Effect of patient position on the incidence of vasovagal response to venous cannulation.

BACKGROUND: This study was undertaken to determine the effect of patient position on the incidence of vasovagal responses to venous cannulation in ambulatory surgery patients. METHODS: Three hundred surgical outpatients, aged 18 to 40 years, were randomly assigned by week to the sitting or recumbent position. Blood pressure and heart rate were recorded during and for 6 minutes following venous cannulation. An observer recorded signs and symptoms suggestive of a vasovagal response. RESULTS: A vasovagal reaction occurred in 12.6% of sitting patients and 2.1% of recumbent patients. Two sitting patients, 1.3%, experienced frank syncope. Symptomatic patients were more likely (39.1%) than asymptomatic patients (8.3%) to have a history of fainting. In symptomatic patients who were sitting, mean arterial pressure fell from 90.4 mm Hg (SD, 10.6) at baseline to 64.4 mm Hg (SD, 14.3) during cannulation. Similarly, heart rate fell from 76.6 beats per minute (SD, 15.6) at baseline to 59.0 beats per minute (SD, 11.7) after cannulation. CONCLUSIONS: The vasovagal response during venous cannulation occurs more frequently in the sitting patient who has a history of fainting and is associated with a significant decline in blood pressure and heart rate.

Reexpansion hypotension. A complication of rapid evacuation of prolonged pneumothorax.

Three cases of hypotension are described that followed rapid evacuation of persistent unilateral pneumothorax. Common features included the presence of a pneumothorax for approximately one week before treatment commenced and profuse unilateral reexpansion edema, a rising hematocrit reading, hypotension, and anuria after evacuation of the pneumothorax in spite of a relatively normal pulmonary capillary wedge pressure. In one case, cardiac output was measured and found to be low (1.54 and 1.65 L/min/sq m), with a pulmonary capillary wedge pressure of 10 to 14 mm Hg. Death due to cardiovascular collapse occurred in one patient; ischemic colitis, acute renal failure, disseminated intravascular coagulation, and ischemic necrosis of both humeral heads occurred in another. The cases presented and the literature reviewed suggest that cardiovascular compromise was the end result of the combined effects of intravascular volume depletion and myocardial depression.

Hemodynamic effects of rapidly evacuating prolonged pneumothorax in rabbits.

Clinical observations suggest that systemic hypotension may be caused by rapid evacuation of persistent pneumothorax. This observation has not been substantiated experimentally and the mechanism(s) are unknown. In this study, we measured systemic hemodynamic parameters in rabbits before and for 2 h during negative pressure evacuation of a right-sided pneumothorax of 7-9 days duration. Three groups of animals were studied: 10 rabbits breathed room air and were hypoxemic during pneumothorax (hypoxemic pneumothorax = HP); 10 rabbits breathed 40% O2-60% N2, which prevented arterial hypoxemia during pneumothorax (supraoxemic pneumothorax = SP); seven normal control animals were untreated during this time period (NC). Pneumothoraces in HP and SP were evacuated by negative pressure applied to the right pleural space for 2 h while animals were anesthetized and mechanically ventilated. The NC group was anesthetized and ventilated without prior pneumothorax. Serial hemodynamic measurements were made before and during pleural suction.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular fluid volume during pneumothorax and hypoxemia in rabbits.

This study was designed to test the hypothesis that persistent pneumothorax of greater than or equal to 6 days duration causes a decrease of extracellular fluid volume (ECF). Such changes are of interest as they may be causally related to persistent hypotension that has occurred in humans following pneumothorax evacuation. Experiments were done in rabbits to determine the effect on ECF of persistent pneumothorax with or without systemic hypoxemia. Animals were divided into four treatment groups: 1) pneumothorax with hypoxemia [fractional concentration of O2 in inspired gas (FIO2) = 0.21, n = 30], 2) pneumothorax without hypoxemia (FIO2 = 0.40, n = 25), 3) hypoxemia alone (FIO2 = 0.14, n = 11), and 4) normal controls (FIO2 = 0.21, n = 15). Measurements of ECF were made in the base-line control state and after 6 days of treatment using the dilution volume of thiocyanate sodium as an estimate of ECF volume. We found a reduction of ECF in 53% of animals with pneumothorax plus hypoxemia (range -47% to +13%) and in 54% of animals with hypoxemia alone (range -26% to +25%). ECF declined in only 7% of normal controls and 20% of animals with pneumothorax without hypoxemia. Arterial O2 tensions after 6 days of treatment were 58 +/- 12.6, 141 +/- 28, 60 +/- 5.1, and 97 +/- 9.3 Torr (mean +/- SD) in groups 1-4, respectively. The results suggest that pneumothorax with hypoxemia or hypoxemia alone may contribute to depletion of ECF, but this response is variable and unpredictable in individual animals.

Endogenous plasma proteins in edematous lungs and alveolar fluid in rabbits.

In this study, we compared two methods of differentiating hydrostatic and permeability types of pulmonary edema. The first method entailed measurement of protein concentrations directly in samples of alveolar fluid (AF); the second method was an indirect technique in which protein concentration in extravascular extracellular water (EVECW) was calculated on the basis of separate measurements of the quantity of protein in the lung and the volume of EVECW. The concentration of albumin (Alb) and gamma-G-globulin was measured in EVECW and alveolar fluid in excised edematous rabbit lungs. Edema was caused by elevation of left ventricular end-diastolic pressure to 25 Torr (hydrostatic edema, HE) or by intravenous oleic acid, 0.09 ml/kg (permeability edema, PE). The volume of distribution of Na+ was utilized as a measure of EVECW in the lung. Protein concentration in EVECW and AF relative to plasma (EV/PL and AF/PL, respectively) was compared in the two types of edema. The EV/PL was 0.61 +/- 0.12 (SD) for Alb in He compared with 1.18 +/- 0.47 in PE (P less than 0.02). The AF/PL was 0.54 +/- 0.12 and 1.25 +/- 0.33 in HE and PE, respectively (P less than 0.001). There was good correlation between EV/PL and AF/PL for Alb (r = 0.74, P less than 0.001) but not for gamma-G-globulin. Thus EV/PL for Alb, AF/PL for Alb, and gamma-G-globulin all differentiated hydrostatic from permeability edema.

Oxygen and resolution of lung injury.

We investigated the effects of varying inspired oxygen concentrations on the resolution of oleic acid-induced lung injury in rabbits. Rabbits were injected intravenously with oleic acid and maintained in room air, or exposed to 60, 70, or 80% oxygen for periods of 7 or 10 days. Oleic acid caused hemorrhagic pulmonary edema with hypoxemia. Hypoxemia was more profound in the oxygen-treated animals, a difference that was significant after 7 days' exposure to 60 and 70% oxygen, and after 4 days to 80% oxygen. Mortality was increased in the animals maintained in 80% oxygen. The data suggest that environmental oxygen concentrations greater than 60% interfere with the return to normal lung function following oleic acid injury in rabbits. The hypoxemia may be due to either mismatching of ventilation and perfusion or to a diffusion block resulting from the increased septal width. There was no evidence of massive pulmonary edema as a cause of the hypoxemia. It was not possible to distinguish between injury primarily caused by oxygen and its interference with the healing process.

Outpatient preanaesthesia evaluation clinics.

In recent years, there has been a paradigm shift from an inpatient to outpatient preanaesthesia evaluation. This has been driven by rising healthcare costs and the increasing popularity of ambulatory and same-day admission surgery. These outpatient preanaesthesia clinics play an important role in enhancing the cost-effectiveness of the perioperative process. This review describes the structure of modern outpatient preanaesthesia evaluation clinics, and the associated benefits, limitations and controversies.

Increased pulmonary vascular permeability as a cause of re-expansion edema in rabbits.

In order to study the mechanism(s) underlying re-expansion edema, we measured the concentration of labeled albumin (RISA) in the extravascular, extracellular water (EVECW) of the lung as a measure of pulmonary vascular permeability. Re-expansion edema was first induced by rapid re-expansion of rabbit lungs that had been collapsed for 1 wk by pneumothorax. The RISA in EVECW was expressed as a fraction of its plasma concentration: (RISA)L/(RISA)PL. The volume of EVECW (ml/gm dry lung) was measured using a 24Na indicator. Results in re-expansion edema were compared with normal control lungs and with oleic acid edema as a model of permeability edema. In re-expanded lungs, EVECW (3.41 +/- SD 1.24 ml/g) and (RISA)L/(RISA)PL 0.84 +/- SD 0.15) were significantly increased when compared with normal control lungs (2.25 +/- 0.41 ml/g and 0.51 +/- 0.20, respectively). Results in oleic acid edema (5.66 +/- 2.23 ml/g and 0.84 +/- 0.23) were similar to re-expansion edema. This suggested that re-expansion edema is due to increased pulmonary vascular permeability caused by mechanical stresses applied to the lung during re-expansion.

Effects of breathing 80% oxygen on water and albumin accumulation in oleic acid-injured rabbit lungs.

This study was done to determine whether breathing 80% oxygen would enhance edema formation in oleic acid (OA) lung injury. Rabbits breathed air (n = 51) or 80% oxygen (n = 51) for 1 to 7 days after OA lung injury (0.09 ml/kg iv). Control groups breathed 80% oxygen (n = 37) or room air (n = 8) without OA injury. Pulmonary vascular permeability was assessed by measuring 131I-albumin (RISA) concentration in extravascular, extracellular lung water (EVECW) relative to plasma (RISAL/RISAPL). EVECW (ml/g dry lung) was measured by 24Na, and total lung water (TLW) by wet/dry weight (g/g dry lung). Air-breathing control values were 4.53 +/- 0.25 (SD) for TLW and 0.40 +/- 0.09 for RISAL/RISAPL. In the air-breathing OA group, TLW and RISAL/RISAPL increased to 8.32 +/- 0.85 and 0.93 +/- 0.16, respectively, 2 h after OA (p less than .001) but by 24 h, were equal to air-breathing controls. TLW and RISAL/RISAPL in the oxygen treated OA group did not differ from the air breathing OA group on days 2 through 7 inclusive, suggesting that 80% oxygen had no effect on edema formation in the OA-injured lung. Breathing 80% oxygen alone, without OA injury, significantly (p less than .005) increased TLW and RISAL/RISAPL on days 5 and 6. Thus, preexisting lung injury had a protective effect against edema formation from a high fraction of inspired oxygen.

Pulmonary arteriovenous shunts during halothane anesthesia in dogs.

The fraction of cardiac output flowing through pulmonary arteriovenous anastomoses (Qav/Qt) was measured in dogs during halothane anesthesia and compared with results obtained in normal awake dogs. Flow through arteriovenous anastomoses was measured using 99mTc-labelled polystyrene microspheres (50 microns diameter). The fraction of cardiac output perfusing pulmonary arteriovenous anastomoses during halothane anaesthesia was 4.1% (+/- SD 1.75) compared with 4.6% (+/- SD 0.73) in air-breathing awake control dogs. In spite of variations in arteriovenous shunt fraction, no significant relationship between the Qav/Qt and Qs/Qt was detected. These results suggest that pulmonary arteriovenous anastomases do not contribute significantly to the physiological shunt observed during halothane anaesthesia.

Extravascular, extracellular water in rabbit lung using Na and sucrose indicators.

We compared the volume of the pulmonary extravascular, extracellular water space using sodium and sucrose indicators in 8 normal and 11 edematous rabbit lungs by steady-state techniques. The volume of the extravascular, extracellular space (EVECW), expressed in milliliters per gram dry lung, was determined from the volume of distribution of 24Na, [3H]sucrose, or total sodium in 1) supernatant solutions obtained by centrifugation of homogenized lung or 2) intact lung fragments. There was no significant difference in EVECW measured in normal lungs [24Na 1.88 +/- (SD) 0.31; [3H]sucrose 1.84 +/- (SD) 0.27] or edematous lungs [24Na 4.78 +/- (SD) 1.44; [3H]sucrose 4.41 +/- (SD) 1.33] when comparing supernate solutions of homogenized lungs. Similarly, there was no significant difference between the volumes of distribution (EVECW) of these two isotopes when measured in intact fragments of normal lung [24Na 2.08 +/- (SD) 0.28; [3H]sucrose 1.68 +/- (SD) 0.37]. The volume of EVECW measured in supernates was less than in fragments with both isotopes. Washing the centrifuged tissue pellet and adding the wash activity to the initial supernate activity yielded results that were equal to the fragment technique. The failure to detect significant differences between 24Na and [3H]sucrose spaces in the lung suggests that the contribution on intracellular sodium to the measurement of lung water is small and relatively insignificant, at least within the confines of this experiment.

Hemodynamic and metabolic effects of aortic unclamping following emergency surgery for traumatic thoracic aortic tear in shunted and unshunted patients.

Nine cases of traumatic aortic tear treated during 1986-1987 were reviewed. Two patients had functioning Gott shunts, six patients had simple crossclamp, and one patient had a Gott shunt placed which was nonfunctional. Anesthetic management was similar in all patients. Clamp times ranged in unshunted patients from 25 to 38 minutes, and in shunted patients from 42 to 50 minutes. The crossclamp time of the patient with the nonfunctional shunt was 42 minutes. Declamping was accompanied in unshunted patients by decreases in core temperature of up to 1 degree C and acute decreases in PaO2. Marked respiratory and metabolic acidosis occurred with declamping. Respiratory acidosis resolved within 30 minutes with hyperventilation, but metabolic acidosis persisted despite bicarbonate therapy (mean = 1.2 mEq/kg) up to 6 hours after declamping. Associated elevations in serum potassium resolved as pH returned to baseline. Acid-base and electrolyte abnormalities were less marked in patients who were shunted.

Vaso-vagal reactions in an ambulatory surgery center.

This prospective study was undertaken to determine the incidence and factors predisposing to vaso-vagal reactions during venous cannulation in an ambulatory surgery population. In 141 ambulatory surgery patients, signs and symptoms of a reaction together with mean arterial pressure and heart rate were recorded at 1-min intervals during and for 6 min after venous cannulation. Overall, 10.6% of patients were symptomatic (95% confidence interval [CI] 6%-17%). The incidence was 16.6% (95% CI 8.4%-24.9%) in patients < or = 40 yr and 33.3% (95% CI 6.7%-60.0%) with a prior fainting history. Young age, duration or number of attempts at venous cannulation, and fainting history were independently associated with increased risk of a reaction (P < 0.03-0.004 by multiple repression analysis). Minimum mean arterial pressure was less in symptomatic patients than in those who were asymptomatic (58 mm Hg +/- 11.3 SD versus 82 mm Hg +/- 14.3 SD, P < 0.0001). We conclude that reactions occur commonly, particularly in the young or in patients with a history of fainting. Reactions are typically associated with significant hypotension that may require treatment.

Factors affecting discharge time in adult outpatients.

UNLABELLED: Discharge time (total recovery time) is one determinant of the overall cost of outpatient surgery. We performed this study to determine what factors affect discharge time. Details regarding patients, anesthesia, surgery, and recovery were recorded prospectively for 1088 adult patients undergoing ambulatory surgery over an 8-mo period. The contribution of factors to variability in the discharge time was assessed by using multivariate linear regression analysis. In the last 4 mo of the study, nurses indicated the causes of discharge delays > or =50 min in Phase 1 or > or =70 min in Phase 2 recovery. When all anesthetic techniques were included, anesthetic technique was the most important determinant of discharge time (R2 = 0.10-0.15; P = 0.001), followed by the Phase 2 nurse. After general anesthesia, the Phase 2 nurse was the most important factor (R2 = 0.13; P = 0.01-0.001). In women, the choice of general anesthetic drugs was significant (R2 = 0.04; P = 0.002). The three most common medical causes of delay were pain, drowsiness, and nausea/vomiting. System factors were the foremost cause of Phase 2 delays (41%), with lack of immediate availability of an escort accounting for 53% of system-related delays. We conclude that efforts to shorten discharge time would best be directed at improving nursing efficiency; ensuring availability of an escort for the patient; and preventing postoperative pain, drowsiness, and emetic symptoms. The selection of anesthetic technique and anesthetic drug seems to be of selective importance in determining discharge time depending on patient gender and type of surgery. IMPLICATIONS: The relative importance of anesthetic and nonanesthetic factors were evaluated as determinants of discharge time after ambulatory surgery. Postoperative nursing care was the single most important factor after general anesthesia; anesthetic drugs, anesthetic technique, and prevention of pain and emetic symptoms were of selective importance depending on patient gender and type of surgery.

Voiding in patients managed with or without ultrasound monitoring of bladder volume after outpatient surgery.

UNLABELLED: The goal of this study was to determine whether recovery room monitoring of bladder volume would affect patient outcome after ambulatory surgery. Incidence of urinary retention and times to void and to discharge were compared in 161 patients managed with ultrasound bladder monitoring versus 173 controls without bladder monitoring. Urinary retention was diagnosed by clinical means or by ultrasound, confirmed by bladder catheterization. Patients were required to void or were catheterized before discharge. In the control patients without underlying risk factors for retention, median time to void was 95 min, and retention occurred in 0.8%, which was not significantly different from the ultrasound group (80 min and 0%, respectively). After hernia/anal surgery or spinal/epidural anesthesia, voiding was delayed (130 and 213 min), incidence of retention was increased (17% and 13%), and there was a trend toward earlier voiding (168+/-99 vs. 138+/-68 min) with bladder monitoring. We conclude that most patients at low risk of retention void within 3 h of outpatient surgery; their outcome is unaffected by bladder monitoring. After hernia/anal surgery and spinal/ epidural anesthesia, the likelihood of urinary retention is increased, and ultrasound monitoring facilitates deciding whether such patients should be catheterized. IMPLICATIONS: Incidence of bladder catheterization and urinary retention were compared in patients managed with and without ultrasound monitoring of bladder volume after outpatient surgery. Monitoring did not alter outcome in patients at low risk of retention, but it facilitated determining when to catheterize patients at high risk of retention (hernia/anal surgery, spinal/epidural anesthesia).

Management of bladder function after outpatient surgery.

BACKGROUND: This study was designed to test a treatment algorithm for management of bladder function after outpatient general or local anesthesia. METHODS: Three hundred twenty-four outpatients, stratified into risk categories for urinary retention, were studied. Patients in category 1 were low-risk patients (n = 227) having non-pelvic surgery and randomly assigned to receive 10 ml/kg or 2 ml/kg of intravenous fluid intraoperatively. They were discharged when otherwise ready, without being required to void. Patients in category 2 (n = 40), also presumed to be low risk, had gynecologic surgery. High-risk patients included 31 patients having hernia or anal surgery (category 3), and 31 patients with a history of retention (category 4). Bladder volumes were monitored by ultrasound in those in categories 2-4, and patients were required to void (or be catheterized) before discharge. The incidence of retention and urinary tract symptoms after surgery were determined for all categories. RESULT: Urinary retention affected 0.5% of category 1 patients and none of category 2 patients. Median time to void after discharge was 75 min (interquartile range 120) in category 1 patients (n = 27) discharged without voiding. Fluids administered did not alter incidence of retention or time to void. Retention occurred in 5% of high-risk patients before discharge and recurred in 25% after discharge. CONCLUSION: In reliable patients at low risk for retention, voiding before discharge appears unnecessary. In high-risk patients, continued observation until the bladder is emptied is indicated to avoid prolonged overdistention of the bladder.

Optimal propofol-alfentanil combinations for supplementing nitrous oxide for outpatient surgery.

BACKGROUND: The combination of propofol and alfentanil with nitrous oxide provides balanced anesthesia with rapid recovery and minimal emetic side effects. The object of this study was to compare recovery parameters at varying proportions of propofol and alfentanil, and to determine the dosing rate and plasma concentration of propofol necessary to supplement nitrous oxide in the presence of varying concentrations of alfentanil METHODS: Forty-eight patients were anesthetized with nitrous oxide, targeted manual infusions of alfentanil (target plasma concentrations of 0, 50, 100, and 150 ng/ml), and propofol at rates that were varied up or down by 25% depending on the response (movement/no movement) of the preceding patient (at the same alfentanil target concentrations) to ulnar-nerve stimulation. The minimum concentrations of propofol and alfentanil required to prevent movement in 50% of patients (EC50) was determined by logistic regression. Speed of emergence and recovery of cognitive function, time to discharge, and incidence of side effects were compared for four different combinations of propofol and alfentanil with nitrous oxide. RESULTS: The EC50 for propofol alone with nitrous oxide was 6.1 microg/ml. AlfentaniL at concentrations of 41+/-17 (SD), 113+/-54, and 130+/-61 ng/mL reduced the EC50 of propofol to 3.3, 2.3, and 2.2 microg/ml, respectively, and decreased emergence time (eye opening) to 8.1, 4.9, and 3.4 min, compared with 24.3 min for propofol alone. Side effects did not differ between groups. CONCLUSIONS: The authors conclude that there is a synergistic effect between propofol and alfentanil, and that combining alfentanil with propofol is associated with faster early recovery.

The effect of bispectral index monitoring on end-tidal gas concentration and recovery duration after outpatient anesthesia.

We performed this study to determine whether instituting monitoring of bispectral index (BIS) throughout an entire operating room would affect end-tidal gas concentration (as a surrogate for anesthetic use) or speed of recovery after outpatient surgery. Primary caregivers (n = 69) were randomly assigned to a BIS or non-BIS Control group with cross-over at 1-mo intervals for 7 mo. Data were obtained in all outpatients except for those having head-and-neck surgery. Mean end-tidal gas concentration and total recovery duration were compared by unpaired t-test. Overall, 469 patients (80%) received propofol for induction and sevoflurane for maintenance. This homogeneous group was selected for statistical analysis. Mean end-tidal sevoflurane concentration was 13% less in the BIS group (BIS, 1.23%; Control, 1.41%; P < 0.0001); differences were most evident when anesthesia was administered by first-year trainees. Mean BIS values were 47 in the BIS-Monitored group. Total recovery was 19 min less with BIS monitoring in men (BIS group, 147 min; Controls, 166 min; P = 0.035), but not different in women. We conclude that routine application of BIS monitoring is associated with a modest reduction in end-tidal sevoflurane concentration. In men, this may correlate with a similar reduction (11%) in recovery duration.

Comparison of desflurane with propofol in outpatients undergoing peripheral orthopedic surgery.

This study was undertaken to compare desflurane with propofol anesthesia in outpatients undergoing peripheral orthopedic surgery. Data were combined from two institutions participating in a multicenter study. Ninety-one patients, ASA physical status I or II, were each randomly assigned to one of four groups. After administration of fentanyl (2 micrograms/kg) and d-tubocurarine (3 mg), intravenous propofol was administered to induce anesthesia in groups I and II and desflurane in groups III and IV. Maintenance was provided by desflurane/N2O in groups I and III, propofol/N2O in group II, and desflurane/O2 in group IV. Emergence and recovery variables, psychometric test results, and side effects were recorded by observers unaware of the experimental treatment. Patients in group II experienced less nausea than other groups (P = 0.002) despite this group having required more intraoperative fentanyl supplementation than groups III and IV (P = 0.01). Time to emergence, discharge, and psychometric test results were similar in all groups. Desflurane appears to be comparable with propofol as an outpatient anesthetic, facilitating rapid recovery and discharge home.