From: http://emedicine.medscape.com/article/304235-overview
Modes of ventilation
Choosing the initial mode of ventilation is based in part on past experience, in part on the capability of ventilators available to provide support, and in part on the condition being treated. Most patients who are provided noninvasive ventilation are provided support with pressure ventilation, with continuous positive airway pressure (CPAP), which is the most basic level of support. CPAP may be especially useful in patients with congestive heart failure or obstructive sleep apnea.Bilevel positive airway pressure (BiPAP) is probably the most common mode of support and requires provision of inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP). The difference between IPAP and EPAP is a reflection of the amount of pressure support ventilation provided to the patient, and EPAP is synonymous with positive end-expiratory pressure (PEEP). Some noninvasive ventilation is provided using proportional-assist ventilation (PAV), which provides flow and volume assistance with each breath. While volume ventilators can be used to provide noninvasive ventilatory support, the previously described modes are preferred because they provide better patient comfort and synchrony and are more tolerant of the leaks that accompany all noninvasive ventilatory interfaces.Initial ventilator settings and adjustmentsAdequate ventilation and oxygenation, correction of respiratory failure, and adequate patient tolerance and comfort are the primary goals of noninvasive ventilation, and adjustments are made to achieve these endpoints. Initial settings focus on achieving adequate tidal volumes, usually in the range of 5-7 mL/kg. Additional support is provided to reduce the respiratory rate to less than 25 breaths/minute. Oxygen is adjusted to achieve adequate oxygenation, with a pulse oximetry goal of greater than 90%. Serial arterial blood gas measurements are essential to monitor the response to therapy and to guide further adjustments in the ventilator.
Initial IPAP/EPAP settings
Start at 10 cm water/5 cm water
Pressures less than 8 cm water/4 cm water not advised as this may be inadequate
Initial adjustments to achieve tidal volume of 5-7 mL/kg (IPAP and/or EPAP)
Subsequent adjustments based on arterial blood gas values
Increase IPAP by 2 cm water if persistent hypercapnia
Increase IPAP and EPAP by 2 cm water if persistent hypoxemia
Maximal IPAP limited to 20-25 cm water (avoids gastric distension, improves patient comfort)
Maximal EPAP limited to 10-15 cm water
FIO2 at 1.0 and adjust to lowest level with an acceptable pulse oximetry value
Back up respiratory rate 12-16 breaths/minute
Predictors of successful noninvasive ventilation
Importantly, recognize that certain parameters may predict successful noninvasive ventilation or failure of noninvasive ventilation, so that patients are not subjected to continued treatment when optimal treatment requires intubation and mechanical ventilation. This includes changes during a trial of noninvasive ventilation. The changes, in turn, are a reflection of the patient's ability to cooperate with noninvasive ventilation, patient-ventilatory synchrony, and noninvasive ventilation effectiveness. Trials of noninvasive ventilation are usually 1-2 hours in length and are useful to determine if a patient can be treated with noninvasive ventilation. Extended trials without significant improvement are not recommended because this only delays intubation and mechanical ventilation (unless patients are do-not-intubate status).
Predictors of success - Response to trial of NIV (1-2 h)
Decrease in PaCO2 greater than 8 mm Hg
Improvement in pH greater than 0.06
Correction of respiratory acidosis
Predictors of failure
Severity of illness
Acidosis (pH <7.25)>80 and pH <7.25)>4 = stuporous, arousal only after vigorous stimulation; inconsistently follows commands)
Encephalopathy score (>3 = major confusion, daytime sleepiness or agitation)
Glasgow Coma Scale score lower than 8
Failure of improvement with 12-24 hours of noninvasive ventilationLate failures (>48 h after initiation of noninvasive ventilation)
Admission predictors of failure
Lower functional status (Activity score < 2 =" dyspnea" href="javascript:showcontent(">2,3
Major criteria (any 1 of the following):
Respiratory arrest
Loss of consciousness with respiratory pauses
Gasping for air
Psychomotor agitation requiring sedation
Heart rate less than 50 bpm with loss of alertness
Hemodynamic instability with systolic blood pressure less than 70 mm Hg
Minor criteria (2 of the following):
Respiratory rate greater than 35 breaths/minute
pH less than 7.30 and decreased from onset
PaO2 less than 45 mm Hg despite oxygen
Increase in encephalopathy or decreased level of consciousness
Intubation guidelines4
Any 1 of the following:
pH less than 7.20
pH 7.20–7.25 on 2 occasions 1 hour apart
Hypercapnic coma (Glasgow Coma Scale score <8>60 mm Hg)
PaO2 less than 45 mm Hg
Cardiopulmonary arrest
Two or more of the following in the context of respiratory distress:
Respiratory rate greater than 35 breaths/minute or less than 6 breaths/minute
Tidal volume less than 5 mL/kg
Blood pressure changes, with systolic less than 90 mm Hg
Oxygen desaturation to less than 90% despite adequate supplemental oxygen
Hypercapnia (PaCO2 >10 mm increase) or acidosis (pH decline >0.08) from baseline
Obtundation
Diaphoresis
Abdominal paradox
