The incidence of and clinical variables associated with vancomycin-resistant enterococcal colonization in mechanically ventilated patients

STUDY OBJECTIVES

(1) To determine in our ICU the incidence of vancomycin-resistant enterococcus (VRE) colonization in mechanically ventilated patients without a history of VRE infection or colonization; and (2) to determine the risk factors and outcome variables associated with VRE colonization in these patients.

DESIGN

A prospective cohort study conducted between January 1996 and March 1998.

SETTING

Medical and cardiac critical care units in a tertiary care urban university hospital.

PATIENTS

Mechanically ventilated patients without evidence of pneumonia at the onset of ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Patients underwent rectal cultures by standard methods on day 1, day 3 or 4, day 6 or 7, and day 14 of intubation to detect VRE. Thirteen of 83 patients (16%) had rectal cultures positive for VRE (VRE+) at some point while being mechanically ventilated during their stay in the ICU. In comparison, approximately 15 of 2,100 medical ICU patients (0.7%) had clinical VRE infections as determined by the hospital's infection control program during a 2-year period. VRE+ patients had a higher incidence of immunosuppression than patients who had rectal cultures negative for VRE (VRE-) (9 of 13 [69%] vs 16 of 70 [23%], respectively; p < 0.01) and neutropenia (4 of 13 [31%] vs 5 of 70 [7%], respectively; p < 0.01). Hospital length of stay (LOS) was longer in VRE+ patients than in VRE- patients (27+/-17 days vs 17+/-14 days, respectively; p = 0.05), whereas pre-ICU hospital LOS and ICU LOS were similar in both patient groups. Five of 67 patients (7%) were VRE+ on day 1 of intubation, suggesting colonization at a prior site of care. Three of 29 patients who had subsequent rectal cultures converted to VRE+ while in the ICU. This group had a higher incidence of immunosuppression and neutropenia, and received more vancomycin compared with the patients who remained VRE- (p < 0.01). However, there was no significant difference in the use of other broad-spectrum antibiotics (such as antipseudomonal penicillins, third-generation cephalosporins, quinolones, and clindamycin), enteral tube feedings, or sucralfate between the two groups. In addition, a topical antibiotic paste (a gentamicin, nystatin, polymixin slurry) that was placed in the oropharynx to prevent bacterial overgrowth was not found to increase the incidence of VRE colonization in this patient population.

CONCLUSIONS

The incidence of VRE colonization was surprisingly high: 16% in mechanically ventilated patients in a hospital in which VRE was not previously known to be endemic. Risk factors for the acquisition of VRE colonization included immunosuppression, neutropenia, and vancomycin use. Increased LOSs and hospital costs were seen in VRE+ patients compared to VRE- patients. Whether VRE colonization is a contributor to severe disease that leads to prolonged hospitalization and increased resource allocation or whether it is simply a marker of disease severity cannot be determined from this study. To the extent that specific antibiotic protocols are used to reduce antibiotic-resistant flora in the ICU, monitoring the incidence of VRE in the stool specimens of immunocompromised, mechanically ventilated patients can be a simple and useful tool to assess one effect of these strategies.

Response to inhaled nitric oxide in patients with acute right heart syndrome

Inhaled nitric oxide (iNO), a selective pulmonary vasodilator, has been shown to decrease pulmonary artery pressures but not increase cardiac output in hemodynamically stable patients with a variety of causes of pulmonary hypertension. The response to iNO in hemodynamically unstable patients with acute right heart syndrome has not been previously described. We determined the response to iNO in 26 critically ill adult patients with acute right heart failure defined by echocardiographic criteria. Patients received iNO through the inspiratory limb of the ventilator in increments of 10 ppm with hemodynamic and gas-exchange measurements made before and after each level. When maximal effect was seen, iNO was discontinued to compare parameters with baseline. iNO significantly increased cardiac output (5.5 +/- 3 to 6.4 +/- 4 L/min), stroke volume (54 +/- 27 to 65 +/- 38 ml), and mixed-venous oxygen saturation (69 +/- 8 to 73 +/- 10%), all p < 0.01. With discontinuation of iNO, all parameters returned immediately to baseline. These parameters of improved perfusion were related to a decrease in pulmonary vascular pressures and resistance. In a subset of approximately 50% of patients, these changes were substantial (> 20%) and in approximately 25% of all patients, the improvement in hemodynamic measures permitted a decrease in other vasoactive drug administration. The mean concentration of iNO required to achieve these effects was 35 ppm, and 85% of patients exhibiting a substantial improvement in hemodynamics did so at a concentration of iNO of less than or equal to 40 ppm. Underlying causes of right heart failure and baseline hemodynamics did not predict response to iNO, but the use of alpha-agonist catecholamines did. We conclude iNO improves hemodynamics in patients with respiratory failure, shock, and right ventricular dysfunction. Although mortality was not a key end point in this pilot study, it was high for both responders and nonresponders to this therapy. Further evaluation of the role of iNO in this patient population is supported by these data.

A comparison of multimedia and standard advanced cardiac life support learning

OBJECTIVES

To compare student performance after Multimedia ACLS Learning System (MM) education compared with that after standard (ST) ACLS education.

METHODS

Final-year medical students were divided into 2 groups based on convenience scheduling and given ACLS instruction either in a standard format or with the MM course. The sizes of the small groups and the times in small-group instruction were identical. All students were evaluated with the same 50-item multiple-choice written examination, a structured evaluation immediately after the management of a mock cardiac arrest, and a second structured evaluation of the same mock arrest (videotaped) by an instructor blinded to the education method. Students were assigned a mark from 1 to 5 in each of 4 domains: assessment, immediate priorities, continual assessment, and leadership.

RESULTS

75 students took the MM and 38 took the ST course. The mean +/- SD mark for the multiple-choice test was 89.3 +/- 4.9% (MM) vs 89.3 +/- 4.8% (ST); the on-site mock arrest evaluation mark (20 maximum) was 14.1 +/- 2.5 (MM) vs 14.1 +/- 2.0 (ST); and the blinded mock arrest evaluation was 13.1 +/- 2.9 (MM) vs 14.4 +/- 2.9 (ST) (p = 0.024). 1/75 (MM) vs 0/38 (ST) did not successfully complete the on-site mock arrest evaluation. More students in the MM group (46% vs 25%) required multiple attempts to successfully complete the mock arrest evaluation (p < 0.02).

CONCLUSION

In medical students with no previous ACLS training, structured access to the multimedia ACLS Learning System provides immediate educational outcomes similar to those of a standard ACLS course. Multimedia computer-interactive learning should be enhanced with a short period of hands-on practice.

Altered neuronal activity rhythm and glutamate receptor expression in the suprachiasmatic nuclei of Trypanosoma brucei-infected rats

The parasites Trypanosoma brucei cause African trypanosomiasis (sleeping sickness), a severe neuropsychiatric disease with marked disturbances of sleep-wake alternation. The sites of brain lesions are not well characterized. The present experimental investigation is focused on the hypothalamic suprachiasmatic nuclei, which play a role of a biological clock entraining endogenous rhythms in the mammalian brain. The electrophysiological properties of these neurons were analyzed in slice preparations from trypanosome-infected rats. The neuronal spontaneous activity, which shows a circadian oscillation, was markedly altered in the infected animals, displaying a reduced firing rate and phase advance of its circadian peak. The direct retinal fibers, which play a pivotal role in entrainment of the circadian pacemaker, displayed a normal density and distribution in the suprachiasmatic nuclei of infected animals after intraocular tracer injections in vivo. At the postsynaptic level, immunohistochemistry and Western blotting revealed in the suprachiasmatic nuclei of infected rats a selective decrease of the expression of glutamate AMPA GluR2/3 and NMDAR1 receptor subunits that gate retinal afferents. These data disclose an impairment of the neuronal functions in the biological clock in African trypanosomiasis, and may serve to unravel functional and molecular mechanisms behind endogenous rhythm disturbances.

Effects of organizational change in the medical intensive care unit of a teaching hospital: a comparison of 'open' and 'closed' formats

OBJECTIVE

To compare the effects of change from an open to a closed intensive care unit (ICU) format on clinical outcomes, resource utilization, teaching, and perceptions regarding quality of care.

DESIGN

Prospective cohort study; prospective economic evaluation.

SETTING

Medical ICU at a university-based tertiary care center. For the open ICU, primary admitting physicians direct care of patients with input from critical care specialists via consultation. For the closed ICU, critical care specialists direct patient care.

PATIENTS

Consecutive samples of 124 patients admitted under an open ICU format and 121 patients admitted after changing to a closed ICU format. Readmissions were excluded.

MAIN OUTCOME MEASURES

Comparison of hospital mortality with mortality predicted by the Acute Physiology and Chronic Health Evaluation II (APACHE II) system; duration of mechanical ventilation; length of stay; patient charges for radiology, laboratory, and pharmacy departments; vascular catheter use; number of interruptions of formal teaching rounds; and perceptions of patients, families, physicians, and nurses regarding quality of care and ICU function.

RESULTS

Mean +/- SD APACHE II scores were 15.4 +/- 8.3 in the open ICU and 20.6 +/- 8.6 in the closed ICU (P=.001). In the closed ICU, the ratio of actual mortality (31.4 percent) to predicted mortality (40.1 percent) was 0.78. In the open ICU, the ratio of actual mortality (22.6 percent) to predicted mortality (25.2 percent) was 0.90. Mean length of stay for survivors in the open ICU was 3.9 days, and mean length of stay for survivors in the closed ICU was 3.7 days (P=.79). There were no significant differences between periods in patient charges for radiology, laboratory, or pharmacy resources. Nurses were more likely to say that they were very confident in the clinical judgment of the physician primarily responsible for patient care in the closed ICU compared with the open ICU (41 percent vs 7 percent; P<.Ol), and nurses were the group most supportive of changing to a closed ICU format before and after the study.

CONCLUSIONS

Based on comparison of actual to predicted mortality, changing from an open to a closed ICU format improved clinical outcome. Although patients in the closed ICU had greater severity of illness, resource utilization did not increase.

A fieldwork model for non-traditional community practice

The purpose of this article is to discuss a fieldwork Level II model developed by the College of St. Catherine in St. Paul, Minnesota for psychosocial practice. Fieldwork, especially psychosocial fieldwork, is undergoing significant change due to the shifting of occupational therapy practice and the demand for sites. This nontraditional group process model was developed in a shelter for the homeless and poor in downtown Minneapolis. The authors will trace the development of the model, its organization and requirements. Program results will be discussed including advantages and disadvantages as seen by students and faculty supervisors who participated in the experience. The authors believe that this collaborative model can develop effective student therapists who are able to work from a client-centered approach and are able to be flexible within a team.

Healing the wounds of war: the Vietnam veteran after Operation Desert Storm

TOPIC

How Operation Desert Storm, and the positive response of the public to this crisis, seemed to stimulate and heighten unresolved feelings for many Vietnam veterans.

PURPOSE

To show that understanding the lived experiences of Vietnam veterans, at time when men and women returning from Operation Desert Storm were welcomed back by their country, would allow for the development of more effective treatment approaches in working with Vietnam veterans.

METHODS

Personal interviews, during and immediately following Operation Desert Storm, with 12 men who served in Vietnam.

FINDINGS

Themes identified and described by Vietnam veterans included repressed fear, shame, isolation and loneliness, disillusionment, permanence of memories, and acceptance.

CONCLUSION

Further exploration and analysis of these themes is recommended.

Persistent and severely mentally ill clients' perceptions of their mental illness

This qualitative, exploratory study examines severely mentally ill clients' perceptions of their illness and the effects of this illness on their lives. The major purpose of this study was to explore the lived experiences of severely mentally ill clients. Subjects included 15 clients in an out patient mental health clinic in a veterans' hospital in the upper midwestern United States. A phenomenologic methodology was used, with subjects being interviewed until common themes emerged. The data were analyzed utilizing a seven-step method. Four major themes emerged in the data analysis. Identification of these themes provided a meaningful way to synthesize the data and identify those concepts that best capture and name the personal perceptions of severely and persistently mentally ill people. The four themes identified were stigmatization and the resulting alienation, loss, a pervasive feeling of distress, and acceptance on two dimensions (a personal acceptance of having a mental illness and a need for acceptance by others). Although the individuality of each client was evident in the data obtained, each theme represents a collective perspective that emerged from the analysis of the data.

Presence of low voltage activated calcium channels distinguishes touch from pressure sensory neurons in the lamprey spinal cord

Touch (T) and pressure (P) primary sensory neurons (dorsal cells) in the lamprey spinal cord differ not only with regard to their mechanoreceptive properties but also in their membrane properties. Touch cells have a significantly shorter time delay to the spike onset on a rebound of a hyperpolarizing current pulse than the pressure cells. Different time constants and input resistances partially explain these findings but cannot fully account for the observed differences between T- and P-cells. A more detailed study of membrane properties was therefore required. 3-D reconstructions of dorsal cells reveal a round shape with few processes and thus that they are suitable for voltage clamp analysis. Voltage activated calcium channels with a low threshold were found in a subpopulation of dorsal cells after administration of tetrodotoxin and K+ channel antagonists. These channels were blocked by addition of Co2+. In the short latency T-cells Co2+ increased the latency under current clamp conditions, and inhibited the facilitatory effect on spike activation upon increased hyperpolarization. This effect of Co2+ was not observed in the long latency P-cells. It is likely that the presence of low voltage calcium channels in T-cells are responsible for the differences observed between T- and P-cells. Voltage activated calcium channels with a higher threshold were observed in dorsal cells of both types. These channels were blocked by Co2+ or cadmium. Late outward 'tail' currents were shown to include calcium dependent potassium channels.

Possible morphological substrates for GABA-mediated presynaptic inhibition in the lamprey spinal cord

Gamma-aminobutyric acid (GABA) neurons intrinsic to the lamprey spinal cord are known to modulate synaptic transmission from interneurons active during locomotion and from mechanosensory dorsal cells. Many of these physiological effects are presynaptic. To establish the morphological substrates for these axo-axonic interactions, an ultrastructural analysis was performed with an antiserum to fixed GABA. The GABA immunoreactivity (ir) was detected by postembedding peroxidase-antiperoxidase and immunogold techniques. GABA-ir terminals were found to make appositions with unlabelled axons located in the dorsal columns and in the ventrolateral aspect of the spinal cord. In the ventrolateral part of the cord, similar appositions between different GABA-ir terminals were also observed. The immunolabelled terminals contained spherical to pleomorphic synaptic vesicles, and also glycogen granules and dense core vesicles. In some cases, the fine structure of the contacts between immunogold-labelled terminals and unlabelled axons suggested a synaptic relationship. Such a relation was found in a relatively small proportion (2-3%) of the appositions studied. These specializations were always observed in close relation to an output synapse of the postsynaptic axon. It is suggested that the axo-axonal contacts described may provide an effective modulation of the synaptic transmission from axons in the lamprey spinal cord.

Subcellular distribution of serotonin in the lamprey spinal cord

The subcellular distribution of serotonin (5-hydroxytryptamine; 5-HT) in the lamprey (Ichtyomyzon unicuspis, Lampetra fluviatilis) spinal cord was investigated by using ultracentrifugation on continuous density gradients combined with an electron microscopic analysis of the gradients and of immunostained tissue. Endogenous 5-HT was analyzed by high-performance liquid chromatography with electrochemical detection. After differential centrifugation, the highest levels of 5-HT were found in the particulate fractions. After ultracentrifugation of lysed synaptosomal fractions on continuous sucrose gradients and the subsequent sedimentation of the individual fractions, 5-HT showed a biphasic distribution in the gradient. The two peaks corresponded to 0.30-0.40 M and 0.85-1.05 M sucrose. Electron microscopy of intact tissue showed that some of the boutons were strongly immunoreactive to 5-HT with dense precipitates over large granular vesicles. The area around these large vesicles, however, also showed reaction product. Large granular vesicles could be clearly distinguished in the immunostained axonal varicosities. In tissue not processed for 5-HT immunoreactivity it was seen that the varicosities contained not only large dense-cored vesicles, but also small agranular vesicles. An electron microscopical analysis of the subcellular fractions revealed that the fraction corresponding to the "light" 5-HT peak contained numerous vesicular structures, which in most cases were electron lucent. In the "heavy" fractions, nerve ending particles containing vesicles of various sizes were observed. The results suggest that 5-HT in the lamprey spinal cord may be distributed in more than one subcellular compartment which, apart from the cytosol, possibly corresponds to small and large synaptic vesicles.

Co-localized GABA and somatostatin use different ionic mechanisms to hyperpolarize target neurons in the lamprey spinal cord

gamma-Aminobutyric acid (GABA) and somatostatin are co-localized in cells close to the central canal in the lamprey. These cells project to the lateral margin of the spinal cord where they form a GABA and somatostatin containing plexus. Stretch receptor neurons (edge cells) are situated along the lateral margin of the spinal cord and their dendrites extend into the GABA and somatostatin containing plexus. To investigate whether GABA and/or somatostatin exert an affect on edge cells, these putative transmitters were applied from extracellular pipettes onto edge cells during intracellular recordings. Both GABA and somatostatin hyperpolarized the edge cells but through different ionic mechanisms. GABA activated a chloride current while somatostatin activated a current most likely carried by potassium which, however, could not be blocked by any of the conventional potassium blockers.

Primary afferents evoke excitatory amino acid receptor-mediated EPSPs that are modulated by presynaptic GABAB receptors in lamprey

1. The primary afferent neurons (dorsal cells) are of two types in lamprey, which are fast (touch) and slowly adapting (pressure), respectively. Intracellular stimulation of such sensory neurons evokes mono- and polysynaptic excitatory postsynaptic potentials (EPSPs) in spinobulbar neurons (giant interneurons) and in unidentified interneurons. Paired intracellular recordings between identified sensory cells and spinobulbar neurons made it possible to study the synaptic transmission in detail. It is shown that both touch and pressure primary afferents utilize excitatory amino acid (EAA) transmission and, furthermore, that these effects are subject to a presynaptic GABAB receptor modulation. 2. The monosynaptic mixed electrical and chemical EPSPs in giant interneurons had a mean peak amplitude of 3.2 +/- 1.3 (SD) mV, a time to peak of 4.7 +/- 1.2 ms, and a duration at one-half peak amplitude of 9.4 +/- 3.2 ms. Corresponding results were obtained with dorsal root or dorsal column stimulation. Seventy percent of the fast-adapting dorsal cells of the "touch" type evoked monosynaptic mixed EPSPs in giant interneurons, whereas only 3% of the slowly adapting "pressure" dorsal cells did. 3. The chemical part of the monosynaptic EPSPs evoked in giant interneurons was, in all cases tested, blocked by application of EAA antagonists, like the nonselective antagonist kynurenic acid (KYAC; 2 mM). The selective kainate/alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 5 microM) had a similar effect, whereas the selective N-methyl-D-aspartate (NMDA) receptor antagonist 2-aminophosphono-5-valeric acid (AP-5; 200-400 microM) did not change the EPSP, even in the absence of magnesium ions. 4. The monosynaptic excitatory synaptic transmission was modulated by application of the selective GABAB receptor agonist L-baclofen (5-10 mM local droplet application or 100-1,000 microM bath applied) or by gamma-aminobutyric acid (GABA; 100-1,000 microM), also when GABAA receptor-evoked effects were blocked by bicuculline (10 microM). L-baclofen or GABA in combination with bicuculline did not evoke any effects in the postsynaptic neuron on membrane potential, input resistance, or spike threshold. Therefore the effects of the GABAB receptor activation most likely occurs at the presynaptic afferent level. 5. In conclusion, the monosynaptic excitation from skin mechanoreceptors evoked in spinobulbar neurons is mediated by EAA receptors of the kainate/AMPA type. GABAB receptor activation causes a depression of this EPSP, most likely because of a presynaptic action. GABA interneurons are known to form close appositions on sensory axons in the lamprey.

Putative GABAergic input to axons of spinal interneurons and primary sensory neurons in the lamprey spinal cord as shown by intracellular Lucifer yellow and GABA immunohistochemistry

GABAergic phasic modulation of the membrane potential occurs in spinal interneurons during fictive locomotion in lamprey presumably indicating a presynaptic inhibition. GABA also modulates synaptic transmission from primary sensory neurons (dorsal cells) at a presynaptic site. From these findings GABA terminals would be expected to be in close contact with phasically modulated axons of spinal interneurons and/or dorsal cells and their axons. To test this supposition intracellular injections of Lucifer yellow into spinal interneurons or dorsal cells were combined with GABA immunohistochemistry. GABA-immunoreactive (ir) varicosities were found to be in close contact (less than 1 micron distance) with axons modulated during fictive locomotion as well as dorsal cell axons. Small GABA-ir bipolar neurons form processes, which are in close contact with the axons of dorsal cells.

Neuropeptide Y-immunoreactive spinal neurons make close appositions on axons of primary sensory afferents

The dorsal cells in the lamprey are primary sensory neurons located in a parasagittal region of the spinal cord. In the same plane neuropeptide Y (NPY) immunoreactivity has been described. To investigate if the dorsal cells were in contact with NPY-immunoreactive (ir) fibers and cell bodies, intracellular injections of Lucifer yellow into identified dorsal cells were combined with NPY immunohistochemistry. NPY-ir varicosities were found to be in close apposition to both the descending and the ascending axon of dorsal cells. No NPY-ir boutons were seen in close contact with the dorsal cell bodies.

5-hydroxytryptamine immunoreactive varicosities in the lamprey spinal cord have no synaptic specializations--an ultrastructural study

The distribution and fine structure of 5-hydroxytryptamine (5-HT) immunoreactive cell bodies and axonal varicosities have been studied in the lamprey spinal cord, using the peroxidase-antiperoxidase (PAP) immunohistochemical technique and subsequent analysis of ultrathin serial sections. Immunostained cell bodies were found in the ventral spinal cord close to the central canal. Immunostained varicosities were found throughout the spinal cord with the highest density in the ventromedial plexus and the dorsal horn. Only large granular vesicles could be clearly distinguished in immunostained cell bodies and varicosities, but it was concluded based on a comparison with unstained normal tissue that these boutons also contained small, pleomorphic agranular vesicles. Immunoreactive varicosities were studied in the ventromedial plexus, the dorsal horn, the dorsal column, the dorsolateral and ventrolateral funiculi and the grey matter. No morphological differences could be observed between varicosities in the different loci. The varicosities were in no case seen to make synaptic contact with surrounding neuronal elements, even when followed through serial sections. Consequently, 5-HT released from boutons in all parts of the spinal cord could be expected to act on 5-HT receptors located on nearby as well as distant receptors.

Three types of GABA-immunoreactive cells in the lamprey spinal cord

Polyclonal antisera raised against conjugated GABA were used to study the distribution of GABAergic neurons in the spinal cords of lampreys (Lampetra fluviatilis and Ichtyomyzon unicuspis) using immunofluorescence and peroxidase-antiperoxidase techniques. Three morphologically distinct types of GABA-immunoreactive (GABA-ir) cell bodies were observed, multipolar neurons in the lateral grey cell column, apparently bipolar cells in the ventral aspect of the dorsal horn, and small liquor-contacting cells surrounding the central canal. A high density of immunoreactive fibers of spinal origin were present in the lateral and ventral funiculi, whereas the dorsal column had a relatively low density. Dense GABA-ir plexuses were situated in the lateral spinal margin, and in the dorsal part of the dorsal horn. A chronic lesion of the rostral spinal cord did not result in any observable loss of GABA-ir fibers below or above the lesion, suggesting that the 3 types of segmental GABA-ir neurons are the main sources of the GABAergic innervation of the lamprey spinal cord.