Comparison of quality and cost-effectiveness in the evaluation of symptomatic cholelithiasis with different approaches to ultrasound availability in the ED.

Ultrasound is the imaging study of choice for the detection of gallstones, but ultrasound through medical imaging departments (MI Sono) is not readily available on an immediate basis in many emergency departments (EDs). Several studies have shown that emergency physicians can perform ultrasound themselves (ED Sono) to rule out gallstones with acceptable accuracy after relatively brief training periods, but there have been no studies to date specifically addressing the effect of ED Sono of the gallbladder on quality and cost-effectiveness in the ED. In this study, we investigated measures of quality and cost-effectiveness in evaluating patients with suspected symptomatic cholelithiasis during three different years with distinctly different approaches to ultrasound availability. The study retrospectively identified a total of 418 patients who were admitted for cholecystectomy or for a complication of cholelithiasis within 6 months of an ED visit for possible biliary colic. The percentage of patients who had gallstones documented at the first ED visit improved from 28% in 1993, when there was limited availability of ultrasound through the Medical Imaging Department (MI Sono), to 56% in 1995, when MI Sono was readily available, to 70% in 1997, when both MI Sono and ED Sono were readily available (P <.001). There were also significant differences over the 3 years in the mean number of days from the first ED visit to documentation of gallstones (19.7 in 1993, 10.7 in 1995, 7.4 in 1997, P <.001); the mean number of return visits for possible biliary colic before documentation of gallstones (1.67 in 1993, 1.24 in 1995, and 1.25 in 1997, P <.001); and the incidence of complications of cholelithiasis in the interval between the first ED visit for possible biliary colic and the date of documentation of cholelithiasis (6.8% in 1993, 5.9% in 1995, 1.5% in 1997, P =.049). The number of MI Sonos ordered by emergency physicians per case of symptomatic cholelithiasis identified increased from 1.7 in 1993 to 2.5 in 1995 and dropped back to 1.7 in 1997, when 4.2 ED Sonos per study case were also done. The cost of ED Sonos was more than offset by savings in avoiding calling in ultrasound technicians after regular Medical Imaging Department hours. The indeterminate rate for ED Sonos was 18%. Excluding indeterminates, the sensitivity of ED Sono for detection of gallstones was 88.6% (95% CI 83.1-92.8%), the specificity 98.2% (95% CI 96.0-99.3%), and the accuracy 94.8% (95% CI 92.5-96.5%). We conclude that greater availability of MI Sono in the ED was associated with improved quality in the evaluation of patients with suspected symptomatic cholelithiasis but also with increased ultrasound costs. The availability of ED Sono in addition to readily available MI Sono was associated with further improved quality and decreased costs. The indeterminate rate for ED Sono was relatively high, but excluding indeterminates, the accuracy of ED Sono was comparable with published reports of MI Sono.

Ultrasound availability in the evaluation of ectopic pregnancy in the ED: comparison of quality and cost-effectiveness with different approaches.

The liberal use of ultrasonography has been advocated in patients with first trimester cramping or bleeding to avoid misdiagnosis of ectopic pregnancy in the emergency department (ED). The cost-effectiveness of different approaches to ultrasound availability has not been previously reported. In this study, we investigated measures of quality and cost-effectiveness in detecting ectopic pregnancy in the ED over a 6-year period, divided into three approximately equal epochs with three distinct approaches to ultrasound availability. The study retrospectively identified 120 cases of ectopic pregnancy seen in the ED over 6 years. There was significant improvement in the percentage of patients with ectopic pregnancy who were documented to have absence of intrauterine pregnancy (IUP) at the first visit from 76% during Epoch 1, when there was limited availability of ultrasound through medical imaging (MI Sono), to 88% in Epoch 2, when MI Sono was readily available, to 96% in Epoch 3, when both MI Sono and ultrasound by emergency physicians (ED Sono) were readily available (P = .02). The estimated number of MI Sonos ordered by emergency physicians in patients at risk for ectopic pregnancy increased from 5.2 per ectopic pregnancy in Epoch 1 to 11.8 per ectopic pregnancy in Epoch 2, and declined to 5.5 per ectopic pregnancy in Epoch 3, when 19.9 ED Sonos per ectopic pregnancy were also done. The cost of ED Sono in Epoch 3 was more than offset by savings from avoiding calling in ultrasound technicians after regular medical imaging department hours. The specificity of ED Sono in ruling in an IUP was 100% (95% CI 98.3 to 100%), but analysis of secondary quality indicators reflecting times from first ED visit to treatment in Epoch 3 raised the possibility that an adnexal mass or signs of tubal rupture may have been missed on some ED Sonos. We conclude that increased availability of ultrasonography leads to improved quality in the detection of ectopic pregnancy in the ED, but at the expense of a disproportionate increase in the number of ultrasound studies done per ectopic pregnancy detected. Our study suggests that the most cost-effective strategy is for emergency physicians to screen all patients with first trimester cramping and bleeding with ED Sonos, and to obtain MI Sonos at the time of the initial ED visit in all cases in which the ED Sono is indeterminate or shows no IUP.

Patient satisfaction and diagnostic accuracy with ultrasound by emergency physicians.

In recent years, there has been considerable interest and controversy concerning the performance of ultrasound by emergency physicians (ED Sono), but patient satisfaction with ED Sono has not been well studied. The primary purpose of this investigation was to assess the level of patient satisfaction with ED Sono and to compare satisfaction with ED Sono with ultrasound by the Medical Imaging Department (MI Sono). A secondary objective was to assess the accuracy of ED Sono at our facility. During a 5-month period, which included the startup phase of a program for ED Sono, emergency physicians prospectively identified patients who were candidates for ultrasound as a part of their workup. Patients were contacted by telephone after their ED visit and asked to rate satisfaction on a 0 to 10 scale for various aspects of their care, including the ultrasound if one was done. The accuracy of ED Sono was determined by comparing ED ultrasound interpretations with surgical pathology, repeat imaging studies, or clinical follow-up. Two hundred forty patients were entered into the study, and 186 (78%) responded to the satisfaction survey. Satisfaction ratings were similarly high for ED Sono (mean, 8.9; 95% Cl, 8.6 to 9.2) and for MI Sono (mean, 8.8; 95% Cl, 8.2 to 9.4). Eighteen percent of ultrasounds performed by emergency physicians were indeterminate. Excluding indeterminate scans and scans for which confirmation was not possible, the accuracy of ED Sono was 99.1% (95% Cl, 95.1% to >99.9%). We conclude that during the startup phase of our ED Sono program, patient satisfaction was high, and the error rate was very low.

Control of ventilation during lung volume changes and permissive hypercapnia in dogs.

We investigated the effect changes in end-expiratory lung volume (EEVL) had on the response to progressive hypercapnia (CO2-response curve) in eight open-chest, anesthetized dogs, in order to clarify the role that vagal lung mechanoreceptors have in altered respiratory drive during permissive hypercapnia. The dogs were ventilated using a positive-pressure ventilator driven by phrenic neural activity. Systemic arterial CO2 tension (PaCO2) was elevated by increasing the fraction of CO2 delivered to the ventilator. EEVL was altered from approximated functional residual capacity ("FRC") to 1.5 and 0.5 "FRC" by changing positive end-expiratory pressure. Although the tidal volume (VT)-PaCO2 and inspiratory time (TI)-PaCO2 relationships were not affected, decreasing EEVL from 1.5 "FRC" to "FRC" and then to 0.5 "FRC" caused a significant (p < 0.01) upward shift in the CO2-response curves for minute ventilation (V I) and frequency (f ), and a significant (p < 0.01) downward shift in the CO2- response curve for expiratory time (TE). We conclude that these shifts were explained by a decrease in the inhibitory activity of slowly adapting pulmonary stretch receptors (PSRs) as EEVL was lowered. In addition, increases in EEVL from 0.5 "FRC" to 1.5 "FRC" caused a significant (p < 0.05) increase in the apneic threshold, which we attribute to an inhibitory effect on central drive caused by increased PSR activity.

Gas exchange and lung mechanics during percutaneous transtracheal ventilation in an unparalyzed canine model.

OBJECTIVE: To compare the efficacy of percutaneous transtracheal ventilation (PTV) in the unparalyzed state with that in the paralyzed state using a sedated nonobstructed canine model. METHODS: Eight mongrel dogs (16.8-32 kg) were anesthetized, instrumented, and placed in a volume plethysmograph. Anesthesia was achieved with pentobarbital sodium (up to 30 mg/kg). The spontaneous respiratory drive was kept intact. PTV was performed using a 13-ga transtracheal catheter and compressed air at 45 psi at an I:E ratio of 1:3 (15 breaths/min). Each dog was sequentially ventilated in both the paralyzed and unparalyzed states. The paralyzed/unparalyzed sequence was alternated among the animals to avoid sequence bias. Paralysis was achieved with succinylcholine (0.1 mg/kg bolus and 0.01 mg/kg/min drip). Reversal of paralysis was achieved by discontinuing the succinylcholine infusion. Key variables, including arterial blood gas, tidal volume, and pulmonary mechanics, were measured and compared for the paralyzed and unparalyzed states. RESULTS: Gas exchanges and lung mechanics were similar between the unparalyzed and paralyzed states. There was no significant difference in mean pH, pCO2, pO2, tidal volume, or peak inspiratory transpulmonary pressure. There was also no significant difference in pulmonary resistance or pulmonary compliance. CONCLUSION: In a sedated nonobstructed canine model, PTV is as efficacious in the unparalyzed state as it is in the paralyzed state. The lung mechanics are also similar in the 2 states. These data suggest that it may be unnecessary to induce paralysis when using PTV for emergency ventilation in the heavily sedated state.

Pulmonary mechanics of dogs during transtracheal jet ventilation.

STUDY OBJECTIVE: To quantify the delivered tidal volume and other selected measurements of pulmonary mechanics in an animal model during transtracheal jet ventilation (TTJV), with comparison to positive-pressure mechanical ventilation (PPMV) and spontaneous breathing. DESIGN: Prospective, nonblinded laboratory animal study. INTERVENTIONS: Seven mongrel dogs weighing 24.5 +/- 3.7 kg were anesthetized, paralyzed, and placed within a specially designed volume plethysmograph with the head and neck externalized. Ventilation was performed using TTJV under variable inspiratory time:expiratory time ratios (TI:TE) (1:1, 1:2, 1:3, 1:4, 1.5:2.5, 2:1, 2:2, 3:1, and 4:1) and variable driving air pressures (40, 45, and 50 psi). The dogs then were ventilated with PPMV. Tidal volume, tracheal pressure, transpulmonary pressure, air flow, arterial pressure, central venous pressure, and arterial blood gases were measured during spontaneous ventilation, TTJV, and PPMV. Quasistatic compliance of the lungs was measured after all methods of ventilation. Statistical significance was accepted at P < .05. RESULTS: There was no significant difference between delivered tidal volume during TTJV (446 +/- 69 mL at a TI:TE of 1:3 and 45 psi) and spontaneous breathing (506 +/- 72 mL). TTJV delivered a tidal volume significantly higher than the standard 15 mL/kg volume used for mechanical ventilation in dogs. Tracheal pressure and transpulmonary pressure were not significantly different between TTJV and PPMV. Variations in TI:TE had no significant effect on most of the measured variables, specifically tidal volume or transpulmonary pressure. Minute ventilation increased significantly and PCO2 decreased significantly as frequency increased during TI:TE settings of 1:1, 1:2, and 2:1. Increases in the driving air pressure during TTJV significantly increased the tidal volume as it was raised from 40 psi to 50 psi. There was no change in quasistatic lung compliance during any method of ventilation. CONCLUSION: TTJV delivers an effective tidal volume comparable to both spontaneous breathing and PPMV in a dog model. In the absence of upper-airway obstruction, there was no significant difference in the pulmonary pressures, resistance, and compliance during TTJV, as compared to mechanical ventilation. Variation in TI:TE during TTJV had no major effect on pulmonary mechanics, except to increase minute ventilation and decrease PCO2 as the frequency was increased significantly. Increasing the driving air pressure to the TTJV apparatus significantly augmented delivered tidal volume due to increased air flow.

Effects of graded upper-airway obstruction on pulmonary mechanics during transtracheal jet ventilation in dogs.

STUDY OBJECTIVE: To quantify the effects of graded upper-airway obstruction on the delivered tidal volume and selected parameters of pulmonary mechanics during transtracheal jet ventilation (TTJV) in a dog model. DESIGN: Laboratory study in which seven dogs were anesthetized, paralyzed, and placed within a volume plethysmograph with the head and neck externalized. INTERVENTIONS: Ventilation was performed using TTJV at 45 psi and a frequency of 15 beats per minute. The upper trachea was occluded progressively using a Foley catheter balloon to induce tracheal pressure levels of approximately 150%, 200%, 250%, and 300% of the tracheal pressure obtained during TTJV-c. Tidal volume, tracheal pressure, transpulmonary pressure, airflow, arterial blood pressure, central venous pressure, and arterial blood gases were measured during all conditions of ventilation. Quasistatic compliance curves of the lungs were measured at the conclusion of spontaneous breathing, TTJV-c, and TTJV (at all levels of obstruction). Minute ventilation and pulmonary flow resistance were calculated for each condition of ventilation. RESULTS: Application of graded upper-airway obstruction during TTJV yielded mean tracheal pressures of 130% (level 1), 190% (level 2), 220% (level 3), and 230% (level 4) of that obtained during TTJV-c (10.9 +/- 2.0 cm H2O). Tidal volume significantly increased with each level of obstruction except between levels 3 and 4 (spontaneous breathing, 506 +/- 72 mL; TTJV-c, 446 +/- 69 mL; level 1, 663 +/- 139 mL; level 2, 780 +/- 140 mL; level 3, 931 +/- 181 mL; and level 4, 944 +/- 135 mL). During TTJV at obstruction level 1, transpulmonary pressure was not significantly higher than either spontaneous breathing or TTJV-c, but did significantly increase during higher levels of obstruction. The mean arterial PCO2 significantly decreased at all levels of obstruction due to significantly increased minute ventilation, with a concomitant increase in arterial pH. There was no significant difference seen in the quasistatic compliance of the lungs among spontaneous breathing, TTJV-c, or TTJV at any level of upper airway obstruction. CONCLUSION: Partial upper-airway obstruction increases the delivered tidal volume, minute ventilation, and transpulmonary pressure of the lungs during TTJV, with consequent decreases in the arterial PCO2 as the amount of obstruction increases. No significant changes were seen in the quasistatic compliance of the lungs, pulmonary flow resistance, or alveolar:arterial gradient, lending support to the position that TTJV is a safe technique under conditions of partial upper-airway obstruction. However, due to significant increases in tidal volume and functional residual capacity and decreases in mean arterial blood pressure, concerns still exist during near-total or total upper-airway obstruction.

Contribution of vagal afferents to respiratory reflexes evoked by acute inhalation of ozone in dogs.

Acute inhalation of ozone induces vagally mediated rapid shallow breathing and bronchoconstriction. In spontaneously breathing anesthetized dogs, we attempted to determine whether afferent vagal C-fibers in the lower airways contributed to these responses. Dogs inhaled 3 ppm ozone for 40-70 min into the lower trachea while cervical vagal temperature was maintained successively at 37, 7, and 0 degrees C. At 37 degrees C, addition of ozone to the inspired air decreased tidal volume and dynamic lung compliance and increased breathing frequency, total lung resistance, and tracheal smooth muscle tension. Ozone still evoked significant effects when conduction in myelinated vagal axons was blocked selectively by cooling the nerves to 7 degrees C. Ozone-induced effects were largely abolished when nonmyelinated vagal axons were blocked by cooling to 0 degree C, breathing during ozone inhalation at 0 degree C being generally similar to that during air breathing at 0 degree C, except that minute volume and inspiratory flow were higher. We conclude that afferent vagal C-fibers in the lower airways make a major contribution to the acute respiratory effects of ozone and that nonvagal afferents contribute to the effects that survive vagal blockade.

Role of vagal afferents in the control of abdominal expiratory muscle activity in the dog.

We examined the contribution of afferent vagal A- and C-fibers on abdominal expiratory muscle activity (EMA). In seven spontaneously breathing supine dogs anesthetized with alpha-chloralose we recorded the electromyogram of the external oblique muscle at various vagal temperatures before and after the induction of a pneumothorax. When myelinated fibers were blocked selectively by cooling the vagus nerves to 7 degrees C, EMA decreased to 40% of control (EMA at 39 degrees C). With further cooling to 0 degrees C, removing afferent vagal C-fiber activity, EMA returned to 72% of control. On rewarming the vagus nerves to 39 degrees C, we then induced a pneumothorax (27 ml/kg) that eliminated the EMA in all the dogs studied. Cooling the vagus nerves to 7 degrees C, during the pneumothorax, produced a slight though not significant increase in EMA. However, further cooling of the vagus nerves to 0 degrees C caused the EMA to return vigorously to 116% of control. In three dogs, intravenous infusion of a constant incrementally increasing dose of capsaicin, a C-fiber stimulant, decreased EMA in proportion to the dose delivered. These results suggest that EMA is modulated by a balance between excitatory vagal A-fiber activity, most likely from slowly adapting pulmonary stretch receptors, and inhibitory C-fiber activity, most likely from lung C-fibers.