Cardiac arrest due to hypoxia and asphyxia

Hypoxia and asphyxiation

• Hypoxia refers to a reduced partial pressure of oxygen in the blood.
• Asphyxia is characterized by insufficient ventilation, leading to hypoxia.

Etiologies of hypoxic cardiac arrest:

1. Trauma and injuries:
   • Direct trauma can cause airway injuries, resulting in obstruction.
   • Central nervous system (CNS) injuries might cause apnea or hypoventilation.
2. Respiratory conditions:
   • Tension pneumothorax
   • Drowning
   • Airway obstruction
   • Hanging
   • Pneumonia
   • High-altitude sickness
   • Aspiration
   • Chronic obstructive pulmonary disease (COPD)
   • Bronchospasm (asthma)
3. Other:
   • Coma
   • Central hypoventilation syndromes
   • Neuromuscular diseases
   • Anemia

The natural course of asphyxia

Should ventilation be entirely inhibited (as seen in acute airway obstructions), a rapid decline in blood oxygen saturation ensues. Within 1-2 minutes, oxygen saturation falls to approximately 60%, leading to unconsciousness. The myocardium responds to hypoxia by downregulating metabolism and thus contractility (a consistent finding in acute coronary syndromes). Between 3-8 minutes, pulseless electrical activity (PEA) develops. PEA progresses to asystole within minutes, as outlined in the studies by DeBehnke et al. and Safar et al. The majority of all asphytic cardiac arrests begin with PEA and progress to asystole. Shockable rhythms (ventricular fibrillation [VF], ventricular tachycardia [VT]) are uncommon in hypoxic cardiac arrest, as evidenced by the fact that only 0.5% of all hangings exhibit VF on the initial ECG recording (Kitamura et al, Deasy et al).

A complete airway obstruction results in PEA and cardiac arrest within 8 minutes.

Cardiac arrest as a result of asphyxia or hypoxia is managed according to the standard CPR algorithm, except that interventions to reoxygenate the patient is of paramount importance.

In cardiac arrest due to asphyxia, the probability of return of spontaneous circulation (ROSC) is high but survival is very low, as is the proportion surviving with good neurological function (Table 1).

Table 1.	Asphyxi	Hanging ning	Case Traumas	Drowning	Road accident	Drug overdose/drugs
Number of individuals	(n=2670)	(n=1999)	(n=1300 1062)	(n=1062)	(n=765)	(n=187)
Pre-Hospital ROSC (%)	17.3	7.2	1.7	3.4	3.7	2.1
Total ROSC (%)	37.6	75.0	93.3	84.2	83.3	76.5
Hospitalized (%)	57.3	22.7	4.8	13.8	12.0	21.4
30-dagars överlevnad (%)	14.3	4.2	0.7	1.1	1.6	3.7
Survival with good neurological function (CPC 1-2,%) |<	2.7	0.9	0.1	0.4	0.8	2.1

References

DeBehnke DJ, Hilander SJ, Dobler DW, Wickman LL, Swart GL. The hemodynamic and arterial blood gas response to asphyxiation: a canine model of pulseless electrical activity. Resuscitation 1995;30:16975.

Safar P, Paradis NA, Weil MH. Asphyxial cardiac arrest. In: Paradis NA, Halperin HR, Kern KB, Wenzel V, Chamberlain DA, editors. Cardiac arrest—the science and practice of resuscitation medicine.

Kitamura T, Kiyohara K, Sakai T, et al. Epidemiology and outcome of adult out-of-hospital cardiac arrest of non-cardiac origin in Osaka: a population-based study. BMJ Open 2014;4:e006462.

Deasy C, Bray J, Smith K, et al. Hanging-associated out-of-hospital cardiac arrests in Melbourne, Australia. Emerg Med 2013;30:3842.

Luna GK, Pavlin EG, Kirkman T, Copass MK, Rice CL. Hemodynamic effects of external cardiac massage in trauma shock. J Trauma 1989;29:1430-3.

Jeffcoach DR, Gallegos JJ, Jesty SA, et al. Use of CPR in hemorrhagic shock, a dog model. J Trauma Acute Care Surg 2016;81:27-33.

Wallmuller C, Meron G, Kurkciyan I, et al. Causes of in-hospital cardiac arrest and influence on outcome. Resuscitation 2012;83:120611.

Wood S. Interactions between hypoxia and hypothermia. Annu Rev Physiol 1991;53:7185.