The Use of CPAP in Acute
CHF
Donald M. Pell M.D. FCCP
The Effects
of CPAP
on Cardio-Respiratory Function
I. Normal Physiology
I. Normal Physiology
• Normal respiratory effort is
handled by the diaphragm.
• Air is drawn into the lungs
when the diaphragm
contracts.
• As diaphragm contracts,
pressure falls in chest and
rises in abdomen
pressurizing venous blood
to return to right heart, (the
thoracic-abdominal pump).
Normal Physiology (con’t.)
• Air is drawn into lungs,
reduced pressure in chest
draws venous blood to right side
of heart (pre-load).
• The expanding lung acts as a pump, pools returning
venous blood in lung circulation, decreases left heart
filling.
• Lung exhales, work is done by stretched elastic tissues
and vessels, no effort.
Normal Physiology (con’t.)
• Lung expands/contracts, air spaces (alveoli) kept open
by surfactant made by the lining cells.
• Negatively charged, walls repel each other, preventing
total collapse of the alveoli when in a near-empty air
position.
• This synchronized effort allows air/blood to flow through
lungs, achieves CO2 transfer and acquires oxygen at
same time.
II. Abnormal Physiology
Acute Heart Failure
(Pulmonary Edema)
Acute Heart Failure
(Pulmonary Edema)
• Most illness involves left heart.
• Right heart is a receiving chamber,
thin and distended accommodating
returning blood volume.
• Left heart 6 times thicker than right
as it pumps higher pressures i.e., 120 systolic,
80 diastolic.
Acute Heart Failure (con’t.)
• With heart failure, stroke volume
(number of cc’s blood/per beat) falls – to make
up for decreased cardiac output, heart rate rises.
• Increased rate/sympathetic tone . . .
- Increases oxygen demand
- Increases myocardial work
Acute Heart Failure (con’t.)
• Usual causes of left heart failure include:
- Arterial sclerosis
- Hypertension
- Vascular Disease
and/or
- Cardiomyopathy . . .
… alcohol
… thyrotoxicosis
… viral
… familial
Acute Heart Failure (con’t.)
• Left heart is thick, can’t distend.
• Right heart continues to pump making:
- lungs become stiff/rigid,
- lungs become harder to
ventilate,
- reduces gas space,
- water fills air sacs,
- gas transfer oxygen decreased,
- O2 level falls.
Acute Heart Failure (con’t.)
• Therapies to improve left heart reduce pre-load . . .
(blood getting to the heart) and therapies that reduce
afterload (resistance to blood flow leaving the left heart).
- Nitroglycerin and ACE Inhibitors
• Drugs to reduce sympathetic tone (autonomic vasoconstriction/fluid retention).
- Aldactone
CPAP Types
Some examples of CPAP Systems . . .
Vitaid
PulmodyneTM
Boussignac
O2-RESQTM
Philips
Respironics
Mercury Medical®
Flow-Safe TM
WhisperFlow ®
There are many types of CPAP systems available today. Some use flow generators, others do not.
The new disposable CPAP systems are cost-efficient, lightweight, convenient and reliable. Most are
available with accessories such as; masks, head straps, T-piece, filters, valves and connectors.
Acute Heart Failure (con’t.)
• CPAP Therapy
- improves abnormal work-of-breathing,
- corrects hypoxia,
- decreases myocardial O2
consumption,
- reduces pre-load/afterload,
- decreases sympathetic tone
reducing cardiac risk,
and decreases cardiac arrhythmia.
What is CPAP?
(continuous positive
airway pressure)
• Pressurizing O2 with a mixture to lungs through
sealed mask device with titratable flow:
- Fast attainment of work reduction
and cardiac stability.
- Decreased need for intubation and
possible consequences.
- misplacement,
- tissue damage/bleeding,
- cardiac arrhythmia,
- dental damage.
What is CPAP? (con’t.)
• Pressure/Flow generators no longer necessary . . .
- disposable CPAP systems require no
pressure/flow generator, only oxygen flow,
- titratable from 2-1/2 cm H2O to 10 cm H2O,
- Improved head straps, coaching, and attaining O2
saturation,
- CPAP is transferred to E.R. along with O2
flow/pressure settings for continued continuity of care.
What is CPAP? (con’t.)
• CPAP?
- It’s like blowing up a balloon
and allowing it to inflate the lungs.
- Set level of pressure is applied to raise
airway pressure and expand alveoli. It will
also restrict air flow out of lung (like pursed
lip breathing).
- Expiratory work done by elastic recoil of lung,
doesn’t require muscle help once CHF
improves.
Respiratory Goals
of CPAP . . .
•
•
•
•
•
•
•
Increased Alveoli gas volume,
Increased PO2,
Decreased work-of-breathing,
Increased O2 transfer,
Lower respiratory muscle oxygen requirement,
Satisfying patient’s respiratory flow needs,
Improving patient’s comfort/clinical status/level
of consciousness.
Cardio-Respiratory Effects
of CPAP
CPAP systems dramatically/beneficially affect
pressure/flow.
• Air is positively pressurized and pushed into airway reducing
inspiratory muscle work, decreasing venous blood flow returning to
right heart as venous flow has to be at higher level than pressure
resisting blood return (CPAP).
• Less blood pooling in lungs/less fluid transferred into air space.
• Decreased sympathetic tone.
• Decreased afterload on left heart.
• Decreased cardiac heart rate.
• Resulting in lowered cardiac work/O2 consumption/reduced cardiac
arrhythmia risk.
When to Use
CPAP . . .
•
•
•
•
•
•
•
Can’t maintain O2 saturation @ 92%/4 liters,
Respiratory distress increasing,
Patient’s level of consciousness decreasing,
Cardiac arrhythmia not responding to drugs,
Respiratory Acidosis increasing (rising PCO2),
Cardiac rate of 120+ not responding to oxygen therapy,
Respiratory rate of 36+ not responding to oxygen
therapy.
Proper Use
CPAP
• Allow patient to hold device in place to feel improvement
in inspiratory ease-of-breathing.
• Once patient is comfortable, titrate pressure upward for
desired results.
• Proper mask fit/nasal fit.
• Adjust head strap once patient is comfortable.
• Stay with patient, coach on improvements attained.
• Adjust flow for patient’s inspiratory flow rates.
• A positive attitude/device can relieve consequences of
CHF.
Goals
of CPAP
• Attain O2 saturation of 92%,
• Decrease work-of-breathing/improve patient’s respiratory
status,
• Decreased cardiac rate of 120 or less,
• Decreased respiratory rate below 30,
• Improved PCO2 level if elevated,
• Improved cardiac arrhythmia,
• Reduced need for in-the-field intubations,
• Improved mental status/cooperation,
• Leave CPAP equipment/settings with patient when
transferred from transport to E.R.
Contraindications
of CPAP
• Facial Trauma/fractures.
• Recent gastric surgery.
• Dense, copious respiratory secretions/frequent
suctioning.
• Patient unable to tolerate mask.
• Respiratory arrest.
• PCO2 greater than 50 in CHF patient/monitor (relative).
• Near lethal cardiac arrhythmia (ventricular tachycardia,
ventricular fibrillation).
• Decreased level of consciousness.
• Persisting vomiting.
• Pneumothorax.
Possible Side Effects
of CPAP
• Nasal bridge skin necrosis (rare).
• Hypotension due to decrease in venous return (rare).
• Claustrophobic (coaching/proper technique),
may eliminate.
What if Diagnosis is Incorrect?
C.O.P.D.
In spite of usual over-inflation of lungs .
..
•
•
•
•
•
CO2 is lowered,
O2 saturation is improved,
LOC improves as PCO2 falls,
Respiratory effort is enhanced,
CO2 production is decreased.
In E.R.
• Excess PO2 can be titrated downward (decrease
pressure slowly), increased PCO2 and low O2 are
corrected).
• Due to dry state, low blood pressure occurs (rarely), to
correct, use rehydration and adjust CPAP pressures
downward.
Asthma
Using CPAP:
• Reduction in inspiratory work.
• Better expansion of previously collapsed alveoli with
reduced CO2 level and increased O2 level.
• Reduced need for intubation.