Week 8 - Mrs Mitchell Flashcards
Define the general terms tachycardia.
You do not need to include parameters
Tachycardia - increased heart rate
Rapid heartbeat
Faster than normal
Define the general terms tachypnea.
You do not need to include parameters
Tachypnea - increased breathing rate
For a 70Kg man what is the amount of total body water and how is this calculated?
Body weight x 60%
70Kg x 60% = 42L
The concentration of what solute in the blood is important for the increased osmolarity when fluid volume decreases that stimulates the hypothalamus
Sodium
If Mrs Michel had been vomitting rather than having diarrhoea what acid base disturbance would she be most likely to have presented with and why?
Metabolic alkalosis (1 mark)
Vomiting leads to the loss of gastric secretions which are rich is hydrochloric acid. (1 mark)
Whenever a hydrogen ion is excreted a bicarbonate ion is gained. (1 mark) in the extracellular space leading to more bicarbonate in the body and therefore alkalosis. (1 mark)
Briefly explain how metabolic acidosis is compensated for both by the lungs and the kidneys? (2 marks)
Lungs: Lowering the PCO2 by hyperventilation
Kidney: Adds more H+ (or NH+) to the urine
What are some common symptoms of metabolic acidosis?
Headache
Decreased BP
Hyperkalemia (normally with quick onset)
Muscle twitching
Warm, flushed skin
Nausea, Vomiting, Diarrhoea
Changes in LOC (Confusion, drowsiness)
Kussmaul Respirations (compensatory hyperventilation)
What are some causes of Metabolic Acidosis?
Severe Diarrhoea
Renal Failure
Shock
What is metabolic acidosis?
Decrease ability of the kidney to excrete acid or conserve base
What pH should our body stay within?
7.35 and 7.45
Why is it important for the pH of the body to be within 7.35 and 7.45?
So enzymes do not denature
Mrs Mitchel is 72 years old and lives in a sheltered accommodation flat. She is admitted to hospital with a one week history of severe diarrhoea. She is weak, lethargic and clinically dehydrated. At the hospital a physician associate takes her blood pressure which is 100/60 mm Hg when lying down and this drops to 70/40 mm Hg when she is sitting up. Her radial pulse is weak, but there was tachycardia and tachypnea. There was reduced urine output.
List Mrs Mitchell’s presenting symptoms when admitted
72 years old
- 1 week of severe diarrhoea
- weak, lethargic, clinically dehydrated
Mrs Mitchel is 72 years old and lives in a sheltered accommodation flat. She is admitted to hospital with a one week history of severe diarrhoea. She is weak, lethargic and clinically dehydrated. At the hospital a physician associate takes her blood pressure which is 100/60 mm Hg when lying down and this drops to 70/40 mm Hg when she is sitting up. Her radial pulse is weak, but there was tachycardia and tachypnea. There was reduced urine output.
What did the physician’s associate find in the hospital?
BP
110/60mmHg (lying down)
70/40mmHg (sitting)
Tachycardia
Tachypnoea
Reduced urine output
What is the definition of tachycardia?
Increased heart rate >100bpm
What is the definition of tachypnoea?
Increased respiratory rate >20 per min
What is Ringer’s Lactate?
Solution for fluid and electrolyte replacement
Isotonic with blood
Lactate has alkaline effect which can help counteract the acidosis (metabolised into HC03-) in blood serum or in urine
What is Creatinine?
Waste molecule generated from metabolism of creatine in muscle
Filtered by kidneys and disposed in urine
What is the anion gap?
It checks the levels of acid in your blood
Measurement of the difference - or gap - between the negatively charged and positively charged electrolytes
If the anion gap is too high or too low, may be a sign of a disorder in your lungs, kidneys, other organ systems
Summarise the 4 different types of acid-base disturbance
Respiratory acidosis - retain CO2, usually because of hypoventilation (not breathing out enough)
Respiratory alkalosis - blow off too much CO2 hyperventilation (fast breathing)
Metabolic acidosis - retain H+ and excrete HCO3- (e.g. diarrhoea)
Metabolic alkalosis - retain HCO3- and excrete H+ (e.g. vomitting)
What acid base disturbance are you likely to have if you have been vomiting?
Metabolic alkalosis
Lose H+ ions in vomitting from the stomach (think about it stomach acid lost, lose H+ ions)
What acid base disturbance are you likely to have if you have been diarrhoea?
Metabolic acidosis
What acid base disturbance are you likely to have if you have been hyperventilating?
Respiratory alkalosis
Lose too much CO2, CO2 is acidic, so the blood becomes alkaline
What acid base disturbance are you likely to have if you have been hypoventilating?
Respiratory acidosis
Retain CO2 and so blood gets acidic
What do Mrs Mitchell’s blood work show when she first arrives?
pH - 7.11
pC02 - 16 (35-45mmHg)
HCO3- 5 (22-26mEq/L)
Hyperchloremic (High chloride levels - 118 (98-106)
pH is low 7.11
pCO2 is low - 16 (35-45)
compensatory hyperventilation
HCO3- is very low - 5 (22-26)
Hypokalaemia was very low but then was corrected 2.5 to 4.2 (3.5-5.5)
If you see a pH of 7.11 and a pCO2 of 16 (35-45mmHg) what does the patient have?
Acidosis
If pCO2 was high it would be respiratory acidosis
But because it is low you can see that the respiratory system was trying to counteract the low pH through hyperventilation so it is
Metabolic Acidosis
What does Mrs Mitchell’s blood work show after the Ringer’s solution?
pH - 7.49
pC02 - 20 (35-45mmHg)
HCO3- 15 (22-26mEq/L)
pH is 7.49
Alkalosis
pCO2 would be high in acidosis and low in alkalosis, which is in line with the high pH
So Respiratory alkalosis
Her body didn’t compensate yet for the Ringer’s solution
What are the 3 compensatory mechanisms that help handle changes in pH?
- Physiologic buffers - a reversible equation where a weak acid is broken down into a base salt or weak base
Examples:
- Bicarbonate-carbonic acid buffer system
- Intracellular protein buffers
- Phosphate buffers in the bone
- Pulmonary compensation - changes in pCO2 driving pH
- Renal compensation - kidneys excrete or retain HCO3-
What are 3 examples of physiological buffers?
Bicarbonate-carbonic acid buffer system
Intracellular protein buffers
Phosphate buffers in the bone
How does pulmonary compensation work?
So when pH is low, increase ventilation gets rid of acidic CO2 and works to increase pH
When pH is high, there is a decrease in ventilatory effort, which increases pCO2 (retains acidic CO2) and lowers pH back towards normal
How does renal compensation work?
Starts 6 hours after sustained acidosis or alkalosis
In acidosis, kidneys excrete H+ and retains HCO3-
In alkalosis, kidneys excrete HCO3- and retain H+ in the form of organic acids
How long does it take for renal compensation to kick in?
6 hours after sustained acidosis or alkalosis
What are the final reserves for acidosis/alkalosis?
Bone
Bone can act as a buffer because it has a large reservoir of bicarbonate and phosphate and can buffer a significant acute acid load
If patients have low albumin levels, bone density due to malnutrition or chronic disease and anaemic patients, buffering ability is compromised
Why does respiratory acidosis occur? Physiological mechanism
The only mechanism is alveolar hypoventilation
(pCO2 is above 45mmHg)
pH is less than 7.35
Alveolar hypoventilation can occur due to paralysis, brain stem disturbances, patient is sedated, elderly unwell and can’t move, respiratory paralysis (Guillain Barre)
Pulmonary emphysema, pulmonary oedema, COPD, bronchitis
Why does respiratory alkalosis occur? Physiological mechanism
pH is high
pCO2 is low (breathed out)
Most common cause is due to increased alveolar ventilation (hyperventilation (anxious), hepatic disease, pregnancy, septicaemia, over ventilated in iCU)
Paper bag in hyperventilation helps to regulate CO2
Why does metabolic acidosis occur? Physiological mechanism
Increase in amount of body acid (excess production of acids or excessive loss of bicarbonate, sodium and potassium)
Lactic acidosis
Diabetic ketoacidosis
Loss of bicarbonate through severe diarrhoea
Bicarbonate wasting through kidneys or GI tract
What are some signs and symptoms of metabolic acidosis?
Headache
Lethargy
Anorexia
Deep, rapid respirations (Kussmaul)
Nausea
Diarrhoea
Abdominal discomfort (severe acidosis)
Coma and dangerous dysrhythmias
What ions are involved in the anion gap?
(Na + K) - (Cl + HCO3)
As sodium is the most dominant cation can do
Na - (Cl + HCO3)
What does a normal anion gap indicate in metabolic acidosis?
You have a very high level of Cl- to make up for the low HCO3- in the equation
Na - (Cl + HCO3)
Why does metabolic alkalosis occur? Physiological mechanism
HCO3- is increased, usually due to an excessive loss of metabolic acids
Diuretics Prolonged vomitting Hyperaldosteronism Cushing's syndrome Exogenous steroids
What are some signs and symptoms for metabolic alkalosis?
Cardiac dysrhythmias as a result of low K
Physical weakness
Muscle cramping
Hyperactive reflexes
Tetany
Convulsions
Confusion
Reasons for an elevated anion gap
Don’t really need to know
Particular medications can cause it to be elevated
Methanol, metformin Ethylene glycol Toluene Alcoholic ketoacidosis Lactic acidosis
Aminoglycosides, other uremic agents
Cyanide, carbon monoxide
Isoniazid, iron
Diabetic ketoacidosis
Generalised seizure-producing toxins
ASA or other salicylate
Paraldehyde, phenformin
Mrs Mitchell’s potassium levels were:
2.5 then 4.2 next day (3.5-5.5 mEq/L)
Though this is not the case for Mrs Mitchell..
How does Acidosis lead to Hyperkalemia?
Hyperkalemia is when potassium levels are higher than normal
H+ ions are taken into the cell from the extracellular fluid, and this is done by exchanging K+ ions to maintain electroneutrality
I.V potassium would still be given to these patients early in treatment despite the often elevated serum potassium levels because the cells themselves don’t have much K+ in them
Mrs Mitchell’s sodium levels were:
137 on admission
137 the next day
(Normal - 135-147 mEq/L)
Explain this?
Normal sodium levels despite everything else changing
The kidneys try to keep sodium by exchanging it for excreted H+ or potassium
Sodium levels are kept quite constant
What is saline responsive?
When you have metabolic alkalosis and you are deciding what treatment to give a patient based on their chloride ion levels in their urine
Saline responsive = less 15mmol/L
Nonsaline responsive = above 25mmol/L
Metabolic acidosis and serum anion gap decreased due to?
Low albumin
Metabolic acidosis and serum anion gap increased diagnosis
Lactic acidosis
or Ketoacidosis
Metabolic acidosis and normal anion gap = ?
Hyperchloraemic metabolic acidosis
Her Chloride levels are in line with this:
118 on admission
114 next day
Normal = 98-106 mEq/L
What are the three major causes of Hyperchloraemic metabolic acidosis and which one applies to Mrs Mitchell?
Renal tubular acidosis
Gastrointestinal losses
Chronic hypoventilation
GI losses applies to Mrs Mitchell
In metabolic acidosis what are the following levels going to be like?
pH
H+
Primary disturbance (HCO3 or pCO2?)
Secondary response (HCO3 or pCO2?)
pH - Low
H+ - High
Primary disturbance - Low HCO3-
Secondary response - Low pCO2
In metabolic alkalosis what are the following levels going to be like?
pH
H+
Primary disturbance (HCO3 or pCO2?)
Secondary response (HCO3 or pCO2?)
pH - High
H+ - Low
Primary disturbance - High HCO3-
Secondary response - High pCO2
In respiratory acidosis what are the following levels going to be like?
pH
H+
Primary disturbance (HCO3 or pCO2?)
Secondary response (HCO3 or pCO2?)
pH - Low
H+ - High
Primary disturbance - High pCO2
Secondary response - High HCO3
In respiratory alkalosis what are the following levels going to be like?
pH
H+
Primary disturbance (HCO3 or pCO2?)
Secondary response (HCO3 or pCO2?)
pH - High
H+ - Low
Primary disturbance - Low pCO2
Secondary response - Low HCO3
Explain generally renal compensation in acidosis/alkalosis
So you secrete or reabsorb H+ or HCO3- in the collecting duct in the kidneys
So you urinate one of the ions out to compensate for what is going on in the body
Longer term solution
What do the Type A intercalated cells in the kidney’s collecting duct do? In what conditions?
In acidosis
The Type A intercalated cells
Excretes: H+
Reabsorbs: HCO3- and K+
What do the Type B intercalated cells in the kidney’s collecting duct do? In what conditions?
In alkalosis
The Type B intercalated cells
Excretes: HCO3- and K+
Reabsorbs: H+
How many ml is Ringers fluid?
1L
What treatment is Mrs Mitchell given?
IV Lactated Ringer’s fluid
Potassium supplementation
What is going on in the next day after Mrs Mitchell is admitted?
Sodium 137 (135-147mEq/L)
Next day: 137
Potassium 2.5 (3.5-5.5 mEq/L)
Next day: 4.2
Chloride 118 (98-106mEq/L)
Next day: 114
Bicarbonate 5 (22-26mEq/L)
Next day: 15
Creatinine 3.1 (0.6-1.1mg/dL women)
Next day: 2.0
Anion gap 10 (Less than 11mEq/L)
Next day: 8
pH 7.11 (7.35-7.45)
Next day: 7.49
pCO2 16 (35-45mmHg)
Next day: 20
So she came in with metabolic acidosis
(Primary problem is HCO3- lost through diarrhoea)
So you can see the Bicarbonate is increasing :D
pCO2 is still much lower than predicted which means she is still hyperventilating
This results in respiratory alkalaemia
This is because the central chemoreceptors in the brain are slow to respond to the reversal in bicarbonate and so you still see compensatory hyperventilation
Bicarbonate will slowly enter the brain over 12-24 hours and central chemoreceptor inhibition will be progressively inhibited
pCO2 back to normal and normal breathing lags behind the increase in bicarbonate
What is the key equation of buffering in the blood?
HCO3- + H+ > H2CO3 > CO2 + H20
What 3 organs regulate fluid balance?
Brain
Adrenal glands
Kidneys
What is the process that happens in the body when the fluid volume decreases?
Concentration of sodium increases in the blood (increased osmolarity)
Hypothalamus has osmoreceptors
Stimulates posterior pituitary to release ADH
ADH goes to the kidneys and they retain water (more concentrated urine, water returned to ECF)
Adrenal glands secrete aldosterone in response to low BP (retain fluid)
How much of the Total Body Water is the Extracellular Fluid Volume?
1/3
How much of the Total Body Water is the Intracellular Fluid Volume?
2/3
What are the primary components of the extracellular fluid?
Interstitial Fluid (3/4) Plasma (1/4) Transcellular Fluid (rest around 0.5L)
What is the recommended daily intake of fluid?
2.5 L
What makes up our intake of fluid?
Drink 1.6L
Food 0.7L
Metabolic water 0.2L
What makes up our outtake of fluid?
Feces (0.2L) Expired air (0.3L) Cutaneous transpirational (0.4L) Sweat (0.1L) Urine (1.5L)
What is the daily output of fluid in L?
2.5L
What are the two types of fluid that patients can get for rehydration?
Crystalloid fluids - water with electrolytes added to it (what Mrs Mitchell was given)
Colloid fluids - bigger molecules so they stay in blood vessels and water is drawn into the blood vessels (e.g. through trauma and scarring)
Different reasons for dehydration?
(Sodium or water loss)
Vomitting and diarrhoea
Inadequate fluid intake
Low-sodium diet or no sodium intake
Diabetes insipidus (rare)
Symptoms for dehydration
Skin turgor Hypovolemia Tachycardia Weak pulse Postural hypotension Confusion
Also: thirst, dry skin, sticky or dry mucous membranes, weight loss, concentrated urine
What is a minimum urine output required for kidney function?
30ml per hour
What is the definition of dehydration?
Lost 1% of body mass
When does performance become impaired with water loss?
Loss 2% in body weight
What are different effects of water loss on performance?
Loss 1% body weight - dehydration
Loss 2% body weight - impaired performance
Loss 4% body weight - capacity for muscular work reduced
Loss 6% body weight - heat exhaustion
Loss 8% body weight - hallucination
Loss 10% body weight - circulatory collapse and heat stroke
ROME?
Respiratory Opposite
Metabolic Equal
In terms of the acidosis and alkalosis
What does high creatinine indicate?
Mrs Mitchel
On admission = 3.1
Next day = 2.0
Normal = 0.6-1.1mg/dL (women)
Decreased Renal Function
Properties of crystalloid fluids?
Saline plus electrolytes
Remain longer in ECF
Isotonic
