Drugs for preventing postoperative nausea and vomiting in adults after general anaesthesia: an abridged Cochrane network meta-analysis

Postoperative nausea and vomiting is a common adverse effect of anaesthesia. Although dozens of different anti-emetics are available for clinical practice, there is currently no comparative ranking of efficacy and safety of these drugs to inform clinical practice. We performed a systematic review with network meta-analyses to compare, and rank in terms of efficacy and safety, single anti-emetic drugs and their combinations, including 5-hydroxytryptamine₃ , dopamine-2 and neurokinin-1 receptor antagonists; corticosteroids; antihistamines; and anticholinergics used to prevent postoperative nausea and vomiting in adults after general anaesthesia. We systematically searched for placebo-controlled and head-to-head randomised controlled trials up to November 2017 (updated in April 2020). We assessed how trustworthy the evidence was using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) and Confidence In Network Meta-Analysis (CINeMA) approaches for vomiting within 24 h postoperatively, serious adverse events, any adverse event and drug class-specific side-effects. We included 585 trials (97,516 participants, 83% women) testing 44 single drugs and 51 drug combinations. The studies' overall risk of bias was assessed as low in only 27% of the studies. In 282 trials, 29 out of 36 drug combinations and 10 out of 28 single drugs lowered the risk of vomiting at least 20% compared with placebo. In the ranking of treatments, combinations of drugs were generally more effective than single drugs. Single neurokinin-1 receptor antagonists were as effective as other drug combinations. Out of the 10 effective single drugs, certainty of evidence was high for aprepitant, with risk ratio (95%CI) 0.26 (0.18-0.38); ramosetron, 0.44 (0.32-0.59); granisetron, 0.45 (0.38-0.54); dexamethasone, 0.51 (0.44-0.57); and ondansetron, 0.55 (0.51-0.60). It was moderate for fosaprepitant, 0.06 (0.02-0.21) and droperidol, 0.61 (0.54-0.69). Granisetron and amisulpride are likely to have little or no increase in any adverse event compared with placebo, while dimenhydrinate and scopolamine may increase the number of patients with any adverse event compared with placebo. So far, there is no convincing evidence that other single drugs effect the incidence of serious, or any, adverse events when compared with placebo. Among drug class specific side-effects, evidence for single drugs is mostly not convincing. There is convincing evidence regarding the prophylactic effect of at least seven single drugs for postoperative vomiting such that future studies investigating these drugs will probably not change the estimated beneficial effect. However, there is still considerable lack of evidence regarding safety aspects that does warrant investigation.

Patient-controlled analgesia with remifentanil vs. alternative parenteral methods for pain management in labour: a Cochrane systematic review

We aimed to assess the effectiveness of remifentanil used as intravenous patient-controlled analgesia for the pain of labour. We performed a systematic literature search in December 2015 (updated in December 2016). We included randomised, controlled and cluster-randomised trials of women in labour with planned vaginal delivery receiving patient-controlled remifentanil compared principally with other parenteral and patient-controlled opioids, epidural analgesia and continuous remifentanil infusion or placebo. The primary outcomes were patient satisfaction with pain relief and the occurrence of adverse events for mothers and newborns. We assessed risk of bias for each included study and applied the GRADE approach for the quality of evidence. We included total zero event trials, using a constant continuity correction of 0.01 and a random-effect meta-analysis. Twenty studies were included in the qualitative analysis; within these, 3713 participants were randomised and 3569 analysed. Most of our pre-specified outcomes were not studied in the included trials. However, we found evidence that women using patient-controlled remifentanil were more satisfied with pain relief than women receiving parenteral opioids (four trials, 216 patients, very low quality evidence) with a standardised mean difference ([SMD] 95%CI) of 2.11 (0.72-3.49), but were less satisfied than women receiving epidural analgesia (seven trials, 2135 patients, very low quality evidence), -0.22 (-0.40 to -0.04). Data on adverse events were sparse. However, the relative risk (95%CI) for maternal respiratory depression for patient-controlled remifentanil compared with epidural analgesia (three trials, 687 patients, low-quality evidence) was 0.91 (0.51-1.62). Compared with continuous intravenous infusion of remifentanil (two trials, 135 patients, low-quality evidence) no conclusion could be reached as all study arms showed zero events. The relative risk (95%CI) of Apgar scores less than 7 at 5 min after birth compared with epidural analgesia (five trials, 1322 participants, low-quality evidence) was 1.26 (0.62-2.57).

Transient neurologic symptoms (TNS) following spinal anaesthesia with lidocaine versus other local anaesthetics

BACKGROUND

Spinal anaesthesia has been in use since the turn of the late nineteenth century. During the last decade there has been an increase in the number of reports implicating lidocaine as a possible cause of temporary and permanent neurologic complications after spinal anaesthesia. Follow-up of patients who received uncomplicated spinal anaesthesia revealed that some of them developed pain in the lower extremities after an initial full recovery. This painful condition that occurs in the immediate postoperative period was named "transient neurologic symptoms" (TNS).

OBJECTIVES

To study the frequency of TNS and neurologic complications after spinal anaesthesia with lidocaine, compared to other local anaesthetics.

SEARCH STRATEGY

We searched the Cochrane Controlled Trials Register (CENTRAL), (The Cochrane Library, Issue 1, 2005); MEDLINE (1966 to January 2005); EMBASE (1980 to week 6, 2005); LILACS (March 2005); and handsearched the reference lists of trials and review articles.

SELECTION CRITERIA

We included all randomized and pseudo-randomized studies comparing the frequency of TNS and of neurologic complications after spinal anaesthesia with lidocaine as compared to other local anaesthetics.

DATA COLLECTION AND ANALYSIS

Two authors independently evaluated the quality of the relevant studies and extracted the data from the included studies.

MAIN RESULTS

Fifteen trials, reporting 1437 patients, 120 of whom developed transient neurologic symptoms, were included in the analysis. The use of lidocaine for spinal anaesthesia increased the risk of developing TNS. There was no evidence that this painful condition was associated with any neurologic pathology; the symptoms disappeared spontaneously by the fifth postoperative day. The relative risk (RR) for developing TNS after spinal anaesthesia with lidocaine as compared to other local anaesthetics (bupivacaine, prilocaine, procaine, levobupivacaine and ropivacaine) was 7.16 (95% confidence interval (CI) 4.02, 12.75).

AUTHORS' CONCLUSIONS

The risk of developing TNS after spinal anaesthesia with lidocaine was significantly higher than when bupivacaine, prilocaine and procaine were used. The term "TNS", which implies a positive neurologic finding, should not be used for this painful condition. One study about the impact of TNS on patient satisfaction and functional impairment demonstrated that non-TNS patients were more satisfied and had less functional impairment after surgery than TNS patients, but this did not influence their willingness to recommend spinal anaesthesia.

Transient neurologic symptoms (TNS) following spinal anaesthesia with lidocaine versus other local anaesthetics

BACKGROUND

Spinal anaesthesia has been in use since the turn of the late 19th century. The most serious complication of this technique is damage to the spinal cord or nerve roots resulting in lasting neurologic sequelae. Such serious adverse effects seldom happen. There has been an increase in the number of reports during the last nine years implicating lidocaine as a possible cause of temporary and permanent neurologic complications after spinal anaesthesia. Follow-up of patients who received uncomplicated spinal anaesthesia revealed that some of them developed pain in the lower extremities after an initial full recovery. This painful condition that occurs in the immediate post-operative period was named "transient neurologic symptoms" (TNS).

OBJECTIVES

The objectives of this review were to study the frequency of TNS and neurologic complications after spinal anaesthesia with lidocaine, compared to other local anaesthetics.

SEARCH STRATEGY

Trials were identified by computerized searches of the Cochrane Controlled Trials Register (4th Quarter 2002), MEDLINE (1966 - January 2003), LILAC database, EMBASE (1980 - week 51, 2002), and by checking the reference lists of trials and review articles.

SELECTION CRITERIA

All randomized and pseudo-randomized studies comparing the frequency of TNS and of neurologic complications after spinal anaesthesia with lidocaine as compared to other local anaesthetics.

DATA COLLECTION AND ANALYSIS

Two reviewers independently evaluated the quality of the relevant studies and extracted the data from the included studies.

MAIN RESULTS

Fourteen trials, reporting 1,349 patients, 117 of whom developed transient neurologic symptoms, were included in the analysis. The use of lidocaine for spinal anaesthesia increased the risk of developing TNS. There was no evidence that this painful condition was associated with any neurologic pathology as it was clearly documented that no positive neurologic findings were present in any patient with TNS; the symptoms disappeared spontaneously by the fifth postoperative day. The relative risk for developing TNS after spinal anaesthesia with lidocaine as compared to other local anaesthetics (bupivacaine, prilocaine, procaine and mepivacaine) was 4.35 (95% Confidence Interval: 1.98, 9.54).

REVIEWER'S CONCLUSIONS

The risk of developing TNS after spinal anaesthesia with lidocaine was significantly higher than when bupivacaine, prilocaine and procaine were used. The term "TNS", which implies a positive neurologic finding, should not be used for this painful condition, which is in fact comparable to another common adverse effect after spinal anaesthesia - lower back pain. How much the pain in the lower extremities influences patient satisfaction is not elucidated clearly in the literature.

Effects of intrathecal morphine on the ventilatory response to hypoxia

BACKGROUND

Intrathecal administration of morphine produces intense analgesia, but it depresses respiration, an effect that can be life-threatening. Whether intrathecal morphine affects the ventilatory response to hypoxia, however, is not known.

METHODS

We randomly assigned 30 men to receive one of three study treatments in a double-blind fashion: intravenous morphine (0.14 mg per kilogram of body weight) with intrathecal placebo; intrathecal morphine (0.3 mg) with intravenous placebo; or intravenous and intrathecal placebo. The selected doses of intravenous and intrathecal morphine produce similar degrees of analgesia. The ventilatory response to hypercapnia, the subsequent response to acute hypoxia during hypercapnic breathing (targeted end-tidal partial pressures of expired oxygen and carbon dioxide, 45 mm Hg), and the plasma levels of morphine and morphine metabolites were measured at base line (before drug administration) and 1, 2, 4, 6, 8, 10, and 12 hours after drug administration.

RESULTS

At base line, the mean (+/-SD) values for the ventilatory response to hypoxia (calculated as the difference between the minute ventilation during the second full minute of hypoxia and the fifth minute of hypercapnic ventilation) were similar in the three groups: 38.3+/-23.2 liters per minute in the placebo group, 33.5+/-16.4 liters per minute in the intravenous-morphine group, and 30.2+/-11.6 liters per minute in the intrathecal-morphine group (P=0.61). The overall ventilatory response to hypoxia (the area under the curve) was significantly lower after either intravenous morphine (20.2+/-10.8 liters per minute) or intrathecal morphine (14.5+/-6.4 liters per minute) than after placebo (36.8+/-19.2 liters per minute) (P=O.003). Twelve hours after treatment, the ventilatory response to hypoxia in the intrathecal-morphine group (19.9+/-8.9 liters per minute), but not in the intravenous-morphine group (30+/-15.8 liters per minute), remained significantly depressed as compared with the response in the placebo group (40.9+/-19.0 liters per minute) (P= 0.02 for intrathecal morphine vs. placebo). Plasma concentrations of morphine and morphine metabolites either were not detectable after intrathecal morphine or were much lower after intrathecal morphine than after intravenous morphine.

CONCLUSIONS

Depression of the ventilatory response to hypoxia after the administration of intrathecal morphine is similar in magnitude to, but longer-lasting than, that after the administration of an equianalgesic dose of intravenous morphine.

Dysphotopsia in phakic and pseudophakic patients: incidence and relation to intraocular lens type(2)

PURPOSE

To determine the relationship between various intraocular lens (IOL) types and the incidence of unwanted light images.

SETTING

The Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

METHODS

A telephone questionnaire was administered to 302 postoperative patients who had received 1 of 6 commonly used IOLs between January and September 1998. Patients were included only if they had uneventful cataract surgery, no additional ocular pathology, and a postoperative best corrected visual acuity of 20/25 or better. A control group of 50 patients with the diagnosis of presbyopia only also participated in the questionnaire. Patients reported on incidence of glare, light sensitivity, and unwanted images. The data were analyzed for statistically significant relationships between incidence of photopsias and IOL type.

RESULTS

The AcrySof 5.5 mm, AcrySof 6.0 mm, and SI-40 groups reported significantly more unwanted images than the control group (P =.0014). The 2 AcrySof groups also reported a greater incidence of light to the side causing a central flash, and the SI-40 group, a higher incidence of glare. The control group was more likely to experience symptoms of glare than any pseudophakic group. Overall, a mean of 49% of patients reported some light-related phenomenon postoperatively. The majority in all groups reported being satisfied with their eyesight despite the light-related problems.

CONCLUSIONS

A significant number of pseudophakic patients reported symptoms of dysphotopsia. Patients who received an acrylic IOL with flattened edges were at increased risk of experiencing images associated with edge reflections. The SI-40 lens group, although less than the AcrySof groups, reported a higher incidence of glare than the non-AcrySof groups; however, it also had the highest number of patients still driving at night. The phakic population commonly experienced glare reported as more severe than several of the IOL groups.

Intrathecal fentanyl is superior to intravenous ondansetron for the prevention of perioperative nausea during cesarean delivery with spinal anesthesia

This study compares intrathecal (IT) fentanyl with IV ondansetron for preventing intraoperative nausea and vomiting during cesarean deliveries performed with spinal anesthesia. Thirty healthy parturients presenting for elective cesarean delivery with standardized bupivacaine spinal anesthesia were randomized to receive 20 microg IT fentanyl (Group F) or 4 mg IV ondansetron (Group O) by using double-blinded methodology. At eight specific intervals during the surgery, a blinded observer questioned the patient about nausea (1 = nausea, 0 = no nausea), observed for the presence of retching or vomiting (1 = vomiting or retching, 0 = no vomiting or retching), and recorded a verbal pain score (0-10, 0 = no pain, 10 = worst pain imaginable). Cumulative nausea, vomiting, and pain scores were calculated as the sum of the eight measurements. Intraoperative nausea was decreased in the IT fentanyl group compared with the IV ondansetron group: the median (interquartile range) difference in nausea scores was 1 (1, 2), P = 0.03. The incidence of vomiting and treatment for vomiting was not different (P = 0.7). The IT fentanyl group had a lower cumulative perioperative pain score than the IV ondansetron group; the median difference in the cumulative pain score was 12 (8, 16) (P = 0.0007). The IT fentanyl group required less supplementary intraoperative analgesia. The median difference in the cumulative fentanyl dose was 100 (75, 100) microg fentanyl, (P = 0.0002).

Multiple dose pharmacokinetics of oral transmucosal fentanyl citrate in healthy volunteers

BACKGROUND

Oral transmucosal fentanyl citrate (OTFC) is a solid form of fentanyl that delivers the drug through the oral mucosa. The clinical utility of multiple doses of OTFC in the treatment of "breakthrough" cancer pain is under evaluation. The aim of this study was to test the hypothesis that the pharmacokinetics of OTFC do not change with multiple dosing.

METHODS

Twelve healthy adult volunteers received intravenous fentanyl (15 microg/kg) or OTFC (three consecutive doses of 800 microg) on separate study sessions. Arterial blood samples were collected for determination of fentanyl plasma concentration by radioimmunoassay. The descriptive pharmacokinetic parameters (maximum concentration, minimum concentration, and time to maximum concentration) were identified from the raw data and subjected to a nonparametric analysis of variance. Population pharmacokinetic models for all subjects and separate models for each subject were developed to estimate the pharmacokinetic parameters of fentanyl after multiple OTFC doses.

RESULTS

The shapes of the profiles of plasma concentration versus time for each dose of OTFC were grossly similar. No change was noted for maximum concentration or time to maximum concentration over the three doses, while minimum concentration did show a significantly increasing trend. Terminal half-lives for intravenous fentanyl and OTFC were similar. A two-compartment population pharmacokinetic model adequately represented the central tendency of the data from all subjects. Individual subject data were best described by either two- or three-compartment pharmacokinetic models. These models demonstrated rapid and substantial absorption of OTFC that did not change systematically with time and multiple dosing.

CONCLUSIONS

The pharmacokinetics of OTFC were similar among subjects and did not change with multiple dosing. Multiple OTFC dosing regimens within the dosage schedule examined in this study can thus be formulated without concern about nonlinear accumulation.

Delays in the detection of hypoxemia due to site of pulse oximetry probe placement

STUDY OBJECTIVES

To determine if there were any differences in the time to detect hypoxemia related to the site of peripheral pulse oximetry (ear, hand, and foot) during the rapid induction of hypoxemia in healthy volunteers.

DESIGN

Repeated-measures, longitudinal, observational study.

SETTING

Anesthesia clinical research area of the Department of Anesthesiology.

PATIENTS

13 healthy volunteers, aged 18 to 44 years.

INTERVENTIONS

Nellcor N-200 (Nellcor, Inc., Pleasanton, CA) oximeter probes were placed at the ear, hand, and foot. All units were turned on simultaneously with averaging times set for 5 seconds and signals sampled at 2 Hz. A computer-controlled anesthesia circuit was employed to induce mild hypercapnia and hyperoxia (end-tidal gas partial pressures: PETCO2 = 42 +/- 2 mmHg and PETO2 = 130 mmHg) for 5 minutes. PETO2 was then decreased to 45 +/- 2 mmHg over 60 seconds and held at that value for 5 minutes.

MEASUREMENTS AND MAIN RESULTS

The mean differences in time (sec) for pulse oximeters to detect hypoxemia (read less than 90%) between probe sites were determined and compared. The following mean differences in time (sec) for pulse oximeters to detect hypoxemia (read less than 90%) between probe sites were found: ear-hand = 6; hand-foot = 57; ear-foot = 63. Paired t-tests revealed statistically significant mean time delay differences of 51 seconds (p < 0.005) and 57 seconds (p < 0.005) for ear-hand versus hand-foot and for ear-hand versus ear-foot, respectively.

CONCLUSIONS

In healthy volunteers, significant delays in the detection of acute hypoxemia by pulse oximetry occur when pulse oximeters are placed at the toe as compared with probes at either the ear or hand.

Rapid onset of ulnar nerve dysfunction during transient occlusion of the brachial artery

Perioperative ulnar neuropathy is a complication that occurs even in patients who seem to be appropriately padded and positioned. The disproportionately high incidence of postoperative ulnar nerve injury compared with the median and radial nerves has largely been attributed to its vulnerability to compression or stretch at the cubital tunnel. Some clinical and laboratory evidence suggests that compromise of perfusion to the upper extremity may also play a role in this complication. To determine whether the ulnar nerve is more sensitive to ischemia of the upper extremity, we studied 10 men during general anesthesia. Somatosensory evoked potentials of the radial, median, and ulnar nerves were simultaneously recorded during general anesthesia with the brachial artery occluded proximal to the cubital fossa. All three nerves showed rapid changes in signal amplitude in response to occlusion of the brachial artery, but the amplitude of the ulnar nerve was affected earlier and to a greater degree. Compared with the median nerve, the change in ulnar nerve signal amplitude during ischemia was significantly greater after 4 min (P = 0.002). This trend persisted at 6 and 8 min (P = 0.008). At 4, 6, and 8 min of ischemia, the ulnar nerve likewise showed a greater decrease in amplitude compared with the radial nerve, with corresponding P values of 0.015, 0.008, and 0.008. We conclude that the ulnar nerve is more sensitive to ischemia of the upper extremity compared with the radial and median nerves. In addition to its increased vulnerability at the elbow, compromise of arterial flow may contribute to some cases of postoperative ulnar neuropathy.

IMPLICATIONS

Postoperative ulnar neuropathy is thought to result from compression or stretch of the ulnar nerve at the elbow. However, patients may sustain this complication despite careful padding and positioning. This study suggests that the ulnar nerve may also be unusually sensitive to decreases in blood supply to the arm. Care should not only to properly position and pad the elbows, but also to ensure adequate perfusion of the upper extremities.

Dose proportionality and pharmacokinetics of oral transmucosal fentanyl citrate

BACKGROUND

The pharmacokinetics of a single dose (15 microg/kg) of oral transmucosal fentanyl citrate (OTFC) have been characterized. A range of doses may eventually be used in clinical practice. The goal of this study was to determine if the pharmacokinetics of OTFC are dose proportional for doses ranging from 200 to 1,600 microg.

METHODS

Twelve healthy male volunteers were studied on four different occasions, receiving 200, 400, 800, and 1,600 microg OTFC in a double-blind, randomized protocol. Venous blood samples were collected at selected times during and after dosing for a 24-h period and assayed for fentanyl using a radioimmunoassay. Maximum concentration, time to maximum concentration, area under the curve, and elimination half-life were determined for each dose administered. In addition, respiratory rate, need for verbal prompting to breathe, and supplemental oxygen requirements were noted.

RESULTS

Mean fentanyl concentration time curves were similarly shaped with increasing doses. Both peak concentrations and area under the curve increased linearly with an increase in dose, whereas time to reach peak serum concentrations did not vary significantly between doses. Except for the 200-microg dose, the apparent elimination half-life remained relatively constant (358-386 min). The incidence of low respiratory rate, supplemental oxygen requirement, and number of breathing prompts significantly increased with increasing doses.

CONCLUSIONS

Oral transmucosal fentanyl citrate exhibits dose-proportional pharmacokinetics over the dose range of 200-1,600 microg.

The dose-response pharmacology of intrathecal sufentanil in female volunteers

The pharmacologic effects of intrathecal sufentanil (ITS) beyond what is clinically administered (10 microg) are not known. We observed 18 healthy, young, adult female volunteers who received 12.5, 25, or 50 microg of ITS in a randomized, double-blind fashion for 11 h. Analgesia was assessed by pressure algometry at the tibia. Respiratory function was assessed by pulse oximetry, respiratory rate, arterial blood gas, the ventilatory response to CO2, and a respiratory intervention score (RIS). The incidence and severity of side effects also were documented. Serum sufentanil levels were measured for 4 h after ITS administration. We found that ITS produced statistically significant changes in algometry, doubling the pressure required to produce moderate pain. However, doses of ITS greater than 12.5 microg failed to produce proportionate increases in the duration or intensity of analgesia. All doses of ITS produced significant respiratory depression, but only the RIS was significantly related to ITS dose. Neither respiratory rate nor sedation reliably predicted hypoxemia. Supplemental oxygen by nasal cannula consistently prevented pulse oximeter readings below 90%. Serum sufentanil concentrations were related to ITS dose in a statistically significant manner, reached clinically significant concentrations, and followed a time course similar to analgesia and measures of respiratory depression. However, there was no significant increase in measured analgesia associated with the increases in serum sufentanil concentrations. We conclude that in our volunteer model of lower extremity pain, administering ITS in doses larger than 12.5 microg does not improve the speed of onset, magnitude, or duration of analgesia and only causes dose-related increases in serum sufentanil concentrations, which may augment respiratory depression.

Duration of intrathecal labor analgesia: early versus advanced labor

Early first-stage labor pain is primarily visceral in origin. Increasing pain intensity and transition to somatic nociceptive input characterizes late first- and second-stage labor pain. The effect of this change in nociceptive input on the duration of intrathecal labor analgesia has not been well studied. This prospective cohort observational study compares the duration of intrathecal labor analgesia after intrathecal injections made in early labor (3- to 5-cm cervical dilation) and those made in more advanced labor (7- to 10-cm cervical dilation). Forty-one parturients (18 in early labor and 23 in advanced labor) received intrathecal sufentanil (10 micrograms) and bupivacaine (2.5 mg) as part of a combined spinal-epidural technique. Patients rated their pain using a 0-10 verbal pain scale prior to intrathecal injection and every 20 min thereafter. Duration of analgesia was defined as the lesser of time until the pain score exceeded 5 or until a request for supplemental epidural analgesia was made. The duration of spinal analgesia was significantly less when intrathecal injection was made in advanced labor (120 +/- 26 min) compared with early labor (163 +/- 57 min, P < 0.01). We conclude that cervical dilation and stage of labor significantly impact the effective duration of intrathecal sufentanil/ bupivacaine labor analgesia.

Transesophageal echocardiography: an objective tool in defining maximum ventricular response to intravenous fluid therapy

Ventricular preload is an important determinant of cardiac function, which is indirectly measured in the clinical setting by the pulmonary capillary wedge pressure (PCWP). Transesophageal echocardiography (TEE) is rapidly gaining acceptance as a monitor of cardiac function. Although it provides high-resolution images of cardiac structures, clinical assessment of ventricular preload using TEE has been subjective, since quantitative measurements have been difficult to perform in a timely fashion. Automated border detection (ABD) is a new technology used in conjunction with TEE that allows quantitative real-time, two-dimensional measurement of cavity areas. To determine whether enddiastolic area (EDA) measured by ABD can be used to determine an appropriate end point for intravenous fluid administration, nine mongrel dogs were studied. Anesthetized animals were hemorrhaged to achieve a central venous pressure of 0-5 mm Hg. Each animal was then given intravenous fluid (autologous blood followed by hetastarch) until a peak in thermodilution cardiac output (CO) was achieved. Measures of PCWP, EDA, CO, and left ventricular stroke work (LVSW) were obtained after each fluid bolus. Bivariate plots displaying administered volume versus CO, LVSW, and EDA revealed parallel curves for each of these variables with peaks evident at cumulative volumes of 50-55 mL/kg. Multiple regression with mixed model analysis of covariance was performed to determine the significance of EDA in relation to changes in CO and LVSW. Analysis was likewise performed comparing the relationship between PCWP and changes in CO or LVSW. A significant relationship was demonstrated when comparing EDA to changes in CO and LVSW (P = 0.03 and P < 0.0001, respectively). Similar analysis comparing PCWP to changes in CO and LVSW failed to demonstrate a significant relationship (P = 0.54 and P = 0.36, respectively). These data suggest that changes in EDA measured using TEE with ABD are related to trends in cardiac function and can suggest an appropriate end point for intravenous fluid administration as defined by maximum CO and LVSW. PCWP did not demonstrate a significant relationship to changes in CO and LVSW.

The effect of prior dural puncture on cisternal cerebrospinal fluid morphine concentrations in sheep after administration of lumbar epidural morphine

Combined spinal epidural anesthesia has become increasingly popular as a method of providing rapid onset of analgesia or surgical block with access for further administration of analgesics or anesthetics. No in vivo studies have evaluated the relationship between dural puncture and drug transfer from the epidural space to the cerebrospinal fluid (CSF). To determine whether morphine administered in the epidural space adjacent to a dural puncture results in increased CSF concentrations at the cisterna magna (CM), 12 adult ewes were studied. Each animal was assigned to one of three groups. Animals in Group 1 served as a control and received no dural puncture. Animals in Group 2 received a dural puncture with a 25-gauge (G) Whitacre needle, while Group 3 animals received a dural puncture with an 18-G Tuohy needle. One hour after dural puncture, each animal was given epidural morphine, 0.2 mg/kg. Six hours after the administration of epidural morphine, CSF from the CM was sampled and analyzed by gas chromatography-mass spectrometry for morphine concentration. The mean morphine concentration at the CM for Group 1 (control) was 22 +/- 12 ng/mL, whereas animals with 25-G and 18-G dural punctures had concentrations of 154 +/- 32 ng/mL and 405 +/- 53 ng/mL, respectively (P = 0.0005). These data demonstrate that a significant increase in CSF morphine concentration at the brainstem will occur when lumbar epidural morphine is administered adjacent to a dural puncture. Furthermore, the increase in CSF morphine concentration is positively correlated with the size of the needle producing the dural puncture. These findings highlight the potential for delayed respiratory depression when epidural opiate administration follows a dural puncture.

A comparison of topical and retrobulbar anesthesia for cataract surgery

PURPOSE

To evaluate and compare the efficacy of topical and retrobulbar anesthesia for cataract extraction with intraocular lens implantation.

METHODS

One hundred thirty-eight patients prospectively were assigned to the topical (group 1; n = 69) or retrobulbar (group 2; n = 69) anesthesia groups by permuted block restricted randomization. Group 1 received topical 0.75% bupivacaine and intravenous midazolam and fentanyl for anesthesia. Group 2 received intravenous methohexital followed by retrobulbar block with an equal mixture of 2% lidocaine and 0.75% bupivacaine plus hyaluronidase (150 U). A visual pain analogue scale was used to assess the degree of pain during the administration of anesthesia, during surgery, and post-operatively. The degree to which eye movement, touch, and light caused patient discomfort was assessed. Complications and surgical conditions were recorded.

RESULTS

There was no difference in the surgical conditions (P = 0.5) or pain during surgery (P = 0.35) between the two groups. There was more discomfort during administration of topical anesthesia (P < 0.0001) and postoperatively (P < 0.05) in the topical group. Chemosis, subconjunctival hemorrhage, and eyelid hemorrhage were seen almost exclusively in the retrobulbar group. One patient in group 2 had a retrobulbar hemorrhage. Although eyeball movement and squeezing of the eyelids were present more frequently in the topical group, neither was a problem to the surgeon.

CONCLUSION

Topical anesthesia can be used safely for cataract extraction. The degree of patient discomfort is only marginally higher during administration of the anesthesia and postoperatively. However, surgical training and patient preparation are the keys to the safe use of topical anesthesia.

Cardiovascular responses to graded doses of three catecholamines during lactic and hydrochloric acidosis in dogs

We have studied the cardiovascular effects of incremental doses of three catecholamines in dogs subjected to lactic (LAC) and hydrochloric (HCl) acidosis. Fifty-four dogs were allocated randomly to one of three groups: control, LAC and HCl acidosis (n = 18 each group). In the acidotic models, 2 mol litre-1 of lactic acid (4 ml kg-1 h-1) or 2 mol litre-1 of HCl (1 ml kg-1 h-1) was infused i.v. until arterial pH was reduced to 7.00 +/- 0.1. Within each group, six dogs received one of three different drugs in logarithmically incremental doses: adrenaline 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 micrograms kg-1 min-1, noradrenaline 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 micrograms kg-1 min-1 and dobutamine 5, 10, 20, 40, 80, 160 micrograms kg-1 min-1. Cardiovascular variables were monitored, with periodic measurements of plasma electrolyte and lactate concentrations. The pH reduction induced by HCl or lactic acid was associated with a statistically significant increase in mean pulmonary arterial pressure (MPAP), prominent especially in the LAC group where MPAP increased from mean 18 (SD 5) to 27 (6) mm Hg. In the acidotic models, the reduction in myocardial responsiveness to adrenaline or noradrenaline was more prominent than that for the control for corresponding doses of drugs. In the LAC group mean cardiac index decreased significantly from 5.2 (1.8) to 2.2 (0.7) litre min-1 m-2 after infusion of adrenaline 3.2 micrograms kg-1 min-1 and decreased from 5.1 (1.1 to 2.4 (0.9) litre min-1 m-2 after infusion of noradrenaline 3.2 micrograms kg-1 min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Buccal absorption of fentanyl is pH-dependent in dogs

BACKGROUND

Analgesia and sedation have been achieved noninvasively by fentanyl administration through the oral and nasal mucosa. In theory, the transmucosal bioavailability and absorption of fentanyl could be improved by converting more fentanyl to the unionized form by adjusting the surrounding pH. The authors tested this hypothesis in dogs.

METHODS

Under general anesthesia, each of six mongrel dogs was given fentanyl on repeated occasions, first intravenously (once), then by application to the buccal mucosa (six times). Buccal fentanyl administration was accomplished by placement of a pH-buffered solution of fentanyl into a specially constructed cell, which was clamped to the dog's buccal mucosa for 60 min. Fentanyl solutions with pHs of 6.6, 7.2, and 7.7 were studied to span a tenfold difference in the unionized fraction of fentanyl. Femoral arterial blood samples were sampled frequently and analyzed for fentanyl using a radioimmunoassay. Peak plasma concentration and the time of its occurrence for each buccal study were noted from the plasma concentration verses time profile. Terminal elimination half-life, bioavailability, and permeability coefficients were calculated using standard pharmacokinetic techniques.

RESULTS

The variables peak plasma concentration, bioavailability, and permeability coefficient increased three- to fivefold as the pH of the fentanyl buccal solution increased and more fentanyl molecules became unionized. There was no difference in terminal elimination half-life after intravenous fentanyl (244 +/- 68 min) or buccal fentanyl administration (pH 7.7, 205 +/- 89 min; pH 7.2, 205 +/- 65 min; pH 6.6, 196 +/- 48 min). In all buccal studies regardless of pH, time to peak plasma concentration occurred within 10 min of removal of the fentanyl solutions from the buccal mucosa.

CONCLUSIONS

The buccal absorption, bioavailability, and permeability of fentanyl are markedly increased as the pH of the fentanyl solution becomes more basic. Most likely, this is because of an increase in the fraction of unionized fentanyl.

Comparison of methohexital and alfentanil on movement during placement of retrobulbar nerve block

We compared the use of methohexital (0.5 mg/kg) with alfentanil (20 micrograms/kg) as a drug for limiting movement and pain during the placement of a retrobulbar block (RBB). Thirty patients (ASA class I-III) were randomly assigned to receive either methohexital or alfentanil (15 patients in each group). All but two patients (87%) treated with alfentanil were awake and responsive to command. All of the patients given methohexital were unresponsive at the time of block placement. However, less movement was observed when patients were treated with alfentanil compared to methohexital (P < 0.0002). None of the patients treated with alfentanil complained of pain during placement of the RBB. No difference was detected in the incidence of respiratory depression. However, one patient who received alfentanil had a prolonged period of apnea (approximately 30 s) with a significant decrease in oxygen saturation. The incidence of nausea and vomiting and the time to discharge from the outpatient department were similar in the two groups. The results of this study suggest that alfentanil may be used as a single drug to limit movement during placement of retrobulbar block for ophthalmic surgery.

Respiratory-related critical events with intravenous patient-controlled analgesia

OBJECTIVE

The objective of this study was to identify the underlying causes of respiratory-related critical events associated with intravenous patient-controlled analgesia (i.v. PCA).

DESIGN

The design is an observation study of prospectively collected data.

SETTING

An Acute Pain Service (APS) was established for the management of all patients receiving i.v. PCA therapy for pain management. As part of ongoing care, all respiratory-related critical events were documented and analyzed by staff members of the APS team.

PATIENTS

All patients receiving i.v. PCA therapy through the APS during the period of May 1990 through October 1992 were enrolled in the study.

INTERVENTIONS

Evaluation of all respiratory-related critical events was attempted to identify the underlying cause of the event and to determine if measures could be taken to prevent recurrence of similar events.

OUTCOME MEASURES

Any clinical event that could have or did lead to adverse patient outcome was used as an outcome measure.

RESULTS

A total of 3,785 patients received PCA therapy for a total of 11,521 patient care days. Fourteen critical events occurred, of which four led to increased patient care. There were eight programming errors (all involving misprogramming of the continuous infusion): three involved a family member activating the device, three were the result of an error in clinical judgment, and one involved a patient tampering with the device (one event involved more than one error). Of the four events that led to increased patient care, two involved a family member activating the device, one was the result of a programming error, and one was the result of an error in clinical judgment. All patients who experienced a critical event had an uneventful recovery.

CONCLUSIONS

Following review of the critical events, it was determined that the design of the PCA device contributed to the misprogramming errors and the device was removed from service. Changes in the training of physicians and nurses were instituted to avoid recurrence of other errors identified. The incidence of serious respiratory-related critical events was 0.1%. i.v. PCA therapy has the risk of potentially serious complications and requires constant physician and nursing care with an active quality assurance program.

Randomized clinical trial of pressure-controlled inverse ratio ventilation and extracorporeal CO2 removal for adult respiratory distress syndrome

The impact of a new therapy that includes pressure-controlled inverse ratio ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from other published survival rates after extracorporeal CO2 removal. Mechanical ventilation patient group survival was significantly higher than the 12% derived from published data (p = 0.0001). Protocols controlled care 86% of the time. Average PaO2 was 59 mm Hg in both treatment groups. Intensity of care required to maintain arterial oxygenation was similar in both groups (2.6 and 2.6 PEEP changes/day; 4.3 and 5.0 FIO2 changes/day). We conclude that there was no significant difference in survival between the mechanical ventilation and the extracorporeal CO2 removal groups. We do not recommend extracorporeal support as a therapy for ARDS. Extracorporeal support for ARDS should be restricted to controlled clinical trials.

Dose-response pharmacology of intrathecal morphine in human volunteers

BACKGROUND

Intrathecal morphine sulfate (ITMS) administration was introduced into clinical practice in 1979. Inadequate information exists delineating ITMS respiratory effects in the dosage range most frequently employed today. This study evaluated 0.2, 0.4, and 0.6 mg ITMS in male volunteers.

METHODS

Twenty healthy, young, adult male volunteers received 0.0, 0.2, 0.4, or 0.6 mg preservative-free ITMS in an isobaric solution administered at the L3-L4 interspace in a double-blind randomized fashion. Respiratory function was assessed by finger pulse oximetry (SpO2), respiratory rate, and arterial blood gas analysis via an indwelling arterial catheter and the slope of the ventilatory response to carbon dioxide (VE/CO2). Analgesia was assessed by the effect of ITMS on moderate pain produced by pressure algometry at the tibia. The need for supplemental oxygen, 2 L/min via nasal cannulae, was determined by the failure of verbal and tactile prompts to maintain subjects' SpO2 > or = 85% on more than two occasions. Heart rate, arterial blood pressure, sedation level, pupil size, and the incidence of adverse effects also were documented. All the above measurements were made before and 30 min after ITMS, hourly for 11 h, and then every 2 h for 12 more h.

RESULTS

ITMS produced significant dose-related decreases in SpO2. Mild desaturations (SpO2 > or = 85 and < 90%) occurred in 2 of 5, 3 of 5, and 4 of 5 subjects receiving 0.2, 0.4, and 0.6 mg ITMS, respectively. Moderate to severe desaturations (SpO2 < 85%) occurred in 0 of 5, 2 of 5, and 4 of 5 subjects receiving 0.2, 0.4, and 0.6 mg ITMS, respectively. The need for supplemental oxygen also was significantly related to ITMS dose, with 0 of 5, 1 of 5, and 4 of 5 subjects requiring oxygen after 0.2, 0.4, and 0.6 mg ITMS, respectively. Nasal oxygen administration consistently alleviated hypoxemia. Increases in arterial carbon dioxide tension (PaCO2) and decreases in pH were significantly related to ITMS dose. Peak mean PaCO2s were 42.4, 44.9, and 50.7 mmHg in the 0.2-, 0.4-, and 0.6-mg groups, respectively. These peaks occurred 6.5-7.5 h after ITMS injection. ITMS produced significant dose-related depression of VE/CO2. Maximum mean depressions of VE/CO2 were to 61%, 63%, and 32% of baseline in the 0.2-, 0.4-, and 0.6-mg groups, respectively. These nadirs occurred 3.5-7.5 h after ITMS injection. Some subjects receiving 0.6 mg ITMS experienced profound (< 20% of baseline) and prolonged (< 50% of baseline for up to 20 h) VE/CO2 depression. Magnitude and duration of analgesia after ITMS were dose-related. Changes in heart rate, systolic blood pressure, and respiratory rate were not significantly related to ITMS dose. Hypoxemia was not related to respiratory rate. Although ITMS produced statistically significant dose-related increases in sedation and decreases in pupil size, these changes were small and did not coincide with hypoxemia. ITMS caused dose-related increases in emesis, but the severity of pruritus and urinary retention was unrelated to dose.

CONCLUSION

ITMS produced dose-related analgesia and respiratory depression in nonsurgical healthy, young, adult male volunteers. Respiratory depression was significant after 0.2 or 0.4 mg and profound and prolonged after 0.6 mg. No clinical signs or symptoms, including respiratory rate, reliably indicated hypoxemia. Pulse oximetry reliably detected hypoxemia after ITMS, and supplemental nasal oxygen (2 L/min) effectively corrected this hypoxemia.

Oral transmucosal fentanyl citrate (OTFC) for the treatment of postoperative pain

Oral transmucosal fentanyl citrate (OTFC) has been used in a variety of clinical situations. This study was designed to determine if OTFC could provide analgesia to patients with acute pain after major surgery. Following written informed consent, 38 ASA Physical Status I-III patients undergoing either a total hip replacement or total knee arthroplasty were studied prospectively. The patients were randomly allocated to receive either OTFC (7-10 micrograms/kg) or a placebo identical in appearance to an OTFC unit. General anesthesia was administered for surgery, and patient-controlled analgesia (PCA) with morphine was initiated in all patients. The PCA interval dose was adjusted to provide adequate analgesia as determined by the patient and physician; the PCA lock-out time was not changed. On the morning after surgery, the most recent 12 h of PCA data (milligrams per hour of morphine and PCA attempts per hour) were recorded. OTFC or placebo units were administered at times 0, 4, and 8 h during a 12-h study, resulting in three identical units being completely consumed. PCA data, as well as incidence and severity of any adverse side effects, were recorded during the study and for the next 12 h. Treatment groups were compared for similarity, and study variables were analyzed. Twenty-eight patients completed the study, 13 in the control group and 15 in the OTFC group. There were no significant differences between the study groups as to patients' age, gender, ASA classification, or surgical procedure. In addition, there were no differences between the groups in the number of PCA attempts or delivered dose of morphine during the prestudy or poststudy periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetic techniques during surgical repair of femoral neck fractures. A meta-analysis

Fracture of the hip typically occurs in older women. These patients usually have serious accompanying chronic illnesses. There is a difference of opinion as to the choice of regional versus general anesthesia for surgery in these patients. This meta-analysis compared survival of patients with traumatic femoral neck fractures undergoing operative repair during regional or general anesthesia. The data sources were articles comparing regional and general anesthesia from peer reviewed journals. Thirteen randomized controlled trials were found. Besides 1-month mortality, variables used were estimated operative blood loss and the incidence of deep venous thrombosis. For dichotomous outcomes, two effect measures were calculated: the difference in probabilities and the odds ratio. For blood loss, a continuous variable, the effect measure was the mean difference in blood loss. A random-effects Bayesian meta-analysis was used to combine study data, estimate parameters and create 95% confidence intervals. Only the incidence of deep venous thrombosis was clearly greater for patients receiving general anesthesia, being 31 percentage points higher than for patients receiving regional anesthesia. By the odds ratio, deep venous thrombosis was almost four times more likely following general anesthesia. There was no difference in estimated operative blood loss. By probability difference, mortality was a non-significant 2.7 percentage points less following regional anesthesia. By odds ratio effect measure, death was 1.5 times more likely following general anesthesia, but the lower bound of the 95% confidence interval was close to 1. Meta-analysis does not allow a conclusion that important differences in mortality exist between regional and general anesthesia for traumatic hip fracture surgery.

Fentanyl and sufentanil increase intracranial pressure in head trauma patients

Although opioids frequently are administered to patients with severe head trauma, the effects of such drugs on intracranial pressure are controversial. Nine patients with severe head trauma were studied for the effects of fentanyl and sufentanil on intracranial pressure (ICP). In all patients, ICP monitoring was instituted before the study. Full neuromuscular blockade was achieved with vecuronium bromide before the administration of either fentanyl (3 micrograms.kg-1) or sufentanil (0.6 microgram.kg-1) as an intravenous bolus over a 1-min period in a masked and random fashion. Patients received the other opioid in the same fashion 24 h later. Arterial blood pressure, heart rate, and ICP were recorded continuously for the 1 h after drug administration. Fentanyl was associated with an average ICP increase of 8 +/- 2 mmHg, and sufentanil with an increase of 6 +/- 1 mmHg. These increases were statistically significant. Both drugs produced clinically mild decreases in mean arterial blood pressure (fentanyl, 11 +/- 6 mmHg; sufentanil, 10 +/- 5 mmHg) that nevertheless were statistically significant. No significant changes in heart rate occurred. These results indicate that modest doses of potent opioids can significantly increase ICP in patients with severe head trauma.

Technology assessment of anesthesia monitors

This essay argues that optimal utilization of anesthesia monitors requires careful technology assessment. This careful assessment is important because monitors may produce spurious or uninterpretable values, or they may damage patients. In addition, resources should be spent only for truly beneficial devices. The types of evidence that this essay describes for use in technology assessment include questions concerning data reliability, data interpretability, and data outcome. Considerable evidence bearing on technology assessment has already been amassed. I propose synthesizing this evidence by meta-analysis. Additional primary studies of technology assessment are also needed.

Iontophoretic delivery of morphine for postoperative analgesia

Iontophoresis is a method of transdermal administration of ionized drugs in which electrically charged molecules are propelled through the skin by an external electrical field. This was a prospective, randomized, single-blind study to determine the effectiveness of iontophoretically delivered morphine HCl for the control of postoperative pain. Thirty-eight patients who underwent total knee or hip replacement completed this clinical trial. Informed consent was obtained before surgery and patients were instructed on the use of a patient-controlled analgesia (PCA) device. Postoperatively, pain in the recovery room was initially controlled with IV meperidine, and thereafter with PCA therapy using meperidine, 2 mg/cc, with a dose of 10 mg IV and a lock-out period of 15 min. The dose was adjusted as necessary and the lock-out period remained the same. The number of patient requests and the dose (mg) administered was recorded hourly. On the morning following surgery, iontophoresis devices were attached for 6 hr to patients who received either morphine HCl or lactated ringers solution. During this period and for 12 hr following completion of iontophoresis, PCA analgesia remained available to patients. Venous blood samples for determination of morphine levels were obtained every 30 min during iontophoresis, then every 60 min for 2 hr following iontophoresis. Of the 38 patients, 17 received iontophoresed morphine, and 21 received iontophoresed lactated ringers. The morphine group utilized the PCA device more than the control group during the baseline period. However, following the institution of iontophoresis and continuing up to 12 hr following completion of iontophoresis, the morphine group used significantly less PCA meperidine to maintain analgesia than the control group (p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Knowledge engineering using retrospective review of data: a useful technique or merely data dredging?

The process of extracting the knowledge or rules for medical decision making is not an easy task. One approach to knowledge engineering is to carefully review how decisions were made in the past with the goal of extracting the rules. The purpose of this project was to use previously collected data from ICU patients to derive the rules for the definition of hemodynamic stability. 97 ICU patients between 9/9/86 and 7/29/90 were included in the analysis. All of these patients had adult respiratory distress syndrome. Their mechanical ventilation was managed by a set of computerized protocols. We retrospectively searched the HELP system database for instructions that were not followed due to hemodynamic reasons. For each patient, we also chose one randomly selected therapy instruction which was followed to act as a control. For each instruction we then selected the corresponding hemodynamic data set. The data was then used in a stepwise logistic regression to determine the rules used for defining hemodynamic instability. We found that several of the hemodynamic parameters we had anticipated to be important were not even measured most of the time. The blood pressures and heart rate were almost identical between the hemodynamicly stable and unstable data sets. We conclude that the decision making process used by physicians has great variation, both between and within physicians. This makes knowledge engineering using retrospective techniques such as this prone to error and probably not very fruitful.

Simultaneous comparison of intraarterial, oscillometric, and finapres monitoring during anesthesia

In 30 patients (15 with normal peripheral vascular status and 15 with peripheral vascular disease, hypertension, or a heavy smoking history), systolic, mean, and diastolic arterial pressures were recorded simultaneously every 5 min using a radial arterial catheter, an oscillometric arm cuff, and a Finapres finger cuff during 1-6 h of anesthesia and operation. The average accuracy of oscillometric and Finapres pressure measurements was good. Comparisons of arterial, oscillometric, and Finapres pressures showed only a small bias in the oscillometric and Finapres pressure estimations. Finapres pressures underestimated arterial pressures by 1 mm Hg more than oscillometric pressures did. Peripheral vascular status had no effect on comparisons made between pressures measured with these two techniques. Although bias was small, precision was often lacking as shown by the large variability of the difference between individual values from the three monitors. However, the precision of Finapres pressure measurements was about the same order of magnitude as that of oscillometric measurements.

Respiratory effects of clonidine alone and combined with morphine, in humans

Because only limited and controversial data exist concerning the respiratory effects of clonidine in humans, the authors evaluated the respiratory effects of clonidine alone and in combination with morphine, in 12 healthy adult males. Subjects received clonidine (0.3-0.4 mg orally), morphine (0.21 mg/kg intramuscularly), or the same doses of the two drugs combined, at three separate sessions in a randomized fashion. The study was balanced for all possible sequences of drug administration. Blood pressure, heart rate, hemoglobin oxygen saturation via finger pulse oximetry, and ventilatory and occlusion pressure responses to CO2 were obtained before and 20, 40, 60, 90, 120, 180, 240, 300, and 360 min after administration of drug or drug combination. Systolic blood pressure decreased significantly only in the clonidine and clonidine plus morphine groups (P less than 0.05). Hemoglobin oxygen saturation decreased by a statistically significant (P less than 0.05), though clinically minor, degree only in the morphine or morphine plus clonidine groups. Clonidine alone did not depress the slope of either the ventilatory or the occlusion pressure response to CO2. In addition, clonidine did not significantly worsen morphine-induced depression of the slope of the ventilatory and occlusion pressure responses in the drug combination group. Both the ventilatory and occlusion pressure responses to CO2 were shifted to the right in all three drug groups (P less than 0.05) but were shifted to a significantly lesser degree by clonidine alone than by morphine and morphine plus clonidine. In healthy young adult males, clonidine alone produces little respiratory depression and does not significantly potentiate morphine-induced respiratory depression.

Oral transmucosal fentanyl citrate for premedication in paediatric outpatients

Two doses (10-15 micrograms.kg-1, Group I, and 15-20 micrograms.kg-1, Group II) of oral transmucosal fentanyl citrate (OTFC) plus a placebo (Group III) were evaluated for premedication in 105 healthy children, aged 2 to 13 yr, undergoing short (less than 1 hr) operations in the hospital short-stay unit. The study was randomized and double-blinded and 91 of the 105 children also received droperidol, 25 micrograms.kg-1 IV, after induction of anaesthesia with halothane and N2O in oxygen. Both doses of OTFC produced significantly greater sedation (first present at 20 min) and anxiolysis (first present in Group I at 40 min) than the placebo. Recovery times were similar in the three groups and analgesic requirements in the recovery room were significantly lower in Group I than Group III. Both OTFC groups took longer to tolerate oral fluids in the postoperative discharge unit than the placebo group and this caused patients in Group I to have a delayed discharge from the hospital compared to Group III. Preoperative pruritus occurred significantly more frequently in Groups I and II (58 and 76 per cent, respectively) than Group III (23 per cent). Although the incidences of nausea and vomiting tended to be slightly higher in the OTFC groups in the preoperative holding and postoperative discharge units, the differences among the groups were not statistically significant. Likewise droperidol did not reduce the incidence of postoperative nausea or vomiting. The data indicate that OTFC may be a safe and effective premedicant in paediatric patients having short operations but delays discharge from the hospital (by 30-50 min) by delaying the time patients tolerate fluids early after operation.

Frequent hypoxemia and apnea after sedation with midazolam and fentanyl

More than 80 deaths have occurred after the use of midazolam (Versed), often in combination with opioids, to sedate patients undergoing various medical and surgical procedures. We investigated the respiratory effects of midazolam (0.05 mg.kg-1) and fentanyl (2.0 micrograms.kg-1) in volunteers. The incidence of hypoxemia (oxyhemoglobin saturation less than 90%) and apnea (no spontaneous respiratory effort for 15 s) and the ventilatory response to carbon dioxide were evaluated. Midazolam alone produced no significant respiratory effects. Fentanyl alone produced hypoxemia in half of the subjects and significant depression of the ventilatory response to CO2, but did not produce apnea. Midazolam and fentanyl in combination significantly increased the incidence of hypoxemia (11 of 12 subjects) and apnea (6 of 12 subjects), but did not depress the ventilatory response to CO2 more than did fentanyl alone. Adverse reactions linked to midazolam and reported to the Department of Health and Human Services highlight apnea- and hypoxia-related problems as among the most frequent adverse reactions. Seventy-eight per cent of the deaths associated with midazolam were respiratory in nature, and in 57% an opioid had also been administered. All but three of the deaths associated with the use of midazolam occurred in patients unattended by anesthesia personnel. We conclude that combining midazolam with fentanyl or other opioids produces a potent drug interaction that places patients at a high risk for hypoxemia and apnea. Adequate precautions, including monitoring of patient oxygenation with pulse oximetry, the administration of supplemental oxygen, and the availability of persons skilled in airway management are recommended when benzodiazepines are administered in combination with opioids.

Transdermal scopolamine reduces nausea and vomiting after outpatient laparoscopy

The authors evaluated the effect of transdermal scopolamine on the incidence of postoperative nausea, retching, and vomiting after outpatient laparoscopy in a double-blind, placebo-controlled study. A Band-Aid-like patch containing either scopolamine or placebo was placed behind the ear the night before surgery. Anesthesia was induced with fentanyl (0.5-2 micrograms/kg iv), thiopental (3-5 mg/kg iv), and succinylcholine (1-1.5 mg/kg iv) and maintained with isoflurane (0.2-2%) and nitrous oxide (60%) in oxygen. Scopolamine-treated patients had less nausea, retching, and vomiting compared with placebo-treated patients (P = 0.0029). Severe nausea and/or vomiting was present in 62% of the placebo group but only 37% of those getting the scopolamine patch. Repeated episodes of retching and vomiting were also less frequent in the scopolamine group compared with the placebo group (23% vs. 41%; P = 0.0213) as was the need for additional antiemetic therapy (13% vs. 32%; P = 0.0013). Patients in the scopolamine group were also discharged from the hospital sooner (4 +/- 1.3 vs. 4.5 +/- 1.5 h; P = 0.0487). Side effects were more frequent among those patients treated with the scopolamine patch (91% vs. 45%; P less than 0.05) but were not troublesome. The authors conclude that transdermal scopolamine is a safe and effective antiemetic for outpatients undergoing laparoscopy.

Cardiovascular effects of large doses of pentamorphone in the dog

The cardiovascular effects of large doses of pentamorphone were evaluated in nine mongrel dogs basally anesthetized with sodium thiopental, 25 to 30 mg/kg, intravenously. All dogs were mechanically ventilated with 100% oxygen, and the PaCO2 was maintained between 35 and 40 mm Hg. Mean arterial pressure (MAP), central venous pressure, heart rate (HR), cardiac output (CO), pulmonary artery pressure, and pulmonary artery occluded pressure were measured, and stroke volume and systemic and pulmonary vascular resistances were calculated. Baseline measurements were obtained, then pentamorphone, 10 micrograms/mL, was given as an intravenous infusion at 2.5 micrograms/kg/min. Additional data were obtained after infusion of 25, 50, 75, 100, 125, 150, 200, 250, 300, and 350 micrograms/kg of pentamorphone. The inspired gases were then changed to 50% nitrous oxide in oxygen, and after a 20-minute equilibration period, an additional set of data was collected. Pentamorphone, 25 micrograms/kg, decreased HR 50%, MAP 65%, and CO 54%. No further changes in any measured or calculated variables were observed with additional doses of pentamorphone. The addition of 50% nitrous oxide to the inspired gas mixture had no effect on any measured or calculated hemodynamic variable. The minimal hemodynamic effects of pentamorphone in the dog suggest that further investigation into its use as an anesthetic is warranted.

Prevention of succinylcholine myalgias: a meta-analysis

Meta-analysis is a term used to describe statistical methods for evaluating a series of research reports; this analysis transcends the limitations that may be inherent in each of the individual studies summarized. Forty-five research reports of clinical trials for the prevention of myalgias after succinylcholine were assembled. Four classes of preventive drugs (nondepolarizing muscle relaxants, benzodiazepines, succinylcholine in "self-taming" doses, and local anesthetics) were reported in detail sufficient to allow for inclusion in a meta-analysis of clinical efficacy. Each study was summarized by determining the difference in the incidence of myalgias on the first postoperative day between treatment and control groups. A random-effects variance components approach was used. Seven meta-analyses were performed (atracurium, d-tubocurarine, gallamine, pancuronium, diazepam, succinylcholine in self-taming doses, and lidocaine). For each meta-analysis there was statistically significant heterogeneity among studies. Atracurium, d-tubocurarine, gallamine, pancuronium, diazepam, and lidocaine all significantly decreased the frequency of myalgias by about 30%. Succinylcholine in self-taming doses alone was not efficacious.

Differences in magnitude and duration of opioid-induced respiratory depression and analgesia with fentanyl and sufentanil

The magnitude and duration of analgesia and respiratory depression induced by fentanyl (1.0, 2.0, and 4.0 micrograms/kg) and sufentanil (0.1, 0.2, and 0.4 microgram/kg) after intravenous administration over 30 s were measured in 30 healthy young adult male volunteers divided into three groups and studied in a double-blind, randomized fashion. Each volunteer received one dose of fentanyl or sufentanil and no sooner than 48 h later, the corresponding equipotent dose of the other opioid. End-tidal CO2 and ventilatory and occlusion pressure responses to CO2 rebreathing were used to measure drug-induced respiratory effects. Analgesic effects were assessed by changes in the pain threshold to electric shock applied to the forearm. Plasma levels of fentanyl and sufentanil were measured by radioimmunoassay. Testing and sampling intervals were 5, 30, 60, 90, 120, 240, 300, and 360 min after drug administration. The magnitude and duration of depression of the ventilatory and occlusion pressure response were significantly less with sufentanil compared with fentanyl, irrespective of dose. Ventilatory and occlusion pressure responses returned to control values by 30 and 30 min, respectively, after sufentanil and by 240 and 120 min, respectively, after fentanyl. Statistically significant elevations of the pain threshold were, however, greater and longer lasting after sufentanil compared with fentanyl. Pain threshold returned to control values 180 min after sufentanil but only 90 min after fentanyl. These results suggest that sufentanil may provide better patient comfort with less respiratory depression than does fentanyl.

Automated sulfur hexafluoride washout functional residual capacity measurement system for any mode of mechanical ventilation as well as spontaneous respiration

A new sulfur hexafluoride (SF6) washout functional residual capacity (FRC) measurement system has been developed which will work with any mode of mechanical ventilation, as well as with spontaneous respiration. This system was evaluated in three different human studies. In the first two studies, the accuracy of the system was compared with He dilution and body plethysmography in 12 spontaneously breathing normal volunteers and in 12 spontaneously breathing chronic obstructive pulmonary disease (COPD) patients. In the third study, the reproducibility and efficacy of using the system in the ICU was tested in 12 adult respiratory distress syndrome (ARDS) patients who were mechanically ventilated with PEEP. In the normal volunteers, there was no significant difference between the three measurement techniques. In the COPD group, there was an overall significant difference between measurement techniques (F[2,28] = 17.18, p less than .0001) and the rank of the magnitude of the FRC measurements from lowest to highest was SF6 washout, He dilution, and body plethysmography. There was a significant difference in accuracy between the COPD and normal volunteer groups (F[2,28] = 12.24, p less than .0002). There were a total of 1,227 FRC measurements made on the 12 ARDS patients. The number of FRC measurements per patient was 102 +/- 13 (SEM). The "stable" periods were 14 +/- 2 h long and ranged from 60 min to 63.5 h. The reproducibility for all 12 patients was 188 +/- 17 ml or 11.7 +/- 0.7%. This automated SF6 washout system should make routine FRC measurements in patients who are being mechanically ventilated simple and easy to do.(ABSTRACT TRUNCATED AT 250 WORDS)

Is there central respiratory depression after intravenous administration of propranolol?

Beta-adrenergic blockers have been reported to depress central ventilatory drive. The authors investigated this possibility in a double-blind, randomized fashion in 12 healthy volunteers who received 0.1 mg.kg-1 of propranolol and normal saline intravenously at two separate study sessions. A modified Read rebreathing technique was used. Both ventilatory and occlusion pressure responses to CO2 were measured to help separate peripheral (airway) from central mechanisms. Significant beta blockade was demonstrated by statistically lower heart rate responses to CO2 rebreathing after propranolol, but not normal saline. Nevertheless, propranolol exerted no significant effect on resting end-tidal CO2 or the ventilatory and occlusion pressure responses to CO2. Although health subjects appear to have minimal alterations in their ventilatory response to CO2 after beta-adrenergic blockade, patients with airway disease may still experience significant changes in ventilation. In addition, drug interaction studies may give further insight into the presence or absence of any respiratory effects of propranolol.

Computerized management of patient care in a complex, controlled clinical trial in the intensive care unit

Acute respiratory distress syndrome (ARDS) is often not responsive to conventional supportive therapy and the mortality rate may exceed 90%. A new form of supportive care, extracorporeal carbon dioxide removal (ECCO2R), has shown a dramatic increase in survival (48%). A controlled clinical trial of the new ECCO2R therapy versus conventional continuous positive pressure ventilation (CPPV) is being initiated. Detailed care protocols have been developed by 'expert' critical care physicians for the management of patients. Using a blackboard control architecture, the protocols have been implemented on an existing hospital information system and will direct patient care and help manage the controlled clinical trial. Therapeutic instructions are automatically generated by the computer from data input by physicians, nurses, respiratory therapists, and the laboratory. Preliminary results show that the computerized protocol system can direct therapy for acutely ill patients.

Implementation of a computerized patient advice system using the HELP clinical information system

A COMputerized Patient Advice System (COMPAS) was designed to test the feasibility of using the HELP clinical information system to direct the respiratory therapy of intensive care (ICU) patients acutely ill with adult respiratory distress syndrome. A modified black-board control architecture allowed the application of knowledge in either a forward or a backward chaining mode. Expert clinicians recommended decision logic and actions for five different modes of ventilatory support. The clinical staff used COMPAS to manage the ICU ventilatory support of five patients for a total of 624 hr. During that time there were 407 decision-making opportunities. COMPAS automatically generated therapy suggestions 379 (93.1%) times and the clinical staff accepted COMPAS's recommendation in 320 (84.4%) of these cases. These results suggest that the ventilatory support of severely ill ICU patients can be managed by a clinical information system using a blackboard control architecture.

The effects of oral transmucosal fentanyl citrate premedication on preoperative behavioral responses and gastric volume and acidity in children

The authors compared the safety, efficacy, and effects on gastric volume and pH of oral transmucosal fentanyl citrate (OTFC) premedication and of placebo lollipop and no premedication in 55 children undergoing elective operations. The patients were randomly assigned to receive no premedication (group A, N = 18); OTFC containing 15-20 micrograms/kg of fentanyl citrate (group B, N = 18); or a placebo lollipop (group C, N = 19). Activity (sedation) and anxiety scores, vital signs (including systolic and diastolic arterial blood pressures, heart and respiratory rates), and pulse oximetry determined oxygen saturation were measured before and at 10-min intervals after premedication until the patients were taken to the operating room. Gastric contents were aspirated via an orogastric tube and analyzed for volume and pH after induction of anesthesia. Quality of induction and recovery were evaluated using scoring schedules; recovery times were measured and side effects recorded. OTFC was readily accepted and provided levels of sedation and anxiolysis significantly greater after 10 min than after no premedication or the placebo lollipop. Arterial blood pressures, heart rate, and oxygen saturations were not different among the three groups. In patients given OTFC, respiratory rates were significantly lower after 10 min than they were in patients having no premedication.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a replenishment type oxygen consumption monitor

This paper describes the testing of a monitor (Oxyconsumeter) which uses a replenishment technique to measure oxygen consumption (VO2). Oxygen is added to the expired gas to replace the oxygen consumed by the patient. The replenishing oxygen flow equals the patients's VO2 when the mixed replenished expired oxygen fraction equals the inspired oxygen fraction. The accuracy of the Oxyconsumeter was assessed using a N2 and CO2 dilution technique. When tested over the operating range specified by the manufacturer, the bias of the Oxyconsumeter was 1.66% of reading. The reproducibility averaged 6.96% of reading. The reproducibility did not change with VO2, FIO2 or minute ventilation. The replenishment technique has the theoretical advantage that an absolute oxygen sensor calibration is not necessary and a respiratory flowmeter is not needed. It appears, from the laboratory testing, that the Oxyconsumeter has sufficient accuracy for use in the critical care setting.

Oral transmucosal fentanyl citrate (lollipop) premedication in human volunteers

The authors determined whether fentanyl incorporated into a candy lollipop, oral transmucosal fentanyl citrate (OTFC), would cross mucosal tissues of the mouth in sufficient quantities during and after dissolution to produce sedation and/or analgesia. Associated respiratory and circulatory changes, side effects, and plasma concentrations of fentanyl were also measured. The evaluations were done in 28 adult volunteers who received fentanyl citrate in doses of 5, 4, 2, 1, and 0.5 mg in OTFC and rapidly sucked the lollipops (N = 20) or allowed them to passively dissolve (N = 8). Rapid consumption of OTFC resulted in more rapid onset of a pleasant feeling (first subjective sensation) but not more rapid onset of objective sedation or analgesia than passive dissolution. There was a significant correlation between dose of OTFC and magnitude of sedation (P less than 0.001, Spearman rank correlation = -0.82). Higher doses of OTFC produced greater and longer lasting analgesia and respiratory depression and a higher incidence of nausea and vomiting than lower doses, but pruritus (33%-87%) was not related to the dose of OTFC. Heart rate and arterial blood pressures were not changed by any dose of OTFC. The data indicate that low doses of OTFC (0.5 and 1 mg, equivalent to 5-20 micrograms.kg-1 of fentanyl citrate) produce analgesia and sedation with minimal side effects and little respiratory depression in adult volunteers and deserve further evaluation in patients.

Oral transmucosal fentanyl citrate premedication in children

The authors evaluated the safety and efficacy of four doses of oral transmucosal fentanyl citrate (OTFC) as a premedicant in 44 children about to undergo elective operations. The patients received 5-10, 10-15, 15-20, or 20-25 micrograms.kg-1 of OTFC in the holding area and had activity (sedation) scores, vital signs (including systolic and diastolic arterial blood pressures, heart, and respiratory rates), and pulse oximetry determined oxygen saturation measured before and at 15-min intervals after premedication until they were taken to the operating room. Cooperation during anesthetic induction, and quality and speed of recovery room emergence were measured and side effects noted. OTFC was readily accepted and provided significant (dose dependent) reductions in preoperative activity starting after 30 min. Onset of sedation was related to dose of OTFC but time to peak effect was not. Vital signs remained unchanged preoperatively in all groups but patients receiving 20-25 micrograms.kg-1 had oxygen saturations that were significantly lower than patients in the other groups 30 min after beginning OTFC consumption. Three of the 12 patients receiving the highest dose of OTFC experienced transient oxygen saturation less than 90% which, however, was easily treated by commands to take a breath. Anesthetic inductions were rated good or excellent in 80% of the patients and recovery times were similar irrespective of the OTFC dose. OTFC caused dose-independent preoperative pruritus in 90% or more of patients and pruritus (33%-70%), nausea (30%-58%), and vomiting (50%-83%) postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

The Utah anesthesia workstation

A prototype anesthesia workstation has been developed to demonstrate the feasibility of a computer-assisted anesthesia workplace. The workstation provides a central display of information and aids the user in controlling and monitoring the anesthesia delivery system. The anesthesiologist interacts with the workstation through a Macintosh computer, which is easy for the clinician to understand and to use. Seventeen sensors and monitors transmit information from the anesthesia delivery system to the computer. The computer monitors this information using a set of rules, evaluated once each breath, to detect changes in the delivery system. If an event is detected, the computer alerts the anesthesiologist with a diagram, a text message, and an audible warning. A laboratory test of the monitoring system was performed to see if it properly identified 26 different critical events during simulated low flow and closed circuit anesthesia. Five hundred and eight-three of 660 simulated critical events (88%) were identified with the unique and correct message. On 35 occasions, multiple messages were displayed, including the correct one. Critical events were misidentified or not detected 42 times. Eight false positive alarms occurred during the 20 h of testing; all occurred as a result of baseline drift in a single transducer. These results demonstrate that a sophisticated monitoring system can reliably diagnose specific anesthesia machine failures.