Continuous versus bilevel positive airway pressure in a patient with idiopathic central sleep apnea

A 57-yr-old man with idiopathic central apnea is reported. He presented at our hospital complaining of excessive daytime sleepiness. Polysomnography, including esophageal pressure monitoring, confirmed central sleep apnea with an apnea index of 27/h. He had mild non-insulin-dependent diabetes mellitus (NIDDM) but no signs of diabetic neuropathy or other background diseases. The ventilatory responses to hypoxia and hypercapnia tested while he was awake indicated increased respiratory chemosensitivity. We applied nasal continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BPAP) in an attempt to compare the possible difference in therapeutic efficacy. Although nasal CPAP completely reversed central apnea, nasal BPAP adversely affected both apnea length and frequency in an applied pressure-dependent manner. Arterial blood gas analyses while he was being treated indicted alveolar hypoventilation with CPAP and hyperventilation with BPAP. Additionally, administration of a mixed gas containing 5% CO2 through a face mask had a significant effect on the disappearance of central apnea in this patient. These findings support the theory that the arterial PCO2 level is critical in generating idiopathic central apnea and that nasal CPAP therapy may be effective in eliminating central apnea by raising the PaCO2.     

Effects of nasal continuous positive airway pressure on breathing pattern and respiratory drive in patients with obstructive sleep apnea syndrome

To examine the influence of continuous positive airway pressure (CPAP) therapy on respiratory center drive in patients with obstructive sleep apnea syndrome (OSAS), 20 normocapnic OSAS patients (group 0) and 20 simple snoring patients were studied. In the first night, diagnostic polysomnography (PSG) was performed. Before and after PSG monitoring, mouth occlusion pressure (P0.1), tidal volume (VT), minute ventilation (VE), respiratory rate (RR), inspiratory time (Ti), expiratory time (Te), total cycle duration (Ttot), inspiratory duty cycle (Ti/Ttot), mean inspiratory flow (VT/Ti) and effective inspiratory impedance (P0.1/VT/Ti, Ieff) were measured while they were breathing room air. In the following night the OSAS patients were treated with nasal CPAP and PSG monitoring and the above mentioned measurements were repeated. The results showed that pre-PSG values of P0.1, RR and P0.1/VT/Ti in the OSAS patients were significantly higher than those in the snoring patients, while VT, Ti, Te and Ttot values were lower. In the first night, the post-PSG P0.1 value in the OSAS patients increased markedly as compared with the pre-PSG. After overnight nasal CPAP therapy, the respiratory disorder index in the OSAS patients decreased markedly, the nadir SaO2 increased markedly, but the post-PSG P0.1 value did not increase significantly. It is concluded that, before sleep, OSAS patients exhibit a higher respiratory drive and a shallow and frequent breathing pattern as compared with simple snoring patients. After nocturnal sleep, the respiratory drive of OSAS patients increases significantly, the breathing pattern becomes more shallow and frequent. Nasal CPAP may effectively relieve the sleep apnea and hypopnea as well as the resulting hypoxemia and therefore correct the changes in breathing pattern and respiratory drive through nocturnal sleep in patients with OSAS.     

Acute effects of nasal continuous positive airway pressure on 24-hour blood pressure and catecholamines in patients with obstructive sleep apnea

OBJECTIVE: To estimate the risk for spina bifida associated with the common mutation C677T of the MTHFR gene in a country with a relatively low prevalence of NTDs. DESIGN: Case-control study. SUBJECTS: Cases: 203 living patients affected with spina bifida (173 myelomeningocele and 30 lipomeningocele); controls: 583 subjects (306 young adults and 277 unselected newborns) from northern and central-southern Italy. SETTING: Cases: three spina bifida centres; young adult controls: DNA banks; newborn controls: regional neonatal screening centres. MAIN OUTCOME MEASURES: Prevalence of the C677T genotypes in cases and controls by place of birth; odds ratios for spina bifida and estimated attributable fraction. RESULTS: The prevalence of T/T, T/C, and C/C genotype was 16.6%, 53.7%, and 29.7% in controls and 25.6%, 43.8%, and 30.6% in cases, respectively. We found no differences between type of defect or place of birth. The odds ratio for spina bifida associated with the T/T genotype v C/C plus T/C was 1.73 (95% CI 1.15, 2.59) and the corresponding attributable fraction was 10.8%. No increased risk was found for heterozygous patients (OR=0.79, 95% CI 0.53-1.18). CONCLUSION: This study, as well as the meta-analysis we updated, shows that homozygosity for the MTHFR C677T mutation is a moderate risk factor in Europe, and even in Italy where there is a relatively low prevalence of spina bifida. The estimated attributable fraction associated with this risk factor explains only a small proportion of cases preventable by periconceptional folic acid supplementation. Thus, other genes involved in folate-homocysteine metabolism, their interaction, and the interaction between genetic and environmental factors should be investigated further.     

Reversal of sinus arrest and atrioventricular conduction block in patients with sleep apnea during nasal continuous positive airway pressure

Sinus arrest and atrioventricular (AV) block have been demonstrated in as much as 30% of patients with sleep apnea (SA). The reversal of heart block after tracheostomy has been shown. Nasal continuous positive airway pressure (nCPAP) now is widely used as the treatment of SA, but little data are available on the effect of nCPAP on heart block in patients with SA. During a 17-mo period 239 patients were found to have SA in an ambulatory study. Heart block was identified in 17 (16 male, one female) of these patients. Standard polysomnography and two-channel long-term ECG before and during nCPAP therapy were performed in order to assess the effect of nCPAP on SA and heart block. Mean age of the 17 patients was 50.7 yr (range, 27 to 78 yr), mean respiratory disturbance index (RDI) was 90/h (SD +/- 36.1) before nCPAP and 6/h (SD +/- 6.2) on the second treatment night. The number of episodes of heart block during sleep decreased significantly (p < 0.001) from 1,575 before therapy to 165 during nCPAP. In 12 patients (70.6%) heart block was totally prevented by nCPAP. In another three patients, there was a 71 to 97% reduction in the number of episodes of heart block on the second treatment night, and in two of them a complete reversal occurred thereafter. Two patients exhibited an increase in block frequency during nCPAP, which was reversed after 4 wk of nCPAP in one but persisted in the other.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of nasal continuous positive airway pressure therapy on respiratory parameters of upper airway patency in patients with obstructive sleep apnea syndrome

OBJECTIVES: To assess whether an initial treatment with nasal continuous positive airway pressure (NCPAP) therapy, applied for one night, had any effect on airway patency. METHODS: In 18 patients with obstructive sleep apnea syndrome (OSAS), we measured the total resistance of the respiratory system (Rrs) and their relevant lung functions before and after polysomnography, with and without NCPAP therapy. The Rrs was measured at 3 Hz with the forced oscillation technique. The overnight changes in the specific respiratory conductance (SGrs=reciprocal of the Rrs per unit lung volume) was also calculated in the sitting position. Since many reports have suggested that obesity, through fat deposits around the pharynx, can affect the mechanical and neuromuscular properties of the upper airway, we also investigated if the degree of obesity was related to the magnitude of improvement in these parameters. RESULTS: After the first night of NCPAP therapy, the Rrs decreased (sitting: 4.8+/-0.4 vs 4.3+/-0.4 cm H20/L/s, p < 0.05; lying: 6.5+/-0.4 vs 5.6+/-0.4 cm H20/L/s, p < 0.05) and the maximal voluntary ventilation increased in the morning (sitting: 101.6+/-5.8% vs 106.4+/-4.5%, p < 0.05; lying: 91.2+/-5.4% vs 97.9+/-4.7%, p < 0.05). The overnight difference in the SGrs showed a significant improvement after the initial treatment with NCPAP therapy (p < 0.05). However, the lung volume, flow volume loop, and closing volume in the morning did not change significantly after the therapy. An overnight decrease in the Rrs following NCPAP therapy is significantly correlated with the body mass index (sitting: r=0.54, p < 0.05; lying: r=0.61, p < 0.01). CONCLUSION: The improvements in Rrs without changes in spirometry may reflect improved upper airway patency after NCPAP therapy. The degree of obesity is suggested to be associated with the treatment effect on upper airway in patients with OSAS.     

Abnormal autonomic stress responses in obstructive sleep apnoea are reversed by nasal continuous positive airway pressure

Obstructive sleep apnoea (OSA) is associated with abnormalities in autonomic stress tests, which are tests of cardiovascular response in the autonomic nervous system (ANS). The level of abnormality has been related to the level of overnight arterial oxygen saturation (Sa,O2). We have studied ANS function pre- and post-treatment with nasal continuous positive airway pressure (nCPAP) in six males with moderately severe or severe OSA (apnoea/hypopnoea index (AHI) median 51 (range 14-74 events.h-1 of sleep). Tests consisted of heart rate responses to Valsalva manoeuvre, deep breathing, and change of posture from lying to standing. In addition, systolic blood pressure (SBP) response to standing and diastolic blood pressure (DBP) response to handgrip were studied. Each abnormal test (compared to published normal values) scored +1.0 and each marginal test result (90-95% confidence interval for normals) scored +0.5. A total score was calculated for the five tests performed in the evening and morning (maximum score 10 per patient). Patients had been receiving treatment for more than 1 year (median 471 (389-624) days) and objective compliance was monitored by a clock counter in the nCPAP machines. Five of six patients had regularly used nCPAP (mean 7.8 h.night-1) and all showed a normalization in ANS test score: pre-nCPAP 2 (1-4.5), post-nCPAP 0.2 (0-0.5) (p < 0.05, Wilcoxon signed rank test). One poorly compliant subject (No. 6; nCPAP 3 h.night-1) had a deterioration in ANS test score: 1 pre-nCPAP to 1.5 post-nCPAP. The improvement in ANS test score in the five compliant patients was positively correlated with an improvement in mean Sa,O2 during sleep posttreatment. We conclude that successful treatment of obstructive sleep apnoea leads to normalization of impaired autonomic stress responses.     

Sleep apnea syndrome in patients with diabetes. Effectiveness of treatment for respiratory assistance at night with continuous positive airway pressure

The group of 30 patients with OSA and diabetes type I or II has been examined. After the first test with MESAM 4, 5 patients with considerable nocturnal desaturation and heart rate disorders during sleep have been found. All diabetes type II. Two polisomnographic studies (the first diagnostic polisomnography and the second study for the settlement of treatment with CPAP) have been performed in the patients. After 6 months of applying CPAP all the patients have been examined again. The apnoea index was decreased (from 87.5 to 11.2) and a better control of both systemic arterial pressure and glycaemia, saturation > 80% has been obtained.     

Therapy with nasal CPAP (continuous positive airway pressure) in patients with obstructive sleep apnea syndrome (OSAS). I: Long-term acceptance of nasal CPAP

BACKGROUND: Nocturnal ventilation with nCPAP has been established as the safest and most efficient nonsurgical treatment for OSAS. Long-term results, however, are determined by the patients' compliance with therapy. The aim of this study was the objective measurement of long-term acceptability of nCPAP therapy in all patients receiving this treatment in our sleep laboratory between January 1990 and March 1995. METHODS: We prospectively investigated 41 patients (36 male, 5 female) with moderate to severe OSAS who received nCPAP therapy. Mean time of follow-up was 20.6 months, ranging from 1.2 to 53.5 months. Therapy was indicated when OSAS was confirmed by cardiorespiratory polygraphy and either (1) the patient complained of daytime sleepiness or (2) the patient possessed an apnea-hypopnea index greater than 30/h or when the mean oxygen desaturation was below 80% regardless of the presenting symptoms. The compliance with treatment was defined as a mean rate of use of over 5 hours per night calculated from the time counter on the nCPAP machine. RESULTS: 33 patients (88.5%) have continued using nCPAP until the present time but only 24 patients (59%) met our criteria for long-term acceptance and this group was identified as responders. We found no significant differences in age, body mass index, apnea-hypopnea index, and nCPAP-pressure between responders and non-responders. CONCLUSION: Although nCPAP is the safest treatment for OSAS, there is still a large group of patients with moderate to severe OSAS who are not efficiently treated with nCPAP because of the low long-term acceptability of this therapy. With respect to this group of patients, surgical approaches have to be considered as an alternative therapy.     

Secondary obstructive sleep apnea syndrome in a patient with tracheal stenosis and bilateral recurrent paresis. Successful treatment with nasal continuous positive airway pressure therapy

HISTORY AND ADMISSION FINDINGS: A 67-year-old woman complained of marked daytime sleepiness, as well as loud snoring and apnoeas during sleep. She was known to have had 3 thyroidectomies for goitre 41, 23 and 12 years ago, with known tracheal stenosis and recurrent nerve palsy for 11 years. Physical examination revealed marked stridor, hoarse voice and slightly enlarged and palpable recurrent right thyroid. INVESTIGATIONS: Polysomnography demonstrated a clearly elevated obstructive sleep apnoea activity (apnoea index: 34/h, apnoea-hypopnea index: 40/h, desaturation index: 31/h, minimal saturation: 63%). Selective tracheal imaging showed subglottic tracheal stenosis with an inspiratory luminal diameter of 4 mm and an expiratory luminal diameter of 8 mm. Lung function analysis revealed marked flattening of the flow-volume curve as sign of a functionally effective tracheal stenosis. These findings indicated a secondary obstructive sleep apnoea (OSA) due to tracheal stenosis and bilateral recurrent nerve palsy. The patient declined further studies, such as bronchoscopy. TREATMENT AND COURSE: As the patient did not want any surgical treatment, nasal continuous positive airway pressure therapy (CPAP) was instituted as a trial. No apnoea occurred at a pressure of 12 mm H2O and this was well tolerated. She has now continued CPAP at home for 12 months and her vigilance was markedly improved. CONCLUSIONS: Tracheal stenosis or recurrent nerve palsy is a rare cause of OSA which can be effectively treated by nasal CPAP.     

Continuous positive airway pressure requirement during the first month of treatment in patients with severe obstructive sleep apnea

OBJECTIVES: (1) To compare the continuous positive airway pressure (CPAP) requirement at the time of diagnosis (T0), after 2 weeks (T2), and after 4 weeks (T4) of CPAP treatment, in patients with severe obstructive sleep apnea (OSA); and (2) to assess whether any alteration in CPAP requirement over the first 4 weeks of CPAP treatment would influence daytime alertness, subjective sleepiness, or mood. DESIGN: A prospective, controlled, single-blind crossover study. SETTING: University teaching hospital. PATIENTS: Ten patients with newly diagnosed and previously untreated severe OSA (aged 52+/-9 years, apnea hypopnea index [AHI] of 99+/-31) and subsequently 10 control patients (aged 52+/-11 years, AHI 85+/-17). MEASUREMENTS: Overnight polysomnography with CPAP titration to determine the CPAP requirement, which was standardized for body position and sleep stage, on all three occasions (T0, T2, T4). Objective sleep quality, daytime alertness, subjective sleepiness (Epworth Sleepiness Scale), and mood (Hospital Anxiety and Depression Scale). RESULTS: CPAP requirement decreased from T0 to T2 (median difference, 1.5 cm H2O, 95% confidence interval [CI], 1.1 to 2.7 cm H2O, p=0.0004) and did not differ between T2 and T4. Use of the lower CPAP pressure during T2 to T4 was associated with a decrease in Epworth scale (mean difference, 2.6, 95% CI, 1.2 to 4; p=0.01) and anxiety (median change, 2; 95% CI, 0.5 to 2.9, p=0.03) scores, as compared with the first 2 weeks. Daytime alertness did not differ between T0 to T2 and T2 to T4. CONCLUSION: CPAP requirement falls within 2 weeks of starting CPAP treatment. A change to the lower required CPAP was not associated with any deterioration in daytime alertness but was associated with small subjective improvements in sleepiness and mood.     

Effects of body position on sleep related disordered breathing in a patient with Steinert's disease

Sudden changes in respiratory patterns observed during polysomnographic studies may suggest a positional form of SAHS (sleep apnea-hypopnea syndrome). We report the case of a 37-year-old patient with Steinert's disease with this form of SAHS. Breathing during sleep could be regularized by a simple positional control.     

Changes in urinary uric acid excretion in obstructive sleep apnea before and after therapy with nasal continuous positive airway pressure

STUDY OBJECTIVE: To assess the utility of urinary uric acid excretion as a marker of nocturnal hypoxia in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) before and after the institution of nasal continuous positive airway pressure (CPAP). DESIGN: Prospective, open. SETTING: Sleep Disorders Laboratory, Veterans Affairs Medical Center. PARTICIPANTS: Thirty consecutive male subjects, 20 with OSAHS and 10 without OSAHS. MEASUREMENTS AND METHODS: Spot morning urine and venous blood samples were obtained in all subjects; samples were also obtained after the application of CPAP in those with OSAHS. Uric acid excretion, normalized to creatinine clearance, was calculated as the product of urinary uric acid and serum creatinine concentrations divided by urine creatinine concentration. In patients with OSAHS, uric acid excretion was 0.55+/-0.1 mg/dL before CPAP therapy and decreased to 0.30+/-0.01 mg/dL after CPAP therapy (p < 0.001). The latter value did not differ significantly from the mean value (0.32+/-0.03 mg/dL) in the control group. Uric acid excretion in OSAHS patients correlated significantly with the apnea-hypopnea index (r=0.42; p<0.0003). CONCLUSION: Uric acid excretion is increased in OSAHS patients and normalizes after CPAP treatment, most likely reflecting differences in tissue oxygenation between the two conditions. Further studies in large number of patients may confirm the usefulness of this simple test for diagnosis and follow-up of patients with OSAHS.     

Cerebral hemodynamic changes in sleep apnea syndrome and effect of continuous positive airway pressure treatment

BACKGROUND AND OBJECTIVE: A clear association among snoring, sleep apnea, and increased risk of stroke has been shown by previous studies. However, the possible role played by sleep apnea in the pathogenesis of cerebrovascular disease is subject to debate. To evaluate the influence of hemodynamic changes caused by obstructive sleep apnea syndrome (OSAS), we investigated cerebrovascular reactivity to hypercapnia in patients with OSAS. METHODS: The study was performed at baseline and after 1 night and 1 month of nasal continuous positive airway pressure (n-CPAP) therapy, with patients in the waking state (8:00 to 8:30 AM and 5:30 to 6:00 PM) with transcranial Doppler ultrasonography. Cerebrovascular reactivity was calculated with the breath-holding index (BHI). RESULTS: In the baseline condition, compared with normal subjects, patients with OSAS showed significantly lower BHI values in both the morning (0.57 versus 1.40, p < 0.0001) and the afternoon (1.0 versus 1.51, p < 0.0001). Cerebrovascular reactivity was significantly higher in the afternoon than it was in the morning in both patients (p < 0.0001) and controls (p < 0.05). In patients, the BHI returned to normal values, comparable with those of control subjects, after both 1 night and 1 month of n-CPAP therapy. CONCLUSIONS: These findings suggest an association between OSAS and diminished cerebral vasodilator reserve. This condition may be related to the increased susceptibility to cerebral ischemia in patients with OSAS, particularly evident in the early morning.     

Nasal fibreoptic tracheal intubation in anaesthetised patients breathing via a modified laryngeal mask airway

A modified laryngeal mask airway was used to facilitate nasotracheal intubation with a fibreoptic laryngoscope. A size 4 laryngeal mask airway was modified by creating a defect at the base of the stem and removing the bars to allow passage of the fibreoptic laryngoscope from the nasopharynx to the larynx. The laryngeal mask airway cuff was split and the cut edges were sealed with silicone. This design allowed the cuff to function normally and allowed removal of the split laryngeal mask airway after the tracheal tube had been 'railroaded' into place. Thirty-four patients were studied. The split laryngeal mask airway was easily inserted with satisfactory airway maintenance in 32 patients. Nasal airway endoscopy and laryngoscopy were successfully achieved with the split laryngeal mask airway in place in 31 of 32 patients. Railroading the tracheal tube over the fibreoptic laryngoscope with the split laryngeal mask airway in place was successful in all 31 of these patients. This prototype split laryngeal mask airway allows good airway maintenance while fibreoptic nasotracheal intubation is performed.     

Long-term evolution of daytime somnolence in patients with sleep apnea/hypopnea syndrome treated by continuous positive airway pressure

We demonstrated in a previous study that excessive daytime sleepiness (EDS) in patients who have sleep apnea/hypopnea syndrome (SAHS) and are undergoing continuous positive airway pressure (CPAP) treatment improved differently in two groups of patients: in group I, multiple sleep latency tests (MSLT) were normalized after 50 days of treatment (individual value > 10 minutes), whereas they remained low (individual value < 10 minutes) in group II, with a significant difference between groups. To evaluate the long-term evolution of daytime somnolence under nasal CPAP treatment, five patients from group I and seven patients from group II underwent a new polysomnography and MSLT 4 years after the previous study. Clinical, polysomnographic and MSLT results obtained at baseline before treatment (T1), after the initial 50-day period of CPAP treatment (T2), and after 4 years (T3) were compared. The significant difference in mean MSLT value between the two groups previously observed at T1 and T2 disappeared at T3 (group I: 12.4+/-5.9 minutes; group II: 9.7+/-5.9 minutes). We found that this long-term improvement in excessive daytime somnolence was independent of the initial MSLT value, the severity of SAHS, and the initial MSLT changes under nasal CPAP. Long-term MSLT evolution was significantly correlated to CPAP compliance. These results demonstrate that even in the absence of a significant increase in MSLT at the beginning of CPAP treatment, further improvement is still possible several years later, which may encourage the regular, long-term use of nasal CPAP by patients.     

Small airway closure and positive end-expiratory pressure in mechanically ventilated patients with chronic obstructive pulmonary disease

The effects of positive end-expiratory pressure (PEEP) on alveolar recruitment and closing volume were studied in ten supine, sedated, and paralyzed patients with chronic obstructive respiratory disease and acute respiratory failure. We applied PEEP (0, 5, 10, and 15 cm H2O) and constructed inflation static volume-pressure (V-P) curves. In all patients, the static V-P curves obtained at different PEEP levels were superimposed on each other, indicating that with PEEP there was no recruitment of previously atelectatic lung units. However, the static V-P curves exhibited an inflection point, which should reflect the critical pressure (Po) required to reopen all closed airways, whilst the corresponding lung volume (Vo) reflects the opening volume. On average, Vo was 0.71 L above the relaxation volume of the respiratory system (Vr). All patients, however, exhibited dynamic hyperinflation, i.e., with zero PEEP (ZEEP) the end-expiratory lung volume (EELV) was 0.54 L above Vr. Nevertheless, in seven patients the EELV on ZEEP was below Vo, resulting in cyclic reopening and closure of small airways with each breathing cycle, with concomitant mechanical stresses on the peripheral airways that may lead to low-volume barotrauma. Such barotrauma may be prevented by increasing with PEEP the EELV to Vo.     

Effects of continuous positive airway pressure on obstructive sleep apnea and left ventricular afterload in patients with heart failure

BACKGROUND: The objectives of this study were to determine the effects of continuous positive airway pressure (CPAP) on blood pressure (BP) and systolic left ventricular transmural pressure (LVPtm) during sleep in congestive heart failure (CHF) patients with obstructive sleep apnea (OSA). In CHF patients with OSA, chronic nightly CPAP treatment abolishes OSA and improves left ventricular (LV) ejection fraction. We hypothesized that one mechanism whereby CPAP improves cardiac function in CHF patients with OSA is by lowering LV afterload during sleep. METHODS AND RESULTS: Eight pharmacologically treated CHF patients with OSA were studied during overnight polysomnography. BP and esophageal pressure (Pes) (ie, intrathoracic pressure) were recorded before the onset of sleep and during stage 2 non-rapid eye movement sleep before, during, and after CPAP application. OSA was associated with an increase in systolic BP (from 120.4+/-7.8 to 131.8+/-10.6 mm Hg, P<0.05) and systolic LVPtm (from 124.4+/-7.7 to 137.2+/-10.8 mm Hg, P<0.05) from wakefulness to stage 2 sleep. CPAP alleviated OSA, improved oxyhemoglobin saturation, and reduced systolic BP in stage 2 sleep to 115.4+/-8.5 mm Hg (P<0.01), systolic LVPtm to 117.4+/-8.5 mm Hg (P<0.01), heart rate, Pes amplitude, and respiratory rate. CONCLUSIONS: In CHF patients with OSA, LV afterload increases from wakefulness to stage 2 sleep. By alleviating OSA, CPAP reduces LV afterload and heart rate, unloads inspiratory muscles, and improves arterial oxygenation during stage 2 sleep. CPAP is a nonpharmacological means of further reducing afterload and heart rate during sleep in pharmacologically treated CHF patients with OSA.     

Comparison of oxygen cost of breathing with pressure-support ventilation and biphasic intermittent positive airway pressure ventilation

OBJECTIVE: To assess the oxygen cost of breathing with either pressure-support ventilation (PSV) or biphasic intermittent positive airway pressure ventilation (BIPAP). DESIGN: Prospective, randomized, crossover study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: Twenty clinically stable and spontaneously breathing patients after long-term mechanical ventilation. INTERVENTIONS: Patients were randomized to start on either PSV or BIPAP, and measurements were performed after an adaptation period of 30 mins. Immediately after, the ventilatory mode was changed and after another 30-min adaptation period, the same measurements were performed. MEASUREMENTS AND MAIN RESULTS: Indirect calorimetry was performed during each ventilatory mode for a period of 30 mins. Oxygen consumption, energy expenditure, CO2 production, and respiratory quotient did not differ significantly between the two ventilatory modes, regardless of the patients' randomization. There were no statistically significant differences with regard to respiratory rate, minute volume, and blood gas analysis. All patients tolerated both ventilatory modes without any signs of discomfort. CONCLUSIONS: Pressure support ventilation and BIPAP are both used for weaning patients gradually from the ventilator. BIPAP may be advantageous in patients not breathing sufficiently with PSV, since no patient effort is necessary with use of this ventilatory mode.