Servo 900C Research Articles

Sevoflurane Therapy for Severe Refractory Bronchospasm in Children.

To describe the effect of inhaled sevoflurane in the treatment of severe refractory bronchospasm in children. Retrospective case series. Two PICUs of tertiary general university hospitals in Spain. Ten patients ranging from 5 months to 14 years old with severe bronchospasm and acute respiratory failure requiring tracheal intubation and mechanical ventilation and treated with sevoflurane from 2008 to 2015. Inhaled sevoflurane therapy was initiated after failure of conventional medical management and mechanical ventilation. In two patients, sevoflurane was administered through a Servo 900C ventilator (Maquet, Bridgewater, NJ) equipped with a vaporizer and in the other eight patients via the Anesthetic Conserving Device (AnaConDa; Sedana medical, Uppsala, Sweden) with a critical care ventilator. Inhaled sevoflurane resulted in statistically significant decreases of PaCO2 of 34.2 torr (95% CI, 8.3-60), peak inspiratory pressure of 14.3 cm H2O (95% CI, 8.6-19.9), and improvement in pH of 0.17 (0.346-0.002) within 6 hours of administration. Only one patient presented hypotension responsive to volume administration at the beginning of the treatment. All patients could be extubated within a median time of 120 hours (interquartile range, 46-216). Inhaled sevoflurane therapy decreases the levels of PaCO2 and peak inspiratory pressure values, and it may be considered as a rescue therapy in patients with life-threatening bronchospasm refractory to conventional therapy.

A porcine model for initial surge mechanical ventilator assessment and evaluation of two limited-function ventilators*

To adapt an animal model of acute lung injury for use as a standard protocol for a screening initial evaluation of limited function, or "surge," ventilators for use in mass casualty scenarios. Prospective, experimental animal study. University research laboratory. Twelve adult pigs. Twelve spontaneously breathing pigs (six in each group) were subjected to acute lung injury/acute respiratory distress syndrome via pulmonary artery infusion of oleic acid. After development of respiratory failure, animals were mechanically ventilated with a limited-function ventilator (simplified automatic ventilator [SAVe] I or II; Automedx, Germantown, MD) for 1 hr or until the ventilator could not support the animal. The limited-function ventilator was then exchanged for a full-function ventilator (Servo 900C; Siemens-Elema, Solna, Sweden). Reliable and reproducible levels of acute lung injury/acute respiratory distress syndrome were induced. The SAVe I was unable to adequately oxygenate five animals with Pao2 (52.0±11.1 torr) compared to the Servo (106.0±25.6 torr; p=.002). The SAVe II was able to oxygenate and ventilate all six animals for 1 hr with no difference in Pao2 (141.8±169.3 torr) compared to the Servo (158.3±167.7 torr). We describe a novel in vivo model of acute lung injury/acute respiratory distress syndrome that can be used to initially screen limited-function ventilators considered for mass respiratory failure stockpiles and that is intended to be combined with additional studies to definitively assess appropriateness for mass respiratory failure. Specifically, during this study we demonstrate that the SAVe I ventilator is unable to provide sufficient gas exchange, whereas the SAVe II, with several more functions, was able to support the same level of hypoxemic respiratory failure secondary to acute lung injury/acute respiratory distress syndrome for 1 hr.

No explicit memory after skin incision without anesthetic except for remifentanil infusion

To the Editor: Awareness and memory during general anesthesia is a serious problem. We experienced no explicit memory in a patient who was accidentally not administered anesthetic during skin incision before abdominal surgery. During that time, remifentanil alone was infused continuously. A 76-year-old woman, height 156.8 cm, weight 52 kg, was scheduled for peritoneal metastatic tumor resection. She had no complications or past history, except for lower anterior resection of the rectum with laparoscopic surgery 24 months prior. No premedication was administered. Anesthesia was induced with 200 mg thiopental and continuous infusion of remifentanil at the rate of 0.5 lg/kg/ min. She underwent tracheal intubation with the aid of 7 mg of vecuronium. The ventilation was controlled with 35% oxygen in air. After the induction of anesthesia, we planned to provide inhaled 3% sevoflurane during mask ventilation and 1% after tracheal intubation. We used the sevoflurane vaporizer 953 for servo 900C ventilator (MAQUET Critical Care AB, Solna, Sweden). This vaporizer requires activation of another switch in addition to adjusting the concentration dial to initiate sevoflurane inhalation (Fig. 1). We inadvertently forgot to activate the vaporizer switch to the ‘‘on’’ position. Accordingly, no sevoflurane was inhaled. After intubation, we decreased the rate of remifentanil infusion to 0.25 lg/kg/min during surgical-site sterilization and draping. Just before skin incision, we increased the rate of remifentanil infusion to 0.5 lg/kg/min. Twenty-four minutes after the administration of thiopental, skin incision was performed as usual. There was no apparent change of blood pressure or heart rate. The laparotomy was then continued, and there were no apparent changes in her vital signs. About 6 min after the skin incision, we noticed that the end-tidal concentration of sevoflurane on the monitor (S5, GE Healthcare Japan, Tokyo) was zero, and activated the vaporizer switch. We initially administered 3% sevoflurane, followed by 1–1.5% sevoflurane with 0.1–0.5 lg/kg/min of remifentanil. No other sedatives were administered. The operation was completed uneventfully with a total operation time of 1 h 39 min. The emergence from anesthesia was uneventful, with a total duration of anesthesia of 2 h 29 min. We asked the patient about her memories of the operation later on that same day and the next day. She had no explicit memory during the operation and expressed her thanks for a good anesthetic experience. The hypnotic that we administered to this patient was 200 mg of thiopental alone. Clinically, patients awaken from a single dose of thiopental about 5–10 min after administration because the drug levels in the brain decrease as a result of redistribution [1]. Accordingly, about 15 min after the end of the hypnotic action of thiopental, the patient was sedated only with remifentanil of 0.25–0.5 lg/kg/min. During the procedure, we had closed the eyelids of the patient using a sticking tape. The ears of the patient were free, but the sound in the operating room was minimal. Accordingly, it is possible that the patient was not aware of any stimuli except for the surgical procedure. Remifentanil has some sedative action and has been used for analgesia-based sedation [2, 3]. No implicit or explicit memory was found when a high concentration of remifentanil combined with low hypnotic concentration of propofol was maintained with high bispectral index (BIS) values [4]. Remifentanil 0.5 lg/kg/min might have been M. Yasuda R. Kubota T. Adachi (&) Department of Anesthesiology, Kitano Hospital, The Tazukekofukai Medical Research Institute, 2-4-20 Ohgimachi, Kita-ku, Osaka 530-8480, Japan e-mail: t-adachi@kitano-hp.or.jp

Halothane, an Effective Infrequently Used Drug, in the Treatment of Pediatric Status Asthmaticus: A Case Report

Asthma is the most common chronic disease of childhood. Despite a better understanding of the disease process and its management, status asthmaticus continues to be a life-threatening event. The use of volatile inhaled anesthetics is infrequently reported as adjunctive therapy to conventional treatment of this condition. We report the use of halothane in a mechanically ventilated pediatric patient with life-threatening status asthmaticus who was admitted to the pediatric intensive care unit (PICU) after failing to respond to standard medical therapy and noninvasive positive pressure ventilation. A 12-year-old African American male was seen in the emergency department and treated with intravenous corticosteroids, beta-agonist therapy. He deteriorated rapidly and required endotracheal intubation and mechanical ventilation. Two hours later, the patient developed an acute, severe respiratory acidosis (pH = 6.97, PaCO2 = 171, PaO2 = 162, BE = 1.7). Halothane was started at 2% by using the Siemens Servo 900C anesthesia ventilator. Improvement in both arterial blood gases and exhaled tidal volume were noted 30 minutes after initiation of the anesthetic gas. The patient remained on halothane for a total of 36 hours. No adverse effects associated with the use of halothane were noted. The patient was extubated to BiPAP 16/6, FiO2 = 0.30 at 68 hours and was discharged home 5 days later.

Pressure-controlled inverse ratio ventilation after cardiac surgery

Background and objective Pressure-controlled inverse ratio ventilation was compared with controlled mechanical ventilation in patients after cardiac surgery. Methods Ten patients were ventilated after sternal closure using a Siemens Servo 900C ventilator to a target end-tidal PCO2 of 4.0 kPa. They were randomized to receive controlled mechanical ventilation or pressure-controlled inverse ratio ventilation. CO2-based data were recorded on a laptop personal computer, which together with arterial PCO2 permitted measurement of the respiratory dead space. Once measurements were complete the ventilator was switched to the other mode and new measurements taken. Results PaCO2 and CO2 were virtually the same in both modes. Peak airway pressure (17.2 ± 2.7 vs. 20.8 ± 2.5 cmH2O, P < 0.01) and minute ventilation (4.9 ± 1.1 vs. 5.3 ± 1.1 cmH2O, P < 0.01) were less during pressure-controlled inverse ratio ventilation. Physiological dead space fraction (0.39 ± 0.06 vs. 0.51 ± 0.05, P < 0.001), airway dead space (56 ± 15 vs. 81 ± 15 mL, P < 0.001) and alveolar dead space fraction (0.25 ± 0.07 vs. 0.31 ± 0.09, P < 0.01) were all less during pressure-controlled inverse ratio ventilation. There were no differences in heart rate or mean arterial pressure. Conclusions The prolonged inspiratory period and pressure-controlled flow pattern of pressure-controlled inverse ratio ventilation reduce the alveolar and airway dead spaces, and give lower peak airway pressures, compared with conventional ventilation, in cardiac surgical patients.

Warning! Suctioning. A lung model evaluation of closed suctioning systems.

Closed system suctioning, CSS, has been advocated to avoid alveolar collapse. However, ventilator manufacturers indicate that extreme negative pressure levels can be obtained during closed system suctioning, impeding the performance of the ventilator. Suctioning with a 12 or 14 Fr catheter with a vacuum level of -50 kPa was either performed with an open technology or a CSS, where the catheter is introduced through a tight-fitting connection through the endotracheal tube, EYT. The lung model was ventilated with a Servo 900C or 300 ventilator with an I:E ratio of 1:2, 1:1 and 2:1 and extrinsic positive end-expiratory pressure (PEEP) at 0 or 10 cm H20. Respiratory volumes and alveolar pressure were measured at the lung model alveolus. The initial suctioning flow was >40 l/min with a 14 Fr catheter. When inserting the catheter through a no. 7 ETT, PEEP rose from 11 to 23 cm H2O during volume control ventilation with an I:E ratio 1:1. During suctioning the alveolar pressure fell to 10 cm H2O below the set PEEP level. CSS during pressure control ventilation had fewer effects. Low tidal volumes, inverse I:E ratio and secretions in the tube resulted in pressures down to -92 cm H2O. CSS should not be used in volume control ventilation due to risk of high intrinsic PEEP levels at insertion of the catheter and extreme negative pressures during suctioning. Pressure control ventilation produces less intrinsic PEEP effect. The continuous positive airway pressure (CPAP) mode offers the least intrinsic PEEP during insertion of the catheter and least sub-atmospheric pressure during suctioning.

Leak compensation in positive pressure ventilators: a lung model study

Leak compensating abilities of six different positive pressure ventilators commonly used to deliver noninvasive positive pressure ventilation, including the bilevel positive airway pressure (BiPAP) S/T-D and Quantum (Respironics Inc, Murrysville, PA, USA), 335 and O'NYX (Mallinckrodt Inc, St Louis, MO, USA), PLV 102 (Respironics), and Siemens Servo 900C (Siemens Inc, Danvers, MA, USA). Using a test lung model, compensatory capabilities of the ventilators were tested for smaller and larger leaks using the assist/control or timed modes. Back-up rate was 20 min(-1), inspiratory pressure was 18 cmH2O, and expiratory pressure was 5 cmH2O. It was found that even in the absence of air leaking, delivered tidal volume differed substantially between the ventilators during use of pressure-targeted modes, depending on inspiratory flows, inaccuracies in set versus delivered pressures, and inspiratory duration. Also during pressure-targeted ventilation, increasing the tI/ttot up to, but not beyond, 0.5 improved compensation by lengthening inspiratory duration, whereas use of a sensitive flow trigger setting tended to cause autocycling during leaking, interfering with compensation. Leaking interfered with cycling of the BiPAP S/T, inverting the I:E ratio, shortening expiratory time, and reducing delivered tidal volume. Volume-targeted modes achieved limited compensation for small air leaks, but compensated poorly for large leaks. To conclude, leak-compensating capabilities differ markedly between ventilators but pressure-targeted ventilators are preferred for noninvasive positive pressure ventilation in patients with substantial air leaking. Adequate inspiratory flows and durations should be used, triggering sensitivity should be adjusted to prevent autocycling, and a mechanism should be available to limit inspiratory time and avoid I:E ratio inversion.

Pressure Control Ventilation: Three Anesthesia Ventilators Compared Using an Infant Lung Model

We compared three ventilators—Servo 900C (Siemens Medical Systems, Danvers, MA), Aestiva 3000 (Datex-Ohmeda, Madison, WI), and NAD 6000 (North American Dräger, Telford, PA)—set to deliver pressure control ventilation using an infant test lung model. Ventilator settings were selected to test “near-maximum” settings that would be used for a neonatal patient (peak inspiratory pressure [PIP] 30 cm H2O) or older child (PIP 60 cm H2O). When adjusted for set inspiratory pressure and compliance, the average tidal volume (Vt) produced by the NAD 6000 was 5.8 mL less than the Servo 900C (P = 0.103), and the average Vt produced by the Aestiva 3000 was 18.9 mL less than the Servo 900C (P < 0.001). The Servo 900C generated increased peak pressures, tending to overshoot the set maximum inflating pressures, especially during rapid respiratory rates with decreased inspiratory times. The Aestiva 3000 did not achieve the set PIP during testing conditions of decreased inspiratory times, and the NAD 6000 was not greatly affected by changes in inspiratory time. All three ventilators measured expiratory Vt to be larger than the actual Vt delivered to the lung; however, the NAD 6000 was more accurate. Implications There are differences in performance of ventilators when set to deliver pressure control ventilation to an infant test lung model.

Accuracy of an indirect calorimeter for mechanically ventilated infants and children: the influence of low rates of gas exchange and varying FIO2.

To test the accuracy and validity of the Deltatrac II MBM-200 metabolic monitor for use in mechanically ventilated infants and children in the pediatric intensive care unit. Laboratory validation of an indirect calorimeter with a ventilated lung model. The influence of low tidal volumes and low levels of oxygen consumption (V(O2)) and carbon dioxide production (V(CO2)) in combination with different levels of inspired oxygen concentrations (F(IO2)) was investigated. University research laboratory. Low tidal volumes were provided with two intermittent flow types of ventilators, a Servo 300 and a Servo 900C. A butane flame with a V(O2) approximating 20 mL/min and 40 mL/min was ventilated. To investigate the effect of different levels of F(IO2) on the accuracy of V(O2), V(CO2), and respiratory quotient (RQ), measurements were performed at F(IO2) target values of 0.25, 0.40, and 0.60. No significant differences were found between the ventilators regarding V(O2), V(CO2), and RQ measurements. The mean deviation of V(O2) increased significantly with increasing F(IO2) to -7.98% with a V(O2) of 21.0 mL/min and to -8.46% with a V(O2) of 38.9 mL/min (F(IO2), 0.558) with a variability (2 SD) of +/- 4.86% and +/- 6.82%, respectively. The mean deviation and variability of V(CO2) in all tests remained within 8%. The mean deviation of RQ increased significantly with increasing F(IO2) to 5.5% with a V(O2) of 21.0 mL/min and to 5.69% with a V(O2) of 38.9 mL/min (F(IO2), 0.558) with a variability (2 SD) of +/- 5.62% and +/- 5.76%, respectively. The minute to minute delivered F(IO2) fluctuated significantly when increasing the level of F(IO2). The Deltatrac II MBM-200 metabolic monitor appears accurate for low levels of V(O2) and V(CO2) during mechanical ventilation with F(IO2) levels up to 0.390. With increasing F(IO2) to 0.558, the increase in deviation of V(O2) for single measurements can be of clinical relevance for mechanically ventilated infants and children. The increased fluctuation of delivered F(IO2) on higher levels of F(IO2) is likely the cause of the inaccuracy.

Second gas effect of N2O on oxygen uptake.

The concept of the second gas effect is well known, however, there have been no studies that showed the relationship between alveolar oxygen concentration and arterial oxygen tension (PaO2) after the inhalation of nitrous oxide (N2O) in humans. The purpose of this study was to examine the changes in both end-tidal oxygen fraction (F(ET)O2) and PaO2 after N2O inhalation in patients under general anesthesia. Fifteen patients scheduled for elective orthopedic surgery were enrolled in this study. Anesthesia was maintained with the continuous infusion of propofol and with nitrogen (N2) and oxygen (O2) (6 L x min(-1), F1O2, 0.33). In all patients, the lungs were ventilated with a Servo 900C ventilator equipped with a gas mixer for O2, N2O, and N2. After obtaining baseline data, N2 was replaced with N2O maintaining FIO2 constant at 0.33. The changes in fractional concentration of O2, N2O, and N2 were continuously measured using mass spectrometer in a breath-by-breath basis. PaO2 and hemodynamic data were obtained at 1, 5, 10, 30 and 60 min after the start of N2O inhalation. Five minutes after N2O inhalation, F(ET)O2 increased from 0.27+/-0.01 to 0.31+/-0.02 (P<0.01) and PaO2 increased from 172.0+/-22.5 mm Hg to 201.0+/-10.3 mm Hg (P<0.01). These effects produced by N2O were observed for 30 min. These results confirm the concept of second gas effect of N2O on oxygen uptake in humans and provide evidence that the PaO2 increase correlated with the increase in F(ET)O2 after N2O inhalation.

Improved flow and pressure capabilities of the Datex-Ohmeda SmartVent anesthesia ventilator

Study Objective: To compare the flow and pressure capabilities of the Datex-Ohmeda SmartVent (Ohmeda 7900, Datex-Ohmeda, Madison, WI) to previous Ohmeda (7810 and 7000, Datex-Ohmeda, Madison, WI) anesthesia ventilators. To determine airway pressure and minute ventilation thresholds for intraoperative use of a critical care ventilator. Design: Three anesthesia ventilators and one critical care ventilator (Siemens Servo 900C, Siemens, Solna, Sweden) were studied in a lung model. Retrospective medical record review. Setting: Research Laboratory and Critical Care Unit of a Level I Trauma Center. Patients: 145 mechanically ventilated patients treated for acute respiratory failure who underwent 200 surgical procedures. Interventions: The effect of increasing pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum minute ventilation was measured at low compliance (10–30 mL/cm H 2O), positive end-expiratory pressure (PEEP) (0–20 cm H 2O), and increased airway resistance (∼19 and ∼36 cm H 2O/L/sec) in a mechanical lung model. Measurements and Main Results: Flow, volume, and pressure were measured with a pulmonary mechanics monitor (BICORE CP-100, Thermo Respiratory Group, Yorba Linda, CA). Preoperative peak airway pressure and minute ventilation (V̇ E) were extracted from the medical record. Mean inspiratory flow declined with increasing pressure in all anesthesia ventilators. The SmartVent and the 7810 produced greater mean inspiratory flow than did the 7000 ventilator. As compliance progressively decreased, the Siemens, the SmartVent, and the 7810 ventilators maintained V̇ E compared to the 7000 ventilator. The Siemens and the SmartVent maintained V̇ E with PEEP, compared to the 7810 and 7000 ventilators. During increased airway resistance, maximal V̇ E was lower for all ventilators. The SmartVent met the ventilation requirements in 90% of the patients compared to 67% of patients with the 7000 ventilator. Conclusion: The improved pressure and flow capabilities of the SmartVent increase the threshold for using a critical care ventilator intraoperatively to a peak airway pressure >65 cm H 2O and/or V̇ E >18 L/min.

Comparison of NAD 6000 and Servo 900C Ventilators in an Infant Lung Model

Comparison of NAD 6000 and Servo 900C Ventilators in an Infant Lung Model

Reliability of Noninvasive Measurement of Cardiac Output Using Partial CO2 Rebreathing: A Comparison with Thermodilution Method

Background: A noninvasive method for estimating cardiac output was tested in dogs. The technique is based on a differential CO₂ Fick equation applied during normal ventilation and 50 seconds of partial rebreathing using additional dead space. We compared the cardiac output measured by the CO₂ rebreathing method vs. the thermodilution technique. Methods: Seven mongrel-dogs (24.6 ± 0.4 kg) were studied, anesthesia was induced and maintained with a pentobarbital 25 mg/kg IV bolus injection followed by an infusion of 5 mg/kg/h. Mechanical ventilation was accomplished with a Servo 900C ventilator with FiO₂ 0.6 to maintain normocarbia. A fiberoptic pulmonary artery catheter was introduced via an external jugular vein for continuous monitoring of the cardiac output by the thermodilution method. Also cardiac output was measured by using partial CO₂ rebreathing method. A continuous infusion of 0.5% bupivacaine was started at 0.5 mg/kg/min via the venous infusion port of the pulmonary catheter. Bupivacaine was infused continuously until mean arterial pressure decreased to 60 mmHg or less for at least 5 seconds. Results: The total measured cardiac outputs (n = 72) were distributed over the range of 1.03 7.72 L/min by thermodilution method and 1.6 7.3 L/min by CO₂ rebreathing. The correlation coefficients between both cardiac outputs was 0.6, the mean difference was 0.27 ± 0.81 L/min. Conclusions: The cardiac output measured by CO₂ rebreathing method was well correlated with cardiac output by thermodilution method.

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

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. The animal laboratory at the Osaka University Medical School. 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 (r2 = 0.514, p<0.001). The value of PEEPi-dyn was dependent on ventilatory settings, and PEEPi-dyn does not necessarily represent the lowest regional PEEPi within the lungs.

Lung volume and oxygenation changes with a closed suction system (CSS) in patients undergoing volume controlled ventilation (VCV)

We wished to measure changes in lung volume (Δ LV), airway pressures, and oxygenation during tracheal suctioning performed with a CSS and with an open suction system (OSS). We enrolled 7 adult patients, sedated and paralyzed, VCV ventilated by a SERVO 900C ventilator (Siemens, Sweden) with PEEP ≥ 5 cmH2O and FiO2 ≥ 0.4. Keeping all remaining ventilarory settings unchanged, we set trigger sensitivity at -2 cmH2O, inspiratory time at 25%, inspiratory pause at 10%. We performed four suctioning manouvers at 20 min intervals using alternatively a CSS and an OSS. With both systems, we used 12 F size catheters. We performed no pre-oxygenation manouvers. Suction was applied for 20 s at a pressure of 100 cmH2O. We continuously recorded signals of respiratory inductance pletismography (RIP. Respitrace Plus. NIMS, FL), arterial oxygen saturation (O2Sat) by pulse oxymetry, and airway pressures. We obtained Δ LV as the change in the RIP signal measured during VCV and during suction. We measured Respiratory Rate (RR), peak inspiratory pressure (PIP), positive end-expiratory pressure (PEEP), and mean airway pressure(MAP) during VCV and during suction with the CSS.

Implementation of a respiratory drive monitor on a Servo Ventilator.

To design and evaluate a clinical monitor of respiratory drive (P0.1) and other respiratory variables in a simple way, using a commercial ventilator. Nine healthy males were studied as they were breathing spontaneously in a Servo 900C Ventilator, at rest and during light exercise (50 W). The ventilator was slightly modified to improve its mechanical performance during spontaneous breathing, and was used as a measuring instrument. All the relevant information was retrieved, calculated and monitored by a PC. Respiratory drive was assessed as occlusion pressures from the inspiratory airway pressure signal. The equipment was compared with a two-way non-rebreathing laboratory system. Furthermore, negative and positive inspiratory pressures were applied from the ventilator, to study respiratory responses to mechanical loads. At rest, the ventilator introduced a minor influence on inspiratory time and P0.1, but not in ventilation, tidal volume, expiratory duration and respiratory frequency. During exercise, the influence was more evident. This effect could also be noticed in the coefficients of variation. The responses to mechanical loads were easily recorded and can be used as a simple test of central load-compensating mechanisms. CONCLUSIONS. The ventilator, with limitations, may be an alternative to conventional techniques, especially in clinical studies of the central inspiratory activity with and without respiratory loading.

Delivery of Inhaled Nitric Oxide Using the Ohmeda INOvent Delivery System

We evaluated the Ohmeda INOvent Nitric Oxide Delivery System, which uses an inspiratory flow sensor to inject a synchronized and proportional nitric oxide (NO) flow into the mechanical ventilator circuit. This system should deliver a constant NO concentration independent of ventilator mode, minute ventilation, fraction of inspired oxygen, or ventilator brand. It should also minimize nitrogen dioxide (NO2) formation. NO delivery by the INOvent and a premixing NO delivery system were compared using two ventilators (Puritan-Bennett 7200 and Servo 900C). NO concentration was measured within the trachea of an attached lung model using a fast-response chemiluminescence NO analyzer. NO concentration was also measured in the inspiratory limb using the electrochemical analyzer of the INOvent. For three NO concentrations (2, 5, and 20 ppm), the ventilators were set for constant flow volume control ventilation, pressure control ventilation, and spontaneous breathing with pressure support ventilation or synchronized intermittent mandatory ventilation. Different tidal volumes (300, 500, 750, and 1,000 mL) and inspiratory times (1 and 2 s) were evaluated. NO2 formation for both ventilators and delivery systems were evaluated at 20 ppm and 95% O2-. Regardless of ventilatory pattern, both systems delivered a constant NO concentration. The error between the target and the delivered NO dose for the INOvent was -1.3+/-3.6% with the Puritan-Bennett 7200 and -3.9+/-4.3% with the Servo 900C. For the premixing system, the error was -5.5+/-4.8% with the Puritan-Bennett 7200 and -6.7+/-6.2% with the Servo 900C. NO2 concentrations were 0.5+/-0.1 ppm during NO delivery by the INOvent, 5.8+/-1.6 ppm when NO was premixed with air, 0.3+/-0.1 ppm when NO was premixed with N2. The INOvent provides a constant NO concentration independent of the ventilatory pattern, and NO2 formation is minimal.

Comparison of Gas Exchange Parmeters between Same Volume of N2-02 and Heliox Inhalation

BACKGROUND: Heliox is known to decrease PaCO2 in patients with increased airway resistance by increasing minute ventilation and reducing work of breathing(WOB). Besides these effect, heliox is expected to decrease functional anatomic dead space owing to improvement of peak expiratory flow rate(PEFR) and enhancement of gas distribution. We investigated whether heliox can decrease PaCO2 even at the same minute ventilation(VE) and WOB with N2-02 to speculate the effect of the heliox on the anatomic dead space. MATERIAL AND METHOD: The subjects were 8 mechanically ventilated patients with asthma or upper airway obstruction(M : F= 5 : 3, 68+/-10years) who were under neuromuscular paralysis. The study was consisted of three 15-minutes phases: basal N2-O2, heliox and washout Heliox was administered via the low pressure inlet of servo 900C, and respiratory parameters were measured by pulmonary monitor(CP-100 pulmonary monitor, Bicore, Irvine, CA, USA). To obtain the same tidal volume(Vt) in heliox phase, the Vt on monitor was adjusted by the factor of relative flow rate of heliox to N2-O2. Dead space was calculated by Bohr equation. RESULTS: 1) Vt, VE, peak inspiratory pressure(PIP) and peak inspiratory flow rate(PIFR) were not different between N2-O2 and heliox. 2) PEFR was higher on heliox(0.52+/-0.19L/sec) than N2-O2(0.44+/-0.13L/sec) (p=0.024). 3) PaCO2(mmHg) were decreased with heliox(56.1+/-14.1) compared to N2-O2(60.5+/-15.9) (p=0.027). 4) Dead space ventilation(%) were decreased with heliox(73+/-9 with N2-O2 and 71+/-10 with heliox) (p=0.026). CONCLUSION: Heliox decreased PaCO2 even at the same VE and WOB with N2-O2, and the effect was considered to be related with the reduction of anatomic dead space.

Ventilatory effects of laparoscopic cholecystectomy under general anesthesia.

To investigate the ventilatory effect of laparoscopic cholecystectomy in patients under general anesthesia with epidural block. We measured arterial blood gas, pulmonary carbon dioxide elimination (0000126;ECO2), the dead space/tidal volume ratio (VD/VT), and the alveolar-arterial PO2 difference [(A-a)DO2] just before and 5, 10, 20, 40, and 80 min after peritoneal insufflation in eight patients who underwent laparoscopic cholecystectomy under general anesthesia with epidural block. The effect of laparoscopic cholecystectomy on these values was evaluated. The patients were ventilated on the controlled mode by Servo 900C with a constant tidal volume (VT 10ml·kg-1) and frequency (respiratory rate 12 breaths·min-1) throughout the study. After starting peritoneal insufflation the PaCO2 showed a sudden increase during the initial 10 min of about 4 mmHg followed by a gradual increase thereafter. The increase in000123;ECO2 was about 30ml·min-1 (20%) on average during the initial 20 min, and a plateau was reached within 20-40 min after peritoneal insufflation. Neither VD/VT nor (A-a)DO2 showed significant changes during the study. These results suggest that (1) transperitoneal absorption of CO2 may be the main cause of hypercarbia, and the hypercarbia is not attributed to the increase in VD/VT; and (2) oxygenation is not impaired during pneumoperitoneum.

Comparison of jet and ultrasonic nebulizer pulmonary aerosol deposition during mechanical ventilation

Increased delivery of aerosol to a model lung (attached to a mechanical ventilator) has been demonstrated with an ultrasonic nebulizer as compared to a jet nebulizer. This study examined whether the increased aerosol deposition with an ultrasonic nebulizer could also be demonstrated in vivo. Seven patients (6 male and 1 female) were studied during mechanical ventilalion (Siemens Servo 900C, Middlesex, UK) after open heart surgery. Two studies were performed in each patient. In the first study, aerosol was delivered via a Siemens Servo 945 nebulizer system (high setting) driving a System 22 Acorn jet nebulizer (Medic-Aid, Sussex, UK) containing 3 mL (99m)technetium-labelled human serum albumin (99mTc-HSA) (50 microg; activity 74 MBq). In the second study, a DP100 ultrasonic nebulizer (DP Medical, Meylan, France) containing 12 mL 99mTc-HSA (50 microg; activity 185 MBq) was used. Pulmonary deposition was quantified using a gamma camera. The humidification of the circuit and the ventilator settings were kept constant according to the patient's clinical requirements. The total lung aerosol deposition (mean+/-SD), as a percentage of initial nebulizer activity, was greater using the ultrasonic nebulizer than using the jet nebulizer (53+/-1.4 vs 2.3+/-0.9%; p<0.002). The ultrasonic nebulizer was also associated with a reduction in the time required to complete nebulization (9 vs 21 min, respectively) (p<0.0001). Use of the DP100 ultrasonic nebulizer more than doubled lung deposition compared with the System 22 jet nebulizers in mechanically-ventilated patients. Their efficiency, speed of drug delivery, and compatibility with mechanical ventilator circuits make ultrasonic nebulizers potentially attractive for use during mechanical ventilation.