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
How to determine if the pt is breathing over the vent?
pt RR on the monitor will be higher than the set RR
Pulmonary complications of mechanical ventilation
-endotracheal tube infection (burn/trauma pt at higher risk)
-alveolar overdistention (results in hypotension and barotrauma –> can cause tension pneumothorax)
-atelectasis
what can endotracheal tube infection lead to?
MC cause of endotracheal tube infection (pathogens)?
-can lead to nosocomial pneumonia if aspiration occurs
in the first 48-72h it is typically d/t S. aureus, H. influenzae, or S. pneumoniae
after 72h, typical causes are P. aeruginosa, Acinetobacter, Enterobacter, & still S. aureus
Other complications of mechanical ventilation include
-VTE (prevent w/ Lovenox & intermittent pneumatic compression stockings)
-GI bleeding d/t stress ulcer (prevent w/ H2 receptor antagonist or PPI)
-Pressure ulcers over bony prominences
-NM weakness (critical illness polyneuropathy (CIP) - diffuse, symmetric flaccid weakness)
ARDS
-acute: w/in 7 days
-CXR shows pulmonary infiltrates, capillary endothelial injury alveolar damage
-PaO2/FIO2 <300
-Pulmonary consultation needed
-NM blocker in first 48h improves 98 day survival
-proning pt at least 8h/day shows benefit in 50-70% of pts (ant/post alveoli take turns working)
