Toshimichi Takahashi

Effect of core body temperature on ventilator-induced lung injury

ObjectiveVentilator-induced lung injury is a risk in patients requiring elevated ventilatory support pressures. We hypothesized that thermal stress modulates the development of ventilator-induced lung injury. DesignExperimental study. SettingUniversity laboratory. SubjectsAnesthetized rabbits. InterventionsTwo experimental studies were designed to determine the role of temperature as a cofactor in ventilator-induced lung injury. In the first study, three groups of anesthetized rabbits were randomized to be ventilated for 2 hrs at core body temperatures of 33, 37, or 41°C while ventilated with pressure control ventilation of 15/3 cm H2O (noninjurious settings—control) or 35/3 cm H2O (potentially injurious settings—experimental). To exclude effects arising from cardiac output fluctuations or from extrapulmonary organs, an isolated lung model was used for the second study, perfused at a fixed rate and studied at either 33°C or 41°C. Measurements and Main ResultsIn the first study, the hyperthermic group compared with the hypothermic animals had significantly reduced mean Pao2 (−114 vs. + 14 mm Hg, p < .05), increased lung edema formation (mean wet weight/dry weight ratio of 8.1 vs. 5.7), and altered pressure-volume curves. The hyperthermic isolated, perfused lungs had an increased ultrafiltration coefficient, formed more edema, and experienced greater alveolar hemorrhage than hypothermic lungs. ConclusionsIn two studies of ventilator-induced lung injury in rabbits, maintaining hyperthermia compared with hypothermia augmented the development of lung injury. Similar results from both the in vivo and isolated, perfused lung studies suggest that the observed effects were not due to cardiovascular factors or consequences of heating nonpulmonary organs.

Heart rate variability during massive hemorrhage and progressive hemorrhagic shock in dogs

Purpose: To investigate the sequential changes in heart rate (HR), autonomic nervous activity presented by the spectral analysis of heart rate variability (HRV), hemodynamics and metabolism during massive hemorrhage and progressive hemorrhagic shock in dogs.Methods: Twelve dogs were subjected to acute massive hemorrhage until mean arterial pressure (MAP) reached 50 mmHg. Then bleeding was stopped and they were allowed to reach a plateau phase. They were divided, post hoc, into bradycardic or tachycardic groups according to their HR response to the acute massive hemorrhage. After reaching a plateau phase, the dogs were further bled to keep their MAP around 50 mmHg (progressive hemorrhagic shock). Their heart rate power spectra were quantified into low-frequency (LF) (0.04–0.15 Hz) and high-frequency (HF) (0.15–0.4 Hz) components.Results: In the bradycardic group, both LF and HF increased after massive hemorrhage, but during progressive hemorrhagic shock these components decreased while HR increased. In the tachycardic group, LF increased after massive hemorrhage, but during progressive hemorrhagic shock LF decreased with continuous suppression of HF.Conclusion: Massive hemorrhage caused two types of HR response: bradycardia and tachycardia. The HRV profile showed differential autonomic characteristics, and could be a valuable tool in assessing various degrees of hemorrhagic shock.RésuméObjectif: Examiner les changements de fréquence cardiaque (FC), l’activité nerveuse autonome selon l’analyse spectrale de la variabilité de la fréquence cardiaque (VFC), l’hémodynamie et le métabolisme pendant une hémorragie massive et un choc hémorragique progressif, chez des chiens.Méthode: Douze chiens ont été soumis à une hémorragie aiguë massive jusqu’à ce que la tension artérielle moyenne (TAM) atteigne 50 mmHg. Puis, on a arrêté le saignement et laissé la pression parvenir à un plateau. On a, en conséquence, réparti les animaux en groupe bradycardie ou tachycardie selon le compotement de la FC pendant l’hémorragie aiguë massive. Un plateau une fois atteint, les chiens ons subi une autre hémorragie pour amener leur TAM autour de 50 mmHg (choc hémorragique progressif). Le spectre de la puissance de la fréquence cardiaque a été quantifié en composantes de basses fréquences (BF) (0,04–0,15 Hz) et de hautes fréquences (HF) (0,15–0,4 Hz).Résultats: Dans le groupe bradycardie, les BF et HF ont augmenté après l’hémorragie massive, mais lors du choc hémorragique progressif, ces composantes ont diminué pendant que la FC augmentait. Dans le groupe tachycardie, les BF ont augmenté après l’hémorragie massive, mais lors du choc, elles ont baissé en même temps que survenait la suppression continue des HF.Conclusion: L’hémorragie massive a causé deux types de réaction de la FC: la bradycardie et la tachycardie. Le profil de VFC a affiché des caractéristiques autonomes différentielles, ce qui en fait un outil valable pour évaluer différents degrés de choc hémorragique.

Effects of different triggering systems and external PEEP on trigger capability of the ventilator

ObjectiveThe triggering capability of both the pressure and flow triggering systems of the Servo 300 ventilator (Siemens-Elema, Sweden) was compared at various levels of positive end-expiratory pressure (PEEP), airway resistance (Raw), inspiratory effort and air leak, using a mechanical lung model.DesignThe ventilator was connected to a two bellows-in-series-type lung model with various mechanical properties. Lung complicance and chest wall compliance were 0.03 and 0.12 l/cmH2O, respectively. Raw was 5, 20 and 50 cmH2O/l/s. Respiratory rate was 15 breaths/min. To compare the triggering capability of both systems, the sensitivity of pressure and flow triggered pressure support ventilation (PSV) was adjusted to be equal by observing the triggering time at 0 cmH2O PEEP and 16 cmH2O of pressure support (PS) with no air leak. No auto-PEEP was developed. In the measurement of trigger delay, the PS level ranged from 16 to 22 cmH2O to attain a set tidal volume (VT) of 470 ml at a Raw of 5, 20 and 50 cmH2O/l/s. The PEEP level was then changed from 0, 5 and 10 cmH2O at a PS level of 17 cmH2O and Raw of 5 and 20 cmH2O/l/s, and the trigger delay was determined. The effect of various levels of air leak and inspiratory effort on triggering capability was also evaluated. Inspiratory effort during triggering delay was estimated by measurements of pressure differentials of airway pressure (Paw) and driving pressure in the diaphragm bellows (Pdriv) in both systems.Measurements and resultsThere were no significant differences in trigger delay between the two triggering systems at the various PEEP and Raw levels. At the matched sensitivity level, air leak decreased trigger delay in both systems, and additional PEEP caused auto-cycling. A low inspiratory drive increased trigger delay in the pressure sensing system, while trigger delay was not affected in the flow sensing system. The Paw and Pdriv differentials were lower in flow triggering than in pressure triggering.ConclusionsWith respect to triggering delay, the triggering capabilities of the pressure and flow sensing systems were comparable with and without PEEP and/or high air-way resistance at the same sensitivity level, unless low inspiratory drive and air leak were present. In terms of pressure differentials, the flow triggering system may require less inspiratory effort to trigger the ventilator than that of the pressure triggering system with a comparable triggering time. However, this difference may be extremely small.

Is out-of-hospital intubation by paramedics valid enough to be continued?

To the Editor: Takei et al. [1] reported that out-of-hospital intubation by paramedics was associated with increased incidence of sustained return of spontaneous circulation comparing with bag-valve-mask ventilation and alternative airway techniques. Their findings are consistent with previous studies, which have provoked the current worldwide trend of reluctance to support out-of-hospital intubation by paramedics. Out-of-hospital intubation by paramedics has been implemented for several decades in an effort to improve outcomes from cardiac arrest and major trauma in Western countries. Increasing evidence suggests that tracheal intubation is not the optimal method of out-of-hospital airway management by paramedics and may be detrimental to patient outcome. For pediatric patients and cases of severe multiple trauma and head injury, a developing body of literature indicates adverse survival outcome of out-ofhospital tracheal intubation by paramedics. The most recent studies have shown that out-of-hospital intubation is associated with decreased survival to hospital discharge among out-of-hospital cardiac arrest patients comparing with bag-valve-mask ventilation [2–4]. In the light of the findings of these reports, a number of articles and guidelines recommend discontinuing the current practices of outof-hospital intubation by paramedics. For instance, a critical review from a scientific UK committee concluded that out-of-hospital intubation by paramedics was more likely to be harmful than beneficial [5]. Other guidelines also recommend that paramedics should not perform tracheal intubation when performing resuscitation [6]. Similar to previous studies, the authors revealed that out-of-hospital intubation did not improve clinically robust outcomes (i.e., survival to discharge and neurological performance). Their data implied that intubation by paramedics might only result in increased burden for hospitals. They might consider that sustained return of spontaneous circulation was a significant measure to evaluate the outcome of cardiac arrests. However, the primary outcome measure has been survival to hospital discharge in most of the current literature investigating the impact of out-ofhospital intubation. They suggested not to discontinue outof-hospital intubation under limited indication criteria, at least in cardiac arrest with noncardiac origin. It is hard to determine the reason why they justified continuing out-ofhospital intubation by paramedics with tenuous or even negative evidence to support it. The authors excluded the cases where attempts of advanced airway management failed because they expected poor prognosis of such cases [1]. In 641 cases, advanced airway management was attempted by intubation-certified paramedics. Of those, advanced airway management failed or was discontinued in 72 cases. That is, intubation-certified paramedics did not successfully handle the airway in more than 10% of the patients requiring advanced airway management. The authors did not depict these failed cases in detail, and they completely abandoned them in their analysis. However, the failed cases after intubation attempts are necessary to be investigated intensely because they might represent the overall skills of intubation and airway management by paramedics. No intubation will be accomplished without an attempt, and any attempts could An answer to this letter to the editor is available at doi:10.1007/s00540-011-1139-y.

Evaluation of dilators for central venous catheterization using an experimental model

PurposeSkin incision before percutaneous central venous catheterization may cause serious hemorrhage and/or skin cicatrization. To minimize these adverse effects, we improved the shape of a dilator and coated it with lubricant to reduce insertion load.MethodsWe selected three types of dilators from different manufacturers. Each brand was widely available on the market in Japan. We redesigned one model with modified multitapering angles. Six types of dilators in total (three manufactured dilators, one manufactured dilator with lubricant, and the newly modified dilator +/− lubricant) were examined regarding load of insertion using pork muscle covered with porcine skin. Among these dilators, two manufactured dilators and the newly modified one with lubricant were also investigated regarding insertion load with or without skin incision.ResultsThe minimum load of insertion was observed in the newly modified dilator with lubricant. The modified dilator attenuated the insertion load by up to 50% of the manufactured dilator, and the lubricant also reduced load by up to 16%. The insertion load of the modified dilator coated with lubricant was comparable to that of the manufactured dilators inserted with a 2-mm skin incision.ConclusionThe lubricant-coated dilator with multitapering angles was associated with decreased insertion load and thus facilitated its insertion without skin incision.

ST segment and T wave changes with the respiratory cycle during anesthesia for coronary artery bypass grafting.

Electrocardiographic changes with myocardial ischemia include ST segment and T wave alterations. In this report, we present a case in which the ST segment and T wave changed synchronously with respiration during coronary artery bypass grafting (CABG) surgery. There has been no report on changes of ST segment morphology along with respiration, the etiology of which may be similar to that of changes in T wave morphology [1,2[. However, this phenomenon may be noteworthy since it occurred during anesthetic management for CABG surgery and required special vigilance over ST segment and T wave changes.

Air ventilation during pulmonary artery banding operation

In pediatric cardiac anesthesia, we usually use high FIo2 to avoid hypoxia due to surgical and/or anesthetic mainpulation. However, it is well known that high FIo2 increases the pulmonary blood flow because of inhibition of hypoxic pulmonary vasoconstrictionl-3 • Thus, theoretically, ventilation with higher FIo2 might be disadvantageous to the patients who have left to right (L-R) shunt. We evaluated the effects of air ventilation and 100% O 2 ventilation on pulmonary and systemic circulation during anesthesia in infants who underwent PA-banding for reducing high pulmonary blood flow due to atrial septal defect (ASD) and/or ventricular septal defect (VSD).