Right ventricular function and pulmonary hemodynamics during dopamine infusion in burned patients

Hemodynamic coherence in patients with burns

Burn shock is characterized by profound hemodynamic alterations mainly associated with rapid loss of intravascular volume related to severe capillary leak. Thus, fluid resuscitation conventionally based on macrocirculatory targets is considered as a corner stone of initial management of patients with burns. Nonetheless, traditional markers such as blood pressure, urinary output, and cardiac output are helpful but do not sufficiently reflect the adequacy of perfusion and oxygenation at the microcirculatory level. Microcirculatory alterations have been identified in patients with severe burns even when macrocirculatory variables are within therapeutic goals. In this review, we discuss the pathophysiology of the microvascular alterations in burn shock, its coherence with macrocirculatory physiologic variables, and potential future implications for the treatment of burn shock.

Changes in cardiac physiology after severe burn injury

Cardiac stress, mediated by increased catecholamines, is the hallmark of severe burn injury typified by marked tachycardia, increased myocardial oxygen consumption, and increased cardiac output (CO). It remains one of the main determinants of survival in large burns. Currently, it is unknown for how long cardiac stress persists after a severe injury. Therefore, the aim of this study was to determine the extent and duration of cardiac stress after a severe burn. To determine persistence of cardiac alteration, the authors determined cardiac parameters of all surviving patients with burns ≥ 40% TBSA from 1998 to 2008. One hundred ninety-four patients were included in this study. Heart rate, mean arterial pressure, CO, stroke volume, cardiac index, and ejection fractions were measured at regular intervals from admission up to 2 years after injury. Rate pressure product was calculated as a correlate of myocardial oxygen consumption. All values were compared with normal nonburned children to validate the findings. Statistical analysis was performed using log transformed analysis of variance with Bonferroni correction and Student's t-test, where applicable. Heart rate, CO, cardiac index, and rate pressure product remained significantly increased in burned children for up to 2 years when compared with normal ranges (P < .05), indicating vastly increased cardiac stress. Ejection fraction was within normal limits for 2 years. Cardiac stress persists for at least 2 years postburn, and the authors suggest that attenuation of these detrimental responses may improve long-term morbidity.

Thermal injury impairs cardiac protein synthesis and is associated with alterations in translation initiation

The purpose of the present study was to determine whether burn injury decreases myocardial protein synthesis and potential contributing mechanisms for this impairment. To address this aim, thermal injury was produced by a 40% total body surface area full-thickness scald burn in anesthetized rats, and the animals were studied 24 h late. Burn decreased the in vivo-determined rate of myocardial protein synthesis and translation efficiency by 25% but did not alter the protein synthetic rate in skeletal muscle. To identify potential mechanisms responsible for regulating mRNA translation in cardiac muscle, we examined several eukaryotic initiation factors (eIFs) and elongation factors (eEFs). Burn failed to alter eIF2B activity or the total amount or phosphorylation status of either eIF2 alpha or eIF2B epsilon in heart. In contrast, hearts from burned rats demonstrated 1) an increased binding of the translational repressor 4E-BP1 with eIF4E, 2) a decreased amount of eIF4E associated with eIF4G, and 3) a decreased amount of the hyperphosphorylated gamma-form of 4E-BP1. These changes in eIF4E availability were not seen in gastrocnemius muscle where burn injury did not decrease protein synthesis. Furthermore, constitutive phosphorylation of mTOR, S6K1, the ribosomal protein S6, and eIF4G were also decreased in hearts from burned rats. Burn did not appear to adversely affect elongation because there was no significant difference in the myocardial content of eEF1 alpha or eEF2 or the phosphorylation state of eEF2. The above-mentioned burn-induced changes in mRNA translation were associated with an impairment of in vitro myocardial performance. Finally, 24 h postburn, the cardiac mRNA content of IL-1 beta, IL-6, and high-mobility group protein B1 (but not TNF-alpha) was increased. In summary, these data suggest that thermal injury specifically decreases cardiac protein synthesis in part by decreasing mRNA translation efficiency resulting from an impairment in translation initiation associated with alterations in eIF4E availability and S6K1 activity.

Burn injury alters beta-adrenergic receptor and second messenger function in rat ventricular muscle

OBJECTIVES

The molecular pharmacologic bases for the attenuated cardiovascular and metabolic responses to catecholamines, after burn injury, have not been elucidated. In the present study, myocardial tissues were used as a model of beta-adrenergic receptors to study burn injury-induced alterations in receptors and in signal transduction.

DESIGN

Prospective study, randomized to treatment and control groups.

SETTING

University-hospital research laboratory.

SUBJECTS

Male Sprague-Dawley rats (180 to 210 g).

INTERVENTIONS

A 50% body surface area burn or sham-burn was administered to the rats.

MEASUREMENTS AND MAIN RESULTS

Myocardial membranes were isolated at 24 hrs, 7 days and 14 days after 50% body surface area scald or sham injury. (-)125I-iodocyanopindolol was used to assess maximal binding capacity and affinity of the beta-adrenergic receptor. Basal and stimulated concentrations of second messenger, cyclic adenosine monophosphate (cAMP), were also assessed. Production of cAMP during isoproterenol stimulation tested the integrity of the beta-adrenergic receptor-mediated signal transduction. Forskolin, which stimulates adenylate cyclase enzyme directly (bypassing the receptor and G protein) to produce cAMP, tested the efficacy of the enzyme itself. Maximal binding capacity was unaltered between the experimental and control groups, but the affinity (mean +/- SEM) was significantly decreased in burned animals at 7 days (125.4 +/- 15.5 picomoles [pmol]; p = .01) and at 14 days (216.7 +/- 50.7 pmol; p = .001) compared with controls (75.5 +/- 8.4 pmol). In different set experimental and control groups, basal concentrations of cAMP in myocardial membranes were significantly decreased in burned animals at 7 days (control 38.6 +/- 4.2 vs. 5.8 +/- 0.9 pmol/mg of protein/min; p = .003) and at 14 days (control 47.4 +/- 3.2 vs 28.3 +/- 6.6 pmol/mg of protein/min; p = .002). The forskolin (direct)-stimulated synthesis of cAMP was decreased in burned animals at 24 hrs (control 339.0 +/- 40.5 vs. 214.4 +/- 16.6 pmol/mg of protein/min; p = .01), at 7 days (control 289.0 +/- 34.4 vs. 32 +/- 13.0 pmol/mg of protein/min; p = .01), and at 14 days (control 322.9 +/- 28.6 vs. 137.0 +/- 46.1 pmol/mg of protein/min; p = .01). The isoproterenol or receptor-mediated stimulation of cAMP production was also significantly (p < .001) impaired in burned animals compared with controls at 24 hrs (control 134.7 +/- 11.9 vs. 83.1 +/- 13.3 pmol/mg of protein/min), and at 14 days (control 128.2 +/- 7.2 vs. 92.8 +/- 17.7 pmol/mg of protein/min).

CONCLUSION

The etiology of the decreased responses in the myocardium to exogenous and endogenous beta-adrenergic receptor agonists after burn injury may be attributed to decreased affinity for ligands, and also to impaired receptor-mediated signal transduction and to decreased adenylate cyclase enzyme activity, resulting in decreased basal and stimulated second messenger (cAMP) production.

Prognostic significance of early cardiac index measurements in severely burned patients

Invasive monitoring during early resuscitation was performed. To compare the heamodynamic results of severely burned patients, the results of 38 patients hospitalized between 1988 and 1991 in the burn centre of Lyon were retrospectively reviewed. Survivors and non-Survivors' data were compared. No difference existed between the two groups in age, unit burn score, fluid requirement and dose of dobutamine. Survivors had a significantly higher cardiac index, O2 delivery and systolic blood pressure index than non-survivors. It is suggested that the ability to sustain a high cardiac index in response to the burn injury plays a role in the outcome of the patients. There is an indication that dobutamine could have a beneficial effect in this way. Further studies are needed to confirm the benefit of the maintenance of high cardiac index levels by the pressors.

Right ventricular function in early septic shock states

OBJECTIVES

To define a variable which could reliably predict when fluid resuscitation as monotherapy is not expected to improve organ perfusion pressure, owing to limitations in cardiac output responsiveness in patients with severe sepsis.

DESIGN

Prospective controlled trial.

SETTING

Anesthesiological ICU in a university hospital.

PATIENTS

Twenty seven patients in early septic shock states (MAP < 60 mmHg).

INTERVENTIONS

Infusion therapy was titrated until no further increase in cardiac index and mean arterial pressure could be achieved. Fluid resuscitation as monotherapy was deemed unsuccessful at the end of 2 h if inotropic or vasoactive pharmacologic support was required to maintain a mean arterial pressure > 60 mmHg.

MEASUREMENTS AND RESULTS

We investigated the hemodynamic course during fluid resuscitation (2850 +/- 210 ml crystalloids) with special emphasis on right heart function using the thermodilution technique. Eleven patients (group A) had a right ventricular (RV) ejection fraction below 45%. In this group positive inotropic and/or vasoactive drugs were obligatory to achieve and maintain a sufficient perfusion pressure (MAP > 60 mmHg) after fluid challenge.

CONCLUSIONS

In 27 septic shock patients investigated, we diagnosed right ventricular dysfunction in 41%. In this specific patient population fluid replacement alone did not succeed in stabilizing hemodynamic variables, therefore necessitating catecholamine therapy.

In vitro validation of a right ventricular thermodilution ejection fraction system

Right ventricular ejection fraction (RVEF) is used clinically as an index of right ventricular (RV) pump function. Clinical measurements of RVEF are complicated by the need for complex imaging equipment to compute RV volumes. Recently, the use of thermodilution (TD) methods have been suggested as a simplified means to measure RVEF (RVEFTD) in patients using rapid response thermistors. Validation, however, by comparison of RVEFTD and other methods in vivo, is difficult. Accordingly, thermodilution derived EF measurements (EFTD) were compared to known values using an in vitro system, with known ejection fractions (EF) set from 17-78% and stroke rates varying independently from 50-100 strokes/min. EFTD was computed by fitting the downslope of the TD curve to a monoexponential function and computing the time constant of thermal decay. A significant correlation existed between EFTD and actual EF over the entire study (r = 0.96, p less than 0.001). Bias analysis showed that the points were within a 95% confidence interval of +/- 12%. Multivariate analysis showed that stroke rate did not significantly affect TD measurements (r = 0.03, p greater than 0.7). This study demonstrates that TD accurately predicts EF using an in vitro system and appears to be independent of stroke rate. Thus, TD methods may provide an accurate, simple and reliable means to serially measure RVEF in the clinical setting.

Efficacy of right atrial infusion of PGE1 in sepsis-induced pulmonary hypertension

In this study we investigated the effects of right atrial infusion of PGE1 (RAIPGE1) in doses from 40 to 500 ng/kg/min on sepsis-induced pulmonary artery hypertension (SIPAH). Thirteen pigs were randomized into a time-course group (n = 6) and a PGE1-treated group (n = 7). Pulmonary hypertension (PAH) was induced with the infusion of Pseudomonas Aeruginosa (PsAr) at a concentration of 2 X 10(8) CFU/20 kg/min in both groups. The infusion of PsAr caused a significant and persistent rise in mean pulmonary artery pressure (MPA), pulmonary vascular resistance (PVRI), right ventricular compliance (RVC), RV dp/dt, and right ventricular stroke work index (RVSWI), 30 min after the onset of infusion (P less than 0.05 vs baseline). Systemic hemodynamics and gas exchange were not affected throughout the 3-hr period of infusion (P = NS); however, left ventricular compliance (LVC) was depressed at a MPA greater than 35 mm Hg. The RAIPGE1 following SIPAH caused a concentration-dependent reduction above 40 ng/kg/min of MPA, PVRI, RVSWI, and RV dp/dt (P less than 0.05, 120 and 500 ng/kg/min vs PAH). RVC returned to baseline values during the infusion of PGE1. Systemic hemodynamics, including oxygen delivery and extraction, were unaffected by the infusion of PGE1, but LVC was improved (P less than 0.05, PGE1 500 vs PAH). The infusion of PGE1 caused a concentration-dependent rise in shunt fraction (Qs/Qt) and alveolararterial oxygen gradients which reached statistical significance during the infusion of 500 ng/kg/min. Our data show that RAIPGE1 is effective in ameliorating RV and pulmonary hemodynamics, but at the largest dose it negatively affects gas exchange.

Thermodilution right ventricular ejection fraction. Catheter positioning effects

Right ventricular (RV) ejection fractions have been difficult to estimate clinically. It has been demonstrated recently that RV ejection fractions can be calculated by thermodilution techniques using a rapid response thermistor and computer. This method critically depends on adequate mixing of the thermal bolus and sensing of the rapid response thermistor. This study examined the effects of the thermistor position within the pulmonary artery and injectate site within the right atrium on RV thermodilution ejection fraction measurements. Ten pigs were instrumented with a RV thermodilution catheter in the pulmonary artery, an injectate catheter in the right atrium, an atrial-pacing electrode, and a systemic arterial catheter. The RV ejection fractions were determined using thermodilution in two ways: (1) with incremental increases in pulmonic valve to thermistor distance, and (2) with incremental increases in injectate port to tricuspid valve. These measurements were obtained at a paced rate of 107 +/- 1 beats per minute (bpm) and then repeated with pacing-induced tachycardia (140 bpm). The highest RV ejection fraction with the lowest coefficient of variation was with the thermistor 2 cm from the pulmonic valve (50 +/- 2 percent), with a significant decline from this value at 10 cm (42 +/- 4 percent, p less than 0.05). This reduction in RV ejection fraction values with increased pulmonic valve to thermistor distance became more pronounced with tachycardia where a significant decline in RV ejection fraction occurred at 4 cm from the valve when compared with 0 cm (38 +/- 6 percent vs 47 +/- 3 percent, respectively, p less than 0.05). There was no significant change in RV ejection fraction at any injectate port to tricuspid valve distance at the lower heart rate. With tachycardia, however, a significant decline in RV ejection fraction occurred with the injectate port located 7 cm from the tricuspid valve (p less than 0.05). These results demonstrate that RV ejection fractions can be reliably obtained using thermodilution. Positioning of the thermodilution catheter is an important consideration for obtaining optimal RV ejection fraction measurements. Care should be taken to position the catheter with the thermistor a minimal distance from the pulmonic valve and the injectate port within the central body of the right atrium.

Thermal trauma alters myocardial cyclic nucleotides and protein content in mice

1. This study tested the hypothesis that the systemic effects of burn include altered metabolic activity in the heart. Metabolic activity was studied by measuring alterations in cyclic nucleotide levels and protein concentrations in atrial and ventricular muscle in mice at 14 and 22 days after a 20% body surface area (BSA) burn. Thermal injury was produced on the dorsal surface of anesthetized male CD mice by immersion in water at 95 degrees C for 8 s. This resulted in a full-thickness, 3 degrees scald burn. In atrial and ventricular tissues, levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) and guanosine 3':5'-cyclic monophosphate (cyclic GMP) were analyzed by 125I-radioimmunoassay. 2. The protein content (mg prot g-1 dry wt) increased in the atria. The cyclic AMP content (nmol g-1 dry wt) was significantly increased fourfold and ninefold at 14 and 22 days, respectively, in atria from burned animals compared to controls. The cyclic AMP/cyclic GMP ratios were similarly increased. 3. In the ventricle, the protein content and cyclic AMP levels were not altered, but the cyclic AMP/cyclic GMP ratios (nmol g-1 dry wt) were increased at both 14 and 22 days. These changes both in atria and ventricles were less prominent when cyclic nucleotide concentrations or ratios were expressed as pmol mg-1 protein. 4. The data confirm the hypothesis that a 20% BSA thermal injury evokes effects in sites remote from burn injury such as in the atria and ventricles. These effects include total body weight loss, elevated cyclic AMP, cyclic AMP/cyclic GMP ratios, and protein levels in the atria, and elevated cyclic AMP/cyclic GMP ratios in both atrial and ventricular tissues at 2 and 3 weeks after thermal injury. To prevent underestimation of cyclic nucleotide levels such changes should preferably be expressed on a prot g- dry weight basis.

Alteration by burn injury of the pharmacokinetics and pharmacodynamics of cimetidine in children

We have studied the mechanisms of the increased dosage requirements of the H2-receptor antagonist cimetidine in paediatric burned patients in a pharmacokinetic and pharmacodynamic study. Cimetidine (10-15 mg.kg-1) was given to 21 burned children and multiple blood samples were obtained for determination of plasma cimetidine concentrations and pharmacokinetic analysis. The relation of gastric pH to plasma cimetidine concentrations was studied in five of these children who had nasogastric tubes. In an additional four patients the effects of cimetidine on gastric pH were studied during a continuous infusion of cimetidine, which maintained steady-state plasma cimetidine concentrations above 0.5 microgram.ml-1. The mean (SEM) clearance of cimetidine in burned children was 16.22 ml.kg-1 and cimetidine half-life was 1.06 h. The cimetidine clearance and half-life values were significantly higher in burned children compared with our previously reported values for normal adult patients, 8.2 ml.min.kg-1 and 2.21 h respectively. Endogenous creatinine clearance normalized to 70 kg in burned children was 190 ml.min-1. In burned children 41% of the dose of intact cimetidine was excreted during 8 h of the study compared with 45% excretion during 24 h in healthy adult controls previously reported. The correlation coefficient between creatinine and cimetidine clearances was 0.93 (r2 = 0.85). The plasma concentration of cimetidine needed to increase gastric pH to greater than or equal to 4.0 was greater than or equal to 1.0 micron.ml-1, which contrasts with the value of greater than 0.5 micron.ml-1 required for adult burned patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopamine vs norepinephrine on hemodynamics in septic shock. Emphasis on right ventricular performance

The effects of continuously infused dopamine and norepinephrine on hemodynamics, oxygen metabolism, and right ventricular (RV) performance were studied by crossover design in ten patients with septic shock who needed treatment with vasoactive drugs after fluid replacement. Standard hemodynamic measurements were obtained and RV performance assessed before and 1 h after the start of the infusion. All but one patient had pulmonary hypertension, and in seven the RV ejection fraction (RVEF) was lower than 50 percent at baseline. Drugs were titrated to a systolic arterial blood pressure of mean 106 +/- 18 mm Hg for dopamine and 116 +/- 20 mm Hg for norepinephrine (NS). Dopamine infusion increased the cardiac index (CI) 16 percent (p less than 0.02), but heart rate and systemic and pulmonary vascular resistances were unchanged. With norepinephrine CI was unchanged, a heart rate decreased 7 percent (p less than 0.05), and systemic and pulmonary vascular resistance increased 35 and 26 percent, respectively (p less than 0.05). With both drugs, RV volumes and RVEF remained unchanged, and systemic oxygen consumption increased equally (by 19 percent for dopamine and 22 percent for norepinephrine, p less than 0.05); systemic oxygen delivery rose by 17 percent during dopamine infusion and was unchanged during norepinephrine infusion. Norepinephrine increased oxygen extraction vs dopamine (p less than 0.05). There were no differences in urinary output. Norepinephrine may improve the RV oxygen supply/demand ratio, but this potentially beneficial effect on RV ejection fraction may be offset by a concomitant increase in pulmonary vascular resistance and RV afterload. Norepinephrine may not adversely affect the peripheral circulation. In short-term treatment of volume-resuscitated, severe septic shock complicated by pulmonary hypertension and impaired RV performance, norepinephrine may be at least as effective as dopamine.

Right ventricular dysfunction in septic shock: assessment by measurements of right ventricular ejection fraction using the thermodilution technique

Right ventricular ejection fraction (RVEF) was measured by the thermodilution technique in a series of 127 consecutive critically ill patients monitored with a modified pulmonary artery (PA) catheter equipped with a fast response thermistor. Thermodilution RVEF was significantly lower in septic shock (23.8 +/- 8.2%, 93 measurements) than in sepsis without shock (30.3 +/- 10.1%, 118 measurements) or in the absence of sepsis or cardiopulmonary impairment (32.5 +/- 7.1%, 62 measurements). Both myocardial depression and pulmonary hypertension could account for this impairment of RV function. RVEF decreased from 35.1 +/- 9.8 to 24.2 +/- 10.4% (P less than 0.01) during development of septic shock and increased from 25.0 +/- 7.6 to 29.8 +/- 8.5% (P less than 0.05) during recovery (14 patients). Initial RVEF in septic shock was 27.8 +/- 8.6% in 11 patients who survived but only 20.9 +/- 6.7% (P less than 0.02) in the 23 patients who eventually died. Thus, RV dysfunction is common during septic shock, is directly related to its severity, and can easily be recognized in patients monitored with a PA catheter.

The right ventricle and critical illness: a review of anatomy, physiology, and clinical evaluation of its function

This paper reviews right ventricular anatomy and physiology in the critically ill patient. The role of right ventricular function during acute pulmonary artery hypertension and the effect of acute myocardial injury upon right ventricular performance are examined. Clinical methods of assessing right ventricular function at the bedside in acutely ill patients are critically reviewed.