The use of noninvasive pressure support ventilation for severe respiratory insufficiency due to pulmonary oedema

Objective: Experimental use of noninvasive pressure support ventilation (NIPSV) in patients with severe pulmonary oedema who would have been intubated if noninvasive ventilation were not available. Design: Open, prospective, within patients non comparative study. Setting: Internal intensive care unit (11 beds) at a university hospital. Patients: 29 patients with severe respiratory distress and confirmed pulmonary oedema. Interventions: NIPSV was applied via a tight fitting face mask delivering between 13 and 24 cmH₂O inspiratory airway pressure and 2 to 8 cmH₂O expiratory airway pressure. Measurements and results: One patient required endotracheal intubation. Mean plethysmographic oxygen saturation rose significantly within 30 min from 73.8 ± 11 to 90.3 ± 5 %, while the oxygen supply was reduced from 7.3 ± 3.7 to 5.1 ± 3 l/min. Mean pH increased significantly (p < 0.01) from 7.22 ± 0.1 before NIPSV to 7.31 ± 0.07 after 60 min of NIPSV. Partial pressure of carbon dioxide was 62 ± 18.5 mmHg but decreased significantly within 60 min to 48.4 ± 11.5 mmHg. Heart rate and blood pressure stabilised continuously during the observation time. Mean duration of NIPSV was 6 h 9 min (range 60 min to 24 h). There were no serious side effects. Four patients died from underlying diseases between 1 and 28 days after NIPSV. Conclusion: NIPSV is a highly effective technique with which to treat patients with severe cardiogenic pulmonary oedema. Received: 29 December 1997 Final revision received: 7 October 1998 Accepted: 9 October 1998     

Physiologie evaluation of non-invasive pressure support ventilation in trauma patients with acute respiratory failure

Objective: To investigate the effectiveness of noninvasive (face mask) versus invasive (endotracheal tube) equal pressure values on blood gases and respiratory pattern and to evaluate the feasibility of using mask ventilation after the short term physiologic study. Design: Open, prospective, physiologic study and uncontrolled clinical study. Setting: Intensive care unit of a trauma center. Patients: 22 intubated trauma patients were studied. Interventions: Patients were intubated and ventilated in a pressure support mode (IPSV) of 13.5 ± 1.5 cmH₂O and a post end-expiratory pressure (PEEP) of 5.8 ± 2.57 cmH₂O. After a T-piece trial to assess patient's ability to breath spontaneously, patients were switched over to noninvasive pressure support (NIPSV). The pressure levels were set as during IPSV. Blood gases and respiratory parameters were measured during IPSV, during the T-piece trial, and after 1 h of NIPSV. After the physiologic study, all patients were asked if they wished to continue on NIPSV. The patient's subjective compliance with IPSV and NIPSV was measured by means of an arbitrary score. A successful outcome was defined as no need for reintubation. Measurements and results: IPSV and NIPSV showed no statistical differences for blood gas and respiratory parameters by using the same values of PSV (13 ± 5 vs 12.8 ± 1.7 cmH₂O, NS) and PEEP (5.8 ± 2.5 and 5.2 ± 2.2 cmH₂O NS). The median length of time on NIPSV was 47 h (range 6 to 144). All patients wished to continue on NIPSV, but 9 patients (40.9 %) were reintubated after 54 ± 54 h. Six of them died after 36 ± 13 days while still on mechanical ventilation. There was no statistically significant difference in compliance score between IPSV and NIPSV. Conclusions: NIPSV is comparable to IPSV in terms of blood gases and respiratory pattern. The clinical uncontrolled study indicates that NIPSV could be used in selected trauma patients. Received: 21 July 1997 Accepted: 12 April 1998     

Noninvasive pressure support ventilation (NIPSV) with face mask in patients with acute cardiogenic pulmonary edema (ACPE)

Objectives: To assess (1) the short-term hemodynamic, respiratory and arterial blood gas effects of NIPSV in patients with ACPE who were likely to require endotracheal intubation, (2) the initial causes of failure and (3) the side effects and the difficulties of this technique. Design: Uncontrolled, prospective clinical study. Setting: Teaching hospital intensive care unit. Patients: 26 consecutive patients with severe ACPE. Interventions: Noninvasive ventilation via a face mask, using a pressure support mode (20.5 ± 4.7 cmH₂O), with an initial fractional inspired oxygen of 93.0 ± 16 % and a positive end-expiratory pressure of 3.5 ± 2.3 cmH₂O. The need to intubate the patients within 48 h was considered as a criterion of failure of the procedure. Measurements and results: Clinical and biological parameters were measured at 15 and 30 minutes, 1 h and 2 h and at 1 h and 2 h, respectively. There were 5 (21 %) failures and 21 (79 %) successes. In both the success and the failure groups, clinical and blood gas parameters improved at the first measure. In the success group, within 15 min of the start of NIPSV, pulse oximetry saturation (SpO₂) had increased from 84 ± 12 to 96 ± 4 % (p < 0.001), the respiratory rate (RR) had decreased from 36 ± 5.3 to 22.4 ± 4.9 breaths/min (p < 0.0001) and within 1 h the arterial oxygen tension and pH, respectively, had increased from 61 ± 14 to 270 ± 126 mmHg (p < 0.0001) and from 7.25 ± 0.11 to 7.34 ± 0.07 (p < 0.01) and the arterial carbon dioxide tension (PaCO₂) had decreased from 54.2 ± 15 to 43.4 ± 6.4 mmHg (p < 0.01). There were no statistical differences between the success and failure groups for the initial clinical parameters: SpO₂, RR, heart rate, mean arterial pressure. The only differences between the success and failure groups were in the PaCO₂ (54.2 ± 15 vs 32 ± 2.1 mmHg, p < 0.001) and the creatine kinase (CPK) (176 ± 149 vs 1282 ± 2080 IU/l, p < 0.05); this difference in CPK activity was related to the number of patients who had an acute myocardial infarction (AMI) (4/5 in the failure group vs 2/21 in the success group, p < 0.05). All patients with AMI in the failure group died. Conclusion: Among patients in acute respiratory failure, those with severe ACPE could benefit from NIPSV if they are hypercapnic, but NIPSV should be avoided in those with AMI. Received: 22 January 1998 Final revision received: 3 September 1998 Accepted: 24 September 1998     

Sequential use of noninvasive pressure support ventilation for acute exacerbations of COPD

Objectives: To compare the efficacy of noninvasive pressure support ventilation (NIPSV) in acute decompensation in chronic obstructive pulmonary disease (COPD) by means of a bi-level positive airway pressure support system (BiPAP) in a sequential mode with medical therapy alone; to assess the short-term physiologic effects of the device on gas exchange; and to compare patients successfully ventilated with NIPSV with those in whom NIPSV failed. Design: A prospective case series with historically matched control study. Setting: A general intensive care unit (ICU) of a university hospital. Patients: We evaluated the efficacy of administration of NIPSV in 42 COPD patients and compared this with standard treatment in 42 matched historical control COPD patients. Interventions: NIPSV was performed in a sequential mode, i. e., BiPAP in the spontaneous mode was used for at least 30 min every 3 h. Between periods of ventilation, patients could be systematically returned to BiPAP when the arterial oxygen saturation was < 0.85 or when the respiratory rate was > 30 breaths/min. Measurements and results: Success rate, mortality, duration of ventilatory assistance, and length of ICU stay were recorded. Eleven of the 42 patients (26 %) in the NIPSV group needed tracheal intubation compared with 30 of the 42 control patients (71 %). The 31 patients in whom NIPSV was successful were ventilated for a mean of 6 ± 3 days. In-hospital mortality was not significantly different in the treated versus the control group, but the duration of ventilatory assistance (7 ± 4 days vs 15 ± 10 days, p < 0.01) and the length of ICU stay (9 ± 4 days vs 21 ± 12, p < 0.01) were both shortened by NIPSV. BiPAP was effective in correcting gas exchange abnormalities. The pH values, measured after 45 min of BiPAP with optimal settings, in the success (7.38 ± 0.04) and failure (7.28 ± 0.04) patients were significantly different (p < 0.05). Conclusions: NIPSV, performed with a sequential mode, may be used in the management of patients with acute exacerbations of COPD. Received: 10 February 1997 Accepted: 14 July 1997     

Feasibility of non-invasive pressure support ventilation in infants with respiratory failure after extubation: a pilot study

Objective  To evaluate the feasibility and effects of non-invasive pressure support ventilation (NIV) on the breathing pattern in infants developing respiratory failure after extubation. Design  Prospective pilot clinical study; each patient served as their own control. Setting  A nine-bed paediatric intensive care unit of a tertiary university hospital. Patients  Six patients (median age 5 months, range 0.5–7 months; median weight 4.2 kg, range 3.8–5.1 kg) who developed respiratory failure after extubation. Interventions  After a period of spontaneous breathing (SB), children who developed respiratory failure were treated with NIV. Measurements and results  Measurements included clinical dyspnoea score (DS), blood gases and oesophageal pressure recordings, which were analysed for respiratory rate (RR), oesophageal inspiratory pressure swing (dPes) and oesophageal pressure-time product (PTPes). All data were collected during both periods (SB and NIV). When comparing NIV with SB, DS was reduced by 44% (P < 0.001), RR by 32% (P < 0.001), dPes by 45% (P < 0.01) and PTPes by 57% (P < 0.001). A non-significant trend for decrease in PaCO₂ was observed. Conclusion  In these infants, non-invasive pressure support ventilation with turbine flow generator induced a reduction of breathing frequency, dPes and PTPes, indicating reduced load of the inspiratory muscles. NIV can be used with some benefits in infants with respiratory failure after extubation.     

Cardiopulmonary responses to continuous positive airway pressure in acute asthma

The effects of nasal continuous positive airway pressure (CPAP) on expiratory flow, arterial blood gas tensions, cardiovascular status, and dyspnea were studied in 21 patients with acute asthma. Therapy consisted of the following CPAP sequence: 30 minutes at 5 cm H₂O, 20 minutes at 0 cm H₂O, 30 minutes at 7.5 cm H₂O, and 20 minutes at 0 cm H₂O. Six control patients were fitted with a CPAP mask but given no positive-pressure therapy. Significant reductions in respiratory rate occurred from a baseline of 22.0 ± 1.0 to 19.8 ± 3.8 breaths/min at CPAP 5 cm H₂O and to 19.4 ± 4.3 breaths/min at CPAP 7.5 cm H₂O (P < .05). No significant change occurred in forced expiratory volume in 1 second (FEV₁), heart rate, mean arterial blood pressure, or arterial blood gas tension with either level of CPAP. Dyspnea, as assessed by a breathlessness score, improved during CPAP therapy (P < .05). These levels of CPAP were tolerated without deleterious side effects. In comparison, the control group showed no change in heart rate, respiratory rate, or breathlessness score during the study period. These data show that application of CPAP in acute asthma reduces respiratory rate and dyspnea with no untoward effects on gas exchange, expiratory airflow, or hemodynamics.     

Noninvasive pressure support ventilation vs. continuous positive airway pressure in acute hypercapnic pulmonary edema

Objective This study compared noninvasive pressure support ventilation (NIPSV) and continuous positive airway pressure (CPAP) in patients with acute hypercapnic pulmonary edema with regard to resolution time.Design and setting Randomized prospective study in an emergency department.Patients and participants We randomly assigned 36 patients with respiratory failure due to acute pulmonary edema and arterial hypercapnia (PaCO₂ >45 mmHg) to NIPSV (n=18) or CPAP through a face mask (n=18).Measurements and results Electrocardiographic and physiological measurements were made over 36 h. There was no difference in resolution time defined as clinical improvement with a respiratory rate of fewer than 30 breaths/min and SpO₂ of 96% or more between CPAP and NIPSV groups. Arterial carbon dioxide tension was significantly decreased after 1 h of ventilation (CPAP, 60.5±13.6 to 42.8±4.9 mmHg; NIPSV, 65.7±13.6 to 44.0±5.5 mmHg); respective improvements were seen in pH (CPAP, 7.22±0.11 to 7.37±0.04; NIPSV, 7.19±0.11 to 7.38±0.04), SpO₂ (CPAP, 86.9±3.7% to 95.1±2.6%; NIPSV, 83.7±6.6% to 96.0±2.9%), and respiratory rate (CPAP, 37.9±4.5 to 21.3±5.1 breaths/min; NIPSV, 39.8±4.4 to 21.2±4.6 breaths/min). No significant differences were seen with regards to endotracheal intubation and in-hospital mortality.Conclusions NIPSV proved as effective as CPAP in the treatment of patients with acute pulmonary edema and hypercapnia but did not improve resolution time.     

Hypercarbia during tracheostomy: a comparison of percutaneous endoscopic, percutaneous Doppler, and standard surgical tracheostomy

Objective: Tracheostomy is one of the most commonly performed surgical procedures in the critical care setting. The early use of tracheostomy as a method of primary airway management has been proposed as a means to decrease pulmonary morbidity and to shorten the number of ventilator, intensive care unit, and hospital days. We set out to (1) determine whether hypercarbia occurs during tracheostomy of the critically ill patient and (2) determine the extent to which the partial pressure of carbon dioxide in arterial blood (PaCO₂) rises during percutaneous endoscopic, percutaneous Doppler, and standard surgical tracheostomy. Design: Prospective, open clinical trial. Setting: Surgical intensive care unit and operating room in teaching hospitals. Patients: During mechanical ventilation, patients underwent either percutaneous endoscopic (PET), percutaneous Doppler (PDT), or standard surgical tracheostomy (ST), based on surgeon preference. Arterial blood gas readings were obtained approximately every 4 min throughout each procedure. Measurements and results: All tracheostomies were successfully performed. No serious complications (including hypoxia) occurred during the study. Significant (p < 0.05 vs PDT and ST) hypercarbia (maximum Δ PaCO₂ 24 ± 3 mmHg) and acidosis (maximum Δ pH – 0.16 ± 0.02) developed during PET. The changes in PaCO₂ and pH during PDT (maximum Δ PaCO₂ 8 ± 2 mmHg; maximum Δ pH – 0.07 ± 0.02) and ST (maximum Δ PaCO₂ 3 ± 1 mmHg; maximum ΔpH – 0.04 ± 0.01) were markedly less pronounced. Conclusions: Continuous bronchoscopy during percutaneous tracheostomy contributes significantly to early hypoventilation, hypercarbia, and respiratory acidosis during the procedure. Percutaneous tracheostomy, when performed using the Doppler ultrasound method to position the endotracheal tube, significantly reduces CO₂ retention when compared to PET. Because of a possible rise in intracranial pressure, the potential for hypercarbia should be considered when choosing the method of tracheostomy in the critically ill and/or head-injured patient, where hypercarbia may be detrimental. If PET is to be performed, steps to minimize occult hypercarbia, such as using the smallest bronchoscope available, minimizing suctioning during bronchoscopy, and minimizing the length of time the bronchoscope is in the endotracheal tube, should be undertaken. Received: 7 October 1996 Accepted: 6 March 1997     

PEEP-induced tricuspid regurgitation

Objective : To determine the presence of tricuspid regurgitation (TR) in patients affected by acute lung injury (ALI) and the adult respiratory distress syndrome (ARDS) during mechanical ventilation with positive end-expiratory pressure (PEEP). Design: A prospective clinical study. Setting: 10-bed general intensive care unit in a University Hospital. Patients: 7 consecutive patients an age 44.7 ± 8.6 years with a diagnosis of ALI or ARDS were studied. All were on mechanical ventilation with PEEP. Interventions: PEEP was increased in steps of 5 cm H₂O until the appearance of TR or up to a limit of 20 cm H₂O. Measurements and results: Right atrial pressure, pulmonary artery pressure, and wedge pressure were measured and cardiac output was determined by thermodilution. TR was graded from 0 to 3. Standard 2D echocardiographic and pulsed-wave images were obtained at each level of PEEP. PEEP was increased from 4 ± 3 to 17 ± 2 cm H₂O. Mean PAP increased from 27.7 ± 2.9 to 36.7 ± 3.5 mm Hg (p < 0.02) when PEEP was increased. Five patients had competent valves and two had mild TR at baseline. In six out of the seven, TR either developed or increased when PEEP was increased. Conclusions: Our study demonstrated the development of TR after the use of PEEP in patients with ALI and ARDS as a consequence of pulmonary hypertension and right ventricular overloading. Since TR may randomly affect cardiac output values and derived parameters, the assessment of cardiac performance by some techniques such as thermodilution should be used with caution. Received: 3 December 1996 Acepted: 5 May 1997     

Distribution of inhaled nitric oxide during sequential and continuous administration into the inspiratory limb of the ventilator

Objectives : The concentrations of nitric oxide (NO) in the ventilatory circuits and the patient's airways were compared between sequential (SQA) and continuous (CTA) administration during inspiratory limb delivery. Design: Prospective controlled study. Setting: 14-bed Surgical Intensive Care Unit of a teaching University hospital. Patients and participants: Eleven patients with acute lung injury on mechanical ventilation and two healthy volunteers. Interventions: A prototype NO delivery device (Opti-NO) and César ventilator were set up in order to deliver 1, 3 and 6 parts per million (ppm) of NO into the bellows of a lung model in SQA and CTA. Using identical ventilatory and Opti-NO settings, NO was administered to the patients with acute lung injury. Measurements and results: NO concentrations measured from the inspiratory limb [INSP-NO_Meas] and the trachea [TRACH-NO_Meas] using fast response chemiluminescence were compared between the lung model and the patients using controlled mechanical ventilation with a constant inspiratory flow. INSP-NO_Meas were stable during SQA and fluctuated widely during CTA (fluctuation at 6 ppm = 61 % in the lung model and 58 ± 3 % in patients). In patients, [TRACH-NO_Meas] fluctuated widely during both modes (fluctuation at 6 ppm = 55 ± 3 % during SQA and 54 ± 5 % during CTA). The NO flow requirement was significantly lower during SQA than during CTA (74 ± 0.5 vs 158 ± 2.2 ml.min^–1 to attain 6 ppm, p = 0.0001). INSP-NO_Meas were close to the values predicted using a classical formula only during SQA (bias = –0.1 ppm, precision = ± 1 ppm during SQA; bias = 2.93 ppm and precision = ± 3.54 ppm during CTA). During SQA, INSP-NO_Meas varied widely in healthy volunteers on pressure support ventilation. Conclusions: CTA did not provide homogenous mixing of NO with the tidal volume and resulted in fluctuating INSP-NO_Meas. In contrast, SQA delivered stable and predictable NO concentrations during controlled mechanical ventilation with a constant inspiratory flow and was economical compared to CTA. However, SQA did not provide stable and predictable NO concentrations during pressure support ventilation. Received: 5 May 1997 Accepted: 20 June 1997     

Intrapulmonary percussive ventilation in tracheostomized patients: a randomized controlled trial

Objective To investigate whether the addition of intrapulmonary percussive ventilation to the usual chest physiotherapy improves gas exchange and lung mechanics in tracheostomized patients.Design and setting Randomized multicenter trial in two weaning centers in northern Italy.Patients and participants 46 tracheostomized patients (age 70 ± 7 years, 28 men, arterial blood pH 7.436 ± 0.06, PaO₂/FIO₂ 238 ± 46) weaned from mechanical ventilation.Interventions Patients were assigned to two treatment groups performing chest physiotherapy (control), or percussive ventilation (IMP2 Breas, Sweden) 10 min twice/day in addition to chest physiotherapy (intervention).Measurements and results Arterial blood gases, PaO₂/FIO₂ ratio, and maximal expiratory pressure were assessed every 5th day for 15 day. Treatment complications that showed up in 1 month of follow-up were recorded. At 15 days the intervention group had a significantly better PaO₂/FIO₂ ratio and higher maximal expiratory pressure; after follow-up this group also had a lower incidence of pneumonia.Conclusions The addition of percussive ventilation to the usual chest physiotherapy regimen in tracheostomized patients improves gas exchange and expiratory muscle performance and reduces the incidence of pneumonia.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.This research was supported by the Italian Ministry of University and Research and Agenzia Italiana del Farmaco.     

Test of 20 similar intensive care ventilators in daily use conditions —evaluation of accuracy and performances

Infrequent control, aging of components, may compromise the accuracy of ICU ventilators. In order to assess the reliability of ventilators during their clinical use, we bench tested a group of 20 CPU₁ ventilators (Ohmeda) sampled at random in several ICU units. We found major leaks in 5 ventilators, attributable to the disposable tubings used in these systems. Mean error in expired tidal volume and corresponding standard deviation (precision) were greater than 100 ml in two. Positive end expiratory pressure measurement comprised a mean error higher than 2 cm H₂O in 40% of the ventilators tested. The valve opening pressure threshold was correlated to the inspiratory flow (r=0.81) contrary to the valve opening delay (average 138±40 ms). These two parameters did not correlate with the age of the ventilator. Our study addresses the need for periodic control of ventilator performance in order to minimize the risks of errors and malfunctions.     

Dynamic measurement of intrinsic PEEP does not represent the lowest intrinsic PEEP

Objective: Dynamic intrinsic PEEP (PEEPi-dyn) is the airway pressure required to overcome expiratory flow and is considered to represent the lowest regional PEEPi. However, there are few data to validate this assumption. We investigated if PEEPi-dyn represents the lowest PEEPi. Setting: The animal laboratory at the Osaka University Medical School. Measurements and results: We compared static PEEPi (PEEPi-stat) and PEEPi-dyn in healthy animals. Five adult white rabbits (2.77 ± 0.05 kg) were anesthetized, tracheostomized, and intubated with several different sizes of endotracheal tubes (ETT) (2.0, 2.5, 3.0, 3.5, or 4.0 mm i. d.). The animals were paralyzed and ventilated (Siemens Servo 900C). Baseline ventilator settings were at a rate of 50/min, inspiratory:expiratory (I:E) ratio of 2:1 or 4:1, and minute ventilation was manipulated to create 3 or 5 cm H₂O PEEPi-stat. PEEPi-stat was measured using the expiratory hold button of the ventilator. PEEPi-dyn showed large variations. In all ventilator settings, PEEPi-dyn was higher than PEEPi-stat (p < 0.001). The larger the ETT, the higher the PEEPi-dyn at an I:E ratio of 2:1 (p < 0.05). The higher the minute ventilation, the greater the difference between PEEPi-stat and PEEPi-dyn. The tidal volume and the difference showed a significant correlation (r ² = 0.514, p < 0.001). Conclusions: The value of PEEPi-dyn was dependent on ventilatory settings, and PEEPi-dyn does not necessarily represent the lowest regional PEEPi within the lungs. Received: 27 April 1998 Final revision received: 18 November 1998 Accepted: 20 November 1998     

Ventilator Y-Piece Pressure Compared with Intratracheal Airway Pressure in Healthy Intubated Children

Objective. Compare airway pressure measurements at the ventilator Y-piece of the breathing circuit (P _Y ) to intratracheal pressure measured at the distal end (P _T ) of the endotracheal tube (ETT) during mechanical ventilation and spontaneous breathing of intubated children. Methods. Thirty children (age range 29 days to 5 years) receiving general anesthesia were intubated with an ETT incorporating a lumen embedded in its sidewall that opened at the distal end to measure P _T . Peak inflation pressure (PIP) was measured at P _Y and P _T during positive pressure ventilation. Just before extubation, all measurements were repeated and imposed resistive work of breathing (WOBi) was calculated at both sites while breathing spontaneously. Results. Average PIP was approximately 25% greater at P _Y (19.7 ± 3.4 cm H₂O) vs. P _T (15.0 ± 2.9 cm H₂O), p < 0.01. During spontaneous inhalation P _T was 59% lower ({bond}8.5 ± 4.0 cm H₂O) vs. P _Y ({bond}3.5 ± 2.0 cm H₂O), p < 0.01. WOBi measured at P _Y (0.10 ± 0.02 Joule/L) was 86% less than WOBi measured at P _T (0.70 ± 0.40 Joule/L), p < 0.01. Conclusions. In healthy children P _Y significantly overestimates PIP in the trachea during positive pressure ventilation and underestimates the intratracheal airway pressure during spontaneous inhalation. During positive pressure ventilation P _T better assesses the pressure generated in the airways and lungs compared to P _Y because P _T also includes the difference in airway pressure across the ETT tube due to resistance. During spontaneous inhalation, P _T reflects the series resistance of the ETT and ventilator circuit, while P _Y reflects only the resistance of the ventilator circuit, accounting for the smaller decreases in pressure. Additionally, P _Y underestimates the total WOBi load on the respiratory muscles. Thus, P _T is a more accurate reflection of pulmonary airway pressures than P _Y and suggests that it should be incorporated into ventilator systems to more accurately trigger the ventilator and to reduce work of breathing.     

Additional inspiratory work of breathing imposed by tracheostomy tubes and non-ideal ventilator properties in critically ill patients

Objective: To determine the tracheostomy tube-related additional work of breathing (WOB_add) in critically ill patients and to show its reduction by different ventilatory modes. Design: Prospective, clinical study. Setting: Medical ICU of a university teaching hospital. Intervention: Standard tracheostomy due to prolonged respiratory failure. Measurements and results: Ten tracheostomized, spontaneously breathing patients were investigated. As the tube resistance depends on gas flow, patients were subdivided according to minute ventilation into a low ventilation group ( = 10 l/min; n = 5) and a high ventilation group ( > 10 l/min; n = 5). The WOB_add due to tube resistance and non-ideal ventilator properties was calculated on the basis of the tracheal pressure measured. Ventilatory modes investigated were: continuous positive airway pressure (CPAP), inspiratory pressure support (IPS) of 5, 10, and 15 cm H₂O above PEEP, and automatic tube compensation (ATC). In the low ventilation group, WOB_add during CPAP was 0.382 ± 0.106 J/l. It was reduced to below 15 % of that value by ATC or IPS more than 5 cm H₂O. In the high ventilation group WOB_add during CPAP increased to 0.908 ± 0.142 J/l. In this group, however, only ATC was able to reduce WOB_add below 15 % of the value observed in the CPAP mode. Conclusions: The results indicate that, depending on respiratory flow rate, (1) tracheostomy tubes can cause a considerable amount of WOB_add, and (2) ATC, in contrast to IPS, is a suitable mode to compensate for WOB_add at any ventilatory effort of the patient. Received: 12 August 1998 Final revision received: 22 February 1999 Accepted: 24 February 1999     

A randomized comparison of the Ambu AuraGain versus the LMA supreme in patients undergoing gynaecologic laparoscopic surgery

Second generation supraglottic airway devices providing high seal airway pressures are suitable for patients undergoing gynecologic laparoscopy. We compared the seal pressure achieved by the new Ambu AuraGain? versus LMA Supreme? following pneumoperitoneum in the Trendelenburg position. Sixty female patients were randomly allocated to ventilation with either the AuraGain or the Supreme. A target-controlled system was used to administer total intravenous anesthesia. Intracuff pressure was maintained below 60 cm H₂O. The following parameters were registered: Time, number of attempts and manoeuvres required for insertion; seal pressure and peak inspiratory pressure at four time points; ease of gastric tube insertion, flexible scope view, complications and postoperative morbidity. Both devices were quick and easily inserted, although the Supreme required less rotation manoeuvres (16 in AuraGain vs. 6 in LMA Supreme; p = 0.01). The AuraGain achieved higher seal pressures (34 ± 5 in AuraGain vs. 29 ± 5 in LMA Supreme; p = 0.0002). Following pneumoperitoneum in head-down position, peak airway pressure increased 9 ± 3 cm H₂O in both groups, exceeding seal pressure in 3 patients in the Supreme group (p = 0.06). The vocal cords were seen through all AuraGain and 90% of the Supreme devices; epiglottis was often visible inside the tube (68%). No differences were found in the incidence of traces of blood on the mask or postoperative symptoms. Both devices allowed effective ventilation in patients undergoing gynaecologic laparoscopic surgery with a low rate of complications. The Ambu AuraGain provided higher seal pressures and a clear view of glottic inlet in all patients offering the possibility to guide direct tracheal intubation if required.     

Non-invasive ventilation in chronic obstructive pulmonary disease patients: helmet versus facial mask

Rationale The helmet is a new interface with the potential of increasing the success rate of non-invasive ventilation by improving tolerance. Objectives To perform a physiological comparison between the helmet and the conventional facial mask in delivering non-invasive ventilation in hypercapnic patients with chronic obstructive pulmonary disease. Methods Prospective, controlled, randomized study with cross-over design. In 10 patients we evaluated gas exchange, inspiratory effort, patient–ventilator synchrony and patient tolerance after 30 min of non-invasive ventilation delivered either by helmet or facial mask; both trials were preceded by periods of spontaneous unassisted breathing. Measurements Arterial blood gases, inspiratory effort, duration of diaphragm contraction and ventilator assistance, effort-to-support delays (at the beginning and at the end of inspiration), number of ineffective efforts, and patient comfort. Main results Non-invasive ventilation improved gas exchange (p< 0.05) and inspiratory effort (p< 0.01) with both interfaces. The helmet, however, was less efficient than the mask in reducing inspiratory effort (p< 0.05) and worsened the patient–ventilator synchrony, as indicated by the longer delays to trigger on (p< 0.05) and cycle off (p< 0.05) the mechanical assistance and by the number of ineffective efforts (p< 0.005). Patient comfort was no different with the two interfaces. Conclusions Helmet and facial mask were equally tolerated and both were effective in ameliorating gas exchange and decreasing inspiratory effort. The helmet, however, was less efficient in decreasing inspiratory effort and worsened the patient–ventilator interaction. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. Financial support: None     

Changes in Arterial Oxygen Tension Correlate with Changes in End-expiratory Carbon Monoxide Level

Objective Carbon monoxide (CO) and oxygen compete for haemoglobin binding sites. While the effects of increased inspiratory oxygen fractions on exhaled carbon monoxide concentrations have been studied previously, the relationships between intravascular oxygen tension, blood carboxyhaemoglobin levels and expiratory CO concentrations remain unclear. We therefore studied the effects of increases in arterial oxygen tension as crucial determinant for the displacement of carbon monoxide from its haemoglobin bond during lung passage. Methods Measurements of end-expiratory CO concentrations (eCO), arterial oxygen tensions and carboxyhaemoglobin concentrations were performed in 19 patients while breathing air and oxygen. Results With increasing PaO₂ (from 11.5 ± 1.9 to 35.2 ± 10.3 kPa) end-expiratory CO concentrations increased from 8.6 ± 4.9 to 16.7 ± 9.4 ppm, p < 0.001, with a mean increase of 0.36 ppm CO per kPa increase in PaO₂ (ΔeCO [ppm] = 0.36 *␣ΔPaO₂ [kPa]). Increases of arterial oxygen tension correlated with increases of end-expiratory CO concentration (r² = 0.33). Arterial carboxyhaemoglobin concentrations decreased from 1.06 ± 0.37 during air breathing to 0.92 ± 0.35 % after 5 minutes of oxygen inhalation (p < 0.001). Conclusions Oxygen-induced increases in exhaled CO correlate with increases in arterial oxygen tensions. Furthermore, oxygen inhalation reduces carboxyhaemoglobin levels, supporting the concept of accelerated CO elimination by oxygen via the lungs. Patrick Schober, M.D., Melanie Kalmanowicz, Lothar A Schwarte, M.D., PhD, Joerg Weimann, Professor, M.D. and Stephan A Loer, Professor, M.D., PhD, M.Sc. Changes in arterial oxygen tension correlate with changes in end-expiratory carbon monoxide level.     

Real time noninvasive estimation of work of breathing using facemask leak-corrected tidal volume during noninvasive pressure support: validation study

We describe a real time, noninvasive method of estimating work of breathing (esophageal balloon not required) during noninvasive pressure support (PS) that uses an artificial neural network (ANN) combined with a leak correction (LC) algorithm, programmed to ignore asynchronous breaths, that corrects for differences in inhaled and exhaled tidal volume (V_T) from facemask leaks (WOB_ANN,LC/min). Validation studies of WOB_ANN,LC/min were performed. Using a dedicated and popular noninvasive ventilation ventilator (V60, Philips), in vitro studies using PS (5 and 10 cm H₂O) at various inspiratory flow rate demands were simulated with a lung model. WOB_ANN,LC/min was compared with the actual work of breathing, determined under conditions of no facemask leaks and estimated using an ANN (WOB_ANN/min). Using the same ventilator, an in vivo study of healthy adults (n = 8) receiving combinations of PS (3–10 cm H₂O) and expiratory positive airway pressure was done. WOB_ANN,LC/min was compared with physiologic work of breathing/min (WOB_PHYS/min), determined from changes in esophageal pressure and V_T applied to a Campbell diagram. For the in vitro studies, WOB_ANN,LC/min and WOB_ANN/min ranged from 2.4 to 11.9 J/min and there was an excellent relationship between WOB_ANN,LC/breath and WOB_ANN/breath, r = 0.99, r² = 0.98 (p < 0.01). There were essentially no differences between WOB_ANN,LC/min and WOB_ANN/min. For the in vivo study, WOB_ANN,LC/min and WOB_PHYS/min ranged from 3 to 12 J/min and there was an excellent relationship between WOB_ANN,LC/breath and WOB_PHYS/breath, r = 0.93, r² = 0.86 (p < 0.01). An ANN combined with a facemask LC algorithm provides noninvasive and valid estimates of work of breathing during noninvasive PS. WOB_ANN,LC/min, automatically and continuously estimated, may be useful for assessing inspiratory muscle loads and guiding noninvasive PS settings as in a decision support system to appropriately unload inspiratory muscles.