepared.
No more than two doses or benzodiazepines should be given (including any doses given before arrival at the hospital)
If still no IV access then obtain intraosseous access (IO).

Step 3 (Ten minutes after step 2)

Senior help along with anaesthetic/ICU help should be sought
Phenytoin 20 mg/kg IV over 20 minutes
If the seizure stops before the full dose of phenytoin is given then the infusion should be completed as this provides up to 24 hours of anticonvulsant effect
In children already receiving phenytoin as treatment for epilepsy then an alternative is phenobarbitone 20 mg/kg IV over five minutes
Once the phenytoin is started, senior staff may wish to give rectal paraldehyde 0.4 mg/kg although this is no longer included in the routine algorithm recommended by APLS.

Step 4 (20 minutes after step 3)

If 20 minutes after starting phenytoin the child remains in status epilepticus then rapid sequence induction of anaesthesia with thiopentone and a short acting paralysing agent is needed and the child transferred to paediatric intensive care.

Serum specific IgE assays against allergen sources/molecules are the most commonly used in vitro diagnostic approach. The measurement of specific IgE recognizing allergenic epitopes can be achieved both through the usage of single reagents (singleplex) or with a pre-defined panel of a number of molecules to be tested simultaneously (multiplex).

Several clinical entities have been described and those occurring immediately after drug exposure are immunoglobulin E (IgE)-mediated and explored by skin testing and by the in vitro measurement of serum-specific IgE. The sensitivity of these tests is not 100% and even for patients with a clear positive history, a drug provocation test may be required in order to confirm the diagnosis. The advantages of the in vitro determination of specific IgE antibodies when compared with in vivo testing are that the former poses no direct risk to the patient and does not require personnel with expertise. Even though in vitro tests are recommended in immediate hypersensitivity reactions, their exact place in the diagnostic procedure is not clear and certain authors do not use this method in daily practice. In one study, in terms of sensitivity, 11 of 26 patients (42%) with negative skin tests and a positive drug provocation challenge (or repeated clinical history) had specific IgE to benzylpenicilloyl or amoxicilloyl (4). The specificity of the test was 95–100%. Therefore, IgE measurements can avoid a potentially harmful drug provocation test.

An elevated serum tryptase does not differentiate between type 1 and type 2 hypersensitivity reaction. It indicates mast cell degranulation.

RAST is a useful aid to improve the overall diagnosis of drug allergies by using radioactive detection. This, however, is now rarely used.

Quantification of basophil activation by CD63 expression can be done by flow cytometry, which forms the basis of experimental drug-induced basophil stimulation tests.

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

Resistance pulmonary arteries constrict in response to alveolar and airway hypoxia, diverting blood to better-oxygenated alveoli.

In atelectasis, pneumonia, asthma, and adult respiratory distress syndrome, hypoxic pulmonary vasoconstriction optimises O2 uptake. Hypoxic pulmonary vasoconstriction helps maintain systemic oxygenation during single-lung anaesthesia.

A redox-based O2 sensor within pulmonary artery smooth muscle cells is involved in hypoxic pulmonary vasoconstriction. The production of reactive oxygen species by smooth muscle cells in the pulmonary artery varies in proportion to PaO2. Hypoxic removal of these redox second messengers inhibits voltage-gated potassium channels, depolarizing smooth muscle cells in the pulmonary artery.

L-type calcium channels are activated by depolarization, which raises cytosolic calcium and causes hypoxic pulmonary vasoconstriction. Some anaesthetics suppress this response, increasing the risk of further deterioration in ventilation perfusion mismatch.

Agents that inhibit HPV are ether, halothane, and desflurane (>1.6 MAC).
Agents with no effect on HPV include thiopentone, fentanyl, desflurane (1MAC), isoflurane (<1.5MAC), sevoflurane(1MAC), and propofol.

The maximum safe amount of bupivacaine is 2mg/kg. Addition of adrenaline slows down absorption of the local anaesthetic and allows a maximum dose of 2.5mg/kg to be used.

The maximum safe dose of bupivacaine for this patient is 125 mg.

A 0.125% solution will contain 0.125g/100mL or 125mg/100 mL.

The maximum volume of local anaesthetic is approximately 80-100 mL.

Dorsal column (ascending tract) – Proprioception, vibration, discriminative

Spinocerebellar (ascending tract) – Subconscious muscle position and tone

Corticospinal (descending tract) – Voluntary muscle

Rubrospinal (descending tract) – Flexor muscle tone

Vestibulospinal (descending tract) – Reflexes and muscle tone

Reticulospinal(descending tract) – Voluntary movements, head position.-

Autonomic – Descending tract.