Restraint and capnography: Lifesaving for patients and career-saving for medics

Understand how capnography identifies respiratory and cardiovascular compromise in restrained patients

By Bob Sullivan

Caring for aggressive and violent patients can be one of the most challenging situations EMS providers face. Patients who are intoxicated, have overdosed, are in drug withdrawal or have psychiatric conditions often present a safety threat to themselves and responding caregivers. Patients with excited delirium face an additional risk of sudden death. After ruling out an underlying medical cause of aggression, such as head injury, hypoglycemia or hypoxia, aggressive patients need to be restrained prior to transport.

In addition to physical restraint, medication for sedation is important for patient and provider safety, though a side effect of several medications used for sedation is respiratory compromise. Close monitoring of restrained patients is important to identify respiratory compromise, as well as to detect changes in circulation and metabolism associated with patient decline during restraint.

Waveform capnography is a valuable tool to monitor respiration, metabolism and perfusion in restrained patients. Capnography provides an objective timeline of patient status for documentation. Here are four things paramedics should know about using capnography for restrained patients.

1. Capnography is practical to apply and provides reliable feedback.
Capnography works by measuring the amount of carbon dioxide in exhaled air through nasal prongs secured to the patient’s face. While the nasal prongs can be difficult to apply while patients are aggressive, once secured they provide accurate measurement of exhaled air, even if the patient continues to resist physical restraint.

Aggressive patients should be physically restrained in the supine or semi-fowler’s position, which allows for better visualization of the patient’s airway, rapid airway access if the patient were to vomit and easier spontaneous respirations. Capnography provides continuous, hands-free monitoring that responds to changes in respiration, perfusion and metabolism. The accuracy of other monitoring devices, such as pulse oximetry, cardiac monitoring and blood pressure measurement, are affected by patient movement, are slower to alert that the patient has become apneic and are less reliable than capnography.

2. Capnography immediately detects respiratory compromise from sedation.
After physically restraining a patient, administering medications for sedation helps keep the patient and providers safe from physical harm, decreases the patient’s metabolic demand while resisting physical restraint and reduces the patient’s anxiety. Waveform capnography immediately detects respiratory compromise that may occur after chemical sedation, to guide treatment of respiratory compromise and to monitor response to treatment.

Midazolam, lorazepam, or diazepam are frequently administered to sedate agitated patients. Respiratory depression is a side effect of these medications, especially when high doses are needed to control aggression [1]. Respiratory depression may present as periods of apnea, decreased respiratory rate with normal tidal volume, or decreased tidal volume with decreased or normal respiratory rate. Each form of respiratory depression can prevent CO2 from being eliminated effectively [2].

Waveform capnography captures changes in respiratory rate and tidal volume in real time. ETCO2, the amount of CO2 present in exhaled air, is normally 35 to 45 mm Hg. In studies of stable patients who received procedural sedation in the emergency department, capnography identified respiratory depression before a change in pulse oximetry [2].

Changes in ETCO2 and waveform shape depend on the form of respiratory depression. Periods of apnea would be detected immediately with a loss of capnography wavefrorm and ETCO2. With decreased respiratory rate and normal tidal volume, ETCO2 and waveform amplitude would rise above 45 mmHG as excess CO2 accumulated in the lungs is exhaled [2]. When tidal volume is compromised, most exhaled air comes from dead space in the upper airway. In this case ETCO2 and waveform amplitude would drop below 35 mmHg and CO2-rich air would continue to accumulate in the lungs [2]. 

For patients with respiratory depression after benzodiazepine administration, first attempt to reposition the patient’s upper airway and attempt verbal or tactile stimulation. If the patient does not respond, assist ventilation with a bag-valve mask and use capnography to guide ventilation  rate. ETCO2 may initially be high after assisted ventilation is initiated as CO2 that accumulated in the lungs is eliminated. Titrate ETCO2 between 35 and 45 mm Hg with assisted ventilation and administer supplemental oxygen to maintain pulse oximetry at 94 percent.

Ketamine is another medication for sedation of aggressive patients. Ketamine is dissociative agent that is fast acting when administered intramuscularly, and it does not cause respiratory depression or hemodynamic compromise [1].

While ketamine has an excellent safety profile, one rare but very serious side effect is laryngospasm, which prevents air from passing through the upper airway. Signs of laryngospasm include stridor and absent breath sounds despite movement of the chest and abdomen. Ventilation during laryngospasm also does not improve after repositioning the upper airway or placing an oral or nasal adjunct [2]. In one published case report, a patient suddenly developed laryngospasm in the emergency department approximately fifteen minutes after receiving intramuscular ketamine by EMS in the field. The patient experienced hypoxia during the episode, and was ventilated effectively with a bag-valve mask [3].

When a patient monitored with capnography develops laryngospasm, the capnography waveform disappears, and ETCO2 and respiratory rate will both display zero [2]. Delivering positive pressure from a bag valve mask can overcome the upper airway obstruction from the laryngospasm. Capnography provides breath-to-breath feedback on how much pressure is needed to assist ventilation effectively during laryngospasm.

3. Capnography helps identify patients at risk of sudden death from excited delirium.
Excited delirium is a condition that causes patients to be irrational, violent, have superhuman strength and be immune to pain. Patients with excited delirium have no control over their aggression and are unlikely to comply with physical restraint measures [1]. As patients continue to resist physical restraint, the body’s demand for energy exceeds its available supply, which leads to metabolic acidosis and hyperthermia.

Patients with excited delirium may literally fight until their death. Prompt recognition and treatment of excited delirium with chemical sedation, oxygen, IV fluids and cooling measures is vital to patient survival [1].

Capnography can be used to identify patients who are at risk of decompensation from excited delirium. Increase in metabolic rate and hyperthermia initially causes ETCO2 to increase, above 45 mm Hg. Once sedated, the patient’s metabolic demand decreases and ETCO2 should normalize. Changes in ETCO2 after effective sedation may indicate that sedative medications are wearing off, and that the patient’s aggression may return.

Continued aggression from excited delirium can lead to anaerobic metabolism and metabolic acidosis. To compensate for metabolic acidosis, the patient’s respiratory rate increases and excess CO2 is blown off, causing low ETCO2, below 35 mm Hg [4]. ETCO2 decreases as metabolic acidosis worsens, which indicates that the patient is decompensating.

Capnography is also useful to identify cardiac arrest from excited delirium. Cardiac arrest from excited delirium usually occurs shortly after a struggle, and may be confused with compliance or adequate sedation. Because ETCO2 reading also depends on perfusion to the lungs, the capnography waveform will disappear immediately after cardiac arrest. Along with assessing pulse and respiration, capnography can quickly confirm cardiac arrest in patients who were previously aggressive.

During CPR, capnography can be monitored through a circuit attached to a bag-valve mask or advanced airway, which helps determine chest compression quality and ventilation rate. ETCO2 above 15 mm Hg indicates that CPR is producing effective circulation. Lower ETCO2 indicates that compression rate, depth, recoil or ventilation rate need to be assessed and adjusted [5]. 

4. Capnography provides a timeline of patient trends for documentation.
Adverse events, most notably sudden death, can occur to restrained patients despite appropriate care. This poses a significant legal risk to EMS services and individual providers. When capnography is applied to restrained patients the continuously acquired ETCO2 data is an objective supplement to the run report. Capnography provides documentation of:

  • The duration of respiratory compromise after sedation
  • How quickly treatment for respiratory compromise was initiated
  • How well the patient responded to treatment
  • The metabolic status of the patient at baseline
  • Trends in metabolism after treatment
  • The time that cardiac arrest occurred
  • How long it took for resuscitation to be initiated
  • Quality of chest compressions and ventilation during resuscitation

This information is also valuable for quality assurance, protocol development and education.

Treatment goals for restrained patients are to keep caregivers and patients safe from harm, to keep the patient as comfortable as possible while maintaining adequate respiration during restraint and managing life threats that may cause the patient’s aggression. Waveform capnography provides continuous feedback about ventilation, perfusion and metabolism, which helps guide treatment decisions and provides a record for documentation. Nasal prongs to continuously monitor ETCO2 should be applied as early as possible to any aggressive patient who requires restraint. 


  1. ACEP Excited Delirium Task Force. White paper report on excited delirium syndrome, 2009.
  2. Krauss B, Hess D. Capnography for procedural sedation and analgesia in the emergency department. Annals of Emergency Medicine. 2007; 50:172-181.
  3. Burnett A, Watters B, Barringer K, Griffith K, Frascone R. Laryngospasm and hypoxia after intramuscular administration of ketamine to a patient with excited delirium. Prehospital Emergency Care. 2011; 16:3, 412-414.
  4. McEvoy M. The critical role of capnography EMS1. 2014 January 31. Retrieved from:
  5. Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardiac life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010; 122 (suppl 3): S729-S767.

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