Mechanical+Ventilation

=Why we need ventilators=
 * when work of breathing is too much
 * when CNS of patient won't breath on own

>* due to loss of surfactant, filling of alveoli with fluids, scarring, Fibrosis
 * Change in compliance can affect work

=Respiratory failure and arrest=
 * Lots of people technically have respiratory failure
 * term reserved for decline in function that will lead to arrest if not corrected
 * Arrest is moment whe e ffective ventilaltion ceases
 * can usually be seen coming in advance

=The Road to Respiratory Failure= >* COPD >* Asthma >* Restrictive lung disease >* Chest wall abnormalities >* Pneumothorax, pleural disease >* Neuromuscular disease >* Untreated hypoxia produces compensatory tachypnea
 * Poor Mechanics
 * Poor gas exchange
 * hypoxia affects bellows like any other organ

=Steps to Taking Over Breathing= >* iintubation not always necessary
 * Gain control over upper airway
 * deliver cyclical postive-pressure 'breaths'
 * supplemental Oxygen
 * makte tolerable for patient

=Details= >* F)2 >* rate >* tidal volume
 * positive pressure ventialtion almost always used
 * ventilators can set to deliver:

=Problems with mchanica venitation= >* Always concern unless deepp sedation >* if not fixed, will icnrease work of breathing, increase anxiety, impair eforts at ventilation >* Triggers >>* Inspiratory triggering when pt tries to breath >* Modes >>* Assist/Control >>>* Regular uniform breaths, plus bonus breaths when pt asks for them >>>* Problems: >>>** Some breaths delivered regardless of whether pt wants them >>>** Bonus breaths same as controlled breaths >>>** Uncomfortable for conscious pts >>>** still used in OR, pts under deep seadtion in ICU
 * patient-ventilatory dyssyncrhony
 * History of ventilation is getting machine to listen to paient

>>* Syncronized intermittent mandatory ventillation (SIMV)

>* 'Bells & Whistles'

>* 8-10ml/kg body mass >* ~12/min in adult >* Higher in pediatric pts neonates >* often 50-100% to start
 * Initiating mechanical ventilation
 * Pick a mode
 * pick a volume
 * Pick a rate
 * Pick a FiO2

=Bells & Whistles=

Positve End-Expiratory Pressure, PEEP
>* Presumably keeps more alveoli open >* 5cm H2O often sufficient >* can significantly improve oxygenation >>* Useful in Acute Respiratory Distress Syndrome, ARDS >>* Useful in CHF with pulmonary edema >* POsitive pressure in thorax reduces return to heart >* decreases cardiac output by this mechanism
 * Ventilator never lets circuit pressures fall below threshold
 * **Drawback**: Venous return to heart impaired!

Inspiratory and Experiatory Ratios
>* COPD alveoli are 'floppy', inflate easily, deflate poorly >* ARDS alveoli are stiff, inflate poorly, deflate easily
 * Diffrent disease affect inflatability vs deflatability

Volume-driven ventilation

 * set ventilator to deliver certain tidal volume
 * pressure develops as function of compliance
 * common strategy...easy to set rate, volume
 * if compliance low, pressure may become too high

pressure-driven venitaltion

 * set ventilator to deliver a peak airway pressure
 * the volume that gets delivered is function of compliance
 * limits 'barotrauma' from ventilator
 * if compliance is low, Vt may be too low

CPAP and BiPAP
both use support //without/// intubation...id est, with a mask

CPAP

 * Continuous Positive Airway Pressure
 * Commonly used for treating acute respiratory failure
 * Provides PEP, so may recruit alveoli

BIPAP

 * Bi-Level Positive Airay Pressure
 * Used in obstructive sleep apnea

Sedation
>* Benzodiazepine >* Propofol >* completely relax chest wall >* improve compliance >* may cause ICU myopathy
 * Patient anxiety of ten limits therapy
 * IV sedation is standard
 * neuromuscular blockers go in and out of style

=Discontinuing Ventilation=
 * atrophy
 * may take hours-months to recondition muscles

=Drawbacks= Iinterrupts upper airways defense >* cough gag, mucus >* colonization


 * muscle wasting
 * bed bound, hospital bound
 * expensive
 * often 'staving off inevitable'
 * many pts state, 'Do not intubate'

=M3 notes=
 * Do Not Touch!
 * FiO2
 * mode
 * rade
 * tidal volume
 * peak airway pressure
 * PEEP