U1 O3 - Emergency diagnostics Flashcards
What is the normal PCV for cats and dogs?
Normal dogs have a PCV of 37-55% and cats 30-45%.
What are reticulocytes?
Reticulocytes are immature, non-nucleated red blood cells that are found in the circulation in increased numbers in regenerative responses.
What is the mean cell volume (MCV) in haematology?
➢ Mean cell (corpuscular) volume (MCV) The mean cell volume provides information about the average size of red blood cells. Cells may be: • macrocytic (bigger than normal), • normocytic (normal size) • microcytic (smaller than normal).
Why would a patient have large circulating erythrocytes?
RBCs become smaller as they develop in the bone marrow- so if immature are released early into the bloodstream e.g. following haemorrhage, they will be relatively large. In regenerative anaemia, immature cells are often released into the circulation and are relatively larger than mature erythrocytes.
Why would a patient have small circulating erythrocytes?
If a patient, has iron deficiency anaemia, the circulating red blood cells are smaller than normal as they have spent longer developing in the bone marrow, due to the lack of iron.
What us the mean cell haemoglobin concentration (MCHC) in haemoatology?
➢ Mean cell (corpuscular) haemoglobin concentration (MCHC)
This is a measurement of the average haemoglobin concentration per red blood cell. Depending on the haemoglobin levels in RBCs, they will be
• normochromic (normal colour = normal haemoglobin concentration)
• hypochromic (paler than normal = reduced haemoglobin).
Immature RBCs contain less haemoglobin- thus regenerative anaemia will usually be hypochromic; whereas non-regenerative anaemia will be normochromic.
What is a white blood cell count made up of?
The white blood cell count is made up of neutrophils, lymphocytes, eosinophils and basophils.
What can a leucogram assist with identifying?
The character of the leucogram (i.e. what combination of white cells is present) can assist in identifying an underlying cause e.g. stress leucogram, inflammatory leucogram etc.
What is an increase in neutrophils usually associated with?
Explain what a left shift is and what a degenerative left shift is?
Neutrophils: an increase in the number of neutrophils is most commonly associated with infection or inflammation. Immature neutrophils are called band cells - an increase in the number of immature neutrophils in the circulation is known as ‘a left shift’. This is seen where neutrophils are involved in an active inflammatory or infectious process; or where there is abnormal neutrophil production. In a normal regenerative response, the number of mature neutrophils will outnumber the band neutrophils- indicating that the immune response is working well. However, if band neutrophils outnumber the mature neutrophils, this indicates that the mature neutrophils are being consumed/destroyed- the immune response is not working as well as we would like or is being overwhelmed. This is called a degenerative left shift.
What is lymphopaenia? and what is it associated with?
Lymphopaenia (decreased circulating lymphocyte numbers) can be seen in association with acute infection or chronic stress e.g. chronic disease or corticosteroid therapy etc. Lymphocytosis (increased numbers of circulating lymphocytes) can be seen with hypoadrenocorticism, leukaemia or prolonged antigenic stimulation. It may also be seen with an acute stress response.
What are lymphocytes T and B associated with?
Lymphocytes (T and B lymphocytes) are associated with the immune response.
What are eosinophils associated with?
Eosinophils are present in relatively small numbers. They are associated with allergic disease and parasitism. Increased numbers may also be seen with specific conditions such as pulmonary infiltration with eosinophilia (PIE) or neoplasia. Eosinopaenia may be a stress response or secondary to corticosteroid treatment.
How common are basophil abnormalities?
Basophils abnormalities in basophil numbers are rarely identified.
What do monocytes develop in to? and what are large number associated with?
Monocytes these large cells are only present in blood for a short time before leaving and developing into macrophages. Increased numbers can be associated with chronic, intracellular infections or a stress response
What is haemostasis?
Haemostasis is the process of stopping bleeding
How can haemostasis occur?
- vasoconstriction
- primary haemostasis - formation of an initial platelet plug
- secondary haemostasis/ clot formation - the platelet plug is stabilised by cross-linked fibrin- clot
- thrombolysis- clot break-down.
What can happen to platelets when a patient is thrombocytopaenic?
thrombocytopaenia can arise due to:
• Increased platelet destruction e.g. immune-mediated thrombocytopaenia (IMHA)
• Increased platelet ‘consumption’: platelets have been used up secondary to haemorrhage or inflammation.
What is primary haemostasis?
Primary Haemostasis
Platelets are required for primary haemostasis (the start of clot formation). Alterations in the platelet numbers occur for many reasons and with various diseases.
What is the monolayer segment of a smear and what is it composed of?
Oil immersion fields are examined in the monolayer segment of the smear. The monolayer segment lies between the feathered edge of the smear and the main body of the smear - it is composed of a single layer of cells.
How many platelets should be seen per field on average on a normal blood smear? What would be considered as dangerously low level of platelets?
Each one platelet, seen in an oil immersion (x100) field, is roughly equivalent to 15x109 platelets/l. Therefore, a normal blood smear should have 11-15 platelets per field on average. Dangerously low levels of platelets would be indicated by less than 3 platelets per oil immersion field (equivalent to 0-45x109/l). A patient with a platelet count of <5 per field should be closely monitored for evidence of bleeding.
What equipment would you need to carry out a true platelet count?
A true platelet count may be done, manually, using a haemocytometer, commercial diluting fluid and a microscope
How do you carry out a true platelet count?
A commercial ammonium oxalate diluent pipette system should be used (e.g. ‘Unopette Micro-collection System for WBC and Platelet Determination’ produced by Becton-Dickinson, Oxford UK). This is filled as directed and lyses the red cells after ~ 10 minutes. A Neubauer modified haemocytometer is then filled with the mixture and left in a humid environment (a small covered dish with a layer of wet filter paper in the bottom) for 5-10 minutes, to allow the platelets to settle to the floor of the haemocytometer.
A platelet count is then performed by examining the haemocytometer microscopically. Platelets can be differentiated from white cells by their smaller size and refractile nature. The total number of platelets, in the central major square on each side of the haemocytometer, is counted. This square is divided into 25 smaller squares, each of which contains 16 further squares. The average of the two major square counts is then the total platelet count in 109/l. Normal values for dogs are 200-700x109/l and for cats are 300-800 x109/l.
Clinically what is the best way to perform platelet function assessment?
Platelet function can be assessed in a laboratory using specific analysers. Clinically, however, the best way is to perform a buccal mucosal bleeding time (BMBT).
How do you carry out a Buccal mucosal bleeding time test?
Buccal mucosal bleeding time - The BMBT requires the use of a commercial device that produces two standardised cuts to the buccal mucosa of the upper lip - 5mm long and 1mm deep. The patient is placed in lateral recumbency, the upper lip is reflected to expose the mucosal surface and held in place by a gauze tape lightly applied around the maxilla, enough to partially block venous return (Oakley, 2007). The BMBT device is then placed on the mucosa and activated. The incisions are then left alone until bleeding stops- the time taken should be recorded. This is assessed by using a swab or filter paper placed near to the incisions (3-4 mm below), but not touching them. Bleeding is judged to have stopped when blood stops being taken up by the clean edge of the swab/filter paper. The BMBT is taken as the mean bleeding time of the two incisions and should normally be less than 4 minutes. The BMBT evaluates primary haemostasis by assessing platelet and vascular aspects of haemostasis.
In what case would you see an increased Buccal mucosal bleeding time?
What are the contraindications?
Instances where BMBT may be increased include:
• thrombocytopaenia
• von Willebrand’s disease
• drug therapy e.g. aspirin.
A BMBT should NOT be performed on dogs that are already known to be thrombocytopaenic- thrombocytopaenia should be confirmed initially on a blood smear, as previously discussed. Thrombocytopaenic animals will have a prolonged BMBT so confirmation with the test is unnecessary.
What is secondary haemostasis?
Secondary Haemostasis
Secondary haemostasis is the process of clot formation using coagulation factors - it follows the formation of an initial platelet plug (Cornell University College of Veterinary Medicine, 2013). It can therefore be affected by deficiency in any clotting factor. These deficiencies may arise from a lack of production (e.g. vitamin K deficiency or haemophiliacs); or consumption of the coagulation factors (e.g. sepsis or trauma).
What is activated partial thromboplastin time (aPTT)?
Activated partial thromboplastin time (aPTT)
This assesses the function of both the intrinsic and common pathways. Activated partial thromboplastin time (aPTT) is measured from blood collected into a citrated plasma tube. The tube MUST be accurately filled as the results will be inaccurate otherwise.
What is prothrombin time (PT)?
Prothrombin time (PT) This identifies deficiencies in the extrinsic (factor VII) and common pathways (fibrinogen, II, V and X). It measures the time for fibrin to be produced after activation of factor VII, then factors X, V and II (prothrombin). Tissue factor and calcium are added to a citrated plasma tube, containing a blood sample, to activate. The tube MUST be accurately filled as an inaccurate result will be obtained otherwise. Fibrin formation, from fibrinogen, is the end point of the assay - this can also be measured using optical or mechanical means.
What percentage of deficiency does aPTT require to produce prolongation of the PT?
As with aPTT, deficiencies of less than 30% are required to produce prolongation of the PT. Factor VII has the shortest half-life of the clotting factors, so PT maybe increased before aPTT in a patient with a coagulopathy.
What effects will rodenticide poisoning have on coagulation factors?
Acquired vitamin K deficiency (rodenticide poisoning) is an example of a condition that can prolong PT. Whilst eventually both PT and APTT will increase, PT will become elevated first-normally within 48-72hrs of ingestion of the rodenticide.
How is activated clotting time measured?
Activated clotting time.
Activated clotting time is measured by taking a blood sample, then discarding the first 0.25-0.5 ml of it. This removes the tissue factor which could otherwise complicate the test. 2ml of the blood sample is put into a tube containing diatomaceous earth (produced by Becton-Dickinson, Oxford). After mixing, the tube is incubated at 37°C for 60 seconds in the dog; and 45 seconds in the cat. After thisthe tube is gently tilted, at 10 second intervals, to determine if a clot has formed. Normal ACT for dogs is 60-110 seconds and for cats is 50-75 seconds.
An in-house test-kit is also available for measuring activated clotting time (ACT).
Sampling technique is important when considering coagulation profiles. Samples should be from a “clean stick”, with minimal dwell time in the vessel and they should be non-haemolysed. Other patient specific factors considerations need to be considered (e.g. a patient with a coagulopathy should not have jugular blood samples taken)
How do you carry out a slide agglutination test?
Slide Agglutination (also called saline dispersion test) A saline dispersion test should be performed to determine if there is true agglutination in a blood sample. N.B. Agglutination can arise with immune-mediated haemolytic anaemia when antibody covered RBCs stick together. In this test, a drop of blood from an EDTA blood tube or capillary tube is put onto a slide- it is assessed for the presence of agglutination (development of obvious flecks within the drop of blood). If agglutination appears to be present, three drops of saline are added to the blood on the slide. This will cause dispersal of RBCs if rouleaux (stacking of RBCS) rather than agglutination was present- the flecks will disappear with rouleaux. If true autoagglutination has occurred, the flecks will still be seen as the RBCs remain stuck together. Autoagglutination is caused by cross-linking of antibodies which are bound to the erythrocyte membranes - this is diagnostic for an immune-mediated component to the haemolysis. It is important to remember that the saline does not induce the agglutination – it merely confirms that it is true agglutination.
What is a coombs test?
Coombs Test
A Direct Antiglobulin Test looking for the auto-immune antibodies that are directed against the red cells (Coombs) can be used to confirm immune mediated haemolytic anaemia. Because the end (positive) result of this test is agglutination, the Coombs test need not be run if the patient is already auto-agglutinating. Blood should be taken for this assay prior to transfusion.
What is a POCUS?
Point of Care Ultrasound
What is the abbreviation FAST?
Focused assessment sonogram for trauma
What is a TFAST?
Thoracic Focused Assessment with Sonography for Trauma
What is an AFAST?
Abdominal Focused Assessment with Sonography for
Trauma
What is the abbreviation COP?
Colloid osmotic pressure
What does an emergency database test include?
• the minimum database
1.3.3.1 Minimum Database
A minimum database consists of the following:
• Packed cell volume (PCV)
• Refractometric total solids (TS) or total protein (TP) **
• Blood glucose (BG)
• Blood urea (BUN)
- blood smear
- electrolytes
- blood gases
- urine specific gravity.
What does a minimum database include?
1.3.3.1 Minimum Database
A minimum database consists of the following:
• Packed cell volume (PCV)
• Refractometric total solids (TS) or total protein (TP) **
• Blood glucose (BG)
• Blood urea (BUN)
• Blood smear
How much blood is required for a minimum database?
The volume of blood required for this database is small (~ 0.2ml depending on
equipment used) and can be collected from the hub of an intravenous catheter at the
time of placement (if the catheter was not flushed with heparinised saline prior to
placement)
Why is it best to get a small amount of blood from the hub of the catheter initially in an emergency situation?
Separate venepuncture to collect blood for a MDB should not be
necessary- merely adding to the patient morbidity. During catheter placement blood
can also be collected for additional laboratory tests such as electrolytes/ venous
blood gases (N.B. arterial blood gas analysis would require placement of an arterial
catheter)
What is the difference between total solids and total protein?
Total solids (TS) versus total protein (TP) - these terms are often used interchangeably but are not quite the same. Total solids (TS) refer to everything
dissolved in plasma (plasma proteins, urea, triglycerides, cholesterol and glucose),
while total protein literally refers to the main plasma proteins (primarily albumin and
globulins).
What does the term total solids refer to?
Total solids (TS) refer to everything dissolved in plasma (plasma proteins, urea, triglycerides, cholesterol and glucose),
What does the term total protein refer to?
total protein literally refers to the main plasma proteins (primarily albumin and
globulins).
Is a refractometer calibrated to give a total protein or total solids measurement?
The value for TP should therefore be slightly lower than TS. Most refractometers have been calibrated to give a TP measurement which is, in fact, the
TS minus a small factor.
What breed and age specifics may cause a variation in PCV?
There are some breed and age specifics where PCV will be higher or lower
(greyhounds/ sighthounds/paediatric patients)
What does a refractometric total solids estimate?
Refractometric TS allows estimation of serum proteins and a rough estimation
of colloid osmotic pressure (COP)
what does a PCV determine?
PCV is used to determine if a patient is anaemic or polycythaemic.
What is an increase in both PCV and TP consistent with?
An increase in both PCV and TS is consistent with dehydration- although this
may only be apparent with severe dehydration. A normal PCV/ TS could be
present in a slightly dehydrated patient
What may an increase in PCV and normal TP be consistent with?
An increase in PCV alone could be normal for the breed e.g. greyhound. It
could be due to polycythaemia, but it could also be stress-induced
(adrenaline/ epinephrine) splenic contraction
What might a decreased PCV and TP be consistent with?
Decreased PCV and TS will often arise following haemorrhage or after aggressive fluid therapy
Why might a PCV/TP be normal in an acute haemorrhage?
A decrease in both PCV and TS is not usually seen during/immediately following haemorrhage. During acute, active haemorrhage, whilst the total blood volume will be decreased, the PCV and TS may be normal because there has
not yet been any fluid shift from the interstitial space to intravascular space (blood vessels). Soon there will be fluid movement from the interstitial space
to the intravascular space causing dilution of the TS; the PCV is likely to be maintained near normal, initially, due to splenic contraction which releases
more erythrocytes to improve oxygen delivering capacity. Therefore, if an animal is presented in shock with a low TS yet normal PCV, haemorrhage is the likely condition needing to be ruled-out. If the haemorrhage continues, both the PCV and TS are likely to decrease.
What might a low TP and normal PCV be consistent with?
Low TS may also arise with a normal PCV if there has been protein loss/decreased production: (Hypoalbinaemia) primarily albumin (Mackin, 2010). This loss may be through the kidneys, GI tract or from the vasculature into a body cavity (thirdspacing) secondary to inflammation (e.g. peritonitis). Failure to produce can be associated with chronic liver disease or malnutrition.
What might a low TP and low PCV be consistent with?
Normal TS with a low PCV is consistent with enhanced erythrocyte destruction or a non-regenerative anaemia (Haemorrage, anaemia and hypoproteinamia)
What might a normal PCV and increased PCV be consistent with?
Hyperglobinaemia
artifactual
What might a low PCV and normal TP be consistent with?
(Chronic anaemia and haemolytic anaemia)
What may be the common cause of hypoglycaemia in an emergency patient?
Pediatric patients Septic patients insulin secreting tumour Hypoadrenocorticism exercise induce (working dogs)
What may be the common cause of hyperglycaemia in an emergency patient?
diabetes mellitus
stress reponse (cats)
In dogs, hyperglycaemia can be associated with head trauma and seizures- it
is a poor prognostic indicator
Patients with severe hypovolaemia or hypoxaemia may have hyperglycaemia
due to the sympatho-adrenal response. However, depending on the individual
patient it is possible they could be hypoglycaemic e.g., severe liver disease
preventing gluconeogenesis
What is azotaemia?
Azotaemia is when there are increased nitrogenous compounds in the
blood stream e.g. urea and creatinine
What is a BUN test used to screen?
Blood urea nitrogen (BUN) can be used as a screening test to identify azotaemic
animals
What should you do if you get a very high BUN reading on a dipstick?
A low BUN result on a dipstick is considered
accurate, but a high value should be supported with additional laboratory tests.
What secondary causes may cause an increase in BUN?
BUN
may be elevated secondary to a pre-renal, renal or post-renal cause e.g.,
dehydration, renal disease or urethral obstruction
What information does a blood smear provide?
A blood smear provides vital information on the number and morphology of cells within blood. A blood smear should always be performed (and interpreted) if a haemotology profile is performed.
What cells can be evaluated on a blood smear?
Erythrocytes, leukocytes and platelets should be evaluated - with attention
paid to both the number and the cell morphology.
Where can cellular morphology be viewed on a blood smear?
Cellular morphology should be viewed in the monolayer.
What might the presence of immature neutrophils indicate on a blood smear?
The presence of immature neutrophils (band cells) should be noted- this can
indicate a severe inflammatory or infectious condition
What changes in leukocytes may be seen on a blood smear if a patient has SIRS or sepsis?
In a patient with SIRS (septic or non-septic), leucocytosis may be present typically with a left shift (immature/ band neutrophils) and toxic changes to the neutrophils (eClinpath, 2013). Leucocytosis and mature neutrophilia can be part of a stress leukogram
Septic patients may also be leucopaenic because of sequestration of white
blood cells at the site of the infection (e.g. pyometra). Leucopaenia can also
be present with viral infections e.g. parvovirus
What toxic changes may be seen in neutrophils on a blood smear?
Toxic changes that can be seen include-
➢ blue granules/ foamy appearance of the cytoplasm
➢ swelling of the nucleus
➢ Dohle bodies (light blue-grey, oval, inclusions in the peripheral cytoplasm)
How do toxic neutrophils occur?
Toxic neutrophils occur when the condition intensely stimulates neutrophil
production, with decreased maturation time in the bone marrow.
What cases might you see a moderately decreased number of platelets?
The platelet count may be moderately decreased in bleeding or septic
patients, secondary to consumption; or severely decreased and the actual
cause of hypovolaemic (haemorrhagic) shock in a patient with blood loss.
What does reducing levels of platelets on a blood smear indicate in a critically ill patient?
Reducing levels of platelets in a critically ill patient can indicate that they are developing disseminated intra-vascular coagulation (DIC). Thrombocytopaenia is one of the earliest indicators of DIC.
How many platelets should be seen per high power field in the monolayer?
• In healthy patients, under oil immersion (x100) microscopic examination, there
should be 11-15 platelets per high power field (h.p.f.) in the monolayer. This
is equivalent to a platelet count of ~ 165 - 225 x109platelets/l. Each platelet
viewed, per h.p.f., equates to 15 x 109
/ l in the bloodstream.
What number of platelets per high power field would be a cause for concern and should be monitored for evidence of bleeding?
A patient with a platelet count of <5 per high power field should be closely
monitored for evidence of bleeding
What number of platelets per high power field would be a cause for concern and intervention would be indicated?
Less than 3 platelets per high power field (equivalent to equivalent to 0-
45x109
/L) is a dangerously low levels of platelets. Intervention would be
indicated.
How can you detect reticulocytes on a blood smear?
If the blood smear is stained with new methylene blue, then reticulocytes
are demonstrated- they have a fine trabecular structure within the cells
(made up of nuclear material and cellular organelles). In cats,
reticulocytes may appear with punctuate dots/ clusters and lines of
condensed organelles. These start out as the aggregate form (clusters
and lines) and mature to the punctuate dots. Therefore, large numbers of
the aggregate form of reticulocyte in cats demonstrates active
regeneration
When might nucleated red cells be seen on a blood smear?
Nucleated red cell may be seen with a strongly regenerative response
Nucleated RBCs may also be seen in cases of splenic disease,
myelodysplastic conditions and lead intoxication
What will be seen on a blood smear from a dog with immune-mediated haemolytic anaemia?
In dogs with immune-mediated haemolytic anaemia, there may be -
Spherocytes- produced when macrophages remove part of the red cell
wall.
Strongly regenerative response
Auto-agglutination
What are schistocytes?
Fragments of red cells (schistocytes)
What might schistocytes on a blood smear be secondary to?
Fragments of red cells (schistocytes) may be secondary to haemangiosarcoma or disseminated intravascular coagulation
What are heinz bodies a result of?
Heinz bodies are the result of oxidative damage
to haemoglobin in red cells- they appear as refractile, poorly staining bodies,
located beneath or protruding from the red cell membrane
What may the presence of heinz bodies on a blood smear suggest?
In cats, the presence of Heinz bodies may suggest intoxication e.g. paracetamol or onion. Heinz bodies may also develop in cats with prolonged
or repeated use of propofol.
In addition, parasites e.g. Mycoplasma haemofelis or Babesia sp. may be present. Mycoplasma haemofelis may be seen as chains, discs or rods on the surface
of erythrocytes. The PCV can decrease rapidly in cats with this condition.
What is the term for too much acid in the body?
Acidosis
What is Acidaemia?
Blood pH < 7.35
What is the term for too much alkali in the body?
Alkalosis
What is Alkalaemia?
Blood pH > 7.45
What can be used to relate the pH
of blood to the bicarbonate buffer system?
Henderson- Hasselbach Equation -
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
What are the main gases in the blood?
The main gases that are present in blood are oxygen (O2) and carbon dioxide (CO2).
What does the partial pressure of oxygen and carbon dioxide represent?
The partial pressure of oxygen and carbon dioxide (PO2 and PCO2) represent the
amount of the gas that is dissolved in blood.
What body systems does blood gas analysis give essential information on?
Blood gas analysis can give essential information on the respiratory and metabolic
status of a patient. It is important to note when considering respiratory status that
arterial blood gases will be more accurate
What part of a blood gas analysis evaluates the acid/base status?
Firstly, the acid/base status can be evaluated by assaying pH, PCO2 and
bicarbonate
What part of a blood gas analysis evaluates the lung function?
Secondly lung function can be assessed by measuring the amount of oxygen
(PaO2) and carbon dioxide (PaCO2) in arterial blood. (N.B. a = arterial; v =
venous)
What type of blood sample is needed for blood gas analysis?
Arterial blood gas analysis (ABG) is preferred when assessing respiratory
status but venous blood gas analysis (VBG) will still yield useful information
regarding metabolic status.
Why is it important to determine the metabolic status of a patient?
Determining the metabolic status of the patient will therefore provide vital clues to aid in the diagnosis of a condition, as well as help in the management/treatment of it.
➢ The presence of acidosis and alkalosis will also determine the type of fluid
and replacement therapies indicated
Why is it important to determine the resiratoy status of a patient?
Analysis of the respiratory component of the blood gas will help in the identification of a specific respiratory condition: as well as guiding therapy/intervention and prognosis. For example, deciding on when to provide
supplemental oxygen. The use of arterial blood gases can help guide oxygen therapy protocols. Whilst oxygen is widely considered to be a benign therapy
there is a risk of hyperoxia and associated complications. Monitoring of the PaO2 allows us to identify when we can reduce FiO2 for individual patients.
N.B. Some figures are measured (e.g. pH) and some are calculated (e.g. BE).
Animals with respiratory fatigue may need ventilation
How is the PH or acidity of the body maintained?
The pH or acidity of the body is maintained within a relatively, narrow range (7.35–
7.45) through expiration of CO2 from the lungs; and the excretion of hydrogen ions
through the kidneys. There are also a series of other buffers such as bicarbonate
which act to keep the pH within narrow limits
What effects can alteration in PH have?
Alterations to pH mean that cells and
metabolic processes are unable to function leading to organ dysfunction, failure and
ultimately death.
What compensatory changes can a variation in PH have?
Any variation in the pH outside of this range will result in compensatory changes such as an increase/decrease in respiratory rate that will
attempt to correct the pH:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
However, these compensatory changes, whilst maintaining pH, can result in
increased energy and oxygen consumption for the patient.
What component is important for the bodys buffering system?
Bicarbonate is very important
for the body’s ‘buffering’ system.
What is respiratory acidosis?
Plasma CO2 levels increase in animals that are hypoventilating- this is RESPIRATORY ACIDOSIS
↑CO2 + H2O → ↑H2CO3 → ↑H+ + ↑HCO3-
Why would a patient with metabolic acidosis be tachypnoeic?
If a patient has METABOLIC ACIDOSIS e.g. diabetic ketoacidosis or lactic acidosis secondary to anaerobic metabolism, caused by hypovolaemia, it will often be
tachypnoeic (rapid, shallow breathing). The tachypnoea is a compensatory response from the respiratory system to try and rid the body of acid (CO2) to maintain pH. This response results in more CO2 being expired and so more H+ ions binding with
HCO3- to maintain equilibrium. With less H+ in circulation, this compensatory
mechanism should assist the blood pH return to neutral.
↓CO2 + H2O → ↓H2CO3 → ↓H+ + ↓HCO3-
How can a patient develop metabolic alkalosis?
If a patient loses excess acid (hydrogen ions H+) through gastric vomiting or has excess bicarbonate, it will develop a METABOLIC ALKALOSIS - which results in the blood becoming more alkaline.
How can a patient develop respiratory alkalosis?
If a patient hyperventilates and expires too much carbon dioxide, it will develop a RESPIRATORY ALKALOSIS. This can also occur in anaesthetised patients undergoing IPPV or those receiving mechanical ventilation.
What organs are involved in maintaining the correct PH?
The kidneys assist in maintaining the correct pH but their response is not as immediate as that obtained by altered ventilation (Lungs)
Why is important to optimise renal function when a patient is acidaemic?
The kidneys assist in maintaining the correct pH but their response is not as
immediate as that obtained by altered ventilation. The kidney function is also
commonly reduced in emergency patients, especially those that are hypotensive or
hypovolaemic on presentation. As such supportive measures may need to be
considered to optimise renal function.
What are assessed when analysing blood gases?
When performing ABG the following are assessed: • pH • PCO2 • Bicarbonate (HCO3 - and ‘base-excess’)
What does a PaCO2 and PvCO2 assess?
If this an arterial blood sample (preferred) PaCO2, is
assessed; if this is a venous blood sample PvCO2, is assessed. carbon dioxide in blood
What is a respiratory acidosis?
Increased CO2 (PCO2) levels in the blood stream decrease the pH
of blood e.g. it becomes more acidic- acidaemia. As discussed
previously, the cause is ineffective ventilation (hypoventilation). The
animal therefore has a respiratory acidosis.
How does respiratory alkalosis occur?
Decreased CO2 (PCO2) levels in the blood stream increase the pH of blood - alkalaemia e.g. it becomes more alkaline- the cause is hyperventilation. The animal therefore has a respiratory alkalosis.
Is bicarbonate in the body high or low in metabolic alkalosis?
metabolic alkalosis, bicarbonate will be increased.
Is bicarbonate high or low in metabolic acidosis?
In metabolic acidosis, bicarbonate will be decreased (less to mop up H+/
hydrogen ions);
What are the causes for altered bicarbonate levels?
Reasons for altered bicarbonate levels are -
o Metabolic causes e.g. lost in diarrhoea, anorexia
o Respiratory causes e.g. hypoventilation
What type of acid-base abnormality does the concept of the base excess identify?
Because bicarbonate levels can be affected by respiration, the concept of
the base excess (BE) was developed to identify metabolic rather than
respiratory causes of acid-base disorders (
What is the base excess?
The base excess (BE) is a calculated figure which estimates the metabolic (rather than respiratory) component of the acid-base balance
Whilst we commonly evaluate pH, PCO2 and HCO3 to
measure acidosis or alkalosis in the blood we can also evaluate BE to differentiate between the metabolic and respiratory components.
It measures the amount of excessive base (alkali) or acid in blood and so gives information on the metabolic aspect of the acid-base balance.
What does the base excess measure?
It measures the amount of excessive base (alkali) or acid in blood and so gives information on the metabolic aspect of the acid-base balance.
It calculates the amount of strong acid (or alkali - base deficit (BD)) that would theoretically have to be added to blood to neutralise it. The normal
range is - 2→ +2
e.g. if a patient’s blood were alkaline for metabolic reasons, it would have too much base (e.g. increased HCO3). To neutralise the blood, strong acid
would in theory be needed. The more alkaline the blood is the more acid would be required. The amount that is required is the base excess and it
is an indication of how alkaline the blood is e.g. + 4 is less alkaline than +8.
What is a base deficit? What would need to be done to correct this?
If the number is more negative than it should be (e.g. -9) the patient has a base deficit. There is an excess of acid/ or lack of ‘base’/alkali in the bloodstream. This means more alkali/base would have to be added to neutralise blood. This shows that the patient’s blood too acidic= metabolic acidosis (more common)
What is a base excess? What can be done to correct this?
If the number is more positive than it should be (e.g. +12) the patient has a base excess- there is an excess of ‘base’ (alkali)/ or lack of acid in the blood stream meaning more acid would have to be added to neutralise blood. This shows that the patient’s blood is
too alkaline = metabolic alkalosis (less common)
How do the kidneys and lungs assist with the body buffering system and what is the onset of action?
As the body buffering system diagram demonstrates, blood CO2 levels (pCO2) can be altered quickly by altering ventilation (almost instantly). The kidneys are also involved in buffering, but this is a slower mechanism (2-3 days).
What is the anion gap calculation used to determine?
The anion gap calculation is used to determine whether metabolic acidosis is due to:
o An increase in the level of acid in the system e.g. diabetic ketoacidosis, uraemic acids, toxins or lactate;
o A loss of alkali (bicarbonate) e.g., from the kidneys.
What are anions?
Anions are negatively charged particles e.g. Cl- + HCO3 - present in extracellular fluid
(ECF) (remember plasma is also part of the ECF);
What are cations?
cations are positively charged particles present in ECF e.g. Na+ + K+
What is the formula to calculate the anion gap?
Anion gap = (Na+ + K+) – (Cl- + HCO3-
What is the normal anion gap for dogs?
The normal value for the anion gap for dogs is 8-25, i.e. normally
dogs have 8-25 more positive ions than negative ions.
What is the normal anion gap for cats?
The normal value for the anion gap for cats 10-27 i.e. normally cats have 10-27 more positive ions than negative ions.
What does an increase in anion gap in cases of acidosis tell you?
An increase in the anion gap (e.g. 40) in cases of acidosis, tells us that there are more anions (e.g. lactate, ketones. present than normal e.g. diabetic ketoacidosis.
What does a normal anion gap in cases of acidosis tell you?
However, a normal anion gap in a case of acidosis (identified from the BE calculation) tells us that the acidosis is due to a loss of bicarbonate (alkali) rather
than increased acid e.g. diarrhoea
What is a blood lactate an indicator of?
Blood lactate is considered a global indicator of tissue perfusion.
What does blood lactate help to assess?
It can be used to assess tissue oxygenation; response to therapy and as a prognostic indicator.
When is lactic acid generated? What is this secondary to?
Lactic acid is generated during anaerobic metabolism. This is most commonly secondary to decreased tissue perfusion, severe hypoxaemia; or a combination of these.
What is the most common cause of metabolic acidosis in veterinary medicine?
Lactic acidosis is the most common
cause of metabolic acidosis in veterinary medicine.
What is the normal serum lactate concentrations in dogs and what would be considered clinically significant?
Normal serum lactate concentrations in dogs should be < 2.5 mmol/L (range 0.3 – 2.5 mmol/L). Concentrations greater than 2.5 mmol/L are considered clinically significant.
What would be considered an intermediate blood lactate and what level would be considered a high?
Lactate levels of 2.5 – 4 mmol/L are intermediate; lactate levels > 4 mmol/L are considered high.
How can blood lactate help to determine prognosis?
Correlations have been made between lactate levels and likely patient mortality/prognosis (Young, 2012). Generally, the higher the lactate level, the poorer the prognosis. It is, however, more important to
monitor trends in lactate levels - a significant decline in lactate would improve the prognosis whereas increasing lactate levels, in a patient, receiving
treatment would give more cause for concern.
What can increase serum lactate concentration even in animals with adequate perfusion?
Prolonged vessel occlusion, excessive restraint, patient struggling, excessive panting, twitching and tremoring and delays in sample analysis will increase the serum lactate concentration, even in animals with adequate perfusion.
What is the most useful monitoring tool for gauging response to resuscitation in patient with shock?
Lactate is most useful as a monitoring tool for gauging response to resuscitation in patients with shock.
How can lactate levels aid the decision in transfusing an anaemic patient?
Severe anaemia will result in a decreased oxygen delivery to tissues with the generation of lactic acid secondary to anaerobic metabolism. The presence of hyperlactataemia may therefore be utilised to aid in the decision to
transfuse anaemic patients.
What will lactate and glucose levels be on abdominal effusion analysis in a septic patient?
Lactate can also be used to analyse effusions from the abdominal cavity. In septic patients lactate levels will be increased in the effusion and glucose will
be decreased due to anaerobic cellular metabolism taking place.
What is the main role of sodium in the body?
Sodium is the main extracellular cation (Na+) in the body. In addition to being involved in blood pressure control, muscle and nerve function, it is important in maintaining intracellular fluid (ICF) and extracellular fluid (ECF) water distribution and balance
What is the concentration of sodium reflect?
The concentration of sodium reflects water balance; abnormalities in sodium are generally a result of gain or loss of water or sodium
Why does sodium change osmotic gradients?
Sodium can change osmotic gradients within the body leading to shifts of water into or out of cells e.g.
cerebral oedema.
What diseases can hyponatraemia occur in?
Hyponatraemia can occur in disease conditions such as intestinal obstruction (sodium is lost with the vomit), hypoadrenocorticism (sodium is lost from the kidneys) or a gain in free water (e.g. inappropriate use of hypotonic fluids).
How can a animal with an intestinal obstruction become hyponatraemic?
(sodium is lost with the vomit
Why can a patient with hypoadrenocorticism become hyponatraemic?
sodium is lost in the kidneys
What cases is hypernatraemia usually seen?
Hypernatraemia can be seen in salt toxicity (gain in salt); a lack of free water (e.g. cat that has been accidentally locked in a shed for multiple days with no access to water) or because of iatrogenic administration of high sodium substances.
Hypernatraemia can also be seen in disease processes e.g. hyperaldosteronism
How does hypernatraemia affect cells?
causes cell dehydration
How does hyponatraemia affect cells?
hyponatraemia results in cell oedema
What signs can animals with hyper and hyponatraemia develop?
Both conditions can affect neuron function potentially causing serious neurological signs. Whilst sodium is only one of the many electrolytes monitored, it is arguably one of the more important -plasma sodium concentration is the major determinant of
plasma osmolality. Extremely high or low sodium levels must be carefully corrected to avoid neurological signs developing and avoid patient mortality.
What is the main role of chloride in the body?
Chloride (Cl -) is an extracellular anion which, along with sodium, is involved in water balance. Along with bicarbonate, it also has an important
role in acid-base balance
