Clinical implication…… Any interference to the delivery of O2 at any point in the cascade, Significant injury can occur downstream
2 TISSUES CaO 2 = (SAT x Hb x 1 . 3 4 ) + .0 0 3(PaO 2 )
Tissue oxygenation depends on:
efficient gas exchange at lung level
adequate circulatory distribution
Failure of any of these 3 elements results in tissue hypoxia
Body compensation for tissue Hypoxia 1 ) Increase in cardiac output 2 ) Tissues extract more Oxygen 3 ) Anaerobic metabolism begins
PaO2 SaO2 OXY (Sat) 98% HAEMOGLOBIN 2 % Dissolved Oxygen O. D. C. PAO2 A.C.I. CaO2 Content of oxygen Ml/100 of blood Delivery Of Oxygen To Tissues DaO2 O2 Cardiac output A.C.I.( Alveolar capillary interface)
Oxygen content CaO2 = 2% Dissolved O2 ( PaO2 0.003 ml ) 98% O 2 is bound to Hb. ( Hb 1.34 SaO2 )
HB% 12 SAT 100% HB% 12 SAT 50% HB 6 SAT 100% HB 13 SAT 90% PaO2 SATURATION O2 content Normal ↓ ↓ ↓ or N
OXYGEN DELIVERY IS A CARDIO-RESPIRATORY FUNCTION
Onloading Oxygen in Lungs Pressure Saturation oxyhemeglobin deoxyhemeglobin pH 7.4 pH 7.45 pH shifts curve to left ‘ onloading’ in lungs Remember: CO 2 [H + ]
If there are obvious signs that the patient is deteriorating – BP, HR & RR it is a good idea to request an ABG analysis even if the SpO2 value is normal.
Is there any single test which will pickup tissue hypoxia early ?
C.P.A.P / PEEP
Improving Oxygenation 2
Table 1. Principle stores of oxygen in the body While breathing AIR While breathing 100% O2 In the lungs (FRC) 450ml 3000ml In the blood 850ml 950ml Dissolved or bound in tissues (FRC) 250ml 300ml Total 1550ml 4250ml
Causes….Mechanism…. D/D of Hypoxia/Hypoxemia…….. Non R E S P I R A T O R Y Does supplemental O2(↑FiO2)increase PaO2 substantially PaO2 SaO2 CaO2 P(A-a)O2 R-L shunt No ANAEMIA N N N NO CO / MethHb N N Possibly ventilation N NO Tissue (histo) N N N N NO
Causes….Mechanism…. D/D of Hypoxia/Hypoxemia…….. R E S P I R A T O R Y Does supplemental O2(↑FiO2)increase PaO2 substantially PaO2 SaO2 CaO2 P(A-a)O2 R-L shunt No (depends on magnitude of shunt) V-Q mismatch Yes Diffusion Barrier Yes ventilation N Yes PiO2 N Yes
LOW FLOW S. HIGH FLOW S. C.P.A.P. HYPERBAIC O2
SIMPLE OX. MASK FIO2 VARIABLE 30 TO 60 % FEEDING PROBLEM REBREATHING……
NASAL CANNULA MAX FLOW……2LIT/MIN FIO2 DIF. TO CONTROL HUMIDI. NOT NEC. MOUTH / NOSE BREAT.?
NASOPHARYN. CATH .
Oclsn of dist Opening.
FiO2 difficult to control.
CATHER MORE THAN 8 FR.
The colour of the mask’s aperture reflects the FiO2 achieved Venturi masks…….. 28% 35% 40% 60%
Can provide 24%-50% oxygen by mixing room air with a precise amount of oxygen thereby delivering a precise FiO2. The size of the port and the oxygen liter flow determine the FiO2. The mask should be fitted to the patient as best as possible to prevent entrainment of room air around the mask which would alter the FiO2.