The effect of cigarette smoking on the hypnotic efficacy of propofol

High daily caffeine intake is associated with lower propofol requirements for anesthetic induction

Background and Aims

There is significant interindividual variation in the dose of propofol required for anesthetic induction. Factors dictating this are poorly described, but understanding them would be useful for anesthetic drug dosing. It has been shown in rats and recently in humans that caffeine administration accelerates recovery from anesthesia, but no study has assessed the effect on anesthetic induction.

Material and Methods

Forty American Society of Anesthesiologists (ASA)-I, 18-65-year-old patients, undergoing day case general anesthesia with propofol and fentanyl took part in this observational study. Total daily caffeine intake (mg) was estimated using the caffeine assessment tool and caffeine content values from the US Department of Agriculture National Nutrient Database. Pharmacokinetic-pharmacodynamic modeling was used to estimate the effect site concentration of propofol at loss of consciousness (Ce(p) LOC).

Results

Median (interquartile range [IQR]) daily caffeine intake was 106 (51-193) mg. Ce(p) LOC was lower in those with caffeine intake greater than or equal to the median of 106 mg (median (IQR) = 0.64 μg/ml (0.51-0.72) vs. 0.70 μg/ml (0.57-1.10), P = 0.04). The effect was robust when controlling for weight-adjusted fentanyl dose, age, smoking status, and alcohol intake (F (1,34) = 4.66, P = 0.04).

Conclusion

High daily caffeine intake is associated with lower propofol requirements for day case anesthetic induction. We propose that high daily caffeine intake may cause lower arousal levels prior to surgery due to a relative caffeine deficit caused by being nil by mouth. As such, assessment of daily caffeine intake preoperatively may aid anesthetic drug dosing.

A Protocol for Propofol-Infusion Drug-Induced Sleep Endoscopy

OBJECTIVE

The objective of this study was to outline a protocol utilizing propofol infusion without an initial bolus during drug-induced sleep endoscopy (DISE). We define normative values for final propofol infusion rate (P^final ) during DISE and sedation depth values at P^final .

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary academic hospital.

METHODS

A review of patients with obstructive sleep apnea who underwent DISE between 2016 and 2020 was performed. The following patient data were recorded: demographics; DISE procedure details, including P^final , time to P^final , frequency and cadence of infusion rate changes, depth of sedation as measured by Bispectral Index and SedLine values, and hemodynamics; and polysomnography details including apnea-hypopnea index severity and minimum oxygen saturation. A mixed linear model adjusted for age and body mass index was performed for the analysis of effects on P^final . Pearson correlation coefficients determined the strength of association between depth of sedation measured and pattern of collapse on DISE and P^final .

RESULTS

There were 246 patients who met inclusion criteria. P^final resembled a normal distribution (mean ± SD, 156.44 ± 26.69 mcg/kg/min; median, 150 mcg/kg/min). Analysis demonstrated that P^final was influenced by male sex, current smoker status, time to P^final , and number of propofol dose changes (P < .05). Depth of sedation categories measured differently between Bispectral Index and SedLine (55-65 vs 45-55, P < .001). The pattern including severity of collapse on DISE was not associated with P^final (P > .05). No patients required intra- or postoperative respiratory support beyond oxygen via nasal canula.

CONCLUSION

We describe a propofol slow-infusion DISE protocol that demonstrates safe and reproducible outcomes.

Does smoking increase the anesthetic requirement?

Background/aim

To examine the effects of active and passive smoking on perioperative anesthetic and analgesic consumption.

Materials and methods

Patients were divided into three groups: group S, smokers; group PS, passive smokers; and group NS, individuals who did not have a history of smoking and were not exposed to smoke. All patients underwent the standard total intravenous anesthesia method. The primary endpoint of this study was determination of the total amount of propofol and remifentanil consumed.

Results

The amount of propofol used in induction of anesthesia was significantly higher in group S compared to groups PS and NS. Moreover, the total consumption of propofol was significantly higher in group S compared to groups PS and NS. The total propofol consumption of group PS was significantly higher than that of group NS (P = 0.00). Analysis of total remifentanil consumption showed that remifentanil use was significantly higher in group S compared to group NS (P = 0.00).

Conclusion

The amount of the anesthetic required to ensure equal anesthetic depth in similar surgeries was higher in active smokers and passive smokers compared to nonsmokers.

Cytochrome P450-mediated drug metabolism in the brain

Cytochrome P450 enzymes (CYPs) metabolize many drugs that act on the central nervous system (CNS), such as antidepressants and antipsychotics; drugs of abuse; endogenous neurochemicals, such as serotonin and dopamine; neurotoxins; and carcinogens. This takes place primarily in the liver, but metabolism can also occur in extrahepatic organs, including the brain. This is important for CNS-acting drugs, as variation in brain CYP-mediated metabolism may be a contributing factor when plasma levels do not predict drug response. This review summarizes the characterization of CYPs in the brain, using examples from the CYP2 subfamily, and discusses sources of variation in brain CYP levels and metabolism. Some recent experiments are described that demonstrate how changes in brain CYP metabolism can influence drug response, toxicity and drug-induced behaviours. Advancing knowledge of brain CYP-mediated metabolism may help us understand why patients respond differently to drugs used in psychiatry and predict risk for psychiatric disorders, including neurodegenerative diseases and substance abuse.

Drug metabolism within the brain changes drug response: selective manipulation of brain CYP2B alters propofol effects

Drug-metabolizing cytochrome P450 (CYPs) enzymes are expressed in the liver, as well as in extrahepatic tissues such as the brain. Here we show for the first time that drug metabolism by a CYP within the brain, illustrated using CYP2B and the anesthetic propofol (2, 6-diisopropylphenol, Diprivan), can meaningfully alter the pharmacological response to a CNS acting drug. CYP2B is expressed in the brains of animals and humans, and this CYP isoform is able to metabolize centrally acting substrates such as propofol, ecstasy, and serotonin. Rats were given intracerebroventricularly (i.c.v.) injections of vehicle, C8-xanthate, or 8-methoxypsoralen (CYP2B mechanism-based inhibitors) and then tested for sleep time following propofol (80 mg/kg intraperitoneally). Both inhibitors significantly increased sleep-time (1.8- to 2-fold) and brain propofol levels, while having no effect on plasma propofol levels. Seven days of nicotine treatment can induce the expression of brain, but not hepatic, CYP2B, and this induction reduced propofol sleep times by 2.5-fold. This reduction was reversed in a dose-dependent manner by i.c.v. injections of inhibitor. Sleep times correlated with brain (r=0.76, P=0.0009), but not plasma (r=0.24, P=0.39) propofol concentrations. Inhibitor treatments increased brain, but not plasma, propofol levels, and had no effect on hepatic enzyme activity. These data indicate that brain CYP2B can metabolize neuroactive substrates (eg, propofol) and can alter their pharmacological response. This has wider implications for localized CYP-mediated metabolism of drugs, neurotransmitters, and neurotoxins within the brain by this highly variable enzyme family and other CYP subfamilies expressed in the brain.

Effect of cigarette smoking on the washout time of sevoflurane anesthesia

Background

Cigarette smoking affects the pharmacodynamic and pharmacokinetic behavior of many drugs and causes deterioration of pulmonary mechanics. We have evaluated the effect of cigarette smoking on washout time after one minimum alveolar concentration-h (1 MAC-h) of sevoflurane anesthesia.

Methods

We investigated the washout time of sevoflurane in 30 non-smoking and 30 healthy cigarette smoking (≥20 cigarettes/day for>1 year) ASA I-II physical status patients, aged 18-63 years, who were candidates for otorhinolaryngologic elective surgery under 1MAC-h standardized sevoflurane anesthesia. At the end of the surgery, the sevoflurane vaporizer was turned off and the time taken for the sevoflurane concentration to decrease to MAC-awake (0.3) and 0.1 MAC levels were recorded. In addition, the ratio of the fractions of inspired concentration (Fi) and expired concentration of sevoflurane (Fexp) at 1 MAC and Fexp of sevoflurane at 0.1MAC were recorded. The patients were mechanically ventilated during the washout time.

Results

We found no difference between the 2 study groups with regard to washout time of sevoflurane. The times of 1MAC down to MAC-awake (106 ± 48 sec in non-smokers vs 97 ± 37 sec in smokers, p > 0.05) and down to 0.1MAC (491 ± 187 sec in non-smokers vs 409 ± 130 sec in smokers, p > 0.05) were similar. Similarly, there were no significant differences in the ratios of Fi/Fexp at 1MAC (1.18 in non-smokers vs. 1.19 in smokers, p > 0.05) and Fexp of sevoflurane at 0.1MAC (0.26 in non-smokers vs. 0.25 in smokers, p > 0.05).

Conclusions

Washout time of 1MAC-h sevoflurane anesthesia is not appear to be effected by cigarette smoking in patients without significant pulmonary disease.

Brain drug-metabolizing cytochrome P450 enzymes are active in vivo, demonstrated by mechanism-based enzyme inhibition

Individuals vary in their response to centrally acting drugs, and this is not always predicted by drug plasma levels. Central metabolism by brain cytochromes P450 (CYPs) may contribute to interindividual variation in response to drugs. Brain CYPs have unique regional and cell-type expression and induction patterns, and they are regulated independently of their hepatic isoforms. In vitro, these enzymes can metabolize endogenous and xenobiotic substrates including centrally acting drugs, but there is no evidence to date of their in vivo function. This has been difficult to demonstrate in the presence of hepatically derived metabolites that may cross the blood-brain barrier. In addition, because of the membrane location of brain CYPs and the rate limiting effect of endogenous heme levels on the activity and appropriate membrane insertion of some induced CYPs, it has been unclear whether sufficient cofactors and coenzymes are present for constitutive and induced CYP forms to be enzymatically active. We have developed a method using a radiolabeled mechanism-based inhibitor of CYP2B1, (3)H-8-methoxypsoralen, to demonstrate for the first time that both the constitutive and induced forms of this enzyme are active in situ in the living rat brain. This methodology provides a novel approach to assess the function of enzymes in extrahepatic tissues, where expression levels are often low. Selective induction of metabolically active drug metabolizing enzymes in the brain may also provide ways to control prodrug activation in specific brain regions as a novel therapeutic avenue.

Tobacco dependence in surgical patients

PURPOSE OF REVIEW

Many patients who smoke cigarettes require anesthesia and surgery. Their smoking can have profound consequences for perioperative management. Efforts to help them quit will be rewarded by both improved immediate postoperative outcomes and the long-term health benefits after surgery. This review will introduce basic concepts important to perioperative tobacco control and cover recent advances in the field.

RECENT FINDINGS

Evidence continues to accumulate regarding how smoking increases perioperative risk, especially of wound-related complications. There is also new information regarding how abstinence from smoking reduces risk, including how the timing of preoperative abstinence affects outcome. Methods to help surgical patients continue to be developed, taking advantage of surgery as a teachable moment for intervention. There is a need to develop methods practical in the surgical setting. Several pharmacological tools to help surgical patients quit smoking are available, including a new partial acetylcholine receptor agonist.

SUMMARY

The fact that the perioperative period represents an excellent opportunity to help surgical patients quit smoking is becoming increasingly apparent. Although these efforts, and the evidence base to support them, are still at an early stage of development, seizing this opportunity will benefit both the short and long-term health of our patients who smoke.

Tobacco control for anesthesiologists

Anesthesiologists daily witness the consequences of tobacco use, the most common preventable cause of death. Smoking-related diseases such as atherosclerosis and chronic obstructive pulmonary disease increase anesthetic risk, and even smokers without overt disease are at increased risk for morbidity such as pulmonary and wound-related complications. Evidence suggests that stopping smoking will reduce the frequency of these complications. Nicotine and the other constituents of cigarette smoke, such as carbon monoxide, have important physiologic effects that may affect perioperative management. In addition, it is now apparent that the scheduling of elective surgery represents an excellent opportunity for smokers to quit in the long term. This review serves as an introduction to tobacco control for anesthesiologists, first examining issues of importance to perioperative management. It then discusses how anesthesiologists and other perioperative physicians can help address tobacco use, both at an individual level with their patients, and by contributing to the implementation of effective public health strategies in their countries. Anesthesiologists can play a key role in helping their patients quit smoking. Effective tobacco control measures applied to surgical patients will not only improve immediate perioperative outcomes but also long-term health.