Endotracheal compared with intravenous injection of 3 mg/kg of lignocaine. Measurement of arterial and venous levels

Lidocaine sprayed down the endotracheal tube attenuates the airway-circulatory reflexes by local anesthesia during emergence and extubation

To determine whether lidocaine sprayed down the endotracheal tube (ETT) would attenuate airway-circulatory reflexes during emergence, we compared the reflex responses after endotracheal or IV lidocaine (IVL) in 75 patients receiving a standardized anesthetic protocol. At the end of surgery, the patients were divided into 3 groups (n = 25 for each group) and given no drug (Group 1), given 1 mg/kg of 2% lidocaine sprayed down the ETT 5 min before (Group 2), or given the same dose of IVL 3 min before extubation (Group 3). Blood pressure and heart rate were recorded at predetermined time points from 5 min (baseline) before until 5 min after extubation. The number of coughs per patient was continuously monitored during this period. The number (mean +/- SD) of coughs was decreased in Group 2 (4.5 +/- 3.7) compared with the control (10.2 +/- 6.0) (P < 0.01) with no difference for the control versus Group 3 (7.8 +/- 4.6). The increase in blood pressure was only attenuated immediately before extubation (P < 0.05), whereas the increase in heart rate was attenuated (P < 0.05) at all (except baseline) time points (P < 0.05) in Group 2 compared with the control with no difference for the control versus Group 3. The results indicate that lidocaine sprayed down the ETT suppresses the reflexes whereas using the same dose IVL does not, which is probably attributable to the mucosa-anesthetizing effect of lidocaine.

IMPLICATIONS

Lidocaine sprayed down the endotracheal tube suppresses the airway-circulatory reflex responses whereas using the same dose IV lidocaine does not. This effect seems to be from the direct local anesthesia rather than from systemic absorption from the airway.

The impact of an endotracheal side port on the absorption of lidocaine

OBJECTIVE

To compare lidocaine levels after administration through an i.v. line, a standard endotracheal (ET) tube, and an ET tube side port (ETSP) designed for medication administration.

METHODS

A double-blind, prospective, triple crossover canine study was performed. Seventeen anesthetized mongrel dogs were given standard doses of 2% lidocaine via i.v. (1.5 mg/kg), endotracheally through the main lumen (3 mg/kg diluted in 10 mL normal saline), and endotracheally through the modified side port (3 mg/ kg diluted in 10 mL normal saline). Arterial blood gases (ABGs) and plasma lidocaine levels were measured at time 0, 30 sec, 1 min, 5 min, 10 min, 20 min, 30 min, and 60 min. Mean lidocaine levels across time, comparing the 3 methods of administration, were analyzed with repeated-measures analysis of variance. The main outcome was the comparison of mean ET and ETSP lidocaine levels at each time point using paired t-tests. The attainment and duration of lidocaine levels considered therapeutic in cardiac arrest (1.4 micrograms/mL) were described. ABGs were measured at each point to describe trends in oxygenation.

RESULTS

Mean lidocaine levels, comparing the 3 methods of administration, were significantly different at all time points except time 0. The ETSP levels were significantly lower than the ET main-lumen levels at 30 sec, 1 min, 5 min, and 10 min. i.v.-administered lidocaine attained quick therapeutic levels and revealed faster elimination. Lidocaine administered through the ET main lumen reached therapeutic levels more slowly, and maintained such levels longer. Lidocaine administered through the ETSP never reached therapeutic levels. Mean PO2S remained > 340 torr throughout each method of administration.

CONCLUSION

This nonarrest canine model suggests that lidocaine levels achieved through an ETSP are lower than levels obtained with the same drug dose via an ET main lumen. Therapeutic lidocaine levels are obtainable by i.v. or ET main-lumen routes, but not via this ETSP.

The effect of topical lignocaine on intubating conditions after propofol-alfentanil induction

BACKGROUND

Recent studies have found satisfactory conditions for intubation of the trachea without using muscle relaxants using an intravenous technique combining propofol and alfentanil. In this study we evaluate intubating conditions with this method and either lignocaine applied topically in the larynx and trachea or placebo.

METHODS

Sixty adult patients of ASA class I were premedicated with diazepam 15-20 mg and randomly allocated to one of two groups. For induction of anaesthesia both groups were given propofol 2.5 mg/kg and alfentanil 30 micrograms/kg. One group received 4 ml of lignocaine 40 mg/ml (< or = 3 mg/kg) topically into the larynx and trachea (group L), the other group an equal amount of isotonic saline (group S) in a double-blind design. Intubation conditions were assessed as excellent, good, moderately good, poor or impossible, scored on the basis of jaw relaxation, ease of insertion of the tube and coughing on intubation.

RESULTS

The total score for group L was significantly better than the score for group S (P < 0.0001) with significant differences with respect to ease of intubation and coughing after intubation.

CONCLUSIONS

Induction of anaesthesia with propofol 2.5 mg/kg and alfentanil 30 micrograms/kg combined with 4 ml of lignocainespray 40 mg/ml into the larynx and trachea offered consistent and satisfactory intubation conditions. We thus recommend this method for tracheal intubation, where the use of muscle relaxants is not indicated.

Plasma lidocaine levels occurring with endotracheal administration during hemorrhagic shock

During the many emergency situations in which venous access is difficult or impossible, endotracheal drug administration is an effective alternative means of delivering life-saving medications. Shock is a commonly encountered emergency situation in which endotracheal drug therapy can and is often used. Yet whether a drug given endotracheally during shock can be absorbed from the lungs and pass into the bloodstream is not known. Forty-five sets of plasma lidocaine levels drawn at 5, 15, 30 and 60 min after the administration of endotracheal lidocaine at a dose of 2 or 4 mg/kg were obtained in dogs either in shock or in a normal control group: Group I = "Non-shock" or normal control, N = 27; Group II = "Shock", N = 18. Significantly higher plasma lidocaine levels occurred in the shock group in all time periods and with either dose of lidocaine (P less than 0.001). Mean plasma lidocaine levels (micrograms/ml) at 5 min were: (at 2 mg/kg dose) Group I = 1.1, Group II = 2.0; and (at 4 mg/kg dose) Group I = 2.3, and Group II = 5.1. The dose of lidocaine, the technique of administration, and the time at which the plasma lidocaine level was drawn as well as whether shock vs. non-shock was present were all highly significant factors (P less than 0.001) in determining plasma lidocaine levels. In summary: (1) endotracheal lidocaine is absorbed during shock and (2) higher plasma lidocaine levels occur during shock than during the non-shock control state. This suggests that the dosage of endotracheal medication may need to be adjusted for various clinical conditions such as shock.

Arterial-venous concentration gradient as a potential source of error in pharmacokinetic studies. Plasma concentration differences of 6-chloro-2-pyridylmethyl nitrate on constant infusion to rats

1. Plasma concentrations of 6-chloro-2-pyridylmethyl nitrate (CPMN) at different sampling sites in the circulation were determined during and after constant infusion in the rat. 2. An arterial-venous CPMN concentration gradient was found and characterized by the following trends. During CPMN infusion into the right atrium, plasma concentrations were higher in arterial (aortic arch) than venous (inferior vena cava) plasma. After cessation of infusion the venous plasma concentrations were significantly higher (P less than 0.05) than those in arterial samples. There was a low concentration gradient between the right atrium and the peripheral artery, but substantial difference between the peripheral artery and the vein. There was a 1.8-2.4 extraction ratio of CPMN across the arterial-venous bed.

The influence of age on lignocaine pharmacokinetics in young puppies

Eight mongrel puppies were studied at intervals of a few weeks. Lignocaine 4 mg/kg was infused over 60 seconds. Frequent samples were taken over 30 minutes for plasma lignocaine assay. Initially the concentrations were significantly higher in the oldest group (178-191 days) but after 10 minutes the youngest group (3-16 days) had significantly higher levels than the other groups. Pharmacokinetic data derived included the rate constants k21, k12 (drug movement between two compartments), k10 (elimination from the central compartment), and the volume of distribution (V beta). The elimination rate constant k10 was significantly lower in Group 1 (3-16 days) than all other groups and Group 2 (37-57 days) was lower than Group 4 (178-191 days). The calculated beta half-life was significantly longer in the youngest group than the others. There was no significant difference in the volume of distribution between these age groups--up to 6 months.

The influence of age on plasma lignocaine levels following tracheal spray in young dogs

A study was conducted in puppies of one litter beginning before they were three weeks old and repeated up to six times in the first four months of life to determine whether any age-related changes in peak plasma lignocaine levels occurred following tracheal spray. These were significantly higher in the youngest group (less than 20 days) than in dogs 2-3 months of age. There was a significant negative correlation between peak plasma levels and age up to four months. The maximum level attained by any puppy was 4.48 ug/ml after 4 mg/kg tracheal lignocaine spray.

Arterial-venous nitroglycerin gradient during intravenous infusion in man

We assessed the concentration of nitroglycerin (GTN) measured in plasma at different sampling sites in the circulation during a constant i.v. infusion. Twenty patients with chronic congestive cardiac failure underwent hemodynamic monitoring during i.v. GTN infusion. Our end point was a reduction in pulmonary capillary wedge pressure by at least 25% of its control value or a 10-fold increment over the initial infusion rate. Nitroglycerin infusion produced no change in heart rate, a reduction in mean arterial pressure from 90 +/- 21 (+/- SD) to 83 +/- 17 mm Hg (p less than 0.001), a fall in total peripheral resistance from 24.3 +/- 10.8 to 20.8 +/- 7.0 units (p less than 0.02), and a substantial reduction in both pulmonary capillary wedge pressure (from 27 +/- 6 to 20 +/- 6 mm Hg, p less than 0.001) and right atrial pressure (from 12 +/- 4 to 8 +/- 4 mm Hg, p less than 0.001). The concentrations of GTN in the pulmonary artery and systemic artery were similar (29.8 ng/ml +/- 52.8 and 25.1 +/- 48.4 ng/ml, respectively) and considerably higher than the concentration in the peripheral vein (7.3 +/- 15.4 ng/ml). There was a 17.4 +/- 19.1% extraction of GTN across the pulmonary vascular bed and a 60.8 +/- 27.2% extraction across the arterial-venous bed (p less than 0.001). There was no relationship between the arterial-venous extraction and the magnitude of arterial plasma (GTN concentration, the duration of the infusion of GTN or the total dose administered. These data show that a better understanding of GTN pharmacokinetics is provided by simultaneous arterial and venous samples.