Evaluation of administration of isoflurane at approximately the minimum alveolar concentration on depression of a nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation in ponies

OBJECTIVE: To investigate effects of isoflurane at approximately the minimum alveolar concentration (MAC) on the nociceptive withdrawal reflex (NWR) of the forelimb of ponies as a method for quantifying anesthetic potency. ANIMALS: 7 healthy adult Shetland ponies. PROCEDURE: Individual MAC (iMAC) for isoflurane was determined for each pony. Then, effects of isoflurane administered at 0.85, 0.95, and 1.05 iMAC on the NWR were assessed. At each concentration, the NWR threshold was defined electromyographically for the common digital extensor and deltoid muscles by stimulating the digital nerve; additional electrical stimulations (3, 5, 10, 20, 30, and 40 mA) were delivered, and the evoked activity was recorded and analyzed. After the end of anesthesia, the NWR threshold was assessed in standing ponies. RESULTS: Mean +/- SD MAC of isoflurane was 1.0 +/- 0.2%. The NWR thresholds for both muscles increased significantly in a concentration-dependent manner during anesthesia, whereas they decreased in awake ponies. Significantly higher thresholds were found for the deltoid muscle, compared with thresholds for the common digital extensor muscle, in anesthetized ponies. At each iMAC tested, amplitudes of the reflex responses from both muscles increased as stimulus intensities increased from 3 to 40 mA. A concentration-dependent depression of evoked reflexes with reduction in slopes of the stimulus-response functions was detected. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthetic-induced changes in sensory-motor processing in ponies anesthetized with isoflurane at concentrations of approximately 1.0 MAC can be detected by assessment of NWR. This method will permit comparison of effects of inhaled anesthetics or anesthetic combinations on spinal processing in equids.

Prevalence and predictors of posttraumatic stress disorder in patients with acute myocardial infarction

OBJECTIVE: We estimated the prevalence of posttraumatic stress disorder (PTSD) and identified predictors of self-rated PTSD symptoms in patients post-myocardial infarction (MI). METHODS: We recruited 400 patients (mean age 60 +/- 12 years, 79% were men) with a previous acute index MI who were referred to a tertiary cardiology clinic. PTSD was assessed by the Clinician-administered PTSD Scale, and self-rated severity of PTSD symptom levels were assessed by the Posttraumatic Diagnostic Scale. RESULTS: Of the 190 patients who completed the Posttraumatic Diagnostic Scale, 34 met the cutoff for clinically significant PTSD symptomatology and 32 agreed to be interviewed. Among these patients, the Clinician-administered PTSD Scale interview yielded a prevalence of full and subsyndromal PTSD of 9.5% (95% confidence interval 7.4-11.6). Retrospectively rated feelings of helplessness (beta = .47, P < .001) and pain intensity during MI (beta = .15, P = .019) independently predicted PTSD symptom level. CONCLUSIONS: Approximately 10% of patients post-MI had full or subsyndromal PTSD. Subjective perception of MI predicted self-rated PTSD symptom level.