Background and Methods The role of noninvasive positive-pressureventilation delivered through a face mask in patients with acuterespiratory failure is uncertain. We conducted a prospective,randomized trial of noninvasive positive-pressure ventilationas compared with endotracheal intubation with conventional mechanicalventilation in 64 patients with hypoxemic acute respiratoryfailure who required mechanical ventilation.
Results Within the first hour of ventilation, 20 of 32 patients(62 percent) in the noninvasive-ventilation group and 15 of32 (47 percent) in the conventional-ventilation group had animproved ratio of the partial pressure of arterial oxygen tothe fraction of inspired oxygen (PaO2:FiO2) (P=0.21). Ten patientsin the noninvasive-ventilation group subsequently required endotrachealintubation. Seventeen patients in the conventional-ventilationgroup (53 percent) and 23 in the noninvasive-ventilation group(72 percent) survived their stay in the intensive care unit(odds ratio, 0.4; 95 percent confidence interval, 0.1 to 1.4;P=0.19); 16 patients in the conventional-ventilation group and22 patients in the noninvasive-ventilation group were dischargedfrom the hospital. More patients in the conventional-ventilationgroup had serious complications (66 percent vs. 38 percent,P=0.02) and had pneumonia or sinusitis related to the endotrachealtube (31 percent vs. 3 percent, P=0.003). Among the survivors,patients in the noninvasive-ventilation group had shorter periodsof ventilation (P=0.006) and shorter stays in the intensivecare unit (P=0.002).
Conclusions In patients with acute respiratory failure, noninvasiveventilation was as effective as conventional ventilation inimproving gas exchange and was associated with fewer seriouscomplications and shorter stays in the intensive care unit.
Noninvasive positive-pressure ventilation is a safe and effectivemeans of improving gas exchange in patients with many typesof acute respiratory failure.1 For example, in patients withacute exacerbations of chronic obstructive pulmonary diseaseand hypercapnic respiratory failure, adding noninvasive ventilationto standard therapy decreased the need for endotracheal intubation2,3,4,5,6,7,8,9and reduced mortality.8 Similarly, noninvasive continuous positiveairway pressure was effective in patients with cardiogenic pulmonaryedema, particularly those with hypercapnia.10,11,12 In patientswith various forms of acute hypoxemic respiratory failure (pneumonia,congestive heart failure, chest-wall impairment, and so forth),6,13this therapy slightly decreased the rate of intubation and improvedsurvival, but the effect was not statistically significant.8The efficacy of positive-pressure ventilation in patients withhypoxemic respiratory failure is not known.
We compared the efficacy of noninvasive ventilation deliveredthrough a face mask with the efficacy of conventional mechanicalventilation delivered through an endotracheal tube in patientswith severe hypoxemia whose condition had not improved withaggressive medical therapy and who required mechanical ventilation.
Methods
Study Design and Patient Selection
We enrolled consecutive adults with acute hypoxemic respiratoryfailure who were admitted to the intensive care unit of La SapienzaUniversity Hospital in Rome. The patients were randomly assignedto receive either conventional mechanical ventilation with endotrachealintubation or noninvasive ventilation through a face mask. Anad hoc ethics committee approved the protocol, and all patientsor their next of kin gave written informed consent.
The criteria for eligibility were acute respiratory distressthat had deteriorated despite aggressive medical management,including severe dyspnea at rest as determined by a clinicianwho was not an investigator; a respiratory rate greater than35 breaths per minute; a ratio of the partial pressure of arterialoxygen to the fraction of inspired oxygen (PaO2 :FiO2) of lessthan 200 while the patient was breathing oxygen through a Venturimask; and active contraction of the accessory muscles of respirationor paradoxical abdominal motion. Patients with any of the followingwere excluded: chronic obstructive pulmonary disease accordingto previously defined criteria5; immunosuppressive therapy;a requirement of emergency intubation for cardiopulmonary resuscitation,respiratory arrest, severe hemodynamic instability, or encephalopathy;respiratory failure caused by neurologic disease or status asthmaticus;more than two new organ failures (e.g., the simultaneous presenceof renal and cardiovascular failure)14; and tracheostomy, facialdeformities, or recent oral, esophageal, or gastric surgery.
Medical management for the conditions causing acute respiratoryfailure was similar in the two groups. We used two types ofmechanical ventilators: the Puritan Bennett 7200 (Puritan Bennett,Overland Park, Kans.) and the Servo 900 C (Siemens Elema, Uppsala,Sweden). The patients underwent continuous electrocardiographyand monitoring of arterial oxygen saturation (Biox 3700, Ohmeda,Boulder, Colo.).
Conventional Ventilation
Patients assigned to the conventional-ventilation group underwentintubation with cuffed endotracheal tubes (internal diam-eter,7.5 to 8.5 mm). The initial ventilator setting was in the assist–controlmode, with a delivered tidal volume of 10 ml per kilogram ofbody weight and a respiratory rate of 14 to 18 breaths per minute,a positive end-expiratory pressure of 5 cm of water, and anFiO2 of 0.8. Positive end-expiratory pressure was increasedin increments of 2 to 3 cm of water up to 10 cm of water, untilthe FiO2 requirement was 0.6 or less. Intravenous diazepam (0.2mg per kilogram) or propofol (2 mg per kilogram) was given forsedation at the time of intubation; none of the patients receiveda paralyzing drug. The head of the bed was kept elevated atan angle of 45 degrees to minimize the risk of aspiration. Whenspontaneous breathing reappeared, the ventilator settings werechanged to intermittent mandatory ventilation (rate, 4 to 7breaths per minute) with pressure support (14 to 20 cm of water),adjusted to achieve a spontaneous tidal volume of 8 to 10 mlper kilogram, a respiratory rate of fewer than 25 breaths perminute, and the disappearance of accessory-muscle activity.15All patients were weaned from the ventilator by reducing thelevel of pressure support by 4 cm of water twice and then decreasingthe ventilatory rate by two breaths per minute at two-hour intervals,as tolerated. Patients who tolerated an intermittent-mandatory-ventilationrate of 0.5 breath per minute, a pressure-support level of 8cm of water, and an FiO2 of 0.5 or less had a two-hour T-piecetrial.16 These patients then underwent extubation if they maintaineda respiratory rate lower than 30 breaths per minute and a PaO2greater than 75 mm Hg.
Noninvasive Ventilation
For patients assigned to noninvasive ventilation, the ventilatorwas connected with conventional tubing to a clear, full-facemask with an inflatable soft-cushion seal and a disposable foamspacer to reduce dead space (Gibeck, Upplands, Sweden). Themask was secured with head straps to avoid an excessively tightfit, and the head of the bed was kept elevated at a 45-degreeangle. In most cases, a hydrocolloid sheet was applied overthe nasal bridge. For patients with a nasogastric tube, a sealconnector in the dome of the mask was used to minimize air leakage.After the mask had been secured, pressure support was increasedto achieve an exhaled tidal volume of 8 to 10 ml per kilogram,a respiratory rate of fewer than 25 breaths per minute, thedisappearance of accessory-muscle activity (as evaluated bypalpation of the sternocleidomastoid muscle),15 and patientcomfort. Continuous positive airway pressure was increased by2 to 3 cm of water repeatedly, up to 10 cm of water, until theFiO2 requirement was 0.6 or less. Ventilator settings were adjustedon the basis of continuous oximetry and measurements of arterial-bloodgases. The patients were not sedated.
The duration of ventilation was standardized according to theprotocol of Wysocki et al.13 During the first 24 hours, ventilationwas continuously maintained until oxygenation and clinical statusimproved. Subsequently, each patient was evaluated daily afterbreathing supplemental oxygen without ventilatory support for15 minutes. Noninvasive ventilation was reduced progressivelyin accordance with the degree of clinical improvement and wasdiscontinued if the patient maintained a respiratory rate lowerthan 30 breaths per minute and a PaO2 greater than 75 mm Hgwith an FiO2 of 0.5, without ventilatory support.
In the patients randomly assigned to receive noninvasive ventilation,the criteria for switching them to endotracheal intubation andconventional ventilation were the failure to maintain a PaO2above 65 mm Hg with an FiO2 of at least 0.6; the developmentof conditions necessitating endotracheal intubation to protectthe airways (coma or seizure disorder) or to manage copioustracheal secretions; hemodynamic or electrocardiographic instability;or an inability on the part of the patient to tolerate the facemask because of discomfort. An attending physician who was notan investigator evaluated these criteria.
End Points and Definitions
The primary end points were the values for gas exchange andthe frequency of complications of mechanical ventilation, includingpneumonia, sepsis, and sinusitis. Arterial-blood gas valueswere determined at base line, at one hour, at four-hour intervalsduring mechanical ventilation, and before discontinuation ofventilatory support. Improvement in gas exchange was definedas the ability to increase the PaO2 :FiO2 ratio to more than200 or an increase in this ratio of more than 100 from baseline.12 Improvement in gas exchange was evaluated within onehour after study entry (initial improvement) and over time (sustainedimprovement). Sustained improvement in gas exchange was definedas the ability to maintain the defined improvement in PaO2 :FiO2until mechanical ventilation was discontinued, as confirmedby serial blood gas measurements.
Patients were monitored for the development of infections orother complications. Sepsis was defined as a systemic inflammatoryresponse to an infectious process, with manifestations includingtachycardia, tachypnea, hyperthermia, and hypothermia, and ahigh white-cell count; positive blood cultures were not required.Severe sepsis was diagnosed when sepsis was associated withevidence of organ dysfunction or hypoperfusion, such as alteredmental status, metabolic acidosis, or oliguria. Severe sepsisassociated with hypotension that was unresponsive to fluid therapywas referred to as septic shock.17
Patients in whom clinical manifestations of pneumonia developed,including radiographic evidence of persistent pulmonary infiltrates,hyperthermia or hypothermia, purulent tracheobronchial secretions,a high white-cell count, and worsening of pulmonary-gas exchange,18,19underwent bronchoscopy with bronchoalveolar lavage. The methodsand laboratory procedures followed consensus guidelines.20,21Pneumonia was diagnosed when at least 100,000 colony-formingunits of bacteria per milliliter were measured in bronchoalveolar-lavagefluids.20 Since infections in patients receiving mechanicalventilation are frequently associated with the presence of aninvasive device,18 an index of invasiveness was establishedby counting the number of devices (central venous, arterial,pulmonary arterial, and urinary catheters; drainage, endotracheal,and nasogastric tubes) per patient at entry to the study.
The secondary end points were survival, the duration of mechanicalventilation, and the duration of the stay in the intensive careunit. The criteria for the diagnosis of the acute respiratorydistress syndrome were those of the American–EuropeanConsensus Conference.22 The simplified acute physiologic scorewas calculated 24 hours after admission to the intensive careunit.23 This score takes into account 14 variables (age, heartrate, systolic blood pressure, body temperature, respiratoryrate or need for ventilatory support, urinary output, white-cellcount, hematocrit, Glasgow coma score, and serum glucose, potassium,sodium, bicarbonate, and urea nitrogen concentrations). A rangeof 0 to 4 is assigned for each variable (range of possible scores,0 to 56). Higher scores indicate a higher risk of death; forinstance, a score of 15 or 16 is associated with a mortalityrate of approximately 32 percent, and for all scores of 21 orhigher, mortality exceeds 80 percent.
Statistical Analysis
Results are given as means ±SD. Demographic and physiologiccharacteristics of the two groups were compared with use ofStudent's t-test for continuous data (separate estimates ofvariance were used when variances differed significantly) andwith the Mantel–Haenszel extended chi-square test forcategorical data. Fisher's exact test (two-tailed) was usedwhen appropriate (when the expected number of cases per cellwas below five). The SPSS package (SPSS, Chicago) was used forall analyses. The odds ratios, relative risks, and 95 percentconfidence intervals are given with chi-square and P valuesto illustrate the amount of risk associated with some of theeffects.24
Results
Between April 1995 and March 1996, 486 patients were admittedto the intensive care unit; 295 had already undergone intubation,19 underwent tracheostomy, and 95 had chronic obstructive pulmonarydisease or were receiving immunosuppressive therapy. Of the77 patients who met the entry criteria, 13 chose not to participate;thus, 64 were enrolled. Thirty-two patients were assigned toeach group. The base-line characteristics of the two groupswere similar (Table 1), with the exception that in the conventional-ventilationgroup the mean arterial pH was significantly lower (P=0.002)and more patients had a partial pressure of arterial carbondioxide (PaCO2) greater than 45 mm Hg (12 vs. 5 patients, P=0.05).The treatments for the conditions precipitating respiratoryfailure and the ventilatory requirements were similar. The meanlevel of applied positive end-expiratory pressure was similar(5.1±1.4 cm of water in the noninvasive-ventilation groupand 5.3±1.2 cm of water in the conventional-ventilationgroup).
Table 1. Base-Line Characteristics of the Patients and Causes of Acute Respiratory Failure.
The patients in the two groups had a similar initial changein PaO2 :FiO2 (Figure 1). Within the first hour of mechanicalventilation, 20 patients (62 percent) in the noninvasive-ventilationgroup and 15 (47 percent) in the conventional-ventilation grouphad an improvement in PaO2 :FiO2 (P=0.21). The PaO2 :FiO2 improvedover time in the 22 patients in the noninvasive-ventilationgroup who did not need intubation (116±25 at base linevs. 250±60 at the end of treatment, P=0.02) and in the17 patients in the conventional-ventilation group who survived(126±25 at base line vs. 241±98 at the end oftreatment, P=0.03). The change in PaCO2 was similar in the twogroups. Ten patients in the noninvasive-ventilation group (31percent) required endotracheal intubation an average of 15±7hours after entry into the study, but none required emergencyintubation. The reasons for intubation were the failure of noninvasiveventilation to maintain the PaO2 above 65 mm Hg (four patients),its inability to correct dyspnea (one patient), its inabilityto manage copious secretions (one patient), intolerance of noninvasiveventilation (two patients), and hemodynamic instability (twopatients).
Figure 1. The Ratio of the Partial Pressure of Arterial Oxygen to the Fraction of Inspired Oxygen (PaO2:FiO2) at Base Line and after One Hour of Mechanical Ventilation in Patients with Acute Respiratory Failure in the Noninvasive-Ventilation and Conventional-Ventilation Groups.
A paired t-test was used for the statistical comparison. The degree of improvement in gas exchange after the start of mechanical ventilation was similar in the two groups. The values shown within the panels are means ±SD.
Overall, 42 patients, including 10 in the noninvasive-ventilationgroup, underwent intubation; 14 had orotracheal intubation,and 28 had nasotracheal intubation. The length of stay in theintensive care unit was shorter for patients in the noninvasive-ventilationgroup (9±7 days, vs. 16±17 days in the conventional-ventilationgroup; P=0.04). Nine patients in the noninvasive-ventilationgroup — all of whom required endotracheal intubation —and 15 in the conventional-ventilation group died in the intensivecare unit. Thus, the rate of survival to discharge from theintensive care unit was 53 percent (17 patients) in the conventional-ventilationgroup and 72 percent (23 patients) in the noninvasive-ventilationgroup (odds ratio, 0.4; 95 percent confidence interval, 0.1to 1.4; P=0.19). Two patients (one in each group) died in thehospital after discharge from intensive care. One, in the noninvasive-ventilationgroup, died of ventricular fibrillation. The other, in the conventional-ventilationgroup, died of cardiogenic shock due to a new myocardial infarction.The other patients were successfully discharged from the hospitalwithout further complications.
The complications and events leading to death are shown in Table 2.More patients in the conventional-ventilation group thanin the noninvasive-ventilation group had serious complications(66 percent vs. 38 percent, P=0.02) and had pneumonia or sinusitisrelated to the endotracheal tube (31 percent vs. 3 percent,P=0.003). The rate of serious complications was higher in patientsin the conventional-ventilation group. Among the patients inthe noninvasive-ventilation group, 12 (38 percent) had seriouscomplications after undergoing endotracheal intubation. Oneof the 12 patients in whom noninvasive ventilation failed hadpneumonia diagnosed six days after undergoing endotracheal intubation.
Table 2. Serious Complications and Complications Resulting in Death.
Further details of patient outcomes are shown in Table 3. Inthe noninvasive-ventilation group, there was a sustained improvementin gas exchange over time in 17 of the 22 patients who did notundergo intubation but in only 2 of the 10 patients who requiredintubation (P=0.003). Avoiding intubation was associated witha lower incidence of septic complications (P=0.006). Among the40 patients who survived to be discharged from the intensivecare unit, the patients in the noninvasive-ventilation grouphad a shorter duration of mechanical ventilation (3±3vs. 6±5 days, P=0.006) and a shorter stay in the intensivecare unit (6.6±5 vs. 14±13 days, P= 0.002) thanthose in the conventional-ventilation group.
Table 3. Characteristics of Patients According to the Success or Failure of Noninvasive Ventilation and Survival or Death in the Conventional-Ventilation Group.
Among the patients in the conventional-ventilation group, thosewho died had a higher simplified acute physiologic score (P=0.02).A post hoc subgroup analysis was performed for patients withsimplified acute physiologic scores lower than 16 and for thosewith scores of at least 16. The 19 patients with simplifiedacute physiologic scores of at least 16 had similar outcomesregardless of the type of ventilation, whereas in the 45 patientswith simplified acute physiologic scores lower than 16, noninvasiveventilation was superior to conventional ventilation (data notshown).
Discussion
We found that, with similar ventilator settings, noninvasiveventilation was as effective as conventional ventilation inimproving gas exchange in patients with acute hypoxemic respiratoryfailure. Furthermore, the rate of serious complications, inparticular those related to intubation (pneumonia and sinusitis),was significantly lower in patients receiving noninvasive ventilation.Successful noninvasive ventilation was associated with shorterstays in the intensive care unit. Ten patients in whom noninvasiveventilation failed (31 percent of the group) required intubationdespite an improvement in gas exchange; this finding agreeswith a prior report.9
Noninvasive ventilation can relieve hypoxemic respiratory failurein patients with pneumonia, cardiogenic pulmonary edema, orpostoperative complications.1 Twenty-nine studies enrolling748 patients described the successful application of noninvasiveventilation in patients with hypoxemic respiratory failure ofvarious causes.1 In one study, gas exchange improved when patientswith hypoxemia had their endotracheal tubes replaced by noninvasiveface masks with similar settings.25
In our study, the noninvasive-ventilation and conventional-ventilationgroups had received a similar number of invasive devices, notcounting the endotracheal tubes in the patients in the conventional-ventilationgroup. Endotracheal intubation is the single most importantpredisposing factor for ventilator-associated pneumonia.26 Weidentified pneumonia using bronchoscopic criteria in eight patientsin the conventional-ventilation group (25 percent). The presenceor absence of nosocomial pneumonia helps determine the outcomeof respiratory failure.26 Two patients in the conventional-ventilationgroup died of ventilator-associated pneumonia. The low rateof ventilator-associated pneumonia among patients in the noninvasive-ventilationgroup is in agreement with other findings.1,5
As in other studies,5,13 the outcome in patients with highersimplified acute physiologic scores was poor, irrespective oftheir randomization group. Among survivors, those in the noninvasive-ventilationgroup had a shorter duration of mechanical ventilation and ashorter stay in the intensive care unit. Factors that may havebeen involved in shortening the duration of mechanical ventilationinclude the avoidance of sedation, elimination of the extrawork of breathing imposed by the endotracheal tube, the lowerrate of ventilator-associated pneumonia, and earlier removalfrom ventilation. There were more patients with respiratoryacidosis in the conventional-ventilation group, and this mayhave affected the duration of mechanical ventilation and theoutcome in this group. However, in an earlier randomized studyof patients without chronic obstructive pulmonary disease, patientswith a PaCO2 greater than 45 mm Hg who were treated with noninvasiveventilation had shorter durations of stay in the intensive careunit and a lower mortality rate than those treated with conventionalventilation.13
In conclusion, we found that noninvasive ventilation was aseffective as conventional ventilation in improving gas exchangein patients with acute hypoxemic respiratory failure, and thatwhen endotracheal intubation was avoided, the development ofventilator-associated pneumonia was unlikely.
Source Information
From the Institute of Anesthesiology and Intensive Care, Università La Sapienza, Policlinico Umberto I, Rome (M.A., G.C., M.R., M.B., R.A.D.B., G.V., A.G.); and the University of Tennessee, Memphis, Lung Research Program, Department of Medicine, Pulmonary and Critical Care Division, Memphis (G.U.M.).
Address reprint requests to Dr. Antonelli at the Istituto di Anestesiologia e Rianimazione, Università La Sapienza, Policlinico Umberto I, Viale del Policlinico 155, 00161 Rome, Italy.
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