Dystonia is characterised by repetitive twisting movements or abnormal postures. They are classified as either primary or secondary.

Primary dystonia is a genetic disorder that is inherited in an autosomal dominant pattern.
Secondary dystonia can be caused by focal brain lesions, Parkinson’s disease, or certain medications.

The following drugs cause the most common drug-induced dystonic reactions:
Antipsychotics, antiemetics (especially prochlorperazine and metoclopramide), and antidepressants.

Following the administration of the neuroleptic prochlorperazine, 16 percent of patients experience restlessness (akathisia) and 4% experience dystonia.

Several published reports have linked the anaesthetics thiopentone, fentanyl, and propofol to opisthotonos and other abnormal neurologic sequelae. Dystonias following a general anaesthetic are uncommon. Tramadol has been linked to serotonin syndrome, while remifentanil has been linked to muscle rigidity.

The following are some of the risk factors:

Positive family history
Male
Children
An episode of acute dystonia occurred previously.
Dopamine receptor (D2) antagonists at high doses and recent cocaine use

Dystonia is treated in a variety of ways, including:

Benztropine (as a first-line therapy):

1-2 mg intravenous injection for adults
Child: 0.02 mg/kg to 1 mg maximum

Benzodiazepines are a type of benzodiazepine (second line treatment).

Midazolam:

1-2 mg intravenously, or 5-10 mg IV/PO diazepam

Antihistamines with anticholinergic activity (H1receptor antagonists):

Promethazine 25-50 mg IV/IM, or diphenhydramine 50 mg IV/IM (1 mg/kg in children) are used when benztropine is not available.

Charles’ Law states that there is a direct correlation between temperature and volume, where pressure and amount gas are constant. As temperature increases, volume also increases.

Boyle’s Law states that Pressure is inversely proportional to volume, assuming that temperature and amount of gas are constant. As volume increases, pressure decreases. In Dalton’s law of partial pressure, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of the gases in mixture.

According to Henry’s Law for concentration of dissolved gases, at a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. An equivalent way of stating the law is that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

Gay-Lussac’s Law states that the pressure of a given mass of gas varies directly with the absolute temperature of the gas, when the volume is kept constant. This law is very similar to Charles’ Law, with the only difference being the type of container. Whereas the container in a Charles’ Law experiment is flexible, it is rigid in a Gay-Lussac’s Law experiment.

These clinical signs suggest that 15-30% of circulating blood volume has been lost.

Pelvic fractures are associated with significant haemorrhage (>2000 ml) that can be concealed. This may require aggressive fluid resuscitation which is initially with crystalloids and then blood. What is also important is including stabilisation of the fracture(s) and pain relief.

The Advanced Trauma Life Support (ATLS) classification of haemorrhagic shock is as follows:

Class I haemorrhage (blood loss up to 15%):
<750 ml of blood loss
Minimal tachycardia
No changes in blood pressure, RR or pulse pressure
Patients do not normally not require fluid replacement as will be restored in 24 hours, but in trauma, this needs to be correct.

Class II haemorrhage (15-30% blood volume loss):
Uncomplicated haemorrhage requiring crystalloid resuscitation
Represents about 750 – 1500 ml of blood loss
Tachycardia, tachypnoea and a decrease in pulse pressure (due to a rise in diastolic component due action of catecholamines).
There are minimal systolic pressure changes.
There may be associated anxiety, fright or hostility

Class III haemorrhage (30-40% blood volume loss):
Complicated haemorrhagic state – crystalloid and probably blood replacement are required
There are classical signs of inadequate perfusion, marked tachycardia, tachypnoea, significant changes in mental state and measurable fall in systolic pressure.
Almost always require blood transfusion, but decision based on patient initial response to fluid resuscitation.

Class IV haemorrhage (> 40% blood volume loss):
Preterminal event patient will die in minutes
Marked tachycardia, significant depression in systolic pressure and very narrow pulse pressure (or unobtainable diastolic pressure)
Mental state is markedly depressed
Skin cold and pale.
Needs rapid transfusion and immediate surgical intervention.

A blood loss of >50% results in loss of consciousness, pulse and blood pressure.

Fluid resuscitation following trauma is a controversial area.

This clinical scenario points to a 15-30% blood loss. However, further crystalloid and blood replacement may be required after assessing the clinical situation. There is increasing evidence to suggest that transfusion of large volumes of crystalloid in the hospital setting are likely to be deleterious to the patient and hypotensive resuscitation and judicious blood and blood product resuscitation is a more appropriate option. A ratio of 1 unit of plasma to 1 unit of red blood cells is used to replace fluid volume in adults.

This patient does not require immediate transfusion of O negative blood and there is time for a formal crossmatch. The argument about colloids versus crystalloids has existed for decades. However, while they have a role in fluid resuscitation, they are not first line.

There is a risk of anaphylaxis, Hypernatraemia, and acute renal injury with colloidal solutions.

Number needed to treat can be defined as the number of patients who need to be treated to prevent one additional bad outcome.

It can be found as:

NNT=1/Absolute Risk Reduction (rounded to the next integer since number of patients can be integer only).

where ARR= (Risk factor associated with the new drug group) — (Risk factor associated with the currently available drug)

So,

ARR= (165/1050)-(132/1044)

ARR= (0.157-0.126)

ARR= 0.031

NNT= 1/0.031

NNT=32.3

Sevoflurane is highly fluorinated methyl isopropyl ether widely used as an inhalational anaesthetic. It is suggested that sevoflurane preconditioning occurs via the opening of mitochondrial Potassium ATP dependent channel similar to that of Ischemic Preconditioning protection.

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.

Nonsteroidal anti-inflammatory drugs (NSAIDs) cause bronchospasm, rhinorrhoea, and nasal obstruction in some asthma patients.

The inhibition of cyclooxygenase-1 (Cox-1) appears to be the cause of NSAID-induced reactions. This activates the lipoxygenase pathway, which increases the release of cysteinyl leukotrienes (Cys-LTs), which causes bronchospasm and nasal obstruction.

The following changes in arachidonic acid (AA) metabolism have been observed in NSAID-intolerant asthmatic patients:

Prostaglandin E2 production is low, possibly due to a lack of Cox-2 regulation.
An increase in leukotriene-C4 synthase expression and
A decrease in the production of metabolites (lipoxins) released by AA’s transcellular metabolism.

Phospholipase A produces membrane phospholipids, which are converted to arachidonic acid.

TXA2 causes vasoconstriction as well as platelet aggregation and adhesion.

PGI2 causes vasodilation and a reduction in platelet adhesion.

PGE2 is involved in parturition initiation and maintenance, as well as thermoregulation.

Thiopental is a new British Approved Name for thiopentone and is thio-barbiturate.
Methohexitone is an oxy- barbiturate. Both thiopental and methohexitone are intravenous induction agents.

Ketamine cannot cause loss of consciousness in less than 30 seconds. At least 30 seconds is needed to cause loss of consciousness following intravenous administration.

Etomidate is an imidazole but it is not used in the Intensive Care unit for sedation because it has an antidepressant effect on the steroid axis.

Adequate humidification is vital to maintain homeostasis of the airway. Heat and moisture exchangers conserve some of the exhaled water, heat and return them to inspired gases. Many heat and moisture exchangers also perform bacterial/viral filtration and prevent inhalation of small particles. Heat and moisture exchangers are also called condenser humidifier, artificial nose, etc. Most of them are disposable devices with exchanging medium enclosed in a plastic housing. For adult and paediatric age group different dead space types are available. Heat and moisture exchangers are helpful during anaesthesia and ventilatory breathing system. To reduce the damage of the upper respiratory tract through cooling and dehydration inspiratory air can be heated and humidified, thus preventing the serious complications. Moreover, they are the most appropriate humidification devices used for routine anaesthesia.

Gases can be bubbled through water to increase humidity. Passing gas through water at room temperature causes the gas to cool due to latent heat of vaporisation. The water bath can be heated. This improves the efficiency of the device and also reduces the incidence of bacterial colonisation.

Nebulisers use a venturi system which employs the Bernoulli effect. A gas at high flow passes through a constriction causing the gas to accelerate, reducing its potential energy allowing other gases or liquids to be entrained. This can include medications or in the case of humidification, water vapour. The size of the water droplet produced by nebulisation determines where in the airway it is deposited. Standard nebulisers produced droplets of 4 microns in diameter and these are deposited in the upper airway and trachea. Efficacy can be improved by passing the droplets over an anvil which further reduces particle size. The most efficient form of nebuliser is the ultrasonic nebuliser. Here a transducer immersed in water and vibrated at a frequency of 3MHz produces1-2micron droplets. These particles easily reach the bronchioles and provide excellent humidification.

Approximately 25% of phase-1 drug reactions is made responsible by CYP2D6.

As much as a 1,000-fold difference in the ability to metabolise drugs by CYP2D6 can happen between phenotypes, and this may result in adverse drug reactions (ADRs).

The metabolism of antiemetics, beta-blockers, codeine, tramadol, oxycodone, hydrocodone, tamoxifen, antidepressants, neuroleptics, and antiarrhythmics is also as a result of CYP2D6.

Patients who take drugs that are metabolised by CYP2D6 but have poor CYP2D6 metabolism are more likely to have ADRs. People with ultra-rapid CYP2D6 metabolism may have a decreased drug effect due to low plasma concentrations of these drugs.

All the other CYP enzymes are subject to genetic polymorphism. Variants are less likely to lead to adverse drug reactions.

Absolute risk reduction = (Control event rate) – (Experimental event rate)

Experimental event rate = 24 / 120 = 0.2

Control event rate = 60 / 240 = 0.25

Absolute risk reduction = 0.25 – 0.2 = 0.05 = 5% reduction

Type I – immediate hypersensitivity reaction

Examples are: Atopy, urticaria, Anaphylaxis, Asthma( IgE mediated).

Type II – Antibody mediated cytotoxic reaction

Examples are: Autoimmune haemolytic anaemia, Thrombocytopenia( IgM or IgG mediated).

Type III – Immune complex mediated reaction

Examples are: Serum sickness,SLE – IgG., Farmers lungs, rheumatoid arthritis

Type IV – Delayed hypersensitivity reaction

Examples are: Contact dermatitis, drug allergies.

Type V – Autoimmune

Graves’
Myasthenia – IgM or IgG.

The peritoneal cavity is made up of the omentum, the ligaments and the mesentery.

The section of the peritoneum responsible for tethering organs to the posterior abdominal wall is the mesentery.

These tethered organs are classified as intraperitoneal, and these include the stomach, spleen, liver, first and fourth parts of the duodenum, jejunum, ileum, transverse, and sigmoid colon.

Retroperitoneal organs are located posterior to the peritoneum and include: the rest of the duodenum, the ascending colon, the descending colon, the middle third of the rectum, and the remainder of the pancreas

The sternocleidomastoid muscle divides the neck into anterior and posterior triangles on both sides of the neck.

The posterior triangle has the following boundaries:
anteriorly – sternocleidomastoid muscle
posteriorly – trapezius
roof – investing layer of deep cervical fascia
floor – prevertebral fascia overlying splenius capitis, levator scapulae, and the scalene muscles

The contents of the posterior triangle are:
1. fat
2. lymph nodes (level V)
3. accessory nerve
4. cutaneous branches of the cervical plexus – greater auricular nerve, transverse cervical nerve, lesser occipital nerve, supraclavicular nerve (A major branch of this plexus is the phrenic nerve, which arises from the anterior divisions of spinal nerves C3-C5)
5. inferior belly of omohyoid
6. branches of the thyrocervical trunk (transverse cervical and suprascapular arteries)
7. third part of the subclavian artery
8. external jugular vein

The extrinsic pathway is best assessed by the PT time.

D-dimer is a fibrin degradation product which is raised in the presence of blood clots.

A 50:50 mixing study is used to assess if a prolonged PT or aPTT is due to factor deficiency or a factor inhibitor.

The thrombin time is a test used to assess fibrin formation from fibrinogen in plasma. Factors that prolong the thrombin time include heparin, fibrin degradation products, and fibrinogen deficiency.

Intrinsic pathway – Best assessed by APTT. Factors 8,9,11,12 are involved. Prolonged aPTT can be seen in haemophilia and use of heparin.

Extrinsic pathway – Best assessed by Increased PT. Factor 7 involved.

Common pathway – Best assessed by APTT & PT. Factors 2,5,10 involved.

Vitamin K dependent factors are factors 2,7,9,10

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.

Propofol is considered a safe drug to use in porphyria because even if causes mild elevation of porphyrins inpatient, it does not cause any symptoms.

Since barbiturates are inducers of ALA synthetase, they are contraindicated in porphyria patients. So, thiopentone most not be used.

Etomidate is a potent inhibitor of adrenal 11 beta-hydroxylase and 17 alpha-hydroxylase reducing cortisol and aldosterone synthesis in the adrenal cortex and has been associated with exacerbations of porphyria in animal studies and it is advisable not to use it in this condition.

Ketamine should be reserved for the hemodynamically unstable patient, however, it is a safe drug.

Diazepam is safe in porphyria but is not usually used for a rapid sequence induction.

Automated blood gas analysers are commonly used to analyse blood gas samples, and they measure specific components of the arterial blood gas sample, whether directly or indirectly.

The following are the components of arterial blood gas:

pH = measured (directly determined) acid-base balance of the blood

PaO2 = measured partial pressure of oxygen in arterial blood

PaCO2 = measured partial pressure of carbon dioxide in arterial blood

HCO3 = calculated (indirectly determined) concentration of bicarbonate in arterial blood

Base excess/deficit = calculated relative excess or deficit of base in arterial blood

SaO2 = calculated arterial oxygen saturation unless a co-oximetry is obtained, in which case it is measured

The costal elements of the seventh cervical vertebrae form projections known as cervical ribs, which are present in approximately 0.5% – 1 % individuals.

A cervical rib commonly comprises of a head, neck and tubercle. The body of the rib varies from person to person. It extends into the posterior triangle of the neck, where it is either free anteriorly, or attached to the first rib / sternum.

Patients with a cervical rib mostly are asymptomatic and it is usually diagnosed as an incidental finding on chest x-ray. However, in some cases, the subclavian artery and the lower trunk of the brachial plexus are compressed where they pass over the cervical rib. This leads to a condition known as ”neurovascular compression syndrome,” in which these neurovascular structures are compressed between the cervical rib and scalenus anterior.

The most common cause of neurogenic symptoms in approximately 80% of the patients with cervical rib is neck trauma.

In most cases, the tingling, numbness and impaired circulation to the upper limb appears only after puberty. This is because the neck elongates, and the shoulders droop slightly.

Wavelength can be computed as follows:

Wavelength = velocity/frequency

In the given problem, the values stated are:

Frequency = 10 x 10^6
Velocity = 1540 meters per second

Wavelength = 1540/(10×10^6)
Wavelength = 1540/10,000,000 meters
Wavelength = 0.15 millimetres

The normal peak inspiratory flow in healthy individuals is 20-30 L/min during each normal tidal ventilation. This is expected to increase with greater respiratory rate and deeper inspiration.

Face masks are used to facilitate the delivery of oxygen from a breathing system to a patient. Face masks can be divided into two types: fixed performance or variable performance devices.

In fixed performance devices (also known as high air flow oxygen enrichment or HAFOE), fixed inspired oxygen concentration is delivered to the patent, independent and greater than that of the patient’s peak inspiratory flow rate (PIFR). No random entrainment is expected to occur at the time of PIFR, hence, the oxygen concentration in HAFOE devices is not dependent on the patient’s respiratory pattern.

Moreover, in HAFOE masks, the concentration of oxygen at a given oxygen flow rate is determined by the size of the constriction; a device with a greater entrainment aperture delivers a lower oxygen concentration. Therefore, a 40% Venturi device will have lesser entrainment aperture when compared to a 31% Venturi. Venturi masks allow relatively fixed concentrations of supplemental oxygen to be inspired e.g. 24%, 28%, 31%, 35%, 40% and 60% oxygen. These are colour coded and marked with the recommended oxygen flow rate.

Variable performance devices deliver variable inspired oxygen concentration to the patient, and is dependent on the PIFR. The PIFR can often exceed the flow rate at which oxygen or an oxygen/air mixture is supplied by the device, depending on a patient’s inspiratory effort. In addition, these masks allow expired air to be released through the holes in the sides of the mask. Thus, with increased respiratory rate, rebreathing of alveolar gas from inside the mask may occur.

The correct answer is the Purkinje fibres, which conducts at a velocity of about 4m/sec.

The electrical conduction system of the heart starts with the SA node which generates spontaneous action potentials.

This is conducted across both atria by cell to cell conduction, and occurs at around 1 m/s. The only pathway for the action potential to enter the ventricles is through the AV node in a normal heart.
At this site, conduction is very slow at 0.05ms, which allows for the atria to completely contract and fill the ventricles with blood before the ventricles depolarise and contract.

The action potentials are conducted through the Bundle of His from the AV node which then splits into the left and right bundle branches. This conduction is very fast, (,2m/s), and brings the action potential to the Purkinje fibres.

Purkinje fibres are specialised conducting cells which allow for a faster conduction speed of the action potential (,2-4m/s). This allows for a strong synchronized contraction from the ventricle and thus efficient generation of pressure in systole.

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.

There are different classes of electrical equipment that can be classified in the table below:

Class 1 – provides basic protection only. It must be connected to earth and insulated from the mains supply

Class II – provides double insulation for all equipment. It does not require an earth.

Class III – uses safety extra low voltage (SELV) which does not exceed 24 V AC. There is no risk of gross electrocution but risk of microshock exists.

Type B – All of above with low leakage currents (0.5mA for Class IB, 0.1 mA for Class IIB)

Type BF – Same as with other equipment but has ‘floating circuit’ which means that the equipment applied to patient is isolated from all its other parts.

Type CF – Class I or II equipment with ‘floating circuits’ that is considered to be safe for direct connection with the heart. There are extremely low leakage currents (0.05mA for Class I CF and 0.01mA for Class II CF)

The diaphragm divides the thoracic cavity from the abdominal cavity. Structures penetrate the diaphragm at different vertebral levels through openings in the diaphragm to communicate between the two cavities. The diaphragm has openings at three vertebral levels:

T8: vena cava, terminal branches of the right phrenic nerve
T10: oesophagus, vagal trunks, left anterior phrenic vessels, oesophageal branches of the left gastric vessels
T12: descending aorta, thoracic duct, azygous and hemi-azygous vein

Iliacus, and Psoas major are the most important muscles that produce flexion at the hip.

They are collectively called the iliopsoas muscle. The iliacus muscle originates from the ilium while the psoas major muscle takes its origin from the lumbar vertebrae and sacrum. Their insertion is the lesser trochanter of the femur. They work together to produce flexion and external rotation of the hip. The nerve supply is from branches of the lumbar plexus (L1, 2, 3) femoral nerve (L2, 3, 4) and short direct muscular branches (T12, L1, L2, L3 and L4).

Sartorius, Rectus femoris, Tensor fasciae latae, and Pectineus muscles are two-joint muscles acting at the knee and having less influence on hip flexion:

Rectus femoris and sartorius are involved in extension of the knee. They are supplied by branches of the femoral nerve.

Myotomes associated with key movement of the lower limb are:

L1/L2 – Hip flexion
L2/L3/L4 – Hip adduction, quadriceps (knee extension)
L4/L5 – Hip abduction
L5 – Great toe dorsiflexion.

Since knee extension is not affected, L2, L3 and L4 are still intact.

The Delphi method relies on expert consensus. This method kicks off with an open ended questionnaire and uses its responses as a survey instrument for the next round in which each of the participants is asked to rate the items that the investigators have summarized on the basis of the data collected in the first round. Any disagreement is further discussed in phases to come on the basis of information obtained from previous phases.

Calcium channel blocker (CCB) blocks L-type of voltage-gated calcium channels present in blood vessels and the heart. By inhibiting the calcium channels, these agents decrease the frequency of opening of calcium channels activity of the heart, decrease heart rate, AV conduction, and contractility.

Three groups of CCBs include
1) Phenylalkylamines: Verapamil, Norverapamil
2) Benzothiazepines : Diltiazem
3) Dihydropyridine : Nifedipine, Nicardipine, Nimodipine, Nislodipine, Nitrendipine, Isradipine, Lacidipine, Felodipine and Amlodipine.

Even though verapamil as good absorption from GIT, its oral bioavailability is low due to high first-pass metabolism.

Nimodipine is a Cerebro-selective CCB, used to reverse the compensatory vasoconstriction after sub-arachnoid haemorrhage and is more lipid soluble analogue of nifedipine

Calcium channel antagonist can potentiate the effect of non-depolarising muscle relaxants.

The structures that pass through the foramen magnum are:

Meningeal lymphatics
Spinal cord
Spinal meninges
Sympathetic plexus of vertebral arteries
Vertebral arteries
Vertebral artery spinal branches
The spinal roots of the accessory nerve.

The jugular foramen contains the vagus nerve, the accessory nerve and glossopharyngeal nerve.

The vertebral veins does not pass into the skull.

Mast cell tryptase is a reliable marker of mast cell degranulation. Tryptase is a protease enzyme that acts via widespread protease-activated receptors (PARs).