Manual of Perioperative Care in Adult Cardiac Surgery by Bojar Robert M

Manual of Perioperative Care in Adult Cardiac Surgery by Bojar Robert M

Author:Bojar, Robert M.
Language: eng
Format: epub
Publisher: John Wiley & Sons, Ltd.
Published: 2011-09-14T16:00:00+00:00


X. Acute Respiratory Insufficiency/Short-Term Ventilatory Support

A. Prolonged mechanical ventilation beyond 48 hours is necessary in about 5–10% of patients undergoing open-heart surgery.18,19 It may be necessary until hemodynamic issues or transient pleuropulmonary insults, such as pulmonary edema, have resolved. It may also be indicated for patients without intrinsic pulmonary problems who are sedated, obtunded, or sustain neurologic insults. These patients may have adequate gas exchange but need an endotracheal tube for airway protection.

B. Acute respiratory insufficiency characterized by inadequate oxygenation (PaO2 <60 torr with an FIO2 of 0.5 or PaO2/FIO2≤120) or ventilation (PCO2>50 torr) during mechanical ventilatory support occurs in up to 10% of patients undergoing surgery on cardiopulmonary bypass.17 This usually results from a severe perioperative cardiopulmonary insult (such as a long duration of CPB or postcardiotomy low cardiac output syndrome) that is superimposed on preexisting lung disease. Predisposing factors to acute pulmonary dysfunction are essentially the same as those that are predictive of the need for prolonged ventilatory support (see pages 396–398).

1. Predisposing factors to acute pulmonary dysfunction immediately after surgery include advanced age, significant COPD, active smoking history, obesity (BMI >30 kg/m2), diabetes, a mean PA pressure ≥20mm Hg, depressed left ventricular function (stroke volume index ≤30mL/m ), low serum albumin, a history of cerebrovascular disease and clinical CHF.17

2. Intraoperative factors include emergency surgery and CPB time ≥140 minutes. The latter is often associated with a significant inflammatory response, due to which patients usually receive a significant amount of volume during and after surgery.

3. The development of acute respiratory insufficiency is associated with more renal dysfunction, gastrointestinal and neurologic complications, nosocomial infections, and the need for prolonged mechanical ventilatory support.18 The development of multisystem organ problems explains the high mortality rate of postoperative respiratory failure, which averages 20–25%.

4. Several logistic models have been created which are predictive of prolonged ventilatory failure (>72 hours).19,20 One simple model found that the combination of a Parsonnet score >7 (Table 3.9, page 158) with a poor ejection fraction, age >65 with pulmonary hypertension, or an emergency reoperation for bleeding or cardiac arrest predicted 50% of patients requiring prolonged ventilation (>24 hours). A more sophisticated bedside model is noted in Figure 10.2.19

C. “Acute lung injury” defined by poor oxygenation is a clinical spectrum that ranges from a transient phenomenon with low risk to that of ARDS, which carries a very high mortality rate. In most patients with a PaO2/FIO2 ratio <200–300 immediately after surgery, a short period of ventilatory support while the patient is hemodynamically supported and diuresed usually results in improvement in oxygenation and the requirement for very short-term ventilation. In contrast, acute lung injury may progress to a chronic phase of ventilatory dependence in fewer than 5% of patients. It is also more likely in older patients with preexisting pulmonary, cardiac, or renal problems that compromise postoperative recovery or when postoperative care is complicated by stroke, bleeding, and multiple blood transfusions.18,19 Chronic respiratory insufficiency/ventilator dependence will be discussed in section XI (pages 413–418).

D. Etiology. During the first 48 hours, oxygenation problems predominate and can produce tissue hypoxia.



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