Hypoxemia is defined as an SaO2 of less than __% lasting for more than ___ seconds.
What is the only way to precisely control FiO2? (2 things)
- 1. must have a closed system with an airtight seal
- 2. must have separation of inspiration and expiration gasses
What % of patients experience severe hypoxia following surgery? (immediate post op)
Why are patients at risk of desaturating in the immediate post operative period?
(List as many things as you can think of!)
Reduction in FRC=atelectasis increases shunting
Decreased clearance of secretions
Shivering: increases O2 consumption: decreases mixed venous PO2
Inhibition of hypoxic pulmoinary vasoconstriction by anesthetics= V/Q Mismatch
Hypoventilation due to narcotics
Why does FRC fall in the immediate post operative period?
as a result of decreased chest wall recoil (from muscle relaxants and anesthesia)- compounded by use of 100% O2 and absorption atelectasis
What are possible causes of decreased clearance of secretions in the immediate post operative period?
- Decreased mucociliary clearance (ex. airway drying, ETT presence)
By what percentage can shivering increased O2 requirements post operatively?
up to 400%!!! holy smokes!!
How is the hypothalamus affected by general anesthesia? (specifically related to thermoregulation)
Hypothalamus is the thermoregulator of the body, GA affects the hypothalamus which will cause the patient to shiver postoperatively even if they're normothermic
Anesthesia gasses are drying.
Can contribute to cause of decreases clearance of secretions and subsequent desaturation risk in immediate post operative period
If a patient is being mechanically ventilated, and a blood gas shows an increase in CO2, what is your next action?
INCREASE your tidal volume! to INCREASE alveolar ventilation
What are some risk factors that predispose patients to hypoxemia in the early postoperative period?
- preexisting heart disease
- extremes of age
- thoracic and high abdominal surgeries
Why are elderly people at risk for hypoxemia in the early post-operative period?
Because the elderly have an increased closing capacity: their airways are more likely to close
Why are infants at risk for hypoxemia in the early post operative period?
- Infants have a SMALL FRC, so their airways are more prone to closure
- *consider surfactant status in premature infant as well
With a low flow oxygen delivery device, you have control over precise FiO2.
- FiO2 intake depends on entrained room air in balance with tidal volume.
Part inspiration from O2
device, part inspiration from room air
What are some examples of high flow devices?
- specially designed face masks
- oxygen nebulizers
- CPAP devices
Which oxygen delivery device has complete control over FiO2, inspiration, and expiration?
What are some examples of low flow devices?
- Nasal Cannula
- Face Mask
- Face Tent
How many L can be delivered with a nasal cannula?
What % FiO2 can be delivered with a nasal cannula?
- Denise: 25-30%
- Chart in Powerpoint: 24-66% (1-6L)
*all depends on amount of entrained air, a mouth breather will obviously have less than optimal Fi
What happens to the patient mucoa at >4L O2 delivery with a nasal cannula?
It dries out! (mucosal drying)
Benefits of a Nasal Cannula
Disadvantages of a Nasal Cannula
- no discomfort of a mask
- patient can eat with these on
- low maximum inspired concentration of O2
- Unpredictability of O2 concentration
How many L delivered in a simple face mask?
What % FiO2 in simple face mask?
Describe the appearance of a simple face mask.
*holes in the side from which a patient entrains air
Why can a nonrebreather delivery higher amount of FiO2 than a rebreather?
Same mask as a rebreather, but because of higher air flow the patient is breathing in delivery O2
and not rebreathing their own dead space.
What is the FiO2 delivered with a partial rebreather?
How many L can be delivered with a partial rebreather?
What FiO2 does a nonrebreather deliver?
What does a partial rebreathing mask look like?
- Same as nonrebreather.
- *Reservoir bag must be inflated for mask to work appropriately ;)
What L/min can a nonrebreather deliver?
True or False
With a partial rebreather, the patient is partially rebreathing dead space air that is caught in the reservoir bag along with delivery O2.
If you need more precision of O2 delivery than a low flow device is offering, you can use a:
- High flow device!
- mechanical ventilation :)
A valve attached to high flow devices controls the amount of:
High Flow devices use the _________ principle.
True or False
In a high flow device, you're more able to control the amount of FiO2 delivered and amount of air being entrained.
True or False:
In a partial rebreather, dead space is high in CO2.
Dead space in a patient using a nonrebreather is high in O2 and NOT CO2 because the air hasn't reached gas exchange.
What is the primary difference between a CPAP and BiPAP?
- CPAP:small positive pressure continuously applied to the airway
- BiPAP:differential pressure on inspiration AND expiration, pressure at end expiratory too- but pressure is higher for inspiratory than expiratory
Increase in PEEP may allow for _____ in O2 concentration.
Insituting PEEP may lessen the risk of oxygen toxicity
True or False
CPAP and BiPAP operate on the same mechanism as PEEP.
Increasing PEEP by 10 cm H2O would increase FRC by:
the concern: squish capillaries (squish capillaries)
In what circumstances can alveoli be damaged by high pressure and high volume?
in a code!... if the smarty pants RT grabs the bag and squeezes too hard.. .
risk of damage with super high PEEP combined with Positive pressure ventilation
Why is PEEP good for patients with edema in their airways?
Fluid is moved into small airways: allowing more ventilation of the lung
How can you increase PO2 in an ARDs patient?
maintained small positive airways pressure at the end of expiration
What are some benefits of intubation and trach's?
- 1. facilitates removal of secretions
- 2. prevent blood/vomitus from pharynx into lung
What are some complications of intubation and trach?
- ulceration of larynx/trachea
- distal end of tube of R mainstem bronchus, and possible atelectasis/collapse of L lung
What clinical situations would CPAP and BiPAP be indicated?
- COPD exacerbation
- cardiogenic pulmonary edema
- acute lung injury
- weaning from mechanical ventilation
What are some benefits of CPAP and BiPAP?
- Increase in alveolar pressure
- redistributes H2O
- Raises PO2 in respiratory Failure
What are the disadvantages of BiPAP and CPAP?
- Decreases CO
- Decreases BP
- Diversion of blood flow away from ventilated regions
*think disadvantages for PEEP :)
What effect does PEEP, CPAP, and BiPAP have on H2O and interstitial edema?
- Redistributes extravascular H2O, interstitial edema
- DOESNT ELIMINATE...ONLY redistributes
What are some complications of PEEP?
What are normal levels of PEEP
5-20 cm H2O
Why can autoPEEP be harmfuL?
in hyperventilation or high frequency ventilation because alveoli don't have time to empty (patient basically isn't exhaling)
Why is autoPEEP helpful in COPD?
- It keeps the alveoli open :)
- Airways are less likely to close because it increases the FRC
- Pursed lip breathing
How does autoPEEP play a role in obstructive lung disease?
Explains why patients are slow to exhale
PEEP decreases Cardiac Output. Especially after:
- hypocapnia (c by overventilation)
What is the venturi principle?
the gas source provides the driving flow
**I might be understanding this wrong, if so... please please PLEASE text me and let me know, and I'll fix my brain and my cards! Thanks!
Name some things that effect cardiopulmonary reserve.
- Vital Capacity
- Tidal Volume
- High BP
- Low BP
- Hemoglobin Levels
- Ventilatory Demand
What RSBI score meets criteria for extubation?
What is the formula for rapid shallow breathing index? (RSBI)
What are some criteria for extubation?
- Inspiratory Pressure
- Tidal Volume
- Vital Capacity
- Rapid Shallow Breathing Index (RSBI)
Below what temperature (in C) would we keep the patient intubated?
- -keep patient on ventilator because we'd be expecting them to shiver and have an increased ventilatory demand
What three things do we look at to discontinue ventilation (make decision to extubate).
- 1. Underlying indication is reversed or improved
- 2. Cardiopulmonary Reserve intact
- 3. Clinical Evaluation and Lab Levels Stable
What are manifestations/symptoms of Pulmonary Barotrauma
What are some miscellaneous hazards of mechanical ventilation?
- Mechanical (power failure, kinking, broken connections)
- Pneumo (especially if ↑ PEEP/ ↑ Tidal Volume)
- Interstitial Emphysema
- Pulmonary Infection
- Cardiac Arrythmias (r/t hypoxemia)
- GI Bleeding (stinky!)
Which ventilator setting has the effect of increasing the mean lung volume?
Inverse Ratio (if we flip I:E to 2:1)
Which patients may benefit from a reverse I:E ratio?
- sick patients
- restrictive lung disease
What are some causes of reaching the pressure limit during mechanical ventilation?
- Coughing on Tube
- Surgical Interactions
What 4 Steps would you take to improve ALVEOLAR VENTILATION in a patient with low compliance in a lap chole?
(start at least invasive/serious change to most serious change)
- 1. Lengthen inspiration by switching setting from 1:3 to 1:2
- 2. Increase plateau time by decreasing amount of time of initial inspiration
- 3. Switch to pressure control-all time is plateau time
- 4. Reverse I:E Ratio
What are the consequences of Increased Plateau time?
- Increased intrathoracic BP (squishes capillaries!)
- BP could fall
What variables can we contorl during ventilation?
- Tidal Volume
- Inspiratory Flow Rate
- Respiration Rate
- Inspirated O2 Concentration
- Duration of I:E
- Minute Volume
*maximym amount of independent controls is 3 (meaning: if we set any 3 of these, it determines the values for the rest)
What is a typical I:E ratio?
- (West says 1:2-1:4)
What patients may benefit from long plateaus in ventilation?
Airways Obstruction patients
What does the waveform look like for pressure vs volume support?
Transport of Gas in High Frequency Ventilation occurs by:
What are the risks associated with high frequency ventilation?
- Injection Injury
- Alveolar Overdistention
Rate of high frequency ventilation:
___-___ per minute with inspiration taking ___-___% of cycle
60-100 per minute with inspiration taking 20-30%
What is the benefit of high frequency ventilation?
- maintain high mean airway pressure
- no high peak airway pressures
- prevents alveoli collapse
What is the most common cause of respiratory failure?
small airways disease
What are four types of respiratory failure?
- 1. Pure Hypoventilation
- 2. COPD, VQ Inequality (Obstructive Diseases)
- 3. Restrictive Disease
- 4. ARDs
What are clinical examples of restrictive disease?
- Severe instersitial disease
In a restrictive disease, what is the relationship between PO2 and PCO2?
Increasingly severe hypoxemia but NO CO2
retention because of the raised ventilation
Very low O2
but breathing fast because their hypoxic so CO2
is NOT high
What is the relationship between CO2 and O2 in ARDs?
may be low, hypoxemia may be extreme
- Very low PO2, breathing very quickly
- Low PO2 due to alveolar collapse and pulmonary edema
- D to E: if you give O2 to these patients, wont help by much: may increase O2 but won't effect CO2
In pure hypoventilation, what is the relationship between PCO2 and PO2?
increases the PO2
decreases in a predictable way
- High PCO2 as PO2 Decreases
What are clinical examples of hypoventilation?
In obstructive lung disease (COPD & VQ Inequality) What is the relationship between PO2 and CO2?
goes up SLIGHTLY (not as severe as pure hypoventilation)
B to F: give O2
can increases PO2
but not really affected the CO2
What clinical scenarios is ventilatory support most often seen in?
- 1. resuscitation following acute apnea
- 2. anesthesia with paralysis
- 3. intensive care
- 4. treatment of chronic ventilatory failure
In general: Arterial PO2 indicates:
the severity of respiratory failure
In general: PCO2 indicates:
The differential diagnosis between ventilatory failure and shunt
What are the four mechanisms of hypoxemia?
- 1. Pure hypoventilation
- 2. VQ Inequality
- 3. Diffusion Impairment
- 4. Shunt
Definition of respiratory failure
said to occur when the lung fails to oxygenate the arterial blood adequately and/or fails to prevent CO2 retention (NOT SHUNTING)
The only way to lower CO2...
INCREASE alveolar ventilation
True or False
There is an absolute definition of PO2 and PCO2 levels that indicate respiratory failure.
Although a PO2 <60 mmHg and PCo2 >50 mmHg often referenced in respirator failure
What is the gold standard of detection of severe hypoxemia?
What tissues are most sensitive (most affected) by hypoxia?
Symptoms of mild hypoxemia
- Slight impairment of mental performance
- diminished visual acuity
- mild HTN
Symptoms of severe hypoxemia
cyanosis, tachycardia, CNS, mental confusion
CNS: HA, somnolence, clouding of consciousness, convulsions, retinal hemorrhages, permanent brain damage
CV: tachycardia, mild HTN, bradycardia, hypotension, symptoms of heart failure
Renal Function: NA and protein in the unine
Pulmonary: pulmonary hypertension because of alveolar hypoxia
Duration of inspiration during IPPV controlled by four things:
- 1. time cycling
- 2. volume cycling
- 3. pressure cycling
- 4. limitation on inspiratory duration
What occurs during inspiration on IPPV?
1. Mouth (airway) pressure is intermittently raised above ambient pressure
2. inspired gas flows into respiratory system
What occurs during exhalation on IPPV?
Airway pressure fails below ambient pressure
In IPPV, the lung is expanded through:
in IPPV, the lung deflates passively to:
Whats another name for IPPV?
Intermittent positive pressure breathing
What type of ventilation is the "basic goal" of ventilator management?
The clinical goal in adults with normal or mildly diseases lungs is delivery of large tidal volumes (___-____ ml/kg) over ___seconds at a rate of ___-___/minute.
How are compliance, O2, and atelectasis affected by large tidal volumes?
COmpliance: near WNL
Atelectasis: incidence is decreased
*also tolerated better in an awake/mildly sedated patient
What is the end expiratory pressure?
AKA inflation hold
ventilator maneuver in which exhalation is delayed for a specific amount of time after the present inspiratory volume has been achieved
(recruitment maneuver is the same, but held LONGER)
When would the peak inspiratory pressure increase?
- airway secretions
- biting on tube
Does peak inspiratory pressure have a predictable relationship to alveolar pressure?
NO (see slide 15)
What are the risks associated with an end expiratory hold or recruitment maneuver? Benefits?
Risk: low BP
Benefit: OPEN alveoli :)
What is a measurement you'd want to look at when concerned about barotrauma?
plateau pressure: >40 cause damage
- Why not PIP?
- -because plateau pressure reflects TRUE alveolar pressure
What is our plateau pressure anesthesia goal?
35 or lower
What are the 3 modes of ventilation?
(West names 4)
- 1. Pressure Control
- 2. Volume Control
- 3. Dual Controlled
- 4. Assisted ventilation (we never use this one because our patients are asleep/paralyzed)
Which ventilation mode is best for a patient with stiff lungs?
pressure control ventilation
What are some disadvantages of pressure control?
- 1. volume affected by lung compliance
- 2. airway resistance could decrease volume delivered
- 3. inspired oxygen concentration varies with inspiratory flow rate
What is the disadvantage of volume control?
high pressure can develop
- Pressure support is same as pressure controlled ventilation but the patient is breathing spontaneously
Why may it be a problem that volume control doesn't have a long plateau?
may not be long enough for the alveoli to open! some patients need the extra plateau time!
What are the triggers for:
- Volume: patient or time
- Pressure: patient or time
Which ventilation setting is suitable for long term ventilation?
What animal says "PEEP"!?