Page 1854 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 132: Diving Medicine and Drowning 1323

Time (minutes)
3 20 5 20 5 20 5 30 15 60 15 60 30
0

Ascent rate
Depth (FSW) 30
(1 ft/min)

Air

Ascent rate O 2
(1 ft/min)

60
Descent rate
(20 ft/min)
285 minutes
periods at 60 FSW and two at 30 FSW
USN Treatment Table 6 can be extended by two O 2
FIGURE 132-2. US Navy Treatment Table 6. This is an oxygen recompression treatment table used to treat decompression sickness and in many instances, arterial gas embolism. Other USN
treatment tables can be found in the US Navy Diving Manual, Volume 5.

USN Treatment Table 6 to treat AGE suggests that equally good results summarizes the information on the pathogenesis of drowning and the
are obtained at 2.8 ATA. This compresses the emboli to about 70% of consequences to the frequently injured systems supported in the ICU.
their original diameter and expedites the release of nitrogen. USN Table
6 is more amenable to hospital-based chambers and is particularly well ■ PATHOPHYSIOLOGY
suited to critically ill patients with AGE at sea level pressure. Like DCS, 41
recurrent or persisting symptoms of gas embolism may respond to daily The consequences of drowning are mainly those of asphyxia. During
Table 6 sessions until the patient’s neurological condition reaches a submersion, the victim’s breath-hold time is exceeded and alveolar
plateau. In general, the prognosis is good with early treatment in expe- hypoxia and hypercapnia supervene. Laryngospasm develops and the
rienced centers. 36 victim frequently swallows large quantities of water. Ultimately, breath
Smaller hospitals may not have the experience or equipment to holding and laryngospasm abate and water usually enters the lungs,
manage critically ill patients in a hyperbaric chamber. In that case, the worsening the hypoxemia. Without restoration of ventilation, most
patient may require transfer to a suitably equipped facility. This can be victims develop bradycardia followed soon thereafter by cardiac arrest.
accomplished by ground or air transportation as long as the aircraft can The key point is that cardiac arrest is a result of alveolar hypoxia and the
be pressurized or fly below 1000 ft of altitude to avoid further increases reversal of hypoxemia is critical to obtaining a return of spontaneous
42
in gas volume. circulation.
The best therapeutic responses for AGE and type II DCS occur with
rapid recompression. Although anecdotal, recompression treatment Lungs: Acute lung injury in drowning is initiated by upper airway
delays of 24 hours and perhaps up to 48 hours appear to show benefit obstruction when freshwater or seawater contacts the respiratory tract
for both conditions in some cases. Advice from a diving medicine mucosa and provokes laryngospasm. Laryngospasm is protective if the
37
physician concerning diving-related injuries is available 24 hours a day duration of hypoxemia is limited by a short immersion time. As many
by calling Duke Dive Medicine (919-684-8111). Duke Dive Medicine as 15% of individuals aspirate trivial amounts of water, but some of these
collects and disseminates information on diving safety and related inju- victims develop sufficient hypoxemia to produce hypoxic encepha-
42
ries and is associated with the hyperbaric treatment center at the Duke lopathy or ventricular arrhythmia from laryngospasm. Aspiration of
University Medical Center. water also induces mechanical airway obstruction with a small airway
component. Small airway obstruction is aggravated by bronchoconstric-
tion, mucosal edema, and plugging by water and suspended debris such
DROWNING as algae, diatoms, sand, mud or by teeth and gastric contents. 43
■ DEFINITION drowning, animal studies and human series have shown that, regardless
Although there are differences between salt water and freshwater
The terminology of drowning has evolved of late in the interest of of the tonicity of the inhaled liquid, hypoxemia is the dominant patho-
standardization and to avoid confusion in reporting. The International physiological process—driven by surfactant loss, alveolar collapse, atel-
Liaison Committee on Resuscitation (ILCOR) defines drowning as ectasis, and intrapulmonary shunting. Small differences in electrolyte
“a process resulting in primary respiratory impairment from submer- values are rarely relevant clinically and require only routine attention.
sion/immersion in a liquid medium.” This definition implies that liquid Aspiration of even small quantities of water immediately decreases
present at the entrance of the airway has prevented the victim from lung compliance and creates persistent areas of low ventilation-
breathing air. The victim may live or not, but whatever the outcome, perfusion ratio and shunt. 42,43 Therefore, the duration of hypoxemia after
he or she has been in a drowning incident. This definition avoids the aspiration of water is usually longer than after laryngospasm alone. The
need for terms such as near-drowning, wet-drowning, or dry-drowning early changes in pulmonary gas exchange have been studied experi-
38
although these descriptions are still encountered in the literature. There mentally and are attributable to loss of surfactant or its activity, damage
are excellent summaries of the demographics and emergency response to the alveolar epithelium and capillary endothelium, and pulmonary
available and those aspects are not covered here. 38-41 This section edema. In humans, vomiting and aspiration of stomach contents during

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