Search

Fiberoptic bronchoscopy revealed an ectopic tracheal bronchus to the right upper lobe arising 3 cm above the carina. An endobronchial blocker (COOPDECH™, Osaka, Japan) was positioned in the proximal right intermediate bronchus, blocking the middle and inferior lobes. Although the right upper lobe was ventilated, it did not obstruct the surgical field via a right anterior thoracotomy. The patient was ventilated using pressure-control ventilation with inspiratory pressure 20 cm H2O, positive end-expiratory pressure (PEEP) 6 cm H2O, and tidal volume 500 mL at an FIO2 1.0 after collapse of the right middle and lower lobes. The femoral artery was cannulated with a 20-Fr arterial cannula and the femoral vein with a 28-Fr venous cannula positioned into the right atrium with the tip in the superior vena cava to establish CPB. An antegrade cardioplegia cannula was inserted into the ascending aorta with a flexible cross-clamp subsequently applied. The heart was arrested initially by using antegrade cold blood cardioplegia. Myocardial protection was provided using mild systemic hypothermia (341C), and antegrade cold blood cardioplegia was given throughout the procedure at 30-minute intervals.

As the use of pulse oximeters increases, the needs for higher performance and wider applicability of pulse oximetry have increased. To realize the full potential of pulse oximetry, it is indispensable to increase the number of optical wavelengths. To develop a multiwavelength oximetry system, a physical theory of pulse oximetry must be constructed. In addition, a theory for quantitative measurement of optical absorption in an optical scatterer, such as in living tissue, remains a difficult theoretical and practical aspect of this problem.We adopted Schuster's theory of radiation through a foggy atmosphere for a basis of theory of pulse oximetry. We considered three factors affecting pulse oximetry: the optics, the tissue, and the venous blood.We derived a physical theoretical formula of pulse oximetry. The theory was confirmed with a full SO2 range experiment. Based on the theory, the three-wavelength method eliminated the effect of tissue and improved the accuracy of Spo2. The five-wavelength method eliminated the effect of venous blood and improved motion artifact elimination.Our theory of multiwavelength pulse oximetry can be expected to be useful for solving almost all problems in pulse oximetry such as accuracy, motion artifact, low-pulse amplitude, response delay, and errors using reflection oximetry which will expand the application of pulse oximetry. Our theory is probably a rare case of success in solving the difficult problem of quantifying optical density of a substance embedded in an optically scattering medium.

We read with great interest the article by Aldrich et al 1 in this issue of CHEST (see page 1484 ). In 2003, we reported our trial of measuring noninvasive arterial saturation during a pulseless situation (cardiopulmonary bypass [CPB]) by inducing a simulated pulse. 2 We were interested in fi nding a way to obtain pulse oximeter function during CPB at the time because we had experienced a mortally instructive cardiac case in which the routine anesthesia practice of turning off the pulse oximeter during CPB resulted in severe hypoxic brain damage.

This observational, prospective pediatric human study was performed to determine the agreement between brain tissue oxygenation indices (TOI) measured by near infrared spatially resolved spectroscopy and jugular bulb oxygen saturation values (SjO(2)).Five cardiac patients without neurological impairment who were admitted into the critical care unit after open-heart surgery with jugular bulb venous catheters were enrolled. Their mean age was 8.6 months and mean body weight was 6.7 kg. Simultaneous measurements of brain TOI using NIR0-300 (Hamamatsu Photonics, Hamamatsu City, Japan) and SjO(2) values from blood samples were recorded.The TOI range was 59+/-9% and the SjO(2) range was 58+/-17%. The correlation coefficient R was 0.64 (p=0.11; n=14). Bland-Altman plotting revealed a bias of -3.4%, and precision of 7.2% (n=14). Intra-class correlation reliability analysis showed kappa of 0.55.Statistically, brain TOI was in reasonable agreement with SjO(2) in pediatric patients with normal brain within the measurement range from 50 to 70%.

The pressure-flow relationships and the longitudinal distributions of pulmonary vascular resistance in normal and heartworm-infected (HWI) dogs were compared in an isolated, blood perfused preparation. The pulmonary circulation was partitioned into pulmonary arterial, middle, and venous segment based on the concept of a five element lumped model. The pulmonary arterial pressure-flow relationships were found to be non-linear and convex to the pressure axis in both normal and HWI lungs. The pressure-flow relationships of the pulmonary arterial and venous segment were linear and these slopes in the HWI lungs were significantly higher than the normal lungs. The pressure gradient of the middle segment was increased as flow increased at lower flow range, however, it was not increased during higher perfusion range in both lungs. At higher flow, the pressure gradient of the middle segment in the HWI lungs was significantly higher than the normal lungs. These results suggest that the ohmic resistance was almost equal to the sum of the two slopes of the pressure-flow relationships of the pulmonary arterial and venous segment because the pressure gradient of the middle segment was not altered as flow increased during higher perfusion rate. Because the slopes of the pressure-flow relationships of the pulmonary arterial and venous segment were increased with heartworm infection, the ohmic resistance of HWI lungs would be higher than normal lungs. The intercept pressure on the pressure axis of the linear portion of the pulmonary arterial pressure-flow relationship, a critical closing pressure, was regarded as pressure gradient of the middle segment during higher perfusing rate because the intercept pressures of pressure-flow relationships of pulmonary arterial and venous segment were almost equal to zero. Therefore, the critical closing pressure of HWI lungs would be higher than normal lungs. The pulmonary hypertension of filariasis appears to be due to an increase in ohmic resistance and elevated critical closing pressure.

Background: High-frequency oscillatory ventilation (HFOV) has become the preferred method of ventilation for the fragile lungs of neonates and infants because its beneficial effects on lungs are well known; however, its benefits on upper airways are not yet known. We investigated the effects of HFOV and conventional mechanical ventilation (CMV) on the airways of kittens with normal lungs. Methods: Ten healthy cross-bred kittens, 2–3-months-old, with a mean bodyweight of 0.98 kg, were randomly divided into two groups: HFOV and CMV. Kittens were intubated and ventilated for 24 h. A semiquantitative scoring system was used to grade histopathological tissue changes in the cricoid, mid-trachea, carina and left bonchus. The injury scores of the two groups were ranked and compared using a two-tailed Mann–Whitney rank test. Results: Histopathologic changes were similar and mild in both groups under light microscopic examination. There was no significant difference in airway injury between the two groups. Conclusions: We conclude that, in this animal model, HFOV results in minimal airway damage when properly managed and causes no greater tracheobronchial injury than CMV.

Study Design. This study investigated the case of a 17-year-old girl with postpneumonectomy syndrome, complicated by a thoracic lordoscoliosis, who was successfully treated with prosthetic implants, partial vertebrectomies, and anteroposterior spinal fusion. Objective. To report a unique case and describe the authors' method of treatment. Summary of Background Data. Postpneumonectomy syndrome is an uncommon complication of pneumonectomy. Many case reports describe successful treatment with insertion of prosthetic implants into the empty hemithorax to shift the mediastinum to its original position. Thoracic lordoscoliosis reportedly has contributed to pulmonary compromise, but no cases have shown its occurrence in the setting of postpneumonectomy syndrome. Methods. The patient was observed at the National Children's Hospital in Tokyo, referred to Children's Hospital in Los Angeles, California for surgical correction, and followed in Tokyo for the next year. Results. Two prosthetic implants with an injection port for further expansion were positioned in the right hemithorax to restore the mediastinum to its normal position. Anterior discectomies, partial vertebrectomies, and fusion of T5-T10 was performed concurrently. Then 5 days later, posterior spinal fusion of T1-T12 with instrumentation and bone graft were performed to correct the thoracic lordoscoliosis and increase the chest cavity space. At 1 month after the surgery, the patient was extubated after being ventilator dependent for 5 months. At the time of operation, the girl was ventilator dependent and nonambulatory, but 1 year later could participate in all activities of daily living without any oxygen supplementation. Conclusions. Postpneumonectomy syndrome can be treated successfully with prosthetic implants to restore the normal position of the mediastinum. Thoracic lordoscoliosis can complicate the syndrome and may be corrected to help restore normal pulmonary function.

Heart transplantation is increasingly becoming accepted worldwide as therapy for end-stage heart failure not only in adult patients but also in pediatric practice. The new law in Japan for organ transplantation from brain-dead patients was established on 16 October 1998, but there is no definite law or protocol for brain death in children under the age of 6 years and children less than 15 years of age cannot become donors. These facts make organ transplantation from the cadavers of neonates, infants and young children almost impossible in Japan, even though there are children who need heart or heart-lung transplantation. The present authors have to date transferred 8 patients to the USA or Germany for heart transplantation: 4 successfully underwent heart transplantation, but 4 died during the waiting period overseas. There are many things to consider; not only the medical problems involved in transportation, but also the financial issues when transferring patients to other countries. This report details the experience with the 8 cases that were transferred overseas for heart transplantation, and highlights the problems that need to be considered.

To evaluate the role of tumor necrosis factor (TNF)-alpha in the pathogenesis of ventilator-induced lung injury, we 1) measured TNF-alpha production in the lung caused by conventional mechanical ventilation (CMV) and 2) evaluated the protective effect of anti-TNF-alpha antibody (Ab) in saline-lavaged rabbit lungs. After they received saline lung lavage, rabbits were intratracheally instilled with 1 mg/kg of polyclonal anti-TNF-alpha Ab in the high-dose group (n = 6), 0.2 mg/kg of anti-TNF-alpha Ab in the low-dose group (n = 6), serum IgG fraction in the Ab control group (n = 6), and saline in the saline control group (n = 7). Animals then underwent CMV for 4 h. Levels of TNF-alpha in lung lavage fluid were significantly higher after CMV than before in both control groups. Pretreatment with intratracheal instillation of high and low doses of anti-TNF-alpha Ab improved oxygenation and respiratory compliance, reduced the infiltration of leukocytes, and ameliorated pathological findings. CMV led to TNF-alpha production in the lungs, and intratracheal instillation of anti-TNF-alpha Ab attenuated CMV-induced lung injury in this model.

Background/Purpose: Blood perfusion to the coronary artery (CA) during venoarterial (VA) extracorporeal membrane oxygenation (ECMO) was examined to determine whether it was receiving highly oxygenated ECMO blood or desaturated blood from the pulmonary circulation of diseased lungs. Methods: In the first experiment, left ventricle output and oxygen saturation in the left ventricle (LV) and CA were measured in dogs placed on VA ECMO. In the second experiment, dogs with an artificial subclavian-pulmonary artery shunt were placed on VA ECMO at 100 mL/kg/min, and oxygen saturation was measured as the shunt flow increased. Results: Without an artificial shunt, a substantial portion of coronary perfusion was found to be supplied by the left ventricle (54 + 30%), even at a high ECMO flow rate of 100 mL/kg/min and low LV output (22 + 17%) relative to ECMO flow. With a shunt, oxygen saturation in the CA was more than 95%, even when shunt flow was only 7.5% of ECMO flow and output from the left ventricle was less than 25% of the ECMO flow rate. Conclusions: These results suggest that an excessive "lung rest" strategy during VA ECMO may produce suboptimal coronary oxygenation possibly leading to myocardial damage. The presence of a small left-to-right shunt may prevent coronary hypoxia.

嚥下協調障害,胃食道逆流による慢性誤嚥を呈する患者群では,軽微な気道感染症から急性呼吸窮迫症候群(acute respiratory distress syndrome, ARDS)への進展を経験することが少なくないが,その病態は十分には解明されていない。慢性誤嚥が小児ARDSの発症に関与している実態の把握を目的として後方視的検討を行った。小児集中治療室全収容患者570症例中ARDS症例は15症例であり,そのうち慢性誤嚥が発症,増悪に関与したと推定された症例は3症例(0.53%)であった。これら3症例では,従来のARDSの危険因子は関与しておらず,基礎疾患として慢性誤嚥を認め,軽微な気道感染症に伴って急激に悪化した。なお,こうした症例群ではARDS再発の危険性が残るため,遠隔期まで見込んだ治療計画が求められる。

Capnometry is the standard of care to measure the amount of carbon dioxide in the proximal airway, detect apnea, tracheal tube dislodgement, and effectiveness of ventilation during invasive mechanical ventilation in critically ill infants, children and adults [1]. Capnometry is not yet standard practice for non-invasively supported or ventilated patients, due to dead space ventilation, inspiratory gas washout, gas entrainment, and potential for rebreathing of gas. Potential capnometry use in non-intubated patients could identify impending respiratory failure, obstructed airways, and improve the safety and effectiveness of non-invasive support for infants and children [2].Copyright © 2013 by ASME

A safe clinical system for nitric oxide (NO) inhalation therapy was developed. The system consists of three parts: a NO controller, a NO monitor, and a patient circuit. NO gas flow and carrier gas flow are controlled by a special rust-proof thermal mass flowmeter. Standard gas quality NO gas (10,000 ppm, balance nitrogen) is used. The outlet of the NO gas tank is connected to the distal end of a heated humidifer that is very close (12 mL) to the patient, to decrease acidic water precipitation and decrease contact time between NO and oxygen (O2). Fail-safe mechanisms to prevent the delivery of a hypoxic mixture or excessive NO concentration are incorporated. Inspiratory NO concentration is continuously monitored by a modified electrochemical NO meter. The patient circuit consists of a breathing circuit and a ventilator with a scavenging unit. A modified Mapleson D type circuit is used. Fresh gas, humidified and mixed with NO, is introduced to the patient connection port. A mechanical ventilator, either of conventional or of high-frequency oscillation type, is connected to the expiratory limb of the Mapleson D circuit. A coaxial scavenging unit including activated charcoal is placed in between the expiratory limb and the ventilator. The adjustment of inspiratory NO concentration (y) was accurate over a wide range (1-80 ppm) of concentrations (x) (y = 0.36 + 0.96x, R2 = 0.999, n = 45) and showed good agreement with the chemiluminescence method. Inspiratory nitrous oxide (NO2) concentration was less than 0.3 ppm, and acidic water accumulation as measured by NO2- and NO3- was less than 5 ppm, even at an extremely high NO concentration of 80 ppm with an FiO2 of 1.0 and 10 L/min of fresh gas flow. Environmental NO and NO2 concentrations in the ICU remained below 0.005 and 0.05 ppm, respectively. This system was used clinically on 214 pediatric patients and proved to be accurate, safe, and useful.

To compare the pathophysiologic changes occurring during drowning in cold fresh water and cold salt water with reference to viability.Randomized, prospective, controlled submersion experiments in two contrasting cold liquids.A laboratory at a large university-affiliated medical institution.Thirteen healthy, anesthetized mongrel dogs. Three dogs served as controls and were immersed but not submerged. The remainder were submerged in cold fresh water or cold salt water (4 degrees C).Catheters were placed in the femoral artery, right carotid artery and right internal jugular vein. Electrocardiogram, pneumogram, and rectal temperatures were measured continuously during submersion/immersion.Cold water submersion with drowning produced a large initial decrease in carotid artery temperature (approximately 7.5 degrees C in the first 2 mins) compared with a minor decrease (approximately 0.8 degrees C with immersion). No significant differences were noted in the rate of decrease of temperature between drowning in fresh water and salt water. During cold fresh water drowning, aspiration produced gross hemodilution with an average increase in body weight of 16.5%. Hematocrit values, serum sodium concentrations, and osmolality decreased while serum potassium concentrations, catecholamines, and free hemoglobin increased. All measured biochemical data (except PaO2) remained at viable levels. By contrast, during cold salt water drowning, average body weight increased by only 6%, with hemoconcentration and a shrinkage of vascular volume. Hematocrit and hemoglobin values increased by 30%, but initial plasma free hemoglobin values remained unchanged. Serum sodium concentrations, osmolality, and potassium concentrations increased rapidly to critical levels.On submersion in cold water, all of the experimental animals developed tachypnea immediately, followed by aspiration with predictable effects. The biochemical and pathophysiologic changes in cold water drowning approximated those changes reported for warm water drowning for both fresh and salt water with one exception and continued aspiration of cold water produced extremely rapid core cooling as long as the circulation remained intact. This process of acute submersion hypothermia may protect the brain temporarily from lethal damage, as reported in cases of cold fresh water drowning. Concentrations of circulating catecholamines increased exponentially in both groups of test animals. Clinically, their acute effects on the circulation, compounded by significant hypothermia and extreme anoxia, must hamper the detection of residual circulation at rescue and may play a role in sudden death from cold water in the absence of drowning.

The effects of intratracheal administration of MKS 492, a selective phosphodiesterase (PDE) III inhibitor, were studied in five anesthetized bronchoconstricted cats. The animals were challenged by four repeated doses of intratracheal methacholine (67 micrograms/kg), and the degree of bronchoconstriction was assessed from increases in respiratory system resistance (Rrs). All animals demonstrated good bronchoconstrictive responses (i.e., 86-99% increases in Rrs) to methacholine without tachyphylaxis. On a separate day, the cats received the same four doses of methacholine after being pretreated with either intratracheal saline or three different doses of MKS 492 (0.17, 1.7, and 17 micrograms/kg). The increases in Rrs with 1.7 micrograms/kg [52.6 +/- 8.4% (SE)] and 17 micrograms/kg of MKS 492 (44.4 +/- 10.1%) were smaller than those with saline pretreatment (88.1 +/- 16.8%) (P < 0.05). There were no treatment-associated changes in mean arterial pressure or heart rate during administration of MKS 492. We conclude that intratracheal MKS 492 effectively reduced methacholine-induced bronchoconstriction in a dose-dependent fashion without substantial systemic effects. These preliminary results suggest that inhalation of isozyme-selective PDE inhibitors may deserve consideration for clinical trials provided that more extensive preclinical investigations justify such trials.

To study the effects of ketamine on structurally remodeled pulmonary arteries from rats with hypoxic pulmonary hypertension (PH) and the effects of ketamine on endothelium-dependent and -independent relaxation, rats were exposed to hypobaric hypoxia (air at 380 mm Hg for 10 days). We measured the responses to ketamine, acetylcholine, and sodium nitroprusside (SNP) in prostaglandin F2 alpha-precontracted ring segments from a left extrapulmonary artery (EPA, 1.4-1.6 mm in outside diameter [OD] and an intrapulmonary artery (IPA, 0.7-1.1 mm OD) obtained from control and PH rats. The effects of acetylcholine and SNP were decreased in EPA and IPA rings from PH rats compared with control rings. In contrast, ketamine produced a greater relaxation response in rings from PH rats at 3 x 10(-5) -3 x 10(-4) in the EPA and at 10(-4) -10(-3) M in the IPA compared to control rings. A nitric oxide synthase inhibitor, nitro-L-arginine (10(-4) M), inhibited the relaxation in response to acetylcholine in both control and PH rats. Pretreatment with ketamine (10(-4) M) had no effect on the relaxation response to any concentration of acetylcholine or SNP in either control or PH rats. We conclude that nitric-oxide-mediated relaxation, but not ketamine-induced relaxation, was impaired in structurally remodeled hypertensive pulmonary arteries. Ketamine had no effects on nitric oxide-mediated relaxation in either normal or PH rats.

Capnometer has been widely used as a respiratory monitor. Stable carbon dioxide (CO 2 ) monitoring of non-intubated patient is especially problematic due to the frequent occurrence of tube obstruction and it could be even more difficult when oxygen is being administered. Oxygen is often administered by an oxygen mask or oxygen nasal cannula; however there are some problems with these methods. For oxygen masks, it is necessary to provide high-flow oxygen to prevent rebreathing of exhaled CO 2 , and as for oxygen nasal cannula, it is incapable of increasing the oxygen concentration and patient may feel uncomfortable during oxygen administration because it could dry nasal mucous. To solve these problems, we developed a novel mainstream capnometer system, which provides stable monitoring of exhaled CO 2 while administering oxygen. This capnometer system has a mask with an opening large enough to facilitate the observation of patient's nose and mouth and the procedures such as daily oral care. Furthermore, the outer rim of the mask is designed to effectively retain oxygen flow without causing rebreathing.

Access to artificial surfactant and high frequency oscillatory ventilation (HFO) in Japan seems to affect the actual indications for extracorporeal membrane oxygenation (ECMO). The relation between the methods of treatment and survival and/or neurological sequelae of 27 neonates with severe respiratory failure who would have met the US ECMO entry criteria in the Neonatal Intensive Care Unit of National Children's Hospital, Tokyo between January 1988 and May 1992 were retrospectively analyzed. Out of 27 neonates, conventional treatment including artificial surfactant was successful in 6 cases (22%). High frequency oscillatory ventilation was used for the 21 cases who did not respond to conventional treatment and it was effective in 5 cases (19% of total). Extracorporeal membrane oxygenation was used on 11 (40% of total) of 16 cases who did not respond to HFO. Eight (29% of total or 73% of ECMO cases) of these cases survived and 3 cases (11% of total) died. The remaining 5 cases (19% of total) who met the exclusion criteria of ECMO died. No patient with respiratory distress syndrome (RDS) became ill enough to meet the US ECMO entry criteria. Six out of 8 congenital diaphragmatic hernia cases were saved on a delayed surgery protocol with HFO. Only about 1% of the neonates who were admitted to our NICU during the last 4 years needed ECMO treatment. Forty-one per cent of the patients who would have met the US ECMO entry criteria were treated successfully without ECMO. The necessity for ECMO is less in Japan than in the US because other methods can often be used successfully to treat severe respiratory disorders.

Inflammatory chemical mediators, platelet-activating factor (PAF), thromboxane (TX) B2, and 6-keto-prostaglandin (PG)F1 alpha, were extracted from lung lavage fluid after conventional mechanical ventilation (CMV) and high frequency oscillatory ventilation (HFOV) to clarify the relation between mode of ventilation and lung injury in surfactant-depleted rabbit lungs. Anesthetized adult rabbits were tracheostomized, and surfactant depletion was induced by repeated saline lavage. Lung lavage for measurement of mediators was performed after 4 h of CMV at an FIO2 of 1.0 and a mean airway pressure of 15 cm H2O or HFOV (15 Hz) at an FIO2 of 1.0 or 0.21 and a mean airway pressure of 15 cm H2O. The number of total cells and polymorphonuclear leukocytes (PMN) and the levels of PAF, TXB2, and 6-keto-PGF1 alpha were measured by radioimmunoassay. Total respiratory compliance (Crs) was measured by the passive flow-volume curve method. The numbers of PMN, and the levels of PAF and TXB2 in lung lavage fluid were significantly greater during CMV than during HFOV. HFOV resulted in decreased production of PAF and TXB2 in a surfactant-depleted rabbit lung. Crs was significantly less during CMV than during HFOV. These results suggest that HFOV could prevent the release of such inflammatory chemical mediators and result in less lung injury than CMV.

To analyze longitudinal distribution of pulmonary vascular resistance, we proposed a five element lumped model which partitioned pulmonary circulation into pulmonary arterial, middle and pulmonary venous segment. The validity and anatomical correlation of the model were tested in an isolated, perfused, canine lung lobe preparation with inflow/outflow occlusion techniques. With arterial occlusion, pulmonary arterial pressure fell rapidly and then exponentially. With venous occlusion, pulmonary venous pressure rose suddenly and then exponentially. Theoretical pressure profiles produced by computer simulation of the model well approximated the general characteristics of the experimental traces. Serotonin increased the pressure gradient across the pulmonary arterial segment (delta Pa), whereas histamine increased the gradient across the pulmonary venous segment (delta Pv). Neither drug altered the gradient across the middle segment (delta Pm). The results suggest that the lumped model is a useful concept to understand the longitudinal distribution of pulmonary vascular resistance, and that delta Pa, delta Pm and delta Pv reflect the resistance distribution of anatomical pulmonary arteries, alveolar vessels and pulmonary veins, respectively.

Summary A report of our experience with a complete switchover from halothane (HAL) to sevoflurane (SF) in 1550 paediatric cases over a period of 17 months is presented. SF became the sole inhalational anaesthetic in our institution in July 1990. Induction of anaesthesia with SF was performed with the overpressure technique by administering rapid increases of concentration and assisted pulmonary ventilation with a large fresh gas flow (6 l·min−1 of nitrous oxide and 3 l·min−1 of oxygen). SF concentration was increased rapidly up to 5 or 7% in increments of 2% in every 2–3 breaths. Induction time as measured in 60 cases (3–6 years) was 50 ± 5 (mean ± SD) sec for loss of eyelash reflex and 119 ± 10 (mean ± SD) sec for loss of movement to venepuncture at 7% SF concentration. No serious complications were observed. Peak serum levels of inorganic fluoride were within a safe range (less than 30 μmol·l−1) in all 7 cases in which this was studied. The results suggest that SF is a useful anaesthetic agent in paediatric anaesthesia, particularly because of its smooth and rapid inhalation induction.

A multicenter randomised trial was conducted in nine neonatal centers in Japan to re-evaluate the safety and the efficacy of high frequency oscillatory ventilation using the piston type oscillator (Hummingbird) in the treatment of respiratory failure in preterm infants weighing between 750 and 2000 g at birth. A total of 92 infants were enrolled in the study. Forty-six infants were allocated to high frequency oscillatory ventilation and 46 infants to conventional mechanical ventilation. There were no differences in sex, birth weight, gestation and Apgar score between groups. The study was begun 2.0 ± 1.6 h (mean ± S.D.) after birth in the high frequency oscillation group and 1.7 ± 1.5 h after birth in the conventional mechanical ventilation group. The absence of intraventricular hemorrhage was confirmed by echography in all cases before beginning ventilation. Mortality was similar in high frequency oscillatory ventilation and conventional mechanical ventilation (0 and 2%). The incidence of intraventricular hemorrhage was also similar in the high frequency and conventional mechanical ventilation groups (15 and 13% overall; 4 and 2% in grades III and IV, respectively). Nine percent of the infants in high frequency oscillatory ventilation and 13% in conventional mechanical ventilation developed bronchopulmonary dysplasia, but the difference was not significant. The frequency of air leaks was also equal in both groups. Periventricular leukomalacia was detected in 9% of infants on conventional mechanical ventilation and 2% on high frequency oscillation, but the difference was not significant. Mean airway pressure was significantly higher in the high frequency oscillatory ventilation group and the infants on high frequency oscillation showed a significantly higher arterial to alveolar oxygen tension ratio after 6 h of treatment. These results suggest that high frequency oscillatory ventilation does not increase the risk of severe complications such as air leaks, intraventricular hemorrhage or periventricular leukomalacia when it is used by experienced neonatologists. Indeed high frequency oscillatory ventilation helps provide better oxygenation with higher mean airway pressure without increasing the risk of bronchopulmonary dysplasia and severe complications such as air leaks and intraventricular hemorrhage.

The KATS catheter (continuous arterial thermodeprivation system catheter) measures the blood flow velocity of the pulmonary artery (PA) by thermodeprivation which enables continuous determination of cardiac output. The accuracy of this system may depend on the degree of uniformity of flow velocity in the PA, because small movements of the catheter within the PA are inevitable with a beating heart. We evaluated the flow velocity profile of the PA in seven anaesthetized open-chest dogs to assess these potential errors. A custom-made stiff catheter, at the tip of which was incorporated the flow velocity sensor of the KATS catheter, was used to penetrate the main PA in the short axis direction (perpendicular to flow direction) or the long axis direction (along flow direction). The stiff catheter was moved in increments of 2.5 mm, and flow velocity was recorded. The wall-to-wall distance of the PA along each direction was divided into five sections (S1 to S5 for the short axis, and L1 to L5 for the long axis). Flow velocity data for each section were averaged and presented as relative values against the control mid-point velocity. Along the short axis, flow velocity was 0.41 ± 0.20 (SD), 1.00 ± 0.10, 1.03 ± 0.10, 1.08 ± 0.13 and 0.49 ± 0.26 from S1 to S5, i.e., lower in S1 and S5 which were close to the vascular walls (P < 0.05) but uniform in other areas. Along the long axis, flow velocity was 0.28 ± 0.28, 0.88 ± 0.09, 0.94 ± 0.08, 1.06 ± 0.25 and 1.28 ± 0.50 from L1 to L5. Thus, flow velocity was lower in L1 which was close to the bifurcation (P < 0.05), slightly higher in L5 close to the pulmonary valve, but uniform in other areas. These results suggest that the profile of blood flow velocity is relatively uniform within the main PA except in areas close to the vessel walls or valve. We conclude that movement of the catheter within the vessel would not substantially influence the accuracy of the KATS catheter system as long as the flow velocity sensor of the catheter stays within the main PA.

A modified thermodilution catheter (KATS catheter) capable of monitoring continuous cardiac output by thermodeprivation and preserving its conventional function was devised. The KATS catheter has a thermistor incorporated closer to the tip of the catheter in addition to the usual thermistor used for conventional thermodilution. This additional thermistor is heated by a constant electric current but is capable of measuring its own temperature. The degree of heat deprivation is detected as the cooling of the thermistor, which is proportionally larger with larger blood velocity. Since blood flow is not the only source of heat deprivation, the actual formula was empirically derived by performing in vitro studies. Cardiac output can be determined by assuming the cross sectional area of the pulmonary artery is stationary. Calibration can be derived from a cardiac output measurement by the usual thermodilution method with the same catheter. The KATS catheter readings correlated significantly with conventional thermodilution values and electromagnetic flowmeter readings in anesthetized dogs. Continuous cardiac output measurement by the KATS catheter appears to be a promising technique.

従来の呼吸生理学の上では気管壁は吸気時に拡張するとされる。ところが実際の胸腔内中枢気道狭窄性疾患の人工呼吸管理では吸気性呼吸困難を呈する症例がみられる。われわれは気管壁の動きが気管内外差圧に支配されることに着目し, 自発呼吸下の気管内圧, 気管周囲圧および胸腔内圧を気管内挿管されたイヌにおいて同時測定した。結果として, 気管壁は呼気時に拡張方向, 吸気時に狭窄方向の力を受けることが示された。また気管周囲圧は胸腔内圧とほぼ平行に動き, 気管内圧は呼吸流量と同じ時相で変動した。今回の結果は古典的呼吸生理学から理論的に考えられる気管内外差圧の動きとは逆であった〇また, 今回の現象は, 最大吸気流量が中枢気道性疾患に於て特異的に低下するとの以前のわれわれの臨床報告を裏付けるものである。

Background: Pediatric anesthesia in Japan is in the developing stage. The aim of this study was to review pediatric anesthesia training in Japan and to discuss the future prospects for this field. Methods: We sent questionnaires to assess current pediatric anesthetic practice and training to all 106 university hospitals [UHs; response rate, 66% (70/106)] and all 17 children's hospitals [CHs; response rate, 87.5% (15/17)] in Japan. We also sent questionnaires to assess attitudes towards pediatric anesthetic training, to all 280 representatives of the Japanese Society of Anesthesiologists [JSA; response rate, 57.9% (162/280)]. Results: The hospital survey revealed the number of pediatric anesthesia cases encountered in 15 CHs (25 009 cases) to be almost equivalent to that in 70 UHs (29 031 cases). In 19 of these UHs, there were no newborn surgical cases. Forty-nine UHs reported that no special training program existed for pediatric anesthesia, and only five UHs mandated training at CHs. Sixty-six percent of the representative JSA members considered it premature for pediatric anesthesia to become a subspecialty, but 87% considered experience in pediatric anesthesia mandatory for anesthesia board qualification. Conclusions: This survey revealed that although pediatric anesthesia training is considered mandatory, university hospitals lack adequate numbers of pediatric cases and children's hospitals suffer from a shortage of staff positions and anesthesiologists, and hence are unable to satisfy this demand. Most representative members of our society consider it too early to subspecialize pediatric anesthesia in Japan.

Mirror syndrome is a preeclampsia-like disease first described in a case of severe hydrops fetalis caused by rhesus isoimmunization, later reported in some cases of nonimmunological fetal hydrops. Twin-twin transfusion syndrome (TTTS) is a severe complication associated with monochorionic pregnancies, in particular, severe TTTS with one hydropic fetus leading to a poor prognosis. We report here a case of mirror syndrome that occurred after selective fetoscopic laser photocoagulation in severe TTTS at 24 weeks’ gestation.

OBJECTIVES Pulse dye densitometry (PDD), based on the principles of pulse oximetry and dye-dilution technique, is a less invasive method of measuring cardiac output (CO). We have developed prototype equipment to measure CO in pediatric patients using this technique. The purpose of our study was to evaluate the accuracy of this new PDD system using three wavelengths for pediatric application by comparing measurement with an ultrasound flowmeter. DESIGN Laboratory investigation. SETTING Hospital physiology research laboratory. SUBJECTS A total of 15 young piglets weighing approximately 10 kg each. INTERVENTIONS Measurement of CO by PDD was performed using general anesthesia. Indocyanine green, 0.2 mg/kg, was administered intravenously, and CO was calculated from the dye dilution curve obtained by the PDD system. The ultrasound flowmeter probe was placed on the ascending aorta in the animal, and CO was simultaneously calculated. MEASUREMENTS AND MAIN RESULTS The two CO values, simultaneously obtained by the ultrasound flowmeter and PDD, were compared during various hemodynamic states. The bias between the CO measured by the ultrasound flowmeter and the CO measured by the PDD system using the reflection-type probe at the central site was 33.8 mL/min and the precision was 293.4 mL/min, indicating that CO measured by PDD had a good correlation with measurements obtained with the ultrasonic method. CONCLUSION We measured CO in young piglets at an acceptable level of bias and precision using a prototype PDD device. CO measurement by this new PDD system using three wavelengths can be useful and beneficial for critically ill infants and children. It is simple to perform, requiring an injection of dye into a peripheral intravenous catheter, and it will provide a less invasive bedside measurement of CO.

This study compared pathophysiological and biochemical indexes of acute lung injury in a saline-lavaged rabbit model with different ventilatory strategies: a control group consisting of moderate tidal volume (Vt) (10–12 ml/kg) and low positive end-expiratory pressure (PEEP) (4–5 cmH2O); and three protective groups: 1) low Vt (5–6 ml/kg) high PEEP, 2–3 cmH2O greater than the lower inflection point; 2) low Vt (5–6 ml/kg), high PEEP (8–10 cmH2O); and 3) high-frequency oscillatory ventilation (HFOV). The strategy using PEEP > inflection point resulted in hypotension and barotrauma. HFOV attenuated the decrease in pulmonary compliance, the lung inflammation assessed by polymorphonuclear leukocyte infiltration and tumor necrosis factor-α concentration in the alveolar space, and pathological changes of the small airways and alveoli. Conventional mechanical ventilation using lung protection strategies (low Vt high PEEP) only attenuated the decrease in oxygenation and pulmonary compliance. Therefore, HFOV may be a preferable option as a lung protection strategy.

The effect of steady-state increases in abdominal pressure (Pab) on cardiac performance was studied in seven acutely instrumented swine with pneumoperitoneum (PP). The animal was placed on volume-preset ventilation, and PP was created by air insufflation. Cardiac output (CO), right atrial (Pra), left atrial (Pla), pericardial (Ppe), and abdominal inferior vena cava pressures (Pivc) were measured while Pab was increased from baseline to 7.5, 15, and 30 mmHg (PP7.5, PP15, and PP30, respectively). Cardiac function curves of the right and left ventricle (RV and LV, respectively) were compared between baseline and PP30. CO presented biphasic changes, with an inital slight increase at PP7.5 followed by a fall at PP30. A significant discrepancy was observed between Pra and Pivc at PP15 and PP30, consistent with development of a “vascular waterfall.” Transmural Pla (Pla − Ppe) showed parallel changes with CO, whereas transmural Pra (Pra − Ppe) exhibited a sustained increase. The RV cardiac-function curve was more depressed than was that of the LV at PP30; this suggests an increased RV afterload produced by the elevated airway pressure. These results support the hypothesis that our previously proposed concept of abdominal vascular zone conditions (M. Takata, R. A. Wise, and J. L. Robotham. J. Appl. Physiol. 69: 1961–1972, 1990) is also applicable to steady-state hemodynamic analyses. The abdominal zones appear to play an important role in determining CO, with increases in Pab, by modulating systemic venous return and the LV preload. Simultaneous measurements of Pra and Pivc may provide useful information in the hemodynamic care of patients with elevated Pab.

Background/Purpose: To develop practical and less invasive techniques for fetal endoscopic surgery, new methods of lifting the uterine wall to allow fetal surgery without maternal laparotomy were developed and assessed. Methods: Fetal endoscopic surgical procedures, including tracheostomy and umbilical vascular cannulation, were performed using one of the three methods to enter the uterus without maternal laparotomy in pregnant goats (n = 6; 105 to 115 days' gestation): (1) direct uterine lifting with an air-cushion device; (2) indirect uterine lifting, in which the uterine wall was fixed to the maternal abdominal wall using balloon tip ports inserted percutaneously by Seldinger's method, then the maternal abdomen was lifted mechanically; and (3) combined method, in which low pressure CO 2 (5 mm Hg for initial inflation and 2 mm Hg for maintenance) was insufflated into the uterus in addition to the indirect uterine lifting cited above. Results: The direct uterine lifting caused massive injury of myometrium and uterine membranes. The creation of intrauterine space and the protection of the membranes were not accomplished effectively by the indirect uterine lifting only. The combined method provided the adequate intrauterine space and excellent endoscopic visibility for completion of the endoscopic procedures with minimal uterine injury. Conclusion: The fetal endoscopic surgery may be accomplished simply and safely by the combined method, a novel technique of uterine lifting to allow fetal surgery without maternal laparotomy.

The effects of conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation (HFO) on intraalveolar expression of the tumor necrosis factor-alpha (TNF-alpha) gene were studied in surfactant-depleted rabbits. After lung lavage with saline, 13 rabbits were administered either CMV (n = 6) or HFO (n = 7) for 1 h at an FiO2 of 1.0 and a mean airway pressure of 13 cm H2O. Lung lavage was then repeated. The rabbits' RNA was extracted from the lavage cells, and mRNA for TNF-alpha was quantitated by reverse-transcription polymerase chain reaction using glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as an internal standard. At 1 h of ventilation, PaO2 was slightly lower with CMV than HFO, while lavage cell counts and cytology were similar between the two groups. The ratio of TNF-alpha mRNA to GAPDH mRNA increased with CMV (control, 0.48 +/- 0.04 [SE] versus 1 h, 1.02 +/- 0.14, p0.01) but did not change with HFO (0.55 +/- 0.07 versus 0.73 +/- 0.09). In a separate series of experiments, ten surfactant-depleted rabbits continued to be ventilated for 4 h either by CMV (n = 5) or HFO (n = 5). Conventional mechanical ventilation resulted in a progressive hypoxemia, decreased lung compliance, increased number of neutrophils in lung lavage fluid, and substantial morphological changes including hyaline membrane formation and neutrophil accumulation, whereas HFO was associated with minimal changes in such physiological and pathological abnormalities. These results suggest that activation of alveolar macrophages and production of proinflammatory cytokines may play a pivotal role in the early stage of ventilator-induced lung injury, and that ventilator mode (CMV or HFO) substantially modulates macrophage activation and hence the degree of lung injury.

A new heparin binding method was applied to a miniature extracorporeal membrane oxygenation (ECMO) system with a nonporous membrane oxygenator (the priming volume, 45 mL; the membrane surface area, 0.4 m2; maximal flow rate, 2 L/min) that is resistant to plasma leakage. The authors evaluated the stability of the immobilized heparin in vitro and the feasibility of this system in animals. Samples of hollow fibers and tubing were rinsed at 40 degrees C for 4 days in normal saline, Ringer's lactate, and 1 mol/L NaCl solution. Heparin activities on hollow fibers after rinsing were 99 +/- 2.3% (mean +/- SD), 96 +/- 3.9%, and 93 +/- 2.0% of the control in each solution, while those of the tubing were 87 +/- 4.1%, 86 +/- 3.1%, and 76 +/- 8.6%, respectively. Veno-arterial ECMO using this heparin-coated system was performed on five beagles (8 to 12 kg) for 10 hours. Neither major thrombus formation nor plasma leakage was detected during the procedure in spite of a low flow rate (300 mL/min) and a reduced activated clotting time (mean, 128 seconds). Platelets decreased to 52% of the control (P < .01) at 1 hour, but no progressive decrease was seen thereafter. Antithrombin-III decreased (P < .01) and thrombin/antithrombin III complex increased (P < .05 at 4 hours and P < .01 at 6, 8, and 10 hours) during bypass, but the changes of fibrinogen and fibrinopeptide A were not significant. Fibrinogen/fibrin degeneration products, fibrinopeptide B beta 15-42, and plasma-free hemoglobin levels did not rise significantly. O2 transfer of the oxygenators at a flow rate of 300 mL/min were 12.3 +/- 0.4 mL/min at 30 minutes, 14.3 +/- 1.2 mL/min at 5 hours, and 14.7 +/- 1.7 mL/min at 10 hours (no statistical difference). Histological examination of the brains and the kidneys showed no evidence of thromboembolic sequela in any of the animals. These results suggest that this new system is a promising device for long-term ECMO in which the amount of systemic heparinization can be reduced with the minimal possibility of plasma leakage.

Objective. To develop and to assess the clinical impact of a near-television quality home digital videophone system (Integrated Services Digital Network [ISDN] 64, 320 × 200 resolutions, 10 to 12 frames per second), which would provide respiratory care specialists’ resources to primary care physicians and their pediatric patients receiving home respiratory care. Method. A prospective study comparing the preceding 6 months and following 6 months of implementation of a videophone system on seven pediatric home respiratory care patients (group I) and a prospective analytical study of three patients (group II) being introduced to home ventilatory care were carried out. Clinical effectiveness and time-saving benefits were studied. Results. There were large reductions in the number of house calls by the physicians (from 5 to 0), unscheduled hospital visits by patients (from 24 to 5), and hospital admission days (from 22 to 10), with a fivefold increase in phone calls (from 11 to 58) in group I. This reduced the net number of hours spent by both patients and physicians in unscheduled medical care by 95 hours for the patients and 51.2 hours for the physicians. A total of 45 videophone calls, of which 27 were related to mechanical concerns and 18 to medical concerns, were made in group II. There were 7 mechanical and 10 medical problems of clinical significance, but all were directly handled by physicians by videophone. The majority (35 of 45) of videophone calls were made in the first 3-month period, indicating a decrease in nonspecific concerns after this period. The specifications of the system we used were found acceptable by both patients and health care professionals. The system seemed to be useful in effectively using the time of specialists and in relieving the anxieties of families. No deleterious effects were noted. The current initial cost is substantial but rapidly falling. The running cost is similar to a regular telephone bill when one ISDN 64 line is used. Conclusions. The videophone system using ISDN 64 can now be considered a practical and effective tool to recruit specialist resources into home care and to improve the quality of pediatric home ventilatory care. This study encourages the use of videophones to help establish designated home care support systems that may extend beyond national borders and time zones. home care, videophone, telemedicine, Integrated Services Digital Network.

The longitudinal distribution of pulmonary vascular compliance was evaluated in isolated canine lung lobes using arterial-(AO), venous-(VO), and double-occlusion (DO) techniques. Total vascular compliance (Ctau) was separated into pulmonary arterial (Ca) and venous compliance (Cv) in lumped model of pulmonary circulation. Under constant pulmonary venous pressure (Pv) at 5 mmHg, blood inflow to the lobe (Q) was gradually increased by changing pulmonary arterial pressure (Pa) from 10 to 22 mmHg at 4 mmHg ranges. Changes in vascular blood volume (deltaV) with each increment in Q were determined by decreased reservoir blood volume of perfusion system. DO was performed at each level of Q and allowing all vascular pressures to equilibrate at the same static pressure (Ps), which was equal to the compliance-weighted average pressure in the circulation. Ctau was obtained from the slope of the relationship between Ps and deltaV. When Pa and Pv were 14 and 5 mmHg, AO, VO, and DO were performed to measure pressures at Ca (Pca) and Cv (Pcv) and Ps. The arterial-to-venous compliance ratio (Ca/Cv) was evaluated using Pca, Pcv, and Ps measurements. Ctau was 0.113 +/- 0.012 ml/kg/mmHg. Ca/Cv was 0.30. Ca and Cv were 0.026 +/- 0.013 and 0.087 +/- 0.007 ml/kg/mmHg, respectively. These data demonstrated the usefulness of AO, VO, and DO techniques in evaluating the longitudinal distribution of compliance in canine pulmonary vasculature.

Venoarterial extracorporeal membrane oxygenation (ECMO) was performed in five dogs without systemic heparinization to assess the feasibility of heparin-free ECMO. The surfaces of the inverted hollow-fiber-type oxygenator and circuit of the ECMO system were coated with heparin by the endpoint-attached (covalent-bonded) technique. No heparin was administered to the animal except for a small dose to maintain patency of the arterial line (1 IU/h). ECMO was run for 24 h at a pump flow of 50 ml/kg · min and was successful throughout the experiment in four of the five dogs. Scanning electron microscopy did not detect any blood clots in the oxygenator or circuit except for inside and outside the cannulas that were not coated with heparin in the carotid artery and jugular vein. Activated clotting time (ACT), fibrinogen, and anti-thrombin III (AT-III) activity remained within the normal physiological range. Serum heparin concentrations were low throughout the experiment, indicating minimal heparin release. Platelet levels decreased and fibrinopeptide B β15-42 (FPB β15-42) increased significantly after 6 h ECMO. D-dimer levels did not change throughout the experiment. ECMO was discontinued in one case after successful a 23-h run because of macroscopic clot formation at the oxygenator blood inlet. ACT had suddenly increased to 160 s approximately 1 h prior to this clot formation. These results suggest that the amount of systemic heparinization required can be substantially reduced by a heparin-coated ECMO system. Total abolishment of heparin administration in pediatric venoarterial ECMO may be possible by refinement of this technique. Monitoring of AT-III and FPB β15-42 in addition to ACT may be useful for early diagnosis of latent but ongoing coagulopathies during ECMO.

Persistent pulmonary hypertension of the newborn (PPHN) may occasionally require an invasive treatment with extracorporeal membrane oxygenation (ECMO). Inhaled nitric oxide (NO) has recently been introduced as a selective pulmonary vasodilator for treatment of PPHN. We describe a case of PPHN in which neither inhaled NO nor ECMO was effective in reversing pulmonary hypertension. The clinical course of the patient suggested a potential role of NO inhalation in predicting the outcome of ECMO treatment for PPHN.

Various respiratory monitoring methods have been used as a part of home respiratory care, but none has been accepted as a universal method. Impedance pneumography is the most popular method at present and is used in the form of cardiorespiratory monitoring, but it has limitations for diagnosing obstructive airway problems and a high incidence of false alarms. We evaluated a new investigational method, inductance pneumography, in terms of the incidence of false alarms (waveform out of range), using infants recovering from general anesthesia. They were used for this study because they go through all the stages of sleep in a short period and their relatively long period of light sleep was advantageous in evaluating motion artifact interference. Waveforms went out of range 24.6 ± 2.9% of the time with impedance pneumography and 15.9 ± 4.5% with pulse oximeter, but 11.0 ± 3.4% with inductance pneumography. These differences are statistically significant (P < 0.01). Electrocardiography electrodes for impedance pneumography dislodged briefly in one case but the Respiband dislodged in four cases and the Flex II probe dislodged in three cases, indicating the need for better fixation of sensors. It was found that inductance pneumography, in addition to being able to detect obstructive apnea, has a significantly lower incidence of false alarms. Further elaboration of this method is warranted for better home respiratory monitoring.

We studied the pressure-volume (PV) relationships of the total respiratory system, lung and chest wall in 8 anesthetized and paralyzed normal adult cats. The PV relationships of the total respiratory system had a sigmoid shape with a relatively linear portion with an alveolar pressure between 0 to +15 cmH2O. The relative impact of the lung and chest wall to the total elastic recoil forces of the respiratory system was approximately equal within a physiological pressure range. The results suggest that measurements of PV relationships of the respiratory system may offer a physiologic basis for accurate interpretation of pulmonary functions, leading to a better therapeutic strategy in animals with lung diseases.

Controversy exists as to whether high frequency oscillation (HFO) increases the risk of intraventricular hemorrhage (IVH) compared with conventional mechanical ventilation (CMV). We compared the risk of intracranial hemorrhage after phenylephrine-induced hypertension, combined with a hypovolemic, hypotensive insult followed by rapid volume replacement in two groups of newborn beagle puppies (one group on a piston pump HFO and the other on CMV). A total of 12 beagle puppies (6 on HFO and 6 on CMV) survived the protocol. Arterial blood gas analysis and arterial blood pressures through the study were of the same magnitude in both groups. The length of time for which the puppies remained hypertensive and hypotensive also did not vary significantly between the groups. Intraventricular hemorrhages were observed in two of six CMV puppies and two of six HFO puppies. One animal in each group had a white matter hemorrhage. Subarachnoid hemorrhages were seen in 4 animals on CMV and 3 on HFO. This study indicated that HFO does not increase the risk of any kind of intracranial hemorrhage, including IVH, in beagle puppies.

We developed a rebreathing system for measuring response to carbon dioxide (CO2) of newborns and infants for use at the bedside. The system based on Read's method is small, easy to operate, and includes a computer-controlled gas switching sequence, computerized calculation, and display functions. © 1992 Wiley-Liss, Inc. We measured the CO2 response in 11 infants with or without apnea, who were born at 26–33 weeks gestation and were 12 to 215 days old at the time of the study. Our results suggest that the presence of apnea in premature infants may correspond to a low CO2 response. The method was convenient for clinical use because it allowed an investigator to carry out bedside tests in only a few minutes. With our system we were able to assess respiratory center function in newborns and infants.

OBJECTIVES Since the introduction of a humidifier with a heating wire, we have frequently experienced severe upper airway obstruction from consolidation of secretions, previously unencountered when a humidifier without a heating wire was used. Such problems led to the suspicion that the heating wire incorporated into the breathing circuit of the heated humidifier might be the cause. Therefore, we scheduled an experiment to assess the hypothesis that relative humidity, rather than absolute humidity, is a dominant factor in the case of drying secretions in the upper airway when using such a humidifier. DESIGN Three clinical case reports and an experiment with a tracheal model. SETTING Intensive care units at Saitama Medical Center, Saitama Medical School, Saitama, Japan. PATIENTS Three intubated patients. MEASUREMENTS AND MAIN RESULTS An experiment with a tracheal model showed that gas with a higher temperature and lower relative humidity (35 degrees C, 48%) deprived the tracheal model of significantly more water (5.9 +/- 0.2 [SD] g) than gas with a lower temperature and higher relative humidity (24 degrees C, 87%) (2.9 +/- 0.4 g; p less than .01), even though the gases contained the same amount of water vapor (19 mg H2O/L) minus the same absolute humidity. CONCLUSIONS A heated humidifier with a heating wire incorporated into the breathing circuit may be dangerous when only temperature is monitored and controlled. Relative humidity, rather than absolute humidity, is a dominant factor in the case of drying secretions in the upper airway when using such a humidifier.

Respiratory Inductance Plethysmography (RIP) has become popular in critical care respiratory monitoring. However, the primary use has been in the evaluation of breathing pattern, and there has been little emphasis placed upon looking at the shape of the respiratory curves, which closely resemble volume curves. We introduce a new method of loop analyses, which is potentially useful in diagnosing the airway function and quantitating phase lag between diaphragmatic and rib cage compartments of breathing in infants and children.