MECHANICAL VENTILATION Marc Charles Parent

Presentation Different settings to consider Monitoring of the patient Different type of patient COPD, Asthma ARDS Trouble shooting

Ventilator settings

Ventilator settings Ventilator mode Respiratory rate Tidal volume or pressure settings Inspiratory flow I:E ratio PEEP FiO2 Inspiratory trigger

CMV

A/CV

SIMV

PSV(pressure support ventilation) Spontaneous inspiratory efforts trigger the ventilator to provide a variable flow of gas in order to attain a preset airway pressure. Can be used in adjunct with SIMV.

Respiratory Rate What is the pt actual rate demand?

Tidal Volume or Pressure setting Maximum volume/pressure to achieve good ventilation and oxygenation without producing alveolar overdistention Max cc/kg? = 10 cc/kg Some clinical exceptions

Inspiratory flow Varies with the Vt, I:E and RR Normally about 60 l/min Can be majored to 100- 120 l/min

I:E Ratio 1:2 Prolonged at 1:3, 1:4, … Inverse ratio

FIO2 The usual goal is to use the minimum Fio2 required to have a PaO2 > 60mmhg or a sat >90% Start at 100% Oxygen toxicity normally with Fio2 >40%

Inspiratory Trigger Normally set automatically 2 modes: Airway pressure Flow triggering

Positive End-expiratory Pressure (PEEP) What is PEEP? What is the goal of PEEP? Improve oxygenation Diminish the work of breathing Different potential effects

PEEP What are the secondary effects of PEEP? Barotrauma Diminish cardiac output Regional hypoperfusion NaCl retention Augmentation of I.C.P.? Paradoxal hypoxemia

PEEP Contraindication: No absolute CI Barotrauma Airway trauma Hemodynamic instability I.C.P.? Bronchospasm?

PEEP What PEEP do you want? Usually, 5-10 cmH2O

Monitoring of the patient

Look at your patient Question your pt Examine your pt Monitor your pt Look at the synchronicity of your pt breathing

Pressures

Compliance pressure (Pplat) Represent the static end inspiratory recoil pressure of the respiratory system, lung and chest wall respectively Measures the static compliance or elastance

Pplat Measured by occluding the ventilator 3-5 sec at the end of inspiration Should not exceed 30 cmH2O

Peak Pressure (Ppeak) Ppeak = Pplat + Pres Where Pres reflects the resistive element of the respiratory system (ET tube and airway)

Ppeak Pressure measured at the end of inspiration Should not exceed 50cmH2O?

Auto-PEEP or Intrinsic PEEP What is Auto-PEEP? Normally, at end expiration, the lung volume is equal to the FRC When PEEPi occurs, the lung volume at end expiration is greater then the FRC

Auto-PEEP or Intrinsic PEEP Why does hyperinflation occur? Airflow limitation because of dynamic collapse No time to expire all the lung volume (high RR or Vt) Expiratory muscle activity Lesions that increase expiratory resistance

Auto-PEEP or Intrinsic PEEP Auto-PEEP is measured in a relaxed pt with an end-expiratory hold maneuver on a mechanical ventilator immediately before the onset of the next breath

Auto-PEEP or Intrinsic PEEP Adverse effects: Predisposes to barotrauma Predisposes hemodynamic compromises Diminishes the efficiency of the force generated by respiratory muscles Augments the work of breathing Augments the effort to trigger the ventilator

Different types of patient

COPD and Asthma Goals: Diminish dynamic hyperinflation Diminish work of breathing Controlled hypoventilation (permissive hypercapnia)

Diminish DHI Why?

Diminish DHI How? Diminish minute ventilation Low Vt (6-8 cc/kg) Low RR (8-10 b/min) Maximize expiratory time

Diminish work of breathing How: Add PEEP (about 85% of PEEPi) Applicable in COPD and Asthma.

Controlled hypercapnia Why? Limit high airway pressures and thus diminish the risk of complications

Controlled hypercapnia How? Control the ventilation to keep adequate pressures up to a PH > 7.20 and/or a PaCO2 of 80 mmHg

Controlled hypercapnia CI: Head pathologies Severe HTN Severe metabolic acidosis Hypovolemia Severe refractory hypoxia Severe pulmonary HTN Coronary disease

A.R.D.S. Ventilation with lower tidal volume as compared with traditional volumes for acute lung injury and the ARDS The Acute Respiratory Distress Syndrome Network N Engl J Med 2000;342:1301-08

Methods March 96 – March 99 10 university centers Inclusion: Exclusion Diminish PaO2 Bilateral infiltrate Wedge < 18 Exclusion Randomized

Methods A/C 28d or weaning 2 groups: End point: 1. Traditional Vt (12cc/kg) 2. Low Vt (6cc/kg) End point: 1. Death 2. Days of spontaneous breathing 3. Days without organ failure or barotrauma

Results The trails were stopped after 861 pt because of lower mortality in low Vt group

Trouble Shooting

Trouble Shooting Doctor, doctor, his pressures are going up!!! What is your next step?

Trouble Shooting Call the I.T., he will take care of it! Where is the staff? I dont know this pt, and run! Ask which pressure is going up

Trouble Shooting Ppeak is up Look at your Pplat

Trouble Shooting If your Pplat is high, you are faced with a COMPLIANCE problem If your Pplat is N, you are faced with a RESISTIVE problem DD?

Trouble Shooting

Trouble Shooting Doctor, doctor, my patient is very agitated! What is your next step?

Trouble Shooting Give an ativan to the nurse! Give haldol 10mg to the patient! Take 5mg of morphine for yourself! Look at your pt!

Trouble Shooting At the time of intubation, fighting is largely due to anxiety But what do you do if pt is stable and then becomes agitated?

Trouble Shooting Remove pt from ventilator Initiate manual ventilation Perform P/E and assess monitoring indices Check patency of airway If death is imminent, consider and treat most likely causes Once pt is stabilized, undertake more detailed assessement and management

Trouble Shooting

Conclusion