Mechanical Ventilation & Noninvasive Ventilatory Support Flashcards
What are the physiological changes that occur from transition to negative to positive pressure ventilation?
PPV = increase intrathoracic pressure = reduced venous return & preload = decreased cardiac output = decreased pressure gradient between LV and aorta.
Resulting in relative hypotension.
What are the different ventilator modes?
- Continuous Mechanical Ventilation (CMV) - aka assisted-control - provides full ventilatory support. Disadvantage = patient initiated breaths are not proportional to patient effect; may results in hyperventilation, air trapping, poor synchrony & hypotension
- Intermittent Mandatory Ventilation (SIMV) - Mandatory breath given at preset rate. But the vent synchronises with spontaneous patient breaths as much as possible. Ideal for patients who are sedation but have weak resp effort
- Continuous Spontaneous Ventilation (CSV) - breaths ONLY delivered on a patient initiated trigger. Option for CSV include PSV (intubated patient) or CPAP/BiPAP (NIV)
Describe the set parameters, variable targets, benefits and clinical applications of pressure-controlled ventilation (PCV)?
PCV = delivers a set pressure with each breath; variable TV
- Set parameters: Pressure target, inspiratory time, Resp Rate, PEEP.
- Variable Targets: Tidal volume (becomes function of lung compliance); inspiratory flow rate.
- Benefit: prevents barotrauma; impede ventilator synchrony in patient with high respiratory drive
- Clinical application: asthma, COPD, salicylate toxicity.
Describe the set parameters, variable targets, benefits and clinical applications of volume-controlled ventilation (VCV)?
VCV = delivers a set volume with each breath; variable pressure
- Set parameters: Tidal volume, Resp rate, inspiratory flow rate, inspiratory time
- Variable Targets: Peak Inspiratory Pressure, End expiratory alveolar Pressure. (thus need to check plateau pressure to ensure no barotrauma)
- Benefit: useful in patients with decreased chest wall complicated (burns, obesity) or when strict control of TV in beneficial (ARDS)
- Clinical application: ARDS, obesity, severe burns.
What conditions benefit from NIV?
Strong evidence to suggest benefit of NIV in acute exacerbation of COPD and APO (obviates intubation in more than 50% of cases and improves survival)
NIV has been shown to improved pre-oxygenation prior to intubation; but NIV should not delay the decision to intubation as this has demonstrated increased mortality
No established role for NIV in pneumonia at this stage. Presence of pneumonia is an independent risk factor for failure of NIV.
What are the relative contraindications to NIV?
- Altered or diminished LOC
- Lack of respiratory drive
- Increased secretions
- Haemodynamic instability
- Facial trauma
- Impending respiratory failure despite trial of NPPV (must reassess frequently)
CPAP v. BiPAP
CPAP = continuous non-varying positive pressure during the entire respiratory cycle
BiPAP = continuous pressure varies throughout out inspiratory (IPAP) and expiratory (EPAP) phase of the respiratory cycle
No clear benefit of one over the other. However, some evidence exists that notes greater benefits with BiPAP rather than CPAP in the patient with CHF.
What initial settings do you us for NIV?
Full face mask recommended over nasal mask
Inspiratory support (IPAP) initiated at 10 cmH2O (max: 20 cmH2O due to risk of gastric insufflation)
Expiratory support (EPAP) initiated at 5 cmH2O
Titrated based on tolerative, RR, O2 sats, consider adjusting EPAP (for oxygenation) and IPAP (to reduce hypercabia) by 1-2 cmH2O at a time.
How is treatment failure of NIV in AECOPD defined?
GCS < 11
Sustained arterial pH < 7.25
Tachypnea >35 BrPM
What is the Richmond Agitation-Sedation Scale (RASS) and what is it used for?
See picture
What is your target RASS scores for sedated patients post-intubation?
A target score of -2 to 0 avoids both over and under sedation.
What analgesic agents and sedatives are commonly used for post-intubation management?
Goal = maximise patient comfort and promote patient-ventilator synchrony
Analgesia = opioids (fentanyl v. morphine); fentanyl preferred in renal impairment
Sedation = BNZ v. propofol; propofol has limited pharmacokinetic changes in the critically ill and some evidence to suggest benefit over benzodiazepines in mechanically-ventilated patients
Others = dexmedetomidine & haloperidol (can’t use as single agent)
How do you troubleshoot a ventilator?
See Flowchart (Fig. 2.1)
“Disconnect the vent and bag with 100% O2”
What is auto-PEEP?
The term “auto-PEEP” or “iPEEP” refers to a physiologic and intrinsic positive-end expiratory pressure; results from the accumulation of end-expiratory volume when the patient cannot completely exhale.
Common in acute asthma or AECOPD = “breath stacking”
Can result in increase PIP, hypotension and circulatory collapse
Address by reduced RR and increasing expiratory time
Outline your approach to ventilator settings for normal patient?
TV = 6-8ml/kg of IBW (lung protective)
Flow rate as per pt comfort
RR = 12-14bpm (ventilation)
PEEP: 5 (oxygenation)
FiO2 = Start at 100% and down titrated with aim PaO2 55-80mmHg or SpO2 88-85% (oxygenation)
