Lecture 20: Mechanical Ventilation (Exam 3) Flashcards
What is normal ventilation
- Movement of gas in & out of the alveoli & is defined as the maintenance of norm arterial blood CO2 concentration (PaCO2) of 35-45 mmHg
- Also should have a norm respiratory effort, rate, & rhythm
Label the diagram
What are the 4 different volumes & capacities the air in the lungs can be divided into
- Tidal volume (Vt)
- Inspiratory reserve vol (IRV)
- Expiratory reserve vol (ERV)
- Residual vol (RV)
- Inspiratory capacity (IC)
- Functional residual capacity (FRC)
- Vital capacity (VC)
- Total lung capacity (TLC)
What is the equation for inspiratory capacity
TV + IRV
What is the equation for functional residual capacity
ERV + RV
Equation of vital capacity
IRV + TV + ERV
Equation of total lung capacity
IRV + TV + ERV + RV
What is min ventilation (Ve)
- Tidal vol (Vt) x respiratory frequency
- mL per min
Answer the example
3,000 mL/min
Why do we care about ventilation
- Ax drugs can alter the px ability to norm ventilate - this could lead to inadequate gas exchange, hypoventilation & eventually respiratory arrest or cardiac arrest
- Ventilation is req for inhalant ax to be properly taken up & eliminated (controlled ventilation can maintain a smooth & stable plane of ax)
What are the effects of hypercapnia
- Directly causes vasodilation of peripheral arterioles & myocardial depression which can cause slow heart rate, cardiac arrest, & intracranial pressure
- Indirectly increases circulating catecholamines which can lead to cardia arrhythmias, tachycardia, increased myocardial contractility, & BP elevation
- Narcosis @ paCO2 above 95 mmHg
- Induces complete ax @ 245 mmHg
Define IPPV
- Intermittent positive pressure ventilation
- positive pressure maintained only during inspiration
Define IMV
- Intermittent mandatory ventilation
- Operator sets a predetermined # of positive breaths but the px can also breathe spontaneously
Define PEEP
- Positive end-expiratory pressure
- Airway pressure at the end of expiration is maintained above ambient pressure
- Peep is applied when positive pressure is maintained btw/ inspirations that are delivered by a ventilator
What is CPAP
- Continuous positive airway pressure
- Spontaneous breathing w/ positive pressure during both inspiratory & expiratory cycles
Define HF(N)OT
- High flow (nasal) oxygen therapy
- Admin of warm humidified oxygen via nasal prongs using a commercially ava unit to deliver higher flow rates of O2 & an FiO2 up to 100%
Describe how IPPV is performed by closing/occluding the pop-off valve
- close/occlude the pop off valve & squeezing the reservoir bag until 10 to 20 cm H2O is reached
- The pop off valve is reopened so the px can passively expire
- “manual”
- Preferred method is to utilize the safety occlusion valve instead of actually closing the APL valve (pop off)
Describe is IPPV is by machine (“mechanical ventilator”) convenient
- B/c it frees your hands to to do other things
- Can do harm to px if not used correctly
What are the reasons a px may require mechanical ventilation
- Simply the px has failure to oxygenate or ventilate
- Respiratory center depression
- Inability to adequately expand thorax
- Cardiopulmonary arrest
- Pulmonary edema or pulmonary insufficiency
What are specific indications for IPPV during ax
- Thoracic sx (lungs cannot be inflated when the chis is open)
- Neuromuscular blocking drugs (If you paralyze the ocular m you paralyze the diaphragm)
- Prolonged ax ( > 60 min)
- Chest wall or diaphragmatic trauma ( px w/ flail chest)
- Maintain a more stable ax plane
- Obesity & special px positing (more like to hypoventilation or have V-Q mismatch)
- Control of intracranial pressure
- Convenience
When should IPPV be started in health SA px
When the ETCO2 reaches the mid 50s
What are the neg CV effects of mechanical ventilation
- Neg pressure is not generated inspiration so venous return to the heart is not enhanced
- IPPV may actually physically impede venous return to the right side of the heart (decreased stroke volume, CO, & arterial BP)
- Exacerbated by prolonged inspiratory time, PEEP/CPAP, obstruction to exhalation, & an excessively rapid respiratory rate
How can CV effect w/ IPPV be overcome
Expansion of the extracellular fluid vol & admin of inotropic drugs
What are the other effects of IPPV
- Excessive or sustained pressure can lead to over expansion & volutrauma which in return causes alveolar membrane disruption, dev of interstitial air, & eventual transfer to air to mediastinum, pleural space, or abdomen
- Also alters neurohormonal systems like ADH release, sympathetic outflow, renin-angiotensin axis, & ANP production which can caused decreased RBF/GFR & retention w/ oliguria
Describe a mechanical ventilator
- Compliant pleated compressible bellows connected to an ax breathing circuit
- Needs power (electricity)
- Needs a driving force (oxygen)
What is a double circuit ventilator
- Refers to two gas sources
- The driving gas circuit outside the bellows which compresses the bellows & the px gas circuit inside the bellows that originates in the ax machine & provides oxygen & ax gases to the px
What are the guideline for IPPV
- Vt is usually increased above norm spont Vt to compensate for pressure mediated increases in volume of the breathing system & airway
- PIP: how much pressure is given w/ each breath
- I to E ratio: How long in inspiration & expiration; want to spend twice as long in expiratory phase than inspiratory
- Px w/ lung trauma, diaphragmatic hernia, or GI distention may need to have an increased respiratory rate to maintain Ve w/o creating excessive inspiratory pressures
Fill out the chart
Answer the example
Answer is C
What are the steps of an IPPV
What does the amount of gas delivered to the px depend on
- Resistance & compliance of breathing system
- Pxs respiratory sys
What increases resistance? What can decrease compliance?
- Increasing resistant: Obstructive dx that narrow airways; like COPD, chronic bronchitis, bronchiectasis, asthma, & emphysema
- Decrease compliance: restrictive dx that reduce expandability; like pleural effusion, pneumothorax, morbid obesity, trauma, abdominal distension, & pulmonary fibrosis
T/F: Although inspiratory pressure may not vary of time the Vt may changes as the compliance of the respiratory system changes
True
What happens after IPPV is discont.
- If PaCO2 is low spontaneous ventilation may not return b/c a certain level of PaCO2 is req to stimulate ventilation
- Opioids, axs, neuromuscular blocking drugs, hypothermia, or hypovolemia may delay return of consciousness & therefore spontaneous ventilation
- Px should continue to receive supllemental O2 & can be manually ventilated @ 1 to 4 bpm until spont ventilation has returned and stabilized (norm Vt & f)
Describe volume cycled ventilators & what is the disadvantage
- Inflate lungs to predetermined vol
- Inspiratory pressure may increase if compliance decreases during ventilation
Describe pressure cycled ventilators & what is the disadvantage
- Inflate lungs to a predetermine pressure
- Vt delivered may may decrease if respiratory compliance decreases in px
Describe time cycled ventilators
- Inflate lungs for a preset time at a predetermined gas flow rate
- Most ax ventilators are time cycled
Describe self inflating resuscitation sys (ambu bag)
Used for IPPV of small animals w/ room for supplemental O2 components
Describe demand valve
- Inserted on proximal end of endotracheal tube & delivers IPPV (O2 only)
- Demand from a px initiated breath or from operator assistance
What are recruitment maneuvers (RM) used for? What do they induce
- Used to reinflate collapsed alveoli by applying sustained pressure above norm PIP & using PEEP to prevent derecruitment
- Induces a temporary improvement in lung fxn in healthy dogs under general ax
So what can you do?
- Admin a “sigh” (a large pos pressure breath held for 10 to 15 sec) once every 5 mins
- Consider adding PEEP
- May be useful to recruit collapsed alveoli & might improve oxygenation
Describe oxygen toxicity (Hyperoxia)
- Rare but can dev w/ prolonged exposure to high O2 conc
- Reversible in the early stages
- Can lead to pulmonary dysfunction, pulmonary edema, & death
- Significant species & indiv variation (recommendation is 100% O2 should not be admin for > 12 H)
- 40 to 50% O2 is generally safe for prolonged admin but higher concentration may be needed to maintain px PaO2 @ ~ 90 to 100 mmHg
