PBL Topic 2 Case 9 Flashcards
What is an acid?
- A molecule containing hydrogen atoms that can release protons
What is a strong acid? Give an example of a strong acid
- One that rapidly dissociates and releases large amounts of protons
- Hydrochloric acid
What is a weak acid? Give an example of a weak acid
- One that has a lower tendency to dissociate protons
- Carbonic acid
What is a base?
- A molecule that can accept a proton
What is a strong base? Give an example of a strong base
- One that reacts rapidly and strongly with protons
- Hydroxide ion
What is a weak base? Give an example of a weak base?
- One that reacts much more weakly with protons
- Bicarbonate ion
How does one calculate pH from [H+]?
pH = -log [H+]
What is the normal pH of blood?
7.4
Why is the pH of venous blood lower than that of arterial blood?
- Carbon dioxide is released from tissues to form carbonic acid
Why is intracellular pH lower than plasma pH?
- Metabolism of cells produced carbonic acid
Identify three systems that help regulate [H+]
- Buffer systems
- Respiratory centre
- Kidneys
What is a buffer?
- Any substance that can reversible bind H+
What is Ka and how is it calculated?
- The concentration of the acid relative to its dissociated ions
- Ka = [H+][A-] / [HA]
What is pKa and how is it calculated?
- Negative log of the Ka value
- pKa = -log [Ka]
What is the pKa in the bicarbonate buffer system?
- 6.1
Give the Henderson-Hasselbalch Equation
pH = 6.1 + log [HCO3-] / (0.03 x [PCO2])
In the Henderson-Hasselbalch Equation:
Why is [CO2] calculated rather than H2CO3?
- H2CO3 rapidly dissociated into CO2
- Which is proportional to the amount of undissociated H2CO3
Using the Henderson-Hasselbalch Equation:
What is the result of an increase in [HCO3-]
- pH increases
- Shift towards alkalosis
Using the Henderson-Hasselbalch Equation:
What is the result of an increase in pCO2
- pH decreases
- Shift towards acidosis
Why is a change in the [HCO3-] referred to as a metabolic disturbance?
- [HCO3-] is regulated by the kidneys
Why is a change in the pCO2 referred to as a respiratory disturbance?
- PCO2 is controlled by the rate of respiration
An increase in [HCO3-] is termed a [A]
A decrease in pCO2 is termed a [B]
An increase in pCO2 is termed a [C]
A decrease in [HCO3-] is termed a [D}
- [A] Metabolic alkalosis
- [B} Respiratory alkalosis
- [C] Respiratory acidosis
- [D] Metabolic acidosis
What is the effect of increased ventilation on [H+]
- Reduced CO2 from extracellular fluid
- Reduced [H+]
What is the effect of decreased [H+] on ventilation
- Alveolar ventilation decreases
- Reduced [H+]
Explain why respiratory acidosis occurs in emphysema
- Loss of elastic recoil
- Airflow limitation
- Build up of CO2
Outline the mechanism by which the kidneys excrete acidic or basic urine
- HCO3- is filtered into the tubules, thus removing base from the blood
- H+ is filtered into the tubules, thus removing acid from the blood
- Net effect is based on relative concentrations in tubular lumen
How does the removal of HCO3- raise the extracellular [H+] in alkalosis
- Kidneys fail to reabsorb HCO3-
- Increased excretion of bicarbonate
- Decrease in HCO3- shifts acid base balance towards acidosis (Henderson-Hasselbalch equation)
How does the reabsorption of HCO3- reduce the extracellular [H+] in acidosis
- Increase in HCO3 shifts acid base balance towards alkalosis (Henderson-Hasselbalch equation)
In which region of the kidneys does HCO3- reabsorption and H+ secretion not occur?
- Loop of Henle
Outline the features of metabolic acidosis
- pH < 7.4
- PO2 > 40 mm Hg
What is the compensatory mechanism for metabolic acidosis?
- Increased ventilation
- Reduced pCO2
- Reduced H+
- Increased pH
Outline the features of a respiratory acidosis
- pH < 7.4
- HCO3- <24 mEq/L
What is the compensatory mechanism for respiratory acidosis?
- Increased H+ secretion
- Increased reabsorption of bicarbonate
- Increased pH
Outline the features of a metabolic alkalosis
- pH > 7.4
- PO2 < 40 mm Hg
What is the compensatory mechanism for metabolic alkalosis?
- Decreased ventilation
- Increased CO2
- Increased H+
- Reduced pH
Outline the features of a respiratory alkalosis
- pH > 7.4
- HCO3- > 24 mEq/L
What is the compensatory mechanism for respiratory alkalosis?
- Reduced H+ secretion
- Reduced reabsorption of HCO3-
- Reduced pH
Define circulatory shock
- Generalised inadequate blood flow
- Damage to body tissues due to lack of oxygen and other nutrients
Outline the three stages of shock
- Non progressive / compensatory stage
- Progressive stage
- Irreversible stage
What is meant by the term hypovolaemia?
- Reduced blood volume
What is the most common cause of hypovolaemia?
- Haemorrhage
How does haemorrhage result in shock?
- Reduced filling pressure
- Reduced venous return
- Reduced cardiac output
Identify the sympathetic reflexes that occur as a result of decreased arterial pressure after haemorrhage
- Arterioles constrict, increasing total peripheral resistance
- Veins and venous reservoirs constrict, increasing venous return
- Increased heart rate
Identify the role of baroreceptors in non-progressive shock
- Elicit powerful sympathetic stimulation of the circulation
Identify the role of the CNS ischaemic response in non-progressive shock
When is this response activated?
- Elicits even more powerful sympathetic stimulation of the circulation
- When the arterial pressure falls below 50 mm Hg
What is the role of reverse stress-relaxation in non-progressive shock ?
- Contraction of blood vessels around the diminished blood volume
What is the role of angiotensin in non-progressive shock ?
- Constriction of peripheral arteries
- Decreased output of water and salt by the kidneys
What is the role of ADH in non-progressive shock ?
- Constricts arteries and veins
- Greatly increases water retention by the kidneys
What causes cardiac depression?
- Fall in arterial pressure
- Reduced coronary blood flow
- For adequate nutrition of the myocardium
- Weakness of the heart muscle
What causes vasomotor failure?
- Reduced cardiac output
- Reduced blood flow to the vasomotor centre
How does failure of the vasomotor centre cause a decreased cardiac output?
- Vascular dilation
- Venous pooling of blood
- Decreased venous return
Identify three effects of sluggish blood flow
- Tissue metabolism continues despite low flow
- Large amounts of acid continue to empty into the local vessels and increase the acidity of the blood
- Resulting in agglutination and blood clots
- Leading to plugging of small vessels
Why is there increased capillary permeability and what is the effect of this?
- Due to hypoxia
- Decreased cardiac output
Explain what occurs to the phosphate reserves in irreversible shock
- Creatine phosphate is degraded
- ATP is degraded to ADP
- ADP is degraded to AMP
- AMP is degraded to adenosine
- Which diffuses out of cells and is converted to uric acid
- Uric acid cannot re=enter the cells
Explain how intestinal obstruction can result in hypovolaemic shock
- Distension of intestine block venous return
- Increase in capillary pressure
- Fluid leakage from capillaries into intestinal wall and lumen
- Reduced plasma volume
Explain how severe burns can result in hypovolaemic shock
- Loss of plasma through the denuding skin
Why does blood viscosity increase in hypovolaemic shock? What is the effect of this?
- Increased red cell concentration
- Increased sluggishness of blood
Identify four causes of hypovolaemic shock caused by dehydration
- Excessive sweating
- Fluid loss in diarrhoea or vomiting
- Fluid loss by nephrotic kidney
- Inadequate intake of fluid and electrolytes
Outline the pathophysiology of neurogenic shock
- Loss of vasomotor tone
- Massive dilation of veins
- Reduced mean systemic filling pressure
- Reduced venous return
- Increased venous pooling
Explain how anaesthesia causes neurogenic shock
- Blockage of sympathetic nervous outflow from nervous system
Explain how brain damage causes neurogenic shock
- Brain ischaemia is prolonged
- Inactivation of vasomotor centre
Identify a cause of compartment syndrome
- Bone fracture
Outline the pathophysiology of compartment syndrome
- Tissue hypoxia
- Release of histamine like substances
- Causing vasodilation
- Increased endothelial permeability
- Transudation of plasma into the intramuscular compartment
- Swelling and oedema
What causes the collapse of a vessel in compartment syndrome?
- Increased critical closing pressure
Outline the treatment of compartment syndrome
- Incision through the deep fascia
- To open up the compression
- To cause decompression
Outline the pathophysiology of anaphylactic shock
- Antigen-antibody reaction
- Release of basophils and mast cells
- Release of histamine
- Increased venous dilation and decreased venous return
- Dilation of arterioles and reduced arterial pressure
- Increased capillary permeability
- Loss of fluid into the tissue spaces
What is the main cause of sepsis?
- ‘Blood poisoning’
- Caused by bacterial infection
Outline the clinical features of hypovolaemic shock stemming from inadequate perfusion
- Cold, pale and clammy skin with slow capillary refill
- Anuria and oliguria
- Drowsiness, confusion and irritability
Outline the clinical features of hypovolaemic shock stemming from increased sympathetic tone
- Tachycardia
- Hypotension
- Sweating
Outline the clinical features of cardiogenic shock
- Raised jugular venous pressure
- Pulmonary oedema
- Gallop rhythm
- Basal crackles
- Pulmonary oedema
Outline the clinical features of anaphylactic shock
- Low blood pressure and tachycardia (vasodilation)
- Bronchospasm
- Oedema of the face, pharynx and larynx
- Nausea, vomiting, abdominal cramps and diarrhoea
Outline the clinical features sepsis
- Pyrexia and rigors
- Nausea and vomiting
- Hypotension
- Bounding pulse
Outline the management of shock
- Oxygen (via endotracheal tube where necessary)
- Antibiotics for sepsis
- Fluid Replacement by wide-bore intravenous cannula
What is packed cell volume?
- Proportion of blood made up of red blood cells
- Essentially the same thing as hematocrit
When giving fluid replacement what is the optimal packed cell volume and why is this the case?
- 30-35%
- Balance oxygen carrying capacity
- And tissue flow
A massive transfusion involves the transfer of how many units of blood?
- 80 > 100 units of red cells
Why can blood transfusion cause hypothermia?
- Bank blood is stored at four degrees celsius
Why can blood transfusion cause coagulopathy
- Bank blood contains few platelets or clotting factors
Why can blood transfusion cause hypocalcaemia?
- Citrate stored in blood binds to calcium ions reducing ionised calcium levels
Why can blood transfusion cause increased oxygen affinity
- 2,3-BPG in stored blood is reduced
- Oxygen dissociation curve shifts to the left
- Increased affinity and reduced unloading
What do crystalloid fluids involve? Identify an example of a crystalloid
- Addition of volume to blood
- Addition of electrolytes
- Saline
What do colloid fluids involve? Identify an example of a colloid
- Volume expanders resulting in an increase in blood volume, blood flow, cardiac output and oxygen transportation
- Gelofusine
Which are preferred colloids or crystalloids?
- Colloids
- Since the volume of crystalloid needed to produce the same effect as colloid is far greater
Identify two potential sites of heart block
- AV Block in AV node or Bundle of His
- Bundle Branch Block in lower conductive system
What is a Stokes-Adams attack?
- Associated with heart block
- Causes syncope
What is seen on an ECG with first degree heart block?
- Prolongation of PR interval greater than 0.22
Identify three types of second degree AV block
- Mobitz 1 Block (Wenckeback block)
- Mobitz II Block
- 2:1 or 3:1 Block
What is seen on an ECG with Mobitz 1 block
- Progressive PR prolongation
- Until P wave fails to conduct
Where is Mobitz I block most likely to occur?
- AV Node
What is seen on an ECG with Mobitz II block?
- A dropped QRS complex
- Not preceded by PR interval prolongation
Where is Mobitz II block most likely to occur?
- Bundle of His
What is seen on an ECG with a 2:1 or 3:1 advanced block?
- Every second or third P wave conducts to the ventricles
Identify two types of third degree AV block
- Congenital complete heart block
- Acquired complete heart block
What is seen on an ECG with a congenital complete AV block?
- QRS complex is narrow
- QRS rate is rapid
What is seen on an ECG with an acquired complete AV block?
- QRS complex is broad
- QRS complex is slow
What is seen in right bundle branch block on an ECG?
- Deep S waves in leads I and V6
- Tall R wave in lead V1
What are the clinical features of right bundle branch block?
- Splitting of the second heart sound
What is seen in left bundle branch block on an ECG?
- Deep S wave in lead V1
- Tall R wave in leads 1 and V6
What are the clinical features of right bundle branch block?
- Reverse splitting of the second heart sound
Identify the two functioning systems that determine consciousness
- Ascending Reticular Activating System (ARAS)
- Cerebral Cortex
Identify the three principal causes of coma
- Diffuse brain dysfunction e.g. traumatic brain injury or drug overdose
- Direct effect within brainstem e.g. haemorrhage or infarction
- Pressure effect on brainstem e.g. tumour, oedema, abscess
What does Glasgow Coma Scale record?
- Best Eye, Verbal and Motor Responses
A Glasgow Come Scale score of less than which value denotes a coma?
- 8
What is meant by the term delirium?
- Confusion state
- Reduced attention
- Altered behaviour
What is a Swan-Ganz catheter?
- Balloon Flotation Catheter
- Used to determine pulmonary artery pressure
Identify two locations where the Swan-Ganz catheter may be inserted?
- Femoral Vein
- Antecubital Fossa
Identify three conditions that can be diagnosed using a Swan-Ganz catheter
- Cardiac tamponade
- Pulmonary hypertension
- Cardiomyopathy
Identify three conditions that are often monitored using a Swan Ganz catheter
- Heart failure
- Cardiogenic Shock
- Doubtful fluid status
Why is the pulmonary artery pressure recorded a reasonable reflection of left atrial pressure?
- Catheter becomes so wedged
- Due to fluid between the catheter lumen and left atrium
Identify two invasive means of ventilating a patietn
- Endotracheal tube
- Tracheostomy
Explain how sedation, muscle anaesthesia and muscle relaxation can cause hypotension
- Loss of sympathetic drive
- Vasodilation
Explain how positive pressure ventilation can cause hypotension
- Increased intrathroacic pressure
- Reduced venous return
- Reduced cardiac output
When is a tracheostomy performed?
- When endotracheal intubation is likely to be required for a prolonged period
- Typically over 14 days
What is IPPV and how is it achieved?
- Intermittent Positive Pressure Ventilation
- Intermittent inflation of lungs with positive pressure
- Air is forced into lungs
- Elastic recoil carries out expiration
When is CMV used and outline two ways in which it is achieved
- Controlled Mechanical Ventilation
- With patients in whom respiratory efforts are absent
- Volume controlled ventilation
- Pressure controlled ventilation
Outline the process of volume controlled ventilation
- Tidal volume and respiratory rate are preset
- Airway pressure varies according to the ventilator setting and the lung mechanics (e.g. resistance and compliance)
Outline the process of pressure controlled ventilation
- Inspiratory pressure and respiratory rate are preset
- Tidal volume varies according to patient’s lung mechanics
What is IMV ?
- Intermittent mandatory ventilation
- Allows patient to breathe spontaneously between the mandatory tidal volumes delivered by ventilator
- Timed to coincide with patients own respiratory efforts
What is weaning?
- Process of progressively reducing and eventually removing external ventilatory support
How is the decision made to wean a patient from artificial ventilation?
- Subjective criteria including responses to short periods of spontaneous breathing
- Objective criteria based on blood gas analysis, lung mechanics and muscular strength
- Patient’s mood, and consciousness level, as well as any drugs
Identify two causes of a fall in cardiac output associated with artificial ventilation
- Positive pressure to the lungs impeded venous return
- Stretching of pulmonary capillaries causing a rise in pulmonary vascular resistance
What is barotrauma and how is it associated with artificial ventilation
- Damage to body tissues caused by a difference in pressure
- Caused by high tidal volumes and PEEP
- Which may rupture alveoli and cause air to dissect along the perivascular sheath
Identify three sets of signs of a tension pneumothorax associated with artificial ventilation
- Hypoxia and hypercapnia
- Hypotension and tachycardia
- Mediastinal shift and tracheal displacement
How may ventilator associated pneumonia occur?
- Leakage of infected oropharyngeal secretions
- Promoted by regurgitation of colonised gastric fluid
Identify three organisms associated with ventilator associated pneumonia
- Pseudomonas aeruginosa
- Klebsiella pneumoniae
- Staphylococcus aureus
Identify a specific marker that be may helpful when there is suspected ventilator associated pneumonia
- Serum procalcitonin
Outline the pathophysiology of disseminated intravascular coagulation
- Endothelial damage results in platelet aggregation
- Tissue injury results in thrombin
- Vascular occlusion and consumption of platelets
Outline how tranexamic acid is used in disseminated intravascular coagulation
- Inhibits plasminogen activation
- Prevents fibrinolysis
- Given orally or by IV injection
What is an opioid?
- Any substance that produces morphine like effects
Identify a drug that blocks opioids
- Naloxone
What is the function of u receptors?
- Analgesic effects of opioids
Outline the mechanism of action of opioids
- Opening of inward K+ channels causing hyperpolarisation
- Closure of Na+ channels resulting in reduced Ca2+ entry
Outline how opioids can result in physical dependence
- Inhibition of adenylyl cyclase and MAP activation
Identify three regions of the brain where analgesics have an effect
- Insular cortex
- Amygdala
- Hypothalamus
What is diamorphine?
- Prodrug that has a high analgesic potency
-
Why does diamorphine give a greater ‘buzz’ than morphine
- Greater lipid solubility
- More easily crosses the blood brain barrier
How is diamorphine metabolised?
- By glucuronide in the liver
- Metabolised to 6-monoacetylmorphine
Why does morphine cause respiratory depression?
- Decrease in sensitivity of receptors to arterial PCO2
Why does morphine cause constipation?
- Increased tone
- Reduced motility in GI system
Why does morphine cause urticaria and itching?
- Release of histamine from mast cells
Why are opioids unsuitable for asthmatic patients?
- Release of histamine from mast cells
- Causing bronchoconstriction and hypotension
