Respiratory Devices: Incentive Spirometers, Vaporizers and Intermittent Positive Pressure Breathing Machines

Number: 0479

Table Of Contents

Policy
Applicable CPT / HCPCS / ICD-10 Codes
Background
References

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Policy

Scope of Policy

This Clinical Policy Bulletin addresses respiratory devices: incentive spirometers, vaporizers, and intermittent positive pressure breathing machines.

1. Medical Necessity

   Aetna considers the following medically necessary:

   1. Incentive spirometers as durable medical equipment (DME) for post-operative use for members with neuromuscular or chest wall diseases;
   2. Intermittent positive pressure breathing (IPPB) machines as DME for members with asthma, chronic obstructive pulmonary disease (COPD) and other respiratory diseases;
   3. A fluidic breathing assistor as DME when IPPB is used for nebulization or aerosolization.

2. Experimental and Investigational

   Aetna considers the following procedures experimental and investigational because the effectiveness of these approaches has not been established:

   1. The SpiroTimer (an incentive spirometer user reminder) 
   2. Incentive spirometers for all other indications (including the following; not an all-inclusive list) because its effectiveness for indications other than the ones listed above has not been established:
      
      
      • Improvement of oromotor and pulmonary functions in children with Down's syndrome
      • Pre-operative use to prevent post-operative decrease in lung function following bariatric surgery
      • Prevention of atelectasis following laparotomy/upper-abdominal surgery, neurosurgery, or after coronary artery bypass graft surgery
      • Treatment of acute chest syndrome in individuals with sickle cell disease.

   3. Intermittent positive pressure breathing (IPPB) for all other indications (including the following; not an all-inclusive list):

      • Improvements in lung function and ventilation in persons with spinal cord injury
      • Treatment of croup in children.

3. Policy Limitations and Exclusions

   Aetna does not cover vaporizers because they are not considered primarily medical in nature. 

4. Related Policies

   • CPB 0067 - Chest Physiotherapy and Airway Clearance Devices

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Table:

CPT Codes / HCPCS Codes / ICD-10 Codes

Code	Code Description
CPT codes covered if selection criteria are met:
94640	Pressurized or nonpressurized inhalation treatment for acute airway obstruction for therapeutic purposes and/or for diagnostic purposes such as sputum induction with an aerosol generator, nebulizer, metered dose inhaler or intermittent positive pressure breathing (IPPB) device
Other CPT codes related to the CPB:
43631 - 43635	Gastrectomy and Vagotomy [preoperative use of incentive spirometer prior to bariatric surgery to prevent postoperative decrease in lung function]
43644 - 43645	Laparoscopy, surgical, gastric restrictive procedure [preoperative use of incentive spirometer prior to bariatric surgery to prevent postoperative decrease in lung function]
43770 - 43775	Laparoscopy, surgical, gastric restrictive procedure [preoperative use of incentive spirometer prior to bariatric surgery to prevent postoperative decrease in lung function]
43842 - 43848	Gastric restrictive procedure [preoperative use of incentive spirometer prior to bariatric surgery to prevent postoperative decrease in lung function]
61000 - 64999	Surgery/nervous system
94010 - 94621, 94642 - 94799	Pulmonary medicine
HCPCS code covered if selection criteria are met:
E0487	Spirometer, electronic, includes all accessories
E0500	IPPB machine, all types, with built-in nebulization; manual or automatic valves; internal or external power source
HCPCS codes not covered for indications listed in the CPB:
SpiroTimer (an incentive spirometer user reminder) – No specific code
E0605	Vaporizer, room type
Other HCPCS codes related to the CPB:
A9284	Spirometer, nonelectric, includes all accessories
E0550 - E0585	Humidifiers/compressors/nebulizers for use with oxygen IPPB equipment
S8096	Portable peak flow meter
ICD-10 codes covered if selection criteria are met:
J00 - J99	Diseases of the respiratory system
ICD-10 codes not covered for indications listed in the CPB (not all inclusive):
D57.01, D57.211, D57.431, D57.451, D57.811	Sickle cell disease with acute chest syndrome
J05.0	Acute obstructive laryngitis [croup]
Q90.0 - Q90.9	Down syndrome [improvement of oromotor and pulmonary functions]
S12.000A – S12.691S, S12.9XXA – S12.9XXS, S14.0XXA – S14.159S, S22.000A – S22.089S, S24.0XXA – S24.159S, S32.000A – S32.2XXS, S34.01XA – S34.139S, S34.3XXA – S34.3XXS	Fracture of vertebral column with spinal cord injury
S14.0xxS - S14.159S S24.0xxS - S24.159S S34.01xS - S34.139S	Spinal cord injury, sequelae
S14.0XXA – S14.3XXS, S24.0XXA – S24.2XXS, S34.01XA – S34.4XXS	Injury to spinal cord

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Background

Atelectasis is a common problem in post-operative patients and those with neuromuscular or chest wall disease.  Because atelectasis in some patients appears to be due to repeated small inspirations, deeper breaths may be helpful.  Incentive spirometers encourage expansion of the lungs as much as possible above spontaneous breathing; these have proved to be beneficial in controlled studies.

The use of intermittent positive pressure breathing (IPPB) has been declining because the benefit has been difficult to demonstrate in most patients.  Although sometimes used to deliver bronchodilator medications, IPPB is usually intended to prevent or treat atelectasis.  In objective studies, patients can improve atelectasis if and only if IPPB can increase the depth of breathing more than the patient alone can achieve.  Intermittent positive pressure breathing can be tried in patients with respiratory muscle weakness due to neuromuscular disease, those with chest wall abnormalities, and after abdominal surgery.  In general, the literature suggests that incentive spirometry should be tried first and IPPB used only when there is proof that larger inspired volumes can be reached with this technique.  Intermittent positive pressure breathing is contraindicated in persons with untreated tension pneumothorax.

In a systematic review, Pasquina et al (2003) examined if respiratory physiotherapy, including IPPB, prevented pulmonary complications after cardiac surgery.  The authors concluded that the usefulness of respiratory physiotherapy for the prevention of pulmonary complications after cardiac surgery remains unproved.  Large randomized studies are needed with no intervention controls, clinically relevant end points, and reasonable follow-up periods.  Indeed, the American Association for Respiratory Care (AARC)'s clinical practice guideline on IPPB (Sorenson et al, 2003) did not list prophylactic respiratory physiotherapy following cardiac surgery as a recommended indication for IPPB.

Pasquina and colleagues (2006) examined the efficacy of respiratory physiotherapy for prevention of pulmonary complications after abdominal surgery.  These investigators searched in databases and bibliographies for articles in all languages through November 2005.  Randomized trials were included if they investigated prophylactic respiratory physiotherapy and pulmonary outcomes, and if the follow-up was at least 2 days.  Efficacy data were expressed as risk differences (RDs) and number needed to treat (NNT), with 95 % confidence intervals (CIs); 35 trials tested respiratory physiotherapy treatments.  Of 13 trials with a "no intervention" control group, 9 studies (n = 883) did not report on significant differences, and 4 studies (n = 528) did: in 1 study, the incidence of pneumonia was decreased from 37.3 to 13.7 % with deep breathing, directed cough, and postural drainage (RD, 23.6 %; 95 % CI: 7 % to 40 %; NNT, 4.3; 95 % CI: 2.5 to 14); in 1 study, the incidence of atelectasis was decreased from 39 % to 15 % with deep breathing and directed cough (RD, 24 %; 95 % CI: 5 % to 43 %; NNT, 4.2; 95 % CI: 2.4 to 18); in 1 study, the incidence of atelectasis was decreased from 77 % to 59 % with deep breathing, directed cough, and postural drainage (RD, 18 %; 95 % CI: 5 % to 31 %; NNT, 5.6; 95 % CI: 3.3 to 19); in 1 study, the incidence of unspecified pulmonary complications was decreased from 47.7 % to 21.4 - 22.2 % with IPPB, or incentive spirometry, or deep breathing with directed cough (RD, 25.5 % to 26.3 %; NNT, 3.8 to 3.9).  A total of 22 trials (n = 2,734) compared physiotherapy treatments without no intervention control subjects; no conclusions could be drawn.  The authors concluded that there are only a few trials that support the usefulness of prophylactic respiratory physiotherapy.  The routine use of respiratory physiotherapy after abdominal surgery does not seem to be justified.

In an unblinded, randomized cross-over study, Laffont et al (2008) examined if IPPB improved lung compliance, work of breathing, and respiratory function in patients with recent high spinal cord injury (SCI).  A total of 14 patients with SCI caused by trauma within the last 6 months and located between C5 and T6 were included in the study.  Two months of IPPB and 2 months of conventional treatment were evaluated prospectively in random order in patients with SCI.  Non-invasive lung function tests and arterial blood gas measurements were obtained repeatedly in all patients.  Repeated measurements of dynamic lung compliance and work of breathing as measured by computing the area enclosed between the inspiratory esophageal pressure-tidal volume curve, and the theoretical chest wall static pressure-volume curve were performed in 7 patients.  Intermittent positive pressure breathing had no long-term effects on vital capacity (52.1 % +/- 11.3 % versus 54.5 % +/- 12.5 %, after conventional treatment and IPPB, respectively; p = 0.27), lung compliance (66.4 +/- 48.9 ml/cmH(2)O versus 70.3 +/- 38.4 ml/cmH(2)O; p = 0.56), or other lung function tests.  Intermittent positive pressure breathing did not exert short-term effects on lung compliance or work of breathing.  The authors concluded that IPPB produced no immediate or long-term improvements in lung function or ventilatory mechanics in patients with recent SCI.

In a Cochrane review, Guimaraes and colleagues (2009) evaluated the effects of incentive spirometry (IS) compared to no such therapy (or other therapy) on all-cause post-operative pulmonary complications (atelectasis, acute respiratory inadequacy) and mortality in adult patients admitted for upper abdominal surgery.  These investigators searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2006, Issue 3), MEDLINE, EMBASE, and LILACS (from inception to July 2006).  They included randomized controlled trials of IS in adult patients admitted for any type of upper abdominal surgery, including patients undergoing laparoscopic procedures.  Two authors independently assessed trial quality and extracted data.  These researchers included 11 studies with a total of 1,754 subjects.  Many trials were of only moderate methodological quality and did not report on compliance with the prescribed therapy.  Data from only 1,160 patients could be included in the meta-analysis.  Three trials (n = 120) compared the effects of IS with no respiratory treatment; 2  trials (n = 194) compared IS with deep breathing exercises; 2 trials (n = 946) compared IS with other chest physiotherapy.  All showed no evidence of a statistically significant effect of IS.  There was no evidence that IS is effective in the prevention of pulmonary complications.  The authors concluded that there is no evidence regarding the effectiveness of the use of IS for the prevention of post-operative pulmonary complications in upper abdominal surgery.  They noted that this review underlines the urgent need to conduct well-designed trials in this field.  There is a need for large randomized trials of high methodological rigour in order to define any benefit from the use of IS regarding mortality.

Ludwig and colleagues (2011) examined if atelectasis can be avoided and if post-operative lung function is improved following major lung resections with the use of IPPB.  Prospective analysis was carried out in 135 patients operated on between 2007 and 2009; 55 received IPPB and 80 did not receive IPPB.  Pre- and post-operative lung function tests were similar in both groups.  Pulmonary complications were observed in 19 % of patients without IPPB and 27 % of those who received this treatment.  The authors were unable to find evidence that additional improvement in post-operative pulmonary function is achieved when adding IPPB to the standard physical therapy.

Cattano et al (2010) examined if a systematic use of IS prior to surgery could help patients to preserve their respiratory function better in the post-operative period.  A total of 41 morbidly obese (body mass index [BMI] greater than 40 kg/m²) candidates for laparoscopic bariatric surgery were consented in the study.  All patients were taught how to use an incentive spirometer but then were randomized blindly into 2 groups.  The control group was instructed to use the incentive spirometer for 3 breaths, once-daily.  The treatment group was requested to use the incentive spirometer for 10 breaths, 5 times per day.  Twenty experimental (mean BMI of 48.9 +/- 5.67 kg/m²) and 21 control patients (mean BMI of 48.3 +/- 6.96 kg/m²) were studied.  The initial mean inspiratory capacity (IC) was 2,155 +/- 650.08 (SD) cc and 2,171 +/- 762.98 cc in the experimental and control groups, respectively.  On the day of surgery, the mean IC was 2,275 +/- 777.56 cc versus 2,254.76 +/- 808.84 cc, respectively.  On post-operative day 1, both groups experienced a significant drop of their IC, with volumes of 1,458 +/- 613.87 cc (t-test, p < 0.001) and 1,557.89 +/- 814.67 cc (t-test, p < 0.010), respectively.  The authors concluded that these findings suggested that pre-operative use of the IS does not lead to significant improvements of inspiratory capacity and that it is a not a useful resource to prevent post-operative decrease in lung function.

Carvalho et al (2011) performed a systematic review to evaluate the evidence of the use of IS for the prevention of post-operative pulmonary complications and for the recovery of pulmonary function in patients undergoing abdominal, cardiac and thoracic surgeries.  Searches were performed in the following databases: Medline, Embase, Web of Science, PEDro and Scopus to select randomized controlled trials in which IS was used in pre- and/or post-operative in order to prevent post-operative pulmonary complications and/or recover lung function after abdominal, cardiac and thoracic surgery.  Two reviewers independently assessed all studies.  In addition, the studies quality was assessed using the PEDro scale.  A total of 30 studies were included (14 abdominal, 13 cardiac and 3 thoracic surgery; n = 3,370 patients).  In the analysis of the methodological quality, studies achieved a PEDro average score of 5.6, 4.7 and 4.8 points in abdominal, cardiac and thoracic surgeries, respectively.  Five studies (3 abdominal, 1 cardiac and 1 thoracic surgery) compared the effect of the IS with control group (no intervention) and no difference was detected in the evaluated outcomes.  The authors concluded that there was no evidence to support the use of IS in the management of surgical patients.

The AARC's clinical practice guideline on "Incentive spirometry" (Restrepo et al, 2011) provided the following recommendations:

• IS alone is not recommended for routine use in the pre-operative and post-operative setting to prevent post-operative pulmonary complications
• Routine use of IS to prevent atelectasis in patients after upper-abdominal surgery is not recommended
• Routine use of IS to prevent atelectasis after coronary artery bypass graft surgery is not recommended.

Contraindications of IS include:

• Patients who can not be instructed or supervised to assure appropriate use of the device
• Patients in whom co-operation is absent or patients unable to understand or demonstrate proper use of the device
  
  
  • Very young patients and others with developmental delays
  • Patients who are confused or delirious
  • Patients who are heavily sedated or comatose
     
• Patients unable to deep breathe effectively due to pain, diaphragmatic dysfunction, or opiate analgesia
• Patients unable to generate adequate inspiration with a vital capacity less than 10 ml/kg or an inspiratory capacity less than 33 % of predicted normal.

In a Cochrane review, Freitas et al (2012) compared the effects of IS for preventing post-operative pulmonary complications in adults undergoing coronary artery bypass graft (CABG).  These investigators searched CENTRAL and DARE on The Cochrane Library (Issue 2 of 4 2011), MEDLINE OVID (1948 to May 2011), EMBASE (1980 to Week 20 2011), LILACS (1982 to July 2011) , the Physiotherapy Evidence Database (PEDro) (1980 to July 2011), Allied & Complementary Medicine (AMED) (1985 to May 2011), CINAHL (1982 to May 2011).  Randomized controlled trials comparing IS with any type of prophylactic physiotherapy for prevention of post-operative pulmonary complications in adults undergoing CABG were selected.  Two reviewers independently evaluated trial quality using the guidelines of the Cochrane Handbook for Systematic Reviews and extracted data from included trials.  For continuous outcomes, they used the generic inverse variance method for meta-analysis; and for dichotomous data they used the Peto Odds Ratio.  This update of the 2007 review included 592 participants from 7 studies (2 new and 1 that had been excluded in the previous review in 2007.  There was no evidence of a difference between groups in the incidence of any pulmonary complications and functional capacity between treatment with IS and treatment with physical therapy, positive pressure breathing techniques (including continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP) and IPPB, active cycle of breathing techniques (ACBT) or pre-operative patient education.  Patients treated with IS had worse pulmonary function and arterial oxygenation compared with positive pressure breathing.  Based on these studies there was no improvement in the muscle strength between groups who received IS demonstrated by maximal inspiratory pressure and maximal expiratory pressure.  The authors concluded that this review suggested that there is no evidence of benefit from IS in reducing pulmonary complications and in decreasing the negative effects on pulmonary function in patients undergoing CABG.  In view of the modest number of patients studied, methodological shortcomings and poor reporting of the included trials, these results should still be interpreted cautiously.  An appropriately powered trial of high methodological rigor is needed to determine if there are patients who may derive benefit from IS following CABG.

do Nascimento et al (2014) assessed the effect of IS, compared to no such therapy or other therapy, on post-operative pulmonary complications and mortality in adults undergoing upper abdominal surgery.  Secondary objectives were to evaluate the effects of IS, compared to no therapy or other therapy, on other post-operative complications, adverse events, and spirometric parameters.  These investigators searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 8), MEDLINE, EMBASE, and LILACS (from inception to August 2013).  There were no language restrictions.  The date of the most recent search was August 12, 2013.  The original search was performed in June 2006.  These researchers included randomized controlled trails (RCTs) of IS in adult patients admitted for any type of upper abdominal surgery, including patients undergoing laparoscopic procedures.  Two authors independently assessed trial quality and extracted data.  They included 12 studies with a total of 1,834 participants in this updated review.  The methodological quality of the included studies was difficult to assess as it was poorly reported, so the predominant classification of bias was “unclear”; the studies did not report on compliance with the prescribed therapy.  They were able to include data from only 1,160 patients in the meta-analysis.  Four trials (n = 152) compared the effects of IS with no respiratory treatment.  These researchers found no statistically significant difference between the participants receiving IS and those who had no respiratory treatment for clinical complications (relative risk (RR) 0.59, 95 % CI: 0.30 to 1.18).  Two trials (n = 194) compared IS with deep breathing exercises (DBE).  In the meta-analysis, there were no statistically significant differences between participants receiving IS compared to those receiving DBE for respiratory failure (RR 0.67, 95 % CI: 0.04 to 10.50).  Two trials (n = 946) compared IS with other chest physiotherapy.  These researchers found no statistically significant differences between the participants receiving IS compared to those receiving physiotherapy in the risk of developing a pulmonary condition or the type of complication.  There was no evidence that incentive spirometry is effective in the prevention of pulmonary complications.  The authors concluded that there is low quality evidence regarding the lack of effectiveness of IS for prevention of post-operative pulmonary complications in patients after upper abdominal surgery.  They stated that this review underlined the urgent need to conduct well-designed trials in this field.

Tyson and colleagues (2015) noted that changes in pulmonary dynamics following laparotomy are well documented.  Deep breathing exercises, with or without IS, may help counteract post-operative decreased vital capacity (VC); however, the evidence for the role of IS in the prevention of post-operative atelectasis is inconclusive.  Furthermore, data are scarce regarding the prevention of post-operative atelectasis in sub-Saharan Africa.  In a RCT, these researchers determined the effect of the use of IS on pulmonary function following exploratory laparotomy as measured by forced vital capacity (FVC).  This was a single-center, RCT performed at Kamuzu Central Hospital, Lilongwe, Malawi.  Study participants were adult patients who underwent exploratory laparotomy and were randomized into the intervention or control groups (standard of care) from February 1 to November 30, 2013.  All patients received routine post-operative care, including instructions for deep breathing and early ambulation.  These researchers used bi-variate analysis to compare outcomes between the intervention and control groups.  Adult patients who underwent exploratory laparotomy participated in post-operative deep breathing exercises.  Patients in the intervention group received incentive spirometers.  These investigators assessed pulmonary function using a peak flow meter to measure FVC in both groups of patients.  Secondary outcomes, such as hospital length of stay and mortality, were obtained from the medical records.  A total of 150 patients were randomized (75 in each arm).  The median age in the intervention and control groups was 35 years (interquartile range of 28 to 53 years) and 33 years (interquartile range of 23 to 46 years), respectively.  Men predominated in both groups, and most patients underwent emergency procedures (78.7 % in the intervention group and 84.0 % in the control group).  Mean initial FVC did not differ significantly between the intervention and control groups (0.92 and 0.90 L, respectively; p = 0.82 [95 % CI: 0.52 to 2.29]).  Although patients in the intervention group tended to have higher final FVC measurements, the change between the first and last measured FVC was not statistically significant (0.29 and 0.25 L, respectively; p = 0.68 [95 % CI: 0.65 to 1.95]).  Likewise, hospital length of stay did not differ significantly between groups.  Overall post-operative mortality was 6.0 %, with a higher mortality rate in the control group compared with the intervention group (10.7 % and 1.3 %, respectively; p = 0.02 [95 % CI: 0.01 to 0.92]).  The authors concluded that education and provision of IS for unmonitored patient use does not result in statistically significant improvement in pulmonary dynamics following laparotomy.  They would not recommend the addition of IS to the current standard of care in this resource-constrained environment.

In a Cochrane review, Bjornson et al (2013) evaluated the effectiveness (measured by croup scores, rate of intubation and health care utilization such as rate of hospitalization) and safety (frequency and severity of side effects) of nebulized epinephrine versus placebo in children with croup, evaluated in an emergency department (ED) or hospital setting.  These investigators searched CENTRAL 2013, Issue 6, MEDLINE (1966 to Week 3 of June 2013), EMBASE (1980 to July 2013), Web of Science (1974 to July 2013), CINAHL (1982 to July 2013) and Scopus (1996 to July 2013); RCTs or quasi-RCTs of children with croup evaluated in an ED or admitted to hospital were selected for analysis.  Comparisons were: nebulized epinephrine versus placebo, racemic nebulized epinephrine versus L-epinephrine (an isomer) and nebulized epinephrine delivered by IPPB versus nebulized epinephrine without IPPB.  Primary outcome was change in croup score post-treatment.  Secondary outcomes were rate and duration of intubation and hospitalization, croup return visit, parental anxiety and side effects.  Two authors independently identified potentially relevant studies by title and abstract (when available) and examined relevant studies using a priori inclusion criteria, followed by methodological quality assessment.  One author extracted data while the second checked accuracy.  These researchers used the standard methodological procedures expected by the Cochrane Collaboration.  A total of 8 studies (225 participants) were included.  In general, children included in the studies were young (average age of less than 2 years in the majority of included studies).  Severity of croup was described as moderate-to-severe in all included studies.  Six studies took place in the inpatient setting, 1 in the ED and 1 setting was not specified.  Six of the 8 studies were deemed to have a low-risk of bias and the risk of bias was unclear in the remaining 2 studies.  Nebulized epinephrine was associated with croup score improvement 30 minutes post-treatment (3 RCTs, standardized mean difference (SMD) -0.94; 95 % CI: -1.37 to -0.51; I(2) statistic = 0 %).  This effect was not significant 2 and 6hours post-treatment.  Nebulized epinephrine was associated with significantly shorter hospital stay than placebo (1 RCT, MD -32.0 hours; 95 % CI: -59.1 to -4.9).  Comparing racemic and L-epinephrine, no difference in croup score was found after 30 minutes (SMD 0.33; 95 % CI: -0.42 to 1.08).  After 2 hours, L-epinephrine showed significant reduction compared with racemic epinephrine (1 RCT, SMD 0.87; 95 % CI: 0.09 to 1.65).  There was no significant difference in croup score between administration of nebulized epinephrine via IPPB versus nebulization alone at 30 minutes (1 RCT, SMD -0.14; 95 % CI: -1.24 to 0.95) or 2 hours (SMD -0.72; 95 % CI: -1.86 to 0.42).  None of the studies sought or reported data on adverse effects.  The authors concluded that nebulized epinephrine is associated with clinically and statistically significant transient reduction of symptoms of croup 30 minutes post-treatment.  Evidence does not favor racemic epinephrine or L-epinephrine, or IPPB over simple nebulization.  Moreover, they noted that data and analyses were limited by the small number of relevant studies and total number of participants and thus most outcomes contained data from very few or even single studies.

An UpToDate review on “Croup: Pharmacologic and supportive interventions” (Woods, 2014a) stated that “Administration of epinephrine does not alter the natural history of croup in the short (>2 hours) or longer term (24 to 36 hours).  In the studies described above, racemic epinephrine was administered either by nebulization alone or by nebulization combined with intermittent positive pressure breaths.  Another study compared these two methods [nebulization alone or by nebulization combined with IPPB] of administration and found them to be similarly effective”.  Furthermore, an UpToDate review on “Croup: Approach to management” (Woods, 2014b) does not mention IPPB as a therapeutic option.

Moradian and colleagues (2019) noted that atelectasis and hypoxemia are frequently reported following CABG surgery.  Some studies confirmed the benefits of breathing exercises on pulmonary complications; however, the effectiveness of pre-operative breathing exercises in patients undergoing CABG is controversial.  In a single-blinded randomized clinical trial, these researchers examined the effect of pre-operative breathing exercises on the incidence of atelectasis and hypoxemia in candidates for CABG surgery.  A total of 100 patients who were undergoing CABG were randomly allocated into 2 groups of experimental and control, each consisted of 50 patients.  Before the operation, experimental group patients were enrolled in a protocol including deep breathing, cough and IS.  In the control group, hospital routine physiotherapy was implemented.  All the patients received the hospital routine physiotherapy once-daily for 2 to 3 mins in the first 4 days post-operatively.  Arterial blood gases and atelectasis were compared between groups.  There was no significant difference between groups in terms of atelectasis and hypoxemia (p > 0.05).  The authors concluded that pre-operative breathing exercise (including IS) did not reduce pulmonary complications in patients undergoing CABG surgery.

Sweity and associates (2021) stated that PPCs often occur following cardiac operations and are a leading cause of morbidity, inhibit oxygenation, and increase hospital LOS and mortality.  Although clinical evidence for PPCs prevention is often unclear and crucial, there are measures to reduce PPCs.  One device usually used for this reason is IS.  In a prospective, randomized study, these researchers examined the effect of pre-operative IS for the prevention of PPCs, improvement of post-operative oxygenation, and reduction in hospital LOS following CABG surgery.  A total of 80 patients were selected as candidates for CABG at An-Najah National University Hospital, Nablus-Palestine.  Patients were randomly assigned into 2 groups: IS group (IS) – IS performed before surgery (study group) and control group, pre-operative IS was not performed.  The 40 patients in each group received the same protocol of anesthesia and ventilation in the operating room.  The study findings showed a significant difference between the IS and control groups in the incidence of post-operative atelectasis.  There were 8 patients (20.0 %) in IS group and 17 patients (42.5 %) in the control group (p = 0.03).  Mechanical ventilation duration was significantly less in IS group.  The median was 4 hours versus 6 hours in the control group (p < 0.001).  Hospital LOS was significantly less in IS group, and the median was 6 days versus 7 days in the control group (p < 0.001).  The median of the amount of arterial blood oxygen and oxygen saturation was significantly improved in the IS group (p < 0.005).  The authors concluded that pre-operative IS for 2 days along with the exercise of deep breathing, encouraged coughing, and early ambulation following CABG were associated with prevention and reduced incidence of atelectasis, hospital LOS, mechanical ventilation duration and improved post-operative oxygenation with better pain control.  A difference that can be considered both significant and clinically relevant.  The findings of this study were confounded by the combined uses of exercise of deep breathing, encouraged coughing, and IS.  Moreover, these researchers stated that this study was carried out on patients who received IS for 2 days pre-operative and did not have lung problems; thus, it is recommended to perform a clinical study to examine IS with deep breathing and cough in patients who will undergo CABG surgery with lung problems (e.g., asthma and COPD).

Furthermore, an UpToDate review on “Coronary artery bypass surgery: Perioperative medical management” (Aranki et al, 2022) does not mention incentive spirometry as a management option.

Sullivan et al (2021) state that consensus on the effectiveness of incentive spirometry (IS) following cardiac, thoracic, and upper abdominal surgery has been based on randomized controlled trials (RCTs) and systematic reviews of lower methodological quality. To improve the quality of the research and to account for the effects of IS following thoracic surgery, in addition to cardiac and upper abdominal surgery, the authors performed a meta-analysis with thorough application of the Grading of Recommendations Assessment, Development and Evaluation scoring system and extensive reference to the Cochrane Handbook for Systematic Reviews of Interventions. The objective of this study was to determine, with rigorous methodology, whether IS for adult patients (18 years of age or older) undergoing cardiac, thoracic, or upper abdominal surgery significantly reduces30-day post-operative pulmonary complications (PPCs), 30-day mortality, and length of hospital stay (LHS) when compared to other rehabilitation strategies. Thirty-one RCTs involving 3,776 adults undergoing cardiac, thoracic, or upper abdominal surgery were included. By comparing the use of IS to other chest rehabilitation strategies, we found that IS alone did not significantly reduce 30-day PPCs (RR = 1.00, 95% CI: 0.88-1.13) or 30-day mortality (RR = 0.73, 95% CI: 0.42-1.25). Likewise, there was no difference in LHS (mean difference = -0.17,95% CI: -0.65 to 0.30) between IS and the other rehabilitation strategies. None of the included trials significantly impacted the sensitivity analysis and publication bias was not detected. The authors concluded that this meta-analysis showed that IS alone likely results in little to no reduction in the number of adult patients with PPCs, in mortality, or in the LHS, following cardiac, thoracic, and upper abdominal surgery.

Incentive Spirometry After Pulmonary Resection

Chang et al (2022) noted that post-operative pulmonary complications (PPCs) most commonly occur following thoracic surgery.  Not only prolonged stay in the hospital and increased financial expenses, but also morbidity and even mortality may be troublesome for patients with PPCs.  In a systematic review and meta-analysis, these investigators examined available evidence on the effectiveness of (IS to reduce PPCs and shorten hospital LOS.  This systematic review and meta-analysis included 5 RCTs and 3 retrospective cohort studies (a total of 10,322 patients) in PubMed, Embase and Cochrane Library until September 31, 2021.  They evaluated the effectiveness of IS using hospital LOS, PPCs, post-operative pneumonia, and post-operative atelectasis with meta-analysis, meta-regression and trial sequential analysis (TSA).  With this meta-analysis, the hospital LOS in patients undergoing IS was significantly shorter (1.8 days) than that in patients not receiving IS (MD = -1.80, 95 % CI: -2.95 to -0.65).  Patients undergoing IS also had reduced risk of PPCs (32 %) and post-operative pneumonia (17.9 %) with statistical significance than patients not undergoing IS (PPC: OR = 0.68, 95 % CI: 0.51 to 0.90) (pneumonia: OR = 0.821, 95 % CI: 0.677 to 0.995).  In meta-regression, the benefits of undergoing IS in patients with pre-operative predicted FEV1 of less than 80 % in a linear fashion with decreasing PPCs.  IS was an effective modality to improve the quality of post-operative care for patients after pulmonary resection, compared with the control group without using IS; and applying IS has favorable outcomes of shorter hospital LOS (1.8 days) and lower occurrence of PPCs (32 % of risk reduction), which were conclusive and robust based on validation via TSA.  Moreover, the IS device was more beneficial for patients with pre-operative predicted FEV1 of less than 80 % than that in others.  Moreover, these researchers stated that despite these striking findings, further investigation is needed to examine the use of this adjunct among patients receiving pulmonary resection.

The authors stated that this meta-analysis had several drawbacks.  First, although focusing on employing IS for patients receiving pulmonary resection, the definite timing of using IS (pre- and post-operatively), the employed protocols, and analgesic management post-operatively remain diverse among these enrolled studies, which would contribute to the substantial heterogeneity observed in this analysis.  Second, the protocols of care implemented were also different between intervention and control groups and among the enrolled studies.  Some studies used the same protocol between intervention and control groups, except for IS; however, some studies din not include chest physiotherapy in the control group, which may be confounding factors.  Third, the clinical heterogeneity of included participants, such as different co-morbidities, smoking status, surgical approach, and extent of resection, was a critical confounding factor that should be considered (e.g., the post-operative courses were different between the patients undergoing pneumonectomy, wedge resection or lobectomy/segmentectomy).  Fourth, patient adherence is crucial for the success of IS.  The bedside request from the physician in charge and the patient's health literacy may have contribution to the compliance of IS, which were not reported in the enrolled studies.  Fifth, despite the comprehensive searches of major databases, only a few studies and small patient numbers were enrolled with different evidence level, patient numbers and study design (In this study, both RCTs and retrospective study were included).  A paucity of clinical trials that examined the benefits of IS was observed in patients who underwent pulmonary resection.  As a result, a cautious interpretation of results from this meta-analysis is needed.

Incentive Spirometry After Bariatric Surgery

Pantel and colleagues (2017) stated that the combination of obesity and foregut surgery puts patients undergoing bariatric surgery at high risk for post-operative pulmonary complications.  Post-operative IS was a ubiquitous practice; however, little evidence exists on its effectiveness.  In a randomized, non-inferiority, clinical trial, these researchers determined the effect of post-operative IS on hypoxemia, arterial oxygen saturation (Sao2) level, and pulmonary complications after bariatric surgery.  This study enrolled patients undergoing bariatric surgery from May 1, 2015, to June 30, 2016.  Patients were randomized to post-operative IS (control group) or clinical observation (test group) at a single-center tertiary referral teaching hospital.  Analysis was based on the evaluable population.  The controls received the standard of care with IS use 10 times every hour while awake.  The test group did not receive an IS device or these orders.  The primary outcome was frequency of hypoxemia, defined as an Sao2 level of less than 92 % without supplementation at 6, 12, and 24 post-operative hours.  Secondary outcomes were Sao2 levels at these times and the rate of 30-day post-operative pulmonary complications.  A total of 224 patients (50 men [22.3 %] and 174 women [77.7 %]; mean [SD] age of 45.6 [11.8] years) were enrolled, and 112 were randomized for each group.  Baseline characteristics of the groups were similar.  No significant differences in frequency of post-operative hypoxemia between the control and test groups were found at 6 (11.9 % versus 10.4 %; p = 0.72), 12 (5.4 % versus 8.2 %; p = 0.40), or 24 (3.7 % versus 4.6 %; p = 0.73) post-operative hours.  No significant differences were observed in mean (SD) Sao2 level between the control and test groups at 6 (94.9 % [3.2 %] versus 94.9 % [2.9 %]; p = 0.99), 12 (95.4 % [2.2 %] versus 95.1 % [2.5 %]; p = 0.40), or 24 (95.7 % [2.4 %] versus 95.6 % [2.4 %]; p = 0.69) post-operative hours.  Rates of 30-day post-operative pulmonary complications did not differ between groups (8 patients [7.1 %] in the control group versus 4 [3.6 %] in the test group; p = 0.24).  The authors concluded that post-operative IS did not demonstrate any effect on post-operative hypoxemia, Sao2 level, or post-operative pulmonary complications.  They stated that based on these findings, the routine use of IS should not be recommended after bariatric surgery in its current implementation.

Incentive Spirometers for Prevention of Atelectasis Following Neurosurgery

Sah and colleagues (2017) noted that volume controlled ventilation with low PEEP is used in neuro-anesthesia to provide constant PaCO2 levels and prevent raised intra-cranial pressure.  Thus, neurosurgery patients are prone to atelectasis formation, however, these investigators could not find any study that evaluated prevention of post-operative pulmonary complications in neurosurgery.  In a prospective RCT, these researchers examined the efficacy of CPAP and IS on respiratory functions during the post-operative period following supratentorial craniotomy.  A total of 79 ASAI-II patients aged between 18 and 70 years scheduled for elective supratentorial craniotomy were included in the study.  Patients were randomized into 3 groups after surgery.  The Group IS (n = 20) was treated with IS 5 times in 1 min and 5 min per hour, the Group CPAP (n = 20) with continuous positive airway pressure 10 cm H2O pressure and 0.4 FiO2 via an oro-nasal mask 5 min per hour, and the Group Control (n = 20) 4L·min-1O2 via mask; all during the 1st 6 hours post-operatively.  Respiratory functions tests and arterial blood gases analysis were performed before the induction of anesthesia (baseline), 30 minutes, 6 hours, 24 hours post-operatively.  The IS and CPAP applications had similar effects with respect to FVC values.  The post-operative 30-min forced expiratory volume in 1 second (FEV1) values were statistically significantly reduced compared to the baseline in all groups (p < 0.0001).  FEV1 values were statistically significantly increased at the post-operative 24 hours compared to the post-operative 30-min in the Groups IS and CPAP (p < 0.0001).  This increase, however, was not observed in the Group Control, and the post-operative 24- hour FEV1 values were statistically significantly lower in the Group Control compared to the Group IS (p = 0.015).  The authors concluded that although this study was under-powered to detect differences in FEV1 values, the post-operative 24-hour FEV1 values were significantly higher in the IS group than the Control group and this difference was not observed between the CPAP and Control groups.  They stated that there might be a favorable effect of IS in neurosurgery patients; however, larger studies are needed to make a certain conclusion.

Incentive Spirometers for Improvement of Oromotor and Pulmonary Functions in Children With Down's Syndrome

Ibrahim and colleagues (2019) examined the effect of incentive spirometry training on oromotor and pulmonary functions in children with Down's syndrome.  A total of 34 children with Down's syndrome were randomly divided into 2 groups; the children were of both sexes and aged between 6 and 12 years.  Group A received only oromotor exercises, while Group B received oromotor exercises and IS training.  The pulmonary function test (PFT) was performed using computerized spirometry model master screen that assessed pulmonary functions (peak expiratory flow, FVC, and FEV1), while the orofacial myofunctional evaluation with score (OMES) was used to evaluate oromotor function before and after treatment.  The post-treatment results showed significant difference in oromotor and pulmonary functions within both groups, but no significant differences were found between the 2 groups. The authors concluded that oromotor exercises were more effective than IS training in improving both oromotor and pulmonary functions in children with Down's syndrome.  The main drawback of this study was that the intellectual disability of the children with Down’s syndrome made it difficult for them to follow instructions, therefore, these researchers spent a long time teaching them to follow the instructions well.

Incentive Spirometers for Reduction of Pulmonary Complications in Patients With Traumatic Rib Fractures

An UpToDate review on the initial evaluation and management of rib fractures (Karlson & French, 2019) states that "respiratory care, including use of incentive spirometry to prevent atelectasis and its complications, is often important "

In a RCT, Sum and colleagues (2019) examined the effect of IS on lung function and pulmonary complication rates in patients with rib fractures.  Between June 2014 and May 2017, a total of 50 adult patients with traumatic rib fractures were prospectively investigated.  Patients who were unconscious, had a history of COPD or asthma, or an Injury Severity Score (ISS) of greater than or equal to 16 were excluded.  Patients were randomly divided into a study group (n = 24), who underwent IS therapy, and a control group (n = 26).  All patients received the same analgesic protocol.  Chest X-rays and PFTs were performed on the 5th and 7th days after trauma.  The groups were considered demographically homogeneous.  The mean age was 55.2 years and 68 % were male.  Mean pre-treatment ISSs and mean number of ribs fractured were not significantly different (8.23 versus 8.08 and 4 versus 4, respectively).  Of 50 patients, 28 (56 %) developed pulmonary complications, which were more prevalent in the control group (80.7 % versus 29.2 %; p = 0.001).  Altogether, 25 patients had delayed hemothorax, which was more prevalent in the control group (69.2 % versus 29.2 %; p = 0.005); 2 patients in the control group developed atelectasis, 1 patient developed pneumothorax, and 5 patients required thoracostomy.  PFT results showed decreased FVC and FEV1 in the control group.  Comparing pre- and post-treatment FVC and FEV1, the study group had significantly greater improvements (p < 0.001).  The authors concluded that the use of an IS reduced pulmonary complications and improved PFT results in patients with rib fractures.  The IS was a cost-effective device for patients with rib fractures and its use has clinical benefits without harmful effects.

The authors stated that this study had several drawbacks.  First, the relatively small sample size (n = 26 I the IS group) may not be representative of the population of rib fracture patients in Taiwan.  These researchers included only patients who were admitted to hospital and it was likely that patients who were not admitted also suffered from delayed pulmonary complications.  This may limit the generalizability of these findings to wider populations.  In the future, these investigators may consider extending the inclusion criteria to include out-patients and patients attending an ED.  Second, these researchers carried out PFTs only within 1 week of trauma, so the outcomes reported were relatively short-term.  Further studies on long-term outcomes and on training on IS compliance following discharge would aid to further the knowledge of the benefits of IS.  Third, the interventional procedures were challenging to blind, but the effort would be worthwhile by avoiding bias.  However, blinding was reported to be successful in only a few interventional studies (13/63; 21 %).

Incentive Spirometeres for the Management of Acute Chest Syndrome in Patients with Sickle Cell Disease

Niazi et al (2022) noted that acute chest syndrome (ACS) accounts for the highest mortality in patients with Sickle cell disease (SCD).  Early diagnosis and timely management of ACS results in better outcomes; however, the effectiveness of most treatment modalities for ACS management has not been established.  To review the treatment modalities management protocols and highlight the effectiveness of each option, these investigators carried out a literature search.  RCTs that examined the effectiveness of different treatment modalities in ACS management in SCD patients were chosen and reviewed.  A total of 11 RCTs were found that examined the effectiveness of IS, positive expiratory pressure (PEP) device, intravenous (IV) dexamethasone, oral versus IV morphine, inhaled nitric oxide (INO), unfractionated heparin (UFH), and blood transfusion in the prevention or treatment of ACS.  Although there are guidelines for ACS treatment, the available evidence is very limited to delineating the effectiveness of various interventions in ACS management.  The authors concluded that more high-quality studies and trials with a larger patient population can benefit this research area to support the recommendations with stronger evidence.

SpiroTimer - Incentive Spirometer Patient Reminder

Eltorai and associates (2019) stated that IS was developed to reduce atelectasis and are in widespread clinical use; however, without IS use adherence data, the effectiveness of IS cannot be determined.  In a randomized, clinical trial, these researchers examined the effect of a use-tracking IS reminder on patient adherence and clinical outcomes following coronary artery bypass grafting (CABG) surgery.  This study was carried out from June 5, 2017 to December 29, 2017, at a tertiary referral teaching hospital; and included 212 patients who underwent CABG, of whom 160 subjects were randomized (intent-to-treat), with 145 completing the study per protocol.  Subjects were stratified by surgical urgency (elective versus non-elective) and sex (men versus women).  A use-tracking IS add-on device (SpiroTimer) with an integrated use reminder bell recorded and time-stamped subjects' inspiratory breaths.  Patients were randomized by hourly reminder "bell on" (experimental group) or "bell off" (control group).  Incentive spirometer use was recorded for the entire post-operative stay and compared between groups.  Radiographic atelectasis severity (score, 0 to 10) was the primary clinical outcome; secondary respiratory and non-respiratory outcomes were also evaluated.  A total of 145 per-protocol participants (112 men [77 %]; mean age of 69 years [95 % confidence interval [CI]: 67 to 70]; 90 [62 %] undergoing a non-elective procedure) were evaluated, with 74 (51.0 %) in the bell off group and 71 (49.0 %) in the bell on group.  The baseline medical and motivation-to-recover characteristics of the 2 groups were similar.  The mean number of daily inspiratory breaths was greater in bell on (35; 95 % CI: 29 to 43 versus 17; 95 % CI: 13 to 23; p < 0.001).  The percentage of recorded hours with an inspiratory breath event was greater in bell on (58 %; 95 % CI: 51 to 65 versus 28 %; 95 % CI: 23 to 32; p < 0.001).  Despite no differences in the 1st post-operative chest radiograph mean atelectasis severity scores (2.3; 95 % CI: 2.0 to 2.6 versus 2.4; 95 % CI: 2.2 to 2.7; p = 0.48), the mean atelectasis severity scores for the final chest radiographs conducted before discharge were significantly lower for bell on than bell off group (1.5; 95 % CI: 1.3 to 1.8 versus 1.8; 95 % CI: 1.6 to 2.1; p = 0.04).  Of those with early post-operative fevers, fever duration was shorter for bell on (3.2 hours; 95 % CI: 2.3 to 4.6 versus 5.2 hours; 95 % CI: 3.9 to 7.0; p = 0.04).  Having the bell turned on reduced non-invasive positive pressure ventilation use rates (37.2 %; 95 % CI: 24.1 % to 52.5 % versus 19.2 %; 95 % CI: 10.2 % to 33.0 %; p = 0.03) for subjects undergoing non-elective procedures.  Bell on reduced the median post-operative length of stay (LOS; 7 days; 95 % CI: 6 to 9 versus 6 days; 95 % CI: 6 to 7; p = 0.048) and the intensive care unit (ICU) LOS for patients undergoing non-elective procedures (4 days; 95 % CI: 3 to 5 versus 3 days; 95 % CI: 3 to 4; p = 0.02).  At 6 months, the bell off mortality rate was higher than bell on (9 % versus 0 %, p = 0.048) for subjects undergoing non-elective procedures.  The authors concluded that incentive spirometer reminder improved patient adherence, atelectasis severity, early post-operative fever duration, non-invasive positive pressure ventilation use, ICU and LOS, and 6-month mortality in certain patients.  These researchers stated that incentive spirometers could be clinically effective, but perhaps only when adherence was high.  To their knowledge, the benefit of IS without a reminder is still unknown, and further studies are needed to examine if incentive spirometry without a reminder is cost-effective or of any clinical use.

The authors stated that this study had several drawbacks.  This trial did not directly examine the effectiveness of IS on outcomes.  To do so, a future study would need to compare a treatment group (high-adherence reminder IS) with a negative control condition (no IS).  Such a study may not be feasible given the widespread use and promotion of IS as standard of care and may be not be permissible in light of the data from this study due to the improved outcomes in the bell on group.  Masking the reminder bell sound (the intervention) is not possible for participants, clinicians, and researchers with intact hearing.  The objective of the study was to examine the effect of the un-maskable reminder on clinical outcomes in a real clinical setting.  Atelectasis severity, as the primary clinical outcome measure, was scored by 2 masked radiologists.  The primary non-clinical outcome measure, IS use, was measured by the SpiroTimer machine.  Clinician-directed endpoints (e.g., CPAP/BiPAP use and LOS) were determined by standardized objective criteria and clinical protocols that were the same between groups.  The research team was independent from the clinicians and not involved in patient treatment decisions.  If unmasked clinicians responded to the reminder bell (consciously or unconsciously) to help patients use their incentive spirometers more, use CPAP/BiPAP less, or be more aggressive in discharge timing, then the reminder bell still caused the observed clinical improvements.  Furthermore, although the target threshold inspiratory volume may under-estimate the number of breath events (e.g., subjects may have taken subthreshold breaths), the method was used in both groups and represented how clinicians instruct patients.  Several secondary outcomes were not observed to be different between the conditions.  The lack of observed effects on certain secondary outcomes was not unexpected given that the study was only powered to detect a difference in atelectasis between groups.  It would be interesting to examine the effect of various peri-operative factors (e.g., surgical techniques, graft type, anesthesia, post-operative pain scores, transverse sternal fracture, rib fracture, type of sternal closure, circulatory arrest times, and skeletonized versus pedicle fashion graft) on immediate post-operative atelectasis, IS use, and SpiroTimer effectiveness.  For example, future IS studies of patients undergoing CABG could randomize on variables such as bilateral internal mammary artery use and/or skeletonization of internal mammary artery.  Studies aimed at different patient populations that are powered to detect additional outcomes are needed to help further clarify and define IS applications and indications.  Furthermore, IS protocol optimization studies are needed to examine what parameters have the greatest effect on outcomes.

Pangborn and colleagues (2020) noted that the SpiroTimer was developed to address the problem of IS non-compliance.  In a recent randomized clinical trial, the SpiroTimer improved IS use compliance, LOS, and mortality.  For successful, safe, and effective implementation of a new medical device, human factors and usability must be examined.  These investigators examined the SpiroTimer's human factors as they pertain to intended users, use environments, as well as uses.  Immediately following the completion of the randomized clinical trial of the SpiroTimer, before the providers were informed of the results of the study, a human factors and usability survey was distributed in-person to all nurses involved in the trial.  Variations in nurse user perspectives were evaluated.  A total of 52 nurses (100 % response rate) completed the survey.  In general, most nurses felt IS use compliance was poor (65 %; 34/52, p = 0.0265) and should be improved (94 %; 49/52, p < 0.001).  Nurses agreed the SpiroTimer ameliorated patient IS use compliance (82 %; 41/50, p < 0.001), IS effectiveness (74 %; 37/50, p < 0.001), and patient engagement in their own care (88 %; 44/ 50, p < 0.001).  Nurses reported the SpiroTimer helped remind them to work with their patients on IS (70 %; 35/50, p = 0.0047) while reducing the number of times they had to remind their patients to use their IS (70 %; 35/50, p = 0.0047).  They felt that they would use the SpiroTimer with all their patients (82 %; 41/50, p < 0.001) and that they would recommend the SpiroTimer to a colleague (74 %; 37/50, p < 0.001).  Finally, most nurses believed the SpiroTimer should become part of routine patient care (78 %; 39/50, p < 0.001).  The authors concluded that based on human factors feedback from intended users in an intended environment, the SpiroTimer has the potential to be usable and effective.

The authors stated that this study had several drawbacks.  As a survey study, this trial was subject to the weaknesses of surveys; however, it was able to attain a 100 % response rate; thus, could reflect the whole population of nurses who had clinically interacted with the SpiroTimer to-date.  Although surveys represent subjective data, the nature of human factors and usability is based on human-perceived interface.  These researchers stated that future SpiroTimer human factor investigations may examine different groups of users (e.g., respiratory therapists, nursing aides, patients, and patient families) in various clinical settings.

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References