SIVAUK Education Section

Arterial pressure (AP) monitoring should be accurate, easy to use, free of risks, and ideally continuous. The continuous non-invasive arterial pressure (CNAP) device is non-invasive and provides continuous pressure readings. This study was performed to compare the agreement of CNAP and invasive AP monitoring.

Ninety patients undergoing surgery under general anaesthesia were enrolled. Invasive pressure monitoring was established at the radial artery. CNAP monitoring using a finger sensor recording was begun before induction of anaesthesia. Statistical analysis was conducted with the Bland–Altman method for comparisons of repeated measures.

We obtained 16 843 valid pressure readings from 85 patients. Mean (sd) bias during maintenance of anaesthesia was: systolic AP: 4.2 (16.5) mm Hg; mean AP (MAP): –4.3 (10.4) mm Hg; and diastolic AP: –5.8 (6) mm Hg. The results of a subgroup analysis of patients who had a mean intra-arterial pressure of <70 mm Hg were as follows: systolic pressure: –0.3 (9.7) mm Hg; mean pressure: –6.8 (7.6) mm Hg; and diastolic pressure: –7.9 (7.2) mm Hg. Bias and percentage error during the induction period were greater in both the main and subgroup analyses, probably due to recalibration being omitted after induction.

The CNAP monitor showed an acceptable agreement and was interchangeable with invasive pressure monitoring for MAP during normotensive conditions. During induction of anaesthesia and when the AP was low, the agreement was less good and interchangeability was not achieved. These results suggest that CNAP is not statistically equivalent to invasive monitoring during all periods of anaesthesia but may be a useful additional AP monitor.

In the intensive care unit, intra-abdominal hypertension (IAH) is a frequently encountered, life-threatening condition. The aim of this animal study was to evaluate the effect of IAH on left ventricular (LV) relaxation (i.e. the active phase of diastole).

Seven male rabbits were anaesthetized before mechanical ventilation. A 20 mm Hg increase in intra-abdominal pressure (IAP) was then induced by intraperitoneal infusion of 1.5% glycine solution. Haemodynamic parameters were recorded and the relaxation time constant tau (considered to be the best index of left ventricle relaxation) was calculated. All haemodynamic measurements were recorded at baseline and then after induction of IAH.

A 20 mm Hg increase in IAP was not followed by a significant change in arterial pressure, but was associated with increases in central venous pressure (from 2 [–2 to 6] to 7 [–2 to 12] mm Hg, P= 0.03), LV end-diastolic pressure (from 7 [6–8] to 15 [11–19] mm Hg, P= 0.04) and the relaxation time constant tau (from 16 [14–18] to 43 [34–52] ms, P= 0.048).

In this animal study, a 20 mm Hg increase in IAP impaired LV relaxation. Further studies are necessary to identify the causes of this impairment.

Re-exploration for bleeding after cardiac surgery is an indicator of substantial haemorrhage and is associated with increased hospital resource utilization. This study aimed to analyse the costs of re-exploration and estimate the costs of haemostatic prophylaxis.

A total of 4232 patients underwent isolated, first-time, coronary artery bypass graft (CABG) surgery during 2005–8. Each patient re-explored for bleeding (n=127) was matched with two controls not requiring re-exploration (n=254). Cost analysis was based on resource utilization from completion of CABG until discharge. A mean cost per patient for re-exploration was calculated. Based on this, the net cost of prophylactic treatment with haemostatic drugs for preventing re-exploration was calculated.

Patients undergoing re-exploration had higher exposure to clopidogrel before operation, prolonged stays in the intensive care unit, and more blood transfusions than controls. The mean incremental cost for re-exploration was 6290 [95% confidence interval (CI) 3408–9173] per patient, of which 48% [3001 (95% CI 249–2147)] was due to prolonged stay, 31% [1928 (95% CI 1710–2147)] to the cost of surgery/anaesthesia, 20% [1261 (95% CI 1145–1378)] to the increased number of blood transfusions, and <2% [100 (95% CI 39–161)] to the cost of haemostatic drugs. A cost model, at an estimated 50% efficacy for recombinant activated clotting factor VIIa and a 50% expected risk for re-exploration without prophylaxis, demonstrated that to be cost neutral, prophylaxis of four patients needed to result in one avoided re-exploration.

The resource utilization costs were substantially higher in patients requiring re-exploration for bleeding. From a strict cost-effectiveness perspective, clinical interventions to prevent haemorrhage might be underutilized.

Remote ischaemic preconditioning (RIPC) can reduce ischaemic–reperfusion injury in distant organs. The myocardial and pulmonary protective effect of RIPC in infants with pulmonary hypertension remains unclear. We conducted a randomized controlled trial to evaluate the effect of RIPC in infants receiving ventricular septal defect (VSD) repair.

We studied 55 infants with pulmonary hypertension undergoing VSD repair (RIPC group, n=27; control group, n=28). RIPC consisted of four 5 min cycles of lower limb ischaemia and reperfusion. Serum troponin I (TnI) concentrations were measured after induction of anaesthesia and at 1, 6, 12, and 24 h after surgery. Other clinical data such as inotropic score, lung compliance, alveolar–arterial oxygen gradient, oxygen index, mechanical ventilation time, and length of intensive care unit stay were also recorded at each interval.

No differences in patient or surgical characteristics were observed between the two groups. There were no significant differences in postoperative TnI levels according to time (P=0.35) or the total amount of TnI release, expressed as the area under the curve over the 24 h after surgery [RIPC vs control: 207.6 (134.0) vs 274.6 (263.7) h ng ml^–1, P=0.24]. All other clinical data were also comparable.

RIPC does not reduce the postoperative TnI release after VSD repair in infants with pulmonary hypertension. Additionally, it is difficult to find significant clinical benefits of RIPC in this population. The effect of RIPC varies according to clinical situation and patient condition.

Clinical trial registration: ClinicalTrials.gov, NCT01313832.

Cognitive errors are thought-process errors, or thinking mistakes, which lead to incorrect diagnoses, treatments, or both. This psychology of decision-making has received little formal attention in anaesthesiology literature, although it is widely appreciated in other safety cultures, such as aviation, and other medical specialities. We sought to identify which types of cognitive errors are most important in anaesthesiology.

This study consisted of two parts. First, we created a cognitive error catalogue specific to anaesthesiology practice using a literature review, modified Delphi method with experts, and a survey of academic faculty. In the second part, we observed for those cognitive errors during resident physician management of simulated anaesthesiology emergencies.

Of >30 described cognitive errors, the modified Delphi method yielded 14 key items experts felt were most important and prevalent in anaesthesiology practice (Table 1). Faculty survey responses narrowed this to a ‘top 10’ catalogue consisting of anchoring, availability bias, premature closure, feedback bias, framing effect, confirmation bias, omission bias, commission bias, overconfidence, and sunk costs (Table 2). Nine types of cognitive errors were selected for observation during simulated emergency management. Seven of those nine types of cognitive errors occurred in >50% of observed emergencies (Table 3).

Cognitive errors are thought to contribute significantly to medical mishaps. We identified cognitive errors specific to anaesthesiology practice. Understanding the key types of cognitive errors specific to anaesthesiology is the first step towards training in metacognition and de-biasing strategies, which may improve patient safety.

Complete and fast recovery of neuromuscular function is very important in morbidly obese patients because of the possible influence of postoperative residual curarization (PORC) on respiratory function in the postoperative period. Recent reports underline incidences of the residual influence of neuromuscular blocking agents.

Seventy morbidly obese (BMI >40 kg m^–2) patients requiring general anaesthesia and receiving rocuronium for muscle relaxation were randomly assigned into two groups: at the end of the anaesthetic procedure, one group received sugammadex 2 mg kg^–1 of corrected body weight (Group SUG) and the other group received neostigmine 0.05 mg kg^–1 of CBW (Group NEO). At the end of surgery and when response reached a train-of-four (TOF) score of 2, patients received the study drugs. The neuromuscular function was recorded and time to achieve 90% of TOF (safe extubation) was measured. Patients were examined directly after arrival to the post-anaesthesia care unit (PACU) by a blinded investigator for the presence of PORC.

Thirty-five patients received sugammadex and 35 neostigmine. Mean dose of rocuronium was 87.9 vs 85.6 mg (P>0.05), mean time to 90% of TOF was 2.7 vs 9.6 min (P<0.05), and TOF at the PACU was 109.8% vs 85.5% (P<0.05) in Groups SUG and NEO, respectively.

Administration of sugammadex provides fast recovery of neuromuscular function and prevents PORC in the morbidly obese, however neostigmine does not.

TOF-Watch^® monitors are designed to display train-of-four (TOF) count when neuromuscular block is intense, and to display TOF ratio when it is less intense. In dogs recovering from non-depolarizing neuromuscular block, when all four twitches are easily visible and apparently of similar magnitude, TOF-Watch^® monitors often display TOF counts and not TOF ratios, as would be expected. We have never encountered this problem when the monitor was calibrated before neuromuscular blocking agent administration.

Fourteen healthy female dogs undergoing ovariohysterectomy were investigated. Recovery from neuromuscular block was assessed with a calibrated TOF-Watch SX^® monitor. When the TOF ratio returned to 90%, the TOF-Watch SX^® was replaced with an uncalibrated TOF-Watch^® monitor. The output obtained from the uncalibrated TOF-Watch^® was compared with that of the calibrated device.

The median TOF ratio measured by the calibrated TOF-Watch SX^® unit at recovery was 91 (86–100)% (n=14). The uncalibrated TOF-Watch^® monitor displayed TOF counts in six dogs [2 (0, 4)] and TOF ratios in the remaining eight dogs [91 (79, 98)%], that is, the uncalibrated device failed to display appropriately >40% of the time.

TOF-Watch^® monitors must be calibrated before neuromuscular blocking agents are administered to dogs. When these devices are not so calibrated, they default to a reference value for twitch magnitude that was defined in healthy adult people. Even though neuromuscular transmission was restored in these dogs, we surmise that they did not achieve the default reference value, causing the monitor to display TOF counts rather than TOF ratios.

This study aimed at comparing total i.v. anaesthesia (TIVA) with monitored anaesthesia care (MAC) during day-surgery operative hysteroscopy regarding: operation time, time to mobilization and discharge, and patient satisfaction.

Ninety-one healthy women were randomized to MAC with paracervical local anaesthesia and remifentanil or to TIVA with propofol and remifentanil. Time from arrival to leaving the operating theatre, time from arrival in the recovery room to mobilization and discharge readiness, and patient satisfaction with MAC and TIVA were observed.

Time from arrival to leaving the operating theatre showed no significant difference between groups (P=0.6). The time to mobilization {MAC: 53 min [inter-quartile range (IQR) 40–83], TIVA: 69 min (IQR 52–96) (P=0.017)} and the total time from arrival to discharge readiness [MAC: 118 min (IQR 95–139), TIVA: 138 (IQR 120–158) (P=0.0009)] were significantly reduced for patients in the MAC group. More patients in the MAC group 45 (91.8%) than in the TIVA group 24 (64.9%) responded positively to the question: would you like to receive the same kind of anaesthesia for a similar procedure in the future? (P=0.003).

Paracervical local anaesthesia combined with remifentanil is suitable for operative hysteroscopy in day surgery.

Microcirculatory and mitochondrial dysfunction are important factors in the development of septic shock. In this study, we investigated the effects of fluid resuscitated endotoxaemic shock and norepinephrine treatment on intestinal microcirculation and mitochondrial function in sheep.

Eight anaesthetized sheep received an i.v. infusion of endotoxin. After 24 h, mean arterial pressure (MAP) was restored to baseline levels with a norepinephrine infusion. Five sheep served as sham experiments. Central and regional haemodynamics were monitored, and ileal microcirculation was evaluated with laser Doppler and sidestream dark-field videomicroscopy techniques. Gut mucosal acidosis was assessed by air tonometry, and ileal wall biopsies were analysed for mitochondrial activity.

After 24 h of endotoxaemia, the animals had developed hyperdynamic shock with systemic and mucosal acidosis. Although superior mesenteric artery (SMA) flow was higher than the baseline values, ileal microcirculatory perfusion and mitochondrial complex I activity decreased. After norepinephrine was started, SMA flow, ileal microcirculation, and mucosal acidosis remained unchanged. Although no statistically significant difference could be demonstrated, norepinephrine increased mitochondrial complex I activity in five of the six animals from which ileal biopsies were taken.

Although fluid resuscitated endotoxaemic shock increased regional blood flow, microcirculatory and mitochondrial alterations were still present. Restoring MAP with norepinephrine did not affect ileal microcirculation or mucosal acidosis, indicating that perfusion pressure manipulation is of limited importance to the intestinal microcirculation in established endotoxaemic shock.

While producing good-quality analgesia, µ-opioid (MOP) receptor activation produces a number of side-effects including tolerance. Simultaneous blockade of -opioid (DOP) receptors has been shown to reduce tolerance to morphine. Here, we characterize a prototype bifunctional opioid H-Dmt-Tic-Gly-NH-Bzl (UFP-505).

We measured receptor binding affinity in Chinese hamster ovary (CHO) cells expressing recombinant human MOP, DOP, k-opioid (KOP), nociceptin/orphanin (NOP) receptors. For activation, we measured the binding of GTP³⁵S to membranes from CHO_hMOP, CHO_hDOP, rat cerebrocortex, and rat spinal cord. In addition, we assessed ‘end organ’ responses in the guinea pig ileum and mouse vas deferens.

UFP-505 bound to CHO_hMOP and CHO_hDOP with (binding affinity) pK_i values of 7.79 and 9.82, respectively. There was a weak interaction at KOP and NOP (pK_i 6.29 and 5.86). At CHO_hMOP, UFP-505 stimulated GTP³⁵S binding with potency (pEC₅₀) of 6.37 and in CHO_hDOP reversed the effects of a DOP agonist with affinity (pK_b) of 9.81 (in agreement with pK_i at DOP). UFP-505 also stimulated GTP³⁵S binding in rat cerebrocortex and spinal cord with pEC₅₀ values of 6.11–6.53. In the guinea pig ileum (MOP-rich preparation), UFP-505 inhibited contractility with pEC₅₀ of 7.50 and in the vas deferens (DOP-rich preparation) reversed the effects of a DOP agonist with an affinity (pA₂) of 9.15.

We have shown in a range of preparations and assays that UFP-505 behaves as a potent MOP agonist and DOP antagonist; a MOP/DOP bifunctional opioid. Further studies in dual expression systems and whole animals with this prototype are warranted.

The ability to measure haemoglobin (Hb) real-time and non-invasively offers important clinical value in the assessment of acute changes in maternal Hb during the peripartum period. This study evaluates the Masimo Rainbow SET^® Radical-7 Pulse CO-Oximeter in a pregnant population undergoing Caesarean section (CS).

Fifty patients undergoing elective CS were enrolled in this prospective, controlled study and followed for 48 h after surgery. Non-invasive Masimo Hb (SpHb) values were compared with laboratory Hb values from venous blood samples drawn at baseline, immediately post-CS, and 24 h post-CS using the Bland–Altman plots. Longitudinal analysis of SpHb changes over time was performed using mixed-effects regression modelling.

For the comparison between SpHb and laboratory Hb, SpHb displayed a significant positive bias at baseline {1.22 g dl^–1 [95% confidence interval (CI): 0.89–1.54]} and at 24 h post-CS [1.36 g dl^–1 (95% CI: 1.04–1.68)]. The bias immediately post-CS was 0.14 g dl^–1 (95% CI: –0.18 to 0.46). The limits of agreement at baseline, immediately post-CS, and at 24 h post-CS were: –0.9 and 3.33, –2.35 and 2.56, and –0.55 and 3.27 g dl^–1, respectively. The mean decrease in SpHb from baseline to 48 h post-CS was ~1 g dl^–1.

The variability in bias and limits of agreements of the Rainbow SET^® Radical-7 Pulse CO-Oximeter SpHb may limit its clinical utility for assessing Hb concentration in patients undergoing elective CS. Modifications are needed in the calibration of the device to improve accuracy and precision in an obstetric setting.

The study was registered at clinicaltrials.gov (NCT01108471) before participant enrolment: URL=http://clinicaltrials.gov/ct2/show/NCT01108471?term=butwick&rank=1.

As general anaesthesia may compromise the immune system, it has been hypothesized that latent varicella-zoster virus is more likely to be reactivated and cause herpes zoster in mothers after Caesarean deliveries under general anaesthesia. Our study was thus aimed at investigating the risk of herpes zoster among women during the first year after Caesarean deliveries under either general or regional anaesthesia.

Two nationwide population-based data sets were utilized, including the Taiwan birth certificate registry and the Taiwan National Health Insurance Research Dataset. From 2001 to 2003, a total of 162 495 women underwent Caesarean delivery. Among them, 21 454 women received general anaesthesia, whereas 141 041 patients received regional anaesthesia. Each individual was followed for 1 yr to identify the subsequent occurrence of herpes zoster. Cox's proportional hazards regressions were performed for analysis.

During the 1 yr follow-up period, 0.46% of the women receiving general anaesthesia experienced an episode of herpes zoster, compared with 0.34% of women receiving regional anaesthesia. In Caesarean deliveries, the use of general anaesthesia compared with regional anaesthesia was independently associated with a 1.29-fold (95% confidence interval=1.04–1.61) increase in the 1 yr risk of herpes zoster, after adjusting for maternal and infant characteristics.

In this series, there was a small increased risk of herpes zoster in the year after Caesarean delivery with general anaesthesia. Future studies are needed to further investigate these findings.

The aim of this study was to investigate ECG and haemodynamic alterations provoked by a test dose of bupivacaine, epinephrine, and their combination.

Paediatric patients undergoing general anaesthesia were randomized into three groups. After anaesthesia induction and tracheal intubation, 0.2 ml kg^–1 (max. 3 ml) of the corresponding test solution was i.v. injected: bupivacaine 0.125% (Group B), bupivacaine 0.125% plus epinephrine 1:200 000 (Group BE), or epinephrine 1:200 000 (Group E). ECG was printed and analysed post hoc. Non-invasive arterial pressure (AP) was measured at 1 and 2 min after test dose injection. Increases in T-wave of ≥25%, in heart rate (HR) of ≥10 beats min^–1, and in systolic AP of ≥15 mm Hg above baseline value were considered a positive result.

A total of 105 children aged 0.2–16 (median 6.8) yr were enrolled. Test dose injection provoked T-wave elevation in 0%, 85%, and 89% of patients in Groups B, BE, and E, respectively. A positive increase in HR was found in 0%, 68%, and 76%. A positive increase in AP at 1 min was found in 0%, 88%, and 94% and at 2 min in 0%, 42%, and 59%. A decrease in HR of ≥10 beats min^–1 was observed in 6%, 76%, and 69%. Alterations in T-wave and HR were significantly influenced by age.

ECG and haemodynamic alterations after i.v. injection of a local anaesthetic test dose were significantly influenced by epinephrine. T-wave elevation, increase in AP, and changes in HR are highly reliable variables, particularly when age is taken into account.

The establishment of peripheral venous access in infants is the most common invasive technique in paediatric anaesthesia. Venous puncture can be challenging due to the small size of vessels in this patient population. The present study was designed to investigate the practicability of ultrasound-guided vascular access to the great saphenous vein (GSV) at the level of the medial malleolus in infants ≤12 months.

Ninety consecutive infants ≤12 months undergoing elective surgery were included in this prospective study and divided into two age groups (0–6 and 7–12 months). After anaesthesia induction with sevoflurane, an ultrasound investigation of both GSVs at the level of the medial malleoli was performed. Subsequently, venous access in one GSV was established under direct ultrasound control. Anatomical ultrasound data and success rates of venous accesses were analysed.

While not deeper relative to the skin, the GSV was significantly larger in older infants. The success rate in infants ≤6 months was 96%, whereas in older infants, the success rate was 100%. The overall success rate in all infants was 98%.

Ultrasound facilitates venous puncture of the GSV in the vast majority of infants ≤12 months. Direct visualization via ultrasound is a promising technique for the establishment of venous access in the GSV at the level of the medial malleolus in infants.

Reports conflict on optimal postoperative analgesic treatment in children with intellectual disability. We retrospectively compared postoperative analgesics consumption between neonates with and without Down's syndrome in relation to anaesthesia requirements and pain scores.

We analysed hypnotic and analgesic drug administration, pain scores [COMFORT-Behaviour (COMFORT-B) scale], and duration of mechanical ventilation during the first 48 h after surgical repair of congenital duodenal obstruction in neonates, between 1999 and 2011. Data of 15 children with Down's syndrome were compared with data of 30 children without Down's syndrome.

General anaesthesia requirements did not differ. The median (inter-quartile range) maintenance dose of morphine during the first 24 h after operation was 9.5 (7.8–10.1) µg kg^–1 h^–1 in the Down's syndrome group vs 7.7 (5.0–10.0) µg kg^–1 h^–1 in the control group (P=0.46). Morphine doses at postoperative day 2 and COMFORT-B scores at day 1 did not significantly differ between the two groups. COMFORT-B scores at day two were lower in children with Down's syndrome (P=0.04). The duration of postoperative mechanical ventilation did not statistically differ between the two groups (P=0.89).

In this study, neonates with and without Down's syndrome received adequate postoperative analgesia, as judged from comparable analgesic consumption and pain scores. We recommend prospective studies in children of different age groups with Down's syndrome and in other groups of intellectually disabled children to provide further investigation of the hypothesis that intellectual disability predisposes to different analgesic requirements.

Incorrect placement of epidural catheters causes medical complications. We used linear discriminant analysis (LDA) to develop an intelligent recognition system (i-RS) in order to guide epidural placement and reduce physician error.

We analysed real-time dual-wavelength fibreoptic data recorded from the end of an epidural needle in a live porcine model. Two categories of tissue layers were necessary for correct placement of catheter: epidural space and ligamentum flavum. The data were tested using linear, quadratic and logistic parametric analysis to identify which method could distinguish the two anatomical structures.

LDA was the best fit for our model. There was ~80% sensitivity and specificity for correct anatomical identification. Error rates based on cross-validation were 17.0% for the epidural space and 18.6% for ligamentum flavum. Error rates were greater with the 532 nm compared with 650 nm wavelength.

The sensitivity and specificity of LDA for identifying the correct anatomical structure was similar to a physician who is an expert in epidural placement. Overall performance of an i-RS could be improved by expanding the database for decision-making and adding a category of uncertainty. This would reduce complications caused by incorrect epidural placement.

Parallel-walled spinal needles ≤22 G are routinely used for lumbar puncture, despite a reported ≥32% incidence of post-dural puncture headache. A tapered spinal needle (22 G shaft, 27 G tip) is in use in our institution. We hypothesized that despite the smaller dural puncture hole, this needle has similar cerebrospinal fluid (CSF) pressure equilibration times and CSF sampling times to a standard 22 G needle and assessed a range of spinal needles using an experimental pulsatile CSF reservoir.

The pulsatile CSF reservoir had an oscillating pressure varying between 25 and 15 cm H₂O at a cycle frequency of 80 s^–1. We tested seven parallel-walled spinal needles (18–27 G) and the tapered 22/27 G needle. CSF pressure was measured every 2 s by manometry. The time to collect 1 ml CSF samples was measured. Saline 0.9% and mannitol 20% were tested separately. One-way ANOVA with Bonferroni post-hoc test was used to compare 22G, 27G and 22/27G needles.

The mean [standard deviation (sd)] CSF pressure equilibration time (saline) was 40.7 (6.4), 108.7 (6.1), and 51.3 (4.6) s for the 22, 27, and 22/27 G needles (P< 0.0001 for comparisons between 27 G and other needles). The mean (sd) CSF sampling time (saline) was 40.3 (3.1), 225.3 (10.0), and 63.0 (5.2) s for the 22, 27, and 22/27 G needles (P< 0.0001 for comparisons between 27 G and other needles, and P= 0.019 between 22 and 22/27 G needles). Saline was different from mannitol for both measurements and all needles (P< 0.0001).

A 22/27 G tapered spinal needle has similar flow properties to the 22 G needle, despite a 27 G tip.

Respiratory monitoring is standard after anaesthesia and surgery. Abnormal respiratory rate is a sensitive indicator of respiratory problems, even in patients receiving supplemental oxygen, but the best method for its continuous measurement in spontaneously breathing patients is unclear. This study compared respiratory rate assessment by capnometry using a new oxygen mask with a carbon dioxide sampling port (Capnomask^®) and thoracic impedance pneumography with clinical measurement (used as a reference method) in extubated patients receiving supplemental oxygen.

Adult males admitted to the post-anaesthesia care unit after general anaesthesia were studied. Immediately after extubation, a Capnomask^® connected to a capnometer was positioned appropriately. Respiratory rate was measured by visual inspection of chest movement for 1 min, by capnometry, and thoracic impedance pneumography. One set of measurements was obtained for every patient receiving supplemental oxygen at different flow rates.

Twenty men, mean (inter-quartile range) age 54 (23–66) yr and BMI 25 (21–31) kg m^–2, were studied. Compared with visual inspection, the bias and limits of agreement were 0.0 (1.0 to –1.0) bpm for the Capnomask^® and –2.2 (2.0 to –6.5) bpm for the impedance pneumography. The accuracy of respiratory rate assessment using Capnomask^® was not influenced by the supplemental oxygen flow rate.

In extubated patients, continuous assessment of respiratory rate with the Capnomask^® is more accurate than by thoracic impedance pneumography even when supplemental oxygen is delivered at a high flow rate.