Cerebral CO2 vasoreactivity evaluation by transcranial Doppler ultrasound technique: a standardized methodology.

OBJECTIVE: In normal subjects cerebral CO2 vasoreactivity is measured during spontaneous hyperventilation, breathholding, or adding CO2 to inspiratory gases. The correlation between CO2 and cerebral blood flow may, however, be invalidated by the effects of a modified respiratory pattern on venous return, sympathovagal balance, and cathecolamine release. Moreover, the duration of the test, usually not considered, may play an important role. This may justify the scattering of values found in literature. We evaluated a new standardized method for overcoming these confounding factors. DESIGN: Experimental. PARTICIPANTS: Twenty-one healthy volunteers. METHODS: Subjects were connected through a mouthpiece to a mechanical ventilator set in the intermittent positive pressure ventilation mode. The ventilator was fed by two 40-1 tanks, one of which contained 5% CO2. The inspiratory CO2 concentration was varied at fixed time intervals from 0% to 5% without modifying ventilator settings. End-tidal CO2 was measured at the mouthpiece. Mean blood velocity (V(m)) and pulsatility index (PI) in the middle cerebral artery were measured by means of transcranial Doppler ultrasound. RESULTS: The test was easily applicable and well tolerated. No hemodynamic alterations were observed during the tests. The correlation between CO2 and V(m) was always linear and highly significant (R2 > 0.8, p < 0.0001). A low intersubject variability was observed. No difference was found between the two hemispheres, nor between the sexes. CONCLUSIONS: The strict standardization of the technique, avoiding hemodynamic interference, may explain the low intersubject variability. The value of this technique in ventilated neurosurgical patients is still speculative, but it might allow the collecting of valuable data together with a reduction in exposure to CO2, and hence cerebral blood flow modifications.

A new active model lung.

A new model lung with the capacity for simulated spontaneous breathing is described. It consists of a modified commercial mechanical ventilator (Kontron ABT 4100), connected in parallel to a compliant system, a cylindric acrylic box with a latex thin membrane substituting for the top. Volume and compliance of the model are 2500 ml and 50 ml cmH2O-1, respectively. The modified ventilator simulates physiologic inspiratory flow at a rate of 10 to 30 min-1 and tidal volume up to 1000 ml, with an inspiratory to expiratory time ratio continuously variable between 1:4 and 4:1. The model has been tested under different respiratory assist techniques, connected either to continuous positive airway pressure proved to be reliable, versatile and bearing satisfactory resemblance to human ventilatory physiology.

Early onset pneumonia: a multicenter study in intensive care units.

A prospective multicenter study concerning the incidence, onset time, risk factors and mortality of pneumonia was carried out by the Intensive Care Units Collaborative Group for Infection Control in Lombardy, Northern Italy. Out of 1304 patients admitted over 3 months in 16 intensive care units (ICUs), 441 met the criteria for the protocol (no previous pulmonary infection or irreversible terminal illness, ICU stay greater than 48 h). The incidence of acquired pneumonia was 21.3% (94/441), with 54.2% of cases diagnosed within 4 days of admission (early onset pneumonia). Impairment of airway reflexes on admission and more than 24 h respiratory assistance were shown as significant risk factors (RR) for early onset pneumonia (respectively RR = 12.4, with 95% confidence interval (CI) = 5.3-28.9 and RR = 3.3, with 95% CI = 1.8-5.9). A suggested pathogenetic mechanism is aspiration of oropharyngeal contents at the onset of acute illness, due to depression of protective reflexes with delayed clearance of bacterial contamination. No protection was offered by routinely applied prophylactic antibiotic therapy.

Comparison of high-frequency jet to conventional mechanical ventilation in the treatment of severe smoke inhalation injury.

The pathophysiology of smoke inhalation includes surfactant inhibition and pulmonary vascular injury leading to a high permeability pulmonary oedema. It has been shown in surfactant deficient animal models that methods of ventilation (i.e. high-frequency ventilation - HFV) avoiding a large pressure excursion (i.e. pressure change from end expiration to peak inspiration) improves oxygenation and decreases hyaline membrane formation. Therefore, we compared HFV with conventional mechanical ventilation (CMV) on lung function in an acute animal model of smoke inhalation (SI). Mongrel dogs were anaesthetized, surgically prepared for haemodynamic and blood gas monitoring, and placed on either CMV (n = 6) or HFV (n = 7). Following baseline (BL) measurements both groups were ventilated with wood smoke for 10 min. Ventilator settings were not adjusted from baseline following smoke inhalation in either groups; positive and expiratory pressure (PEEP, approximately 6 mmHg) was added in both groups following smoke exposure. At the conclusion of the study (4 h postsmoke inhalation) lung samples were taken for surfactant function and lung water measurements. Smoke inhalation immediately increased the A-a gradient (CMV-BL = 6.9 +/- 2.4 to CMV-SI = 77.3 +/- 1.9; HFV-BL = 10.5 +/- 2.7; HFV-SI = 72.8 +/- 3.7 mmHg), venous admixture (CMV-BL = 6.9 +/- 2.8 to CMV-SI 69.8 +/- 6.6; HFV-BL = 7 +/- 1.7 to HFV-SI = 60.4 +/- 7.9 per cent) and decreased Pao2 (CMV-BL = 110 +/- 3.4 to CMV-SI = 28 +/- 3.5; HFV-BL = 103 +/- 3.6 to HFV-SI = 31 +/- 1.7 mmHg) to a similar level in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic changes during hypnosis: a heart rate variability power spectrum analysis as a marker of sympatho-vagal balance.

Spectral analysis of beat-to-beat variability in electrocardiography is a simple, noninvasive method to analyze sympatho-vagal interaction. The electrocardiogram is analyzed by means of an automatic, autoregressive modeling algorithm that provides a quantitative estimate of R-R interval variability by the computation of power spectral density. Two major peaks are recognizable in this specter: a low-frequency peak (LF, -0.1 Hz), related to the overall autonomic activity (ortho+parasympathetic) and a high-frequency peak (HF, -0.25 Hz), representative of the vagal activity. The LF/HF ratio is an index of the sympatho-vagal interaction. This technique was applied, using a computer-assisted electrocardiograph, to 10 healthy volunteers (6 high and 4 low hypnotizable subjects as determined by the Stanford Hypnotic Susceptibility Scale, Form C) in randomized awake and neutral hypnosis conditions. Preliminary results indicated that hypnosis affects heart rate variability, shifting the balance of the sympatho-vagal interaction toward an enhanced parasympathetic activity, concomitant with a reduction of the sympathetic tone. A positive correlation between hypnotic susceptibility and autonomic responsiveness during hypnosis was also found, with high hypnotizable subjects showing a trend toward a greater increase of vagal efferent activity than did low hypnotizables.

Diagnosis of macular pseudoholes and lamellar macular holes: is optical coherence tomography the "gold standard"?

AIM: To assess fundus autofluorescence (AF) for differential diagnosis of macular pseudoholes (MPH) and lamellar macular holes (LMH) evaluated by optical coherence tomography (OCT) as the "gold standard". METHODS: The files on 50 eyes of 46 consecutive patients diagnosed by OCT as having a foveal defect with residual retinal tissue at the bottom were reviewed. Retinal thickness was measured at the foveal centre and 750 microm temporally and nasally to differentiate further MPH and LMH. The corresponding corrected AF images were then evaluated. Eyes with either macular pucker or stage 1a impending macular hole served as controls. RESULTS: OCT measurements allowed the classification of two different profiles: 28 eyes classified with MPH had macular centres and perifoveal retinas that were significantly thicker than the 22 eyes classified with LMH. The corrected value of the foveal AF intensity was not significantly different between the two groups. In addition, the AF did not correlate with the thickness of the retinal tissue at the base of either MPH or LMH eyes. None of the control eyes showed foveal AF. CONCLUSIONS: The findings suggest that OCT data must be interpreted with caution when differentiating between MPH and LMH. In this series, the two groups showed similar foveal AF. AF imaging may add useful information to the differential diagnosis of MPH from LMH: the presence of foveal AF is consistent with a loss of foveal tissue and therefore a diagnosis of LMH.

Sleep and delirium in the intensive care unit.

Intensive Care Unit (ICU) patients almost uniformly suffer from sleep disruption. Even though the role of sleep disturbances is not still adequately understood, they may be related to metabolic, immune, neurological and respiratory dysfunction and could worsen the quality of life after discharge. A harsh ICU environment, underlying disease, mechanical ventilation, pain and drugs are the main reasons that underlie sleep disruption in the critically ill. Polysomnography is the gold standard in evaluating sleep, but it is not feasible in clinical practice; therefore, other objective (bispectral index score [BIS] and actigraphy) and subjective (nurse and patient assessment) methods have been proposed, but their adequacy in ICU patients is not clear. Frequent evaluation of neurological status with validated tools is necessary to avoid excessive or prolonged sedation in order to better titrate patient-focused therapy. Hypnotic agents like benzodiazepines can increase total sleep time, but they alter the physiological progression of sleep phases, and decrease the time spent in the most restorative phases compared to the phases normally mediated by melatonin; melatonin production is decreased in critically ill patients, and as such, exogenous melatonin supplementation may improve sleep quality. Sleep disruption and the development of delirium are frequently related, both because of sleep scarcity and inappropriate dosing with sedatives. Delirium is strongly related to increased ICU morbidity and mortality, thus the resolution of sleep disruption could significantly contribute to improved ICU outcomes. An early evaluation of delirium is strongly recommended because of the potential to resolve the underlying causes or to begin an appropriate therapy. Further studies are needed on the effects of strategies to promote sleep and on the evaluation of better sleep in clinical outcomes, particularly on the development of delirium.

Epidemiology and risk factors of pneumonia in critically ill patients. Intensive Care Unit Group for Infection Control.

Risk factors for pneumonia were analysed in a large population of critically ill patients, collected in two prospective multicentre "pneumonia studies" in Italy. Twenty-three intensive care units were involved and the study time was 150 unit months. Only patients without previous pulmonary infection, with intensive care unit stay greater than or equal to 48 hours and no rapidly irreversible illness at admission were included. The incidence of pneumonia in the 1475 selected patients was 15% (220 cases). 239 patients died in ICU; the mortality rate was significantly higher in patients developing pneumonia (p less than 0.0001); pneumonia was found to be an independent highly significant risk factor for death in critically ill patients (OR = 3.88; p less than 0.0001). Multivariate analysis of seven risk factors for pneumonia showed a significantly higher risk in patients with neuromuscular disease (OR = 3.8, p less than 0.002), impairment of airway reflexes at admission (OR = 2.93, p less than 0.0001), and greater than or equal to 24h respiratory assistance (OR = 3.05, p less than 0.0001). Impairment of airway reflexes at admission to the emergency room or intensive care unit identifies the population who will experience 3/4 of the overall lower respiratory tract infections. Rapid recognition of at-risk patients seems clinically important and may improve awareness programs and preventive approaches.

Long-term respiratory support and risk of pneumonia in critically ill patients. Intensive Care Unit Group of Infection Control.

In 724 critically ill patients who had received prolonged (greater than 24 h) ventilatory assistance since admission to the ward, we analyzed the relationship between artificial ventilatory support and pulmonary infection. Two different approaches were used. The first, plotting the incidence of pneumonia versus the duration of ventilatory support, confirms previous data: the incidence rises from 5% in patients receiving one day of respiratory assistance to 68.8% in patients receiving more than 30 days. In the second approach, the same data were computed as an actuarial life table with the day of pneumonia onset as terminal event. This different approach, focusing on the onset of infection rather than on incidence, allows a new insight into the problem of nosocomial infection: pneumonia in patients with respiratory support is an early occurrence with a high and constant rate of acquisition and, therefore, a high risk of infection in the first eight to ten days. Later pneumonia acquisitions were rare, and the risk after ten days of ventilatory support is low.

Prevention of pneumonia in an intensive care unit: a randomized multicenter clinical trial. Intensive Care Unit Group of Infection Control.

In a randomized multicenter clinical trial on antibiotic prophylaxis, 1,319 patients in 23 ICUs were enrolled over a 4-month period. The end-point of the study was the prevention of early onset pneumonia (EOP), defined as acquired pneumonia diagnosed within 4 days of ICU admission; this accounted for greater than 50% of overall pneumonia. Patients eligible for the study were divided into three groups which received either cefoxitin (2 g iv for three doses/8 h), penicillin G (2 million U iv for four doses/6 h), or no antibiotic (control group). In the overall population, the incidence of EOP was 6.1% in the prophylaxis recipients vs. 7.2% in the control group (a 15.3% reduction). No statistically different rates of pneumonia or death were found among the groups. Patients with impaired reflexes on admission or prolonged ventilatory support were noted to have a lower incidence of EOP and an improved outcome when treated with cefoxitin.

Postoperative pain control by transdermal fentanyl. Preliminary comparison of two dosages to a fixed-interval i.m. morphine regimen.

The efficacy of postoperative pain control with two doses of transdermal fentanyl were compared to a fixed-interval intramuscular (i.m.) morphine regimen in 21 patients undergoing orthopedic surgical procedures. The two transdermal fentanyl patches with delivery rates of 70-80 micrograms/hr and 90-100 micrograms/hr, groups one and two, respectively, were compared to an i.m. morphine regimen of 150 micrograms/kg every 6h, group three. Transdermal patches were applied one hour prior to surgery and removed after 24h. Analgesia, safety scores, side effects, and a global postoperative evaluation were recorded by a blinded physician at frequent intervals up to 36h. No significant difference in pain intensity, evaluated by the visual analog scale, were found between the three groups. Group two had the lowest discomfort score. Groups one and two had a significantly lower respiratory rate than group three. Although there were isolated significant differences in peripheral hemoglobin saturations, these differences were not consistent. This is the first study in which transdermal fentanyl was compared to a fixed-interval i.m. morphine protocol without supplementation with other narcotics. The results show that fentanyl by a transdermal route can provide analgesia comparable to i.m. morphine. No clinically important adverse side effects were found in any of the study groups.

Pulmonary mechanical and vascular responses after acute hyperbaric oxygen exposure.

Pulmonary mechanical and vascular responses were studied in Sprague-Dawley rats exposed to hyperbaric oxygen (HBO, 100% O2 at 2.8 atm (1 atm = 101.325 kPa) for 6 h). Two groups of animals were examined after HBO exposure: group HBO comprised rats examined immediately after exposure and group R consisted of rats left recovering while breathing air for 24 h before being studied. Both groups were compared with control rats, group C, not exposed to HBO. Pulmonary mechanical responses were measured by quantitating static lung compliance (Cs), wet to dry weight ratio (W/D) of lung tissue, and surface tension (ST) of broncho-alveolar lavage as a measurement of lung surfactant. Cs and W/D did not change significantly after exposure to HBO. ST was slightly lower in group R compared with group C (18.46 +/- 1.46 vs. 22.47 +/- 0.91 dynes/cm (1 dyne = 10 microN); p < 0.05). The effects of HBO on the pulmonary vasculature were studied in an isolated perfused lung preparation. Pulmonary vascular responses to hypoxia were recorded repeatedly over a period of 1 h. The percent increase in pulmonary vascular resistance (PVR) with hypoxia was blunted in group HBO and returned to the normal level in group R (8.2 +/- 2.4% in group HBO vs. 44.2 +/- 7.2% in group C and 42.9 +/- 11.2% in group R; p < 0.001). In a subgroup of rats, to assess the vascular smooth muscle contractility, 0.1 mL of KCl (15 mmol/L) was added to the perfusate and the pulmonary vascular responses were also recorded.(ABSTRACT TRUNCATED AT 250 WORDS)

Noninvasive monitoring of respiratory volume. Experimental evaluation of a breath monitoring device.

The authors studied the accuracy of the noninvasive breath monitor (Voltek Enterprise, Willowdale, Ontario, Canada) in predicting the tidal volumes in five healthy human volunteers. The signals of the breath monitor were compared with the volumes estimated by a calibrated pneumotachograph. The results show that the breath monitor is considerably accurate and can be accepted as a reliable device for clinical applications.

Surgical removal of subfoveal choroidal neovascular membranes in high myopia.

BACKGROUND: A study was carried out to elucidate the anatomical and functional outcome after surgical excision of subfoveal choroidal neovascular membranes in high myopia. METHODS: Sixty-five patients with high myopia (> or =6 diopters), well-defined subfoveal neovascular membranes on fluorescein angiography and preoperative visual acuity < or =20/100 were selected for surgery. A standardized surgical technique was used in all cases, by a single surgeon. The main outcomes assessed were Snellen visual acuity, surgical retinal pigment epithelium defect and postoperative perfusion of the choriocapillaris. Multifactor analysis of variance and chi-square/Fisher's exact test statistics were used to assess the association between patients' pre- and postoperative characteristics and outcome measures. RESULTS: Follow-up ranged from 6 to 48 months (mean 16 months). Mean postoperative visual acuity (0.18) was significantly better than mean preoperative visual acuity (0.09). Visual acuity improved by at least two lines in 29 eyes (45%) and was unchanged in 24 (37%). Overall, 43 eyes (66%) had visual acuity of 20/200 or better and 15 (23%), 20/60 or better. Predictive factors with a significant effect on final visual acuity were mean visual acuity, preoperative status of retinal pigment epithelium and postoperative perfusion of the choriocapillaris. Postoperative perfusion was detected in 31 (48%) of the total 65 eyes and in 12 (67%) of the 18 eyes with normal retinal pigment epithelium at baseline. The mean postoperative retinal pigment epithelium defect was 4.6 times larger than the original neovascular membrane. In selected patients, SLO macular scotometry showed areas of retained retinal sensitivity within the atrophic scar. CONCLUSION: The natural history of subfoveal neovascularization in high myopia is rarely visually restorative. By contrast, surgical excision of the membranes is feasible and may restore visual acuity in selected patients. This therapeutic approach merits a formal multicenter clinical trial.

[Respiratory failure caused by myopathy in severe sepsis]. / Insufficienza ventilatoria da miopatia in corso di sepsi severa.

OBJECTIVE: To describe a generalized myopathic disorder occurred in the convalescence phase of illness of a critically ill patient. SETTING: Neurological Intensive Care Unit. PATIENT: A 43-year-old man with acute leukoencephalopathy and severe sepsis complicated by sustained and prolonged cardiovascular, respiratory and renal failure. After 15 days of complete respiratory autonomy, the patient presented an acute ventilatory failure associated with generalized muscle weakness. Neither a relapse of sepsis nor neurological worsening were detected. MEASUREMENTS AND RESULTS: Electromyogram resulted in normal conduction velocity in both motor and sensitive nervous fibers. Muscular biopsy showed marked fiber size variability with several hypotrophic fibers type II fiber grouping, several areas of degeneration-necrosis with macrophage invasion, dishomogeneous oxidative enzymatic activity, no increase in glycogen or lipid content. CONCLUSIONS: These results excluded critical illness polyneuropathy and all the other known myopathies. Prolonged period of sepsis with multiple organ failure can result in a direct generalized myopathy. This possibility should be kept in mind while treating long term critically ill survivors.

[Adequacy of admission in neurosurgical intensive care]. / Appropriatezza dei ricoveri in terapia intensiva neurochirurgica.

OBJECTIVE: The Intensive Care Units of Milano metropolitan area are characterized by difficulties of hospitalization for acutely injured patients due to the low bed availability. We evaluated the problem trying to find out possible solutions. DESIGN: On the day of achieved neurological and neurosurgical stability-defined as the day when the intracranial pressure and jugular venous oxygen saturation monitoring, hyperventilation, osmotic therapy were considered no longer needed--the monitoring procedures and instrumental and/or pharmacological treatments that the patients received were recorded and classified as follows: 1) intensive, 2) intermediate, 3) non-intensive. PATIENTS: All the acutely injured patients admitted at five Neurosurgical ICUs during June-July and October-November 1994 have been studied. Only one of these ICUs had a "sub-intensive unit". MEASUREMENTS AND MAIN RESULTS: 391 patients (29.9%) aneurysms and arteriovenous malformations, 25.1% tumours, 2.8% head injuries, 8.7% spontaneous intracranial haematomas, 13.5% various pathologies) were studied. Out of them 358 had an acute brain failure. 16.5% died during brain failure and 83.5% reached neurological stability within 3 days. When neurological stability was reached 32.1% of patients could be classified as "intensive", 63.6% as "intermediate" and 4.3% as "unintensive". In the four ICUs, without sub-intensive ward facilities, 361 patients were admitted with a total amount of 2292 days of hospitalization. Among them 61.9% were spent for a) patients with no brain injury (32 pts/113 days), b) postoperative patients (113 pts/167 days), c) patients in stable neurological conditions (159 pts/1139 days). Therefore, only 38% of the days recorded were given to patients that needed neurointensive care. CONCLUSION: Out data suggest that the receptivity for acute injured patients could be increased creating recovery room units and intermediate post-intensive units together with a better interchange between general and neurosurgical ICUs.