Which examination position has the patient lying on their back face up with the knees bent?

Knee-Chest Position.

In the knee-chest position, the patient lies on the side with both knees bent, with the top leg brought closer to the chest (Fig. 19.38). A variation of this position would allow the patient to lie with the bottom leg straightened while the top leg is still bent close to the chest. Insert the speculum with the handle pointed in the direction of the patient's abdomen or back. Because the patient is lying on the side, be sure to angle the speculum toward the small of the patient's back and not straight up toward the head. Once the speculum has been removed, the patient will need to roll onto the back.

The assistant may provide support for the patient while on the examination table, help the patient straighten the bottom leg if the preferred variation of this position, or support the patient in rolling onto the back for the bimanual examination. If the patient cannot separate the legs, the assistant may help elevate one leg.

The knee-chest position does not require the use of stirrups. It is particularly good for a patient who feels most comfortable and balanced lying on a side.

A. Prenatal Exercises

Studies in which patients assumed the knee-chest position with chest and head against the floor or bed and hips elevated, accompanied by gentle pelvic rocking for 20 minutes three times a day, demonstrate version rates greater than control patients.6,7 This posture allows the fetus to “fall forward” out of the pelvis and promotes turning. If the knee-chest position is uncomfortable, the patient may achieve the same effect by lying supine with her hips supported on several firm pillows. A Cochrane metaanalysis, however, has demonstrated an overall nonsignificant trend toward reduction in breech presentation with these exercises.8

Male Patient, Bending Forward (Lateral Decubitus or Knee-Chest Positions Are Also Possible)

Assist male patients in leaning over examining table (or into knee-chest position or lateral decubitus position if preferred) (Fig. 25.11). Examiner is behind patient. Ask the patient, unlike in this illustration, to point his toes inward and to put his arms and chest on the table to help relax the buttocks and make the examination easier.

Inspect sacrococcygeal and perianal areas.

Perform rectal examination:

Palpate sphincter tone and surface characteristics; palpate circumferentially for rectal mass.

Obtain rectal culture if needed.

Palpate prostate gland and seminal vesicles.

Note characteristics of stool when gloved finger is removed. Test for occult blood.

Approach to the Physical Examination

An infant or very young child can be examined most easily while she is semirecumbent on her mother's lap with her hips flexed and abducted. Put lateral and downward pressure on the labia majora so that you can visualize the introitus, hymen, and lower third of the vagina (Fig. 18–1). An alternative, equally effective technique is to hold the labia majora gently between your thumbs and forefingers and gently draw them forward (Figs. 18–2 and 18–3).

A child who is age 2 years or older can also be examined in the knee-chest position. The child holds her bottom in the air with her knees 10 to 15 cm (about 4 to 6 inches) apart, allowing her stomach to sag against her thighs. Have an assistant or parent gently retract the labia majora on one side laterally and upward while you do likewise on the other side. This positioning facilitates the inspection of the external genitalia and causes the pubococcygeus muscle to relax, allowing the vagina to fall open. You can visualize the entire length of the vagina and frequently identify the cervix. Use the otoscope (without a speculum) to provide magnification and good illumination along the length of the vagina. Do not allow the otoscope to touch the external genitalia or to enter the vagina.

Key Point

The technique for the examination of the genitalia must be tailored to the child's age.

Management

The overall treatment goals for tet spells are to increase the SVR, to abolish the hyperpnea, and to correct the metabolic acidosis (Box 170.8). Give supplemental oxygen and increase the child's SVR by placing him in a knee-to-chest position; older children may be placed in the squatting position, if tolerated. Both maneuvers are believed to increase SVR and to decrease the pathologic right-to-left shunting of blood. Analgesics should be given to calm the child, decrease the catecholamine surge, and decrease the respiratory rate. Morphine (0.1 to 0.2 mg/kg) intramuscularly has been a traditional option but has the possible untoward effect of systemic vasodilation (further decreasing the SVR) by endogenous histamine release. Fentanyl and midazolam are newer options without the potential risk of endogenous histamine release.22 Both may be given via the intranasal route and may be less distressful than intramuscular morphine. Ketamine (1 to 2 mg/kg IV or 3 to 5 mg/kg IM) is a good choice for its analgesic and sedative effects; it is an excellent choice to improve SVR.23-26 In the event of clinically suspected or documented (pH <7.4) metabolic acidosis, sodium bicarbonate (1 mEq/kg IV) may be given to break the cycle of hypoxemia, acidosis, and worsening hypotension and perfusion. Most infants respond to these measures and exhibit an improvement in their oxygenation and a decrease in their degree of cyanosis.

Infants whose condition does not improve with these measures may require a vasopressor (such as, phenylephrine) to increase the SVR and thereby to decrease the degree of right-to-left shunting across the VSD. An intravenous fluid bolus may also be considered to increase the volume of blood flow through the pulmonary artery. If the aforementioned pharmacologic interventions are not successful, consider propranolol (0.1 to 0.25 g/kg IV) administered slowly and repeated if needed every 10 to 15 minutes (possibly reduces infundibular spasm at the right ventricular outflow tract) or phenylephrine (5 to 20 mcg/kg IV) administered slowly and repeated if needed every 10 to 15 minutes (alpha-antagonist to increase SVR).

Palliative surgical procedures to increase the amount of blood flow temporarily to the pulmonary arteries are performed in infants with severe cyanotic tetralogy of Fallot. The most commonly performed procedure is the modified Blalock-Taussig shunt, in which an anastomosis is created between the subclavian artery and the ipsilateral pulmonary artery. Definitive surgical repair consists of closing the VSD and opening the right ventricular outflow tract obstruction by resection of the infundibular tissue. The mortality rate is 5% to 10% within the first 2 years after definitive surgical repair in uncomplicated tetralogy of Fallot cases. Complications that can occur after definitive surgical repair include complete heart block, ventricular dysrhythmias, and right bundle branch block (secondary to the right ventriculotomy).

Medical Management

When called to a child undergoing a hypercyanotic crisis, the first actions should be to place the child in the knee-chest position and administer oxygen by face mask. If the child is extremely restless, an intravenous line should be inserted, and a small dose of morphine sulphate, at 0.1 mg per kg, may be all that is required to abort the crisis. If this fails, treatment with a β-blocking agent such as propranolol will reduce tachycardia and increase systemic resistance. It may also have an effect to reduce hypercontractility in response to endogenous release of catecholamine, but there is no evidence for a specific effect to reduce infundibular muscular spasm. The drug should be administered intravenously. Half of this should be given rapidly, and the remaining half more slowly over the next few minutes. If this fails to lead to prompt improvement, then arterial blood gases should be assessed. Accompanying metabolic acidosis should be corrected. Intubation and ventilation may be required in extreme cases, and at this stage an intravenous vasoconstrictor, such as phenylephrine, is often effective. Exceptionally, it will be necessary to construct an emergency systemic-to-pulmonary shunt. In any case, the patient should immediately be referred for definitive intervention, with treating orally with propranolol during the interim.

Hypercyanotic Episodes

Hypercyanotic spells are episodes of cyanosis that occur in 20% to 70% of untreated children. They may be initiated by crying or feeding and may even occur during anesthesia. The cause of these spells is unclear, but metabolic acidosis, increased Paco2, circulating catecholamines, and surgical stimulation have all been implicated.

Management of a tet spell requires urgent intervention. Simple measures (e.g., morphine to reduce infundibular spasm, Valsalva maneuver or legs-to-knee chest position to increase SVR) may be effective. Early and aggressive use of a vasoconstrictor is essential (e.g., metaraminol or phenylephrine). Phenylephrine should be premixed and in a syringe for immediate use. Management may require any of the following:

100% oxygen and hyperventilation

IV fluid bolus

Sedation or analgesia (e.g., fentanyl, morphine) and paralysis

Sodium bicarbonate

Vasoconstriction

Phenylephrine is given as a 1-µg/kg bolus and doubled at 1-minute intervals until a satisfactory response is achieved (doses required in small preterm infants may be up to 30 µg/kg); this is followed by an infusion at 1 to 5 µg/kg per minute.

Norepinephrine is given at a rate of 0.01 to 0.2 µg/kg per minute, if central venous access is available.

β-Blockers are administered to relax infundibular spasm and reduce the heart rate.

Propranolol 15–20 µg/kg is given as a slow intravenous injection (max 100 µg/kg), and repeated depending on clinical effect.

Esmolol is given as a 500-µg/kg loading dose administered over 1 minute, followed by a continuous infusion at a rate of 50 to 250 µg/kg per minute.

Tetralogy of Fallot

The classic description of TOF includes the following four abnormalities: VSD, pulmonary stenosis (PS), right ventricular hypertrophy (RVH), and overriding of the aorta. From a physiologic point of view, TOF requires only two abnormalities—a VSD large enough to equalize systolic pressures in both ventricles and a stenosis of the right ventricular outflow tract (RVOT) in the form of infundibular stenosis, valvular stenosis, or both. RVH is secondary to PS, and the degree of overriding of the aorta varies widely and it is not always present. The severity of the RVOT obstruction determines the direction and the magnitude of the shunt through the VSD. With mild stenosis, the shunt is left to right, and the clinical picture resembles that of a VSD. This is called acyanotic or pink TOF (Fig. 11-8, A). With a more severe stenosis, the shunt is right to left, resulting in “cyanotic” TOF (Fig. 11-8, B). In the extreme form of TOF, the pulmonary valve is atretic, with right-to-left shunting of the entire systemic venous return through the VSD. In this case, the PBF is provided through a patent ductus arteriosus (PDA) or multiple collateral arteries arising from the aorta. In TOF, regardless of the direction of the ventricular shunt, the systolic pressure in the RV equals that of the LV and the aorta (see Fig. 11-8, A and B). The mere combination of a small VSD and a PS is not TOF; the size of the VSD must be nearly as large as the annulus of the aortic valve to equalize the pressure in the RV and LV.

In acyanotic TOF, a small to moderate left-to-right ventricular shunt is present, and the systolic pressures are equal in the RV, LV, and aorta (see Fig. 11-8, A). There is a mild to moderate pressure gradient between the RV and PA, and the PA pressure may be slightly elevated (because of a less severe stenosis of the right ventricular outflow tract). Because the presence of the PS minimizes the magnitude of the left-to-right shunt, the heart size and the pulmonary vascularity increase only slightly to moderately. These increases are indistinguishable from those of a small to moderate VSD. However, unlike VSDs, the ECG always shows RVH because the RV pressure is always high. Occasionally, LVH is also present. The heart murmurs are caused by the PS and the VSD. Therefore, the murmur is a superimposition of an ejection systolic murmur of PS and a regurgitant systolic murmur of a VSD. The murmur is best audible along the lower left and mid-left sternal borders, and it sometimes extends to the upper left sternal border. Therefore, in a child who has physical and radiographic findings similar to those of a small VSD, the presence of RVH or BVH on the ECG should raise the possibility of acyanotic TOF. (A small VSD is associated with LVH or a normal ECG rather than with RVH or BVH). Right aortic arch, if present, confirms the diagnosis. Infants with acyanotic TOF become cyanotic over time, usually by 1 or 2 years of age, and have clinical pictures of cyanotic TOF, including exertional dyspnea and squatting.

In infants with classic cyanotic TOF, the presence of severe PS produces a right-to-left shunt at the ventricular level (i.e., cyanosis) with decreased PBF (see Fig. 11-8, B). The PAs are small, and the LA and LV may be slightly smaller than normal because of a reduction in the pulmonary venous return to the left side of the heart. Therefore, chest radiograph films show a normal heart size with decreased pulmonary vascularity. The systolic pressures are identical in the RV, LV, and aorta. The ECG demonstrates RVH because of the high pressure in the RV. The right-to-left ventricular shunt is silent, and that the heart murmur audible in this condition originates in the PS (ejection-type murmur). The ejection systolic murmur is best audible at the mid-left sternal border (over the infundibular stenosis) or occasionally at the upper left sternal border (in patients with pulmonary valve stenosis). The intensity and the duration of the heart murmur are proportional to the amount of blood flow through the stenotic valve. When the PS is mild, a relatively large amount of blood goes through the stenotic valve (with a relatively small right-to-left ventricular shunt), thereby producing a loud, long systolic murmur (Fig. 11-9, A). However, with severe PS, there is a relatively large right-to-left ventricular shunt that is silent, and only a small amount of blood goes through the PS, thereby producing a short, faint systolic murmur (see Fig. 11-9, A). In other words, the intensity and duration of the systolic murmur are inversely related to the severity of the PS. These findings are in contrast to those seen in isolated PS (Fig. 11-9, A and B). Because of low pressure in the PA, the P2 is soft and often inaudible, resulting in a single S2. The heart size on chest radiograph films is normal in TOF because none of the heart chambers handle an increased amount of blood. If a cyanotic infant has a large heart on the chest radiograph films, especially with an increase in pulmonary vascularity, TOF is extremely unlikely unless the child has undergone a large systemic-to-PA shunt operation. Another important point is that an infant with TOF does not develop CHF. This is because no cardiac chamber is under volume overload, and the pressure overload placed on the RV (not higher than the aortic pressure, which is under baroreceptor control) is well tolerated.

The extreme form of TOF is that associated with pulmonary atresia, in which the only source of PBF is through a constricting PDA or through multiple aortic collateral arteries (feeding into pulmonary arteries). All systemic venous return is shunted right to left at the ventricular level, resulting in a marked systemic arterial desaturation. Probably the more important reason for such severe cyanosis is the markedly reduced PBF, with resulting reduction of pulmonary venous return to the left side of the heart. Unless the patency of the ductus is maintained, the infant may die. Infusion of prostaglandin E1 has been successful in keeping the ductus open in this and other forms of cyanotic congenital heart defects that rely on the patency of the ductus arteriosus for PBF. Heart murmur is absent, or a faint murmur of PDA is present. RVH is present on the ECG as in other forms of TOF. Chest radiographs show a small heart and a markedly reduced PBF.

It is important to understand what determines the amount of PBF, which in turn determines the degree of cyanosis, in patients with TOF because this concept relates to the mechanism of the “hypoxic” spell of TOF. Because the VSD of TOF is large enough to equalize systolic pressures in both ventricles, the RV and LV may be viewed as a single chamber that ejects blood to the systemic and pulmonary circuits (Fig. 11-10). The ratio of flows to the pulmonary and systemic circuits (Qp/Qs) is related to the ratio of resistance offered by the right ventricular outflow obstruction (shown as pulmonary resistance [PR] in Fig. 11-10) and the systemic vascular resistance (SVR). Either an increase in the pulmonary resistance or a decrease in the SVR will increase the degree of the right-to-left shunt, producing a more severe arterial desaturation. On the contrary, more blood passes through the right ventricular outflow obstruction when the SVR increases or when the pulmonary resistance decreases. Although controversies exist over the role of the spasm of the RVOT as an initiating event for the hypoxic spell, there is no evidence that the spasm actually occurs as a primary event. Pulmonary valve stenosis has a fixed resistance and does not produce spasm. The infundibular stenosis, which consists of disorganized muscle fibers intermingled with fibrous tissue, is almost nonreactive to sympathetic stimulation or catecholamines. Hypoxic spell also occurs in patients with TOF with pulmonary atresia in which the presence or absence of spasm would have no role in the spell. Therefore, it is more likely that changes in the SVR plays a primary role in controlling the degree of the right-to-left shunt and the amount of PBF. A decrease in the SVR increases the right-to-left shunt and decreases the PBF with a resulting increase in cyanosis. In this case, the RVOT dimension may decrease, but it is likely secondary to the decreased amount of blood flowing through it rather than primary spasm. Conversely, an increase in SVR decreases the right-to-left shunt and forces more blood through the stenotic RVOT. This results in an improvement in the arterial oxygen saturation. Therefore, the likelihood of the RVOT spasm initiating the right-to-left shunt is remote. Also, excessive tachycardia or hypovolemia can increase the right-to-left shunt through the VSD, resulting in a fall in the systemic arterial oxygen saturation. The resulting hypoxia can initiate the hypoxic spell. Tachycardia or hypovolemia may narrow down the RVOT, and hypovolemia with reduction of blood pressure can initiate a hypoxic spell by increasing right-to-left ventricular shunt. Slowing of the heart rate by β-adrenergic blockers, volume expansion, or interventions that increase the SVR have all been used to terminate the hypoxic spell.

The hypoxic spell, also called the cyanotic spell, tet spell, or hypercyanotic spell, occurs in young infants with TOF. It consists of hyperpnea (i.e., rapid and deep respiration), worsening cyanosis, and disappearance of the heart murmur. This occasionally results in complications of the CNS and even death. Any event such as crying, defecation, or increased physical activity that suddenly lowers the SVR or produces a large right-to-left ventricular shunt may initiate the spell and, if not corrected, establishes a vicious circle of hypoxic spells (Fig. 11-11). The sudden onset of tachycardia or hypovolemia can also cause the spell as discussed earlier. The resulting fall in arterial Po2, in addition to an increase in Pco2 and a fall in pH, stimulates the respiratory center and produces hyperpnea. The hyperpnea, in turn, makes the negative thoracic pump more efficient and results in an increase in the systemic venous return to the RV. In the presence of fixed resistance at the RVOT (i.e., pulmonary resistance) or decreased SVR, the increased systemic venous return to the RV must go out the aorta. This leads to a further decrease in the arterial oxygen saturation, which establishes a vicious circle of hypoxic spells (see Fig. 11-11).

Treatment of hypoxic spells is aimed at breaking this circle by using one or more of the following maneuvers:

Picking up the infant in such a way that the infant assumes the knee–chest position and traps systemic venous blood in the legs, thereby temporarily decreasing systemic venous return and helping to calm the baby. The knee–chest position may also increase SVR by reducing arterial blood flow to the lower extremities.

Morphine sulfate suppresses the respiratory center and abolishes hyperpnea.

Sodium bicarbonate (NaHCO3) corrects acidosis and eliminates the respiratory center–stimulating effect of acidosis.

Administration of oxygen may slightly improve arterial oxygen saturation.

Vasoconstrictors such as phenylephrine raise SVR and improve arterial oxygen saturation.

Ketamine is a good drug to use because it simultaneously increases SVR and sedates the patient. Both effects are known to help terminate the spell.

Propranolol has been used successfully in some cases of hypoxic spell, both acute and chronic. Its mechanism of action is not entirely clear. When administered for acute cases, propranolol may slow the heart rate and perhaps reduce the spasm of the RVOT (although not likely as discussed earlier). More important, propranolol may also increase SVR by antagonizing the vasodilating effects of β-adrenergic stimulation. The successful use of propranolol in the prevention of hypoxic spells is more likely the result of the drug’s peripheral action. The drug may stabilize vascular reactivity of the systemic arteries, thereby preventing a sudden decrease in SVR (see Chapter 14).

Infants and toddlers with untreated TOF often assume a squatting position after playing hard. During playing, these infants become tachypneic and dusky. When they assume a squatting position and rest a little while, these symptoms disappear, and then they resume playing. What is the mechanism of recovery from these symptoms during squatting? The squatting position is the same as the knee–chest position (which is used to treat hypoxic spells). Squatting or the knee–chest position increases systemic arterial oxygen saturation as shown in an experimental study (Fig. 11-12). Three mechanisms may be involved. First, reduction of the systemic venous return by trapping venous blood in the lower extremities reduces right-to-left shunt at the ventricular level (evidenced by a reduced arterial lactate levels in Fig. 11-12). Second, a reduced arterial blood flow to the legs reduces venous washout from the leg muscles. Third, squatting might also increase SVR, a known mechanism to reduce right-to-left ventricular shunt.

Cardiovascular Changes

Using a noninvasive cardiac output monitor, both cardiac index (CI) and venous return20 decreased in unanesthetized, healthy volunteers in the prone position. CI decreased compared with the supine position as follows: knee-chest position (20%), on pelvic props from a modified Relton-Hall frame under the anterior superior iliac spines and padded support under the chest (17%), on an evacuatable mattress (11%), and on pillows (3%; one pillow under the thorax and one under the abdomen, leaving the abdomen free to move). Toyota and Amaki21 studied transesophageal echocardiograms in 15 healthy patients undergoing prone-position lumbar laminectomy. The prone position caused left ventricular volume and compliance to decrease. These changes were attributed to a decrease in the venous return due to inferior vena caval compression, and decreased left ventricular compliance due to increased intrathoracic pressure in the prone position. These results had been confirmed by other studies using thermodilution pulmonary artery catheters to measure the cardiac index when transferring from the supine to the prone position. Cardiac output decreased in these studies by 17% to 24%. The reduction in cardiac output in the prone position also leads to a decrease in the metabolism of propofol.22 A reduction in propofol metabolism while in the prone position could also explain the results of Sudheer and colleagues,23 who showed a significant reduction in cardiac output in the prone position during maintenance of anesthesia using propofol compared with isoflurane. Pearce24 observed vena caval pressures to be 0 to 40 mm H2O in patients in the prone position with the abdomen hanging free. In contrast, patients with abdominal compression had vena caval pressures greater than 300 mm H2O. Increased venous pressure not only increases bleeding during spine surgery owing to congestion of vertebral veins but also can impair spinal cord perfusion.

The use of the prone position with abdominal compression was identified as a plausible cause of spinal cord ischemia leading to neurologic deficits after cervical laminectomy. The authors of this case series recommended the avoidance of abdominal compression and hypotension, especially in myelopathic patients for whom maintenance of spinal cord perfusion pressure is of paramount importance.25

Tumors Involving S3 And Below Posterior Approach2

This approach is suitable for lower sacral tumors whose superior limit can be reached on digital rectal examination (Fig. 42-2). A purse-string suture is performed around the anus. A modified knee-chest position is set, and a midline skin incision is made. The skin and subcutaneous tissue are prepared and reflected, exposing the sacrum, the sacroiliac ligament, the origin of the gluteus maximus, and the medial attachment of the sacrotuberous ligament. The sacral periosteum should not be incised or dissected.3 These ligaments and muscles are divided on both sides close to their sacral attachment. The insertion of the gluteus maximus muscle is cut up to the edge of the sacroiliac joint (Fig. 42-3).

This allows exposure of the inferior roots of the sciatic nerves, the piriformis muscles, and the posterior margin of the pelvic portion of the tumor.2

At the deeper level, the piriformis muscle and the sacrospinous and anococcygeal ligaments are found and divided. The rectum is gently detached from the presacral lamina and from the tumor, which always protrudes anteriorly. The upper level section of the sacrum is decided on the basis of radiological findings. At the chosen level, a careful digital dissection of the anterior soft tissue is performed on both sides through the greater sciatic notch below the lower margins of the ilium and alae of the sacrum. The bulky tumor usually remains well covered by the periosteum, and careful finger dissection prevents dramatic injury to the gluteal vessels (Fig. 42-4). The pudendal nerves exiting the greater sciatic foramen and reentering the lesser foramen also should be identified and protected, except when they are too intimate with the tumor to be spared (see Fig. 42-4).

The lower roots, including S3, are removed en bloc with the tumor mass. The removed specimen includes the sacrum, coccyx, lower sacral roots, and resected surrounding soft tissue. An osteotomy is performed between the S2 and S3 dorsal foramina.4

The tumor mass is freed circumferentially and can be removed en bloc. Bleeding from the sacral stump is controlled with bone wax. Bleeding in the presacral soft tissue may be severe. The median and lateral sacral arteries and veins are usually the main sources of this bleeding. In these types of resection, reconstruction is not necessary because the sacroiliac joints are not excised. For smaller lesions of the mid-sacrum and distal sacrum, the resection of the sacroiliac joint is not required.3 Wound closure generally can be achieved without a rotational flap or other reconstructive procedures.

It is impossible to dissect the soft tissue of the upper presacrum safely via the posterior approach. A posterior approach to the upper sacrum may cause major vascular injury or inadvertent entry into the rectum, or violate the tumor capsule during an attempt to osteotomize the ventral sacrum and sacroiliac joints from behind.

These difficulties are best addressed by combining the dorsal sacrectomy via a ventral approach for the lesions requiring amputation through the level of the sacroiliac joints.