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Wide variation in responses to neuromuscular blocking agents is well described but typically underappreciated in clinical practice. We present 2 patients with unexpected responses to rocuronium, despite being otherwise unremarkable. Quantitative neuromuscular monitoring provided clear documentation of the events, providing illustrations of these atypical responses.

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BACKGROUND: We have developed an automated algorithm to allow the measurement of respiratory rate directly from the photoplethysmogram (pulse oximeter waveform). AIM: To test the algorithm's ability to determine respiratory rate in children. METHODS: A convenience sample of patients attending a paediatric Accident and Emergency Department was monitored using a purpose-built pulse oximeter and the photoplethysmogram (PPG) recorded. Respiration was also recorded by an observer activating a push-button switch in synchronization with the child's breathing. The switch marker signals were processed to derive a manual respiratory rate that was compared with the wavelet-based oximeter respiratory rate derived from the PPG signal. RESULTS: Photoplethysmograms were obtained from 18 children aged 18 mo to 12 y, breathing spontaneously at rates of 17 to 27 breaths per minute. There was close correspondence between the wavelet-based oximeter respiration rate and the manual respiratory rate, with the difference between them being less than one breath per minute in all children. CONCLUSION: Our automated algorithm allows the accurate determination of respiratory rate from photoplethysmograms of a heterogeneous group of children. We believe that our automated wavelet-based signal-processing techniques could soon be easily incorporated into current pulse oximetry technology.

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OBJECTIVE: To determine if an automatic algorithm using wavelet analysis techniques can be used to reliably determine respiratory rate from the photoplethysmogram (PPG). METHODS: Photoplethysmograms were obtained from 12 spontaneously breathing healthy adult volunteers. Three related wavelet transforms were automatically polled to obtain a measure of respiratory rate. This was compared with a secondary timing signal obtained by asking the volunteers to actuate a small push button switch, held in their right hand, in synchronisation with their respiration. In addition, individual breaths were resolved using the wavelet-method to identify the source of any discrepancies. RESULTS: Volunteer respiratory rates varied from 6.56 to 18.89 breaths per minute. Through training of the algorithm it was possible to determine a respiratory rate for all 12 traces acquired during the study. The maximum error between the PPG derived rates and the manually determined rate was found to be 7.9%. CONCLUSION: Our technique allows the accurate measurement of respiratory rate from the photoplethysmogram, and leads the way for developing a simple non-invasive combined respiration and saturation monitor.

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Bradykinin, an endogenous nonapeptide and an important mediator of inflammation, is also implicated in the initiation and maintenance of pain. Both des-Arg(8), Leu(8)-bradykinin (dALBK) and HOE-140, the prototypic bradykinin B1 and B2 receptor antagonists, respectively, have been shown to reduce pain behaviors and inflammation in animal models of persistent nociception. We studied them for activity against incision-induced pain behaviors in a rat model for postoperative pain. A 1-cm plantar incision was made in the hind paw of halothane-anesthetized rats and closed with 5-0 nylon. Withdrawal responses to punctate and nonpunctate mechanical stimuli were tested with von Frey filaments and a plastic disk attached to a von Frey filament, respectively. Withdrawal latency to radiant heat was also tested. Rats were tested 1 day before the incision, 1 h after the incision, and 0.5, 1, 1.5, and 2.5 h after the injection of the drug. They were then retested at the same times before and after the injection of the drug on each of the first 2 postoperative days. The rats received the saline vehicle dALBK (0.1, 0.3, 1.0, or 3.0 mg/kg) or HOE-140 (0.1, 0.3, 1.0, or 3.0 mg/kg) IV. Another group of rats had the drug injected 1 h before incision and tested as above. Statistical significance (P < 0.05) was determined with Kruskal-Wallis test and a two-way analysis of variance. None of the doses of either dALBK or HOE-140 affected the responses to punctate or blunt mechanical stimulation or heat, either as a pretreatment or as a posttreatment. These data support the unique mechanisms for incision-induced pain relative to inflammation-related pain. Although inflammation may represent a component of incisional pain, the etiology of inflammation and its role seem different than in other models.

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OBJECTIVE: The purpose of this study was to establish the usefulness of capillary refill time when measured during the initial assessment of children. METHODS: All children with spontaneous illness attending a paediatric accident and emergency department over a 7-month period were eligible for entry into the study. Capillary refill time was measured at the fingertip, using a standard technique, as part of the initial assessment. Each child was then followed up to ascertain clinical progress, including the need for admission, intravenous fluids, length of stay and diagnosis, as well as the white cell count when this was available. The value of capillary refill time as a predictor of the markers of illness severity was then assessed. RESULTS: Capillary refill time measurements were recorded on 4878 children. There was no significant association of capillary refill time with meningococcal disease, other significant bacterial illness or the white cell count. A prolonged capillary refill time was associated with a more urgent triage category, the administration of a fluid bolus and the length of hospital stay (P<0.0001). The best performance was obtained when a capillary refill time of 3s or more is taken to be 'prolonged'. However, this gave positive predictive values of only 9% for a triage category of 1 or 2 (negative predictive value 97%), 11% for requiring a fluid bolus (negative predictive value 99%), 55% for hospital admission (negative predictive value 65%) and 22% for stay over 2 days/death (negative predictive value 91%). CONCLUSION: The prolongation of capillary refill time is a poor predictor of the need for intravenous fluid bolus or hospital admission.

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