Buttons on a Ventilator

Awani DeshmukhPGY3

(Aspiring Intensivist)

Just to state a few

Airway protection (Coma) Excessive work of breathing (COPD

exacerbation) Depressed respiratory drive (drug overdose)

Why use a Ventilator

What is the normal respiratory physiology

Negative Pressure Ventilation

Positive Pressure Ventilation

Oxygenation control = Control O2

Ventilation control = Control CO2

Aim of Ventilation

Barotrauma Oxygen toxicity Respiratory muscle weakness Ventilator acquired pneumonia Auto PEEPing Decreased cardiac output

Adverse Effects of MV

1. Trigger

2. Tidal Volume

3. Respiratory rate

4. PEEP

5. Fio2

6. Flow rate and flow pattern

7. Inspiratory time

Settings on a Ventilator

Tidal Volume

Respiratory rate

PEEP

Fio2

PCO2

O2

Trigger

Control

Cycle

3 Variables that Define a Ventilator Mode

Determines how the ventilator determines how to initiate a machine driven breath

Trigger sensitivity

Common option:1. Time triggered2. Pressure triggered3. Flow triggered

Trigger

Determines when the ventilator initiates the breath

Common option:1. Flow control2. Pressure control3. Volume control

Control

Determines when the ventilator stops the inspiration

Common option:1. Flow cycle2. Time cycle 3. Volume cycle

Cycling

Breath Type Trigger Ventilator support

Mandatory Ventilator Full

Assisted Patient or ventilator (time, volume, flow)

Partial or full

Spontaneous Patient (none) None

Types of Breaths

Assist Control (A/c)

Synchronized Intermittent Mandatory Ventilation

Pressure Support ventilation

Common Ventilator Modes

Mix of mandatory and assisted breaths. All breaths once triggered are fully assisted by the ventilator and get the maximum Vt (tidal volume) set

Trigger : Time, Flow, Volume Control: Flow (Volume)

Cycle: Time

Assist Control (A/C)

Advantages Guarantees a set minute ventilation

Low work of breathing

Disadvantages Respiratory alkalosis, auto PEEP, Hypotension

Indications Who need full ventilatory supportVt cannot be variable

Assist Control

A mix of breaths some of which are mandatory and assisted breaths

Different from A/C is assisted breaths get no support from ventilator

Syncronized Intermitted Mandatory Ventilation (SIMV)

Pressure Support Ventilation

No mandatory breaths. Patient has to initiate all breaths

Trigger: Pressure / Flow Control: Pressure

Cycle: Flow

Advantages Patient comfort

Disadvantages Patient must trigger all breathsNo guaranteed Vt

Not comfortable during sleepIncomplete ventilatory support

Indications “Stepping stone” for extubation

Pressure Support Ventilation

Low Tidal Volumes : Cuff leak, Biting , Coughing

High Peak Pressure: Biting, Kinking, Mucus plugging, elevated plateau pressure ( pulmonary edema, ARDS, pneumothorax)

Ventilator disconnect

Apnea : In patients who trigger own breaths

Ventilator Alarms

VENTILATION WITH LOWER TIDAL VOLUME (Vt) AS COMPARED WITH TRADITIONAL Vt

FOR ACUTE LUNG INJURY AND ARDS

New England Journal of Medicine May 2000

Journal Presentation

Bilateral infiltrates on CXR/ CT consistent with pulmonary edema

PaO2/ FiO2< 300 (has staging for severity) No need to rule out heart failure Should start in under 7 days of insulting

etiology

What is ARDS

Large Vt leading to excess stretching and lung injury

Trial conducted to determine of lower volumes could improve the clinical outcome

of these patients

Can we actually not given ARDS to a patient with ARDS?

Need for the Trial

Multicenter Randomized From March 1996- March 1999 Approved by IRB’s All centers except one had informed

consent

Method-Study design

Inclusion criteria Anyone who was

intubated and on a ventilator who met criteria for ARDS. They all got volume assist control ventilation

Exclusion criteria > 36 hours since onset of

ARDS < 18 years Participated in other trials

in last 30 days Pregnant Increased ICP NM disease Burns > 30 % BSA Liver disease (CPC C) Estimated mortality < 6

months

Study population

Patients were randomized to receive a high or a low tidal volume calculated from predicted

body weight (height and sex dependent)

Intervention

High tidal volumes Low tidal volumes

Vt of 12 ml/kg Vt of 6 ml/kg

Minimum Plateau pressure of 45 cm H2O

Minimum Plateau pressure of 30 cm H2O

Patients monitored until day 28 until death or for signs of system failure:

Circulatory failure: SBP ≤90mmHg or need for vasopressor

Coagulation failure: platelets ≤80,000 mm3 Hepatic failure: serum bilirubin ≥2mg/dL Renal failure: serum creatinine ≥2mg/dL

Primary Endpoint

Death before discharge Ventilator free days , defined as the number

of days from day 1 to day 28 on which a patient breathed without assistance

Breathing without assistance by day 28

Outcomes

Secondary endpoints

Days without non-pulmonary organ or system failure (circulatory , coagulation failure)

Barotrauma defined as any new pneumothorax, pneumomediastinum, or subcutaneous emphysema, or a pneumatocele that was more than 2 cm in diameter.

Mortality rate was 39.8 % in group treated with traditional Vt and 31.0% in group treated with lower Vt (P= 0.007; 95% confidence interval for difference between groups 2.4 to 15.3%)

The number of days without nonpulmonary organ failure was higher in group treated with lower Vt (P= 0.006)

Results

The trial was stopped after the fourth interim analysis because the use of lower tidal volumes was found to be efficacious (P=0.005 for the difference in mortality between groups)

Incidence of barotrauma after randomization was similar in the two groups

There was no significant differences between groups in the percentages of days on which neuro muscular blocking agents were used

Trait Low VT Traditional VT

RR High Low

Vt Low High

Pplt Low High

PaO2/FiO2 High Low

PEEP High Low

Fio2 High Low

Vent free days High Low

Study design appropriate Randomized , multicenter trail IRB approved Informed consent at all centers except 1 Proved that lower Vt had mortality and

morbidity benefit as compared with higher Vt

Critiques/Strong Points of the Study

Ethical values of the trial have been questioned

Unfair to the patients getting traditional Vt Hypercapneic acidosis

Negative points

Application of ARMA trial

The use of a written protocol outlining how to provide lung protective mechanical ventilation is associated with enhanced compliance with LTVV in patients with ARDS

This approach should be considered in all institutions that provide care to such patients

Me during my first MICU rotation

Hopefully after today rest of y’all

Thank you

NEJM Uptodate PubMed ARDSNET.COM American Thoracic Society guidelines Multiple YouTube videos

References