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Biomedical subjects

M C Norris

Publications and source records attributed to M C Norris.

At least 55 records · Page 3Linked to original sources
PubMed1990

Incidence of electrocardiographic changes during cesarean delivery under regional anesthesia.

Serial electrocardiograms were obtained on 93 healthy ASA physical status I and II term parturients during nonemergent cesarean delivery under regional anesthesia. Electrocardiographic changes occurred in 44 of the 93 patients (47.3%); in 35 of these 44 patients, the changes were characteristic, or suggestive, of myocardial ischemia. Symptoms of chest pain, pressure, and dyspnea occurred in 15 of the 44 patients with electrocardiographic changes; no patient without electrocardiographic change developed symptoms of chest pain, pressure, or dyspnea. Small but statistically significant differences were noted in heart rate, diastolic and systolic arterial pressures, and rate-pressure product between the patients with electrocardiographic changes and those without. The authors speculate that myocardial ischemia is a likely cause of both the electrocardiographic changes seen in these patients and of the symptoms of chest pain and dyspnea that they sometimes experience.

Adult↗
PubMed1989

Evaluation of a continuous noninvasive blood pressure monitor in obstetric patients undergoing spinal anesthesia.

A noninvasive blood pressure monitor (Finapres) that continuously displays the arterial waveform using the Penaz methodology has recently been introduced into clinical practice. We compared this device with an automated oscillometric blood pressure monitor (Dinamap 1846SX) in 20 patients during spinal anesthesia for nonemergency cesarean section according to a procedure suggested by the Association for the Advancement of Medical Instrumentation. After administration of the spinal anesthetic, the Finapres monitor produced systolic, mean, and diastolic pressure measurements greater than those of the Dinamap monitor (6.6 +/- 12.5, 3.3 +/- 10.4, and 7.2 +/- 9.8 mm Hg, respectively). In most patients, the Finapres measurements were similar to those determined by the Dinamap; however, in 4 patients, mean systolic differences were greater than 20 mm Hg. These patients did not differ from the others in age, height, weight, or baseline blood pressure, and the pressure values recorded by the Finapres monitor were substantially higher than those measured by auscultation in the labor room. In 30% of the patients, the offset between Dinamap and Finapres blood pressure measurements changed markedly over the course of the surgical procedure. The Finapres monitor occasionally stopped working and had to be restarted. In 1 patient (not included in this analysis), the Dinamap monitor was unable to determine the blood pressure due to patient shivering; this did not appear to interfere with the Finapres. We conclude that the Finapres monitor does not consistently provide blood pressure information equivalent to that of the Dinamap in obstetric patients undergoing spinal anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Denitrogenation in pregnancy.

This study measured nitrogen washout in ten pregnant and nine non-pregnant women to understand better how pregnancy effects denitrogenation. Nitrogen concentration was monitored continuously while the women breathed 100 per cent O2 for three minutes and took four deep breaths of 100 per cent O2 using a circle anaesthesia system and 8 L.min-1 fresh gas flow. Parturients achieved 95 per cent denitrogenation significantly (P less than 0.0005) faster than non-pregnant women (54.5 +/- 17.8 vs 110.8 +/- 35.7 sec). In parturients, denitrogenation for three minutes lowered expired N2 concentration to 1.0 +/- 0.2 per cent while four deep breaths lowered it to 5.1 +/- 1.7 per cent (P less than 0.0001). This difference, while statistically significant, is predicted to supply only 10-15 sec of extra protection against hypoxaemia, and thus is probably not clinically significant. The authors conclude that either two minutes of tidal breathing or four deep breaths of 100 per cent O2 provide adequate denitrogenation and similar protection against apnoeic hypoxaemia in normal parturients.

Adult↗
PubMed1989

Anesthesia for perinatal surgery.

A 30 year gravida 3 para 2002 woman presented at 28 weeks' gestation with polyhydramnios. Ultrasound revealed a single fetus with a large anterior neck mass. With halothane general anesthesia providing uterine relaxation and maintaining placental and umbilical blood flow, an otolaryngologist attempted to secure the airway. We discuss the rationale for our anesthetic management and suggest its use in similar situations in which surgical intervention may be required in the immediate perinatal period.

Anesthesia, General↗
PubMed1989

Needle bevel direction and headache after inadvertent dural puncture.

To study the effect of needle bevel direction on the incidence and severity of headache following inadvertent dural puncture occurring during the identification of the epidural space, the authors randomly assigned obstetric anesthesia residents to identify epidural space with the bevel of the epidural needle oriented either parallel or perpendicular to the longitudinal dural fibers. If dural puncture occurred, an observer unaware of the needle bevel direction, daily assessed the presence and severity of any subsequent headache. Of the 1,558 women who received epidural analgesia during this study, 41 women suffered dural puncture, 20 with the needle bevel oriented perpendicular to the longitudinal dural fibers and 21 with the needle bevel inserted parallel to the dural fibers (NS). Fourteen of 20 women in the group in which the needle bevel was perpendicular to dural fibers developed a moderate to severe headache, whereas only five of 21 in the group in which the needle bevel was parallel to dural fibers did so (P less than 0.005). Similarly, we administered a therapeutic blood patch to ten of 20 women in the perpendicular group but to only four of 21 in the parallel group (P less than 0.05). Thus, identifying the epidural space with the needle bevel oriented parallel to the longitudinal dural fibers limits the size of the subsequent dural tear and, therefore, lowers the incidence of headache should dural perforation occur.

Analgesia, Epidural↗
PubMed1989

Isoproterenol is an effective marker of intravenous injection in laboring women.

The purpose of this randomized, double-blind study was to determine if isoproterenol 5 micrograms iv produces a consistent, noticeable tachycardia in healthy, laboring women. Maternal heart rate, fetal heart rate, and uterine contractions were continuously recorded and maternal blood pressure was measured every minute for 10 min before and after each patient received either normal saline (NS group; n = 10) or isoproterenol 5 micrograms (ISO group; n = 10) iv. The data-collecting investigator and a nurse palpating the patient's radial artery determined which solution they thought had been administered. The authors analyzed the maternal heart rate tracings using baseline-to-peak (a greater than or equal to 25 beat/min maternal heart rate increase occurring within 120 s of drug injection and lasting greater than or equal to 15 s) and peak-to-peak (a greater than or equal to 10 beat/min increase in the maximum maternal heart rate during the 2-min postinjection over the maximum maternal heart rate during the 2 min preinjection) criteria for detection of an intravascular marker. Mean maternal heart rate in the ISO group was significantly higher than in the NS group 20, 30, 40, 50, and 60 s following the injection (P less than 0.01). The peak-to-peak criterion and the data-collecting investigator correctly classified all patients. Five ISO group patients were not identified by the baseline-to-peak criterion. The nurse palpating the mother's radial artery misidentified two patients. Systolic blood pressure was significantly higher in ISO group than in NS group patients 1 min (P less than 0.05) and 2 min (P less than 0.01) following drug injection. Diastolic and mean blood pressures did not change. No fetal distress occurred. Isoproterenol 5 micrograms is an effective marker of intravascular injection in laboring women; however, the safety and efficacy of epidural isoproterenol must be demonstrated in animals before isoproterenol can be incorporated in an epidural anesthesia test dose.

Anesthetics, Local↗
PubMed1988

Height, weight, and the spread of subarachnoid hyperbaric bupivacaine in the term parturient.

Using a standardized technique, spinal anesthesia was induced in 50 term parturients to study the correlation between patient height, weight, and body mass index (BMI) and the spread of sensory blockade. All patients received 12 mg hyperbaric bupivacaine while in the right lateral decubitus position on a horizontal operating table. Immediately after drug injection, the women were turned to the supine horizontal position with left uterine displacement. Fifteen minutes after drug injection, the level of analgesia to pinprick was measured. Linear regression analysis revealed no significant correlation between height (146-175 cm), weight (57.3-93.6 kg), or body mass index (21-38 kg/m2) and the spread of spinal anesthesia (T7-C8). It is concluded that, in term parturients, patient height, weight, or BMI does not significantly affect the spread of hyperbaric spinal anesthesia.

Anesthesia, Obstetrical↗
PubMed1987

Effect of gravity on the spread of extradural anaesthesia for caesarean section.

The effect of gravity on the spread of extradural anaesthesia was evaluated in a series of parturients undergoing elective Caesarean section. Following placement of an extradural catheter, 25 patients were placed 30-40 degrees head-up for 20 min during the administration of the local anaesthetic drug; 25 additional patients remained supine during injection. Extradural anaesthesia was induced with 3% 2-chloroprocaine 23 ml and analgesia to pinprick assessed at 5-min intervals. Additional drug was given after 20 min, if required. There were no differences in the rate of onset of sacral blockade or in the extent of neural blockade between the two groups. The semi-upright position was not necessary to ensure adequate sacral anaesthesia for Caesarean section.

Adult↗
PubMed1986

Nifedipine or verapamil counteracts hypertension in gravid ewes.

Hypertension frequently complicates endotracheal intubation in the severely preeclamptic parturient. The calcium entry-blocking drugs nifedipine (N) and verapamil (V) are effective antihypertensive agents in nonpregnant patients. The authors studied the maternal and fetal hemodynamic effects of these drugs in chronically instrumented gravid ewes made hypertensive with an infusion of norepinephrine (NE). Initially NE was infused to increase maternal mean arterial pressure (MAP) by 20%. The NE infusion was continued and either N, 2 mg, or V, 10 mg, was administered intravenously. MAP decreased promptly to control values following both drugs. Maternal heart rate (MHR) decreased significantly following NE infusion. MHR returned to control values following V administration, and increased significantly above control following N administration. Uterine blood flow decreased 50-60% during NE infusion, and there was no further change following either N or V. Fetal hemodynamics were unchanged throughout the study. These results suggest that both N and V may be effective antihypertensive agents in the parturient. V did not produce maternal tachycardia and may be the preferable drug.

Animals↗