respiratory monitoring Flashcards
what are simple observation monitoring techniques?
- chest rise and fall
- circuit bag movement and feel of the bag
- Vt and end expiratory Vt
- color of lips, nails, blood, conjunctiva
- accessory respiratory muscles, increased work of breathing
- respiratory rate and depth
- rocking = obstruction
- puffing = patent
- airway noise
- air felt on palm
- precordial stethoscope sounds
- tube fog
what is gas exchange?
addition of O2 to the blood and the elimination of CO2 from the blood
how can assessment of oxygenation and ventilation be invasive and non invasive?
non invasive: observation of chest rise and fall;
invasive: ETT insertion and direct measurement of ETCO2, Vt, etc
what respiratory monitors are provided by the anesthesia machine monitor?
- Vt
- FiO2 and FeO2
- PiP meter, value and waveform
- FiCO2 and ETCO2 and capnograph
- RR (indicator of CO2 response curve)
- Vm
- gas analysis
- inspiratory flow rates
- misc. values like inspiratory trigger can tell you whether pt. has weak effort
describe the precordial and esophageal stethoscopes.
- heavy weight chest piece placed on skin or esophageal temp probe used
- custom fitted ear piece connects the tubing to either the chest piece or esophageal probe
- confirms ventilation by breath sounds
what can the precordial and esophageal stethoscopes detect?
-stridor
-wheezing (bronchospasm)
-abnormal heart sounds (arrhythmias, new murmur from
air emboli)
-S3 gallop (CHF)
-absence of heart sounds (cardiac arrest, PEA)
*cannot detect diffusion abnormalities
when are esophageal stethoscopes contraindicated?
esophageal varicies
where is the correct placement of precordial and esophageal stethoscopes?
at the 4th intercostal space and left sternal border
what are you looking for when monitoring tidal volumes?
- ensure achieving Vt between 6-8 ml/kg IBW
- do not exceed PiP > 35-40 cmH2O
- monitor bilaterally equal chest rise and fall
- Vt need to be enough to control ETCO2, keep alveoli expanded, and deliver volatile anesthetic drugs
- bellows descend and ascend
what are arterial blood gases?
measurement of PaO2, PaCO2, pH, Oxyhgb saturation, base excess and bicarb levels
- assessment of oxygenation: PaO2 and Oxyhgb Sat
- assessment of ventilation: PaCO2
- assessment of acid-base status: pH, bicarb, base excess
what is hypoxemia?
decreased blood oxygen levels resulting from decreased delivery of oxygen from atmosphere to the blood (obstruction, decreased hypoventilation)
what is hypoxia?
decreased delivery of oxygen to the tissues (caused by hypoxemia)
what are the four categories of hypoxia?
1) hypoxemia: low FiO2, hypoventilation, V/Q mismatch,
shunt, diffusion limitations
2) anemic hypoxia: not enough Hgb (RBCs) picking up
O2 to take to tissues
3) circulatory hypoxia: not enough cardiac output to push
Hgb with O2
4) histiocystic hypoxia: cell won’t accept the delivery of
the O2 (cyanide poisoning)
what are some causes of hypoxemia?
-decreased inspired oxygen (altitude)
-hypoventilation (resp. center depression, NM disease,
resp. failure)
-shunt: pulm. (atelectasis, pneumonia, pulm. edema,
ARDS) or cardiac (patent foramen ovale)
-V/Q mismatch (airway secretions, bronchospasm)
what are some causes of hypoxia?
- hypoxemia (lower than normal PaO2)
- anemia
- circulatory hypoxia (decreased CO, dec. local perfusion)
- affinity hypoxia (dec. release of O2 from Hgb tissues)
- histotoxic hypoxia (cyanide poisoning; won’t accept O2)
how do you estimate O2 consumption and O2 delivery to the lungs?
- average O2 consumption is 3 ml O2/kg/min
- current monitors allow you to determine if O2 delivery is adequate to meet O2 consumption
- VO2 (consumption) = FiO2-FeO2 x Vm/wt in kg
- DO2 (delivery to lungs) = FiO2 x Vm / wt in kg
whether O2 gets to the tissues depends on what?
- Hgb
- cardiac output
- if sat is near 100%, increasing FiO2 will have little effect on delivery of O2 to lungs; cardiovascular system is the limiting factor in delivery O2 to tissue
describe pulse oximetry.
- dual wavelengths of light (660 nm and 940 nm) pass through tissue and vascular beds via LED
- tissue and blood absorb light passing through
- a ratio is calculated at the two wavelengths of light
- requires pulsatile blood flow (SpO2)
- can be placed on finger, toe, earlobe, forehead; infants on hand and foot
what are some causes of error in pulse oximetry?
- elevated Hgb species other than Hgb and Oxyhgb
- improper fitting probe causing light shunt as light is reflected from skin results in falsely low SpO2
- SaO2 < 60% results in falsely low SpO2
- poorly perfused areas
- Hgb concentration (anemia and hypoxemia falsely low)
- IV methylene blue dye (dramatic falsely low)
- blue nail polish w/ light absorbance near 660 nm lead to falsely low
- ambient fluorescent light
- excessive motion
what can result in a falsely high SpO2?
-elevated Hgb species other than Hgb and Oxyhgb
*COHgb absorbs light similarly, resulting in false high
*MetHgb similar to Hgb: if SaO2 > 85% SpO2 will be
low, if SaO2 is < 85% SpO2 will be high
*not affected by fetal hgb or sickle cell
-ambient fluorescent light
what can result in a falsely low SpO2?
- improper fitting probe
- SaO2 <60%
- poorly perfused areas
- low flow in cardiac arrest and vasoconstriction
- low flow hypothermia, low CO
- anemia and hypoxemia
- IV methylene blue dye
- blue nail polish
- excessive motion
what are some oximetry probe sites?
- finger (most common)
- toe (desat/ resat detection not as fast)
- nose (hypothermia, vasopressors; central location makes desat/resat better than peripheral; unreliable with trendelenberg)
- earlobe (useful when finger, toes not available; failure right higher)
- tongue (burn pts.; desat/resat quicker than finger)
- cheek (more accurate than finger; good for poor perfusion states; desat/resat rapid)
describe gas and agent analysis.
- some newer gas analyzers are able to recognize different agents while older models can’t
- older gas analyzers require the anesthetist to select which agent they use and calibrate
- *failure to select the appropriate agent can cause OD or underdose of agent
- gas analyzers are pre-calibrated for specific agents
- most newer analyzers calibrated for volatiles and N2O and will calculate MAC and additive MAC if N2O in use
what is capnography?
measurement of CO2 during ventilatory cycle
**CO2 is affected by VO2 (O2 consumption), CO2 transport, alveolar ventilation
describe capnography.
- CO2 is measured by infrared absorption
- CO2 gas is measured and a waveform over time is created using the CO2 value
- mainstream: measurement chamber is placed directly at the airway
- sidestream: airway gas is aspirated through tubing to a measurement chamber
what causes CO2 production, increasing ETCO2?
- fever
- physical activity
- seizures
- sepsis
- hyperthyroidism
- trauma and burns
- high carbohydrate diet
what causes decreased elimination of CO2, increasing ETCO2?
hypoventilation
what decreases ETCO2 due to inability to get CO2 back to the lungs for elimination?
-hypotension and decreased CO: not carrying CO2 back
from tissues to heart and lungs
-right to left pulmonary shunt: bypasses the lungs
what decreases CO2 production, decreasing ETCO2?
- hypothyroidism
- paralysis, motionless
- hypothermia
what causes an increase in CO2 elimination, decreasing ETCO2?
hyperventilation
if there is a sudden decrease in ETCO2, what should you suspect?
-no flow, like with a drop in blood pressure
what mirrors CO2 level?
VO2
how does VO2 indicate what ETCO2 will show?
bigger O2 consumption (bigger difference in FiO2 and FeO2) end in larger ETCO2 (increased metabolic state)
cardiac status and ventilator settings affect what with CO2?
-elimination and evacuation of CO2
patient metabolic status affects what with CO2?
production
describe the normal capnograph.
Phase I: dead space, expiration (no CO2 d/t no gas exchange)
Phase II: mixed dead space and alveolar gas exchange (CO2 rising)
Phase III: alveolar gas expiration; plateau (CO2 peaks)
Phase IV: upswing that may be seen at end of III
Phase 0: inspiration (CO2 drops down to 0)
describe the capnograph in non-intubated patients.
- use special nasal cannula designs that allow sidestream ETCO2 measurement
- nasal cannula sidestream connection can be created with normal cannula
- mixed gases of air and oxygen occur
- inadequate sampling
- mouth breathers will cause low readings
- inaccurate low readings and waveforms are common d/t contaminated exhaled gases are mixed with ambient air
- ETCO2 wave usually has no plateau phase
what causes increased PiP and plateau pressure (PP)?
- increased tidal volume
- decreased pulmonary compliance
- pulmonary edema
- trendelenburg
- pleural effusion
- ascites
- abdominal packing
- peritoneal gas insufflation
- tension pneumothorax
- endobronchial intubation
what causes increased Pip with unchanged Pplat?
- increased inspiratory gas flow rate
- increased airway resistance
- kinked ETT
- bronchospasm
- secretions
- foreign body aspiration
- airway compression
- ETT cuff herniation
what is static lung compliance?
- during times of NO gas flow
- measured using plateau pressure (end inhalation prior to exhalation; always lower than Peak pressure)
- measure of lung compliance
- constant unless lung compliance changes
what is dynamic lung compliance?
- during times of gas flow (active inspiration)
- measured using peak pressure
- measures lung compliance plus airway resistance
- airway resistance contributes to a decrease in dynamic compliance
- airway resistance can change from breath to breath
what is Peak inspiratory pressure (PiP)?
highest circuit pressure during inspiratory cycle
*indicator of dynamic compliance when flow is occurring
what is plateau pressure (Pplat)?
pressure during inspiratory pause, no flow
- indicator of static lung compliance
- never greater than PiP
an increase in Pplat indicates what?
- decreased compliance of lungs
- stiff and rigid, no recoil OR too much volume
- pt moved to trendelenburg; opioids lead to stiff chest; insufflated abdomen during lap chole
an increase in Pip indicates what?
- increased inspiratory flow
- increased airway resistance
- increased secretions or kinks
describe pressure volume loops.
- indicator of lung compliance (change of volume for a given change in pressure)
- yields info regarding leaks, lung over inflation, and obstruction
- loops move based on positive or negative pressure
- counter-clockwise during positive pressure ventilation
- clockwise during spontaneous respiration
- slope indicate compliance
how does pressure move loops?
higher pressure moves loop farther right
how does slope indicate lung compliance?
- flatter slope indicates decreased compliance
- steeper slope indicates increased compliance
describe flow volume loops.
- normal loop looks like an upside down ice cream cone
* clockwise direction
what changes with flow volume loop in restrictive lung disease?
- normal shape
- lung volumes are smaller
- flows are reduced
what changes with flow volume loop in obstructive lung disease?
- shape is caved in which indicates expiratory obstruction
- lung volumes are larger
- flows are reduced
- *obstructed flow will always yield a flatter, less round shape as air flow is impeded
what three types of obstructions can be seen on flow volume loops?
- fixed (tumor) obstruction in and out: impedes inspiration and expiration
- extrathoracic : airway collapses on inspiration d/t increased negative pressure and opens on expiration with positive pressure (inspiratory impeded)
- inrathoracic: airway collapse on expiration with positive pressure (COPD and emphysema) (expiratory impeded)
