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NIPPV refers to mechanical ventilation delivered to a patient without placement of an endotracheal or
Figure 75-11
The effect of changing respiratory system compliance
on a dual-control mode that switches the control parameter "breath to breath." The
target tidal volume in this illustration is set at 500 mL. CL
, compliance;
VT
, tidal volume.
By far the most widely used form of noninvasive ventilation today is NIPPV with a mask and a device to deliver positive pressure. Numerous studies have shown that NIPPV may reduce the need for intubation, complication rates, and even mortality in specific respiratory failure scenarios.
NIPPV can be delivered via nasal mask, nasal pillow, or full facemask. Chiumello and associates have described the use of a helmet to assist in the delivery of NIPPV.[83] No patient-machine interface has been shown to be superior, and selection depends on patient comfort. Straps hold the mask firmly to the patient's face to create a seal. Some degree of air leak is tolerated, because strapping the mask too tightly can cause patient discomfort or skin breakdown.
NIPPV can be delivered from a CPAP or BiPAP machine or a standard ICU ventilator.[81] Older BiPAP machines have some disadvantages. Because they are completely
CPAP can be delivered from a CPAP or BiPAP machine or a standard ICU ventilator. It increases FRC and improves oxygenation but gives no direct ventilatory assistance.[82] Its most common use is in the treatment of chronic obstructive sleep apnea at home. In the acute setting, it is most commonly used to treat acute cardiogenic pulmonary edema. CPAP is usually set at 5 to 12 cm H2 O.[81]
Using BiPAP in the spontaneous mode, the clinician sets an inspiratory positive airway pressure (IPAP) and an expiratory positive airway pressure (EPAP). The machine maintains the EPAP (which is analogous to CPAP) until it senses inspiratory effort. It then cycles to the IPAP. The increased pressure is terminated either at a preset time or when flow rate falls below a certain level.[81] [82] Newer BiPAP machines can deliver the IPAP at a preset rate independent of patient effort. Typical settings are an IPAP of 8 to 20 cm H2 O and an EPAP of 4 to 5 cm H2 O. The IPAP should be titrated to give an expiratory tidal volume of about 7 mL/kg and a respiratory rate of less than 25.[86]
Using a standard ICU ventilator, a patient can be ventilated with the pressure support, pressure control, or volume control mode. Pressure support with a standard ventilator is nearly identical to BiPAP, except that the terminology is different. A pressure support of 5 cm and a PEEP of 5 cm is equivalent to an IPAP of 10 cm and an EPAP of 5 cm. Thus the pressure support setting denotes the pressure above PEEP/CPAP that is delivered at inspiration. As with BiPAP, pressure-support ventilation is fully dependent on the patient to initiate breaths, and the pressure support is terminated when flow falls below a certain threshold. In the pressure control mode, the ventilator will deliver breaths independent of patient effort. The breath is terminated after a preset inspiratory time. Usual noninvasive pressure support or pressure control settings are about 8 to 20 cm H2 O with a PEEP of 0 to 6 cm H2 O.[81] Initial pressure settings should be low and they should be titrated up to the same goals described for BiPAP.[86] Noninvasive volume-control ventilation is less frequently used because of concerns about high pressures exacerbating air leaks and causing patient discomfort.
Weaning patients from NIPPV is accomplished by gradually decreasing pressures or increasing the amount of time the patient spends without NIPPV each day. These "rest periods" may be started early after initiation in patients with mild respiratory failure, but only after about 24 hours in patients with more severe respiratory failure.[6] Neither method of weaning has been shown to be superior.
NIPPV has been studied in various populations of patients with both hypercapnic and hypoxic respiratory failure. Studies regarding NIPPV and specific disease processes are discussed later. When deciding whether to treat a patient in acute respiratory failure with NIPPV, one should keep in mind that NIPPV requires a conscious and cooperative patient and that it offers no airway protection. Patient selection criteria are listed in Table 75-8 .[86]
Complications reported with noninvasive ventilation include serious air leaks, skin breakdown, gastric distension, and drying of eyes. A serious air leak will compromise the effectiveness of NIPPV. In addition, it may excessively prolong inspiratory pressure when using BiPAP or pressure support because the inspiratory phase in these modes is terminated by a drop in flow. This problem can be addressed by changing masks or tightening the seal. Limiting inspiratory pressure, when possible, will also reduce air leakage. Finally, changing to pressure-control ventilation, which has a set inspiratory time, will alleviate the problem of a prolonged inspiratory phase caused by an air leak. Facial skin breakdown can be avoided by using occlusive dressings on pressure points on the face and by changing mask position.[86] The potential for gastric distention prohibits NIPPV use in patients with recent gastric or esophageal operations.
NIPPV was first used on a widespread scale to treat chronic respiratory failure in neuromuscular disease and chronic lung disease. It is also the established treatment of choice for obstructive sleep apnea.[87] Recent research suggests that nasal CPAP also may be beneficial in patients with sleep-disordered breathing and chronic heart failure.[88] Claman and colleagues provide an excellent review of the use of noninvasive ventilation for chronic diseases.[89]
| • Conscious and cooperative patient (chronic obstructive pulmonary disease patients may be an exception) |
| • No need for urgent endotracheal intubation to protect the airways or remove copious secretions |
| • No acute facial trauma |
| • No recent gastroesophageal surgery |
| • No active gastrointestinal bleeding |
| • No impaired swallowing |
| • Hemodynamic and rhythm stability |
| • Facemask adequately fitted |
| Adapted from Antonelli M, Conti G: Noninvasive positive pressure ventilation as treatment for acute respiratory failure in critically ill patients. Crit Care 4:15–22, 2000. |
Anesthesiologists are more likely to use NIPPV in the acute setting. Acute respiratory failure due to exacerbation of COPD is the most established indication for NIPPV. Since Meduri and colleagues first reported the use of NIPPV for acute COPD, numerous randomized studies have followed.[90] Brochard and coworkers reviewed a prospective multicenter randomized, controlled trial of patients with acute respiratory failure from COPD.[91] They found that NIPPV reduced need for intubation, overall complications, hospital length of stay, and hospital mortality.[91] A recent meta-analysis of trials using NIPPV in acute respiratory failure from COPD produced the Forest plot, which shows mortality benefit ( Fig. 75-12 ).[92] Based on these results, the authors recommended that, unless there are contraindications, NIPPV should be used routinely for severe acute exacerbations of COPD.
NIPPV has also been studied in the setting of severe respiratory distress from acute pulmonary edema. These studies have demonstrated a decreased need for intubation but no clear mortality benefit.[93] [94] [95] [96] [97] Some clinicians avoid the use of BiPAP or noninvasive pressure support, as opposed to CPAP, based on a study by Mehta and associates comparing BiPAP with CPAP in patients with acute cardiogenic pulmonary edema.[98] This study was terminated at interim analysis because of an excessive number of myocardial infarctions in the BiPAP group. However, more patients in the BiPAP group than the CPAP group presented with chest pain.[98] This indicates that more patients in the BiPAP group presented in the context of an acute myocardial infarction.
Immunosuppressed patients with acute hypoxic respiratory failure are another population studied using NIPPV. These patients have reported mortality rates of 80% to 100% if intubated.[99] [100] Hilbert and colleagues reviewed a randomized trial of 52 patients with immunosuppression of varying etiology (e.g., AIDS, organ transplant, chemotherapy) and acute hypoxic respiratory failure with bilateral pulmonary infiltrates.[101] Of note, these patients were randomized relatively early in their
Figure 75-12
Forest plot summarizing hospital mortality as expressed
by risk difference (absolute risk reduction) for individual trials, pooled results
of nine trials of patients with severe exacerbations, and two trials of patients
with nonsevere exacerbations. Unit of expression equates a reduction of 1.0 as equal
to a 100% risk difference or absolute risk reduction. NPPV, noninvasive positive-pressure
ventilation. (Adapted from: Keenan SP, Sinuff J, Cook DJ, et al: Which
patients with acute exacerbation of COPD benefit from noninvasive PPV? Ann Intern
Med 138:861–870, 2003.)
No studies have been done specifically evaluating the use of NIPPV in postoperative patients. However, Antonelli and colleagues reported a randomized, controlled trial of NIPPV in patients with acute hypoxemic respiratory failure from various causes in which about half of the patients were postoperative.[102] The control patients in this study were intubated and mechanically ventilated. The NIPPV patients showed a decreased rate of serious complications such as pneumonia, sinusitis, and sepsis. The NIPPV patients also had a decreased length of ICU stay.
A more recent study of mechanically ventilated patients who had failed a weaning trial for three consecutive days randomized them to either extubation and NIPPV or a conventional weaning approach.[103] The trial was stopped early because of significant benefits in the intervention arm. The NIPPV patients had a decrease in ventilator days, ICU length of stay, hospital length of stay, need for tracheostomy, and incidences of septic shock and nosocomial pneumonia. They also had improved ICU and 90-day survival rates. These provocative results require duplication in follow-up studies before there is widespread acceptance of such an aggressive approach.
When initiating NIPPV, it is useful to consider which patients are at highest risk of failure and subsequent need for endotracheal intubation. Antonelli and associates carried out a prospective cohort study of patients who received NIPPV for hypoxic respiratory failure.[104] The patients who were most likely to fail NIPPV and require
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