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describe acid production in the body

• Cellular respiration
o Produces CO2 which reacts with water to form carbonic acid

• Metabolic processes
o Give rise to non-volatile acids: ketones, lactate etc
o ~60 mmol non-volatile acids per day
o In 14L this would make the body pH 2.3


describe how acid homeostasis is maintained

• Buffers (rapid)
o Bind to protons to reduce acidity
o Proteins e.g. Hb
o Bicarbonate

• Lungs (fast)
o Remove CO2
o Limited by HCO3 reserves

• Kidneys (slow)
o Excrete H into urine
o Recover HCO3


what happens in hypoventilation

• Increased CO2  respiratory acidosis
• Lung disease, airway obstruction, neurological problem leading to depressed breathing such as head injury or opiate overdose


what happens in hyperventilation

• Less CO2  respiratory alkalosis
• Panic attack in response to pain or asthma


how can you get metabolic acidosis

• Increased protons
o Over production of acid such as lactic acidosis (tissue hypoxia) or ketoacidosis (diabetes, starvation, alcohol)
o Impaired excretion
 Acute kidney injury or CKD

• Losing bicarbonate
o Severe diarrhoea
o Fistula formation in small bowel
o renal tubular acidosis type II


how can you get metabolic alkalosis

• Unusual loss of protons
o Vomiting
o Severe hyperkalaemia
o Hyperaldosteronism
• Unusual ingestion of bicarbonate


what are the compensation mechanisms for each acid base disturbance

metabolic acidosis
- increased RR to lower CO2
- increased renal recovery of HCO3

metabolic alkalosis
- decreased RR to increase CO2
- decreased renal recovery of HCO3
- usually marginal

respiratory acidosis
- increased renal recovery of HCO3

respiratory alkalosis
- decreased renal recovery of HCO3
- usually marginal


how is HCO3 calculated

using the henderson-hasselbalch equation

CO2 + H2O H2CO3 H + HCO3


what is important to remember about arterial blood gases

Blood gases often performed on the radial artery – can damage artery
Need to be analysed asap and not sent by pneumatic tube – pressure
We only need H, pO2, pCO2 and HCO3
Base excess and HCO3 are calculated by the analyser
Base excess is the amount of H per L of blood, required to return the pH to reference range at pCO2 of 5.3kPa
Should only be deranged where a metabolic disorder is present


describe standardised bicarbonate

• What the HCO3 conc would be if pCO2 were reference range (5.3kPa)
• Std bicarb should only be deranged where a metabolic disorder is present
• Purely metabolic disorder - approx. equivalent to actual bicarb
• Mixed resp-meta disorder - significant difference to actual bicarb


what are the effects of metabolic acidosis

• Cardiovascular
o Negative inotropic effect (if severe)

• Oxygen delivery
o Acutely – H causes R-shift of oxyHb dissociation curve (facilitates oxygen delivery)
o After several hours – H reduces 2,3-DPG causing L-shift of curve (impairs O2 delivery)

• Nervous system
o Impaired consciousness

• Potassium homeostasis
o H leakage from cells causing high plasma K, may also be lost renally
o If above sustained, total body K can be depleted

• Bone
o If chronic, acidosis can get buffered by bone
o Leads to decalcification


describe the relationship between metabolic acidosis and anion gap

some causes have anion gap and some done

o lactic acidosis
o salicylate overdose
o ethylene glycol, methanol poisoning
o renal failure

o severe diarrhoea
o high intestinal fitula output
o renal tubular acidosis


what are the effects of respiratory acidosis

hypercapnia -
o shortness of breath
o neurological - anxiety, coma, headache, myoclonus
o systemic vasodilation

o hypoxia


what are the effects of metabolic alkalosis

not usually significant
K moves into cells

beware effect of IV bicarbonate in CKD as metabolic acidosis is common in CKD - acute fall in acidity can reduce solubility of calcium salts and increase risk of systemic calcification

Remember the compensation for alkalosis is limited


what are the effects of respiratory alkalosis

acute hypocapnia
o cerebral vasoconstriction - light headedness, fits, confusion, syncope
o fall in ionised calcium -perioral, peripheral parasthesia

o increased heart rate
o vasoconstriction - possible angina in those with coronary artery disease

Remember the compensation for alkalosis is limited


how can you get respiratory acidosis

o airway obstruction
o cardio-resp arrest
o infective exacerbation of COPD
o pneumonia
o neurological - opiate toxicity, guilllain barre syndrome, myasthenia gravis

o obstructive - obesity
o restrictive - pulmonary fibrosis
o neurological - MND, myopathy


how can you get respiratory alkalosis

usually acute in nature
o asthma, COPD. PE
o pain, panic attack
o iatrogenic
o altitude sickness

o inappropriate stimulation of respiratory centre
• head injury
• raised ICP
• local tumour
• metabolic e.g. hepatic encephalopathy, poisoning

o pregnancy - mild resp alkalosis compensated by minor metabolic acidosis


what are the immune systems normal functions?

Recognition of ‘non-self’or ‘abnormal self’
Protection from pathogens (bacteria, viruses etc)
Surveillance for tumours


what are the components of the immune system

Innate immune system

Complement & natural antibodies (IgM)

Adaptive immune system

Dendritic cells (antigen presentation)
T cells (helper and cytotoxic T cells)
Natural Killer (NK) cells - cytotoxic
B cells (antibody generation & memory)


describe MHC (Major Histocompatibility Complex)

MHC in humans called Histocompatibility Locus Antigen (HLA)
These molecules imprint ‘individuality’ on cells and are pivotal in the generation of immune responses
HLA genes are very polymorphic i.e. there are many different variations possible at each gene locus

Class I molecules: HLA-A, -B and -C
Expressed by most somatic cells of body
Used to present peptides from internally processed proteins
Class II: HLA-DP, -DQ and –DR
Expressed by Antigen Presenting Cells (DCs etc) that constantly ’sample’ their microenvironment
Used to present antigenic peptides derived from digested material (including pathogens, abnormal or foreign cells)

Class I: HLA-A, -B and -C
If Class 1 HLA molecule is associated with virus-derived protein then the cell is recognised as infected
Infected cell will be killed by cytotoxic T cells

Class II: HLA-DP, -DQ and –DR
Used by Antigen Presenting Cells (DCs etc) to present antigenic peptides derived from digested and processed material
Cell surface expression of a peptide derived from a pathogen or foreign cell will stimulate a T cell immune response


what are the key principles of transplant immunology

Rejection of Tx is directed at specific proteins called antigens
Rejection is donor specific
Rejection may be both Cell or Antibody mediated
Rejection exhibits ‘memory’ i.e. a 2nd similar Tx is rejected MORE RAPIDLY and this results from the rapid generation of cytotoxic antibodies that recognise the Tx


describe HLA profiling

Performed using molecular biological and serological techniques
e.g. HLA-A1 and A3,
HLA-B44 and B44
HLA-DR7 and DR15
The HLA tissue types of all patients on the Kidney Transplant waiting list is held on a central UK database and the ‘best match’ chosen when kidneys become available
Used to allocate kidneys but less important for other organs such as liver (less immunogenic)
If all HLA-A, -B and –DR loci are the same the it is a 0-0-0 mismatch
If they are all different then it is a 2-2-2 mismatch


describe immunosuppressive treatment

Kill lymphocytes
Interfere with T cell activation and gene transcription
Powerful anti-inflammatory agents

Calcineurin inhibitors (CNI) – Tacrolimus
Inhibit T cell activation by interfering with intracellular signaling pathways

Anti-proliferative agents - mycophenolate mofetil (MMF)
Inhibit clonal expansion of T cells

Various monoclonal and polyclonal antibodies directed against:
IL-2 receptor blockers (IL-2 stimulates clonal expansion of T cells)
T cells (cytotoxic complement fixing Abs)
Co-stimulatory molecules


which organs are transplantable

Pancreas (complete organ or pancreatic islets)
Small Bowel
Faces, arms etc


what needs to be assessed in patients needing a transplant

Age important (biological vs chronological!) - frailty
Primary cause of renal failure e.g. polycystic kidneys versus conditions which can recur in a Tx (e.g. aHUS, FSGS)
Comorbid disease e.g. cardiovascular disease (IHD, PVD), diabetes etc
History of infections
History of tumours (need tumour free period)
Urological disease e.g. bladder dysfunction

Additional investigations:

CARDIAC - exercise ECG, myocardial perfusion studies
Angiography (need decent vessels for the anastomosis)
Urodynamic studies
Tumour markers, imaging etc


what are the types of transplant?

Cadaveric Tx (commonest) e.g. subarachnoid haemorrhage
• DCD = donated after cardiac death
• DBD = donation after brain death
Living related donor Tx
• Sibling, spouse, altruistic
Typically a kidney Tx

Live donation lasts longer than cadaveric


what are the criteria for a kidney Tx to go ahead?

Blood group (ABO) compatible (RIE now has an ABO incompatible programme)
Immunological ‘X-match negative’
• Take serum from the recipient and donor lymphocytes
• Add a complement e.g. vital dye which will enter killed cells and turn them a colour if they are matched to recipient antibodies


describe anti-HLA antibodies

If a person is exposed to a foreign HLA molecule, they can produce an HLA antibody against this e.g. patient is A1, A24 and with exposure to A31 generating an anti-A31 antibody

Approximately 30% patients on renal waiting list have anti-HLA antibodies
The ‘specificity’ of these antibodies has to be defined (e.g. A31, B8, DR3 etc)

Highly sensitised patients exhibit high levels of cytotoxic Abs to many HLA antigens that may be derived from:
• Previous transfusions (WBC filtered)
• Pregnancies
• Previous Transplantation


why do anti-HLA antibodies matter?

HLA antibody status requires careful consideration
- make a successful X-match less likely (long wait for Tx)
- can lead to antibody mediated rejection
- Consider desensitisation/antibody removal or paired exchange Tx


what types of rejection are there

Hyperacute rejection (should not happen)
Acute rejection
Chronic rejection