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Biomedical subjects

J H Tinker

Publications and source records attributed to J H Tinker.

At least 19 recordsLinked to original sources
PubMed1995

The cost efficacy of hypothetically eliminating adverse anesthetic outcomes from high-risk, but neither low- nor moderate-risk, surgical operations.

We tested whether hypothetical improvements in the quality of perioperative care can decrease hospital costs for elective surgical operations. Our case series was constructed retrospectively of consecutive patients who underwent one of the following elective operations at our tertiary care center: lung lobectomy (137), coronary artery bypass (339), kidney transplant (251), total hip replacement (305), laparoscopic cholecystectomy (203), or cesarean section (649). Only hospital costs were included in our study. Eliminating adverse anesthetic outcomes (identified by chart review) entirely would decrease total hospital costs (i.e., for all patients in that group) by less than 0.5% (95% confidence bound < 1.2%) for kidney transplant, 1.8% (< 3.5%) for total hip replacement, 0% for laparoscopic cholecystectomy, and 2.2% (< 6.2%) for cesarean section. In contrast, a hypothetical quality improvement that would have the effect of decreasing costs for the 10% most expensive patients just to the group median would decrease total costs by 30% (15%-44%) for lung lobectomy and 16% (10%-21%) for coronary artery bypass. We conclude that for low- and moderate-risk procedures, hypothetical improvements in the quality of anesthetic care will not reduce costs. However, improving the quality of perioperative care may be cost efficient for high-risk operations.

Anesthesia↗
PubMed1995

Decreases in anesthesia-controlled time cannot permit one additional surgical operation to be reliably scheduled during the workday.

We tested whether anesthesiologists can decrease operating room (OR) costs by working more quickly. Anesthesia-controlled time (ACT) was defined as the sum of 1) the time starting when the patient enters an OR until preparation or surgical positioning can begin plus 2) the time starting when the dressing is finished and ending when the patient leaves the OR. Case time was defined as the time starting when one patient undergoing an operation leaves an OR and ending when the next patient undergoing the same operation leaves the OR. An actual case series was constructed of 709 consecutive patients who underwent one of 11 elective operations at a tertiary care center. Statistical analysis of measured OR times showed that ACt would have to be decreased by more than 100% to permit one additional scheduled, short (30-min) operation to be performed in an OR during an 8-h workday after a prior series of cases, each lasting more than 45 min. Anesthesiologists alone cannot reasonably decrease case times sufficiently to permit one extra case to be reliably scheduled during a workday. Methods to decrease ACT (e.g., using preoperative intravenous catheter teams, procedure rooms, and/or shorter acting drugs) may simply increase costs.

Ambulatory Surgical Procedures↗
PubMed1995

Analysis of strategies to decrease postanesthesia care unit costs.

BACKGROUND: The goal of this study was to identify interventions that anesthesiologists can make to decrease total costs of a postanesthesia care unit (PACU). METHODS: Data were collected retrospectively from patients who underwent ambulatory surgery at our tertiary care center. RESULTS: Supplies and medications accounted for only 2% of PACU charges. Personnel costs, which depend on the peak number of patients in the PACU, accounted for almost all PACU costs. If nausea and vomiting could have been eliminated in each patient who suffered this complication, without causing sedation, the total time to discharge for all patients would have been decreased by less than 4.8% (95% confidence interval < 7.3%). Arrival rates to and times to discharge from the PACU followed triangular and log-normal distributions, respectively. Computer simulations, using published times to discharge for drugs with "faster recovery," such as propofol, showed that the use of these drugs would only decrease PACU costs if operating rooms were consistently scheduled to run later each day. Such earlier discharge also might be beneficial if used at night, but only if the PACU could close after a single patient leaves. However, reasonably achievable decreases in the times to discharge for all patients undergoing general anesthesia are unlikely to substantively decrease PACU costs. In contrast, arranging an operating room schedule to optimize admission rates would greatly affect the number of PACU nurses needed. CONCLUSIONS: Anesthesiologists have little control over PACU economics via choice of anesthetic drugs. The major determinant of PACU costs is the distribution of admissions.

Ambulatory Surgical Procedures↗
PubMed1995

Comparisons between desflurane and isoflurane or propofol on time to following commands and time to discharge. A metaanalysis.

BACKGROUND: Anesthesiologists can best decide whether to use desflurane based on the magnitudes of its effects compared to other general anesthetics. The goal of this study was to estimate the mean decrease in times to following commands when desflurane was being used instead of isoflurane or propofol. The mean decrease in time to hospital discharge after ambulatory surgery when desflurane was used instead of propofol also was examined. METHODS: Published studies that met entry criteria were collected up to November 1994. Included are studies in which patients were randomly assigned to groups, extubation was planned at the end of surgery, and general anesthesia was induced with an intravenous agent. We used random-effects metaanalysis to calculate confidence intervals for pooled mean differences. RESULTS: Six studies (with 229 patients) that compared desflurane to propofol met the inclusion criteria. Eight studies (with 316 patients) compared desflurane to isoflurane. A statistically significant difference in the time to following commands after discontinuation of desflurane versus propofol (mean difference 0.7 min (propofol minus desflurane), 95% confidence interval -0.2 to 1.7 min) was not found. Patients who received propofol were discharged to home a mean of 17 min (4-30 min) more quickly than patients who received desflurane. Patients who received desflurane followed commands a mean of 4.4 min (3.3-5.4 min) more quickly than did patients who received isoflurane. CONCLUSIONS: There are only minor clinically important differences between desflurane and isoflurane or propofol with respect to time to following commands and time to discharge.

Anesthetics, Inhalation↗
PubMed1994

Inhibition of volatile sevoflurane degradation product formation in an anesthesia circuit by a reduction in soda lime temperature.

BACKGROUND: Sevoflurane reacts with carbon dioxide absorbents, such as soda lime, to release the volatile products compounds A and B. These two products, which have been detected in anesthesia circuits, are among five formed when sevoflurane is degraded by soda lime at increased temperature; the others, compounds C, D, and E, have been detected only in heated sealed systems. The current study attempted to determine the influence of soda lime temperature on compounds A and B generation in an anesthesia circuit and whether a decrease in soda lime temperature could eliminate product formation in the circulating gases. METHODS: Sevoflurane (1.5% in oxygen) was circulated (6 l/min) in a partially closed, low-flow (215 ml/min fresh gas) anesthesia circuit that included a canister containing 1.2 kg fresh soda lime. Carbon dioxide was introduced into the circuit at 200 ml/min, and gas samples for analysis of sevoflurane, compounds A, B, C, and D, and carbon dioxide were taken at the opening of an attached artificial lung. The circuit was operated for 8 h under conditions whereby the soda lime temperature could increase freely or the soda lime was chilled with ice. RESULTS: A maximum core soda lime temperature of about 46 degrees C was measured when the experiment was run under conditions whereby the soda lime temperature was allowed to increase. Compounds A and B increased with time to a maximum of 23 and 9 ppm, respectively. At 4.5 h of circuit operation, compound C/D was found. Chilling of the soda lime canister, which produced a maximum core soda lime temperature of 25 degrees C, resulted in neither compound B nor C/D being detected during the 8-h period. Compound A was present in the circuit at all times at approximately 10 ppm; however, its concentration did not increase as occurred when the experiment was conducted under nonchilled conditions. Carbon dioxide levels at the opening of the lung remained at a constant 5% for 8 h with or without soda lime chilling. CONCLUSIONS: This study demonstrates that the release of volatile sevoflurane degradation products in an anesthesia circuit is highly dependent on soda lime temperatures. A reduction of the temperature of soda lime may be a feasible method of preventing the release of significant levels of sevoflurane degradation products without interfering with carbon dioxide absorption or altering the sevoflurane concentration.

Absorption↗
PubMed1993

Hypothermic acid-base management does not affect cerebral metabolic rate for oxygen at 27 degrees C. A study during cardiopulmonary bypass in rabbits.

BACKGROUND: It has been contended that, during cardiopulmonary bypass at 27 degrees C, pH-stat management decreases cerebral metabolic rate for oxygen (CMRO2) more than alpha-stat management. In contrast, other studies have not found CMRO2 to differ between techniques. Using each animal as its own control, the authors assessed the effect of alpha-stat versus pH-stat management of CMRO2, cerebral blood flow (CBF), and brain oxygen extraction during cardiopulmonary bypass at 27 degrees C. METHODS: Fourteen New Zealand White rabbits, anesthetized with fentanyl and diazepam, underwent cardiopulmonary bypass at 27 degrees C (membrane oxygenator, centrifugal pump, and bifemoral arterial perfusion). Group 1 animals (n = 7) had alpha-stat management for the initial 65-70 min of bypass, and were then changed to pH-stat management for the remaining 30 min of bypass. Group 2 animals (n = 7) had pH-stat management for the initial 65-70 min of bypass, and were then changed to alpha-stat management for the remaining 30 min. Measurement of CBF (radiolabeled microspheres), CMRO2 (CBF x brain arterial-venous oxygen content difference), brain temperature, systemic hemodynamics, and arterial blood gases were made in each animal under both alpha-stat and pH-stat conditions. RESULTS: CMRO2 did not differ between alpha-stat and pH-stat conditions (1.4 +/- 0.3 ml.100 g-1.min-1; median +/- quartile deviation), and was independent of order of determination. Changes in CBF between alpha-stat and pH-stat conditions were associated with proportional opposite changes in cerebral oxygen extraction. Cerebral blood flow was significantly greater with pH-stat management than with alpha-stat management (37 +/- 5 vs. 30 +/- 3 ml.100 g-1.min-1, respectively). The CBF response to changing PaCO2 was significantly greater when going from alpha-stat to pH-stat conditions (group 1) than in the reverse order (group 2). CONCLUSIONS: During cardiopulmonary bypass at 27 degrees C, hypothermic acid-base management has no measurable effect on CMRO2. CMRO2 was neither extraction limited nor dependent on either PaCO2, CBF, or hemoglobin oxygen affinity differences between alpha-stat and pH-stat management. Cerebral blood flow responses to changing CMRO2 depend on the "starting" conditions, with alpha-stat management appearing to better preserve CBF reactivity than pH-stat management.

Acid-Base Equilibrium↗
PubMed1992

Dose-response relationship of isoflurane and halothane versus coronary perfusion pressures. Effects on flow redistribution in a collateralized chronic swine model.

The authors studied the redistribution of myocardial blood flow in a collateral-dependent (CD) zone as a function of coronary perfusion pressure (CPP) during isoflurane and halothane anesthesia. A swine model with CD myocardium distal to a chronically occluded left anterior descending coronary artery was developed and studied. Sixteen piglets were allowed to grow for 8-10 weeks after banding of the left anterior descending coronary artery. They were randomly anesthetized with either isoflurane (n = 8) or halothane (n = 8) as the sole anesthetic, which was used to regulate specific CPP. The resultant regional myocardial blood flows were measured using radiolabeled microspheres. Four randomly allocated CPPs, of 30, 40, 45, and 55 mmHg, were studied in each animal. Four additional collateralized animals were anesthetized with alpha-chloralose, and the same CPPs were obtained using an intravenous adenosine infusion (1-5 microM kg-1) to validate this model. There was a proportional decrease in heart rate and blood pressure in both the isoflurane and and the halothane group with CPP. Cardiac output was significantly decreased in the halothane group at 30 mmHg when compared to 55-mmHg CPP, but it was maintained in the isoflurane group. Systemic vascular resistance was significantly lower in the isoflurane group at 30 and 40 mmHg when compared to 55-mmHg CPP. Both the isoflurane and the halothane group showed a proportional and significant decrease in endo-, mid-, and epicardial blood flows at 30-mmHg CPP when compared to baseline. In both CD and normal perfusion zones, isoflurane consistently sustained a higher endocardial blood flow than halothane (5.7-41.1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Brain blood flow and metabolism do not decrease at stable brain temperature during cardiopulmonary bypass in rabbits.

Cerebral blood flow (CBF) during human hypothermic cardiopulmonary bypass has been reported to decrease with time, suggesting that progressive cerebral vasoconstriction or embolic obstruction may occur. We tested the hypotheses: 1) that observed CBF reductions were due to continued undetected brain cooling and 2) that CBF during cardiopulmonary bypass would be stable after achievement of constant brain temperature. Anesthetized New Zealand White rabbits underwent cardiopulmonary bypass (membrane oxygenator, centrifugal pump, bifemoral arterial perfusion) and were assigned to one of three bypass management groups based on perfusate temperature and PaCO2 management: group 1 (37 degrees C, n = 8); group 2 (27 degrees C, pH-stat, n = 9); and group 3 (27 degrees C, alpha-stat, n = 8). Systemic hemodynamics, and cerebral cortical, esophageal, and arterial perfusate temperatures were recorded every 10 min for the first hour of bypass and again at 90 min. CBF and masseter blood flow (radiolabeled microspheres) were determined at 30, 60, and 90 min of bypass, while the cerebral metabolic rate for oxygen (CMRO2) was determined at 60 and 90 min. Groups were comparable with respect to mean arterial pressure, central venous pressure, hematocrit, and arterial oxygen content throughout bypass. Cortical temperature was stable in normothermic (group 1) animals, and there was no significant change in CBF between 30 and 90 min of bypass: 68 +/- 18 versus 73 +/- 20 ml.100 g-1.min-1 (mean +/- SD). In the hypothermic groups (2 and 3), cortical temperature equilibration (95% of the total change) required 41 +/- 6 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Efficacy of prior skin puncture in preventing i.v. catheter damage.

The efficacy, with respect to preventing i.v. catheter damage, of creating a skin entry site by first piercing the skin with a large gauge needle through which an over-the-needle teflon catheter is then placed was evaluated. In 50 adult volunteers two 22-gauge i.v. catheters and two 24-gauge catheters were placed through the forearm skin into the subcutaneous tissue. One catheter of each size was placed through an entry site created by piercing the skin with an 18-gauge disposable, stainless steel needle. One catheter of each size was inserted through nearby skin without creation of an entry site. Two to three weeks after insertion all catheters, along with 50 catheters of each size that had not been inserted, were examined under a microscope for evidence of damage. Intravenous catheter damage was more prevalent in the 24-gauge catheters than the 22-gauge catheters (P less than 0.05). No differences in frequency of damage were noted for either gauge catheter inserted through an entry site compared with those inserted without a prior skin puncture. Twenty-four-gauge catheters, but not 22-gauge catheters, placed into the subcutaneous tissue were damaged more frequently than were catheters that had never been inserted (control catheters). This study demonstrated that 24-gauge catheters are more likely to be damaged during insertion into the subcutaneous tissue than are 22-gauge catheters. We also demonstrated that creation of a skin entry site by piercing the epidermis with a needle of larger gauge than the catheter to be placed is not efficacious in preventing intravenous catheter damage during insertion.

Adult↗
PubMed1991

Differences in cerebral blood flow between alpha-stat and pH-stat management are eliminated during periods of decreased systemic flow and pressure. A study during cardiopulmonary bypass in rabbits.

Prior reports suggest cerebral blood flow (CBF) responses to changing bypass (systemic) flow rates may differ between alpha-stat and pH-stat management. To compare the effect of blood gas management upon CBF responses to changing systemic flow and pressure, 15 New Zealand White rabbits, anesthetized with fentanyl and diazepam, underwent nonpulsatile cardiopulmonary bypass at 25 degrees C. One group of animals (n = 8) was randomized to alpha-stat blood gas management that maintained arterial carbon dioxide tension (PaCO2) approximately 40 mmHg when measured at 37 degrees C. A second group (n = 7) was managed with pH-stat technique, maintaining PaCO2 approximately 40 mmHg when corrected to the animal's actual temperature. Bypass was initiated at a flow rate of 100 ml.kg-1.min-1 and, after approximately 20 min, control hemodynamic and CBF measurements (radioactive microspheres) were made. Thereafter, bypass flow rate was changed in random order at 15-min intervals to 50, 70, and 100 ml.kg-1.min-1. CBF and hemodynamic measurements were repeated at the end of each period of altered bypass flow. Groups differed significantly with respect to both pHa and PaCO2. There were no significant differences between groups with respect to bypass flow rate, mean arterial pressure (MAP), central venous pressure, temperature, hematocrit, arterial oxygen tension (PaCO2), or bypass duration at any measurement point. MAP decreased significantly, from approximately 80 to approximately 65 mmHg with decreasing bypass flow (P = 0.0001). Over the entire range of bypass flows, CBF decreased with decreasing bypass flow (P = 0.001), and the degree of change was equivalent among regions and between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗