The effect of a ketamine constant rate infusion on cardiovascular variables in sheep anesthetized at the minimum alveolar concentration of sevoflurane that blunts adrenergic responses

OBJECTIVE To evaluate the effect of a constant rate infusion of ketamine on cardiac index (CI) in sheep, as estimated using noninvasive cardiac output (NICO) monitoring by partial carbon dioxide rebreathing, when anesthetized with sevoflurane at the previously determined minimum alveolar concentration that blunts adrenergic responses (MACBAR). ANIMALS 12 healthy Dorset-crossbred adult sheep. PROCEDURES Sheep were anesthetized 2 times in a balanced placebo-controlled crossover design. Anesthesia was induced with sevoflurane delivered via a tight-fitting face mask and maintained at MACBAR. Following induction, sheep received either ketamine (1.5 mg/kg IV, followed by a constant rate infusion of 1.5 mg/kg/h) or an equivalent volume of saline (0.9% NaCl) solution (placebo). After an 8-day washout period, each sheep received the alternate treatment. NICO measurements were performed in triplicate 20 minutes after treatment administration and were converted to CI. Blood samples were collected prior to the start of NICO measurements for analysis of ketamine plasma concentrations. The paired t test was used to compare CI values between groups and the ketamine plasma concentrations with those achieved during the previous study. RESULTS Mean ± SD CI of the ketamine and placebo treatments were 2.69 ± 0.65 and 2.57 ± 0.53 L/min/m2, respectively. No significant difference was found between the 2 treatments. Mean ketamine plasma concentration achieved prior to the NICO measurement was 1.37 ± 0.58 µg/mL, with no significant difference observed between the current and prior study. CLINICAL RELEVANCE Ketamine, at the dose administered, did not significantly increase the CI in sheep when determined by partial carbon dioxide rebreathing.

Superiority of OxyMask™ with Less Carbon Dioxide Rebreathing in Children

Despite the growing importance of oxygen-delivery devices worldwide, there are only a few reports of physiological data on various oxygen masks in children. OxyMask KidTM (Southmedic Inc. Canada; hereafter OxyMask) is expected to reduce carbon dioxide rebreathing even at low oxygen flow rates because of its structural features. Biological data using OxyMask in children have not been well investigated. Measured respiratory parameters of OxyMask with those of a simple oxygen mask in healthy children were compared. Ten subjects were enrolled, with a median age of 5.4 years. All of them used both OxyMask and a simple oxygen mask. The fraction of inspiratory oxygen (FIO2), partial pressure of inspiratory carbon dioxide (PICO2), and partial pressure of end-tidal carbon dioxide were measured using a side-stream gas-sampling monitor in all subjects. The oxygen-flow rate was set at 1, 3, 5, and 10 L/min. FIO2 levels were higher with OxyMask than with the simple oxygen mask at 3L/min of oxygen. PICO2 levels were significantly lower with OxyMask than with the simple oxygen mask (1.5 mmHg vs. 3.7 mmHg at 1 L/min, P = .005; 1.0 mmHg vs. 2.7 mmHg at 3 L/min, P = .005, respectively), whereas PICO2 levels were higher at low oxygen-flow rates with both masks. ConclusionOur results showed that higher FIO2 and less CO2 rebreathing were achieved with OxyMask than with a simple oxygen mask at low-flow rates of oxygen in healthy children.

Multilevel allometric modelling of maximal stroke volume and peak oxygen uptake in 11–13-year-olds

Purpose To investigate (1) whether maximal stroke volume (SVmax) occurs at submaximal exercise intensities, (2) sex differences in SVmax once fat-free mass (FFM) has been controlled for, and, (3) the contribution of concurrent changes in FFM and SVmax to the sex-specific development of peak oxygen uptake $$ \left( {{\dot{\text{V}}\text{O}}_{2} } \right) $$V˙O2. Methods The peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 s of 61 (34 boys) 11–12-year-olds were determined and their SV determined during treadmill running at 2.28 and 2.50 m s−1 using carbon dioxide rebreathing. The SVmax and peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 of 51 (32 boys) students who volunteered to be tested treadmill running at 2.50 m s−1 on three annual occasions were investigated using multilevel allometric modelling. The models were founded on 111 (71 from boys) determinations of SVmax, FFM, and peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2. Results Progressive increases in treadmill running speed resulted in significant (p < 0.01) increases in $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2, but SV levelled-off with nonsignificant (p > 0.05) changes within ~ 2–3%. In the multilevel models, SVmax increased proportionally to FFM0.72 and with FFM controlled for, there were no significant (p > 0.05) sex differences. Peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 increased with FFM but after adjusting for FFM0.98, a significant (p < 0.05) sex difference in peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 remained. Introducing SVmax to the multilevel model revealed a significant (p < 0.05), but small additional effect of SVmax on peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2. Conclusions Fat-free mass explained sex differences in SVmax, but with FFM controlled for, there was still a ~ 5% sex difference in peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2. SVmax made a modest additional contribution to explain the development of peak $$ {\dot{\text{V}}\text{O}}_{2} , $$V˙O2, but there remained an unresolved sex difference of ~ 4%.

Nasal high flow reduces minute ventilation during sleep through a decrease of carbon dioxide rebreathing

Nasal high flow (NHF) is an emerging therapy for respiratory support, but knowledge of the mechanisms and applications is limited. It was previously observed that NHF reduces the tidal volume but does not affect the respiratory rate during sleep. The authors hypothesized that the decrease in tidal volume during NHF is due to a reduction in carbon dioxide (CO2) rebreathing from dead space. In nine healthy males, ventilation was measured during sleep using calibrated respiratory inductance plethysmography (RIP). Carbogen gas mixture was entrained into 30 l/min of NHF to obtain three levels of inspired CO2: 0.04% (room air), 1%, and 3%. NHF with room air reduced tidal volume by 81 ml, SD 25 ( P < 0.0001) from a baseline of 415 ml, SD 114, but did not change respiratory rate; tissue CO2 and O2 remained stable, indicating that gas exchange had been maintained. CO2 entrainment increased tidal volume close to baseline with 1% CO2 and greater than baseline with 3% CO2 by 155 ml, SD 79 ( P = 0.0004), without affecting the respiratory rate. It was calculated that 30 l/min of NHF reduced the rebreathing of CO2 from anatomical dead space by 45%, which is equivalent to the 20% reduction in tidal volume that was observed. The study proves that the reduction in tidal volume in response to NHF during sleep is due to the reduced rebreathing of CO2. Entrainment of CO2 into the NHF can be used to control ventilation during sleep. NEW & NOTEWORTHY The findings in healthy volunteers during sleep show that nasal high flow (NHF) with a rate of 30 l/min reduces the rebreathing of CO2 from anatomical dead space by 45%, resulting in a reduced minute ventilation, while gas exchange is maintained. Entrainment of CO2 into the NHF can be used to control ventilation during sleep.

Carbon dioxide rebreathing induced by crib bumpers and mesh liners using an infant manikin

ObjectivesQuantify impaired respiration in currently marketed crib bumpers (CBs), mesh liners (MLs) and alternative products (ALTs) used to attenuate the interaction between the baby and the crib sides and elucidate the relationship between impaired respiration and permeability.MethodsWe experimentally quantified carbon dioxide rebreathing (CO2RB) via an infant manikin and air permeability via previously published test protocols, in commercially available CBs, MLs and ALTs.ResultsDifferences in CO2RB in ML (median [m]=8.2%, 25th percentile [P25]=6.8, 75th percentile [P75]=8.6), ALT (m=10.5%, P25=9.8, P75=10.7) and CB (m=11.6%, P25=10.2, P75=14.3) were significant (p<0.0001). For comparison, manikin tests with a pacifier yielded CO2RB of 5.6%–5.9%, blanket draped over the face/torso yielded CO2RB of 7.7%–8.6% and stuffed animal in various positions yielded CO2RB from 6.1% to 16.1%. Differences in permeability between ML (m=529.5 cubic feet per minute [CFM], P25=460, P75=747.5), ALT (m=29.0 CFM, P25=27.7, P75=37.7) and CB (m=46.6 CFM, P25=30.1, P75=58.7) groups were significant (p<0.0001). CO2RB was poorly correlated with air permeability (max R2=0.36). In a subset of tests, CB CO2RB increased by 50%–80% with increasing penetration force, whereas the ML CO2RB was nominally unchanged.ConclusionsGovernment agencies and standards organisations are presently considering regulation of bedding including CBs. As paediatricians are consulted in the development of such regulations, our findings that permeability by itself was a poor predictor of CO2RB should be considered.

Carbon dioxide rebreathing in non-invasive ventilation. Analysis of masks, expiratory ports and ventilatory modes

Background and Aim. Carbon dioxide (CO2) rebreathing is a complication of non-invasive ventilation (NIV). Our objectives were to evaluate the ability of masks with exhaust vents (EV) to avoid rebreathing while using positive pressure (PP) NIV with different levels of expiratory pressure (EPAP). Concerning volume-cycled NIV, we aimed to determine whether cylindrical spacers located in the circuit generate rebreathing. Materials and methods. 5 healthy volunteers were evaluated. Bi-level PP was used with 3 nasal and 2 facial masks with and without EV. Spacers of increasing volume attached to nasal hermetic masks were evaluated with volume NIV. Inspired CO2 fraction was analyzed. Results. Rebreathing was zero with all nasal masks and EPAP levels. Using facial masks 1 volunteer showed rebreathing. There was no rebreathing while using all the spacers. Conclusions. In healthy volunteers, nasal and facial masks with EV prevent rebreathing. In addition, the use of spacers did not generate this undesirable phenomenon.