Efficacy of metered-dose inhaler administration of albuterol in intubated infants

Effects of Chest Physiotherapy in Preterm Infants with Respiratory Distress Syndrome: A Systematic Review

Preterm birth carries a higher risk of respiratory problems. The objectives of the study are to summarize the evidence on the effect of chest physiotherapy in the treatment of respiratory difficulties in preterm infants, and to determine the most appropriate technique and whether they are safe. Searches were made in PubMed, WOS, Scopus, Cochrane Library, SciELO, LILACS, MEDLINE, ProQuest, PsycArticle and VHL until 30 April 2022. Eligibility criteria were study type, full text, language, and treatment type. No publication date restrictions were applied. The MINCIR Therapy and PEDro scales were used to measure the methodological quality, and the Cochrane risk of bias and Newcastle Ottawa quality assessment Scale to measure the risk of bias. We analysed 10 studies with 522 participants. The most common interventions were conventional chest physiotherapy and stimulation of the chest zone according to Vojta. Lung compression and increased expiratory flow were also used. Heterogeneities were observed regarding the duration of the interventions and the number of participants. The methodological quality of some articles was not adequate. All techniques were shown to be safe. Benefits were described after conventional chest physiotherapy, Vojta's reflex rolling, and lung compression interventions. Improvements after Vojta's reflex rolling are highlighted in the comparative studies.

Bronchodilators for bronchiolitis

BACKGROUND

Bronchiolitis is an acute, viral lower respiratory tract infection affecting infants and is sometimes treated with bronchodilators.

OBJECTIVES

To assess the effects of bronchodilators on clinical outcomes in infants (0 to 12 months) with acute bronchiolitis.

SEARCH METHODS

We searched CENTRAL 2013, Issue 12, MEDLINE (1966 to January Week 2, 2014) and EMBASE (1998 to January 2014).

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing bronchodilators (other than epinephrine) with placebo for bronchiolitis.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial quality and extracted data. We obtained unpublished data from trial authors.

MAIN RESULTS

We included 30 trials (35 data sets) representing 1992 infants with bronchiolitis. In 11 inpatient and 10 outpatient studies, oxygen saturation did not improve with bronchodilators (mean difference (MD) -0.43, 95% confidence interval (CI) -0.92 to 0.06, n = 1242). Outpatient bronchodilator treatment did not reduce the rate of hospitalization (11.9% in bronchodilator group versus 15.9% in placebo group, odds ratio (OR) 0.75, 95% CI 0.46 to 1.21, n = 710). Inpatient bronchodilator treatment did not reduce the duration of hospitalization (MD 0.06, 95% CI -0.27 to 0.39, n = 349).Effect estimates for inpatients (MD -0.62, 95% CI -1.40 to 0.16) were slightly larger than for outpatients (MD -0.25, 95% CI -0.61 to 0.11) for oximetry. Oximetry outcomes showed significant heterogeneity (I(2) statistic = 81%). Including only studies with low risk of bias had little impact on the overall effect size of oximetry (MD -0.38, 95% CI -0.75 to 0.00) but results were close to statistical significance.In eight inpatient studies, there was no change in average clinical score (standardized MD (SMD) -0.14, 95% CI -0.41 to 0.12) with bronchodilators. In nine outpatient studies, the average clinical score decreased slightly with bronchodilators (SMD -0.42, 95% CI -0.79 to -0.06), a statistically significant finding of questionable clinical importance. The clinical score outcome showed significant heterogeneity (I(2) statistic = 73%). Including only studies with low risk of bias reduced the heterogeneity but had little impact on the overall effect size of average clinical score (SMD -0.22, 95% CI -0.41 to -0.03).Sub-analyses limited to nebulized albuterol or salbutamol among outpatients (nine studies) showed no effect on oxygen saturation (MD -0.19, 95% CI -0.59 to 0.21, n = 572), average clinical score (SMD -0.36, 95% CI -0.83 to 0.11, n = 532) or hospital admission after treatment (OR 0.77, 95% CI 0.44 to 1.33, n = 404).Adverse effects included tachycardia, oxygen desaturation and tremors.

AUTHORS' CONCLUSIONS

Bronchodilators such as albuterol or salbutamol do not improve oxygen saturation, do not reduce hospital admission after outpatient treatment, do not shorten the duration of hospitalization and do not reduce the time to resolution of illness at home. Given the adverse side effects and the expense associated with these treatments, bronchodilators are not effective in the routine management of bronchiolitis. This meta-analysis continues to be limited by the small sample sizes and the lack of standardized study design and validated outcomes across the studies. Future trials with large sample sizes, standardized methodology across clinical sites and consistent assessment methods are needed to answer completely the question of efficacy.

Albuterol delivery in an in vitro pediatric ventilator lung model: comparison of jet, ultrasonic, and mesh nebulizers

OBJECTIVE

To determine the influence of nebulizer types and nebulization modes on bronchodilator delivery in a mechanically ventilated pediatric lung model.

DESIGN

In vitro, laboratory study.

SETTING

Research laboratory of a university hospital.

INTERVENTIONS

Using albuterol as a marker, three nebulizer types (jet nebulizer, ultrasonic nebulizer, and vibrating-mesh nebulizer) were tested in three nebulization modes in a nonhumidified bench model mimicking the ventilatory pattern of a 10-kg infant. The amounts of albuterol deposited on the inspiratory filters (inhaled drug) at the end of the endotracheal tube, on the expiratory filters, and remaining in the nebulizers or in the ventilator circuit were determined. Particle size distribution of the nebulizers was also measured.

MEASUREMENTS AND MAIN RESULTS

The inhaled drug was 2.8% ± 0.5% for the jet nebulizer, 10.5% ± 2.3% for the ultrasonic nebulizer, and 5.4% ± 2.7% for the vibrating-mesh nebulizer in intermittent nebulization during the inspiratory phase (p < 0.01). The most efficient nebulizer was the vibrating-mesh nebulizer in continuous nebulization (13.3% ± 4.6%, p < 0.01). Depending on the nebulizers, a variable but important part of albuterol was observed as remaining in the nebulizers (jet and ultrasonic nebulizers), or being expired or lost in the ventilator circuit (all nebulizers). Only small particles (range 2.39-2.70 µm) reached the end of the endotracheal tube.

CONCLUSIONS

Important differences between nebulizer types and nebulization modes were seen for albuterol deposition at the end of the endotracheal tube in an in vitro pediatric ventilator-lung model. New aerosol devices, such as ultrasonic and vibrating-mesh nebulizers, were more efficient than the jet nebulizer.

Respiratory syncytial virus: diagnosis, treatment and prevention

Respiratory Syncytial Virus (RSV) is a common virus that infects children and adults; however, children younger than two years of age tend to develop more serious respiratory symptoms. RSV is responsible for thousands of outpatient visits (e.g., emergency room/primary care physician), hospitalizations and can result in death. Treatment is primarily supportive care and the illness resolves without complications in most children. RSV prophylaxis with palivizumab is an option for high-risk infants and children, which can decrease hospitalization and length of stay. Immunocompromised patients are a special population of which ribavirin and palivizumab may be used for treatment. Currently, no medication or vaccine available has been able to show a reduction in mortality from RSV. Future vaccines are in the developmental stage and will hopefully decrease the symptomatic and economic burden of this disease.

Bronchodilators for bronchiolitis

BACKGROUND

Bronchiolitis is an acute, viral lower respiratory tract infection affecting infants and often treated with bronchodilators.

OBJECTIVES

To assess the effects of bronchodilators on clinical outcomes in infants with acute bronchiolitis.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 1) which contains the Acute Respiratory Infections Group's Specialized Register, MEDLINE (1966 to March week 2 2010) and EMBASE (2003 to March 2010).

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing bronchodilators (other than epinephrine) with placebo for bronchiolitis.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial quality and extracted data. Unpublished data were obtained from trial authors.

MAIN RESULTS

We included 28 trials (1912 infants) with bronchiolitis. In 10 inpatient and 10 outpatient studies, oxygen saturation did not improve with bronchodilators (mean difference (MD) -0.45, 95% confidence interval (CI) -0.96 to 0.05, n = 1182). Outpatient bronchodilator treatment did not reduce the rate of hospitalization (12% in bronchodilator group versus 16% in placebo, odds ratio (OR) 0.78, 95% CI 0.47 to 1.29, n = 650). Inpatient bronchodilator treatment did not reduce the duration of hospitalization (MD 0.06, 95% CI -0.27 to 0.39, n = 349). In seven inpatient and eight outpatient studies, average clinical score decreased slightly with bronchodilators (standardized mean difference (SMD) -0.37, 95% CI -0.62 to -0.13, n = 1006).Oximetry and clinical score outcomes showed significant heterogeneity. Including only studies at low risk of bias significantly reduced heterogeneity measures for oximetry (I(2) statistic = 17%) and average clinical score (I(2) statistic = 26%), while having little impact on the overall effect size of oximetry (MD -0.38, 95% CI -0.75 to 0.00, P = 0.05) and average clinical score (SMD -0.26, 95% CI -0.44 to -0.08, P = 0.005).Effect estimates for outpatients were slightly larger than for inpatients for oximetry (outpatients MD -0.57, 95% CI -1.13 to 0.00 versus inpatients MD -0.29, 95% CI -1.10 to 0.51) and average clinical score (outpatients SMD -0.49, 95% CI -0.86 to -0.11 versus inpatients SMD -0.20, 95% CI -0.43 to 0.03). Adverse effects included tachycardia and tremors.

AUTHORS' CONCLUSIONS

Bronchodilators do not improve oxygen saturation, do not reduce hospital admission after outpatient treatment, do not shorten the duration of hospitalization and do not reduce the time to resolution of illness at home. The small improvements in clinical scores for outpatients must be weighed against the costs and adverse effects of bronchodilators.

Infection control in mass respiratory failure: preparing to respond to H1N1

The first hints of a global public health crisis emerged with the identification of a new strain of H1N1 influenza A in March and April 2009 in Mexico City. By June 11, the World Health Organization had declared the outbreak of 2009 H1N1 a global pandemic. Now, with the continued growing presence of 2009 H1N1 on the global scene, much attention has been focused on the key role of personal protective equipment in healthcare infection control. Much less emphasis has been placed on specific interventions that may minimize the increased infectious risk commonly associated with critical care delivery. Given the frequency of high-risk respiratory procedures such as intubation and delivery of aerosolized medications in the intensive care unit, the delivery of critical care presents unique infection control challenges and unique opportunities to augment usual infection control practice with specific source-control efforts. Here, we summarize data regarding risks to critical care healthcare workers from previous respiratory virus outbreaks, discuss findings from the early 2009 H1N1 experience that suggest reasons for increased concern for those delivering critical care, and review best available evidence regarding strategies for source control in respiratory and critical care delivery.

In vitro deposition properties of nebulized formoterol fumarate: effect of nebulization time, airflow, volume of fill and nebulizer type

OBJECTIVE

The aim of this study was to investigate in vitro the delivery of a new long-acting beta2-agonist (LABA) drug formoterol fumarate inhalation solution (20 microg/2 mL) nebulized with and without ipratropium bromide (0.5 mg/2.5 mL) at different administration times (2.5-22.5 min), airflows (5-28.3 L/min), nebulizer fill volumes (2-6 mL),and nebulizer brands (Pari LC+, Ventstream and DeVilbiss).

METHOD

Formoterol fumarate with and without ipratropium bromide was aerosolized at different administration times, airflows, nebulizer fill volumes, and nebulizer brands. The drug deposited on the throat, filter and stage plates was collected and analyzed by HPLC to determine the aerodynamic profiles of the nebulized drugs under each variable.

RESULTS

In addition to altering the aerosol characteristics,increasing the nebulizer fill volume including the addition of ipratropium bromide produced a significant(p50.05) increase in the drug output. As expected, sputtering time was significantly longer at low airflows, and vice versa at higher airflows but with a significant loss of drug delivered presumably due to greater solvent evaporation at higher airflows. Airflows between 10 and 28.3 L/min and a nebulization time of approximately 10 min appear sufficient for producing aerosols within the respirable range (1-5 mm MMAD) with the nebulizer/compressor combination used.While the drug output varied significantly (p50.05) among the three brands of nebulizers tested, the LC+ nebulizer appears to produce aerosols (2.7 0.1 microm MMAD) capable of penetrating more deeply into the lung than the other nebulizers evaluated under the current test conditions. This study did not attempt to evaluate different nebulizer/compressor combinations. Also, the cascade impaction data may not necessarily reflect aerosol deposition in the airways in vivo, which may be different depending on the health status of the patient.

CONCLUSION

The results demonstrated that administration of nebulized formoterol fumarate require proper selection of a delivery system/method for safe and effective therapy of the medication with and without ipratropium bromide.

Device Selection and Outcomes of Aerosol Therapy: Evidence-Based Guidelines

BACKGROUND

The proliferation of inhaler devices has resulted in a confusing number of choices for clinicians who are selecting a delivery device for aerosol therapy. There are advantages and disadvantages associated with each device category. Evidence-based guidelines for the selection of the appropriate aerosol delivery device in specific clinical settings are needed.

AIM

(1) To compare the efficacy and adverse effects of treatment using nebulizers vs pressurized metered-dose inhalers (MDIs) with or without a spacer/holding chamber vs dry powder inhalers (DPIs) as delivery systems for beta-agonists, anticholinergic agents, and corticosteroids for several commonly encountered clinical settings and patient populations, and (2) to provide recommendations to clinicians to aid them in selecting a particular aerosol delivery device for their patients.

METHODS

A systematic review of pertinent randomized, controlled clinical trials (RCTs) was undertaken using MEDLINE, EmBase, and the Cochrane Library databases. A broad search strategy was chosen, combining terms related to aerosol devices or drugs with the diseases of interest in various patient groups and clinical settings. Only RCTs in which the same drug was administered with different devices were included. RCTs (394 trials) assessing inhaled corticosteroid, beta2-agonist, and anticholinergic agents delivered by an MDI, an MDI with a spacer/holding chamber, a nebulizer, or a DPI were identified for the years 1982 to 2001. A total of 254 outcomes were tabulated. Of the 131 studies that met the eligibility criteria, only 59 (primarily those that tested beta2-agonists) proved to have useable data.

RESULTS

None of the pooled metaanalyses showed a significant difference between devices in any efficacy outcome in any patient group for each of the clinical settings that was investigated. The adverse effects that were reported were minimal and were related to the increased drug dose that was delivered. Each of the delivery devices provided similar outcomes in patients using the correct technique for inhalation.

CONCLUSIONS

Devices used for the delivery of bronchodilators and steroids can be equally efficacious. When selecting an aerosol delivery device for patients with asthma and COPD, the following should be considered: device/drug availability; clinical setting; patient age and the ability to use the selected device correctly; device use with multiple medications; cost and reimbursement; drug administration time; convenience in both outpatient and inpatient settings; and physician and patient preference.

Two administration methods for inhaled salbutamol in intubated patients

AIMS

To compare serum concentrations and effects on respiratory mechanics and haemodynamics of salbutamol administered by small volume nebuliser (SVN) and metered dose inhaler (MDI) plus spacer.

METHODS

Blinded, randomised, crossover study in 12 intubated infants and children (mean age 17.8 months) receiving inhaled salbutamol therapy. Subjects received salbutamol as 0.15 mg/kg by SVN and four puffs (400 microg) by MDI plus spacer at a four hour interval in random order. Passive respiratory mechanics were measured by a single breath/single occlusion technique, and serum salbutamol concentrations by liquid chromatography-mass spectrometry at 30 minutes, 1, 2, and 4 hours after each dose. Haemodynamics (heart rate and blood pressure) were recorded at each measurement time.

RESULTS

There was no difference in percentage change in respiratory mechanics or haemodynamics between the two methods of administration. Mean area under the curve (AUC(0-4)) was 5.86 for MDI plus spacer versus 4.93 ng/ml x h for SVN.

CONCLUSIONS

Serum concentrations and effects on respiratory mechanics and haemodynamics of salbutamol were comparable with the two administration methods under the conditions studied. Future studies are needed to determine the most effective and safe combination of dose and administration method of inhaled salbutamol in mechanically ventilated infants and children.

Delivery of salbutamol pressurized metered-dose inhaler administered via small-volume spacer devices in intubated, spontaneously breathing rabbits

Little is known about the ability of small-volume valved spacer devices to deliver a significant amount of an aerosolized drug to the lungs of babies. This study compared the in vitro delivery of salbutamol administered via Aerochamber-Infant (145 mL), Babyhaler (350 mL), and metallic NES-spacer (250 mL), as well as the in vivo delivery using an animal model. The lung deposition study of technetium-99m-labeled salbutamol was conducted in six anesthetized, intubated (3.0-mm endotracheal tube simulating oropharyngeal deposition), spontaneously breathing New Zealand White rabbits, a model for 3-kg babies. Each rabbit was studied on three separate occasions, once with each spacer device. The amount of radioactivity deposited in the spacer device, the endotracheal tube, the lungs, or the body was measured by a gamma camera and expressed as a percentage of the emitted labeled dose. The emitted dose and particle size distribution of salbutamol via the three spacer devices were measured using unit dose sampling tubes and an eight-stage Anderson cascade impactor, respectively. The results were compared by ANOVA or Student-Newman-Keuls test when indicated. In vitro, the NES-spacer and Babyhaler were equivalent for delivering particles <5.8 microm in diameter (NES-spacer = Babyhaler > Aerochamber-Infant; p < 0.05). In vivo, the lung and body deposition was low with all spacer devices (range: 0.52-5.40% of the delivered dose) but greater with the NES-spacer than with the Aerochamber-Infant or the Babyhaler (5.40 +/- 2.40%, 2.91 +/- 0.86%, 0.52 +/- 0.46%, respectively; p = 0.002). These results suggest the metal-valved spacer device may be preferable for delivering pressurized aerosols to spontaneously breathing infants.

Mechanical ventilatory support in infants with respiratory syncytial virus infection

OBJECTIVE: To present a review of current knowledge of the use of mechanical ventilatory support in the management of infants with respiratory failure secondary to infection with respiratory syncytial virus (RSV). DATA SOURCES: MEDLINE and manual search for case reports and clinical trials that address management strategies for respiratory support of infants with RSV infection. Data Extraction and Synthesis: Critical appraisal of reported epidemiologic and clinical data regarding risk factors, pathophysiology, and efficacy of respiratory therapy. There is an increasing number of hospital admissions for RSV infection with a variable proportion of infants who need mechanical ventilatory support. The mortality rate is estimated to be <1% in infants without preexisting respiratory or cardiac disorders vs. <5% in those with preexisting respiratory or cardiac disorders. Optimal ventilator settings need to be refined according to the dominant obstructive or restrictive pattern with the aim to avoid barovolutrauma. The role of noninvasive ventilation and additional therapies (heliox, beta(2) agonists, surfactant) is not conclusively established. The indications for high-frequency oscillatory ventilation with the possible adjunction of inhaled nitric oxide deserve further study. Extracorporeal membrane oxygenation plays a minor role in severe cases that are refractory to conventional treatment. CONCLUSIONS: Conventional ventilation strategies are usually adequate for treating infants with severe RSV infection. Particular attention must be paid to the dominant pathophysiologic mechanism in a given condition. Prospective trials are needed to validate alternative therapeutic options and to improve the outcome of the rare but most severe cases that are difficult to control.

Rationale for the choice of an aerosol delivery system

The choice of an aerosol delivery system depends on numerous factors such as the drug itself, the characteristics of the aerosol generator, the patient and his or her disease, the physician, and the clinical setting, notably an emergency situation or not. Some rules always apply: an ultrasonic nebulizer should not be used to aerosolize a drug suspension; whenever possible, the same type of aerosol generator should be used for all inhaled medications received by a given patient; for outpatients, education is a major factor to ensure treatment efficacy. When the deposition of the aerosolized drug is aimed at the terminal respiratory units, nebulizers that generate micronic aerosols should be chosen. When the deposition of the aerosolized drug is aimed at the conducting airways, the metered dose inhaler (MDI) is the first choice. However, the MDI is often ill-used, notably in children and elderly people. Therefore, other inhalation devices have been developed: spacers, dry-powder inhalers, breath-actuated MDIs and, more recently, piezo-electric devices. They have been shown to increase lung deposition of drugs in poor coordinators but they all have limitations, which may affect their clinical efficacy. These limitations include the cumbersome dimensions of spacers, the dependency of lung deposition of dry powders on the inspiratory flow rate, the need for reformulation of breath-actuated or not MDIs with CFC-free gases. Nebulization of drugs should be considered only when no portable device is available for the considered drug, or in case of failure of other forms of aerosol administration.

Accumulation of CO(2) in reservoir devices during simulated neonatal mechanical ventilation

Aerosolized albuterol is frequently administered to mechanically ventilated neonates by metered dose inhaler (MDI) and a reservoir device. These reservoirs are often placed between the Y-piece and endotracheal tube, thereby creating mechanical dead space and increasing the risk of rebreathing carbon dioxide (CO(2)). The objectives of this study were: 1) to quantify CO(2) accumulation in two commonly used reservoirs (ACE(R), Aerochamber(R)-MV) and a bidirectional nonreservoir actuator (Airlife(R) Minispacer) during mechanical ventilation of a neonatal lung model; and 2) to determine the effect of tidal volume (V(T)) on CO(2) accumulation. We hypothesized that the accumulation of CO(2) in these devices is clinically insignificant at the small tidal volumes used in mechanically ventilated premature neonates. The model was constructed to simulate CO(2) exhalation by a ventilated neonate and consisted of a neonatal ventilator circuit (rate = 40/min; peak inspiratory pressure (PIP) = 20 cm H(2)0) attached to a reservoir/actuator and neonatal test lung. The ventilator delivered inspiratory gas (room air) to the test lung, which was vented into the atmosphere by a small adjustable leak. Expiration was simulated by manually ventilating 7.1% CO(2) (partial pressure of CO(2) (PCO(2)) = 48 mm Hg) back through the model. Accumulation of CO(2) within the reservoir/actuator was measured using an end-tidal CO(2) monitor. Each 4-min experiment was conducted at three V(T) (7.5 mL, 15 mL, and 25 mL), and the median PCO(2) was calculated in 0.5-min increments. For V(T) = 7.5 mL, CO(2) accumulated slowly in the ACE(R) and Minispacer(R) and reached a maximum at 4.0 min (PCO(2) = 2.3 mm Hg and 7.3 mm Hg, respectively). In contrast, the Aerochamber(R)-MV rapidly reached a PCO(2) of 9.5-10.0 mm Hg by 1-1. 5 min. A similar trend occurred with V(T) = 15 mL; however, higher partial pressures (approximately 10-12 mm Hg) were achieved with all devices. At V(T) = 25 mL, PCO(2) rose rapidly with the ACE(R), Aerochamber(R)-MV, and Minispacer(R), reaching peaks of 17.2, 12.3, and 20.3 mm Hg, respectively (P < 0.05). In conclusion, accumulation of CO(2) in reservoir/actuator depends on V(T) as well as the chamber design and internal volume. Due to the short duration of use when administering drugs via MDI, accumulation of CO(2) in these devices is not likely to be clinically relevant for the majority of ventilated newborns.

Bronchodilators for bronchiolitis

OBJECTIVES

Bronchiolitis is an acute, highly communicable lower respiratory tract infection. Bronchodilators are commonly used in the management of bronchiolitis in North America, but not in the United Kingdom. The objective of this review was to assess the effects of bronchodilators for bronchiolitis.

SEARCH STRATEGY

We searched MEDLINE, EMBASE, Reference Update, reference lists of articles, and the files of two of the authors up to June 1998.

SELECTION CRITERIA

Randomised trials comparing bronchodilators with placebo in the treatment of bronchiolitis.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Unpublished data were requested from authors when necessary.

MAIN RESULTS

In eight trials with 394 children, 46% demonstrated an improved clinical score with bronchodilators compared to 75% with placebo (odds ratio for no improvement 0.29, 95% confidence interval 0.19 to 0.45). However, the inclusion of studies that enrolled people with recurrent wheezes may have biased these results in favour of bronchodilators. Bronchodilator recipients did not show improvement in measures of oxygenation, the rate of hospitalisation (18% versus 26%, odds ratio 0.70, 95% confidence interval 0.36 to 1.35) or duration of hospitalisation (weighted mean difference 0.12, 95% confidence interval -0.3 to 0.5).

REVIEWER'S CONCLUSIONS

Bronchodilators produce modest short-term improvement in clinical scores. This small benefit must be weighed against the costs of these agents.