John T. Martin

Peri-MAC Depression of a Nociceptive Withdrawal Reflex Is Accompanied by Reduced Dorsal Horn Activity with Halothane but not Isoflurane

Background Anesthetics act in the spinal cord to suppress movement evoked by a noxious stimulus, although the exact site is unknown. Methods This study investigated sensorimotor processing in hind limb withdrawal reflexes, and effects of two general anesthetics, halothane and isoflurane, on simultaneously recorded responses of single dorsal horn neurons and hind limb withdrawal force, elicited by graded noxious thermal hind paw stimulation in rats. Minimum alveolar anesthetic concentration (MAC) needed to block gross movement to a supra-maximal mechanical stimulus was determined for each animal. Results Between 0.9 and 1.1 MAC, halothane and isoflurane greatly reduced or abolished withdrawal force (79 and 89% reduction, respectively). Halothane (0.75–1.4 MAC) depressed heat-evoked neuronal responses in a concentration-related manner (41% reduction between 0.9 and 1.1 MAC averaged across all stimulus temperatures, P < 0.05) and decreased stimulus-response function slopes, with corresponding reductions in withdrawal force. In contrast, isoflurane did not reduce neuronal responses in the 0.75–1.4 MAC range and slightly facilitated responses (by 16%) when concentration increased from 0.9 to 1.1 MAC, despite a concurrent withdrawal force reduction. Anesthetic depression of heat-evoked withdrawal force correlated well with MAC determination using a supra-maximal mechanical stimulus. At sub-MAC anesthetic concentrations, some units exhibited firing rate changes that preceded and paralleled moment-to-moment changes in force during a given withdrawal. Conclusions Halothane reduces noxious-evoked movement at least partly via depression of dorsal horn neurons, whereas isoflurane suppresses movement by an action at more ventral sites in the spinal cord.

Compartment syndromes : concepts and perspectives for the anesthesiologist

ompartment syndromes have been discussed infrequently in literature familiar to anesthesiC ologists ( 1 4 ) . Reports of compartment syndromes following vascular punctures in patients receiving anticoagulant therapy (5,6), plus recent allegations by plaintiffs that patient positioning can be a factor in causing postoperative compartment syndromes, establish a need to review the pathophysiology of compartmentaI ischemia and develop perspectives for the anesthesiologist. Matsen (7) defined a compartment syndrome as a condition “in which the circulation and function of tissues within a closed space are compromised by increased pressure within that space.” Dense osseofascial planes in extremities establish relatively unyielding boundaries that compartmentalize groups of muscles, nerves, and blood vessels. Blood flow through such a compartment can be disturbed by remote perfusion failure (vascular obstruction or systemic hypotension) or by increases in resistance to flow within the compartment itself (Table 1). Compartmental resistance may be increased by (a) an external application of pressure that decreases the effective size of the compartment and compresses its contents or (b) by an enlarged mass of compartment contents that crowds against rigid walls and elevates tissue pressure within the space. If compartmental ischemia is prolonged, it eventually initiates the sequence of events listed in Table 2. Neural dysfunction and muscle injury follow. UsuaIly, prompt surgical decompression of the affected compartments is the only means of minimizing the functional impairment and structural damage of their contents. Remote perfusion failure (Table 1) disrupts driving pressure whether due to systemic hypotension or

Safety of regional anesthesia in Eisenmenger's syndrome.

Background and Objectives Eisenmenger’s syndrome is characterized by right-to-left or bidirectional shunting and pulmonary hypertension. Perioperative risk is high for noncardiac surgery, and many clinicians avoid regional anesthesia because of the potential deleterious hemodynamic effects. We determined perioperative mortality based on published reports describing anesthetic management in patients with Eisenmenger’s syndrome. Methods A literature search identified 57 articles describing 103 anesthetics in patients with Eisenmenger’s syndrome. An additional 21 anesthetics were identified in patients receiving regional anesthesia for labor. Results Overall perioperative mortality was 14%; patients receiving regional anesthesia had a mortality of 5%, whereas those receiving general anesthesia had a mortality of 18%. This trend favored the use of regional anesthesia but was not statistically significant. A better predictor of outcome was the nature of the surgery (and presumably the surgical disease). Patients requiring major surgery had mortality of 24%, whereas those requiring minor surgery had mortality of 5% (P < .05). Patients in labor receiving regional anesthesia had a mortality rate of 24%, and most of these occurred several hours after delivery. Conclusions This review of anesthesia and surgery in patients with Eisenmenger’s syndrome reveals that most deaths probably occurred as a result of the surgical procedure and disease and not anesthesia. Although perioperative and peripartum mortalities are high, many anesthetic agents and techniques have been used with success.

Postoperative Isolated Dysfunction of the Long Thoracic Nerve: A Rare Entity of Uncertain Etiology

A “winged” scapula is a rare, poorly understood, and potentially disabling curiosity following anesthesia and surgery. It is produced by dysfunction of the long thoracic nerve and consequent paralysis of the serratus anterior muscle. A survey of senior anesthesiologists indicated a consistent lack of familiarity with the entity. This article presents six cases of postoperative long thoracic nerve palsy. In a literature review of 111 instances of long thoracic nerve palsy, 51 were trauma-related, 47 were either idiopathic or of debatable origin, and 13 appeared following a surgical or obstetrical procedure. Unprovable etiologic contentions were frequent. Considerations of the etiologies of postoperative long thoracic nerve palsies must include a coincidental infectious neuropathy (“neuralgic amyotrophy”) as a valid alternative to the assertion that a preventable injury occurred during anesthesia.

Neuroanesthetic adjuncts for surgery in he sitting position. II. The antigravity suit.

ATIENTS anesthetized and placed in the P sitting position for surgical procedures have the effects of gravity added to the usual drug-induced stresses upon their circulatory system, Above the level of the heart, gravity aids venous return and opposes arterial perfusion of the brain; below the heart venous return is impeded. Depression of the autonomic nervous system by anesthetics decompensates, to varying degrees, the compensatory reflexes which support circulation. Controlled intermittent-positive-pressure ventilation and the effects of osmotic diuretics upon circulating volume augment the circulatory embarrassment in many instances. Of principal concern is the amount of blood which reaches the brain, for perfusion pressures adequate for the supine patient may be untenable if he is sitting.

Isoflurane, but not halothane, depresses c-fos expression in rat spinal cord at concentrations that suppress reflex movement after supramaximal noxious stimulation

We investigated the effects of isoflurane and halothane on the induction of fos-like immunoreactivity (FLI) in the rat lumbosacral spinal cord after supramaximal noxious mechanical stimulation of the hindpaw. Compared with unstimulated controls (0.9% isoflurane), noxious stimulation at 0.9%–1.5% elicited significant (0.9%–1.5% isoflurane) increases in FLI bilaterally. FLI was distributed mainly in the superficial dorsal horn (laminae I–III) and, to a lesser extent, in the deep dorsal horn (laminae IV–VI) and intermediate zone (lamina VII), with three- to fivefold greater labeling ipsilaterally. At 1.8% isoflurane, mean FLI counts in all laminar regions were significantly smaller (1.7 ± 1.3 per section) compared with the other concentrations (11.4 ± 9.5, 7.5 ± 6.8, and 9.7 ± 6.6 at 0.9%, 1.2%, and 1.5%, respectively) but were not different from unstimulated controls. At sacral levels, we observed a bilateral distribution of FLI primarily in superficial laminae in unstimulated controls that was not significantly different at any isoflurane concentration. FLI counts were not significantly different across groups receiving halothane (0.9%–1.5%). FLI was reduced only at isoflurane concentrations that depressed both gross, purposeful movement and reflex withdrawal, whereas halothane did not cause depression even at concentrations that depressed withdrawal reflexes. Isoflurane and halothane may have differing effects on neuronal function and responses to noxious stimulation.

Neuroanesthetic adjuncts for patients in the sitting position. 3. Intravascular electrocardiography.

HE HAZARD of air embolism in patients T whose surgical incisions are above the level of the heart can be minimized if a means is available to remove embolized air as it enters the right atrium. Michenfelder and associates1 described successful evacuation of air from the atrium using a transvenous catheter which had been placed to sample mixed venous blood and atrial pressures during surgical exploration of the posterior cranial fossa. The tip of the catheter was positioned accurately, using the intravascular electrocardiogram derived from the catheter itself. In the manner described by Robertson and associates,2 P-wave changes on the intravascular lead were obsewed until a biphasic wave was encountered. Experience with this system of diagnosing and treating air embolism has been recounted elsewhere.3 This paper enlarges upon the technique of recording and interpreting the electrocardiogram to assure proper mid-atrial localization of the catheter.

Neuroanesthetic adjuncts for surgery in the sitting position. I. Introduction and basic equipment.

NE OF the most complex tasks con0 fronting the anesthesiologist is that of setting up and supporting the anesthetic for a patient who is to be operated upon after being placed in the sitting position. Since our neurosurgical colleagues frequently require such an operative position, its problems should be common knowledge and techniques aimed at their solution should be widely understood. This paper begins a four-part series which will examine mechanical techniques in use at the Mayo Clinic to support the physiologic functions of the patient who is anesthetized and placed in the sitting position for surgery upon the cervicodorsal spine and the posterior and lateral cranial fossae. In addition to the present comments on basic problems, subsequent articles will discuss the anti-gravity suit, the use of intravascular electrocardiography to place a catheter in the right atrium, and a current-limiting device known as the isolation amplifier which is designed to protect the myocardium from accidental electrical insults during intravascular cardiography.

PLASTIC DEVICES FOR INTRAVASCULAR THERAPY.

HE DEVELOPMENT of plastic tubing acT ceptable for intravascular use has been a significant event in the management of patients requiring multiple injections of drugs, continuous parenteral nutrition, or prolonged diagnostic procedures. Previous to this, repeated administrations of anticoagulants produced trauma to vessels or to sites of injection, and prolonged intravenous therapy required immobilization of an extremity for many hours. The result was uncomfortable for the patient and inconvenient for the attending personnel. Various efforts to improve this situation have led to the development of three categories of plastic devices: (1) “cutdown” tubings, (2) catheters introduced through a “percutaneous” needle, and (3) “plastic” needles.

Anesthesia & Analgesia: seventy-five years of publication.

T he first issue of Current Researches in Anesthesia and Analgesia appeared in August 1922 as a bimonthly publication of the National Anesthesia Research Society (NARS), the organizational precursor (1919-1925) of the International Anesthesia Research Society (IARS). The linear descendent, Anesfhesiu 8 Analgesia, now produced monthly, is the oldest active publication devoted specifically to the specialty of anesthesiology. The 75th anniversary of Anesthesia t? Analgesia provides an opportunity to review its history, as well as that of the IARS, and to celebrate the achievements of both. The early history of the Journal and the Society was documented by Dr. T. H. Seldon on the occasion of the 50th anniversary of the Journal, then titled Anesthesia and Analgesia. . .Cuwenf Researchers (1). Enough of that earlier information is included in this article to provide continuity for the more recent history. Also recalled is the key role played by the IARS in the creation of the World Federation of Societies of Anaesthesiologists tWFSA) and in the first WFSA Congress. Several newer programs of the Journal and Society include the 1983 establishment of the IARS Research Awards Program, affiliations beginning in 1994 between Anesthesia b Analgesia and several subspecialty societies in anesthesiology, and the 1996 development of The Electronic Anesthesiology Library (TEAL) project. A tentative look at the future concludes this historical review.