EMS World

AUG 2011

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Page 43 of 71

CAPNOGRAPHY IN EMS indication of the loss of proper position or function. As with endotracheal intubation, when using alternative airways it is critical to continuously monitor the airway and assess ventilatory status. Waveform capnography is able to support those clinical assessment needs and can indicate the need to adjust ventilatory support.2 Chest Compressions Capnography provides valuable infor- mation in the assessment of resuscitative efforts. In the cardiac arrest patient, EtCO2 directly correlates with cardiac output. No carbon dioxide in exhaled air indicates either an improperly placed tube or no cardiac output. Systemic and pulmonary perfusion during cardiac compressions transports CO2 Therefore, as long as the cardiac arrest victim has residual metabolic production of CO2 , EtCO2 how EtCO2 serves as a measure of the effectiveness of chest compressions.5–7 Studies as early as the 1980s discuss can be used as a noninva- sive measurement of cardiac output during cardiac arrest.6 During CPR, EtCOc production by cellular metabolism remains constant; therefore, EtCO2 can assist in showing the paramedic the effectiveness of chest compressions. The AHA (American Heart Association) Guidelines call for quality compressions (“push hard, push fast, push deep”)2 and direct rescuers to switch places every two minutes to main- tain effective CPR. By analyzing the EtCO2 waveform, a clinician can detect rescuer fatigue before the rescuer is aware of tiring. EMS providers can position the monitor so the compressors can view the EtCO2 readings as well as the ECG waveform generated by their compressions. It is impor- tant to encourage prehospital personnel to perform quality chest compressions to keep the EtCO2 of circulation of tissues that were not being circulated due to the ineffi - ciency of chest compressions (approximately 25%–30%), as compared with intrinsic cardiac contraction.8 A recent study found the EtCO2 Figure 1: A capnograph indicating bronchospasm. increased on average 13.5 mmHg with sudden ROSC before returning to a normal range.9 sudden increase in EtCO2 to the alveolar space. If paramedics encounter a during resuscita- tion, accompanied by a rhythm appearing capable of supporting perfusion, CPR should be briefl y interrupted for a pulse check. If no pulses are present, CPR should be aggres- sively resumed, as ROSC may be near. It is important to note, however, that adminis- tration of sodium bicarbonate could also produce a “bump” in the EtCO2 of bicarbonate ion conversion to CO2 as a result during correction of acidosis. Clinical Death Confi rmation While EtCO2 can be used to gauge the effectiveness of resuscitation, it can also be used as a determining factor in the decision to cease resuscitative efforts. In 1997, a study in the New England Journal of Medicine established that an end-tidal carbon dioxide level of 10 mmHg or less measured 20 minutes after the initiation of advanced cardiac life support accurately predicts death in patients with cardiac arrest associated with electrical activity but no pulse. Patients with an EtCO2 of number as high as possible. This represents effective cellular perfusion, allowing cells to metabolize and circula- tion to deliver carbon dioxide to the lungs. Return of ROSC A rapid rise in EtCO2 during chest compressions can be the fi rst indicator of return of spontaneous circulation (ROSC), possibly even before a pulse is detectable. This rapid rise is likely due to the recruitment 40 AUGUST 2011 | EMSWORLD.com less than 10 mmHg at the 20-minute interval had 100% mortality. The study suggests that cardiopulmonary resuscita- tion may reasonably be terminated in such patients.10 efforts. In the induced hypothermia patient, the metabolic rate will be lowered, thus diminishing the production of cellular CO2 A guideline for CPR termination based on an EtCO2 of less than 10 mmHg for 20 minutes may not be adequately conser- vative for those patients receiving hypo- thermia treatment during CPR. Head-Injury Patients Capnography can help paramedics optimize ventilation in intubated patients with suspected increased intracranial pres- sure (ICP). Avoiding hypo- and hyperventila- tion in these patients is absolutely critical and diffi cult. Increased ICP may be caused by a head injury, . intracerebral hemor- rhage, a tumor or mass, or an infection. Hyperventilation of patients with increased ICP has been associated with increased mortality.11 Hyperventilation decreases intracranial pressure by decreasing intra- cranial blood fl ow, thereby increasing the risk of cerebral ischemia. In a recent study of head-injury patients, those patients with EtCO2 hyperventilation. A target EtCO2 monitoring had a lower incidence of recommen- dation is outside the scope of this article, but ventilation should be tightly controlled in this patient population, using local protocol. Caution must be taken, however, that rescuers are not hyperventilating the patient if capnography is used as a deter- minant for termination of efforts. With the advent of induced hypo- thermia in the treatment of cardiac arrest patients, new research is now needed to set guidelines for the use of EtCO2 in determining when to cease resuscitation Non-Intubated Patients Capnography can be used to differ- entiate between the varying causes of respiratory distress often seen by para- medics in the field, such as asthma, COPD exacerbation and CHF. It can also provide paramedics with early warning signs of hypoventilation, apnea, airway obstruction and hypercarbia before compensatory changes are seen in heart

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