Apparatus Dead Space Research Articles

Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses.

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500mL, in 5-7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT:spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [-15% (-46-32)] and expiratory [10% (-32-20)] flows and inspiratory [-6% (-25-18)] and expiratory [5% (-9-20)] times. Agreement for nadir flows was poor [-22% (-87-369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horses.

Effects of apparatus dead space on volumetric capnograms in neonates with healthy lungs: a simulation study.

Volumetric capnography in healthy ventilated neonates showed deformed waveforms, which are supposedly due to technological limitations of flow and carbon dioxide sensors. This bench study analyzed the role of apparatus dead space on the shape of capnograms in simulated neonates with healthy lungs. We simulated mechanical breaths in neonates of 2, 2.5, and 3 kg of body weight using a neonatal volumetric capnography simulator. The simulator was fed by a fixed amount of carbon dioxide of 6 mL/kg/min. Such simulator was ventilated in a volume control mode using fixed ventilatory settings with a tidal volume of 8 mL/kg and respiratory rates of 40, 35, and 30 breaths per minute for the 2, 2.5 and 3 kg neonates, respectively. We tested the above baseline ventilation with and without an additional apparatus dead space of 4 mL. Simulations showed that adding the apparatus dead space to baseline ventilation increased the amount of re-inhaled carbon dioxide in all neonates: 0.16 ± 0.01 to 0.32 ± 0.03 mL (2 kg), 0.14 ± 0.02 to 0.39 ± 0.05 mL (2.5 kg), and 0.13 ± 0.01 to 0.36 ± 0.05 mL (3 kg); (p < .001). Apparatus dead space was computed as part of the airway dead space, and therefore, the ratio of airway dead space to tidal volume increased from 0.51 ± 0.04 to 0.68 ± 0.06, from 0.43 ± 0.04 to 0.62 ± 0.01 and from 0.38 ± 0.01 to 0.60 ± 0.02 in the 2, 2.5 and 3 kg simulated neonates, respectively (p < .001). Compared to baseline ventilation, adding apparatus dead space decreased the ratio of the volume of phase III to VT size from 31% to 11% (2 kg), from 40% to 16% (2.5 kg) and from 50% to 18% (3 kg); (p < .001). The addition of a small apparatus dead space artificially deformed the volumetric capnograms in simulated neonates with healthy lungs.

Total dead space in children under general anesthesia.

Total dead space in children under general anesthesia.

Alveolar target ventilation and dead space in children under anaesthesia: The proventiped cohort study.

Ventilator settings in children under anaesthesia remain difficult because of the changes in the physiology and the high dead space. To determine the alveolar minute-volume to sustain normocapnia in children under mechanical ventilation. A prospective observational study. This study was performed between May and October 2019 in a tertiary care children's hospital. Children between 2 months and 12 years, weighing between 5 and 40 kg, admitted for general anaesthesia. Volumetric capnography was used to estimate the alveolar and dead space volume (Vd). Total and alveolar minute ventilation in (ml kg-1 min-1) over 100 breaths. Sixty patients were included comprising 20 per group: 5 to 10 kg (group 1), 10 to 20 kg (group 2), 20 to 40 kg (group 3). Seven patients were excluded for aberrant capnographic curves. After normalisation to weight, the median [IQR] tidal volume per kilogram was similar between the three groups: 6.5 ml kg-1 [6.0 to 7.5 ml kg-1], 6.4 ml kg-1 [5.7 to 7.3 ml kg-1], 6.4 ml kg-1 [5.3 to 6.8 ml kg-1]; P = 0.3. Total Vd (in ml kg-1) was negatively correlated to weight (r = -0.62, 95% confidence interval -0.41 to -0.76, P < 0.001). The total normalised minute ventilation (ml kg-1 min-1) to obtain normocapnia was higher in group 1 than in group 2 and in group 3; 203 ml kg-1 min-1 [175 to 219 ml kg-1 min-1], 150 ml kg-1 min-1 [139 to 181 ml kg-1 min-1] and 128 ml kg-1 min-1 [107 to 157 ml kg-1 min-1]; P < 0.001 (mean ± SD), but (mean ± SD) alveolar minute ventilation was similar between the three groups; 68 ± 21 ml kg-1 min-1. Total dead space volume (including apparatus dead space) represents a major component of tidal volume in children less than 30 kg, when using large heat and moisture exchanger filters. The total minute ventilation necessary to achieve normocapnia decreased with increasing weight, while the alveolar minute ventilation remained constant. ClinicalTrials.gov, identifier: NCT03901599.

A comparison of the breathing apparatus deadspace associated with a supraglottic airway and endotracheal tube using volumetric capnography in young children.

BackgroundSupraglottic airway (SGA) devices including the air-Q® are being used with increasing frequency for anesthesia in infants and younger pediatric patients. To date, there is minimal research documenting the potentially significant airway deadspace these devices may contribute to the ventilation circuit when compared to an endotracheal tube (ETT). The aim of this study was to evaluate the airway apparatus deadspace associated with an air-Q® versus an ETT in young children.MethodsIn a prospective cohort study, 59 patients between 3 months and 6 years of age, weighing between 5 and 20 kg, scheduled for outpatient urologic or general surgery procedures were recruited. An air-Q® or ETT was inserted at the discretion of the attending anesthesiologist, and tidal volume, positive end expiratory pressure, respiratory rate, and end-tidal CO2 were controlled according to protocol. Airway deadspace was recorded using volumetric capnography every 2 min for 10 min. ResultsGroups were similar in demographics. There was a significant difference in weight-adjusted deadspace volume between the air-Q® and ETT groups, 4.1 ± 0.8 ml/kg versus 3.0 ± 0.7 ml/kg, respectively (P < 0.001). Weight-adjusted deadspace volume (ml/kg) increased significantly with decreasing weight for both the air-Q® and ETT groups.ConclusionsIn healthy children undergoing positive pressure ventilation for elective surgery, the air-Q® SGA introduces significantly greater airway deadspace than an ETT. Additionally, airway deadspace, and minute ventilation required to maintain normocarbia, appear to increase with decreasing patient weight irrespective of whether a SGA or ETT is used.

Optimal management of apparatus dead space in the anesthetized infant.

Mechanical ventilation of the anesthetized infant requires careful attention to equipment and ventilator settings to assure optimal gas exchange and minimize the potential for lung injury. Apparatus dead space, defined as dead space resulting from devices placed between the endotracheal tube and the Y-piece of the breathing circuit, is the primary source of dead space controlled by the clinician. Due to the small tidal volumes required by infants and neonates, it is easy to create excessive apparatus dead space resulting in unintended hypercarbia or increased minute ventilation in an effort to achieve a desirable PCO2 . The goal of this review was to evaluate the apparatus that are commonly added to the breathing circuit during anesthesia care, and develop recommendations to guide the clinician in selecting apparatus that are best matched to the clinical goals and the patient's size. We include specific recommendations for apparatus that are best suited for different size pediatric patients, with a particular focus on patients <5 kg.

Current methodological and technical limitations of time and volumetric capnography in newborns.

Although capnography is a standard tool in mechanically ventilated adult and pediatric patients, it has physiological and technical limitations in neonates. Gas exchange differs between small and adult lungs due to the greater impact of small airways on gas exchange, the higher impact of the apparatus dead space on measurements due to lower tidal volume and the occurrence of air leaks in intubated patients. The high respiratory rate and low tidal volume in newborns, especially those with stiff lungs, require main-stream sensors with fast response times and minimal dead-space or low suction flow when using side-stream measurements. If these technical requirements are not fulfilled, the measured end-tidal CO2 (PetCO2), which should reflect the alveolar CO2 and the calculated airway dead spaces, can be misleading. The aim of this survey is to highlight the current limitations of capnography in very young patients to avoid pitfalls associated with the interpretation of capnographic parameters, and to describe further developments.

Impact of Software Settings on Multiple-Breath Washout Outcomes.

Background and ObjectivesMultiple-breath washout (MBW) is an attractive test to assess ventilation inhomogeneity, a marker of peripheral lung disease. Standardization of MBW is hampered as little data exists on possible measurement bias. We aimed to identify potential sources of measurement bias based on MBW software settings.MethodsWe used unprocessed data from nitrogen (N2) MBW (Exhalyzer D, Eco Medics AG) applied in 30 children aged 5–18 years: 10 with CF, 10 formerly preterm, and 10 healthy controls. This setup calculates the tracer gas N2 mainly from measured O2 and CO2concentrations. The following software settings for MBW signal processing were changed by at least 5 units or >10% in both directions or completely switched off: (i) environmental conditions, (ii) apparatus dead space, (iii) O2 and CO2 signal correction, and (iv) signal alignment (delay time). Primary outcome was the change in lung clearance index (LCI) compared to LCI calculated with the settings as recommended. A change in LCI exceeding 10% was considered relevant.ResultsChanges in both environmental and dead space settings resulted in uniform but modest LCI changes and exceeded >10% in only two measurements. Changes in signal alignment and O2 signal correction had the most relevant impact on LCI. Decrease of O2 delay time by 40 ms (7%) lead to a mean LCI increase of 12%, with >10% LCI change in 60% of the children. Increase of O2 delay time by 40 ms resulted in mean LCI decrease of 9% with LCI changing >10% in 43% of the children.ConclusionsAccurate LCI results depend crucially on signal processing settings in MBW software. Especially correct signal delay times are possible sources of incorrect LCI measurements. Algorithms of signal processing and signal alignment should thus be optimized to avoid susceptibility of MBW measurements to this significant measurement bias.

When Does Apparatus Dead Space Matter for the Pediatric Patient?

Physiologic dead space is defined as the volume of the lung where gas exchange does not occur. Apparatus dead space increases dead space volume, causing either increased PaCO2 or the need to increase minute ventilation to maintain normocapnia. Children are especially vulnerable because small increases in apparatus dead space can significantly increase dead space to tidal volume ratio (Vd/Vt). The effect of changes in dead space on arterial CO2 (PaCO2) and required minute ventilation were calculated for patients weighing 2 to 17 kg that corresponds to 0 to 36 months of age. Apparatus volumes for typical devices were obtained from the manufacturer or measured by the volume of water required to fill the device. The relationship between the fraction of alveolar CO2 (FaCO2) and dead space volume (Vd) was derived from the Bohr equation, FaCO2 = VCO2/(RR*(Vt - Vd)), where VCO2 is CO2 production, RR is respiratory rate, and Vt is tidal volume. VCO2 was estimated by using Brody's equation for humans aged up to 36 months, (VCO2 = 5.56*(wt)), where weight is in kilogram. Initial conditions were Vt = 8 mL/kg, Vd/Vt = 0.3, and a RR of 20 breaths per minute. The relationship between PaCO2 and dead space was determined for increasing Vd. Rearranging the Bohr equation, the RR required to maintain PaCO2 of 40 mm·Hg was determined as dead space increased. The apparatus Vd of typical device arrangements ranged from 8 to 55 mL, and these values were used for the dead space values in the model. PaCO2 increased exponentially with increasing apparatus dead space. For smaller patients, the PaCO2 increased more rapidly for small changes in Vd than that in larger patients. Similarly, RR required to maintain PaCO2 of 40 mm·Hg increased exponentially with increasing dead space. Increasing apparatus Vd can lead to exponential increases in PaCO2 and/or RR required to maintain normal PaCO2. The effect on PaCO2 is less as patient weight increases, but these data suggest it can be significant for typical circuit components up to at least 17 kg or aged 36 months.

Dead space reduction by Kolobow’s endotracheal tube does not justify the waiving of volume monitoring in small, ventilated lungs

In ventilated preterm infants the flow sensor contributes significantly to the total apparatus dead space, which may impair gas exchange. The aim of the study was to quantify to which extent a dead space reduced Kolobow tube (KB) without flow sensor improves the gas exchange compared with a conventional ventilator circuit with flow sensor [Babylog 8000 (BL)]. In a cross-over trial in 14 tracheotomized, surfactant-depleted (saline lavage) and mechanically ventilated newborn piglets (age <12h; body weight 705-1200g) BL and KB was applied alternately for 15min and blood gases were recorded. The inner diameter of the endotracheal tube was 3.6mm and the apparatus dead space of BL and KB including the endotracheal tube were 3.0 and 1.34mL. Despite a 50% apparatus dead space reduction with KB compared to BL statistically significant improvements were only observed for body weights <900g. In this weight group median paCO2 was decreased by 5mmHg (p<0.01), whereas the improvement decreased with decreasing baseline paCO2. Furthermore, median paO2 was increased by 4mmHg (p<0.05) and O2 saturation was increased by 2.5% (p<0.05). No significant changes were seen in the circulatory parameters. In very small, ventilated lungs the use of KB improved the gas exchange; however, the improvement was moderate and does not justify the waiving of volume monitoring.

Apparent Dead Space with the Anesthetic Conserving Device, AnaConDa®

The anesthetic conserving device (ACD) reduces consumption of volatile anesthetic drug by a conserving medium adsorbing exhaled drug during expiration and releasing it during inspiration. Elevated arterial CO2 tension (PaCO2) has been observed in patients using the ACD, despite tidal volume increase to compensate for larger apparatus dead space. In a test lung using room temperature dry gas, this was shown to be due to adsorption of CO2 in the ACD during expiration and release of CO2 during the following inspiration. The effect in the test lung was higher than in patients. We tested the hypothesis that a lesser dead space effect in patients is due to higher temperature and/or moisture attenuating rebreathing of CO2. The lungs of 6 postoperative cardiac surgery patients were ventilated using a conventional heat and moisture exchanger (HME) or an ACD. The ACD was studied with a test lung at varying temperatures and moistures. Infrared spectrometry was used to measure apparent dead space by the single-breath test for CO2 as well as rebreathing of CO2. In patients, the median apparent dead space was 136 mL (95% confidence interval [CI,] 120-167) larger using the ACD compared with an HME (after correction for difference in internal volume 100 and 50 mL, respectively). Median rebreathing of CO2 using the ACD was 53% (range 48-58) of exhaled CO2 compared with 29% (range 27-32) with an HME. The median difference in CO2 rebreathing was 23% (95% CI, 18-27). In the test lung apparent dead space using ACD was unaffected by body temperature but decreased from 360 to 260 mL when moisture was added. This decreased rebreathing of CO2 from 62% to 48%. The use of an ACD increases apparent dead space to a greater extent than can be explained by its internal volume. This is caused by adsorption of CO2 in the ACD during expiration and release of CO2 during inspiration. Rebreathing of CO2 was attenuated by moisture. The dead space effect of the ACD could be clinically relevant in acute respiratory distress syndrome and other diseases associated with ventilation difficulties, but investigations with larger sample sizes would be needed to determine the clinical importance.

Carbon dioxide rebreathing with the anaesthetic conserving device, AnaConDa®

The anaesthetic conserving device (ACD) AnaConDa(®) was developed to allow the reduced use of inhaled agents by conserving exhaled agent and allowing rebreathing. Elevated has been observed in patients when using this ACD, despite tidal volume compensation for the larger apparatus dead space. The aim of the present study was to determine whether CO(2), like inhaled anaesthetics, adsorbs to the ACD during expiration and returns to a test lung during the following inspiration. The ACD was attached to an experimental test lung. Apparent dead space by the single-breath test for CO(2) and the amount of CO(2) adsorbed to the carbon filter of the ACD was measured with infrared spectrometry. Apparent dead space was 230 ml larger using the ACD compared with a conventional heat and moisture exchanger (internal volumes 100 and 50 ml, respectively). Varying CO(2) flux to the test lung (85-375 ml min(-1)) did not change the measured dead space nor did varying respiratory rate (12-24 bpm). The ACD contained 3.3 times more CO(2) than the predicted amount present in its internal volume of 100 ml. Our measurements show a CO(2) reservoir effect of 180 ml in excess of the ACD internal volume. This is due to adsorption of CO(2) in the ACD during expiration and return of CO(2) during the following inspiration.

Influence of tidal volume on pulmonary gas exchange during general anaesthesia

Background and objective: General anaesthesia impairs respiratory function. The present studies were performed to compare arterial concentration of sevoflurane, oxygen and carbon dioxide in normal and overweight patients ventilated with increased tidal volume (VT), or normal tidal volume with and without PEEP. Methods: Prospective, randomised, clinical studies. ASA І and II abdominal surgery patients were randomly assigned to be ventilated with normal VT (NVT) with and without PEEP to 10 cmH2O or with increased VT (IVT) achieved by increasing inspired plateau pressure 0.04 cm H2O kg-1. Extra apparatus dead space was added to maintain PETCO2 at 4.5 kPa. Arterial oxygenation, sevoflurane tension (Pasevo, Fisevo, PETsevo), PaCO2, PETCO2, stroke volume, cardiac output, VT and airway pressure were measured. Results: The groups of patients compared were similar regarding gender, age, and BMI. Arterial oxygen and sevoflurane tension was generally higher in the IVT group (P < 0.05) whereas mean FiO2 and PETsevo did not differ between the groups. Arterial carbon dioxide was significantly lower with IVT than NVT ventilated without PEEP but in the presence of PEEP in the NVT group, the groups were similar. Cardiac output decreased significantly less in the IVT group compared to the NVT group with PEEP (5 and 33 % respectively). Conclusion: Isocapnic ventilation with larger tidal volumes maintained with added apparatus dead-space increases the arterial oxygen and sevoflurane tension as well as carbon dioxide elimination in normal and overweight patients, and in overweight patient also preserves cardiac output better than in the presence of PEEP. (Less)

Increased apparatus dead space and tidal volume increase blood concentrations of oxygen and sevoflurane in overweight patients: a randomised controlled clinical study

General anaesthesia impairs respiratory function in overweight patients. We wanted to determine whether increased tidal volume (V(T)), with unchanged end-tidal carbon dioxide partial pressure (P(ET)CO₂), affects blood concentrations of oxygen and sevoflurane in overweight patients. The present study is a prospective, randomised, clinical study. American Society of Anesthesiologists physical status I and II patients with BMI over 25 scheduled for elective surgery of the lower abdomen were randomly assigned to one of two groups with 10 patients in each. One group was ventilated with normal V(T) (NV(T)) and one group with increased V(T) (IV(T)) achieved by increasing inspired plateau pressure 0.04 cmH₂O kg⁻¹ above initial plateau pressure. Extra apparatus dead space was added to maintain P(ET)CO₂ at 4.5 kPa. Respiratory rate was set at 15 min⁻¹, and sevoflurane was delivered to the fresh gas by a vaporiser set at 3%. Arterial oxygenation, sevoflurane tensions (P(a)sevo, F(i)sevo, P(ET)sevo), paCO₂, P(ET)CO₂, V(t) and airway pressure were measured. The two groups of patients were similar with regard to sex, age, weight, height and BMI. Arterial oxygen tension (mean ± SD) was significantly higher in the IV(T) group (15 ± 4.3 vs. 10 ± 2.7 kPa after 60 min of anaesthesia, P < 0.05). Mean PETsevo did not differ between the groups, whereas arterial sevoflurane tension (mean ± SD) was significantly higher in the IVT group (1.74 ± 0.18 vs. 1.43 ± 0.19 kPa after 60 min of anaesthesia, P < 0.05). Ventilation with larger tidal volumes with isocapnia maintained with added apparatus dead space increases the tension of oxygen and sevoflurane in arterial blood in overweight patients.

Measurement of Dead Space in Subjects Under General Anesthesia Using Standard Anesthesia Equipment

Pulmonary dead space is the volume of gas that is delivered to the lungs but does not participate in gas exchange. Knowing pulmonary dead space in patients under general anesthesia is clinically useful because it can aid in detecting disease processes such as pulmonary emboli or low cardiac output states. Dead space can be simply calculated by using the Bohr equation; however, it is difficult to measure mixed exhaled carbon dioxide (PECO(2)) with a standard anesthesia machine. Previously, a study at our institution demonstrated the carbon dioxide (CO(2)) concentration in the bellows of a standard anesthesia machine is an accurate approximation of PECO(2). In this study, we used the bellows PECO(2) measurement and arterial CO(2) (PaCO(2)) to calculate pulmonary dead space. We verified the technique by adding known apparatus dead space volumes during anesthesia. Subjects were under general endotracheal anesthesia. A sampling line was positioned inside the ventilator bellows and connected to a capnometer. Measurements of PECO(2) and PaCO(2) from an arterial catheter were taken at baseline and after adding 100 mL and 200 mL of dead space to the endotracheal tube. Dead space was calculated using the Bohr equation (alveolar dead space/tidal volume = [PaCO(2) - PECO(2)]/PaCO(2)) at baseline and after adding 100 mL and 200 mL of apparatus dead space. The dead space at baseline was 265 ± 47 mL (mean ± SD) in 10 study subjects. After adding 100 mL of dead space to the endotracheal tube, the measured dead space increased by 110 ± 46 mL. The measured dead space increased by 158 ± 39 mL after adding 200 mL. Our baseline dead space measurements were in the expected range under general anesthesia. When dead space was added, we were able to calculate that an increase in dead space occurred. Our calculation was more accurate after adding a 100-mL volume than after adding 200 mL. We present a simple way to detect trends in dead space in ventilated patients using a Narkomed GS anesthesia machine (Dräger Medical, Lübeck, Germany).

Larger tidal volume increases sevoflurane uptake in blood: a randomized clinical study

The rate of uptake of volatile anesthetics is dependent on alveolar concentration and ventilation, blood solubility and cardiac output. We wanted to determine whether increased tidal volume (V(T)), with unchanged end-tidal carbon dioxide partial pressure (P(ET)CO(2)), could affect the arterial concentration of sevoflurane. Prospective, randomized, clinical study. ASA physical status (2) and II patients scheduled for elective surgery of the lower abdomen were randomly assigned to one of the two groups with 10 patients in each: one group with normal V(T) (NV(T)) and one group with increased V(T) (IV(T)) achieved by increasing the inspired plateau pressure 0.04 cmH(2)O/kg above the initial plateau pressure. A corrugated tube added extra apparatus dead space to maintain P(ET)CO(2) at 4.5 kPa. The respiratory rate was set at 15 min(-1), and sevoflurane was delivered to the fresh gas by a vaporizer set at 3%. Arterial sevoflurane tensions (P(a)sevo), F(i)sevo, P(ET)sevo, P(ET)CO(2), P(a)CO(2), V(T) and airway pressure were measured. The two groups of patients were similar with regard to gender, age, weight, height and body mass index. The mean P(ET)sevo did not differ between the groups. Throughout the observation time, arterial sevoflurane tension (mean ± SE) was significantly higher in the IV(T) group compared with the NV(T) group, e.g. 1.9 ± 0.23 vs. 1.6 ± 0.25 kPa after 60 min of anesthesia (P<0.05). Ventilation with larger tidal volumes with isocapnia maintained with added dead-space volume increases the tension of sevoflurane in arterial blood.

The effect of increased apparatus dead space and tidal volumes on carbon dioxide elimination and oxygen saturations in a low-flow anesthesia system

Study objective To determine if a large tidal volume ( V T), with an unchanged end-tidal carbon dioxide partial pressure (P ET co 2), could improve arterial carbon dioxide elimination, oxygen saturation (Sp o 2), and arterial blood oxygenation. Design Prospective, randomized, clinical study. Setting Single university hospital. Patients 60 ASA physical status I and II patients scheduled for elective urologic or general surgery. Interventions Patients were randomly assigned to one of two treatments: patients in group 1, nondead space (NDS), received a fresh gas flow of 1 L/min without added apparatus dead space volume. Patients in group 2, dead space (DS), received ventilation using an added dead space volume between the Y-piece and tracheal tube. In both groups, patients' lungs were ventilated to a fixed P ET co 2 value of 33.8 mmHg. Patients in the DS group were ventilated with V Ts to maintain an airway plateau pressure (P plateau) of 0.04 cm H 2O/kg over initial plateau pressure. The corrugated tube was then adjusted to maintain a fixed P ET co 2. Measurements Dead space volumes, P ET co 2, arterial CO 2 tension (Pa co 2), SpO 2, arterial O 2 tension (Pa o 2), V Ts, and airway pressures were measured. Main Results Arterial CO 2 tension was significantly lower in the DS group, 36 ± 2.3 mmHg, compared with the NDS group, 37.5 ± 2.3 mmHg ( P < 0.05), and the difference between P ET co 2 and Pa co 2 was lower in the DS group than in the NDS group ( P < 0.001). Oxygen saturation was 99% ± 1.0% in the DS group compared with 98.5% ± 1.5% in the NDS group ( P < 0.05). Arterial O 2 tension was 13.2 ± 25.5 mmHg in the DS group and 119.1 ± 30.2 mmHg in NDS group (not significant). Conclusion Larger V Ts, with an unchanged P ETCO 2 concentration created by an added apparatus dead space volume, improved arterial carbon dioxide elimination.

Problems in the measurement of functional residual capacity

Accurate assessment of lung volume in infancy is important to determine the impact of disease and the efficacy of therapies. A new generation of infant plethysmographs with lower apparatus deadspace has been produced, but gives lower volume results than those from older traditional plethysmographs. We hypothesized that the new plethysmographs might have greater sensitivity to the adiabatic effect and hence they, rather than the traditional plethysmographs, produced erroneous results. Our aim was to assess the influence of the adiabatic effect on the results of a contemporary plethysmograph, an older traditional plethysmograph and a helium gas dilution system using a lung model. Altering the amount of copper wool within the lung model allowed the influence of the adiabatic effect on the plethysmographic results to be assessed. The measured compared to the actual volumes were significantly lower for the contemporary plethysmograph compared to the traditional plethysmograph (p < 0.001) and to the helium gas dilution system (p < 0.001). Under optimal testing conditions the contemporary plethysmograph under-recorded by 11–13%, whereas the other two systems gave similar results to the actual volumes. As the effect of the adiabatic effect was increased, the discrepancy between the results of the contemporary and the traditional plethysmographs increased. We conclude, the contemporary plethysmograph is more sensitive to adiabatic effects and hence under-records.

Dead-space washout by split-flow ventilation. A new method to reduce ventilation needs in premature infants

Chronic lung disease caused by volutrauma is one of the most important consequences of preterm delivery. In this pilot study a new method is presented that consists of flushing part of the dead space with fresh gas in order to reduce high tidal volumes, the chief cause of volutrauma. The aim of the study was to evaluate if the new method could reduce ventilatory effort in preterm infants by diminishing dead space. In split-flow ventilation, gas required for dead-space washout is split off from the regular ventilation circuit. The split flow bypasses the apparatus dead space and fills it retrogradely with fresh breathing gas, mainly in the pause between exhalation and inspiration. The mean per-minute ventilation and ventilation index after 12 h of conventional ventilation were compared with corresponding mean values after 12 h of split-flow ventilation in 17 preterm infants weighing <2,000 g. Statistical analysis was performed using the T -test for matched pairs. After switching from conventional ventilation to split-flow ventilation, the mean per-minute ventilation per kilogram of body weight decreased significantly from a mean value of 0.314+/-0.097 l/kg/min to 0.190+/-0.043 l/kg/min ( p <0.001), while the ventilation index decreased significantly from 28.47+/-7.48 to 16.10+/-4.13 ( p <0.001). Split-flow ventilation significantly reduces apparatus dead space during ventilation in preterm infants. This leads to reduced ventilatory effort.

Is the Effect on Elimination of Apparatus Dead Space Different according to Ventilation Modes?

Background: The objective of this study was to observe that the effect on the elimination of apparatus dead space was different according to modes of ventilation. Methods: In 30 patients undergoing esophageal surgery, we placed a double-lumen endobronchial tube in the midtrachea and used the bronchial lumen with a conventional Y connector while the tracheal lumen was clamped for conventional ventilation (CV) or used both lumens with special connectors that separated the inspiratory limb and the expiratory limb for separated ventilation (SV). Four ventilation modes were used in each patient. Type CV10 is a mode with 10 ml/kg of tidal volume, and a frequency of 10/min, and type CV5 is a mode with 5 ml/kg of tidal volume, and a frequency of 20/min. Except for the special connectors, type SV10 and SV5 are the same as CV10 and CV5, respectively. Results: The means ﾅ standard deviations of PaCO2 in CV10, SV10, CV5, and SV5 were 34.8 K 5.7 mmHg, 32.3 5.1 mmHg, 39.2 6.6 mmHg, and 34.9 5.9 mmHg, respectively. The PaCO2 in SV10 and SV5 decreased significantly when compared with that seen in CV10 and CV5, respectively (P 0.001), showing the effect of the elimination of apparatus dead space. Moreover, the PaCO2 difference observed between CV5 and SV5 (4.4 4.1 mmHg) was significantly greater than that observed between CV10 and SV10 (2.5 2.4 mmHg) (P = 0.014). Conclusions: The elimination of apparatus dead space to improve CO2 removal can be more beneficial in a ventilation mode with 5 ml/kg of tidal volume, and a frequency of 20/min rather than in 10 ml/kg of tidal volume, and a frequency of 10/min.