Influence of respiratory and metabolic acidosis on epinephrine-inotropic effect in isolated guinea pig atria

Pharmacokinetic and pharmacodynamic evaluation of various vasopressin doses and routes of administration in a neonatal piglet model

Epinephrine is the only recommended vasopressor during neonatal cardiopulmonary resuscitation. However, there are concerns about the potential adverse effects of epinephrine, which might hamper efficacy during cardiopulmonary resuscitation. An alternative might be vasopressin, which has a preferable adverse effect profile, however, its optimal dose and route of administration is unknown. We aimed to compare the pharmacodynamics and pharmacokinetics of various vasopressin doses administered via intravenous (IV), intraosseous (IO), endotracheal (ETT), and intranasal (IN) routes in healthy neonatal piglets. Forty-four post-transitional piglets (1-3 days of age) were anesthetized, intubated via a tracheostomy, and randomized to receive vasopressin via intravenous (control), IO, ETT, or IN route. Heart rate (HR), arterial blood pressure, carotid blood flow, and cardiac function (e.g., stroke volume, ejection fraction) were continuously recorded throughout the experiment. Blood was collected prior to drug administration and throughout the observation period for pharmacodynamics and pharmacokinetic analysis. Significant changes in hemodynamic parameters were observed following IO administration of vasopressin while pharmacokinetic parameters were not different between IV and IO vasopressin. Administration of vasopressin via ETT or IN did not change hemodynamic parameters and had significantly lower maximum plasma concentrations and systemic absorption compared to piglets administered IV vasopressin (p < 0.05). The IV and IO routes appear the most effective for vasopressin administration in neonatal piglets, while the ETT and IN routes appear unsuitable for vasopressin administration.

Comparison of various vasopressin doses to epinephrine during cardiopulmonary resuscitation in asphyxiated neonatal piglets

BACKGROUND

Current neonatal resuscitation guidelines recommend epinephrine for cardiac arrest. Vasopressin might be an alternative during asphyxial cardiac arrest. We aimed to compare vasopressin and epinephrine on incidence and time to return of spontaneous circulation (ROSC) in asphyxiated newborn piglets.

DESIGN/METHODS

Newborn piglets (n = 8/group) were anesthetized, intubated, instrumented, and exposed to 30 min of normocapnic hypoxia, followed by asphyxia and asystolic cardiac arrest. Piglets were randomized to 0.2, 0.4, or 0.8IU/kg vasopressin, or 0.02 mg/kg epinephrine. Hemodynamic parameters were continuously measured.

RESULTS

Median (IQR) time to ROSC was 172(103-418)s, 157(100-413)s, 122(93-289)s, and 276(117-480)s for 0.2, 0.4, 0.8IU/kg vasopressin, and 0.02 mg/kg epinephrine groups, respectively (p = 0.59). The number of piglets that achieved ROSC was 6(75%), 6(75%), 7(88%), and 5(63%) for 0.2, 0.4, 0.8IU/kg vasopressin, and 0.02 mg/kg epinephrine, respectively (p = 0.94). The epinephrine group had a 60% (3/5) rate of post-ROSC survival compared to 83% (5/6), 83% (5/6), and 57% (4/7) in the 0.2, 0.4, and 0.8IU/kg vasopressin groups, respectively (p = 0.61).

CONCLUSION

Time to and incidence of ROSC were not different between all vasopressin dosages and epinephrine. However, non-significantly lower time to ROSC and higher post-ROSC survival in vasopressin groups warrant further investigation.

IMPACT

Time to and incidence of ROSC were not statistically different between all vasopressin dosages and epinephrine. Non-significantly lower time to ROSC and higher post-ROSC survival in vasopressin-treated piglets. Overall poorer hemodynamic recovery following ROSC in epinephrine piglets compared to vasopressin groups. Human neonatal clinical trials examining the efficacy of vasopressin during asphyxial cardiac arrest will begin recruitment soon.

Vasopressin Associated With an Increase in Return of Spontaneous Circulation in Acidotic Cardiopulmonary Arrest Patients

Background: During respiratory and metabolic acidosis, the vasoconstrictive effects of epinephrine may be blunted, whereas the response to vasopressin remains unchanged. The impact of this effect during advanced cardiac life support (ACLS) remains unclear. Objective: Determine if vasopressin therapy in combination with epinephrine was associated with improved outcomes in patients with cardiac arrest compared to epinephrine alone. The primary outcome was difference in rate of return of spontaneous circulation (ROSC). Secondary outcomes included evaluation of rates of ROSC for patients with an initial pH <7.2 and by initial pulseless rhythm. Methods: Single-center, retrospective review conducted from July 2010 to July 2012. Patients ≥18 years of age with documented cardiac arrest requiring ACLS and vasopressor therapy were included. Results: A total of 101 patients met inclusion criteria. There was no difference in rate of ROSC (56% vs 60%, P = 0.68) or survival to hospital discharge (9% vs 5%, P = 0.46) between patients who received vasopressin in combination with epinephrine (n = 43) compared to epinephrine alone (n = 58). Subgroup analysis of ROSC in patients with an arterial pH of <7.2 (n = 35) showed an increased rate of ROSC (63% vs 37%, P = 0.01) in the vasopressin plus epinephrine group versus the epinephrine alone group, respectively. Subgroup analysis by initial cardiac rhythm showed no difference in rate of ROSC. Conclusions: Vasopressin in combination with epinephrine demonstrated improved ROSC in cardiac arrest patients with initial arterial pH <7.2 compared with epinephrine alone, without improving survival to hospital discharge.

Mild metabolic acidosis impairs the β-adrenergic response in isolated human failing myocardium

INTRODUCTION

Pronounced extracellular acidosis reduces both cardiac contractility and the β-adrenergic response. In the past, this was shown in some studies using animal models. However, few data exist regarding how the human end-stage failing myocardium, in which compensatory mechanisms are exhausted, reacts to acute mild metabolic acidosis. The aim of this study was to investigate the effect of mild metabolic acidosis on contractility and the β-adrenergic response of isolated trabeculae from human end-stage failing hearts.

METHODS

Intact isometrically twitching trabeculae isolated from patients with end-stage heart failure were exposed to mild metabolic acidosis (pH 7.20). Trabeculae were stimulated at increasing frequencies and finally exposed to increasing concentrations of isoproterenol (0 to 1 × 10(-6) M).

RESULTS

A mild metabolic acidosis caused a depression in twitch-force amplitude of 26% (12.1 ± 1.9 to 9.0 ± 1.5 mN/mm(2); n = 12; P < 0.01) as compared with pH 7.40. Force-frequency relation measurements yielded no further significant differences of twitch force. At the maximal isoproterenol concentration, the force amplitude was comparable in each of the two groups (pH 7.40 versus pH 7.20). However, the half-maximal effective concentration (EC50) was significantly increased in the acidosis group, with an EC50 of 5.834 × 10(-8) M (confidence interval (CI), 3.48 × 10(-8) to 9.779 × 10(-8); n = 9), compared with the control group, which had an EC50 of 1.056 × 10(-8) M (CI, 2.626 × 10(-9) to 4.243 × 10(-8); n = 10; P < 0.05), indicating an impaired β-adrenergic force response.

CONCLUSIONS

Our data show that mild metabolic acidosis reduces cardiac contractility and significantly impairs the β-adrenergic force response in human failing myocardium. Thus, our results could contribute to the still-controversial discussion about the therapy regimen of acidosis in patients with critical heart failure.

Influence of mild metabolic acidosis on cardiac contractility and isoprenaline response in isolated ovine myocardium

The postoperative course after major surgical procedures such as cardiothoracic operations is often accompanied by acute metabolic abnormalities due to large volume and temperature shifts. In general, those intervention-induced trauma might cause the use of catecholamines to stabilize hemodynamics. Within the cardiac community, there are still controversial discussions about standardized medical therapy to treat postoperative acidosis, for example, buffering versus nonbuffering for improving catecholaminergic response of myocardial contractility. The aim of this study was to investigate the influence of mild (and thus clinically relevant) acidosis on myocardial contractility and catecholamine response in explanted trabeculae of ovine hearts. Intact trabeculae (n = 24) were isolated from the right ventricle of healthy sheep hearts. Two different groups (group 1: pH = 7.40, n = 9 and group 2: pH = 7.20, n = 13) were investigated, and force amplitudes were measured at frequencies between 30 and 180 beats per minute and increasing catecholamine concentrations (isoprenaline 0-3 × 10(-6) mM). Force-frequency relation experiments in the presence of a physiological and/or mild acidotic pH solution showed no significant differences. Mean force amplitudes normalized to the lowest frequency showing no significant differences in force development between 0.5 and 3 Hz (n = 9 vs. 13, P = n.s.) (0.5 Hz absolute values 3.1 ± 2.6 for pH = 7.40 vs. 3.8 ± 2.6 mN/mm(2) for pH = 7.20, P = n.s.). Moreover, there was no significant difference in relaxation kinetics between the two groups. Furthermore, the experiments showed similar catecholamine responses in both groups. Force amplitudes normalized to baseline and maximum force showed no significant differences in force development between baseline and maximum isoprenaline concentrations (n = 6 vs. 9, P = n.s.) (baseline absolute values 4.3 ± 4.0 for pH = 7.40 vs. 3.9 ± 1.2 mN/mm(2) for pH = 7.20, P = n.s.). Additionally, relaxation kinetics did not show differences after catecholamine stimulation. The presented experiments revealed no significant negative inotropic effects on isometrically contracting ovine trabeculae with mild metabolic acidosis (pH = 7.2) compared with physiological pH (7.4). Additionally, similar catecholamine responses were seen in both groups. Further investigations (e.g., in vivo and/or in failing hearts with reduced compensatory reserves) will be necessary to examine optimal medical treatment for metabolic abnormalities after cardiac surgery.

Effect of pH and lidocaine on beta-adrenergic receptor binding. Interaction during resuscitation?

Epinephrine and other beta-adrenergic receptor (beta AR) agonists are often administered during cardiopulmonary resuscitation, a time when acid-base abnormalities and arrhythmias also commonly occur. We tested whether beta 2AR binding is influenced by pH or the antiarrhythmic drug lidocaine, and whether pH might influence the interaction of lidocaine with beta 2ARs. With institutional review board approval and informed consent, 32 venous blood samples were obtained from volunteers. Lymphocytes (which bear beta 2ARs similar to those found in heart) were isolated by density gradient centrifugation. Specific binding of the beta AR ligand 3H-dihydroalprenolol (3H-DHA) was determined with lidocaine concentrations ranging from 10(-6) to 10(-2) mol/L (n = 18 experiments), and with and without lidocaine (n = 10 experiments), 100 mumol/L, and with and without QX314 (a permanently charged lidocaine derivative), 1 mmol/L (n = 4 experiments). Data are presented as percent of control-specific binding measured at a pH of 7.4. Statistical analysis consisted of Spearman's rank-test. 3H-DHA-specific binding increased (p < .001) with pH. Thus, alkaline conditions favored binding of 3H-DHA to the receptor. Lidocaine inhibited 3H-DHA binding to beta 2ARs in a concentration-dependent manner. The concentration that inhibited specific binding of 3H-DHA by 50% was 3.1 x 10(-4) mol/L (95% confidence limits, 1.3 x 10(-4) to 7.5 x 10(-4) mol/L). Lidocaine potency at inhibiting beta 2AR binding also increased with increasing pH; thus, there was limited benefit (in terms of increasing binding to beta 2ARs) to increasing pH when lidocaine was present. QX314, despite being present in a 10-fold greater concentration than lidocaine, had no effect on 3H-DHA binding at any tested pH. The affinity of beta 2 ARs for both 3H-DHA and lidocaine increased with pH. Thus, the response to beta 2AR agonists (when no lidocaine is present) might be expected to be greater with normal or alkalotic pH than under acidotic conditions, supporting the correction of metabolic acidosis to achieve optimal effects from beta 2AR agonists during resuscitation.

Sodium bicarbonate versus Carbicarb in canine myocardial hypercarbic acidosis

The objective of this study was to compare the in vivo effects of sodium bicarbonate (NaHCO3) and Carbicarb infusion on regional contractile performance and acid-base status in the setting of hypercarbic acidosis. Animals (N = 9) were anesthetized and paralyzed using sodium pentothal, halothane, and pancuronium bromide, and mechanically ventilated with an air-O2 mixture so that arterial PO2 was > or = 300 mm Hg. Following beta-adrenergic blockade, alveolar ventilation was gradually reduced over a 50-minute period to increase arterial PCO2 to 60 to 80 mm Hg. Each of the following solutions was then infused in consecutive order directly into the left anterior descending artery coronary artery for 15 minutes: (1) 8.4% NaHCO3 at 2 mL/min; (2) 5% sodium chloride at 2 mL/min, equivalent to NaHCO3 in osmolality; (3) 6.3% Carbicarb at 0.5 mL/min, equivalent to NaHCO3 in buffer capacity; and (4) 6.3% Carbicarb at 2 mL/min, equivalent to NaHCO3 in volume. Regional stroke work analog (ultrasonic dimension transducers), interstitial myocardial pH (Khuri electrode), coronary blood flow (doppler flow probe), and hemodynamic/metabolic variables (heart rate, blood pressure, arterial and coronary venous blood gases) were measured at 1, 5, 10, and 15 minutes during each infusion and 10 minutes after the infusion was discontinued, ie, at 25 minutes. Animals were allowed to recover for 45 minutes between interventions. Values at each time point were compared with baseline for statistical significance. Small reductions in interstitial myocardial pH (P < .05) and stroke work (P > .05) were observed within 1 minute of NaHCO3 administration. Both parameters increased significantly from baseline levels thereafter, ie, interstitial myocardial pH at 5 minutes and stroke work at 15 minutes. Infusion of Carbicarb invariably was associated with an increase (P < .05) in interstitial myocardial pH. Stroke work increased (P < .05) during low-dose Carbicarb administration, but infusion of the higher dose was accompanied by a biphasic response, ie, an increase (P < .05) from 0 to 5 minutes, followed by a gradual decrease that achieved statistical significance 10 minutes after termination of the infusion. End-diastolic length was inversely proportional to changes in stroke work, and coronary blood flow varied directly with changes in coronary venous Pco2. Myocardial O2 consumption decreased (P < .05) during Carbicarb infusion, but changes during NaHCO3 did not reach statistical significance. Our findings lend support to the hypothesis that intramyocardial pH determines myocardial function independent of CO2 production by buffer therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of metabolic acidosis and alkalosis on the response to sympathomimetic drugs in dogs

Sympathomimetic drugs are commonly used in many circumstances to increase cardiac output, blood pressure, and myocardial contractility. However, factors such as acidosis or alkalosis are known to influence the action of these drugs. This study looked at the response to the administration of epinephrine, norepinephrine, dopamine, dobutamine, isoproterenol, and glucagon at normal pH and under acidotic (pH 7.2 +/- 0.01) and alkalotic (pH 7.59 +/- 0.01) conditions in 17 dogs. Acidosis was produced with an infusion of hydrochloric acid and alkalosis by infusion of sodium bicarbonate. The infusions were given over one hour followed by a 15- to 30-minute stabilization period. With the administration of each sympathomimetic drug at each pH level, hemodynamic parameters and measurements of myocardia; contractility were recorded. Epinephrine increased cardiac output at normal pH, but decreased cardiac output under conditions of both acidosis and alkalosis; the net change from values at pH 7.40 was nearly 3 L/min. The only other drug to demonstrate this reversal of cardiac output, though to a lesser degree, was dopamine, 10 microg/kg/min, and only in the alkalotic state. Dobutamine was the only drug that decreased contractility under acidotic conditions, while all other drugs caused an increase. In sum, epinephrine was the only drug markedly affected by metabolic acidosis and alkalosis. Isoproterenol's hemodynamic effects were altered the least by changes in acid-base balance. Alkalosis had an equally adverse effect on the cardiovascular system as compared with acidosis.

Direct antilipolytic effect of acidosis in isolated rat adipocytes

The possibility that acidosis inhibits lipolysis indirectly by causing ionic shifts or by favouring the accumulation of an inhibitor has been tested in isolated fat cells. Lipolysis induced by 3 muM noradrenaline (NA) was inhibited by 40-60% and that induced by 1 mM theophylline (THEO) by about 75% when the pH was reduced to 6.6. Lipolysis induced by NA + THEO was inhibited by 20-30%. Changing the concentration of Ca++ or Mg++ did not alter the degree of inhibition. Reducing the K+-ion concentration enhanced the inhibitory effect of low pH on lipolysis induced by NA or NA + THEO, whereas cyclic AMP accumulation was uninfluenced. Omitting glucose from the incubation medium caused a slight enhancement of pH-induced inhibition of lipolysis (from 60 to 70%, p less than 0.01). Reducing the concentration of albumin, which binds inhibitory substances such as FFA, reduced lipolysis more at normal than at reduced pH. At high FFA/albumin ratios (5 or above) lipolysis was similar at normal and reduced pH. The antilipolytic effect of decreased pH was equally pronounced in perifused fat cells, where inhibitory substances are not allowed to accumulate. Our results suggest that the antilipolytic effect of acidosis is mainly a direct effect of the increase in H+ ion concentration. The inhibitory effect of acidosis on various responses to beta-adrenoceptor stimulation may be caused by a decreased formation of cyclic AMP in turn caused directly by the decrease in pH.

Dissociation of theophylline uptake and inotropic effect in myocardial tissue: influence of temperature, pH and calcium

1. The myocardial uptake and the positive inotropic effect of theophylline (100 mug/ml; 0.56 mM) were studied in isolated electrically driven guinea-pig hearts perfused by the Langendorff technique under various extracellular conditions. [3H]-theophylline was used. 2. Variations in temperature, hydrogen ion and calcium ion concentrations of the perfusion media changed the time course and magnitude of the effect of theophylline on myocardial twitch tension but did not affect the time course and amount of theophylline uptake. 3. Under all conditions, the build-up of the positive inotropic effect of theophylline was about three times faster than the uptake of the drug into the heart. 4. Since no relationship could be found between theophylline uptake and inotropic effect, the cardiac positive inotropic response to theophylline is thought unlikely to be due mainly to an interaction of the drug with intracellular receptor sites but is assumed to occur via an effect of the drug on the sarcolemma, that is at a site which the drug reaches before it enters the intracellular space.