R.A. Little

Muscle wasting and energy balance in critical illness.

BACKGROUND In nine patients with multiple organ failure ultrasound was able to identify muscle wasting despite the presence of oedema (Campbell et al., J Clin Nutr 62 (1995) 533). AIMS The purpose of the present study was twofold: one was to determine whether this technique was applicable to a much larger ICU population, many of whom were not as ill as the original subjects. The second reason was to determine whether a relationship could be identified between rates of wasting and energy balance. METHODS Serial measurements of both mid-upper arm circumference (MAC) and muscle thickness, using ultrasound, were made at 1-3 day intervals between 5 and 39 (median 7) days in 50 critically ill patients. RESULTS Muscle thickness decreased in 48 of the 50 patients at a median rate of 1.6%/day with a range of 0.2-5.7%/day. In 33 patients, in whom MAC did not change significantly with time, muscle thickness decreased by between 0.3 and 4.2 (median 1.6)%/day. In three patients MAC increased significantly with time but muscle thickness decreased by between 1.3 and 5.7 (median 2.6)%/day. Twelve patients showed a significant decrease in MAC with time and muscle thickness in this group decreased by between 0.2 and 4.0 (median 1.3)%/day. The percentage decrease in muscle thickness between the groups, in whom MAC decreased or did not change, was not significantly different (P = 0.475). CONCLUSION We have demonstrated that an ultrasound technique devised to identify muscle wasting in the presence of severe fluid retention works in the majority (48/50) of patients when applied to a wider ICU population. Energy balance made no difference to the rate of wasting.

Estimation of errors in determining intrathoracic blood volume using the single transpulmonary thermal dilution technique in hypovolemic shock

Background: The transpulmonary thermal dilution technique has been widely adopted for monitoring cardiac preload and extravascular lung water in critically ill patients. This method assumes intrathoracic blood volume (ITBV) to be a fixed proportion of global end-diastolic volume (GEDV). This study determines the relation between GEDV and ITBV under normovolemic and hypovolemic conditions and quantifies the errors in estimating ITBV. Methods: Nineteen pigs allocated to control (n = 9) and shock (n = 10) groups were studied. Shock was maintained for 60 min followed by volume resuscitation. The dual dye–thermal dilution technique was used to measure GEDV and ITBV (ITBVm) at baseline (time 0), shock phase (30 and 90 min), and after resuscitation (150 min). The regression equations estimated from paired GEDV and ITBVm measurements under normovolemic and hypovolemic conditions were used to estimate ITBV from the corresponding GEDV, and the estimation errors were quantified. A more simplified equation, used in a commercially available clinical monitor (ITBV = 1.25 × GEDV), was then used to estimate ITBV. Results: The regression equation in the control group was ITBVm = 1.21 × GEDV + 99 (r 2 = 0.89, P < 0.0001) and in the shock group at 30 and 90 min was ITBVm = 1.45 × GEDV + 0.6 (r 2 = 0.95, P < 0.0001). The 95% confidence interval for the y-intercept was relatively wide, ranging from 31 to 168 and −47 to 49, respectively, for the two equations. The equation estimated in the control group led to overestimation of ITBV and a significant (P < 0.05) increase in errors in the shock group at 30 and 90 min. Errors in estimating ITBV using the simplified commercial algorithm were less than 15% under normovolemic and hypovolemic conditions. Conclusions: The linear relation between GEDV and ITBV is maintained in hypovolemic shock. Even though the relation between GEDV and ITBV is influenced by circulatory volume and cardiac output, the mean errors in predicting ITBV were small and within clinically tolerable limits.

Testing the validity of the ATLS classification of hypovolaemic shock

AIM The Advanced Trauma Life Support system classifies the severity of shock. The aim of this study is to test the validity of this classification. METHODS Admission physiology, injury and outcome variables from adult injured patients presenting to hospitals in England and Wales between 1989 and 2007 and stored on the Trauma Audit and Research Network (TARN) database, were studied. Patients were divided into groups representing the four ATLS classes of shock, based on heart rate (HR) systolic blood pressure (SBP), respiratory rate (RR) and Glasgow Coma Score (GCS). The relationships between variables were examined by classifying the cohort by each recorded variable in turn and deriving the median and interquartile range (IQR) of the remaining three variables. Patients with penetrating trauma and major injuries were examined in sub-group analyses. RESULTS In blunt trauma patients grouped by HR, the median SBP decreased from 128 mmHg in patients with HR<100 BPM to 114 mmHg in those with HR>140 BPM. The median RR increased from 18 to 22 bpm and the GCS reduced from 15 to 14. The median HR in hypotensive patients was 88 BPM compared to 83 BPM in normotensive patients and the RR was the same. When grouped by RR, the HR increased with increasing RR but there were no changes in SBP. CONCLUSION In trauma patients there is an inter-relationship between derangements of HR, SBP, RR and GCS but not to the same degree as that suggested by the ATLS classification of shock.

Systemic arterial pressure wave reflections during acute hemorrhage

Objective:To determine the effects of hemorrhage on wave-reflection-induced systolic pressure augmentation in the aorta. Design:Randomized, controlled laboratory experiment. Setting:University research laboratory. Subjects:Twenty-five anesthetized pigs randomized to surgical controls (n = 7), hemorrhage (n = 9, H), and hemorrhage with reinfusion (n = 9, HR). Interventions:Hemorrhage of 1 mL/kg/min over 20 mins followed by observation (H) or reinfusion (HR) of shed blood. Measurements and Main Results:High-fidelity systemic arterial pressure waveforms, from ascending aorta to femoral artery, were transduced and archived digitally using intravascular semiconductor catheter-tipped pressure transducers. Wave-reflection-induced systolic pressure augmentation was determined using the augmentation index in the ascending aorta (AIaa) and distal descending aorta (AIda). Pulse wave velocity, wave travel times, and lumped pressure wave reflection sites were also calculated. AI values were positive at baseline with greater decreases in AIda compared with AIaa observed following hemorrhage, with negative values achieved for AIda alone. AI returned to control values following reinfusion. Lumped reflection site positions and pressure contour maps suggested that a single lumped reflection site (lower abdomen/pelvis) at baseline was replaced by two discrete sites (upper abdomen and pelvis) following hemorrhage, which only recovered following reinfusion. Hemorrhage was associated with hemodynamic conditions that favored late return of wave reflection from the trunk and with the absence of significant changes in systemic vascular resistance. Conclusions:Hemorrhage-induced early return of pressure wave reflection from the abdominal vasculature is associated with systolic pressure augmentation in the ascending aorta and has the potential to worsen afterload conditions and decrease coronary artery perfusion and cardiac performance. Hemorrhage-induced splanchnic vasoconstriction causing pressure wave reflection may explain these loading conditions in the ascending aorta, and systolic pressure augmentation may be a more useful guide to left ventricular afterload than systemic vascular resistance.

The use and misuse of meta-analysis.

OBJECTIVE: To demonstrate how the results of a meta-analysis can confuse rather than clarify therapeutic dilemmas if clinical heterogeneity among trials is ignored. Then to further discuss the qualities emergency physicians should expect from published meta-analyses if they are to affect clinical practice. SUBJECTS AND METHODS: The data and results were examined from 23 randomised controlled trials of selective decontamination of the digestive tract (SDD), which have been combined in a previous meta-analysis. These were reviewed to take account of clinical heterogeneity, particularly with regard to severity of patient illness. RESULTS: Severity of patient illness predicts degree of reduction in mortality with SDD in a regression analysis: log odds ratio (OR) of death with SDD = -0.0074 - (0.0035 x control group mortality rate), P = 0.017. This is also true when trials are stratified into more and less severely ill patients: pooled OR (a) for CMR > 41% = 0.69 (0.54 to 0.89), with (b) CMR < 3% = 1.02 (0.86 to 1.21). This difference was not suggested by the original meta-analysis result. CONCLUSIONS: Failure to take account of clinical heterogeneity between trials can mean a meta-analysis result ignores important differences in the effect of a treatment on different groups of patients. The discussion indicates how emergency physicians might guard against basing clinical practice on misleading meta-analysis results.

Change in bioelectrical impedance following laparoscopic and open abdominal surgery

The effect of surgery, and in particular, the relative effects of open and laparoscopic abdominal surgery on whole body bioelectrical impedance (BI) has been investigated. Repeated measurements of BI were performed over a 60 h period in 12 patients undergoing laparoscopic surgery (group A) and in 12 patients undergoing elective open abdominal surgery for benign conditions (group B). Control measurements were performed upon 4 healthy adult subjects over the same time period. Attempts were made to relate postoperative changes in BI in group A and group B to changes in net postoperative fluid balance. The postoperative disturbance in BI was significantly greater in group B than group A (P < 0.001 Mann-Whitney-U test) and differed significantly from the minor fluctuations of BI observed in the control group (P < 0.001 Mann-Whitney-U test). The fluctuations in BI observed after laparoscopic surgery were not significantly greater than those seen in the control group (P = 0.1 Mann- Whitney U test). Changes in BI in both group A and B did not correlate with changes in net postoperative fluid balance, which suggests that the effect of surgery upon BI was related to changes of body water distribution rather than changes in total body water volume.