不同潮气量对体重超重或肥胖患者肺氧合功能的影响

目的分析不同潮气量对体重超重或肥胖患者机械通气肺氧合功能的影响,探索一种肺保护通气模式。方法选取体重超过重或肥胖拟择期非心脏手术患者80例,将其随机分成男性实验组、女性实验组、男性对照组、女性对照组。两组均采用丙泊酚复合瑞芬太尼靶控静脉输注,顺阿曲库铵诱导。喉镜明视下气管插管后,对照组的潮气量:潮气量=体重(kg)×8 ml/kg,实验组潮气量=平均体重指数×身高(m)2×8 ml/kg,R11次/min,I∶E=1∶2,行机械通气。丙泊酚复合瑞芬太尼持续靶控输注;顺阿曲库铵间断静注。分别在机械通气开始、机械通气后1 h作血气分析。结果①实验组潮气量低于对照组(P0.05)。②实验组机械通气1 h氧合指数(1 h OI)高于对照组(P0.05);男性对照组1 h OI300发生率高于实验组(分别是9例,2例,P0.05),女性对照组机械通气1 h OI300发生率高于实验组(分别是8例,1例,P0.05)。③实验组机械通气1 h二氧化碳分压(1 h PaCO2)高于对照组(P0.05)。结论较小的潮气量可明显减少肺氧合功能障碍发生的风险,是一种有效地肺保护通气模式。     

Theoretical estimation of retinal oxygenation during retinal artery occlusion

The aim of the present work was to simulate the oxygenation of the whole retina under normal conditions as well as during retinal ischemia. A differential equation describing how oxygen is transported from blood to tissue, diffuses through the tissue and is consumed according to Michaelis-Menten kinetics was constructed. The outer retina was divided into three regions of which one was set to have consumption. The inner retina was considered as one uniform region with respect to maximal rate of oxygen consumption and blood flow. The results suggest that extreme hyperoxia would be needed to make the choroid capable of supplying the whole retina during total retinal artery occlusion and moreover confirm that light might to some extent be beneficial. As supplying 100% oxygen by nose cannula or common oxygen mask can hardly increase the arterial oxygen tension to the levels needed to rescue the whole retina, the effects of oxygen treatment of total retinal artery occlusion are expected to be modest, both in darkness and light, unless a non-rebreather face mask system is used.     

单肺通气时持续气道正压对动脉氧合的影响

目的 利用自制的气道正压装置,对单肺通气下开胸病人的无通气肺施加志气道正压,观察无通气肺接受不同水平的持续气道正压时对动脉氧合的影响。方法 １９例需在单肺通气下开胸手术的病人（ＡＳＡ：１－２级）,随机分成２组,组１（ｎ＝１０）,对无通气肺施加０．２９４ｋＰａ（３ｃｍＨ２Ｏ）的气道持续正压（ＣＰＡＰ－３）,组２（ｎ＝９）;对无 敢肺施加０．４９０ｋＰａ（５ｃｈｍＨ２Ｏ）的气道持续正压（ＣＰＡＰ－５）     

Sildenafil attenuates pulmonary arterial pressure but does not improve oxygenation during ARDS

Objective  

Pulmonary hypertension is a characteristic feature of acute respiratory distress syndrome (ARDS) and contributes to mortality. Administration of sildenafil in ambulatory patients with pulmonary hypertension improves oxygenation and ameliorates pulmonary hypertension. Our aim was to determine whether sildenafil is beneficial for patients with ARDS.     

The oxygenation ratio during mechanical ventilation in children: The role of tidal volume and positive end-expiratory pressure

Objective

The objective of this study is to analyze the role of tidal volume (Vt) and positive end-expiratory pressure on the oxygenation ratio (OR) (Pao₂/Fio₂) during mechanical ventilation (MV) in children with a normal pulmonary gas exchange on admission.

Methods

A retrospective cohort study of children with an admission OR greater than 300 mm Hg and duration of MV greater than 48 hours (n = 96) was done. We analyzed Vt, Fio₂, Pao₂, and positive end-expiratory pressure and calculated Vt (mL/kg) and Pao₂/Fio₂ based on the measured Vt and weight. Patients were divided into group 1, Vt less than 9 mL/kg (n = 24); 2, Vt 9 to 12 mL/kg (n = 58); and 3, Vt 12 mL/kg or higher (n = 14).

Results

Baseline characteristics and OR were comparable. Forty-one percent of patients developed OR less than 300 mm Hg. The proportion of patients developing an OR less than 300 mm Hg was lowest in group 1 and highest in group 3, and differences became more pronounced with longer MV duration: 56%, 58%, and 89% on day 5; 29%, 65%, and 100% on day 7 (P = .05); 0%, 40%, and 100% on day 10 (P = .03). In patients maintaining an OR greater than 300 mm Hg during 10 days of MV, Vt was 9.3 ± 1.0 vs 12.7 ± 4.8 mL/kg in patients developing an OR less than 300 mm Hg (P = .05). Mechanical ventilation duration was longer in children developing OR less than 300 mm Hg (P < .01). Positive end-expiratory pressure levels were not significantly different between groups.

Conclusion

In ventilated children, Vt was greater than 9 mL/kg were associated with increased development of an OR less than 300 mm Hg and longer duration of MV.     

The pulmonary distress syndrome during acute arterial occlusion of the lower extremities]

After surgery for acute arterial occlusion in the lower extremities 59 patients have developed tachypnea, respiratory alkalosis and arterial hypoxemia. These symptoms persisted over the whole postoperative period. In 66% of dead patients pulmonary changes have been observed and only in 34% of patients who died suddenly the lungs were unaffected. Morphological changes in the lungs are most marked in long-standing ischemia and have the signs of the "shock lung" (adult respiratory distress syndrome). Pronounced changes in the respiratory function, acid-base balance, blood gas composition can account for a more severe course of the disease, deteriorate the prognosis, predetermine multiorgan failure in the early postoperative period.     

Effect of remifentanil on arterial oxygenation during one-lung ventilation

This study was designed to assess the dose-related effects of remifentanil on arterial oxygenation during one-lung ventilation (OLV) under total intravenous anaesthesia with propofol. A total of 104 patients scheduled for elective lung resection surgery requiring OLV were randomly assigned to one of four groups with a target effect-site concentration (Ce) of remifentanil of 0.5, 1, 2 or 4 ng/ml. Patients were anaesthetized with propofol and remifentanil in 100% oxygen. Arterial blood gas analysis was performed after 15 min of two-lung ventilation (TLV15, baseline) and after 15 and 30 min of OLV (OLV15 and OLV30). Mean arterial oxygen tension (PaO2) decreased significantly at OLV15 and OLV30 compared with baseline in all groups, but was comparable in the four groups at each time point, suggesting that remifentanil infusion with a Ce < or =4 ng/ml can be successfully used for anaesthesia with propofol during OLV in lung surgery without any significant changes in PaO2.     

Influence of leg position and environmental temperature on segmental volume expansion during venous occlusion plethysmography

Blood flow determinations by venous occlusion plethysmography applying the strain-gauge technique are frequently used. A problem with the strain-gauge technique is that the relationship between venous volume and transmural pressure is not linear and, furthermore, changes with the sympathetic tone. The present study tests the hypothesis that these factors lead to a redistribution of venous blood, which may impair the accuracy of the technique. The relative volume expansion rates of four leg segments were studied with the leg in different positions and at disparate temperatures, thereby inducing varying venous pressures and sympathetic tone ( n =6). With elevated leg and relaxed veins (at 50 degrees C), the distal thigh showed a relatively low expansion rate (25.8+/-4.5 ml.min(-1).l(-1)), whereas values in the calf segments were higher (34.5-39.0 ml.min(-1).l(-1)). With lower initial transmural pressure, calf segments can increase their volume much more during occlusion compared with the distal thigh. In a higher transmural pressure region (lowered leg), the difference in compliance between limb segments is less. In this case, compliance and volume expansion rate was higher in the distal thigh (14.2, 13.5 and 22.2 ml.min(-1).l(-1) at 10, 20 and 50 degrees C respectively) than in the calf segments (for the distal calf: 6.4, 7.7 and 16.2 ml.min(-1).l(-1) respectively). There was a significant interaction ( P <0.001) between temperature and leg position, indicating a higher degree of sympathetic vasoactivity in the calf. It is concluded that blood flow determination by strain-gauge plethysmography is less accurate, due to a potential redistribution of the venous blood. Therefore possible influences of variations in sympathetic tone and venous pressure must be considered even in intra-individual comparisons, especially in interventional studies.     

Determinants of tidal volume during high-frequency oscillation

OBJECTIVE: High-frequency oscillation has been proposed for use in adult acute respiratory distress syndrome. However, limited data are available on the effect of pressure amplitude and rate (Hz) on tidal volumes delivered during high-frequency oscillation in adults. DESIGN: Prospective, animal model, lung injury study. SETTING: Large-animal laboratory of a university-affiliated medical center. SUBJECTS: Nine sheep (29.2 +/- 2.4 kg). INTERVENTIONS: Severe lung injury was induced by repeated saline lung lavage. After stabilization, high-frequency oscillation was initiated at a mean airway pressure equal to the point of maximum curvature on the deflation limb of the pressure-volume curve (26 +/- 1.9 cm H2O). Tidal volume at all combinations of rates of 4, 6, 8, and 10 Hz, pressure amplitudes of 30, 40, 50, and 60 cm H2O, and inspiratory/expiratory ratios of 1:1 and 1:2 (using the Sensormedics 3100B oscillator) were measured. Flow was measured by a pneumotachometer, amplified and digitized at 1000 Hz. Three breaths were analyzed at each setting. MEASUREMENTS AND MAIN RESULTS: At both inspiratory/expiratory ratios, tidal volume was directly proportional to pressure amplitude and inversely proportional to frequency. During an inspiratory/expiratory ratio of 1:1, at 60 cm H2O pressure amplitude and 4 Hz, a tidal volume of 129.1 +/- 34.8 mL (4.4 +/- 1.2 mL/kg) was delivered. CONCLUSIONS: At low rates and high-pressure amplitudes in this model, tidal volumes approaching conventional mechanical ventilation can be delivered during high-frequency oscillation.     

Clinical significance of pulmonary artery occlusion pressure

BACKGROUND: Ppao values are routinely used to assess pulmonary vascular status and LV performance. Regrettably, under many common clinically relevant conditions, even when Ppao values are measured accurately, Ppao values at baseline and in response to therapy often reflect an inaccurate measure of cardiovascular status. RESULTS AND CONCLUSIONS: Thus, caution should be used when applying measures of Ppao in determining therapy if changes in RV volume, hyperinflation, or LV diastolic compliance are simultaneously occurring.     

Lamellar body depletion in dogs undergoing pulmonary artery occlusion.

We have investigated the relationship between pulmonary artery occlusion (PAO) and the surfactant system of the lung by studying the ultrastructural responses of type II alveolar pneumocytes to PAO of 4-12 h duration in 16 mongrel dogs. In six of these animals, the occluded lung was allowed to reperfuse for 6 h before killing and in four animals subjected to PAO of 4 h duration, the occluded lung was ventilated with 5% CO2 balance air. PAO by itself resulted in a dramatic 80% reduction in the volumetric density of lamellar bodies (LB) in the type II cells. This resulted predominantly from a decrese in volume of the individual LB. Although reperfusion was associated with an increase in LB volume density toward normal, 6 h of reperfusion was insufficient to re-establish normal type II cellular morphology. Ventilation of the occluded lung with 5% CO2 prevented LB depletion indicating that alveolar CO2 tension may affect the release and/or synthesis of LB in type II pneumocytes.     

Rupture of pulmonary artery induced by balloon occlusion pulmonary angiography

A case of pulmonary artery rupture induced by balloon occlusion pulmonary angiography (BOPA) is reported. A flow-directed pulmonary artery catheter had been inserted for hemodynamic monitoring in a septic shock patient complicated by acute respiratory distress syndrome. To check for pulmonary damage, BOPA was performed immediately after hemodynamic measurement. Just as the hand injection of contrast medium was ending, the patient began to cough and a small amount of hemoptysis was observed. The angiogram showed the extravasation of contrast medium from the distal pulmonary artery to the situation of catheter tip. Pulmonary hemorrhage was controlled with mechanical ventilatory support with 10 cmH₂O positive end-expiratory pressure and no specific therapy was required. This complication should be kept in mind and using a power injector to avoid injurious transient high pressure pulse is recommended.     

Surfactant application during extracorporeal membrane oxygenation improves lung volume and pulmonary mechanics in children with respiratory failure

Introduction  

This study was performed to determine whether surfactant application during extracorporeal membrane oxygenation (ECMO) improves lung volume, pulmonary mechanics, and chest radiographic findings in children with respiratory failure or after cardiac surgery.     

Effects of bronchoalveolar lavage volume on arterial oxygenation in mechanically ventilated patients with pneumonia

OBJECTIVE: To assess the effect of bronchoalveolar lavage (BAL) volume on arterial oxygenation in critically ill patients with pneumonia. DESIGN: Randomized clinical comparison. SETTING: Six-bed respiratory intensive care unit of a 850-bed tertiary care university hospital. PATIENTS: Thirty-seven intubated and mechanically ventilated patients with clinical suspicion of pneumonia. INTERVENTIONS: Bronchoscopically guided protected specimen brush (PSB) followed by either a "high volume" BAL (n = 16, protected catheter, mean volume: 131 +/- 14 ml) or a "low volume" BAL (n = 21, protected double-plugged catheter, 40 ml volume for all patients). MEASUREMENTS: Arterial oxygen tension/fractional inspired oxygen (PaO2/FIO2) and mean arterial pressure (MAP) before and up to 24 h after the intervention. Bacterial growth in quantitative cultures. Analysis of variance for repeated measurements with inter-subject factors. RESULTS: All patients showed a lower PaO2/FIO2 ratio and higher MAP after the diagnostic procedure, without differences between the study arms (p = 0.608 and p = 0.967, respectively). Patients with significant bacterial growth (p = 0.014) and patients without preemptive antibiotic (p = 0.042) therapy showed a more profound and longer decrease in arterial oxygenation after the diagnostic procedure. CONCLUSIONS: A decrease in the PaO2/FIO2 ratio was observed in all patients after a combined diagnostic procedure, independent of the BAL volume used. A significant bacterial burden recovered from the alveoli and no preemptive antibiotic therapy were associated with a larger and longer-lasting decrease in arterial oxygenation.     

Central venous pressure, pulmonary artery occlusion pressure, intrathoracic blood volume, and right ventricular end-diastolic volume as indicators of cardiac preload

Central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP) and right ventricular end-diastolic volume (RVEDV) are often regarded as indicators of both circulating blood volume and cardiac preload. To evaluate these relationships, the response of each variable to induced volume shifts was tested. The relationships between these variables and cardiac index (CI) and stroke volume index (SVI) was also recorded to assess the utility of each variable as an indicator of cardiac preload. The responses of the new variable intrathoracic blood volume (ITBV) to the same maneuvers was also tested. To examine the effects of changes in cardiac output alone on ITBV, the effects of infusing dobutamine were studied.

Ten anesthetized piglets were studied during conditions of normovolemia, hypovolemia, and hypervolemia. The effects of an infusion of dobutamine were examined under normovolemia and hypovolemia. Cardiac output was measured by thermodilution, and ITBV was measured by double-indicator dilution.

CI was correlated to CVP with r² = .42 (P ≤ .01), to PAOP with r² = .43 (P ≤ 5.01), to RVEDV index with r² = .21 (P ≤ .01), and to ITBV with r² = .78 (P ≤ .01) (pooled absolute values). Bias (mean difference of the percent changes with NORMOVOLEMIA = 100%) ± 1 SD; for SVI - ITBV index was 1 ± 22%, for SVI — CVP it was −128 ± 214%; for SVI — PAOP it was −36 ± 46%; and for SVI -RVEDV index it was 1 ± 29%. Dobutamine infusion increased heart rate (to about 190 × min⁻¹) and CI by 30% in normovolemia and hypovolemia, while ITBV remained basically unchanged.

Under the experimental conditions choosen neither CVP, PAOP, nor RVEDV reliably indicated changes in circulating blood volume, nor were they linearly and tightly correlated to the resulting changes in SVI. ITBV reflected both changes in volume status and the resulting alteration in cardiac output. The possibility that ITBV might be cardiac output-dependent was not supported. ITBV, therefore, shows potential as a clinically useful indicator of overall cardiac preload.     

Physiology in medicine: importance of hypoxic pulmonary vasoconstriction in maintaining arterial oxygenation during acute respiratory failure

Hypoxic pulmonary vasoconstriction continues to attract interest more than half a century after its original report because of persistent mystery about its biochemical mechanism and its exact physiological function. Recent work suggests an important role for pulmonary arteriolar smooth muscle cell oxygen-sensitive voltage-dependent potassium channels. Inhibition of these channels by decreased PO₂ inhibits outward potassium current, causing membrane depolarization, and calcium entry through voltage-dependent calcium channels. Endothelium-derived vasoconstricting and vasodilating mediators modulate this intrinsic smooth muscle cell reactivity to hypoxia. However, refined modeling of hypoxic pulmonary vasoconstriction operating as a feedback mechanism in inhomogeneous lungs, using more realistic stimulus-response curves and confronted with direct measurements of regional blood flow distribution, shows a more effective than previously assessed ability of this remarkable intrapulmonary reflex to improve gas exchange and arterial oxygenation. Further studies could show clinical benefit of pharmacological manipulation of hypoxic pulmonary vasoconstriction, in circumstances of life-threatening hypoxemia.