Environmental emergencies

Asthma and the diver

Self-contained underwater breathing apparatus (scuba) diving has grown in popularity, with nearly 9 million sport divers in the United States alone. Approximately 7% of the population has been diagnosed with asthma, which is similar to the percentage of divers admitting they have asthma. Numerous concerns exist regarding subjects with asthma who choose to participate in recreational diving. Among these concerns are pulmonary barotrauma, pneumomediastinum, pneumothorax, arterial gas embolism, ear barotrauma, sinus barotrauma, and dental barotrauma. Despite these concerns, a paucity of information exists linking asthma to increased risk of diving complications. However, it has long been the norm to discourage individuals with asthma from participating in recreational scuba diving. This article examines the currently available literature to allow for a more informed decision regarding the possible risks associated with diving and asthma. It examines the underlying physiological principles associated with diving, including Henry's law and Boyle's law, to provide a more intimate understanding on physiological changes occurring in the respiratory system under compressive stress. Finally, this article offers a framework for guiding the patient with asthma who is interested in scuba diving. Under the right circumstances, the patient with asthma can safely participate in recreational diving without apparent increased risk of an asthma-related event.

A Randomized, Controlled Trial Comparing Arteriovenous to Venovenous Rewarming of Severe Hypothermia in a Porcine Model

BACKGROUND

The purpose of this study was to evaluate active rewarming using continuous arteriovenous rewarming (CAVR) and continuous venovenous rewarming (CVVR) methods during severe hypothermia using an electromagnetic fluid warmer. Rapid rewarming using these techniques is superior to passive rewarming and is possible with commercially available equipment.

METHODS

Eighteen swine (55-65 kg) were assigned to CAVR, CVVR, or control. Vascular access was obtained via central lines (8.5-French) in all subjects. Subjects were cooled to 27 degrees C (80.6 degrees F) in an ice bath, and then dried, covered, and connected to the rewarming device. The carotid artery (CAVR) or internal jugular vein (CVVR) was used for circuit inflow. Warmed 39 degrees C (102.2 degrees F) blood was returned via the femoral vein. Hemodynamic parameters and temperatures (pulmonary artery and rectal) were recorded until reaching an endpoint of a pulmonary artery temperature of 37 degrees C (98.6 degrees F).

RESULTS

Mean rewarming time in the CAVR group was 2 hours 14 minutes, with a mean rewarming rate of 4.5 degrees C/h (8.1 degrees F/h, 0.034 degrees C/kg/h). Total circulating volume averaged 65 L. CVVR averaged 3 hours 8 minutes, with a mean rewarming rate of 3.2 degrees C/h (5.8 degrees F/h, 0.024 degrees C/kg/h). Total circulating volume averaged 67 L. Controls averaged 10 hours 42 minutes, with a mean rate of 0.9 degrees C/h (1.7 degrees F/h, 0.007 degrees C/kg/h). The CAVR group was faster than the CVVR group in both the rewarming rate and total time to rewarming (p = 0.034 and p = 0.040, respectively). Both experimental groups were significantly different from controls in rewarming rate and total time to rewarming (p < 0.001).

CONCLUSION

CAVR offers the most rapid rate of rewarming. CVVR offers a rapid rate using less invasive procedures. Both techniques are markedly superior to passive rewarming methods typically used during early resuscitation.

Accidental hypothermia

Individuals at extremes of age and those who have certain underlying medical conditions are at greatest risk for hypothermia. Hypothermia may occur during any season of the year and in any climate. Prompt recognition of hypothermia and early institution of the rewarming techniques are imperative for a successful outcome with minimal complications. Several rewarming techniques are available and the decision to use any of them depends on the degree of hypothermia, the condition of the patient, and the rewarming rate possible with the technique chosen.