CPAP- SCIENCE INDICATION AND APPLICATION

PRESENTED BY

DR NISHANT PRABHAKAR

MD PEDIATRICS

DEFINITION

Also called continuous distending pressure (CDP)

Maintenance of an increased (positive)transpulmonary pressure during the inspiratory &expiratory phase of respiration in a spontaniouslybreathing baby.

By which alveoli are kept open which increasethe functional residual capacity(FRC) of the lungsresulting in better gas exchange.

HISTORY

Harrison 1968: described grunting in neonates asnaturally producing end expiratory pressure

Gregory et al, 1971: introduced the clinical use ofdistending pressure in neonates.(via endotrachialtube or a head box)

Kattwinkel reported successful use of nasal prongs inneonates with RDS.

Reports of significant lower incidence of chronic lungdisease from columbia university that used moreCPAP as compared to north american centre have ledto resurgence of interest in CPAP over the last 15years.

PHYSIOLOGY OF CPAP

Increases FRC

Decreases V/Q mismatch

Splints upper airway - airway resistance

Increase tidal volume

Decrease work of breathing

Conserves surfectant

Increase lung compliance

DISADVANTAGES OF CONVENTIONAL VENTILATION

High pressure- Barotrauma

Tidal volumes- Volutrauma

Atelectotrauma

Inflammation & infection- Biotrauma

CV ruptures the interalveolar septa thusdecrease the surface area of gasexchange despite increasing lung volume.

Effect of Ventilator on Preterm Lamb Lung

At 0 hour

24 hour after ventilation

Limitations of premature lung

1.Underdeveloped architect tohold the lung open

2.Thicker and few septa so less SAfor gas exchange

Pinkerton KE, et al J Appl Physiol, 1994

Preterm Lambs at 72 Hours Distal

Airspace Wall Thickness -

CV nCPAP

VENTILATOR INDUCED LUNG INJURY (VILI)

Biotrauma with tube

atelectotrauma

VENTILATOR INDUCED LUNG INJURY (VILI)

Barotrauma

Volutrauma

ADVANTAGE OF CPAP

1. Effect on lung growth- increased protein and DNA

2- increased lung compliance

PVR Increases at Lung Volumes Below and Above FRC

PVR

Lung Volume

FRC

HMD MAS

CPAP MAGIC

Opens lung at FRC

Keeps it open at minimum constant pressure least atelecto & barotrauma

Pulmonary arterial pressure are leasthence less V/Q mismatch less pressurerequired.

No ET tube- no biotrauma

Larger alveolus

r = 1.5

T = 3

P = (2 x 3) / 1.5

P = 4

Smaller alveolus

r = 1

T = 3

P = (2 x 3) / 1

P = 6

CPAP

Law of LaPlace : P = 2T/rP : pressure T : surface tension r : radius

How does CPAP works

Stretches lung pleura and upper airway

CPAP

Prevents collapse of alveoli with

marginal stability

Stabilizes the chest wall

Splints open upper airway

Improves pH

Reduces airway resistance

Recruitment of alveoli

PaO2PaCO2

Improves V/Q mismatch and reduces intrapulmonary shunt

Increased alveolar surface area for gas exchange

Maintains lung at FRC

Reduces work of breathing

Reduces mixed and central apnea

Reduces obstructive apnea

Stimulates stretch receptors

INDICATION OF CPAP

COMMON

Respiratory distress syndrome

Apnea of prematurity (specially obstructive apnea)

Post-extubation in preterm VLBW infants

Transient tachypnea of newborn (TTNB)

OTHER INDICATION

Pneumonia

Meconium aspiration/other aspiration syndrome

Pulmonary edema/pulmonary hemorrhage

Laryngomalacia/tracheomalacia/bronchomalacia

Early CPAP in RDS

was proved to be more beneficial in the atelectaticdisease

lower peak pressure required in infants treated with CPAP

enhance surfactant conservation

reduce the need for IMV by 20%, except infants with birth weight <1500 g.

improve mortality and decrease the incidence of BPD

prevent need for prolong intubation which reduce the incidence of acquired subglottic stenosis

Failure of CPAP therapy in RDS

very low birth weight infant

late application of CPAP

severity of RDS

associated disease e.g. sepsis, hypotension

infants with severe degree of extrapulmonary shunt

(Fox and coworkers, 1977)

CPAP in apnea of prematurity

the application of low-level CPAP decrease the incidence of apnea of prematurity (compared to other forms of stimulation)

improve oxygenation

stimulation or inhibition of pulmonary reflexes

alveolar stabilization

mechanical splinting of airway; reduce supraglotticresistance in both inspiration and expiration

some investigators recommended the early use of CPAP as a preventive measure of apnea of prematurity

CPAP IN INFANTS WITH MAS

pathology of meconium aspiration

atelectasis

large airway obstruction

V/Q abnormalities

application of low-to moderate level CPAP

resolution of atelectasis

stabilization of terminal airway

incidence of pneumothorax: not increased

precautions in case with PPHN

C0NTRAINDICATION OF CPAP

Progressive respiratory failure with PaCO2 levels >60mmhg and/or inability to maintain oxygenation(PaCO2 <50 mmHg)

Certain congenital malformation of the airway(choanal atresia, cleft palate, tracheoesophagealfistula, congenital diaphragmatic hernia,etc)

Severe cardiovascular instability (hypotension)

Poor respiratory drive (frequent apnea andbradycardia) that is not improved by CPAP.

ESSENTIALS OF CPAP

CPAP MACHINES

An ideal CPAP delivery system consists of:

A continuous supply of warm, humidified, blended gases at a flow rate of 2-3 times the infant minute ventilation.

A device to connect CPAP circuit to infants airway.

Means of creating a positive pressure in CPAP circuit.

CPAP DELIVERY SYSTEM

Ventilator : ideal system to provide CPAP but very costly

CPAP system : should have

1. End expiratory pressure of 0-15 cm of water.

2. Humidification of upto 100%

3. Gas flow 5-8 L/min

4. Warming of gases to 34-37˚c

5. Blending oxygen-air mixture FiO20.21-1.0

6. Low noise compressor

7. Compatibility to run days & weeks

8. Reasonable cost

PATIENT INTERFACE FOR PROVIDING CPAP

Nasal prongs

1-Fisher & paykel 2-Hudson 3-Argyl nasal prong

CPAP DEVICES

SETTING PRESSURE, FLOW & FiO2

1. Pressure- regulated by depth of immersion ofexpiratory limb(water level being constant).startwith 5 cm water in case of RDS or pneumonia and 4cm water for apnea management.(range- 4-8)

2. Flow- it should be minimal to produce bubbling inthe bubble chamber(2-5 L/min is sufficient)

3. FiO2- start with a FiO2 of 40 to 50% and afteradjusting the pressure,titrate FiO2 to maintain SpO2between 89% to 94%.

MONITORING ADEQUACY AND COMPLICATION OF CPAP

MONITORING THE INFANT CONDITION

Recommended monitoring:

• Respiratory status (RR, work of breathing)

• Pre ductal oxygen saturation

• Cardiovascular status (HR, BP, perfusion)

• GI status (abdominal distention, bowel sounds)

• Neurological state (tone, activity, responsiveness)

• Thermoregulation (temp)

WEANING FROM CPAP

It is considered when clinical conditionfor which CPAP was indicated ispassive.

e.g. in case of RDS we have to see forimprovement in Silverman Andersonscore i.e. if score is less than 4 we cantry weaning

SILVERMAN ANDERSON SCORE Score >7 –respiratory failure

Score 4-7 –respiratory distress

WEANING FROM CPAP

CPAP for apnea may be removed after 24 -48 hrs of apneafree interval.

If the baby is stable on CPAP,first wean off the oxygen insteps of 5% and then wean PEEP to minimum of 4cm instep of 1cm/change.

When baby is in FiO2<30%, PEEP 4cm, with normalsaturation and minimal retraction CPAP can be removed.

CPAP FAILURE

CPAP failure is considered if FiO2 required is>60% and PEEP required is > 7cm of water.

If baby is continuing to have retraction,grunting and apnea is considered fomechanical ventilation.

If PaO2<50%, SpO2<85%, and PaCO2>60%on CPAP with FiO2>60% and PEEP >7cm ofwater is also considered for mechanicalventilation.

BEFORE CONSIDERING CPAP FAILURE ENSURE THE FOLLOWING

Maintaining Optimal Airway Care: Humidification

• Maintain adequatehumidification of thecircuit to preventdrying of secretions.

• Adjust settings tomaintain gashumidification at orclose to 100%.

• Set the humidifiertemperature to 36.8-37.3o C.

Complications associated with bubble nasal CPAP

● Pneumothorax / PIE

- more in the acute phase

- not a contraindication for continuing CPAP

● Nasal obstruction

- Remove secretions and check for proper positioning of the prongs

● Nasal septal erosion or necrosis

- Keep prongs away from the septum

● Gastric distension

Intermittent or continuous aspiration of the stomach

● Feeding intolerance

Preventing Complications: Gastric Distention

• NCPAP is not acontraindication toenteric feeding.

• Infants mayexperience mildabdominaldistention duringNCPAP deliveryfrom swallowing air.

CPAP BELLY

Preventing Complications: Gastric Distention

To prevent gastric distention:

• Assess the infant’s abdomen regularly

• Pass an oro-gastric tube to aspirate excess air before feeds q 2-4 hr

• An 8 Fr oro-gastric tube may be left indwelling to allow for continuous air removal

CASE STUDY

Antenatal steroid

Arrangement before birth

Exercise