Critical care

Question 1

What equation governs acid-base balance?

Answer 1

Henderson-Hasselbach equation
H20 + CO2 H2CO3 HCO3- + H+
Mediated by carbonic anhydrase

Question 2

How does CO2 travel in blood?

Answer 2

1) dissolved in solution
2) buffered with water as carbonic acid
3) bound to proteins (e.g. haemoglobin)

Question 3

What is the chloride shift?

Answer 3

Exchange of bicarbonate and chloride across red blood cell membranes.

Question 4

What is a buffer?

Answer 4

They limit the change in pH by binding or releasing H+.

Bicarbonate & Hb are most important

Question 5

Causes of metabolic acidosis?

Answer 5

Normal anion gap: renal tubular acidosis, tubular damage, diarrhoea, ileostomy, hyperparathyroidism, hypoaldosteronism.

Increased anion gap: sepsis, cardiac arrest, hypotension, methanol, uraemia, diabetes (insulin deficiency), metformin, starvation, salicylates.

Question 6

Causes of metabolic alkalosis?

Answer 6

Vomiting, renal loss of H+, low chloride states, diuretics, excess antacid,

Question 7

Causes of respiratory acidosis?

Answer 7

Neurological: myasthenia gravis, Guillain-Barre, polio, head trauma, opiates
Lung: Pneumonia, pulmonary oedema, airway obstruction, ARDS, flail segment, lung contusion

Question 8

Causes of respiratory alkalosis?

Answer 8

Hyperventilation- Anxiety, pain, altitude, excess mechanical ventilation, salicylate overdose, PE, asthma

Question 9

What is acute respiratory distress syndrome?

Answer 9

A clinical syndrome comprising acute respiratory failure and non-cardiogenic pulmonary oedema. This leads to hypoxaemia and a decreased lung compliance that is refractory to oxygen therapy

Question 10

What are the key characteristics of ARDS?

Answer 10

1. Diffuse bilateral pulmonary infiltrates on chest radiograph
2. Normal pulmonary artery wedge pressure (PAWP < 18mmHg)
3. PaO2/FiO2 ratio of < 26.6kPa

Question 11

Potential causes of ARDS?

Answer 11

Primary lung causes:
Trauma
Pneumonia
Aspiration
Fat embolism
Smoke inhalation

Others:
Multiple trauma
Generalised sepsis
Massive transfusion
DIC
Cardio-pulmonary bypass

Question 12

Management of ARDS?

Answer 12

Supportive
Treat the underlying cause

Other potentials:
NIV and PEEP to keep alveoli open
Increase ratio of inspiration to expiration
Prone ventilation to reduce V/Q mismatch

Question 13

How and why do patients lose heat intraoperatively?

Answer 13

Convection- moving air in surroundings cools body surface
Conduction- direct contact
Evaporation- water, mucosal surfaces
Radiation- surroundings

Question 14

Define hypothermia

Answer 14

Core body temperature lowering to <35°C (rectal temp)

Question 15

What is the body’s response to hypothermia?

Answer 15

Sympathetic response, inducing piloerection, shivering and peripheral vasoconstriction.

Question 16

Risk factors for intraoperative and postoperative hypothermia?

Answer 16

ASA grade
A preop temp less than 36 degrees
Combined general and regional anaesthetic
Major surgery
Exposed surgery

Question 17

Complications of hypothermia:

Answer 17

Increase in morbidity.

Intraoperatively: A reduction in cardiac output and an increase in Hb oxygen affinity ->decreased tissue oxygen delivery-> myocardial ischaemia -> arrhythmias, cerebral ischaemia.
Decreased drug metabolism ->prolonged duration of action.
Coagulopathy, as the enzymes involved in the clotting cascade are affected. Platelet function is temperature dependent, promoting intra- and postoperative haemorrhage.

Shivering increases oxygen consumption and myocardial work.
Metabolism falls-> wound breakdown & infection.
May develop limb or bowel ischaemia, pancreatitis, renal failure

Question 18

How to avoid hypothermia?

Answer 18

Bair hugger, theatre temp 21 degrees, warm fluids, patient exposed only as needed.

Patient should not leave recovery unless core temperature >36 degrees.

Question 19

Causes of CKD

Answer 19

Diabetes
Hypertension & arteriopathic disease
Glomerulonephritis
Infective/obstructive/reflux nephropathy
Systemic disease with kidney involvement e.g. SLE, amyloid
Family history e.g. polycystic kidneys
Drugs e.g. NSAIDs
Malignancy

Question 20

When do you consider renal replacement therapy?

Answer 20

Acidaemia
Electrolyte imbalance
Intoxication- drug overdose
Oedema, oliguria/anuria
Uraemia (pericarditis, encephalopathy)

Question 21

What are they types of transplant rejection?

Answer 21

Hyperacute (minutes to hours)
Preformed antibody against tissue
Lymphocytotoxic cross matching minimizes risk

Acute (weeks)
T cell mediated
HLA typing minimizes risk

Chronic (months to years)
Unknown aetiology or possibly due to recurrent acute episodes

Question 22

Which diseases are blood transfusions screened for in UK?

Answer 22

Hepatitis B
Hepatitis C
HIV
HTLV
Syphilis

Question 23

How long and at what temperature can RBC/platelets/fresh frozen plasma & cryoprecipitate be stored?

Answer 23

RBC / 35 days / 2-6C
Platelets / 5 days / 20-24C
FFP/cryoprecipitate / 1yr / -30C

Question 24

Constituents of FFP & cryoprecipitate

Answer 24

FFP = albumin, all clotting factors, complement, fibrinogen, vWF
Cryoprecipitate = Factor VIII, Factor XIII, fibrinogen, vWF

Question 25

Types of blood transfusion reaction?

Answer 25

Acute

Acute haemolytic reaction
TRALI (transfusion related acute lung injury)
Bacterial contamination
Allergic (includes febrile non-haemolytic transfusion reaction and anaphylaxis
Fluid overload
Coagulopathy & DIC
Hyperkalaemia
Hypocalcaemia (due to citrate binding calcium)

Delayed

Delayed haemolytic transfusion reaction (>24 hours)
Graft versus host
Post transfusion purpura
Infection

Question 26

Layers for lumbar puncture

Answer 26

Skin
Subcutaneous fat
Superficial fascia
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space containing internal vertebral venous plexus
Dura mater
Arachnoid mater
CSF