HYPOTHERMIA
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THE BIG CHILL: HYPOTHERMIC TREATMENT FOR SCI

Laurance Johnston, Ph.D.

In a season-opening game, Buffalo Bills tight end Kevin Everett sustained a cervical C3-4 injury from tackling an opponent. While still in the ambulance, an ice-cold saline solution was injected into Everett putting him into a neuroprotective, hypothermic state. He soon regained significant function, which may (or may not) have resulted from the cooling.

Cooling the acutely injured cord is not a recent development, and, as reviewed by Miami-Project investigators Drs. Alberto Martinez-Arizala and Barth Green (1992) and Drs. James Guest and Dalton Dietrich (2005), various permutations have been tried over the years.  Observations dating back to the 1950s suggest that lowering central-nervous-system (CNS) temperature can mitigate the harmful effects of restricted blood flow and oxygen deficiency during, for example, CNS-blood-flow-disrupting operations. Based on the observations, hypothermic cooling procedures were developed to save neurological function after acute spinal cord injury (SCI).

Supposedly, the procedures protect the injured cord by reducing its metabolic and energetic requirements. Like putting the injured neurons on life support, they donít need as much viable cellular processes to keep functioning in the cooled state and, therefore, may survive longer. Similar to an ice-pack on a sprain, cooling reduces neuron-damaging, injury-site swelling and bleeding.

Although SCI studies suggest intriguing potential, care must be taken in over-generalizing results in humans because the studies 1) involved limited cases, 2) lacked controls, 3) reported only generalized improvement during a period in which some gain is not unusual, 4) varied in the time from injury to when cooling was started, and 5) were potentially confounded by the concomitant use of other treatments.

Although the neuroprotective potential of cooling is being revisited, most clinical experience was acquired in the 1960-70s. By the 1980s, enthusiasm cooled off because of ambiguous results, technical complexity, and decreased use of emergency laminectomy needed to expose the injured cord to cooling. [laminectomy removes function-compromising, cord-compressing tissue or bone fragments].

Essentially, procedures can be categorized as either systemic (i.e., whole body) hypothermia or localized cooling:

LOCALIZED COOLING

1) Dr. Gaston Acosta-Rua (Iowa City, IA) treated two men (17 & 21) with thoracic injuries from motor-vehicle accidents with spinal-cord cooling (1970). After a decompressive laminectomy, the cordís outer membrane was opened, and the cord cooled for three hours with recirculated, ice-cold saline. The time from injury to cooling was two days in the first case and several hours in the second. Both patients improved.

2) Dr. Y. K. Demian et al (Cleveland, OH) treated three patients (age 15, 17, & 18) with cervical injuries (1971). After laminectomy, the cord was cooled for 1.5 - 3 hours with ice-cold saline.  In two cases, the time from injury to cooling was about five hours; in one, it was over 12 hours. Recovery was noted in all.

3) Dr. Robert Selker (Chicago, IL) used hypothermic cooling to treat four acutely injured patients (2 cervical & 2 thoracic; 3 from gunshot) within three hours of injury (1971). Although two died several months later, the other two regained some function.

4) Dr. Dexter Koons and colleagues (Tucson, AZ) treated five patients with cervical (2) and thoracic (3) injuries with hypothermic procedures (1972). After a decompressive laminectomy 3-7 hours after injury, the cordís outer membrane was opened, and the cord was cooled with a saline slush for 30 minutes. Most patients did not regain function.

5) Drs. William Meacham and Warren McPherson (Nashville, TN) treated 14 patients with spinal-cord cooling within eight hours of injury (1973). Age ranged from 16 to 56; all but three were male; and 12 and 2 had cervical and thoracic injuries, respectively. After a wide decompressive laminectomy, the cord was cooled by cold saline for three hours. Four patients died. Of the 10 survivors, seven had some improvement, including improved sensation, motor control, and bladder functioning.

6) Dr. Juan Negrin (New York, NY) treated three patients with delayed cooling (1975). With the first patient, who sustained a thoracic injury five hours before laminectomy, the cord was cooled without opening its membrane for three, 45-minute periods two, three, and four days after surgery. No improvement was reported.  With the second patient, who had a laminectomy a day after injury, the cord was cooled for one hour after opening the covering membranes. Several weeks later when the cord needed to be opened once more, cooling was carried out again for another hour. The patient regained considerable function. Due to delayed complications, the third patientís decompressive laminectomy was undertaken a year after acquiring a cervical injury. After opening the covering membranes, cooling was carried out for 45 minutes. Improvement was noted.

7) Dr. Charles Tator (Toronto, Ontario) irrigated the acutely injured spinal cord of 11 patients (7 cervical & 4 thoracic; age 16-56) with either cooled or body-temperature solutions (1979). He suggested that non-cooling irrigation still provides benefits because the solution provides oxygen to the injured tissue, creates a biochemically supportive environment, and flushes out noxious substances. The time from injury to surgery varied from 3-8 hours. The irrigations were carried out with covering membranes widely opened. Three patients recovered some sensation, one of whom also regained some motor function (toe wiggling).

8) Dr. Robert Hansebout and colleagues (Hamilton, Ontario) treated seven males and three females (6 thoracic and 4 cervical injuries) within 8.5 hours of injury (1984). After decompression, a cooling saddle was placed lightly against the cordís outer membrane for four hours. Followed for at least six months, three patients accrued some motor or sensory recovery (one died).

SYSTEMIC COOLING

Due to a rise in body temperature after injury, Everett was systemically cooled, a procedure that has been more extensively used in traumatic brain injury (TBI). Even with TBI, however, the benefits of such cooling have been ambiguous. For example, a study completed in 1998 involving 392 patients with TBI did not demonstrate significant benefits, except in younger, quickly treated patients.

For SCI, medications used to prevent shivering interfere with monitoring neurological function and promote health complications. Addressing this issue, Dr. Jogi Inamasu and colleagues (2003; Tokyo, Japan) stated ďÖ patients with cervical SCI, who are most vulnerable to respiratory infection, hypotension, and bradycardia [slow heart rate] may be further compromised by induction of systemic hypothermia,Ē further noting that the prolonged use of sedatives and muscle relaxants essential during systemic hypothermia may worsen the respiratory function of these ďfragile patients.Ē

Nevertheless, because animal studies suggest that post-injury elevated body temperatures are detrimental, Miami-Project investigators have started using state-of-the-art technology to treat acutely injured patients with mild hypothermia, producing a several degree drop in body temperature. Basically, a catheter is placed in the patientís blood vessel, and a thermo-regulating device closely monitors and adjusts blood temperature as it passes by the catheter.  The study will follow long-term benefits by assessing improvements in motor and sensory function and acquisition of daily-living skills.

CONCLUSION

The still-to-be-defined neuroprotective benefits associated with cooling the acutely injured spinal cord must be carefully weighed relative to potential risks. Because the results of various animal and human studies have been ambiguous and often contradictory, more definitive studies are needed.

Adapted from article appearing in December 2007 Paraplegia News (For subscriptions, call 602-224-0500) or go to www.pn-magazine.com

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