1) Hypoxia can lead to decreased ATP synthesis, lactic acidosis, impaired protein synthesis, and irreversible cell changes due to increased cytosolic calcium. 2) Pao2, Sao2, and oxygen content are important measures of oxygen levels in the blood. Pulse oximetry can monitor Sao2 non-invasively but has limitations. 3) Arterial blood gas analysis precisely measures oxygen, carbon dioxide, pH, and bicarbonate levels to assess oxygenation and ventilation.

1. Monitoring hypoxia and oxygen
supplementation
Dr. Uttam Laudari
MS First year Resident
Department of Surgery

2. Consequences of hypoxia
1. Decrease synthesis of ATP
2. Anerobic glycolysis used for ATP synthesis
– Lactic acidosis ( denaturation of structural and enzymatic protein)
– Na-K ATPase pump impaired ( cellular swelling)
3. Decrese protein synthesis
4. Irreversible cell changes -Increase cytosolic calcium

3. Pao2
• pressure keeping O2 dissolved in the plasma of arterial blood
• reflects the tension or pressure that is exerted by oxygenwhen it is
dissolved in plasma.
• A high PO2 is required to dissolve even small amounts of oxygen in
plasma
• Contributing factors-
– percentage of O2 in inspired air
– Normal O2 exchange in lung
• Significance
– Reduced in hypoxemia
– Driving force for movement of O2 from capillaries into tissue by diffusion

4. Sao2
• Average percentage of 02 bound to hemoglobin
• Contributing factors-
– Pao2 and valence of heme iron in each of four heme group
– Ferrous iron binds to O2 but ferric does not
• Significance
– Sa02< 80% produces cyanosis of skin and mucous
membrane
– When SpO2 (or SaO2) exceeds 90% (PaO2 > 60 mm
Hg), the curve begins to flatten, and larger changes
in PaO2 are accompanied by smaller changes in SpO2

5. Oxygen content
• Total amount of oxygen carried in blood
• Oxygen content=(Hb x 1.34 x SaO2) + (0.0032 x
PaO2)
• Contributing factors
– Hemoglobin concentration in RBCs
– PaO2
– Sao2
• Significance-
– Hb being important carrier of blood
– Hb concentration determines total amount of O2
delivered to tissue

6. • PULSE OXIMETRY
• Non invasive method of monitoring hypoxia (SaO2)
• Oximetry emits light at specified wave lengths that identifies
oxyhemoglobin and dexyhemoglobin
• Cannot identify dyshemoglobin such as methhemoglobin
and carboxyhemoglobins shows falsely high record
• It is related to PaO2 through the sigmoid shaped O2-Hb
dissociation curve but should not be interpreted as direct
substitute for PaO2

7. • Principle-photodetector senses only lightof alternating
intensity (analogous to an AC amplifier)
• At SaO2 above 70%, the O2 saturation recorded by pulse
oximeters (SpO2) differs by less than 3% from the actual
SaO2
• SpO2 can be a sensitive marker of inadequate ventilation (a
low PaO2) when patients are breathing room air, but not when
they are breathing supplemental oxygen

8. • The association segment of the curve, or upper portion, is
essentially flat and represents oxygen uptake in the lung.
• In this portion of the curve, changes in PO2 levels between
60 and 100 mm Hg cause only small changesin oxygen
saturation.

9. • This is advantageous in the lung where fluctuations
in alveolar PO2, and subsequently arterial PO2, do
not affect oxygen loading until PO2 falls significantly
lower than normal.

10. • The lower portion of the curve (below 45 mm Hg)
corresponds to the PO2 levels of venous blood
• This steep part of the curve is referred to as
the dissociation segment and represents the release of oxygen to
the tissues.
• In this low range of PO2 values, even small changes in oxygen
tension produce large alterations in oxygen saturation
• This is advantageous to the tissue because large quantities of
oxygen can be extracted from the blood for relatively small
decreases in PO2

11. • When SpO2 (or SaO2) exceeds 90% (PaO2 > 60 mm Hg), the
curve begins to flatten, and larger changes in PaO2 are
accompanied by smaller changes in SpO2
• supplemental O2 can be safely withheld if the SpO2 is92% or
higher on room air

12. ABG
• The ABG analyser measures:
• Hydrogen ion concentration, reported as either hydrogen ion
concentration [H+] or pH (-log10[H+] ) .
• A lower pH value is more acidotic
• Oxygen tension (PaO2), reported in kilopascals (kPa) or mmHg.
• Carbon dioxide tension (PaCO2) (kPa or mmHg)
• bicarbonate [HC03-] expressed in mmol l-1 and Base Excess/Deficit
(BE/D), are calculated

13. • Base Deficit is the amount of base that would be needed to
correct the pH of the sample to 7.4.
• Base excess is the amount of acid needed to correct to pH 7.4
• PaO2 is a measure of arterial oxygen, a balance between
oxygen delivery (a function of the cardiorespiratory system)
and uptake by the tissues (aerobic metabolism).
• This varies normally with age and living at altitude,
abnormally in cardio-respiratory disease

14. • The level of PaCO2 is a balance between
production (cellular aerobic metabolism) and
clearance.
• CO2 is cleared in two ways.
– First, by ventilation (acute adaption over seconds)
and second,
– metabolic compensation (renal excretion) after
conversion to HCO3- (chronic, over hours and days).
[HCO3-] level indicates the adaptive responses to
acidosis or alkalosis.
– Low [HCO3-] indicates acidosis, high alkalosis

15. Mixed venous oxygen
• SvO2 represents the end result of both oxygen delivery and
consumption at the tissue level
• SvO2 = Oxygen Delivered – Oxygen Consumed
(SaO2, Hb, CO) (VO2)
• When a threat to normal oxygen supply/demand occurs, the
body attempts to compensate, and its success is immediately
reflected by SvO2
• If the SvO2 value is low, then either the oxygen supply is
insufficient or the oxygen demand is elevated

16. Mixed venous oxygen
• The SvO2 is measured in pulmonary artery blood, and is a marker of
the balance between whole-body O2 delivery (DO2) and O2
consumption
• Normal range- 70 to 75 %
• A decrease in SvO2 below the normal range of 70 to 75% identifies
a state of inadequate O2 delivery relative to O2 consumption that
could be the result of a decreased DO2 (from low cardiac output,
anemia, or hypoxemia)
• a greater than 5% variation in SvO2 that persists for longer than 10
minutes is considered a significant change

17. • If SvO2 falls below 60%, a decrease in oxygen delivery and/or
an increase in oxygen consumption should be suspected
• When SvO2 falls below 40%, the body’s ability to compensate
is limited, and oxygen is relatively unavailable for use by the
tissues

18. • High SvO2
↑ Oxygen delivery ↑ FIO2 Hyperoxia
↓ Oxygen demand
Hypothermia,Anesthesia,Pharmacologic paralysis Sepsis
• Low SVO2
– Decrese oxygen deleivery
• Decrease hemogolbin- anemia hemorrage
• Decrese SaO2-hypoxia, suctioning
• Decrease cardiac output-hypovolemic shock, arrthymia
– Increase oxygen demand
• Hyperthermia pain
• Shivering, seizures

19. A-a gradient
• Difference in Partial pressure of oxygen between the alveolar Po2 and
Arterial Po2
• A-a gradient is due to V/Q mismatch
• Used in differentiating the cause of hypoxemia
• Hypoxemia due to pulmonary cause increases A-a gradient while
extrapulmonary cause has normal A-a gradient
• Normal PAo2 = 100 mmHg
•
Normal Pao2= 95mm HG
• So normal A-a gradient =5 mm Hg

20. • Medically significant A-a gradient > 30 mmHG
• Hypoxemia + increased A- Gradient ventilation,perfusion,
diffusion defect, right to left cardiac shunts
• Hypoxemia + normal A-a gradient- depressed respiratory
center, upper airway obstrution and chest bellows disease

21. Oxygen delivery system
• Oxygen delivery systems are classified as low-flow or high-
flow systems
• Low-flow delivery systems, which include nasal prongs, face
masks, and masks with reservoir bags, provide a reservoir of
oxygen for the patient to inhale
• In contrast to thevariable FiO2 with low-flow systems, high-
flow oxygen delivery systems provide a constant FiO2

22. Nasal Prongs
• Nasal prongs deliver a constant flow of oxygen to the
nasopharynx and oropharynx, which acts as an oxygen
reservoir (average capacity = 50 mL
• As the oxygen flow rate increases from 1 to 6 L/min, the FiO2
increases from 0.24 to 0.46
• Nasal prongs are easy to use and well tolerated by most
patients.
•
• major disadvantage of nasal prongs is the inability to achieve
high concentrations of inhaled O2 in patients who have a high
minute ventilation.

23. Low flow oxygen mask
• Face masks add 100 to 200 mL to the capacity of the oxygen reservoir
• These devices fit loosely on the face, which allows room air to be inhaled,
if needed
• Standard face masks deliver oxygen at flow rates between 5 and 10 L/min
• Low-flow oxygen masks can achieve a maximum FiO2 of approximately
0.60
• Standard face masks can provide a slightly higher maximum FiO2 than
nasal prongs
• face masks are considered to have the same drawbacks as nasal prongs

24. Masks with Reservoir Bags
• The addition of a reservoir bag to a standard face mask increases the
capacity of the oxygen reservoir by 600 to 1000 mL
• If the reservoir bag is kept inflated, the patient will inhale only the gas
contained in the bag
• This device allows the gas exhaled in the initial phase of expiration to
return to the reservoir bag
• The initial part of expiration contains gas from the upper airways
(anatomic dead space), so the gas that is rebreathed is rich in oxygen and
largely devoid of CO2
• Partial rebreather devices can achieve a maximum FiO2 of 70 to80%.

25. • principal advantage of the reservoir bags is
the greater ability to control the composition
of inhaled gas
• Disadvantage
• because the masks must create a tight seal on the
face, it is not possible to feed patients by mouth
or nasoenteral tube
• Aerosolized bronchodilator therapy is also not
possible with reservoir bag

26. High-Flow Oxygen Masks
• High-flow oxygen inhalation devices provide complete control of
the inhaled gas mixture
• deliver a constant FiO2 regardless ofchanges in ventilatory pattern
• Oxygen is delivered to the mask at low flow rates, but at the inlet of
the mask, the oxygen is passed through a narrowed orifice, and this
creates a high-velocity stream of gas
• The volume of room air thatmoves into the mask (which
determines the FiO2) can be varied by varying the size of the
openings (called entrainment ports) on the mask

27. • Advantage
– deliver a constant FiO2
– This feature is desirable in patients with chronic
hypercapnia because an inadvertent increase in FiO2 in
these patients can lead to furtherCO2 retention
• Disadvantage
– inability to deliver high concentrations of inhaled O2

28. • Thank you