I85PREP
⌘ K
Arab Board Anesthesia Part 1 study materials
Arab Board Anesthesia Part 1 study resources

Arab Board Anesthesia Part 1 practice questions

One question at a time. Build your Arab Board Anesthesia Part 1 understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Applied Anatomy

The cricothyroid membrane, the standard site for emergency front-of-neck airway access, is located between which two structures?

  1. The thyroid cartilage and the cricoid cartilage Correct answer.
  2. The arytenoid cartilages and the thyroid cartilage
  3. The cricoid cartilage and the first tracheal ring
  4. The hyoid bone and the thyroid cartilage

Explanation

The cricothyroid membrane spans the gap between the inferior border of the thyroid cartilage and the superior border of the cricoid cartilage. It is relatively avascular and superficial, which is why it is the preferred puncture site in a cannot-intubate cannot-oxygenate situation.

Question 2Applied Anatomy

Which nerve provides sensory innervation to the mucosa of the vocal cords?

  1. The recurrent laryngeal nerve
  2. The external branch of the superior laryngeal nerve
  3. The internal branch of the superior laryngeal nerve Correct answer.
  4. The glossopharyngeal nerve

Explanation

The internal branch of the superior laryngeal nerve pierces the thyrohyoid membrane and supplies sensation to the laryngeal mucosa above the vocal cords, including the cords themselves. This is why topical anesthesia of this nerve blunts the gag and cough response during awake intubation.

Question 3Applied Anatomy

A patient develops hoarseness after thyroid surgery. Which nerve is most likely injured given its course in the tracheoesophageal groove?

  1. The superior laryngeal nerve
  2. The recurrent laryngeal nerve Correct answer.
  3. The hypoglossal nerve
  4. The phrenic nerve

Explanation

The recurrent laryngeal nerve ascends in the tracheoesophageal groove close to the thyroid gland and is vulnerable during thyroidectomy. Injury causes vocal cord paresis and hoarseness; bilateral injury can cause airway obstruction.

Question 4Applied Anatomy

The dural puncture during a spinal anesthetic most commonly occurs at which vertebral level in an adult?

  1. L2–L3 or L3–L4 Correct answer.
  2. L1–L2
  3. L5–S1
  4. T12–L1

Explanation

The conus medullaris ends around L1–L2 in adults, so the spinal cord is safely above the L2–L3 and L3–L4 interspaces. These lower lumbar levels are therefore the standard sites for lumbar puncture and spinal anesthesia.

Question 5Applied Anatomy

During a lumbar epidural, the needle passes through several layers. Which structure must be pierced to enter the epidural space from posterior approach?

  1. The annulus fibrosus
  2. The ligamentum flavum Correct answer.
  3. The pia mater
  4. The posterior longitudinal ligament

Explanation

The ligamentum flavum is the last ligamentous layer before the epidural space in the midline posterior approach. Loss of resistance to saline or air is felt as the needle traverses it into the epidural space.

Question 6Applied Anatomy

Which vessel is most likely to be inadvertently cannulated during attempted internal jugular vein catheterization because it lies immediately posterolateral to the vein?

  1. The carotid artery Correct answer.
  2. The subclavian artery
  3. The external jugular vein
  4. The vertebral artery

Explanation

The common carotid artery lies medial and slightly posterior to the internal jugular vein within the carotid sheath. Needle passage beyond the vein can therefore enter the carotid, which is why ultrasound guidance and aspiration checks are used.

Question 7Applied Anatomy

The subclavian vein is commonly approached during central line placement. Which structure lies immediately posterior to the vein and is at risk of injury?

  1. The phrenic nerve
  2. The subclavian artery Correct answer.
  3. The first rib
  4. The apex of the lung

Explanation

The subclavian artery lies immediately posterior and superior to the subclavian vein as they cross the first rib behind the clavicle. Advancing the needle too far posteriorly can puncture the artery.

Question 8Applied Anatomy

The brachial plexus is most reliably blocked at the interscalene level, but this approach commonly spares which nerve?

  1. The ulnar nerve Correct answer.
  2. The median nerve
  3. The musculocutaneous nerve
  4. The radial nerve

Explanation

At the interscalene level the plexus is still in the neck, and the lower trunk (C8–T1) fibers that form the ulnar nerve are often missed. This is why interscalene block is unreliable for the ulnar distribution of the hand.

Question 9Applied Anatomy

Which anatomical landmark best identifies the site for an axillary brachial plexus block?

  1. The pulsation of the axillary artery Correct answer.
  2. The coracoid process
  3. The medial epicondyle
  4. The deltoid tuberosity

Explanation

At the axilla the brachial plexus cords surround the axillary artery, so arterial pulsation is the key landmark. Needle placement is aimed just around the artery within the axillary sheath.

Question 10Applied Anatomy

A femoral nerve block is performed in the inguinal region. The femoral nerve lies in which relation to the femoral artery?

  1. Medial to the femoral artery
  2. Lateral to the femoral artery Correct answer.
  3. Anterior to the inguinal ligament
  4. Posterior to the femoral vein

Explanation

In the femoral triangle the nerve lies lateral to the artery, which in turn lies lateral to the vein (NAVY from lateral to medial). This lateral position guides needle placement for femoral block.

Question 11Applied Anatomy

The sciatic nerve is classically blocked in the popliteal fossa. Which landmark defines the level at which the nerve divides into tibial and common peroneal components?

  1. The head of the fibula
  2. The adductor hiatus
  3. The apex of the popliteal fossa Correct answer.
  4. The popliteal crease

Explanation

The sciatic nerve typically bifurcates near the apex of the popliteal fossa, above the popliteal crease. Blocking at or above this level ensures coverage of both tibial and common peroneal territories.

Question 12Applied Anatomy

The diaphragm is innervated by the phrenic nerve. From which spinal segments does the phrenic nerve arise?

  1. C1–C3
  2. C3–C5 Correct answer.
  3. T1–T3
  4. C5–T8

Explanation

The phrenic nerve arises from ventral rami of C3, C4, and C5 ("C3-4-5 keeps the diaphragm alive"). It descends through the neck and thorax to innervate the diaphragm.

Question 13Applied Anatomy

Which structure marks the carina, the bifurcation of the trachea, in an adult?

  1. The jugular notch
  2. The xiphisternal joint
  3. The second rib anteriorly
  4. The sternal angle (angle of Louis) Correct answer.

Explanation

The carina lies approximately at the level of the sternal angle (T4–T5) and is an important landmark during bronchoscopy and for confirming tracheal tube depth.

Question 14Applied Anatomy

During one-lung ventilation with a double-lumen tube, correct placement of the right-sided tube requires particular care because of which anatomical feature?

  1. The trachea is shorter on the right
  2. The right upper lobe bronchus arises very close to the carina Correct answer.
  3. The right lung has three lobes
  4. The left main bronchus is shorter

Explanation

The right upper lobe bronchus arises close to the carina from the right main bronchus, so a right-sided double-lumen tube can easily occlude it. This is why right-sided tubes are more prone to malposition and require bronchoscopic confirmation.

Question 15Applied Anatomy

The aortic valve is best auscultated at which location?

  1. The left second intercostal space at the sternal edge
  2. The right second intercostal space at the sternal edge Correct answer.
  3. The left fifth intercostal space at the midclavicular line
  4. The lower left sternal border

Explanation

The aortic valve sounds are best heard in the right second intercostal space adjacent to the sternum, the aortic area. The mitral area is at the apex, the pulmonary area at the left second space, and the tricuspid area at the lower left sternal border.

Question 16Applied Anatomy

The coronary sinus drains most of the cardiac venous blood and empties into which chamber?

  1. The left ventricle
  2. The left atrium
  3. The right atrium Correct answer.
  4. The right ventricle

Explanation

The coronary sinus opens into the right atrium near the inferior vena cava. This is relevant because coronary sinus catheters and retrograde cardioplegia access the right atrium.

Question 17Applied Anatomy

During central venous cannulation, the right internal jugular vein is preferred partly because of which anatomical relationship?

  1. It has no valves
  2. It has a straight course to the superior vena cava Correct answer.
  3. It is the largest vein in the neck
  4. It lies lateral to the carotid artery

Explanation

The right internal jugular vein and right brachiocephalic vein form an almost straight line to the superior vena cava, easing catheter advancement. The left side has a more angulated course.

Question 18Applied Anatomy

The anterior approach to the sciatic nerve block in the supine patient relies on which landmark relationship?

  1. The nerve lies medial to the femoral artery
  2. The nerve lies between the greater trochanter and ischial tuberosity Correct answer.
  3. The nerve lies anterior to the greater trochanter
  4. The nerve lies posterior to the lesser trochanter of the femur

Explanation

The sciatic nerve exits the pelvis through the greater sciatic foramen between the greater trochanter and the ischial tuberosity. This relationship guides both posterior and anterior approaches.

Question 19Applied Anatomy

The cricoid cartilage is the only complete cartilaginous ring of the airway. At which vertebral level does it lie in an adult?

  1. C6 Correct answer.
  2. C4
  3. C2
  4. T1

Explanation

The cricoid cartilage lies at about the level of C6, just below the thyroid cartilage. This level is used as a landmark for emergency airway access and for identifying the trachea.

Question 20Applied Anatomy

A patient undergoing awake fiberoptic intubation receives topical anesthesia of the airway. Blockade of which nerve is most important to suppress the cough reflex from the trachea and carina?

  1. The glossopharyngeal nerve
  2. The vagus nerve Correct answer.
  3. The hypoglossal nerve
  4. The recurrent laryngeal nerve

Explanation

Sensory fibers from the trachea and carina travel via the vagus nerve, so topical vagal blockade (for example, transtracheal or via the fiberoptic channel) suppresses the cough reflex. The glossopharyngeal nerve covers the posterior tongue and pharynx.

Question 21Applied Physiology

At sea level, the partial pressure of oxygen in humidified tracheal gas at 37 degrees Celsius is closest to which value?

  1. 159 mmHg
  2. 149 mmHg Correct answer.
  3. 100 mmHg
  4. 40 mmHg

Explanation

Humidification adds water vapour pressure of 47 mmHg at 37 degrees Celsius, so dry inspired PO2 of 0.21 x 760 = 159 mmHg is reduced to 0.21 x (760 - 47) = about 149 mmHg. This humidified value is the starting point of the alveolar gas equation.

Question 22Applied Physiology

Which change most increases the oxygen-carrying capacity of blood?

  1. A rise in arterial PO2 from 60 to 100 mmHg
  2. A rise in haemoglobin concentration from 10 to 15 g/dL Correct answer.
  3. A rise in body temperature
  4. A fall in arterial PCO2

Explanation

Oxygen-carrying capacity depends almost entirely on haemoglobin concentration, since each gram of haemoglobin binds about 1.34 mL of oxygen. Adding haemoglobin adds binding sites and therefore capacity.

Question 23Applied Physiology

According to the oxyhaemoglobin dissociation curve, what is the approximate P50 in normal adult blood?

  1. 27 mmHg Correct answer.
  2. 60 mmHg
  3. 40 mmHg
  4. 97 mmHg

Explanation

P50 is the PO2 at which haemoglobin is 50% saturated, and in standard adult blood it is about 26-27 mmHg. This value shifts right with acidosis, hypercapnia and hyperthermia.

Question 24Applied Physiology

In a healthy adult at rest, which fraction of total body oxygen consumption is normally attributable to the kidneys?

  1. 20%
  2. 50%
  3. 7% Correct answer.
  4. 2%

Explanation

Although the kidneys receive about a fifth of cardiac output, their oxygen consumption is modest, around 7% of the total because much of their flow is destined for filtration rather than oxidative metabolism. Skeletal muscle and the heart account for much larger shares during exercise.

Question 25Applied Physiology

A patient has an arterial PCO2 of 60 mmHg. Using the alveolar gas equation with a respiratory quotient of 0.8 and a humidified inspired PO2 of 149 mmHg, the alveolar PO2 is closest to which value?

  1. 99 mmHg
  2. 54 mmHg
  3. 74 mmHg Correct answer.
  4. 89 mmHg

Explanation

The simplified alveolar gas equation is PAO2 = PiO2 - PaCO2/R. Substituting gives 149 - (60/0.8) = 149 - 75 = 74 mmHg. Alveolar oxygen falls sharply as carbon dioxide rises because the two gases compete for the same alveolar volume.

Question 26Applied Physiology

Which statement best explains why the oxyhaemoglobin dissociation curve has a sigmoid shape?

  1. Oxygen dissolves in plasma in proportion to its partial pressure
  2. Haemoglobin exists as a single polypeptide chain with one oxygen-binding site
  3. Binding of oxygen to one haem group reduces the affinity of the remaining haem groups
  4. Binding of oxygen to one haem group increases the affinity of the remaining haem groups Correct answer.

Explanation

The sigmoid curve reflects positive cooperativity: binding of the first oxygen molecule promotes a conformational change that raises the affinity of the remaining sites. This makes the curve steep in the middle and flat at the top, giving a safety margin at high PO2.

Question 27Applied Physiology

During a rightward shift of the oxyhaemoglobin dissociation curve, which change occurs?

  1. Reduced delivery of oxygen to exercising muscle
  2. Increased oxygen release to tissues at any given PO2 Correct answer.
  3. Reduced P50
  4. Increased oxygen affinity of haemoglobin

Explanation

A rightward shift means reduced affinity, so a higher PO2 is needed for any given saturation and more oxygen is unloaded at tissue PO2. This is advantageous in exercising muscle, where acidosis and warmth shift the curve right.

Question 28Applied Physiology

Which factor in stored blood most reduces its oxygen-carrying capacity shortly after donation?

  1. Depletion of 2,3-diphosphoglycerate Correct answer.
  2. Loss of plasma albumin
  3. Reduction in platelet count
  4. Rise in plasma potassium

Explanation

2,3-DPG falls during storage, shifting the dissociation curve left and impairing oxygen unloading until it is regenerated after transfusion. Oxygen-carrying capacity is little affected by albumin or potassium changes.

Question 29Applied Physiology

Which statement about carbon dioxide transport in blood is correct?

  1. Carbamino compounds account for the majority of carbon dioxide carriage
  2. Carbon dioxide is mainly dissolved in plasma as the free gas
  3. Most carbon dioxide is carried bound to haemoglobin at the same site as oxygen
  4. Most carbon dioxide is transported as bicarbonate after carbonic anhydrase activity in red cells Correct answer.

Explanation

About 70% of carbon dioxide is carried as bicarbonate generated by carbonic anhydrase within red cells, with chloride shift maintaining electroneutrality. Carbamino binding and dissolved gas account for smaller fractions.

Question 30Applied Physiology

A patient with chronic obstructive pulmonary disease has a haemoglobin of 18 g/dL. What is the approximate arterial oxygen content if saturation is 90% and PaO2 is 60 mmHg?

  1. 21.7 mL/dL Correct answer.
  2. 18.6 mL/dL
  3. 24.1 mL/dL
  4. 15.2 mL/dL

Explanation

Arterial oxygen content is (1.34 x haemoglobin x saturation) plus (0.003 x PaO2). This gives (1.34 x 18 x 0.90) + (0.003 x 60) = 21.7 + 0.18, approximately 21.7 mL/dL.

Question 31Applied Physiology

Which statement about pulmonary vascular resistance is correct?

  1. It is higher than systemic vascular resistance at rest
  2. It rises steeply as pulmonary artery pressure increases within the physiological range
  3. It is lowest when lung volume is near functional residual capacity Correct answer.
  4. It increases when alveolar oxygen tension rises

Explanation

Pulmonary vascular resistance is lowest near functional residual capacity because extra-alveolar and alveolar vessels are both relatively relaxed. It rises at both high and low lung volumes and is much lower than systemic resistance.

Question 32Applied Physiology

Hypoxic pulmonary vasoconstriction serves which physiological purpose?

  1. Increasing blood flow to poorly ventilated lung regions
  2. Reducing pulmonary artery pressure during hypoxia
  3. Diverting blood flow away from poorly ventilated alveoli Correct answer.
  4. Increasing oxygen delivery to the bronchial circulation

Explanation

Small pulmonary arteries constrict when alveolar oxygen falls, redirecting blood towards better-ventilated regions and improving ventilation-perfusion matching. This mechanism is unique to the pulmonary circulation, unlike systemic vessels which dilate with hypoxia.

Question 33Applied Physiology

In the upright lung, which region receives the greatest ventilation per unit volume?

  1. Mid-zone
  2. Apex
  3. Base Correct answer.
  4. Hilum

Explanation

Gravity causes pleural pressure to be less negative at the base, so basal alveoli are less expanded at end-expiration and have greater compliance, receiving more ventilation. Perfusion increases even more steeply toward the base.

Question 34Applied Physiology

Which statement best describes the effect of general anaesthesia on functional residual capacity?

  1. It falls, promoting airway closure and atelectasis Correct answer.
  2. It falls only when neuromuscular blockade is used
  3. It remains unchanged in supine patients
  4. It increases because of bronchodilation

Explanation

Anaesthesia reduces functional residual capacity through loss of respiratory muscle tone, cephalad diaphragmatic displacement and altered chest wall mechanics. The reduction promotes dependent atelectasis and airway closure, particularly in obese and elderly patients.

Question 35Applied Physiology

Which change in lung mechanics occurs in a patient with emphysema?

  1. Increased surface tension with alveolar collapse
  2. Reduced airway resistance with normal recoil
  3. Increased elastic recoil with reduced compliance
  4. Loss of elastic recoil with increased compliance Correct answer.

Explanation

Emphysema destroys alveolar walls and elastin, reducing elastic recoil and increasing compliance, which leads to air trapping and dynamic hyperinflation. The loss of radial traction also increases small airway resistance.

Question 36Applied Physiology

Which statement about closing capacity is correct?

  1. It increases with age and may exceed functional residual capacity in the elderly Correct answer.
  2. It equals residual volume at all ages
  3. It decreases with age and is unrelated to smoking
  4. It is the volume at which airways are maximally dilated

Explanation

Closing capacity rises with age as elastic recoil falls, and in older or supine patients it can exceed functional residual capacity, causing airway closure during tidal breathing and impaired gas exchange. Smoking accelerates this rise.

Question 37Applied Physiology

Which nerve is the principal motor supply to the diaphragm?

  1. Vagus nerve
  2. Recurrent laryngeal nerve
  3. Intercostal nerves
  4. Phrenic nerve Correct answer.

Explanation

The phrenic nerve, arising from cervical roots C3 to C5, provides the motor innervation to the diaphragm. Preserved phrenic function explains why hiccups and diaphragmatic breathing persist in some high cervical lesions.

Question 38Applied Physiology

Central chemoreceptors respond primarily to which stimulus?

  1. Arterial PO2
  2. Cerebrospinal fluid hydrogen ion concentration Correct answer.
  3. Plasma bicarbonate concentration directly
  4. Arterial pH measured in the carotid body

Explanation

Central chemoreceptors lie on the ventral medulla and respond to hydrogen ions in cerebrospinal fluid, which change when carbon dioxide diffuses across the blood-brain barrier. Because carbon dioxide crosses readily but hydrogen and bicarbonate do not, the central response is effectively to arterial PCO2.

Question 39Applied Physiology

A patient breathing room air has an arterial PO2 of 55 mmHg and a normal chest radiograph. Which finding most suggests a shunt rather than hypoventilation as the cause?

  1. A normal alveolar-arterial oxygen gradient
  2. A low mixed venous oxygen saturation
  3. An elevated alveolar-arterial oxygen gradient that does not correct with supplemental oxygen Correct answer.
  4. A raised arterial PCO2

Explanation

A true shunt produces an elevated alveolar-arterial gradient that responds poorly to supplemental oxygen because shunted blood bypasses ventilated alveoli. Pure hypoventilation raises PCO2 and lowers PO2 but leaves the gradient normal.

Question 40Applied Physiology

Which statement about diffusion of oxygen across the alveolar membrane is correct?

  1. Oxygen diffusion is limited during exercise even in healthy people
  2. Diffusion capacity increases during exercise in healthy adults Correct answer.
  3. Oxygen uptake is normally perfusion-limited rather than diffusion-limited
  4. Carbon dioxide diffuses less readily than oxygen

Explanation

In healthy adults, oxygen uptake is perfusion-limited at rest, but during exercise increased cardiac output and recruitment of capillaries raise diffusion capacity so that equilibration is maintained. Carbon dioxide diffuses about twenty times more readily than oxygen.

Question 41Applied Physiology

Which factor most increases the risk of hypoxaemia during one-lung ventilation?

  1. Use of positive end-expiratory pressure to the dependent lung
  2. Increased hypoxic pulmonary vasoconstriction in the non-ventilated lung
  3. Lateral decubitus positioning with the operative side up
  4. Administration of a pulmonary vasodilator Correct answer.

Explanation

Hypoxic pulmonary vasoconstriction diverts blood away from the non-ventilated lung, and drugs that reverse it increase shunt and worsen hypoxaemia. Measures that support hypoxic pulmonary vasoconstriction or reduce shunt improve oxygenation.

Question 42Applied Physiology

Which statement about the Haldane effect is correct?

  1. It describes the effect of temperature on carbon dioxide solubility
  2. Oxygenated blood carries less carbon dioxide than deoxygenated blood at the same PCO2 Correct answer.
  3. Deoxygenated blood carries less carbon dioxide than oxygenated blood at the same PCO2
  4. It describes the effect of pH on oxygen affinity

Explanation

The Haldane effect describes how oxygenation of haemoglobin reduces its capacity to carry carbon dioxide, so oxygenated blood holds less carbon dioxide at a given PCO2. In tissues, oxygen unloading therefore promotes carbon dioxide uptake, and in the lungs oxygen uptake promotes carbon dioxide release.

Question 43Applied Physiology

Which statement about the Bohr effect is correct?

  1. A fall in pH reduces haemoglobin oxygen affinity Correct answer.
  2. A rise in pH increases oxygen unloading at tissues
  3. A rise in PCO2 shifts the dissociation curve left
  4. It describes carbon dioxide carriage by haemoglobin

Explanation

The Bohr effect is the reduction in oxygen affinity caused by acidosis and raised PCO2, shifting the curve right and enhancing unloading in metabolically active tissue. Alkalosis has the opposite effect.

Question 44Applied Physiology

Which change in respiratory physiology occurs at high altitude after acclimatisation?

  1. A fall in 2,3-diphosphoglycerate with a leftward shift of the curve
  2. A fall in erythropoietin secretion
  3. A rise in 2,3-diphosphoglycerate with a rightward shift of the curve Correct answer.
  4. A fall in ventilation due to alkalosis

Explanation

Acclimatisation raises red cell 2,3-DPG, shifting the dissociation curve right and improving oxygen unloading despite lower arterial saturation. Ventilation increases and erythropoietin secretion rises, not falls.

Question 45Applied Physiology

Which statement about the pulmonary surfactant system is correct?

  1. Its effect is greatest in large alveoli
  2. It is produced mainly by alveolar macrophages
  3. It reduces surface tension and increases lung compliance Correct answer.
  4. It increases alveolar surface tension and promotes collapse

Explanation

Surfactant, secreted by type II pneumocytes, lowers surface tension, which increases compliance and stabilises alveoli of differing sizes. Its effect is greatest in small alveoli where surface tension would otherwise be highest.

Question 46Applied Physiology

Which structure is the primary site of resistance to airflow in the normal adult tracheobronchial tree?

  1. The trachea
  2. Terminal bronchioles
  3. Medium-sized bronchi Correct answer.
  4. The alveolar ducts

Explanation

Airway resistance is greatest in the medium-sized bronchi, where cross-sectional area is still relatively small; as branching continues, total cross-sectional area rises steeply and resistance falls. The trachea has a large calibre and low resistance, and bronchioles and alveolar ducts are so numerous that their aggregate resistance is small.

Question 47Applied Physiology

A patient has an arterial PCO2 of 60 mmHg and a measured arterial bicarbonate of 24 mmol/L. Using the Henderson-Hasselbalch relationship, the arterial pH is closest to which value?

  1. 7.50
  2. 7.20 Correct answer.
  3. 7.40
  4. 7.30

Explanation

Applying the Henderson-Hasselbalch equation with a normal bicarbonate and a PCO2 of 60 mmHg gives a pH of approximately 7.20, reflecting acute respiratory acidosis. Each 10 mmHg rise in PCO2 above 40 lowers pH by roughly 0.08 acutely, so a 20 mmHg rise predicts a fall of about 0.16 from 7.40.

Question 48Applied Physiology

Which statement about the renal regulation of acid-base balance is correct?

  1. It regulates pH solely by excreting fixed acids without changing plasma bicarbonate
  2. It buffers hydrogen ions only within the intracellular fluid
  3. It corrects pH changes within seconds by altering ventilation
  4. It adjusts bicarbonate reabsorption and hydrogen ion excretion over hours to days Correct answer.

Explanation

The kidney achieves acid-base correction by reabsorbing filtered bicarbonate and excreting hydrogen ions, a process that develops over hours to days. This makes it the slow but definitive regulator, whereas chemical buffers and ventilation act much faster.

Question 49Applied Physiology

A patient with a large arteriovenous shunt is breathing room air. Which statement best explains why raising the inspired oxygen concentration produces only a limited rise in arterial oxygen tension?

  1. The alveolar-arterial gradient is abolished by hyperoxia
  2. The haemoglobin is fully saturated and cannot take up additional oxygen
  3. Diffusion of oxygen across the alveolar membrane is impaired
  4. Shunted blood does not contact ventilated alveoli and retains its low oxygen content Correct answer.

Explanation

In true shunt, blood bypasses ventilated alveoli, so its oxygen content stays low regardless of the inspired concentration. Adding oxygen raises the content of the ventilated lung units, but the mixing of shunted blood limits the increase in arterial oxygen tension.

Question 50Applied Physiology

During a nitrous oxide-based anaesthetic, a patient's body temperature falls from 37 °C to 35 °C. Which change in the oxyhaemoglobin dissociation curve is expected at the lower temperature?

  1. A reduction in the maximum oxygen content of haemoglobin at full saturation
  2. A leftward shift, so haemoglobin binds oxygen more avidly and releases less to the tissues Correct answer.
  3. No shift, because temperature affects only carbon dioxide carriage
  4. A rightward shift, so haemoglobin releases oxygen more readily to the tissues

Explanation

Hypothermia reduces the metabolic activity of the red cell and stabilises the relaxed oxyhaemoglobin conformation, shifting the dissociation curve to the left. This increases oxygen affinity, so at any given tissue PO2 less oxygen is unloaded. The same principle explains why hyperthermia shifts the curve to the right and improves tissue unloading.