Statistical analysis of total labor pain using the visual analog scale and application to studies of analgesic effectiveness during childbirth.
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Analgesia, Obstetrical↗
Biomedical subjects
F Dexter
Publications and source records attributed to F Dexter.
Recovery of evoked potential amplitude after cerebral arterial air embolism in the rabbit: a comparison of the effect of cardiopulmonary bypass with normal circulation.
BACKGROUND: Cerebral arterial air embolism (CAAE) may cause neurologic injury during cardiac surgery. It is not known whether cardiopulmonary bypass (CPB) increases or decreases brain injury from CAAE compared with the normal circulation. METHODS: A model of CAAE was produced by injection of 50 microl/kg air into the internal carotid artery of methohexital-anesthetized New Zealand white rabbits. Somatosensory-evoked potential (SSEP) amplitude was measured serially as a marker of neurologic recovery. In experiment A, saline rather than air was injected to control for surgical manipulation and time in CPB (n = 4) and nonheparinized non-CPB (n = 4) animals. In experiment B, 50 microl/kg air was injected in CPB (n = 11) and nonheparinized non-CPB (n = 11) animals. In experiment C, non-CPB animals (n = 6) were given heparin according to the same protocol as for CPB. RESULTS: In experiment A, SSEP latencies and amplitudes did not differ between CPB and non-CPB conditions. In experiment B, there was no SSEP recovery 5 min after CAAE in either CPB or non-CPB animals. Thereafter, SSEP recovery was less in CPB animals than in non-CPB animals at 30 min (9 +/- 12% vs. 29 +/- 20%; P = 0.009) and 60 min (18 +/- 15% vs. 39 +/- 22%; P = 0.030) after CAAE. Ninety-minute SSEP recovery did not differ between CPB and non-CPB groups (at 24 +/- 19% vs. 39 +/- 24%, respectively; P = 0.146). In experiment C (heparinized non-CPB), SSEP recovery 5, 30, 60, and 90 min after CAAE was 67 +/- 48%, 72 +/- 47%, 80 +/- 35%, and 77 +/- 35%, respectively. CONCLUSIONS: Somatosensory-evoked potential recovery after CAAE is no better (and is probably worse) during CPB than during normal circulation. The adverse effect of CPB occurs despite heparinization, which, under non-CPB conditions, appears to be protective. Therapies in addition to heparin are needed during CPB to reduce neurologic injury from CAAE.
Animals↗
Interactions between hypothermia and the latency to ischemic depolarization: implications for neuroprotection.
BACKGROUND: The authors postulated that hypothermic neuroprotection can be attributed to a delayed onset of ischemic depolarization. METHODS: Halothane-anesthetized rats were prepared for near-complete forebrain ischemia. Direct current (DC) potential microelectrodes were placed in hippocampal CA1. The pericranial temperature was maintained at 31 degrees C, 33 degrees C, 35 degrees C, or 37 degrees C (n = 6 per group). Bilateral carotid occlusion with systemic hypotension was initiated for 10 min. The time to onset of the DC shift was recorded. In a second experiment, rats were assigned to 37 degrees C or 31 degrees C for 10 min of ischemia, or to 31 degrees C for 14 min of ischemia (n = 8 per group). These durations of ischemia were defined to allow 9 min of ischemic depolarization in the 37 degrees C-10 min and 31 degrees C-14 min groups. Neurologic and histologic outcomes were examined 7 days later. RESULTS: Hippocampal CA1 time to depolarization increased with decreasing temperature (P < 0.0001). Time to depolarization was increased by approximately 4 min in the rats maintained at 31 degrees C compared with those at 37 degrees C. Time to repolarization during reperfusion was not affected by temperature. Increasing the duration of ischemia from 10 min to 14 min with the pericranial temperature maintained at 31 degrees C resulted in a duration of depolarization that was equivalent in the 37 degrees C-10 min and 31 degrees C-14 min groups. However, hippocampal CA1 damage was not increased (31 degrees C-10 min = 4 +/- 1% dead neurons; 31 degrees C-14 min = 6 +/- 1% dead neurons, 95% CI, -1% to 3%; 37 degrees C-10 min = 90 +/- 17% dead neurons). CONCLUSIONS: Despite similar durations of DC depolarization, outcome in hypothermic rats was markedly improved compared with normothermic rats. This indicates that hypothermic neuroprotection can be attributed to mechanisms other than the delay in time to onset of ischemic depolarization.
Animals↗
A method to compare costs of drugs and supplies among anesthesia providers: a simple statistical method to reduce variations in cost due to variations in casemix.
BACKGROUND: Comparison of costs among anesthesia providers using "cost per case" does not adjust for variations in casemix (such as the type of procedure and patient condition). The authors propose an alternative method for comparing costs using the American Society of Anesthesiologists' Relative Value Scale (ASARVS) system, which incorporates basic units (for the procedure), modifier units (for the patient's physical condition), "other" units (such as for the placement of invasive monitors), and time units (proportional to the case duration). METHODS: Data were obtained from a series of 3,340 anesthetics performed at a tertiary hospital. Administered and discarded drug, supply, and fluid costs were used. RESULTS: Costs expressed as dollars per ASARVS unit had 54% less variability than costs expressed as dollars per case (P < 0.0001). Pearson correlations between demographic variables and cost per ASARVS unit ranged from -0.10 to 0.13. Total (e.g., quarterly) costs for simulated sets of cases were predicted within 0.0 +/- 2.3% by multiplying (1) their sum of units and (2) a like set of case's sum of costs divided by sum of units. CONCLUSIONS: Costs of anesthetic supplies and drugs of a case were more accurately reported as "cost per unit" than as "cost per case." This method of calculating the cost of anesthetic drugs and supplies has several applications, including (1) comparison of costs among anesthesia providers and (2) benchmarking costs among hospitals and anesthesia groups. By design, anesthesia providers' time is quantified by their ASARVS units. Together anesthesia costs (personnel, supplies, and drugs) are better reported as "cost per unit" than as "cost per case."
Adult↗
Cerebrovascular relaxation responses to endothelium-dependent and -independent vasodilators after normothermic and hypothermic cardiopulmonary bypass in the rabbit.
BACKGROUND: Cardiopulmonary bypass causes activation of leukocytes and increased concentrations of proinflammatory mediators, which may result in endothelial dysfunction. Because hypothermia attenuates many inflammatory processes, the authors hypothesized that hypothermic cardiopulmonary bypass would be associated with better endothelial function than normothermic cardiopulmonary bypass. METHODS: Isoflurane-anesthetized New Zealand White rabbits were randomized to undergo 90 min of either normothermic (37 degrees C, n=9) or hypothermic (27 degrees C, n=9) cardiopulmonary bypass with terminal rewarming. A third group served as anesthetized normothermic non-cardiopulmonary bypass surgical controls (n=8). Basilar artery and descending thoracic aorta were isolated from each animal. In vitro vessel relaxation responses to increasing concentrations of acetylcholine (which induces endothelial release of nitric oxide) and nitroprusside (which provides exogenous nitric oxide) were measured in phenylephrine-precontracted vessel rings. RESULTS: There were no differences in vessel relaxation responses between normothermic and hypothermic cardiopulmonary bypass groups in basilar artery or aorta. In contrast, basilar arteries from non-cardiopulmonary bypass controls had increased relaxation responses to both acetylcholine (P=0.004) and nitroprusside (P=0.031) compared with the pooled cardiopulmonary bypass animal data. CONCLUSIONS: The authors observed no differences in endothelial or vascular smooth muscle function between normothermic and hypothermic cardiopulmonary bypass groups. Compared with non-cardiopulmonary bypass controls, cardiopulmonary bypass appeared to decrease basilar artery smooth muscle relaxation in response to endogenous and exogenous nitric oxide.
Acetylcholine↗
Differential effects of anesthetic agents on outcome from near-complete but not incomplete global ischemia in the rat.
BACKGROUND: It has been postulated that anesthetic agents that reduce cerebral metabolic rate will protect the brain against ischemia when electroencephalographic (EEG) activity is persistent, but will provide no protection when ischemia is severe enough to cause EEG isoelectricity. No outcome studies have addressed this issue. The authors studied anesthetic agents to determine if they provide differential effects on outcome from global cerebral ischemic insults that cause either an attenuated or isoelectric EEG. METHODS: Fasted rats were subjected to either (1) incomplete ischemia (attenuated EEG; 20 min of mean arterial pressure [MAP] = 50 mmHg and bilateral carotid occlusion) or (2) near-complete ischemia (isoelectric EEG; 10 min of MAP = 30 mmHg and bilateral carotid occlusion) while anesthetized with 1.4% isoflurane, 1 mg x kg(-1) x min(-1) ketamine, or 25 microg x kg(-1) x h(-1) 70% nitrous oxide and fentanyl. The brain was maintained at normothermia during ischemia and for 22 h after ischemia. Five days later, hippocampal CA1 and cortical injury were measured. RESULTS: There was no difference among anesthetic agents during incomplete ischemia for mean +/- SD percentage dead CA1 neurons (fentanyl, 38%+/-20%; isoflurane, 31%+/-10%; ketamine, 40%+/-19%; P = 0.38). During near-complete ischemia, there was a difference among anesthetic agents (fentanyl, 88%+/-9%; isoflurane, 37%+/-20%; ketamine, 70%+/-28%; P = 0.00008). Isoflurane was protective compared with fentanyl (P = 0.00007) and ketamine (P = 0.0061). There was no difference between fentanyl and ketamine (P = 0.143). Similar observations were made in the cortex. Neurologic function correlated with histologic damage. CONCLUSIONS: Outcome from near-complete but not incomplete cerebral ischemia depended on the anesthetic agent administered during the ischemic insult.
Anesthesia↗
Method to assist in the scheduling of add-on surgical cases--upper prediction bounds for surgical case durations based on the log-normal distribution.
BACKGROUND: A problem that operating room (OR) managers face in running an OR suite on the day of surgery is to identify "holes" in the OR schedule in which to assign "add-on" cases. This process necessitates knowing the typical and maximum amounts of time that the case is likely to require. The OR manager may know previous case durations for the particular surgeon performing a particular scheduled procedure. The "upper prediction bound" specifies with a certain probability that the duration of the surgeon's next case will be less than or equal to the bound. METHODS: Prediction bounds were calculated by using methods that (1) do not assume that case durations follow a specific statistical distribution or (2) assume that case durations follow a log-normal distribution. These bounds were tested using durations of 48,847 cases based on 15,574 combinations of scheduled surgeon and procedure. RESULTS: Despite having 3 yr of data, 80 or 90% prediction bounds would not be able to be calculated using the distribution-free method for 35 or 49% of future cases versus 22 or 22% for the log-normal method, respectively. Prediction bounds based on the log-normal distribution overestimated the desired value less often than did the distribution-free method. The chance that the duration of the next case would be less than or equal to its 90% bound based on the log-normal distribution was within 2% of the expected rate. CONCLUSIONS: Prediction bounds classified by scheduled surgeon and procedure can be accurately calculated using a method that assumes that case durations follow a log-normal distribution.
Algorithms↗
Computer simulation of microscopic cerebral air emboli absorption during cardiac surgery.
Microscopic cerebral arterial air emboli (MCAAE) cause neurologic injury during cardiac surgery. We used a mathematical model of gas absorption to gain a preliminary assessment of what physical or physiologic parameters affect MCAAE absorption in the setting of cardiac surgery with its unique set of normal values. Simulated MCAAE of radii 50 and 200 microns have absorption times of 2 and 32 min, respectively. Predicted absorption times depend dramatically on PaN2. MCAAE are predicted to be absorbed twice as quickly at a PaN2 of 0 vs. 380 mmHg (FiO2 approximately equal to 0.50). Moderate hypothermia (27 degrees C) is predicted to cause only small decreases in absorption time. Changes in cerebral blood flow (for example, as affected by hemoglobin concentration, PaCO2, PaO2, collateral circulation, anesthetics, or cerebral metabolism) probably have only small effects on absorption time. Intravascular perfluorocarbons are predicted to cause small-to-moderate decreases in absorption time. In conclusion, there is probably only one important determinant of MCAAE absorption time during normothermic or moderately hypothermic CPB: arterial nitrogen partial pressure.
Absorption↗
A statistical method for predicting postanesthesia care unit staffing needs.
When predicting staffing requirements for postanesthesia care units (PACUs), nurse managers are expected to satisfy standards, meet patient care needs, staff PACUs to accommodate surgeons' and facilities' needs, and contain costs. The authors present a statistical method that offers reliability and accuracy in forecasting future patient numbers and related PACU staffing requirements. Nurse managers can use this method to decide how frequently they will satisfy staffing standards, how many shifts of RNs to schedule each day, and how many months in the future to schedule staff members. Future peak numbers of patients for each daily shift are based on previous daily peak numbers of patients, and staffing requirements can be planned from these predicted peak numbers of patients, using a facility's PACU staffing standards.
Data Interpretation, Statistical↗
The brain uses mostly dissolved oxygen during profoundly hypothermic cardiopulmonary bypass.
BACKGROUND: During profoundly hypothermic cardiopulmonary bypass, cerebral venous oxygen saturation increases (eg, to 98% at 15 degrees C). We reanalyzed results of clinical studies to learn why. METHODS: One hundred sixty-eight cerebral oxygen transport measurements were available from 96 infants and children undergoing profoundly hypothermic cardiopulmonary bypass during repair of congenital heart defects. RESULTS: Dissolved oxygen accounted for 2% to 17% of arterial oxygen content, depending on the arterial oxygen partial pressure and hemoglobin concentration. The fraction of the cerebral metabolic rate for oxygen obtained from dissolved oxygen depended on pump flow, temperature, hemoglobin concentration, and arterial oxygen partial pressure (all p < 10(-3)). For "full-flow" cardiopulmonary bypass, temperatures less than 18 degrees C, and arterial oxygen partial pressure measurements more than 180 mm Hg, the mean +/- standard deviation of the fraction of cerebral metabolic rate for oxygen obtained from dissolved oxygen equaled 77% +/- 19%. CONCLUSIONS: Dissolved oxygen satisfies most of the brain's oxygen requirements during profound hypothermic cardiopulmonary bypass. This result reflects four properties of profound hypothermic cardiopulmonary bypass: (1) increases in hemoglobin's oxygen affinity due to profound hypothermia (which impairs oxygen transfer from hemoglobin to cerebral tissue), (2) use of hemodilution, (3) use of high arterial oxygen partial pressure, and (4) low cerebral metabolic rate of oxygen.
Brain↗
Measuring productivity of the phase I postanesthesia care unit.
Most of the costs of operating a PACU are for the salaries of the nurses. Therefore, the only way to significantly decrease costs of a PACU, without decreasing salaries, is to increase labor productivity. This article discusses the benefits of measuring labor productivity of the PACU. Approaches that a nurse manager of a phase I PACU can use to increase productivity are considered. One way to measure a PACU's productivity is described, which uses data that some PACUs already collect for billing purposes. The measure of productivity considers heterogeneity in nursing requirements among patients (ie, patient acuity). Measuring productivity in this manner encourages hospital managers to maintain quality, in part by following ASPAN standards.
Bias↗
Performance of anesthesia machines' devices that are not part of the Food and Drug Administration's daily checkout.
OBJECTIVE: The Food and Drug Administration's (FDA) checkout recommendations are to be applied, at least daily, on anesthesia machines. Devices included in the checkout are crucial to the safe operation of the machine. Remaining devices do not need to be checked as often. However, they should be checked at some appropriate interval. We calculated the reliability of the non-FDA checkout devices, to predict failure rates of these devices. METHODS: The study included 36 North American Drager Narkomed anesthesia machines that were in service a total of 109,410 days at a university hospital. Reliability (i.e., statistical) analyses were done using in-house data recorded by biomedical technicians during 3359 monthly machine inspections. If any one device was operating outside of the limits of the manufacturer's specifications, the machine was labeled as having failed its inspection. RESULTS: Assumptions of the failure analysis were satisfied. The mean time between failures equaled 1351 days or 3.7 years (lower 95% confidence bound 1123 days or 3.1 years). The mean daily probability of one or more devices failing to perform within the manufacturer's specification between inspections equaled 1.1, 2.2%, and 4.4% for inspections every 1, 2, or 4 months, respectively. Probabilities that a machine would fail on demand between inspections were approximately equal to the mean daily probabilities of machine failure. The mean number of days per year that a machine would be operating with a device that is outside of the limits of its specifications equaled 4, 8, and 12, days, respectively. The mean daily probabilities of failure and the probabilities of failure on demand were both directly proportional to the inspection interval. CONCLUSIONS: Our failure analysis provides a rational basis for choosing an appropriate inspection interval for anesthesia machines' devices that are not included in the FDA's checkout recommendations.
Anesthesiology↗
Effect of haemoglobin concentration on brain oxygenation in focal stroke: a mathematical modelling study.
Acute perioperative anaemia may affect neurological injury from permanent focal ischaemic insults. We modelled the opposing effects of haemodilution (increasing cerebral blood flow, decreasing arterial oxygen content) on oxygen availability and uptake in the ischaemic penumbra. First, we validated a mathematical model of regional cerebral oxygen uptake by using published arterial oxygen content and cerebral blood flow values from normal rabbits with progressive anaemia. Then we applied the model to the problem of interest (i.e. the ischaemic penumbra of a focal embolic stroke). We re-analysed published experimental data giving the cerebral blood flow response to anaemia in the ischaemic penumbra. Penumbral extraction reserves were nearly exhausted at a haemoglobin concentration of approximately 10g 100ml-1. Oxygen uptake in the ischaemic penumbra decreased progressively when haemoglobin concentrations decreased to less than 10g 100ml-1. We conclude that, given the available clinical and experimental literature, and until a suitable randomized clinical study has been performed, a haemoglobin concentration of 10 g 100 ml-1 is the rational transfusion "trigger" for the acutely anaemic stroke patient.
Anemia↗
Recommendations for hyperbaric oxygen therapy of cerebral air embolism based on a mathematical model of bubble absorption.
Transcranial doppler studies show that microscopic cerebral artery air emboli (CAAE) are present in virtually all patients undergoing cardiac surgery. Massive cerebral arterial air embolism is rare. If it occurs, hyperbaric oxygen therapy (HBO) is recommended as soon as surgery is completed. We used a mathematical model to predict the absorption time of CAAE, assuming that the volumes of clinically relevant CAAE vary from 10(-7) to at least 10(-1) mL. Absorption times are predicted to be at least 40 h during oxygenation using breathing gas mixtures of fraction of inspired oxygen approximately equal to 40%. When CAAE are large enough to be detected by computerized tomography, absorption times are calculated to be at least 15 h. Decreases in cerebral blood flow caused by the CAAE would make the absorption even slower. Our analysis suggests that if the diagnosis of massive CAAE is suspected, computerized tomography should be performed, and consideration should be given to HBO therapy if the CAAE are large enough to be visualized, even if patient transfer to a HBO facility will require several hours.
Absorption↗
Heart rate variability, respiratory sinus arrhythmia, and mathematical modeling of acetylcholine pharmacokinetics/pharmacodynamics in sinus node neuroeffector junctions.
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Acetylcholine↗
Does early extubation ("fast-tracking") of coronary artery bypass graft surgery patients truly decrease perioperative costs?: Appropriate analysis of direct variable costs.
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Coronary Artery Bypass↗
Doxycycline reduces early neurologic impairment after cerebral arterial air embolism in the rabbit.
BACKGROUND: Previous studies indicate leukocytes play a role in the pathogenesis of cerebral arterial air embolism. Because doxycycline inhibits numerous leukocyte activities, the authors hypothesized doxycycline would decrease neurologic impairment after cerebral arterial air embolism. METHODS: New Zealand White rabbits anesthetized with methohexital received either intravenous saline (n = 7) or 10 mg/kg doxycycline (n = 7) 1 h before administration of 100 microl/kg of air into the internal carotid artery. Somatosensory-evoked potentials (SSEPs) were recorded at 30-min intervals for the next 2 h. After the final recording, the anesthetic was discontinued, and animals recovered. Animals were neurologically evaluated 4 h after air embolism on a scale of 0 (normal) to 99 (coma) points. RESULTS: At 4 h, doxycycline animals had lesser neurologic impairment (46 +/- 23; median, 41) than animals that received saline (77 +/- 20; median, 81); P = 0.007. SSEP amplitude was greater in the doxycycline group at 60, 90, and 120 min after air embolism; P = 0.001, 0.006, 0.026, respectively. SSEP amplitudes at 30, 60, 90, and 120 min inversely correlated with 4 h neurologic impairment; tau = -0.43, -0.75, -0.85, -0.79, respectively. CONCLUSIONS: Doxycycline decreased electrophysiologic and neurologic abnormalities after cerebral air embolism. Because groups could be distinguished electrophysiologically as soon as 1 h after air embolism and because SSEP amplitude inversely correlated with neurologic impairment, doxycycline appears to inhibit a key early (approximately 1 h) process in the pathophysiology of cerebral air embolism.
Animals↗
Development of a measure of patient satisfaction with monitored anesthesia care: the Iowa Satisfaction with Anesthesia Scale.
BACKGROUND: The authors describe development of the Iowa Satisfaction with Anesthesia Scale (ISAS) for monitored anesthesia care (MAC). Patients complete the self-administered written questionnaire before discharge from the hospital. The authors designed the ISAS to measure satisfaction with MAC itself, not the perioperative experience. Patients respond to eleven statements (e.g., "I felt pain") by placing a mark along a six-choice vertical response column (e.g., "Disagree moderately") below each statement. The mean of their responses to each of the 11 statements gives a single number, which is a quantitative measure of a patient's satisfaction with their MAC. METHODS: Adult, English-speaking patients completed the questionnaires following admission to a phase II postanesthesia care unit after MAC. RESULTS: Response rate for MAC was 92% (86 of 94 patients). Patients completed the questionnaire in 4.6 +/- 2.3 min. Internal consistency, Cronbach's alpha, equaled 0.80. Patients' scores were positively correlated with those predicted by their anesthesia provider (r2 = 0.23) and with responses to the question "I was satisfied with my anesthetic care" (Kendall's tau = +0.41). Scores on initial and repeat questionnaires were positively correlated (r2 = 0.74). Scores on initial questionnaires and those completed within 4.4 +/- 1.7 days postoperatively were positively correlated (r2 = 0.76). CONCLUSIONS: The authors have developed and tested an internally consistent, reliable, and valid measure of patient satisfaction with MAC.
Adult↗