ABC’s of Mechanical Ventilation

By Robert Gales, RRT-NPS

Indications for Mechanical Ventilation

Apnea

Hypoxemia

Hpyercapnea or Hypoventilation

Normal Arterial Blood Gas Values

Common Ventilator Modes

Volume Control4-7 ml/kg

Pressure Control15-20 cmh20

High Frequency

Pressure Support

Time Parameters

• Rate or number of breaths/unit of time• Cycle-time or time/breath

• Ti = Inspiratory Time• Te = Expiratory Time• I:E Ratio = Ti/Te

• Cycle Time = Ti + Te

• Only need to set 2 of these variables

Setting Rate using Inspiratory time and Expiratory Time• Confirm desired rate

• Divide by 60= total cycle time• From this number, subtract the inspiratory time (Ti)

This gives you expiratory time that you need to set the rate

Order: Rate of 40, and Ti of .35. What is your Expiratory time (Te)

60/40= 1.5 (total cycle time)1.5-.35=1.15

Expiratory time is 1.15 for a rate of 40 with an I-time (Ti) of .35

Pressure Parameters

• Peak Inspiratory Pressure = “PIP” • Pressure achieved at peak inspiration

• Positive End-Expiratory Pressure = “PEEP”• Pressure maintained during Te

• Needed to prevent atelectasis• PIP – PEEP = ΔP [“Amplitude”]

“Effect of positive end-expiratory pressure and tidal volume on lung injury induced by alveolar instability.”

• Protective mechanical ventilation strategies must take into consideration the need to stabilize alveoli in order to prevent ventilator induced lung injury.

• Both lowering Vt and increasing PEEP will stabilize alveoli.

• However, the combination of reduced Vt and increased PEEP needed to reduce alveolar instability and prevent VILI optimally has not been determined.

Volutrauma from PIP and PEEP

Ryu J, et al. Clin Perinatol 2012; 39:603–12.

Compliance and Resistance

• Compliance• The elasticity or distensibility of the respiratory systemCompliance =Volume/pressure

• Resitance• The capability of the airways and endotracheal tube to oppose airflow; expressed as the change in pressure per unit change in flowResistance= Pressure/Flow

Plateau Pressure

• Pressure applied to small airways and alveoli

• Measured at end inspiration

• To measure, apply Inspiratory hold on ventilator for 1-2 seconds

• Plateau Pressures >35 cmh20 • associated with barotrauma• Alveolar distention• Ventilator associated lung

injury

Compliance and PEEP

• PEEP determines FRC• FRC-volume of air in lungs after end of passive expiration

• CL varies with FRC• low FRC → atelectasis• high FRC → hyperexpansion• both decrease compliance

Compliance Waveforms

•PIP ↑ → VT ↑•High PIP → Hyperexpansion

• Loss of compliance• Risk of Volutrauma

• Pneumothorax• PIE• CLD

Non-Invasive Ventilatory Support

• Continous Positive Airway Pressure (CPAP)• Least invasive• RDS, Pneumonia• Usually 4-6 cmh20• Overcomes initial opening pressure• Decreases work of breathing• Increases functional residual capacity (FRC)

Non-Invasive Ventilatory Support

• Non-Invasive Positive Pressure Ventilation (NIPPV)• CPAP with a rate• Adds machine breaths (PIP) to CPAP• Rate, PIP and Ti are set

Standard Modes of Ventilation

• Controlled Mandatory Ventilation [CMV]• Intermittent Mandatory Ventilation [IMV]• Synchronized IMV [SIMV]• Assist/Control [A/C]• Pressure Support [PS]

CMV

SIMV

Modes of Mechanical Ventilation

• Synchronized Intermittent Mandatory Ventilation (SIMV)• Synchronizes mechanical breaths with patient breaths• “intermittent mandatory” delivers breaths set by

provider• the patient is allowed to take additional breaths in

between the mechanical breaths. The patient's own breaths are called "spontaneous breaths". The size of these breaths may be large or small, depending upon the patient's abiltiy.

Modes of Mechanical Ventilation

• SIMV Set Parameters• Rate• Ti• PIP• PEEP

Modes of Mechanical Ventilation

• Assist/Control• Set number of breaths ventilator will deliver• Synchronized with patients effort• Delivers assisted breath with same settings as A/C breath

Assist Control (AC)

Modes of Mechanical Ventilation

• Assist Control Set Parameters• Rate (minimum)• Ti• PIP• PEEP

Modes of Mechanical Ventilation

• Volume Guarantee (VG)• Adds safety limit to pressure control ventilation (PCV)• Used in conjunction with SIMV or AC modes• Ordered in ml/kg• Assses previoUs breaths to determine minimal PIP to

achieve desired tidal volume (VT)

Modes of Mechanical Ventilation

• Pressure Support Ventilation (PSV)• Duration is determined by patient effort• Pressure ordered is added to PEEP• Maximim inspiratory pressure is peep +set pressure

support• Comfortable mode for stable and chronic patients

Ventilator Adjustments

• PEEP1. Starting PEEP is usually 4-6 cm H202. Less compliant lungs may need increased PEEP3. As lung function improves, PEEP is decreased to

avoid gas trapping and hyperinflation4. Increasing PEEP recruits more lung surface area for

gas exchange

Ventilator Adjustments

• PIP1. Starting PIP is usually 15-20 cmh20 range2. Less compliant lungs may require higher PIP (25-30)3. As lung function improves, lower PIP to avoid over

distention, volutrauma and air leaks4. Increasing PIP increases tidal volume5. Usually first maneuver to improve ventilation

Ventilator Settings

• Tidal Volume1. VLBW (very low birth weight) 4-5 ml/kg2. Larger Premies 5-6ml/kg3. Sick term Infants 6-8 ml/kg

Ventilator Adjustments

• Rate1. Starting rate is usually around 35-40 with either AC

or SIMV2. Increaseing rate increases minute ventilation which

impoves ventilation3. Decrease rate as lung function improves4. In SIMV, Pressure support allows patient to breath

between PC breaths with less work of breathing, and improves ventilation

Ventilator Adjustments

• I time (Ti) Start with .35 seconds1. Longer Ti’s have been associated with increased

incidence of air-leaks2. Severe acute lung disease, or chronic lung disease

complicated by increased airway resistance, longer Ti’s may be needed

3. Increasing Ti is another method for improving oxygenation

4. Pay Close attention to I:E ratio

Ventilator Adjustments

• Oxygenation (to increase Pa02 or Sp02)1. Increase Fi022. Increase PEEP3. Increase PIP4. Increase Ti

Ventilator Adjustments

• Ventilation (lower PaC02)1. Increase Rate2. Increase PIP or Volume3. Decrease PEEP

Troubleshooting

• High airway pressure (Common Causes)1. Kinked or obstructed ETT2. Mucous Plugging3. Bronchospasm4. ETT is too small

Weaning

• Extubation should be considered when all the following criteria are met.

• PaCO2 below 55 mm Hg with a pH higher than 7.25. • FIO2 below 35%. • Demonstration of adequate respiratory reserve• Trial of PSV VG for 15 min- hour• trial of CPAP

Criteria may vary!

The END

Guven S, et al. J Matern Fetal Neonatal Med 2013; 26:396–401.