Section 2 Flashcards

Question

What is open- and closed-angle glaucoma?

Answer 1

○ Open-angle glaucoma (chronic glaucoma) is the condition in which aqueous fluid drains very slowly due to clogging of the trabecular mesh. ○ Closed-angle glaucoma, also called acute glaucoma, is an ophthalmologic emergency. •This occurs when the iris completely blocks fluid access to the trabecular meshwork. •The pressure builds up, causing the patient excruciating eye pain, and vision is lost quickly. ○ In normal tension glaucoma optic nerve damage is present but with normal IoP. •The cause is mainly familial and history of systemic heart disease such as irregular heart rhythm.

Answer 2

IoP is dependent on • Contents, such as volume of aqueous, vitreous, and blood • Scleral compliance • Tone of extra ocular muscles • Drainage of aqueous, which depends on venous pressure Normal IoP = 16+/− 5 mmHg; >25 mmHg is pathological.

Answer 3

Yes. In open-angle and normal tension types, the IoP can be normal. The sclera adapts to increased volume, and hence IoP is normal.

Answer 4

○ Normally the aqueous humour produced by the ciliary body is drained to the veins through the Canal of Schlemm. ○ If the angle between iris and cornea is acute/blocked, then the drainage is affected, resulting in increased intraocular pressure. • Pain and loss of sight in extreme conditions; “silent thief of sight” Avoid drugs that dilate the pupils as this also can close the angle. See Figure 2.6

Answer 5

Consider IoP equivalent to ICP and structure your answers similarly. Any increase in volume and pressure intraocularly and obstruction to venous drainage would cause an increase in IoP. • IV induction drugs: decrease IOP except ketamine. • Muscle relaxants: suxamethonium increases IOP up to 10 mmHg due to extraocular muscle twitching. This can be overcome by giving adequate dose of IV induction agents. Nondepolarising muscle relaxants decrease IoP. • Hypoxia, hypercarbia, neck ties/coughing: increase IOP

Answer 6

General • Head up tilt • Avoid neck ties/coughing/vomiting, etc. • Maintain oxygenation, and avoid hypercarbia and hypotension. Drugs • Acetazolamide • Mannitol • Propofol

Answer 7

1. Pupillary (light) reflex ○ Afferent—Optic nerve, which terminates in the pretectal area of midbrain. ○ Axons from here then radiate bilaterally to terminate in the Edinger-Westphal nucleus ⊙Ciliary ganglion parasympathetic postganglionic axons travel in the short ciliary nerve and end on the iris sphincter. ○ Efferent—Oculomotor nerve ○ Ganglion—Ciliary ganglion ○ Central mediator—Occipital lobe of brain 2. corneal reflex ○ Afferent—Ophthalmic or nasociliary division of trigeminal nerve trigeminal nerve trigeminal ganglion spinal trigeminal tract spinal trigeminal nucleus ○ Efferent—Facial motor neurons facial nerve branch to orbicularis oculi ○ Ganglion—Trigeminal ganglion ○ Central mediator—Pons

Answer 8

The spinal cord derives its blood supply from a single anterior spinal artery (ASA), paired posterior spinal arteries (PSA), and by the communicating segmental arteries and the pial plexus. AsA Single artery formed at the foramen magnum by the union of each vertebral artery. Blood flows centrifugally supplying the anterior two-thirds of the spinal cord in front of the posterior grey column. PsA Derived from the posterior inferior cerebellar artery (PICA) or vertebral artery, with blood flowing centripetally in this arterial system. The arteries lie along the postero lateral surface of the spinal cord medial to the posterior nerve roots. Pial arterial plexus Surface vessels branch from the ASA and PSA forming an anastomosing network that penetrates and supplies the outer portion of the spinal cord. segmental branches Segmental or radicular branches arise from various arteries—vertebral, deep cervical, costo cervical, aorta, and the pelvic vessels. Arteria radicularis magna, or the artery of Adamkiewicz Arises from the thoracolumbar part of the aorta, usually on the left, and enters the spinal cord at the level of L1. Various regions of spinal cord are vascularised unevenly. The cervical and lumbosacral parts are well vascularised whereas the thoracic part of the spinal cord, especially the anterior region, derives the branches from intercostal and iliac arteries, which vary in location and numbers making it prone to ischaemic damage. See Figures 2.7 and 2.8.

Answer 9

○ Radicular and spinal veins drain into the internal vertebral venous plexus and later drain into the azygos system and the superior vena cava. ○ The plexus communicates with the basilar sinus in the brain and with the pelvic veins and inferior vena cava. ○ So in patients with increased intra-abdominal pressure, blood is diverted from the inferior vena cava to the plexus, leading to engorgement of epidural veins. a. This increases the risk of accidental venous puncture during the conduct of epidural anaesthesia. b. It also decreases the effective epidural space volume, thereby requiring a smaller volume of local anaesthetic

Answer 10

○ Watershed effect occurs when two streams of blood flowing in opposite directions meet. ○ This happens where the radicular artery unites with the ASA, where blood courses upward and downward from the entry point, thus leaving a watershed region between the adjacent radicular areas where blood flows in neither direction. ○ The watershed effect is maximum in the mid-thoracic area due to the greater distance between the radicular arteries

Answer 11

1. Trauma 2. Rupture of aortic aneurysm 3. Dissection of the aorta 4. Inflammation of aorta—vasculitis, collagen disorders 5. Venous hypertension 6. Degenerative spinal diseases and disc herniation 7. Severe atherosclerosis and luminal narrowing 8. Iatrogenic • Vasoconstrictors in epidural space • Surgical cross clamping of the aorta • Coeliac plexus block • Deliberate/accidental hypotension

Answer 12

○ According to recent statistics, incidence of spinal cord ischaemia following thoracoabdominal aortic aneurysm repair is 3% –18% despite improved surgical technique, transfusion, and perfusion technology. ○ The factors that determine the neurological outcome after aortic cross clamping are: 1. Presence of predisposing factors, such as atherosclerosis, diabetes, and renal disease 2. Extent of aneurysm 3. Duration of cross clamp 4. Surgical difficulty 5. Previous aortic surgery 6. Severity of perioperative hypotension

Answer 13

1. Mild systemic hypothermia (32°–34°C): The most reliable protective adjunct and helps by decreasing metabolic demands and attenuating inflammatory response to ischaemia. 2. Maintaining spinal cord perfusion pressure (SCPP) depends on the mean arterial pressure and cerebrospinal fluid pressure (CSFP). SCPP = MAP − CSFP Cross-clamping leads to proximal hypertension and increased cerebrospinal fluid pressure. So controlling the arterial pressure with vasopressors or decreasing CSFP via lumbar drains plays a significant role in maintaining SCPP. 3. Distal aortic shunting through femorofemoral bypass and left heart bypass increases the blood flow to the distal aorta. 4. Pharmacological neuroprotection: Agents such as free radical scavengers, barbiturates, steroids, opiate antagonists, etc., have been evaluated in decreasing the risk of ischaemic damage of the cord. 5. Monitoring spinal cord function with MEPs/SSEPs have proved effective in preventing damage by avoiding important radicular arteries.

Answer 14

○ ASA syndrome—problems in the anterior spinal artery territory resulting in critical ischaemia of the anterior part of the spinal cord. ○ The characteristic findings are Motor • Loss of motor function bilaterally below the level of lesion due to the involvement of corticospinal tracts Sensory • Loss of spinothalamic tracts resulting in bilateral thermoanaesthesia • But intact light touch, vibration, and proprioception due to preservation of posterior columns Autonomic • Sexual dysfunction; loss of bladder and bowel function due to the effect on descending autonomic tract See Figure 2.9.

Answer 15

• Hypoventilation • Rebreathing • Sepsis • Malignant hyperpyrexia (MH) • Skeletal muscle activity/hypermetabolism • CO2 insufflation

Answer 16

• Increase ventilation • Change soda lime or increase flows • Increase depth of anaesthesia, muscle relaxants • Specific treatment of MH

Answer 17

• Hypoventilation • CO2 insufflation • CO2 embolism

Answer 18

• Hypoventilation • CO2 insufflation • CO2 embolism

Answer 19

Medical contraindications to laparoscopic surgery are always relative. Successful laparoscopic surgery has been performed on anticoagulated, pregnant, and morbidly obese patients.

Answer 20

• Cardiovascular ° ‚cardiac index: ‚venous return due to compression of IVC and Trendelenburg position ° ·SVR: Aortic and splanchnic compression ° ·MAP ° Ischaemia: alteration in supply and demand ° Arrhythmia: Vagally mediated and ventricular due to high Co2 ° Cardiac failure • Respiratory ° ‚FRC - Diaphragmatic splinting and cephalad displacement - Atelectasis - Pulmonary shunting - Hypoxaemia ° ·Airway pressures: barotrauma or pneumothorax ° ·Co2: Rises by 1 kPa—needs 25% increase in minute volume ° Endobronchial intubation ° Gas embolism: Rare and Co2 is safe • Renal effect: ‚Renal blood flow and GFR • Acid aspiration

Answer 21

>20 mmHg >30 mmHg, Cardiac index might fall by 50%

Answer 22

• Head up: Hypotension and cerebral hypoperfusion • Head down: Cerebral oedema, retinal detachment (long operations) • Soft tissue damage due to pressure; e.g. Brachial plexus injury with pressure on the shoulder and neck if used with harness to prevent the patient from slipping down with extreme head down.

Answer 23

Pros: • Pulmonary function better preserved following laparoscopic surgery; FVC‚ 27% after laparoscopic surgery and by 48% after open surgery • Less painful, earlier discharge from hospital • Cosmetic appealing surgical scars cons: • Postoperative nausea and vomiting—50% of patients require antiemetics, so prophylactic antiemetics may be given routinely • Pain following laparoscopic surgery consists of early transient vagal abdominal and shoulder discomfort due to peritoneal irritation by residual carbon dioxide

Answer 24

• Volume of gas entrainment: The closer the vein of entrainment is to the right heart, the smaller the lethal volume. - As little as 0.5 mL in Lt anterior descending artery or 2 mL in cerebral circulation is fatal. Traditional estimation is 5 mL/kg • Rate of accumulation: > 0.30 mL/kg/min • Patient’s position at the time of the event

Answer 25

• Pressure effect: Air entering the systemic venous circulation puts a substantial strain on the right ventricle, and rise in pulmonary artery pressures. This increase in PA pressure can lead to right ventricular outflow obstruction and decrease pulmonary venous return to the left heart, which in turn would lead to resultant decreased cardiac output and eventual systemic cardiovascular collapse. • Inflammatory effect: The air embolism effects on the pulmonary vasculature can lead to serious inflammatory changes in the pulmonary vessels such as direct endothelial damage and accumulation of platelets, fibrin, neutrophils, and lipid droplets. Secondary injury as a result of the activation of complement and the release of mediators and free radicals can lead to capillary leakage and eventual noncardiogenic pulmonary edema. • V/Q mismatch: Alteration in the resistance of the lung vessels and ventilation-perfusion mismatching can lead to intra-pulmonary right-to-left shunting and increased alveolar dead space with subsequent arterial hypoxia and hypercapnia.

Answer 26

History • Anaesthetic history, paying particular attention to cardiac and respiratory function • Smoking history examination • Signs of weight loss and cachexia • Cardiovascular and respiratory examination investigations • Routine bloods, cross matching • Arterial blood gas • Lung Spirometry, diffusion capacity (DLCO), predicted postoperative FEV1 • Cardiopulmonary exercise testing (CPET)

Answer 27

DLCo is the diffusion capacity and is calculated by measurement of carbon monoxide taken up by p

Answer 28

○ The predicted or estimated postoperative (epo) values of FEV1, FVC, and diffusion capacity can be obtained by consideration of the lung volume removed at surgery. ○ For lobectomy, the simple calculation uses the number of bronchopulmonary segments removed compared with the total number (19) in both lungs. Example: Consider a patient with a preoperative FEV1 of 1.6 litre, which is 80% of predicted normal. For right middle lobectomy (two segments), epo-FEV1 = 1.6 × 17/19 = 1.43 litre ppo-FEV1% = 80% × 17/19 = 71% ○ often a V/Q scan is used to measure how much the lung that will not be operated on contributes to lung function and then combine with a formula to calculate postoperative FEV1.

Answer 29

○ The flow chart in Figure 2.5 is an amalgamation of the British Thoracic Society and American College of Chest Physicians’ guidelines. ○ The initial screening tool is of preoperative measured FEV1 with >2 litre required for pneumonectomy and >1.5 litre for lobectomy. ○ If there is no diffuse lung disease and no comorbidity, achievement of the appropriate lung volume is sufficient. ○ When these threshold lung volumes are not present, full respiratory function testing allows calculation of the predicted postoperative FEV1 and DLCo. ○ If both are >40% and the oxygen saturation is >90% on air, the patient is in an average risk group. If either (or both) the predicted postoperative FEV1 or DLCo are <40%, the patient should undergo formal CPET. ○ The threshold Vo2 max of 15 ml/kg/min delineates between high- and medium-risk patients. ○ This patient is undergoing a thoracotomy and lung resection.

Answer 30

For thoracotomy, one lung ventilation is desired and hence you can use a double lumen tube (DLT) or bronchial blocker.

Answer 31

• Commonly used tube is left-sided Mallinckrodt. Size 39–41 for male and 37 for female. • Insert with stylet, pass vocal cords, then remove stylet, and rotate the tube to 90 degrees and advance. once resistance is felt, inflate tracheal cuff and check both lungs. • Then inflate bronchial cuff and clamp off tracheal lumen. Confirm single lung ventilation. Repeat on opposite side. • Gold standard: Check with fibreoptic scope before and after positioning. on the left side, blue bronchial cuff should just be visible below carina; on the right side, also check that right upper lobe corresponds to opening “slit” in distal bronchial lumen.

Answer 32

• Systemic • Paracetamol, NSAIDs, IV opioids • Neuraxial ° Epidural—Gold standard but failure rate and hypotension from bilateral sympathetic blockade. ° Intrathecal—Not often used. ° Paravertebral—Getting more popular, can be placed by surgeon by direct vision or anaesthetist. Single-side blockade makes for less incidence of hypotension. ° Intercostal and intrapleural—Can be used but the limited effectiveness makes its use not as popular.

Answer 33

• Soda lime - Commonly used, it has been proven that presence of sodium hydroxide, at any level, provides the basis for anaesthetic agent dehalogenation, which can lead to formation of compound A and carbon monoxide. • Baralyme or barium lime - It is made of 80% calcium hydroxide and 20% barium hydroxide. This is less efficient than soda lime and also produces compound A more quickly. • Litholyme or lithium lime - Also an effective carbon dioxide absorbent, litholyme is free of the strong bases (NaoH, KoH) and does not produce compound A or carbon monoxide. - Lithium chloride acts as the catalyst to accelerate the formation of calcium carbonate. • Amsorb - Contains calcium hydroxide and calcium chloride and is not associated with the formation of carbon monoxide or compound A. • Amsorb Plus - It is a new generation carbon dioxide absorbent, free from strong alkali metal hydroxides. - It utilizes calcium hydroxide as the active base with minor constituents that promote speed and capacity of absorption. - Amsorb Plus is specifically designed for low and minimal flow anaesthesia. • Dragersorb and Medisorb - These are produced by Drager and GE healthcare, respectively, with varying proportions of constituents.

Answer 34

○ Soda lime consists of 94% calcium hydroxide, 5% sodium hydroxide, and a small amount of potassium hydroxide (0.1%) and silica to prevent disintegration. ○ A dye or colour indicator such as ethyl violet is also added, which changes the colour when the soda lime is exhausted. - This happens at pH < 10. pH 13.5 ○ Moisture content 14%–19% ○ 1 kg absorbs 120 L of carbon dioxide ○ When exhaled gases reach the canister, carbon dioxide absorption takes place and heat and water are produced. The warmed and humidified gas rejoins the fresh gas flow (FGF). ○ In a patient with tidal ventilation of 6 L/min and Co2 production of 250 ml/min, the soda lime will be exhausted in 6 hours at FGF of 1 L/min and in 8 hours if the FGF is 3 L/min.

Answer 35

Co2 + H2o H2Co3 then H2Co3 + 2 KoH - K2Co3 + 2 H2o + Energy then K2Co3 + Ca(oH)2 - CaCo3 + 2KoH oR Co2 + 2NaoH Na2Co3 + H2o + heat then Na2Co3 + Ca(oH)2 CaCo3 + 2NaoH Each mole of Co2 (44 g) reacted produces one mole of water (18 g). The overall reaction is Ca(oH)2 + Co2 CaCo3 + H2o + heat

Answer 36

compound A • Is a fluoro methyl ether produced when sevoflurane is used with soda lime due to dehydrohalogenation in the presence of KoH. • Factors that increase the production of compound A are ° High sevoflurane ° Increasing temperature ° Low FGF ° Use of baralyme carbon monoxide • Occurs when inhalational agents with CHF2 moiety such as desflurane, enflurane, and isoflurane are used with desiccated soda lime granules. This happens when the system is left unused for a long time. This can lead to formation of carboxyhaemoglobin and can be significant in smokers especially when very low flows are used. • Factors increasing the production of CO include ° Type of inhaled anaesthetic agent (magnitude of Co production from greatest to least is desflurane > enflurane > isoflurane > sevoflurane) ° High absorbent dryness ° Type of absorbent (at a given water content, baralyme produces more Co than soda lime) ° Increased temperature ° Higher anaesthetic concentration • Other insignificant substances like methane, acetone, ethanol, etc.

Answer 37

The typical size is expressed as between 4–8 mesh. It means the granules will pass through a mesh with 4–8 strands per inch in each axis. The uniformity in size is necessary to provide a smooth flow. They should provide larger surface area but lesser resistance to flow. Bigger molecules would cause gas channelling, and smaller granules can increase the resistance to gas flow

Answer 38

• Anaesthetic use • Non anaesthetic use—in submarines and recompression chambers • Metabolic monitoring—in alkaline fuel cells to extract carbon dioxide as it affects the measurement Advantages • Permits low flows without rebreathing carbon dioxide, making the system cost effective • Less waste and pollution • Humidification of inspired gases due to the inherent exothermic reaction

Answer 39

No. The decrease in pH causes the indicator to change colour, so any product that causes a decrease in pH can mimic an exhausted soda lime. In partial exhaustion, the carbonic acid levels increase and cause the change in colour of the indicator. If the soda lime is unused, then the free hydroxyl ions from the depth of the canister migrate to the surface and neutralise the acid, reverting the colour change. As a result, the soda lime appears fresh although it is partially exhausted.

Answer 40

No. The decrease in pH causes the indicator to change colour, so any product that causes a decrease in pH can mimic an exhausted soda lime. In partial exhaustion, the carbonic acid levels increase and cause the change in colour of the indicator. If the soda lime is unused, then the free hydroxyl ions from the depth of the canister migrate to the surface and neutralise the acid, reverting the colour change. As a result, the soda lime appears fresh although it is partially exhausted.

Answer 41

• Increased spontaneous respiratory rate in the absence of muscle relaxant • Increase in sympathetic drive • Respiratory acidosis • Increased surgical bleeding due to hypertension and coagulopathy

Answer 42

Advantages • Economy of anaesthetic consumption • Warming and humidification of the inspired gases • Reduced atmospheric pollution Disadvantages • Unstable if closed-system is used • Slow changes in the inspired anaesthetic concentration with low flows and out-of-circuit vaporiser

Answer 43

• CO2 absorber canister • Breathing bag • Unidirectional inspiratory and expiratory valves • Fresh gas supply • Pressure-relief valve • Corrugated hoses and a Y-piece The body of the absorber is connected to the patient by means of inspiratory and expiratory tubes and a Y-piece the size of which is important when anaesthetising paediatric patients as very small tidal volumes may not generate enough pressure to open the valves effectively. The effective dead space of the Y-piece is larger than it appears, and so there can be rebreathing of exhaled gas. These difficulties are overcome by the use of purpose-built infant absorbers and paediatric tubing and Y-pieces.

Answer 44

This is one of the difficult questions but keeps reappearing at the FRCA. control of disease progression • Cytotoxics immunosuppressants • Immunoglobins, anti-lymphocytes such as cyclosporine and tacrolimus control of symptoms • Analgesics • Antiemetics • Anxiolytics • Antisialogogues Prevent/treat metastasis • Bone-modifying drugs (e.g., Alendronic acid)

Answer 45

• Alkylating agents Act by chemically altering DNA by adding alkyl groups to the electronegative groups of cancer cells. (e.g. Cisplatin, Carboplatin, Chlorambucil, Cyclophosphamide) • Anti-metabolites The anti-metabolites function as the building blocks of DNA by imitating the role of purine or pyrimidine and stop cell division. (e.g. Methotrexate, cytarabine) • Plant alkaloids They block cell division by inhibiting microtubule function. (e.g. vinca alkaloids) • Topoisomerase inhibitors Topoisomerases are enzymes that are essential to maintain the topology of the DNA. Interfering with these enzymes prevents the normal functions of the DNA, such as transcription, replication, and repair. (e.g. amasacrine and etoposide) • Antitumour antibiotics (e.g. Dactinomycin, daunorubicin, doxorubicin) • Hormones Prednisone and dexamethasone in high doses can damage lymphoma cells. Tamoxifen is a selective oestrogen receptor modulator. Finasteride is a 5 alpha reductase inhibitor. • Monoclonal antibodies Monoclonal antibodies attach themselves to tumour-specific antigens, thereby increasing immune response to tumour cell. (e.g. rituximab, cetuximab, trastuzumab)

Answer 46

Pulmonary toxicity • Infection due to neutropenic myelosuppression • Pneumonitis: methotrexate and cyclophosphamide • Pulmonary fibrosis: bleomycin cardiac toxicity • Arrhythmias, myocardial infarction, congestive cardiac failure, cardiomyopathy, myocarditis, and pericarditis: cyclophosphamide • Torsades de Pointes: cisplatin and anthracyclines Renal toxicity • Acute and chronic renal failure: cisplatin and carboplatin Hepatotoxicity • Fatty change, cholestasis, and hepatocellular necrosis: methotrexate and cyclophosphamide neurotoxicity • Peripheral and cranial neuropathy, autonomic dysfunction, and seizures: Vinca alkaloids and methotrexate Haematological toxicity • Myelodepression and neutropenic sepsis: most agents

Answer 47

Water and sodium retention, hypokalaemia, hypertension, hyperglycaemia, diabetes, osteoporosis, proximal myopathy, dyspepsia, peptic ulcer, euphoria, depression, infection, poor wound healing, Cushing’s, etc

Answer 48

Increased infection, abnormal LFTs, thrombocytopenia, photosensitivity

Answer 49

It is a group of metabolic complications that can occur after treatment of cancer, usually lymphomas and leukaemias. Precipitating medication includes combination chemotherapy or steroids, and it sometimes occurs without any treatment and is known as ‘spontaneous tumour lysis syndrome’.

Answer 50

Hyperkalaemia High turnover of tumour cells leads to spill of potassium into the blood. • Cardiac conduction abnormalities (can be fatal) • Severe muscle weakness or paralysis Hyperphosphataemia Causes acute renal failure because of deposition of calcium phosphate crystals in the renal parenchyma Hypocalcaemia Calcium precipitates with phosphate to form calcium phosphate, leading to hypocalcaemia. • Tetany • Seizures • Emotional instability/agitation/anxiety • Myopathy Hyperuricaemia Acute uric acid nephropathy (AUAN)

Answer 51

• Adequate IV hydration • Alkalinisation of urine • Prophylactic oral or IV allopurinol • Rasburicase as an alternative to allopurinol

Answer 52

Simple analgesics: Paracetamol and nonsteroidal agents Weak opioids: tramadol and codeine Strong opioids: morphine, diamorphine in oral, parenteral, transdermal and neuraxial routes Special drugs: gabapentin, pregabalin Nerve blocks

Answer 53

Breakthrough pain is defined as pain of moderate or severe intensity occurring against a background of controlled chronic pain. It could be spontaneous, incidental, or procedural. As with any cancer pain, treatment relies on detailed assessment and formulation of a multidisciplinary therapy plan. Rapid acting opioids have been successfully used to treat breakthrough pain, but it remains a difficult therapeutic problem.

Answer 54

• Hypoventilation • Rebreathing • Sepsis • Malignant hyperpyrexia (MH) • Skeletal muscle activity/hypermetabolism • CO2 insufflation

Answer 55

• Increase ventilation • Change soda lime or increase flows • Increase depth of anaesthesia, muscle relaxants • Specific treatment of MH

Answer 56

• Hypoventilation • CO2 insufflation • CO2 embolism

Answer 57

Medical contraindications to laparoscopic surgery are always relative. Successful laparoscopic surgery has been performed on anticoagulated, pregnant, and morbidly obese patients

Answer 58

• Pneumoperitoneum and its effects • Positioning: extreme head up or head down • Surgical issues: trauma of a viscus, vascular trauma

Answer 59

• Cardiovascular ° ‚cardiac index: ‚venous return due to compression of IVC and Trendelenburg position ° ·SVR: Aortic and splanchnic compression ° ·MAP ° Ischaemia: alteration in supply and demand ° Arrhythmia: Vagally mediated and ventricular due to high Co2 ° Cardiac failure • Respiratory ° ‚FRC - Diaphragmatic splinting and cephalad displacement - Atelectasis - Pulmonary shunting - Hypoxaemia ° ·Airway pressures: barotrauma or pneumothorax ° ·Co2: Rises by 1 kPa—needs 25% increase in minute volume ° Endobronchial intubation ° Gas embolism: Rare and Co2 is safe • Renal effect: ‚Renal blood flow and GFR • Acid aspiration

Answer 60

>20 mmHg >30 mmHg, Cardiac index might fall by 50%

Answer 61

• Head up: Hypotension and cerebral hypoperfusion • Head down: Cerebral oedema, retinal detachment (long operations) • Soft tissue damage due to pressure; e.g. Brachial plexus injury with pressure on the shoulder and neck if used with harness to prevent the patient from slipping down with extreme head down.

Answer 62

Pros: • Pulmonary function better preserved following laparoscopic surgery; FVC‚ 27% after laparoscopic surgery and by 48% after open surgery • Less painful, earlier discharge from hospital • Cosmetic appealing surgical scars cons: • Postoperative nausea and vomiting—50% of patients require antiemetics, so prophylactic antiemetics may be given routinely • Pain following laparoscopic surgery consists of early transient vagal abdominal and shoulder discomfort due to peritoneal irritation by residual carbon dioxide

Answer 63

• Volume of gas entrainment: The closer the vein of entrainment is to the right heart, the smaller the lethal volume. As little as 0.5 mL in Lt anterior descending artery or 2 mL in cerebral circulation is fatal. Traditional estimation is 5 mL/kg • Rate of accumulation: > 0.30 mL/kg/min • Patient’s position at the time of the even

Answer 64

• Pressure effect: Air entering the systemic venous circulation puts a substantial strain on the right ventricle, and rise in pulmonary artery pressures. This increase in PA pressure can lead to right ventricular outflow obstruction and decrease pulmonary venous return to the left heart, which in turn would lead to resultant decreased cardiac output and eventual systemic cardiovascular collapse. • Inflammatory effect: The air embolism effects on the pulmonary vasculature can lead to serious inflammatory changes in the pulmonary vessels such as direct endothelial damage and accumulation of platelets, fibrin, neutrophils, and lipid droplets. Secondary injury as a result of the activation of complement and the release of mediators and free radicals can lead to capillary leakage and eventual noncardiogenic pulmonary edema. • V/Q mismatch: Alteration in the resistance of the lung vessels and ventilation-perfusion mismatching can lead to intra-pulmonary right-to-left shunting and increased alveolar dead space with subsequent arterial hypoxia and hypercapnia.