POSTOPERATIVE AND CRITICAL CARE Flashcards
Which of the arterial blood gas analyses shown below would most likely be seen with a patient who has a pulmonary embolus?
A рН 7.64, рОз 10.0 кРа pC02 2.8 k₽a, НСОз 20
B pH 725, po 8.5 pco 3.2; НСОз 10
C pH 7.20, p02 6.2, pCO2 6.2, HCOз 27
D pH 7.60, pO2 8.2, pC02 5.8, НСОз 40
E рН 7.50, р02 7.2, pC02 2.5, НСОз 24
E PH 7.50, p02 7.2, pCO2 2.5, HCOз 24
A combination of hypoxia and respiratory alkalosis should suggest a pulmonary embolus. The respiratory alkalosis is due to hyperventilation associated with the pulmonary embolism.
Metabolic alkalosis
• Usually caused by a rise in plasma bicarbonate levels.
• Rise of bicarbonate above 24 mmol/L will typically result in renal excretion of excess bicarbonate.
• Caused by a loss of hydrogen ions or a gain of bicarbonate. It is due mainly to problems of the kidney or gastrointestinal tract
Causes
: Vomiting/aspiration (eg. Peptic ulcer leading to pyloric stenosis, nasogastic suction)
• Liquorics, carbenoxolon
Primary hyperaldosteronism
Bartter’s syndrome
• Cushing’s syndrome
Congenital adrenal hyperplasia
Mechanism of metabolic alkalosis
Activation of the renin angiotensin II Aldosterone system is a key factor. Aldosterone causes reabsorbtion of Na in exchange for H in the distal convoluted tubule.
ECF depletion (vomiting, diuretics) -Na and Cl loss-activation of RAA system-raised aldosterone levels
• In hypokalaemia, K* shift from cells - ECF, alkalosis is caused by shift of H* into cells to maintain neutrality
Which of the following conditions is most likely to be associated with these arterial blood gas sample results:
pH: 7.48
pO2: 10.1
НСО3: 30
pCO2: 4.5
Cl: 96mEq
A Respiratory alkalosis
B Metabolic acidosis with normal anion gap
C Metabolic alkalosis
D Metabolic acidosis with increased anion gap
E Type 2 respiratory failure
C Metabolic alkalosis
These arterial blood gas results are classically seen in situations where there is metabolic alkalosis such as may occur following prolonged vomiting.
A 22 year old lady is admitted to the intensive care unit following a laparotomy. She has a central line, pulmonary artery catheter and arterial lines inserted. The following results are obtained:
Pulmonary artery occlusion pressure: Low
Cardiac output: High
Systemic vascular resistance: Low
How may these findings be best interpreted?
A Hypovolaemia
B Septic shock
C Normal
D Fluid overload
E Cardiogenic shock
B Septic shock
Decreased SVR is a major feature of sepsis. A hyperdynamic circulation is often present. This is the reason for the use of vasoconstrictors.
Pulmonary artery occlusion pressure monitoring
The pulmonary artery occlusion pressure is an indirect measure of left atrial pressure, and thus filling pressure of the left heart. The low resistance within the pulmonary venous system allows this useful measurement to be made.
The most accurate trace is made by inflating the balloon at the catheter tip and ‘floating’ it so that it occludes the vessel. If it is not possible to occlude the vessel in this way then the measurement gained will be the pulmonary artery end diastolic pressure.
Interpretation of PAOP
Normal: mmHg
8-12
Low <5 mmHg Scenario: Hypovolemia
Low with Pulmonary oedema Scenario: ARDS
High >18 mmHg Scenario: Overload
When combined with measurements of systemic vascular resistance and cardiac output it is possible to accurately classify patients. Systemic vascular resistance
Derived from aortic pressure, right atrial pressure and cardiac output
SVR=80(mean aortic pressure-mean right atrial pressure)/cardiac output
Which of the drugs listed below confers the greatest risk of malignant hyperthermia?
A Decamethonium halides
B Suxamethonium
C Benzquinonium
D Gallamine
E Vecuronium
B Suxamethonium
Muscle relaxants
Suxamethonium
• Depolarising neuromuscular blocker
• Inhibits action of acetylcholine at the neuromuscular junction
• Degraded by plasma cholinesterase and acetylcholinesterase affected by lack of acetylcholinesterase)
• Fastest onset and shortest duration of action of all muscle relaxants
• Produces generalised muscular contraction prior to paralysis
• Adverse effects include hyperkalaemia, malignant hyperthermia, delayed recovery
Atracurium
• Non depolarising neuromuscular blocking drug
• Duration of action usually 30-45 minutes
• Generalised histamine release on administration may produce facial flushing, tachycardia and hypotension. Not excreted by the liver or kidney Just broken down in tisues by hydrolysis
•Reversed by Neostigmine
Vecuronium
• Non depolarising neuromuscular blocking drug
•Duration of action approximately 30-40 minutes
•Degraded by liver and kidney and effects prolonged in organ disfunction
•Effects may be reversed by Neostigmine
Pancuronium
• Non depolarising neuromuscular blocker
• Onset of action approximately 2-3 minutes and duration of action is up to 2 hours
• Effects may be partially reversed with drugs such as nostigmine
Which of the agents listed below is a phosphodiesterase inhibitor?
A Milrinone
B Metaraminol
C Dopamine
D Dobutamine
E Adrenaline
A Milrinone
Circulatory support of the critically ill
Impaired tissue oxygenation may occur as a result of circulatory shock. Shock is considered further under its own
Patients requiring circulatory support require haemodynamic monitoring. At its simplest level this may simply be in the form of regular urine output measurements and blood pressure monitoring. In addition ECG monitoring with allow the identification of cardiac arrhythmias. Pulse oximeter measurements will allow quick estimation haemoglobin oxygen saturation in arterial blood.
Invasive artenal blood pressure monitoring is undertaken by the use of an indwelling arterial line. Most arterial sites can be used although the radial artery is the commonest. It is important not to cannulate end arteries. The arterial trace can be tracked to ventilation phases and those patients whose systolic pressure varies with changes in intrathoracic pressure may benefit from further intravenous fluids.
Central venous pressure is measured using a CVP line that is usually sited in the superior vena cava via the internal jugular route. The CVP will demonstrate right atrial filing pressure and volume status. When adequate intra vascular volume is present a fluid challenge will typically cause a prolonged rise in CVP (usually greater than 6-8mmHg).
To monitor the cardiac output a Swan-Ganz catheter is traditionally inserted (other devices may be used and are less invasive). Inflation of the ustar balloon will provide the pulmonary artery occiusion pressure and the pressure distal to the balloon will equate to the left atrial pressure. This gives a measure of left ventricular preload. Because the swan-Ganz catheter ce
• Stroke volume
• Systemic vascular resistance
Inotropes
In patients with an adequate circulating volume but on-going circulatory compromise a vasoactive drug may be considered. These should usually be administered via the central venous route. Commonly used inotropes include:
Agent and Mode of action
Noradrenaline: a agonist Vasopressor action, minimal effect on cardiac output
Adrenaline: a and ß receptor agonist Increases cardiac output and peripheral vascular resistance
Dopamine: ß1 agonist Increases contractility and rate
Dobutamine: ß1 and 32 agonist Increases cardiac output and decreases SVR
Milrinone: Phosphodiesterase inhibitor Elevation of cAMP levels improves muscular contractility, short half life and acts as vasodilator
A 56 year old man is on the ward 5 days following a high anterior resection for a carcinoma of the recto sigmoid junction. Over the past 12 hours, he has developed increasing lower abdominal pain, a fever of 37.8°C and fast atrial fibrillation. Of the investigations listed below, which is likely to be the most useful?
A Abdominal X-ray
B Abdominal ultrasound scan
C Abdominal CT scan
D Echocardiogram
E Measurement of cardiac enzymes in the blood
C Abdominal CT scan
New AF following a colonic resection is most likely to represent an anastomotic leak and this will be best seen on
CT scanning.
A 4 week old preterm neonate is due to have surgery for an inguinal hernia. Which of the following fluids should be administered whilst they are nil by mouth?
A 10% dextrose
B 50% dextrose
C 5% dextrose
D 25% dextrose
E Hartmanns solution
A 10% dextrose
Neonates are at considerable risk of hypoglycaemia following surgery and should receive 10% dextrose.
In the Uk the GiAsuP and NICE guidelines were derived to provide some consensus guidance as to how intravenous fluids should be administered. A decade ago it was a commonly held belief that little harm would occur as a result of excessive administration of normal saline and many oliguric postoperative patients received enormous quantities of IV fluids. As a result they developed hyperchloaremic acidosis. With greater understanding oi this potential complication, the use of electrolyte balanced solutions (Ringers lactate/ Hartmans) is now favored over normal saline.
The other guidance includes:
• Fluids given should be documented clearly and easily available
• Assess the patient’s fluid status when they leave theatre
• If a patient is haemodynamically stable and euvolaemic, aim to restart oral fluid intake as soon as possible
• Review patients whose urinary sodium is < 20
• If a patient is oedematous, hypovolaemia if present should be treated first. This should then be followed by a negative balance of sodium and water, monitored using urine Na excretion levels
• Solutions such as Dextran 70 should be used in caution in patients with sepsis as there is a risk of developing acute renal injury
A 53 year old man has an arterial blood gas sample taken and the following results are obtained, he is breathing room air.
pH: 7.49. PO2: 8.5 HCO3 22 pCO2 2.4. Cl <10meq
Which of the conditions listed below is most likely to account for these findings?
A Respiratory alkalosis
B Type 2 respiratory failure
C Metabolic acidosis with increased anion gap
D Metabolic alkalosis
E Metabolic acidosis with normal anion gap
To interpret the arterial blood gas (ABG) results, let’s analyze each component:
ABG Results:
• pH: 7.49 (alkalosis) • pO2: 8.5 kPa (low, indicating hypoxemia) • HCO3: 22 mmol/L (normal) • pCO2: 2.4 kPa (low) • Cl: <10 mEq/L (abnormally low)
Interpretation:
• pH (7.49): Indicates alkalosis. • pCO2 (2.4 kPa): Low pCO2 indicates respiratory alkalosis. • HCO3 (22 mmol/L): Normal bicarbonate level, which is not consistent with metabolic alkalosis or acidosis.
Conditions to Consider:
• Respiratory Alkalosis: Characterized by an elevated pH and a low pCO2, typically due to hyperventilation. • Type 2 Respiratory Failure: Characterized by hypercapnia (high pCO2), which is not present here. • Metabolic Acidosis with Increased Anion Gap: Would show low pH and low HCO3. • Metabolic Alkalosis: Would show high pH and high HCO3. • Metabolic Acidosis with Normal Anion Gap: Would show low pH and low HCO3.
Given the ABG values, the most fitting diagnosis is respiratory alkalosis due to the combination of high pH and low pCO2, while the bicarbonate level is normal, which is a compensatory response.
Answer:
A Respiratory alkalosis
44 year old man undergoes a distal gastrectomy for cancer. He is slightly anaemic and therefore receives a transfusion of 4 units of packed red cells to cover both the existing anaemia and associated perioperative blood loss. He is noted to develop ECG changes that are not consistent with ischaemia. What is the most likely cause?
A Hyponatraemia
B Hyperkalaemia
C Hypercalcaemia
D Metabolic alkalosis
E Hypernatraemia
B Hyperkalaemia
The transfusion of packed red cells has been shown to increase serum potassium levels. The risk is higher with large volume transfusions and with old blood.
Blood transfusion reactions
Acute transfusion reactions present as adverse signs or symptoms during or within 24 hours of a blood transfusion.
The most frequent reactions are fever, chills, pruritus, or urticaria, which typically resolve promptly without specific treatment or complications. Other signs occurring in temporal relationship with a blood transfusion, such as severe dyspnoea, pyrexia, or loss of consciousness may be the first indication of a more severe potentially fatal reaction.
The causes of adverse reactions are multi-factorial. Immune mediated reactions, some of the most feared, occur as a result of component mismatch, the commonest cause of which is clerical error. More common, non immune mediated, complications may occur as a result of product contamination, this may be bacterial or viral.
Transfusion related lung injury is well recognised and there are two proposed mechanisms which underpin this.
One involves the sequestration of primed neutrophils within the recipient pulmonary capillary bed. The other proposed mechanism suggests that HLA mismatches between donor neutrophils and recipient lung tissue is to blame.
The table below summarises the main types of transfusion reaction.
Immune mediated
Pyrexia
Alloimmunization
Thrombocytopaenia
Transfusion associated lung injury
Graft vs Host disease
Urticaria
Acute or delayed haemolysis
ABO incompatibility
Rhesus incompatibility
Non immune mediated: Hypocalcemia, Hyperkalaemia, Infections
Which of the following muscle relaxants will tend to incite neuromuscular excitability following administration?
A Atracurium
B Suxamethonium
C Vecuronium
D Pancuronium
E None of the above
B Suxamethonium
Suxamethonium may induce generalised muscular contractions following administration. This may raise serum potassium levels.
Which of the variables listed below is not considered in the sequential organ failure assessment (SOFA) tool?
A Bilirubin
B Urea
C Mean arterial pressure
D Platelet count
E Creatinine
B Urea
Urea is not one of the variables considered.
A SOFA score of 2 or more reflects an overall mortality risk of approximately 10% in a general hospital population with suspected infection. Even patients presenting with modest dysfunction can deteriorate further, emphasizing the seriousness of this condition and the need for prompt and appropriate intervention, if not already being instituted.
The qSOFA score (also known as quickSOFA) is a bedside prompt that may identify patients with suspected infection who are at greater risk for a poor outcome outside the intensive care unit (ICU). It uses three criteria, asiain nagin for low or pressure (SP 100 mH,), high respratoy rat (-22 breats per min) or atored
QSOFA score
Respiratory rate 22/min
Altered mentation
vasopressors to maintain MAP 65 mm Hg and having a serum lactate level >2 mmol/L (18mg/dit) despite adequate volume resuscitation. With these criteria, nospaai morality is in excess ot 40%.
Severe infections
Sepsis is a multifaceted syndrome which arises as a result of an infective process. Historically, the main focus was on the pro-inflammatory nature of the process, accordingly, 2 of the 4 SIRS criteria were related solely to inflammatory excesses. More modern systems take into account the fact that some of the effects of sepsis are suppressive from an immunological perspective and effects on organ function can be widespread. Sepsis is now defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. This new definition emphasizes the primacy of the non homeostatic host response to infection, the potential lethality that is considerably in excess of a straightforward infection, and the need for urgent recognition. To help identify and categorise patients the Sequential (Sepsis-Related) Organ Failure Assessment Score (SOFA) is increasingly used.
The score grades abnormality by organ system and accounts for clinical interventions. However, laboratory variables, namely, Pa02, platelet count, creatinine level, and bilirubin level, are needed for full computation.
A 23 year old man is recovering from an appendicectomy. The operation was complicated by the presence of perforation. He is now recovering on the ward. However, his urine output is falling and he has been vomiting. Which of the following intravenous fluids should be initially administered, pending analysis of his urea and electrolyte levels?
A Hartmans solution
B Dextran 70
C Pentastarch
D Gelofusin
E 5% Dextrose
Correct Answer:
A. Hartmann’s solution
Explanation:
In the setting of post-operative care, particularly following a complicated appendicectomy with perforation, it is essential to maintain adequate fluid and electrolyte balance. Given the patient’s falling urine output and vomiting, it is likely he is experiencing hypovolemia and potential electrolyte disturbances.
Hartmann’s solution (also known as Ringer’s lactate) is the most appropriate initial fluid choice in this scenario for the following reasons:
• Electrolyte Balance: Hartmann’s solution contains electrolytes (sodium, potassium, calcium, and chloride) and lactate, which help to replenish lost electrolytes and correct acid-base disturbances. • Volume Expansion: It is an isotonic crystalloid solution, which effectively expands the intravascular volume, improving urine output and stabilizing hemodynamics. • Safety: It is generally well-tolerated and safe in most clinical scenarios, including post-operative care.
Other options such as Dextran 70, Pentastarch, and Gelofusin are colloid solutions and are typically reserved for more specific indications like severe hypovolemia or shock. 5% Dextrose is a hypotonic solution that is not suitable for initial resuscitation as it does not provide electrolytes and can lead to further electrolyte imbalances.
73 year old man develops disseminated intravascular coagulation following an abdominal aortic aneurysm repair. He receives an infusion of cryoprecipitate. What is the major constituent of this infusion?
A Factor VIII
B Factor IX
C Protein C
D Protein S
E Factor V
A Factor VIII
Cryoprecipitate
• Blood product made from plasma
• Usually transfused as 6 unit pool
• Indications include massive haemorrhage and uncontrolled bleeding due to haemophilia
Agent. Quantity
Factor VIII: 100IU
Fibrinogen: 250mg
von Willebrand factor: Variable
Factor XIII: Variable
A 32 year old man presents to the acute surgical unit with acute pancreatitis. Over the next few days he becomes dyspnoeic and his saturations are 89% on air. A CXR shows bilateral pulmonary infiltrates. His CVP pressure is 16mmHg. What is the most likely diagnosis?
A Cardiac failure
B Pneumococcal pneumonia
C Staphylococcal pneumonia
D Pneumocystis carinii
E Adult respiratory distress syndrome
E Adult respiratory distress syndrome
Acute pancreatitis is known to precipitate ARDS. ARDS is characterised by bilateral pulmonary infiltrates and hypoxaemia. Note that pulmonary oedema is excluded by the CVP reading < 18mmHg.
Adult respiratory distress syndrome
Defined as an acute condition characterized by bilateral pulmonary infiltrates and severe hypoxemia (Pa02/FiOz ratio < 200) in the absence of evidence for cardiogenic pulmonary oedema (clinically or pulmonary capillary wedge pressure of less than 18 mm Hg).
It is subdivided into two stages. Early stages consist of an exudative phase of injury with associated oedema. The later stage is one of repair and consists of fibroproliferative changes. Subsequent scarring may result in poor lung function.
Causes
• Sepsis
• Direct lung injury
• Trauma
• Acute pancreatitis
Long bone fracture or multiple fractures (througin fai ernioulism
• Headinjury (causes sympathetic erous stimulatiz. which leads to acute pulmonary hypertension)
Clinical features
• Acute dyspnoea and hypoxaemia hours/aays after event
MRCS Made Easy
• Auto ventiony pressures
Management
• Treat the underlying cause
• Antibiotics (if signs of sepsis)
• Negative fluid balance i.e. Diuretics
• Mechanical entain sue using eventil on us, as corie ina xpra olymes may cause lung injury
(only treatment found to improve survival rates)
Which of the anaesthetic agents below is most likely to induce adrenal suppression?
A Sodium thiopentone
B Midazolam
C Propofol
D Etomidate
E Ketamine
D Etomidate
Etomidate is a recognised cause of adrenal suppression, this has been associated with increased mortality when used as a sedation agent in the critically ill.
Anaesthetic agents
Propofol
• Rapid onset of anaesthesia
• Pain on IV injection
• Rapidly metabolised with little accumulation of metabolites
• Proven anti emetic properties
• Moderate myocardial depression
• Widely used especially for maintaining sedation on ITU, total IV anaesthesia and for daycase surgery
Sodium thiopentone
• Extremely rapid onset of action making it the agent of choice for rapid sequence of
induction
• Marked myocardial depression may occur
• Metabolites build up quickly
• Unsuitable for maintenance infusion
• Little analgesic effects
Ketamine
• May be used for induction of anaesthesia
• Has moderate to strong analgesic properties
• Produces little myocardial depression making it a suitable agent for anaesthesia in those who are haemodynamically unstable
• May induce state of dissociative anaesthesia resulting in nightmares
Etomidate
• Has favorable cardiac safety profile with very little haemodynamic instability
• No analgesic properties
• Unsuitable for maintaining sedation as prolonged (and even brief) use may result in adrenal suppression
• Post operative vomiting is common
