Section 1 Flashcards

Question

other potential questions for this case

Answer 1

Physiology of cardiac conduction Hazards associated with diathermy ICD and anaesthesia—NPSA guideline

Answer 2

Nasogastric tube is above the diaphragm and follows the course of the right lower lobe bronchus

Answer 3

National Patient safety Agency alert/nice guideline • Use pH paper. ° pH < 5.5 indicates gastric placement. ° If > 5.5, or no aspirate, change patient position and check in an hour. • X-ray is recommended only if the pH test fails. The position of all nasogastric tubes should be confirmed after placement and before each use by aspiration and pH graded paper (with X–ray if necessary) according to the NPSA guideline.

Answer 4

○ Measuring energy use requires sophisticated equipment, so nutrition requirements are estimated using formulae. ○ The Harris Benedict Equation estimates basal metabolic rate (BMR) in kcal/day. • In men: BMR = 13.75 × weight (kg) + 5 × height (cm) − 6.78 × age (years) + 66 For women: BMR = 9.56 × weight (kg) + 1.85 × height (cm) − 4.68 × age (years) + 655 For an afebrile healthy individual, this is around 25 kcal/kg/day. Conditions such as fever, sepsis, surgery, and burns increase the requirements. european society of Parenteral and enteral nutrition (esPen) The total energy requirements of critically ill patients are given in recent guidelines issued by the ESPEN in 2006. • Acute initial phase of critical illness: 20–25 kcal/kg/day • Recovery/anabolic phase: 25–30 kcal/kg/day • Protein around 1.5 g/kg/day (2g/kg/day in severely catabolic patients). • lipid should be limited to 40% of total calories. • Carbohydrate makes up the remaining calorie requirements. ○ Glutamine, arginine, fish oils, and ribonucleotides; antioxidants including Vitamins C and E; selenium and other trace elements are considered useful for immunonutrition. Sodium 1.0–2.0 mmol/kg/day Potassium 0.7–1.0 mmol/kg/day Calcium 0.1 mmol/kg/day Magnesium 0.1 mmol/kg/day Chloride 1–2 mmol/kg/day Phosphate 0.4 mmol/kg/day

Answer 5

Malnutrition is the condition that develops when the body does not get the right amount of vitamins, minerals, and other nutrients it needs to maintain healthy tissues and organ function.

Answer 6

Malnutrition is associated with increased morbidity and mortality. • Increased risk of infection and pulmonary oedema • Reduced ventilatory drive • Impaired production of surfactant • Prolonged weaning due to muscle fatigue • Impaired wound healing • Delayed mobilisation resulting from weak muscles

Answer 7

Mechanical • Obstruction, discomfort • Ulceration Metabolic • Dehydration or overhydration • Hyperglycaemia • Electrolyte imbalance Gastrointestinal • Gastric stasis/retention, nausea, vomiting, diarrhoea, bloating • Aspiration pneumonia due to gastro-oesophageal reflux

Answer 8

○ Group of metabolic disturbances that occur after reinstitution of nutrition in a patient who has been malnourished for a prolonged period. • Usually starts 4 days after initiating feeding • Characterised by severe hypophosphataemia and life-threatening complications such as cardiac and respiratory failure, seizures, coma, rhabdomyolysis, and haematological disturbances

Answer 9

• Shift occurs from fat to carbohydrate metabolism • This causes sudden increase in insulin levels, which in turn increases cellular uptake of phosphate and precipitous fall in extracellular phosphate • Levels of K, Mg also fall, leading to heart failure

Answer 10

The presence of the following features suggest nonabsorption of feeds: • Increased aspirate from NG tube • Nausea and vomiting • Bloating, abd

Answer 11

• Check correct position of NG tube. • Ensure 45° head-up position. • Use prokinetics. • Institute a high-fibre diet for diarrhoea. • Start parenteral route.

Answer 12

ECT, having been in clinical use since the late 1930s, is the treatment for various psychiatric disorders and involves artificially inducing a brief generalised tonic-clonic seizure. The exact mechanism is still unclear, although a common (and probably oversimplified) view is that a tonic-clonic seizure ‘resets’ or ‘jumpstarts’ neuronal transmission (in a similar way DC cardioversion does for the heart).

Answer 13

• Depressive illness: failed medical therapy • Mania: refractory cases • Schizophrenia • Parkinson’s disease • Neuroleptic malignant syndrome • Delirium

Answer 14

In the UK, it involves induction of general anaesthesia, and usually partial muscle relaxation, before inducing a generalised tonic-clonic seizure by passing a brief current of 30–45 J between two electrodes on either side of the patient’s skull (bilateral ECT), or more commonly over one side only (unilateral) over 0.5–1.5 seconds

Answer 15

Remote site anaesthesia • Unfamiliar environment and staff • Potentially old/unfamiliar equipment (which may not have been checked recently) • Inconsistent anaesthetic support (ODP) The overall aims of anaesthesia are • To induce rapid onset, brief general anaesthesia, with partial muscle relaxation to reduce the risk of limb injury during convulsions • To avoid raising the seizure threshold (which may make seizures harder to induce and/or shorter in duration, which in turn may make the ECT less effective) • To minimise physiological effects of ECT

Answer 16

This is because of the autonomic surges that happen at the onset and maintenance of ECT, which is described below. only parasympathetic symptoms are shown in the ECG

Answer 17

cardiac • Initial parasympathetic discharge, lasting 10–20 seconds; bradycardia, hypotension, and asystole may occur. • Followed by sympathetic surge, leading to increased heart rate, blood pressure, and myocardial oxygen demand. • Potential for myocardial ischaemia or infarction, especially in those with preexisting LV impairment or coronary artery disease. cerebral • Increased cerebral O2 consumption, blood flow, and ICP • Post-procedure cognitive deficits are common: post-ictal confusion, drowsiness, retrograde and anterograde amnesia commonly occur. other • Raised intraocular and intragastric pressure are not thought to be clinically significant. • Dental damage, tongue/lip lacerations may occur due to jaw clenching. • Headache and myalgia. • Fractures are rare now, due to widespread use of muscle relaxants.

Answer 18

• Often poor historians with multiple comorbidities (IHD, COPD, etc) • No absolute contraindications exist, but most anaesthetists would consider an MI or CVA within the previous 3 months, or raised ICP, to place the patient at high risk of further cardiac or cerebral events • Drug therapy may have anaesthetic implications (lithium, MAOI, etc) • Patients may not have followed fasting instructions • All patients should ideally be investigated and optimised as for any procedure; however, if ECT is deemed semi-urgent, the risks of delay must again be balanced against the benefits of optimising comorbidities

Answer 19

induction • Check patient, full monitoring, appropriate assistance and equipment as per AAGBI • Intravenous access and pre-oxygenation • Induction agent: ‘minimal sleep dose’, to minimise effects on raising seizure threshold. Methohexital used to be commonly employed but is no longer available; propofol is a common choice; etomidate reduces seizure threshold but affects adrenal hormone synthesis • Short-acting opioids may allow dose of induction agent to be reduced and blunt haemodynamic responses • Muscle relaxants: suxamethonium 0.5 mg/kg commonly used. If contraindicated, consider mivacurium (or rocuronium followed by emergence • Once seizure terminates, ventilation can be supported manually until anaesthesia and muscle relaxation start to wear off and spontaneous ventilation resumes • Keep oxygen applied, and transfer to recovery • Monitor standards and recovery facilities same as in a normal postoperative care unit • Anticipate post-op confusion/agitation sugammadex if available)

Answer 20

• Check monitoring still attached • Feel for pulse • Give atropine 3 mg stat bolus (followed by 10–20 mL flush!) • Commence CPR and put out crash call if no pulse palpable • Document on anaesthetic chart and consider prophylactic glycopyrrolate next time

Answer 21

Lithium • Used mainly in bipolar disorder • Decreases the central and peripheral neurotransmitters and may prolong depolarising neuromuscular blockade • May cause nephrogenic diabetes insipidus • Has a narrow therapeutic index and signs develop at > 2.0 mmol/L. Signs of toxicity include lethargy or restlessness initially; then tremor, ataxia, weakness and muscle twitching, hypokalaemia, arrhythmias, renal failure, convulsions, and coma ssRis • May cause SIADH: low [Na+] MAois • Potential for hypertensive crisis if used with sympathomimetics (mainly indirectly acting, i.e. metaraminol, ephedrine) • Caution with opioids (unpredictable effects with pethidine; morphine and fentanyl thought to be safe) • Irreversibly inhibit MAO, so consider stopping 2 to 3 weeks pre- procedure if concerned about anaesthetic interactions

Answer 22

Remote site anaesthesia

Answer 23

• Vertebral level Anatomical level of T10 vertebra • Dermatomal level ° Dermatome is the area of skin whose sensory innervation is derived from a single spinal nerve (dorsal root) ° Not the same as vertebral body level but refers to the cutaneous area at the level of umbilicus • Myotomal level ° Muscle distribution of a single spinal nerve (ventral root) ° T10 myotome includes the abdominal muscles ° Useful in clinical and electromyographic localisation of radicular lesion causing motor defect

Answer 24

Diagnosis: Intraperitoneal and retroperitoneal free gas Tip: Using lung windows makes free gas easier to visualise.

Answer 25

spontaneous • Perforated hollow viscus • Secondary to bowel obstruction • Secondary to peptic ulcer iatrogenic • Endoscopic perforation • Secondary to mechanical ventilation • After laparotomy and laparoscopy Miscellaneous • In females, the fallopian tube acts as a conduit between the vagina and the peritoneal cavity

Answer 26

Diffuse fatty liver. The liver is of low density in keeping with fatty infiltration. (Tip: Use the spleen for comparison. The liver density should be equal to or higher than the spleen.)

Answer 27

Benign lesions • Simple cysts • Abscesses • Hepatic adenoma • Focal nodular hyperplasia Malignant lesions • Hepatocellular carcinoma • Cholangiocarcinoma • Angiosarcoma Miscellaneous • Fatty liver • Cirrhosis

Answer 28

The liver is the second largest organ (second to skin). Weight is 1500 g, which accounts for 2.5% of body weight. • Hepatocytes are polyhedral epithelial cells arranged in sheets separated from each other by spaces filled with hepatic sinusoids • Hepatic sinusoids are vessels that arise at the portal triad and run between sheets of hepatocytes receiving blood from the portal triad to deliver to central vein

Answer 29

Anatomical division • Divided into right and left lobes by the falciform ligament, with the caudate and quadrate lobes arising from the right lobe • No clinical or surgical significance Surgical divisions (corinaud’s classification) • Total of eight independent segments • Each segment has its own blood supply and biliary drainage, so they can be resected without damage to the adjacent segments Functional classification Liver lobule is the structural unit of liver. See Figure 1.8 • Classic lobule ° Based on direction of blood flow ° Hexagonal structure with the central vein in the middle and portal triad (branches of portal vein, hepatic artery, and bile duct) in the six corners. The hepatic arterial and portal venous blood flows from portal triad to the central vein • Portal lobule ° Based on direction of bile flow ° The portal triad is in the middle and the central veins form the corners of the triangle • Hepatic acinus ° Based on changes in oxygen and nutrient content as blood flows from the portal triad to the central vein ° It is rhomboid tissue as shown in the image, containing two triangles of adjacent classic lobule, whose apices are the central veins ° Hepatocytes in the acinus are divided into three zones ° Zone 1 or periportal zone, where the blood supply is the highest. This zone is susceptible to damage by blood-borne toxins and infection ° Zone 2 or intermediate zone ° Zone 3 or centrilobular zone is closer to the central vein. This area is higher in CYP 450 levels but gets the least blood supply and is susceptible to ischaemia

Answer 30

Liver has a dual blood supply. Total liver blood flow = 1200–1400 mls/min = 25% of cardiac output It contains 10%–15% of the total blood volume, thereby acting as a powerful reservoir. Hepatic artery • High-pressure/high-resistance system • Branch of the coeliac trunk (branch of abdominal aorta) • Carries oxygenated blood • 20%–30% of total blood supply • 40%–50% of total oxygen supply Portal vein • Low pressure/low resistance • Formed by the union of superior mesenteric vein and splenic vein • Carries oxygen-poor but nutrient-rich blood from the abdominal viscera • 70%–80% of total blood supply • 50%–60% of total oxygen supply Deoxygenated, detoxified blood exits the liver via hepatic veins to join the inferior vena cava.

Answer 31

Like any other ‘factors affecting blood flow’ question, have a general classification of factors. (I have listed here the factors in no order of importance.) Myogenic autoregulation • Applicable only to the hepatic arterial system in metabolically active liver Metabolic/chemical control • CO2, o2, and pH changes can alter the hepatic blood flow • Postprandial hyperosmolarity increases the hepatic arterial and portal venous blood flow neural control • Autonomic nervous system via the vagus and splanchnic nerves also control the hepatic blood flow • An important example is the stimulation of the sympathetic system in haemorrhage resulting in constriction of arterioles and expulsion of blood into the general circulation, thus acting as a major reservoir of blood Humoral control • Adrenaline, angiotensin II, and vasopressin are the main constrictors of the arterial and venous system Hepatic arterial buffer response (HABR) • Phenomenon where decrease in portal venous blood flow increases the hepatic arterial blood flow and vice versa so that a constant oxygen supply and total blood flow is maintained • The mechanism of HABR is unknown, but the local production of adenosine is predicted to be one of the causative factors

Answer 32

• Immune responses: formation of plasma cells and lymphocytes • Phagocytosis • Haematopoiesis: in foetus • Lymphopoiesis: throughout • Storage of red cells: 8% of the circulating red cells are present in spleen

Answer 33

• Infection: malaria, infectious mononucleosis • Malignancy: lymphomas, leukaemia • Portal hypertension • Sickle cell disease • Collagen vascular diseases • Polycythemia

Answer 34

• Trauma ° Commonest organ injured in blunt abdominal trauma ° Associated with lower rib fractures • Hypersplenism ° Hereditary spherocytosis ° Idiopathic thrombocytopenic purpura • Tumour ° Lymphoma or leukaemia • Surgical ° Along with gastrectomy, pancreatectomy, etc. • Others ° Splenic cysts and abscess ° Hydatid cysts

Answer 35

overwhelming post-splenectomy infections (oPSI) • Infection due to encapsulated bacteria: 50% mortality • Organisms ° Strep. Pneumoniae ° Haemophilus influenza ° Neisseria meningitides • Occurs post-splenectomy in 4% patients without prophylaxis Prevention of oPSI • Antibiotic prophylaxis ° Penicillin (amoxicillin) ° Lifelong ° Prophylaxis required in children up to 16 years • Immunisation ° Pneumococcal, haemophilus, and meningococcal ° Perform 2 weeks prior to planned operation ° Immediately post-op for emergency cases ° Repeat every 5 to 10 years

Answer 36

The reasons for the altered pathophysiology of the heart-beating brainstem dead person can be due to • Primary pathology suffered by the patient • Complications of ITU treatment (mainly the resuscitation of the injured brain) • Specific physiological changes and a systemic inflammatory response caused by the brainstem death cardiovascular changes • Initial changes: The first change to occur is the increase in intracranial pressure (ICP). Mean arterial pressure increases to maintain cerebral perfusion in parallel with the increasing ICP. Later brain herniation causes ischaemic changes in brainstem and a hyper-adrenergic state. This in turn increases both pulmonary and systemic vascular resistance. Episodes of ‘sympathetic storm’ of variable duration occur with tachycardia, vasoconstriction, and hypertension, which can lead to myocardial ischaemia. Hypertension and bradycardia (Cushing’s reflex) occur in some patients secondary to reflex baroreceptor activation and activation of the parasympathetic nervous system • Subsequent changes: Cerebral herniation leads to loss of spinal cord sympathetic activity, reducing vasomotor tone, preload, and cardiac output. This is more consistent and called ‘syndrome with marked vasodilation and relative hypovolaemia’. Myocardial perfusion can be affected due to low aortic diastolic pressure other changes • Ischaemia to pituitary causes diabetes insipidus, fluid and electrolyte loss, leading to further cardiovascular instability • Reduced metabolic rate, loss of hypothalamic control and vasodilatation results in heat loss and hypothermia • Coagulation abnormalities can occur due to original pathology and release of coagulation activators from the necrotic brain tissue and hypothermia • Posterior pituitary function is lost, but anterior pituitary function is preserved. There is reduction in T3 levels with normal TSH levels

Answer 37

In order to ensure that donations are as safe as possible, the donor’s medical and behavioural history is reviewed to reduce the risk of transmitting disease to a patient. There are many absolute contraindications for various tissue donations, but there are only two absolute contraindications for organ donation along with organ specific contraindications. Absolute contraindications for organ donation • Known or suspected new variant CJD and other neurodegenerative diseases • Known HIV disease, not HIV infection alone Relative contraindications for organ donation • Disseminated malignancy • Treated malignancy within 3 years (except non-melanoma skin cancer) • Age >70 years • Known active TB • Untreated bacterial sepsis organ and tissue specific contraindications Lungs • Donor age >65 • Previous intra-thoracic malignancy • Significant, chronic destructive or suppurative lung disease • Chest X-ray evidence of major pulmonary consolidation Liver • Acute hepatitis (AST >1000 IU/L) • Cirrhosis • Portal vein thrombosis Kidney • Chronic kidney disease (CKD stage 3B and below; eGFR <45) • Long-term dialysis • Renal malignancy • Previous kidney transplant (> 6 months previously) Pancreas • Insulin-dependent diabetes (excluding ICU-associated insulin requirement) • History of pancreatic malignancy Heart • Age >65 • Documented coronary artery disease • Median sternotomy for cardiac surgery • LVEF ≤ 30% on more than one occasion • Massive inotropic or vasopressor support

Answer 38

Referral: Early referral and communication with Donor Team (Specialist Nurse for organ Donation – SN-oD) should be done once decision is made to test for brainstem death. Each acute trust in the UK has a nominated SN-oD. If out of hours, the on-call SN-oD can be contacted. Patient/relatives: once notified, the SN-oD will collect all the information about the patient and his or her relatives. The specialist nurse will do a detailed assessment of the patient for suitability of organ donation. Decision is made on this assessment and after considering factors such as coroner and relatives’ views. Transplant centre: A check on organ donation is then made by contacting the NHS Blood and Transplant Duty office. ITU: once decision is made, optimal organ support is continued in the ITU and specific therapies are initiated to enhance the likelihood of successful transplantation.

Answer 39

General care Care should always take place in critical care environment. once the brain death had been confirmed, the care is mainly organ centred rather than patient centred, as patient is legally dead. Hence, in the brain-dead donor, it is appropriate to insert new lines for invasive monitoring if indicated for organ optimisation. Continue all the basic critical care management including enteral feeding, essential drugs and antimicrobial therapy, correction of electrolytes, glucose control with insulin, prevention of hypothermia, and blood product transfusion to correct significant anaemia and coagulopathy. organ specific management Cardiovascular system: Restoration of circulating volume without overload is essential. Short-acting drugs are used during the periods of Cushing’s reflux and sympathetic storm such as esmolol, GTN, and sodium nitroprusside infusions. Vasopressin is preferred to noradrenaline as this treats diabetes insipidus and minimises catecholamine requirements. T3 replacement can improve cardiac function. Haemodynamic targets include HR of 60–120/min, MAP of > 70 but < 95 mmHg, CVP of 10–15 mmHg, cardiac index of > 2.1 L/min/m2, and mixed venous saturation > 60%. Respiratory system: Methyl prednisolone 15 mg/kg given intravenously at the earliest opportunity as this is proven to reduce extra pulmonary lung water. Use lung protective ventilation with low tidal volumes of 6–8 mL/kg, inspiratory pressures limited to < 30 cmsH2o, use of PEEP and recruitment manoeuvres on regular intervals. Fio2 is adjusted to maintain Spo2 of > 90% or a Pao2 > 8.0 kPa. Endocrine management: T3 supplementation is part of many protocols but it is beneficial only in patients with poor cardiac performance after fluid loading and vasopressin. Desmopressin is also used if diabetes insipidus persisted. Insulin may be useful as anti-inflammatory and reduces cytokines in addition to glycaemic control. Renal and fluid management: Early assessment of overall fluid status is vital as hypervolemia is associated with poor liver graft function. Fluid overload and pulmonary congestion causes poor oxygenation, which makes the lung unsuitable for transplantation. Polyuria is common due to diabetes insipidus, diuretics use, and hypothermia. Nephrotoxic drugs should be stopped and blood pressure should be maintained to ensure adequate renal perfusion.

Answer 40

DBD—Donation after Brainstem Death DcD—Donation after cardiac Death DCD refers to the retrieval of organs and tissues for the purposes of transplantation after death that is confirmed using ‘traditional’ cardio- respiratory criteria. This pathway refers exclusively to ‘controlled’ DCD; that is, donation which follows a cardiac death that is the result of the withdrawal or nonescalation of cardio-respiratory support. Controlled DCD is where retrieval of organs is planned before death occurs. In uncontrolled DCD, decision for organ donation is made only after death. The main difference is in the duration of warm ischaemia time (WIT). Warm ischaemia starts when perfusion and oxygenation are inadequate after cardiac arrest or withdrawal of treatment. This period continues until cold ischaemia starts during organ retrieval. Cold perfusion slows down metabolism and ischaemic injury to the organs. This can be started earlier to reduce ischaemic injury.

Answer 41

Kidneys, liver, pancreas, lung, and tissues such as cornea, bone, skin, and heart valves. Renal donors are the major group with a WIT of up to 2 hours or sometimes longer. Liver and pancreas are increasingly used, but WIT is only 30 min. Lung is an ideal organ as it can tolerate lack of circulation for longer times if oxygenation is provided.

Answer 42

Dopamine is a neurotransmitter of the catecholamine family and is formed by removing a carboxyl group from a molecule of L–DoPA. Phenylalanine Phenylalanine hydroxylase L-Tyrosine Tyrosine hydroxylase (rate limiting step) L-DoPA DoPA decarboxylase Dopamine Dopamine β-hydroxylase Noradrenaline PNMT (Phenylethanolamine N-methyltransferase) Adrenaline

Answer 43

Dopamine is converted to noradrenaline and adrenaline, which are in turn metabolised by Catechol-o-methyltransferase (CoMT) and Monoamine oxidase (MAos)

Answer 44

Parkinsonism is characterised by the triad of tremor, rigidity, and bradykinesia. It has multiple causes, of which 85% is Parkinson’s disease. other causes of Parkinsonism Pharmacological: • Drugs affecting dopamine synthesis, storage, and release; e.g. reserpine • Drugs blocking dopamine receptor; e.g. prochlorperazine Vascular: e.g. arteriosclerosis, multi-infarct disease Infection: e.g. post-encephalitis Structural lesion: e.g. tumour, trauma (repeated head injury), normal pressure hydrocephalus Metabolic: e.g. hypoparathyroidism, Wilson’s disease Post–trauma: e.g. repeated head injury

Answer 45

1) Dopamine precursors with peripheral dopa decarboxylase inhibitor (DDI) Dopamine precursors (e.g. Levodopa) undergo conversion peripherally and within the CNS. DDI (e.g. benserazide) is administered together to reduce peripheral dopaminergic side effects (tachycardia, nausea, vomiting, dysrhythmias). 2) Dopamine agonists Examples: Ropinirole, Apomorphine. They mimic actions of dopamine at the dopamine receptors. 3) MAo-B inhibitors Example: Selegiline. Prevents breakdown of dopamine in CNS by MAo-B. 4) CoMT inhibitors Example: Entacapone. Used with Levodopa and DDI in combination to smooth out end-of-dose ‘off’ periods where symptoms return only a few hours after the last dose. 5) Anticholinergics Example: orphenadrine. Antagonises the unopposed excitatory effects of cholinergic pathways. 6) Atypical agents Example: Amantadine. Mechanisum of action not fully understood. May be useful as monotherapy in early Parkinson’s disease.

Answer 46

In general, it is advisable for patients to stop their drugs as late as possible preoperatively and restart it as soon as possible in the postoperative period. This is not always possible in patients who are unable to swallow or maintain enteral feeding (post major abdominal surgery). Levodopa can be administered via nasogastric or nasojejunal tubes. Patients can be commenced on apomorphine intravenous infusion and continue it throughout the operative period. The bolus dose of apomorphine can be determined by an apomorphine challenge—dose required to abolish the symptoms and to check that no severe adverse effects occur (e.g. profound hypotension).

Answer 47

• Pethidine should be avoided as it can cause hypertension and muscle rigidity in patients on selegiline • Antiemetics are of importance as nausea/vomiting can hinder restarting enteral Parkinson’s disease drugs. Metoclopramide, droperidol, and prochlorperazine are unsafe as they will worsen the symptoms and cause extra pyramidal effects. The antiemetic of choice is domperidone as it does not cross the blood brain barrier and therefore does not cause extra pyramidal effects • Antidepressants: tricyclic antidepressants may potentiate Levodopa- induced arrhythmias • Antipsychotics (e.g. phenothiazines, butyrophenones, piperazine derivatives) may worsen symptoms. It is best to use atypical antipsychotics (e.g. sulpiride, clozapine) • Antihypertensives may cause severe hypotension (due to postural hypotension, hypovolaemia) • Centrally acting anticholinergic drugs can precipitate central anticholinergic syndrome. Glycopyrrolate is the anticholinergic of choice

Answer 48

• Unpaired protons in the body (mostly H+ atom in water—abundant) align randomly and act as bar magnets • When placed in an external static magnetic field (A), the protons align • When another magnetic field (B) is applied, the protons are turned out of alignment • When this magnetic field is intermittently turned off and on, the radiofrequency energy taken up by the protons are released before the realignment takes place. Also there is some ‘Precession’—a wobbling motion that occurs when a spinning object is subject to an external force. • This energy released is measured by a set of 3-dimensional orthogonal gradient coils in the MRI machine • The energy released by protons in different tissues is different, and hence a 3-dimensional image with varying intensity is formed some numbers • Earth’s magnetic field = 0.5–1.0 Gauss • 10,000 Gauss = 1 Tesla • MRI requires magnetic fields between 0.2–3 Tesla (30,000 times the earth’s magnetic field) • MRI Safe zone < 5 Gauss • > 5 Gauss—pacemakers will malfunction and all personnel need screening • MRI Conditional zone—50 Gauss • > 50 gauss—ferro magnetic objects become projectiles and monitors malfunction

Answer 49

• ‘T’ is the relaxation time constant. • T1 weighted (early image)—few milliseconds after the electro magnetic field is removed • T2 weighted (later image)—later than T1 • Protons in hydrogen take a long time to decay to original position, so fluid will appear dark (minimal signal) in T1 but white (better signal) in T2

Answer 50

• Patient factors ° Patients needing anaesthesia are usually ITU patients, paediatric patients, patients with learning difficulties, seizures, or movement disorders ° Pregnancy: Currently recommended that pregnant women should ideally not be scanned during the first trimester of pregnancy due to magnetic field problems, noise, and also unscavenged anaesthetic gas issues ° Patients with implants: Pacemakers, cochlear implants, intraocular foreign body, and ferromagnetic aneurysm clips are absolute contraindications. Modern implants such as joint prosthesis, surgical clips, heart valves, and sternal wires are deemed safe. All patients and staff need screening • MRI factors ° Presence of strong magnetic field - Exert large forces on any ferromagnetic materials in the proximity - Induce currents in metallic objects and cause local heating - Interfere with monitoring - Magnetic field in the vicinity can also derange the quality of images produced - < 5 Gauss is the safe zone ° Noise such as that due to the gradient coils switching on and off - > 85 dB (above safe level) - Patient and staff should be protected - Can mask the monitor alarms ° Heat: That produced by the radiofrequency radiation is absorbed by patient. • Anaesthetic equipment factors ° MRI safe: Equipment will not pose a danger to patients and staff but does not guarantee that it will function correctly ° MRI compatible: Equipment is both safe to enter the MR examination room and will operate normally without interference to the MR scanner ° Anaesthetic machines, cylinders, circuits, ventilators, vapourisers and scavenging are now available as MRI-compatible ° Infusion pumps fail if field strength is > 50 Gauss • Anaesthetic monitoring factors ° MRI-compatible short (15 cms) braided ECG leads and insulated pulse oximetry cables are necessary ° NIBP—plastic connectors; IBP—pressure transducer cabling is passed through the wave guides or use MRI-compatible pressure transducers ° Capnography and airway pressure monitoring requires longer sample lines with a 20-second delay ° Monitoring screens should be in the control room and carbon fibre cables passed via the wave guide port • Location factors ° Usually remote ° Difficult to access in case of emergency

Answer 51

Faraday’s cage is a radiofrequency shield built into the fabric of the MR room. To allow infusion lines or monitoring cables to enter the MR room, a hollow brass tube or ‘waveguide’ is built into the Faraday cage passing through into the control room. Mechanism: An external static electrical field causes the electric charges within the cage’s conducting material to be distributed such that they cancel the field’s effect in the cage’s interior. Examples: Microwave oven, MR room.

Answer 52

The coils used in MR magnets need to be kept cold (liquid helium) in order to maintain superconductivity. Quenching is a process involving the rapid boil-off of the cryogen that causes an immediate loss of superconductivity. This can happen spontaneously, due to error or installation, or deliberately such as in order to switch the scanner off. This produces a large volume of helium gas, which is vented to the outside atmosphere through a quench pipe. In the event of damage to the quench pipe, the buildup of helium could potentially lead to asphyxiation.