J. Qvist

Hemodynamic responses to mechanical ventilation with PEEP: the effect of hypervolemia.

The hemodynamic effects of prolonged mechanical ventilation with positive end-expiratory pressure (PEEP), with and without blood volume augmentation, were studied in 18 beagles anesthetized with halothane (0.7 per cent end-tidal). Addition of 12 cm H2O PEEP during mechanical ventilation in normavolemic dogs was associated with reductions of transmural cardiac filling pressures, cardiac index and stroke index to 50 per cent of control values. Circulatory adaptation did not occur. Filling pressures and flow remained unchanged during the ensuing 8 hours when PEEP was maintained. They returned to control levels when PEEP was discontinued, except for the transmural right ventricular end-diastolic pressure, which remained elevated above control levels. Systemic vascular resistance was unchanged, but pulmonary vascular resistance doubled upon addition of PEEP. Following autologous whole blood transfusion (25 ml/kg) during mechanical ventilation with PEEP, cardiac index returned to, and remained at, control levels. After PEEP was discontinued, cardiac index increased acutely and remained elevated for the remainder of the study period (as long as 7 hours). Comparable transfusion during mechanical ventilation without PEEP elevated cardiac index only transiently. Right atrial, pulmonary capillary wedge, and right and left ventricular end-diastolic pressures showed marked increases relative to atmospheric with PEEP and after transfusion. Calculated transmural pressures demonstrated clear reductions with application of PEEP, followed by increases to control levels with transfusion and further increases to above control when PEEP was discontinued. Study of ventricular function curves revealed that changes in filling pressures and not to changes in ventricular contractility. Transmural pulmonary arterial diastolic pressure rose throughout the 12 hours of study, despite return of pulmonary vascular resistance to control level with removal of PEEP. Thus, acute decreases in cardiac filling pressure, cardiac index, and stroke index persist consequent to application of PEEP, and circulatory adaptation does not occur. The apparent hemodynamic deterioration may be reversed by blood volume augmentation, but when PEEP is discontinued, hypervolemia with consequent increases in filling pressures and a move along a ventricular function curve will occur. Changes in cardiac index will depend upon the overall state of right and left ventricular contractility.

Interhospital comparisons of patient outcome from intensive care: importance of lead-time bias

We studied 432 admissions to two Danish ICUs by using a standard severity of illness classification system to assess utilization and outcome. Substantial differences in utilization were found. The patients in Hospital 2 were younger, had better previous health records, and were admitted significantly more often for active treatment as opposed to monitoring than the patients in Hospital 1. Although their measured severity of illness was similar, patients at Hospital 2 received significantly more therapy and their mortality exceeded that of the patients at Hospital 1. The mortality rate of Hospital 2 also exceeded that predicted from a recent survey of U.S. hospitals. We found, however, that 35% of the patients at Hospital 2 had been transferred to the ICU from other ICUs. This created the possibility of an adverse selection and lead-time bias for the patients at Hospital 2. These findings indicate that although national and international comparisons of intensive care are now possible using common classification systems, this progress has created a new need for more precise measurement of potential confounding biases, such as the duration of intensive care services received before formal ICU admission.

Pulmonary vascular lesions in the adult respiratory distress syndrome caused by inhalation of zinc chloride smoke : a morphometric study

Two soldiers were fatally injured by accidental inhalation of zinc chloride (ZnCl2) from a smoke bomb. Although exposed to a relatively short but high smoke concentration, acute injury was minor and for 10 days the patients were clinically satisfactory. Unexpectedly, both then rapidly developed features typical of severe adult respiratory distress syndrome with pulmonary hypertension. Intubation and mechanical ventilation were instigated on day 15 (patient no. 1) and day 12 (patient no. 2) after the inhalation, but death followed at days 25 and 32, respectively. Lung vascular injury was assessed by angiography and morphometric techniques. The lungs showed extensive interstitial and intra-alveolar space fibrosis. Vessels showed a significant lumen reduction by contracture (that is, reduction in vessel external diameter) affecting preacinar and intraacinar arterial and venous segments, the extent of injury suggesting that hexite causes more severe venous injury than seen in other types of adult respiratory distress syndrome. In microvessels there was obliteration and widespread occlusion by endothelial cell proliferation and clot. No evidence of infection was identified during life or at autopsy. It is unclear whether the long lag time was due to the fact that the infection was not a complicating event or because steroids, administered prophylactically, had sufficed to delay, but not to prevent, the amplification of injury that seems responsible for the adult respiratory distress syndrome.

Pulmonary metabolism during diving: conditioning blood for the brain.

During experimental diving by the awake Weddell seal, blood glucose concentration falls consistently. A large fraction of the glucose consumed from the central circulating blood appears as lactate. During diving, the lung utilizes blood lactate in preference to blood glucose as a source of both carbon and energy, and it is able to release glucose into pulmonary venous blood to supplement the supply available for brain metabolism.

Transient compartment syndrome of the forearm after attempted radial artery cannulation

Radial artery cannulation for continuous intraoperative monitoring of arterial blood pressure is considered a safe procedure. One complication of arterial cannulation is hematoma formation at the time of insertion or removal of the catheter. Bleeding is usually self-limited or will stop with compression without significant sequelae, even in the anticoagulated patient. We describe a case of hematoma with a transient compartment syndrome of the forearm after attempts to cannulate the radial artery for intraoperative monitoring purposes.

Positive airway pressure in lambs spontaneously breathing air and oxygen

The effects of 10 cm H2O positive endexpiratory pressure (PEEP) were studied in 26 unrestrained Hampshire and Corriedale lambs, breathing spontaneously air or pure oxygen. No changes in lung morphology, pulmonary mechanics or arterial blood gas tensions were detected after air breathing with 10 cm H2O PEEP for one week. No changes were found in mean pulmonary artery pressure, pulmonary capillary wedge pressure, pulmonary vascular resistance or cardiac output in oxygen breathing lambs until minutes before death. Addition of PEEP to oxygen breathing accelerated the development of respiratory acidemia and death (PEEP group mean lifespan 5434 hr, without PEEP mean lifespan 7134 hr). Morphologic changes of acute oxygen toxicity were present in oxygen breathing lambs and lung water was increased. Oxygen breathing lambs died from apnea with hypercarbia and a markedly increased (A-a) DO2. An increase in pulmonary vascular resistance or right ventricular failure do not appear to be major factors in the syndrome of fulminant acute respiratory insufficiency due to oxygen toxicity in lambs.

Arterial Oxygen Tensions and Hemoglobin Concentrations of the Free Diving Antarctic Weddell Seal

Diving physiology has interested scientists for over a century (Blix and Folkow 1983). The mammals and birds which dive to great depths for long periods to exploit food sources deep in the ocean have developed remarkable evolutionary adaptations to optimize their diving ability. Some of the respiratory accommodations are obvious to casual inspection, such as a small-lung-volume-to-body-size ratio, thoracic cage mobility, and circular bronchial cartilages (Kooyman 1981). Some respiratory and circulatory adaptations have been observed in the laboratory; captive seals have been forced to dive while monitored by invasive instrumentation (Swan Ganz catheters, left ventricular catheters) (Zapol et al. 1979) or have been subjected to the pressure of depth (hyperbaric chamber) (Kooyman et al. 1972). However, it has been clear for over 10 years that laboratory diving forces an abnormally profound diving reflex, including intense bradycardia and marked regional arterial vasoconstriction (Blix and Folkow 1983; Zapol et al. 1979). This intense bradycardia is far slower than that recorded in free-swimming seals with an electrocardiogram (ECG) and breakoff leads (Kooyman and Campbell 1972).

Dilatation of the trachea treated with the NL-tracheostomy tube

The NL-tracheostomy tube has a large diameter, large residual volume cuff with automatic and instant cuff pressure regulation. It has been shown in clinical studies to prevent mucosal damage; and depending on airway pressure, it should in theory prevent or delay the onset of trachea dilatation. The authors report 2 patients who developed severe tracheal dilatation with use of standard low volume cuffs during prolonged mechanical ventilation. Placement of the NL-tracheostomy tube with a special long intratracheal leg and cuff positioned below the dilatation abolished the acute problems of air leakage. Tracheal dilatation at the new cuff site did not develop in 1 patient and was slowed in onset in the 2nd patient, who needed high inflation pressures.

REGIONAL BLOOD FLOW DURING SIMULATED DIVING OF THE CONSCIOUS ANTARCTIC WEDDELL SEAL

Publisher Summary This chapter discusses a study to analyze regional blood flow during the simulated diving of the conscious Antarctic Weddell seal. This study used 25 micra radioactive carbon microsphere techniques. Four isotopic labels were serially injected into the left ventricle of the awake seal during control and breath-hold diving. Organ blood flow distribution was sampled and counted on a gamma spectrometer. Fifteen adult pregnant and male seals (300–500 kg) were captured on the fast ice off Turtle Rock and taken by sledge to the laboratory. After Ketamine injection, under spontaneous Halothane anesthesia, a flipper artery and a left ventricular or proximal aortic catheter was passed. In 5 gravid seals, a fetal flipper artery was also catheterized at caesarian section. It was observed that cardiac output and left ventricular blood flow were reduced by 85% after 8–12 min during diving despite PaO 2 32 mmHg. Cerebral blood flow was unchanged, while adrenal blood flow was maintained at a reduced level. In 3 late gestation seals, descending aorta microsphere injection revealed an increase from 8 to 38% of the injected dose lodged in the placenta during diving.