# 05 - SECTION 2 Shock and Cardiac Arrest

## SECTION 2 Shock and Cardiac Arrest

TABLE 313-4  Main Types and Key Features of Extracorporeal Gas Exchange
TERM
DESCRIPTION
KEY FEATURES
IMPORTANT TECHNICAL NOTES
VA-ECMO (venoarterial extracorporeal 
membrane oxygenation)
Deoxygenated blood drains via venous catheter 
to a pump and membrane oxygenator; blood is 
then returned to the arterial system
VV-ECMO (venovenous-ECMO)
Deoxygenated blood drains via venous catheter 
to a pump and membrane oxygenator; blood is 
then returned to the venous system
ECCO2R (extracorporeal CO2 removal)
Venous catheter drains blood to a CO2 removal 
device; blood then returns via a venous catheter
is indicated for patients with hypercapnia after extubation, high-flow 
oxygen support for all other patients may be preferable given similar 
efficacy to NIV in preventing reintubation and generally better patient 
comfort. Although many factors can cause a patient to fail an SBT or 
require reintubation and continued mechanical ventilation, common 
processes perpetuating mechanical ventilation include critical ill­
ness myopathy and polyneuropathy, myocardial ischemia, congestive 
heart failure, vascular and extravascular volume overload, delirium, 
malnutrition, and electrolyte abnormalities (hypophosphatemia, hypo­
kalemia, and hypomagnesemia). These processes should be evaluated 
and treated, as necessary, in patients failing attempts to discontinue 
mechanical ventilation.
EXTRACORPOREAL GAS EXCHANGE
Despite interventions to optimize oxygenation and alveolar ventilation 
on mechanical ventilation, some patients suffer life-threatening hypox­
emia, refractory respiratory acidosis, and barotrauma, and may be 
candidates for salvage therapy with extracorporeal gas exchange, a pro­
cedure whereby blood continuously circulates outside the body through 
a device that oxygenates it, removes CO2, and then returns blood to the 
patient’s circulation. Although often referred to as ECMO, modern gas 
exchange membranes both deliver oxygen and remove CO2, replacing 
the gas exchange function of the lung. The main components of an 
ECMO “circuit” include vascular cannulas to remove and return blood 
to the patient, a pump to circulate blood, and a gas exchange mem­
brane. ECMO can provide varying levels of both respiratory and circu­
latory support depending on the clinical situation (Table 313-4). In a 
patient both in shock and requiring full respiratory support, the ECMO 
circuit would include a central venous cannula (V) to remove blood 
and a central arterial cannula (A) to return oxygenated blood at rela­
tively high flow rates (up to 6 L/min) providing mechanical circulatory 
support, so-called VA-ECMO. In the absence of shock, both the drain­
ing and return vascular cannulas can be central venous, or VV-ECMO, 
but blood flow is still relatively high (2–5 L/min) to provide adequate 
oxygen delivery to tissues. In situations where a patient’s lungs can pro­
vide adequate oxygenation but insufficient CO2 removal, such as severe 
obstructive lung disease exacerbations, a venovenous circuit with low 
blood flows (0.25–2 L/min) is often adequate to remove CO2 and treat 
refractory respiratory acidosis, a process called extracorporeal CO2 
removal (ECCO2R). ECMO continues to evolve, including the use of 
hybrid circuits. For example, if patients on traditional VA-ECMO have 
asymmetric hypoxia in the upper body, an additional venous return 
catheter can be placed in an internal jugular vein to deliver additional 
oxygenated blood; this hybrid circuit would be V (removal)-VA (dual 
arterial and venous return)-ECMO. Moreover, several ECMO centers 
now have mobile ECMO equipment and teams, allowing patients who 
are too unstable for transfer to an ECMO center to start on ECMO and 
facilitate transfer to an ECMO center for further care.
Although technologic advances in the ECMO pumps, gas exchange 
membranes, and even vascular catheters have reduced ECMO-related 
complications, the procedure is resource-intensive and still associated 
with several adverse events, including cannula site hemorrhage and 
vascular injury, catheter-related infection, pneumothorax, pulmonary 
and gastrointestinal hemorrhage, limb ischemia, intracranial hemor­
rhage, and disseminated intravascular coagulation (DIC). Clinical 
outcomes for ECMO patients remain promising, including for patients 

Circulatory and respiratory 
support
Requires large vascular catheters (16–30 Fr)
Higher blood flow rates (2–6 L/min)
Respiratory support
Requires large vascular catheters (20–30 Fr)
Higher blood flow rates (2–5 L/min)
Partial respiratory support, 
CO2 removal only
Requires smaller vascular catheters (14–18 Fr)
Lower blood flow rates (0.25–2 L/min)
with severe respiratory failure from SARS-CoV-2 infection treated 
with ECMO. However, the overall mortality benefit from ECMO, 
especially in ARDS, remains unclear. Selecting patients most likely to 
benefit from ECMO, therefore, is very important, and in addition to 
exhausting traditional mechanical ventilatory support, patients being 
considered for ECMO should have a reversible underlying illness or 
be eligible for organ transplant (heart and/or lung), no chronic severe 
end-organ disease (e.g., severe kidney disease), no contraindication to 
systemic anticoagulation, a good functional status before the acute ill­
ness requiring ECMO, and a good neurologic prognosis.
CHAPTER 314
Approach to the Patient with Shock 
■
■FURTHER READING
Acute Respiratory Distress Syndrome Network et al: Ventilation 
with lower tidal volumes as compared with traditional tidal volumes 
for acute lung injury and the acute respiratory distress syndrome. 
N Engl J Med 342:1301, 2000.
Barrot L et al: Liberal or conservative oxygen therapy for acute respi­
ratory distress syndrome. N Engl J Med 328:999, 2020.
Bertini P et al: ECMO in COVID-19 patients: A systematic review and 
meta-analysis. J Cardiothorac Vasc Anesth 36:2700, 2022.
Girard T et al: An official American Thoracic Society clinical practice 
guideline: Liberation from mechanical ventilation in critically ill 
adults. Rehabilitation protocols, ventilator liberation protocols, and 
cuff leak tests. Am J Respir Crit Care Med 195:120, 2017.
Hernandez G et al: Effect of post extubation high-flow nasal can­
nula vs non-invasive ventilation on reintubation and post extubation 
respiratory failure in high-risk patients: A randomized clinical trial. 
JAMA 316:1565, 2016.
Moss M et al: Early neuromuscular blockade in the acute respiratory 
distress syndrome. N Engl J Med 380:1997, 2019.
Murphy PB et al: Effect of home noninvasive ventilation with oxygen 
therapy vs oxygen therapy alone on hospital readmission or death 
after an acute COPD exacerbation. A randomized clinical trial. 
JAMA 317:2177, 2017.
Tramm R et al: Extracorporeal membrane oxygenation for critically ill 
adults. Cochrane Database Syst Rev 1:CD010381, 2015.
Section 2	 Shock and Cardiac Arrest
Rebecca M. Baron, Anthony F. Massaro

Approach to the Patient 

with Shock
Shock is the clinical condition of organ dysfunction resulting from 
an imbalance between cellular oxygen supply and demand result­
ing in cellular and tissue hypoxia. This life-threatening condition is 
common reason for requiring care in the intensive care unit (ICU).