The Patient in Shock

Alan C. Heffner

THE CLINICAL CHALLENGE

Airway management and hemodynamic support are defining priorities of critical care. Intubation is among the most complicated emergency resuscitation procedures and both preintubation hypotension and postintubation hypotension (PIH) during emergency airway control are associated with increased risk of adverse events and death. A clear understanding of pertinent principles and priorities helps to minimize and rapidly manage shock in the peri-intubation period. In this chapter, we focus on the interplay between the shock state, intubation technique, medication selection, and postintubation management. Comprehensive discussions of shock resuscitation can be found in standard emergency medicine and critical care textbooks.

Shock is the final common pathway for many life-threatening diseases. Unfortunately, shock recognition is not always straightforward. Shock is defined by inadequate tissue perfusion in which oxygen delivery is insufficient to meet metabolic needs. Contrary to popular use, the term is not synonymous with perfusion pressure. Systemic blood pressure is an unreliable indicator of adequate oxygen delivery and perfusion. Normal or even elevated blood pressure does not assure normal organ perfusion. Inadequate perfusion in the setting of normotension is termed compensated shock. The difficulty in identifying these patients has spawned the terms occult hypoperfusion and cryptic shock to describe hemodynamically stable patients with microvascular insufficiency. The majority of critically ill patients present in compensated shock with normal or near-normal blood pressure.

Uncompensated shock is characterized by hypotension, which is a late sign of hypoperfusion that develops when physiologic mechanisms to maintain normal perfusion pressure are overwhelmed or exhausted. Mean arterial pressure (MAP) <65 mm Hg, systolic blood pressure (SBP) <90 mm Hg or MAP >20 mm Hg below baseline should raise clinical concern even in the absence of overt clinical hypoperfusion. Both the degree and duration of hypotension are directly correlated with likelihood of adverse outcomes. Similarly, brief self-limited hypotension represents progressive failure of cardiovascular compensation and is a common first sign of uncompensated shock. This transient hypotension is an important clue, as it is a marker of adverse outcome and often heralds further hemodynamic deterioration in the absence of effective intervention.

AIRWAY MANAGEMENT OF THE PATIENT IN SHOCK

Airway management of the patient in cardiovascular crisis is a high-risk situation. Determining the need for, and timing of, intubation requires balancing respiratory and cardiovascular considerations in these fragile patients. The airway manager should optimize conditions to achieve first attempt intubation success as prolonged airway management, including the need for multiple laryngoscopy attempts, is associated with increased risk of clinical deterioration. Box 35-1 summarizes some important practical issues and modifications required for safe airway management of patients in shock.

Timing of Airway Management

Patients in shock exhibit the same primary indications for airway management as those without hemodynamic compromise. Failures of airway maintenance, airway protection, oxygenation, or ventilation are often related to the patient’s primary disease. Concomitant shock simply adds complexity to the airway management plan of such cases. However, often the airway is maintained and protected and oxygenation and ventilation are (at least marginally)
adequate. The primary indication for intubation in most cases derives from the anticipated clinical course, which is one of increasing metabolic debt, progressive patient fatigue, worsening hypoxemia, and respiratory failure. Prioritization of immediate airway management versus hemodynamic support is a common clinical dilemma. Four main considerations may assist with the decision:

Box 35-1. Implications of Shock during Airway Management

Hemodynamic monitoring and optimizing preintubation status
- Monitor for precipitous hemodynamic decline
- Adequate IV access
- Empiric fluid loading prior to airway management
- When appropriate, delay intubation to improve hemodynamic status
- Immediate availability and use of vasopressor support to avoid or treat hypotension
Preoxygenation
- Ineffective spontaneous breathing may limit preoxygenation
- Limited preoxygenation resulting from high systemic oxygen extraction
- Rapid desaturation limiting period of apneic normoxia for laryngoscopy
RSI and drug use
- Greater untoward cardiovascular effects of RSI drugs
- Need for reduced dose sedative-hypnotic agent
- Slower onset of action of RSI drugs
Postintubation management
- Attention to controlled, slow, low-tidal volume ventilation
- Avoid dynamic hyperinflation and auto-PEEP
- Low-dose titrated sedation

The severity of respiratory compromise

Inadequate spontaneous ventilation and oxygenation are late-stage sequelae of shock. Respiratory failure, particularly sudden hypoventilation (especially bradypnea or apnea) often signifies impending cardiac arrest and requires immediate attention. Prompt intubation is indicated, and ideally, airway and cardiovascular support are coordinated. Less severely ill patients may benefit from supplemental oxygen or bag-valve-mask support to optimize preoxygenation, while critical minutes for improvement of cardiovascular status are gained through administration of crystalloid and vasopressor support.
The risk of intubation at the patient’s current cardiovascular state and the benefit of hemodynamic support

Preintubation shock increases the likelihood of severe complications, including cardiac arrest, during or following intubation. Intubation and mechanical ventilation can have substantial negative impact on fragile cardiovascular status. Medications and positive-pressure ventilation may reduce cardiovascular performance and precipitate irreversible decompensation. Cardiac arrest rates as high as 15% are described during airway management of patients in hypotensive shock. If the patient is adequately oxygenated, fluid and catecholamine support is advised before initiating the intubation sequence.

Cardiac tamponade represents an extreme example where the ABC priorities must be reordered to minimize the risk of precipitating cardiac arrest with intubation. In the absence of apnea or cardiac arrest, volume loading and support of spontaneous ventilation may provide sufficient time to perform pericardiocentesis or enable rapid transfer
to the operating room, for immediate surgical intervention, if needed, at the time of intubation.
The anticipated clinical course of the patient with shock

Many critically ill patients demonstrate a biphasic early course wherein early resuscitation slows the spiral of hypotension, malperfusion, and organ dysfunction, only to have the patient deteriorate a few hours later. In most instances, hypotension and organ malperfusion are improved, but not entirely reversed by initial therapy. Interstitial edema from volume resuscitation, the progression of end-organ dysfunction (including acute lung injury), cumulative work of breathing, and metabolic debt combine with other factors to exhaust the patient’s physiologic reserve leading to respiratory failure minutes or hours following initial “successful” resuscitation. Frequent reassessment is required, with particular attention to respiratory parameters. Declining oxygen saturation or increasing respiratory work or rate signals the diffusion compromise and decreasing lung compliance of acute lung injury. Hemodynamic status may also subtly, but progressively deteriorate, indicated by malperfusion or escalating vasopressor support. Intubation should occur early when this downward cycle is identified, and should not wait for overt cardiovascular or respiratory failure.