Fractional OxyHb= oxyHb/[HHb +OxyHb+ COHb + MetHb]
What is fractional Hb saturation?
Functional OxyHb = OxyHb/[HHb + OxyHb]
What is functional Hb saturation?
660 nm
*
Pulse ox will read COHb as functional oxyHb --> false elevation
*
What wavelengths do OxyHb and COHb have absorption coefficients for?
940 nm
Corresponds with an SpO2 of ~85%
What wavelength does MetHb have an affinity for?
Low perfusion state
Dysfunctional Hb
Dyes
Nail polish
Skin Pigmentation
Ambient light (sunlight vs fluorescent lights, heat lams etc)
List 5 reasons why you might get a falsely SpO2 reading
How are mainstream capnographs different from sidestream capnographs?
See picture
Explain the phases of a capnograph
Phase 1: Expiratory baseline --> beginning of exhalation, corresponds to exhaltion of CO2 free dead space gas from the larger conducting airways
Phase 2: Expiratory upstroke --> exhalation of mixed alveolar and decreaseing dead space gas
Phase 3: Expirato
How is the capnograph of an obstructive or bronchospasmic process appear?
Alterations to phase 3 - increasing slope due to slow emptying of alveoli
What is a curare cleft?
A dip in phase III due to mechanically ventilated patients with spontaneous breathing. Seen commonly in patients emerging from a neuromuscular blockade.
Indicates a small amount of fresh gas being drawn over the detector
How does rebreathing appear on capnograph?
Failure of the capnogram to return to baseline
What is a single-breath CO2 curve and what does it measure?
It meausrues expiratory and inspiratory tidal volum and is generally divided into 3 areas ( anatomic dead-space volume), transitional phase II volume and phase III alveolar volume. Sum of volumes = Vt
The vertical axis represents PCO2
What is considered normal P(a-et)CO2?
4-6 mmHg
Can be increased by COPD, left-sided heart failure, pulmonary embolism (caused by an increase in physiologic dead space)
What is mean airway pressure and how can it be calculated?
Mean airway pressure (Paw) represents the average pressure recorded during the respiratory cycle.
Influenced by PIP, PEEP, inspiratory time, total cycle time
Paw= 1/2 [(PIP-PEEP) x (Ti/TCT)] + PEEP
can be obtained by integrating the area under the pressur
What conditions can increase CO2 production?
Increases in metabolic rate: sepsis, fever, severe, burns, trauma, increased work of breaking (muscles produce additional CO2)
Factors that influence the amount of CO2 exhaled:
-CO2 production
-perfusion of the lungs
-diffusion
-ventilation