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
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
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.
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
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 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
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.
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.
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