The visual analog scale for pain: clinical significance in postoperative patients.

BACKGROUND: The visual analog scale is widely used in research studies, but its connection with clinical experience outside the research setting and the best way to administer the VAS forms are not well established. This study defines changes in dosing of intravenous patient-controlled analgesia as a clinically relevant outcome and compares it with VAS measures of postoperative pain. METHODS: Visual analog scale measurements were obtained from 150 patients on the morning after intraabdominal surgery. On the same afternoon, 50 of the patients provided a VAS score on the same form used in the morning, 50 on a new form, and 50 were not asked for a second VAS measurement. RESULTS: Visual analog scale values and changes in value were similar for patients who were given a new VAS form in the afternoon and those who used the form that showed the morning value. The proportions of patients requesting additional analgesia were 4, 43, and 80%, corresponding to afternoon VAS scores of 30 or less, 31-70, and greater than 70, respectively. Change from morning VAS score had no apparent influence on patient-controlled analgesic dosing for patients with afternoon values of 30 or less or greater than 70, but changes in VAS scores of at least 10 did discriminate among patients whose afternoon values were between 31 and 70. CONCLUSIONS: When pain is an outcome measure in research studies, grouping final VAS scores into a small number of categories provides greater clinical relevance for comparisons than using the full spectrum of measured values or changes in value. Seeing an earlier VAS form has no apparent influence on later values.

Anesthetic considerations for thoracic neurosurgical procedures.

Anesthetic considerations for thoracic and thoracoscopic neurosurgical procedures are considered, emphasizing the need to provide anesthetic stability during prolonged periods of one-lung ventilation, while optimizing conditions for intraoperative monitoring of spinal cord integrity.

The use of propofol, nitrous oxide, or isoflurane does not affect the reproductive success rate following gamete intrafallopian transfer (GIFT): a multicenter pilot trial/survey.

BACKGROUND: Whether anesthetic agents administered during gamete intrafallopian transfer (GIFT) affect reproductive outcome is controversial. This multicenter pilot trial and survey had two purposes: to evaluate the effect of propofol, nitrous oxide, midazolam, and isoflurane on pregnancy outcome after GIFT, and to determine if a larger prospective, randomized study is warranted. METHODS: A written invitation was mailed to all 50 fertility programs in the United States that are members of the Society for Assisted Reproductive Technology and perform more than 30 GIFT procedures per year. They were invited to contribute information from the medical records of women who underwent GIFT during the calendar years 1993 and 1994. They were asked to document whether propofol, nitrous oxide, midazolam, a potent inhaled anesthetic agent was used during the GIFT procedure; if the woman became pregnant; and if she delivered at least one live neonate. RESULTS: Seven medical centers participated and contributed data from 455 women. The clinical pregnancy rate (number of pregnancies/total number of GIFT procedures) and the delivery rate (number of women who delivered at least one live baby/total number of GIFT procedures) were 35% and 32%, respectively. A statistically significant difference could not be found in the clinical pregnancy or delivery rates between those women who received propofol, nitrous oxide, midazolam, or isoflurane during GIFT and those who did not. CONCLUSIONS: No agent-related differences in pregnancy rates were found when propofol, nitrous oxide, isoflurane, or midazolam was used as part of the anesthetic technique for GIFT. Therefore, a more extensive prospective trial does not appear to be warranted.

Hypoxic pulmonary vasoconstriction.

Hypoxic pulmonary vasoconstriction is a local reflex in the lung that diverts blood away from poorly oxygenated regions. Improvements in understanding of modulators of this response have led to pharmacologic methods whereby V/Q matching may potentially be improved in certain types of pulmonary pathology and during anesthesia for thoracic surgical procedures.

Prolonged surgery increases the likelihood of admission of scheduled ambulatory surgery patients.

STUDY OBJECTIVE: To identify variables influencing the likelihood of unanticipated admission following scheduled ambulatory surgery. DESIGN: Retrospective case-controlled chart review study. SETTING: A large academic tertiary care hospital. PATIENTS: 8,549 ASA physical status I, II, III, and IV patients who underwent scheduled ambulatory surgery in 1991. MEASUREMENTS AND MAIN RESULTS: Of the 8,549 patients, 216 were admitted, with complete medical record information available for 167 of the admitted patients. The most common reasons for admission among the 167 were surgical (43%), anesthetic (28%), and medical (17%) complications. Odds for admission following long surgery (of at least 60 minutes) were 7.5 times (p < 0.001) greater than following short surgery (under 60 minutes). Among long cases, independent variables influencing admission were: general anesthesia [odds ratio 20.8; 95% confidence interval (CI) 4.4 to 45.6], and monitored anesthesia care or regional anesthesia (combined odds ratio 8.3; 95% CI 1.7 to 40.8). ASA physical status and patient age did not significantly influence admission rate for long cases. For short cases, patients over 65 years (odds ratio 5.6; 95% CI 2.6 to 12.0), ASA physical status III or IV (odds ratio 4.8; 95% CI 2.0 to 11.6), use of general anesthesia (odds ratio 4.7; 95% CI 1.5 to 14.2), and monitored anesthesia care or regional anesthesia (odds ratio 3.1; 95% CI 1.0 to 10.1) independently influenced the likelihood of admission. Type of surgery and gender had no detectable effect on admission. CONCLUSIONS: Surgery duration of 60 minutes or longer was the most important predictor of unanticipated admission following scheduled ambulatory surgery.

Positive end-expiratory pressure during one-lung ventilation improves oxygenation in patients with low arterial oxygen tensions.

OBJECTIVE: The application of 10 cm H2O of positive end-expiratory pressure (PEEP10) to the ventilated lung during one-lung ventilation (OLV) has an unpredictable effect on PaO2. It was hypothesized that patients with a low PaO2 (< 80 mmHg) during OLV may benefit from application of PEEP. DESIGN: Prospective, open. SETTING: A university medical center. PARTICIPANTS: Eighteen patients were studied who were undergoing OLV for pulmonary resection. All were anesthetized with thiamylal, N2O/O2 (50%/50%), isoflurane, and pancuronium. INTERVENTIONS: Application of PEEP10 during one-lung ventilation. MEASUREMENTS AND MAIN RESULTS: Hemodynamics and oxygenation were measured during two-lung ventilation in the lateral position, OLV, and OLV plus application of PEEP10. Overall, PEEP10 during OLV failed to produce significant changes in PaO2, Qs/Qt%, cardiac output (CO), SvO2, or mean arterial pressure. However, in 11 patients whose PaO2 was less than 80 mmHg during OLV, application of PEEP10 significantly increased PaO2, decreased Qs/Qt%, and decreased CO (p < 0.05). In the 7 patients whose PaO2 was greater than 80 mmHg on OLV, the authors did not find a significant effect of PEEP10 on the hemodynamic or oxygenation parameters measured. CONCLUSIONS: In patients with a low PaO2 (< 80 mmHg) during OLV with F1O2 = 0.5, PaO2 is increased by the application of PEEP10. This maneuver may be useful in situations in which application of continuous positive airway pressure (CPAP) to the nonventilated lung is not possible.

Propofol permits tracheal intubation but does not affect postoperative myalgias.

STUDY OBJECTIVE: To determine the effect of propofol without succinylcholine on intubating conditions and postoperative myalgias in ambulatory surgical patients undergoing general anesthesia. DESIGN: Prospective, double-blind, randomized study. SETTING: Ambulatory surgery adult patients. PATIENTS: 56 ASA physical status I and II adult patients undergoing general endotracheal anesthesia. INTERVENTIONS: Group 1 patients received thiamylal plus succinylcholine, Group 2 patients received propofol plus succinylcholine; and Group 3 patients received propofol plus saline. All patients received fentanyl, lidocaine, and nitrous oxide plus isoflurane in oxygen. MEASUREMENTS AND MAIN RESULTS: Incidence and severity of fasciculations, tracheal intubating conditions, and myalgias on the first and third postoperative days were measured. Propofol did not affect the incidence or severity of fasciculations following succinylcholine, or the incidence of myalgias. Of patients who received propofol without succinylcholine, intubation was successful in 85%. CONCLUSIONS: Propofol did not affect the incidence or severity of postoperative myalgias following succinylcholine.

Predictors of pulse oximetry data failure.

BACKGROUND: Pulse oximeters have been reported to fail to record data in 1.12-2.50% of cases in which anesthesia records were handwritten. There is reason to believe that these may be underestimates. Computerized anesthesia records may provide insight into the true incidence of pulse oximetry data failures and factors that are associated with such failures. METHODS: The current study reviewed case files of 9,203 computerized anesthesia records. Pulse oximetry data failure was defined as the presence of at least one continuous gap in data > or = 10 min in duration in a case. A multivariate logistic regression model was used to identify predictors of pulse oximetry data failure, and a modified case-control method was used to determine whether extremes of blood pressure and hypothermia during the procedure were associated with pulse oximetry data failure. RESULTS: The overall incidence of cases that had at least one continuous gap of > or = 10 min in pulse oximetry data was 9.18%. The independent preoperative predictors of pulse oximetry data failure were ASA physical status 3,4, or 5 and orthopedic, vascular, and cardiac surgery. Intraoperative hypothermia, hypotension, hypertension, and duration of procedure were also independent risk factors for pulse oximetry data failure. CONCLUSIONS: Pulse oximetry data failure rates based on review of computerized records were markedly greater than those previously reported. Physical status, type of surgery, and intraoperative variables were risk factors for pulse oximetry data failure. Regulations and expectations regarding pulse oximetry monitoring should reflect the limitations of the technology.

Performance of erroneously filled sevoflurane, enflurane and other agent-specific vaporizers.

OBJECTIVE: Erroneous filling of an agent-specific anesthesia vaporizer may result in concentration and potency outputs that are very different from those expected from the concentration dial setting. Enflurane and sevoflurane have relatively similar saturated vapor pressures (SVPs 175 mmHg and 160 mmHg, respectively, at 20 degrees C) and potencies (MACs 1.68% and 2%, respectively). We derived an equation to relate the vapor concentration output of an agent-specific vaporizer to the gas inflow splitting ratio (SR) created by the vaporizer and the SVP of the potent inhaled agent. METHODS: To test the validity of this equation, we filled an Enfluratec 4 enflurane vaporizer with sevoflurane and a Penlon PPV Sigma sevoflurane vaporizer with enflurane and compared the vapor concentration outputs with our predictions. RESULTS: The equation accurately predicted the vapor concentration outputs of the erroneously filled enflurane and sevoflurane vaporizers. The potency (MAC) output of the erroneously filled Enfluratec 4 vaporizer decreased by 22%-33%, and that of the Penlon PPV Sigma sevoflurane vaporizer increased by 21%-31% from those expected from the concentration dial settings. CONCLUSION: When an agent-specific variable bypass vaporizer is erroneously filled, the vapor concentration outputs can be predicted from the splitting ratio created by setting the vaporizer concentration dial and the SVP of the agent.

Surgical patients' attitudes regarding participation in clinical anesthesia research.

We designed a questionnaire to identify the factors influencing both day of admission surgery (DAS) and ambulatory (AMB) patients in their decision whether to participate in and give informed consent for clinical anesthesia research. On the day of surgery, 276 patients were approached to complete a questionnaire and a visual analog scale (VAS) to assess anxiety. The data collected were observational and are presented as percentages for each group (DAS and AMB). One hundred eighty-two patient (60 DAS and 122 AMB) completed questionnaires. Both DAS and AMB patients desired 20-30 min to read a consent form. Preferred conditions for enrollment by both groups were as follows: interview at the time of preadmission testing; after consulting with their physician; in a private setting while dressed in street clothes; and with assurance that the investigator would also participate in the study, if eligible. Unacceptable conditions were as follows: research associated with any risk and interview in the operating room holding area. All patients responded that they were capable of making the decision whether to participate in research on the day of surgery. Most AMB and DAS patients found it acceptable to be recruited on the day of surgery, if approached appropriately.

Postoperative pain control with a new transdermal fentanyl delivery system. A multicenter trial.

BACKGROUND: A new transdermal delivery system for fentanyl is available in two strengths: 70-80 and 90-100 micrograms.kg-1.h-1 (40- and 60-cm2 patches, respectively). Their short onset and 24-h drug delivery make them attractive for postoperative pain control. METHODS: Both doses of the new transdermal fentanyl patches were evaluated for the relief of postoperative pain in 143 patients after gynecologic exploratory laparotomy. The study was conducted at four centers using a prospective, randomized, placebo-controlled, double-blind format. Patients were randomly assigned to one of three study groups: group 1 patients received two placebo patches: group 2 patients received a 40-cm2 fentanyl patch and a 60-cm2 placebo patch; and group 3 patients received a 60-cm2 fentanyl patch and a 40-cm2 placebo patch. Patient-controlled morphine use and pain, sedation, and comfort scores were assessed postoperatively every 4 h for 36 h after patch placement. RESULTS: Patients' assessment of their analgesia was significantly (P < or = 0.05) better in group 2 at 16 and 24 h and in group 3 at 8, 12, 16, 20, and 24 h postoperatively, compared with the patients in group 1. Patients in groups 2 and 3 required less supplemental morphine to maintain satisfactory analgesia than did the patients in group 1. Patients in groups 2 and 3 had greater incidences of pruritus, erythema, and respiratory depression than did those receiving placebo. CONCLUSIONS: Concern exists regarding the side effects of this this new transdermal fentanyl patch. Therefore, this new patch will need further research before it can be recommended as an adjunct in controlling postoperative pain.

Erroneous mass spectrometer readings caused by desflurane and sevoflurane.

OBJECTIVE: Medical mass spectrometers are configured to detect and measure specific respiratory and anesthetic gases. Unrecognized gases entering these systems may cause erroneous readings. We determined how the Advantage 1100 (Perkin-Elmer, now Marquette Gas Systems, Milwaukee, WI) and PPG-SARA (PPG Biomedical Systems, Lenexa, KS) systems that were not configured to measure desflurane or sevoflurane respond to increasing concentrations of these new potent volatile anesthetic agents. METHODS: Desflurane 0% to 18% in 3% increments or sevoflurane 0% to 7% in 1% increments in 5-L/min oxygen was delivered to the Advantage and PPG-SARA mass spectrometry systems. For each concentration of each agent, the displayed gas analysis readings and uncompensated collector plate voltages were recorded. RESULTS: The Advantage 1100 system read both desflurane and sevoflurane mainly as enflurane and, to a lesser extent, as carbon dioxide and isoflurane. For enflurane(E) readings < 9.9%, the approximate relationships are: %Desflurane = 1.6E; %Sevoflurane = 0.3E. These formulas do not apply if E > 9.9% because of saturation of the summation bus. PPG-SARA read desflurane mainly as isoflurane(I) and, to a lesser extent, as nitrous oxide. PPG-SARA read sevoflurane mainly as enflurane(E) and, to a lesser extent, as nitrous oxide and halothane. The approximate relationships are: %Desflurane = 1.11 (for I < 9%); %Sevoflurane = 2.1E. CONCLUSIONS: Advantage 1100 and PPG-SARA systems not configured for desflurane or sevoflurane display erroneous anesthetic agent readings when these new agents are sampled. Advantage 1100 also displays falsely elevated carbon dioxide readings when desflurane is sampled.

Improving patient-controlled analgesia: adding droperidol to morphine sulfate to reduce nausea and vomiting and potentiate analgesia.

Opioid-related side effects, including nausea and vomiting, are common in patients using morphine in patient-controlled analgesia for postoperative pain relief. The purpose of this study was to determine if the addition of droperidol to a morphine sulfate delivery system could decrease the incidences of nausea and vomiting without increasing droperidol-related side effects. Forty ASA 1 and 2 patients scheduled to undergo peripheral orthopedic surgery were randomized to receive either morphine sulfate (2 mg/mL), or morphine sulfate (1.9 mg/mL) plus droperidol (0.125 mg/mL) for postoperative self-controlled analgesia. Visual analogue scores for pain, nausea, and sedation were obtained from each patient immediately after surgery and each morning and evening until patient-controlled analgesia was discontinued approximately 48 hours later. Total patient-controlled use of morphine sulfate was recorded at each visual analogue rating. The patients who used morphine sulfate plus droperidol had significantly less nausea and vomiting and used significantly less morphine. No patient experienced droperidol-related side effects. We conclude that the routine addition of droperidol to morphine sulfate in self-controlled analgesia improves the comfort of patients following peripheral orthopedic surgery.

Adverse effects of nondepolarising neuromuscular blocking agents. Incidence, prevention and management.

Nondepolarising muscle relaxants block neuromuscular transmission, acting as antagonists of the nicotinic receptors at the neuromuscular junction. Their undesired effects are frequently caused by interaction with acetylcholine receptors outside this junction, and autonomic cardiovascular effects may result. Other adverse effects include anaphylactic or anaphylactoid reactions, and histamine release. Various disease states may present specific considerations in the use of nondepolarising muscle relaxants. Although many complications of these drugs (such as prolonged block or resistance) are easily treated, others may necessitate immediate intervention and vigorous therapy. Careful selection of an appropriate relaxant for a particular patient will usually prevent the occurrence of complications.

Adverse effects of depolarising neuromuscular blocking agents. Incidence, prevention and management.

Muscle relaxants block neuromuscular transmission, acting at nicotinic acetylcholine receptors of the neuromuscular junction. Suxamethonium (succinylcholine) is a depolarising agent, whereas all other relaxants in clinical use are nondepolarising. The desired neuromuscular block results from the structural similarity of muscle relaxants to acetylcholine, enabling the interaction with receptors at the neuromuscular junction. Adverse effects of suxamethonium are generally related to its agonist mode of action. Autonomic cardiovascular effects may result. Other adverse effects include anaphylactic or anaphylactoid reactions, and histamine release. Various disease states may present specific considerations in the use of muscle relaxants. Although many complications of muscle relaxants (such as prolonged block or resistance) are easily treated, others may require immediate intervention and vigorous therapy. Careful selection of appropriate relaxants for particular patients will usually prevent the occurrence of complications.