A loss-of-resistance-to-negative-pressure test for subarachnoid puncture with narrow-gauge needles.

BACKGROUND AND OBJECTIVES: Approximately 5-10% of attempted myelograms are spoiled by partial subdural injection. Similar spillage of local anesthetics may underlie the wide variability of segmental spread reported for spinal anesthesia. A technique of applied negative pressure to avoid accidental subdural injection and to facilitate subarachnoid puncture with narrow gauge needles is described. METHODS: Hydraulic circuitry was designed to measure saline flow rates through spinal needles at hub-to-tip differential pressures of 55 mm Hg and 650 mm Hg. A model of dura and arachnoid membranes was constructed to demonstrate the effects of applied negative pressure on the subdural space during the passage of Quincke-tip and pencil-point needles. Cisternal puncture in 38 dogs and thoracic or lumbar subarachnoid puncture in 680 patients were performed using applied negative pressure to the needle hub. RESULTS: A sustained vacuum of -650 mm Hg at the hub of air-filled spinal needles was transmitted beyond the tip but fell to zero at the tip as the shaft filled with saline. Flow rates through the Quincke needles, ranging from 22-gauge to 29-gauge, rose 22- to 33-fold when a vacuum of -650 mm Hg was applied at the hub. Model dura and arachnoid membranes were separated by air-filled tips at atmospheric pressure but were juxtaposed by negative pressure applied to the hub. CONCLUSIONS: Negative pressure applied to the needle hub is transmitted to the tip without decrement in air-filled needles but not in fluid-filled needles. Clinical application of this principle by exertion of strong negative pressure at the hub during needle advancement facilitates rapid identification of cerebrospinal fluid, avoids unintentional subdural injection of local anesthetics or contrast media, and increases the safety of subarachnoid punctures above the termination of the spinal cord.

Pulse oximetry: a review of the theory, accuracy, and clinical applications.

Pulse oximetry has emerged as a clinical tool in anesthesia and newborn monitoring within the last 7 years as a result of recent technological and theoretical advances. Oximeters measure the different absorption spectra of oxygenated and deoxygenated hemoglobin. Electronic measures of oxygenation at the peak of the pulse allow computation and display of oxygen saturation of the arterial blood almost instantly. Correlation coefficients between pulse oximetry and direct blood oxygen saturation measurement range from 0.77-0.99 when oxygen saturation is greater than 60%. The method is noninvasive (a clip or tape on a finger), simple to operate, and adaptable to various patient populations. Pulse oximetry monitors continuously and instantaneously, is responsive to change, and is accurate. Factors adversely affecting the accuracy of pulse oximeter output include transducer movement, peripheral vasoconstriction, a nonpulsating vascular bed, hypotension, anemia, changes in systemic vascular resistance, hypothermia, presence of intravascular dyes, and nail polish. Pulse oximetry has been used to monitor oxygen saturation intraoperatively in the adult and neonatal intensive care units and to monitor pregnant patients and their infants at delivery. Once the advantages and limitations of pulse oximetry are recognized, this monitoring technique can play an important role in the care of patients with cardiovascular and respiratory compromise.

Prevention of fetal movement during invasive procedures with pancuronium bromide.

The use of fetal intramuscular pancuronium (0.5 mg) to temporarily arrest fetal movement during antenatal intervention in six instances is reported. Successful arrest of movement without adverse side effects was observed. The use of this technique eliminates the need for the excessive and potentially dangerous maternal sedation currently used to minimize fetal movement.

Advantages and disadvantages of regional anesthesia for cesarean section. A review.

Both epidural and spinal anesthesia have advantages and disadvantages for cesarean section. Compared to general anesthesia, regional offers reduced maternal mortality, the ability to use fewer drugs, more direct experience of childbirth and the capability to decrease blood loss and provide excellent postoperative pain control. The disadvantages of regional anesthesia include hypotension, intraoperative discomfort, post-lumbar-puncture headache and the potential for neurologic and cardiac toxicity from local anesthetics. The choice of which anesthetic technique to employ must depend on maternal preference, the experience and skills of the anesthesiologist, and the obstetric indication for the cesarean section.

Problems associated with epidural anesthesia in obstetrics.

Toxic reactions to bupivacaine and 2-chloroprocaine recently have been reported in parturients receiving epidural analgesia. Neurotoxicity has occurred after the accidental subarachnoid injection of large doses of 2-chloroprocaine. Cardiac arrest and death have occurred after the accidental intravascular injection of bupivacaine. Obstetricians should be aware of these hazards and how to avoid them by the use of proper technique.

Anesthesiologists' practice of obstetric anesthesiology.

Physicians trained in obstetric anesthesia and no longer practicing it were questioned regarding conditions that were responsible for their leaving the field. A questionnaire was prepared to determine whether the physicians' activity in obstetric anesthesia continued after fellowship training. The survey yielded a response rate of 76%. Forty-two percent of the respondents spend more than 40% of their clinical anesthesia time in obstetric anesthesia, and 58% spend less than 40% in it. The reasons for less of an emphasis on obstetric anesthesia were finances, personal matters, lack of recognition, long hours and too much call, and lack of stimulation.

Anaesthesia for fetal surgery.

Anaesthesia for fetal surgery is described as used for thirteen procedures in seven patients. Analgesia was accomplished by local infiltration of lignocaine 1% by the surgeons and small incremental doses of intravenous medication by the anaesthetist as needed to make the mother comfortable and reduce fetal movement. There were no maternal or fetal complications. Ethical issues of this therapy are described.

Hyperkalemia and cardiovascular collapse after verapamil and dantrolene administration in swine.

The cardiovascular and neuromuscular interactions of verapamil and dantrolene were evaluated in 20 chloralose-anesthetized swine. The animals were randomly divided into three groups. Group I, ten animals, received a bolus intravenous injection of 0.1 mg . kg-1 of verapamil followed by the continuous infusion of 5 micrograms . kg-1 . min-1. This group was then randomly divided into two equal subgroups. Five of these animals, Group Ia, continued to receive the verapamil infusion alone. The other five animals, Group Ib, received dantrolene in incremental doses of 1.0, 3.3, and 5.6 mg . kg-1 while the verapamil infusion was continued. An additional group of five animals, Group II, received the same incremental doses of dantrolene but did not receive verapamil. Five control animals, Group III, received the alpha-chloralose anesthetic without dantrolene or verapamil. Neuromuscular function, as measured by twitch height, was affected only by dantrolene, which produced a dose-dependent depression. Verapamil resulted in initial decreases in heart rate, arterial blood pressure, cardiac output, left ventricular dP/dt, and an increase in PR interval. Dantrolene alone produced a mild increase in arterial blood pressure. Dantrolene administration to verapamil-pretreated animals resulted in a profound depression in cardiac function, marked elevation in serum K+ (8.0 +/- 0.7 mEq . l-1), and no change in arterial pH (7.39 +/- 0.02). Cardiac arrest preceded by complete atrioventricular heart block occurred in one animal before and in four animals after the final dantrolene dose was given to animals pretreated with verapamil. Although we cannot extrapolate data from our porcine model to humans, further studies are indicated to help evaluate a possible fatal drug interaction before verapamil and dantrolene are used concomitantly in a clinical setting.

The influence of 2-chloroprocaine on the subsequent analgesic potency of bupivacaine.

Isolated rat sciatic nerves were used to study the interaction between 2-chloroprocaine (2-CP) and bupivacaine (BP). Five nerves studied as controls were treated with 5 X 10(-4) M BP and the amplitude of the compound action potential (CAP) evoked by suprathreshold stimulation was measured. This concentration of BP completely blocked nerve conduction; but, following washout with normal Krebs-Ringer solution, the CAP amplitude recovered to 50% of initial values in 50 (+/- 4) min with a rate of recovery of 1.7 (+/- 0.6) %/min. In another series of experiments, five nerves were blocked first with 5 X 10(-4) M 2-CP, allowed to fully recover, and then were blocked with BP under the same conditions as the controls. Under these conditions, the half time for the recovery of CAP amplitude following BP was shortened to 25 (+/- 5) min, with a rate of recovery of 2.8 (+/- 0.3) %/min. When five nerves were exposed to a 5 X 10(-4) M solution of a 2-CP metabolite, 4-amino-2-chlorobenzoic acid, no nerve blockade was produced. When these nerves subsequently were blocked with BP, recovery to 50% of initial values occurred in 22 (+/- 5) min, with a rate of recovery of 2.0 (+/- 0.2) %/min. Although pretreatment with either 2-CP or 4-amino-2-chlorobenzoic acid significantly shortened the duration of BP-induced nerve blockade, neither drug had a significant effect on the rate of recovery once the CAP amplitude returned to measurable values.

Reflex apnea from laryngeal chemo-stimulation in the sleeping premature newborn lamb.

The laryngeal chemoreflex was studied during quiet and REM sleep and wakefulness in premature newborn lambs. The response to reflex stimulation with a 5 sec-water infusion was evaluated during 30 sec, as % change in ventilation, heart rate and blood pressure. Apnea, hypertension and bradycardia were more pronounced during sleep than during wakefulness, when arousal was not associated with the stimulation. The response was similar during quiet and REM sleep. Arousal, which occurred in 24 and 31% of the tests respectively, resulted in a response comparable to that seen during wakefulness. The respiratory drive was evaluated by measurement of the mean inspiratory flow and was found to be decreased during both sleep states when compared to wakefulness. We propose that during sleep in the newborn period there is a decreased ability to respond to asphyxia possibly due to a functional immaturity of the arterial chemoreceptors. This results in a low incidence of arousal and a delayed termination of the pronounced poststimulus apnea resulting from laryngeal chemoreflex stimulation.

Spinal anaesthesia for Caesarean section. The influence of hypotension on neonatal outcome.

The effect upon the neonate of a short period of maternal hypotension sustained during the initiation of spinal analgesia for Caesarean section was studied. Babies born to mothers with hypotension were significantly more acidotic than controls although acid-base levels were still within normal limits. Neurobehavioural studies were found to be normal in both groups at 4 and 24 hours. It was concluded that a short period (less than 2 minutes) of hypotension was not harmful to the neonate.

Epidural anesthesia for cesarean section: a comparison of bupivacaine, chloroprocaine, and etidocaine.

The authors studied three groups of patients undergoing elective cesarean section during lumbar epidural anesthesia with bupivacaine, 0.75 per cent (15 patients), chloroprocaine, 3 per cent (15 patients) or etidocaine, 1 per cent (ten patients). Excellent sensory and motor block were obtained with chloroprocaine and bupivacaine; sensory anesthesia was inadequate with etidocaine in most patients. Onset of anesthesia, induction--delivery interval, and stay in the recovery room were all longer with bupivacaine when compared with chloroprocaine. Fetal outcomes, as determined by Apgar scores, acid--base status and neurobehavioral testing, were equally good in all groups. At delivery, fetal/maternal concentration ratio of bupivacaine was 0.31 and that of etidocaine, 0.25. The umbilical artery--umbilical vein blood concentration difference for etidocaine was significantly higher than that for bupivacaine. Excellent clinical results were obtained using either bupivacaine, 0.75 per cent, alone, or chloroprocaine, 3 per cent- for induction and maintenance of anesthesia, supplemented with bupivacaine, 0.25 per cent, before removal of the catheter.

Neurobehavioural responses of the newborn. The effect of different forms of maternal analgesia.

A neurobehavioural assessment made of infants within 4 hours of delivery revealed that infants born to mothers receiving pethidine and promazine showed significantly worse overall scores than babies of mothers receiving either no analgesia or a lumbar epidural using bupivacaine.