16. Mechanical Ventilation

Best Practices Clinical Guidelines for Mechanical Ventilation in Neonates

Mammady Al maghayrehDate: October 17-19, 2011

Venue: Pr. Rahma Hospital/Auditourium

Introduction It is an invasive life-support procedure with many

effects on the cardiopulmonary system The goal is to optimize both gas exchange and clinical

status at minimum FiO2 and ventilator pressure. The ventilator strategy employed to accomplish this goal depends in part on the infant disease process.

Conventional positive pressure ventilation remains the mainstay of assisted ventilation in neonates despite the development of new ventilatory techniques.

2

Physiologic functions of the lung

VentilationThe movement of air between the atmosphere and the

respiratory portion of the lungs

PerfusionThe flow of blood through the lungs

DiffusionThe transfer of gases between the air-filled spaces in the

lungs and the blood.

Ventilation

Depends on the conducting airways:

Nasopharynx and oropharynxLarynxTracheobronchial tree

Open AlveoliFunction:

Moves air in and out of the lung, warms and humidifes. Airways do not participate in gas exchange.

Lung ComplianceThe ease with which lungs can be expandedSpecifically, the measure of the change in lung

volume that occurs with a given change in transpulmonary pressure

Determined by two main factors Distensibility of the lung tissue and

surrounding thoracic cage Surface tension of the alveoli

Pulmonary Mechanics during Assisted Ventilation

Compliance (ml/cmH2O) =Distensible nature of lungs and chest wall. = Change in volume (ml) X change in

pressure (cmH2O)Neonates have greater chest wall

CompliancePremature infants with RDS have stiffer lungs

(poorly compliant lungs).

Neonatal lung Normal 0.003-0.006 L/cm H2Owith RDS 0.0005-0.001 L/cm H2O

Resistance

10

Resistance (cmH2O/L/sec)= Property of airways and lungs to resist gas. = Change in pressure (cmH2O) X Change in flow

(L/sec) Time constant of the respiratory system = Resistance x

Compliance

Resistance in infants with normal lungs ranges from 25 to 50 cm H2O/L/sec.It is increased in intubated babies and ranges from 50 to 100 cm H2O/L/sec.

Pulmonary mechanics

Time constant The time taken for the airway pressure (and

volume) changes to equilibrate throughout the lung is proportional to the compliance and resistance of the respiratory system

Time constant = Compliance x Resistance

Pulmonary mechanics

Almost full equilibration: 3-5 time constants

100

80

60

40

20

01 2 3 4 5 Time constants

Cha

nge

in p

ress

ure

)%(

6386

95 98 99

14

Time ConstantInspiratory time must be 3-5 X time constant1(„ One time conststant = time for alveoli to discharge 63% of its volume through the airway.2(„Two time constant = 84% of the volume leaves3(„ Three time constant = 95% of volume leaves.

Lung Mechanics Differ in Different Disease States

DiseaseCompliance

ml/cm H2O

Resistance

(cm/H2O/ml/s)

Time

Constant(s)

FRC

(ml/kg)

V/Q

Matching

Work

Normal

Term4-620-400.2530------

RDSDecreasedDecreasedDecreasedDecreasedDecreasedIncreased

Meconium

AspirationDecreasedIncreasedIncreasedIncreasedDecreasedIncreased

BPDIncreased/

DecreasedIncreasedIncreasedIncreasedDecreasedIncreased

Air leakDecreasedIncreasedIncreasedIncreasedDecreasedIncreased

VLBW apnea

DecreasedDecreasedDecreasedDecreasedDecreasedIncreased

15

Basic Ventilator Parameters

FiO2

Fractional concentration of inspired oxygen delivered expressed as a % (21-100)

Breath Rate (f)The number of times over a

one minute period inspiration is initiated (bpm)

Tidal volume (VT)

The amount of gas that is delivered during inspiration expressed in mls or Liters. Inspired or exhaled.

FlowThe velocity of gas flow or

volume of gas per minute

Phase Variables

Trigger (start)- begins inspiratory flowCycling (end)- ends inspiratory flowLimiting (continue)- places a maximum value on a

“control variable”pressurevolumeflow

time

Breath Type… Only Two (for now)!

MandatoryVentilator does the workVentilator controls start and stop

SpontaneousPatient takes on workPatient controls start and stop

Trigger Variable- Start of a Breath

Time - control ventilationPressure - patient assistedFlow - patient assistedVolume - patient assistedManual - operator control

The Control Variable-Inspiratory Breath Delivery

Flow (volume) controlledpressure may vary

Pressure controlledflow and volume may vary

Time controlled (HFOV)pressure, flow, volume may vary

Inspiratory - delivery limits

Maximum value that can be reached but will not end the breath-VolumeFlowPressure

Expiratory - baseline

Positive End Expiratory PressureExpiratory RetardNegative End Expiratory PressureExpiratory HoldTime Limited Exhalation

PEEP

DefinitionPositive end expiratory pressureApplication of a constant, positive pressure such that at end

exhalation, airway pressure does not return to a 0 baseline

Used with other mechanical ventilation modes such as A/C, SIMV, or PCV

Referred to as CPAP when applied to spontaneous breaths

PEEP

Increases functional residual capacity (FRC) and improves oxygenationRecruits collapsed alveoliSplints and distends patent alveoliRedistributes lung fluid from alveoli to perivascular

space

55 cm cm HH22OO

PEEPPEEP

Gas Exchange during Assisted Ventilation

Carbon Dioxide (CO2)

Diffuses rapidly from the blood into the alveoli. Its elimination depends largely on alveolar

ventilation.Minute alveolar ventilation= (Tidal volume –

Dead space) x Frequency.Tidal volume is determined by the pressure

gradient between inspiration and expiration.

25

CPAP

DefinitionContinuous positive airway pressureApplication of constant positive pressure throughout the

spontaneous ventilatory cycle

No mechanical inspiratory assistance is provided Requires active spontaneous respiratory drive

Same physiologic effects as PEEP

Gas Exchange during Assisted Ventilation (cont.)

Carbon Dioxide (CO2) - (cont.)

Inspiratory duration may partially determine the tidal volume

Tidal volume can be decreased by shortening the inspiratory time.

Changes in ventilator frequency have a strong effect on CO2 elimination

27

OxygenOxygen exchange depends on matching perfusion

with ventilation. Oxygenation is determined by the mean airway

pressure applied. Paw = (PIP –PEEP) [Ti/ (Ti +Te)] + PEEP

28


Mean airway pressure will be augmented by increasing any of the following: Inspiratory flowPIP I:E ratioPEEPFrequency (or rate) by shortening Te

29


The effect of mean airway pressure on oxygenation is related to:Optimizing the lung volumePreventing atelectasis and consequently

improving ventilation perfusion relationships.

30


Conventional Neonatal Ventilator

31

Volume-Cycled Ventilators

Less used to ventilate neonates Deliver a fixed volume irrespective of pressure Flow and I:E ratio determine the tidal volume Does not work well for RDS patient

32

Pressure-Limited, Time-Cycled

Peak inspiratory pressure, and inspiratory timing are selected

Continuous flow of fresh heated humidified gas It allows the infant to make spontaneous

respiratory efforts Fighting neonates may face air leak syndrome

33

Patient Triggered Ventilation

Neonate is able to initiate ventilatory breath by:1) „ Abdominal motion2) „ Chest wall impedance3) „ Airway flow4) „ Great degree of synchronacy between patient and

ventilator

34

Patient–Triggered Ventilators (PTV)

The patient is able to initiate ventilator breaths by1) Abdominal motion2) „ Chest wall impedance3) „ Airway flow4) „ Great degree of synchronacy between patient and ventilator

Triggering the ventilator setting detector The system support the patient if it didn't breath improved tidal volume and blood gases It can be Synchronized (SIMV) or Assisted/ control (A/C) modes Weaning is by reducing the PIP Cerebral blood flow is controlled Reduce the duration of ventilation and ease weaning

35

Troubleshooting Changes in Tidal Volume during Pressure Ventilation of the Neonate

Tidal Volume Change

Possible CuesSolutions

Increase Increased compliance, decreased resistance, decreased PEEP, increased inspiratory time, decreased leak.

Reduce peak inspiratory pressure.

Decrease Decreased compliance, increased resistance, decreased peak inspiratory pressure, increased PEEP, decreased inspiratory time, increased leak.

Suction airway

Administer surfactant.

Increase inspiratory pressure, performing a transillumination to check for pneumothorax, obtaining chest radiography, and check tube positioning.

36

Indications for Mechanical Ventilation

Absolute indicationsSevere hypoxemia with a PaO2 less than 50mm

Hg despite FiO2 of 0.8Respiratory acidosis with pH of less than 7.20 to

7:25 or PaCO2 above 60mm Hg.Severe prolonged apnea

37

USAID-Funded Health Systems Strengthening II Project 38

Relative indicationsFrequent intermittent apnea unresponsive to

drug therapyEarly treatment when use of mechanical

ventilation is anticipated because of deteriorating gas exchange

Relieving work of breathing in an infant with signs of respiratory difficulty

Initiation of exogenous surfactant therapy in infants with RDS

39

Indications for Mechanical Ventilation (cont.)

Volume vs… Pressure Control Ventilation

Volume Ventilation

Volume delivery constant Inspiratory pressure

varies Inspiratory flow constant Inspiratory time

determined by set flow and VT

Pressure Ventilation

Volume delivery varies Inspiratory pressure

constant Inspiratory flow varies Inspiratory time set by

clinician

The Effects of Ventilator Setting Changes on Blood Gases

Effects on Blood Gas Tensions

Ventilator setting changesPaCO2PaO2

Increase PIPDecreaseIncrease

Increase PEEPIncreaseIncrease

Increase FrequencyDecreaseIncrease

Increase I:E Ratio------Increase

Increase FiO2------Increase

Increase FlowDecreaseIncrease

41

Starting Ventilator Settings

Guidelines for Endotracheal Tube Size

Infant Weight (gm)Endotracheal Tube Internal Diameter

< 1,0002.5mm

1,000-2,0003.0mm

2,000-3,0003.5mm

> 3,0003.5 - 4.00mm

42

Initial Settings for mechanical ventilationSettingInstructions for Use

Peak inspiratory pressure (PIP)As needed to provide tidal volume of 5-7ml/kg.

Positive end-expiratory pressure (PEEP)

3-5cm H2O

Rate40- 60/minute.

Inspiratory time0.3- 0.4 seconds

Fractional inspired oxygen concentration (FiO2)

maintain SpO (88-93%)

Flow8-12L/minute.

43

Starting Ventilator Settings (cont.)

The subsequent settings for mechanical ventilation

Subsequent SettingsPEEPPIP

Low PaO2, low PaCO2Increase

Low PaO2, high PaCO2Increase

High PaO2, high PaCO2Decrease

High PaO2, low PaCO2Decrease

44


Monitoring the infant during mechanical ventilation First blood gas after 15-30 mins Blood gas after 15-30 mins of every change Regularly blood gas every 6 hrs Continuous vital sings monitoring

45


Deterioration during Mechanical Ventilation

Sudden clinical deterioration Mechanical or electrical ventilator failure Disconnected tube or leaking connection Endotracheal tube displacement or blockage Pneumothorax

46

Deterioration during Mechanical Ventilation (cont.)

Gradual deterioration Inappropriate ventilator setting Intraventricular hemorrhage Baby fighting against the ventilator PDA Anemia Infection

47

Paralysis and Sedation

The use of neuromuscular blockade is not routinely indicated

Sedation is restricted to cases when agitation interferes with ventilatory support and when infants fight the ventilator.

It is necessary to increase ventilator pressure after initiation of neuromuscular blockade.

48

Weaning

When the patient is stable, FiO2 and PIP are weaned first.

Decrease PIP as tolerated and as chest rise diminishes.

When PIP is around 20, attention is directed to FiO2 and then to the respiratory rate alternating with each other

As frequency is decreased, Te should be prolonged For larger infants, endotracheal CPAP when PIP 15-

18 cm H2O and FiO2 40%

49

Weaning (cont.)

The infant can be weaned to oxygen hood when PEEP is 4cm H2O

For less than 1.750gm, when PIP is less than 15cm and FiO2 30% decrease respiratory rate to 15-20/ min then to nasal CPAP

In most infants, when ventilator frequency of approximately 15 breaths per minute is tolerated, endotracheal CPAP may be tried for a short period of time before extubation.

50

Weaning (cont.)

Atelectasis after extubation is common in preterm infants recovering from RDS.

Use of nasal CPAP may prevent atelectasis. Steroids are not routine before extubation, but if

there was prolonged intubation or previous failed attempts of extubation, a short course of steroids may facilitate extubation.

If strider developed epinephrine aerosols and steroids may be helpful

51

Complications of Mechanical Ventilation

Endotracheal tube complications and tracheal lesions

Airway injury Air leak Chronic lung disease/Oxygen toxicity Intraventricular hemorrhage Decreased cardiac output Feeding intolerance

52

Pulmonary Hygiene

Chest physiotherapy

Suction

53

Goals of Pulmonary Hygiene

Maintain a patent airway by clearing secretions Promote optimal pulmonary oxygenation and

ventilation Prevent pulmonary infection from accumulated

secretions Facilitate removal of pulmonary debris

54

Chest Physiotherapy Indication

Intubated neonates: Chest physiotherapy should only be applied if it is

clearly indicated. No CPT after surfactant administration CPT in early RDS increases incidence of

intraventricular hemorrhage Post-extubation Chronic lung disease of prematurity

55

Physiotherapy and surgeryAfter abdominal or cardiac surgery Postoperative physiotherapy should never be

“routine” but should be used judiciously.

56

Chest Physiotherapy Indication (cont.)

Chest Physiotherapy Technique

Positioning

Vibration

57

When It Is Indicated

During intubation and ventilation Post ex-tubation Premature with chronic lung disease After abdominal and chest surgery

58

Suction

Methods of suctioning: Open Closed

Catheter suction ca be: Deep Shallow

Suctioning should be performed under strict sterile preparation

59

Suction Procedure

Shallow suction is recommended to prevent trauma Deep suction may cause apnea and vagal

stimulation Duration of suction should be 15 seconds

60

Follow-up Care

Hyper-oxygenation for at least 1 min especially for hypoxemic infants

Hyperventilation should not be routinely used. The patient should be monitored for adverse

reactions

61

Indications

Secretions in peripheral airways should not be directly removed by endotracheal suctioning

Suctioning should be performed only when clinically indicated

To remove accumulated pulmonary secretions To maintain the patency and integrity of the

artificial airway

62

Signs of Increased Pulmonary Secretions

Increased peak inspiratory pressure during volume-controlled mechanical ventilation

Decreased tidal volume during pressure-controlled ventilation

Deterioration of oxygen saturation and/or arterial blood gas values

Visible secretions in the airway Acute respiratory distress Suspected aspiration of gastric or upper-airway

secretions The need to obtain a sputum specimen

63

Complications Decrease in dynamic lung compliance and functional

residual capacity Atelectasis Hypoxia/hypoxemia Tissue trauma Bronchoconstriction/bronchospasm Increased microbial colonization Changes in cerebral blood flow and increased

intracranial pressure Hypertension or hypotension Cardiac dysrhythmias

64

Assessment of Outcome

Improvement in appearance of ventilator graphics and breath sounds

Decreased need for ventilation support Improvement in arterial blood gas values or

saturation Removal of pulmonary secretions

65

The following should be monitored prior to, during, and after the procedure:Breath soundsOxygen saturationPulse rateSkin colorRespiratory rate and patternSputum characteristics: color, volume,

consistency, and odorVentilator

66

Monitoring during suction (cont.)

Recommendations

Endotracheal suctioning should be performed only when secretions are present and not routinely. (1C)

Pre-oxygenation should be considered if the patient has a clinically important reduction in oxygen saturation with suctioning. (2B)

Performing suctioning without disconnecting the patient from the ventilator (2B)

Use of shallow suction (2B)

67

Routine use of normal saline instillation prior to endotracheal suction should not be performed. (2C)

A suction catheter is used that occludes less than 70% of the lumen of the ETT in infants. (2C)

The duration of the suctioning event be limited to less than 15 seconds. (2C)

68

Recommendations (cont.)

High Frequency Ventilation(HFV)

Rescue following failure of conventional ventilation (PPHN, Meconium).2,3

Air leak syndromes (pneumothorax, pulmonary interstitial emphysema) 4

To reduce barotrauma when conventional ventilator settings are high

Frequency

•High frequency ventilation rate (Hz, cycles per second)

MAP

•Mean airway pressure (cmH2O) Amplitude

•delta P or power is the variation around the MAP

Oxygenation is dependent on MAP and FiO

2

•MAP provides a constant distending pressure equivalent to CPAP. •This inflates the lung to a constant and optimal lung volume maximising the area for gas exchange and preventing alveolar collapse in the expiratory phase. •Ventilation is dependent on amplitude and to lesser degree frequency. •Thus when using HFV CO2 elimination and oxygenation are independent

The clinician sets

The amplitude . Frequency of the pressure wave generated by the

ventilator piston or diaphragm Mean airway pressure (MAP) Inspiratory time. Fractional inspired concentration (FiO2)

USAID-Funded Health Systems Strengthening II Project 71

Optimal lung volume strategy(aim to maximise recruitment of alveoli).

Set MAP 2-3 cmH2O above the MAP on conventional ventilation

MAP in 1-2 cmH2O steps until oxygenation improves

Set frequency to 10 Hz

HFV

Low volume strategy(aim to minimise lung trauma)

Set MAP equal to the MAP on conventional ventilation

Set frequency to 10 Hz Adjust amplitude to get an adequate chest

wall vibration.

Making adjustments once established on HFVMaking adjustments once established on HFV

Poor Oxygenatio

n

Over Oxygenatio

n

Under Ventilation

Over Ventilation

Increase FiO2

Decrease FiO2

Increase Amplitude

Decrease Amplitude

Increase MAP

(1-2cmH2O)

Decrease MAP

(1-2cmH2O)

Decrease Frequency (1-2Hz)

if Amplitude Maximal

Increase Frequency (1-2Hz)

if Amplitude Minimal

16. Mechanical Ventilation

Documents

Transcript of 16. Mechanical Ventilation