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Paradox of age: older patients receive higher age-adjusted minimum alveolar concentration fractions of volatile anaesthetics yet display higher bispectral index values.

ABSTRACT: BACKGROUND:Minimum alveolar concentration (MAC) and MAC-awake decrease with age. We hypothesised that, in clinical practice, (i) end-tidal MAC fraction in older patients would decline by less than the predicted age-dependent MAC decrease (i.e. older patients would receive relatively excessive anaesthetic concentrations), and (ii) bispectral index (BIS) values would therefore be lower in older patients. METHODS:We examined the relationship between end-tidal MAC fraction, BIS values, and age in 4699 patients > 30 yr in age at a single centre using unadjusted local regression (locally estimated scatterplot smoothing), Spearman's correlation, stratification, and robust univariable and multivariable linear regression. RESULTS:The end-tidal MAC fraction in older patients declined by 3.01% per decade (95% confidence interval [CI]: 2.56-3.45; P<0.001), less than the 6.47% MAC decrease per decade that we found in a meta-regression analysis of published studies of age-dependent changes in MAC (P<0.001), and less than the age-dependent decrease in MAC-awake. The BIS values correlated positively with age (?=0.15; 95% CI: 0.12-0.17; P<0.001), and inversely with the age-adjusted end-tidal MAC (aaMAC) fraction (?= -0.13; 95% CI: -0.16, -0.11; P<0.001). CONCLUSIONS:The age-dependent decline in end-tidal MAC fraction delivered in clinical practice at our institution was less than the age-dependent percentage decrease in MAC and MAC-awake determined from published studies. Despite receiving higher aaMAC fractions, older patients paradoxically showed higher BIS values. This most likely suggests that the BIS algorithm is inaccurate in older adults.

SUBMITTER: Ni K

PROVIDER: S-EPMC7104362 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Paradox of age: older patients receive higher age-adjusted minimum alveolar concentration fractions of volatile anaesthetics yet display higher bispectral index values.

Ni Katherine K Cooter Mary M Gupta Dhanesh K DK Thomas Jake J Hopkins Thomas J TJ Miller Timothy E TE James Michael L ML Kertai Miklos D MD Berger Miles M

British journal of anaesthesia 20190703 3

<h4>Background</h4>Minimum alveolar concentration (MAC) and MAC-awake decrease with age. We hypothesised that, in clinical practice, (i) end-tidal MAC fraction in older patients would decline by less than the predicted age-dependent MAC decrease (i.e. older patients would receive relatively excessive anaesthetic concentrations), and (ii) bispectral index (BIS) values would therefore be lower in older patients.<h4>Methods</h4>We examined the relationship between end-tidal MAC fraction, BIS values ...[more]

PMID: 31279479

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Project description:BackgroundSpontaneous breathing during mechanical ventilation improves gas exchange by redistribution of ventilation to dependent lung regions. Neurally adjusted ventilatory assist (NAVA) supports spontaneous breathing in proportion to the electrical activity of the diaphragm (EAdi). NAVA has never been used in the operating room and no studies have systematically addressed the influence of different anaesthetic drugs on EAdi.ObjectivesThe aim of this study was to test the feasibility of NAVA under sedation and anaesthesia with two commonly used anaesthetics, sevoflurane and propofol, with and without remifentanil, and to study their effects on EAdi and breathing mechanics.DesignA crossover study with factorial design of NAVA during sedation and anaesthesia in pigs.SettingUniversity basic science laboratory in Uppsala, Sweden, from March 2009 to February 2011.AnimalsNine juvenile pigs were used for the experiment.InterventionsThe lungs were ventilated using NAVA while the animals were sedated and anaesthetised with continuous low-dose ketamine combined with sevoflurane and propofol, with and without remifentanil.Main outcome measuresDuring the last 5? min of each study period (total eight steps) EAdi, breathing pattern, blood gas analysis, neuromechanical efficiency (NME) and neuroventilatory efficiency (NVE) during NAVA were determined.ResultsEAdi was preserved and normoventilation was reached with both sevoflurane and propofol during sedation as well as anaesthesia. Tidal volume (Vt) was significantly lower with sevoflurane anaesthesia than with propofol. NME was significantly higher with sevoflurane than with propofol during anaesthesia with and without remifentanil. NVE was significantly higher with sevoflurane than with propofol during sedation and anaesthesia.ConclusionNAVA is feasible during ketamine-propofol and ketamine-sevoflurane anaesthesia in pigs. Sevoflurane promotes lower Vt, and affects NME and NVE less than propofol. Our data warrant studies of NAVA in humans undergoing anaesthesia.

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Paradox of age: older patients receive higher age-adjusted minimum alveolar concentration fractions of volatile anaesthetics yet display higher bispectral index values.

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Paradox of age: older patients receive higher age-adjusted minimum alveolar concentration fractions of volatile anaesthetics yet display higher bispectral index values.

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