Perioperative Problems

*  Negative-pressure pulmonary edema: A phenomenon unique to the postextubation period and thus pertinent to the PACU is negative-pressure pulmonary edema. As with other causes of pulmonary edema, findings include coarse breath sounds and production of pink frothy sputum. Typically in the PACU setting hypoxia and hypertension precede the telltale physical signs.

·         Recruitment maneuver, Also known as a vital capacity (VC) maneuver, the technique consists of giving multiple manual positive-pressure "sigh" breaths and maintaining pressure at 40 cm H2O for 5-10 seconds in an effort to open, or "recruit," atelectatic alveoli. Nearly all patients experience atelectasis under general anesthesia. A VC maneuver resolves this atelectasis, but it will recur within 5 minutes or so of breathing 100% oxygen. Atelectasis recurs more slowly if a lower fraction of inspired oxygen (FiO2) is used (e.g., > 45 minutes for FiO2 of 0.30).

·         Diffusion hypoxia is a decrease in PO2 usually observed as the patient is emerging from an inhalational anesthetic where nitrous oxide (N2O) was a component. The rapid outpouring of insoluble N2O can displace alveolar oxygen, resulting in hypoxia. All patients should receive supplemental O2 at the end of an anesthetic and during the immediate recovery period.

·         Commonly cited criteria for intubation and mechanical ventilation in adults include the following:

PaO2/FiO2 ratio < 300 mmHg

PaCO2 > 50 mmHg in the absence of metabolic alkalosis (also consider chronicity)

Dead space to tidal volume ratio (Vd/Vt) > 0.6

Respiratory rate > 35

Insufficient negative inspiratory force (NIF) > -20 mm H2O

Tidal volume < 5 mL/kg

Vital capacity

·         Methylmethacrylate, a cement used in joint replacement, undergoes an exothermic reaction that causes it to adhere to imperfections in the bony surface. Hypotension usually occurs 30-60 seconds after placement of the cement but can occur up to 10 minutes later. Postulated mechanisms include tissue damage from the reaction, release of vasoactive substances when it is hydrolyzed to methacrylate acid, embolization, and vasodilation caused by absorption of the volatile monomer.

·         DIFFERENTIAL DIAGNOSIS FOR A NARROW COMPLEX TACHYCARDIA

Sinus tachycardia

Atrial flutter

Atrial fibrillation

Multifocal atrial tachycardia

Atrial tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT)

Atrioventricular reentrant tachycardia (AVRT)

Junctional tachycardia

·         Despite its short half-life, adenosine can provoke severe exacerbations of bronchospasm, and it should be used with caution in patients with a history of asthma or reactive chronic obstructive pulmonary disease.

·         DIFFERENTIAL DIAGNOSIS FOR A WIDE COMPLEX TACHYCARDIA

1. Ventricular tachycardia
2. Supraventricular tachycardia with aberrant conduction, such as with a bundle branch block
3. Tachycardia with activation of the ventricles via an accessory pathway (Wolff-Parkinson-White syndrome)

·         Monomorphic ventricular tachycardia is common in patients with structural heart disease (such as a previous Q wave myocardial infarction), but it is generally not due to acute ischemia. Polymorphic VT may be seen in a variety of settings. Patients may have a long QT interval associated with polymorphic ventricular tachycardia, commonly referred to as torsades de pointes. This may arise from medications, electrolyte derangements, a congenital predisposition (long QT syndrome), severe bradycardia, or myocardial ischemia.

·         TEMPERATURE DISTURBANCES

1. Hypothermia is an extremely common event in the operating room because the environment and the effects of anesthetics increase heat loss. Anesthetics also decrease the ability to generate a response to hypothermia (shivering and vasoconstriction).
2. Even mild hypothermia has a negative influence on patient outcome, increasing wound infection rates, delaying healing, increasing blood loss, and increasing cardiac morbidity threefold.
3. The best method to treat hypothermia is use of forced air warming blankets. Warm all fluids and blood products. Cover all body surfaces possible, including the head, to further reduce heat loss.

·         A phenomenon unique to the postextubation period and thus pertinent to the PACU is negative-pressure pulmonary edema. As with other causes of pulmonary edema, findings include coarse breath sounds and production of pink frothy sputum. Typically in the PACU setting hypoxia and hypertension precede the telltale physical signs. The cause of the edema is the patient's vigorous ventilatory effort against a partially closed glottis or occasionally a small endotracheal tube. The clinical presentation follows a rapid emergence, often when the patient has been intoxicated at the time of induction. This phenomenon should be anticipated in young muscular individuals but may occur in any patient with some degree of laryngospasm after extubation.