Severe heart failure leads to hypoxemia, increased myocardial work, and increased work-of-breathing (Table 23-2). Mechanical ventilation in this setting is indicated to reverse the hypoxemia, reduce the work-of-breathing, and decrease myocardial work. Some patients with severe heart failure develop acute hypercarbia. Therefore the initial treatment includes noninvasive continuous positive airway pressure (CPAP).
Table 23-2Indications for Mechanical Ventilation in Patients With Cardiovascular Failure ||Download (.pdf) Table 23-2 Indications for Mechanical Ventilation in Patients With Cardiovascular Failure
• Increased work of the myocardium
• Increased work–of-breathing
Continuous Positive Airway Pressure
The use of mask CPAP in the patient presenting with acute left ventricular failure and pulmonary edema reduces the work-of-breathing and the work of the myocardium. It also increases Pao2, decreases Paco2, reduces the need for intubation, and increases survival. In many patients, CPAP provides sufficient unloading of myocardial and respiratory work while pharmacologic treatment modifies cardiovascular function, avoiding invasive management. Generally, CPAP is most useful in patients who are awake, oriented, and cooperative. If the CPAP mask further agitates the patient, it should be removed and invasive ventilatory support considered. Initial CPAP settings are generally 10 cm H2O with 100% oxygen.
Noninvasive ventilation (NIV) has also been used to avoid intubation of patients with acute congestive heart failure. For many such patients, the outcomes with CPAP or NIV are equivalent. The specific indication for NIV is hypercarbic ventilatory failure along with the hypoxemic ventilatory failure. However, NIV should be avoided in patients with acute MI, hemodynamic compromise, significant cardiac arrhythmias, and depressed mental status. In these patient presenting with respiratory failure, invasive ventilatory support should be provided rather than NIV.
Since spontaneous breathing potentially diverts blood flow to the respiratory muscles, continuous mandatory ventilation (A/C) should be used (Figure 23-1). Either pressure-control or volume-control ventilation is acceptable. In spite of the pulmonary edema that may be present at the time of initiating ventilatory support, pharmacologic treatment results in rapid resolution. Tidal volumes of 6 to 8 mL/kg ideal body weight are usually adequate with respiratory rates greater than 15/min to achieve eucapnia. Plateau pressure should be less than 30 cm H2O. Inspiratory time should be short (≤ 1 second). Fio2 should initially be set at 1 and then titrated per Spo2 and blood gases. PEEP of 5 to 10 cm H2O should be applied as support for the failing heart. Care must be exercised with the titration of PEEP because of the complex effects of PEEP on cardiac function. However, most patients with severe left ventricular failure benefit by the application of PEEP (Table 23-3).
Table 23-3Initial Ventilator Settings for Acute Congestive Heart Failure ||Download (.pdf) Table 23-3 Initial Ventilator Settings for Acute Congestive Heart Failure
|Setting ||Recommendation |
|Mode ||A/C (CMV) |
|Rate ||14-18/min |
|Volume/pressure control ||Pressure or volume |
|Tidal volume ||6-8 mL/kg and plateau pressure ≤ 30 cm H2O |
|Inspiratory time ||≤ 1 s |
|PEEP ||5-10 cm H2O |
| ||1.0 |
An algorithm for mechanical ventilation of the patient with cardiac failure.
Hemodynamics are monitored during pharmacologic therapy and mechanical ventilation (Table 23-4). Pulse oximetry is used to ensure that patients are well oxygenated. Periodic arterial blood gases are needed. Plateau pressure should be monitored. In addition, urine output, and fluid and electrolyte balance should be carefully monitored.
Table 23-4Monitoring for the Mechanically Ventilated Patient With Cardiovascular Failure ||Download (.pdf) Table 23-4 Monitoring for the Mechanically Ventilated Patient With Cardiovascular Failure
• Central venous pressure
• Pulse oximetry and periodic arterial blood gases
• Urine output and fluid and electrolyte balance
• β-type natriuretic peptide
Provided no underlying chronic pulmonary disease or secondary pulmonary problems develop and the left heart failure is appropriately managed, weaning can be a relatively easy process. However, in these patients cardiovascular system function is most optimal with increased mean intrathoracic pressure. The elimination of mechanical ventilatory support during a spontaneous breathing trial might result in an increase in left ventricular preload and pulmonary edema. Weaning may progress rapidly to low level pressure support and CPAP, but pulmonary edema may develop when positive pressure ventilation is discontinued. Some patients may develop ischemic changes during weaning. In this case, ventilatory support must be continued until therapy is successful at improving cardiac function (eg, diuresis, afterload reduction).