Respiratory Flashcards
Where is the anatomical location of the larynx in the adult?
located anterior to 3rd-6th cervical vertebrae
Where is the anatomical location of the larynx?
At birth: level at C3-4
What is the normal A-O extension (Atlanto Occipital)?
normally 35 degrees
Mallampati classification?
Pt sitting, neck extended, mouth opened fully, tongue protruded, no phonation.
MP Class. 1: full view of uvula and tonsillar pillars, soft palate
MP Class. 2: partial view of uvula or uvular base, partial view of tonsils, soft palate
MP Class. 3: soft palate only
MP Class. 4: hard palate only
What is the PUSH acronym?
Referes to mallampati assessment
Pillars and everything
Uvula
Soft palate
Hard palate
Irritation of which nerve stimulates laryngospasm?
Internal branch Superior Laryngeal nerve (CNX) – mucus membrane above the VC’s, glottis – stimulation is laryngospasm
Does the recurrent laryngeal nerve innervate above or below the vocal chords?
The trachea BELOW VC’s
What are the nerves of LarynxSuperior Laryngeal Nerve?
Vagus Nerve (X) Branch
SLN divides into two nerves:
*Internal SLN provides sensation to supraglottic & ventricle compartment, STIMULATION CAUSES LARYNGOSPASM
*External SLN provides motor innervation of cricothyroid muscle
The Nerves of LarynxRecurrent Laryngeal Nerve
Vagus Nerve Branch (CN X):
Left RLN passes @ Aortic Arch
Provides Sensory innervation to infraglottis
Motor innervation to all larynx except cricothyroid muscle
Stimulation causes abduction of VC
Damage to RLN cause VC adduction
What is the tightest part of the airway in children?
The cricoid ring – can use uncuffed tube when intubating kids
Facts about the trachea
Flexible cylindrical tube supported by 20-25 C-shaped cartilages
18-20mm diameter
12.5-18cm length
Extends from C6 to T5
At carina (level T5-7) divides into 2 bronchi @ 25cm from teeth
Where does gas exchange begin to occur?
The respiratory bronchioles
Where is smooth muscle the thickest?
Smooth muscle is thickest in the bronchioles
What nerve transmits motor stimulation to the diaphragm?
The phrenic nerve (C 3,4,5) transmits motor stimulation to the diaphragm
What nerves send motor innervation to the external intercostal muscles?
Intercostal nerves (T 1-11)
Is the act of inhaling positive pressure or negative pressure ventilation?
Negative pressure
Does the diaphragm move up or down with inspiration?
DOWN with inspiration and UP with expiration
Is pleural pressure always negative?
YES
What is perhaps the most important spirometry value?
FRC - it is what is left when the patient goes apneic
What are some things that decrease FRC?
steep trendelenberg, laparoscopic case, obesity
What is normal tidal volume?
6-8 ml/kg. Normal amount of air moved with each breath
What is minute ventilation?
Tidal volume x respiratory volume
What is normal alveolar ventilation?
(tidal volume - dead space) x respiratory rate
Inspiratory reserve volume?
the volume of gas that can be forcefully inhaled after a tidal breath (about 3L)
Expiratory reserve volume
Amount of air that can be forcefully exhaled after tidal breathing (1,100ml)
Residual volume
Volume of gas that remains in the lungs after a complete exhale (1200ml)
Total lung capacity
IRV + TV + ERV + RV (5800ml)
Vital capacity
IRV + TV + ERV (4500ml)
Inspiratory capacity
IRV + TV (3500ml)
Functional residual capacity (FRC)
ERV + RV (2300ml)
Is tidal volume based on actual body weight or ideal?
Ideal. Basing it on actual body weight would result in very large tidal volumes for obese patients
Can spirometry measure residual volume?
Spirometry cannot measure Residual Volume (RV) thus Functional Residual Capacity (FRC) and Total Lung Capacity (TLC) cannot be determined using spirometry alone.
Since RV, FRC, TLC cannot be determined by spirometry, what can determine these?
FRC and TLC can be determined by 1) Helium dilution, 2) Nitrogen washout, or 3) body plethysmography
Flow volume loops
Intrathoracic - blocks exhalation
Extrathoracic - blocks inhalation
What does surfactant do?
Lowers surface tension of alveoli & lung
Increases compliance of lung
Reduces work of breathing
Promotes stability of alveoli
300 million tiny alveoli have tendency to collapse
Surfactant reduces forces causing atelectasis
Assists lung parenchyma ‘interdependant’ support
Prevents transudation of fluid into alveoli
Reduces surface hydrostatic pressure effects
Prevents surface tension forces from drawing fluid into alveoli from capillary
Poiseuille’s Law
R = (8 * L * h) / (p * r4)
R is resistance to flow in a tube
L is length of tube
h is viscosity of the fluid
p = 3.14
r is radius of tube (to 4th power)
**reducing r by 16% will double the R
**reducing r by 50% will increase R 16-fold
Is the pulmonary system low pressure?
Very low pressure, very distensible, acts as a volume capacitor and helps maintain preload/C.O
Pulmonary recruitment and distention
Recruitment: opening of previously closed vessels
Distention: increase in caliber of vessels
These are responsible for the decrease in pulmonary vascular resistance that occurs as vascular pressures are raised
Increased PRESSURE or flow IN THE PULMONARY SYSTEM DECREASES resistance from recruitment and distention…….recruitment most important
The Pulmonary Capillaries
Functional capillary volume
Capillary volume increases by opening closed segments (recruitment)
70 ml (1 ml/kg body weight) normal volume at rest
200 ml at maximal anatomical volume
Zone 1
Not ideal. No blood flow and no gas exchange
PA > Pa > Pv
V/Q > 1
Zone 2
Intermittent exchange
Pa > PA > Pv
V/Q = 1
Zone 3
Ideal
Pa > Pv > PA
Ventilation AND perfusion are highest at the base
V/Q < 1
Factors Affecting Vasomotor Tone - vasoconstrictors
Reduced PAO2
Increased PCO2
Thromboxane A2
α-adrenergic catecholamines
Histamine
Angiotensin
Prostaglandins
Neuropeptides
Leukotrienes
Serotonin
Endothelin
Norepinephrine
Factors Affecting Vasomotor Tone - vasodilators
Increased PAO2
Prostacyclin
Nitric oxide
β-adrenergic catecholamines
Acetylcholine
Bradykinin
Dopamine
Isoproterenol
What is hypoxic pulmonary vasoconstriction?
Alveolar hypoxia produces hypoxic pulmonary vasoconstriction (HPV)
Localized response of pulmonary arterioles
Caused by hypoxia and enhanced by hypercapnia & acidosis
Contraction of smooth muscle in small arterioles in hypoxic region
Opposite reaction than systemic circulation to hypoxia
HPV is an important mechanism of balancing V/Q ratio
Shift of flow to better ventilated pulmonary regions
Results from decreased formation & release of
Nitric Oxide by pulmonary endothelium in hypoxic region
What is oxygen consumption at rest?
250 ml/min
Co2 production at rest?
200
What is normal alveolar Po2 and co2?
Po2: 100 mmHg
Co2: 40 mmHg
Expired air
Combination of dead space & alveolar air
Dead space air is first portion which consists of humidified air
Second portion is mixture of both
Alveolar air is expired at end of exhalation
Fick’s Law
The bigger the area the bigger the gas exchange
Physiologic Shunt - V/Q is below normal
Mucous plug is an example
Shunt = perfusion but no ventilation
Blood is being shunted from pulmonary artery to pulmonary vein without participating in gas exchange
Inadequate ventilation with a fraction of deoxygenated blood passing through capillaries and not becoming oxygenated
Shunted blood is not oxygenated
Physiologic shunt is total amount of shunted blood per minute
The greater physiologic shunt the greater the amount of blood that fails to be oxygenated in lungs
Physiologic Dead Space - V/Q greater than normal
Pulmonary embolus
Dead space = ventilation but no perfusion
Ventilation to alveoli is good but blood flow is low
More available oxygen in alveoli than can be transported away by flowing blood
Physiologic dead space includes:
- Wasted ventilation
- Anatomical dead space
When physiologic dead space is great much of work of breathing is wasted effort because ventilated air does not reach blood
Saturation (Hb) and PaO2
Saturation PO2
100 100+
95 75
90 60
75 40 (mixed venous)
60 30
50 27 (Hb 50 point)
Very rough rule – PaO2: 40,50,60 for Sat.: 70,80,90
Hemoglobin dissociation curve
Right shift - less affinity and releases o2
Left shift - more affinity and holds onto 02
What shift the hemoglobin curve to the right?
Increase co2, increase temperature, increase H+, increase 2,3 DPG, decrease in PH
Right shift = Hb has less affinity for O2, releases O2, saturation will be less for a given PO2
What shift the hemoglobin curve to the left?
Decrease co2, decrease temperature, decrease H+, decrease 2,3 DPG, increase pH
Left shift = Hb has higher affinity for O2, binds O2, saturation will be higher for a given PO2
O2 Content in blood (CaO2)
The sum of O2 carried on Hb and dissolved in plasma
CaO2 = (SO2 * [Hb] * 1.31) + (PO2 * 0.003)
Example: Pt with sat. of 97%, Hb 15, and PO2 200: CaO2 = (0.97 * 15 * 1.31) + (200 * 0.003) CaO2 = (19) + (0.6) ml/dL
DO2 (oxygen delivery) = CaO2 * CO (cardiac output)
How is most co2 transported?
As bicarb
What group is responsible for breathing at rest?
The Dorsal Respiratory Group
The DRG controls inspiration & respiratory rhythm
The DRG extends most of length of medulla with most of DRG neurons contained in Nucleus of the tractus solitarius
Vagal (X) & Glossopharyngeal (IX) nerves deliver sensory information to DRG
Receives peripheral sensory signals for aid in control of respiration
DRG receives signals from three sources:
Peripheral chemoreceptors
Baroreceptors
Lung receptors
Chemo-sensitive Area of Brainstem
Highly sensitive area on the ventral medulla surface = central chemoreceptors
Responsive to changes in blood Pco2 or H ion concentration
Stimulates other portions of the respiratory center
Effects of Blood Carbon Dioxide
Respiratory center activity is increased very strongly by elevations in blood carbon dioxide levels
CO2 has potent direct effect, via [H], on the chemosensitive area
CO2 is highly permeable to blood-brain barrier so blood & brain concentrations are equal
CO2 reacts with H2O to form carbonic acid which dissociates into hydrogen & bicarbonate ions in interstitial fluid of medulla or CSF
The released hydrogen ions in brain stimulate respiratory center activity
*High co2 in the blood means high co2 in the brain…triggers chemosensitive area of brainstem which triggers ventilation
Peripheral Chemoreceptors
Backup stimulation to breath…stimulated by low o2 (hypoxia).. Will see this more with copd’ers because they chronically have high co2 so they ignore it
Chemoreceptors located mostly in carotid & aorta
Special high flow arterial blood supply exposure, stimulated by hypoxemia
Carotid bodies:
-Bifurcations in common carotid
-Afferent nerve fibers pass via CN IX to act on DRG
Aortic bodies:
-Aortic arch
-CN X to DRG
More on chemoreceptors
Stimulation of chemo-receptors is caused by decreased arterial oxygen content
Impulse rate is sensitive to drops in PaO2 from a range of 60 mmHg to 30 mmHg (hypoxia)
This range is when hemoglobin-oxygen saturation decreases rapidly
High risk PFT results
FEV1 < 2L
FEV1/FVC < 0.5
VC < 15cc/Kg in adult & < 10cc/Kg in child
VC < 40 to 50% than predicted
Intubation criteria:
Mechanics: RR>35, VC <15cc/Kg in adult or <10cc/Kg in child, MIF more neg. than -20cmH2O
Oxygenation: PaO2 < 70mmHg on FiO2 of 40%, A-a gradient > 350mmHg on 100% O2
Ventilation: PaCO2 > 55 (except in chronic hypercarbia), Vd/Vt > 0.6 (remember normal dead space is 30%)
Clinical: airway burn, chemical burn, epiglottitis, mental status change, rapidly deteriorating pulmonary status, fatigue, angioedema
Extubation criteria:
VSS, awake & alert, resp. rate < 30
ABG on FiO2 of 40% PaO2 >70 and PaCO2 <55
MIF is more negative than -20cm H2O
Vital capacity (VC) > 15cc/Kg
ABG normal values
pH: 7.35 – 7.45
PCO2: 35 – 45 mmHg
PO2: 75 – 105 mmHg
Bicarbonate: 20 – 26 mmoles/L
Base excess: -3 to +3 mmoles/L
Co2 rule
Rule: an increase of PCO2 by 10 mmHg causes a decrease in pH by 0.08, likewise, a decrease of PCO2 by 10 mmHg will increase pH by 0.08
So an acute increase in CO2 to 60 should cause a drop in pH to 7.24
A-a gradient
A-a gradient – a measure of efficiency of lung
PAO2 = (PB-PH2O)(FiO2) – (PaCO2/0.8)
PAO2 = (760-47)(0.21) – (40/0.8) = 100
PAO2 = (760-47)(0.5) – (40/0.8) = 306
PAO2 = (760-47)(1) – (40/0.8) = 663
Normal A-a = approximately (Age / 3)
A-a gradient is widened during anesthesia and with intrinsic lung Dz: PTX, PE, shunt, V/Q mismatch, diffusion problems
A-a gradient is normal with hypoventilation or low FiO2
Tx is supplemental O2, adjust ventilation, tx atelectasis, add PEEP, tx underlying cause
Bicarb rule
Rule: a decrease in bicarb. by 10 mmoles decreases the pH by 0.15, likewise, an increase in bicarb. By 10 mmoles increases pH by 0.15
A bicarb. of 13 would result in a pH of 7.25
Total body bicarb. deficit = (base deficit * wt in Kg * 0.4), in mEq/L, usually replace ½ of deficit
What is used to calculate base excess
Base excess is calculated directly using PaCO2, pH, and bicarbonate values
Pulse oximetry
Mandatory intraoperative monitor
Oximetry depends upon the observation that oxygenated and deoxygenated hemoglobin differ in their absorption of red and infrared light
Measures a difference between background absorption in diastole and peak absorption during systole, plethysmography displays as a waveform the differences in absorption during arterial pulsation in systole
Involves transillumination of tissue with two frequencies of light (two light-emitting diodes & one light detecting photodiode)
940nm = infrared light, oxyhemoglobin absorbs more of this light, corresponds to 100% saturation
660nm = red light, deoxyhemoglobin absorbs more of this light, corresponds to 50% saturation
Pulse ox and Carboxyhemoglobin (COHb) (carbon monoxide)
from CO poisoning is viewed as oxyhemoglobin by pulse ox. and shows a SpO2 of 100%, this is an overestimation of the true oxygenation, co-oximeter used to distinguish between the two
Pulse ox and Methemoglobin (MetHb)
Fe in Hb is oxidized to +3 form and cannot transport O2, cyanosis seen when 15% of Hb is in methemoglobin form, caused by nitrates, nitrites, sulfonamides, benzocaine (hurricane spray), nitroglycerine (NTG), nitroprusside (SNP), absorbs equally at both wavelengths, 1:1, shows a SpO2 of 85%, Tx’d with low dose methylene blue or ascorbic acid (vit C)
Do Fetal hemoglobin and bilirubin affect pulse oximetry?
No
What is the gold standard for tracheal intubation?
+ EtCO2 is gold standard for tracheal intubation***
Does capnography rapidly detect endobronchial intubation?
*Rapidly and reliably indicates esophageal intubation but does not reliably detect endobronchial intubation
