Philipp K. Buehler

Gastric pH and residual volume after 1 and 2 h fasting time for clear fluids in children

INTRODUCTION Current guidelines suggest a fasting time of 2 h for clear fluids, which is often exceeded in clinical practice, leading to discomfort, dehydration and stressful anaesthesia induction to patients, especially in the paediatric population. Shorter fluid fasting might be a strategy to improve patient comfort but has not been investigated yet. This prospective clinical trial compares gastric pH and residual volume after 1 vs 2 h of preoperative clear fluid fasting. METHODS Children (1-16 yr, ASA I or II) undergoing elective procedures in general anaesthesia requiring tracheal intubation were randomized into group A with 60 min or B with 120 min preoperative clear fluid fasting. To determine gastric pH and residual volume, the gastric content was sampled in supine, left and right lateral patient position using an oro-gastric tube after intubation. Data are median (interquartile range) for group A or B (P<0.05). RESULTS In total, 131 children aged 1.01-16.23 yr were included; gastric pH was determined in 120 cases. Patient characteristic data were similar between the two groups, except for gender (46/33 males in group A/B; P=0.02). Despite significantly shorter fasting times for clear fluids in group A compared with group B (76/136 min; P<0.001), no significant difference was observed regarding gastric pH [1.43 (1.30-1.56)/1.44 (1.29-1.68), P=0.66] or residual volume [0.43 (0.21-0.84)/0.46 (0.19-0.78) ml kg(-1), P=0.47]. CONCLUSION One hour clear fluid fasting does not alter gastric pH or residual volume significantly compared with 2 h fasting. CLINICAL TRIAL REGISTRATION The study was approved by the local ethics committee (KEK-ZH-Nr. 2011-0034) and registered with ClinicalTrials.gov (NCT01516775).

Gastric ultrasound as a preoperative bedside test for residual gastric contents volume in children.

Emergency situations and conditions with impaired gastric emptying enhance the risk of perioperative pulmonary aspiration due to increased residual gastric contents volume (GCV). Gastric ultrasonographic (US) measurement of the gastric antral cross‐sectional area (CSA) has been proposed to estimate preanesthetic GCV. However, only few healthy children and fasted pediatric patients have been investigated so far, predicting GCV with considerable imprecision. This study aimed to compare GCV assessed by US in different patient positions for measuring CSA, using magnetic resonance imaging (MRI) as reference, and to evaluate its potential as diagnostic test.

Sex-dependent differences in the in vivo respiratory phenotype of the TASK-1 potassium channel knockout mouse

TASK-1 potassium channels have been implicated in central and peripheral chemoreception; however, the precise contribution of TASK-1 for the control of respiration is still under debate. Here, we investigated the respiration of unrestrained adult and neonatal TASK-1 knockout mice (TASK-1-/-) using a plethysmographic device. Respiration in adult female TASK-1-/- mice under control (21% O2), hypoxia and hypercapnia was unaffected. Under acute hypoxia male TASK-1-/- mice exhibited a reduced increase of the respiratory frequency (fR) compared to wildtypes. However, the tidal volume (VT) of male TASK-1-/- mice was strongly enhanced. The volatile anesthetic isoflurane induced in male TASK-1-/- and male wild type mice (TASK-1+/+) a similar respiratory depression. Neonatal TASK-1-/- mice demonstrated a 30-40% decrease of the minute volume, caused by a reduction of the fR under control condition (21% O2). Under hypoxia, neonatal TASK-1-/- mice more frequently stopped breathing (apnea>3s) suggesting an increased hypoxia-sensitivity. As reported before, this increased hypoxia sensitivity had no influence on the survival rate of neonatal TASK-1-/- mice. In adult and neonatal mice, TASK-1 gene deletion induced a significant prolongation of the relaxation time (RT), which is a parameter for expiration kinetics. Additionally, screening for mutations in the human TASK-1 gene in 155 cases of sudden infant death syndrome (SIDS) was inconclusive. In conclusion, these data are suggestive for an increased hypoxia-sensitivity of neonatal TASK-1-/- mice, however, without causing an increase in neonatal lethality. In adult female TASK-1-/- mice respiration was unaffected, whereas adult male TASK-1-/- mice showed a modified breathing pattern. These results are suggestive for sex-specific mechanisms for compensating the inactivation of TASK-1 in mice.

Performance of adjustable pressure-limiting (APL) valves in two different modern anaesthesia machines.

The ability to gently ventilate a patients lungs using a self‐inflating bag requires a properly working adjustable pressure‐limiting (APL) valve. We compared the performance of the APL valves of the GE Aisys CS2 and the Draeger Fabius anaesthetic machines during closure and opening from 1‐20 and from 20‐1 cmH2O, using standardised experimental baby and adolescent patient lung models. Airway pressures and inspiratory tidal volumes were measured using an ASL‐5000 test lung and a GE Aisys CS2 near‐patient spirometry sensors. In both lung models, the GE Aisys CS2 APL valves demonstrated non‐linear behaviours for airway pressures and for inspiratory tidal volumes, with a sharp increase at set APL pressure levels of 8–10 cmH2O. With further closure of the GE Aisys CS2 APL valves up to 20 cmH2O, inspiratory tidal volumes decreased to ~50% of the highest values measured. Airway pressures in the Draeger Fabius APL valves demonstrated a near linear increase and decrease. Airway pressure values measured in the Draeger Fabius were never higher than those set by the APL valves, whereas in the GE Aisys CS2, they considerably exceeded set pressures (by up to 27 cmH2O). We conclude that the performance of the GE Aisys CS2 APL valve does not allow safe bag‐assisted ventilation of a patients lungs.

Abnormal respiration under hyperoxia in TASK-1/3 potassium channel double knockout mice

Despite intensive research, the exact function of TASK potassium channels in central and peripheral chemoreception is still under debate. In this study, we investigated the respiration of unrestrained TASK-3 (TASK-3-/-) and TASK-1/TASK-3 double knockout (TASK-1/3-/-) adult male mice in vivo using a plethysmographic device. Ventilation parameters of TASK-3-/- mice were normal under control condition (21% O2) and upon hypoxia and hypercapnia they displayed the physiological increase of ventilation. TASK-1/3-/- mice showed increased ventilation under control conditions. This increase of ventilation was caused by increased tidal volumes (VT), a phenomenon similarly observed in TASK-1-/- mice. Under acute hypoxia, TASK-1/3-/- mice displayed the physiological increase of the minute volume. Interestingly, this increase was not related to an increase of the respiratory frequency (fR), as observed in wild-type mice, but was caused by a strong increase of VT. This particular respiratory phenotype is reminiscent of the respiratory phenotype of carotid body-denervated rodents in the compensated state. Acute hypercapnia (5% CO2) stimulated ventilation in TASK-1/3-/- and wild-type mice to a similar extent; however, at higher CO2 concentrations (>5% CO2) the stimulation of ventilation was more pronounced in TASK-1/3-/- mice. At hyperoxia (100% O2), TASK-1-/-, TASK-3-/- and wild-type mice showed the physiological small decrease of ventilation. In sharp contrast, TASK-1/3-/- mice exhibited an abnormal increase of ventilation under hyperoxia. In summary, these measurements showed a grossly normal respiration of TASK-3-/- mice and a respiratory phenotype of TASK-1/3-/- mice that was characterized by a markedly enhanced tidal volume, similar to the one observed in TASK-1-/- mice. The abnormal hyperoxia response, exclusively found in TASK-1/3-/- double mutant mice, indicates that both TASK-1 and TASK-3 are essential for the hyperoxia-induced hypoventilation. The peculiar respiratory phenotype of TASK-1/3 knockout mice is reminiscent of the respiration of animals with long-term carotid body dysfunction. Taken together, TASK-1 and TASK-3 appear to serve specific and distinct roles in the complex processes underlying chemoreception and respiratory control.

Comparison of a paediatric emergency ruler with a digital algorithm for weight and age estimation

Emergency tapes like the “Paediatric‐Emergency‐Ruler” (PaedER) provide drug dosing and recommend medical airway equipment based on estimated patient bodyweight and age. Previous studies have revealed unsatisfactory accuracy in bodyweight estimation, due to the tapes′ length‐based weight categories. Therefore, we developed a digital algorithm allowing continuous length‐based estimation of weight and age. The aim of this study was to compare the new algorithm with the PaedER regarding accuracy in estimating bodyweight and recommendation of medical airway equipment.

The in vivo respiratory phenotype of the adenosine A1 receptor knockout mouse.

The nucleoside adenosine has been implicated in the regulation of respiration, especially during hypoxia in the newborn. In this study the role of adenosine A1 receptors for the control of respiration was investigated in vivo. To this end, respiration of unrestrained adult and neonatal adenosine A1 receptor knockout mice (A1R(-/-)) was measured in a plethysmographic device. Under control conditions (21% O2) and mild hypoxia (12-15% O2) no difference of respiratory parameters was observed between adult wildtype (A1R(+/+)) and A1R(-/-) mice. Under more severe hypoxia (6-10% O2) A1R(+/+) mice showed, after a transient increase of respiration, a decrease of respiration frequency (fR) and tidal volume (VT) leading to a decrease of minute volume (MV). This depression of respiration during severe hypoxia was absent in A1R(-/-) mice which displayed a stimulated respiration as indicated by the enhancement of MV by some 50-60%. During hypercapnia-hyperoxia (3-10% CO2/97-90 % O2), no obvious differences in respiration of A1R(-/-) and A1R(+/+) was observed. In neonatal mice, the respiratory response to hypoxia was surprisingly similar in both genotypes. However, neonatal A1R(-/-) mice appeared to have more frequently periods of apnea during hypoxia and in the post-hypoxic control period. In conclusion, these data indicate that the adenosine A1 receptor is an important molecular component mediating hypoxic depression in adult mice and it appears to stabilize respiration of neonatal mice.

Sedation for magnetic resonance imaging using propofol with or without ketamine at induction in pediatrics-A prospective randomized double-blinded study

Deep sedation using propofol has become a standard technique in children. This double‐blinded randomized clinical trial aims to compare the clinical effects of propofol‐mono‐sedation vs a combination of propofol and ketamine at induction and a reduced propofol infusion rate for maintenance in children undergoing diagnostic magnetic resonance imaging.

Tube tip and cuff position using different strategies for placement of currently available paediatric tracheal tubes

Background Tracheal tube tip and cuff positions of different cuffed paediatric tracheal tube brands in the trachea can vary with design. Methods Data from three clinical studies with measured tracheal lengths were pooled in a database including 422 children aged from birth to 16 yr. Dimensional data of seven cuffed paediatric tracheal tube brands (ID 3.0–7.0 mm) were recorded. Positions of tracheal tube tip and upper cuff border were calculated for each of the 422 tracheas using depth mark based tracheal tube placement, placement of the tracheal tube tip at a calculated safety distance above the carina, and mid‐tracheal tube placement. Percentage of accidental bronchial intubations and tracheal tube cuff positions in the subglottic or supraglottic region were calculated. Results Depth mark based tracheal tube placement resulted in accidental bronchial intubation of up to 18% of cases and tracheal tube cuffs being placed in the subglottic region in up to 91%. Tracheal tube tip placement at a calculated safety distance resulted in up to 54% of tube cuffs placed too high. Mid‐tracheal tube placement led to 100% subglottic or supraglottic tracheal tube cuff positions. Conclusions All studied cuffed paediatric tracheal tubes have major design flaws potentially leading to airway complications. Tracheal tube manufacturers are urgently asked to improve the design of cuffed paediatric tracheal tubes. Alternative strategies for tracheal tube placement can allow safe tracheal tube placement of uncuffed but not of cuffed tracheal tubes.

Length-based body weight estimation in paediatric patients: The impact of habitus-A clinical observational trial

Paediatric emergency tapes provide drug dosing based on the patients estimated body weight. Unfortunately, published data revealed an unsatisfactory accuracy. A newly developed digital algorithm for weight estimation (CLAWAR) allowing a three‐staged habitus adaptation (normal, obese, or cachectic; CLAWAR‐3) demonstrated a higher accuracy for weight estimation compared to paediatric emergency tapes. However, the incidence of incorrectly evaluated habitus was 27%. A five‐staged habitus adaptation with figural images was suggested by Wells et al to improve habitus and weight estimation. Therefore, CLAWAR was modified with five habitus stages including figural images (CLAWAR‐5). We hypothized CLAWAR‐5 improves the accuracy of weight estimation.