Acute Respiratory Failure Flashcards
Acute Respiratory Failure & types
syndrome in which either oxygenation or CO2 elimination fail
Type I: acute HYPOXEMIC RF (MC)
-pt can’t properly oxygenate blood
-PaO2 <60; PaCO2 is not elevated
Type II: acute HYPERCAPNIC RF
-pt has difficulty in removing CO2 from blood
-PaCO2 >45 (pH often acidic)
*can occur w/ OSA, COPD, asthma (obstructive lung dz)
Pathogenesis of hypoxemic RF
V/Q mismatch is MC cause:
-usu d/t atelectasis
-pneumonia, pneumothorax, PE
Pathogenesis of hypercapnic RF
-inability to move air in & out of lungs d/t shallow breathing or low RR
-stroke, ALC, spine injury, chest wall d/o, OD
Hypoxemia: S/S
-dyspnea
-drowsiness
-confusion
-cyanosis
Results of hypoxia on CNS: HA, somnolence, confusion, convulsions; permanent encephalopathy if severe hypoxia (aka anoxic insult)
Results of hypoxia on CV: (if mild) tachycardia & HTN as body tries to push O2 to organs; (if severe) bradycardia, hypotension - signs of shock
Hypercapnic: S/S
-same as hypoxemia (dyspnea, drowsy, confusion, cyanosis)
-acute elevation of CO2 –> confusion, HA, convulsions, coma, coarse tremor, coarse tremor, agitation, slurred speech, asterixis (activated muscles suddenly relax), papilledema
ARF workup (dx tests)
-take a good H&P
-assess for multiple etiologies
-CXR
-SpO2 (fast but not always reliable)
-EKG
-Bronchoscopy
-ECHO (if cardiac cause suspected, like cardiogenic pulmonary edema)
*remember ARF is failure to oxygenate, ventilate, or both
ARF workup (labs)
-ABG to assess for hypoxemia, hypercapnia, or both
-CBC (anemia can contribute to tissue hypoxia; polycythemia indicates chronic hypoxia)
-sputum, blood, urine culture
-blood electrolytes (K, Mg, Ph abnormalities can compound RF)
-thyroid panel (hyperthyroidism is a reversible cause of RF)
ARF: Possible findings on CXR
CXR often reveals the cause: pneumonia, cardiogenic pulm edema, ARDS, atelectasis
A clear CXR in pt w/ ARF may indicate: acute COPD, acute asthma, PE, NM dysfunction
*white, hazy appearance indicates fluid or infection
*normal lung should be black on XR
If there’s any suspicion of a PE what dx test should you order?
CTA of the chest
Bicarbonate Buffer System
CO2 + H2O <-> H2CO3 <-> HCO3- + H+
increase CO2 -> decreased pH (opposite direction)
increase HCO3- -> increased pH (same direction)
What is normal FIO2 and SpO2
Normal FIO2 (fraction of inspired O2 = [O2] in air): 21%
*room air = 21% O2 + 78% N + small amt of CO2, Ne, & H
*FIO2 tells us how much supplemental O2 the pt needs
Normal SpO2: >90%
What do you need to document to dx ARF w/ hypoxia
document “dyspnea”
“Rule of 4s” equation used to calculate FIO2
(Liters of O2 x 4) + 21% = FIO2
ex. (4 x 4) + 21 = 37%
Tx for hypoxic pt: non-rebreather mask vs. oxygen blender system
Non-rebreather mask: corrects hypoxia in pt who IS breathing
Oxygen blender system: medical device which mixes medical grade oxygen and medical air in a variable ratio (dial to calculated FIO2)
PaO2/FIO2 ratio
-used as a guide to see if there is sig RF or ARDS developing
(pt can be in RF and have a normal ABG)
400+ normal
<400 hypoxemia
<300 RF
<250 severe RF
<200 critical RF
**look at slide
Indications for mechanical ventilation
-failure of supplemental oxygen to increase PaO2
-apnea w/ respiratory arrest
-RR >30
-disturbed consciousness/coma
-hemodynamic instability
-hypercapnia w/ arterial pH <7.25
-ARDS
Management of ARF
- Ensure airway patency (intubate & mech vent if needed)
- Restore PaO2 (50-70mmHg but aim for 80mmHg; SpO2 90-93%) (may increase FIO2 to accomplish this)
*remember ABCs (airway, breathing, circulation)
Indications for Non-invasive Ventilation
-acute exacerbation of COPD***
-cardiogenic pulm edema
-post-extubation RF
-OSA & NM d/o
Non-Invasive Ventilation: BiPAP
BiPAP (Bilevel Positive Airway Pressure) helps w/ oxygenation and ventilation (different pressures for inhale & exhale)
*CPAP only helps w/ oxygenation (Continuous Positive Airway Pressure = same pressure on inhale & exhale)
when to consider intubation/invasive ventilation
-ARF
-inadequate oxygenation or ventilation
-airway protection/decreased mental status
-unconscious pts
-requiring surgery
-need for short term hyperventilation to manage increased intracranial pressure
Ventilator modes: 2 main ways to ventilate
- Volume mode: set tidal volume w/ variable peak inspiratory pressure (monitor P)
- Pressure mode: set peak inspiratory pressure w/ variable tidal volume which depends on compliance
Normal ventilation vs Ventilator
Normal ventilation:
-extra effort not applied
-NEGATIVE pressure
Ventilator:
-vol/breath
-POSITIVE pressure
-6-8 ml/kg target
-may affect PCO2 and O2
PEEP
(Positive End Expiratory Pressure)
-SUPPORTS OXYGENATION
-pressure left at end of exhalation
-reflects FRC
-maintains airway pressure above atmospheric pressure
-keeps alveoli open for gas exchange
-start at 5-10 cm H2O
Managing FIO2
-titrate to keep FIO2 >90% or >88% if COPD
-once >60%, will need to increase PEEP if still hypoxemic
