James V. Snyder

Global Ischemia in Dogs: Intracranial Pressures, Brain Blood Flow and Metabolism

Our earlier studies showed no secondary postischemic (PI) rise in cisterna magna pressure (CMP) for ten hours and no significant reduction in CBF (integrated N2O desaturation technique) for three and one-half hours after 15 minutes of systemic circulatory arrest. However, transtentorial pressure gradients may have developed, and CBF changes may have been masked by limitations of the N2O method in low flow states. In this study, 12 dogs were subjected to 15 minutes of aortic occlusion and studied for two hours PI. Immediately after restoration of circulation, cisterna magna, supracortical and lateral ventricle pressures rose to 35 to 40 torr, concomitant with a threefold increase in cerebral blood flow (133Xe clearance technique). By 30 minutes postischemia, cisterna magna and supracortical pressures had returned to control values but lateral ventricular pressures normalized slower. CBF decreased to and remained at 50% of preischemic values after 40 minutes PI. Cerebral glucose uptake increased markedly immediately PI, then fell significantly below control values at 45 minutes. Cerebral O2 uptake was significantly reduced, although less than for glucose, between 30 and 60 minutes PI. Global ischemia for 15 minutes is followed neither by a secondary rise in intracranial pressure nor by a cerebrospinal fluid pressure gradient but rather by hypoperfusion and defective glucose metabolism.

Cardiorespiratory Effects of Flexible Fiberoptic Bronchoscopy in Critically III Patients

The flexible fiberoptic bronchoscope is used increasingly often as a multipurpose instrument in critical care medicine. In poor risk patients who need continuous mechanical ventilation, rigid open tube bronchoscopy is a problem. With the flexible fiberoptic bronchoscope, however, diagnostic and therapeutic procedures can be carried out without interruption of ongoing mechanical ventilation. This procedure offers the possibility of bronchoscopy with reduced risk in debilitated patients. However, in these critically ill patients, the cardiopulmonary system is functioning at the borderline of its ability. Therefore, even the small changes in ventilation pattern caused by flexible fiberoptic bronchoscopy (FFB) may in some cases cause dangerous cardiopulmonary distress. For example, changes of intrabronchial pressure, tidal volume, PaO2, PaCO2 and cardiac output may be caused by the procedure. Further, it is of great importance to restrict suction through the instrument to short periods to avoid dangerous alterations in the ventilation perfusion relationship. Since serious complications may occur, it is mandatory that the bronchoscopist be aware of the potential pathophysiologic effects of FFB during mechanical ventilation of critically ill patients.

Evaluating outcome from intensive care: a preliminary multihospital comparison.

To contrast mortality for groups of ICU patients treated in different hospitals, we surveyed 795 consecutive ICU admissions in 5 ICUs using a general severity of illness classification system. After obtaining information from the medical record on age, sex, indication for ICU admission, and severity of illness, we used a logistic multiple regression equation to project death rates for each ICU based on data from a sixth reference hospital. There were substantial differences in severity of acute illness among the hospitals which accounted for most of the variation in death rates. In all ICUs, however, projected death rates were quite similar to observed deaths. These findings suggest that the use of a general severity of illness index and multivariate statistical techniques could, after further refinement and validation, improve interhospital comparisons of the outcome of acutely ill patients.

Development of the University of Pittsburgh Medical Center Policy for the Care of Terminally Ill Patients Who May Become Organ Donors after Death Following the Removal of Life Support

In the mid 1980s it was apparent that the need for organ donors exceeded those willing to donate. Some University of Pittsburgh Medical Center (UPMC) physicians initiated discussion of possible new organ donor categories including individuals pronounced dead by traditional cardiac criteria. However, they reached no conclusion and dropped the discussion. In the late 1980s and the early 1990s, four cases arose in which dying patients or their families requested organ donation following the elective removal of mechanical ventilation. Controversy surrounding these cases precipitated open discussion of the use of organ donors pronounced dead on the basis of cardiac criteria. Prolonged deliberations by many committees in the absence of precedent ultimately resulted in what is, to our knowledge, the countrys first policy for organ donation following elective removal of life support. The policy is intricate and conservative. Care was taken to include as many interested parties as possible in an effort to achieve representative and broad based support. This paper describes the development of the UPMC policy on non-heart-beating organ donation.

Total brain ischaemia in dogs: cerebral physiological and metabolic changes after 15 minutes of circulator arrest

Cross-clamping of the ascending aorta in dogs for 15 min produced severe neurological deficit, observed for up to 20 h. Immediately after restoration of the circulation, the intracranial pressure in the cisterna magna increased transiently to a mean peak of 22.8 Torr (SD +/- 1.7) because of a compensatory increase in systemic arterial pressure, without a fall in cerebral perfusion pressure. The intracranial pressure returned to control values 15-30 min after ischaemia and showed no secondary rise during the 8 h of observation. The electroencephalogram became isoelectric 34 +/- 6.5 s (mean +/-SD) after circulatory occlusion, and was abnormal when it reappeared 5 h 36 min (SD +/- 2 h 4 min) after the circulation was restored. The electrical impedance of the brain increased immediately after ischaemia and returned rapidly towards pre-ischaemic values during re-perfusion. The cerebral water had not increased measurably 4 h after ischaemia. After ischaemia, the lactate concentration in the cerebrospinal fluid increased to 4.7 mequiv./1(SEM +/-0.1) and the pH decreased to 7.17 (SEM +/-0.02); both returned to control values after 3.5 h. The cerebral glucose uptake was decreased 35 min after ischaemia, cerebral oxygen uptake remained unchanged but cerebral blood flow decreased (P less than 0.05 at 90 min). Immediately after cardiac arrest, recovery was impaired more by the presence of focal abnormal brain perfusion than by intracranial hypertension.

Comparison of high frequency jet ventilation to conventional ventilation during severe acute respiratory failure in humans

High frequency jet ventilation (HFJV) was compared to conventional (high tidal volume, low frequency) ventilation in 9 patients with acute respiratory failure (ARF). Alveolar ventilation was comparable or lower with HFJV in all but one case. When comparisons were made at the same concentration of ox

Flexible fiberoptic bronchoscopy in critical care medicine: Diagnosis, therapy and complications

Flexible fiberoptic bronchoscopy was evaluated in 71 procedures in 55 patients. Two-thirds of these procedures were carried out in patients with ongoing mechanical ventilation as their respiratory failure contraindicated rigid bronchoscopy. A wide variety of important diagnostic information was obtained. FFB caused no mortality or serious complications. Transient tachycardia occurred in several patients, cardiac arrhythmia in two and mediastinal emphysema in one patient. Retained secretions and atelectasis were the indications for 53 FFBs; 43 (81%) of these procedures were successful in improving aeration as evaluated with radiography.

Observations of withdrawal of life-sustaining treatment from patients who became non-heart-beating organ donors.

Objective Non-heart-beating organ donation for transplantation is increasing despite the concern whether all the donors are dead. This concern is based on the adequacy of documentation of death and the appropriate duration that circulation and respiration should be absent before death certification. No studies have examined the documentation and deaths of patients who became non-heart-beating organ donors. Design Retrospective study of observational data. Patients All non-brain-dead patients who became non-heart-beating organ donors at the University of Pittsburgh Medical Center from January 1, 1993, to June 30, 1998, were identified. Records for 15 of 16 patients were available for review. Measurements and Main Results Adequacy of documentation, extubation time, onset of severe hypotension, duration of absent circulation before death was certified, and the time of incision for organ procurement were ascertained. Twelve of 15 records had all required clinical documentation. The mean age of patients was 46.5 ± 5.7 yrs. All 15 patients were extubated before death and had femoral arterial catheters; one had a biventricular assist device discontinued. The time of hypotension and pulselessness was not documented for one and three patients, respectively. All 12 patients with documentation had ≥2 mins of absent circulation. Time from certification to incision for procurement was 1.1 ± 2.3 mins. Conclusions In a small study of non-heart-beating organ donation, circulation never resumed after >1 min of absent circulation, suggesting that 2 mins of absent circulation is sufficient to certify death. Three of 15 patients had inadequate documentation. Gaps and inconsistencies in documentation may raise concern about the potential for abuse.

Cheyne-Stokes respiration revisited: controversies and implications.

Investigation of the periodic crescendo-decrescendo alterations in tidal volume in Cheyne-Stokes respiration (CSR) has provided remarkable insight into the physiology of respiratory control. Many patients with periodic breathing have both cardiac and neurologic disease. Considerable controversy has surrounded determination of the relative importance of cardiac and neurologic mechanisms in the genesis of this breathing abnormality. Several investigators have considered the respiratory center as a chemostat model with three basic components: the controller system (chemoreceptors), the controlled system (gas tensions of O2 and CO2), and the feedback loop (arterial circulation from the lung to the brain). If the relationship between these cardiac and neurologic components is altered, stability of the respiratory control system is lost. Such disturbance in the control system may arise by prolongation of the circulation time, or by the system becoming more dependent on its O2, rather than the CO2 component. Earlier investigators considered periodic breathing as a forewarning of ominous developments. In recent studies, mild degrees of periodic breathing, easily missed on physical examination, are often found in otherwise normal subjects, particularly during sleep. Generally no therapy is required, although aminophylline, O2 or CO2 administration has been shown to abolish periodic breathing.

Do periodic hyperinflations improve gas exchange in patients with hypoxemic respiratory failure

Prolonged artificial ventilation may result in worsening gas exchange and pulmonary compliance in patients with otherwise normal lungs. Prolonged hyperinflations to 40 cm H2O can completely reverse deterioration of gas exchange and compliance in such patients. Similar efforts have effectively recruited atelectatic lung regions in critically ill patients. Less aggressive hyperinflations have not improved lung function in patients with abnormal lungs with hypoxemia. However, sustained exaggerated hyperinflations may successfully open collapsed lung units in these patients when standard recruitment techniques fail. We compared periodic hyperinflations of 40 cm H2O lasting 15 to 30 sec associated with body positioning (directed recruitment [DR]) to standard bag-sigh-suctioning (BSS) for their effects on gas exchange and pulmonary compliance in 16 stable surgical ICU patients with hypoxemic respiratory failure of 24-h duration or longer. Patients were sequentially alternated between DR and BSS (group 1, BSS followed by DR; group 2, DR followed by BSS). Neither technique, alone or in sequence, resulted in a sustained (greater than or equal to 5 min) improvement or deterioration in either gas exchange or pulmonary compliance. We conclude that neither BSS nor DR reliably affects gas exchange or compliance in patients with established hypoxemic respiratory failure.