Stress failure of the blood-gas barrier

Benefits and harms of increased inspiratory oxygen concentrations

PURPOSE OF REVIEW

The topic of perioperative hyperoxia remains controversial, with valid arguments on both the 'pro' and 'con' side. On the 'pro' side, the prevention of surgical site infections was a strong argument, leading to the recommendation of the use of hyperoxia in the guidelines of the Center for Disease Control and the WHO. On the 'con' side, the pathophysiology of hyperoxia has increasingly been acknowledged, in particular the pulmonary side effects and aggravation of ischaemia/reperfusion injuries.

RECENT FINDINGS

Some 'pro' articles leading to the Center for Disease Control and WHO guidelines advocating perioperative hyperoxia have been retracted, and the recommendations were downgraded from 'strong' to 'conditional'. At the same time, evidence that supports a tailored, more restrictive use of oxygen, for example, in patients with myocardial infarction or following cardiac arrest, is accumulating.

SUMMARY

The change in recommendation exemplifies that despite much work performed on the field of hyperoxia recently, evidence on either side of the argument remains weak. Outcome-based research is needed for reaching a definite recommendation.

Pulmonary Complications After Spontaneous Aneurysmal Subarachnoid Hemorrhage: Experience from Barrow Neurological Institute

OBJECTIVE

Because the clinical course of spontaneous aneurysmal subarachnoid hemorrhage (aSAH) can be compromised by pulmonary complications, we sought to review posttreatment outcomes in aSAH patients with and without pulmonary complications.

METHODS

Patient demographic, clinical, and outcome data (March 2003-January 2007) were analyzed retrospectively. Patients underwent microsurgical or endovascular treatment for aSAH; pulmonary complications were reported. Outcomes were assessed using the Glasgow Outcome Scale (GOS) scores at the 1-year, 3-year, and 6-year follow-up visits.

RESULTS

The cohort comprised 471 patients (mean age, 53.7 ± 12.4 years; men, 332/471 [70%]). The mean Glasgow Coma Scale (GCS) score at presentation was 11.9 ± 3.0. Of 471 patients, 47% (n = 223) presented with a Hunt and Hess score of ≥3 and 76% (n = 357) with a Fisher grade of 3. Treatment was clipping for 69% (279/407) and coiling for 31% (128/407) of patients. Pulmonary complications occurred in 210 of 471 (45%) patients. Nearly one-half of patients were discharged to home (215/471, 46%), and more than one-half had a good outcome defined as a GOS score of 5 at their 1-year (226/403, 56%), 3-year (217/397, 55%), and 6-year (203/380, 53%) follow-up visits. Logistic regression showed age and GCS scores as outcome predictors at all time points, whereas pulmonary complications predicted poor outcome only at the 1-year follow-up visit.

CONCLUSIONS

Pulmonary problems represent the most common nonneurologic medical complications after aSAH. Despite advances in critical care, pulmonary complications represented predictors of short-term poor outcome only at the 1-year follow-up visit, whereas the medical history of the patient became more relevant for prognosis in long-term follow-up.

Strategies for whole lung tissue engineering

Recent work has demonstrated the feasibility of using decellularized lung extracellular matrix scaffolds to support the engineering of functional lung tissue in vitro. Rendered acellular through the use of detergents and other reagents, the scaffolds are mounted in organ-specific bioreactors where cells in the scaffold are provided with nutrients and appropriate mechanical stimuli such as ventilation and perfusion. Though initial studies are encouraging, a great deal remains to be done to advance the field and transition from rodent lungs to whole human tissue engineered lungs. To do so, a variety of hurdles must be overcome. In particular, a reliable source of human-sized scaffolds, as well as a method of terminal sterilization of scaffolds, must be identified. Continued research in lung cell and developmental biology will hopefully help identify the number and types of cells that will be required to regenerate functional lung tissue. Finally, bioreactor designs must be improved in order to provide more precise ventilation stimuli and vascular perfusion in order to avoid injury to or death of the cells cultivated within the scaffold. Ultimately, the success of efforts to engineer a functional lung in vitro will critically depend on the ability to create a fully endothelialized vascular network that provides sufficient barrier function and alveolar-capillary surface area to exchange gas at rates compatible with healthy lung function.

Non-cardiogenic pulmonary edema complicating electroconvulsive therapy: short review of the pathophysiology and diagnostic approach

Acute pulmonary edema complicating electroconvulsive therapy is an extremely uncommon event that has rarely been described in the literature. Different theories, including one suggesting a cardiogenic component, have been proposed to explain its genesis. The present report describes a classic presentation of this condition with review of its potential mechanisms and diagnostic approach. After successful completion of a session of electroconvulsive therapy, a 42-year-old woman with major depressive disorder developed acute systemic high blood pressure, shortness of breath, and hemoptysis. A chest radiograph demonstrated diffuse bilateral pulmonary infiltrates. Initially cardiogenic pulmonary edema was presumed, but an extensive diagnostic work-up demonstrated normal systolic and diastolic left ventricular function, and with only supportive measures, a complete clinical and radiographic recovery was achieved within 48 hours. The present case does not support any cardiogenic mechanism in the genesis of this condition.

Mechanisms of disease/hypothesis: neurogenic left ventricular dysfunction and neurogenic pulmonary oedema

BACKGROUND

Acute onset of cardiovascular dysfunction may be the result of insults to the central nervous and autonomic system. Several cerebral regions (insular cortex, lateral, hypothalamus, and brain stem) have been identified as part of the "central autonomic network". The brain stem plays an integral role in controlling and mediating autonomic tone.

PATIENT AND METHODS

Case reports.

RESULTS

These two case reports demonstrate the intimate connectivity between the cardiovascular/pulmonary system and the central nervous system in a 13-year-old girl with occipital angiomatosis, but no history of heart disease who developed profound left ventricular dysfunction and pulmonary oedema following pontine haemorrhage, and in a 5-year-old girl who developed severe pulmonary oedema after suffering from status epilepticus.

CONCLUSIONS

The two case reports suggest that cardiovascular dysfunction secondary to central nervous insults and neurogenic pulmonary oedema are not two separate clinical entities, but may very well encompass two different presentations of central autonomic disturbances.

Neurogenic pulmonary edema

Neurogenic pulmonary edema (NPE) is usually defined as an acute pulmonary edema occurring shortly after a central neurologic insult. It has been reported regularly for a long time in numerous and various injuries of the central nervous system in both adults and children, but remains poorly understood because of the complexity of its pathophysiologic mechanisms involving hemodynamic and inflammatory aspects. NPE seems to be under-diagnosed in acute neurologic injuries, partly because the prevention and detection of non-neurologic complications of acute cerebral insults are not at the forefront of the strategy of physicians. The presence of NPE should be high on the list of diagnoses when patients with central neurologic injury suddenly become dyspneic or present with a decreased P(a)o(2)/F(i)o(2) ratio. The associated mortality rate is high, but recovery is usually rapid with early and appropriate management. The treatment of NPE should aim to meet the oxygenation needs without impairing cerebral hemodynamics, to avoid pulmonary worsening and to treat possible associated myocardial dysfunction. During brain death, NPE may worsen myocardial dysfunction, preventing heart harvesting.