Physiologic Evaluation of Pressure Support Ventilation by Nasal Mask in Patients with Stable COPD

Physiologic Evaluati~n of Pressure Support Ventilation .by Nasal Mask in Patients with Stable COPO* N. Ambrosino , M.D .; S. Naoa, M.D. ; P. Bertone, P.T.; C. Eracchia, M.D .; and C. Rampulla, M.D.

We evaluated the physiologic effects of pressure support ventilation by nasal route (NPSV) in eight patients with severe stable COPD and chronic hypercapnia who were randomly submitted to 2-h sessions of NPSV both with a portable ventilator (Respironics BIPAP device) and with a standard ventilator (Bird 6400ST device) at an inspiratory airway pressure of 22 cm Two sessions with each ventilator were performed using an FI<>s of 0.21 in each patient on two consecutive days. One patient did not tolerate either form of ventilation. Comparison of spontaneous with BIPAP ventilation showed a significant improvement in pH, PaCO., and PaO •• Ventilatory pattern assessed by a respiratory inductive plethysmograph showed a significant increase in minute ventilation (VE), VT, and Ttot. Integrated surface diaphragmatic EMG activity measured only during BIPAP device ventilation decreased from that measured during spontaneous breathing. Similar changes in blood gases and ventilatory pattern were observed during venti-

lation by the Bird 6400ST except for VTffi ratio, which significantly increased. Comparison of baseline with measurements performed 12 h after the whole cycle of treatment showed a significant increase in pH and VE and a decrease in PaCO.. We conclude that short-term NPSV may be usefUl in improving respiratory pattern and blood gases in stable COPD patientS with chronic hyperCapnia. (Chest 1992; 101:385-91)

Intermittent positive pressure ventilation applied through a nasal mask (NPPV) has been showiJ. to be useful in the treatment of chronic respiratory failure resulting from neuromuscular, chest wall, and chronic obstructive pulmonary diseases. It is usually delivered by standard volume-cycled ventilators in assisted or controlled mode. I~ Pressure support ventilation (PSV) is an assisted mode of ventilation that supplies a constant set level of positive airway pressure during spontaneous inspiratory efforts. PSV allows the patient to maintain Control of inspiratory time (1i) and expiratory time (Te)and to interact with set pressure to determine the ultimate flow and tidal volume (VT).7.8 PSV has been used during weaning from mechanical ventilationv'" and in the immediate period after cardiac surgery, 11 and it is being more and more frequently applied in acute respiratory failure, also by facial mask I2• 1• To our knowledge, no report has been given on the use of nasal PSV (NPSV) in stable COPD patients with chronic hypercapnic respiratory failure. The aim of

this study was to evaluate the acute physiologic effects of NPSV delivered by a portable device specifically conceived for NPPV in stable COPD patients with chronic hypercapnia.

u.0.

*From the Fondazione Clinica del Lavoro IRCCS and the Centro Medico di Riabilitazione di Montescano, Pavia, Italy. Manuscript received January 14; revision accepted June 4. Reprint requests:Dr. Ambrosino,Centro MediCo, 27040Montescano

(lbt>la), Italy

ABD = abdomen; APRV= airway pressure-release ventilation; CPAP=cOntinuous positive airway pressure; Edi=integrated electromyogram .of the diaphragm; INPV = intermittent negative-pressure ventilation; IPPB = intermittent positive-pressure breething; NPPV = intermittent positive-pressure ventilation applied through a nasal mask; NPSV= misal pressure support ventilation· PIP = peak inBatioo pressure; PSV=pressure support ven~ I\C=rib cage; RIP = respiratory inductive plethysmography; Te=expiratory time; Ti=inspiratory titne; Ttot = total respiratory time; VE= minute ventilation; VT= tidal volume

METHODS

Subjects Studies were carried out on eight male patients (mean age; 64.6±11.6 [SO) years; weight , 64.0±8.5 kg; height , 162±9 em), all of whom were smokers or exsmokers with chronic hypercapnia. The physiologic characteristics of the studied population are shown in 'DIble 1. Patient 5 also suffered from a fibrothorax. During the study, the patients were in a stable condition, without exacerbations of respiratory symptoms or any relevant acute disease . All of the patients received long-term oxygen therapy, oral long-acting aminophylline , and inhaled bronchodilators. No change in medical and oxygen therapy had been made the week preceding the study. No patient had ever been submitted to any form of mechanical ventilation before the study. All of the patients gave their informed consent to participate in the study. Dynamic lung volumes were evaluated by means of a water spirometer (Biomedin, Padua, Italy) with the patient in the seated posture, and static lung volumes were assessed by means of helium dilution method . The predicted values were according to Quanier.IS An automated analyzer (Radiometer ABL 30, Copenhagen) was used to measure blood gases in arterialized blood from the ear lobe. Airflow was measured by a pneumotachograph (Screen mate , Jaeger, Hachburg, Germany) connected between the inlet tube and CHEST I 101 12 I FEBRUARY, 1992

385

Table I-Pull7WflQry Function Values· Patient

VC, %prd

FEV" L

FEV" %prd

FEV,IFVC , %

RV, %prd

PaD" mm H~

PaCO" mm H~

pH

1 2 3 4 5 6

38 29 45 21 30 36 35 15 31 10

0.63 0.45 0 .95 0 .39 0 .82 0 .63 0.47 0 .33 0.58 0 .21

20 15 40 14 26 22 23 II 21

38 34 63 45 60 43

276 119 168 124

66 54

45

I>

10

162 319 164 90

45 55 47 56 60 49 48 42 50 6

7.34 7.34 7.38 7.32 7.35 7.37 7.35 7.41 7.36 0.03

t

I> Mean SO

38 46

*%prd = percentage of predicted value . the nose mask . Ventilatory pattern and separate contribution of rib cage (RC) and abdomen (ABO), VT, and respiratory frequency were obtained by respiratory inductive plethysmography (RIP) (Ambulatory Monitoring Inc, Ardsley, NY) in the DC mode . The two recording bands were placed on the middle RC about 10 em above the xiphoid process of the sternum and on the ABO just above the umbilical line, respectively. The calibration was performed with the isovolume maneuver and the patient in a sitting posture .!" Integrated electromyogram (EMG) of the diaphragm (Edi) was recorded via bipolar surface electrodes placed on the sixth and seventh intercostal spaces, close to the anterior costal border. The EMG signals were filtered (0.2 to 1.6 kHz), full-wave rectified, and integrated by means of a leaky integrator with a time constant of 0 .03 s." The pressures developed by the ventilators at the mask were measured by a 7o-cm-long catheter connected to a pressure transducer (:!: 300 ern 11,0) (Honeywell, Freeport, III). RC and ABO displacement , VT, Edi, airflow, and the pressure developed at the mask by the ventilator were recorded on a six-channel strip chart recorder (Battaglia Hangoni , Casaleechio di Reno , Italy). Stuefy Protocol

After baseline measurements, performed during I h of spontaneous breathing with the mask on, each patient underwent two sessions of NPSV with a portable ventilator (BIPAP, Respironics, Monroeville, Pal while in a sitting posture. The BIPAP device is a nasal continuous positive airway pressure (CPAP) blower modified with a solenoid system that allows delivery of positive airway pressure at two different levels in both "spontaneous" (assisted) and " timed" (controlled) mode, which has been extensively described

46

lOS

53

71 63 57 63 57 61 6

elsewhere" and is depicted in Figure 1. In the timed mode, the principles ofBIPAP ventilation are similar to those seen with airway pressure-release ventilation (APRV)." .,. In the spontaneous mode, inspiratory positive peak inflation pressure (PIP), up to a maximum of 22 cm H,O, and expiratory positive airway pressure can be set by a care-giver, but it is the patient who triggers inspiration and expiration in a manner similar to that used in PSv.· ·I • Once pneumotachograph , RIP bands, and EMG electrodes had been positioned and baseline measurements performed, NPSV was applied through a comfortable, tightly fitted nasal mask (Respironics Inc). The BIPAP device was set in the spontaneous mode with the maximal PIP value tolerated by the patients that was able to induce a VT ranging from 10 to 15 rnl/kg, Expiratory positive airway pressure was set to zero on the ventilator, which , due to the fact that the flow of the machine is continuous, means a negligible positive pressure at the mask (I cm H,O) . Ventilatory sessions were performed using an Flo, of 0.21. To validate the effectiveness of BIPAP as a device able to effectively deliver NPSV, changes in blood gases and in respiratory pattern were assessed in the same patients also randomly undergoing two sessions of NPSV by means of a standard ventilator (Bird 6400 S1') set in PSV mode at the same PIP as with BIPAP device. Efforts were made to reduce unnecessary noise and distractions and to encourage maximal relaxation. Instructions were given to keep the mouth closed. Each session lasted about 2 h over two consecutive days .

Data Analysis Edi was measured as millimeters of deflection from baseline and then expressed as a percentage of control deflections. Edi and respiratory pattern were analyzed on a breath-by-breath basis for 15 consecutive breaths during spontaneous breathing and during

FIGlJRE 1. BIPAP device used to deliver NPSV.

386

Pressure Support Ventilation by Nasal Mask (Ambrosino et 81)

Table 2-Changes in Ventilatory Pattern during BIPAP Device and Bird 6400ST Ventilation BaselineBIPAP Device 8.2 (1.8) VE. Umin Vr v ml 408 (119) Respiratory freque ncy. bpm 21 (4) Ttot , s 3.0 (0.6) Ll (0.6) 11. s 37 (2) TJII'tot. % VTITI. ml/s 363 . (83) Bird6400ST VE. Umin 9.2 (1.5) vrml 443 (61) Respirat ory frequency. bpm 21 (4) Ttot , s 2.9 (0.5) Ll (0.2) 11. sec TJII'tot. % 38 (3) VTITI. ml/s 400 (62)

p Value

Ventilation" , '

<0.05 <0.05 <0.05 <0.05 <0.05 NS NS

ILl (2.6) 790 (98) (2) 14 4.5 (0.8) 1.9 (0.4) (6) 43 436 (148)

<0.05 <0.05 <0.05 <0.05 <0.05 NS <0.05

11.9 779 15 3.9 1.7 40 494

(2.0) (157) (2) (0.4) (0.2) (6) (52)

-Values are expressed as mean (SO); bpm = breaths per minute.

800

BIPAP

.~to:i...

600 E

~

~400

200

t··

800

..

600

E

3

2

4

RESULTS

One subject (No.8) was unable to tolerate both ventilators. He suffered from a more severe degree of

5

T1_ •• c.

.t:i

BIRD6400 ST

-.

c...... ..............

~400

NPSVat the 3rd . 10th , and 20th minutes. Respiratory pattern was analyzed by the RIP tracings, measuring VT. 11. total respiratory time (Ttot), respiratory frequency. the Tv Ttot ratio. and mean inspiratory Bow (VTITI) for the same breaths in which EMG signals were analyzed . Minute ventilation (VE) was measured as the product VTx mean lIftot of those breaths. Baseline and ventilation measurements were expre ssed as the mean of values from two sessions with each ventilator. which were found to be highly reproducible. Significance of the differences between control and NPSV values was analyzed by Wilcoxon signed-rank test . A two-tailed p value <0.05 was considered to be statistically significant. All results are reported as mean (SO).

.........,

200 O.f:---+----+--~_+_-----_+_--__l

o

2

5

FIGURE 2. Changes in ventilatory pattern (mean [SO)) obse rved during NPSV delivered by BIPAP device (upper panel) and Bird 6400ST (lower panel). Solid line and open bars represent baseline data. Dashed line and solid bars represent data obtained during ventilation .

hyperin8ation than the other patients (Table 1). This subject was not included for further analysis. The other seven patients tolerated NPSV with both ventilators without discomfort or complications and all

Table 3-Changes in Blood Gases During BIPAP Device and Bird 6400ST Ventilation Patient No. 1

2

3

4

5

6

7

Mean

SO

7.38 7.40

7.35 7.41

7.36 7.40

0.02 0.03

p Value

BIPAP Device pH Baseline Ventilation PaO•• mm Hg Baseline Ventilation PaCO•• mm Hg Baseline Ventilation pH Baseline Yentilation PaO•• mm Hg Baseline Ventilation PaCO•• mm Hg Baseline Ventilation

<0.05 7.35 7.38

7.35 7.38

7.38 7.45

7.35 7.35

7.34 7.43

<0.05

46 52

53 60

66 58

52 50

47 53

57

58 60

64

51 55

50 55

52 57

5 4

55

63 50

59 52

6 6

<0.05 53

45

60 61

66 49 Bird6400ST

54

<0.05 7.32 7.36

7.34 7.38

7.39 7.40

7.37 7.48

7.36 7.49

7.38 7.44

7.35 7.43

7.36 7.43

0.02 0.05 <0.05

41 50

52 56

45 50

69 55

56 52

50 50

50 57

51

62

57 68

61 45

63 43

56 49

54

53

50 57

5 7

64 49

60 49

6 4

<0.05

CHEST I 101 12 I FEBRUARY, 1992

387

IUIUII ,

..

..• . ··i· • .. .

.

;~~~ :

IIr ....

.;....

.

J-V

I',.., ........

.. ... .•._

... .•.•... --0;'-._ ••-

.

",

-

. ~.$lfl.Jl

._;..

I"

-

. I ·

.::.:;:~:;=~~.:J.:::~.:.~:.

t_

,

tolerated a PIP of 22 em H 20. The actual pressure delivered measured at the mask ranged from 17 to 20 cm H 20 without any differences between the two ventilators. Changes in ventilatory pattern and blood gases observed during BIPAP device and Bird ventilation are shown in Tables 2 and 3, respectively. Comparison of baseline with BIPAP device ventilation showed a significant improvement in blood gases and pH and a significant increase in VE resulting from an increase in VTdespite a decrease in respiratory frequency. Ventilation by Bird 6400 ST showed similar changes except for VTlfi ratio , which significantly increased.

::J 140 oa:

!z oo

120

~ 100 ~ ~

80 60 40 20 O+------l----~------f--

eTR

3"

10"

20"

FIGURE 4. The effect of NPSV by BIPAP device on the mean amplitudes of diaphragmatic surface EMG is shown for six individual patients. Measurements performed during spontaneous breathing (erR) and at the 3rd . 10th. and 20th min of NPSV are shown.

388

_ ._ _ ._ .._. _ ., .

FIGURE 3. Polygraphic recordings during spontaneous breathing (baseline) and NPSV by BIPAP device in a representative patient. Top to bottom: Airflow (inspiration downward). airway pressure• integrated surface diaphragmatic electromyography (Edi), and VT from sum signal of RIP (inspiration upward).

Figure 2 shows the pattern of ventilation obtained by both ventilators. EMG changes were assessed in only six patients receiving BIPAP device ventilation. In almost all of the patients, the application of BIPAP device ventilation induced a very irregular response in the phasic EMGs in the first few minutes. In this period, four patients did indeed noticeably increase the EMG amplitude in comparison to spontaneous breathing up to 40 percent. After about 5 min, however, almost all the patients showed a substantial reduction from baseline in the EMG, as observed in a representative patient in Figure 3 and for all patients assessed in Figure 4, which depicts the mean change in Edi observed in patients during BIPAP device ventilation. It should be noted that in one subject, NPSV did not induce any significant change even after several minutes of ventilation. One patient (No. 7) showed an abdominal paradox as evidenced by a negative RCIABD ratio in the baseline measurement performed before a BIPAP device ventilation session. This paradox disappeared during ventilation. On the whole no change in RCI ABD ratio was observed during ventilation with both ventilators. Twelve hours after the whole trial (that is, four 2-h sessions ofNPSV by both ventilators), patients showed a significant increase in pH (7.35±0.03 [SD] to 7.37±0.02) and in VE (7.2± 1.9 to 9.7± 1.6 Umin, p
The results of this study show that NPSV may be of clinical utility in COPD patients with chronic hypercapnia. PIessurB SUpport Ventilationby Nasal Mask (Ambrosino sf 81)

Noninvasive ventilatory support for patients with chronic respiratory failure has been widely used in patients with neuromuscular or chest wall disease'" or with COPD.oo,21 Intermittent negative-pressure ventilation (INPV) with body ventilators has given conflicting results in COPD patients, the sustained improvements in ventilatory function observed by some authors being generally attributed to resting fatigued inspiratory muscles.22-24 NPPV delivered in assisted or controlled mode may be an alternative noninvasive method providing intermittent ventilation with ease of application and good patient acceptance. Long-term use of NPPV has resulted in an improvement in clinical status and parameters of ventilatory function between treatments.1,3-6 PSV is an assisted mode of ventilation supplying a set level of positive airway pressure during spontaneous inspiratory efforts. PSV can either totally or partially unload ventilatory muscles during spontaneous breathing.8 , l1 ,25 Total unloading occurs when the only effort made by the patient is to trigger the breath. Muscle contractions beyond this point are accompanied by enough PIP and machine flow such that no appreciable muscle tension generation or mechanical work is performed. Total unloading is reflected by virtually no ventilatory muscle oxygen consumption." Clinically total unloading is reported to be related to levels of inspiratory pressure assist that result in VTof 10 to 12 ml/kg" in relaxed patients. In our study, integrated Edi was reduced during BIPAP device ventilation in comparison to control, giving objective information on the degree of inspiratory muscle rest. Carrey et al26 used NPPV in control mode in patients with chronic ventilatory failure due to restrictive or obstructive respiratory disorders. In this study NPPV resulted in marked reductions of phasic Edi amplitude. Belman et al27 observed that NPPV in control mode was more effective than INPV in reducing diaphragmatic activity in patients with COPD. Other investigators' have allowed the NPPV rate to be determined by patient triggering (assist/control mode) with a set backup rate. Studies with conventional positive-pressure ventilation in intubated patients28 ,29 have shown that once the inspiratory muscles have begun to contract, they continue to perform work even after the ventilator has been triggered. It is noteworthy to underline the differences between PSV and intermittent positive-pressure breathing (IPPB).30 PSv, but not IPPB, is able to reduce the effort of breathing.31 During IPPB, inspiration stops when a preset airway pressure is reached that may induce a deleterious active expiratory efforfl2; during PSv, however, the assistance is cycled according to the inspiratory flow and stops before the flow drops to zero, no expiratory effort being required from the

patient. Brochard et al'" studied the ability of PSV to promote a nonfatiguing respiratory muscle activity in eight patients unsuccessful at weaning from mechanical ventilation and with EMG signs of incipient diaphragmatic fatigue. During ventilation at increasing levels ofPS the work of breathing gradually decreased together with the oxygen consumption of the respiratory muscles. Furthermore, electrical signs suggesting diaphragmatic fatigue were no longer present. In addition, intrinsic positive end-expiratory pressure was progressively reduced. For each patient the optimal level of PS was found to be as much as 20 em H 20 . In another study, Brochard et al14 evaluated the physiologic effects and therapeutic efficacy of a noninvasive ventilatory-assistance apparatus in providing PSV by means of a face mask in patients with acute exacerbations of COPD. They found that inspiratory positive airway pressure by face mask can obviate conventional mechanical ventilation. To our knowledge, our study is the first one performed in stable COPD patients with chronic hypercapnia and confirms the ability ofPSV,even if delivered by nasal route, to reduce electrical activity of inspiratory muscles. The reduction in Edi, however, did vary among patients and may have depended on the ability to relax completely. In similar patients, Carrey et al26 found a greater degree of decrease in the Edi by nasal IPPV only when the patients were breathing with their mouths closed . However, this may not have been the case for all our patients, as they were not controlled as to whether their mouths were constantly closed . We did not measure respiratory work, but previous studies have demonstrated that diaphragmatic electrical activity is proportional to diaphragmatic oxygen consumptionr" therefore, the observation of a reduction in phasic activity of the diaphragm should reflect a decrease in energy expenditure, inasmuch as NPSV assumed at least part of the work of breathing. The use of surface electrodes to record diaphragmatic electrical activity may limit the study, even if in a previous study we found a good agreement between recordings performed by surface and esophageal eleetrodes.'? This study shows that NPSV is able to induce an increase in VE through an increase in VT and a reduction in respiratory frequency. An increase in VE by an increase in VT and a reduction in respiratory frequency is associated with an increase in alveolar ventilation and indeed is reflected by the decrease in PaC02 observed during ventilation. This confirms the results of clinical studies demonstrating that as the level of the inspiratory pressure assist is increased, the consequent VT increases and respiratory frequency decreases.8 ,9 ,34 ,35 For both types of ventilators, CHEST I 101 121 FEBRUARY, 1992

389

we used the maximal PIP tolerated by the patients that was able to induce a VT ranging from 10 to 15 ml/ kg. However, we did not measure the mechanical properties ofRC and lung of the patients. The maximal PIP tolerated and applied was found to be 22 cm H 20, which was the maximal available by BIPAP ventilator. The actual pressure measured at the mouth ranged from 15 to 17 cm H 20, indicating that the leaks were small with both ventilators. Recently, MacIntyre and Leatherman.P" using a computer respiratory system model with varying ventilation demands and impedance characteristics, estimated that the level of PIP able to induce a reduction of work of breathing to zero (PSmax) ranged from 5 to 41 cm H 2O. They supported the concept that high levels of PSV virtually totally unload ventilatory muscles; they suggested that under nonfatiguing conditions, the muscle load and ventilatory pattern response to levels of PSV has two distinct phases: a partially loaded phase at lower PIP and an unloaded phase at higher PIP levels. They conclude that clinical application of PIP levels greater than PSmax are unnecessary. The physiologic effects of the two ventilators were found to be similar, confirming that the BIPAP device may deliver effective NPSV. Nevertheless, an interesting result of this study comparing the two types of ventilators was that Vr/Ti ratio significantly increased only during ventilation by Bird 6400 ST. The reason for this difference is not clear. It might be related to differences in the mode of cycling of the devices: (1) Inspiration by Bird 6400ST ventilator is triggered by an airway pressure sensor (that is, the inspiratory effort is sensed as a drop in circuit airway pressure). Inspiration by BIPAP ventilation is triggered when inspiratory flow reaches a value of 40 ml/s for a minimum of 30 ms; this is a flow trigger. (2) With the Bird 6400ST, support termination signal is 25 percent of inspiratory peak flow. With the BIPAP device, support termination is determined by the meeting of an inspiratory flow signal with a signal increasing at a rate proportional to the increasing patient's flow rate. In this way the expiratory trigger threshold adapts to the size of the breath under normal conditions when there is a steady leak . If there has been a sudden increase in the leak, the expiratory offset signal will rise more quickly to prevent inspiratory hang-up. (3) These two ventilators are different as far as the devices delivering ventilation are concerned: with the BIPAP device the patient breathes on a continuous flow through a single tube, while ventilation by Bird 6400-ST is performed on an intermittent flow through a double tube. The level and pattern of VE delivered by BIPAP device was effective in inducing a significant improvement in blood gases. Interestingly, but still to be 390

confirmed, was the observation that 12 h after the end of the trial, patients showed an improvement in basal VE, pH, and PaC02 • No significant relationship was found between the degree of improvement in basal ventilation and the degree of inspiratory muscle rest induced by PSv. Our study shows that by cyclically delivering a level of PIP in the range of PSmax as suggested by MacIntyre and Leatherman." the BIPAP device, used in the spontaneous mode, functions as an effective PSV ventilator and thus appears to be ideal for application in patients requiring only intermittent ventilatory assistance via a nose mask. A limit to this device may be that the maximal PIP delivered is 22 em H 20 (that is, 17 to 18 cm H 20 at the mask), which may not be adequate for some patients. Our trial carried out on eight stable COPD patients demonstrated that the BIPAP device was well tolerated and functioned as effectively as the Bird 64OOST, a standard ventilator with the ability to deliver PSv. ACKNOWLEDGMENTS: The authors wish to thank Antonio Braschi, M.D., for useful talks and Miss Jacqueline McKay for kindly reviewing the English of the manuscript.

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n,

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