Non-steady state monitoring by respiratory gas exchange

Traditionally, the study of CO₂ and O₂ kinetics in the body has been mostly confined to equilibrium conditions. However, the peri-anesthesia period and the critical care arena often involve conditions of non-steady state. The detection and explanation of CO₂ kinetics during non-steady state pathophysiology have required the development of new methodologies, including the CO₂ expirogram, average alveolar expired PCO₂, and CO₂ volume exhaled per breath. Several clinically relevant examples of non-steady state CO₂ kinetics perturbations are examined, including abrupt decrease in cardiac output, application of positive end-expiratory pressure during mechanical ventilation, and occurrence of pulmonary embolism. The lesser known area of non-steady state O₂ kinetics is introduced, including the measurement of pulmonary O₂ uptake per breath. Future directions include the study of the respiratory quotient per breath, where the anaerobic threshold during anesthesia is identified by increasing respiratory quotient. This revised version was published online in July 2006 with corrections to the Cover Date.     

Circulatory and diuretic effects of dopexamine infusion in low-birth-weight infants with respiratory failure

Objective To investigate the effects of infusion of dopexamine hydrochloride, a new synthetic catecholamine, on cardiopulmonary status and urine output in neonates with respiratory and circulatory failure.Design Prospective clinical study with each patient serving as his own control.Setting Intensive care unit (14 beds) in a 300-bed paediatric teaching hospital.Patients Seventeen neonates with low birth weight (LBW) requiring mechanical ventilation in the first 4 days of life, who initially had two of the following symptoms: hypotension, oliguria, metabolic acidosis with base deficit >10 and failure to respond to volume loading.Interventions Cardiopulmonary variables, diuresis and acid-base status were measured before and after volume loading, in patients who did not improve infusion of dopexamine was started at a dose of 2g kg^–1 min^–1 which was titrated to achieve blood pressure, urine output, and base deficit in normal range. Observations were continued for a period of 5 h.Measurements and results Systolic blood pressure increased significantly after 3 h. of dopexamine infusion and remained elevated up to the end of the study period. Diastolic and mean blood pressure increased slightly (NS). Diuresis increased significantly from the 4th h of dopexamine infusion. Arterial blood pH increased significantly from baseline at 5 h after the start of dopexamine administration. There was also a significant imporovement in the PtcO₂/PaO₂ index.Conclusion In neonates with respiratory and circulatory failure, dopexamine increases blood pressure and improves arterial pH and urine output.The work described was also presented in part at the First Congress of Pediatric Intensive Care, Baltimore, Md., USA in June 1992     

咖啡因对犬膈肌疲劳的治疗作用

用１４只实验犬观察咖啡因对膈肌疲劳的作用，以跨膈压曲线（ＰｄｉＦ曲线）作为评价膈肌收缩力的指标。膈肌疲劳模型用连续电刺激两侧膈神经的方法制备。结果：咖啡因（２０ｍｇ／ｋｇ）可显著增强疲劳后膈肌的收缩力，而且，咖啡因对膈肌的正性肌力作用与心输出量、肺总阻力及动态肺顺应性变化无关。作者讨论了咖啡因对膈肌肌力影响的可能机制，指出咖啡因在治疗慢性阻塞性肺病呼吸肌疲劳方面可能有一定临床价值     

Circulatory support for OPCAB procedures

During off-pump coronary artery bypass grafting (OPCAB) which allows complete revascularization through a median sternotomy, revascularization of the lateral and posterior walls requires the verticalization of the heart, which may cause haemodynamic disturbance. This concern has stimulated the development of circulatory support with mini-pumps. Initially, these pumps were designed for the right side of the heart, which was found to be the main contributor to haemodynamic instability under experimental conditions. The three types of mini-pumps that have been developed so far - two for the right side of the heart and one for both sides - are reviewed as well as a new concept of integrated cardiopulmonary bypass (CPB) circuit with reduced surface and priming volume. However, with increasing experience and improved methods of exposition, OPCAB has become a procedure that can be performed without support in the majority of the cases. Nevertheless, the concept of miniaturization and the possibility to insert these devices through a peripheral access has opened the way to new indications, mainly short-term circulatory support for acute heart failure. This development is welcome in a field where available devices are invasive and plagued with a heavy morbidity.     

Circulatory strain in everyday life of paraplegics.

Circulatory strain encountered in everyday life was low, taxing 15-24% of HRR. Similar results (Th8-Th12) was estimated from their heart rates (fH) recorded continuously by portable tape recorders for up to 48 h. The degree of strain was expressed in per cent of the individual's heart rate reserve (HRR), i.e. of the span between resting and maximal fH. The average strain of everyday life was low, taxing 15-24% of HRR. Similar results were obtained in a rehabilitated patient (subj. 5, Th12) at the hospital. fH higher than 50% of HRR which could be expected to have a training effect on the circulatory system was recoreded only when ambulating with crutches, driving wheelchair uphill, playing basketball, or during specific training (arm cranking in subj. 6 (Th2) who attended a post-rehabilitation course). The results confirm that daily life activities with no additional training are not intense enough to maintain the circulatory and physical fitness of rehabilitated paraplegics.     

Extracorporeal gas exchange for acute respiratory failure in adult patients: a systematic review

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2015 and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/annualupdate2015. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.     

反比通气与常规通气治疗犬呼吸窘迫综合征时的呼吸动力学比较

目的：探索反比通气的临床应用价值，观察反比通气对呼吸窘迫综合征时呼吸动力学的影响。方法：应用犬油酸型急性呼吸窘迫综合征（ＡＲＤＳ）模型，Ｓｉｅｍｅｎｓ９００Ｃ呼吸机和ＨＰ１１６５Ａ监护系统，观察反比通气时的气道峰压、气道阻力、平均气道压和动态胸肺顺应性变化。结果：反比通气组的气道峰压和气道阻力显著低于常规通气组（Ｐ均＜０．０１），平均气道压和动态胸肺顺应性显著高于常规通气组（Ｐ均＜０．０１～０．０５）。结论：反比通气在改善ＡＲＤＳ呼吸动力学方面明显优于常规通气，对ＡＲＤＳ的治疗有一定的临床应用价值。     

Low dose almitrine bismesylate improves pulmonary gas exchange during canine one-lung hypoxia

The effects of low dose almitrine bismesylate on pulmonary gas exchange, venous admixture, and pulmonary perfusion were examined in a canine one-lung hypoxic model. The left lung was ventilated with 10.4% oxygen, 89.3% nitrogen, and 0.3% halothane, while the right lung was ventilated with 99.7% oxygen and 0.3% halothane. Group 1 (n = 8) was given no other drug for 60 min. In group 2 (n = 10), consecutive almitrine doses of 0.5, 1, and 2 micrograms/kg.min were administered iv for 20 min/dose. Blood gas and central hemodynamic values remained unchanged in group 1. In group 2, significant increases in PaO2 and significant decreases in venous admixture, dependent on the dose administered, were observed. Mean PaO2 increased from 222 +/- 78 (SD) to 292 +/- 75 torr, and mean venous admixture decreased from 22 +/- 7% to 18 +/- 6% at 2 micrograms/kg.min. Both the decrease in mean left pulmonary blood flow and the increase in mean right pulmonary blood flow were slight, although the cardiac output was unchanged. These results indicate that iv infusion of 2 micrograms/kg.min of almitrine weakly enhances pulmonary vasoconstriction in a hypoxic area and improves pulmonary gas exchange in a moderately hypoxic condition.     

Prostaglandin E2 production by dispersed canine fundic mucosal cells. Contribution of macrophages and endothelial cells as major sources.

Endogenous prostaglandins (PGs) influence resistance of the gastric mucosa to injury, but the source of PGs is unknown. Using radioimmunoassay, we studied PG production by dispersed canine fundic mucosal cells. PGE2 production, stimulated by bradykinin, epidermal growth factor, zymosan, and calcium ionophore, was greater in the small-cell elutriator fraction (SCEF) than in the medium and large cell fractions, which contained mucous, chief, and parietal cells. Linear density gradients of SCEF cells revealed maximal PGE2 production in cells of light density. Mast, endocrine, and endothelial cells did not account for this PGE2 production. Macrophages, identified by uptake of acetylated-LDL, immunoreactivity with antibodies to the human Ia antigen, and phagocytosis of fluorescent latex particles, were enriched in the SCEF and correlated with PGE2 production in the density gradient. Magnetic separation of cells in the SCEF-ingesting iron particles enriched PGE2 production. Fractions enriched in endothelial cells present in intact capillary fragments, but depleted of macrophages, also produced PGE2. Regulation of PGE2 production differed among cell types. Fibroblasts were easily cultured from submucosa, but were not detected in the SCEF. We conclude that macrophages and capillary endothelial cells are major producers of PGE2 in the canine fundic mucosa.     

Plasma exchange for systemic lupus erythematosus.

Efficacy of plasma exchange in patients with systemic lupus erythematosus has not been supported by the results of the first non-controlled and retrospective studies. Nonetheless, they remain relevant for some selected patients with life-threatening manifestations and/or severe therapy-resistant manifestations. They can be used as an adjuvant therapy in combination with corticosteroids and, when required, other immunosuppressant(s) for refractory renal disease, alveolar hemorrhage, some neuropsychiatric manifestations, thrombotic thrombocytopenic purpura, catastrophic antiphospholipid syndrome, hyperviscosity syndrome or symptomatic cryoglobulinemia. The use of newer technologies, like immunoadsorption, possibly in combination with recent biologics, might, in the future, offer some new perspectives for extracorporeal therapy of systemic lupus erythematosus.     

Surfactant treatment impairs gas exchange in a canine model of acute lung injury

The effectiveness of surfactant (SURF) treatment in acute lung injury in the adult is controversial. In this study, we tested the effectiveness of early surfactant treatment in a commonly used animal model of acute lung injury, phorbol-myristate acetate (PMA), to see if it would attenuate the progression of lung injury. We measured the effect on lung compliance and whether positive end-expiratory pressure (PEEP) (10 cm H2O) during SURF administration had a synergistic effect. METHODS: Four groups of anesthetized dogs were studied: a) normals; b) PMA injury only; c) PMA injury + SURF; and d) PMA + SURF + PEEP. Lung injury was induced with 25-30 microg/kg of PMA. Responses were measured over 7 hrs. Surfactant was administered in the form of Survanta, 4 x 25 mg/kg doses via tracheal instillation 2.5 hrs after PMA. For the group receiving PEEP, 10 cm H2O PEEP was begun 1.5 hrs after PMA, 1 hr before SURF. Postmortem, the left lung was excised and inflated three times to total lung capacity (volume at 30 cm H2O) and expiratory compliance was measured with 25-100 mL volume increments. The trachea was then clamped and trapped volume was determined by water displacement. RESULTS: PMA-induced lung injury significantly reduced expiratory compliance and total lung capacity (p < .05 from normal). Wet/dry lung weights did not differ between groups. SURF without PEEP further decreased lung compliance as compared with PMA only. CONCLUSIONS: SURF administration after PMA injury causes marked reductions in lung compliance when no PEEP is coadministered. However, the loss of static expiratory lung compliance appears partly ameliorated by application of PEEP + SURF. Given that tracheal instillation of SURF is known to acutely elevate lung impedance in the first few hours after administration, coadministration of PEEP appears to be critically important in counteracting these early effects of surfactant instillation on the lung.