Journal of clinical monitoring and computing
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J Clin Monit Comput · Dec 2011
Impact of central hypovolemia on photoplethysmographic waveform parameters in healthy volunteers part 2: frequency domain analysis.
The photoplethysmographic (PPG) waveforms are modulated by the respiratory, cardiac and autonomic nervous system. Lower body negative pressure (LBNP) has been used as an experimental tool to simulate loss of central blood volume in humans. The aim of our research is to understanding PPG waveform changes during progressive hypovolemia. ⋯ The pulse oximeter waveform contains a complex mixture of the effect of cardiac, venous, autonomic, and respiratory systems on the central and peripheral circulation. The occurrence of autonomic modulation needs to be taken into account when studying signals that have their origins from central sites (e.g. ear and forehead).
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J Clin Monit Comput · Dec 2011
Impact of central hypovolemia on photoplethysmographic waveform parameters in healthy volunteers. Part 1: time domain analysis.
Our study sought to explore changes in photoplethysmographic (PPG) waveform param- eters, during lower body negative pressure (LBNP) which simulated hypovolemia, in spontaneously breathing volunteers. We hypothesize that during progressive LBNP; there will be a preservation of ear PPG parameters and a decrease in finger PPG parameters. ⋯ PPG waveform parameters may prove to be sensitive and specific as early indicators of blood loss. These PPG changes were observed before profound decreases in arterial blood pressure. The relative sparing of central cutaneous blood flow is consistent with the increased parasympathetic innervation of central structures.
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'Standard' or 'extracellular' base excess (SBE) is a modified calculation using one-third the normal hemoglobin concentration. It is a 'CO(2)-invariant' expression of meta- bolic acid-base status integrated across interstitial, plasma and erythrocytic compartments (IPE). SBE also integrates conflicting physical chemical influences on metabolic acid-base status. ⋯ The impact of assum- ing fixed relationships between arterial and venous acid-base and saturation values in sepsis, anaemia and in differing shock states is unclear. Clinicians are also unlikely to accept that unique, accurate IPE volume determinations can be derived from a single set of blood gas and biochemistry results. Nevertheless, volume determinations aside, the tool is likely to become a valuable addition to the diagnostic armamentarium.
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J Clin Monit Comput · Dec 2011
Randomized Controlled TrialSkin conductance for monitoring of acute pain in adult postoperative patients: influence of electrode surface area and sampling time.
Aim of this prospective randomized study was to determine the influence of the electrode surface area and sampling time on the accuracy of the number of fluctuations in skin conductance per second to distinguish different states of acute pain. These methodological issues have been previously suggested as an explanation for contradictory data related to the accuracy of the skin conductance monitor. A total of 541 pain ratings on a numeric rating scale (0-10) were obtained from 120 adult postoperative patients. ⋯ However, the latter was found improved when the smaller surface area electrodes were used. A combination of small surface area electrodes and a 30 s sampling time resulted in the highest area under the curve in the receiver operating curve analysis of the method to identify states of moderate to severe pain (numeric rating scale > 3): 0.68 vs. e.g. 0.55 [data from all patients combined]). We conclude that the type of electrodes used but only to a lesser degree the sampling time influence the accuracy of the number of fluctuations in skin conductance per second to identify states of moderate or severe postoperative pain.
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J Clin Monit Comput · Dec 2011
Evaluation of a CO2 partial rebreathing functional residual capacity measurement method for use during mechanical ventilation.
There is a need for an automated bedside functional residual capacity (FRC) measurement method that does not require a step change in inspired oxygen fraction. Such a method can be used for patients who require a high inspired oxygen fraction to maintain arterial oxygenation and for patients ventilated using a circle breathing system commonly found in operating rooms, which is not capable of step changes in oxygen. We developed a CO(2) rebreathing method for FRC measurement that is based on the change in partial pressure of end-tidal carbon dioxide and volume of CO(2) eliminated at the end of a partial rebreathing period. This study was designed to assess the accuracy and precision of the proposed FRC measurement system compared to body plethysmography and nitrogen washout FRC. ⋯ The CO(2) rebreathing method for FRC measurement provides acceptable accuracy and precision during stable ventilation compared to the gold standards of body plethysmography and nitrogen washout. The results based on periods of stable ventilation best approximate the performance of the system in the likely areas of application during controlled mechanical ventilation. Further study of the CO(2) rebreathing method is needed to evaluate accuracy in a larger group of controlled mechanical ventilation patients, including patients with respiratory insufficiency and significant lung injury.