Mechanical ventilation and NIV Flashcards
Describe physiology of a normal breath
Contraction of the diaphragm and intercostal muscle increase the intrathoracic volume creating -ve pressure in the chest cavity – initiated inhalation
Relaxation and recoil allow the volume to return to normal and to initiate exhalation
During spontaneous inspiration decreased intrathoracic pressure augments venous return and preload. Cardiac output is increased and there is a increased pressure gradient between the LV and the aorta
Discuss the physiological effects of positive pressure ventilation
Positive pressure ventilation reduces venous return and preload and there is a decreased pressure gradient between the LV and the aorta. This change in physiology can lead to hypotension when positive pressure ventilation is started and can be exacerbated by pre-exisiting pathology
Discuss pressure controlled ventilation
a set amount of pressure is applied to the expand the lung for a specified amount of time.
Target pressure and inspiratory time are set
Particularly important in patient in whom you want to prevent barotrauma
Increased ventilator synchrony
Unable to guarantee tidal volume or limit it if lung compliance either improves or worsens acutely – also unable to garantee minute ventialtion
Provides advantages over VCV when patient have potentional to develop dynamic hyperinflation and instrinsic PEPP
Benifical in conditions in which airway pressures need to be monitored – severe asthma, COPD, salicylate toxicity
As inspiratory flow rate is not limited in pressure controlled ventilation it may be benificial in patient with intrinsically high RR to reduce desyncrony (salicylates)
Discuss volume control ventilation
Defined by a set tidal volume. Inspiratory volume and flow rate are set inhalation ends once a present tidal volume is delievered.
Lung pressures (Peak inspiratory pressures (PIP) and end inspiratory alevolar pressures) vary based on lung compliance and set tidal volume .
Can lead to peaks in inspiratory pressure and barotrauma if lung compliance changes acutedly
Particularly useful in patient in whom tidal volume is stricly controlled (ARDS) and in those with decreased chest wall compliance (morbid obesity or severe chest wall burns)
Discuss ventilator modes
Specifies how much respiratory support the ventilator offers . Most commonly can be divided into CMV (continous) IMV (intermediate) and CSV (spontaneous).
CMV and IMV give a preset number of breaths
CSV gives no mandatory breaths by augments patients spontaneous breaths.
Discuss CMV
Intended to provide full ventilatory support for patient with little to no spontaneous breathing
If a patient generates negative pressure vent will detect and assist breath. This will reset time until next breath. For this reason also called assist control ventilation.
Any -ve pressure generated by the patient will cause a full breath to be delivered, as patient initiaed breaths are not proporitonal to patient effort and can lead to hyperventilation
To achieve adequate synchrony patient need to be deeply sedated
Discuss IMV
Synchronized intermittent mandatory ventilation (SIMV) provide intermittent ventilatory support to patient by delivering spont and mandatory breaths.
Similar to A/C patient will recieve at least the preset number of breaths. Mandortory breaths are given at a preset rate but the breath is synchronized as much as possible with spont breathing
If a patient has a rate of spont breathing higher than the set rate the vent will deliver all preset full breaths. All breaths above this rate will be dependent on patient effort
Useful for patient who are sedated but who have weak respiratory efforts. The delivery of extra breaths consistent with patient respiraotry efforts attenuates air trapping and hyperventialtion seen with A/C
Discuss CSV
On deliveres pressure support on patient spont breathing. Amount of pressure to maintain a breath is dependent on patient effort and differes from breath to breath. When inspiratory flow stops pressure is ceased and allows exhalation.
Rarely used in the ED as people dont breath there
Discuss PEEP
Referes to maintenance of postive airway pressure after completion of passive exhalation.
Increased FRC, improves O2 and decreases intrapulmonary shunting. Reduced portion of non aerated lung that mya contribute to the development of VILI
Increases intrapulomnary and intrathoracic pressure abd affect pulmonary and cardiovascular physiology
Discuss relative contraindications for NIV
Cardiac or respiratory arrest Inability to protect airway - decreased or coma state, excessive secretion or inability to clear Upper airway obstruction untreated pneumothoax Marked HD instability Recent upper GI surgery Maxillofacial surgery or trauma Base of skull fracture Patient refusal Intractable vomiting
Discuss how CPAP works in patients with APO
Elevation in intrathoracic pressure that decrease LV ejection pressure and LV transmural pressure which results in afterload reduction.
Decrease in RV preload may improve LV compliance via ventricular interdependence (a phenomenon whereby the function of one ventricle is altered by changes in the filling of the other ventricle.)
BiPap leads to fast clinical improvement wihtout increased risk of MI
In general Ipap increases tidal volume and minute venitlation and leads to a decrease in CO2
EPAP reduces atelecasis and promotes alveolar recruitment improved o2 saturation
Ipap greater than 20 should be avoided as leads to gastric insufflation
Discuss pressures in invasive ventilation
Two main pressure PIP and Platue
PIP measures the maximum amount of pressure in the venilator circuit during a breath. It reflects lung compliance and airway resistance
P-plat is measured at the end of inspiration with an inspiratory hold. It measure maximum alevolar pressure. Pressure = (flow x R) +(volume/compliance +Peep)
Discuss sedation in a ventilated patient
Should be used to keep patient comfortable and maintain synchrony
Intubation and ventilation is a large source of anxiety and pain for patient
Multiple sedation scores are used included Richmond Agitation-sedation score (RASS) and patient should be aimed to be kept between 0 and -5 on this score
Need to be aware that when roc is used deep enough sedation is given as duration of paralysis is longer than sux. Once adequetly sedated their is usually nil further need to paralyse the patient so long as vent synchrony is maintained
Opiates a mainstay of sedation in the vented patient and have the added benefit of respiratory depression if synchrony is an issue. Care with morphine and its active metabolites in patient with renal disease
Benzo good agent for sedation due to anxiolysis -however in critically unwell patients with repeated doses altered PK can lead to tissue accumulation and patient may take days to metabolise enough to eb extubated. Also interferes if neurolgical exam is needed
Prop nil anxiolytic function but fast on and off - best agent if patient going to be intubated for a short period of time or neurolgoical exams are require. Can precipitate hypotension and increase in venous capacitamce
Discuss reduction in secretion and risk of VAP
Head up semi-recumbent position
frequent suctioning balancing between adequate suction and interruption of ventilation
Discuss the Richmond Agitation sedation scale
4+ - combative – punchy
3+ very agitated - pulling shit out
2+ agitated- moving non purposful
1+ restless- anxious minimal movement
0 calm and alert
-1 Drowsy - spont awakening but not fully alert
-2 light sedation - eyes to voice with tracking for 10
-3 moderate sedation - eyes to voice nil trackin
-4 deep sedation -eyes to pain
-5 unarousable - notta
