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(Chest. 2004;126:165-172.)
© 2004 American College of Chest Physicians

The Use of Noninvasive Ventilation in Acute Respiratory Failure at a Tertiary Care Center*

Elizabeth S. Paus-Jenssen, MD; John K. Reid, MD; Donald W. Cockcroft, MD, FCCP; Karen Laframboise, MD and Heather A. Ward, MD, FCCP

* From the Department of Medicine, Royal University Hospital, Saskatoon, SK, Canada.

Correspondence to: Heather A. Ward, MD, FCCP, Division of General Internal Medicine, Box 109, Royal University Hospital, 103 Hospital Dr, Saskatoon, SK, Canada, S7N 0W8; e-mail: heather.ward{at}saskatoonhealthregion.ca


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Objective: Financial constraints and bed limitations frequently prevent admission of ill patients to a critical care setting. We surveyed the use of treatment with noninvasive ventilation (NIV) in clinical practice by physicians in a tertiary care, university-based teaching hospital and compared our findings with published recommendations for the use of NIV.

Methods: Data were collected prospectively on all patients with acute respiratory failure (ARF) for whom NIV was ordered over a 5-month period. The respiratory therapy department was responsible for administering NIV on written order by a physician. The respiratory therapist completed a survey form with patient tracking data for each initiation of NIV. The investigators then surveyed the clinical chart for clinical data.

Results: NIV was utilized for the treatment of ARF on 75 occasions during the 5-month period. Fourteen patients (18%) received NIV for a COPD exacerbation, and 61 patients (82%) received it for respiratory failure of other etiologies. NIV was initiated in the emergency department in 32% of patients, in a critical care setting in 27% of patients, in a ward observation unit in 23% of patients, and on a general medical or surgical ward in 18% of patients. Arterial blood gases (ABGs) were measured on 68 occasions prior to the initiation of NIV, and 51 patients had an ABG measurement within the first 6 h of treatment. The mean pH at baseline was 7.29, and 33% of patients had a baseline pH of < 7.25. Seven patients required endotracheal intubation (ETI) [13%], and there were 18 deaths (24%) with patients having do-not-resuscitate orders, accounting for 12 deaths.

Conclusion: NIV is commonly used outside of a critical care setting. Our outcomes of ETI and death were similar to those cited in the literature despite less aggressive monitoring of these patients.

Key Words: acute respiratory failure • clinical practice • noninvasive ventilation • outcomes


   Introduction
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 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Acute respiratory failure (ARF) occurs when there is inadequate gas exchange or ventilation, which are manifested primarily by hypoxemia and hypercarbia, respectively. Medical management may be ineffective at this point, and some form of ventilatory support is often required. The use of noninvasive ventilation (NIV) and continuous positive airway pressure (CPAP) has become increasingly common, and they may obviate the need for mechanical ventilation.

Controversy exists as to whether NIV is appropriate in all forms of ARF. The largest proven benefit is confined to patients with severe exacerbations of COPD who present with hypercarbia.12345 While results from patients with hypoxemic respiratory failure are conflicting,5678910111213 the outcome of interest has been the avoidance of endotracheal intubation (ETI) and its potential complications.

In the last 10 years, there have been several studies published12345678911141516171819202122 that have supported the use of NIV in patients with ARF. Scientific studies optimize patient selection, clinical expertise, and careful monitoring of patients. The results of carefully controlled trials may not be generalizable to clinical practice as these ideal conditions may not be present in actual practice. Furthermore, many doctors may have limited experience with the initiation and monitoring of NIV. One study5 reported the results of NIV in patients with ARF in clinical practice. However, all patients had been admitted to the ICU. Financial constraints and bed limitations frequently prevent the admission of ill patients to a critical care setting. We are not aware of any study that has looked at the effectiveness of NIV outside of an ICU or emergency department setting.

To answer this question, we surveyed the use of NIV in a university-based, tertiary care teaching hospital. The only policy governing the use of NIV in our hospital was that there be a written order from a physician. NIV could be initiated and maintained on any ward in the hospital without a mandatory consultation to the pulmonary service or the ICU. The purpose of our study was to compare the patient selection and clinical outcomes of NIV use in this setting with those of the published literature.


   Materials and Methods
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 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
Between June 6 and November 1, 2001, 81 consecutive applications of NIV at the Royal University Hospital in Saskatoon, Canada, were prospectively followed. The inclusion criterion was that NIV be initiated for the treatment of ARF on the decision of the ordering physician. The exclusion criterion was the initiation of NIV for suspected or established sleep-disordered breathing (SDB). Individual patients were eligible to be included in the study on more than one occasion if there were separate hospital admissions.

NIV was defined as any form of ventilatory support without an endotracheal tube that was available as either bilevel positive airway pressure or CPAP. The respiratory therapy department was responsible for administering NIV on written order by a physician. As there was no formal NIV protocol in place, the individual physician providing care determined the type of NIV, its settings, and the monitoring of patients. All admitting physicians at this facility have privileges to order NIV. No consultation to respiratory medicine or ICU is required.

The respiratory therapists completed a survey form with patient tracking data on each initiation of NIV. The investigators followed the patients until NIV was discontinued and then completed a chart audit of outcomes at hospital discharge. The investigators did not intervene in the management of these patients.

The primary outcomes were the need for mechanical ventilation and mortality. In addition to standard demographic data, the following variables were collected: reason for hospital admission; reason for NIV; location of the initiation of NIV; specialty of physician ordering NIV; type of NIV; and resuscitation status of patients. Arterial blood gas (ABG) values prior to the initiation of NIV, within 2 h of NIV initiation, and within 6 h of NIV initiation were recorded (if available). The hours of continuous use from the initiation of NIV and the total duration of use were recorded.

Statistical analysis was completed using a statistical software package (SPSS, version 11.0; SPSS; Chicago, IL). Categoric variables were compared using {chi}2 test and Fisher exact test. Continuous variables were compared using a t test. Statistical significance was set at p ≤ 0.05.


   Results
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 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
During the study period, 77 patients received NIV. Six were excluded for SDB. Seventy-one patients received NIV for the treatment of ARF. Of these patients, two had two separate hospital admissions and one patient had three separate hospital admissions for ARF requiring NIV. In total, 75 records were reviewed. As each utilization of NIV occurred during a separate hospital admission, each record was considered as a separate patient (75 records). Baseline characteristics of the patients are shown in Table 1 .


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  		Table 1. Patient Characteristics*

 
NIV was initiated most frequently by an internist (35% of cases), followed by an intensivist (20%), and emergency physician (12%), surgeon (12%), or cardiologist (12%). A respirologist initiated NIV for only four patients (5%), and an anesthetist initiated NIV in 4% of patients (Fig 1 ). The median initial pressure settings were 10 cm H2O for CPAP and 12/6 cm H2O for bilevel pressure ventilation.



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  		Figure 1. Specialties of physicians ordering NIV.

 
The majority of patients had NIV initiated in the emergency department (32%) or a critical care setting (27%), while 41% were located in a ward observation bed or a general medical or surgical ward bed (Fig 2 ). NIV was initiated for "shortness of breath" in 18 patients. Other indications were COPD exacerbation, hypoxemic respiratory failure, hypercarbic respiratory failure, and congestive heart failure (CHF). Five patients used NIV for postextubation respiratory distress or to assist with weaning from mechanical ventilation, and another five patients used NIV for either hypoventilation or atelectasis postoperatively (Fig 3 ).



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  		Figure 2. Location in the hospital where NIV was initiated. ER = emergency department.

 


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  		Figure 3. Physician indications for NIV initiation. SOB = shortness of breath.

 
Of the 18 patients who had NIV initiated for "shortness of breath/respiratory failure," 7 were eventually identified as having atelectasis, two as having CHF, and one each having COPD exacerbation, pneumonia, lung transplant rejection, muscular dystrophy, graft-vs-host disease, bilateral pleural effusions, and SDB. The reason for the shortness of breath was not clearly established in two patients.

Ninety-one percent of patients (68 patients) had their ABG levels measured prior to the initiation of NIV. Thirty-six patients (48%) had undergone an ABG measurement within 2 h of the initiation NIV, and 30 patients (40%) had undergone an ABG measurement within 6 h. Eighteen patients had ABG measurements within both 2 h and 6 h of NIV initiation. Of the 68 patients with initial ABG measurements, 21 (31%) were normocarbic and 47 (69%) had a PCO2 ≥ 45 mm Hg (Table 2 ). Acid-base status was normal in 15 patients. There was primary respiratory acidosis in 40 patients, primary metabolic acidosis in 7 patients, respiratory and metabolic acidosis in 4 patients, and compensated metabolic alkalosis in 2 patients. The mean pH was 7.29 at baseline, 7.33 at 2 h after NIV initiation, and 7.34 at 6 h after NIV initiation. Of the 18 patients who died in this study, the mean pH was 7.28 at baseline, 7.33 at 2 h after NIV initiation, and 7.28 at 6 h after NIV initiation. The pH was < 7.25 at baseline in 34% of all patients who had undergone an initial ABG measurement (Fig 4 ).


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  		Table 2. Outcome of Normocarbic vs Hypercarbic Patients

 


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  		Figure 4. pH values prior to the initiation of NIV.

 
In our study, 23 of 68 patients with a baseline ABG measurement had a pH < 7.25 prior to NIV initiation. Of these patients, 16 improved after treatment. Seventeen patients had a pH of 7.15 to 7.24 (shortness of breath/respiratory failure, 5 patients; CHF, 5 patients; COPD, 5 patients; pneumonia, 1 patient; postextubation, 1 patient). Of these patients, 11 survived to hospital discharge. Five patients had a pH in the range of 7.05 to 7.14, and four patients survived to hospital discharge. Two survivors had NIV initiated for CHF and two for hypercarbia, and the one who did not survive had NIV initiated for hypoventilation. The one patient with a pH of < 7.05 received a diagnosis of CHF and survived to hospital discharge. Ten of these 23 patients were treated in the emergency department with only two deaths, while 6 patients were managed on the ward (two deaths), four were managed in an observation unit (two deaths), and three were managed in a critical care unit (one death) [Table 2].

Bilevel pressure therapy was used in 64 patients, and CPAP was used in 11 patients. NIV was discontinued in < 24 h in 35 patients (47%) and was continued for > 96 h in 20 patients (27%). Fifty-three patients had "full resuscitation" status. Seven of these patients (13%) were intubated, and four of these patients developed hospital-acquired pneumonia. There were 18 deaths (24%) among patients with do-not-resuscitate (DNR) patients, accounting for two thirds of deaths. Patients with DNR orders included individuals who requested that either intubation or cardiac resuscitation, or both, be withheld. Six deaths occurred in the full-resuscitation group (11%), and 12 deaths occurred in the DNR group (55%). Three patients died while receiving mechanical ventilation. Of the 18 deaths, NIV was initiated outside of a critical care setting or emergency department in 10 patients.


   Discussion
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
To the best of our knowledge, this is the first report of how NIV is being used in a tertiary care hospital in a nonstudy setting. Girault et al5 recently published an observational retrospective cohort study that assessed the outcomes of NIV in daily practice in a non-protocol-driven study, but those patients were all managed in a medical ICU.

Studies utilize NIV protocol strategies in closely monitored locations with experienced staff. Monthly training sessions on NIV are given to rotating housestaff, fellows, nurses, and respiratory therapists.9 Protocols frequently outline initial pressure settings, monitoring, subsequent adjustments to NIV based on clinical status and gas exchange, and criteria for ETI.5912 In our institution, the nurse/patient ratios range from 1:1 in a critical care unit to 1:10 in the general ward. Regular formal teaching sessions are not provided to housestaff, and a formal NIV protocol is not in place. Decision making for NIV was left to the discretion of the individual physicians providing care. The absence of protocols and varying physician experience with NIV would be expected to result in a less uniform approach to the use of NIV than has been documented in previous studies.

All studies of NIV thus far have involved treatment with NIV in a critical care unit, emergency department, or respiratory ward. A 1997 survey23 of hospitals in the United Kingdom showed that NIV was being used on a general ward in 16% of patients, on a respiratory ward in 24% of patients, on an observation unit in 12% of patients, in an ICU in 13% of patients, and in combination in 34% of patients. Patient outcomes from these hospitals are unknown. In our study, 20 patients were in a critical care setting (ie, ICU, coronary care unit, or pediatric ICU) prior to the initiation of NIV. Another 10 patients were transferred to a critical care unit after initiation. Seven of 28 patients (25%) died in a critical care setting, 4 of 13 patients (31%) died in an observation unit, 4 of 21 patients (19%) died in the emergency department, and 3 of 13 patients (23%) in a general ward bed.

The British Medical Society has published guidelines for the use of NIV.20 Prior to this, numerous controlled and uncontrolled studies have reported the success of NIV in managing patients with various causes of respiratory failure. With few exceptions, patient selection in this observational study was consistent with that of most published trials. Despite less intensive monitoring of patients, ETI rate (13%) and mortality rate (24%) were similar to those found in the literature (ETI rate range, 15 to 31%; mortality rate range, 10 to 28%, respectively).4679

Several studies1234 have established the benefit of NIV in hypercapnic respiratory failure secondary to COPD. Not only were improvements noted in respiratory rate, PCO2, pH, and dyspnea scores, but ETI decreased from 27 to 67% with standard medical care down to 9 to 26% with NIV therapy.1234 Furthermore, the mortality rate decreased from 20 to 30% with standard care down to 10% with NIV therapy.124

Although the admitting physician identified only 14 patients in our study as having COPD, 47 patients (of the 68 who had undergone ABG measurements) were hypercarbic. Of these 47 patients, the mortality rate was 18%, while a mortality of 32% was seen in the 21 patients with a normal PCO2 (Table 2).

Hypoxemic respiratory failure is a common indication for NIV. Antonelli et al6 randomized 64 patients with hypoxemic respiratory failure to receive either NIV or ETI. Only 31% of the NIV patients required intubation, and there was a trend toward decreased mortality rate (27 vs 45%) in NIV patients. A randomized, controlled trial7 of 61 patients found a decreased intubation rate with NIV therapy as opposed to standard medical care (7.5 vs 22.6 intubations per 100 ICU days, respectively), although there was no difference in mortality rate. Meduri et al9 assessed the effect of NIV as a first-line intervention in 158 patients with heterogeneous forms of ARF, 41 of whom had hypoxemic respiratory failure. Fourteen patients (34%) with hypoxemic respiratory failure required intubation, and the mortality rate was 22%, with a predicted mortality of 40% based on the acute physiology and chronic health evaluation (APACHE) II score.9

The results of a study of 56 patients with severe community-acquired pneumonia who had been assigned to either conventional treatment or NIV therapy yielded a significant decrease in ETI (21% vs 50%, respectively) in the NIV group compared to the conventional treatment group. A mortality benefit at 2 months was seen in the subgroup of patients with coexisting COPD.24 Antonelli et al11 studied 354 patient with acute hypoxemic respiratory failure who had been treated with NIV. Thirty percent of the patients required intubation. The following factors were identified as independently associated with the lack of response to NIV: age > 40 years; simplified acute physiology score (SAPS) II score of > 35; ARDS or community-acquired pneumonia; or a PaO2/fraction of inspired oxygen ratio of < 146 after 1 h of treatment. In a smaller study, Wysocki et al25 found that NIV was unsuccessful in the majority of patients with a PCO2 < 45 mm Hg. A larger follow-up study found that NIV resulted in decreased ETI and mortality only after a post hoc analysis excluded patients with a PCO2 of < 45 mm Hg.26

Earlier studies demonstrated CPAP to be effective in preventing ETI in patients with acute cardiogenic pulmonary edema.272829 NIV has since been shown to be advantageous as well, especially if the patient is hypercarbic.8263031 In the only published trial comparing CPAP to NIV therapy in patients with acute CHF,10 the rates of ETI and mortality were similar, but the myocardial infarction rate was higher in the NIV group (71% vs 31%, respectively), resulting in the early termination of the study. However, there were concerns regarding the adequacy of patient randomization as more patients in the NIV group had chest pain on entry. Levitt32 subsequently looked at the use of therapy with bilevel pressure vs therapy with high-flow oxygen by mask in patients with severe acute CHF in the emergency department. No true differences were detected between groups for ETI (bilevel pressure therapy, five patients; high-flow O2 therapy, seven patients) or myocardial infarction rate (bilevel pressure therapy, four patients; high-flow O2 therapy, five patients). Of the 14 patients admitted to the hospital with CHF in our study, the three deaths occurred in patients receiving bilevel pressure ventilation. Only four patients with CHF were treated with CPAP.

Randomized, controlled trials3334 have shown a role for NIV therapy in immunocompromised patients, as it has been shown to avoid ETI and, thus, to reduce infectious and hemorrhagic complications. There has been success in using NIV to facilitate weaning from mechanical ventilation353637 or for postextubation respiratory failure.5938 Nine patients in our study were successfully weaned or avoided reintubation, and one patient died after the initiation of NIV. Although it is controversial, NIV may have a role in the treatment of patients who refuse ETI.3940 At our center, NIV is considered part of "full medical therapy" and is not precluded by a "no-intubation" or DNR directive. These patients were identified as having DNR orders. Our results showed that 10 of the 22 patients with DNR orders were ultimately discharged from the hospital after treatment with NIV.

Study protocols for NIV require an ABG measurement at baseline, and most include repeat measurements at 1 h, 4 h, and varying intervals thereafter.456789111213 We found that ABG sampling did not occur nearly as frequently as in clinical trials. One could speculate that following clinical status is adequate as these patients had the same outcomes as those cited in the literature. However, it could also be postulated that if ABG measurements had been followed more closely, it may have resulted in still better patient outcomes.

It is not clear from the literature what level of severity of respiratory acidosis would contraindicate the use of NIV. Furthermore, the threshold may vary depending on the etiology and duration of respiratory failure, as well as on an individual patient’s comorbidities. Wood et al12 found that a pH of < 7.30 in conjunction with clinical status was supportive of the need for ETI. Plant et al4 specifically excluded patients with a pH of < 7.25 in their study of NIV use on the respiratory ward for patients with acute exacerbations of COPD. Subgroup analysis suggested that patients with a hospital admission pH of < 7.30 had higher rates of both ETI and in-hospital mortality. They concluded that this group of patients might benefit by management in a closely monitored or critical care setting. The authors acknowledged, however, that their study was not powered for subgroup analysis. The guidelines of the British Medical Society state that a pH of < 7.25 is more likely to result in a lack of response to NIV therapy.20 Contrasting with this, Meduri et al9 studied 52 hypercapneic patients, with a mean pH of 7.23. Forty-six of these patients showed ABG improvement after treatment with NIV. In our study, 23 of 68 patients with a baseline ABG had a pH of < 7.25 prior to NIV, and the conditions of 16 of these patients improved after treatment.

A low pH indicates patients with severe disease who should be managed in a closely monitored, if not critical care, setting. A European Respiratory Task Force survey suggests that a respiratory intermediate care unit would be beneficial in providing close monitoring for individuals requiring NIV but not ETI.41 Although a respiratory intermediate care unit would be ideal, we do not have such a unit in our hospital. An extreme shortage in critical care bed availability at our center often mandates that patients not requiring therapy with vasoactive drugs or ETI be monitored outside of the ICU. The patients in our study therefore received care in several different units, including the emergency department, general ward, the observation unit, as well as the critical care unit.

Survivors were younger and had a lower mean SAPS II score (Table 1). Method of ventilation, gender, or baseline pH did not significantly differ between survivors and nonsurvivors (Table 1). Mean SAPS II scores and age were more important clinical factors in determining outcome than was baseline pH.

The observational design of our study has several limitations. Some studies have noted that relying on NIV may delay the implementation of ETI and result in worse outcomes.1213 We did not assess whether this was indeed the case in the six deaths of patients in the full-resuscitation group. We did not observe patients after hospital discharge and are thus unaware of post-hospital discharge mortality. This was an observational study without control subjects, and as such we are unable to conclude that patient outcomes were changed by the application of NIV.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
Our audit of NIV use in a university-based, tertiary care teaching hospital revealed results that were similar to those found in the literature. Several patients with significant respiratory acidosis and those not fit for ETI were discharged from the hospital after treatment with NIV. Patients in whom NIV was initiated outside of a critical care unit did not appear to have worse outcomes.


   Acknowledgements
 
Special thanks to the respiratory therapy department at Royal University Hospital for their assistance in collecting data.


   Footnotes
 
Abbreviations: ABG = arterial blood gas; APACHE = acute physiology and chronic health evaluation; ARF = acute respiratory failure; CHF = congestive heart failure; CPAP = continuous positive airway pressure; DNR = do not resuscitate; ETI = endotracheal intubation; NIV = noninvasive ventilation; SAPS = simplified acute physiology score; SDB = sleep-disordered breathing

Received for publication June 10, 2003. Accepted for publication January 21, 2004.


   References
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

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