Noninvasive Ventilation

The Big Asthma Lie

Asthma Holistic Treatment

Get Instant Access

Marked increase in inspiratory and expiratory airflow obstruction leads to dynamic hyperinflation in severe AA (137) (Fig. 2). The cumulative cost of this is respiratory muscle fatigue that, along with the associated increase in dead space, may lead to hypercarbic respiratory failure. Noninvasive positive pressure ventilation (NIPPV) has been extensively reported to be beneficial in other forms of hypercapnic respiratory failure (138-142). While only a minority of patients with AA requires mechanical ventilation (143), such patients suffer significantly high morbidity. Unfortunately, the literature on NIPPV for AA treatment is fairly limited.

The goals of NIPPV in asthma are to reduce work of breathing and potentially decrease the degree of hyperinflation, with mechanical support conducted long enough for pharmacologic therapies to take effect. The former is accomplished in two ways. Application of continuous positive airway pressure (CPAP) or expiratory positive airway pressure (EPAP) when matched to the raised intrathoracic pressure seen as a consequence of dynamic hyperinflation [and assessed by the measurement of intrinsic positive end expiratory pressure (PEEP)] allows inspiratory flow to be initiated with lower intrathoracic pressure swings. This reduces the ''inspiratory threshold load'' on breathing in a dynamically inflated state. Adding inspira-tory pressure support assists the exhausted asthmatic in generating adequate tidal volume and further reduces work of breathing and risk of progression to ventilatory failure. Furthermore, the addition of positive pressure may lead to decreased inspiratory time and extension of expiratory time; to the extent this occurs, gas trapping may be reduced.

Meduri et al. (144) reported findings associated with the early implementation of NIPPV in patients with severe asthma exacerbations. Tolerance of NIPPV was excellent. All but one of the 17 patients had improvements in gas exchange as measured by blood-gas analysis, and the majority had a reduction in respiratory and heart rate. While not a

Table 1 Overview of Pharmacotherapy

Standard therapies Albuterol

Corticosteroids Oxygen

Anticholinergics

Adjunctive therapies for Magnesium

Montelukast (IV)

Heliox Antibiotics

Theophylline

Epinephrine

0.5mL of 0.5% solution (2.5mg) in 2.5mL normal saline by nebulization every 20 minutes x 3 or 4-6 puffs by MDI with spacer every 10 minutes initially then every 20 minutes; for intubated patients, consider 10-15 mg/hr continuously and titrate to physiologic effect or side effects. The role of levalbuterol (1.25 mg by nebulization) as replacement for albuterol in patients with side effects is promising yet requires further validation.

Methylprednisolone/prednisone/prednisolone 120-180mg/day over 3-4 doses for the first 48hours, then 60-80mg/day until PF reaches 70% predicted or personal best.

1-3 L/min by nasal cannula; titrate using pulse oximeter to goal saturation > 90% and consider addition of humidification.

Ipratropium bromide 0.5 mg by nebulization every 20 minutes or 4-8 puffs by MDI with spacer as frequently as every 10 minutes initially. (Used in addition to b-agonist, not as first line therapy.)

consideration in severe acute asthma

2gm IV over 10-15 minutes along with standard therapy. Benefit is seen in patients with PF < 20% of predicted.

7 mg IV along with standard therapy. Benefit may beseen in patients who do not have substantial PF improvement with initial standard therapy.

80:20, 70:30, or 60:40 helium:oxygen. Higher helium concentrations are needed for optimal effect.

Use in patients with bacterial sinusitis or patients with appropriate comorbid conditions and fever with purulent sputum.

5mg/kg intravenously over 30 minutes loading dose in patients not receiving theophylline followed by 0.4 mg/kg/hr intravenous maintenance dose. Check serum level within 6 hours of loading dose. Watch for drug interactions and disease states that alter clearance rates.

0.3-0.5mL of a 1:1,000 solution subcutaneously every 20 minutes x 3; terbutaline (0.25 mL) is favored in pregnant patients when parenteral therapy is indicated.Use with caution in patients older than 40 years of ageand in patients with coronary artery disease.

Source: Adapted from Ref. 16.

PRESSURE (cmHjO)

Figure 2 Dynamic hyperinflation significantly increases the work of breathing. In the absence of hyperinflation, a person taking a 0.5 L breath at the usual functional residual capacity (FRC) expends a workload equal to the shaded area (a). As a consequence of incomplete alveolar emptying due to limitation in airflow, asthmatic patients may begin inspiration at a less advantageous FRC. At this dynamically determined FRC, the work of breathing is the sum of the energy expended to bring alveolar pressures below zero (shaded area b) and the workload at a less compliant portion of the pressure-volume curve (shaded area c). Source: From Ref. 137.

PRESSURE (cmHjO)

Figure 2 Dynamic hyperinflation significantly increases the work of breathing. In the absence of hyperinflation, a person taking a 0.5 L breath at the usual functional residual capacity (FRC) expends a workload equal to the shaded area (a). As a consequence of incomplete alveolar emptying due to limitation in airflow, asthmatic patients may begin inspiration at a less advantageous FRC. At this dynamically determined FRC, the work of breathing is the sum of the energy expended to bring alveolar pressures below zero (shaded area b) and the workload at a less compliant portion of the pressure-volume curve (shaded area c). Source: From Ref. 137.

randomized or blinded study, the patients who received NIPPV received less sedation and had a shorter length of ICU and hospital stay than a cohort of intubated, mechanically ventilated patients.

More recently, Soroksky et al. (145) showed in a prospective, randomized study that the implementation of bi-level, nasal NIPPV in the ED improved both PF in the short term and reduced hospitalization rates. Their control group included 15 patients who also wore nasally fitted masks but received sham therapy at 1 cm of IPAP and EPAP through tubing that was purposefully interrupted. Notably, inhaled therapies were administered to both intervention and control groups during brief periods of mask ventilation. This methodology allowed the investigators to evaluate the direct benefits of NIPPV use and avoid any potentially conflicting profit related to greater bronchodilator delivery with NIPPV-administered breaths.

The growing body of evidence suggests that the use of NIPPV can be attempted in AA and respiratory embarrassment. Caution should be employed in selecting appropriate patients for this ventilation modality as not all patient populations are ideal candidates for NIPPV. Patients with excessive oral secretions, recent upper airway or GI surgery, and patients who are uncooperative should not be treated with NIPPV. In addition, hemodynamic instability and inability to protect the airway are further contraindications to initiating mask ventilation (139) (Table 2). Close attention to worsening respiratory status and the need for escalation to controlled ETI is imperative if NIPPV is attempted.

Initiating NIPPV requires first fitting the mask to allow the most minimal air leak possible. Evidence exists that greater reduction in hypercapnia can be accomplished with the use of a full oronasal mask over nasal masks alone (146). Patient comfort may be higher with nasal masks or newer helmet devices over tight oronasal mask delivery of NIPPV (146,147). Patient compliance may increase if the mask is hand-placed firmly over the nose and mouth for several minutes to allow a period of accommodation before the straps are secured around the head. The appropriate snugness of the straps should be tailored to minimize air leak yet ensure comfort. Initial inspiratory and expiratory pressure ranges are 8-10 and 4-5 cm of H2O, respectively. Since hypoxemia is uncommon in AA, the reason to titrate expiratory pressures is to offset intrinsic PEEP (PEEPi) and ease effort of breathing (148). Inspiratory pressures should be appropriately adjusted so adequate tidal volumes (>7mL/kg) are achieved and, maybe more importantly, a low respiratory rate (< 20 per minute) in order to minimize air trapping (27). Total inspiratory pressures above 20 cm of H2O are poorly tolerated, require very tight fitting masks, and can result in skin breakdown and excessive gastric insufflation.

Lacking larger prospective RCTs, current evidence suggests that among the most severe cases of AA, a trial of several hours of NIPPV may avoid ETI and prolonged hospitalization. If embarked upon, NIPPV use should be followed with early assessment of improvement or deterioration. The use of heliox in concert with NIPPV has not been thoroughly

Table 2 Contraindications to NIPPV

After respiratory arrest

Medically unstable

Unable to protect airway

Excessive secretions

Uncooperative or agitated

Recent airway or gastrointestinal surgery

Source: From Ref. 139.

investigated, but both expert opinion and anecdotal experiences seem to favor the use of this low-risk, adjunctive therapy if a brief trial is rapidly feasible.

Was this article helpful?

0 0
Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

Get My Free Ebook


Post a comment