S8C65 - Respiratory Distress Flashcards
Life-threatening causes of dyspnea
- obstruction/FB/angioedema/hemorrhage
- Tension pneumothorax
- pulmonary embolism
- neuromuscular weakness: myasthenia gravis, GBS, botulism
- fat emobolism
Targets for treatment of dyspnea
- PaO2 >60mmHg
- SaO2 >90 %
Hypoxemia
PaO2
Formula to determine PAO2 on room air at sea level
PAO2 = 0.21 x (760-47) - PaCO2/0.8
Formula for determining A-a gradient on room air at sea level
P(A-a)O2 = 149 - PaCO2/0.8 - PaO2
simplified: P(A-a)O2 = 145 - PaCO2 - PaO2
Hypoxemia: hypoventilation
- increased PaCO2
- normal A-a O2 gradient
Hypoxemia: R to L shunt
- 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
Hypoxemia: V/Q mismatch
- causes: PE, PNA, asthma, COPD, extrinsic vascular compression
- increased A-a O2 gradient
- hypoxemia improves with supplemental O2
Hypoxemia: diffusion impairment
- A-a O2 gradient is increased
- hypoxemia improves with supplemental O2
Hypoxemia: low inspired O2
- causes: altitude, non-obstructive asphyxia
- A-a O2 gradient is normal
- improves with supplemental O2
Hypercapnea
- 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
Hypercapnea and bicarbonate
- 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
Wheeze: DDx
- 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
Bedside assessment of Airflow obstruction:
PEF
FEV1
> 80 is normal
50-80 is mid airflow obstruction
25-50% is moderate
Cough
Acute cough = 8w
upper airway cough syndrome = PND
Bronchitis
-usually a productive cough
pna is often non-productive
Cough DDx
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
Subacute cough
- postiinfectious cough is most likely
- postviral airway inflm with bronchial hyperresponsiveness, mucus hypersecretion, PND, asthma
Antitussives
- 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
Pertussis
-macrolide or septra for 7d and those exposed should also be treated
Chronic cough algorythm:
- reduce exposure to irritants, d/c ACEi/ARB/BB
- treat PND with an antihistamine/decongestant +/- inhaled nasal steroid
- evaluate and treat for asthma
- obtain chest and sinus imaging
- evaluate and treat for GERD
- refer to specialist, CT of chest, bronchoscopy
95% of pts will have resolution of their cough with this approach
Hiccups
-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
Hiccups: dx
- persistent during sleep? (if yes then organic cause, if no then psychogenic)
- check ext auditory canal
- CXR for pathology
Hiccups: DDx
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
Hiccups: Tx
chlorpromazine
metoclopramide
- should work w/in 30 mins
- other: nifedipine, valproic acid, baclofen
Cyanosis: DDx
- 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
Cyanosis
- 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
Pleural Effusion
- 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
Transudative pleural effusion : ddx
- heart failure *** most common cause of any pleural Eff.
- cirrhosis
- peritoneal dialysis
- nephrotic syndrome
Exudative pleural effusion: ddx
- 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
Pleural Effusion: Dx
- 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
