RS Flashcards
How many total lobes, segments and sub-segments in lungs? Why you care?
5 lobes (3 Rt, 2Lt)
19 segments (10 Rt, 9 Lt)
42 sub-segments (22 Rt, 20 Lt)
Important for estimating postop predictive FEV1
FRC is sum of …? And normal number is?
ERV + RV
40 mL/kg
VC is sum of ? And normal number is …?
ERV + TV + IRV
70 mL/kg
TLC is sum of … and normal number is …
RV + ERV + TV + IRV
90 mL/kg
Conditions that decreases FRC?
PANGOS
Pregnancy Ascites Neonates GA Obesity Supine
Why Inhalational induction results into rapid induction
Due to decrease FRC secondary to decrease in RV
What is closing capacity and factors that increases it?
A dynamic volume where airway closure occurs and result into shunting. Prohibition of distal to closure from participating in ventilation.
If closing capacity > FRC then shunting occurs with tV breathing (bad)
Smoking, age, surgery
Surfactant benefits
Increases pulmonary compliance Prevent collapse at end of expiration Keep alveoli dry Regulates alveoli size Play role in host defense
Laplace law describes
How distending pressure of liquid bubble is influenced by
1) surface tension (proportional)
2) size/radius of bubble (inverse)
Surfactant aids in counteracting Laplace law to keep small alveoli open
Poiseuille’s law describes
Flow propositional to Pressure and Radius (to the fourth)
Inversely propositional to length and viscosity
Describes the charstistics of flow in tube (airway resistance)
Turbulent flow created with
High flow rate & pressure gradient
Flow volume loops for intrathoracic vs extrathoracic vs fixed lesions
Blunting of exhalation-> mediastinal mass
Blunting inhalation-> extrathoracic
Blunting of both -> tracheal stenosis
Flow Volume Loops
- Exhalation above X-axis, inhalation below X-axis
- Extrathoracic lesion blunts inspiratory limb • Intrathoracic lesion blunts expiratory limb
- Fixed lesion blunts both inspiratory and expiratory limbs
V/Q matching equation
Vd/Vt = (PaCO2-PEtCO2)/PaCO2
• Normal Vd/Vt <0.3
example: if ptn has HR 70 with SV 70 and TV 500, RR 12, and dead space 100?
The V/Q ratio can be quantified for the entire lung by taking into consideration the patient’s alveolar ventilation and the cardiac output. The alveolar ventilation is calculated by subtracting the estimated dead space from the estimated tidal volume. In this instance, the alveolar ventilation is 400ml (500ml-100ml). The difference is then multiplied by the breathing rate which is 4800 ml (4.8 L) The cardiac output is calculated by multiplying the stroke volume by the heart rate. In this instance, the cardiac output is 70 ml X 70 beats/minute which is 4.9. Therefore, the V/Q ratio is therefore: 4.8/4.9 = 0.97.
Dead Space Ventilation
Gas that does not reach alveoli/not effective
- Ventilation without perfusion – Anatomic dead space • Conducting airways: nose, mouth, trachea – Alveolar dead space • Ventilated but not perfused alveoli (PE) – Physiologic dead space • Anatomic + alveolar
- Normal 0.2 to 0.4 L
V/Q Matching under GA due to
• Expanded A-a gradient under GA – Cardiac output is decreased – Airway resistance is increased – Chest wall compliance is decreased – Neuromuscular blockade results in an alteration of V/Q matching in West zone 3, shifting ventilation preferentially to West zone 1 (dead space ventilation) – FRC is decreased
V/Q matching differences from apex to base of lung
• Perfusion increases with as one goes “down” the lung • Ventilation also increases as one goes “down” the lung • Rate of increase of perfusion»_space;> ventilation resulting in relative shunt in dependent areas of lung
What are the five causes of hypoxemia? which ones demonstrate a normal A-a gradient?
– Hypoventilation – Low FiO2 – Diffusion limitation – Shunt – Ventilation-perfusion mismatch
Hypoventilation and Low FiO2
Widened A-a Gradient
• Shunt is the most common cause of a widened A-a gradient – PAO2= FiO2(Pbar-PH2O)-(PaCO2)/0.8
On room air, the normal gradient is 5 to 10 mmHg
• On 100% FiO2, the gradient may increase to 30 mmHg
– If shunt is only 10% to 20%, increasing FiO2 will help increase PaO2, once shunt hits 30%, increasing FiO2 is ineffective
dead space vs shunt vs HPV
Hallmark of dead space ventilation is PE • Hallmark of shunt is OLV • Hypoxic Pulmonary Vasoconstriction can reduce blood flow to poorly ventilated regions
PFT in obstructive vs restrictive
Of the pulmonary function tests given, a decreased total lung capacity would be most likely in a patient with restrictive lung disease. Increased FRC and FVC would be seen in a patient with obstructive lung disease. Decreased FEV1/FVC is also consistent with a patient with obstructive lung disease. Increased DLCO can be seen with exercise, supine position, and increased alveolar PCO2.
Cormack- Lehane grading system for laryngoscopic view.
grade 1 view is visualization of the entire laryngeal aperture.
grade 2a view gives only a partial view of the glottis.
grade 2b view, only the posterior extremity of glottis is seen or only arytenoid cartilages.
grade 3 view is visualization of only the epiglottis and none of the glottis.
A grade 4 view is no visualization of the epiglottis or larynx. The difficulty of intubation increases as the numbers increase, with a grade 3 or 4 view indicating difficult intubation.
The equation for shunt fraction is
(CCO2-CaO2)/(CCO2-CvO2).
CCO2 refers to pulmonary capillary content of O2. The equation for arterial O2 content is as follows: CaO2 = (1.34 x HgB x Sat) + (0.003 x PaO2)
oxyHb dissociation curve facts
- CaO2 = (1.34 x HgB x Sat) + (0.003 x PaO2)
- 90% sat = PaO2 of 60 mmHg • P50 of the adult (nonpregnant) = 27 mmHg
- P50 of the infant = 19 mmHg
- P50 of term pregnant = 30 mmHg
- Pre-eclampsia results in L shift of cur
OxyHb dissociation curve rt vs left?
- Increased temperature, decreased pH, increased 2,3-DPG, and increased PaCO2 cause rightward shift of curve – Release O2 more easily
- Decreased temperature, increased pH, decreased 2,3-DPG, and decreased PaCO2 AND hemoglobinopathies cause leftward shift of curve – Hold O2 more avidly
CO2 Response Curve
- Peripheral and central response to changing levels of CO2 – N.B. CO2 sensor is the H+ sensor in the medulla, O2 sensor is in the carotid body (and aortic arch)
- Most commonly tested are causes of R shift of the curve – Narcotics – Volatile anesthetics – Metabolic alkalosis
Brainstem Control of Respiration
- Pons – Apneustic center: stimulate apneustic breathing (prolonged inspiration/breath hold) – Pneumotaxic center: receive stretch impulse (cranial nerve [CN] X) from lungs to stop inspiration and initiate exhalation
- Medulla oblongata – Dorsal respiratory groups: basic rhythm of breathing (trigger rate of 12 to 15 breaths per minute [bpm]) – Ventral respiratory groups: inspiratory and expiratory functions. Inactive with normal breathing but sends impulses to muscles of exhalation and accessory muscles of inspiration with exercise
Chemoreceptor Influence on Respiration
- Carotid bodies (via CN IX) have primarily ventilatory effects – As opposed to aortic bodies [via CN X], which have primarily circulatory effect
- Located at carotid bifurcation
- Threshold for increased ventilation is PaO2 of 60 to 65 mmHg (rate and volume)
- Inhibition by volatile anesthetics
Brainstem controls rhythm of breathing • Sensor in medulla assesses pH of CSF to increase respiratory rate (RR) during acidosis • Carotid body (CN IX) increases RR based on low PaO2
Key
Carboxyhemoglobinemia
CO binds to Hb with an affinity 210 times that of O2 and prevents O2 transport
• Headache, dizzy, N/V, “cherry red skin” = COHb >40%
• Monday morning carbon monoxide exposure
– Desiccated CO2 absorbent
– Baralyme use
– High volatile concentration
– High temperatures
– Desflurane»»>Sevoflurane
Airway Nerve Injury
• Unilateral RLN Injury
– Normal cord can compensate
– No stridor
– Affected cord typically paramedian
• Bilateral RLN Injury
– Total Thyroidectomy – Stridor
– Both cords paramedian
• Bilateral RLN/SLN Injury
– Cords flaccid and motionless
– Aphonia and high risk for aspiration
Narrowest point of airway
peds ->
Adults ->
Sub-glotticregion
At level of vocal cord
Agents affects asthmatic patients
Propofol reduces airway resistance
– Ketamine with smooth muscle relaxation
– Sevoflurane known to cause bronchodilation
Worsens asthma:
– Morphine gives histamine release
– NMB: mivacurium associated with histamine release
-BBs
Calculating dead space
The fraction of tidal volume that is delivered to all dead spaces can be calculated using the Bohr equation.
VD/VT = (PaCO2 - PCO2) / PaCO2.
What other tricks to do beside preoxygenation to prevent desaturation upon induction
In addition, to preoxygenation as described, other measures that can sometimes delay this expected desaturation, permitting more time for intubation, include reverse Trendelenberg positioning, to move abdominal contents away from the diaphragm. Application of CPAP during preoxygenation may have some positive effects on the rate of post-induction desaturation as well. The Emergency Room doctors may be on to something here - they routinely keep nasal oxygen going during intubation so the patient at least gets a little apneic oxygenation during our intubation efforts. Alternatively (this is a GREAT trick), you can hold a #2 mask (peds mask) over the nose with a black face strap with CPAP on. This will prevent the very desaturation that occurred in this case. Try it, it really works!
DLCO increases in …
Increased DLCO can be seen with exercise, supine position, and increased alveolar PCO2.
Decreased DLCO is seen with alveolar fibrosis and decreased hemoglobin concentration.
Widened QRS with a fusion of QRS-T and loss of ST segments
B. ST depression and flattening of T waves and a possible U-wave
C. Shortening of the QT interval with possible Osborn (J) waves
D. Increased PR and QTc, and a prolonged QRS
This case is describing a patient with severe (>12 mg/dL) hypercalcemia secondary to malignancy. The most common finding on an ECG associated with hypercalcemia is the shortening of the QT interval primarily secondary to a decrease in phase 2 of the ventricular action potential and a resultant decrease in the ST segment duration. Other findings may include Osborn waves and ventricular irritability leading to VF arrest. As such, option C is the correct choice.
Option A is listing the typical findings for a patient with hyperkalemia.
Option B, ST depression with possible U-waves is most commonly associated with hypokalemia.
Finally, Option D, increased PR and QTc, are the ECG findings of hypermagnesemia.
If Hgb is 10 and on 100 O2, what’s the oxygen carrying capacity of
The oxygen carrying capacity of blood is 13.4 ml/dl. The amount of oxygen that binds to hemoglobin is referred to as the oxygen carrying capacity of the blood. 1g of hemoglobin can be bound by 1.39 ml O2. The amount of oxygen bound to hemoglobin can be calculated as follows: 1.34 X Hb X SpO2. Therefore, 1.34 X 10 X100/100 = 13.4 ml oxygen/dl.
What’s the compression volume for patient with Tv 750, RR 10 and measured MV 6L with peak of 30
The correct compression factor is 5 ml/ (cmH2O).
The following formula is used to calculate the compression volume from which a compression factor for a ventilator delivery system can be calculated: Compression Volume = (V delivered - measured)/ Respiratory rate)/ Peak Airway Pressure (cm H2O).
In this instance, the ventilator is set to deliver a volume of 750 ml/l at a rate of 10 breaths per minute meaning that each minute 7.5 L is delivered.
The measured minute volume of the ventilator is 6 L hence leaving a residual 1.5 L that must be absorbed into the breathing system at a 10/minute rate. This value is known as the compression volume. To obtain a compression factor the compression volume is divided by the peak airway pressure which is 30 cm H2O in this case. Hence giving a compression factor of 5 ml /(cmH2O).
Conditions cause right shift curve of CO2 response
Fentanyl, sleep, and hyperthermia all cause a rightward shift of the CO2 response curve. Doxapram stimulates respiration by its action on peripheral carotid chemoreceptors (leftward shift of the curve)
PFT results in scoliosis
silicosis will cause a restrictive pattern on pulmonary function tests (PFTs) with a decrease in FEV1, a decrease in FVC, a decrease in DLCO.
Expected lung volumes in COPD
Total lung capacity (TLC) increases in COPD patients, but a large contribution is made by increased residual volume (RV).
Vital capacity (VC) is largely unchanged.
DLCO is reduced with COPD.
Management of CF intraoperative
Use inhaled anesthetic and hemodification of gas to make their secretions less viscous and volatiles decreases airway reactivity
Also hydrate them & Avoid anticholenergics.
They produce dehydrated thick and viscous secreations that might obstruct airways.
Intubation grades
- Grade 1: entire larynx
- Grade 2a: partial view of Glottis
- Grade 2b: only posterior glottis or arytenoids
- Grade 3:only epiglottis, none of glottis
- Grade 4: no epiglottis
Shunt equation
The equation for shunt fraction is as follows:
(CCO2-CaO2)/(CCO2-CvO2).
CCO2 refers to pulmonary capillary content of O2.
The equation for arterial O2 content is as follows:
CaO2 = (1.34 x HgB x Sat) + (0.003 x PaO2).
Ventilation in humans is controlled primarily via which mechanism?
A. Arterial partial pressure of carbon dioxide by chemoreceptors on the carotid bodies
B. Arterial partial pressure of carbon dioxide by central chemoreceptors on the medulla oblongata
C. Arterial partial pressure of oxygen by central chemoreceptors on the pons of the brainstem
D. Arterial partial pressure of carbon dioxide by central chemoreceptors on the hypothalamus
Answer B is correct because ventilation of the lungs in humans is regulated by the respiratory centers when chemoreceptors on the anterior surface of the medulla oblongata detect changes in the partial pressure of carbon dioxide.
Answer A is incorrect because the carotid bodies are the peripheral blood gas chemoreceptors which are sensitive to the arterial partial pressure of oxygen primarily thought they may respond weakly to the partial pressure of carbon dioxide.
Answer C is incorrect because the pons has blood gas chemoreceptors which respond to the arterial partial pressure of carbon dioxide, not the arterial partial pressure of oxygen.
Answer D is incorrect because there are no chemoreceptors on the hypothalamus which respond to alteration in either oxygen or carbon dioxide partial pressures. The hypothalamus does not directly control ventilation.
