Anesthesia Effects on Respiratory System Flashcards
The supine position decreases FRC by ___
30%
The induction of GA decreases FRC by ___. Why?
15-20%
Loss of inspiratory muscle tone
Increased expiratory muscle tone
Diaphragm moves cephalad 4 cm
Chest wall rigidity changes
Decrease the transpulmonary pressure
Promotes alveolar collapse
Obesity and FRC
Decreases it due to:
decreased chest wall compliance &
increased airway collapsibility
Pregnancy and FRC
Decreases it due to:
Diaphragm shifts cephalad as a result of the gravid uterus
Decreased chest wall compliance
Neonates and FRC
Less alveoli leads to decreased lung compliance
Cartilaginous ribcage that is prone to collapse
Advanced age and FRC
Decreased elastic lung tissue leads to air trapping which results in increased residual volume and thus INCREASED FRC
Which positions increase FRC?
Prone, sitting, lateral
Paralysis and FRC
Decreases due to diaphragm moving cephalad which decreases lung volumes
Inadequate anesthesia and FRC
Straining leads to forceful expirations which decreases lung volumes
Excessive IV fluids and FRC
Decreases it
Fluid accumulation in dependent lung favors zone 3
High FiO2 and FRC
Decreases it
Absorption atelectasis, conversion of low V/Q unit, shunt unit
Reduced Pulmonary Compliance and FRC
Decreases it
Conditions like acute lung injury, pulmonary edema, pulmonary fibrosis, atelectasis, pleural effusion
Obstructive Lung Disease and FRC
Increases it
Air trapping increases residual volume which increases FRC
PEEP and FRC
Increases it
Recruits collapsed alveoli
Partially overcomes effects of GA
decreases venous admixture which increases PaO2
Sigh breaths and FRC
Increases it
Recruits collapsed alveoli
Prevention of Atelectasis happens through _____.
Recruitment Maneuvers
1)PEEP
2) Sigh breaths
How do you figure out PEEP values for different patients?
BMI below 25 = 6 cm H2O
BMI up to 30 = 8 cm H2O
10 cm H2O consistently reopens collapsed lung tissue
What are components of a sigh breath?
Doubling of Vt (tidal volume)
Sustained inflation of lungs to 30 cm H2O
To open all collapsed lung tissue 40 cm H2O is required
BMI > 45 will require more
The closing capacity is the sum of ___.
the closing volume and the residual volume
Closing capacity is normally well below ____.
FRC, but it rises steadily with age.
What is closing capacity?
The volume at which small airways begin to close in the dependent parts of the lungs.
Intrapulmonary shunting of deoxygenated blood promotes _____.
hypoxemia
Factors that Increase Closing volume
“CLOSE-P”
- COPD
- LV failure
- Obesity
- Extremes of age
- Pregnancy
General facts about V/Q Ratio
V/Q = alveolar ventilation/cardiac output
V/Q = (4 L/min)/(5 L/min)
V/Q are perfectly matched where the lines intersect
V > Q towards the apex
V < Q towards the base
Zone 1
Dead Space: PA > Pa > Pv
V/Q = ∞
Zone 2
Waterfall: Pa > PA > Pv
V/Q = 1
Zone 3
Shunt: Pa > Pv > PA
V/Q = 0
West Lung Zones
During anesthesia, arterial oxygenation is impaired in which patient populations?
Elderly – obese – smokers
Resp function during anesthesia for young to middle aged patients
Shunt 10%
V/Q ratio scatter is small to moderate
Patients with H/O pulmonary disease
V/Q low
Increase shunt
Respiratory Patterns with different types of anesthesia: inadequate, light, moderate, deep etc.
Inadequate Anesthesia can cause hyperventilation or breath holding.
As the depth of anesthesia approaches MAC, respirations progress from irregular to a more regular pattern with an increase in Vt
Moderate levels respirations increase but are shallow
Deep anesthesia with halogenated agents cause rapid shallow breathing
Very deep anesthesia with inhaled agents causes a “rocking boat” type of movement**
Nitrous-narcotic anesthesia – slow and deep
Mechanisms of Hypoxemia during Anesthesia
Mechanical failure of anesthesia apparatus to deliver O2 to the patient
Mechanical failure of the ETT
Hypoventilation – (Decreased Vt)
Decrease in FRC
Mechanisms of Hypoxemia during Anesthesia
Intraoperative conditions that cause hypoxemia
Surgical position
Lithotomy – jackknife – kidney bar
Massive blood loss
Surgical retraction on the lung
Mechanisms of Hypercapnia
Hypoventilation
Increased dead space ventilation
Increased CO2 production
Issues with CO2 absorber
Hypoxic Pulmonary Vasoconstriction
HPV occurs in Pulmonary Arterioles located very close to the small bronchioles & alveoli. This permits rapid & direct detection of alveolar hypoxia.
3 ways HPV works in Humans
Life at High Altitudes
Hypoventilation, Atelectasis, any Low V/Q state
Chronic Disease
In response to alveolar hypoxia, the alveolar arterioles ____.
constrict, thereby decreasing shunt blood flow.
What inhibits the hypoxic pulmonary vasoconstriction response?
Direct-acting vasodilators inhibit HPV response, which increases shunt and decreases PaO2.
Volatile Agents inhibit HPV response at higher concentrations. (> one MAC)
Basics of Pulse Oximetry
Two Wavelengths of light, 660nm (red) & 990nm(infrared).
Infrared absorbed by Oxyhemaglobin.
Red absorbed by deoxyhemoglobin.
Operates based on Beer’s Law. In optics, the Beer–Lambert law is an empirical relationship that relates the absorption of light to the properties of the material through which the light is travelling.
When won’t pulse oximetry work?
Applied to thumb
Vasoconstriction
Hypothermia
Hypotension
Methylene Blue/ Indigo Carmine
Anemia of sickle cell
CO Poisoning
Methemoglobinemia- impairs unloading of O2
Basics of capnography
CO2 may be expressed as a number (capnometery).
CO2 seen as a wave (capnography).
Gas is sampled at two different infrared wavelengths (2600nm & 4300nm)
Place sampling line as close as possible to alveolar gas. ( i.e. elbow of circuit)
Label the different parts of the capnography waveform
Basic Concepts of an ABG and the idea of compensation
Basic Concepts
H+(mEq/L) = 24X [PCO2/HCO3-]
Physiologic goal is to compensate to a normal pH.
Compensation is not synonymous with correction
Compensatory Response
Respiratory system responds immediately to metabolic disorders.
Kidneys provide the compensation for Respiratory disorders and begins in6 to 12 hours and requires a few days to reach maximum compensation.
When the primary disorder is respiratory acidosis, what is the compensation?
When ↑PCO2 (Resp. Acidosis), the compensation is ↑HCO3- .
When the primary disorder is respiratory alkalosis, what is the compensation?
When ↓PCO2 (Resp. Alkalosis), the compensation is ↓HCO3- .
When the primary disorder is metabolic acidosis, what is the compensation?
When ↓HCO3- (Met. Acidosis), the compensation is ↓PCO2.
When the primary disorder is metabolic alkalosis, what is the compensation?
When ↑HCO3- (Met. Alkalosis), the compensation is ↑PCO2.
A Primary Metabolic disorder is present if ___.
The pH and PCO2 change in the same direction, or
The pH is abnormal but the PCO2 is normal.
The following equations will identify an associated respiratory disorder.
For Metabolic Acidosis: Expected PCO2 = 1.5(HCO3-) +8 (± 2)
For Metabolic Alkalosis: Expected PCO2= 0.7(HCO3-) + 20 (± 1.5)
A primary respiratory disorder is present if ___.
the pH and the PCO2 change in the opposite direction.
The relationship between the change in PCO2 and the change in pH can be used to identify ______.
an associated metabolic disorder or an incomplete compensatory response.
A mixed metabolic-respiratory disorder is present if ____.
the pH is normal and the PCO2 is abnormal.
Anion Gap
Used to assess metabolic acidosis
Unmeasured anions and cations – based on measurable anions and cations
Sodium – Chloride – Bicarbonate
Normal Range 8 - 16
Normal anion gap with metabolic acidosis
8 - 16
Loss of bicarbonate
Diarrhea, isotonic saline infusion, renal tubular acidosis, acetazolamide – Addison’s disease
High Anion Gap Metabolic Acidosis
> 16
Excess acid
Lactic acidosis
Ketoacidosis (diabetic – alcoholic – starvation)
Uremic (ESRD)
Alcohols (ethanol) –salicylate toxicity – CO toxicity
Decreased Anion Gap
Decreased unmeasured anions – albumin
Increased unmeasured cations – calcium – magnesium – lithium
Capnography waveform when ETT placed in esophagus
Capnography waveform when there’s an inadequate seal around the ETT
Capnography waveform for hypoventilation
Capnography for hyperventilation
Capnography for rebreathing
Capnography for obstruction
Capnography for Curare Cleft
Capnography for Faulty Ventilator
Faulty Ventilator circuit valve
- baseline elevated
- allows pt to rebreathe
nmb wearing off aka curae clefts
obstruction in airway / circuit - shark fin
- ett kinked
- foreign body
- bronchospasm
rebreathing
- faulty expiratory valve
- inadequate inspiratory flow
- insufficient expiratory time
- co2 absorber system malfunction
hyperventilation
- increased RR and TV
- decreased temp and metabolic rate
hypoventilation
- deceased RR and TV
- increased temp and metabolic rate
inadequate seal around ETT
esophageal ett
