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A study of carotid sinus massage and head-up tilt table testing in patients with syncope and near-syncope.

Patients with syncope of unknown origin are commonly evaluated using several diagnostic tools. It has been suggested that there is a significant overlap between the results of head-up tilt table testing (HUT) and carotid sinus massage (CSM). We retrospectively studied the association between tilt table test results and CSM outcome in 136 patients with syncope or near-syncope who underwent both tests. Carotid sinus massage was performed prior to the tilt test, with the patient supine. The patient was then tilted to 60 degrees for up to 30 minutes. If this did not elicit a symptomatic abnormal hemodynamic response, the tilt was repeated for up to 30 minutes with intravenous isoproterenol. An abnormal response on HUT was elicited in 18% of patients and carotid sinus syndrome was diagnosed in 13%. Mild carotid sinus sensitivity was seen in 14%. Both tests were positive in 4 patients (3%; 11% of patients with a positive test). There was no significant relationship between HUT outcome and CSM result (p = 0.03). Patients with an abnormal CSM result were older (p < 0.001) and more likely to have prior cardiovascular diagnoses (p = 0.01). The opposite applied to patients with abnormal HUT (p = 0.02 and p = 0.0048, respectively). In conclusion, we did not find a concordance between HUT and CSM outcomes in patients with syncope or near-syncope of undetermined origin.

Adolescent↗

Influence of time and therapy on ventricular defibrillation in dogs.

Factors that may influence energy requirements for ventricular defibrillation include the duration of fibrillation and the mode of resuscitation. The present study assesses the effect of these influences on the energy needed for defibrillation. Dogs were anesthetized, and arterial blood pressure and Lead II of the ECG were continuously recorded. Ventricular fibrillation was electrically induced in each dog for a period of 1, 3, 5, or 9 min. Three resuscitation techniques were evaluated: precountershock artificial ventilation (AV) and closed-chest cardiac massage (CCCM); precountershock AV/CCCM and epinephrine, 1 mg IV; and countershock without preliminary AV/CCCM or epinephrine. Each animal was shocked with successive doses of 1, 2, 4, and 8 J/kg, ceasing when either electrical conversion occurred or after the maximum dose had been delivered. If defibrillation was unaccompanied by resumption of spontaneous circulation (systolic pressure greater than 60 mm Hg greater than 2 min), AV/CCCM was administered for 1 min. In general, the incidence of defibrillation was inversely proportional to the duration of fibrillation. Epinephrine had no significant effect on the energy dose needed for conversion. After 2 min of fibrillation, however, epinephrine became increasingly important for restoration of circulation. The technique of immediate countershock was effective for episodes of fibrillation limited to approximately 3 min. Regardless of therapy, for intervals of fibrillation of up to 6 min, Gompertz data curves indicated that a delivered energy of 4--5 J/kg is the approximate energy dose associated with the maximum achievable incidence of defibrillation within the limits of this experimental protocol.

Animals↗

End-tidal CO2 measurement in the detection of esophageal intubation during cardiac arrest.

Measurement of end-tidal carbon dioxide (ETCO2) has been used to detect accidental esophageal tube placement in noncardiac arrest situations. The purpose of our study was to determine whether ETCO2 measurement could distinguish tracheal from esophageal tube placement during closed-chest massage (CCM). Twelve large dogs were anesthetized, and endotracheal tubes were placed in both the trachea and the esophagus. Placement was verified by fiberoptic endoscopy. Ventricular fibrillation was induced by a 60-Hz discharge through a right ventricular pacemaker. After four minutes of cardiac arrest, CCM was initiated and continued for 20 minutes. The dogs were divided into two groups: Group A was ventilated through the tracheal tube, and group B was ventilated through the esophageal tube. Unused tubes were removed. ETCO2 was recorded continuously beginning two minutes before arrest until the end of the experiment. There were no significant between-group differences in mean arterial pressure, weight, blood loss, IV fluid volume administered, or prearrest arterial blood gases. ETCO2 differed significantly between the two groups throughout CCM (P = .001). In group A, ETCO2 ranged from 13 to 34 mm Hg (median, 20 mm Hg). In group B, ETCO2 ranged from 2 to 11 mm Hg (median, 3 mm Hg). In this experimental model, measurement of ETCO2 reliably distinguished esophageal from tracheal intubation during cardiac arrest and CCM. If confirmed in human beings, this may prove to be a quick, reliable method of detecting esophageal intubation during cardiac arrest.

Animals↗

The biphasic mechanism of blood flow during cardiopulmonary resuscitation: a physiologic comparison of active compression-decompression and high-impulse manual external cardiac massage.

STUDY OBJECTIVE: Dismal survival in patients receiving standard manual CPR provided the rationale for the investigation of alternate methods of closed-chest circulatory support. Active compression-decompression (ACD) and high-impulse CPR are alternatives to standard manual CPR. This study was designed to test the hypothesis that ACD CPR provides superior cardiopulmonary hemodynamics due to an active decompression phase when compared with high-impulse manual CPR. PARTICIPANTS: Hemodynamics were studied during ACD and high-impulse CPR in eight adult beagles. DESIGN: Four animals were chronically instrumented and four were studied acutely. In an additional four animals, ACD was compared with sham ACD CPR. Each CPR technique was performed sequentially for 2 minutes, in random order, at a rate of 120, 50% duty cycle, and 1.5 to 2.0 in of compression depth. Measurements obtained included aortic, right atrial, left ventricular, and coronary perfusion pressures (in mm Hg); pulmonary artery flow, and left ventricular dimension. RESULTS: ACD maximized cardiopulmonary hemodynamics, including coronary perfusion pressure and stroke volume, compared with both high-impulse manual and sham ACD CPR. ACD CPR also increased left ventricular pressure change per unit time during decompression, and these changes correlated well with left ventricular volume changes. CONCLUSION: In the intact dog, ACD CPR generates physiologically and statistically superior hemodynamics when compared with high-impulse manual CPR. Improved blood flow seems to be related to more efficient ventricular filling and emptying. These findings emphasize the biphasic nature of CPR and the importance of active decompression.

Animals↗

Insertion of the minimally invasive direct cardiac massage device (MIDCM): training on human cadavers.

OBJECTIVE: Recently, a new device for minimally invasive direct cardiac massage (MIDCM) has been developed. In animal models of cardiopulmonary resuscitation MIDCM has been shown to provide better organ perfusion than external chest compressions (ECC) massage. Since this device has been developed to improve cardiopulmonary resuscitation in humans, its use must be simple. Thus, we measured the time required for the insertion of the MIDCM device on human cadavers. DESIGN: After a 1 h theoretical course, physicians and surgeons were asked to use the MIDCM device on human cadavers. We measured the time from the cutaneous incision to the first direct cardiac compression. MAIN RESULTS: The mean time required for the insertion of the MIDCM device was 16+/-11 s (range 8-58 s). The insertion time required for each group of physicians were as follows, 15+/-8 s for anaesthesiologists (range 8-28 s), 11+/-2 s for cardiac surgeons (range 9-15 s), 42+/-14 s for cardiologists (range 27-58 s), and 12+/-4 s for intensive care physicians (range 8-18). All participants compared the insertion of the MIDCM device favorably with the insertion of a chest drain. CONCLUSION: The MIDCM device can be placed in a few seconds in human cadavers by physicians familiar with chest drain insertion. Theoretical course and training with the device may be useful especially for those who are not familiar with chest drain insertion.

Cadaver↗

The effects of methoxamine and epinephrine on survival and regional distribution of cardiac output in dogs with prolonged ventricular fibrillation.

This study compares the effects of methoxamine, a pure alpha 1-agonist, and epinephrine on cerebral and myocardial blood flow, central hemodynamics, and survival in a randomized placebo-controlled fashion during prolonged ventricular fibrillation (VF) in a canine model. Twenty-four anesthetized and ventilated adult mongrel dogs were instrumented for regional blood flow determinations using radio-labeled microspheres. The dogs were randomized to receive either 20 mg of methoxamine as a single intravenous bolus or repeated boluses of 0.02 mg/kg of epinephrine, 0.2 mg/kg of epinephrine, or normal saline solution placebo beginning at three minutes following induction of VF and initiation of closed chest cardiac massage (CCCM). Organ blood flow measurements were determined during normal sinus rhythm and after five and 20 minutes of VF. All six dogs receiving methoxamine were successfully resuscitated in contrast to only one in each of the epinephrine-treated groups and none of the dogs receiving placebo (p less than .01). Although epinephrine was associated with significantly higher blood pressures than placebo during cardiopulmonary resuscitation (CPR), blood pressures achieved with methoxamine were significantly higher than those observed in the other three treatment groups (p less than .001). Cerebral blood flow was significantly higher with both methoxamine and high-dose epinephrine (p less than .05). Mean left and right ventricular myocardial flows were highest with methoxamine but this did not achieve statistical significance. In contrast, organ flows measured in the animals receiving the lowest dose of epinephrine were not significantly higher than those associated with placebo. Cardiac output after 20 minutes of CPR was significantly lower with high-dose epinephrine than with methoxamine or placebo (p less than .05). Our results suggest that methoxamine significantly improves regional cerebral blood flow and survival during CPR and although high-dose epinephrine is associated with comparable improvements in regional cerebral blood flow, this treatment is associated with deterioration in central hemodynamics during prolonged VF and does not enhance survival.

Animals↗

Effects of epinephrine and norepinephrine on cerebral oxygen delivery and consumption during open-chest CPR.

The effect of epinephrine and norepinephrine on cerebral oxygen delivery and consumption after five minutes of cardiopulmonary arrest and three minutes of open-chest cardiac massage was studied in 21 pigs. Norepinephrine, like epinephrine, has a marked alpha- and beta 1-sympathomimetic activity, but compared with epinephrine, the degree of beta 2-stimulation is weak. Epinephrine probably stimulates cerebral oxygen and glucose consumption by its beta 2-adrenergic effect. After three minutes of CPR, three groups of seven animals each blindly received either placebo (control group), 45 micrograms/kg epinephrine, or 45 micrograms/kg norepinephrine. During CPR but before drug administration, cerebral blood flow was 23 +/- 14 mL/min/100 g in the control group, 30 +/- 7 mL/min/100 g in the epinephrine group, and 30 +/- 11 mL/min/100 g in the norepinephrine group. At 90 seconds after epinephrine, cerebral blood flow increased to 54 +/- 14 mL/min/100 g and after norepinephrine, to 58 +/- 22 mL/min/100 g (P less than .05). Cerebral perfusion pressure for both drugs was significantly higher than the control group. Compared with mechanical measures alone, cerebral oxygen delivery rose from 4.3 +/- 1.2 to 7.4 +/- 1.7 mL/min/100 g after epinephrine and from 3.7 +/- 1.4 to 7.3 +/- 2.7 mL/min/100 g after norepinephrine (P less than .05). There was no increase in cerebral oxygen consumption after both catecholamines, and cerebral oxygen extraction ratio decreased. Cerebral glucose delivery increased in relation to glucose consumption, and extraction ratio did not change significantly after both catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Regulation of right atrial beta-adrenoceptors after cardiopulmonary resuscitation in pigs.

OBJECTIVE: to test the hypothesis that right atrial beta-adrenoceptors are down-regulated after CPR and administration of beta-adrenergic agents. METHODS: after 3 min of ventricular fibrillation and 3 min of cardiac massage, 6 pigs received adrenaline (45 micrograms/kg) intravenously before defibrillation. After restoration of spontaneous circulation, dopamine was given in order to maintain the mean arterial blood pressure stable. Right atrial beta-adrenergic binding sites were determined by an equilibration binding assay using (-)-125Iodocyanopindolol. RESULTS: plasma adrenaline (mean +/- S.E.M.) was 1.1 +/- 0.9 ng/ml (6.0 +/- 4.9 nmol/l) pre-arrest and increased to 63.8 +/- 45.8 (348.2 +/- 250.0 nmol/l) (P < 0.05) and 1034 +/- 344 ng/ml (5644 +/- 1878 nmol/l) (P < 0.05) during CPR before and after adrenaline administration. At points in time 30 and 120 min after successful CPR, plasma adrenaline was 2.4 +/- 0.5 and 1.3 +/- 0.3 ng/ml (13.1 +/- 2.7 and 7.1 +/- 1.6 nmol/l). Compared to pre-arrest, the density of high-affinity beta-adrenoceptors was 29.0 +/- 12.8 fmol/mg pre-arrest and was 69.4 +/- 21.6 and 84.2 +/- 16.7 fmol/mg (P < 0.05 vs. pre-arrest) 30 and 120 min after CPR. The density of low-affinity as well as of total binding sites was not significantly changed after CPR. CONCLUSIONS: it is concluded that markedly elevated plasma catecholamine concentrations after CPR and administration of adrenaline and dopamine do not lead to a decrease in the total density of beta-adrenoceptors but to an increase in high-affinity beta-adrenoceptors in right atrial cells.

Adrenergic beta-Agonists↗

Regional cerebral blood flow with manual internal cardiac massage versus direct mechanical ventricular assistance.

STUDY HYPOTHESIS: Previous studies have not discerned the best method for generating regional cerebral blood flow during internal cardiac massage. We hypothesized that regional cerebral blood flow generated by a mechanical method--direct mechanical ventricular assistance (DMVA)--would be superior to manual internal cardiac massage (MAN). STUDY POPULATION: Twelve adult Yucatan minipigs weighing more than 44 kg each were studied. METHODS: Swine were instrumented for regional cerebral blood flow measurements using tracer microspheres. After 15 minutes of ventricular fibrillation, swine were randomized to receive either MAN or DMVA. Regional cerebral blood flow was measured during normal sinus rhythm and at one minute (VF-1) and six minutes (VF-2) after initiation of circulatory support. Regional cerebral blood flow values were compared using a Wilcoxon rank sum test. RESULTS: During VF-1, there was a tendency for DMVA to produce greater regional cerebral blood flow than MAN, although these differences were not statistically significant (DMVA vs MAN as mL/min/100 g): cerebral cortex, 28 versus 11; cerebellum, 49 versus 22; midbrain, 43 versus 16; pons, 55 versus 18; medulla, 55 versus 19; and spinal cord, 33 versus 10. During VF-2, DMVA produced greater regional cerebral blood flows than were produced by MAN: cerebral cortex, 39 versus 12 (P less than .06); cerebellum, 58 versus 20 (P less than 0.5); midbrain, 50 versus 18 (P less than .05); pons, 52 versus 22 (P less than .06); medulla, 53 versus 20 (P less than .05); and spinal cord, 31 versus 12 (P less than .05). CONCLUSION: DMVA produces greater regional cerebral blood flow than is produced during MAN after 15 minutes of ventricular fibrillation. DMVA is effective at maintaining regional cerebral blood flow after a prolonged cardiac arrest.

Animals↗

Open-chest CPR improves survival and neurologic outcome following cardiac arrest.

STUDY OBJECTIVE: To determine if 15 min of open-chest cardiac massage (OC-CPR) versus closed-chest compressions (CC-CPR) improves 72-h survival and neurologic outcome (behavioral and histologic) after 5 min of untreated cardiac arrest. METHODS: Mongrel dogs were anesthetized and instrumented. Cardiac arrest was induced by KCl injection and after a 5-min period of non-intervention, dogs were randomized to receive either CC-CPR (N = 7) or OC-CPR (N = 5) performed for 15 min. The dogs were then resuscitated and physiologic data was recorded. Surviving dogs were scored at 72 h using canine neurodeficit score of Safar et al. (NDS; 0 = behaviorally normal, 500 = brain death). Dogs that could not be resuscitated or died before 72 h were assigned a score of 500. Brain histology was performed on all survivors. RESULTS: All OC-CPR dogs were successfully resuscitated and were behaviorally normal at 72 h (NDS = 0). Histology in OC-CPR dogs showed little to no injury. Only three out of the seven CC-CPR dogs survived to 72 h. Of the survivors, one dog exhibited minor ataxia (NDS = 15), and two had incapacitating deficits (both NDS = 180). Two dogs died within 24 h after extubation, and one could not be resuscitated and the other could not be weaned from the ventilator (each NDS = 500). Histology of the CC-CPR survivors revealed moderate to severe lesions. NDS between groups was statistically significant (p < 0.0079). CONCLUSION: In our canine model of cardiac arrest, OC-CPR significantly improved 72-h survival and neurologic outcome when compared to CC-CPR.

Animals↗

Direct cardiac massage without major thoracotomy: feasibility and systemic blood flow.

BACKGROUND: Open-chest cardiac massage (OC-CM) provides higher blood pressure and flow than closed-chest compression and may improve the probability of successful resuscitation from cardiac arrest. Its clinical use has been limited by its requirement for a major thoracotomy. The present pilot study tested the technical feasibility of performing effective direct cardiac massage without a major thoracic incision, by using a simple, manually-powered plunger-like device, inserted through a small thoracic incision, to cyclically compress the cardiac ventricles. The method was termed minimally-invasive direct cardiac massage (MID-CM). Systemic blood flow using MID-CM was compared to that with OC-CM, by both direct systemic hemodynamic measurements, cumulative metabolic indicators of the ratio of whole body oxygen delivery and oxygen consumption, and a metabolic index of pulmonary blood flow. METHODS: In 12 large swine, baseline systemic and pulmonary hemodynamic measurements were performed. Arterial and mixed venous blood gases and metabolic indicators of systemic blood flow were measured. Ventricular fibrillation was induced and after 4 min, animals underwent either bimanual OC-CM (N = 6) or MID-CM (N = 6). At 10, 20 and 30 min, hemodynamic and metabolic measurements were repeated. RESULTS: Systemic Blood Pressure: Aortic systolic and diastolic blood pressures were reduced from baseline levels with both OC-CM and MID-CM. No difference in pressure was noted between OC-CM and MID-CM groups. Pulmonary Artery Pressure: Pulmonary artery systolic pressure was elevated from baseline during OC-CM and MID-CM. Pulmonary artery diastolic pressures remained constant throughout the resuscitation period in both groups. No differences in pulmonary systolic or diastolic pressure were noted between OC-CM and MID-CM groups. A trend towards higher pulmonary systolic pressures appeared with MID-CM. Thermodilution Blood Flow: Cardiac index fell from baseline levels with OC-CM and MID-CM. No difference in cardiac index was noted between OC-CM and MID-CM groups. Metabolic Indices: Mixed venous O2 saturation decreased from baseline levels during resuscitation in both experimental groups, with a further decrease at 30 min compared to 10- and 20-min levels. No difference was noted between OC-CM and MID-CM groups at any point. Arterial pH was reduced from baseline levels at 30 min in both groups compared to baseline but no difference was noted between groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Efficacy of continuous insufflation of oxygen combined with active cardiac compression-decompression during out-of-hospital cardiorespiratory arrest.

BACKGROUND: During experimental cardiac arrest, continuous insufflation of air or oxygen (CIO) through microcannulas inserted into the inner wall of a modified intubation tube and generating a permanent positive intrathoracic pressure, combined with external cardiac massage, has previously been shown to be as effective as intermittent positive pressure ventilation (IPPV). METHODS: After basic cardiorespiratory resuscitation, the adult patients who experienced nontraumatic, out-of-hospital cardiac arrest with asystole, were randomized to two groups: an IPPV group tracheally intubated with a standard tube and ventilated with standard IPPV and a CIO group for whom a modified tube was inserted, and in which CIO at a flow rate of 15 l/min replaced IPPV (the tube was left open to atmosphere). Both groups underwent active cardiac compression-decompression with a device. Resuscitation was continued for a maximum of 30 min. Blood gas analysis was performed as soon as stable spontaneous cardiac activity was restored, and a second blood gas analysis was performed at admission to the hospital. RESULTS: The two groups of patients (47 in the IPPV and 48 in the CIO group) were comparable. The percentages of patients who underwent successful resuscitation (stable cardiac activity; 21.3 in the IPPV group and 27.1% in the CIO group) and the time necessary for successful resuscitation (11.8 +/- 1.8 and 12.8 +/- 1.9 min) were also comparable. The blood gas analysis performed after resuscitation (8 patients in the IPPV and 10 in the CIO group) did not show significant differences. The arterial blood gases performed after admission to the hospital and ventilation using a transport ventilator (seven patients in the IPPV group and six in the CIO group) showed that the partial pressure of arterial carbon dioxide (PaCO2) was significantly lower in the CIO group (35.7 +/- 2.1 compared with 72.7 +/- 7.4 mmHg), whereas the pH and the partial pressure of arterial oxygen (PaO2) were significantly higher (all P < 0.05). CONCLUSIONS: Continuous insufflation of air or oxygen alone through a multichannel open tube was as effective as IPPV during out-of-hospital cardiac arrest. A significantly greater elimination of carbon dioxide and a better level of oxygenation in the group previously treated with CIO probably reflected better lung mechanics.

Adolescent↗

Office and operating room management of cardiac arrest.

Management of cardiac arrest depends on a four-minute period of potential reversibility. Success depends on immediate diagnosis, documentation of the onset of cardiac arrest, and establishment of treatment priorities. Pupillary dilation, complete in two minutes, serves to verify the onset and duration of cardiac arrest. Treatment involves two phases--the emergency phase of oxygenation and perfusion and the definitive phase of restoring the spontaneous effective heartbeat. The two mechanisms of cardiac arrest, ventricular fibrillation and asystole, are characterized, and the conditions necessary for each to occur are listed. The treatment of ventricular fibrillation is defibrillation, whereas ventricular asystole responds to cardiac stimuli--a precordial blow, epinephrine, or calcium. The mnemonic "SALT CAN ADD GOOD TIME" is suggested as a guide for drug dosage, and a treatment flowchart is outlined.

Emergencies↗