Functional responses to extremely high plasma epinephrine concentrations in cardiac arrest

OBJECTIVE

To evaluate the action of high-dose epinephrine by measuring simultaneously its vasopressor and norepinephrine releasing effects in humans during cardiac arrest.

DESIGN

A prospective study on consecutive patients admitted with cardiac arrest.

SETTING

Emergency Department in a large, urban hospital.

PATIENTS

Eighteen patients with out-of-hospital cardiac arrest undergoing cardiopulmonary resuscitation (CPR).

INTERVENTIONS

Catheterization of both the aorta and right atrium for the recording of pressure and collection of blood samples. Throughout the study period (12.5 mins), 18 patients received epinephrine at both the standard dose (1 mg, approximately 0.015 mg/kg) and high dose (0.2 mg/kg). Blood samples were drawn five times, every 2.5 mins.

MEASUREMENTS AND MAIN RESULTS

Plasma epinephrine and norepinephrine concentrations; aorta, right atrial, and coronary perfusion pressures. Epinephrine concentrations (normal at rest = 160 +/- 10 [SEM] pmol/L) were increased at the time of the first sample (2.5 mins) by approximately 3,000-fold (to approximately 0.5 mumol/L), and, increased further to 12,000-fold (approximately 2.0 mumol/L) during the study. Aortic pressure increased from 20 +/- 3 to 28 +/- 3 mm Hg (p < .001), and coronary perfusion pressure increased from 4 +/- 3 to 10 +/- 3 mm Hg (p < .001). Simultaneous plasma norepinephrine concentrations were 30-fold higher than the normal resting value of 1.30 +/- 0.04 nmol/L, and increased by 90-fold during the study (p < .001). The spectral distributions of the individual correlations between plasma epinephrine and norepinephrine concentrations were segregated into high correlations (r > .83) in 12 of 18 patients and low r values (r = .29 to .79) in the remaining six patients. The distribution of the correlations was nonuniform by the Kolmogorov-Smirnov goodness-of-fit test with p < .001; this profile suggests that norepinephrine responsiveness to epinephrine can separate two populations, one of which (r > .83) would have preserved viability of the corresponding epinephrine receptors. The correlations between plasma epinephrine concentrations and coronary perfusion pressures were distributed more evenly, also in a nonuniform pattern (p < .02 by Kolmogorov-Smirnov goodness-of-fit test) and the relationship between the two sets of correlations was not significant.

CONCLUSIONS

Despite the very high prevailing plasma epinephrine concentrations during cardiac arrest, further epinephrine increases still elicit biological responses. The present work provides physiologic support for the use of large doses of epinephrine during the course of CPR.

Venous hyperoxia after cardiac arrest. Characterization of a defect in systemic oxygen utilization

BACKGROUND

Supranormal mixed venous oxygen saturation (mixed venous hyperoxia), although reported, has never been characterized in humans resuscitated from cardiac arrest (postarrest cardiogenic shock). By contrast, cardiogenic shock without cardiopulmonary arrest (primary cardiogenic shock) is accompanied by mixed venous hypoxia under similar conditions of low oxygen delivery (DO2). The appearance of mixed venous hyperoxia indicates an excessive supply relative to demand in perfused tissue or cellular impairment of oxygen utilization, ie, low systemic oxygen consumption (VO2). Failure to improve VO2 has been associated with a poor outcome in other shock states.

STUDY OBJECTIVE

This study evaluates the clinical significance of mixed venous hyperoxia and its implications for impaired systemic oxygen utilization. The oxygen transport patterns in surviving and nonsurviving cardiac arrest patients are compared for their prognostic and therapeutic implications.

STUDY DESIGN

Consecutive, nonrandomized series.

SETTING

Large urban emergency department (ED).

PARTICIPANTS

Adult normothermic, nontraumatic out-of-hospital cardiac arrest patients presenting to the ED who develop a return of spontaneous circulation (ROSC).

INTERVENTIONS

On arrival to the ED, a fiberoptic catheter was placed in the central venous position for continuous central venous oxygen saturation monitoring (ScvO2). A proximal aortic catheter was placed via the femoral artery for blood pressure monitoring. Upon ROSC, the fiberoptic catheter was advanced to the pulmonary artery. Mean arterial pressure (MAP), cardiac index (CI), VO2, DO2, systemic oxygen extraction ratio (OER), and systemic vascular resistance index (SVRI-dynes.s/cm5.m2) were measured immediately and every 30 min. The duration of cardiac arrest (DCA) in minutes and amount of epinephrine (milligrams) administered during ACLS was recorded.

MEASUREMENTS AND RESULTS

Twenty-three patients were entered into the study. Survivors (living more than 24 h) and nonsurvivors (living less than 24 h) were compared.

CONCLUSIONS

These findings indicate an impairment of systemic oxygen utilization in postarrest cardiogenic shock patients. In spite of a lower DO2 than survivors, the OER in nonsurvivors remained lower than expected. Venous hyperoxia is a clinical manifestation of this derangement. Epinephrine dose may have a causal relationship. The inability to attain a VO2 of greater than 90 ml/min.m2 after the first 6 h of aggressive therapy was associated with a 100 percent mortality in 24 h.

Continuous central venous oximetry and shock index in the emergency department: use in the evaluation of clinical shock

Initial therapy of shock in the emergency department (ED) emphasizes the normalization of physiologic variables such as heart rate (HR), mean arterial pressure (MAP), and central venous pressure (CVP) rather than restoration of adequate tissue oxygenation. After hemodynamic stabilization of MAP, CVP, and HR, the authors examined tissue oxygenation as indicated by continuous central venous oximetry (SCVO2), lactic acid concentration, and shock index (SI). Sixteen consecutive nonrandomized patients presenting to the ED of a large urban hospital in shock (MAP < 60 mm Hg, HR > 120 beats/min, and altered sensorium) were initially resuscitated with fluid, blood, inotropes, and/or vasoactive drug therapy to normalize MAP, CVP, and HR. In addition, SCVO2, arterial lactate concentration, and SI were measured after completion of resuscitation in the ED. Eight patients (group no. 1) had inadequate tissue oxygenation reflected by low SCVO2 (less than 65%). Four patients in group no. 1 had elevated arterial lactic acid concentration. All group no. 1 patients had an elevated SI (> 0.7) suggesting persistent impairment of left ventricular stroke work. Eight patients (group no. 2) had normal or elevated SCVO2 (> 65%). In group no. 2, arterial lactic acid concentration was elevated in six and SI in seven patients. Normalization of hemodynamic variables does not adequately reflect the optimal endpoint of initial therapy in shock in the ED. Most (94%) of these patients continue to have significant global ischemia and cardiac dysfunction as indicated by reduced SCVO2 and elevated lactic acid concentration and SI. Systemic tissue oxygenation should be monitored and optimized in the ED in these critically ill patients.(ABSTRACT TRUNCATED AT 250 WORDS)

The clinical implications of continuous central venous oxygen saturation during human CPR

STUDY OBJECTIVE

The purpose of this study was to observe, measure, and describe the changes in central venous oxygen saturation during CPR and immediately after return of spontaneous circulation. It also was to examine the clinical utility of continuous central venous oxygen saturation monitoring as a indicator of return of spontaneous circulation during CPR in human beings.

DESIGN AND SETTING

Eight-month, prospective, non-outcome, observational, nonrandomized case series in the ED of a large urban hospital. TYPES OF PATIENTS: Adult normothermic, nontraumatic, out-of-hospital cardiopulmonary arrests.

INTERVENTIONS

All patients were managed according to advanced cardiac life support guidelines. A proximal aortic and double-lumen central venous catheter was placed. Central venous oxygen saturation was measured continuously spectrophotometrically with a fiberoptic catheter in the central venous location.

MEASUREMENTS

Aortic blood pressure and central venous oxygen saturation were simultaneously measured throughout each resuscitation. Return of spontaneous circulation was defined as a systolic blood pressure of more than 60 mm Hg for more than five minutes.

RESULTS

One hundred patients who experienced 68 episodes of cardiac arrest were studied. Patients with return of spontaneous circulation had a higher initial and statistically higher mean and maximal central venous oxygen saturation than those without return of spontaneous circulation (P = .23, .0001, and .0001, respectively; P less than .05 is significant). No patient attained return of spontaneous circulation without reaching a central venous oxygen saturation of at least 30%. Only one of 68 episodes of return of spontaneous circulation was attained without reaching a central venous oxygen saturation of at least 40%. A central venous oxygen saturation of greater than 72% was 100% predictive of return of spontaneous circulation.

CONCLUSION

Continuous central venous oxygen saturation monitoring can serve as a reliable indicator of return of spontaneous circulation during CPR in human beings.

Aortic pressure during human cardiac arrest. Identification of pseudo-electromechanical dissociation

We measured aortic pressure during clinically apparent cardiac electromechanical dissociation (EMD). Patients with pulse pressures were designated as having pseudo-EMD; those without, as having true EMD. Of the 200 patients studied, 54 presented with EMD, and 40 others developed it during resuscitation. Of the 94 with EMD, 39 were found to have pseudo-EMD. We compared the two types of EMD for electrocardiographic duration, return of palpable pulses, and response to standard- and high-dose epinephrine. The mean resting aortic pressure was 18 +/- 11 mm Hg in patients with true EMD and 28 +/- 11 mm Hg in those with pseudo-EMD. The mean pulse pressure in patients with pseudo-EMD was 6.3 +/- 3.5 mm Hg. Patients with pseudo-EMD had a higher proportion of witnessed arrests, higher PaO2, and lower PaCO2 than patients with true EMD. Patients with pseudo-EMD had shorter QR and QRS durations than patients with true EMD. They had a better response to standard- and high-dose epinephrine than patients with true EMD. Many patients diagnosed clinically to be in EMD have mechanical cardiac activity; this should be considered when interpreting the results of cardiac arrest research.

Effects of arterial and venous volume infusion on coronary perfusion pressures during canine CPR

Intraarterial (IA) volume infusion has been reported to be more effective than intravenous (IV) infusion in treating cardiac arrest due to exsanguination. A rapid IA infusion was felt to raise intraaortic pressure and improve coronary perfusion pressure (CPP). The purpose of this study was to determine if IA or IV volume infusion could augment the effect of epinephrine on CPP during CPR in the canine model. Nineteen mongrel dogs with a mean weight of 26.3 +/- 4.2 kg were anesthetized and mechanically ventilated. Thoracic aortic (Ao), right atrial (RA) and pulmonary artery catheters were placed for hemodynamic monitoring. Additional Ao and central venous catheters were placed for volume infusion. Ventricular fibrillation was induced and Thumper CPR was begun after 5 min (t = 5). At t = 10, all dogs received 45 micrograms/kg IV epinephrine. Six animals received epinephrine alone (EPI). Five dogs received EPI plus a 500 cc bolus of normal saline over 3 min intravenously (EPI/IV). Another group (n = 8) received EPI plus the same fluid bolus through the aortic catheter (EPI/IA). Resuscitation was attempted at t = 18 using a standard protocol. There was a significant increase in CPP over baseline in all groups. The changes in CPP from baseline induced by EPI, EPI/IV and EPI/IA were 20.6 +/- 3.7, 22.8 +/- 4.2 and 22.2 +/- 2.4 mmHg, respectively. Volume loading did not augment the effect of therapeutic EPI dosing. By increasing both preload and afterload, volume administration may in fact be detrimental during CPR.

Aortic-carotid artery pressure differences and cephalic perfusion pressure during cardiopulmonary resuscitation in humans

OBJECTIVE

Animal studies have shown an aortic-carotid artery pressure difference during cardiopulmonary resuscitation (CPR), which compromises cerebral perfusion. This pressure difference is most marked with prolonged CPR and can be abolished with administration of high doses of epinephrine. To better understand the mechanism of cerebral blood flow during CPR in humans, we determined the aortic-carotid artery pressure difference, the cephalic perfusion pressure (the carotid artery-jugular vein pressure difference), and thoracic inlet venous "valving" (the central venous-jugular vein pressure difference), while administering standard doses of epinephrine.

DESIGN

Prospective study with randomization as to which side the carotid artery was catheterized.

SETTING

The resuscitation room of a large urban hospital's emergency department.

PATIENTS

Fifteen adults in normothermic, nontraumatic prehospital cardiac arrest treated according to Advanced Cardiac Life Support guidelines, including administration of 1 mg epinephrine iv every 5 mins.

INTERVENTIONS

The descending aorta, cervical common carotid artery, internal jugular vein, and central venous system were catheterized. Pressures were recorded during standard CPR for 5 mins after administration of 1 mg epinephrine iv.

MEASUREMENTS AND MAIN RESULTS

Most patients received CPR for greater than 20 mins before the first epinephrine dose and for greater than 45 mins before pressure recording as described above. There was no significant difference between aortic and carotid artery compression and relaxation phase pressures. The mean +/- SD compression central venous-jugular vein pressure difference was 22.1 +/- 15.0 mm Hg, and the mean cephalic perfusion pressure was 20.8 +/- 19.5 mm Hg.

CONCLUSIONS

There is no clinically important aortic-carotid artery pressure difference during human CPR using the standard dose of epinephrine, even with prolonged CPR. Despite carotid artery patency and thoracic inlet venous valving, the cephalic perfusion pressure is low during CPR in humans.

Cerebral lactate uptake during cardiopulmonary resuscitation in humans

Animal studies have shown cerebral lactate uptake under conditions of anoxia and ischemia. Cerebral lactate uptake in humans during cardiopulmonary resuscitation (CPR) has not been previously reported in the literature. Forty-five patients receiving CPR underwent simultaneous sampling through jugular venous bulb, right atrial, and central aortic catheterization. The mean net cerebral lactate uptake (central aortic minus jugular venous bulb) was 0.76 +/- 1.86 and 0.80 +/- 2.03 mM on initial measurement and 10 min later, respectively. Both measurements were statistically significant (p = 0.01) compared to normal controls who have net cerebral output of lactate of -0.18 +/- 0.1 mM. Seventy-one percent of all patients had a cerebral uptake on initial sampling and this gradient persisted upon sampling 10 min later in 68% of the remaining 40 patients who did not have a return of spontaneous circulation. Among multiple variables measured, patients who exhibited a cerebral lactate uptake were 13.2 years younger (p = 0.004), received an additional 7.6 min of CPR (p = 0.05), and had a mean arterial lactate concentration of 4.8 mM higher (p = 0.005) than the nonuptake group. The pathophysiologic explanation of cerebral lactate uptake during CPR is multifactorial and includes utilization and/or diffusion.

Nuclear magnetic resonance spectroscopy study of human brain after cardiac resuscitation

We used 31P nuclear magnetic resonance spectroscopy to study the cerebral metabolic function of eight patients with severe postischemic anoxic encephalopathy secondary to cardiac arrest. Spectroscopy was performed at 18 +/- 13 and 64 +/- 20 hours after resuscitation. Glasgow Coma Scale scores at the time of initial and repeat spectroscopy were 3.6 +/- 1.2 and 3.5 +/- 1.2, respectively. In those patients whose spectra were of adequate quality to monitor pH, all demonstrated tissue alkalosis in at least one brain region. The mean brain pH at initial spectroscopy was 7.14 +/- 0.09 and was significantly alkalotic when compared with age- and sex-matched normal controls (pH = 6.98 +/- 0.04, p less than 0.0001). Five of the eight patients showed at least one region of persistent alkalosis at repeat spectroscopy, whereas one patient demonstrated severe acidosis with a pH of 6.42. Spectra demonstrated marked metabolic heterogeneity, ranging from normal in appearance to complete obliteration of all high-energy phosphates with only inorganic phosphate remaining.

The effect of standard- and high-dose epinephrine on coronary perfusion pressure during prolonged cardiopulmonary resuscitation

We studied the effect of standard and high doses of epinephrine on coronary perfusion pressure during cardiopulmonary resuscitation in 32 patients whose cardiac arrest was refractory to advanced cardiac life support. Simultaneous aortic and right atrial pressures were measured and plasma epinephrine levels were sampled. Patients remaining in cardiac arrest after multiple 1-mg doses of epinephrine received a high dose of 0.2 mg/kg. The increase in the coronary perfusion pressures was 3.7 +/- 5.0 mm Hg following a standard dose, not a statistically significant change. The increase after a high dose was 11.3 +/- 10.0 mm Hg; this was both statistically different than before administration and larger than after a standard dose. High-dose epinephrine was more likely to raise the coronary perfusion pressure above the previously demonstrated critical value of 15 mm Hg. The highest arterial plasma epinephrine level after a standard dose was 152 +/- 162 ng/mL, and after a high dose, 393 +/- 289 ng/mL. Because coronary perfusion pressure is a good predictor of outcome in cardiac arrest, the increase after high-dose epinephrine may improve rates of return of spontaneous circulation.

Plasma chromogranin A as a marker of sympathochromaffin activity in humans

The extent to which the sympathochromaffin system compared with other endocrine/neuroendocrine tissues contributes to the plasma chromogranin A pool has not been defined. To test the hypothesis that the sympathochromaffin system is the major source of circulating chromogranin A only when that system is activated markedly, we measured chromogranin A concentrations in 200 human plasma samples known to have a broad range of norepinephrine and epinephrine concentrations, reflecting therefore a broad range of sympathochromaffin activity at the time of sampling. Plasma chromogranin A and norepinephrine concentrations were highly correlated when the sympathochromaffin system was activated markedly (cardiac arrest samples, n = 13, r = 0.8392, P less than 0.0005) and when there was release of large amounts of norepinephrine from tumors (pheochromocytoma samples, n = 17, r = 0.8132, P less than 0.001). However, when the sympathochromaffin system was activated less markedly, resulting in plasma catecholamine concentrations that spanned the physiological and lower pathophysiological range (nonpheochromocytoma noncardiac arrest samples, n = 170), correlations between plasma chromogranin A and norepinephrine (r = 0.2877, P less than 0.0001) and epinephrine (r = 0.3814, P less than 0.0001) levels were relatively weak, although still statistically significant. Thus, at basal through moderate stress levels, norepinephrine and epinephrine concentrations accounted for only approximately 10-15% of the variance in plasma chromogranin A levels. We conclude that, although plasma chromogranin A concentrations are a valid marker of sympathochromaffin activity in humans, they are not a sensitive marker under physiological conditions.

Plasma epinephrine levels in resuscitation with cardiopulmonary bypass

Since the highest plasma epinephrine levels have been recorded during resuscitation, we evaluated the isolated effect of cardiac arrest upon adrenomedullary secretion. We determined plasma epinephrine in dogs resuscitated with cardiopulmonary bypass (CPB) after cardiac arrest periods of 12 (CPB-12; n = 4) or 16 min (CPB-16; n = 5). Through 2 h of CPB and the following 6 h of critical care, there was no difference between CPB-12 and CPB-16 regarding most cardiopulmonary functional variables. Plasma epinephrine was markedly elevated immediately after initiation of CPB (p less than .01 at 1 min CPB vs. basal) and returned rapidly to basal concentrations. Comparison of plasma epinephrine levels between CPB and standard CPR groups showed that responses to cardiac arrest were similar (p greater than .05 at 1 min CPB vs. 11.5 min CPR). We conclude that cardiac arrest is the main or sole determinant of the plasma epinephrine elevation of resuscitation.

Effect of epinephrine on end-tidal carbon dioxide monitoring during CPR

End-tidal carbon dioxide (ETCO2) has been shown to correlate with coronary perfusion pressure (CPP) during CPR and has been proposed as a useful noninvasive monitor of CPR efficacy. The effects of therapeutic epinephrine dosing on ETCO2 and CPP in six dogs were examined. Ventricular fibrillation was induced and left untreated for five minutes before CPR was initiated. After five minutes of CPR, epinephrine 0.045 mg/kg IV was administered. CPP and ETCO2 were compared immediately before and two minutes after epinephrine administration. There was a significant increase in CPP from 12.2 +/- 9.6 to 26.8 +/- 7.1 mm Hg (P = .006) after epinephrine. This was accompanied by a significant decrease in ETCO2 from 8.2 +/- 2.9 to 3.8 +/- 2.0 mm Hg (P = .01). These data indicate that after epinephrine administration, caution must be exercised in using ETCO2 as an indicator of CPP.

Characterization of cerebral energetics and brain pH by 31P spectroscopy after graded canine cardiac arrest and bypass reperfusion

Recovery of cerebral energy metabolism is used to indicate CNS viability after ischemia. This study utilized 31P nuclear magnetic resonance (NMR) spectroscopy to measure cerebral energy state and intracellular pH in dogs subjected to 8, 12, or 16 min of cardiac arrest and reperfusion using cardiopulmonary bypass. Spectra were obtained throughout ischemia and initial reperfusion and repeated at 30 and 144 h post ischemia. Neurologic deficit scoring was performed at 12 and 24 h post insult and then daily. High-energy phosphates were depleted by the end of all ischemic intervals. Recovery occurred within 60 min of reperfusion and persisted with no differences in the rate of return between groups (p greater than 0.05). Brain pH (pHb) decreased by the end of ischemia in all groups (p less than 0.0001). Neither the pHb nadir nor its recovery differed between groups (p greater than 0.05). Although longterm neurologic outcome differed between groups, the spectra were similar. Assessment of cerebral energy state using 31P NMR spectroscopy does not appear to be a sensitive indicator of neurologic outcome after global ischemia in dogs. Return of high-energy phosphates may be a necessary but not sufficient condition for cerebral recovery after ischemia. The return of high-energy phosphates after a 16-min cardiac arrest, however, indicates a potential for neurological recovery.

CPR-dependent consciousness: evidence for cardiac compression causing forward flow

We present the case of a patient with cardiac arrest and resuscitation in whom, consistent with direct cardiac compression, large aortic-to-right atrial systolic pressure gradients occurred. Forward blood flow during CPR was sufficient for the patient to maintain consciousness. Although aortic-to-right atrial diastolic gradients adequate to maintain coronary perfusion in experimental models were generated, in our patient, cardiac function could not be restored and the resuscitation was ultimately unsuccessful.

Simultaneous aortic, jugular bulb, and right atrial pressures during cardiopulmonary resuscitation in humans. Insights into mechanisms

Pressure gradients across and between the head and chest were studied during mechanical cardiopulmonary resuscitation (CPR) in 22 humans. Patients in medical cardiac arrest, managed by ACLS guidelines, underwent placement of aortic arch (Ao), jugular venous bulb (JVB), and right atrial (RA) catheters. Simultaneous pressures were measured, and intercatheter gradients were calculated. The JVB to RA pressure difference is the gradient between the cervical and central venous circulations. It was negative when averaged throughout the CPR cycle and was more negative during compression than relaxation, -19 +/- 12 and -2 +/- 6 mm Hg, respectively. This indicates that the intrathoracic pressure rise was not transmitted to the jugular venous system, supporting the concept of a competent jugular valve mechanism during CPR. It is consistent with the thoracic pump model of cerebral perfusion. JVB to RA was positive only during early relaxation, allowing blood return from the head. The Ao to JVB gradient, although not equal to cerebral perfusion pressure, is the maximum potential pressure gradient for blood flow across the cerebral vasculature. It was positive throughout CPR, 25 +/- 17 during compression, and 9 +/- 10 mm Hg during relaxation. The Ao to RA gradient during the relaxation phase is CPR coronary perfusion pressure. In most patients, it was minimally positive in both phases of the CPR cycle: 7 +/- 14 in compression and 7 +/- 9 mm Hg during relaxation. This appears to be inadequate in providing sufficient blood flow to meet the metabolic needs of the myocardium. Four patients had larger gradients during compression suggestive of cardiac compression.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of cardiopulmonary bypass resuscitation on cardiac arrest induced lactic acidosis in dogs

The adequacy of end organ blood flow following a cardiac arrest varies depending on the artificial reperfusion technique utilized and may critically affect patient outcome. Both oxygen consumption (VO2) and arterial lactate values have previously been used to assess tissue perfusion. Cardiopulmonary bypass resuscitation (CPB) is a reperfusion technique capable of providing near normal end organ blood flow. The purpose of this investigation was to study the effect of femoro-femoral veno-arterial CPB resuscitation compared to standard CPR on VO2 and arterial lactic acid values after a prolonged cardiac arrest. Ten mongrel dogs were electrically fibrillated and left in cardiopulmonary arrest without therapy for 12 min. Resuscitation was attempted according to a standardized protocol utilizing either CPB (n = 5) or standard external CPR (n = 5). Oxygen consumption values and arterial lactic acid samples were obtained at baseline, at timed intervals throughout resuscitation and after return of spontaneous circulation in successfully resuscitated dogs. Baseline hemodynamic and biochemical measurements were similar in both treatment groups (P greater than 0.05). Oxygen consumption (440 +/- 50 ml/min/M2) and mean arterial lactic acid values (7.44 +/- 2.25 mmol/l) were significantly higher at 1 min of resuscitation in CPB-treated dogs compared to dogs treated with CPR (60 +/- 10 ml/min/M2) (3.16 +/- 0.69 mmol/l) respectively (P less than 0.05). Mean arterial lactic acid values rose significantly at each sampling interval during CPR (P less than 0.05) but began to decrease after 5 min of resuscitation in the CPB animals and were not significantly different than baseline after 60 min of bypass (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of CO2 and non-CO2-generating buffers on cerebral acidosis after cardiac arrest: A 31P NMR study

There is controversy regarding the use of alkalinizing agents during reperfusion after cardiac arrest. The potential deleterious effects of sodium bicarbonate (bicarb) administration, including paradoxic cerebral acidosis, have led to the search for alternative agents. Tromethamine (tris) is a non-CO2-generating buffer that has been proposed for use during cardiopulmonary resuscitation. The purpose of this experiment was to compare the ability of tris with bicarb to correct brain pH (pH B) during reperfusion after a 12-minute cardiac arrest. Adult mongrel dogs were instrumented and placed in the bore of a Bruker Biospec 1.89 tesla superconducting magnet system. Ventricular fibrillation was induced; after 12 minutes, cardiopulmonary bypass was initiated and maintained for two hours with minimum flows of 80 mL/kg/min. Bicarb (n = 5) or tris (n = 5) were administered to correct arterial pH as rapidly as possible. 31P NMR spectra were obtained at baseline and throughout ischemia and reperfusion. The pH B was determined with the inorganic phosphate relative to the phosphocreatine resonance signal shift. Profile analysis indicates a difference between groups (P less than .02) related to an initial delay in pH B correction in the tris group. By 48 minutes of reperfusion, pH B did not differ between the groups. Moreover, there was no evidence of paradoxic cerebral acidosis in the bicarb group. Although tris corrects blood pH as quickly as bicarb, it is less effective in correcting pH B. Absence of paradoxic acidosis may be caused by efficient elimination of CO2 by cardiopulmonary bypass.

Hyperkalemia during human cardiopulmonary resuscitation: incidence and ramifications

Although hypokalemia has been reported after cardiac arrest and successful resuscitation, experimental data indicate that potassium is released from cells during ischemia. The purpose of this investigation was to study serum potassium concentration ([K+]) during closed chest cardiopulmonary resuscitation (CC-CPR) in humans. Twenty-two patients presenting to the emergency department (ED) in cardiopulmonary arrest had simultaneous measurement of central venous and arterial [K+] and blood gases during CC-CPR utilizing current advanced cardiac life support protocols and a pneumatic chest compressor and ventilator. Mean arterial and central venous [K+] were 5.0 +/- 1.3 and 5.6 +/- 2.9 mEq/L, respectively, (p greater than .05) with 7 patients having [K+] of greater than 6 mEq/L. Significant hyperkalemia does occur in some patients during cardiac arrest and CC-CPR. Because poor tissue perfusion during CC-CPR impairs exchange between the interstitial and intravascular compartments, increases in interstitial [K+] would be expected to be even greater. Interstitial hyperkalemia may play a role in the genesis of wide complex electromechanical dissociation (EMD) seen after prolonged cardiac arrest. Since calcium has long been known to be beneficial in the treatment of hyperkalemia-induced dysrhythmias, the success of calcium chloride in treating wide complex EMD may be on the basis of this phenomenon.

Lactic acidosis during closed-chest CPR in dogs

Survival after out-of-hospital cardiac arrest is intimately related to the time from cardiovascular collapse to the initiation of CPR, or downtime. Furthermore, the reperfusion technique that optimizes coronary and cerebral blood flow after cardiac arrest may also be dependent on downtime. Peak blood lactate levels have been shown to be unchanged throughout resuscitation and predictive of downtime in dogs subjected to cardiopulmonary arrest and open cardiac massage. The purpose of this study was to determine the course of arterial lactate levels in dogs subjected to a fibrillatory cardiopulmonary arrest and conventional closed-chest CPR (CCPR). Fourteen dogs were subjected to five minutes of cardiopulmonary arrest and 30 minutes of CCPR. Resuscitation was performed according to a standardized protocol. Arterial lactic acid samples were collected at timed intervals throughout the experiment. Mean arterial lactic acid levels increased significantly with each sampling interval during 30 minutes of CCPR (overall P less than .05). In nine dogs successfully resuscitated, there were no significant differences in mean arterial lactic acid levels after the return of spontaneous circulation (ROSC). Open-chest resuscitation after five minutes of ventricular fibrillation in dogs results in peak lactic acid levels that do not change significantly once internal cardiac massage is initiated. In contrast, CCPR in similarly arrested dogs does not appear to provide adequate tissue oxygenation and/or perfusion to prevent continuous lactic acid accumulation.