Hemodynamic assessment of local anesthetic administration by laser Doppler flowmetry.

OBJECTIVE: The hemodynamic effects of local anesthetic administration with and without a vasoconstrictor were compared by using laser Doppler flowmetry. STUDY DESIGN: Seventeen people participated in a single study session in which they were given 2 intraoral injections. The injections, which were administered in random order, consisted of 1.8 mL lidocaine (2%) with epinephrine (1:100,000) and mepivacaine (3%). Hemodynamic parameters consisting of blood pressure, heart rate, and laser Doppler flowmetry were reordered at regular intervals. RESULTS: The laser Doppler flowmeter detected changes in the peripheral perfusion of the finger that were not detected by changes in blood pressure and heart rate. The greatest change was associated with anxiety and occurred just before the injection. The inclusion of epinephrine in the local anesthetic resulted in a persistence of these changes. CONCLUSION: This investigation has confirmed the sensitivity of laser Doppler flowmetry as an investigational tool for assessing hemodynamic changes associated with anxiety and the administration of local anesthesia.

Assessment of the economic impact of an overage reduction program in the operating room.

STUDY OBJECTIVES: To delineate excessive supply preparation in the operating rooms (ORs) of Yale-New Haven Hospital, and to measure the reduction in such overage as a result of nursing and administration cost-containment efforts. DESIGN: Before and after trial. SETTING: Inpatient ORs of Yale-New Haven Hospital. INTERVENTIONS: After the initial documentation of overage, several cost-containment measures were instituted, including nursing education, review of overage data, and updating of surgical request lists. MEASUREMENTS AND MAIN RESULTS: The hospital cost of case-specific overage generated by all surgical procedures performed during two 2.5-month periods in 1992 and 1994 (before and after the interventions) were compared. One-thousand three hundred eighteen cases in 1992 were compared with 1,367 cases in 1994. A 45% reduction in mean per case overage occurred between the two assessment periods. Extrapolation of the data to the incidence of similar cases throughout the United States projected a comparable savings. CONCLUSIONS: Efforts to increase the efficiency of OR supply management can be measured, in part, by overage evaluation, which can serve as a resource for focusing efforts at cost-containment.

Focused versus operating room-wide recovery of unused supplies for overseas reconstructive surgery.

Proliferation of programs that recover surplus operating room supplies may effectively address the needs of volunteer overseas surgical efforts. However, these programs tend to garner supplies highly heterogeneous in nature. In order to evaluate the nature and quantity of supplies generated by plastic and reconstructive procedures, we extrapolated the inventory of 71 consecutive cases from our 33,000-case database. Additionally, we examined the recovery of 7 specific supplies from all cases performed at Yale-New Haven Hospital over a 3-year period. Though consistency is unlikely when only plastic and reconstructive surgical cases are examined, operating room-wide recovery may be a reliable source of usable materials.

Pulse width, stimulus intensity, electrode placement, and polarity during assessment of neuromuscular block.

BACKGROUND: Although the intensity of neurostimulation (i.e., charge) is a product of current intensity and pulse duration, the effects of the latter on the amplitude of evoked response and subjective discomfort are unknown. Therefore, the authors investigated the effects of current intensity and pulse width, and their interaction with electrode placement and polarity, on force translation (FTR), accelerography (ACG), and electromyography (EMG) at the adductor pollics muscle. METHODS: Ulnar stimulating electrodes were applied in one of two configurations: over the distal forearm and olecranon groove ("A") or 5 cm apart on the distal forearm ("B"). Stimuli for FTR and EMG with current intensities of 20, 40, 60, and 70 mA and pulse widths of 0.05, 0.1, 0.2, and 0.4 msec resulted in 16 different charges. These combinations were delivered in each of four orientations: "A-" ("A" configuration with negative electrode distal); "A+", "B-", and "B+" (n = 64 stimuli). Eight stimulus combinations (n = 32 stimuli) were used for ACG. For each monitoring technique, the effects of current intensity, pulse width, electrode polarity, and placement were analyzed with repeated measures ANOVA. Pain responses were scored on a 0-100-mm verbal analog scale and analyzed with ANOVA and Fisher's exact test. RESULTS: The evoked response amplitude varied directly with current intensity and pulse width. In both electrode placement configurations, the response was greater when the negative electrode was distal. The electrode positioning ("A" vs. "B") had less of an impact on evoked responses than did polarity, regardless of monitoring technique. The evoked pain varied directly with the amplitude of evoked neuromuscular response in all electrode position-polarity combinations. CONCLUSIONS: The total current charge required for evoking a supramaximal neuromuscular response is much higher than previously appreciated, and electrode polarity is important in attaining a supramaximal plateau. Failure to attain (and maintain) a supramaximal stimulus allows changes in the effectiveness of neurostimulation, thus influencing the magnitude of the evoked neuromuscular response and confounding measurements of neuromuscular block.

Real time versus slow-motion train-of-four monitoring: a theory to explain the inaccuracy of visual assessment.

The present study was undertaken to determine why visual assessment of thumb adduction in response to train-of-four (TOF) stimulation of the ulnar nerve commonly overestimates the ratio that is obtained mechanographically. In patients undergoing general endotracheal anesthesia plus vecuronium for relaxation, 73 data sets were collected at different depths of neuromuscular block in response to supramaximal TOF stimulation. Each data set consisted of: (i) visual estimation of the TOF ratio by an experienced observer; (ii) mechanographic measurement of the TOF ratio with an adductor pollicis force transducer; and (iii) determination of the TOF ratio by measuring the slow-motion thumb displacement recorded on videotape. The last 23 data sets also included visual assessment and videotape recording of evoked responses at low stimulating current (30 mA). Visual inspection at 60 mA overestimated the mechanographic ratio by 0.20 units (48%). Videotape review provided a ratio that was 0.23 units (56%) greater than that determined mechanographically. However, after the first three twitches (T1-3), the thumb did not return to the same resting position as the (original) baseline prior to the first twitch. When the change in thumb position as a result of T1-3 was taken into account, the measured height of T4 was 40% less than it was when measured from the original baseline, and the T4/T1 ratio was identical to that obtained mechanographically. For the 23 data sets obtained at low current visual assessment overestimated the mechanographic value to a lesser degree than when obtained at high current. Again, correction for the T1-3 baseline shift improved the accuracy of videotape analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cost-effective use of operating room supplies based on the REMEDY database of recovered unused materials.

It is estimated that $200 million worth of prepared materials are discarded unused in operating rooms in the United States each year. Although some of these materials have been successfully recovered for overseas donation, they nevertheless constitute an undesirable burden on health care efficiency. This situation has prompted a reevaluation of the procedures that result in the overpreparation of surgical supplies, in the hope of reducing hospital, patient, and third-party payer expenditures. A database, which was initially developed to track the overseas donation of recovered supplies from Yale-New Haven Hospital, is now being applied to measure approaches to waste reduction. This report summarizes the application of this database to an integrated program designed to modify nursing procedures and physician prespecified supply lists.

Peripheral assessment of phenylephrine-induced vasoconstriction by laser Doppler flowmetry and its potential relevance to homeostatic mechanisms.

BACKGROUND: Cutaneous laser Doppler flowmetry enables monitoring of changes in skin perfusion by quantifying the phase shift of laser light induced by moving red blood cells under a fiberoptic probe. It thus can identify the presence of and response to a vasoconstrictive stimulus. However, aspects of the technique must be defined before it can be used with maximum effectiveness. We evaluated the responses of two different laser Doppler outputs, the concentration of moving blood cells (CMBC) and red cell flux (CMBC times cell velocity), and the responses at two sites of probe application, the finger and forearm, during systemic infusions of phenylephrine. METHODS AND RESULTS: Eight healthy volunteers were monitored with a brachial blood pressure cuff, ECG, and laser Doppler flowmeter probes applied to the palmar surface of the fourth finger and volar forearm of the arm opposite the pressure cuff. After baseline readings were obtained, the subjects received three 10-minute intravenous infusions of phenylephrine at rates of 0.4, 0.8, and 1.6 micrograms.kg-1.min-1. The two parameters, flux and CMBC, trended similarly. Flux and CMBC at the finger declined significantly in response to each infusion (P < .05 using repeated-measures ANOVA with Duncan's multiple range test). In contrast, flux and CMBC of the forearm had highly variable responses, with an overall increase during each infusion (P < .05 for % delta of forearm versus % delta of finger readings during the 0.4 microgram.kg-1.min-1 infusion). Heart rate declined significantly during each infusion, consistent with a baroreceptor-mediated response, even though systolic and diastolic blood pressures each increased by less than 2 mm Hg during the 0.4 microgram.kg-1.min-1 infusion. CONCLUSIONS: As expected, laser Doppler readings at the finger decreased during infusion of an alpha 1-agonist. Although, like the digital vessels, forearm vessels have the potential to constrict, the increases in forearm readings suggest that these vessels are highly susceptible to homeostatic responses. The increase in CMBC (a parameter that is sensitive primarily to local changes in vascular caliber) suggested vasodilation of the underlying vessels. The forearm vasodilation and the concomitant decline in heart rate most likely represented vagally mediated baroreceptor activity, which was altered even though blood pressure changed minimally during the 0.4 microgram.kg-1.min-1 infusion. Thus, integrated assessment of skin perfusion at the finger and forearm may provide valuable information about the direct and indirect effects of a vasoactive stimulus. The present application of laser Doppler flowmetry suggests activation of vasodilatory reflexes despite minimal changes in blood pressure.

Visual and tactile assessment of neuromuscular fade.

The accuracy of visual and tactile assessment of the neuromuscular fade in response to train-of-four (TOF) and double-burst stimulation (DBS) were compared to assess their relative utility in the clinical setting. For each of 74 data sets with a mechanographic TOF ratio less than 0.70, an observer (blinded to the presence or degree of fade) performed visual and tactile assessments of fade in response to TOF, DBS3,3, and DBS3,2 stimuli at low current (20 and 30 mA) and high current (50 and 60 mA). For the range of mechanographic TOF ratios between 0.41 and 0.70, visual assessment failed to identify TOF, DBS3,3, and DBS3,2 fade in 46%, 18%, and 14% of cases at high current and in 23%, 5%, and 0% of cases at low current, respectively. Tactile assessments failed to identify fade in 55%, 23%, and 14% of cases at high current and in 23%, 14%, and 14% of cases at low current. Overall, the ability to detect fade was comparable for visual and tactile assessments regardless of the method of neurostimulation (P = NS with paired t-test). However, the degree of overestimation of the fade ratio (i.e., quantitative assessment) tended to be less when using tactile means; the difference achieved significance for TOF at low current and DBS3,3 at both low and high currents. We conclude that the differences between the visual and tactile means of assessment are relatively small compared to the differences among the TOF and DBS patterns of neurostimulation. Both subjective techniques are often inadequate in settings in which assurance of full recovery of neuromuscular function is critical.

Assessment of double-burst monitoring at 10 mA above threshold current.

We compared fade measurements in response to double-burst stimulation (DBS) at 10 mA above the threshold for the second response (D2) to that for DBS at 60 mA in order to determine the utility of low-current DBS testing. In 20 healthy adults undergoing general endotracheal anesthesia with isoflurane 0.5-1% end-tidal, a vecuronium infusion (0.25-1.5 micrograms.kg-1 x min-1) was delivered until a stable train-of-four (TOF) response to ulnar nerve stimulation was documented with an adductor pollicis force transducer. Then DBS responses were recorded, and the D2/D1 ratios were determined at 60 mA and at 10 mA above the D2 threshold current (TS + 10 mA). The mean difference (bias) between D2/D1 /TS+10 mA and D2/D1 / 60 mA was -0.02 (P < 0.05); the 95% limits of agreement were from -0.12 to +0.08. The bias and limits of agreement were similar to those for T4/T1 of train-of-four. A strong correlation was noted between the degrees of fade determined at the low and high currents (r = 0.95). We conclude that, although stimulation at 10 mA above the D2 threshold is associated with a slight negative bias, it is virtually interchangeable with testing at higher current in the clinical setting. This technique thus may be used effectively to monitor neuromuscular fade in settings where neurostimulation with low current is deemed desirable.

Case-by-case assessment of recoverable materials for overseas donation from 1318 surgical procedures.

OBJECTIVE: To provide a mechanism for addressing the need for consistency and projection in overseas donation of surgical supplies, we conducted a case-by-case inventory of unused materials recovered from all surgical procedures in our facility over a 2.5-month period. DESIGN: Unused surgical supplies were recovered in coded bags from individual cases and inventoried. SETTING: Inpatient operating rooms at Yale-New Haven Hospital. MAIN OUTCOME MEASURE: The weight and dollar value of recovered materials were tallied for each case type; these were then extrapolated according to the frequency with which each procedure is performed in the United States to provide an estimate of the impact of a nationwide recovery program. RESULTS: The value of supplies recovered ranged from $1 (bone marrow transplant) to greater than $40 (liver and vulva/perineum procedures). By extrapolation to case-specific data from the National Hospital Discharge Survey (1990), we estimate that a nationwide recovery program could yield more than $193 million in charitable material and reduce operating room waste by more than 1.7 million kilograms (1948 tons). CONCLUSIONS: Consistency and organization would contribute greatly to efforts to alleviate existing medical supply needs in the developing world. This case-by-case assessment should enable participating centers to project more effectively the outcome of such collections and allow the coordination of efforts. Though unlikely to be adopted by all operating theaters in the United States, the potential charitable contributions from a nationwide recovery program are significant.

Visual assessment of train-of-four and double burst-induced fade at submaximal stimulating currents.

The influence of current intensity on visual assessment of fade in response to train-of-four (TOF) and two modes of double-burst stimulation (DBS) was determined to assess the utility of low-current neurostimulation. Each of 150 sets of assessments (in 51 patients) included a mechanographic TOF at 60 mA followed by visual assessments of TOF, DBS3,3 (two minitetanic bursts of three stimuli each), and DBS3,2 (a burst of three followed by a burst of two impulses) at 20, 30, 50, and 60 mA in random order. For the range of mechanographic TOF ratios between 0.41 and 0.70, visual assessment of TOF fade failed to identify fade in 33%, 36%, 44%, and 58% of cases at 20, 30, 50, and 60 mA, respectively. Corresponding false-negative rates for DBS3,3 were 11%, 17%, 36%, and 33%, and for DBS3,2 they were 6%, 6%, 17%, and 28%. Within each method, P less than 0.05 (by Mantel-Haenszel analysis) for a linear trend of increasing accuracy as current decreased. For the range between 0.41 and 0.70, quantitative assessment overestimated the actual ratio at all currents for TOF, at 30, 50, and 60 mA for DBS3,3, and at 50 and 60 mA for DBS3,2 (P less than 0.05 by Wilcoxon signed rank test). At each current tested, DBS was more sensitive in detecting fade visually than TOF. The accuracy of visual fade detection was not influenced significantly by level of observer training. In conclusion, visual assessment of fade by novice and expert observers is improved by testing at low currents.

Elevated intravesical pressure causes arterial hypoperfusion in canine colocystoplasty: a fluorometric assessment.

Since 1988 there have been 15 reported cases of late, spontaneously ruptured intestinal cystoplasties at bowel sites remote from the anastomosis. Ischemic necrosis has been suggested as a possible etiology. We examined this hypothesis by quantifying the uptake of intravascular fluorescein in the augmented bowel of adult mongrel canines. There was a statistically significant decrease in fluorescein uptake at high intravesical pressures, which appeared to be most pronounced at the antimesenteric border. This laboratory study supports a recent clinical report of histological changes pathognomonic for chronic ischemia in the augmented bowel of patients with spontaneous rupture.

Assessment of residual curarization using low-current stimulation.

The present study employed train-of-four (TOF) stimulation at a current of 20 mA to assess the incidence and degree of residual neuromuscular blockade in 64 randomly selected Post Anesthesia Care Unit (PACU) patients. Group C (Control, n = 10) had received anaesthesia without nondepolarizing muscle relaxant; Group V (n = 25) had received vecuronium; and Group P (n = 29) had received pancuronium. At the end of surgery, each patient had been considered by his anaesthetist to have adequate neuromuscular function on the basis of clinical signs and tactile or visual evaluation of responses to TOF stimulation. However, upon testing in the PACU 15 min later, 45% (13 of 29) of Group P patients and 8% (2 of 25) of Group V patients had a TOF ration less than 0.70. This study indicates that residual curarization may be commonly encountered following long-acting relaxants despite qualitative intraoperative TOF monitoring. The present incidence, detected at a current of 20 mA, is consistent with previous reports which employed supramaximal TOF stimulation. We conclude that despite intraoperative monitoring, residual curarization following long-acting nondepolarizing agents is common and that it may be detected with TOF at a low stimulating current (20 mA).

Fluorescence assessment of skin perfusion after oral fluorescein.

This study evaluated oral ingestion as the route of fluorescein administration for fluorescence assessment of skin perfusion. In 10 anesthetized rats, dorsal pedicle flaps were raised to produce graded perfusion; then fluorescein (7.5 mg/kg) was administered via an oropharyngeal tube. Quantification of skin fluorescence, performed with the fiberoptic fluorometer 45 minutes after dye ingestion, delineated a significant difference between the perfusion of flap regions that remained viable and those that subsequently became dystrophic (p less than 0.05). The precision was equivalent to that previously reported after intravenous dye. In addition, the gradual delivery of dye after oral administration permitted monitoring of slope of uptake and time to peak. Each of these pharmacokinetic parameters delineated a significant difference between viable and nonviable sections. As measures of relative change in fluorescence, they are independent of skin color and thickness. This feature suggests that the oral route actually may improve the accuracy and reliability of the fluorescein test.

Comparative assessment of blood flow to canine island flaps.

Fluorometric quantification of dye delivery, laser Doppler flowmetry, and transcutaneous measurement of tissue oxygen level were evaluated in canine island flaps subjected to vascular occlusion. Each technique readily identified the clamping insult. Relative fluorescein delivery to the flap (compared with a reference area) decreased from 66% before clamping to almost zero during clamping. Laser Doppler readings rapidly declined from an average of 230 to an average of 31 mV. Oxygen readings rapidly declined from 57 to 1 mm Hg. Laser Doppler flowmetry and transcutaneous oxygen monitoring seem best suited for continuous monitoring of trends at a single site. Fluorometry is more precise and can be used to monitor multiple sites. One should weigh the benefits of this technique against the need for dye injection.

Clinical assessment of flap perfusion by fiberoptic fluorometry.

Perfusion fluorometry, a method which quantifies tissue fluorescence after intravenous fluorescein injection, has been highly predictive of skin flap survival in animals. It is advantageous because it is objective, simple, noninvasive, repeatable, and can be used to monitor flap perfusion constantly by following both uptake and elimination of dye. We applied this method clinically to a variety of flaps used in head and neck surgery. All flaps with good fluorometric values survived totally. Based on experience with 37 flaps, fluorometric indices have been established that accurately predict necrosis. Serial dye injections have been used to document transient flap ischemia in the early postoperative period. Representative cases illustrating the advantages of fluorometry in flap assessment are presented.

Assessment of delay in bilateral thoracoabdominal island flaps in the rat.

This study demonstrates improved perfusion and viability following surgical delay in a bilateral paired flap model that minimizes the effects of systemic variables in the rat. Surgical delay was achieved in one of two paired thoracoabdominal island flaps by ligating and cutting the inferior epigastric (distal) pedicle three days before flap construction. This created a hypoperfused zone. Within three days of delay, perfusion of the delayed region, as documented by quantification of tissue fluorescein delivery, increased markedly and often exceeded nondelayed values. Construction of 2 X 11-cm island flaps based on the superior epigastric pedicle at this time was associated with an average of 1.1-cm necrosis, compared with 2.6 cm in nondelayed flaps.

Assessment of neovascularization and timing of flap division.

These studies were undertaken to determine if perfusion fluorometry can provide an accurate, reliable means of monitoring neovascularization and predicting optimal time of flap division. An animal model was developed that permitted daily assessment of neovascularization of the flap using fluorescein injections and the fluorometer. An increase in fluorescence of the pedicle-occluded flap of approximately 12 percent the normal skin fluorescence was associated with 100 percent flap survival. This occurred after only 4 days in the rat. Fluorometry proved valuable in the evaluation of clinical flaps. The fluorescence of flaps during pedicle occlusion was observed to increase with each successive fluorometric evaluation performed at 3- to 7-day intervals. It appears that flaps after pedicle occlusion exhibiting at least 25 percent of the fluorescence of normal skin will tolerate pedicle division. Based on the neovascularization studies of the clinical flaps, all pedicles were severed earlier than originally anticipated. Two cross-leg flaps were successfully divided after 11 days. Quantitative assessment of serial fluorescein injections allows reliable evaluation of neovascularization in clinical interpolation flaps and is useful in the timing of flap division.

Fiberoptic fluorometer for skin flap assessment.

The fiberoptic fluorometer permits quantitative measurement of fluorescence after intravenous administration of fluorescein. Accurate assessment of tissue fluorescence can be made at any time after the injection, and both uptake and elimination of fluorescein can be followed. The instrument provides instantaneous digital readout of the fluorescence measured in dye fluorescence (DF) units and an index predictive of viability called the dye fluorescence index (DFI). The unit is portable, can be sterilized for operating room use, and can be operated by paramedical personnel with ease. We have used the instrument extensively in clinical and laboratory investigations, where it has been highly reliable in predicting survival and necrosis of a wide variety of flaps. Little or no operating time is added, and serial, low-dose fluorescein injections may be used to monitor a flap in the recovery room or at the bedside in the early postoperative period.