Respiratory Flashcards
What three inputs control the respiratory pattern in the conscious patient?
- pH of CSF surrounding medulla/midbrain (CO2 crosses BBB easily)
- PaCO2 level from peripheral chemoreceptors
- PaO2 level from peripheral chemoreceptors
- The cortex has a mild inhibitory influence on the respiratory centres, hence why stroke patients can develop Cheyne-Stokes.
Who have worse outcomes. ARDS patients from a systemic source, or pulmonary source?
If ARDS is the result of pulmonary disease (aspiration, pneumonia), they have worse mortality rates than those who develop ARDS from something like sepsis.
What are the three main physiological consequences of developing ARDS?
- Impaired diffusion/gas exchange
- Decreased lung compliance
- Increased pulmonary artery pressures
What P:F ratios define mild, moderate and severe ARDS?
Mild: 200-300 (27% mortality)
Moderate: 100-200 (32% mortality)
Severe: <100 (45% mortality)
What is the P:F ratio and what is normal?
It’s the patient’s PaO2 divided by the FiO2 they were receiving at the time of the ABG.
N: 400-500
Normally, only a small volume of fluid is allowed into the pulmonary interstitium in order to keep the alveoli dry. The mechanisms that maintain this are:
- Oncotic gradient
- Interstitial lymphatics can return a large volume
- Tight alveolar-epithelial junctions prevent leakage (sigma factor)
List some pro-inflammatory cytokines and their role in ARDS:
TNF-a, IL-1, IL-6, IL-8
They recruit neutrophils to the lungs where they become activated and release toxic mediators (O2 species, proteases) that damage the capillary endothelium and alveolar epithelium. This results in permeability and loss of oncotic gradient. Lymphatics overrun. Surfactant washed out->atelectasis.
Most common causes of ARDS
Sepsis Pneumonia Aspiration Blood transfusions (TRALI) Trauma (lung contusion, fat embolus) Drugs (ASA, cocaine, opioids, TCAs)
Broadly speaking, what is the definition of ARDS?
Bilateral lung infiltrates with hypoxemia despite a PEEP of at least 5 cmH2O, and no other explanation.
What is the A-a gradient?
‘A’ denotes alveolar oxygenation while ‘a’ denote arterial oxygenation (PaO2).
Calculate the PAO2 and get the PaO2 from an ABG.
What does increasing FiO2 do to the A-a gradient.
It increases it.
How does hypoventilation affect oxygenation?
Both PaCO2 and PACO2 build up causing displacement of O2 from the alveoli. O2 can’t diffuse into bloodstream until CO2 is forced out since there isn’t a strong enough concentration gradient for CO2 to dissipate into atmosphere.
What is Winter’s formula?
Expected PaCO2 = (HCO3 x 1.5) + (8 +/-2)
PaCO2 > Cal PCO2 = Superimposed respiratory acidosis
PaCO2 < Cal PCO2 = Superimposed respiratory alkalosis
In the setting of SCI, what vital capacity should you consider intubating?
Anything less than 20cc/kg
Oxygenation requires these three processes:
Concentration gradient
Surface area
Cardiac output
A reduced wall thickness also helps
Does PEEP recruit alveoli?
No, it simply maintains it. A lack of PEEP, however, can collapse the FRC.
Does PFO shunt blood from right to left or left to right? Why?
Mostly, it shunts blood from left to right because the LA has higher pressures than the RA.
In the setting of pulmonary HTN, this process can be reversed.
What is HPVC and what does it lead to?
Hypoxic Pulmonary Vasoconstriction
Leads to pulmonary hypertension
What is the equation to measure compliance?
Delta V divided by Delta P
Think cowgirl. V over P
There are three types of compliance:
Pulmonary (atelectasis)
Thoracic (Burns, MSK)
Extra-thoracic (ACS)
How can you estimate deadspace using an ABG?
A difference greater than 10mm/Hg between the PaCO2 and the EtCO2.
*This could also be seen in low cardiac outputs.
Is peri-bronchial cuffing and air bronchograms found in CXRs a sign of consolidated or atelectic parenchyma?
Consolidated
Early ABx for pneumosepsis:
Remember, Strep-A can cause your pneumoseptic patient to go from 0 to 50mcg/min of levophed in a hurry, but early ABx can improve mortality significantly!
Ceftriaxone
Azithromycin
Piptaz (if they’re sick)
Vancomycin + Miropenim + anti-fungal (if they’re dying in front of you)
When fluid resuscitating sepsis, what indicators can you use to determine adequacy?
- Passive leg raise
- IVC diameter/collapsibility <50%
- Lactate < 4.0?
- Delta P <10%
- Urine output > 80mL/hr
Berlin criteria for ARDS:
- Acute onset (<1wk)
- Bilateral lung opacities on CXR not explained by other pathology
- Decreased P:F ratio, despite at least 5cmH2O PEEP
- Not explained by HF (BNP/ECG) or volume overload
Goals for treating ARDS patients:
Target PaO2 > 80 for flight, > 60 for ground
- Prevent volutrauma (4-8mL/kg with PLATs < 30)
- Prevent cyclic atelectasis (PEEP)
- Prevent O2 toxicity/nitrogen washout (PEEP ladder)
- Prevent biotrauma (ET cuff pressure, suction)
Oxygenation strategies for failing ARDS patients:
- Sedate and paralyze (reduce O2 demand)
- ACV with increased FiO2
- PC with increased PEEP
- Inverse ratio ventilation with increased Ti
- Lung recruitment maneuvers
- Prone ventilation
- Don’t forget suction, ETT placement, PTXs
- V-V ECMO
* Don’t forget to consider a fluid bolus to turn WZ I into WZ II or III.
What are the main causes of ARDS?
Pulmonary: CAP, aspiration
Systemic: Sepsis, trauma, TRALI, pancreatitis
What is the sigma factor?
The sigma factor is what keeps the epithelial junctions together in the face of hydrostatic pressure. An acute reaction to injury is transient loss of sigma factor. This allows fluid and protein to escape into the interstitial space, reversing the oncotic gradient and leading to hypoalbumenia and edema. Most ICU patients are edemous and have an albumin level of approx 20 upon admittance.
Does oxygenation occur during inspiration or exhalation?
Both… Except in COPD/asthma when bronchioles collapse on expiration. Also, this is what contributes to elevated CO2 levels. As this builds up, CO2 displaces O2 from alveoli since it has a higher gradient and oxygenation fails as well.
Treatment for COPD exacerbation:
- Oxygen to target SpO2 to 88-94%
- Bronchodilators (ventolin, atrovent)
- Steroids (prednisone or methylpred)
- Consider ABx
- CPAP (PEEP matching)
- Paralyze and intubate, put in pressure control
- Pop them off the vent in peri-arrest situations to allow long exhale
What is the reasoning as to why asthmatics are so dangerous to intubate?
Asthmatics rely on active exhalation to force air out. If you intubate them, they must rely on passive exhalation which will likely kill them.
*COPDers, on the other hand, have their shitty lung architecture splinted open by PEEP which actually helps them.
Asthma treatment:
- Bronchodilators (salbutamol, atrovent)
- Steroids
- ZEEP to 3cm/H2O
- Ketamine
- MgSO4
- Epinephrine
DDx for peri-arrest COPD/asthmatics:
- DOPE
- Airway obstruction
- Tension PTX
- Hyperinflation
Discuss the hemodynamics of PE…
- Decreased pulm flow = increased RV afterload and decreased LV preload. Cardiac output is reduced.
- Bulging RV distends septum into LV, further worsening CO.
- Less CO + increased RA pressure = bad coronary blood flow gradient. RV becomes hypoxic and stiff. RV contractility worsens.
- Patient tries to compensate with tachycardia.
If PE patients are RV preload dependant, why not bolus them?
- Yes, hypotension will kill PE patients, but increasing RA pressure will only worsen Ohm’s law (coronary gradient).
- Consider Milrinone or vasopressin to improve BP.