Hemodynamic effects in dogs of nitrous oxide-meperidine and meperidine, respectively, in comparison with nitrous oxide

Pre-anesthetic meperidine: associated vomiting and gastroesophageal reflux during the subsequent anesthetic in dogs

OBJECTIVE

To determine the effect of meperidine administered prior to anesthesia on the incidence of vomiting before, and gastroesophageal reflux (GER) and regurgitation during, the subsequent period of anesthesia in dogs.

STUDY DESIGN

Randomized, controlled trial.

ANIMALS

A total of 60 healthy dogs, 4.3 +/- 2.3 years old, and weighing 35.5 +/- 13.1 kg.

METHODS

Dogs were admitted to the study if they were healthy, had no history of vomiting, and were scheduled to undergo elective orthopedic surgery. The anesthetic protocol used was standardized to include thiopental and isoflurane in oxygen. Dogs were randomly selected to receive one of the following pre-medications: morphine (0.66 mg kg(-1) IM) with acepromazine (0.044 mg kg(-1) IM), meperidine (8.8 mg kg(-1) IM) with acepromazine (0.044 mg kg(-1) IM) or meperidine alone (8.8 mg kg(-1) IM). A sensor-tipped catheter was placed to measure esophageal pH during anesthesia. Gastro-esophageal reflux was judged to have occurred if there was a decrease in esophageal pH below four or an increase above 7.5.

RESULTS

No dogs vomited after the administration of meperidine, but 50% of dogs vomited after the administration of morphine. When compared with morphine, treatment with meperidine alone or combined with acepromazine before anesthesia was associated with a 55% and 27% reduction in absolute risk of developing GER, respectively. Dogs receiving meperidine alone were significantly less sedate than other dogs in the study, and required more thiopental to induce anesthesia. Arterial blood pressure and heart rate were not significantly different between groups at the start of the measurement period. Cutaneous erythema and swelling were evident in four dogs receiving meperidine.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of meperidine to healthy dogs prior to anesthesia was not associated with vomiting and tended to reduce the occurrence of GER, but produced less sedation when compared with morphine. Meperidine is not a useful addition to the anesthetic protocol if prevention of GER is desired.

The use of pethidine as pre-medication to prevent anoxic spells in patients with tetralogy of Fallot

OBJECTIVE

The aim of this study was to determine whether morphine-HCl or pethidine-HCl differ as pre-medication to prevent anoxic spell in patients with tetralogy of Fallot (TOF) at catheterization.

METHODS

A 3 year retrospective case notes review study of 46 consecutive patients who underwent cardiac catheterization from 1998 to 2001 was conducted. In a prospective 1 year randomized control study, 10 patients diagnosed as TOF and admitted to Tokyo Women's Medical University, The Heart Institute of Japan, Tokyo, in 2002 were randomized to receive morphine or pethidine as pre-medication for cardiac catheterization. The incidence of anoxic spell before and after cardiac catheterization was investigated in both studies.

RESULTS

In the case notes review, a total of 10 out of the 46 patients showed anoxic spell study: eight out of 24 patients in the morphine group and two out of 22 in the pethidine group. The difference in the incidence was statistically significant (P < 0.05, Fisher's exact test). Four patients in the prospective study showed anoxic spell: three out of six in the morphine group and one out of four in the pethidine group (odds ratio = 3.0). Overall, 14 out of 56 patients had anoxic spell: 11 out of 30 in the morphine group and three out of 26 in the pethidine group (P = 0.03).

CONCLUSION

The incidence of hypoxic spells in patients with TOF undergoing cardiac catheterization is reduced by the use of pethidine-HCl as pre-medication compared to morphine. This has important clinical implications.

A descriptive tool to characterize nonlinear kinetics, with applications to meperidine and lidocaine

We describe an explorative data analysis tool which can detect and describe the presence of nonlinearities in multiple dose kinetics studies. The method is nonparametric (i.e. not dependent on modeling assumptions), uses regression to estimate the functions representing the kinetics, and makes the detection of nonlinearity a part of the model selection process. Flexible functions (splines) are used to describe the kinetics corresponding to the lowest given dose, and to describe the (possible) departure of the kinetics corresponding to higher doses from the reference kinetics. The estimated kinetics and departures can be examined to offer possible insight into the nature of the nonlinearity. The methodology is applied to the analysis of meperidine and lidocaine kinetics through the lungs and the heart. We find that the lung kinetics of lidocaine and meperidine are linear. However their myocardial kinetics are complex and nonlinear.

Effects of nitrous oxide/oxygen inhalation on the maternal circulation during vaginal delivery

The hemodynamic changes occurring during the first stage of labor were studied in 24 healthy pregnant women during inhalation of different nitrous oxide/oxygen (N2O/O2) gas mixtures (intermittent 70/30, 40/60, 0/100 and continuous 40/60). Cardiac output increased (P less than 0.01) from 6.6 +/- 0.2 l/min between uterine contractions to 8.5 +/- 0.3 l/min during contractions. Heart rate, stroke volume, systolic, diastolic and mean arterial pressures were increased (P less than 0.01) and total peripheral vascular resistance was reduced (P less than 0.01) during contractions compared to measurements performed between contractions. The maternal circulation was influenced by the use of N2O/O2. During intermittent inhalation, higher concentrations of N2O were associated with a decrease (P less than 0.01) in heart rate, cardiac output and arterial pressure as well as an increase (P less than 0.01) in stroke volume. The degree of pain relief also increased (P less than 0.01) with increasing concentrations of inhaled nitrous oxide. The circulatory influence of intermittent inhalation given during uterine contractions was also apparent during the interval between contractions when N2O/O2 was not administered. The most obvious effects on both circulation and pain were demonstrated during continuous inhalation of N2O/O2. There was a close association between analgetic and cardiovascular effects indicating that the latter, at least partly, were due to pain relief. However, it was not possible to exclude or confirm possible direct pharmacological effects of N2O/O2 on maternal circulation.