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

Transcutaneous carbon dioxide monitoring during prolonged apnoea with high-flow nasal oxygen

BACKGROUND

The duration of apnoeic oxygenation with high-flow nasal oxygen is limited by hypercapnia and acidosis and monitoring of arterial carbon dioxide level is therefore essential. We have performed a study in patients undergoing prolonged apnoeic oxygenation where we monitored the progressive hypercapnia with transcutaneous carbon dioxide. In this paper, we compared the transcutaneous carbon dioxide level with arterial carbon dioxide tension.

METHODS

This is a secondary publication based on data from a study exploring the limits of apnoeic oxygenation. We compared transcutaneous carbon dioxide monitoring with arterial carbon dioxide tension using Bland-Altman analyses in anaesthetised and paralysed patients undergoing prolonged apnoeic oxygenation until a predefined limit of pH 7.15 or PCO₂ of 12 kPa was reached.

RESULTS

We included 35 patients with a median apnoea duration of 25 min. Mean pH was 7.14 and mean arterial carbon dioxide tension was 11.2 kPa at the termination of apnoeic oxygenation. Transcutaneous carbon dioxide monitoring initially slightly underestimated the arterial tension but at carbon dioxide levels above 10 kPa it overestimated the value. Bias ranged from -0.55 to 0.81 kPa with limits of agreement between -1.25 and 2.11 kPa.

CONCLUSION

Transcutaneous carbon dioxide monitoring provided a clinically acceptable substitute for arterial blood gases but as hypercapnia developed to considerable levels, we observed overestimation at high carbon dioxide tensions in patients undergoing apnoeic oxygenation with high-flow nasal oxygen.

Fluid Therapy During Cardiopulmonary Resuscitation

Cardiopulmonary arrest (CPA), the acute cessation of blood flow and ventilation, is fatal if left untreated. Cardiopulmonary resuscitation (CPR) is targeted at restoring oxygen delivery to tissues to mitigate ischemic injury and to provide energy substrate to the tissues in order to achieve return of spontaneous circulation (ROSC). In addition to basic life support (BLS), targeted at replacing the mechanical aspects of circulation and ventilation, adjunctive advanced life support (ALS) interventions, such as intravenous fluid therapy, can improve the likelihood of ROSC depending on the specific characteristics of the patient. In hypovolemic patients with CPA, intravenous fluid boluses to improve preload and cardiac output are likely beneficial, and the use of hypertonic saline may confer additional neuroprotective effects. However, in euvolemic patients, isotonic or hypertonic crystalloid boluses may be detrimental due to decreased tissue blood flow caused by compromised tissue perfusion pressures. Synthetic colloids have not been shown to be beneficial in patients in CPA, and given their documented potential for harm, they are not recommended. Patients with documented electrolyte abnormalities such as hypokalemia or hyperkalemia benefit from therapy targeted at those disturbances, and patients with CPA induced by lipid soluble toxins may benefit from intravenous lipid emulsion therapy. Patients with prolonged CPA that have developed significant acidemia may benefit from intravenous buffer therapy, but patients with acute CPA may be harmed by buffers. In general, ALS fluid therapies should be used only if specific indications are present in the individual patient.

The effect of 0.9% saline versus plasmalyte on coagulation in patients undergoing lumbar spinal surgery; a randomized controlled trial

INTRODUCTION

In multi-level lumbar spinal fusion surgery yielding a large amount of blood loss, choice of fluid for volume resuscitation is an important issue since it can influence acid-base status, coagulation, and patients' outcome. This study compared the effect of plasmalyte to 0.9% saline on coagulation assessed by rotation thromboelastometry (ROTEM) and acid-base balance in the aforementioned patients.

METHODS

Fifty patients were randomly allocated to receive either 0.9% saline or plasmalyte during operation and until postoperative 12 h. ROTEM was performed at 10 min after anesthetic induction and end of surgery. Arterial blood gas analyses were serially performed from 10 min after anesthetic induction until postoperative 12 h. Fluid balance, blood loss, and transfusion requirement were assessed.

RESULTS

ROTEM variables showed sporadic deterioration in both groups after surgery without intergroup differences. Intraoperatively, arterial pH, base excess, and bicarbonate concentrations were lower and serum chloride concentrations were higher in the 0.9% saline group compared with the plasmalyte group. The differences in base excess and bicarbonate concentrations persisted until postoperative 12 h. Fluid balance, blood loss, and transfusion requirement were similar between the groups while urine output was greater in the plasmalyte group compared with the 0.9% saline group (3.2 ± 1.6 ml/kg/h vs. 1.8 ± 1.1 ml/kg/h, p = 0.001).

CONCLUSION

In contrast to plasmalyte, fluid therapy with 0.9% saline resulted in transient hyperchloremic acidosis in patients undergoing multi-level lumbar spinal fusion, while coagulation assessed by ROTEM analysis and the amount of blood loss were similar between the groups.

Half-molar sodium lactate infusion improves cardiac performance in acute heart failure: a pilot randomised controlled clinical trial

Introduction

Acute heart failure (AHF) is characterized by inadequate cardiac output (CO), congestive symptoms, poor peripheral perfusion and end-organ dysfunction. Treatment often includes a combination of diuretics, oxygen, positive pressure ventilation, inotropes and vasodilators or vasopressors. Lactate is a marker of illness severity but is also an important metabolic substrate for the myocardium at rest and during stress. We tested the effects of half-molar sodium lactate infusion on cardiac performance in AHF.

Methods

We conducted a prospective, randomised, controlled, open-label, pilot clinical trial in 40 patients fulfilling two of the following three criteria for AHF: (1) left ventricular ejection fraction <40%, (2) acute pulmonary oedema or respiratory failure of predominantly cardiac origin requiring mechanical ventilation and (3) currently receiving vasopressor and/or inotropic support. Patients in the intervention group received a 3 ml/kg bolus of half-molar sodium lactate over the course of 15 minutes followed by 1 ml/kg/h continuous infusion for 24 hours. The control group received only a 3 ml/kg bolus of Hartmann’s solution without continuous infusion. The primary outcome was CO assessed by transthoracic echocardiography 24 hours after randomisation. Secondary outcomes included a measure of right ventricular systolic function (tricuspid annular plane systolic excursion (TAPSE)), acid-base balance, electrolyte and organ function parameters, along with length of stay and mortality.

Results

The infusion of half-molar sodium lactate increased (mean ± SD) CO from 4.05 ± 1.37 L/min to 5.49 ± 1.9 L/min (P < 0.01) and TAPSE from 14.7 ± 5.5 mm to 18.3 ± 7 mm (P = 0.02). Plasma sodium and pH increased (136 ± 4 to 146 ± 6 and 7.40 ± 0.06 to 7.53 ± 0.03, respectively; both P < 0.01), but potassium, chloride and phosphate levels decreased. There were no significant differences in the need for vasoactive therapy, respiratory support, renal or liver function tests, duration of ICU and hospital stay or 28- and 90-day mortality.

Conclusions

Infusion of half-molar sodium lactate improved cardiac performance and led to metabolic alkalosis in AHF patients without any detrimental effects on organ function.

Trial registration

Clinicaltrials.gov NCT01981655. Registered 13 August 2013.

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.

Physiological effects of hyperchloraemia and acidosis

The advent of balanced solutions for i.v. fluid resuscitation and replacement is imminent and will affect any specialty involved in fluid management. Part of the background to their introduction has focused on the non-physiological nature of 'normal' saline solution and the developing science about the potential problems of hyperchloraemic acidosis. This review assesses the physiological significance of hyperchloraemic acidosis and of acidosis in general. It aims to differentiate the effects of the causes of acidosis from the physiological consequences of acidosis. It is intended to provide an assessment of the importance of hyperchloraemic acidosis and thereby the likely benefits of balanced solutions.

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)