S8C65 - Respiratory Distress

Question 1

Life-threatening causes of dyspnea

Answer 1

• obstruction/FB/angioedema/hemorrhage
• Tension pneumothorax
• pulmonary embolism
• neuromuscular weakness: myasthenia gravis, GBS, botulism
• fat emobolism

Question 2

Targets for treatment of dyspnea

Answer 2

• PaO2 >60mmHg

- SaO2 >90 %

Question 3

Hypoxemia

Answer 3

PaO2

Question 4

Formula to determine PAO2 on room air at sea level

Answer 4

PAO2 = 0.21 x (760-47) - PaCO2/0.8

Question 5

Formula for determining A-a gradient on room air at sea level

Answer 5

P(A-a)O2 = 149 - PaCO2/0.8 - PaO2

simplified: P(A-a)O2 = 145 - PaCO2 - PaO2

Question 6

Hypoxemia: hypoventilation

Answer 6

• increased PaCO2

- normal A-a O2 gradient

Question 7

Hypoxemia: R to L shunt

Answer 7

• occurs when blood enters systemic arteries w/o passing through ventilated lung
• causes: pulmonary consolidation, pulmonary atelectasis, vascular malformations
• normally: coronary veins and bronchial arteries are a normal R-L shunt
• causes increase in A-a O2 gradient
• does not increase PaCO2 (may be low)
• dx: failure of improvement in arterial O2 levels with application of supplemental oxygen

Question 8

Hypoxemia: V/Q mismatch

Answer 8

• causes: PE, PNA, asthma, COPD, extrinsic vascular compression
• increased A-a O2 gradient
• hypoxemia improves with supplemental O2

Question 9

Hypoxemia: diffusion impairment

Answer 9

• A-a O2 gradient is increased

- hypoxemia improves with supplemental O2

Question 10

Hypoxemia: low inspired O2

Answer 10

• causes: altitude, non-obstructive asphyxia
• A-a O2 gradient is normal
• improves with supplemental O2

Question 11

Hypercapnea

Answer 11

• PaCO2 >45 mmHg
• a result of alveolar hypoventilation
• never results from increased CO2 production, strictly a lung ventilation problem

DDx:

• depressed central drive: brainstem lesion, drugs (opioids, sedatives, anesthetic), tetanus
• thoracic d/o: kyphoscoliosis, morbid obesity
• neuromuscular impairment: MG, GBS, botulism, organophosphates
• lung dz with incr dead space: COPD
• upper airway obstruction

-decreased RR, decr tital volume, incr dead space

Question 12

Hypercapnea and bicarbonate

Answer 12

• acutely, bicarb witll increase by 1mEq/L for each increase of 10mmHg in PaCO2 1:10
• chronic hypercapnea, HCO3 increases by 3.5mEq/L for each rise of 10mmHg in PaCO2 3.5:10

Question 13

Wheeze: DDx

Answer 13

• upper airway: (more likely stridor but may have element of wheeze) angdioedema, FB, infxn
• lower airway: asthma, bronchiolitis, COPD, FB
• cardiovascular: cardiogenic pulmonary edema (cardiac asthma), ARDS, PE
• psychogenic

Question 14

Bedside assessment of Airflow obstruction:

Answer 14

PEF

Question 15

FEV1

Answer 15

> 80 is normal
50-80 is mid airflow obstruction
25-50% is moderate

Question 16

Cough

Answer 16

Acute cough = 8w

upper airway cough syndrome = PND

Question 17

Bronchitis

Answer 17

-usually a productive cough

pna is often non-productive

Question 18

Cough DDx

Answer 18

Acute: URTI, LRTI (bronchitis/PNA), allergic rxn, asthma, irritants, FB, transient airway hyperresponsiveness

Chronic: smoking, chronic bronchitis, postnasal d/c, asthma, GERD, ACEi, ARB, pertussis, post-infectious

Other chronic dx: CHF, bronchiectasis, lung Ca, emphysema, occupational irritants, recurrent aspn, chronic FB, pyschiatric, CF, insterstitial lung dz

Question 19

Subacute cough

Answer 19

• postiinfectious cough is most likely

- postviral airway inflm with bronchial hyperresponsiveness, mucus hypersecretion, PND, asthma

Question 20

Antitussives

Answer 20

• no evidence for dextromethorphan or codeine
• opioid antitussives can be use on short-term basis (morphine SR)
• herbal agents: menthol, pepper, mustard, garlic, radish, onions
• for intractable coughing in ED: 1-2% 4cc nebulized lidocaine

Question 21

Pertussis

Answer 21

-macrolide or septra for 7d and those exposed should also be treated

Question 22

Chronic cough algorythm:

Answer 22

1. reduce exposure to irritants, d/c ACEi/ARB/BB
2. treat PND with an antihistamine/decongestant +/- inhaled nasal steroid
3. evaluate and treat for asthma
4. obtain chest and sinus imaging
5. evaluate and treat for GERD
6. refer to specialist, CT of chest, bronchoscopy
   95% of pts will have resolution of their cough with this approach

Question 23

Hiccups

Answer 23

-benign hiccups: due to gastric distension from food, drink, air, EtOH (relaxes relationship b/w inspiration and glottic closure making reflex easier to trigger)

• persistent/intractable hiccups: d/t injury/irritation to a branch of vagus or phrenic nerve
  eg. FB (hair) in ext auditory canal pressing on TM and stimulating vagus nerve branch
• steroids and benzos can also cause hiccups

Question 24

Hiccups: dx

Answer 24

• persistent during sleep? (if yes then organic cause, if no then psychogenic)
• check ext auditory canal
• CXR for pathology

Question 25

Hiccups: DDx

Answer 25

Acute: gastric distention, EtOH, excessive smoking, change in temp, pyschogenic

Chronic/persistent: CNS lesion, vagal/phrenic irritation, metabolic (uremia, hyperglycemia), general anesthesia, surgery (thoracic, abdo, prostate, craniotomy, FB in ear

Question 26

Hiccups: Tx

Answer 26

chlorpromazine
metoclopramide

• should work w/in 30 mins
• other: nifedipine, valproic acid, baclofen

Question 27

Cyanosis: DDx

Answer 27

• central: hypoxemia, V/Q mismatch, R-L shunt, abnormal pigmentation (heavy metals, drugs: phenothiazine, minocycline, amiodarone, chloroquine), hemoglobin abnormalities (methemoglobinemia, sulfhemoglobinemia, carboxyhemoglobinemia)
• peripheral: decr CO, cold extremities, distributive shock, arterial/venous obstruction

Question 28

Cyanosis

Answer 28

• does not necessarily mean low arterial oxygenation, it just means there is a high amount of deoxygentated Hb in the blood
• usually present when deoxygenated HB >5 grams/dL
• methemoglobinemia - will only read 80-85% pulse ox and wont’ change with supplement O2 or with worsening oxygenation, it just stays fixed
• in carboxyhemoglobinemia the pulse ox reads carboxyhemoglobin as oxyhemoglobin
• therefore ABG is imperative for analysis of cyanosis
• if methemo. or carboxyhemo. the PaO2 and calculated O2 sat will be normal however the measured O2 sat will be decreased
• if measured PaO2 normal then think skin pigmentation

Question 29

Pleural Effusion

Answer 29

• either from increased fluid production or interference with fluid absorption
• exudative: d/t pleural dz from inflm or neoplasia, active fluid secretion occurs or leakage with high protein content can occur
• transudative: d/t imbalance b/w hydrostatic (CHF) and oncotic (Nephrotic syndrome) pressures, results in ultrafiltrate with low protein content

Question 30

Transudative pleural effusion : ddx

Answer 30

• heart failure *** most common cause of any pleural Eff.
• cirrhosis
• peritoneal dialysis
• nephrotic syndrome

Question 31

Exudative pleural effusion: ddx

Answer 31

• cancer
• bacteral PNA
• PE
• viral/fungal/mycobacterial/parasitic infxn
• systemic SLE/RA
• uremia/pancreatitis
• postcardaic surgery
• radiotherapy
• drugs: amiodarone
• diuretics or PE can cause transudative or exudative
• diuretics can make a transudative effusion seem like an exudative effusion

Question 32

Pleural Effusion: Dx

Answer 32

• takes 150-200cc to be seen on CXR
• can do a thoracentesis and examine the fluid
• only drain 1-1.5L at a time

Exudative criteria:
-pleural fluid/serum protein ratio >0.5
or pleural fluid/serum LDH ratio >0.6

-other tests: gm stain, culture, cell count, glucose, cytology, pH