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(Chest. 2003;124:857-862.)
© 2003 American College of Chest Physicians

Kyphoscoliotic Ventilatory Insufficiency*

Effects of Long-term Intermittent Positive-Pressure Ventilation

Cruz Gonzalez, MD; Gloria Ferris, MD, PhD; Juan Diaz, RN; Inmaculada Fontana, RN; Julio Nuñez, MD and Julio Marín, MD, PhD, FCCP

* From the Departments of Pneumology (Drs. Gonzalez, Ferris, and Marin, Mr. Diaz, and Ms. Fontana) and Cardiology (Dr. Nuñez), Hospital Clínico Universitario, Universidad de Valencia, Valencia, Spain.

Correspondence to: Julio Marín, MD, PhD, FCCP, Departamento de Medicina, Facultad de Medicina, Avda Blasco Ibáñez 15, E-46010 Valencia, Spain; e-mail: marinj{at}uv.es


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Objectives: To determine the effects of long-term nocturnal intermittent positive-pressure ventilation (NIPPV) on symptoms, pulmonary function test results, sleep, and respiratory muscle performance in patients with ventilatory insufficiency due to severe kyphoscoliosis.

Design: A prospective study in which 16 severe kyphoscoliotic patients were treated with NIPPV delivered by volume-cycled and pressure-cycled ventilators, over a period of 36 months.

Interventions and measurements: At baseline, pulmonary function tests, blood gas measurements, polysomnography, and respiratory muscle strength (measured by noninvasive indexes) were obtained. Symptoms and the number of hospitalizations in the previous 6 months also were recorded. Patients then began using a ventilator for > 1 to 2 days, in order to select the type of ventilator and the appropriate interface. Patients returned for evaluation (in outpatient setting) every 6 months for a follow-up period of 3 years. At 6 months, polysomnography was repeated, and by the third year clinical and functional parameters had been reassessed.

Results: All symptoms improved significantly with NIPPV therapy, when compared with the baseline values. The mean (± SD) PaO2 and FVC values increased at 36 months compared with baseline values (62.6 ± 7.1 vs 67.8 ± 8.8 mm Hg, respectively; and 37.9 ± 7.2% vs 47.5 ± 11.9%, respectively; p < 0.05 for both). There were significant improvements in mean maximal inspiratory pressure (55.8 ± 17.4 to 78.5 ± 17.5 cm H2O), maximal expiratory pressure (53.8 ± 17.7 to 72.3 ± 11.0 cm H2O), mouth pressure (0.28 ± 0.08 to 0.22 ± 0.02 cmH2O), and pressure-time index (0.18 ± 0.05 to 0.11 ± 0.02; p < 0.05 for all comparisons). There were no significant differences in breathing pattern and ventilatory drive. After 6 months, nocturnal oxyhemoglobin saturation improved, however, there was no significant change in sleep architecture. All patients subjectively perceived a better quality of life after beginning ventilation, which persisted over the course of the study.

Conclusions: Long-term NIPPV therapy improves daytime blood gas levels, respiratory muscle performance, and hypoventilation-based symptoms in patients with severe kyphoscoliosis.

Key Words: kyphoscoliosis • mechanical ventilation • noninvasive indexes • respiratory muscle strength


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Changes in the mechanical properties of the rib cage and the respiratory system lead to loss of functional capacity in patients with scoliosis.1 Studies performed in adult patients showed an important reduction in pulmonary compliance2 and the existence of inspiratory muscle weakness, mainly in the diaphragm,1 the most probable cause of which is deformity of the rib cage, with changes in the length and orientation of the respiratory muscles.

The magnitude of the restrictive disorder seems to be related to the severity of the deformity.3 Accordingly, some authors1 have shown that spinal curvature < 50° to 70° are still associated with normal lung volumes, however, some other studies4 have shown significant pulmonary volume abnormalities with spinal curvatures of 30° to 40°. Smyth et al5 have suggested that at the onset of the disease, with spinal curvatures of <= 30°, the reduced vital capacity that may be found in patients with mild scoliosis is not determined by the degree of curvature. Thus, they concluded that a more important determinant appeared to be related to respiratory muscle strength.5

Nocturnal intermittent positive-pressure ventilation (NIPPV) has been shown6 7 8 to improve arterial blood gas levels in the treatment of chronic and acute ventilatory insufficiency. Some of the mechanisms by which NIPPV treatment has a positive impact on symptoms and gas exchange in patients with restrictive thoracic disorders include improved pulmonary mechanics and respiratory muscle rest.9 These mechanisms are interrelated, but together they have not been the object of a long-term study. Therefore, this prospective study was designed to evaluate the effects of long-term NIPPV therapy on respiratory muscle strength, pulmonary function, symptoms, and sleep patterns over 3 years of treatment in patients with severe kyphoscoliosis who have chronic hypoventilation.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Patients
The study group consisted of 16 patients affected by kyphoscoliosis without any concurrent pulmonary parenchymal disease. The causes of kyphoscoliosis in these patients were as follows: Pott disease, six patients; idiopathic kyphoscoliosis, seven patients; trauma of the spine, two patients; and postpoliomyelitis, one patient.

All patients included in the protocol were initially assessed in an outpatient setting for eligibility. After informed consent had been obtained and inclusion/exclusion criteria were applied, clinical parameters and gasometry were measured. In order to be included in the study, the patients had to be in stable condition and to fulfill at least one of the following criteria to begin NIPPV therapy: PaCO2, >= 45 mm Hg; arterial oxygen saturation (SaO2), <= 88% for 5 consecutive minutes, nocturnal oximetry; maximal inspiratory pressure (Pimax), < 60 cm H2O; or FVC, < 50% of predicted. Exclusion criteria included bronchial hyperreactivity, symptomatic cardiovascular disease, current history of smoking, and refusal to use nasal ventilation. As a baseline evaluation, chest radiography, ECG, hemogram, and biochemical blood tests were performed, as well as exploratory pulmonary function tests, including flow-volume curve, static lung volumes, breathing patterns, and respiratory pressures followed by nocturnal polysomnography. Hospitalization days due to respiratory difficulties in the previous 6 months also were recorded. After the baseline evaluation, the patients then were referred to the respiratory care unit where the adaptation to NIPPV was performed. The study procedures were approved by the ethical research committee of our hospital.

Measurements
During the initial evaluation, the NIPPV protocol was explained to the patient, and symptoms of dyspnea, morning headache, diurnal drowsiness, and perceived sleep quality were quantified using a visual analog scale (VAS) of 0 to 100. Respiratory muscle strength was assessed by measuring the PImax, the maximal expiratory pressure (PEmax), and the pressure-time index (PTI) using an electromanometer (Siebelmed 163; Siebel; Barcelona, Spain) connected to a recorder (x-y Servogor 731; Goertz Metrawatt; Nuremberg, Germany). Values of PImax and PEmax were obtained at close to residual volume and total lung capacity levels, respectively, the maximal peak value of three reproducible trials was recorded (intratest reliability, < 10%), and the results were compared with the predicted values reported by Black and Hyatt.10 PTI was derived from the following equation:

where TI is inspiratory time, TTOT is total breathing cycle time, and Pawo represents the mean airway pressure measured at the mouth, and was obtained from the pressure signal curve registered during spontaneous and regular breathing. The pressure signal was recorded over a period of approximately 15 min, at a paper speed of 6 cm/min. The mean airway pressure then was calculated by adding the pressure values of sequential millisecond intervals and was expressed as the mean value of all breaths taken over the whole interval. TI and TTOT were measured on the pneumotachograph, separating the inspiratory from the expiratory line by a return of the volume signal to resting levels at point zero airflow. The TI/TTOT ratio was calculated as the average of 20 to 30 cycles at a rate of 30 cm/min and was expressed as a percentage.

Ventilatory drive was evaluated by measuring the inspiratory occlusion pressure for the first 100 ms of inspiration (P0.1) with the patient sitting at rest and breathing room air, in a module (Masterlab; E. Jaeger; Friedberg, Germany). The valve was closed for the 0.1 s immediately before a spontaneous inspiratory effort. The pressure data were collected and were expressed as the average of six separate measurements. The indexes derived from the measured data included the following: effective inspiratory impedance (ie, P0.1/tidal volume [VT]/TI)11 ; active elasticity (ie, P0.1/VT)12 ; and P0.1/PImax.13

FVC, FEV1, and flow-volume curves were obtained using a calibrated pneumotachograph (Micro S-2000; C. Schatzman; Madrid, Spain). A minimum of three measurements was obtained, and the highest values of FVC and FEV1 were used in the final calculation.

Arterial blood gas levels were measured at rest while the patient was breathing room air (Radiometer ABL 500; Radiometer; Copenhagen, Denmark). Blood samples were analyzed for PaCO2, PaO2, bicarbonate level, and pH.

Eight-channel polysomnography was performed (Sleep IT; CNS; Chanhassen, MN). The channels included electroencephalography, electrooculogram, electromyogram, wrist activity, tracheal noise, thoracic and abdominal movement belts, and SaO2 (Oxipulse Oximeter; Radiometer). The sleep stages were analyzed following the standard criteria.14 Apneas and hypopneas of > 10 s duration were recorded. Oxyhemoglobin desaturations were defined by SaO2 decreases of at least 4% from the baseline value, and lasting at least 8 s. Baseline SaO2 values, together with the lowest SaO2 reading and the amount of time during which the SaO2 was < 90%, were recorded. The apnea/hypopnea index (ie, the total number of apneas plus hypopneas divided by the total sleep time, in hours) and sleep efficiency (ie, total sleep time divided by total bed time) also were calculated.

Protocol
The patients were gradually accustomed to using the NIPPV under the close supervision of medical and nursing staff (2 to 3 h in morning sessions). After 1 to 2 days, the ventilator type and the interface were selected. The mask that was best suited to the patient’s anatomic characteristics and the ventilator that provided the greatest comfort were selected. Using the monitoring the levels of SaO2 and transcutaneous CO2 as references, the requirements of the patients and the responses to the parameters established (ie, VT, breath frequency [BF], and inspiratory/expiratory ratio) were interpreted and the modifications were made to the volumetric ventilators. In the case of pressure-cycled ventilators, tolerance of pressure increases was assessed while checking for leaks. Portable volume-cycled ventilators were used in seven patients (Monnal-D [Electrocare Systems & Services Pvt, Ltd; Mylapore, India], seven patients; Taema [Paris, France], five patients; Airox-Home [Bio-Ms; Pau, France], two patients). On the other hand, a pressure-cycled ventilator was used on the other nine patients (DP90 [Taema], seven patients; O'NYX [Pierre Medicale; Verrieres, France], two patients). A nasal interface (Sullivan; ResCare; San Diego, CA) was used by 12 patients, and the oronasal interface (Hans-Rudolph; Kansas City, MO) was used by 4 patients. The assist-control mode was used for volume-cycled ventilation (PV501; Breas Medical AB; Mölndal, Sweden), and the time-cycled mode, with a backup rate of 15 cycles per minute, was used for pressure-cycled ventilation.

After the training period ended, the patients were admitted to a ventilator unit for 2 to 3 nights for introduction to and monitoring of nocturnal ventilator use. The inspiratory positive airway pressure and the delivered volumes for the volume-cycled ventilator users were set to maximize patient comfort, to maintain nocturnal SaO2 at > 90% for at least 90% of the night, to keep the transcutaneous PaCO2 at < 45 mm Hg, to normalize the daytime PaCO2, and to alleviate symptoms.

Initially, the values recommended for ventilation were as follows: (1) for volume-cycled ventilators: VT, 10 to 15 mL/kg; BF, 15 to 25 cycles per minute; inspiratory/expiratory rate range, 1/1 to 1/2; maximum pressure, 50 cm H2O; (2) for pressure-cycled ventilators: expiratory pressure, 4 cm H2O (less if expiratory valve); inspiratory pressure; 15 to 22 cm H2O; BF, 15 to 25 cm H2O.

The efficacy of the treatment was evaluated by blood gas values, with the aim of achieving a pH between 7.35 and 7.50, a PaCO2 level < 45 mm Hg, and a PaO2 level > 60 mm Hg. If an SaO2 of > 90% was not obtained with the parameters previously obtained, the fraction of inspired oxygen (FIO2) was increased by means of supplemental oxygen.

Finally, the settings for the volume-cycled ventilator were as follows: mean (± SD) rate, 16 ± 1 cycles per minute; minute ventilation, 13 ± 2 L/min; and delivered volume, 14.5 ± 3 mL/kg. The settings for the pressure-cycled ventilators were as follows: inspiratory positive airway pressure, 15.3 ± 2.8 cm H2O and 15 cycles per minute. The settings for the volume-pressure cycled ventilators were as follows: VT, 0.6 ± 0.1 mL/kg; mean (± SD) BF, 16 ± 1 cycles per minute. Initially, six patients received nocturnal supplemental O2 at a rate of 1 L/min to maintain a nocturnal SaO2 of > 90%.

Once the initial evaluation was finished, the patients were scheduled to return for outpatient examination every 6 months for a total follow-up of 3 years. Six months after beginning NIPPV therapy, polysomnography was reassessed and after 3 years, symptoms, number of hospitalizations, pulmonary function test results, breathing patterns, and physical status again were assessed. In the meantime, all the study subjects had access to the medical staff by telephone.

Statistical Analysis
The data are summarized as the mean ± SD for continuous variables or the percentage for categoric variables. Because of the pretreatment/posttreatment design, continuous variables were compared using a paired t test. Additionally, values obtained from volume-cycled and pressure-cycled ventilators at baseline were compared using analysis of variance. All analyses were two-sided, and we considered differences to be significant at p < 0.05.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
The baseline characteristics of the study patients are shown in Table 1 . All patients in the study who received NIPPV showed significant improvement in all clinical parameters evaluated by the VAS (Table 2 ). After 3 years, during the outpatient reexamination and without discontinuing the ventilation, the patients were asked whether they had returned to ventilation and whether they considered that there had been a general improvement in their well-being, and all answered affirmatively to both questions. It is important to mention that the 36-item health survey short form quality-of-life questionnaire, which has been used by Simonds and Elliot15 on kyphoscoliosis patients, was not applied in our study because it was not yet known by the time our protocol had started.


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  		Table 1.. General Characteristics of the Patients*

 

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  		Table 2.. Nasal IPPV and Clinical Outcomes*

 
The mean (± SD) number of hospitalization days for respiratory difficulties decreased from 10.9 ± 13.3 days (range, 0 to 37 days) to 0 days per patient per year after 6 months of treatment, and this was sustained throughout the follow-up period. The one exception was admission to a respiratory care unit (2 to 3 nights) due to changes or adjustments in ventilator parameters or nasal interface. During the course of the study, changes in the type of ventilator and interface were necessary due to excessive noise, insufficient pressure, or deterioration of blood gas levels. Seven patients were changed to a volume-pressure-limited cycle ventilator (the PV501), which was specially designed for long-term home treatment, and one patient was change to a pressure-cycle ventilator (the O’NYX) and a volume-cycled ventilator (the Airox-Home and Monnal-D) at rest. Polysomnography results showed no significant differences after 6 months of treatment, except for improvements in SaO2, (Table 3 ).


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  		Table 3.. Polysomnographic Variables*

 
Table 4 shows the improvements in blood gas levels, with significant changes in PaO2 and PaO2/FIO2 rate. The pulmonary function test results showed significant increases in FVC (38 to 47%; p < 0.05) and a rise, although not significant, in FEV1 values (41 to 46%; p = 0.06). Ventilatory data are listed in Table 5 . No significant differences were found for VT, respiratory rate, and VT/TI rate with respect to baseline values. The PImax and PEmax showed significant rises (p < 0.05) in absolute values (50.11 ± 21.72 vs 72.66 ± 20.32 cm H2O, and 97.44 ± 40.66 vs 124.22 ± 46.83 cm H2O, respectively) and as percentages (55.8 ± 17.4% vs 78.5 ± 17.5% and 53.8 ± 17.7% vs 72.3 ± 11.0%, respectively) [Table 5 ]. Thus, parallel with changes in the Pawo/PImax rate and the PTI, these results show improvement in respiratory muscle strength. The ventilatory drive measured by the P0.1 and its derived indexes showed no significant differences with treatment, although the P0.1/PImax rate decreased with respect to pretreatment values. No differences were found between the data from volume-cycled and pressure-cycled ventilator users.


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  		Table 4.. Blood Gas Levels and Lung Function*

 

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  		Table 5.. Breathing Pattern and Respiratory Muscle Strength*

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
We studied the effect of NIPPV on 16 patients with severe kyphoscoliosis on clinical and functional pulmonary parameters. The important findings of the present study are as follows: (1) the patients receiving NIPPV experienced significant improvements in clinical symptoms; and (2) favorable changes in blood gas levels and respiratory muscle performance, which translated into a better outcome as measured by a reduction in the number of hospitalization days for respiratory insufficiency.

All study patients had severe functional alterations and hypercapnia, justifying the nocturnal use of nasal intermittent positive-pressure ventilation. They had a diminished FVC value (37.9%), a very high ventilatory drive (mean, 3.75 ± 0.93 cm H2O), and a significant reduction in maximum pressures as a result of mechanical abnormalities of the rib cage. They also showed impaired sleep efficiency as well as abnormal sleep architecture, associated with deterioration in nocturnal oxygenation parameters.

The effectiveness of volume-cycled and pressure-cycled ventilators has been shown in previous studies,6 and both techniques can be used at home.16 The parameters used were similar to those in the study by Leger17 with volume-cycled ventilators, and Hill et al,6 except that we maintained the expiratory positive airway pressure at low levels (ie, 4 cm H2O) to prevent CO2 rebreathing from the nasal interface.

Consistent with the results of previous studies,7 17 our results confirm the effectiveness of NIPPV in relieving symptoms and improving daytime arterial blood gas levels and nocturnal SaO2 levels, while decreasing the number of nocturnal oxyhemoglobin desaturation episodes. The impairment in sleep efficiency and architecture, which are associated with decreases in nocturnal SaO2 levels, that has been described previously in kyphoscoliosis patients18 was not significantly improved by NIPPV therapy after 6 months. However, this was consistent with the results of two previous studies19 20 of NIPPV for patients with restrictive chest walls, who showed no significant improvements in the quantity and quality of sleep.

After 6 months, a fall in the number of nocturnal desaturation episodes and sleep time with a saturation < 90% was observed, but not a fall in the number of apneas-hypopneas. Nevertheless, there was a striking improvement in symptoms related to nocturnal hypoventilation, with a large decrease in daytime sleep and morning headaches measured on the VAS.

Oxygenation was improved without an increase in PaCO2 by supplemental oxygen administration. This finding is important because respiratory acidosis has been shown to be associated with reduced diaphragmatic contractility and endurance.21 Knowing the causal association between episodes of nocturnal hypoxia and an increase in the pulmonary arterial pressure, the fact that we achieved an optimal nocturnal oxygenation in our patients without an increase in the PaCO2 represents a significant prognostic improvement.22

The improvements in PaO2 and in PaO2/FIO2 ratio, which are consistent with those in other studies,7 and the changes in clinical outcomes, dyspnea, hypersomnolence, and morning headaches were significantly related to the PaO2/FIO2 ratio before treatment but not with the PaCO2 level. The better oxygenation may be due to alveolar recruitment and the decrease in the number of nocturnal desaturations. In addition, both mechanisms lead to a reduction in symptoms of chronic hypoventilation. The PaCO2 value decreased, but the change was not significant. This result suggests that the degree of hypercapnia did not seem to be a factor in the etiology of the symptoms before treatment.

The significant increases in PImax (23%) and PEmax (16%), and the decrease in Pawo with a slight increase in the mean inspiratory flow suggest improvements in respiratory muscle strength.23 The Pawo/PImax rate decreased, along with the PTI, principally due to an increase in PImax. The changes in PTI measured at the mouth adequately reflect the tension-time index and the root mean square of diaphragmatic electromyography during CO2 stimulation,24 and the index provides important information regarding mechanical load and functional reserve of the respiratory muscles.25 The resting of the respiratory muscles with nocturnal ventilation has been demonstrated in reports such as that of Carrey et al,26 who showed a reduction in the electromyographic activity of the diaphragm. However, an increase of respiratory muscle pressure was not shown in all studies.6 7 The respiratory muscle pressure improved in our series by 32% for PImax and by 16% for PEmax. Goldstein et al,19 in a previous study in restrictive patients who were treated with NIPPV showed that the improvements in nocturnal and daytime oxygenation were related to better respiratory muscle condition.

FVC showed a significant increase after treatment (37.9 to 47.5%). This improvement could have resulted from alveolar recruitment as well as from better muscular condition. Maximum respiratory pressures as an index of respiratory muscle strength have been found to be reduced in patients with severe idiopathic scoliosis, and the correlation between respiratory muscle strength and reduction in lung volume is strong.26 The values of P0.1 and the indexes derived from it (the inspiratory load is represented by the effective impedance of the respiratory system) remained above normal after the long-term treatment, showing no improvement in the physical properties of the lung and chest wall.23 There were no changes in total lung capacity after the treatment. Long-term NIPPV therapy does not seem to affect breathing pattern or ventilatory drive in this subset of patients.

Nine of the 16 patients had experienced at least one hospitalization for respiratory insufficiency during the 6 months before beginning NIPPV therapy. No patient required hospitalization after ventilation, and this improvement is consistent with that reported by other studies.17 20

Consequently, our patients demonstrated better mechanical condition after treatment, with a small increase in dynamic lung volumes and a significant improvement in muscular strength. Better exchange of gases, reflected by increases in PaO2 levels without an increase in PaCO2 levels, provides a more suitable condition for efficient muscular performance. In conclusion, our results show that long-term NIPPV therapy may significantly improve physiologic parameters and symptoms in patients with severe kyphoscoliosis and ventilatory insufficiency.


   Acknowledgements
 
We thank Eduardo Núñez, MD, MPh, for editing the manuscript and for editorial assistance.


   Footnotes
 
Abbreviations: BF = breath frequency; FIO2 = fraction of inspired oxygen; NIPPV = nocturnal intermittent positive-pressure ventilation; Pawo = mean airway pressure at the mouth; PEmax = maximum expiratory pressure; PImax = maximal inspiratory pressure; P0.1 = occlusion pressure during the first 100 ms of inspiration; PTI = pressure-time index at the mouth; SaO2 = arterial oxygen saturation; TI = inspiratory time; TTOT = total breathing cycle time; VAS = visual analog scale; VT = tidal volume

Received for publication November 19, 2001. Accepted for publication February 12, 2003.


   References
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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