Slow Rewarming Research Articles

Evaluation of the efficacy of a forced-air warmer (bair hugger) during spinal surgery in children

To evaluate the efficacy of a forced-air warmer during spinal surgery for correction of scoliosis in children. Prospective randomized study (group allocation based on the availability of the warming device). Children's teaching hospital. 51 ASA physical status I and II children (mean age, 15 years; mean weight, 45 kg) scheduled for posterior spinal fusion with general anesthesia. Study group (warmed; n = 26)--legs covered with the forced-air warmer (Bair Hugger, Augustine Medical, Inc., Eden Prairie, MN) after installation of the patient in prone position--versus control group (n = 25)--400W heat lamp placed over the head during surgery as is usually done in our institution. Rectal temperature was taken every 15 minutes during surgery and during the first 2 hours in the recovery room. Time required for the wake-up test, time to extubation, and blood loss also were noted. Temperature profiles were very different in the 2 groups. In the control group, rectal temperature decreased during the first 180 minutes to a minimum of 34.8 degrees C +/- 0.6 degrees C, followed by a slow rewarming phase. In the warmed group, the lowest temperature (35.6 degrees C +/- 0.5 degrees C) was recorded 45 minutes after placement of the forced-air warmer, followed by an effective warming phase. At the end of surgery, temperature was significantly higher in the warmed group than in the control group (36.5 degrees C +/- 0.8 degrees C vs. 35.4 degrees C +/- 0.9 degrees C). However, time required for the wake-up test, time to extubation, and blood loss did not differ between groups. The forced-air warmer (Bair Hugger) is effective during spinal surgery, although only about 20% of body surface area can be covered.

Cryopreservation of cold-acclimated shoot tips of pear in vitro cultures after encapsulation-dehydration

Cryopreservation of axillary shoot-tips of pear in vitro cultures ( Pyrus communis L. cv Beurré Hardy) was performed after encapsulation in alginate beads. Encapsulated shoot-tips were first precultured in medium enriched with sucrose and then dried in a sterile air flow and cooled in liquid nitrogen. After slow rewarming in air at room temperature, alginate beads were transferred to solid culture medium for 1 week before removal of shoot-tips from beads and subculture onto fresh medium. Shoot recovery from cryopreserved shoot-tips was greatly improved by 8–12 weeks of cold acclimation at 0 °C of donor in vitro cultures. The best results (80% shoot recovery) were obtained using 0.75 M sucrose for preculture and 4-h dehydration (giving 20% residual water). The resistance of encapsulated and dehydrated shoot-tips to liquid nitrogen did not depend on cooling rate. Apical shoot-tips about 3 mm in length with several axillary buds were also cryopreserved successfully (47% shoot recovery).

Ulnar artery thrombosis and the role of interposition vein grafting: Patency with microsurgical technique

Eight consecutive cases of chronic ulnar artery thrombosis at the wrist managed with microsurgical interposition vein grafting were evaluated for long-term patency and clinical results. At a minimum of one-year follow-up, seven of eight vein grafts (88%) were patent by Doppler and Allen's tests. For the patent grafts, functional results were excellent in four (57%) and improved in three. For the nonpatent graft, the function was not improved. Patent vein grafts restored the pulse volume recording amplitudes in painful digits to normal in six of seven cases, although slow rewarming after ice immersion suggested residual vasospastic disease in two. The most favorable outcomes were in (1) nonsmokers, with (2) a single, distinctly recalled history of trauma to the palm, and (3) preoperative symptoms of less than 5 months' duration before treatment. Interposition vein grafts can be used to restore pulsatile digital blood flow to painful digits after thrombosis of the ulnar artery.

Treatment of experimental frostbite with urokinase

An experimental model of frostbite using a standard cold injury in rats was used to test the therapeutic usefulness of the fibrinolytic agent urokinase. Control groups included rapid rewarming, slow rewarming, and slow rewarming followed by saline infusion. Urokinase was administered through an intra-arterial catheter 30 minutes after cold injury and slow rewarming. Optimum results were obtained with rapid rewarming of the extremity at 43°C. However, with rewarming at room temperature eventual tissue loss was significantly decreased with the infusion of urokinase compared with either no treatment or saline infusion. In the clinical situation where the patient with frostbite is seen after slow rewarming, we believe that clinical trials of the use of a fibrinolytic agent are warranted.

Hemodynamic and morphologic alterations after experimental administration of protamine sulfate

The hemodynamic, hematologic, and morphologic effects induced by protamine sulfate have been studied in 28 dogs divided into 6 groups. All of the groups were given heparin (3 mg/kg body weight) and Groups I, II, III, and IV were given protamine (5 mg/kg body weight). Group I (control group) was not subjected to extracorporeal circulation. The other groups had the following interventions: Group II, cardiopulmonary bypass without aortic clamp, hypothermia, or cardioplegia; Groups III and V, hypothermia of 25 degrees C, aortic clamping for 25 minutes, administration of cardioplegic solution, and slow rewarming; and Groups IV and VI, the same as Groups III and V, but with rapid rewarming. After injection of protamine sulfate, there was a decrease in mean arterial pressure due to peripheral vasodilation and an increase in the mean pulmonary pressure due to increased pulmonary vascular resistance; marked diminution of the number of circulating platelets aside from the extracorporeal circulation; a decrease in the contractility of both ventricles with augmented right ventricular work and decreased cardiac output; and right ventricular edema in Groups I, II, III, and IV. These alterations were most evident in Groups III and IV.

ECC Sources of Gaseous Microemboli

We have tried to locate sources of gaseous microemboli during the ECC using a newly developed ultrasonic detector. The detector was calibrated with filters of known pore size and the recorder setting was kept constant at all times. We studied, at the oxygenator, the effect of low and high fill volume, refilling with or without air into the cardiotomy line, mechanical disturbance, rewarming and high p02. Arterial line filters were examined for their capacity to retain microemboli. All bubble oxygenators tested released microemboli, especially at low fill volume when operated at high blood flows. Any mechanical interference (shock) either to the oxygenator or the filter will cause massive release of microemboli. This was also seen during fast rewarming of the blood, fast refilling of the oxygenator and high p02. Slow rewarming of the blood as well as slow refilling of the oxygenator, even with air in the cardiotomy line, did not cause any excessive microemboli. All filters tested retained microemboli to a great extent. Membrane oxygenators demonstrated no measurable microbubble formation at normal flows or with mechanical interference (shock) to the unit. Microemboli detection during ECC has helped to trace various sources of gaseous microemboli which could be avoided using better perfusion techniques. Arterial line filters do reduce the amount and the size of gaseous microemboli during ECC.

Effects of hypothermia on the cat brain-stem auditory evoked response

Effects of systematic hypothermia on the brain-stem auditory evoked resposes (BAERs) in 4 pentobarbital anesthetized adult cats placed on total cardiopulmonary bypass were investigated. Hypothermia was achieved by slowly cooling the bypass blood through a heat exchanger. Serial BAERs were recorded at 2 min intervals as brain temperature was lowered from 37 to 22°C and then rewarmed over a 1–2 h period. Temperatures were recorded from the brain, esophagus and rectum. Three effects were produced by controlled systemic hypothermia. First, latencies of each component wave (I–V) of the BAER increased exponentially as brain temperature was lowered to 19°C. Latencies of earlier waves (I–III) increased less than those of the later waves (IV–V). Arrhenius plots of inverse latency (rate) versus reciprocal of the absolute temperature generated a family of straight lines of similar slope for each of the 5 component waves of the BAER. The activation energy for each of the 5 BAER waves was derived from the slope of the Arrhenius plot. The mean and standard deviation of the activation energy of all 5 waves was 9.7 ± 0.5 kcal/mole°C. The fact that the activation energy was similar for each BAER component wave (I–V) indicated that the increase in latencies for all 5 waves was governed by the same rate-limiting, temperature-dependent process(es). Second, the rise time and duration of each of the component waves of the BAER increased with decreasing temperature, Third, wave amplitudes increased from 37 to 32°C in a quasiparabolic relation and then, decreased at approximately a linear rate. The BAER wave form completely disappeared below 20.3°C. Slow rewarming of the brain to its initial temperature restored the BAER component waves to their original latencies and amplitudes.

Accidental hypothermia

Knowledge of the effects of hypothermia has increased greatly over the past 25 yr. Thousands of patients have been cooled intentionally in the operating room, and hundreds of thousands of living hearts have been temporarily stopped by cold cardioplegia and restarted without difficulty or apparent ill-effect. Yet in spite of the acquisition of this vast body of clinical experience an aura of mystery stills surrounds the patient who becomes hypothermic accidentally. The best treatment in any particular case is not always clear, and published accounts do not always give the impression that the hypothermic patient is treated with the same rational approach with which other sick and comatose patients are treated. In summarizing, therefore, conclusions that might be reached from reviewing past experience several important points emerge. The severely hypothermic patient should be treated in an intensive care unit where appropriate monitoring of temperature, cardiovascular function and respiratory function are available, and where full respiratory support including assisted ventilation can be given. The final outcome depends upon the etiology. The young healthy victim of exposure has a good chance of surviving. The patient poisoned by alcohol or barbiturates has a good chance of surviving provided the level of intoxication is not itself lethal. The elderly without severe underlying disease have a good chance of surviving. The patient with severe underlying disease of the endocrine, cardiovascular or neurologic system probably has, at best, a 50% chance of surviving and, at worst, a chance of only 10-20%, depending upon the associated disease. There is no statistical evidence that any one method of rewarming is significantly better than any other. But there is anecdotal evidence that in the absence of full monitoring and support systems slow rewarming is safer than over-energetic external rewarming. Internal rewarming, peritoneal dialysis, hemodialysis, inhalation of warmed oxygen and extracorporeal circulation are effective in severe cases and can be used with safety. The causes of, and triggering mechanism for, ventricular fibrillation are still largely unknown but the onset of ventricular fibrillation in a very cold patient may often be an irreversible complication. The place of modern anti-arrhythmic drugs in the prevention and management of this complication has yet to be elucidated. Cardiopulmonary resuscitation is difficult in profoundly hypothermic patients but should be maintained until a body temperature of 30 degrees C has been achieved.(ABSTRACT TRUNCATED AT 400 WORDS)

Cryoprotectant penetration and supercooling in the eggs of salmonid fishes

1. 1. The freezing point of isolated, unfertilized eggs of rainbow trout ( Salmo gairdneri) is −1.7 °C. 2. 2. Experiments using radiolabeled cryoprotectants show that the degree of permeation of methanol, dimethyl sulfoxide, and glycerol is inversely proportional to the molecular weights of the compounds; glycerol does not penetrate the egg, while methanol, which penetrates with the greatest rapidity, achieves no more than 23% of the expected equilibrium concentration after 2 hr exposure at 0 °C. 3. 3. Eggs treated with 10% DMSO and 10% sucrose in Fish Ringer resist intracellular freezing longer when cooled at 0.01 °C/min than do those in Fish Ringer alone; intracellular freezing is, however, inevitable with both cryoprotectants, although eggs that have remained unfrozen for several hours appear viable upon slow rewarming. These results make it likely that earlier studies reporting survival of “cryopreserved eggs” have in fact been dealing with supercooled eggs. 4. 4. Scanning electron micrographs of cooled and frozen DMSO-treated eggs show a progressive deterioration of the outermost layer of the zona radiata following cooling and freezing, and suggest that intracellular freezing is occurring following nucleation by way of pore canals in the zona that are exposed as cooling progresses.

Lethal Freeze-Dehydration Injury of Dogwood Stem Tissue Does Not Change the Activation Energy of Water Permeability

The Arrhenius activation energy for water permeability, (DeltaE(a,H(2)O)) through stem cortical tissue of red osier dogwood (Cornus sericea L.) was determined after treatments which cause membrane rupture as well as after a lethal slow freeze and subsequent slow rewarming. The latter value was higher than the former, but was indistinguishable from the DeltaE(a,H(2)O) found for healthy tissue. It was concluded that membrane permeability to water is not altered during the first 24 to 48 hours after exposure of nonacclimated red osier dogwood to lethal freeze dehydration injury.

Latent injury in frozen-thawed bacteriophage T4Bo.

Two interesting new phenomena have been observed in suspensions of T4Bo bacteriophage which were frozen to temperatures below the eutectic temperature of the salt (sodium chloride) in the suspending medium. Approximately 10% of the phage appeared to survive such a phase change as determined by plaque titre. However, exposure of these survivors to ultrasonic vibration or repeated freezing showed them to be hypersensitive and thus latently injured. The hypersensitivity was lost on incubating the phage at 37 degrees C. for 3 hr. Furthermore, following a eutectic phase change, the surviving phage could be inactivated by rapid cooling to -90 degrees C. followed by slow rewarming. Such inactivation cannot be accounted for by accepted theories of freezing injury.

Effect of freezing and freeze-drying on the viability and storage of Lilium longiflorum L. and Zea mays L. pollen

The freeze-preservation of pollen is dependent on the interaction of several factors such as freezing rate, thawing rate, freeze-drying temperature and duration, storage temperature and environment and rehydration rates. Changes in any of these variables affects the others directly or indirectly. Rapid freezing of pollen at rates of approximately 200 °C/min maintains the highest degree of viable pollen in combination with rapid thawing rates of 218 °C/min. Rapid cooling and slow rewarming resulted in a substantial loss of pollen viability. This might indicate that intracellular ice crystals formed during rapid cooling perhaps grow into larger ice masses during slow rewarming or storage at temperatures above −50 °C. The germinability of pollen freeze-dried at temperatures below −50 °C was also prolonged over that of the controls. Germination values for unfrozen pollen stored for 30 days at 0–5 °C averaged 50% for lily and 20% for corn. Freeze-dried pollen stored for 30 days at the same temperature yielded considerably higher viability percentages for both lily and corn pollen. Drying time is an important factor, perhaps indicating that residual moisture is critical. Freeze-dried pollen can be stored at higher temperatures than frozen and control pollen. Freeze-dried material stored for five months at 0–5 °C, upon slow rehydration yielded intact grains which has average germination percentages of 25 for lily and 15 for corn. The same pollen upon rapid rehydration showed rupturing of 20–40% of the cells and practically no germination.

COLD INJURY OF THE NEWBORN IN AUSTRALIA A STUDY OF 31 CASES

Despite the temperate climate of Sydney, 31 cases of infantile hypothermia were seen from 1961 to 1972. The majority of these infants presented in the winter months and the average age of presentation in the group was higher than that seen in colder regions. One–third of the babies died, making this condition a significant problem in infancy. Fourteen of the babies were born more than two weeks prematurely. The commonest clinical features were coldness to touch, slowness or refusal to eat, lethargy or drowsiness, cyanosis and vomiting. Coldness to touch and cyanosis were the most important specific features of this disease. Treatment consisted of slow rewarming in a humidicrib, with correction of any biochemical imbalances. Thirty–two per cent of the babies died, although on their admission to hospital these showed no differences in symptoms and signs from those who survived. Post–mortem examination revealed bronchopneumonia, pulmonary haemorrhage and congestion of most other organs. The follow–up study suggested that those babies who survived showed no neurological abnormality which could be attributed to the hypothermia.

Influence of various cooling and warming temperatures on survival after thawing of cryopreserved Plasmodium berghei

Heavy concentrations of viable P. berghei in the natural milieu [20% ( v v ) parasitized red blood cells, or 20% ( w v ) homogenate of splenic tissue in which malarial cells sequestered wer suspended in a serum-free, protective medium. Various rates of cooling are designated as low (1.3 °C/min) and intermediate (4 °C/ min) on exposure in cold gas evolving from liquid nitrogen refrigerant to −70 °C, and this followed by direct immersion in the low temperature refrigerant (−196 °C). Cooling designated high was accomplished by abrupt immersion of the sealed vials with the live malaria-bearing tissue in the liquid nitrogen refrigerant. Rates of warming and thawing were designated low (after slow rewarming of frozen tissue in air at 25.5 °C) and high (after rapid rewarming and thawing in a water bath at 40 °C). Strip chart recordings were made of the complete cooling and freezing wave patterns of the suspending medium to −70 ° C. The functional survivals of the freeze-thaw P. berghei malaria were measured by a special infectivity titration method. None of the cooling and freezing treatments adversely influenced the parasite survivals. Our data showed the optimum cooling velocity that maximally protected this highly lethal P. berghei strain within the host erythrocyte matrix was 1.3 ° C/min to −70 to −196 ° C. The functional survivals of two RBC stabilates with P. berghei, after retrieval from 25 days storage in the liquid nitrogen refrigerant, excelled by more than 100-fold the infectivity titer found by viability assay in the pool of the 0-days nonfrozen infected RBC. The precise factors favoring the maximal survivals of the freeze-thaw P. berghei are unclear. Several factors, singly or in combination, may have played key roles in protecting the living P. berghei from the freeze-thaw damage. These factors are: The composition of the suspending medium fortified by additions of bicarbonate, glucose, lactalbumin hydrolysate and yeastolate; the presence of naturally occurring peptide-containing materials surrounding the parasites in the host red cell milieu; and the protective glycerol agent. Any of these constituents singly or combined possess potential for reducing freeze-thaw injury to the parasites to produce maximal survivals.

Vascular responses to temperature in the foot of the giant fulmar,Macronectes giganteus

1. Blood circulation to the leg of an antarctic bird, the giant fulmar,Macronectes giganteus, has been studied in response to changing the temperature of the ambient environment including immersion of the feet in ice water. 2. Measurements done include blood flow to the leg by an electromagnetic flow meter, blood pressure in the carotid artery and locally in a leg artery and vein, intravenous and arterial blood temperatures in the leg in addition to foot subcutaneous temperature and core temperature (deep pectoral temperature). 3. Blood flow to the lower leg varied between 10 ml/min and 40 ml/min during resting thermoneutral conditions. 4. Raising the core temperature by heating the central body increased foot blood flow to maximum values around 40 ml/min or 160 ml/min/100 g tissue. 5. Quick warming of the cold feet by immersion in hot water caused only slight increase in leg blood flow, whereas slow rewarming in air gave increasing leg blood flow when the local temperature of the foot increased from near zero to 35.6° C. 6. Sudden immersion of the foot in ice water (T = −2.0° C) elicited an immediate flow increase and a transient increase in foot arterial blood temperature. Venous pressure in the foot increased with blood flow while foot arterial pressure was unaltered. 7. The vasodilatation on ice immersion, termed the “cold flush” was followed by a gradual increase in vasoconstriction and reduced blood flow. After about 3 minutes fluctuations “huntings” appeared in leg blood flow and local temperatures in the foot. 8. The described circulatory changes are discussed in relation to thermal homeostasis of the bird and protection of the naked feet from cold shock and impairment of function on sudden cold exposure. Special reference is given to the phenomenon of cold vasodilatation earlier described on cold exposure of extremeties in mammals.

Survival of Plant Tissue at Super-Low Temperatures. IV. Cell Survival with Rapid Cooling and Rewarming

Thin unmounted cortical tissue sections from winter twigs of the mulberry tree were held with a thin forceps and rapidly immersed in liquid nitrogen from room temperatures without prefreezing. They were rewarmed; rapidly in water at 10 degrees to 40 degrees , or slowly, in air at room temperatures. In those sections rapidly rewarmed, all survived. None survived in those sections rewarmed slowly in air.Tissue sections mounted between coverglasses with water were extracellulary prefrozen at the temperatures low enough to dehydrate almost all of the freezable water in cells. These sufficiently prefrozen cells could survive immersion in liquid nitrogen, and the survival value was very little affected by the rates of cooling to and rewarming from super-low temperatures. With insufficient prefreezing at higher temperatures, however, the rewarming process seriously influenced the survival value of cells frozen at super-low temperatures. Slow rewarming in air destroyed all of the cells, while rapid rewarming in water at 30 degrees did not affect them. An abrupt decrease in the survival value in insufficiently prefrozen cells during rewarming was also observed at temperatures above approximately -50 degrees following immersion in liquid nitrogen. Very little decrease in the survival value was observed in any of the cells that had been sufficiently prefrozen.These results indicate that cells which are insufficiently prefrozen may contain freezable water which nucleates during rapid cooling in liquid nitrogen and then grows during the subsequent slow rewarming into ice masses which destroy the viability of the cells. Such fatal intracellular freezing rarely occurs in sufficiently prefrozen cells, irrespective of the rate of cooling to or rewarming from super-low temperatures.

Cardiovascular functions in the dog rewarmed rapidly and slowly from deep hypothermia.

Heart rate, blood pressure, cardiac output and cardiac minute work were measured in pentobarbitalized dogs prior to induction of hypothermia, at rectal temperatures of 25°C or 20°C and following rapid rewarming in warm water or slow rewarming by wrapping in heated sheeting. During rapid rewarming from either 25°C or 20°C no consistent failure in recovery of normal cardiovascular function was observed, although 1 out of 10 dogs did suffer cardiovascular collapse during rapid rewarming. Slow rewarming from 25° and 20°C resulted in consistent failure of some or all of these functions to recover to prehypothermic levels. Moreover, 5 out of 15 slowly rewarmed dogs suffered cardiovascular collapse during the rewarming process. In five dogs slowly rewarmed from 20°C saline was infused into the superior vena cava. This procedure resulted in moderate increases in blood pressure but dramatic increases in cardiac output and minute work (200% and 270%, respectively), thereby negating myocardial failure as the primary cause of the occasionally observed cardiovascular failure.