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Anesthesiology > Respiratory Physiology and Critical Care > Flashcards

Respiratory Physiology and Critical Care Flashcards

1
Q

What is the most common cause of cyanide toxicity? What is the treatment?

A

Cyanide toxicity is often due to smoke inhalation during home or commercial fires.

First-line treatment is with hydroxocobalamin

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1
Q

What is the equation for Pulmonary Vascular Resistance?

A

PVR = (mean PA pressure - wedge pressure) / (cardiac output x 80)

Normal PVR is 50 to 150

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2
Q

Describe functional residual capacity

A

FRC = Expiratory reserve volume + Residual volume

Decreases with pregnancy, ascites, neonates, general anesthesia, obesity, and supine position

Increased with PEEP

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3
Q

During apnea, how fast will PaCO2 rise?

A

6 mm Hg during the first minute and then 3 to 4 mm Hg each minute after

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4
Q

What is the equation for BMI?

A

kg/m^2

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5
Q

Define anatomic dead space, alveolar (functional) dead space, and physiologic dead space

A

Anatomic dead space - volume of gas in the conducting airways of the lungs

Alveolar dead space - volume of gas in ventilated, but not perfumed alveoli

Physiologic dead space - sum of anatomic and alveolar dead space

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6
Q

What is the normal O2 requirement in adults?

A

3 to 4 mL/kg/min

250 mL/min in typical adult

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8
Q

What is the equation for O2 Content?

A

(1.39 x Hgb x Sat) + (0.003 x PaO2)

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9
Q

What is the Bohr dead space equation?

A

Dead space ratio (VD/VT) = (PaCO2 - EtCO2) / PaCO2

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10
Q

What is the mechanism for the compensatory shift of the oxyhemoglobin dissociation curve in response to chronic acid base abnormalities?

A

Altered metabolism of erythrocyte-2,3-DPG

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11
Q

What is the P50 of adult hemoglobin?

A

27 mm Hg

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12
Q

What is mixed venous O2 saturation (SvO2)? What is the equation? What would cause a decreased SvO2? An increased SvO2?

A

Mixed venous oxygen saturation is the percentage of oxygen bound to hemoglobin in the blood that returns to the right side of the heart
- Measured from a pulmonary artery catheter and includes all of the venous blood returning from the SVC, IVC, and coronoary sinus

SvO2 = SaO2 - VO2/(13.9 x CO x Hgb)

SvO2 is decreased by:

  • Increased O2 consumption (hyperthermia, pain)
  • Decreased CO (MI, hypovolemia)
  • Decreased hemoglobin
  • Decreased SaO2

SvO2 is increased by:

  • Increased hemoglobin (transfusion)
  • Increased SaO2
  • Decreased O2 consumption (cyanide, sepsis, CO poisoning)
  • Increased CO (sepsis, L to R shunt)
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12
Q

A change in PCO2 of 10 mm Hg will alter the pH by what amount?

A

~0.1 pH units

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13
Q

What is normal vital capacity in an adult?

A

60 to 70 mL/kg

About 5L in the average adult

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15
Q

How do you calculate the amount of bicarbonate that needs to be given to correct acidosis?

A

Total body weight (kg) x base deficit x 0.2

When administering sodium bicarbonate, 1/2 calculated dose is given and measurements are repeated

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16
Q

What is the magnitude of compensatory reaction to respiratory alkalosis?

A

Maximum decrease in [HCO3-] of 5 mEq/L for 10 mm Hg decrease in PCO2 under 40 mm Hg

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17
Q

What is the P50 of sickle cell hemoglobin?

A

31 mm Hg (decreased affinity for oxygen)

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18
Q

List some conditions that cause a rightward shift of the oxy-hemoglobin dissociation curve

A

Results in decreased affinity, increased unloading of oxygen

Acidosis
Hyperthermia
Increased 2,3-DPG
Pregnancy
Abnormal hemoglobins (sickle, thalassemia)
Volatile anesthetics
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19
Q

List some conditions that cause a leftward shift of the oxy-hemoglobin dissociation curve

A

Results in increased affinity, decreased unloading of oxygen

Alkalosis
Hypothermia
Different hemoglobin species
Decreased 2,3-DPG

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20
Q

List the O2 saturation at specific PaO2 values

A

PaO2 of 27 mm Hg = 50% sat

PaO2 of 40 mm Hg = 75% sat

PaO2 of 60 mm Hg = 90% sat

PaO2 of 100 mm Hg = 98% sat

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21
Q

What is a general estimation of shunt fraction?

A

A-a gradient / 20

21
Q

In a healthy, resting adult, what % of total body O2 consumption is due to the work of breathing?

A

1 to 3%

22
Q

Describe Ventilation/Perfusion ratios in the lungs

A

Because alveoli in the dependent portion of the lungs are more compliant than alveoli in the non-dependent lung, alveolar ventilation increases from top to bottom. Pulmonary blood flow also increases from top to bottom, but more so than alveolar ventilation,

Ultimately, ventilation/perfusion ratios are higher in the non-dependent areas of the lung and low in the dependent areas of the lung.

Thus, PaO2 and pH are higher in the apex and PCO2 is higher at the base

23
Q

How much anatomic dead space does an average adult have?

A

2 mL/kg

In an average adult, dead space is 150 mL

24
Q

A change of 10 mm Hg of PCO2 results in what magnitude of change in plasma [K+]?

A

0.5 mEq/L in the same direction

25
Q

A change in [HCO3-] of 10 mEq/L will alter the pH by what amount?

A

0.15 pH units

27
Q

Describe the negative effects of acidosis

A

CNS depression

Increased ICP

Cardiovascular depression

Cardiac dysrhytmias

Vasodilation

Hypovolemia

Pulmonary HTN

Hyperkalemia

28
Q

Describe Organophosphate poisoning

A

Organophosphates bind with acetylcholinesterase and produce signs of excess parasympathetic activity:

  • Diarrhea
  • Urination
  • Miosis (pinpoint)
  • Bronchocontriction
  • Emesis
  • Lacrimation
  • Salivation

Treatment is with atropine and pralidoxime

28
Q

How does recombinant human activated protein C (Xigris) work? What is it used for?

A

APC is indicated for the treatment of septic shock

It works via inhibition of factors Va and VIIIa, reducing inflammation and microthrombi. It also blocks production of TNF.

Major side effect is hemorrhage.

29
Q

Describe transfusion related lung injury (TRALI)

A

A serious potential complication of transfusing any product containing plasma, usually diagnosed 1 to 2 hours later
- leading cause of transfusion-related mortality

Key features:
Wide A-a gradient
Non-cardiogenic pulmonary edema
Leukopenia (2/2 lung sequestration)
Fever
Hypotension
30
Q

Describe the difference between dead space and shunt

A

Dead space - ventilation without perfusion
Leads to elevated PCO2

Shunt - perfusion without ventilation
Leads to decreased PO2 and widened A-a gradient

31
Q

What are some causes of dead space?

A 
PE
COPD
ARDS
Fibrosis
Shock
32
Q

Define closing capacity

A

= closing volume + residual volume

The volume at which small airways begin to close

Increases with age, bronchitis, LV failure, surgery, and smoking

At 44 y/o, CC = FRC when supine
At 66 y/o, CC = FRC when standing

33
Q

Describe Flow-Volume Loops

A

Expiratory above, Inspiratory below
TLC to RV (left to right)

Fixed lesions: reduction in both inspiratory and expiratory components

Extrathoracic lesions: reduce inspiratory component

Intrathoracic lesions: reduce expiratory component

34
Q

List the lung volumes and capacities

A

Tidal volume (TV) - volume of air inhaled/exhaled during normal breathing

Inspiratory reserve volume (IRV) - maximum volume of gas that can be inhaled after normal inspiration

Expiratory reserve volume (ERV) - maximum volume of gas that can be exhaled after normal expiration

Residual volume (RV) - volume of gas remaining in lungs after a forced exhalation

Vital capacity (VC) = IRV + TV + ERV - maximum volume of gas that can be exhaled after maximum inhalation

Inspiratory capacity (IC) = IRV + TV - maximum amount of gas that can be inhaled after normal expiration

Functional residual volume (FRC) = ERV + RV - remaining lung volume at the end of normal expiration

Total lung capacity (TLC) = IRV + TV + ERV + RV - lung volume after maximum inspiration

35
Q

How much deoxyhemoglobin is required to appear cyanotic?

A

At least 5g deoxyhemoglobin

36
Q

How does carbon monoxide exert its toxic effects? What are the symptoms? What will an ABG look like? What is the treatment?

A

Carbon monoxide effects:

  • Impaired mitochondrial oxidative phosphorylation
  • Impaired muscle oxygen utilization from impaired myoglobin function
  • Functional anemia and leftward shift of oxygen-Hb curve
  • Vasodilation 2/2 release of NO

Initial symptoms include headache, nausea, dizziness, and vomiting
- Cyanosis is NOT common

An ABG will show a metabolic acidosis with a normal PaO2 and a falsely elevated calculated SaO2 and measured SpO2
- PaO2 is not reliable in setting of carboxyhemoglobinemia since it is only a measure of dissolved oxygen and not bound oxygen

Treatment is O2
- Hyperbaric O2 only indicated for coma, cardiac ischemia, or levels over 40%

37
Q

What is Diffusing Capacity of the Lungs (DLCO)?

A

A measure of the gas exchange capacity of the lungs

Influenced by the volume of blood in the pulmonary circulation

Decreased by:

  • Anemia
  • Hypovolemia
  • Emphysema
  • Pulmonary HTN
  • Pulmonary edema
  • Cystic fibrosis

Increased by:

  • Supine position
  • Exercise
  • Obesity
  • Left to right shunt
  • Polycythemia
  • Asthma
38
Q

How will an air bubble effect an ABG?

A

It will result in elevated PO2 and decreased PCO2

39
Q

What is the equation for the A-a Gradient?

A

A-a gradient = PAO2 - PaO2
PAO2 = FiO2(713) - PaCO2/0.8

Normal A-a gradient = age/4 + 4

40
Q

How is ARDS diagnosed?What is the treatment?

A

Characterized by acute onset, bilateral infiltrates on chest X-ray, and hypoxemia (PaO2/FIO2 ratio less than 300)

Treatment is mainly supportive, while underlying cause is identified:

  • Intubation and ventilation
  • Low tidal volumes (permissive hypercapnia)
  • Low PIP
  • High FiO2
  • High PEEP

Conservative fluid management is advised

Long-term antibiotics are NOT recommended

41
Q

What are some causes of elevated peak pressure? What about plateau pressure?

A

Elevated peak pressures is indicative of high airway resistance:

  • Bronchospasm
  • Kinked ET tube
  • Mucus plug
  • Foreign body

Elevated plateau pressure is indicative of an issue with system compliance:

  • Poor positioning
  • Pulmonary fibrosis
  • Pneumothorax
  • Obesity
  • Insufflation
42
Q

What will the pulse oximetry be in a patient with methemoglobinemia? How is the PaO2 affected? What is the treatment?

A

Pulse oximetry will read ~85% regardless of true oxygen saturation
- need co-oximetry for proper analysis

PaO2 will be normal or unchanged

Treatment is with methylene blue
- Patients with G6PD can be treated with ascorbic acid

43
Q

What is the equation for oxygen delivery (DO2)?

A

= CO x CaO2

= [HR x SV] x [(SaO2)(Hgb x 1.34) + (0.003 x PaO2)]

44
Q

How does positive pressure ventilation cause oliguria?

A

Decreased preload 2/2 increased intrathoracic pressure

  • decreased venous return
  • increased CVP
  • increased release of ADH from posterior pituitary

Increased sympathetic nervous system stimulation
- activation of renin-angiotensin system

Release of inflammatory cytokines

46
Q

How can antibiotics used to treat sepsis potentially worsen hypotension?

A

If sepsis is due to gram-negative bacteria, antibiotics may lead to cell wall lysis and release of lipopolysacharide (LPS)

LPS induces immune response, release of cytokines, and production of NO, leading to vasodilation

47
Q

What is refeeding syndrome? What is the mechanism behind it? What are the manifestations?

A

Hypophosphatemia seen during refeeding in alcoholic, malnourished, or debilitated patients

Caused by glucose loading
- increased secretion of insulin leads to cellular uptake of glucose and phosphate

Can result in AMS, hemolytic anemia, and arrythmias
- can be a cause of failed weaning from ventilator

48
Q

What drug can be given to intubated patients to reduce the incidence of ventilator associated pneumonia

A

Sucralfate

H2-blockers or PPIs can actually increase the risk as they reduce gastric acidity, thus increasing bacterial growth

49
Q

What is the RSBI? How is it used?

A

The Rapid Shallow Breathing Index is a test used in the weaning of mechanical ventilation in ICUs

RSBI = (respiratory frequency)/(tidal volume)

An RSBI less than 65 is considered an indication of weaning readiness

50
Q

What is respiratory quotient? How does diet affect it?

A

RQ is the amount of CO2 produced per unit of oxygen consumed from specific energy substrates

Carbohydrates have a Q of 1
Proteins have a Q of 0.8
Lipids have a Q of 0.7

51
Q

Percutaneous tracheostomy has many advantages over the open approach. However, what are the absolute contraindications of the percutaneous approach?

A
  • Active infection at the site of trach
  • Uncontrolled bleeding disorder
  • Unstable cardiopulmonary status
  • Patient unable to stay still
  • Abnormal tracheolaryngeal anatomy

Anesthesiology (12 decks)

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