Page 238 - Clinical Application of Mechanical Ventilation

204 Chapter 7

pressures varies greatly. Some equipment detects snoring while others detect inspi-
ratory flow patterns or airway vibration. In patients with uncomplicated OSA, un-
attended autotitration of CPAP may be suitable for the relief of airway obstruction.
Autotitration should be used following thorough medical screening and complete
patient education on the use of the prescribed CPAP device (Berthon-Jones et al.,
1996; Teschler et al., 1996).
Unattended autotitration should not be used in patients with central sleep apnea,
cerebral vascular accident, prolonged hypoventilation, hypovolemia, or cardiac fail-
ure. Other potential contraindications to autotitrating CPAP equipment include
uncontrolled asthma, epilepsy, angina, fluid and electrolyte disturbances, noctur-
nal myoclonus, and other parasomnias. Severe air leak around the mask should be
corrected before implementing autotitrating CPAP (Teschler et al., 1998).

Ramp

Ramp is a feature in which the starting pressure (i.e., preset or adjustable) gradually in-
creases over time (e.g., up to 45 min) until the desired pressure is reached. This feature
is ideal for patients who may have trouble tolerating a sudden onset of high pressure.

C-flex™

C-Flex™ is a method of delivering CPAP for the treatment of OSA. A common
complaint by patients is that they have trouble exhaling against the continuous
positive pressure. This problem may result in frequent awakening during sleep,
sleep fragmentation, and occasional noncompliance in the use of the equipment.

C-Flex™ provides pressure relief during exhalation. This reduces the continuous
pressure which the patient must overcome during exhalation.
C-Flex™ is titrated in the same way as conventional CPAP. During use, the equip-
ment monitors the airflow during exhalation and reduces expiratory pressure pro-
portional to expiratory flow. The relief pressure is provided on a breath-to-breath
basis, depending on the actual expiratory airflow. Prior to the end of expiration
and start of inspiration, the preset CPAP level is restored. Three levels of C-Flex™
(1, 2, 3) are available and each higher level provides progressively increased pressure
relief.

TITRATION Of BIlEVEl POSITIVE AIRwAy PRESSURES

When positive airway pressure is used to support acute respiratory failure, the IPAP
and EPAP levels are set independently. Bilevel refers to the inspiratory and ex-
piratory positive airway pressure settings. For example, a bilevel positive airway
A typical starting point
TM
for BiPAP is 8/4 (8 cm H 2 O pressure setting of 8 and 4 means that the IPAP is 8 cm H O and the EPAP is
2
inspiratory and 4 cm H 2 O 4 cm H O. Common initial pressure settings are IPAP from 8 to 12 cm H O and
expiratory) and titrated to an 2 2
appropriate level. EPAP from 4 to 5 cm H O (Hill, 2004). The procedure for titration of IPAP and
2
EPAP (ResMed Corp., 1998a) is outlined in Table 7-6.

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