Oximetry of retinal vessels by dual-wavelength imaging: calibration and influence of pigmentation.

A method for noninvasive measurement of Hb O2 saturation (SO2) in retinal blood vessels by digital imaging was developed and tested. Images of vessels were recorded at O2-sensitive and O2-insensitive wavelengths (600 and 569 nm, respectively) by using a modified fundus camera with an image splitter coupled to an 18-bit digital camera. Retinal arterial SO2 was varied experimentally by having subjects breathe mixtures of O2 and N2 while systemic arterial SO2 was monitored with a pulse oximeter. Optical densities (ODs) of vascular segments were determined using a computer algorithm to track the path of reflected light intensity along vessels. During graded hypoxia the OD ratio (ODR = OD600/OD569) bore an inverse linear relationship to systemic SO2. Compensation for the influence of choroidal pigmentation significantly reduced variation in the arterial SO2 measurements among subjects. An O2 sensitivity of 0.00504 +/- 0.00029 (SE) ODR units/%SO2 was determined. Retinal venous SO2 at normoxia was 55 +/- 3.38% (SE). Breathing 100% O2 increased venous SO2 by 19.2 +/- 2.9%. This technique, when combined with blood flow studies in human subjects, will enable the study of retinal O2 utilization under experimental and various disease conditions.

Can bacteremia be predicted in surgical intensive care unit patients?

OBJECTIVES: To determine which clinical features are associated with bacteremia in a SICU. To determine if infections are identified prior to bacteremia via culturing of other body fluids. To determine if antibiotic regimens are changed after the results of the blood culture were obtained. DESIGN: A retrospective, unit-based, case control study. SETTING: A 10 bed SICU in a 552-bed, tertiary care and Level I Trauma center. PATIENTS: All SICU patients with one or more positive blood cultures over a 2 year period (n = 24) were matched by diagnosis, procedure, and age to SICU patients with negative blood cultures (n = 48). MEASUREMENTS AND RESULTS: Bacteremic and control patients had similar APACHE II scores though death was more likely in bacteremic patients (p < 0.05) and they had higher hospital charges (p < 0.02). There was no difference in any of the clinical variables studied (minimum and maximum temperature, maximum white blood cell count, minimum mean arterial blood pressure) between the bacteremic and control groups on the days leading up to and the day of the positive blood culture. Coincident infections of lung, bladder, wound, and central venous catheters were identified in 42% of bacteremic patients. The identification of organisms found in the blood had a direct impact on the antibiotic regimen of 54% of the bacteremic patients. CONCLUSIONS: A better screen for obtaining blood cultures in this SICU was not identified. If antibiotics are begun empirically before the results of blood cultures are known, the results of other body fluid cultures can be used to guide therapy initially. However, the data obtained from positive blood cultures was often helpful in changing empirical therapy. Therefore, blood cultures remain important diagnostic tools.

Selective application of cardiopulmonary resuscitation improves survival rates.

This study is a retrospective review of all patients who died without cardiopulmonary resuscitation (CPR) or who sustained a sudden cardiopulmonary arrest in the hospital and received CPR during a 2-yr period at a large medical center. Based on a review of Current Procedural Terminology codes, patients were classified into one of the ten disease categories: multiple medical problems, acute disease, procedure-related, congenital disease, neoplasm, metastatic neoplasm, trauma, burn, acquired immunodeficiency syndrome, and dementia. A total of 1206 patient deaths without a CPR effort were identified. CPR was administered to another 550 patients who had a sudden cardiopulmonary arrest, of which 71% survived the resuscitative attempt initially, but only 25% survived CPR until discharge from the hospital. CPR was applied less frequently than the mean in the metastatic neoplasm (P < 0.0001), trauma (P = 0.013), and dementia (P = 0.0003) groups and more frequently in the acute disease (P < 0.0001) and procedure-related (P < 0.0001) groups. Survival to discharge from the hospital was more frequent than the mean in the congenital disease group (P = 0.0004) and less frequent in the neoplasm group (P = 0.0425). The other groups had survival rates comparable to the mean. Patients 70 yr of age and older were less likely to receive CPR than those younger than 70 (P < 0.0001). However, if they did receive CPR, they were just as likely to survive to discharge from the hospital as the younger patients (P = 0.3404).(ABSTRACT TRUNCATED AT 250 WORDS)

A controlled trial of scheduled replacement of central venous and pulmonary-artery catheters.

BACKGROUND: The incidence of infection increases with the prolonged use of central vascular catheters, but it is unclear whether changing catheters every three days, as some recommend, will reduce the rate of infection, It is also unclear whether it is safer to change a catheter over a guide wire or insert it at a new site. METHODS: We conducted a controlled trial in adult patients in intensive care units who required central venous or pulmonary-artery catheters for more than three days. Patients were assigned randomly to undergo one of four methods of catheter exchange: replacement every three days either by insertion at a new site (group 1) or by exchange over a guide wire (group 2), or replacement when clinically indicated either by insertion at a new site (group 3) or by exchange over a guide wire (group 4). RESULTS: Of the 160 patients, 5 percent had catheter-related bloodstream infections, 16 percent had catheters that became colonized, and 9 percent had major mechanical complications. The incidence rates (per 1000 days of catheter use) of bloodstream infection were 3 in group 1, 6 in group 2, 2 in group 3, and 3 in group 4; the incidence rates of mechanical complications were 14, 4, 8, and 3, respectively. Patients randomly assigned to guide-wire-assisted exchange were more likely to have bloodstream infection after the first three days of catheterization (6 percent vs. 0, P = 0.06). Insertions at new sites were associated with more mechanical complications (5 percent vs. 1 percent, P = 0.005). CONCLUSIONS: Routine replacement of central vascular catheters every three days does not prevent infection. Exchanging catheters with the use of a guide wire increases the risk of bloodstream infection, but replacement involving insertion of catheters at new sites increases the risk of mechanical complications.

Influence of political power, medical provincialism, and economic incentives on the rationing of surgical intensive care unit beds.

OBJECTIVE: To determine factors influencing rationing decisions in a surgical ICU during a temporary nursing shortage when two to six of the unit's 16 beds were closed. DESIGN: Blinded, concurrent data collection, retrospective chart review. SETTING: Surgical ICU. PATIENTS: All patients (n = 308) for whom a surgical ICU bed was requested were studied during a 3-month period. MEASUREMENTS AND MAIN RESULTS: Admitting patterns did not change and no attempts were made to limit admissions to more severely ill patients during times of the greatest shortage of surgical ICU beds. Contrary to findings in previous reports, the severity of illness of patients admitted to the surgical ICU decreased as bed availability and bed census decreased. Bed allocation across surgical services was influenced by factors other than medical suitability. Of major users, cardiothoracic surgery experienced the highest percentage (59%) of all patient admissions and lowest percentage (1.6%) of all denied admissions. General surgery experienced the lowest percentage (15%) of all admissions and highest percentage (10.4%) of all denied admissions, although these patients had the highest average Acute Physiology and Chronic Health Evaluation (APACHE II) scores for all patients admitted (17.7) and for patients denied admission (15.8). CONCLUSIONS: Surgical attending physicians rarely used other open inhouse ICU beds when surgical ICU beds were unavailable. Political power, medical provincialism, and income maximization overrode medical suitability in the provision of critical care services.

Hemodynamic and metabolic effects of dobutamine in 18 patients after open heart surgery.

Low cardiac output syndrome frequently follows cardiopulmonary bypass (CPB) surgery. In the present study, we used dobutamine to increase cardiac index (CI) and oxygen delivery (DO2) in 18 patients after open heart surgery. Using increasing doses of dobutamine up to 10 micrograms/kg.min-1, we observed statistically significant (p less than .01) increases in mean CI (2.50 +/- 0.10 to 3.56 +/- 0.18 L/min.m2) and in mean heart rate (HR) (83 +/- 3 to 105 +/- 3 beat/min). Mean systemic vascular resistance index decreased significantly (p less than .01) in all patients (2271 +/- 101 to 1648 +/- 83 dyne.sec/cm5.m2). Pulmonary vascular resistance index did not change in the ten coronary artery bypass graft patients, but decreased significantly (p less than .01) in the eight valve replacement patients (561 +/- 98 to 421 +/- 79 dyne.sec/cm5.m2). Mean DO2 increased in all patients, although there was no concomitant increase in oxygen consumption (VO2) in four patients. We observed a significant (p less than .01) increase in mean VO2 in the remaining 14 patients (110 +/- 6 to 148 +/- 12 ml/min.m2), in spite of significant decreases in PaO2 and increases in right-to-left intrapulmonary shunting. Although increases in HR and ventricular arrhythmias may limit its use, dobutamine increases CI and DO2 in patients after CPB. In the present study, dobutamine's varying metabolic effect exemplifies the need for close monitoring of hemodynamic and metabolic variables when using vasoactive drugs in the postoperative period.

Hemodynamic effects of rapid vancomycin infusion in critically ill patients.

The rapid infusion of vancomycin produces histamine release resulting in rash ("red-man's" syndrome) and hypotension. Because this phenomenon has been described primarily in healthy subjects, we prospectively studied the rapid infusion of vancomycin in 16 critically ill patients after open heart surgery in an attempt to document histamine release with resulting hemodynamic changes, and to see if there is any correlation with vancomycin levels. After establishing baseline hemodynamic stability and histamine levels, 1 g vancomycin diluted in 50 mL of 5% dextrose was infused over 30 min. Cardiac index, heart rate, blood pressure, pulmonary venous pressures, and systemic and pulmonary vascular resistances remained unchanged during the infusion. Although the mean plasma vancomycin level increased to a peak of 69 +/- 20 micrograms/mL after 20 min of the infusion before declining, mean plasma histamine levels in 15 of the 16 patients remained within the normal range during the infusion. In one patient a baseline histamine level (2.8 ng/mL) more than three times the normal before the vancomycin infusion increased further during the infusion (3.0, 4.9, and 5.0 ng/mL at t = 10, 20, and 30 min, respectively), and remained elevated (2.9 ng/mL) 30 min after the infusion. This patient developed the red-man's syndrome, although there were no hemodynamic changes. There was no evidence of myocardial depression in any of the patients. In conclusion, we safely infused a concentrated solution of vancomycin into critically ill patients over 30 min without any adverse hemodynamic changes. One patient developed the red-man's syndrome. There was no correlation between peak vancomycin levels and the release of histamine in this patient population.

Hemodynamic effects of dobutamine in patients following mitral valve replacement.

Mitral valve replacement is frequently complicated by a low cardiac output syndrome and elevated pulmonary arterial pressures. In the present study, we used dobutamine to increase cardiac index and measured the pulmonary hemodynamic effects in 10 patients with increased pulmonary vascular tone following mitral valve replacement. Using increasing doses of dobutamine up to 10 micrograms.kg-1.min-1, we observed a statistically significant increase in mean cardiac index (from 2.39 +/- .14 liters.min-1.m-2 to 3.52 +/- .33, P less than 0.01) and mean heart rate (from 71.6 +/- 5.2 beats.min-1 to 84.3 +/- 8.1, P less than 0.01). This was associated with stable mean systemic arterial pressures and mean pulmonary arterial pressures. Both mean systemic and pulmonary vascular resistances decreased significantly (from 1210 +/- 99 dynes.sec.cm-5 to 809 +/- 90 [P less than 0.01], and from 195.9 +/- 30.6 dynes.sec.cm-5 to 129.4 +/- 41.2 [P less than 0.01] respectively) with dobutamine. Intrapulmonary shunt flow increased significantly in the five patients studied. Though increases in heart rate and pulmonary shunt flow may limit it use, dobutamine increases cardiac output and decreases pulmonary vascular resistance in patients with increased pulmonary arterial pressure following mitral valve replacement.

Efficacy of an attachable subcutaneous cuff for the prevention of intravascular catheter-related infection. A randomized, controlled trial.

We performed a randomized controlled trial of an attachable subcutaneous cuff for the prevention of central vascular catheter-related infection among patients receiving intensive care. Catheters were placed percutaneously into new sites with or without a cuff and were dressed with polyantibiotic ointment containing polymyxin, neomycin, and bacitracin. Microbial colonization developed in 34.5% of 29 control and 7.7% of 26 cuffed catheters. Catheter-related bloodstream infection occurred with 13.8% of control vs 0% of cuffed catheters. The cuff was not associated with adverse effects. An unexpectedly large proportion (75%) of catheter infections were due to Candida albicans. This may have been due, in part, to the use of polyantibiotic ointment, as suggested by a pooled analysis of previous trials that demonstrated increased Candida colonization of catheters with the ointment, which is not fungicidal. These data suggest that the cuff can reduce the incidence of catheter-related infection among high-risk patients receiving catheter site care with an antibacterial ointment.