Case Report: Novel Monitoring for Anaerobic Conditions Detected by Respiratory Quotient in a Critically Ill Pediatric Patient

BACKGROUND

Hyperlactemia after cardiopulmonary bypass is associated with adverse events during the early postoperative period in children. Serum lactate levels, a standard marker of anaerobic metabolism, are determined by the production, conversion and clearance of lactate, and may lag behind the anaerobic response. Here, we report a neonatal case under anaerobic conditions after cardiac surgery, whose expired gas parameters dramatically changed before a rise in blood lactate.

CASE PRESENTATION

A 23-day-old girl with tetralogy of Fallot was admitted to the pediatric intensive care unit after modified Blalock-Taussig shunt operation. As hemoconcentration increased and pleural fluid and ascites accumulated, we performed partial exchange transfusion to prevent shunt occlusion. Ten minutes after partial exchange transfusion, oxygen uptake and carbon dioxide production measured by indirect calorimetry suddenly dropped, while the respiratory quotient began to rise steeply before hyperlactatemia developed a few hours later.

CONCLUSION

Analysis of expired gas in critically ill children can detect the transition from aerobic to anaerobic conditions before hyperlactatemia.

Metabolic effects of beta-blockers in critically ill patients: A retrospective cohort study

BACKGROUND

Beta-blockers have potential protective features during critical illness. Heart rate reduction, with limited effect on blood pressure and beneficial effects on metabolism, organ function and inflammation have been reported. We examined metabolic effects of beta-blockers among ICU patients, to address the effect on the estimated energy expenditure, measured by carbon dioxide production (VCO₂). Furthermore, we investigated effects on organ function and inflammation.

METHODS

A retrospective study in adult patients admitted to our 17-beds mixed medical-surgical ICU from January 2013 to March 2016. Mechanically ventilated patients who commenced beta-blockers were eligible for inclusion. Exclusion criteria were: beta-blocker therapy in the 7 previous days, treatment duration <48 h, therapeutic hypothermia, and no VCO₂ measurements. Outcome parameters were obtained at 6 different time points from 24 h before until 48 h after beta-blocker commencement. Linear mixed models were used to evaluate trends.

RESULTS

In total 58 patients were included. Various types of beta-blockers were administered, with a median equivalent daily dose to metoprolol of 50.0 mg (IQR 25.0-62.5). The mean heart rate decreased from 103 ± 20 to 91 ± 19 beats per minute after 48 h (p < 0.001), with unaltered blood pressures. Metabolic and other parameters did not show significant differences over time, or parameter changes were due to trends that had already started before beta-blocker commencement.

CONCLUSIONS

No changes in VCO₂ after beta-blocker commencement were demonstrated suggesting no alterations in energy expenditure. Heart rates significantly decreased with unaltered blood pressures. Other parameters did not show trends that could be attributed to beta-blockers effects.

Metabolic equivalents fail to indicate metabolic load in post-myocardial infarction patients during the modified Bruce treadmill walking test

AIM

To investigate the suitability of metabolic equivalents (METs) for determining exercise intensity in phase-IV post-myocardial infarction (MI) men during the modified Bruce treadmill walking test (MBWT).

METHODS

Twenty phase-IV post-MI men (mean±SD, aged 64.4±5.8 years) and 20 healthy non-cardiac male controls (59.8±7.6 years) participated. Participants performed a MBWT. Throughout the participants' heart rate (HR), heart rhythm, expired air parameters and ratings of perceived exertion (RPEs) were measured. MET values were compared between groups and those currently ascribed to each stage of the MBWT.

RESULTS

General linear model analysis found no significant differences between groups during the MBWT for VO2, VCO2, HR, METs or RPEs (Borg 6-20 scale). Ascribed METs did not differ from mean METs of post-MIs or controls other than at stage 5 where post-MI METs were significantly lower. Irrespective, the post-MI group worked at a higher percentage of their anaerobic threshold (AT) (respiratory exchange ratio, RER=1.0) (F(2,5)=7.22, p<0.008), higher RER (F(2,5)=11.25, p<0.001) with increased breathing frequency (F(2,5)=7.22, p<0.001). Regression analysis revealed AT to be VO2 25.6 (mL/kg/min) for post-MI versus VO2 31.1 (mL/kg/min) for controls. Gross energy expenditure (kcal/min) was greater for the post-MI group compared with controls (F(2,5)=11.22, p<0.001). Throughout the MBWT, post-MI group worked at a higher %AT/MET than controls (F(2,196)=211.76, p<0.01). Body composition did not strongly influence %AT/MET, parameters of VO2, METs or RPE.

CONCLUSION

During the MBWT, post-MI men worked more anaerobically per MET (%AT/MET) than controls. Therefore, current METs based on non-cardiac individuals appear unsuitable in determining the full metabolic load of the exercise intensity for cardiac patients during the MBWT.

Energy expenditure in critically ill patients estimated by population-based equations, indirect calorimetry and CO2-based indirect calorimetry

Background

Indirect calorimetry (IC) is the reference method for measurement of energy expenditure (EE) in mechanically ventilated critically ill patients. When IC is unavailable, EE can be calculated by predictive equations or by VCO₂-based calorimetry. This study compares the bias, quality and accuracy of these methods.

Methods

EE was determined by IC over a 30-min period in patients from a mixed medical/postsurgical intensive care unit and compared to seven predictive equations and to VCO₂-based calorimetry. The bias was described by the mean difference between predicted EE and IC, the quality by the root mean square error (RMSE) of the difference and the accuracy by the number of patients with estimates within 10 % of IC. Errors of VCO₂-based calorimetry due to choice of respiratory quotient (RQ) were determined by a sensitivity analysis, and errors due to fluctuations in ventilation were explored by a qualitative analysis.

Results

In 18 patients (mean age 61 ± 17 years, five women), EE averaged 2347 kcal/day. All predictive equations were accurate in less than 50 % of the patients with an RMSE ≥ 15 %. VCO₂-based calorimetry was accurate in 89 % of patients, significantly better than all predictive equations, and remained better for any choice of RQ within published range (0.76–0.89). Errors due to fluctuations in ventilation are about equal in IC and VCO₂-based calorimetry, and filtering reduced these errors.

Conclusions

This study confirmed the inaccuracy of predictive equations and established VCO₂-based calorimetry as a more accurate alternative. Both IC and VCO₂-based calorimetry are sensitive to fluctuations in respiration.

Functional iron deficiency and diastolic function in heart failure with preserved ejection fraction

BACKGROUND

Functional iron deficiency (FID) is an independent risk factor for poor outcome in advanced heart failure with reduced EF, but its role in heart failure with preserved EF (HFPEF) remains unclear. We aimed to investigate the impact of FID on cardiac performance determined by pressure-volume loop analysis in HFPEF.

METHODS

26 HFPEF patients who showed an increase in LV stiffness by pressure-volume (PV) loop analysis obtained by conductance-catheterization, performed exercise testing, echocardiographic examination including tissue Doppler and determination of iron metabolism: serum iron, ferritin and transferrin saturation. HFPEF patients who provided ferritin <100 μg/l or ferritin of 100-299 μg/l in combination with transferrin saturation <20% were defined as having FID. In 14 patients the expression of transferrin receptor was determined from available endomyocardial biopsies.

RESULTS

Fifteen out of 26 HFPEF patients showed FID without anemia. Compared to control subjects and HFPEF patients without FID, HFPEF patients with FID showed an up-regulation of the myocardial transferrin receptor expression (p<0.05). No differences between HFPEF patients with and without iron deficiency were found in heart dimensions, systolic and diastolic function obtained by PV-loop and echocardiography analysis. According to the linear regression analysis, LV stiffness was correlated with peak oxygen uptake (r=-0.636, p<0.001) but not with the ferritin level or transferrin saturation. No relation was found between FID and exercise capacity. The association of LV stiffness with exercise performance was independent from the level of iron deficiency.

CONCLUSION

In non-anemic HFPEF patients, cardiac dysfunction and impaired exercise capacity occur independently of FID.