Mitochondrial myopathies: an unusual cause of hypotonia in infants and children.

Children frequently undergo muscle biopsy for the workup of hypotonia under general anaesthesia which poses unique risks in patients with undiagnosed muscle disease. Mitochondrial myopathies are a relatively newly recognized cause of myopathy and multisystem disease in both adults and children. The diagnosis is complex. In addition to causing myopathy, there are metabolic derangements present in some cases that may be life-threatening. We present three cases of children with hypotonia where the diagnosis was suspected in two patients, and confirmed in the third. The question of whether patients with mitochondrial myopathies are at increased risk for developing malignant hyperthermia is discussed.

Enalaprilat effects renin-angiotensin and adrenergic response to induced hypotension in the rabbit.

The effects of enalaprilat on the renin-angiotensin system and sympathetic nervous system during sodium nitroprusside (SNP)-induced hypotension and halothane anesthesia were studied in three groups of New Zealand white rabbits. Two groups of rabbits (E and EH) were treated with an infusion of enalaprilat at 3.5 micrograms/kg/min i.v. One enalaprilat-treated group (EH) and the third, untreated group (H) received SNP to induce hypotension. In these two groups, the mean arterial blood pressure (MAP) was reduced by 40% for 150 min. Group E did not undergo SNP-induced hypotension and served to document the effects of enalaprilat alone during the 150-min study period. Arterial blood samples for norepinephrine (NE), epinephrine (EPI), and plasma renin activity (PRA) were drawn prior to and during hypotension, and during the recovery period. The SNP dose required to maintain the hypotension was continuously recorded. NE, EPI, and PRA all increased in group H, indicating activation of both the renin-angiotensin system and the sympathetic system during hypotension. The amount of SNP required by group H to maintain a 40% reduction in MAP correlated with circulating NE levels (p less than 0.001) and not PRA. In group EH, PRA levels rose sharply and remained elevated. Plasma NE and EPI levels increased slightly with a decline in the SNP dose requirement. Group E demonstrated a rise in PRA levels, accompanied by unchanged NE and EPI levels and MAP during the study period.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of captopril on the renin-angiotensin system and the sympathetic nervous system during sodium nitroprusside-induced hypotension in the halothane-anesthetized rabbit.

Three groups of New Zealand white rabbits were used to study the effects of captopril on the renin-angiotensin system and sympathetic nervous system during sodium nitroprusside (SNP)-induced hypotension and halothane anesthesia. Two groups of rabbits (C and CH) were treated with captopril 2 mg/kg i.v. One captopril-treated group (CH) and the third, untreated group (H) received SNP to induce hypotension. In these two groups, the mean arterial blood pressure (MAP) was reduced by 40% for 150 min. Group C did not undergo SNP-induced hypotension and served to document the effects of captopril alone during the 150-min study period. Arterial blood samples for norepinephrine (NE), epinephrine (EPI), and plasma renin activity (PRA) were drawn prior to, during hypotension, and in the recovery period. The SNP dose required to maintain the hypotension was continuously recorded. NE, EPI, and PRA all increased in group H, indicating activation of both the renin-angiotensin system and the sympathetic system during hypotension. This was accompanied by a dramatic increase in SNP dose requirement. In the CH group, PRA levels rose sharply and remained elevated. Plasma NE levels increased, while EPI levels remained unchanged with a decline in the SNP dose requirement. The C group demonstrated a rise in PRA levels, accompanied by unchanged NE and EPI levels and MAP during the study period. Captopril administration decreased the SNP dose requirement and significantly decreased the sympathetic response (measured by NE and EPI levels) in group CH as compared to the H group.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of two methods for heparin monitoring: a semi-automated heparin monitoring device and activated clotting time during extracorporeal circulation.

Two methods of heparin monitoring, semi-automated in-vivo heparin protamine titration (HPT) and activated clotting time (ACT), were compared in each of sixteen adult patients undergoing extracorporeal circulation (ECC) for coronary artery bypass surgery. The HPT method determined the initial and maintenance level of heparin for ECC, as well as, the amount of protamine needed for neutralization of heparin. ACT determinations were made in parallel to calculate heparin levels, heparin sensitivity, and protamine requirements. ACT determinations increased from 502 +/- 31 seconds after heparinization to 739 +/- 49 seconds (p less than 0.05) five minutes after the start of ECC. The HPT method determined heparin sensitivity to be 153 +/- 17 secs/mg/kg and this did not change after the institution of ECC. The increase in ACT observed after the start of ECC resulted in an increase in heparin sensitivity from 151 +/- 13 secs/mg/kg initially, to 247 +/- 17 secs/mg/kg after the institution of ECC (p less than 0.01). During ECC, the HPT method reported heparin levels which remained near the initial value of 2.40 +/- 0.12 mg/kg. The ACT method's initial heparin level of 2.66 +/- 0.12 mg/kg rose after the start of ECC to 4.39 +/- 0.55 mg/kg (p less than 0.05). The HPT method adequately predicted protamine requirements, 2.66 +/- 0.15 mg/kg protamine vs. 3.47 +/- 0.14 mg/kg actual dose while the ACT method predicted excess: 5.02 +/- 0.34 mg/kg (p less than 0.01). In-vivo heparin-protamine titration method provided more consistent information during ECC and directed a significantly smaller dose of protamine for heparin neutralization.

Effect of halothane concentration on tachyphylaxis to sodium nitroprusside.

The relationship between halothane concentration and tachyphylaxis to sodium nitroprusside (SNP) was studied in a rabbit model. Three groups of six rabbits (groups A, B, and C) were anesthetized with halothane at 0.75, 1.0, and 1.25 vol% end-tidal, respectively. SNP-induced hypotension was maintained for 135 min or until a cumulative total dose of 12 mg/kg had been infused (defined as "marked tachyphylaxis"). Plasma norepinephrine (NE), epinephrine (EPI) levels, and plasma renin activity (PRA) were measured. Initial mean arterial pressure (MAP) (72 +/- 2 mm Hg), heart rate (325 +/- 12 beats/min), and the amount of SNP required to induce 40% hypotension (19 +/- 4 micrograms/kg/min) did not differ significantly among the three groups. In group A, five out of six animals exhibited "marked tachyphylaxis." In group B, only one animal showed "marked tachyphylaxis"; the remaining five required a dose rate of 104 +/- 38 micrograms/kg/min at 135 min to maintain a 40% reduction in MAP. In group C, none of the animals showed "marked tachyphylaxis"; the dose rate of SNP required after 135 min was 29 +/- 14 micrograms/kg/min. In all groups, SNP dose rate was found to best correlate (p less than 0.0005, r = 0.79) with NE levels and not with PRA or arterial blood pH. This implies that reflex sympathetic activation is the measured mediator of SNP tachyphylaxis. Halothane blunted the tachyphylaxis (sympathetic response) to SNP-induced hypotension at higher concentrations.

Reduced narcotic requirement by clonidine with improved hemodynamic and adrenergic stability in patients undergoing coronary bypass surgery.

The authors examined the effect of clonidine, a preferential alpha 2-adrenergic agonist, upon narcotic requirements, hemodynamics, and adrenergic responses during the perioperative period in patients undergoing CABG surgery. Anesthesia was provided by sufentanil supplemented with isoflurane; sodium nitroprusside was given as needed for hemodynamic control. Ten patients received oral clonidine preoperatively at the time of premedication, and again intraoperatively by nasogastric tube. Another group of ten untreated patients were otherwise managed identically. Intergroup differences in required anesthetic and vasoactive drug doses and recovery times were measured and evaluated, as well as hemodynamics and plasma catecholamines prior to induction, after intubation, and at intervals intra- and postoperatively. Patients who received clonidine required less diazepam prior to induction, and received 40% less sufentanil during the anesthetic period, than did untreated controls. More control patients required the addition of isoflurane to prevent hypertension. Mean blood pressures and heart rates were elevated at many sampling points in patients not treated with clonidine. Four of the clonidine-treated group required atropine for treatment of bradycardia in the pre-incision period. Plasma catecholamines were significantly lower throughout most of the study period in patients treated with clonidine. After cardiopulmonary bypass and postoperatively, cardiac outputs were significantly higher in the treated group. Patients who had received clonidine were extubated significantly earlier, and fewer of them shivered postoperatively. We conclude that perioperative treatment with clonidine reduced narcotic and anesthetic requirements, improved hemodynamics, reduced plasma catecholamines, and shortened the period of postoperative ventilation in patients undergoing coronary artery surgery.

Mitral valve replacement complicated by unsuspected pheochromocytoma.

This report describes the case of a 65-year-old woman who underwent elective mitral valve replacement complicated by a malignantly vasoactive pheochromocytoma. The early recognition of this condition and the importance of immediate and aggressive pharmacologic intervention are discussed.

Assessment of digital blood flow and palmar collateral circulation. Allen's test vs. photoplethysmography.

Collateral circulation of the hand and digits was evaluated in 20 healthy male volunteers using a modified Allen's test and photoelectric plethysmography. A borderline (7-14 sec) Allen's test was present in 12.5% and 2.5% required more than 15 seconds for thenar flush. Photoplethysmography was then used to compare the relative contributions of ulnar artery flow to total arterial flow into the hand. This ratio, (ulnar/total) was termed the flow index (FI). Average FI for the first digit (thumb) was 0.59, and for the second digit (index) was 0.64. The FI difference between the first digit and that of the third, fourth and fifth digits was statistically significant (p less than 0.01). The FI difference between the second digit and the third, fourth and fifth digits was also statistically significant (p less than 0.05). These results imply that Allen's test may be misleading, indicating adequate collateral circulation when in fact collateral blood flow to the digits may be poor or nonexistent.