Repeated simulation-based training for performing general anesthesia for emergency cesarean delivery: long-term retention and recurring mistakes.

BACKGROUND: The percentage of women undergoing cesarean delivery under general anesthesia has significantly decreased, which limits training opportunities for its safe administration. The purpose of this study was to evaluate how effective simulation-based training was in the learning and long-term retention of skills to perform general anesthesia for an emergent cesarean delivery. METHODS: During an eight-week obstetric anesthesia rotation, 24 residents attended lectures and simulation-based training to perform general anesthesia for emergent cesarean delivery. Performance assessments using a validated weighted scaling system were made during the first (pre-test) and fifth weeks (post-test) of training, and eight months later (post-retention test). Resident's competency level (weighted score) and errors were assessed at each testing session. Six obstetric anesthesia attending physicians, unfamiliar with the simulation scenario, generated a mean attendings' performance score. The results were compared. RESULTS: At one week of training, residents' performance was significantly below mean attendings' performance score (pre-test: 135±22 vs. 159±11, P=0.013). At five weeks, residents' performance was similar to mean attendings' performance score (post-test: 159±21) and remained at that level at eight months (post-retention test: 164±16). Of the important obstetric-specific tasks, left uterine displacement was missed by 46% of residents at eight months. CONCLUSION: Following lectures and simulation-enhanced training, anesthesia residents reached and retained for up to eight months a competency level in a simulator comparable to that of obstetric anesthesia attending physicians. Errors in performance and missed tasks may be used to improve residency training and continuing medical education.

Screen-based anesthesia simulation with debriefing improves performance in a mannequin-based anesthesia simulator.

BACKGROUND: Previous investigations have established the need for improved training for management of anesthetic emergencies. Training with inexpensive screen-based anesthesia simulators may prove to be helpful. PURPOSES: We measured the effectiveness of screen-based simulator training with debriefing on the response to simulated anesthetic critical incidents. METHODS: Thirty-one 1st-year clinical anesthesia residents were randomized into 2 groups. The intervention group handled 10 anesthetic emergencies using the screen-based anesthesia simulator program and received written feedback on their management, whereas the traditional (control) group was asked to study a handout covering the same 10 emergencies. All residents then were evaluated on their management of 4 standardized scenarios in a mannequin-based simulator using a quantitative scoring system. RESULTS: The average point score for the simulator-with-debriefing group was 52.6 +/- 9.9 out of 95 possible points. The traditional group average point score was 43.4 +/- 5.9, p = .004. CONCLUSIONS: Residents who managed anesthetic problems using a screen-based anesthesia simulator handled the emergencies in a mannequin-based anesthesia simulator better than residents who were asked to study a handout covering the same problems. Computer simulations with feedback are effective as a supplement to traditional residency training methods for the management of medical emergencies.

Use of a computerized advanced cardiac life support simulator improves retention of advanced cardiac life support guidelines better than a textbook review.

OBJECTIVE: To determine whether an advanced cardiac life support (ACLS) computer simulation program improves retention of ACLS guidelines more effectively than textbook review. DESIGN: Randomized, controlled trial. SETTING: Academic medical center. PARTICIPANTS: Forty-five anesthesia residents and faculty tested 10 to 11 months after ACLS provider course training. INTERVENTION: Participants were randomized and asked to prepare for a mock resuscitation (Mega Code) with either textbooks or a computerized ACLS simulation program. MAIN OUTCOME MEASURE: Performance on a standardized Mega Code examination that required application of supraventricular tachycardia, ventricular fibrillation, and second-degree Type II atrioventricular block algorithms. Mega Code sessions were administered by an instructor who was blinded as to the subject group. The sessions were videotaped and scored by two evaluators who also were blinded as to the subject group. RESULTS: Participants who used the ACLS simulation program scored significantly higher (mean 34.9 +/- 5.0 [SD] of 47 possible points) than participants who reviewed using a textbook (29.2 +/- 4.9); p < .001. Pass-fail rates for the algorithms were also higher for the group that reviewed with the simulator (mean 2.5 +/- 0.5 of 3 possible passes) than the group that used the textbook (1.6 +/- 1.0); p = .001. CONCLUSIONS: Use of a computerized ACLS simulation program improves retention of ACLS guidelines better than textbook review.

A multidimensional comparison of morphine and hydromorphone patient-controlled analgesia.

Although patient-controlled analgesia (PCA) pumps have been in use for more than a decade, the optimal PCA analgesic has yet to be identified. Many drugs are used; however, morphine remains the "gold standard" of opioid analgesics worldwide. The present study evaluated morphine and hydromorphone (Dilaudid) PCA with respect to analgesic efficacy, side effects, mood, and cognitive function. Sixty-one opioid naive patients undergoing lower abdominal surgery participated in the double-blind protocol. Verbal rating scores, use of medication, and side effects for the two medications were recorded. Cognitive functioning was assessed by computation of Digit Symbol and Trails Making B Tests. Self-reported affective state (mood) was measured by Profile of Mood States (POMS) inventory. Both medications provided adequate analgesia without a difference in side effects. Cognitive performance was poorer in the hydromorphone group (P < 0.05). Patients receiving hydromorphone reported less anger/hostility (P < 0.01) and generally better mood elevations on the other subscales than those receiving morphine. A similar incidence of side effects and dose medication can be anticipated with morphine and hydromorphone. When considering cognitive effects, morphine had less adverse consequences, while hydromorphone appeared to result in improved mood. We conclude that hydromorphone may provide a suitable alternative to morphine.

Buffered local anesthetics and epinephrine degradation.

Lidocaine with epinephrine is currently the most common local anesthetic agent used for facial soft tissue surgery. This combination is generally safe and effective in providing complete anesthesia and adequate hemostasis. Because epinephrine is unstable at physiologic pH, the commercial preparation is formulated with a low pH (3.5-5.5). Unfortunately, this acidic pH causes significant pain during infiltration. To reduce pain, clinicians sometimes buffer acidic local anesthetic agents with sodium bicarbonate. However, little is known about the stability of epinephrine when the pH of epinephrine is clinically altered. Using high pressure liquid chromatography (HPLC), epinephrine levels were measured after the addition of sodium bicarbonate. Our results indicate a significant amount of epinephrine degradation occurs in some of these specimens. Recommendations regarding the use of buffered local anesthetic agents are made.

Local anesthetic distribution in a spinal model: a possible mechanism of neurologic injury after continuous spinal anesthesia.

BACKGROUND AND OBJECTIVES: Cauda equina syndrome has been reported recently in patients receiving continuous spinal anesthesia using newly developed microcatheters (28 gauge). Failure of microcatheters to allow adequate mixing of local anesthetic was studied as a possible mechanism of the neurologic injury reported with these catheters. METHODS: A spinal canal model was developed and the distribution of hyperbaric lidocaine was measured after injection through catheters typically used for continuous spinal anesthesia (i.e., 20, 28, and 32 gauge). RESULTS: Lidocaine distribution was less uniform and lidocaine concentration and osmolarity in the dependent portions of the model were significantly higher after injection through microcatheters compared to the 20-gauge catheter. CONCLUSIONS: Dependent drug concentrations were greater than those reported in the literature, capable of producing permanent neurologic injury. Directing the catheter tip in the nondependent direction and injecting lidocaine rapidly or through catheters with multiple end holes improved mixing and decreased dependent drug concentration.

Sprotte needle for obstetric anesthesia: decreased incidence of post dural puncture headache.

BACKGROUND AND OBJECTIVES: Reports have emphasized the importance of spinal needle tip configuration in the development of post dural puncture headache (PDPH). METHODS: Charts from 366 consecutive obstetric patients receiving spinal anesthesia for labor, cesarean delivery, postpartum surgical procedures, or postpartum tubal ligations were reviewed retrospectively for evidence of PDPH in the five days after dural puncture. Spinal anesthesia was administered to these patients using 25-gauge Quincke (n = 74), 26-gauge Quincke (n = 160), or 24-gauge Sprotte (n = 132) spinal needles. RESULTS: The groups were well matched demographically. The incidence of PDPH in the three groups was 9%, 8%, and 1.5%, respectively. Half of the patients developing PDPH in each group were treated with an epidural blood patch. CONCLUSIONS: Our data indicate that the Sprotte spinal needle, with its non-cutting tip, results in a significantly lower (p less than 0.05) incidence of PDPH than Quincke cutting-tip needles of smaller gauge.

Fetal heart rate variability and cerebral oxygen consumption in fetal sheep during asphyxia.

This study was designed to examine the relationship between fetal heart rate variability and fetal cerebral oxygen uptake. Fetal sheep were chronically prepared with catheters and electrodes to determine cerebral blood flow (microsphere method), cerebral arteriovenous oxygen difference, and the electrocardiogram. An adjustable occluder was placed on the maternal common internal iliac artery to induce fetal asphyxia by reducing uterine blood flow. Fetal heart rate variability tended to decrease in the first 11 min of asphyxia, when cerebral oxygen consumption was approximately 53% of control. Despite stable cerebral oxygen consumption and worsening metabolic acidosis, however, fetal heart rate variability progressively returned towards normal by 36 min. There was no relationship between the depression of FHR variability and the degree of reduction of cerebral oxygen consumption. Nor was there any relationship between an alteration in regional cerebral blood flow or myocardial blood flow and the return of FHR variability with increasing duration of asphyxia. We conclude that there is an association between loss of fetal heart rate variability and reduced cerebral oxygen consumption, but the reduced variability does not persist with time at this degree of reduced cerebral metabolism in fetal sheep. This appears to be at variance with human clinical experience. Among the explanations for this may be insufficiently severe asphyxia, a species difference, removal of an inhibitor to FHR variability, or progressive use of other substrates for metabolism.

A comparison of postcesarean epidural morphine analgesia by single injection and by continuous infusion.

To assess the relative efficacy and incidence of side effects of a single injection versus a continuous infusion of epidural morphine sulfate (MS) in the postcesarean population, the authors report a prospective, randomized, double-blind study. Thirty-one patients received either a 5-mg MS bolus and subsequent saline infusion (n = 13) or a 2.6-mg MS bolus and subsequent MS infusion at 0.1 mg/hour (n = 18), such that after 24 hours both groups had received a total MS dose of 5 mg. No statistically significant differences were found between the two groups in overall satisfaction with analgesia, verbal pain scores, level of activity, need for supplemental opioids, or incidence of sedation during the 24-hour study period. The authors conclude that in this population, continuous epidural morphine infusion offers no obvious advantage over single morphine bolus therapy. However, the theoretical merits of continuous opioid infusion therapy are discussed.

pH-adjusted 2-chloroprocaine for epidural anesthesia in patients undergoing postpartum tubal ligation.

PIP: The effect of added sodium bicarbonate on 2-chloroprocaine epidural anesthesia in women having postpartum tubal ligation was compared to the commercial product in a double-blind, randomized study. The rationale for the comparison was the reported hastened onset of anesthesia when the pH of bupivacaine and lidocaine are raised. Anesthetic solutions were prepared no more than 20 minutes before use by adding 1 ml sterile 8.4% sodium bicarbonate or 1 ml sterile saline to 27 ml commercial product (3% solution). The pH of the commercial solution was 3.82; that of the saline diluted drug was 3.74; and the pH of the bicarbonate diluted drug was 7.08. Groups of 15 subjects received 23 ml of either diluted anesthesia by a standardized protocol. There were no differences in the matched groups in age, height, weight, or postpartum interval. There were no differences in anesthetic variables, i.e., time of onset of anesthesia, time to T4 level, time to maximum level, or duration of anesthesia, between the groups.^ieng

Regional blood flow during cardiopulmonary resuscitation in dogs using simultaneous and nonsimultaneous compression and ventilation.

We studied regional blood flow (QR) using radiolabeled microspheres and measured hemodynamic variables in 20 anesthetized dogs in normal sinus rhythm and during ventricular fibrillation treated with cardiopulmonary resuscitation (CPR). Nonsimultaneous compression and ventilation CPR (NSCV-CPR) was performed in seven dogs with a pneumatic piston that gave 50 chest compressions/min with an open airway with 10 ventilations at an airway pressure of 33 mm Hg interposed between each fifth and sixth compression. Simultaneous compression and ventilation (SCV-CPR) was performed in seven dogs with the piston and in six other dogs with a circumferential pneumatic vest. Both devices gave 30 compressions/min simultaneously with 30 ventilations that elevated airway pressure to 80 mm Hg., The abdomen was bound during SCV-CPR. Regional blood flow (mean +/- SD) to the cerebral hemispheres, cardiac ventricles, and kidneys, expressed as ml/min/100 g tissue, was 3.1 +/- 4.0, 3.4 +/- 3.3 and 1.5 +/- 1.5, respectively, during NSCV-CPR; 11.5 +/- 5.9, 4.9 +/- 4.7 and 2.7 +/- 2.7 during SCV-CPR (vest); and 16.2 +/- 7.2, 11.0 +/- 4.0 and 20.1 +/- 20.2 during SCV-CPR (piston) (all p less than 0.05 compared with NSCV-CPR). These results indicate that QR to all organs studied is reduced below normal sinus rhythm levels during CPR for ventricular fibrillation, QR to the brain is proportionately greater than QR to the heart and kidneys, and QR to the brain is greater with both forms of SCV-CPR than with NSCV-CPR.

Increased hemoglobin-oxygen affinity does not decrease skeletal muscle oxygen consumption.

The importance of hemoglobin-oxygen affinity (HOA) in affecting skeletal muscle oxygen consumption (VO2) was reevaluated using an isolated canine gracilis muscle. HOA of the blood [normal O2 half-saturation pressure of hemoglobin (P50) = 30 Torr] was increased by refrigerated storage (P50 = 22 Torr), incubation in sodium metabisulfite (P50 = 24 Torr), or in sodium cyanate (P50 = 14 Torr). Stored blood caused a significant fall in VO2 to 80% of control, with no change in venous O2 partial pressure (PvO2), substantiating previous studies. However, in contrast, blood incubated in sodium metabisulfite or sodium cyanate resulted in no impairment of VO2, with a fall in PvO2 in the latter case indicating that a critical PvO2 did not cause the reduction in VO2 with stored blood. To substantiate further the lack of existence of a critical PO2, fresh and increased HOA blood was perfused at constant flow rates and varying arterial oxygen saturations. Stored blood showed a marked reduction in VO2 as compared with normal blood over a wide range of saturations. However, carbamylated blood VO2 was identical to fresh blood VO2 values. The data suggest that the position of the oxygen dissociation curve may not be as important as originally thought in determining skeletal muscle oxygen delivery. The drop in VO2 caused by perfusion with stored blood is due to some other factor unrelated to HOA.

New developments in cardiopulmonary resuscitation.

The traditional concept of cardiopulmonary resuscitation (CPR) is that the heart is squeezed between the sternum and the spine during external cardiac massage to create a pressure gradient that forces blood from the heart to the periphery. Although the heart may actually be squeezed in some persons by this maneuver, a newer view of CPR holds that closed-chest compression produces a generalized rise in intrathoracic pressure that is applied to the pulmonary vascular bed as well as the heart. Thus, the heart does not serve primarily as a pump during external cardiac massage but instead acts as a conduit for blood from the lungs. Furthermore, flow into extrathoracic vessels depends on their tendency to remain open or to collapse: forward flow occurs across the head during CPR because a pressure gradient is developed between the carotid artery and the more compressible jugular vein. These ideas have potential clinical implications and greatly increase our understanding of the physiology of CPR.

Lack of ozone effects on oxygen hemoglobin affinity.

Ozone exposure has been shown to cause erythrocyte damage and thus may be affecting oxygen delivery by the red cell. Oxyhemoglobin affinity, heme-oxygen binding site interaction (Hill coefficient), and red cell 2,3-diphosphoglycerate concentrations were measured in a total of twenty-two New Zealand white rabbits exposed to ozone. Ozone exposures of 1 and 3 ppm for 4 hr in rabbits had no significant (P greater than .05) effect, immediate or delayed, on the parameters measured.

Comparison of cardiovascular reflexes of the newborn and adult opossum.

Neural control of the cardiovascular system was compared in the newborn and adult opossum by measuring changes in blood pressure and heart rate following carotid arterial occlusion and vagal stimulation. The percent change in blood pressure of the newborn was not significantly different from that of the adult following these procedures. This would indicate that even though the newborn opossum is incompletely developed for some time after birth, its neural development was adequate for control of the cardiovascular system.

Gas exchange abnormalities produced by venous gas emboli.

Bubbles of either He, N2 or SF6 were infused intravenously into anesthetized dogs at a rate of 0.2 ml/kg/min. Alterations in pulmonary gas exchange were quantitated by the invert gas elimination method during control, steady state infusion and resolution phases. The hypoxemia produced was predominantly due to regions of low VA/Q rather than pure shunt, and the increase in physiological dead space was due to the addition of high VA/Q regions rather than 'pure' dead space. The VA/Q distribution returned to normal within 30 minutes of stopping the He or N2 bubbles, but remained abnormal for longer periods with SF6 bubbles. The net elimination of insoluble gases (such as He or N2) was only slightly impaired by bubble emboli, provided the cardiac output remained constant. Early pulmonary edema from bubble embolization was documented by increased wet weight/dry weight ratio, but the increased lung water was not apparent on histological examination. This form of pulmonary embolus is unique in that there is a constant fraction of the vasculature blocked although any given region with embolus is undergoing continuous resportion of the bubble. This produced a partial obstruction of the affected gas exchange units which manifests as regions of high VA/Q rather than pure dead space.

Scanning electron microscopy of normoxic and hyperoxic hyperbaric exposed lungs.

Lungs from adult guinea pigs exposed to 1 ATA He-O2 with 200 mm Hg PO2 and 20 ATA He-O2 with 200, 400, and 600 mm Hg PO2 were studied with scanning electron microscopy. The appearance of normal alveoli is described. Even before pulmonary O2 toxicity became symptomatic, subtle changes occurred in the alveoli, such as an increase in macrophages and a marked increase in length of alveolar type-II cell microvilli. These changes occurred in animals exposed to 400 mm Hg PO2, heretofore considered below toxic levels. With increased toxic involvement, the number of alveolar type-II cells increased. A thick layer of material appeared in some of the alveoli, obscuring the Kohns pores and type-I and -II cell surfaces. The alveolar-capillary network with underlying erythrocytes was no longer observable. Lungs with the greatest toxic involvement possessed large numbers of macrophages encompassed by a fibrin-like matrix. The alveolar walls were broken down in many instances, and the alveoli were no longer discrete units but took on the appearance of an amorphous mass of lung tissue.