physiology 2 Flashcards
- how to calculate anion gap
- what is the normal anion gap
- anion gap= NA-Cl-HCO3 e.g 135-110-18 = 7
- normal anion gap = <12
what are causes of high anion gap in metabolic acidosis?
high anion gap (>12) = MUDPILES
These are things not measured in anion gap calc
e.g lactate, ketones
Methanol
Uraemia
DKA
Paracetamol/ propylene glycol
Isoniazid (Tx TB)
Lactic acid
Ethylene glycol
Salicylates
what are causes of low anion gap in metabolic acidosis?
normal anion gap in metabolic acidosis:
Hyperalimentation (excessive nutrition e.g caused by TPN)
Acetazolamide (hyperchloraemic met acidosis- compensatory)
Renal tubular acidosis
Diarrhoea (loose all- Na, CL, K, HCO3)
Uterosigmoid fistula
Pancreatic fistula
what is respiratory quotient
RQ= CO2 given out/02 taken in
RQ 1= carbs
RQ 0.9= protein
RQ 0.7=fats
Glucose has a simple 1:1 ratio and RQ value of 1
C6H12O6 +O2=> 6CO2 + 6H20
RQ > 1: Indicates excessive carbohydrate metabolism or overproduction of CO₂, which might be seen in conditions like hyperventilation or sepsis.
RQ < 0.7: May indicate fat utilization predominates, which can be seen in starvation or diabetic ketoacidosis.
whats the alveolar gas equation
The alveolar gas equation is used to estimate the partial pressure of oxygen in the Alveoli (PAO₂)
- what is the oxygen consumption (VO2) equation?
- what is the CaO2 (arterial oxygen content) equation to allow oxygen consumption to be calculated
- What is the DO2 (oxygen delivery) equation
- Oxygen consumption (VO2)
VO2= CO x (CaO2 - CvO2)
V stands for volume
VO2= O2 consumption
CaO2 = arterial oxygen content
CvO2= venous oxygen content
CO= SV x HR
- Arterial oxygen content (CaO2)
= (1.34 x Hb x SaO2) + (0.023 x PaO2)
units are ml/O2/DL of blood
1.34 is the O2-carrying capacity of 1g of Hb
0.023 is the solubility of Oxygen in plasma
CvO2 uses same formula but input SvO2( instead of SpO2) and PvO2 instead of PaO2)
*kpa use 0.023, mmHg use 0.003
- Oxygen delivery (DO2)
DO2 = CO x CaCO2
What is Ficks principle?
Fick’s Principle is a method used to measure cardiac output (CO) based on the relationship between oxygen consumption (VO₂) and the differences in oxygen content between arterial blood and venous blood.
CO= VO2/ (CaO2-CvO2)
what shifts O2 dissociation curve right?
and left
right: release
->dissociates more/ releases O2
- increased temp
- increased 2,3 DPG
- increased H+
- increased CO2
-HbS (sickle cell HbS has lower affinity for O2 than HbA- normal adult Hb)
Left (low): latches on
-Decreased H+
-Decreased 2,3 DPG
-Decreased temp
-Decreased pCO2
-Carbon monoxide!!!
-Fetal Hb (binds more readily to O2, lower tendency to release it to tissues)
-MetHb
what structural changes occur in sickle cell
Valine is substituted for glutamic acid at position 6 of the beta-globin chain, causing sickle shaped cells that tend to clump together
-increased risk of vaso-occlusion leading to ischaemia, pain and organ damage
- what is CC?
- how do you calculate closing capacity?
CC is the point at which lung volume falls enough for small airways to collapse
CC=CV + RV
CV = volume of gas between RV and CC
what are dependent lung zones?
dependent lung zones are the lower zones- these receive the most blood dur eto gravity pulling blood downward. they also recieve the highest ventilation. VQ is more balanced in lung bases in a healthy person.
When supine, the posterior regions become the dependent lung zones/
why avoid PEEP in neuro cases?
PEEP reduced venous return, which also reduces venous drainage from the brain, thus can raise ICP.
what has the most effect on reducing Et CO2? increasing RR by 20% or increasing VT by 20%?
increasing VT because more of the deadspace may be ventilated. Increasing RR just affects anatomical deadspace.
whats the normal range for fibrinogen?
what should you aim to keep it at in pregnant patients
1.5-4.5 g/l
aim >2 in pregnant pts bleeding
1.what is anatomical deadspace and what is it normally around in adults?
- how is anatomical deadspace measured?
1.anatomical deadspace is that not taking part in gas exchange (nose, pharynx, trachea, bronchi)
- normally around 150ml (2ml/kg) and is influenced by body size and age.
- It can be calculated using Fowlers Method (nitrogen washout technique)
- attach patient to pneumotachograph to measure flow over time (volume), and a nitrogen sensor (will initially read around 79% to reflect percentage of nitrogen in air.
- take breath of 100% O2- this will fill anatomical dead space.
- exhale and measure nitrogen over three phases
-P1: beginning of expiration- no N2-> pure O2
-P2:exhaled nitrogen con increases rapidly. This represents gas from fast time-constant alveoli mixing with gas from more distal airways.
-P3 plateau of nitrogen rich from last stages of exhalation from mainly contents of gas-exchanging alveoli
-Phase 4 has a further rise in nitrogen. This represents closing capacity as small airways in more compliant regions of the lung close, and only poorly compliant alveoli continue to exhale their nitrogen-rich gas.
-NEXT use midpoint of rising nitrogen slopw and compare area a and b above and below curve to predict anatomical deadspace volume
how to measure physiological deadspace (equation)
deadspace is the fraction of tidal volume which does not participate in gas exchange.
Alveolar ventilation = RR x (VT -deadspace)
Physiological deadspace= alveolar DS + anatomical DS
- The Bohr equation
VD/VT= (PACO2 -PECO2)/ PACO2
-using difference between Alveolar and Expired CO2
-Enghoff modification of Bohrs equation uses arterial CO2 instead of exhaled CO2.
whats the inital first change up a mountain
hyperventilation. as peer alveolar gas equation, we hyperventilate to decrease PaCO2 and increase PaO2
Alveolar gas equation
PAO2= (FiO2 x[Patm-PH2O]) + PCO2/RQ
WOB
what is the ratio of energy to overcome elastic forces verses flow-resistive work
WOB is a major source of caloric expenditure and O2 expenditure
70% of WOB is to overcome elastic forces
30% is flow-resistive work
The total area of hysteresis pressure volume curve represents the flow-resistive WOB. During an asthma attack the area of expiratory resistive work increases making the compliance curve larger in area. the larger the area the greater the work required to breathe.
peptide hormones
e.g include hypothalamic and some pituitary hormones.
-mostly lipophobic (unlike steroids) therefore interact with cell surface.
LNRH can be used in prostate ca.
synthesised through recombinant DNA techniques.
what is the primary physiological role of phosphate in the body?
regulation of intracellular pH through buffering mechanisms, maintaining cellular homestasis
