PBL 8

Question 1

Tachycardia

Answer 1

increased heart rate greater than 100bpm, this is greater than what is normal

Question 2

Tachypnoea

Answer 2

increase respiratory rate increased from what is normal

Question 3

Ringer’s Lactate

Answer 3

– solution for fluid and electrolyte replacement. Isotonic with blood. Lactate has alkaline effect which can help counteract the acidosis (it is metabolised into HCO3-).

Question 4

Anion gap

Answer 4

difference between primary measured
cations (Na+ and K+) and primary measured anions
(Cl- and HCO3-) in blood serum or in urine.

Question 5

Creatine

Answer 5

waste molecule generated from
metabolism of creatine in muscle. Filtered by
kidneys and disposed in urine.

Question 6

What kind of acidosis did she have

Answer 6

hyperchloraemic metabolic acidosis

Question 7

describe her results and what they mean 
pH 
HCO3
pCO2
Anion gap

Answer 7

pH - acidosis
HCO3- = 5 (very low)
-> metabolic acidosis – fits with history of diarrhoea and high creatinine in bloods
pCO2 = 16 (low)
-> respiratory compensation (hyperventilation to blow off excess CO2)

Anion gap = 10 (normal) with high chloride -> hyperchloraemic metabolic acidosis

Question 8

Causes of high versus normal anion gap

Answer 8

Normal anion gap (hyperchloraemic metabolic acidosis):
Severe diarrhoea (loss of HCO3-)
Reduced kidney H+ excretion
(HCO3- decreased, Cl- increased to compensate)

High anion gap:
Lots of causes but main ones:
Ketoacidosis
Lactic acidosis
(HCO3- decreased, unmeasured anions increase so high anion gap).

Question 9

How do you compensate for acid base distrubances

Answer 9

Physiological buffers (super fast)

• Bicarbonate-carbonic acid buffering system
• Protein buffers (intracellular and extracellular)
• Phosphate buffers in the bone

Pulmonary compensation (slower) – ventilation

Renal compensation (really slow, starts 6h after sustained acidosis/alkalosis)

Question 10

Describe haemoglobin buffer system/bicarbonate

Answer 10

In tissues: 
CO2 + H2O  H2CO3  H+ + HCO3-
H+ + Hb  HHb
In lungs: HHb releases H+ (and takes up O2)
Then ....H+ + HCO3-  H2CO3  H2O + CO2

Question 11

describe and explain her blood results

• Low potassium
• High Cl-
• high creatinine

Answer 11

• K+ low – in acidosis, high H+ in blood (acidaemia). H+ moves into cells (buffers) so K+ moves out of cells to maintain electroneutrality. But in this case, K+ lost due to diarrhoea.
• High Cl- - compensatory increase in Cl- due to loss of HCO3-.
• High creatinine – decreased renal function

Question 12

Explain the blood pressure

Answer 12

Also note BP changes indicating postural hypotension due to dehydration. Postural hypotension = abnormal fall in BP at least 20mmHg systolic and/or fall of 10mmHg diastolic within 3 min of standing upright

Question 13

How do you replace fluid

Answer 13

Usually use crystalloids – saline, Lactated Ringers etc
Remain longer in ECF
Isotonic

Question 14

describe the fluid balance homeostasis

Answer 14

Fluid volume decreases
-> increased Na+ concentration in blood
-> increased osmolarity
-> detected by hypothalamus (an osmoreceptor)
-> stimulates posterior pituitary to secrete ADH (anti-diuretic hormone)
-> feel thirsty so drink
kidneys retain water -> reduced volume of concentrated urine
water conserved in ECF

Question 15

what are the symptoms of metabolic acidosis

Answer 15

• headache
• decreased blood pressure e
• muscle twitching
• warm flushed skin
• nausea, vomitting, diarrhoea

Question 16

what are the causes of metabolic acidosis

Answer 16

DKA
severe diarrhoea - causes loss of bicarbonate 
renal failure 
shock 
- diabetic ketoacidosis

Question 17

what was her metabolic acidosis complicated by

Answer 17

dehydration

Question 18

describe respiratory compensation

Answer 18

• A drop in pH, results in increased ventilation to blow off excess CO2.
• An increase in pH decreases ventilatory effort, which increases PCO2 and lowers pH back towards normal.

Question 19

describe renal compensation

Answer 19

In acidosis, kidneys excrete H+ in urine and retain HCO3-.

• In alkalosis, kidneys excrete HCO3- and retain H+ in the form of organic acids.

Question 20

what also acts as a buffer

Answer 20

• Lastly, bone may also serve as a buffer because it contains a large reservoir of bicarbonate and phosphate and can buffer a significant acute acid load. Patients who have low albumin levels and bone density due to malnutrition or chronic disease, and anaemic patients, have an ineffective buffering capability.

Question 21

describe potassium in metabolic acidosis

Answer 21

• In presence of an H+ load, H+ ions move from the extracellular fluid into the intracellular fluid. For this to occur, potassium moves outside the cell into the extracellular fluid to maintain electroneutrality

• So I.V. potassium is given to patients early in treatment, despite the often-elevated serum potassium level

Question 22

what is the compensation in the kidney that is used to treat metabolic acidosis

Answer 22

Acute
• Blood buffers
• Nonvolatile buffers absorb excess H+
• Compensation
• Respiratory
•
• rate increased, eliminates CO2 Renal
• Secrete H+ and reabsorb and generate HCO3-

Question 23

what is respiratory alkalaemia caused the next day

Answer 23

• In this case the central chemoreceptors
are slow at responding to the reversal in bicarbonate and so the compensatory hyperventilation is still functional
• Bicarbonate will slowly enter the brain interstitial fluid over about a 12 to 24 hour period and the central chemoreceptor inhibition will be progressively eliminated.
• The recovery of pCO2 to normal lags behind the rise in the bicarbonate.

Question 24

how do you do simple dehydration check

Answer 24

• dehydration urine colour chart

Question 25

describe the effect of water loss on performance

Answer 25

• 1% loss of body mass = dehydration
• 2% = impaired performance
• 4% capacity for muscular work reduced
• 6% heat exhaustion
• 8% hallucination
• 10% circulatory collapse and heat stroke