Biologically variable ventilation prevents deterioration of gas exchange during prolonged anaesthesia.

We have studied the time course of changes in gas exchange and respiratory mechanics using two different modes of ventilation during 7 h of isoflurane anaesthesia in pigs. One group received conventional control mode ventilation (CV). The other group received biologically variable ventilation (BVV) which simulates the breath-to-breath variation in ventilatory frequency (f) that characterizes normal spontaneous ventilation. After baseline measurements with CV, animals were allocated randomly to either CV or BVV (FIO2 1.0 with 1.5% end-tidal isoflurane). With BVV, there were 376 changes in f and tidal volume (VT) over 25.1 min. Ventilation was continued over the next 7 h and blood gases and respiratory mechanics were measured every 60 min. The modulation file used to control the ventilator for BVV used an inverse power law frequency distribution (I/fa with a = 2.3 +/- 0.3). After 7 h, at a similar delivered minute ventilation, significantly greater PaO2 (mean 72.3 (SD 4.0) vs 63.5 (6.5) kPa) and respiratory system compliance (1.08 (0.08) vs 0.92 (0.16) ml cm H2O-1 kg-1) and lower PaCO2 (6.5 (0.7) vs 8.7 (1.5) kPa) and shunt fraction (7.2 (2.7)% vs 12.3 (6.2)%) were seen with BVV, with no significant difference in peak airway pressure (16.3 (1.2) vs 15.3 (3.7) cm H2O). A deterioration in gas exchange and respiratory mechanics was seen with conventional control mode ventilation but not with BVV in this experimental model of prolonged anaesthesia.

Biologically variable pulsation improves jugular venous oxygen saturation during rewarming.

BACKGROUND: Conventional pulsatile (CP) roller pump cardiopulmonary bypass (CPB) was compared to computer controlled biologically variable pulsatile (BVP) bypass designed to return beat-to-beat variability in rate and pressure with superimposed respiratory rhythms. Jugular venous O2 saturation (SjvO2) below 50% during rewarming from hypothermia was compared for the two bypass techniques. A SjvO2 less than 50% during rewarming is correlated with cognitive dysfunction in humans. METHODS: Pigs were placed on CPB for 3 hours using a membrane oxygenator with alpha-stat acid base management and arterial filtration. After apulsatile normothermic CPB was initiated, animals were randomized to CP (n = 8) or BVP (roller pump speed adjusted by an average of 2.9 voltage output modulations/second; n = 8), then cooled to a nasopharyngeal temperature of 28 degrees C. During rewarming to stable normothermia, SjvO2 was measured at 5 minute intervals. The mean and cumulative area for SjvO2 less than 50% was determined. RESULTS: No between group difference in temperature existed during hypothermic CPB or during rewarming. Mean arterial pressure, arterial partial pressure O2, and arterial partial pressure CO2 did not differ between groups. The hemoglobin concentration was within 0.4 g/dL between groups at all time periods. The range of systolic pressure was greater with BVP (41 +/- 18 mm Hg) than with CP (12 +/- 4 mm Hg). A greater mean and cumulative area under the curve for SjvO2 less than 50% was seen with CP (82 +/- 96 versus 3.6% +/- 7.3% x min, p = 0.004; and 983 +/- 1158 versus 42% +/- 87% x min; p = 0.004, Wilcoxon 2-sample test). CONCLUSIONS: Computer-controlled BVP resulted in significantly greater SjvO2 during rewarming from hypothermic CPB. Both mean and cumulative area under the curve for SjvO2 less than 50% exceeded a ratio of 20 to 1 for CP versus BVP. Cerebral oxygenation is better preserved during rewarming from moderate hypothermia with bypass that returns biological variability to the flow pattern.

Ethical and practical considerations of withdrawal of treatment in the intensive care unit.

PURPOSE: To discuss the medical, ethical and legal basis of decisions to discontinue life-support therapy in the adult intensive care unit (ICU), and to provide practical guidelines for the discontinuation of life support therapy. SOURCE: Relevant articles were retrieved through Medline (1991-present; terms: ethics, life support discontinuation, double effect, beneficence, non-maleficence). Other sources include legal references, and personal files. PRINCIPAL FINDINGS: Understanding the legal and ethical principles of autonomy, beneficence, non-maleficence and double effect are crucial when withdrawing life support therapy. The law respects a competent patient's right to direct his/her healthcare but does not uphold his/her right to demand futile care. Surrogate decision makers can be used when the patient is incompetent, provided they are acting in the patient's best interest. Euthanasia is illegal and the distinction between discontinuation of therapy and euthanasia is legally clear. Skillful administration of palliative therapy cannot be construed as euthanasia when the aforementioned ethical principals are respected. The various practical methods of discontinuing therapy are discussed. Every ICU should develop its own guidelines and a checklist to help caregivers during this difficult time. Caregivers must anticipate the mechanism of death and direct interventions at the symptoms that are likely to cause discomfort. Drugs and dosages must be individualized, and depend on the underlying disease, anticipated mechanism of death, and the patient's pharmacological history. When prescribing a drug, the intention should be clear. CONCLUSIONS: Appropriate discontinuation of therapy in the ICU allows patients a dignified and comfortable death.

Localization of a presumed catecholamine-secreting glomus tumor by 123I-metaiodobenzyl guanidine (MIBG) single photon emission computed tomography (SPECT) scanning.

We present an unusual case of a 41-year-old woman with a known glomus tumor, an adrenal mass, hypertension, and elevated catecholamines. The glomus tumor was shown to be the site of excessive catecholamine production in what we believe to be one of the few descriptions of 123I-metaiodobenzylguanidine (MIBG) scanning for this uncommon tumor. The diagnostic difficulties of such a case are discussed. A literature review of catecholamine-secreting glomus tumors and a systematic approach to catecholamine-secreting tumor localization in such patients is presented. Therapeutic options of surgery, radiation therapy, and embolization are reviewed. We conclude that the management of patients with functioning glomus tumors needs to be individualized. A careful, systematic approach is required if needless surgery is to be avoided. Further, the use of 123I-MIBG scanning deserves consideration to help localize catecholamine production in such patients.