INITATION OF MECHANICAL VENTILATION

INITIATION OF MECHANICAL VENTILATION PRIMARY GOAL

TO ACHIEVE A MINUTE VENTILATION THAT MATCHES THE PATIENTS METABOLIC NEEDS

A heathy person at rest has a total oxygen consumption (VO2) of about _

250 mL/min

A healthy person at rest has A carbon dioxide production (VCO2) of about _

200 mL/min

AS THE PATIENTS METABOLIC RATE INCREASES __________ TO MEET THE NEED FOR INCREASED OXYGEN UPTAKE AND CO2 REMOVAL

VENTIALTION MUST CHANGE

AS THE PATIENTS METABOLIC RATE INCREASES, VENTIALTION MUST CHANGE TO _

MEET THE NEED FOR INCREASED OXYGEN UPTAKE AND CO2 REMOVAL

Metabolic rate is directly related to

body mass and surface area in humans

Metabolic rate is estimated on the basis of an

individual's gender and body surface area (BSA)

BSA can be calculated using the DuBois BSA formula:

BSA = 0.007184 × Ht0.725 × W0.425

Minute Ventilation ( VE ) calculation

• Men VE =4 × body surface area (BSA) - Women VE = 3.5 × BSA

Minute ventilation is increased by if above 99° F or if above 37° C

5% 10%

Minute ventilation is increased by _ for metabolic acidosis

20%

if resting energy expenditure is equally increased

50% to 100%

Minute ventilation is decreased by if between 35° C and 37° C

10%

Tidal volume is Minimum of ideal body weight, Maximum of _ IBW

• 6 mL/kg - 8 mL/kg

Keep alveolar pressure <30 cm H2O

Tidal volume

Respiratory Frequency (f) Calculation:

f = V E / V T

Respiratory rate typically ranges from

12 to 18 breaths per minute

The normal spontaneous VT for a healthy adult is about with a spontaneous respiratory rate of 12 to 18 breaths/min.

5 to 7 mL/kg

The normal spontaneous VT for a healthy adult is about 5 to 7 mL/ kg with a spontaneous respiratory rate of ________

12-18 breaths/min

VE is about ____ of ideal body weight

100 mL/kg

When determining VT for ventilated patients, a range of ________ of IBW is typically used for adults

6-8 ml/kg

When determining VT for ventilated patients, a range of _____________ of IBW is typically used for infants and children

4-8 ml/kg

Lower VT rates (e.g., 4 mL/kg IBW) have been successfully used to _ of adult patients with acute respiratory distress syndrome (ARDS)

Ventilate the lungs

Lower VT rates (e.g., 4 mL/kg IBW) have been successfully used to

ventilate the lungs of adult patients with

An alternative method for calculating initial VT settings is to use _ rather than calculations of IBW.

predicted values for body weight

The predicted body weight of male patients can be calculated using the following equation:

50 + 0.91 (centimeters of height - 152.4).

For female patients the predicted body weight can be deter- mined using the following equation:

45.5 + 0.91 (centimeters of height × 152.4)

Recommended tidal volumes for ventilated patients vary depending on the _

lung pathology

For patients with normal lungs, such as patients with a drug overdose or patients with the postoperative effects of anesthesia, an initial VT of and a rate of __ is generally accepted

• 6 to 8 mL/kg - 10 to 20 bpm

In patients with chronic obstructive pulmonary disease (COPD) and asthma, in which airway obstruction and resistance are high, an initial VT of with a rate of _ is acceptable

• 6 to 8 mL/kg - 8 to 12 breaths/min

In patients with chronic or acute restrictive disease such as pulmonary fibrosis or ARDS, an initial VT of with a rate of _ is indicated

• 4 to 6 mL/kg - 15 to 25 breaths/min

The VT should be adjusted to maintain plateau pressure less than and rates adjusted to minimize

• 30cm H2O - auto PEEP

A VT of more than 9 to 10 mL/kg is not recommended because of the:

- risk of high pressures - accompanying over - trauma to the lungs

Low volume settings (4 to 8 mL/kg) are beneficial in ______ and may help prevent high pressures and alveolar overdistention.

Restrictive disease

Regardless of the method used for selecting the VT for a patient, it is important for clinicians to be aware of four risks during the setup of:

1. Overdistention of lung tissue 2. Repeated opening and closing (recruitment/ derecruitment) of alveoli 3. Atelectasis formation 4. Inadequate VT setting

Calculating Ideal Body Weight (IBW) Women:

IBW (lbs) = 105 + 5(H − 60), where H is height in inches.

Calculating Ideal Body Weight (IBW) men:

IBW (lbs) = 106 + 6(H − 60).

When setting tidal volume (VT) and rate, the goal is not to focus so much on the exact VT and rate, but to focus on _____

using settings that do not harm the patient.

Maintaining plateau pressure lower than ______ is very important

30 cm H2O

In some cases it may even be necessary to let ___________ to avoid lung injury

PaCO2 rise and pH fall outside the patient's normal values

The VT set on the ventilator control panel represents the amount of ______

gas sent to the ventilator circuit

Some of the gas volume will not be delivered to the patient because of ______ .

leaks and the effects of tubing compliance.

Reflects the volume (in milliliters) of gas compressed in the ventilator circuit for every centimeter of water pressure generated by the ventilator during the inspiratory phase

Tubing compliance or system compressibility

CT =

change in volume divided by change in pressure (ΔV/ΔP) in mL/cm H2O

Exhaled volume from the ventilator tubing and the patient's lungs pressure builds in the ventilator circuit during inspiration, the circuit expands along with the patient's lungs; therefore:

The total volume that goes to the circuit never reaches the patient.

the volume of gas trapped under pressure in the patient circuit is referred to as ______

compressible volume, or the volume lost as a result of CT.

The compressible volume varies depending on the _____

type of circuit used

Another consideration when setting the VT is defined as the _____

volume of gas that is rebreathed during ventilation.

For example, to add flexibility to the patient-ventilator connection, clinicians sometimes add a _____ between the Y-connector and the endotracheal tube connector

6 inch piece of corrugated tubing

Number of devices can ______ the amount of VDmech added to the breathing circuit.

Decreased or increase

the use of an endotracheal tube slightly reduces Vdmech by about _____ because the tube bypasses the upper airway (mouth and nasal passages)

1 mL/kg IBW

the use of an endotracheal tube slightly reduces Vdmech by about 1 mL/kg IBW because the ______

tube bypasses the upper airway (mouth and nasal passages).

In contrast, the addition of a Y-connector between the ventilator and the patient may add about _____

75 mL of VDmech

Heat-moisture exchanger (HME) inserted between _____ adds VDmech to the circuit (20 to 90 mL)

Endotracheal tube and y-connector

Respiratory therapists added VDmech to increase the ______ of patients who were _______ and developed a ________ that could not be corrected by other methods

- PaCO2 - hyperventilating - RESPIRATORY ALKALOSIS

During ____ , the clinician may have the option to select a variety of ventilator flows and flow patterns.

VC-CMV

-The flow setting on a mechanical ventilator determines how fast the ______

inspired gas will be delivered to the patient.

During ________, high flows shorten TI and may result in higher peak pressures and poor gas distribution.

controlled mechanical ventilation

slower flows may:

- reduce peak pressures - improve gas distribution - increase Paw at the expense of increasing TI

Shorter expiratory time can lead to:

- air trapping - and using a longer TI may also cause cardiovascular side effects

In general the goal of inspiratory flow should be to _______.

use the shortest TI possible

Selecting the most appropriate flow pattern and ventilator rate depends on the _____

Patients lung condition

For example, postoperative patients recovering from anesthesia may have _______ , whereas a young adult with pneumonia and a strong hypoxemic drive would have a ______

- very modest flow demands - very strong flow demand

The most common flow patterns used clinically are the _______

constant flow and descending (decelerating) flow waveforms

Clinicians often select the ________ simply because it is most familiar to them, or it is the only one available on the ventilator in use.

Constant flow pattern

Constant flow patterns are also called ______

rectangular and square waveform.

For initiating ventilation, a ______ pattern is acceptable

Rectangular flow

Generally a constant flow pattern provides the _______ with an equivalent peak flow rate setting.

shortest TI of all the available flow patterns

The amount of gas flow delivered at the beginning of the breath is probably the _____

major determinant of patient effort and work of breathing

A descending (decelerating) flow waveform has a distinct advantage compared with other wave- form patterns. With a descending pattern, flow is greatest at the ________

beginning of inspiration, when patient flow demand is the highest

The descending waveform occurs naturally in ______

Pressure Ventilation

The ascending ramp provides a ______

progressive increase in flow

The ascending ramp is currently not ______, and is available only on a _____

- used by most clinicians
- few older-generation ventilators.

There are no compelling studies that support the use of the ______

ascending flow ramp.

_______ produces a tapered flow at the end of inspiratory phase.

The sine flow pattern

Although it has been suggested that this type of flow pattern may contribute to a more even distribution of gas in the lungs than the flow of the constant flow ventilator, it is not commonly used clinically and additional clinical studies will be required to verify its efficacy

Sine flow pattern

When initiating mechanical ventilation, most clinicians will choose to start with a ______ or _______

- descending (decelerating) ramp
- constant (rectangular) waveform

most clinicians will choose to start with a descending (decelerating) ramp or a constant (rectangular) waveform for the following reasons:

•The mean airway pressure is higher with descending flow waveforms.
•The peak inspiratory pressure is higher with ascending flow waveforms and lower with descending flow waveforms
•Descending waveforms improve gas distribution.
•Descending waveforms improve arterial oxygenation.

In patients with normal lung function, flow pattern selection is ______

not a critical issue

In patients with hypoxemia and low lung compliance (CL), the descending flow pattern may be beneficial by ______

- maintaining low peak
- pressures and high Paw
- improving gas distribution.

In patients with ______, the descending pattern is more likely to deliver a set VT at a lower pressure and provide for better distribution of air through the lung than a constant flow

high airway resistance

In patients with high airway resistance, the _______ is more likely to deliver a set VT at a lower pressure and provide for better distribution of air through the lung than a constant flow

descending pattern

_______ provides a set pressure to the patient during breath delivery, whereas VT can vary from _______

- Pressure-targeted ventilation
- breath to breath

Volume-targeted ventilation has the advantage of ______ however, it has the disadvantage of ______ as CL decreases or Raw increases

- guaranteeing volume delivery
- increasing PIP

______ have the advantages of providing flow on demand and potentially limiting pressures to avoid overinflation.

Pressure targeted breaths

With pressure-targeted breath delivery, rapid initial flows may cause ______ with differing lung inflation characteristics (time constants).

frictional forces (shearing) between adjacent alveoli

Functional residual capacity (FRC) frequently decreases when a patient is ______

intubated or placed in a supine position.

It is appropriate to use minimum levels of PEEP ______ to help preserve a patient's normal FRC

3 to 5 cmH2O

In any pressure-targeted breath the difference in pressure (ΔP) between baseline (PEEP + auto-PEEP) And PIP determines ______

what is set to establish VT delivery

PIP determines what is ______

is set to establish VT delivery

PSV is started after the patient has been on ______ and is being changed to partial support to begin the process of discontinuing ventilation

Full ventilatory support

PSV is used to ______ when IMV or spontaneous/CPAP modes are used

support spontaneous breaths in a patient with an artificial airway

PSV pressure is set at a level sufficient to prevent a ______

fatiguing workload on the respiratory muscles

The level of PSV can then be adjusted once it has been ______

initiated to an adequate level

Sometimes simply asking the patient if he or she feels it is easy to breathe and if he or she is getting enough air helps in ______

Adjusting initial PSV

Appropriate adjustment of PSV level can be done at the ____

Bedside

The goal of adjusting PSV is threefold

1. To help increase VT (4 to 8 mL/kg)
2. To decrease respiratory rate (to <30 breaths/min)
3. To decrease the WOB associated with breathing through an artificial airwa

For patients with lung disease, PSV levels of ______ are typically used to compensate for additional work associated with breathing through a tube and ventilator system.

8 to 14 cm H2O

For patients without lung disease, about ______ should be adequate to compensate for the additional work of breathing

5 cm H2O

When patients, particularly infants, are receiving CPAP through a ventilator, it is recommended that pressure support is added if a ______

high level of CPAP (10 cm H2O) is being used.